Study Notes Exam 4
- the levels of organization are: cells, tissues, organs, and organ systems
- the structure and function of each level depends on structure and function of organ, tissue, and cell type
- epithelial tissue covers body surfaces and lines body cavities
- connective tissue binds and supports body parts
- muscular tissue causes body parts to move
- nervous tissue responds to stimuli and transmits impulses
- epithelial tissue forms a continuous layer over body surfaces including inner cavities
- squamous epithelium: flat cells (e.g., air sacs of lungs, walls of capillaries)
- cuboidal epithelium: cube-shaped cells
- columnar epithelium: elongated cells resembling columns (e.g., small intestine)
- epithelium varies in the number of cell layers
o simple epithelium has one cell layer; all cells contact a basement membrane
o pseudostratified epithelium appears layered but actually, all cells contact the basement membrane
o stratified epithelium is composed of more than one layer of cells
- ciliated epithelium cells are covered with cilia (e.g., lining of human respiratory tract); cilia can bend and move material over the surface of the epithelium
- secretory epithelia can be unicellular or have multicellular glands
o exocrine glands secrete their products into ducts or directly into a tube or cavity
o endocrine glands secrete their product directly into the bloodstream
- epithelium forms the outer layer of skin of animals
- epithelial tissue cells are packed tightly; they join to one another in one of three ways:
o tight junctions have plasma proteins extending between neighboring cells to bind cells tightly
o adhesion junctions have cytoskeletal elements joining internal plaques in neighboring cells
o gap junctions form when two identical plasma membrane channels of neighboring cells join so that ions and small molecules pass between cells
- connective tissue binds structures together, provides support and protection, fills spaces, stores fat, and forms blood cells
- connective tissue provides source cells for muscle and bone in animals that regenerate
- connective tissue cells are separated widely by a noncellular matrix between cells
- Loose Fibrous and Dense Fibrous Connective Tissues
o fibroblasts are cells spaced apart and separated by a jelly matrix of white collagen fibers and yellow elastic fibers
o collagen fibers provide flexibility and strength; elastic fibers provide elasticity
o loose fibrous connective tissue supports epithelium and provides support, flexibility, and protective covering encasing many internal organs
o dense fibrous connective tissue contains closely packed collagenous fibers; it is found in tendons, which attach muscles to bone, and ligaments, which bind bones to other bones at joints
- Adipose Tissue is loose connective tissue that insulates the body, provides protective padding, and stores fat
o in mammals, adipose tissue is beneath the skin, around the kidneys, and on surface of the heart
- Reticular Connective Tissue is present in lymph nodes, spleen, and bone marrow
o reticular fibers, associated with reticular cells resembling fibroblasts, support free blood cells
- Cartilage and Bone are rigid connective tissues
o structural proteins (cartilage) or calcium salts (bone) are deposited in the matrix
o cartilage cells (chondrocytes) lie in small chambers or lacunae embedded in a strong, flexible matrix
§ in some animals, such as sharks and rays, the entire skeleton is cartilage
§ the human fetal skeleton is entirely cartilage but is gradually replaced by bone
§ cartilage is retained at the end of long bones, the human nose, the framework of the human ear, in the walls of respiratory ducts, and within intervertebral discs
o calcium salts give bone rigidity and protein fibers provide elasticity and strength
§ compact bone has cells called osteocytes that lie within lacunae arranged in concentric circles within osteons (Haversian systems) around tiny tubes called central canals containing nerve fibers and blood vessels
§ nutrients brought by the blood reach all of the cells via minute canals (canaliculi) containing thin processes of osteocytes that connect them with one another and with the central canals
§ spongy bone at end of long bones is designed for strength, and has many long bony bars and plates
- Blood transports nutrients and oxygen to cells and removes CO2 and wastes; blood also has a role in fluid, ion and pH balance and distributes heat
o blood is a connective tissue with cells separated by liquid plasma
o in vertebrates, the blood cells are mainly of two types
§ red blood cells (erythrocytes) carry oxygen
§ white blood cells (leukocytes) aid in fighting infection
o platelets present in plasma are fragments of giant cells found in bone marrow; and play a role in blood clotting
o unlike other connective tissues, the intercellular matrix of blood (i.e., plasma) is not made by cells, but is a mix of molecules entering blood at various locations
Muscular Tissue in vertebrates is composed of cells called muscle fibers
- muscle fibers contain actin and myosin filaments; interactions result in movement
- skeletal muscle attaches by tendons to the bones of the skeleton
o skeletal muscle moves body parts, is under voluntary control, and contracts faster than other types
o skeletal muscle fibers are long, cylindrical, multinucleate cells arising from the fusion of several cells
o skeletal fibers are striated due to the light and dark bands of overlapping actin and myosin filaments
- smooth (visceral) muscle is not striated
o spindle-shaped fibers form layers with the thick middle portion of one fiber opposite the thin ends of adjacent fibers
o smooth muscle is not under voluntary control; it is therefore involuntary
o smooth muscle is in the walls of viscera (e.g., intestine, stomach, etc.) and blood vessels driving intestinal contractions and blood vessel constrictions
- cardiac muscle is only in the heart wall and powers the heartbeat that pumps blood
o cardiac muscle combines the features of both smooth and skeletal muscle
o cardiac muscle fibers are individual cells, each with one central nucleus
o cardiac muscle cells are bound end-to-end at intercalated disks where the folded membranes between two fibers contain desmosomes and gap junctions
o impulses move from cell to cell so the heartbeat is coordinated
Nervous Tissue contains neurons in the brain, spinal cord, and nerves
- neurons (nerve cells) have three parts
o dendrites receive a stimulus and conduct signals to cell body
o the cell body contains most of the cytoplasm and the nucleus of the neuron
o the axon conducts nerve impulses away from cell body; long axons are covered by myelin
- long axons and dendrites bound together by connective tissue form nerves
- the neurons detect stimuli and conduct signals to the brain or spinal cord; nerves can also lead to muscles or glands
- Neuroglia: there are several types of neuroglial cells in the nervous system
o neuroglial cells outnumber neurons nine to one
o microglial cells support neurons and phagocytize bacterial and cellular debris
o astrocytes provide nutrients and produce a growth factor known as glial-derived growth factor that someday may be used to cure diseases of neural degeneration
o oligodendrocytes form the myelin around an axon
Organs and Organ Systems
- organs consist of two or more different tissues performing common functions
- organ systems are many different organs performing common functions
- the skin is considered an integumentary system since it cannot be placed in another system; it is a system composed of skin and accessory organs (i.e., nails, hair, glands, and sensory receptors)
- Skin as an Organ: human skin protects the underlying tissues from trauma, desiccation, radiation damage, and microbial invasion
o the skin produces a precursor molecule that is converted to vitamin D after exposure to UV light
o the skin also helps regulate body temperature
o laden with sensory receptors, the skin collects information about the external environment
- Regions of Skin: the skin has both an outer epidermis and a deeper dermis
o the epidermis is the outer, thinner layer of skin composed of stratified squamous epithelium (mostly keratinocytes)
§ epidermal cells are derived from the basal layer of stem cells that undergo continuous cell division underneath
§ the newly formed cells push to the surface away from their blood supply; they flatten and harden as they accumulate keratin, a hard, waterproof protein
§ eventually, the keratinized cells die and are sloughed off
§ melanocytes located in basal layer produce a melanin pigment that absorbs UV light, protecting deeper cells from radiation damage
§ nails grow from special epidermal cells at the base of the nail in a region called the nail root
· the visible portion of a nail is the nail body
· cells become keratinized as they grow out over the nail bed
· the vascular dermal tissue under nail provides the pink color; the white half-moon area (lunula) is the thicker germinal area
o the dermis is fibrous connective tissue that forms a thicker and deeper skin layer
§ the dermis contains both elastic fibers and collagen fibers; these run parallel with the skin surface
§ a hair follicle contains a nonliving hair shaft and the living hair root that produced it
· the hair shaft is formed of dead, keratinized epidermal cells that protect the surface of the skin
· the arrector pili muscle is a smooth muscle attached to the hair follicle; contracting it causes the hair to erect
· follicles have sebaceous glands producing sebum, an oil secreted to lubricate both the hair and the skin
§ the sweat (sudoriferous) glands are coiled tubules present in most of the regions of skin that secrete a fluid (sweat) onto the surface of skin
§ many small receptors are present in the dermis
· there are separate receptors for pressure, touch, temperature, and pain
· pressure receptors have onionlike sense organs buried deep in the dermis and around joints
· in cats, Pacinian corpuscles are in paws, leg joints, and abdomen
· closely related sensors in the tongue of woodpeckers help them find insects in tree bark
· touch receptors are flat and oval shaped; they are concentrated in fingertips, palms, lips, tongue, nipples, penis, and clitoris
· heat and cold sense organs are encapsulated in sheaths of connective tissue
· nerve fibers branch throughout skin; free nerve endings are pain receptors
§ the dermis has blood vessels that constrict (paleness) and dilate (blushing)
o the subcutaneous layer lies below dermis, composed of loose connective tissue, including adipose tissue
§ adipose tissue helps insulate and gives a rounded appearance to the body
§ the excessive development of adipose tissue occurs with obesity
o Skin Cancer: excessive exposure to UV radiation can convert cells in the basal layer of the epidermis into cancer cells
§ there has been an increase in persons with skin cancer due to sunbathing and use of tanning machines
- Organ Systems carry out life processes common to organisms
o Body Cavities: the human body has two main cavities:
§ the dorsal cavity holds the brain and spinal cord, and the larger ventral cavity
§ the ventral cavity located on front side of body develops from coelom and is divided by a muscular diaphragm in humans and other mammals
· the thoracic (chest) cavity is located in the upper part of the ventral cavity, above a muscular diaphragm, and contains heart and lungs
· the abdominal cavity is located in lower part of ventral cavity, below a muscular diaphragm, and contains the major portions of digestive and excretory systems, and much of the reproductive system.
