Study Notes Exam 5
Overview of Digestive System:
- alimentary canal (gastrointestinal (GI) tract): continuous muscular digestive tube that is open to the outside environment at both ends
o digests (breaks down) food & absorbs digested fragments into blood
o organs: mouth, pharynx, esophagus, stomach, small intestine, large intestine (leads to terminal opening or anus)
- accessory digestive organs: teeth, tongue, gall bladder
o large digestive glands in: salivary glands, liver & pancreas
• produce secretions that help in breakdown of food
- Digestive Processes:
o Ingestion: taking food into digestive tract
o Propulsion: moves food along alimentary canal
• swallowing
• peristalsis: alternate waves of contraction & relaxation of muscles in organ (esophagus, stomach) walls
o mechanical digestion: physically prepares food for enzymatic (chemical) digestion
• includes chewing, mixing with saliva, churning food in stomach & segmentation (rhythmic local constrictions of small intestine
o chemical digestion: complex food molecules broken down by enzymes released by glands of digestive organs
o absorption: passage of digested products from GI tract into blood or lymph
o defecation: elimination of indigestible substances in form of feces
- Digestive System Organs: Relationship & Structural Plan
o Relationship of the Digestive Organs to the Peritoneum:
• Peritoneum: 2-layered serous membrane of the abdominopelvic cavity
⋅ peritonitis: inflammation of peritoneum (can result from wounds, ulcers, burst appendix)
• Mesentery: double-layered peritoneum that extends to the digestive organs from the body wall
• Retroperitoneal Organs: organs such as the pancreas & parts of the large intestine that lie posterior to the peritoneum (no mesentery)
o Blood Supply: The Splanchnic Circulation
• Splanchnic circulation includes arteries that branch off abdominal aorta & serve digestive organs & hepatic portal circulation
o Histology of Alimentary Canal
• from the esophagus to rectum, the walls of the GI tract have the same 4 layers
⋅ mucosa: moist epithelial membrane that lines the lumen composed mostly of simple columnar epithelium with goblet cells (stratified squamous epithelium in esophagus)
⋅ submucosa: dense connective tissue (with elastic fibers) containing blood & lymphatic vessels, lymph nodules & nerve fibers
⋅ muscularis externa: smooth muscle; propels food along GI tract; circular layer has sphincters to prevent backflow
⋅ serosa (visceral peritoneum): outermost layer of areolar connective tissue covered with simple squamous epithelium
o Enteric Nervous System of GI tract
• enteric neurons of intrinsic nerve plexuses regulate digestive system activity
⋅ submucosal nerve plexus & myenteric nerve plexus (in muscularis externa; controls GI tract mobility (segmentation & peristalsis)
Functional Anatomy of Digestive System
Mouth & Associated Organs:
- Mouth (oral or buccal cavity): anterior opening is oral orifice; continuous with oropharynx posteriorly
o epithelium of mouth, hard palate & tongue is slightly keratinized stratified squamous epithelium
o oral mucosa produces antimicrobial peptides called defensins to prevent infection
- Lips & Cheeks: formed by orbicularis oris muscle & buccinator muscles
- Palate: forms roof of mouth
o hard palate: formed from palatine bone & palatine process of maxilla
o soft palate: formed mostly of skeletal muscle
• uvula: projects downward from free edge of soft palate; closes off nasopharynx during swallowing
- Tongue: occupies floor of mouth & fills most of oral cavity
o composed of skeletal muscle that grips & mixes food with saliva to form a bolus
o papillae: peglike projections of tongue mucosae, some of which contain taste buds
- 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
o saliva: mostly water; slightly acidic secretion containing electrolytes (sodium, chloride, bicarbonate... ions), salivary amylase (digestive enzyme), mucin, lysozyme, IgA & metabolic wastes (urea & uric acid)
o control of salivation: primarily controlled by parasympathetic division of ANS
Teeth: lie in sockets (alveoli) in gum-covered margins of maxilla & mandible
- primary function is mastication (chewing)
- dentition: 2 sets of teeth
o deciduous (milk or baby) teeth; set of 20 teeth that first appear at about 6 months & generally last from 6 to 12 years
o permanent teeth: usually 32 teeth including wisdom teeth
- tooth structure:
o gingiva (gum): oral mucosa that surrounds tooth
o crown: exposed part of tooth above gingiva
