Study Notes Exam 4
Body Fluids
- Body Water Content:
o infants „ 73% water; normal adult males ~ 60%; normal adult females ~ 50%; elderly ~ 45%
o skeletal muscle more hydrated (~ 65% water) than adipose tissue (¾ 20% water)
- Fluid Compartments:
o Intracellular fluid (ICF): water within cells of the body; ~ 62% of body¹s water
o Extracellular fluid (ECF): water in the body outside cells
§ Plasma: fluid component of blood; ~ 8% of body¹s water
§ Interstitial fluid (IF): fluid in spaces between tissue cells; ~ 30 of body¹s water
· usually includes lymph, CSF, synovial fluid, serous fluid, etcŠ
- Composition of Body Fluids:
o Solutes: Electrolytes & Nonelectrolytes
§ nonelectrolytes: molecules that have no electrical charge; do not dissociate in water (e.g.: organic molecules such as glucose, lipids, creatinine & urea)
§ electrolytes: molecules that do dissociate in water into charged particles (e.g.: inorganic salts, organic & inorganic acids & bases, some proteins)
· since electrolytes dissociate into 2 or more ions in water, they have the greatest ability to cause osmotic movement of water
o Comparison of Intracellular & Extracellular Fluids
§ extracellular fluid: chief ions are sodium cations (positive ions) & chloride anions (negative ions)
§ intracellular fluid: chief ions are potassium cations & phosphate anions (negative ions)
§ cellular ATP-dependent sodium-potassium pumps maintain balance (keep sodium ions outside cell & potassium ions inside cell)
§ since ions are generally small molecules, proteins & large nonelectrolytes (mostly lipids) are the bulk of the mass of dissolved solutes in body fluids
- Fluid Movement Among Compartments
o exchanges between plasma & interstitial fluid occur across capillary membranes
o exchanges between interstitial & intracellular fluids occur by passive transport (osmosis & diffusion) & active transport
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
- Regulation of water intake: the thirst mechanism
o hypothalamic thirst center stimulated when osmoreceptors lose water by osmosis to ECF; results in sensation of thirst
- Regulation of water output:
o insensible water losses from skin & lungs; sensible water loss through urine output tied to sodium & water balance
- 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
o Edema: atypical accumulation of water in interstitial space, leading to tissue swelling
§ increased fluid movement from blood to interstitial space – can be caused by increased blood pressure or capillary permeability, or hypoproteinemia (low plasma protein levels)
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
§ aldosterone release from the adrenal cortex is regulated by the renin-angiotensin mechanism of the juxtaglomerular apparatus & elevated potassium ion levels in the ECF
o cardiovascular system baroreceptors:
§ decreasing blood volume stimulates baroreceptors (pressure receptors) in the heart & large vessels (aorta & carotid arteries), alerting cardiovascular centers in brain stem
§ 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 potassium ions important for electrical conduction in neurons & muscle cells
o potassium ions also part of the blood buffer system; as hydrogen ions are transported into & out of cells, potassium ions are transported in the opposite direction
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
- Regulation of other ions:
o Calcium & phosphate ion levels are regulated by the interaction of parathyroid hormone & calcitonin
o Chloride ion reabsorption is ordinarily coupled to sodium ion reabsorption & transport (ordinarily nearly all chloride ions reabsorbed)
- 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
§ CO2 + H2O «H2CO3 « H+ + HCO3-
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
- physiological buffer systems:
o respiratory system regulation of hydrogen ion concentration:
§ carbon dioxide from metabolism enters blood & combines with water to form carbonic acid
· carbonic acid unstable & reversibly breaks down into hydrogen & bicarbonate ions
o renal mechanisms of acid-base balance:
§ conserving filtered bicarbonate ions: bicarbonate reabsorption
§ during acidosis: bicarbonate ions generated while excreting hydrogen ions
§ during alkalosis: bicarbonate ion secretion while reabsorbing hydrogen ions
Chapter 27: 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 fascia 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 temperature maintained by contraction & relaxation of dartos & cremaster musclesŠ contraction pulls scrotum closer to body, increasing temperature, while relaxation allows scrotum to assume a lower position, decreasing temperature
- each testis is surrounded by 2 tunics: outer tunica vaginalis formed from peritoneum & inner tunica albuginea, formed from fibrous CT
- septa divide each testis into 250-300 lobules
- each lobule contains 1-4 seminiferous tubules, where sperm is produced
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)
- testicular arteries arise from abdominal aortas & supply blood to testes; testicular veins drain testes
- spermatic cord: connective tissue sheath enclosing blood vessels, lymphatics & nerves
- testicular cancer is most common cancer in young men; treatment is surgical removal of tumor followed by radiation & chemotherapy
Penis: copulatory organ; releases sperm produced by testes
- male external genitalia: penis & scrotum
- male perineum: diamond-shaped region bounded by pubic symphysis, coccyx & ischial tuberosities