Homeostasis is the maintenance of internal conditions in a cell or organism within a normal range; the organ systems of the human body contribute to homeostasis
- the respiratory system adds oxygen and removes carbon dioxide
- the liver removes and stores glucose as glycogen and then replaces the blood glucose levels when they lower
- the hormone insulin is secreted by the pancreas to regulate glucose levels
- the kidneys respond to hormones to excrete wastes and salts and maintain blood pH
- hormones control homeostasis, but it is ultimately controlled by the nervous system
o the brain contains centers that regulate temperature and blood pressure
- a negative feedback mechanism involves a response in which the output is counter to and cancels the input, thus decreasing the process (e.g.: a house thermostat)
o a negative feedback causes the heater or air conditioner to maintain the temperature within narrow limits
- a positive feedback mechanism involves output that intensifies and increases the input, thereby increasing the process
o once childbirth begins, each event makes the process continue until completion
o sequences in blood clotting likewise progress to form a blood clot
- Regulation of Body Temperature: the regulatory center for body temperature is located in the hypothalamus, a part of the brain
- when the body temperature of the blood falls below normal, blood vessels in the skin constrict, rerouting blood to internal organs and reducing heat loss to the external environment; shivering from skeletal muscles generates heat
- in hairy animals, the arrector pili muscles pull hairs erect forming a thicker insulation
- if the body temperature is too warm, the regulatory center directs the skin blood vessels to dilate, which increases blood flow to peripheral tissues increasing heat loss
- the regulatory center activates sweat glands, increasing sweat production and increasing evaporative cooling.
Chapter34: Circulation & Cardiovascular Systems
Transport in Invertebrates
- Transport Mechanisms
o unicellular protozoa make exchanges directly with the environment across the plasma membrane
o some multicellular animals lack an internal transport system & can live without it
o the larger invertebrates usually have open or closed circulatory systems
- Invertebrates Without a Circulatory System
o sea anemones and planaria are organisms with a sac body plan that makes a circulatory system unnecessary (use diffusion through gastrovascular cavity)
o pseudocoelomates such as nematodes use the body cavity to transport fluids
o echinoderms rely on movement of coelomic fluid as a circulatory system
- Invertebrates with an Open or a Closed System Circulatory System
- certain arthropods and molluscs have an open circulatory system
o hemolymph (a mix of blood & interstitial fluid) is pumped by the heart into the body cavity or sinuses (in grasshoppers, blood first enters aorta, then hemocoel)
o hemolymph bathes the internal organs and then drains back to the heart
o hemolymph is colorless (it lacks hemoglobin or other respiratory pigments); a system of tracheae provides oxygen
- some invertebrates, including earthworms and cephalopods, have a closed circulatory system in which blood never leaves the heart or vessels
o valves prevent any backward flow of the blood as it moves through vessels
o earthworms have five pairs of anterior lateral vessels that pump blood to segments
o blood moves in capillaries where an exchange with tissue fluid takes place before returning in veins
o earthworms have a red respiratory pigment hemoglobin dissolved in the blood, not inside blood cells
o with
no special cavity for gas exchange, gas must diffuse across a moist body wall
- Closed Circulatory System
- vertebrates have a closed circulatory system called a cardiovascular system
- the muscular heart keeps blood circulating through the animal body
- the atrium is a chamber of the heart that receives blood; the ventricles pump blood
- there are three kinds of blood vessels: arteries carry the blood away from the heart, capillaries are where the exchange with tissue fluid takes place, and veins return the blood to the heart
o arteries have thick walls, expand to fill with blood and divide into small arterioles
o arteriole constriction and dilation (by nervous system) regulates blood pressure
o capillaries are microscopic blood vessels with a wall formed of one layer of simple squamous cells; gas, nutrient, and waste exchange occurs across the walls
§ capillary beds are so prevalent that, in humans, all cells are within 60-80 µm of a capillary
§ capillaries are so narrow that red blood cells pass through them in single file
o the venules are vessels that take blood from capillaries and join to form a vein
o veins transport blood toward the heart
§ wall of a vein is much thinner than that of arteries; there is low blood pressure
§ one-way valves open in direction of heart; close to prevent backflow
- Comparison of Circulatory Pathways
o fishes have a one-circuit (single-loop circulatory) pathway
§ heart has a single atrium and ventricle and pumps the oxygenated blood under pressure to the gills; after gills, blood pressure and flow are reduced
o other vertebrates have a two-circuit (double-loop circulatory) pathway to breathe air on land; the systemic circulation transports the blood to tissues and the pulmonary circulation pumps the blood to lungs
o in amphibians and most reptiles, the heart has two atria but a single ventricle
o the hearts of some reptiles (crocodiles) and all birds and mammals are divided into two halves
§ with two atria and two ventricles, the oxygenated blood is always separate from the deoxygenated blood
§ the right ventricle pumps blood to the lungs; the ventricle pumps blood to the rest of the body, providing adequate pressure for both circuits
Transport in Humans
- The Human Heart
o the pumping of the heart keeps the blood moving in arteries
o skeletal muscle contraction is responsible for the blood movement in veins
o the heart is a cone-shaped, muscular organ about the size of a fist
o it is located between lungs directly behind the sternum and the apex is tilted to left
o the myocardium is a major portion of the heart consisting mostly of cardiac muscle; its muscle fibers are branched and tightly joined together
o the heart lies within a pericardium sac that contains pericardial fluid which provides cushioning
o the endocardium lines the inner surface of the heart; it consists of connective tissue and endothelial tissue
o an internal wall called the septum separates the heart into right and left halves
o the heart has two upper, thin-walled atria and two lower, thick-walled ventricles
§ atria receive blood from the venous portion of the cardiovascular system
§ ventricles pump blood into the arterial portion of the cardiovascular system
o heart valves direct the flow of blood and prevent any backward movement
§ valves are supported by strong fibrous tendons (chordae tendineae) attached to muscle projections of ventricular walls; they prevent valves from inverting
§ atrioventricular valves between the atria and ventricles prevent any back flow from the ventricle to the atrium
· the tricuspid valve on right side of heart consists of three cusps or flaps
· the bicuspid or mitral valve on left side consists of two cusps or flaps
§ semilunar valves resembling half-moons are located between a ventricle and an artery that prevents any back flow from the artery to the ventricle
· the pulmonary semilunar valve lies between the right ventricle and the pulmonary trunk
· the aortic semilunar valve lies between the left ventricle and the aorta
- Path of Blood Through the Heart
o superior & inferior vena cava (& coronary sinus) ® right atrium ® (tricuspid valve) ® right ventricle ® (pulmonary semilunar valve) ® pulmonary trunk ® pulmonary arteries ® lungs ® pulmonary veins ® left atrium ® (bicuspid valve) ® left ventricle ® (aortic semilunar valve) ® aorta ® body tissues
o since the left side needs to pump blood throughout the body, its walls are thicker
- The Heartbeat
o the heart contracts (beats) about 70 times a minute and each heartbeat lasts about 0.85 seconds
o the heartbeat or cardiac cycle consists of phases: the atria contract first while the ventricles relax (0.15 sec.), then the ventricles contract while atria relax (0.30 sec.), and then all chambers rest (0.40 sec.)