o enamel: acellular brittle material composed of calcium salts
o root: portion of tooth embedded in jawbone (teeth can have from 1 to 3 roots)
o cementum: calcified connective tissue covering outer surface of root
o periodontal ligament: anchors the tooth to the upper & lower jaw bones
o dentin: bonelike material under enamel forming bulk of tooth
o pulp cavity: central cavity containing pulp (connective tissue, blood vessels, nerves)
• root canal: where pulp cavity extends into root
- tooth & gum disease
o dental caries (cavities): result from demineralization of enamel by bacteria in dental plaque
o gingivitis: inflammation of gingival caused by dental plaque & tartar accumulation
o periodontitis (periodontal disease): bacteria invade the bone surrounding a tooth, & immune system response further erodes bone & tooth
Pharynx: food passes from mouth into oropharynx & then laryngopharynx
- stratified squamous mucosa surrounded by 2 skeletal muscle layers to propel food into esophagus
Esophagus: food moving through laryngopharynx is routed into the esophagus as the epiglottis closes off the larynx
- esophagus joins stomach at cardiac orifice
- 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
- rugae: longitudinal folds of mucosa
- cardiac region: region near the heart; surrounds cardiac orifice
o cardiac sphincter
- fundus: dome-shaped region superolateral to cardiac region
- body: midportion
- pyloric region: funnel-shaped region inferolateral to body
o pylorus: continuous with duodenum through pyloric sphincter (valve-like smooth muscle that controls stomach emptying)
- 3 layers of smooth muscle in muscularis externa (has innermost oblique layer)
- mucosa: simple columnar epithelium with goblet cells that secrete a protective alkaline mucus
- mucosa folds inward to form gastric pits & deeper gastric glands that secrete gastric juice
o secretory cells of gastric glands:
o mucous neck cells: in upper "neck" region; secrete acidic mucus
o parietal cells: in middle region; secrete hydrochloric acid (HCl) and intrinsic factor (necessary for vitamin B12 absorption in small intestine)
o chief cells: in basal region; produce pepsinogen (precursor of enzyme pepsin, a protease)
o enteroendocrine cells: a variety of cell types that secrete hormones & hormone-like molecules (including gastrin, histamine, endorphins & somatostatin)
• G cells: secrete gastrin
- gastric ulcer: erosions of stomach wall due to persistent damage to mucosa & underlying tissues
o hypersecretion of HCl appears to be a predisposing factor, but the causative agent in most cases is the bacterium Helicobacter pylori, which destroys mucosal cells with enzymes, toxins & migration of inflammatory cells
• treatment: course of antibiotics in combination with bismuth
Small Intestine: convoluted tube extending from the pyloric sphincter to ileocecal valve; major function is completion of digestion & absorption of nutrients
- 3 subdivisions: duodenum, jejunum & ileum
o duodenum: shortest region; continuous with pylorus of stomach
• hepatopancreatic sphincter (sphincter of Oddi): controls entry of bile & pancreatic juice
o jejunum: extends from duodenum to ileum
o ileum: continuous with large intestine through ileocecal valve
- mesentery: attaches jejunum & ileum to posterior abdominal wall
- plicae circulares (circular folds): deep folds of mucosa & submucosa slowing chyme movement for absorption
- villi: fingerlike projections of mucosa composed of absorptive columnar cells called enterocytes
• mucosa: simple columnar absorptive cells with goblet cells
• intestinal crypts (crypts of Lieberkuhn): tubular intestinal glands between villi
• submucosa: areolar CT containing lymphoid follicles called Peyer's 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
- 4 primary lobes: right (largest lobe), left, quadrate & caudate
- falciform ligament: separates left & right lobes & suspends liver from diaphragm & anterior abdominal wall
- hepatic artery & hepatic portal vein travel through lesser omentum & enter liver
- hepatocytes (liver cells) secrete bile, which leaves liver through right & left hepatic ducts, which lead into common hepatic duct
o common hepatic duct fuses with cystic duct to form (common) bile duct
o hepatic macrophages (Kupffer cells) remove debris & bacteria from blood
- hepatitis: inflammation of liver, most often due to viral infection
- cirrhosis: chronic inflammation of liver often resulting from alcoholism or severe chronic hepatitis
- Composition of 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), aiding in digestion & absorption of fats