- 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 corpus spongiosum: surrounds spongy urethra
o corpora cavernosa: paired dorsal erectile bodies
- 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 anterior to pubic bone into pelvic cavity, 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 (TUNA)
§ Prostate cancer is third most common cancer in men
- Bulbourethral Glands (Cowper¹s 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
- seminalplasmin: antibiotic in semen that destroys bacteria
- contains clotting factors to clot & fibrinolysin to liquefy semen
- 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 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
· tetrads or bivalents ³cross over² at similar regions
§ 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 moves to adluminal compartment & 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)
§ Role of sustentacular cells
· Sustentacular cells (Sertoli cells) surround cells of seminiferous tubules & connect to one another by tight junctions which form 2 compartments (basal & adluminal)
o junctions form blood-testis barrier that prevents immune cell targeting of sperm
- 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 parts of broad ligament (suspensory ligament & mesovarium)
- ovarian ligament anchors ovary to uterus
- ovarian arteries (branch from abdominal aorta) & ovarian branch of uterine arteries serve ovaries
- ovaries surrounded externally by tunica albuginea & germinal epithelium
- 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)
o primordial follicle: one layer of squamous cells enclose oocyte
o primary follicle: 2 or more layers of cuboidal or columnar cells surround oocyte
o secondary follicle: has central fluid-filled cavity (antrum)
o vesicular (Graafian) follicle: follicle bulges from ovary surface; oocyte sits on stalk of granulose cells at one side of antrum
- 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
o infundibulum: open funnel-shaped structure with ciliated fingerlike projections called fimbriae 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 isthmus: constricted region that leads into uterus
o smooth muscle sheets in wall of uterine tube & mucosa with ciliated cells aid in carrying oocyte toward uterus
o uterine tubes are covered by peritoneum & supported by mesentery called mesosalpinx
- Uterus: hollow, thick-walled organ in pelvis that receives, retains & nourishes a fertilized ovum
o consists of fundus, body & cervix from superior to inferior
o cervix (neck) projects into vagina
§ cervical canal communicates with vagina via external os & with uterus via internal os
§ cervical cancer: caused by certain types of human papillomavirus (HPV); can be diagnosed by Pap (Papanicolau) smear
o mucosa contains mucus-secreting cervical glands
o supports of uterus: mesometrium of broad ligament, lateral cervical ligament, uterosacral ligaments & round ligaments
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
· blood supply: uterine arteries->arcuate arteries(myometrium)->radial branches(endometrium)->straight arteries(basal layer) & spiral (coiled) arteries (functional layer)
- 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
o perineum: diamond shaped region surrounding external genitalia
- 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 glands consist of lobes separated form each other by fat & fibrous CT forming suspensory ligaments that support breasts
o lobules within lobes contain alveoli that produce milk when a woman is lactating following childbirth
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)
- 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
§ primordial follicle becomes primary follicle
§ primary follicle becomes secondary follicle
§ secondary follicle becomes vesicular follicle
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 collapses, antrum fills with clotted blood & follicle grows into endocrine gland called 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 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
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
- Extrauterine effects of estrogen & progesterone
o in addition to promotion of oogenesis & follicle growth in ovaries, estrogen also exerts anabolic effects on female reproductive tract (increasing size of the duct system in preparation for childbirth) & promotes appearance of secondary sex characteristics in female
o progesterone inhibits motility of uterus & promotes mammary gland activity
- Male sexual response:
o Erection: results from engorgement of erectile bodies in penis with blood
§ During sexual excitement, a parasympathetic reflex releases nitric oxide, which dilates arterioles supplying erectile tissue
§ Corpora cavernosa expand, enlarging & stiffening penis and compressing drainage veins
o Ejaculation: propulsion of semen from male duct system
§ sympathetic spinal reflex sends impulses to nerves serving genital organs
· reproductive ducts & accessory glands contract, emptying contents into urethra
· bladder sphincter muscle constricts, preventing urine release of reflux of semen into bladder
· bulbospongiosus muscles of penis undergo series of contractions, propelling semen along urethra
- Female Sexual Response
o erectile tissue in clitoris & breasts engorge with blood (similar to male response in penis), while increased activity of vestibular glands lubricates vestibule
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 28: Pregnancy & Human Development
Pregnancy: the events that occur from the time of fertilization (conception) until childbirth