o systole refers to the contraction of heart chambers and diastole is the relaxation of heart chambers
o the familiar lub-dub sound of the heart is heard as the valves of the heart close
§ lub is caused by vibrations of the heart when the atrioventricular valves close
§ dub is heard when the vibrations occur due to the closing of semilunar valves
o a pulse is a wave effect that passes down the walls of arterial blood vessels when the aorta expands and then almost immediately recoils after ventricular systole
o since there is one arterial pulse per ventricular systole, the arterial pulse rate can be used to determine the heart rate
o rhythmic contraction of the heart is due to the cardiac conduction system
§ the sinoatrial (SA) node is the ³pacemaker² found in the upper dorsal wall of the right atrium; it initiates the heartbeat by sending out an excitatory impulse every 0.85 seconds to cause the atria to contract
§ the atrioventricular (AV) node is found in the base of the right atrium very near the septum; when stimulated by impulses from the SA node, it sends out impulses through the septum to cause the ventricles to contract
§ although the beat of the heart is intrinsic, it is regulated by the nervous system which can increase or decrease the heartbeat rate
o an electrocardiogram (ECG or EKG) is a recording of the electrical changes that occur in the myocardium during a cardiac cycle; it is used as a diagnostic tool to identify abnormal cardiac function
o Normal Cardiac Cycle
§ the P wave represents excitation and occurs just before atrial contraction
§ the QRS complex signals that the ventricles are about to contract
§ recovery of ventricular muscle fibers produces the T wave
o ventricular fibrillation: uncoordinated contraction of ventricles; with application of a strong electric current, the SA node may reestablish a coordinated beat
- Vascular Pathways
o The pulmonary circuit circulates blood to the lungs where blood is oxygen-rich
§ oxygen-poor blood from the body collects in the right ventricle, which pumps it through the pulmonary trunk into pulmonary arteries to each lung
§ in the lungs, carbon dioxide (CO2) is unloaded and O2 is picked up by blood
§ oxygen-rich blood is returned through pulmonary veins to the left atrium
o The systemic circuit transports oxygenated blood from the left ventricle through the aorta out to all tissues, and deoxygenated blood returns from all tissues via vena cava
§ arteries contain bright red oxygen-rich blood; the veins contain dull red oxygen-poor blood that appears blue when viewed through the skin
o The coronary arteries serve the heart muscle itself
§ coronary arteries originate at base of the aorta just past aortic semilunar valve
§ coronary arteries lie on the external surface of the heart; they branch into arterioles and capillaries; capillary beds enter the venules that join to form the cardiac veins that empty into the right atrium
o A portal system is a pathway of blood flow that begins and ends in capillaries
§ the hepatic portal vein transports blood from capillaries in small intestinal villi to capillaries in liver
§ the hepatic vein leaves the liver and enters the inferior vena cava
- Blood Pressure
o systolic pressure results from blood being forced into the arteries during ventricular systole
o diastolic pressure is pressure in arteries during ventricular diastole
o human blood pressure is measured as the force pushing against the wall of the brachial artery of the upper arm
§ sphygmomanometer: measures blood pressure using a pressure cuff
o blood pressure is stated in millimeters of mercury (e.g., 120/80 mm Hg) for systolic/diastolic
o arteries: bp ~ 40-120 mm Hg
o capillaries: bp ~ 20-40 mm Hg
§ the total length of human capillaries is estimated at 60,000 miles (quantity)
o veins: bp ~ 0-20 mm Hg
§ skeletal muscle contraction on the walls of veins & valves, preventing backflow of blood, is responsible for the flow of blood in veins
§ varicose veins are abnormal dilations that develop when the valves become weak and ineffective
Cardiovascular Disorders
- Cardiovascular disease (CVD) is the leading cause of untimely death in Western countries; following guidelines for a heart-healthy lifestyle reduces the risk of CVD
- Hypertension (high blood pressure) affects an estimated 20% of Americans
o women have this condition if their blood pressure is significantly higher than 160/95; men under the age of 45 if over 130/90, and beyond the age of 45 if above 140/95; the diastolic pressure is emphasized when medical treatment is considered
o hypertension may not be detected until a stroke or heart attack occurs
o two genes are involved in hypertension for some individuals - one gene codes for angiotensinogen, a plasma protein converted to a vasoconstrictor by the product of a second gene; gene therapy may one day cure this form
- Atherosclerosis (formerly called arteriosclerosis) can cause hypertension
o soft masses of fatty materials (plaque), mostly cholesterol, accumulate beneath the inner linings of arteries and interferes with blood flow
o the symptoms may not appear until after age 50, although plaques present earlier
o plaque can cause a blood clot (thrombus) to form on irregular arterial walls
o if a clot dislodges, it is an embolus, a blood clot that moves in the blood
o in some families, atherosclerosis is inherited as familial hypercholesterolemia
- Stroke, Heart Attack & Aneurysm may result from hypertension & atherosclerosis
o a stroke (cardiovascular accident (CVA)) can result in paralysis or death; a cranial arteriole bursts or is blocked by an embolus (¯ O2 & nutrients to brain)
o warning symptoms that foretell stroke include: numbness in hands or face, difficulty speaking, blindness in one eye, etc.
