Major Endocrine Glands:
Pituitary Gland (Hypophysis): connected to hypothalamus by stalk called infundibulum
- Anterior Pituitary (Adenohypophysis):
o Growth Hormone (GH): stimulates cell division in most cells (major targets are bone & skeletal muscle)
o Prolactin (PRL): stimulates milk production by mammary glands of breasts
o Follicle-stimulating hormone (FSH): stimulates gamete production in gonads (ovaries & testes)
o Leutinizing hormone (LH): promotes production of gonadal hormones (testosterone, estrogen & progesterone)
o Thyroid-stimulating hormone (TSH): stimulates normal development of & secretion of hormones from thyroid gland
o Adrenocorticotropic hormone (ACTH or corticotropin): stimulates release of corticosteroid hormones from adrenal cortex
- Posterior pituitary (Neurohypophysis): receives & stores hormones produced by hypothalamus for later release
o Oxytocin: stimulates uterine contraction during childbirth & milk ejection during nursing
o Antidiuretic hormone (ADH): stimulates kidney tubules to retain water
Thyroid Gland:
- Thyroid Hormone:
o Thyroxine (T4): major hormone released from thyroid follicles (contains 4 iodine molecules)
o Triiodothyronine (T3): (contains 3 iodine molecules); generally formed from T4 by cleaving an iodine molecule
- Calcitonin: produced by parafollicular cells (C cells) of thyroid gland
o lowers blood calcium levels by inhibiting osteoclasts & stimulating calcium uptake by bones
Parathyroid Glands: paired glands on posterior aspect of thyroid gland
- Parathyroid hormone (Parathormone or PTH): raises blood calcium levels by stimulating osteoclasts, enhancing absorption of calcium by kidneys, & increasing absorption of calcium by cells of intestine
o PTH activates the inactive form of vitamin D in the kidneys; vitamin D enhances absorption of calcium by intestine
Adrenal Glands (Suprarenal Glands): pyramid-shaped glands above kidneys
- Adrenal Cortex: releases corticosteroid hormones
o Mineralocorticoids: released primarily by cells of zona glomerulosa; regulate salt concentrations in extracellular fluids
§ Aldosterone: primary mineralocorticoid: enhances sodium (& water) reabsorption from kidney tubules
o Glucocorticoids: influence metabolism of body cells & help resist stressors
§ Cortisol (hydrocortisone) is major glucocorticoid (also cortisone & corticosterone)
§ Glucocorticoids conserve glucose during stress & also prevent water loss from cells into tissue fluids; used as anti-inflammatory agents
o Gonadocorticoids: secondary source of sex hormones; primarily androgens (testosterone), but also estrogens
- Adrenal medulla: releases catecholamines (norepinephrine & epinephrine)
o Release is stimulated by sympathetic nervous system (³fight or flight² response)
o Epinephrine: stimulates heart rate & metabolism
o Norepinephrine: influences peripheral vasoconstriction & blood pressure
Pancreas: releases insulin & glucagons from islets of Langerhans
- Insulin: released by beta cells of islets; lowers blood glucose levels by stimulating glucose storage & uptake of glucose by cells for energy
o Insulin deficiency may lead to diabetes mellitus
- Glucagon: raises blood glucose levels by stimulating glucose removal from glycogen storage deposits in liver cells & gluconeogenesis
Gonads: produce steroidal sex hormones
- estrogens & progesterone: produced by ovary cells; responsible for maturation of female reproductive organs & menstrual cycle
- testosterone: produced by cells of testes; responsible for maturation of male reproductive organs & sperm cell production
Pineal Gland: secretes melatonin
- melatonin appears to be involved in maintenance or sleep/wake (day/night) cycles
Thymus: secretes thymopoietins & thymosins; involved with normal development of T cells (lymphocytes)
Blood Components:
- plasma & formed elements (erythrocytes, leukocytes & platelets)
- hematocrit: % of total blood volume occupied by erythrocytes (normally between 42% and 47% ± 5%)
Blood Characteristics:
- pH of blood is maintained between 7.35 and 7.45 by carbonic acid-bicarbonate ion buffer system
- blood accounts for ~ 8% body weight
- blood volume in adults is normally 5-6 L in males and 4-5 L in females
Blood Functions:
- transport & distribution of oxygen & nutrients, carbon dioxide & metabolic waste, and hormones
- regulation of body temperature, normal pH and fluid volume in cells & tissues
- protection against blood loss (clotting) and infection (white blood cells)
Blood Plasma: fluid component of blood
- mostly (~ 90%) water
- contains over 100 different dissolved solutes, including:
o proteins: albumin, globulins, clotting proteins, etc.
o nutrients: sugars, amino acids, fatty acids, cholesterol, vitamins, etc.
o electrolytes: cations (positive ions) such as sodium, potassium, calcium & magnesium; anions (negative ions) such as chloride, phosphate & bicarbonate
o respiratory gases: oxygen & carbon dioxide
Formed Elements: erythrocytes, leukocytes & platelets
- Erythrocytes: red blood cells (RBCs)
o small cells; biconcave discs (flattened disc shape with thin, depressed centers – look like mini doughnuts)
o anucleate – RBCs have no nucleus
o function in gas transport
o most of contents of RBC (other than water) is the protein hemoglobin
o hematopoiesis (hemopoiesis): blood cell formation; occurs in red bone marrow (in adults, in bones of girdles & proximal epiphyses of humerus & femur)
o destruction of erythrocytes: RBCs last ~ 100-120 days in circulation
§ aged & damaged RBCs are broken down in small channels of the spleen, liver & marrow by macrophages
§ heme is broken from hemoglobin; iron is salvaged & stored and the remainder of the group is degraded to bilirubin (yellow pigment), which is picked up by the liver, converted into bile & excreted
§ globin chains are metabolized are broken down into amino acids for protein synthesis
- Leukocytes: white blood cells (WBCs)
o only formed elements with nucleus & normal organelles
o involved in immune responses; protect the body from damage by bacteria, viruses, parasites, toxins & tumor cells
o Granulocytes: WBCs with membrane-bound cytoplasmic granules
§ Neutrophils: most numerous WBCs (>50% of WBC volume)
· nucleus has from 3-6 lobes (also known as PMNs (polymorphonuclear leukocytes))
· phagocytic cells (kill bacteria & fungi by oxidation), chemically attracted to sites of inflammation
§ Eosinophils: ~ 1-4% of WBC population; about size of neutrophils
· nucleus with 2 lobes; large, red-staining granules
· digest invading parasitic flatworms & roundworms with digestive enzymes
· phagocytic; ingest immune complexes during allergic reactions
§ Basophils: ~ 0.5% of WBC population (rare); about size of neutrophils
· release histamine: inflammatory chemical - vasodilator & chemoattractant
o Agranulocytes: WBCs without visible granules
§ Lymphocytes: small, medium & large sizes
· T lymphocytes: fight virus-infected cells & tumor cells
· B lymphocytes: give rise to plasma cells that produce antibodies (immunoglobulins)
