Lecture: Reproduction & Development Flashcards
Define: gametes.
sex cells;
males: spermatozoon (sperm);
females: ovum (egg)
Explain chromosomal sex determination.
23 pairs of chromosomes: -22 autosomes -1 pair of sex chromosomes; ovum contains X; half of sperm contain X, half contain Y
Does sexual differentiation end with fertilization? Explain.
No: requires an interaction between genetics and hormones;
fetus is “non-committed” until 5-6 weeks
Name the 2 ducts adjacent to gonadal ridges which interact with prenatal hormones to undergo sexual differentiation.
2 pairs of ducts along each mesonephros, or primitive kidney:
1) mesonephric (wolffian) ducts:
2) paramesonephric (mullerian) ducts:
Explain how the mesophrenic (wolffian) ducts interact with prenatal hormones to undergo sexual differentiation.
Y chromosome has a gene called SRY (sex-determining region of the Y) that codes for a protein called testis-determining factor (TDF);
rudimentary testes form in 8-9 weeks and secrete:
-testosterone: causes development of male reproductive tract
-mullerian-inhibiting factor (MIF): causes atrophy of paramesonephric ducts
Explain how the paramesonephric (mullerian) ducts interact with prenatal hormones to undergo sexual differentiation.
absence of testosterone and MIF causes development of female reproductive tract
Define: homologous.
male and female organs that develop from the same embryonic structure
In the embryo, the genitals begin developing from identifical structures in both sexes. Name these 3 structures (present at 6 weeks) and name what they develop into.
1) genital tubercle: penis/clitoris
2) urogenital folds: urethra/labia minora
3) labiosacral folds: scrotum/labia majora
Describe the process of the descent of the testes.
begins around embryonic week 6;
though inguinal canal to scrotum (~7 months);
descent guided by testosterone, but not well understood
Define: inguinal canal.
path of low resistance through the groin that serves as a path for testicular descent
Define: cryptorchidism.
condition present in 3% of boys in which they are born with undescended testes
Name the major structures and functions of the male reproductive system.
scrotum and testes: spermatogenesis;
spermatic ducts and accessory glands: transport;
penis: emission
Describe the contents of the scrotum.
testes; spermatic cord: -ductus deferens (sperm duct) -blood/lymph vessels -nerves mechanisms for temp regulation -cremaster muscle: contracts when cold -dartos muscle: contracts when cold -pampiniform plexus: network of veins that cools warm arterial blood that would inhibit sperm production
Describe the microanatomy of the testes.
tunica albuginea: outer white fibrous capsule;
250-300 lobules: each contains 1-3 seminiferous tubules, which produce sperm;
3 cell types:
interstitial (Leydig) cells: produce testosterone;
germ cells: in process of becoming sperm;
sustenacular (Sertoli): protect germ cells and promote their development; secrete nutrients and inhibin
Describe the 3 special cell types present in the testes.
1) interstitial (Leydig) cells: produce testosterone;
2) germ cells of germinal epithelium: in process of becoming sperm;
3) sustenacular (Sertoli): protect germ cells and promote their development;
secrete nutrients and inhibin;
form blood-testis barrier (BTB)
Define: inhibin.
hormone secreted by sustenacular (Sertoli) cells which regulates the rate of sperm production;
helps to produce a protein called ABP (androgen-binding protein)
Define: blood-testis barrier (BTB).
barrier formed by sustenacular (Sertoli) cells which protects sperm from attack by immune system
Describe the 3 spermatic ducts.
1) efferent ductule carries sperm from posterior testes to epididymis
2) ductus (vas) deferens propels sperm from epididymis to urethra
3) ejaculatory duct: where ductus deferens and seminal vesicle meet;
passes through prostate and empties into urethra
Define: epididymis.
site of sperm maturation and storage
Name the 3 accessory glands associate with the male reproductive system.
1) seminal vesicle
2) prostate gland
3) bulbourethral gland
Explain the role of the seminal vesicle.
mucus-like secretions make up 60% of semen volume;
provides nutrients for sperm;
secretions contain proseminogelin;
Explain the role of prostate gland.
alkaline secretions protect sperm from acidity of vagina;
calcium, citrate, phosphate;
serine protease: liquefies semen;
clotting enzyme activates proseminogelin to seminogelin, which gives sperm its stickiness
Explain the role of bulbourethral gland.
secrete alkaline fluid, which neutralizes the urethra, when sexual arousal first occurs;
lubricates penis
Explain composition and function of the penis.