o a myocardial infarction (MI or heart attack) occurs when a portion of heart muscle dies due to a lack of O2
o a partially blocked coronary artery (due to thromboembolism) causes angina pectoris causing pains or a flash of burning
o nitroglycerin and related drugs dilate the blood vessels and relieve pain
Blood: composed of plasma (fluid) and formed elements (cells and platelets)
- plasma contains water and many types of molecules, including nutrients, wastes, salts, and proteins
- salts & proteins buffer blood (keep pH near 7.4) and maintain blood osmotic pressure
- plasma proteins include blood clotting factors & transport proteins
o lipoproteins that transport cholesterol are globulins
o albumin transports bilirubin, a breakdown product of hemoglobin
- Formed Elements: red blood cells (RBCs), white blood cells (WBCs), and platelets
o Red blood cells (erythrocytes) are small biconcave disks
§ when mature, RBCs lack a nucleus and contain hemoglobin
§ there are 6 million RBCs per mm3 of whole blood
§ each RBC contains about 250 million hemoglobin molecules
· hemoglobin contains four globin protein chains, each with an iron-containing heme group
· the iron atom of a heme group binds with an O2 molecule
· anemia is either a lack of enough RBC or insufficient hemoglobin; an individual suffers from a tired, run-down feeling
§ RBCs are manufactured in the red bone marrow of the skull, ribs, vertebrae, and the ends of long bones
§ erythropoietin produced in kidneys stimulates production of red blood cells; as a drug it helps people with anemia
§ red blood cells have a life span of about 120 days; then they are destroyed chiefly in liver and spleen
· the iron is recovered and returned to bone marrow where it is reused
· the heme is broken down and are excreted by the liver as bile pigments
o White blood cells (leukocytes) are larger than RBCs and have a nucleus
§ granular leukocytes contain cytoplasmic granules and have a lobed nucleus
· neutrophils have granules that stain slightly pink; they are amoeboid, spherical cells that readily squeeze through capillary walls and phagocytize foreign material
· eosinophils have granules that take up the red dye eosin
· basophils have granules that take up a basic dye, staining them deep blue
· a newly discovered stem cell growth factor (SGF) increases the production of all WBCs, which helps patients with low immunity
§ agranular leukocytes lack granules and have a circular or indented nucleus
· monocytes are amoeboid and able to enter tissues where they transform into macrophages that release WBC growth factors and kill bacteria
· lymphocytes play a key role in fighting infection and include two types
o T cells are lymphocytes that directly attack virus-infected cells
o B cells are stimulated to produce antibody against one type of antigen
o an antigen is a substance that stimulates production of antibodies
o antibodies combine with antigens to promote their phagocytosis
o a person is actively immune when many B cells produce specific antibody for an infection
- Platelets (thrombocytes) result from fragmented giant cells (megakaryocytes) in the bone marrow; blood contains 150,000–300,000 platelets per mm3
o platelets are involved in blood clotting or coagulation
o at least 12 clotting factors in the blood participate in blood clotting
o hemophilia is an inherited deficiency of one of the clotting factors; minor bumps can cause internal bleeding; bleeding into the brain causes death in hemophilia
o vitamin K is necessary to produce prothrombin; deficiency of vitamin K causes hemorrhagic disorders
o Blood Clotting: when a blood vessel is damaged, platelets clump at the site of the puncture and partially seal the leak
o platelets and nearby cells release a clotting factor called prothrombin activator, which along with calcium ions, converts prothrombin to thrombin
o thrombin is an enzyme that cleaves a fibrinogen molecule to form fibrin
o fibrin threads wind around the platelet plug and provide a framework for a clot
o RBCs are trapped within the fibrin threads, making the clot appear red
o when blood vessel repair is initiated, plasmin destroys fibrin and restores fluidity
o serum is plasma without fibrinogen (can form by clotting blood in test tube)
- Capillary Exchange: two forces control movement of fluid through capillary walls
o osmotic pressure tends to cause water to move from tissue fluid to the blood
o blood pressure tends to cause water to move from the blood to tissue fluid
o at the arterial end of a capillary, blood pressure is higher than osmotic pressure: water exits and moves into tissues
o along the capillary, O2 and nutrients diffuse out into the tissue fluid, while CO2 and other metabolic wastes diffuse into the capillaries from the tissue fluid
o blood and tissue fluid exchange materials by diffusion through capillary walls
o at the venule end, osmotic pressure is higher than blood pressure and water moves back into blood; almost the same amount of fluid that left the capillary returns to it; there is always some excess tissue fluid collected by the lymphatic capillaries
o lymph returns to the systemic venous blood when lymphatic vessels enter the subclavian veins in the shoulder
o precapillary sphincters shunt blood along various pathways
o through capillary dilation and constriction, blood also distributes heat to body parts and conserves heat when cold
Chapter 35 Lymph Transport & Immunity
Lymphatic System: consists of lymphatic vessels and lymphoid organs
- 3 major functions:
o lymphatic vessels take up excess tissue fluid and return it to the bloodstream
o lacteals receive lipoproteins at the intestinal villi and the lymphatic vessels transport these fats to the bloodstream
o lymphatic system helps defend the body against disease
- lymphatic vessels resemble veins in structure & function - the movement of fluid is dependent upon skeletal muscle contraction and valves to prevent backflow
- the lymphatic system is a one-way system that begins with lymphatic capillaries
o they take up fluid that has diffused out of the capillaries and not been reabsorbed
o excess tissue fluid produced or not absorbed will result in edema (swelling)
- once tissue fluid enters the lymphatic capillaries, it is called lymph
- lymphatic capillaries join as lymphatic vessels that merge to enter one of two ducts
o the larger thoracic duct serves the lower extremities, abdomen, and arm, head, neck, and thoracic region of the left side; it empties into the left subclavian vein
o the right lymphatic duct is smaller serves the right arm, the right side of the head and neck, and the right thoracic region; it empties into the right subclavian vein
- Lymphoid Organs: lymph nodes, spleen, thymus gland, and the red bone marrow
o lymph nodes are small (about 1–25 mm) ovoid or round masses of lymphoid tissue located along lymphatic vessels
§ a lymph node has two regions: the outer cortex and the inner medulla
§ the cortex contains nodules where lymphocytes fight off pathogens
§ macrophages are concentrated in the medulla and cleanse the lymph
§ lymph nodes cluster in certain regions of the body (inguinal nodes in the groin and axillary nodes in the armpits)
o the tonsils are located in a ring around the pharynx
§ the pharyngeal tonsil or adenoids are on posterior wall above the soft palate
§ the larger palatine tonsils are on either side of the posterior oral cavity; they are most apt to be the first to be infected
o the spleen is located in the upper left abdominal cavity just below the diaphragm
§ a capsule divides the spleen into lobules containing sinuses filled with blood
§ a spleen nodule contains the following:
· red pulp contains red blood cells, lymphocytes, and macrophages; it helps to purify blood that passes through by removing microorganisms and worn-out or damaged red blood cells
· white pulp contains mostly lymphocytes
· if the spleen ruptures due to injury, it can be removed; its functions are assumed by other organs
· however, a person without a spleen is more susceptible to infections
o the thymus gland is located along the trachea behind the sternum in the upper thoracic cavity; it is larger in children and may disappear completely in old age
§ it is divided into lobules by connective tissue; lobules are the site of T lymphocyte maturation
§ the interior (medulla) of each lobule consists mostly of epithelial cells which produce thymic hormones (e.g., thymosin), that aid maturation of T cells
o the red bone marrow is the origin for all blood cells including all leukocytes that function in immunity
§ stem cells are pluripotent cells that differentiate into various blood cells
§ most bones of a child have red bone marrow but in adults, red bone marrow is only in skull, sternum, ribs, clavicle, pelvic bones and vertebral column
§ red bone marrow consists of reticular fibers produced by reticular cells packed around thin-walled sinuses
