Question

MCAT Biology Tutorial: Human Development

Answer 1

Note: This tutorial will be covering aspects of human reproduction and development in a purely academic context. Any rude/immature comments will not be tolerated.

Answer 2

\({\bf{The~Human~Reproductive~System,~Basic~Terminology:}}\)
- humans have external & internal genitalia
> internal genitalia: gonads, produce gametes and hormones, called testes in men and ovaries in women
> germ cells: cells in the gonads that produce gametes through meiosis; called spermatagonia in men and oogonia in women
> spermatogenesis: production of male gametes (sperm)
> oogenesis: production of female gametes (ova)

\({\bf{The~Male~Reproductive~System:}}\)
- external components: penis and scrotum
- scrotum: skin that encloses the testes, maintains lower temperature for sperm
- seminiferous tubules: original location of sperm
- Leydig cells: secretes testosterone
- Sertoli cells: protect sperm
- epididymis: tubes where sperm matures and mobilizes
- vas deferens: connects to the epididymis; upon ejaculation sperm travels from the epididymis to the vas deferens
- vas deferens merge with the ejaculatory duct, prostate gland, bulbourethral glands, and urethra; sperm mixes w/ seminal fluids to form semen
- urethra: exit point for both semen and urine

\({\bf{Spermatogenesis:}}\)
- spermatogonia in the seminiferous tubules undergo mitosis until adolescence
- during/post adolescence: spermatogonia differentiate into primary spermatocytes
- primary spermatocytes move to the lumen of the seminiferous tubule, form secondary spermatocytes through meiosis I
- secondary spermatocytes: meiosis II, formation of spermatids --> spermatozoa --> exit through the epidymis

\({\bf{Anatomy~of~a~Sperm~Cell:}}\)
- head region: contains nucleus with very condensed DNA to improve motion
- acrosome: encloses the head region, contains hydrolytic enzymes to puncture the egg
- midpiece + tail in 9+2 microtubule arrangement w/ dynein (see tutorial on cell filaments)
- midpiece contains mitochondria for motion
- axoneme: microtubules + motor proteins in tail

Answer 3

\({\bf{The~Female~Reproductive~System:}}\)
external components:vulva; includes mons pubis, Supermanoris, labia
- mons pubis: area of fat underneath the pubic hair region
- Supermanoris: exposed tissue region anatomically homologous to penis
- labia: folds of skin/fat surrounding the urethra, Supermanoris, and vagina
- vagina (a.k.a birth canal): passage for sperm, infant, menstrual fluid

internal components:
- cervix: opening to the uterus
- uterus: smooth muscle cavity, protects fetus/pushes the infant through the vagina during labor
- endometrium: the lining of the uterus
- menstruation: shedding of the uterine lining
- fallopian tubes: connect the uterus to the ovaries (one on each side), location of fertilization
- fimbriae: move the oocytes off the ovary surface --> movement of the oocytes to the uterus is controlled by cilia/smooth muscle
- placenta: fetal and maternal tissue formation that nourishes the embryo

Answer 4

\({\bf{Oogenesis:}}\)
- stay in prophase I as primary oocytes
- at birth, 1M oocytes, but only 500 are released over the ~40 years of a woman's reproductive capacity
- oocytes reside in the ovarian follicles
- ovarian cycle: restarting of oogenesis on a monthly cycle; start of cycle is spurred by increase in FSH and LH
- ovulation: release of an egg, ~14 days into the cycle

*** important: unlike normal meiosis, oogenesis makes three polar bodies and one large secondary gamete (secondary oocyte) that is arrested at metaphase II

- estradiol: hormone that stimulates LH production and ovulation
- corpus luteum/yellow body: name given to the follicle after ovulation. secretes progesterone and estrogen --> growth of uterine lining

Answer 5

[gonna split this into two parts]

Anyway, that's the end of my tutorial, I hope it was a helpful resource. Source material is the 2nd Edition Barron's Prep book for the new MCAT