§ Monocytes: largest WBCs (2-3x size of RBCs)
· Large U or kidney-shaped nucleus
· differentiate into macrophages - phagocytic cells that destroy bacteria & help in immune response against viruses
o Leukopoiesis: WBC production
§ Hemocytoblast differentiates into either myeloid stem cell or lymphoid stem cell
· Myeloid stem cell differentiates into myeloblast or monoblast
o Myeloblast will form granulocytes
o Monoblast will form monocytes
· Lymphoid stem cell differentiates into lymphoblast, which will form lymphocytes
o Leukocyte disorders:
§ Leukemias: cancer of myeloid or lymphoid cell lines
§ Infectious mononucleosis: highly contagious viral infection
· caused by Epstein-Barr virus (EBV)
- Platelets: cytoplasmic fragments of megakaryocytes with granules containing blood-clotting enzymes
o sometimes referred to as thrombocytes
o stick together to form a plug to prevent blood loss in torn vessels
o Hemostasis: stoppage of bleeding from a torn blood vessel
§ Vascular spasms: result in vasoconstriction
§ Platelet plug formation: in response to blood vessel injury, platelets adhere to exposed collagen fibers surrounding vessel s
§ Coagulation (blood clotting): blood transformed from a liquid to a gel
· Thrombin catalyzes joining of fibrinogen molecules in plasma to form a fibrin mesh that seals vessel
o Clot retraction & repair: within 30-60 minutes after injury, platelets contract to pull ends of torn vessel closer together
o Fibrinolysis: removes unneeded clots after healing has occurred
§ Plasmin is an enzyme that digests fibrin, breaking down clot
Human ABO blood groups:
- type A blood individuals have A surface antigen; type B blood individuals have B surface antigen; type AB blood individuals have both A & B surface antigens; type O blood individuals have neither A nor B surface antigens
- type O blood is the universal donor
- type AB blood is the universal recipient
Lymphatic Vessels (Lymphatics): system of drainage vessels that collects excess protein-containing interstitial fluid (fluid between cells) & returns it to blood
- used to return fluid escaped from blood into tissue spaces back to blood
- lymph is interstitial fluid that has entered lymphatic vessels
- form one-way system; blood flows toward heart
- Lymph capillaries: occur almost everywhere blood capillaries occur (except bones & teeth, bone marrow, & central nervous system (uses CSF to collect fluid))
- Lymph transport: slow transport; lymph is not pumped, but flows by smooth muscle contraction in the walls of the vessels, pressure changes in the thorax during breathing & valves to prevent backflow
o Also, bundling with blood vessels helps along with movements in adjacent tissues
Lymphoid Cells:
- Lymphocytes: T cells & B cells
o T cells direct immune response against virally-infected cells & cancer cells
o B cells produce plasma cells that synthesize antibodies
- Macrophages: phagocytize foreign substances & help activate T cells (along with dendritic cells)
- Reticular cells: provide stroma to nourish cells of lymphoid organs
Lymphoid Tissue:
- reticular connective tissue: forms a network around macrophages & lymphocytes in lymphoid organs
- diffuse lymphatic tissue: scattered reticular tissue elements
- lymphatic nodules: tightly packed reticular elements & cells
o germinal centers: actively dividing B cells & T cells
Lymphoid Organs: lymph nodes, spleen & thymus
Lymph Nodes: hundreds of small organs that cluster along lymphatic vessels
- filter lymph: macrophages in lymph nodes remove debris & destroy microorganisms
- activate immune system: lymphocytes within follicles monitor lymph for foreign antigens & mount responses against them
Spleen: largest lymphoid organ; located in left side of abdominal cavity just below diaphragm
- blood flows through sinuses; spleen removes aged & defective blood cells from circulation & contains macrophages to cleanse blood of foreign matter
- stores breakdown products of red blood cells for later use
- in fetus, produces erythrocytes
- stores blood platelets
- red pulp: most of mass of spleen; concerned with blood-cleansing & removal of old RBCs
- white pulp: contains lymphocytes (B cells)
Thymus: bilobed organ in inferior neck extending into mediastinum
- functions in maturation of T cells; mostly in childhood
- thymocytes (epithelial cells in stroma) secrete hormones (thymosins) for development of T cells
Tonsils: small organs around the entrance to the pharynx
- contain follicles with germinal centers with dividing B cells
- palatine tonsils: paired at posterior end or oral cavity; most likely to be infected
- lingual tonsils: at base of tongue
- tubal tonsils: at openings of auditory tubes into pharynx
Lymphoid Follicle Aggregates:
- Mucosa-associated Lymphatic tissue (MALT)
o Peyer¹s Patches in intestine (ileum)
- Appendix
Chapter 21: The Immune System: Innate & Adaptive Body Defenses
- Surface Barriers (Skin & Mucosae)
o keratinized epithelial cells of skin & epithelial mucosae provide a physical barrier to infection
o protective chemicals secreted by cells of skin & mucosae:
§ acidic (pH 3-5) secretions of skin inhibit bacterial growth & chemicals in sebum are toxic to bacteria
§ stomach mucosa secretes concentrated HCl solution (pH 0.5-2.5) & proteases that kill microorganisms
§ saliva in oral cavity & lacrimal fluid in eyes contain lysozyme protein that kills bacteria
§ mucus of respiratory & digestive mucosae traps microorganisms
- Internal Defenses: Cells & Chemicals
o Phagocytes: cells that ingest large particles & bacteria and break them down
§ Macrophages: develop from monocytes that enter tissues; most dominant phagocytes
· Free macrophages: alveolar macrophages of lungs, dendritic cells of epidermis (Langerhans¹ cells)
· Fixed macrophages: Kupffer cells of liver, microglia of brain
§ Also: neutrophils, eosinophils & mast cells have phagocytic activity
o Natural Killer (NK) Cells: large granular lymphocytes present in blood & lymph that nonspecifically kill cancer cells & virus-infected cells
o Inflammation: response to tissue injury (caused by trauma, heat, chemicals or infection)
§ 4 signs of inflammation: redness, heat, swelling & pain
o Antimicrobial proteins
§ Interferon (IFN): proteins released by virus-infected cells that prevent viral replication in neighboring cells
§ Complement: group of plasma proteins that, when activated, release chemical mediators that amplify inflammatory response, enhance phagocytosis (opsonization) & lyse cells
· membrane attack complex (MAC): group of complement proteins that inserts into cell membrane to cause cell lysis (death)
Adaptive (Specific) Defenses: B cells & T cells that recognize specific foreign substances & act to immobilize, neutralize & destroy them
- adaptive defenses are: antigen-specific, systemic (immune cells present throughout body), & have memory (memory cells enhance response to previously encountered antigens)
- humoral immunity (antibody-mediated immunity): mediated by antibodies in the body¹s ³humors² or fluids (blood, lymph, etc.)