§ differentiated blood cells enter the bloodstream at these bone sinuses
Nonspecific Defenses
- Immunity is the ability to defend against infectious agents, foreign cells, and abnormal cancer cells; immunity includes both nonspecific and specific defenses
o the four nonspecific defenses include barrier to entry, inflammatory reaction, natural killer cells, and protective proteins
- Barriers to Entry: skin and the mucous membranes lining the respiratory, digestive, and urinary tracts are mechanical barriers
o oil gland secretions inhibit the growth of bacteria on the skin
o ciliated cells lining the upper respiratory tract sweep mucous and particles up into the throat to be swallowed
o the stomach has a low pH (1.2–3.0) that inhibits the growth of many bacteria
o the normal harmless bacteria that reside in the intestine or vagina prevent pathogens from colonizing
- Inflammatory Reaction: a series of events that occurs following tissue damage
o the inflamed area has four symptoms: redness, pain, swelling, and heat
o when tissue damage occurs, tissue cells and mast cells (like basophils in blood) release chemical mediators, such as histamine and kinins
o kinins and histamine cause vasodilation and increased permeability of capillaries
o enlarged capillaries produce redness and a local increase in temperature
o the swollen area and the kinins stimulate free nerve endings, causing pain
o neutrophils and monocytes migrate by amoeboid movement to the site of the injury; they escape from the blood by squeezing through the capillary wall
o when monocytes enter tissues, they differentiate into macrophages that ingest huge amounts of pathogens
o macrophages vastly increase leukocyte numbers by releasing colony-stimulating factors, which stimulate the production of WBCs
o pus is the accumulation of dead & living WBCs, tissue, cells, and bacteria
o aspirin, ibuprofen, and cortisone are anti-inflammatory agents that counter the chemical mediators of inflammation
- Natural Killer Cells kill virus-infected cells and tumor cells by cell-to-cell contact; they lack any specificity or memory
- Protective Proteins
o the complement system is a number of plasma proteins designated by the letter C and a subscript; it ³complements² certain immune responses
§ it amplifies an inflammatory reaction by attracting WBCs to site of infection
§ some complement binds to antibodies already on the surface of pathogens, thereby increasing the probability that pathogens will be phagocytized by a neutrophil or macrophage
§ some complement proteins form a membrane attack complex that produces holes in bacterial cell walls and plasma membranes; fluids and salts then enter to the point where the cell bursts
o interferon is a protein produced by virus-infected animal cells
§ interferon binds to the receptors of noninfected cells, producing substances interfering with viral replication
§ interferon is species-specific; only human interferon can be used in humans
Specific Defenses - activate against a specific antigen
- antigens are foreign substances, protein or polysaccharide, that stimulate immune system to react (may be on the surface of viruses, bacteria, cancer cells, foreign cells)
- the immune system can tell ³self² from ³nonself.²
- lymphocytes have antigen receptors that bind to antigen (like a lock and key)
- immunity usually lasts for some time; we do not ordinarily get the same illness twice
- specific immunity is primarily the result of the action of B cells and T cells
o B lymphocytes mature in the bone marrow; T lymphocytes mature in the thymus
o B lymphocytes (B cells) give rise to plasma cells that produce antibodies
o T lymphocytes either kill cells with foreign antigens or regulate immune response
- B Cells and Antibody-Mediated Immunity (Humoral Immunity)
o each type of B cell carries a specific antibody as a membrane (surface) receptor
o clonal selection: B cells in lymph nodes & spleen that encounter antigens are activated to divide, forming a clone of plasma cells producing the same antibody
§ B cells are also stimulated to clone by helper T cell secretions
§ some cloned B cells do not participate in antibody production but remain in the blood as memory B cells
§ apoptosis: programmed cell death; once the threat of infection has passed, development of new plasma cells ceases; those present die
- Antibody Structure: antibodies are Y-shaped proteins with two arms
o each arm has a ³heavy² and ³light² polypeptide chain
o each chain has a constant region and a variable region; the constant region is the same for a class of antibody; the variable region forms the antigen binding site
o the antigen-antibody complex (immune complex) marks the antigen for destruction by being phagocytes, or it may activate complement
o complement may attach to surface antigens on pathogens to enhance phagocytosis
- 5 classes of circulating antibodies or immunoglobulins (Igs)
o IgG: major type in blood; binds to pathogens and toxins & activates complement
o IgM: pentamer; first antibody class secreted upon infection; activates complement
o IgA: dimer; the main type of antibody in bodily secretions
o IgD: antigen receptor on immature B cells
o IgE: involved in immediate allergic reactions; binds basophils & mast cells to release histamine
- T Cells and Cell-Mediated Immunity
o like B cells, T cells have unique antigen receptors
o T cell receptors cannot recognize free antigen; antigen must be presented to them by an antigen-presenting cell (APC)
o when an antigen-presenting cell presents a viral or cancer cell antigen, the antigen is first linked to an MHC protein; together they are presented to a T cell
o human MHC proteins = HLA (human leukocyte antigens); they are self proteins
o HLA proteins are typed to match to increase chances of successful transplants
o clonal expansion of T cells following antigen recognition on APC:
§ helper T cells produce cytokines stimulating immune cell activity
§ cytotoxic T cells destroy cells that possess the antigen with HLA
§ the few T cells that do not undergo apoptosis survive as memory cells
o self-tolerance: apoptosis in the thymus of T cells that recognize self antigen; if apoptosis does not occur, T-cell cancers result (i.e., lymphomas and leukemias)
- Types of T Cells
o cytotoxic T cells destroy antigen-bearing cells (virus-infected or cancer cells)
§ perforin molecules perforate a plasma membrane, causing the cell to burst
o helper T cells release cytokines to improving the response of other immune cells
§ cytokines stimulate helper T cells to clone, stimulate macrophages to phagocytize, stimulate B cells to become antibody-producing plasma cells
§ HIV, the cause of AIDS, infects primarily helper T cells
o memory T cells remain and can speed an immune reaction to same antigen
Immunity in Other Animals
- nonspecific immunity in invertebrates: phagocytes have been observed around a thorn in a starfish; antibacterial peptides in silkmoths
- Specific defense mechanisms only evolved among vertebrates
Induced Immunity
- Active Immunity: production of antibodies following infection or vaccination
o immunization: vaccines use avirulent (inactivated or heat killed) pathogens or pathogen proteins to stimulate antibody production
o the immune response is measured by antibody level in serum - the antibody titer
o primary response: after the first exposure, titer slowly rises, playeaus & declines
o secondary response: after second exposure, titer rises rapidly (³booster²); the high antibody titer should now prevent any disease symptoms upon infection
o memory B and T cells respond quickly to lower doses of antigen
- Passive Immunity: an individual is given prepared antibodies to combat a disease
o it is short-lived because antibodies are not made by individual¹s own B cells
o newborn infants gain immunity from mother¹s IgG antibodies that cross placenta
o breast-feeding also promotes passive immunity - IgA antibodies in milk
o passive immunity is needed when patient is in immediate danger from an infectious disease/toxin - given gamma globulin injection (serum containing IgG)
- Cytokines and Immunity: cytokines are signaling molecules produced by either lymphocytes, monocytes or other cells
o cytokines stimulate white blood cell formation; they may work as adjunct therapy for cancer and AIDS
o interferon and interleukins improve the ability of T cells to fight cancer
o cancer cells with altered proteins on their cell surface should be attacked by cytotoxic T cells
o cellular immunotherapy: T cells are removed from a patient and cultured in the presence of interleukin; the T cells are re-injected into the patient; doses of interleukin then maintain the killer activity of the T cells
o interleukin antagonists may help prevent skin or organ rejection, autoimmune diseases, and allergies when used as adjuncts for vaccines