o bilirubin: bile pigment produced as a waste product of heme of hemoglobin during red blood cell breakdown
Gallbladder: thin-walled green muscular sac in a shallow fossa on the ventral surface of liver
- stores (& concentrates) bile that is not immediately needed; when needed, it is expelled through cystic duct into bile duct
- bile release is stimulated by the intestinal hormone cholecystokinin (CCK) following chyme entry into duodenum
- 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
o anal canal has 2 sphincters (internal & external anal sphincters) that open & close the anus during defecation
- 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
- defecation: defecation reflex initiated by stretching of rectal wall & mediated by spinal cord & parasympathetic fibers
o muscles of rectal wall contract to expel feces
o diarrhea: insufficient water absorbed from waste
o constipation: over-absorption of water from waste
o food poisoning: caused by Salmonella bacteria
- nutrient: substance in food that is used by the body to promote normal growth, maintenance & repair
o major nutrients: carbohydrates, lipids, proteins, vitamins, minerals & water
o essential nutrients: nutrients that cannot be synthesized by chemical reactions in the body, & must be obtained from the diet
- Carbohydrates
o Dietary sources: sugars from fruits, sugar (cane), honey, milk; starch from grains, vegetables; cellulose from most plants (cellulose is indigestible = fiber)
o Uses in the body: glucose is major body fuel; used to make ATP (other sugars such as fructose & galactose are converted to glucose by liver)
- Lipids
o Dietary sources: saturated fats in meats & dairy products (& some plants); unsaturated fats in seeds, nuts & vegetable oils; cholesterol in egg yolks, milk products, meats
o Uses in the body: fats help the body absorb fat-soluble vitamins; triglycerides are major source of energy for hepatocytes & skeletal muscle; phospholipids used to synthesize cellular membranes; fats used as cushioning & insulation in adipose tissue; cholesterol used in plasma membrane, steroid hormone synthesis & bile salts
- Proteins
o Dietary sources: eggs, milk & most meats are complete proteins (contain all essential amino acids); vegetables must be used in combination to obtain all essential amino acids (cereal grains and legumes)
o Uses in the body: functional proteins regulate most chemical reactions in cells; structural proteins important for skin, connective tissue fiber & muscle contraction
- Vitamins: organic compounds needed in small amounts for growth & metabolism
o Vitamins not used for energy, but are critical in energy-producing reactions
o most vitamins function as coenzymes (assist enzyme in its activity)
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)
o water-soluble vitamins: absorbed along with water from GI tract
• includes vitamin C & the B vitamins
o fat-soluble vitamins: bind to ingested lipids & absorbed along with their digestion products
• includes vitamins A, D, E & K
o balanced diet necessary to obtain all required vitamins
o vitamins A, C, & E are antioxidants that neutralize harmful free radicals in body
- Minerals: also not used for energy, but used by other nutrients to carry out necessary cellular reactions
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)
Chapter 16: The Urinary System
- kidneys lie in a retroperitoneal position in superior lumbar region
- renal hilum: depression in concave medial surface of kidneys
o ureters, renal blood vessels, lymphatics & nerves enter & exit kidneys at hilum
- renal capsule: protective layer surrounding kidney containing adipose & connective tissue
- 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: continuous with ureter leaving hilum
• major calyces: branching extensions of pelvis; subdivide into 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
o Glomerular (Bowman's) capsule: end of renal tubule; encloses glomerulus
• parietal layer: simple squamous epithelium
• visceral layer: highly modified branching epithelial cells called podocytes
o proximal convoluted tubule (PCT)
• walls of simple cuboidal epithelial cells with microvilli; actively reabsorbs substances from filtrate & secretes substances into it
o loop of Henle
o 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 into papillary ducts at renal pelvis, which deliver urine to calyces
Ureters: tubes that convey urine from kidneys to bladder