3 divisions:
- root
- shaft: 2 bodies of erectile tissue (corpus spongiosum & corpus cavernosum)
- glans
function: delivery of semen
Explain endocrine control of puberty.
at puberty, hypothalamus begins releasing gonadotropin-releasing hormone (GnRH);
GnRH stimulates anterior pituitary to release FSH and LH
Explain follicle-stimulating hormone’s (FSH) role in puberty.
stimulates sustenacular (Sertoli) cells to secrete androgen-binding protein (ABP); without FSH and ABP, testosterone would have no effect on the testes
Explain luteinizing hormone’s (FSH) role in puberty.
stimulates interstitial (Leydig) cells to release androgens, especially testosterone
What is the role of androgen-binding protein (ABP)?
raises testosterone levels in the seminiferous tubules and epididymis;
without FSH and ABP, testosterone would have no effect on the testes
Name the 7 effects of testosterone.
1) spermatogenesis
2) secondary sex characteristics
3) enlargement of reproductive structures
4) inhibits GnRH, FSH, and LH secretion
5) body growth
6) accelerates erythropoiesis
7) awakens libido
Give an overview of the process of sperm production.
Division of germ cells;
meiosis I:
-parent cell is diploid (2n) (46 chromosomes);
-2 daughter cells are haploid (n) (23 chromosomes);
meiosis II:
-more like mitosis;
-ends with 4 haploid cells (n) (23 chromosomes);
each spermatid undergoes spermatogenesis
Explain spermatogenesis.
primordial germ cells: first stem cells destined to become sperm; after they migrate to the gonadal ridges, they change into spermatagonia, which lie upon the basement membranes of the seminiferous tubules outside of the BTB;
spermatagonia:
-Type A: always remain at basement membrane outside of BTB
-Type B: migrate toward the lumen of the seminiferous tubule and become…
primary spermatocytes, which move through the BTB and undergo meiosis I to become…
-2 haploid secondary spermatocytes, which each undergo meiosis II to become…
-2 spermatids (4 total)
Explain spermiogenesis.
spermatid undergoes spermiogenesis, in which it differentiates into a spermatozoon (sperm):
-sprouts tail (flagellum)
-discards cytoplasm
-takes 74 days
sperm production: 300,000/min, 400million/day
Describe the structure of spermatozoa.
head: -nucleus with tip covered by acrosome, which contain enzymes to penetrate the egg tail: -midpiece, contains mitochondria -principal piece -end piece
Describe the composition and functions of semen.
10% sperm
30% prostatic fluid
60% seminal vesicle fluid
function: nourishment, protection, & activation of sperm
Compare and contrast normal and infertile sperm count.
normal: 50-120 mill/mL
infertile: 20-25 mill/mL
Name the 4 stages of male sexual arousal.
1) excitement
2) plateau
3) orgasm
4) resolution
Describe the excitement stage of male sexual arousal.
vasocongestion;
myotonia: muscle tension;
parasympathetic fibers release nitric oxide, which leads to a relaxation of the deep arteries so that they fill with blood
Describe the plateau stage of male sexual arousal.
effects of excitement stage are maintained
Describe the orgasm stage of male sexual arousal.
ejaculation:
-emission: SNS stimulates peristalsis in the smooth muscle of the ductus deferens;
path of sperm: tail of epididymis, ductus deferens, ampulla, prostatic urethra, urethra;
-expulsion: SNS stimulates expulsion of semen and constricts the urethral bladder
Describe the resolution stage of male sexual arousal.