o B cells produce plasma cells that release antibodies that bind antigens
- cellular immunity (cell-mediated immunity): mediated directly by T cells
o T cell receptors recognize & bind to antigens on virus-infected cells & cancer cells
- antigens: substances that can provoke an immune response
§ MHC (major histocompatibility complex) proteins: self antigens involved in cellular immunity
· In humans, called HLA (human leukocyte antigen) molecules
- Lymphocytes: produced from lymphoid stem cells in bone marrow
o must become immunocompetent (able to bind antigen); where cell becomes immunocompetent determines whether it is a T cell or B cell
o B cells become immunocompetent in bone marrow
o T cells become immunocompetent in thymus
- antigen-presenting cells: one of several cell types that engulfs & digests antigens & presents part of them on its plasma membrane bound to MHC molecules for recognition by T cell receptors
o professional APCs include dendritic cells, macrophages & activated B cells, but most cell types can function as APCs
- Humoral Immune Response: B cells stimulated by antigen; leads to production of antibodies by plasma cells
o Active & Passive Humoral immunity:
§ Active immunity: response by our own B cells to antigen(s)
· Naturally acquired: antigens from bacteria & viral infections
· Artificially acquired: antigens from vaccines
o Passive immunity: antibodies harvested or delivered from immune serum (from human or other animal)
§ Naturally acquired: antibodies pass from mother to child via placenta
§ Artificially acquired: antibodies acquired from injection of immune serum
o Antibodies (immunoglobulins or Igs): gamma globulin component of blood serum
§ Y-shaped proteins produced by activated B cells & plasma cells in response to antigen
§ 5 classes of antibodies:
· IgD: B cell antigen receptor
· IgM: monomer & pentamer forms
o monomer – B cell antigen receptor
o pentamer – circulates in blood plasma; first Ig class secreted; potent agglutinating agent
· IgG: most abundant circulating antibody; protects against bacteria, viruses & toxins; fixes complement; primary antibody of primary & secondary responses; confers naturally acquired passive immunity
· IgA: monomer & dimer forms
o monomer: small amounts in plasma
o dimer: found in secretions (mucus, saliva, sweat intestinal juice, milk), helps to prevent pathogens from entering body
· IgE: normally rarely in plasma (levels rise during allergic reaction), secreted by plasma cells in skin, mucosae of digestive & respiratory tracts, & tonsils; when activated by antigen, binds to mast cells & basophils & causes release of histamine & other mediators of inflammation
- Cell-mediated immune response: T cells stimulated by antigen; leads to lysis of virus-infected cells or cancer cells &/or elevation of immune response
o cytotoxic T cells (CD8 cells or TC cells) lyse target cells
o helper T cells (CD4 cells or TH cells) release chemicals called cytokines that amplify immune response (stimulate production of more B cells & T cells, mobilize phagocytes & attract more WBCs to area)
§ some cells become memory T cells that can mount an immediate response to another encounter with the same antigen
o Cytokines: hormone-like glycoproteins released by activated T cells & macrophages
§ Interleukins (IL-1 & IL-2) act as costimulators of T cells & T cell proliferation
Immunodeficiencies: conditions where the production or function of immune cells, phagocytes or complement is impaired or abnormal
- severe combined immunodeficiency syndrome (SCID): congenital (present from birth) condition resulting from deficits in both T and B cells
- acquired immunodeficiency syndrome (AIDS): infection with human immunodeficiency virus (HIV) destroys helper T cells
Autoimmune diseases: condition in which the body produces antibodies & activated cytotoxic T cells that target & destroy (self) body tissues
- causes include improper negative selection of self-directed lymphocytes in bone marrow & thymus during development, appearance of new antigens on cells, or foreign antigens that resemble self antigens
- examples are systemic lupus erythematosus (SLE), rheumatoid arthritis (RA) & multiple sclerosis (MS)
- treatments include anti-inflammatories to control symptoms & antibodies/chemicals to suppress lymphocyte activity
Layers of heart wall:
- epicardium: visceral layer of serous pericardium; often accumulates fat
- myocardium: cardiac muscle deep to epicardium; bulk of heart tissue
o branched cardiac muscle cells linked by connective tissue fiber bundles (collagen & elastin) – fibrous skeleton of heart
- endocardium: thin inner myocardial surface; sheet of endothelium (squamous epithelium) resting on connective tissue
o lines chambers & valves; continuous with endothelial linings of major vessels
- Atria: receiving chambers for blood
o right atrium receives deoxygenated blood from superior vena cava (from areas above diaphragm), inferior vena cava (from areas below diaphragm), & coronary sinus (from myocardium)
o left atrium receives oxygenated blood from pulmonary veins (4, from lungs)
- Ventricles: discharging (pumping) chambers for blood
o right ventricle pumps blood into pulmonary trunk (to lungs)
o left ventricle pumps blood into aorta (to systemic circulation/body tissues)
Pathway of blood through heart:
- pulmonary circuit: blood vessels that carry blood to & from the lungs
- systemic circuit: blood vessels that carry oxygenated blood to & from all body tissues
- know pathway & vessels
Coronary Circulation: functional blood supply of heart (myocardium)
- coronary arteries: arise from the base of the aorta; carry oxygenated blood to myocardium of atria & ventricles
- cardiac veins: carry deoxygenated blood from myocardium to coronary sinus, which empties into right atrium
- atrioventricular (AV) valves: prevent backflow of blood from ventricles to atria
o tricuspid valve: right AV valve; has 3 cusps (flaps of endocardium reinforced with CT)
o bicuspid (mitral) valve: left AV valve
- semilunar (SL) valves: prevent backflow of blood from great vessels to ventricles
o aortic semilunar valve: prevents blood from flowing back into left ventricle following ventricular contraction
o pulmonary semilunar valve: prevents blood from flowing back into right ventricle following ventricular contraction
Cardiac muscle:
- striated, branched muscle; usually uninucleate cells
- intercalated discs: connections between plasma membranes of adjacent cells
o desmosomes: proteins that hold cells together during contraction
o gap junctions: channel proteins allow ions to pass from cell to cell; allows depolarization to move across entire heart (coordinated contraction – functional syncytium)
Heart Physiology - Electrical Events
- Intrinsic conduction system: noncontractile cardiac cells specialized to initiate & distribute impulses throughout the heart
- Autorhythmic cells: cardiac cells with an unstable resting potential
o spontaneously depolarize due to pacemaker potentials caused by gradual influx of sodium ions
o when threshold is reached, fast calcium ion channels open & calcium ions flood into cell causing action potential
o the impulse is transferred from atria to ventricles in a defined sequence through gap junctions between cells
- sequence of excitation:
o sinoatrial (SA) node: autorhythmic cells here are the fastest to generate impulses (~75/min, called sinus rhythm); hence, this is the heart¹s pacemaker
o atrioventricular (AV) node: receives impulses from SA node; fewer connections between cells delay impulse long enough for atria to complete contraction; also autorhythmic cells here, but slower impulses (~50-60/min, called junctional rhythm), so these cells do not set the pace unless there is damage to SA node cells
o atrioventricular (AV) bundle (bundle of His): electrical connection between atria & ventricles; transmits impulse to ventricles