- pressure increases in bladder during filling normally compress & close the distal ends of the ureters, preventing backflow
- mucosa lined with transitional epithelium; muscularis with inner longitudinal & outer circular smooth muscle sheets; adventitia of fibrous CT
- contraction of smooth muscle propels urine to bladder
- renal calculi (kidney stones): form from crystallization of salts in urine in renal pelvis; can obstruct ureters
o surgical removal has generally been replaced by shock wave lithotripsy (ultrasonic shock breaks up stones)
Urinary Bladder: collapsible muscular sac that stores urine temporarily
- trigone: triagonal region encompassing openings for both ureters & opening for urethra
- mucosa lined with transitional epithelium; muscularis (detrusor muscle) with inner longitudinal, middle circular & outer longitudinal smooth muscle sheets; adventitia of fibrous CT
- very distensible; collapses when no or little urine present & expands to accommodate urine
- normally holds ~ 600 ml urine; urination urge begins at ~ 250 ml
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)
- in males: prostatic urethra, membranous urethra & spongy (penile) urethra lead to external urethral orifice
Micturition (voiding or urination): act of emptying bladder
- when ~ 200 ml or urine has accumulated in bladder, contractions of bladder due to activation of stretch receptors & spinal reflexes in turn activates voiding reflexes
- the micturition center of the pons signals parasympathetic neurons that stimulate contraction of the detrusor muscle & relaxation of the internal & external sphincters, allowing urine expulsion
- voluntary control of the external sphincter allows urine retention
- incontinence: inability to control micturition (normal in infants)
- urinary retention: bladder unable to expel urine (can occur following anesthesia or in males with prostate hypertrophy)
- ~1000-2000 ml blood pass through glomeruli each minute; ~650 ml of this is plasma; ~120-125 ml of plasma is forced into renal tubules
- filtrate: everything in blood plasma except proteins
- urine: mostly metabolic wastes & unneeded substances (filtrate without most water, nutrients & essential ions)
- Glomerular filtration: mostly a passive, nonselective process in which fluids & solutes are forced through a membrane by hydrostatic pressure
- Tubular reabsorption: transepithelial process that reclaims most of tubule contents & returns them to blood
o sodium is actively transported out of the tubule cell by a sodium-potassium ion ATPase pump in the cell membrane & moves passively by diffusion into the peritubular capillaries
o anions (chloride & bicarbonate) are passively reabsorbed
o glucose, amino acids, lactate, vitamins & most cations are transported along with sodium
o nonreabsorbed substances: some substances are not reabsorbed because they lack carriers, are not lipid soluble, or are too large
⋅ most important are urea, creatinine & uric acid
o 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
• secretion important for: disposing of substances not already in filtrate (drugs), eliminating unwanted substances (urea & uric acid), elimination of excess potassium ions & controlling blood pH
- Formation of dilute urine: normal course of filtration; low antidiuretic hormone (ADH) levels & collecting ducts remain impermeable to water
- Formation of concentrated urine: increased release of ADH from posterior pituitary inhibits diuresis (urine output) by increasing reabsorption of water from collecting ducts (by creating water channels - aquaporins)
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
Hormonal Regulation:
- Aldosterone:
o without aldosterone, most sodium (90%) is reabsorbed in the proximal tubules & loop of Henle
o when aldosterone levels are high, nearly all the remaining sodium is actively reabsorbed from the distal tubules & collecting ducts
o if ADH is present, as sodium is reabsorbed, water follows
o aldosterone release from the adrenal cortex is regulated by the renin-angiotensin mechanism (angiotensin II) & elevated potassium ion levels in the ECF
- Antidiuretic Hormone (ADH):
o declining blood pressure & blood volume stimulates release of ADH from the posterior pituitary
o ADH increases water reabsorption from the collecting ducts
- Atrial Natriuretic Peptide (ANP):
o ANP reduces blood pressure & blood volume by inhibiting nearly all events (aldosterone, ADH & baroreceptors) that promote vasoconstriction and sodium & water retention
- Other hormones:
o estrogens & glucocorticoids exhibit aldosterone-like effects & enhance tubular reabsorption of sodium