- Monoclonal antibodies: pure antibody preparations produced from a single B cell clone used in clinical applications
o monoclonal antibodies can be used for quick, reliable diagnosis of pregnancy
o they identify infections, and can distinguish cancerous from normal cells and can be used to carry isotopes or toxic drugs to kill tumors
Immunity Side Effects
- allergies are hypersensitivities to everyday substances such as pollen
- a response to these antigens, called allergens, usually involves tissue damage
- immediate allergic responses: occur within seconds of contact with an allergen; coldlike symptoms are common
o when an allergen binds IgE antibodies on mast cells or basophils, they release large amounts of histamine and other substances, which cause the cold symptoms
o a severe systemic reaction is anaphylactic shock, a sudden drop in blood pressure
o allergy shots sometimes prevent the onset of allergic symptoms - injections of the allergen cause the body to build up high quantities of IgG antibodies, which combine with allergens before they have a chance to bind IgE antibodies
- delayed allergic responses: initiated by sensitized memory T cells contacting allergen
o the allergic response is regulated by the cytokines secreted by both T cells and macrophages
o the tuberculin skin test is an example: positive test shows prior exposure to TB bacilli but requires some time to develop reddening of tissue
- Blood Typing: 4 blood types are designated by antigens present on red blood cells
o individuals have naturally-occurring antibodies to blood type proteins not present on their blood cells
o RBCs with a particular antigen agglutinate (clump) when exposed to corresponding antibodies (transfusion reaction)
o recipients with type AB blood (universal recipient) can receive any type blood
o recipients with type O blood (universal donor) cannot receive A, B, or AB
o recipients with type A blood can receive A or O; type B blood can receive B or O
- Rh System: Rh positive (Rh +) has the Rh factor on red blood cells; Rh negative (Rh -) lacks the Rh antigen on RBCs
o Rh - individuals make antibodies to Rh factor if exposed to Rh + blood
o Rh factor is particularly important during pregnancy
§ hemolytic disease of the newborn may result from Rh - mother & Rh + father
§ the child¹s Rh + RBCs can cause the mother to produce anti-Rh antibodies, which cross the placenta and destroy the RBCs of the Rh + child
§ Rho-Gam (anti-Rh immunoglobulin) can be given to Rh - women midway through the first pregnancy or no later than 72 hours after giving birth to an Rh + child to prevent mother¹s immune response to child¹s RBCs
- Tissue Rejection: occurs because cytotoxic T cells cause disintegration of foreign tissue; this is a correct distinguishing between self and nonself
o selection of compatible organs (match donor & recipient HLA) and administration of immunosuppressive drugs prevent tissue rejection
o cyclosporine and tacrolimus act by inhibiting the response of T cells to cytokines
- Autoimmune Diseases: result when cytotoxic T cells or antibodies mistakenly attack the body¹s own cells as if they bear foreign antigens
o the cause is not known but autoimmune diseases sometimes appear following recovery from an infection
o in myasthenia gravis, the neuromuscular junctions do not work properly and muscular weakness results
o in multiple sclerosis (MS), the myelin sheath of nerve fibers is attacked
o persons with systemic lupus erythematosus present many symptoms before dying from kidney damage
o heart damage from rheumatic fever and type I diabetes are autoimmune diseases
o there are no cures for autoimmune diseases but they are controlled by drugs
Chapter 36: Digestive Systems & Nutrition
Digestive Tracts
- General Digestion
o most animals need to digest food into small molecules that can cross plasma membranes; the nutrients are absorbed & nondigestible waste eliminated
o digestion provides the energy needed to carry out routine metabolic activities and maintain homeostasis
- Incomplete Versus Complete Tracts
o planarians are carnivores with an incomplete gut; the digestive system contains only a mouth, a pharynx, and an intestine
§ planaria feed largely on smaller aquatic animals - the pharynx extends beyond the mouth to take up food; digestion is begun by enzymes extracellularly & completed in digestive cavity; nutrients diffuse to nearby cells
§ the tapeworm lacks a digestive system; they absorb food through a body wall
o the earthworm has a complete gut; the digestive system is composed of a tube with a mouth and an anus; different regions of the gut have specialized functions
§ earthworms feed on decayed organic matter in the soil - a muscular pharynx draws in food; the crop stores food & the muscular gizzard has grinds food
- Continuous Versus Discontinuous Feeders
o clams are continuous feeders, often called filter feeders
§ water moves in through an incurrent siphon and ciliarry action moves particles to the labial palps which direct them into the mouth and into the stomach; enzymes from a digestive gland help amoeboid cells complete digestion
o marine fanworms are sessile filter feeders, while baleen whales are active filter feeders; baleen (fringe) filters small krill from water
o squids are an example of discontinuous feeders
§ two of the ten arms around the head seize the prey and bring it to the mouth where beaklike jaws and a radula (toothy tongue) reduce the food to pieces; the esophagus leads to a stomach that holds food until digestion is complete
§ discontinuous feeders require a storage region in their gut
o Adaptation to Diet
§ animals are herbivores (eat plants) or carnivores (eat animals) or omnivores (eat both)
§ invertebrates demonstrate a wide variety of diets
§ mammal dentition differs according to their mode of nutrition
· omnivore teeth include incisors (shearing), canines (tearing), premolars (grinding), and molars (crushing)
· herbivores have large, flat premolars and molars for grinding plant matter
· grazers (e.g., horses) have sharp incisors for clipping off grass and leaves; some have a rumen to digest grasses; partially digested cud is rechewed
· herbivores may have long and complex digestive tracts and bacteria or protozoa in their digestive tracts that can digest cellulose
· carnivores¹ pointed incisors and canines tear off small pieces to swallow; fewer molars for grinding and a shorter digestive tract with less specialization
Human Digestive Tract
- Human Digestion
o the human digestive tract is a complete tube-within-a-tube system
o each part of the digestive system has a specific function
o digestion of food is an extracellular process; enzymes are secreted into the digestive tract by nearby glands which never contain food themselves
o digestion requires production of hormones and the actions of the nervous system
- Mouth
o human dentition has many specializations because humans are omnivores
o food is chewed in the mouth & mixed with saliva - forms a bolus for swallowing
o 3 pairs of salivary glands secrete saliva by way of ducts into the mouth
§ salivary amylase is the enzyme that breaks down starch to maltose (sugar)
§ food is manipulated by a muscular tongue with touch and pressure receptors
§ taste buds are located on the tongue with some on the surface of the mouth
- The Pharynx and the Esophagus
o the digestive and respiratory passages join in the pharynx, and then separate
o during swallowing, the epiglottis covers the opening into the trachea as muscles move a bolus of food through the pharynx into the esophagus
o the esophagus is a muscular tube that moves food to the stomach by peristalsis
- Stomach
o the stomach stores liters of partially digested food
o the epithelial lining of the stomach has many gastric pits leading to gastric glands
o hydrochloric acid (HCl) lowers pH of the gastric contents to about 2, which stops amylase activity & promotes the activity of the stomach protease pepsin
§ this acid kills most bacteria and other microorganisms
o pepsin is a hydrolytic enzyme that acts on proteins to produce peptides
o a thick layer of mucus protects the wall of the stomach and the first part of the duodenum from HCl and pepsin
o ulcers: digestion of the stomach lining, usually by Helicobacter pylori bacteria
o the stomach produces a thick, soupy mixture called chyme
o cardiac (gastroesophageal) sphincter: a circular muscle valve that delivers chyme to the duodenum (first part of the small intestine) by a neural reflex
- Small Intestine
o the human small intestine is a coiled muscular tube about three meters long
o additional digestion of chyme is aided by secretions from liver and pancreas
o bile is secreted by liver & stored in gallbladder before being sent to duodenum
§ bile emulsifies fat to produce fat droplets that are more easily digested