o right & left bundle branches: sends impulse along cells of interventricular septum toward apex
o Purkinje fibers: extend from inferior aspect of interventricular septum to apex & into outer walls of ventricles
- irregular heart rhythms (arrhythmias):
o fibrillation: rapid & irregular contractions
§ defibrillation: electrical shock to heart to reset rhythm
o ectopic focus: abnormal pacemaker; may be caused by drugs (caffeine, nicotine) or SA node damage
o heart block: damage to AV node interferes with impulse transmission to ventricles
§ artificial pacemakers can be used to deliver impulses
- Electrocardiography
o Electrocardiograph: measures electrical currents generated during heart contraction with a series of electrodes placed on 12 body regions
o Electrocardiogram (ECG or EKG): recording from electrocardiograph
§ P wave: atrial depolarization
§ QRS complex: ventricular depolarization
§ T wave: ventricular repolarization
§ P-Q interval: beginning of atrial depolarization until beginning of ventricular depolarization
§ Q-T interval: beginning of ventricular depolarization until beginning of ventricular repolarization
Developmental aspects of heart:
- pulmonary circuit bypasses due to incomplete lung development in fetus
o foramen ovale: sends blood from right atrium to left atrium
§ closes to become fossa ovalis after birth
o ductus arteriosus: sends blood from pulmonary trunk to aorta
§ closes to become ligamentum arteriosum after birth
Structure of Blood Vessel Walls:
- tunica interna (tunica intima): innermost tunic (layer)
o endothelium (simple squamous epithelium) lining lumen of all vessels
- tunica media: middle tunic
o mostly smooth muscle cells & sheets of elastin fibers
o generally thickest layer in arteries
- tunica externa (tunica adventitia): outermost tunic
o mostly loose collagen fibers; protect & reinforce vessel wall & anchor it to surrounding structures
o contains nerve fibers, lymphatic vessels, & elastin in larger veins
o vasa vasorum: system of blood vessels nourishing tunica externa in larger vessels
- arteries: transport blood away from the heart
o elastic (conducting) arteries: thick-walled arteries near heart (aorta & major branches)
o muscular (distributing) arteries: branch from elastic arteries to distribute blood to body organs
§ includes most named arteries
o arterioles: vary in size; lead from muscular arteries to capillary beds
Capillaries: smallest blood vessels; exchange materials (gases, nutrients, hormones, etc.) in blood with tissues
- only tunica interna (endothelium)
- pericytes: smooth muscle-like cells at intervals to stabilize capillary wall
- capillary types:
o continuous capillaries: most common type; abundant in skin & muscles
§ endothelial cells joined by incomplete tight junctions – leave gaps between cells to allow fluids & small solutes to pass through
o fenestrated capillaries: similar to continuous; some endothelial cells contain pores or fenestrations
§ pores allow greater permeability to fluid & small solutes
§ found where active absorption or filtration occurs (digestive system, kidneys)
o sinusoidal capillaries (sinusoids): highly modified, leaky capillaries found only in certain organs (liver, bone marrow, lymphoid tissue & endocrine organs)
§ allow larger molecules (proteins, etc.) & blood cells to pass through
Venous System:
- veins: transport blood toward heart
o venules: smallest veins; range from postcapillary venules (only tunica interna) to larger venules with additional one or two layers of smooth muscle cells & thin tunica externa
o veins: large vessels with all 3 tunics; vessel walls smaller & larger lumens than corresponding arteries
§ venous valves: formed from folds of tunica externa; flaps that prevent backflow of blood, especially in limbs
Blood Flow: volume of blood flowing through a vessel, organ, or circulation in a given period (ml/min)
Blood Pressure: pressure (force per unit area) exerted on the walls of a vessel by blood
Resistance: opposition to blood flow (friction)
- peripheral resistance (PR): resistance in systemic circulation; contributed by:
o Blood viscosity: thickness of blood (high viscosity in polycythemia; low viscosity in anemia)
§ more viscosity = greater resistance
o Blood vessel length: longer vessel length = greater resistance
o Blood vessel diameter: most likely to alter resistance
§ smooth muscle fibers control blood vessel diameter
§ decreased diameter = greater resistance
- Arterial Blood Pressure:
o Systolic pressure: pressure generated in aorta following (left) ventricular systole (~120 mm Hg)
o Diastolic pressure: pressure in aorta following ventricular diastole (70-80 mm Hg)
o Pulse pressure: systolic pressure – diastolic pressure
o Mean arterial pressure (MAP): average pressure in arterial system
- Capillary Blood Pressure: ~ 20-40 mm Hg; good intermediate pressure range (facilitates exchange without rupturing thin walls)
- Venous Blood Pressure: decreases to ~ 20 mm Hg due to peripheral resistance
o pressure built up during breathing & skeletal muscle contraction aid in venous blood return
Pulse: indirect measure of heartbeat/heart rate (measures arterial pressure during cardiac cycle)
- often for convenience radial artery is monitored (radial pulse)
Blood Pressure: measured from brachial artery with sphygmomanometer
- uses auscultatory method (listening for filling of artery as pressure in cuff drops below arterial pressure)
- normal resting ranges: systolic BP: 110-140 mm Hg; diastolic BP: 75-80 mm Hg
- Hypotension: low blood pressure (systolic BP below 100 mm Hg)
o often due to individual variations, fluctuations
o chronic hypotension may be indicative of poor nutrition
- Hypertension: high blood pressure (sustained arterial pressure > 140/90)
o Acutely due to exercise, illness
o Chronic hypertension may be indicative of increased peripheral resistance (often due to vessel blockage)
§ Primary hypertension: most cases; no known causeŠ factors include diet, obesity, age, race heredity, stress & smoking
§ Secondary hypertension: ~ 10% of cases; due to disorders such as arteriosclerosis & hyperthyroidism
Nose:
- nasal cavity: posterior to external nose
o olfactory mucosa: contains smell receptors
o respiratory mucosa: pseudostratified ciliated columnar epithelium containing goblet cells (secrete mucus) resting on a lamina propria with mucus & serous glands
§ rhinitis: inflammation of nasal mucosa; can be caused by cold viruses, bacteria (streptococcus) & allergens
Pharynx (throat): connects nasal cavity & mouth superiorly with larynx & esophagus inferiorly
- nasopharynx: air passageway; posterior to nasal cavity; continuous with nasal cavity through internal nares
o mucosa of pseudostratified ciliated columnar epithelium
- oropharynx: air & food passageway; posterior to oral cavity; continuous with oral cavity through fauces; extends from soft palate to epiglottis
o mucosa of stratified squamous epithelium
- laryngopharynx: air & food passageway; posterior to epiglottis; extends to larynx; continuous with esophagus posteriorly
o mucosa of stratified squamous epithelium
Larynx (voice box): superiorly attaches to hyoid bone & opens into laryngopharynx; inferiorly continuous with trachea
- epiglottis: flexible elastic cartilage extending from posterior aspect of tongue to thyroid cartilage
o covered by mucosa with scattered taste buds
o switching mechanism for air & food passageways
- voice production: involves intermittent release of expired air and opening & closing of glottis
o intrinsic laryngeal muscles affect the length of the vocal folds & size of glottis
o higher pitches from narrow glottis opening & tenser vocal folds
Trachea (windpipe): descends from larynx through neck into mediastinum
- inferiorly divides into primary bronchi
