LEC 20 - Sexual Reproduction

Sexual reproduction

Combines genes from 2 parents → variation; zygote → embryo → fetus

Meiosis

Cuts chromosome number in half to make gametes (sperm/egg)

Fertilization

Sperm + egg → diploid zygote

Autosomes

22 chromosome pairs; same genes, different alleles

Sex chromosomes

XX=female, XY=male; sperm determines sex

SRY gene/TDF

On Y chromosome; initiates testis development

Barr body

Inactive X chromosome in females

Sertoli cells

Support sperm, blood-testis barrier, secrete inhibin & ABP

Leydig cells

Produce testosterone in response to LH

Cryptorchidism

Undescended testes; impairs sperm production

Klinefelter syndrome

XXY (47 chromosomes); infertile, ↓ testosterone

Turner syndrome

XO (45 chromosomes); infertile, ↓ estrogen

Wolffian duct

Male ducts (epididymis, vas deferens, seminal vesicle)

Müllerian duct

Female ducts (uterus, uterine tubes, upper vagina)

MIF (AMH)

From Sertoli cells; regresses Müllerian ducts

DHT

More potent testosterone; forms male external genitalia

GnRH

Hypothalamus hormone → stimulates FSH & LH

FSH

Stimulates spermatogenesis/oogenesis; follicle growth

LH

Males: testosterone; Females: ovulation & corpus luteum

Inhibin

From Sertoli/granulosa cells; inhibits FSH only

Puberty

↑ GnRH → ↑ LH/FSH → ↑ sex hormones

Secondary sex characteristics

Body changes from testosterone/estrogen during puberty

Testes

Seminiferous tubules make sperm; interstitial tissue makes testosterone

Testosterone

Male development, sperm production, muscle & bone growth

Estradiol (male)

Helps spermatogenesis and bone growth

Spermatogenesis

Spermatogonia → primary → secondary → spermatids → sperm

Spermiogenesis

Spermatids mature into sperm

ABP

Binds testosterone to concentrate it in seminiferous tubules

Epididymis

Sperm maturation and storage

Semen

Sperm + seminal vesicle fluid + prostate fluid

BPH

Enlarged prostate compresses urethra

Erection

Parasympathetic; NO → cGMP → smooth muscle relaxation

Emission

Semen enters urethra; sympathetic

Ejaculation

Semen expelled; sympathetic

Oligospermia

Vasectomy

Cuts vas deferens; testosterone unchanged

Ovary

Makes oocytes, estrogen, progesterone

Uterine tube

Usually site of fertilization

Uterus

Endometrium implants embryo; myometrium contracts

Primary oocyte

Begins meiosis before birth; arrests in prophase I

Graafian follicle

Mature follicle that ovulates

Ovulation

LH surge releases secondary oocyte (~day 14)

Corpus luteum

Secretes progesterone & estrogen after ovulation

Follicular phase

FSH stimulates follicle growth; estrogen rises

Luteal phase

Corpus luteum active; progesterone highest

Menstrual cycle

Menstrual → Proliferative → Secretory

Proliferative phase

Estrogen rebuilds endometrium

Secretory phase

Progesterone thickens/prepares endometrium

Menstrual phase

↓ Estrogen/progesterone → shedding

hCG

From embryo/placenta; maintains corpus luteum early pregnancy

Placenta

Exchanges gases/nutrients; secretes hCG, progesterone, estrogen

Oxytocin

Stimulates uterine contractions & milk ejection

Prolactin

Stimulates milk production