§ bile contains bile salts made from cholesterol & bilirubin from hemoglobin
o pancreatic juice is released by pancreas through pancreatic duct to duodenum
§ contains digestive enzymes: proteases trypsin, chymotrypsin, carboxypeptidase; amylase, lipases & nucleases
§ also contains alkaline sodium bicarbonate to neutralize acidic chyme
o epithelial cells of villi produce intestinal enzymes that complete digestion
§ large molecules of carbohydrates, proteins and fats are broken into small molecules (glucose, amino acids, fatty acids) absorbed by villi
o absorption by villi: projections called villi line the intestinal wall; the surface cells have microvilli that increase surface area for absorption
§ each villus has blood vessels & a lymphatic lacteal that aids in fat absorption
§ sugars & amino acids enter villi cells and are absorbed into bloodstream
§ absorption involves diffusion and active transport requiring energy
- Control of Digestive Juices
o gastrin produced by cells in the gastric glands stimulates HCl secretion and increases gastric motility
o secretin and cholecystokinin (CCK) produced by the duodenal wall stimulate the pancreas to increase pancreatic juice and the liver to increase the output of bile
o gastric inhibitory peptide (GIP) from the duodenal wall inhibits both gastric gland secretion and stomach motility
- Accessory Organs
o Pancreas: extends across abdomen just below the stomach
§ as endocrine gland, it secretes the hormones glucagon and insulin into blood
§ as exocrine gland, it secretes pancreatic juice (see above)
o Liver: large glandular organ; fills upper abdominal cavity, just below diaphragm
§ the liver has numerous functions: 1) detoxifies blood by removing poisons; 2) synthesizes plasma proteins including albumin & fibrinogen. 3) destroys old red blood cells and converts hemoglobin to bilirubin in bile. 4) produces bile stored in the gallbladder 5) stores glucose as glycogen and breaks down glycogen to maintain a constant blood glucose concentration. 6) produces urea from amino groups and ammonia; urea is excreted by kidneys
§ blood vessels from both the large and small intestines lead to the liver as the hepatic portal vein
§ deamination: removal of amino groups to convert amino acids into glucose
§ liver disorders
· jaundice: yellowish skin due to a large amount of bilirubin in blood (in hemolytic jaundice, the RBCs are broken down; in obstructive jaundice, there is blockage of the bile ducts (gallstones) or damage to liver cells)
· viral hepatitis is a viral liver infection
o hepatitis A results from eating contaminated food; hepatitis B and C are spread by blood transfusions, kidney dialysis, and unsterile needle use; all three can be caused from sexual contact
· cirrhosis is a chronic disease where the liver tissue is replaced by fatty tissue and then scar tissue; alcoholics provide too much alcohol for the liver to break down
- Large Intestine
o has four parts: the cecum, colon, rectum, and anal canal
o appendix: wormlike projection extending from cecum; contains immune cells
§ if infected appendix bursts, it results in abdominal infection (peritonitis)
o the large intestine functions in ion regulation, absorbing salts plus water
o inadequate water reabsorption can lead to diarrhea, dehydration & ion loss
o vitamin K (helps form blood clotting factors) is produced by intestinal bacteria
o the large intestine terminates at the anus, an external opening
o feces: waste material (~ 75% water and 25% solid (includes intestinal bacteria)
o intestinal polyps: small growths arising from epithelial lining
§ whether they are benign or cancerous, polyps can be removed surgically
§ a low-fat, high-fiber diet promotes regularity and may provide protection against mutagenic agents
Nutrition: a balanced diet, required for good health, includes a properly proportioned variety of foods
- Vitamins: essential organic compounds the body requires for metabolic activities
o most vitamins function as coenzymes (assist enzyme in its activity)
§ B vitamins niacin & riboflavin act as coenzymes NAD+ & FAD
o most vitamins must be obtained from diet; exceptions are vitamin D made in the skin (see below), vitamin K & some B vitamins synthesized by intestinal bacteria, & vitamin A can be synthesized from beta-carotene (orange-yellow pigment in some vegetables)
o water-soluble vitamins (vitamin C & B vitamins): absorbed by GI tract with water
o fat-soluble vitamins (vitamins A, D, E & K): bind to ingested lipids & absorbed along with their digestion products
o balanced diet necessary to obtain all required vitamins
o vitamins A, C, & E (in fruits & vegetables) are antioxidants that neutralize harmful free radicals (e.g.: superoxide radical O3- formed during metabolism)
§ free radicals damage DNA, proteins, and other molecules by donating an electron; this may cause cancer or plaque in arteries
o vitamin A is a precursor for the visual pigment that prevents night blindness
o vitamin D: skin cells contain a precursor cholesterol molecule converted to vitamin D by brief UV light exposure; it¹s then modified in the kidneys and then in the liver until it becomes calcitriol
§ calcitriol promotes absorption of calcium by the intestines
§ the lack of vitamin D leads to rickets in children; poor mineralization of the skeleton causes bowing of the legs
§ most milk is fortified with vitamin D to prevent rickets
- Minerals
o macrominerals (e.g., calcium, phosphorus) required in amounts over 100 mg/day
§ they are found in cells, body fluids and structural components of tissues
§ calcium is needed to build bones and teeth and for nerve conduction and muscle contraction
o microminerals (e.g., zinc, iron) recommended in amounts less than 20 mg/day
§ iron is needed to produce hemoglobin; adult females need more due to menstrual loss of blood
§ iodine is used to produce thyroxin, a hormone of the thyroid glands
§ minute amounts of molybdenum, selenium, chromium, nickel, vanadium, silicon, and arsenic are essential
§ calcium supplements (1,000–1,500 mg calcium/day is recommended) & exercise have been shown to slow bone loss in the elderly
§ the recommended daily intake of sodium is 400–3,300 mg; average American intake is 4,000–4,700 mg
§ a high sodium intake has been linked to hypertension in some people
Chapter 37: Respiratory Systems
Gas Exchange Surfaces
- respiration is the sequence of events that results in gas exchange between the environment and the body¹s cells
o breathing includes inspiration (bringing air in) and expiration (moving air out)
o external respiration involves gas exchange with the external environment at a respiratory surface
o internal respiration in more complex animals involves gas exchange between the blood and tissue fluid
- Diffusion Accompanies Gas Exchange: an effective gas exchange region must be moist, thin, and large in relation to the size of the body
o small animals are shaped to allow their surface to allow adequate gas-exchange
o larger animals are complex and have a specialized gas-exchange surface
o diffusion improves with vascularization; gas delivery to cells is promoted if the blood contains hemoglobin
- Water Environments
o it is more difficult for animals to obtain O2 from water than from air (water fully saturated with air contains only a fraction of the O2 as the same volume of air)
§ water is more dense than air; therefore aquatic animals must use more energy to breathe (fishes use up to 25% of their energy to breathe; land mammals use only 1–2% of their energy output to breathe)
o hydras and planaria have a large surface area in comparison to their size - gas exchange occurs directly across their body surface
o a tubular shape and vascularized parapodia extensions in polychaete worms provide surface areas for diffusion
o aquatic animals often pass water over gills
§ gills are finely divided vascularized outgrowths of outer/inner body surface
§ ventilation is the result of the combined action of the mouth and gill covers
§ when the mouth is open, the opercula are closed and water is drawn in; the mouth then closes and opercula open, drawing water from the pharynx through gill slits
§ blood in capillaries of gill lamellae flows in a direction opposite to that of water; this countercurrent flow of water and blood increases the amount of O2 and CO2 exchanged and maximizes dissolved O2 drawn in
- Land Environments
o air is a richer source of O2 than water but air dries out the wet respiratory surfaces; humans lose 350 ml of water per day at 50% relative humidity
o the earthworm is an invertebrate that uses its body surface for respiration
o terrestrial insects utilize tracheal systems - oxygen enters at spiracles, valvelike openings; the tracheae branch to end in tracheoles or air sacs located near major muscles to keep air moving in and out of the trachea
§ tracheae transport O2 to cells; circulatory system has no role in gas transport