- wall composed of mucosa (pseudostratified ciliated epithelium with goblet cells), submucosa (connective tissue with seromucous glands) & adventitia (connective tissue reinforced with hyaline cartilage rings)
- carina: extension of last tracheal cartilage; marks split of trachea into primary bronchi
- Conducting Zone
o tissue composition of wall changes as tubes become smaller
§ cartilage support structures change from rings to irregular plates
§ epithelium changes from pseudostratified columnar to columnar to cuboidal in terminal bronchioles
§ amount of smooth muscle increases
- Respiratory Zone:
o respiratory membrane: walls of alveoli together with pulmonary capillaries & their fused basal laminas (also known as air-blood barrier or alveolar-capillary membrane)
§ type I cells: very thin simple squamous epithelium
· participate in gas exchange with pulmonary capillaries
· secrete angiotensin converting enzyme (ACE), which plays a role in blood pressure regulation
§ type II cells: cuboidal cells scattered among the type I cells
· secrete a fluid containing surfactant that coats the alveolar walls
Lungs:
o left lung: 2 lobes
§ cardiac notch (impression): depression in left lung to accommodate heart
o right lung: 3 lobes
Mechanics of Breathing:
- intrapulmonary (intra-alveolar) pressure (Palv): pressure within alveoli of lungs
o rises & falls with breathing, but always equalizes with Patm
- intrapleural pressure (Pip): pressure within pleural cavity
o also varies with breathing, but is always about 4 mm Hg less than Palv (negative with respect to both intrapulmonary & atmospheric pressures)
- pulmonary ventilation: inspiration & expiration
o Inspiration:
§ diaphragm & intercostal muscles contract, so that the volume of the thoracic cavity increases
§ lungs are stretched out & intrapulmonary volume increases; as volume increases, pressure decreases -> flow of gases into lungs to equalize pressure
o Expiration:
§ diaphragm relaxes & intercostal muscles relax, so that the volume of the thoracic cavity decreases
§ elastic lungs passively recoil& intrapulmonary volume decreases; as volume decreases, pressure increases -> flow of gases out of lungs to equalize pressure
Respiratory volumes: tidal volume (TV), inspiratory reserve volume (IRV), expiratory reserve volume (ERV), residual volume (RV):
Respiratory capacities: inspiratory capacity (IC), functional residual capacity (FRC), vital capacity (VC), total lung capacity (TLC):
Transport of Respiratory Gases by Blood:
Oxygen Transport: since oxygen is poorly soluble in water, most (> 98%) of oxygen transported by blood is bound to hemoglobin
- nitric oxide (NO) is a vasodilator that regulates blood pressure
o as oxygen binds hemoglobin in lungs, NO binding to hemoglobin is facilitatedŠ this allows hemoglobin to unload both oxygen & NO at tissues
Carbon dioxide Transport: carbon dioxide transported in blood from tissue cells to lungs in 3 forms:
- gas dissolved in plasma (~7-10%)
- chemically bound to hemoglobin (~20%): hemoglobin with bound CO2 is carbaminohemoglobin (since CO2 binds to amino acids of hemoglobin while oxygen binds to iron of the heme group, CO2 does not compete with O2 for binding)
- as bicarbonate ion in plasma (~70%): most carbon dioxide that diffuses into RBCs combines with water, forming carbonic acid, which dissociates into hydrogen & bicarbonate ions
o this acts as part of the carbonic acid-bicarbonate buffering system in blood
Homeostatic imbalances of respiratory system
- Chronic Obstructive Pulmonary Disease (COPD):
o obstructive emphysema: marked by enlargement of alveoli & destruction of alveolar walls
§ Leads to lung fibrosis & loss of elasticity
o chronic bronchitis: chronic excessive mucus production by lower respiratory tract as well as inflammation & fibrosis
- asthma (bronchial asthma): characterized by episodes of coughing, dyspnea (difficult breathing), wheezing & chest tightness
o periods of acute symptoms followed by symptom-free periods
o treatments changed from inhaled bronchodilators to inhaled steroids
- tuberculosis (TB): infectious disease caused by the bacterium Mycobacterium tuberculosis
Blood Supply: The Splanchnic Circulation
- Splanchnic circulation includes arteries that branch off abdominal aorta & serve digestive organs & hepatic portal circulation
Histology of Alimentary Canal
- mucosa: moist epithelial membrane that lines the lumen
o lining epithelium: mostly simple columnar epithelium with goblet cells (stratified squamous epithelium in esophagus)
o lamina propria: loose areolar or reticular connective tissue
o muscularis mucosae: smooth muscle cells that twitch for local movements & folds mucosa in small intestine
- submucosa: dense connective tissue (with elastic fibers) containing blood & lymphatic vessels, lymph nodules & nerve fibers
- muscularis externa: inner circular layer & outer longitudinal layer of smooth muscle (stomach has additional innermost oblique layer)
- serosa (visceral peritoneum): outermost layer of areolar connective tissue covered with mesothelium (simple squamous epithelium)
Functional Anatomy of Digestive System
Mouth & Associated Organs:
- Mouth (oral or buccal cavity):
o epithelium of mouth, hard palate & tongue is slightly keratinized stratified squamous epithelium
o oral mucosa produces antimicrobial peptides called defensins to prevent infection
- Salivary Glands: glands inside & outside oral cavity that secrete saliva
o Intrinsic salivary glands or buccal glands: throughout oral mucosa
o Extrinsic salivary glands
§ Parotid glands: paired glands anterior to ear between masseter muscle & skin
· Mumps: inflammation of parotid glands; caused by mumps virus
§ Submandibular glands: walnut-sized glands that lie along medial aspect of mandible
§ Sublingual gland: anterior to submandibular gland under tongue
Teeth: lie in sockets (alveoli) in gum-covered margins of maxilla & mandible
- tooth structure:
o gingiva (gum): oral mucosa that surrounds tooth
o enamel: acellular brittle material composed of hydroxyapatite crystals (mostly calcium salts)
o periodontal ligament: anchors the tooth to the bony alveolus of the jaw within joint (gomphosis)
o dentin: bonelike material under enamel forming bulk of tooth
o pulp cavity: central cavity containing pulp (connective tissue, blood vessels, nerves)
Esophagus: food moving through laryngopharynx is routed into the esophagus as the epiglottis closes off the larynx
- cardiac (gastroesophageal) sphincter: smooth muscle valve preventing backflow of food from stomach into esophagus
- heartburn: symptom of gastroesophageal reflux disease (GERD); backflow of acidic gastric juice from stomach into esophagus
Stomach: food entering stomach from esophagus is broken down by chemicals into a paste called chyme; major function is digestion (primarily proteolytic) of contents
- cardiac region: region near the heart; surrounds cardiac orifice
o cardiac sphincter
- Microscopic anatomy of stomach
o 3 layers of smooth muscle in muscularis externa (has innermost oblique layer)
o mucosa: simple columnar epithelium with goblet cells that secrete a protective alkaline mucus
o secretory cells of gastric glands:
§ parietal cells: in middle region; secrete hydrochloric acid (HCl) and intrinsic factor (necessary for vitamin B12 absorption in small intestine)
§ chief cells: in basal region; produce pepsinogen (precursor of enzyme pepsin, a protease)
§ enteroendocrine cells: a variety of cell types that secrete hormones & hormone-like molecules (including gastrin, histamine, endorphins & somatostatin)
Small Intestine: convoluted tube extending from the pyloric sphincter to ileocecal valve; major function is completion of digestion & absorption of nutrients
o duodenum: shortest region; continuous with pylorus of stomach
o jejunum: extends from duodenum to ileum
o ileum: continuous with large intestine through ileocecal valve