Important Electrolytes:
- sodium ions required for nerve impulse conduction & muscle contraction as well as maintaining blood osmolarity
- potassium ions also required for nerve impulse conduction & muscle contraction; low blood potassium can lead to cardiac arrest
- bicarbonate ions (HCO3-) is formed from carbon dioxide in blood, & helps maintain blood pH (buffer)
- calcium & phosphate ions are important for bone formation & metabolism
- 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
- buffers maintain pH
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 protein buffer system: proteins in plasma & within cells can act as weak acids or weak bases
- kidneys can also regulate acid-base balance:
o during acidosis: bicarbonate ions generated while excreting hydrogen ions
o during alkalosis: bicarbonate ion secretion while reabsorbing hydrogen ions
Chapter 17: The Reproductive System
- Reproductive system becomes fully active during puberty
- Primary Sex Organs (Gonads): testes in males & ovaries in females
o Gonads produce gametes & secrete sex hormones
• Testes produce sperm through spermatogenesis
• Ovaries produce ova through oogenesis
- Accessory Reproductive Organs: ducts, glands & external genitalia
Testes: lie within scrotum; produce male gametes (sperm)
- scrotum: sac of skin & superficial fascis that houses testes in left & right compartments
o temperature of scrotum must be ~ 3°C lower than core body temperature for production of viable sperm
o contraction of muscles in scrotum pulls scrotum closer to body, increasing temperature, while relaxation allows scrotum to assume a lower position, decreasing temperature
- each testis divided into 250-300 lobules
- each lobule contains 1-4 seminiferous tubules, where sperm is produced
o sperm travels through system of ducts to epididymis
o spermatogenesis: sperm formation by meiosis in seminiferous tubules of testes
o begins occurring during puberty & continues throughout life
o normally ~ 400 million sperm produced each day
o summary of events in seminiferous tubules
• mitosis of spermatogonia: spermatogonia divide to form 2 cells
⋅ one of the resulting cells becomes a primary spermatocyte, destined to form 4 sperm cells
• meiosis: spermatocytes to spermatids
⋅ meiosis I: primary spermatocyte forms 2 secondary spermatocytes
o reduction in chromosome number from 46 to 23
⋅ meiosis II: each secondary spermatocyte forms 2 spermatids
• Spermiogenesis: spermatids to sperm
⋅ each spermatid undergoes changes to form sperm cell
⋅ 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
⋅ at other end, tail region forms, with a flagellum containing many mitochondria (supplying energy for moving flagellum)
- interstitial cells (Leydig cells): surround seminiferous tubules; produce androgens (testosterone)
- testicular cancer is most common cancer in young men; treatment is surgical removal of tumor followed by radiation & chemotherapy
- Epididymis: coiled tube that delivers immature sperm leaving testis to ductus deferens
o En route, sperm gain ability to swim
- Ductus Deferens (vas deferens): propels live sperm from epididymis to urethra
o ductus deferens is a long tube that runs from epididymis upward, loops over ureter & descends posteriorly along bladder, where it joins with seminal vesicle to form ejaculatory duct
o Ejaculatory duct passes into prostate gland & empties into 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
o sperm & seminal fluid mix in ejaculatory duct & enter prostatic urethra during ejaculation
- 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
o prostate gland hypertrophy affects nearly every elderly male
• treatments include microwaves, drugs & transurethral needle ablation
• prostate cancer is usually second or third most common cancer in men
- Bulbourethral Glands (Cowper's glands): small glands inferior to prostate gland
o produce thick clear mucus prior to ejaculation that neutralizes acidic urine in urethra
Semen: mixture of sperm & accessory gland secretions
- provides nutrients & transport medium for sperm & chemicals that facilitate movement
- fructose provides fuel
- prostaglandins decrease viscosity of mucus at uterine cervix & stimulate reverse peristalsis of uterus & uterine tubes to move sperm through female reproductive tract
- alkalinity of semen due to bases (spermine) helps neutralize acidic environment of male urethra & female vagina
Penis: copulatory organ; releases sperm produced by testes
- male external genitalia: penis & scrotum
