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