- mesentery: attaches jejunum & ileum to posterior abdominal wall
- Histology of wall
o mucosa: simple columnar absorptive cells with goblet cells
o intestinal crypts (crypts of Lieberkuhn): tubular intestinal glands between villi
o submucosa: areolar CT containing lymphoid follicles called Peyer¹s patches and mucus-secreting duodenal glands in duodenum
Liver: largest gland in body; under diaphragm & mostly within rib cage; occupies most of right hypochondriac & epigastric regions
- synthesizes bile: bile is a yellow-green alkaline solution consisting of bile salts, bile pigments, cholesterol, neutral fats, phospholipids & a variety of electrolytes
o bile salts: cholesterol derivates that emulsify fats (suspend in water)
o bilirubin: bile pigment produced as a waste product of heme of hemoglobin
Gallbladder: thin-walled green muscular sac in a fossa on the ventral surface of liver
- stores (& concentrates) bile that is not immediately needed
- gallstones: crystallization of cholesterol in gallbladder due to too much cholesterol or too few bile salts
Pancreas: extends across abdomen under stomach; most is retroperitoneal
- releases pancreatic juice through main pancreatic duct to duodenum
o contains digestive enzymes: proteases trypsin, chymotrypsin, carboxypeptidase; amylase, lipases & nucleases
Large Intestine: major function is to absorb water from indigestible foods & eliminate them from body as feces
- subdivisions: cecum, appendix, colon, rectum, & anal canal
o colon: ascending, transverse, descending & sigmoid subdivisions
o appendicitis: inflammation of appendix caused by blockage (fecal) & bacteria
- microscopic anatomy:
o most of large intestine mucosae is simple columnar epithelium with goblet cells; anal canal mucosa is stratified squamous epithelium
- bacterial flora: bacteria remaining in material from food & entering through anus
- Carbohydrates
o Know basic dietary sources & uses in body
- Lipids
o Know basic dietary sources & uses in body
- Proteins
o Know basic dietary sources & uses in body
- Vitamins: organic compounds needed in small amounts for growth & metabolism
o B vitamins niacin & riboflavin act as coenzymes (NAD+ & FAD) in oxidative phosphorylation
o most vitamins must be obtained from diet; exceptions are vitamin D made in the skin, vitamin K & some B vitamins synthesized by intestinal bacteria, & vitamin A which can be synthesized from beta-carotene (orange-yellow pigment in some vegetables)
- Minerals:
o 7 minerals required in moderate amounts: calcium, phosphorus, potassium, sulfur, sodium, chloride & magnesium
o several minerals also required in trace amounts (e.g.: fluorine, iodine, iron, zinc)
- Carbohydrate metabolism
o Oxidation of glucose: glucose + oxygen -> water + carbon dioxide + 36 ATP + heat
§ Glycolysis: glucose broken down to 2 molecules of pyruvic acid
· occurs in the cytoplasm of cells
· net gain of 2 ATP
· following glycolysis, if oxygen is available pyruvic acid is converted to acetyl coA & carbon dioxide is released in the conversion
· if oxygen is in short supply, pyruvic acid is reduced to lactic acid (anaerobic respiration or fermentation)
§ Krebs Cycle: an 8-step cycle that shuffles carbon atoms while oxidizing sugars to reduce NAD+ & FAD
· occurs in the mitochondrial matrix
· the resulting 3 NADH molecules and 1 FADH2 molecule per acetyl coA will enter the electron transport chain
· net gain of 1 ATP per acetyl coA
§ Electron Transport Chain & Oxidative Phosphorylation: NADH & FADH2 are oxidized on the inner mitochondrial membrane
· the hydrogen ions are sent back across the mitochondrial membrane through an ATP synthase enzyme, releasing energy that is used by the enzyme to produce ATP from ADP & phosphate
- Lipid metabolism: about twice as much energy can be gained from fats as from glucose (most cell types can use fats as an energy source, but some cell types (neurons & red blood cells) rely almost exclusively on glucose for energy)
o Oxidation of glycerol & fatty acids: triglycerides are broken down into fatty acids and glycerol; glycerol enters glycolytic pathway while fatty acids are oxidized to acetic acid
- Protein metabolism: when more protein is ingested than needed for protein replacement, amino acids can be oxidized for energy or converted to fat
o Oxidation of amino acids: amino acids are converted to keto acids, which can then be converted to pyruvic acid & acetyl coA; occurs in liver
o Synthesis of Proteins: protein synthesis is first priority for amino acids absorbed
- Role of Liver in Metabolism:
o Hepatocytes carry out many („ 500) metabolic functions
o Cholesterol metabolism & regulation of plasma cholesterol levels
§ cholesterol is used in synthesis of bile salts, steroid hormones, vitamin D & plasma membrane in all cells; also part of embryonic hedgehog protein
· ~ 15% of cholesterol comes from diet; the rest is synthesized from acetyl coA
§ Lipoproteins & cholesterol transport:
· very low density lipoproteins (VLDLs): transport triglycerides from liver to tissues (primarily adipose tissue)
· low-density lipoproteins (LDLs): transport cholesterol to tissues (bad cholesterol)
· high-density lipoproteins (HDLs): transports excess cholesterol from tissues to liver for use in bile salts
- kidneys lie in a retroperitoneal position in superior lumbar region
- renal hilus: cleft in concave medial surface of kidneys
o the ureters, renal blood vessels, lymphatics & nerves enter & exit kidneys at hilus
- 3 regions to kidney interior:
o renal cortex: most superficial region
o renal medulla: deep to cortex; composed of medullary or renal pyramids
§ renal columns: inward extensions of cortex that separate pyramids
o renal pelvis: lateral to hilus within renal sinus & continuous with ureter leaving hilus
§ major calyces: branching extensions of pelvis; subdivide to form minor calyces
- Nephrons: blood-processing units that form urine; consists of glomerulus associated with a renal tubule
o Glomerulus: tuft of capillaries associated with renal tubule
§ fenestrated capillaries allows fluid (filtrate) to pass from blood into glomerular capsule
o Glomerular (Bowman¹s) capsule: end of renal tubule; encloses glomerulus
§ parietal layer: simple squamous epithelium
§ visceral layer: highly modified branching epithelial cells called podocytes
· podocyte extensions terminate in foot processes
· filtration slits (slit pores): openings between foot processes that allow filtrate to pass into capsular space inside glomerular capsule
§ Renal corpuscle: glomerulus & glomerular capsule
o 3 parts to remainder of renal tubule:
§ proximal convoluted tubule (PCT)
· walls of simple cuboidal epithelial cells with microvilli; actively reabsorbs substances from filtrate & secretes substances into it
§ loop of Henle
· descending limb: cuboidal cells give way to simple squamous cells (thin segment)
· ascending limb: cells of wall again become cuboidal to low columnar (thick segment)
§ distal convoluted tubule (DCT): empties filtrate (urine) into collecting duct
· cuboidal cells mostly lacking microvilli (secretion rather than absorption)
o collecting ducts: receive urine from many nephrons; run through medullary pyramids & fuse to form papillary ducts at renal pelvis, which deliver urine to calyces
Absorptive capabilities of different regions of renal tubules
- PCT cells are most active reabsorbers
- Loop of Henle: reabsorbs water, sodium, chloride & potassium ions
- water can leave descending limb but not ascending limb
- DCT cells can reclaim some water, sodium & chloride ions
o Reabsorption of sodium regulated by aldosterone
Tubular secretion: reverse reabsorption; substances such as hydrogen & potassium ions, creatinine, ammonium ion, & some organic acids can move from blood of the peritubular capillaries through tubule cells into filtrate
Diuretics: chemicals that enhance urinary output through inhibition of water or sodium ion reabsorption or increased osmotic pressure in kidney tubules