- penis made up of attached root & free body or shaft ending in enlarged tip called glans penis
- prepuce (foreskin): cuff of skin covering penis; may be removed by circumcision
- erectile tissue: network of connective tissue & smooth muscle with vascular spaces that become filled with blood during sexual excitement
o nitric oxide: dilates arterioles supplying erectile tissue
o impotence: inability to achieve erection
- Gonadotropin-releasing hormone (GnRH) release from hypothalamus controls release of follicle-stimulating hormone (FSH) & luteinizing hormone (LH) from anterior pituitary
- FSH stimulates sustentacular cells to release androgen-binding protein (ABP), which causes spermatogenic cells to bind testosterone & begin spermatogenesis
- LH binds to interstitial cells & stimulates them to secrete testosterone
- Testosterone feeds back (negative feedback) to hypothalamus & anterior pituitary, inhibiting release of GnRH & tropic hormones
- Inhibin released by sustentacular cells inhibits release of FSH from anterior pituitary & GnRH from hypothalamus
- some target cells require conversion of testosterone to another steroid (dihydrotestosterone (DHT) in prostate, estrogen in brain) to exert its effects
- testosterone also controls appearance of secondary sex characteristics in males & boosts metabolism
Ovaries: female gonads; produce oocytes & female sex hormones (estrogens & progesterone)
- flank uterus on each side; held in place within peritoneal cavity by ligaments
- 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
o follicle matures from a primordial follicle to a primary follicle to a secondary follicle & finally a vesicular (Graafian) follicle
o 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)
• 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
- ovulation: ejection of oocyte from follicle & ovary
- corpus luteum: structure formed from follicle cells following ovulation; eventually degenerates
Genital Tract
- Uterine Tubes (Fallopian tubes or Oviducts): receive ovulated oocyte from ovary & provide site for fertilization
o fimbriae: ciliated fingerlike projections called that drape over ovary
• ovulated oocyte is cast into peritoneal cavity; cilia of fimbriae sweep oocyte into uterine tube
o ampulla: expanded curved portion of uterine tube where fertilization normally occurs
o smooth muscle sheets in wall of uterine tube & mucosa with ciliated cells aid in carrying oocyte toward uterus
o developing embryo ordinarily migrates to & implants in uterus
• ectopic pregnancy: embryo implants in wall of uterine tube (cannot survive)
- Uterus: hollow, thick-walled organ in pelvis that receives, retains & nourishes a fertilized ovum
o cervix (neck) projects into vagina
• cervical cancer: caused by certain types of human papillomavirus (HPV); can be diagnosed by Pap (Papanicolau) smear
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
⋅ stratum functionalis (functional layer): undergoes cyclic changes in response to ovarian hormones; shed during menstruation
⋅ stratum basalis (basal layer): forms new functional layer after menstruation
- Vagina: thin-walled tube between bladder & rectum extending from cervix to body exterior
o provides passageway for delivery of baby, for menstrual flow & for delivery of semen (& sperm) to uterine tube
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)
o hymen: incomplete mucosal partition covering vaginal orifice that is normally ruptured during first sexual intercourse
- External Genitalia (Vulva)
o mons pubis: fatty rounded area overlying pubic symphysis
o labia majora: elongated skin folds running posteriorly from mons pubis & enclosing labia minora
o labia minora enclose recess called vestibule, which contains the external opening of urethra (anteriorly) & vagina (posteriorly)
o clitoris: small protruding erectile tissue (corpora cavernosa) hooded by prepuce formed by junction of labia minora folds
- Mammary Glands
o present in both sexes; normally only function in females
o produce milk & nourish newborn baby
o composed of modified sweat glands contained within a rounded skin-covered breast, anterior to pectoral muscles
o milk collects in lactiferous sinuses & is passed into lactiferous ducts, which open to the outside of the nipple
o invasive breast cancer is the most common cancer of U.S. women
• cancer usually arises from epithelial cells of ducts