- developing offspring called conceptus
- 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)
- 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
- Sperm Transport & Capacitation: only a few thousand of millions of sperm in semen reach uterine tubes; those that do must be capacitated
o capacitation: weakening of sperm membrane so that the acrosome¹s hydrolytic enzymes can be released
- Acrosomal reaction & sperm penetration: corona radiata & zona pellucida of oocyte must be broken down for sperm to gain entry into oocyte
o hundreds of sperm undergo acrosomal reaction, releasing acrosomal enzymes 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
- 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)
o ovum & sperm nuclei become female & male pronucleiŠ their nuclear membranes rupture & release their chromosomes, which combine to form the zygote
o almost immediately, the combined chromosomes replicate & the zygote divides to form 2 cells called blastomeres
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 when mucosa of endometrium is ready, the blastocyst implants – trophoblast cells secrete enzymes against endometrium & inflammatory cells migrate in creating thick lining into which blastocyst burrows
o trophoblast forms 2 layers at point of contact with endometrium
§ cytotrophoblast: inner layer
§ syncytiotrophoblast: outer layer that loses cell boundaries as it invades endometrium
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
o placenta also secretes hormones such as human placental lactogen, human chorionic thyrotropin & relaxin
o placenta is usually fully formed by third month, & sloughs off after childbirth (decidua)
Events of Embryonic Development:
- blastocyst is converted into gastrula, in which the 3 primary germ layers form
- Formation & Roles of Embryonic Membranes:
o amnion: sac that fills with amniotic fluid (from maternal blood & fetal urine) that cushions & protects embryo against trauma & maintains temperature
o 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
o allantois: small outpocketing of yolk sac that is the structural base for umbilical cord formation & forms part of urinary bladder
- Gastrulation: Germ Layer Formation
o during gastrulation, 3 primary germ layers form in embryo from raised groove called primitive streak
§ 3 layers are: ectoderm, mesoderm & endoderm
o some mesodermal cells form a rod called notochord, which serves as axial support for embryo
o endoderm & ectoderm consist of epithelia, while mesoderm consists of mesenchyme (star-shaped cells free to migrate within embryo)
- Organogenesis: Differentiation of Germ Layers
o specialization of ectoderm:
§ neurulation: differentiation of ectoderm to form brain & spinal cord
· induced by chemical signals from notochord
· neural plate forms over notochord, & folds inward as neural groove with neural folds
· superior margins of neural folds fuse to form neural tube
· anterior end of neural tube becomes brain; rest becomes spinal cord
· associated neural crest cells give rise to cranial, spinal & sympathetic ganglia, adrenal medulla & some connective tissues
o specialization of endoderm:
o edges of endoderm fuse around part of yolk sac forming tube called primitive gut, which forms epithelium of GI tract
o mucosae of respiratory tract form from foregut (pharyngeal endoderm)
o thyroid, parathyroid & thymus form from pharyngeal endoderm & liver & pancreas arise from midgut (intestinal mucosa)
o specialization of mesoderm:
§ notochord develops into vertebral column
§ somites: series of paired block of mesoderm around notochord
· sclerotome: produces vertebra & rib
· dermatome: helps form dermis of skin
· myotome: forms skeletal muscles
§ intermediate mesoderm: forms gonads & kidneys
§ lateral mesoderm:
· somatic mesoderm: helps form dermis, parietal serosa & bones, ligaments & dermis of limbs
· splanchnic mesoderm: forms heart, blood vessels & most connective tissue
- Development of fetal circulation:
o Umbilical arteries & vein & 3 shunts
§ ductus venosus: liver bypass
§ foramen ovale: pulmonary circuit bypass from right atrium to left atrium
§ ductus arteriosus: pulmonary circuit bypass from pulmonary trunk to aorta
Events of Fetal Development: see chart page 1080-1081 (no questions on exam)
Prenatal Diagnostic Tests:
- Fetal Ultrasonography: sound waves are passed over the abdomen, & the waves reflected by the fetus are converted to an on-screen sonogram image
o used to confirm pregnancy, determine accurate fetal age, evaluate fetal viability, determine fetal position, identify multiple pregnancies, & identify fetal-maternal abnormalities
- Amniocentesis: amniotic fluid is withdrawn with a hypodermic needle inserted through the mother¹s abdominal wall & into the amniotic cavity within the uterus
o Fluid is then used to test for abnormal protein levels (AFP) or as a source of cells for testing DNA for chromosomal damage or genetic disorders
- Chorionic Villi Sampling: a catheter is guided through the vagina & uterine cervix to chorionic villi (using ultrasound as a guide), & tissue (~ 30 mg) is suctioned out for chromosomal analysis
- Noninvasive Prenatal Tests: tests under development that do not entail penetration of embryonic structures
o maternal alpha-fetoprotein (AFP) test: abnormal (high) levels of AFP in maternal circulation after week 15 may indicate nervous system defects (spina bifida, anencephaly)
Hormones of Pregnancy:
- first 3-4 months: corpus luteum secretes progesterone & estrogens