- alcohol inhibits ADH release, while caffeine & drugs such as Lasix & Diuril inhibit sodium ion reabsorption
Ureters: tubes that convey urine from kidneys to bladder
- mucosa lined with transitional epithelium; muscularis with inner longitudinal & outer circular smooth muscle sheets; adventitia of fibrous CT
- renal calculi (kidney stones): form from crystallization of salts in urine in renal pelvis; can obstruct ureters
Urinary Bladder: collapsible muscular sac that stores urine temporarily
- mucosa lined with transitional epithelium; muscularis (detrusor muscle) with inner longitudinal, middle circular & outer longitudinal smooth muscle sheets; adventitia of fibrous CT
Urethra: muscular tube that drains urine from bladder & conveys it out of body
- epithelium of mucosa changes from transitional to pseudostratified columnar to stratified squamous near external urethral orifice
- internal urethral sphincter: near bladder; smooth muscle (involuntary control)
- external urethral sphincter: near urogenital diaphragm; skeletal muscle (voluntary control)
Water Balance:
- water intake: 60% fluids; 30% water in foods; 10% from metabolism (metabolic water or water of oxidation)
- water output: 60% excreted in urine; 28% vaporizes out of lungs of is lost by diffusion through skin (insensible water loss); 8% lost through perspiration & 4% in fecal waste
- Disorders of water balance:
o Dehydration: water loss exceeds water intake; water is lost from ECF & water moves from cells to ECF to equalize osmolality
o Hypotonic hydration (water intoxication): extreme intake of water or renal insufficiency lead to diluted ECF; water flows into cells by osmosis
Electrolyte Balance:
- Regulation of sodium balance
o Sodium content in the body changes, but sodium concentration in the ECF remains stable due to adjustments in water volume (water follows salt)
o Influence & regulation of aldosterone:
§ without aldosterone, most sodium (90%) is reabsorbed in the proximal tubules & loop of Henle
§ when aldosterone levels are high, nearly all the remaining sodium is actively reabsorbed from the distal tubules & collecting ducts
§ if ADH is present, as sodium is reabsorbed, water follows
o cardiovascular system baroreceptors:
§ decreasing blood volume stimulates baroreceptors (pressure receptors) in the heart & large vessels (aorta & carotid arteries)
§ the response is constriction of afferent arterioles, decreased glomerular filtration rate & decreased sodium & water output
o Influence & regulation of ADH:
§ declining blood pressure & blood volume stimulates hypothalamic osmoreceptors, which effect release of ADH from the posterior pituitary
§ ADH increases water reabsorption from the collecting ducts
o Influence & regulation of Atrial Natriuretic Peptide (ANP):
§ ANP reduces blood pressure & blood volume by inhibiting nearly all events (aldosterone, ADH & baroreceptors) that promote vasoconstriction and sodium & water retention
o Influence of other hormones:
§ Estrogens & glucocorticoids exhibit aldosterone-like effects & enhance tubular reabsorption of sodium
- Regulation of potassium balance:
o cortical collecting ducts predictably excrete ~ 15% of potassium ions in filtrate (~ 85% reabsorbed from tubules & loop of Henle)
o when ECF potassium concentration is low, excretion of potassium can be reduced, & some collecting duct cells can reabsorb some potassium
o in the presence of aldosterone, for each sodium reabsorbed, a potassium ion is secreted to maintain electrolyte balance
- maintaining pH of body fluids important for protein function
- blood pH is normally maintained between pH 7.35-7.45
o alkalosis: blood pH > 7.45
o acidosis: blood pH < 7.35
- chemical buffer systems (chemical acid-base buffers):
o bicarbonate buffer system: mixture of carbonic acid & its salt sodium bicarbonate in the same solution; primary blood buffer
§ carbonic acid reacts with added base to stabilize pH
§ bicarbonate ion reacts with added acid to stabilize pH
o phosphate buffer system: mixture of dihydrogen phosphate (weak acid) & monohydrogen phosphate (weak base)
o protein buffer system: proteins in plasma & within cells can act as weak acids or weak bases
Testes: lie within scrotum; produce male gametes (sperm)
- seminiferous tubules produce sperm through spermatogenesis
o seminiferous tubules from each lobule converge to form tubulus rectus that conveys sperm to posterior rete testis
§ sperm travels then from rete testis to efferent ductules to epididymis
- interstitial cells (Leydig cells): surround seminiferous tubules; produce androgens (testosterone)
- Epididymis: coiled tube that delivers immature sperm leaving testis to ductus deferens
- Ductus Deferens (vas deferens): propels live sperm from epididymis to urethra
Accessory Glands
- Seminal Vesicles: lie on posterior wall of bladder
o secrete seminal fluid: a yellowish viscous alkaline fluid containing fructose (sugar), ascorbic acid, a coagulating enzyme & prostaglandins
- Prostate Gland: encircles urethra just inferior to bladder
o Secretes a milky, slightly acidic fluid containing citrate, enzymes & prostate-specific antigen (PSA) that enters prostatic urethra during ejaculation
- Bulbourethral Glands (Cowper¹s glands): small glands inferior to prostate gland
o produce thick clear mucus prior to ejaculation that neutralizes acidic urine in urethra
- Spermatogenesis: sperm formation by meiosis in seminiferous tubules of testes
o terms:
§ diploid (2n): normal chromosome number in most body cells; 46 in humans, or 23 pairs of homologous chromosomes (paternal & maternal chromosome of same chromosome number)
§ haploid (n): chromosome number in gametes; each human gamete only contains 23 total chromosomes (only 1 of each homologous pair)
§ chromatid: one chromosome of a duplicated chromosome
§ meiosis: forms gametes; reduces chromosome number from 2n to n in gametes
o meiosis I: reduction division (2n to n)
§ synapsis: during prophase, homologous chromosomes pair & exchange genetic information (³cross over²)
§ independent assortment: during metaphase, homologous chromosomes line up in pairs at metaphase plate; either maternal or paternal chromosome of each homologous pair can be on a given side of equator
§ both events lead to genetic variation in gametes
o meiosis II: equatorial division (chromatids distributed equally)
§ mitotic-like division; duplicated chromosomes separated
o Summary of events in seminiferous tubules
§ Mitosis of spermatogonia: forming spermatocytes
· spermatogonia divide to form type A cell & type B cell
· type A cell remains in basal compartment in spermatogonia population
· type B cell becomes primary spermatocyte, destined to form 4 sperm cells
§ Meiosis: spermatocytes to spermatids
· meiosis I: primary spermatocyte forms 2 secondary spermatocytes
· meiosis II: each secondary spermatocyte forms 2 spermatids
§ Spermiogenesis: spermatids to sperm
· each spermatid undergoes changes to form sperm cell
o at one end of nucleus, head region forms, including a tightly enclosed nucleus with an acrosome (contains hydrolytic enzymes for penetration of egg cell) at top
o at other end, tail region forms, with a flagellum forming from centrioles & attached to the head region by a midpiece containing many mitochondria (supplying energy for moving flagellum)
Ovaries: female gonads; produce oocytes & female sex hormones (estrogens & progesterone)
- outer cortex houses follicles; inner medulla contains blood vessels & nerves
- ovarian follicles: in cortex; contain immature egg (oocyte) encased by one or more cell layers (1 layer = follicle cells; more than 1 layer = granulosa cells)
- ovulation: ejection of oocyte from follicle & ovary
- corpus luteum: structure formed from follicle cells following ovulation; eventually degenerates
Female Duct System