• known risk factors include: early onset menses & late menopause; no pregnancies or first pregnancy later in life; previous history of breast cancer; family history of breast cancer (possible risk factors include overexposure to estrogens, cigarette smoking & alcoholism)
• hereditary forms (~ 10% of all cases) often stem from mutations in breast cancer susceptibility genes BRCA1 & BRCA2
• can be detected by breast self-examination & mammography
• treatment includes radiation & chemotherapy, and surgery (radical mastectomy has been mostly replaced by lumpectomy or, if necessary, simple mastectomy)
Female Sexual Response
- erectile tissue in clitoris & breasts engorge with blood (similar to male response in penis), while increased activity of vestibular glands lubricates vestibule
- follicular phase: period of follicle growth; days 1-14
o primordial follicle->primary follicle->secondary follicle->vesicular follicle
- ovulation: bulging ovary wall ruptures & releases secondary oocyte into peritoneal cavity; ~ day 14
o fraternal twins: more than one oocyte ovulated, & each fertilized by different sperm (~1-2% of ovulations are multiple oocytes)
o identical twins: one oocyte fertilized by one sperm, & during early embryogenesis cells divide into separate embryos
- luteal phase: period of corpus luteum activity; days 14-28
o after ovulation, ruptured follicle collapses, antrum fills with clotted blood & follicle grows into endocrine gland called corpus luteum
o corpus luteum secretes progesterone & some estrogen
o if pregnancy occurs, corpus luteum continues to produce hormones until placenta can assume its role; otherwise, corpus luteum degenerates within ~ 10 days
- Hormonal Regulation of Ovarian Cycle
o GnRH released from hypothalamus stimulates FSH & LH release from anterior pituitary
o FSH & LH stimulate follicle growth & estrogen secretion
o estrogen levels rise & feed back to anterior pituitary, inhibiting release (while stimulating production) of FSH & LH; in ovary, estrogen secretion is enhanced by maturation of follicles under the influence of FSH
• inhibin release by granulose cells of follicle also inhibits FSH release
o as estrogen levels peak (about midcycle), a burstlike release of accumulated LH (& FSH) from anterior pituitary stimulates secondary oocyte formation & ovulation; LH also transforms the ruptured follicle into a corpus luteum
o release of progesterone, estrogen & inhibin from corpus luteum inhibits release of FSH & LH from anterior pituitary
o as LH blood levels decline, corpus luteum degenerates, & declining levels of progesterone & estrogen remove block to FSH & LH release; cycle begins again
Uterine (Menstrual) Cycle: cyclic changes in uterine endometrium in response to ovarian hormones in blood
- menstrual phase (days 1-5): uterus sheds all but deepest layer of endometrium; detached tissue & blood pass out through vagina as menstrual flow
- proliferative phase (days 6-14): as estrogen blood levels rise, endometrium rebuilds itself
o ovulation occurs in ovary at end of this phase (day 14)
- 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
Sexually Transmitted Diseases (STDs or Venereal Diseases (VDs): infectious diseases spread through sexual contact
- Gonorrhea: caused by bacterium Neisseria gonorrheae
- Syphilis: caused by bacterium Treponema pallidum
- Chlamydia: caused by parasitic bacterium Chlamydia trachomatis
- Genital Warts: caused by human papillomavirus (HPV) (certain types also cause invasive cervical cancer)
- Genital Herpes: caused by human herpesviruses (herpes simplex virus, Epstein-Barr virus)
- bacterial pathogens treated with antibiotics, while viral pathogens are generally treated with antiviral medications
Puberty: the period of life (between 10-15 years of age) when the reproductive organs grow to their adult size & become functional in response to gonadal hormones
Menopause: the time of life in females (usually between 46-54 years of age) when menstruation (& ovulation) ceases
- gradual decline in estrogen levels causes the reproductive organs & breasts to atrophy, with many other possible effects
- hormone replacement therapy may be used to alleviate the signs & complications, but may increase risk of some hyperproliferative diseases (breast cancer)
Chapter 18: Human Development & Birth
Fertilization: fusion of sperm & egg to form a zygote
- sperm viable from 24 hours up to 72 hours; egg viable for 12-24 hours after ovulation
- only a few thousand of millions of sperm in semen reach uterine tubes; those that do must be capacitated
- corona radiata & zona pellucida of oocyte must be broken down for sperm to gain entry into oocyte