SNS reduces blow flow;
detumescence: penis becomes soft and flaccid again;
refractory period: 10 mins to hours; no erection possible
Name the female reproductive organs.
gonads: ovaries; genitalia: internal -uterine tubes -uterus -vagina external: -labia majora -labia minora -clitoris -vestibular glands
Describe the function and structure of ovaries.
functions: produce gametes and sex hormones structure: -capsule: tunica albuginea (like testes) -cortex: contains follicles -medulla: contains blood vessels
Describe the composition of the uterine tubes.
a.k.a. oviducts or fallopian tubes; infundibulum with fimbriae; tissue layers: -middle: smooth muscle -mucosa: cilia and secretory cells held by ligaments
Describe the function and structure of the uterus.
function: nourishment of zygote;
regions: fundus, body, cervix;
cervix contains cervical glands which secretes mucus;
layers: perimetrium, myometrium, endometrium
Describe the functions and structure of the vagina.
functions:
-discharge of menstrual fluid
-intercourse
-childbirth
structures:
-vaginal orifice
-hymen
-dendritic cells: antigen-presenting cells, a route by which HIV from infected semen invades the female body
Describe the female external genitalia.
mons pubis: area where pubic hair grows above pubic symphysis;
labia majora;
labia minora;
vestibule: area enclosed by labia minora
-clitoris: erectile tissue
-vestibular glands: lubrication
-paraurethral glands: similar to prostate
Describe the composition of the mammary glands.
breasts composed of lobes of glandular tissue;
lobes converge to form lactiferous duct, which dilate to form a lactiferous sinus opening into the nipple
Describe the cascade of hormones which cause female puberty.
hypothalamus secretes GnRH, which stimulates anterior pituitary to release FSH and LH:
-FSH stimulates development of ovarian follices, which in turn stimulates secretion of ovarian hormones
What are the 3 noticeable effects of female puberty?
1) thelarche: onset of breast development
2) pubarche: appearance of pubic and axillary hair
3) menarche: first menstrual period
Define: climacteric.
midlife change in hormone secretion, accompanied by menopause, the cessation of menstration
Give an overview of the female reproduction.
oogenesis: egg production; sexual cycle: -ovarian cycle: events in ovaries -menstrual cycle: events in uterus reproductive cycle: events from fertilization to birth
Describe the process of oogenesis.
haploid gametes produced by meiosis;
cyclic event that releases one egg/month;
germ cells arise from the embryonic yolk sac and differentiate into oogonia;
6-7 million present shortly prefer birth;
oogonia transform into primary oocytes;
however, atresia (degeneration) occurs:
only about 400,000 primary oocytes remain by puberty
Name the 4 stages of female sexual arousal.
1) excitement
2) plateau
3) orgasm
4) resolution
Describe the excitement stage of female sexual arousal.
vasocongestion: -clitoris -labia majora & minora -vaginal transduate: serous fluid that lubricates canal myotonia
Describe the plateau stage of female sexual arousal.
effects of excitement stage are maintained;
tenting effect: uterus stands vertical instead of tilting forward toward the urinary bladder
Describe the orgasm stage of female sexual arousal.
clitoris: sensory nerve endings
paraurethral glands (homologous to male prostate): “female ejaculation”;
uterus exhibits peristaltic contractions which may help to draw semen from the vagina
Describe the resolution stage of female sexual arousal.
unlike men, no refractory period, so women may experience multiple orgasms ;)
Describe the 4 hormones that play a role in pregnancy.
1) human chorionic gonadotropin (HCG)
- secreted by placenta
- detected by home pregnancy tests
2) estrogen
- stimulates tissue growth
3) progesterone
- secreted by placenta and corpus luteum
- prevents follicle development & menstruation
4) human chorionic somatommotropin (HCS)
- not understood, thought to contribute to growth and development of
Give a brief overview of the key elements of childbirth.
childbirth = parturition; Braxton Hicks contractions = weak contractions that occur throughout gestation; labor induced by positive feedback: -cervical stretching >>> oxytocin secretion >>> uterine contraction >>> cervical stretching 3 stages: -dilation -expulsion -placental
Explain lactation.
synthesis and ejection of milk;
estrogen, progesterone, prolactin, and GH cause development of mammary glands during pregnancy;
in late pregnancy, colostrum secretion begins;
prolactin governs milk synthesis; its levels cycle between infant feedings;
milk synthesis also requires GH, cortisol, insulin, and PTH;
milk ejection: mechanical stimulation (suckling) stimulates oxytocin