- Uterine Tubes (Fallopian tubes or Oviducts): receive ovulated oocyte from ovary & provide site for fertilization
- Uterus: hollow, thick-walled organ in pelvis that receives, retains & nourishes a fertilized ovum
o uterine wall: composed of 3 layers:
§ perimetrium: outermost serous layer; visceral peritoneum
§ myometrium: middle smooth muscle layer; contraction of muscle bundles expels baby during childbirth
§ endometrium: mucosal lining of uterine cavity; simple columnar epithelium; site of implantation of embryo for development
- Vagina: thin-walled tube between bladder & rectum extending from cervix to body exterior
o urethra is embedded in anterior wall
o wall consists of outer fibroelastic adventitia, smooth muscle muscularis & mucosa of stratified squamous epithelium with ridges (rugae)
o cervical mucous glands supply mucus to mucosa; pH of vagina is normally acidic due to metabolism of sugars by resident bacteria (prevents infection)
- Oogenesis: ovum formation by meiosis in follicles of ovaries
- Oogonia in fetal period in females rapidly divide & transform into primary oocytes in primordial follicles (~ 2 million by birth)
o primary oocytes begin meiosis I, but arrest in prophase I
- starting at puberty, one follicle is chosen each month (from ~ 400,000 remaining) to complete meiosis I, resulting in a secondary oocyte receiving most of the cytosol & a small polar body
- the secondary oocyte begins meiosis II, but arrests in metaphase II (awaiting fertilization in oviduct to complete meiosis II); the polar body may divide to form 2 smaller polar bodies
- the secondary oocyte is ovulated & is picked up by uterine tube; if fertilization occurs, following sperm entry meiosis II is completed, forming the ovum and another polar body
- the end result of complete oogenesis is 3 small polar bodies & one very large ovum (only the ovum is a functional female gamete); the ovum contains most of the cytosol, with ample nutrients for the 7 day journey to the uterus
o follicular phase: period of follicle growth; days 1-14
o ovulation: bulging ovary wall ruptures & releases secondary oocyte into peritoneal cavity; ~ day 14
§ fraternal twins: more than one oocyte ovulated, & each fertilized by different sperm (~1-2% of ovulations are multiple oocytes)
§ identical twins: one oocyte fertilized by one sperm, & during early embryogenesis cells divide into separate embryos
o luteal phase: period of corpus luteum activity; days 14-28
§ after ovulation, ruptured follicle grows into endocrine gland - corpus luteum
§ corpus luteum secretes progesterone & some estrogen
§ if pregnancy occurs, corpus luteum continues to produce hormones until placenta can assume its role; otherwise, corpus luteum degenerates
- Uterine (Menstrual) Cycle: cyclic changes in uterine endometrium in response to ovarian hormones in blood
o Menstrual phase (days 1-5): uterus sheds all but deepest layer of endometrium; detached tissue & blood pass out through vagina as menstrual flow
o Proliferative phase (days 6-14): as estrogen blood levels rise, endometrium rebuilds itself
§ ovulation occurs in ovary at end of this phase (day 14)
o Secretory phase (days 15-28): increasing progesterone levels prepare endometrium for embryo implantation, creating blood vessels & stimulating nutrient secretion from uterine glands; also, cervical plug of mucus reforms to block further sperm entry
- Accomplishing Fertilization: sperm viable from 24 hours up to 72 hours; egg viable for 12-24 hours after ovulation
o Fertilization: fusion of sperm & egg to form a zygote
- Blocks to polyspermy: following initial sperm entry, two mechanisms assure monospermy (only one sperm enters into egg):
o fast block to polyspermy: membrane depolarizes due to sodium ion entry through open sodium channels
o cortical reaction: cortical granules within oocyte release enzymes that destroy sperm receptors
- Completion of Meiosis II & Fertilization: as sperm nucleus enters oocyte (tail & midpiece are lost), oocyte completes meiosis II to form the ovum nucleus (and second polar body, which is ejected)
Preembryonic Development
- Cleavage & Blastocyst Formation:
o Cleavage: period of rapid mitotic divisions of the zygote following fertilization
o Blastomeres divide to form 4 cells, then eight, then 16 as preembryo moves toward uterus
o Morula: berry-shaped cluster of 16 or more cells
o Blastocyst: fluid-filled hollow sphere composed of trophoblast & inner cell mass
§ trophoblast cells take part in placenta formation
§ inner cell mass becomes the embryonic disc, which forms the embryo
- Implantation: when blastocyst reaches uterus, it floats in uterus for several days, receiving nourishment from uterine secretionsŠ 6-7 days later, implantation begins
o implantation takes about a weekŠ by this time, menstruation would normally occur
§ trophoblast cells begin secreting human chorionic gonadotropin (hCG), which prompts the corpus luteum to continue secretion of estrogen & progesterone, bypassing normal controls & menses
- Placentation: placenta arises from trophoblast & endometrial tissue
o Trophoblast gives rise to chorion which begins formation of placenta, with chorionic villi, forming spaces that will be surrounded by blood vessels feeding fetal circulation
o placenta continues secretion of hCG, & eventually takes over secretion of estrogen & progesterone, which encourage growth & differentiation of mammary glands
Parturition (Birth):
- Initiation of Labor: as estrogen levels rise, myometrial cells form oxytocin receptors & quieting effects of progesterone are inhibited
o May result in false labor (Braxton Hicks contractions)
o As birth nears, fetal cells produce oxytocin, which causes placenta to release prostaglandins
§ Both are uterine muscle stimulants that initiate contractions
Lactation: production of milk by hormone-prepared mammary glands
- rising levels of placental hormones stimulate hypothalamus to release prolactin-releasing hormone (PRH)
- PRH stimulates anterior pituitary to release prolactin
- After 2-3 days, milk production begins
Inheritance: the passage of hereditary traits from one generation to the next
- genotype: genetic makeup for a trait or traits
- alleles: alternative forms of a gene that code for the same trait at the same location on homologous chromosomes
- mutation: a permanent heritable change in an allele that produces a different variant of the same trait
- homozygous: an individual with the same alleles on homologous chromosomes
- heterozygous: an individual with different alleles on homologous chromosomes
- phenotype: physical or outward expression of a gene
- carrier: heterozygous individuals that carry a recessive gene but do not express it, and can pass the gene on to their offspring
- variations on dominant-recessive inheritance
o incomplete dominance: neither member of an allelic pair is dominant over the other, & the heterozygote has an intermediate phenotype between dominant & recessive phenotypes
§ sickle-cell disease (SCD) is a disorder that exhibits incomplete dominance in humans
- multiple-allele inheritance: traits with more than 2 alleles
o example: ABO blood groups
o codominance: more than 2 alleles fully expressed
§ since type AB blood has both A & B antigens, both IA & IB alleles are dominant
- autosomes, sex chromosomes & sex determination
o autosomes: every chromosome except the sex chromosomes (chromosome pairs 1-22)
o sex chromosomes: chromosome pair 23 (XX in females; XY in males)
o sex-linked inheritance: traits inherited from genes on the X chromosome
§ examples: red-green color blindness & hemophilia
§ sex-linked traits are more commonly expressed in males, since they only have 1 copy of the X chromosome
§ if a mother has a sex-linked recessive disorder, all of her sons will have the disorder
Teratogens: an agent that causes developmental defects in the embryo