o hundreds of sperm release enzymes from acrosome that break down protective covering of oocyte
o once path is cleared, one sperm is able to contact oocyte receptors & its nucleus is pulled into oocyte cytoplasm
o cortical granules within oocyte release enzymes that destroy sperm receptors to prevent further sperm entry
- 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)
- ovum & sperm nuclei combine to form the zygote
- almost immediately, the zygote begins cell division on its way from the uterine tube to the uterus
- cleavage: period of rapid mitotic divisions of the zygote following fertilization
o zygote->2 cell stage->4 cell stage->8 cell stage->morula->blastocyst
- implantation: when blastocyst reaches uterus, it embeds itself in the prepared uterine lining, or endometrium
o cells surrounding embryo begin secreting the hormone human chorionic gonadotropin (hCG), which prevents menstruation
o physical signs of pregnanc include: cessation of menstruation, increased frequency of urination, morning sickness, & increase in size/tenderness of breasts
o early pregnancy tests detect hCG in the urine (can be detected as early as 14 days after fertilization)
• false negatives can be due to testing too soon or ectopic pregnancy; false positives can be due to excess protein in blood or urine or a rare form of uterine cancer
- Pregnancy: the events that occur from the time of fertilization (conception) until childbirth
- gestation period: time of development; from last menstrual period until birth
- preembryo: first 2 weeks of development
- embryo: third through eighth weeks (embryonic period)
- fetus: ninth week through birth (fetal period)
Extraembryonic Membranes:
- amnion: sac that fills with amniotic fluid (from maternal blood & fetal urine) that cushions & protects embryo against trauma & maintains temperature
- yolk sac: sac that hangs from ventral surface of embryo that forms part of the gut, produces earliest blood cells & vessels and is the source of primordial germ cells that form gonads
- allantois: small outpocketing of yolk sac that is the structural base for umbilical cord formation & forms part of urinary bladder
Placenta arises from trophoblast & endometrial tissue
- trophoblast cells of embryo give rise to chorion which begins formation of placenta, with chorionic villi, forming spaces that will be surrounded by blood vessels feeding fetal circulation
- placenta continues secretion of hCG, & eventually takes over secretion of estrogen & progesterone, which encourage growth & differentiation of mammary glands
- the ovarian cycle & menstruation do not occur during pregnancy
- placenta is usually fully formed by third month, & sloughs off after childbirth
- umbilical cord: transports fetal blood to & from the placenta
o contains umbilical arteries & umbilical veins
Embryonic & Fetal development: see table 18.1, page 368
- Anatomical Changes: female reproductive organs become larger, increasingly vascularized & engorged with blood
- Metabolic Changes: placental hormones stimulate maturation of breasts for lactation & increased metabolic rate
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
- Stages of Labor:
- Dilation Stage: time from labor's onset until cervix is fully dilated by baby's head (~ 10 cm)
- Expulsion Stage: lasts from full dilation until childbirth
o Crowning: when largest dimension of baby's head distends vulva
o Vertex (head-first) presentation: skull of baby dilates cervix
o Breech (buttock-first) presentation: delivery may require forceps
o Caesarian (C) section: delivery of infant through abdominal & uterine walls
- Placental Stage: delivery of placenta (afterbirth), within 30 minutes of childbirth
Lactation: production of milk by hormone-prepared mammary glands
- Prolactin-releasing hormone (PRH) from hypothalamus stimulates anterior pituitary to release prolactin
- after 2-3 days, milk production begins
- suckling (& other stimuli, such as baby's cry) stimulates oxytocin release from the posterior pituitary
- oxytocin causes release of milk into mammary ducts via milk ejection reflex
- frequent lactation can inhibit ovulation (by inhibiting GnRH, FSH & LH release) during the first few months following childbirth
- benefits of breast-feeding to newborn:
o beneficial cells: white blood cells in milk help to fight infection
o beneficial molecules: immunoglobulins (IgA), lysozyme & interferons also help fight infection; B12-binding protein binds vitamin B12 & lactoferrin binds iron, so that bacteria can't use them for growth