Biology 110

Study Notes Exam 5

 

Chapter 15: The Digestive System

 

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

 

Nutrition

-       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

 

Kidney Anatomy

-       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)

 

Kidney Physiology: Mechanisms of Urine Formation

-       ~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

 

Regulation of Urine Concentration & Volume

-       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

 

Acid-Base 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

-       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

 

Anatomy of the Male Reproductive System

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

 

Male Duct System

-       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

 

Hormonal Regulation of Male Reproductive Function

-       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

 

Anatomy of Female Reproductive System

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