o terrestrial vertebrates have evolved lungs for gas exchange
§ lungs are vascularized outgrowths of the lower pharyngeal region
§ amphibian lungs are simple sacs connected to the external environment by two bronchi which connect to a short trachea
· amphibian gas exchange occurs through a moist skin (frogs use positive pressure to force air in)
§ reptiles, birds, and mammals use negative pressure to move air into lungs
· ribs are raised and the muscular diaphragm is flattened to expand the lungs
· as the thoracic cavity expands, the lung volume increases; air flows in due to the difference in air pressure
· by lowering the ribs, pressure is exerted on the lungs, which forces air out
§ the lungs of reptiles, amphibians and mammals are not completely emptied during each breathing cycle - incomplete ventilation, entering air mixes with used air in lungs; conserves moisture but decreases gas-exchange efficiency
§ high oxygen requirements of flying birds requires complete ventilation system
Human Respiratory System: includes everything that conducts air to and from the lungs; the lungs lie deep within the thoracic cavity for protection from drying out
- air moves into nose, then flows past pharynx to trachea, bronchi and lungs
- this process filters debris, warms air, and adds moisture
- the trachea and bronchi are lined with cilia that beat upward carrying mucus, dust, and any food particles that went the wrong route
- the hard and soft palates separate nasal cavities from mouth
- the air and food passages cross in pharynx; the real danger of choking is offset by providing an alternative path for breathing during congestion, and also increasing air intake during exercise
- air flows past the pharynx through the glottis and into the larynx, which is protected by the epiglottis
- at the edges of the glottis are vocal cords; as air passes across them, these tissues vibrate creating sounds
- from the larynx, air flows down the trachea to the bronchi
o the larynx is held open by cartilage that forms the Adam¹s apple
o the trachea walls are reinforced with C-shaped rings of cartilage
o as food is swallowed, the larynx rises and the glottis is closed by the epiglottis
o uvula of soft palate covers entrance to nasal passages; this directs food downward
- the trachea divides into two bronchi; C-rings of cartilage diminish as bronchi branch
- within the lungs, each bronchus branches into numerous bronchioles that conduct air to alveoli (microscopic air sacs)
- Breathing: humans breathe using negative pressure similar to all other mammals
o during inhalation, lowering the diaphragm and raising the ribs forms a negative pressure by increasing the volume of the thoracic cavity; the air under greater outside pressure flows into the lung
o increases in the CO2 and H+ concentrations in the blood are the primary stimuli increasing the breathing rate
§ chemoreceptors in aorta and carotid arteries are sensitive to increases in CO2 and H+ concentrations of blood, but minimally sensitive to decreases in O2
o information from these goes to a respiratory center in the medulla oblongata increasing the breathing rate when CO2 or H+ concentrations increase
- Gas Exchange and Transport
o gas exchange between the air in the alveoli and the blood in the pulmonary capillaries is primarily by diffusion
o CO2 diffuses from higher concentration in the blood across the walls of alveolar capillaries to lower concentration in the air in the alveoli
o oxygen diffuses from higher concentration in alveoli across the walls of the alveolar capillaries to the lower concentration in blood
- Transport of Oxygen and Carbon Dioxide
o most O2 entering pulmonary capillaries combines with hemoglobin (Hb) to form oxyhemoglobin (HbO2)
o each hemoglobin molecule has four globin polypeptide chains; each chain folds over an iron-containing heme; each RBC has 250 million hemoglobin molecules
o the iron atom of a heme group loosely binds with an O2 molecule
o partial pressure is the pressure exerted by a particular gas in a mixture of gases
o at a normal partial pressure of O2 in lungs, hemoglobin becomes nearly saturated with O2; but at the O2 partial pressures in the tissues, oxyhemoglobin quickly unloads much of its O2
o the acid pH and warmer temperature of the tissues also promote this dissociation
o in tissues, some hemoglobin combines with CO2 to form carbaminohemoglobin
o however, most CO2 is transported in form of bicarbonate ion (HCO3-)
o CO2 + H2O « H2CO3 « H+ + HCO3- (carbonic acid/bicarbonate buffer in blood)
o carbonic anhydrase, an enzyme in red blood cells, speeds this reaction
o release of H+ ions could drastically lower blood pH; however, the hydrogen ions are absorbed by the globin portions of hemoglobin and the HCO3- diffuses out of the RBCs and into the plasma
o hemoglobin combines with H+ ions as reduced hemoglobin (HHb); HHb plays a vital role in maintaining normal blood pH
o as blood enters the pulmonary capillaries, most of the CO2 is in plasma as HCO3; the little free CO2 remaining diffuses out of the blood and into alveoli
o any decrease in plasma CO2 concentration causes the reverse of the above reaction as hemoglobin unloads H+ and more CO2 is produced
Respiration and Health
- Upper Respiratory Tract Infections (URI)
o the upper respiratory tract consists of nose, pharynx and larynx
o strept throat is a severe infection caused by the bacteria Streptococcus pyogenes resulting in high fever and difficulty swallowing; it can lead to systemic infection
o sinusitis is infection of the sinuses; accompanies 1–3% of URI
o tonsillitis occurs when the tonsils and adenoids of the pharynx are inflamed as a first line of defense
o laryngitis is an infection of the larynx causing hoarseness and an inability to talk
o persistent hoarseness without any URI is one of the warning signs of cancer
- Lower Respiratory Tract Disorders
o acute bronchitis is an infection of the primary and secondary bronchi and is usually preceded by a viral URI
o pneumonia is usually caused by a bacterial or viral lung infection
§ the bronchi and alveoli fill with fluid; can be localized in specific lobules
§ AIDS patients are subject to a rare form of pneumonia caused by the protozoan Pneumocystis carinii
o pulmonary tuberculosis (TB) is caused by the bacillus bacterium Mycobacterium tuberculosis
§ it is a highly contagious disease that create capsules called tubercules in lungs
§ a TB skin test is a highly diluted extract of the bacilli injected into the patient¹s skin; if a person has been exposed, the immune response will cause an area of inflammation; a chest X ray detects active tubercles
§ teatment involves 6-12 month course of antibiotics to kill bacteria
§ resurgence has accompanied increases in AIDS, homeless, and poor; the new strains are resistant to standard antibiotics
- Pulmonary Disorders
o Pulmonary Fibrosis results in a build up of fibrous connective tissue; so the lungs cannot inflate properly
§ caused by inhaling particles of silica, coal dust, fiberglass and asbestosThese agents
o Chronic Bronchitis: airways are inflamed and filled with mucus; often a cough brings mucus up; the bronchi degenerate, losing cilia and normal cleansing action and making an infection likely
§ smoking cigarettes and cigars is most common cause; but other pollutants also
o Emphysema is a chronic and incurable disorder; it involves distended and damaged alveoli; the lungs often balloon due to trapped air
§ emphysema is often preceded by chronic bronchitis
§ reduced lung elasticity & narrow airways makes expiration difficult
§ insufficient O2 reaches the heart and the brain; can lead to heart condition
§ lack of oxygen to the brain makes patient feel depressed, sluggish, irritable
§ exercise, drug therapy, and supplemental oxygen may relieve the symptoms and slow the progress
o Asthma is a disease of the bronchi and bronchioles; it causes wheezing, breathlessness and a cough
§ the airways are sensitive to specific allergens (e.g., pollen, dust, cold air, etc.)
§ exposure to the irritant causes bronchial inflammation and muscle spasms reducing the diameter of the airways
§ special Inhalers can control the inflammation and sometimes prevent an attack; other inhalers can stop muscle spasms
o Lung Cancer: one of most common cancers & causes of death due to smoking
§ lung cancer develops in the lung tissue in steps: cells lining the bronchi callus & lose cilia (dust & dirt get to lungs); tumor cells with atypical nuclei form in lungs; if tumor cells break free and penetrate other tissue (metastasis), the cancer spreads
§ a tumor may block bronchus, cutting off the air supply to the lungs; the entire lung then collapses; infections can cause pneumonia or lung abscess
§ the only treatment is surgery (pneumonectomy) where a lobe or whole lung is removed before the cancer has been able to spread