- third month through end of pregnancy: placenta secretes progesterone & estrogens
- chorion secretes human chorionic gonadotropin (hCG) into blood, which stimulates hormone release from corpus luteum & prevents menstruation
- chorion also secretes progesterone & estrogens, but after the third month, the placenta is the primary source
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
- relaxin released by corpus luteum, & later, placenta, increases flexibility of joints (pubic symphysis & ligaments of sacroiliac & sacrococcygeal joints) & helps dilate uterine cervix during labor – both actions facilitate delivery
- human chorionic somatomammotropin (hCS) secreted by the chorion is thought to help prepare mammary glands for lactation, increase mother¹s protein synthesis for growth & metabolism
- corticotropin-releasing hormone produced by the placenta (usually produced by the hypothalamus) is thought to be the clock that establishes the timing of birth
- 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 labor¹s onset until cervix is fully dilated by baby¹s head (~ 10 cm)
- Expulsion Stage: lasts from full dilation until childbirth
o Crowning: when largest dimension of baby¹s 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
- 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
o colostrum, a milky fluid with fewer nutrients, is produced late in pregnancy & the first few days after birth & can substitute until milk is produced
- milk produced by glandular cells is stored until the baby begins suckling
- suckling (& other stimuli, such as baby¹s cry) stimulates oxytocin release from the posterior pituitary
- oxytocin causes release of milk into mammary ducts via milk ejection reflex
- suckling also inhibits release of prolactin-inhibiting hormone (PIH) from the hypothalamus, which increases PRH (& prolactin) release
- 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 can¹t use them for growth
o decreased incidence of diseases later in life: studies show reduced incidence of several diseases that occur later in life in children that breast-fed
o miscellaneous benefits: optimal growth & enhanced development, fosters mother-infant relationship, better sources of nutrients, etcŠ
Chapter 29: Heredity
Inheritance: the passage of hereditary traits from one generation to the next
- genetics: the branch of biology that deals with inheritance
- 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
- Punnett square: a representation of the possible combinations of gametes from 2 parents
- dominant allele: an allele that masks presence of another allele & is fully expressed
- recessive allele: an allele whose presence is completely masked
- 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
- genomic imprinting: a situation where the phenotype for a trait depends on the parental origin of the inherited allele
- nondisjunction: failure of homologous chromosomes or sister chromatids to separate during meiosis I or II
- aneuploid: abnormal number of chromosomes
- translocation: nonhomologous chromosomes break & exchange portions
- 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
· the disease is caused by a mutation in the gene for hemoglobin
· normal hemoglobin is HbA; sickle-cell hemoglobin is HbS
· individuals with the homozygous dominant genotype (HbAHbA) form normal hemoglobin & have normal red blood cells
· individuals with the homozygous recessive genotype (HbSHbS) have sickle-cell disease (sickle-shaped red blood cells) & severe anemia
· individuals with the heterozygous genotype (HbAHbS) have sickle cell trait (some normal red blood cells, some sickle-shaped red blood cells) & normally only mild anemia
- multiple-allele inheritance: traits with more than 2 alleles
o example: ABO blood groups
o alleles: IA, IB, i
§ IA allele produces A antigen
§ IB allele produces B antigen
§ I allele produces neither A nor B antigen
o type A blood: IAIA or IAi
o type B blood: IBIB or IBi
o type AB blood: IAIB
o type O blood: ii
o codominance: more than 2 alleles fully expressed
§ since type AB blood has both A & B antigens, both IA & IB alleles are dominant
- polygenetic inheritance: traits controlled by the combined effects of 2 or more genes
o includes most inherited traits
o complex inheritance: traits controlled by the combined effects of many genes & environmental factors
§ skin color, hair color, eye color, height, etc,
- 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-determining region of Y (SRY): prime male-determining gene on Y chromosome
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
- x-chromosome inactivation (lyonization): one X chromosome in females is randomly & permanently inactivated early in development, & most of the genes of the inactivated X chromosome (Barr body) are not expressed
Teratogens: an agent that causes developmental defects in the embryo
- chemicals & drugs: alcohol, pesticides, industrial chemicals, LSD cocaine & numerous prescription drugs (antibiotics, antitumor agents, thalidomide, etcŠ)
- cigarette smoking: studies show strong correlation between mothers who smoke & low birth weight, increased infant mortality & ectopic pregnancy, as well as a number of developmental abnormalities
o exposure to secondhand smoke during pregnancy or while nursing predisposes baby to increased incidence or respiratory problems
- irradiation: exposure to x-rays & radioactive isotopes during embryonic developmental stages of pregnancy may cause microcephaly, mental retardation & skeletal malformations