3. Sexual reproduction in humans

scrotum

external sac containing testes and maintains temperature

testis

produces gametes and testosterone

epididymis

store sperm for a short time while they become motile

vas deferens

where motile sperm is passed into and carries it towards the penis

seminal vesicle

secrete mucus into the vas deferens

what does the prostate gland secrete

zinc-containing fluid

urethra

carry semen through the penis

penis

reproductive organ that reposits semen in vagina

why is semen alkaline?

to neutralise acidity of urine in urethra and the acidity of the vaginal tract

nutrients in semen

amino acids, zinc ions, fructose

what does acrosome contain?

enzymes used in fertilisation

ovary

where oocytes mature and are released during ovulation with hormones

fallopian tubes (oviducts)

ciliated epithelial cells convey the secondary oocyte to the uterus where fertilisation occurs

uterus role

receive and implant a fertilised egg, develop embryo, facilitate waste removal

endometrium

innermost layer of uterus that builds up and is shed in a monthly cycle

cervix

narrow ring of connective tissue and muscle where uterus opens up into the vagina

vagina

where semen is deposited

where does spermatogenisis occur?

seminiferous tubules in the testes

order of stages in spermatogenisis

germinal eptithelium → spermatagonium (mitosis)→ primary spermatocyte (mitosis)→ secondary spermatocyte (meiosis I) → spermatids (meiosis II) → spermatozoa (spermiogenisis)

role of sertoli cells

nourish (provide nutrients), support and protect developing sperm cells

what do leydig cells secrete?

testosterone

order of stages in oogenesis

germinal epithelium → oogonia (mitosis) → primary oocyte (enlargement) → meiosis stops at prophase I and restarts at puberty → polar body and secondary oocyte produced → meiosis II of secondary oocyte into a polar body and mature ovum if fertilisation occurs

name for a mature follicle in oogenesis

Graafian follicle

what is left of the secondary oocyte after ovulation?

corpus luteum

How does is acidity neutralised in ejactualtion?

The prostate gland produces alkaline secretions

The seminal vesicle secretes alkaline mucus that also contains fructose as an energy source

Where does ejactualtioon go?

Seminiferous tubules - epididymis - vas deferens - urethra - vagina

1st stage of fertilisation

Capacitation - removal of cholestrol and glycoprotein layer from sperm head, membrane infront of acrosome made more permeable, motility increased

2nd stage of fertilisation

Sperm binding - spermatozoa burros through corona radiata and binds to zona pellucida

3rd stage of fertilisation

Acrosome reaction - releases enzymes (hydrolases) by exocytosis which digest a path through the zona pellucida

4th stage of fertilisation

Cell membrane fusion - membranes of spermatozoa and secondary oocyte fuse, male nucleus released into cytoplasm of 2ndry oocyte

5th stage of fertilisation

Oocyte activation - meiosis II restarts from metaphase II which produces the ovum and the second polar body

6th stage of fertilisation

Cortical reaction - is triggered by CM fusion, calcium ions are released, vesicles containing cortical granules fuse with CM, these modify the zona pellucida to form the fertilisation membrane to prevent polyspermy

7th stage of fertilisation

Ovum nucleus and spermatazoan nucleus fuse to form the zygote

what is cleavge?

series of rapid mitotic divisions following fertilisation, where the zygote splits into smaller cells (blastomeres) without overall growth

Steps of implantation

cleavage increases number of cells

blastocytes embed in endometrium

trophoblast (outer layer) forms

function of trophoblast

amnion forms amniotic sac and fluid acts as shock absorber

chorion forms chorionic villi which secretes hCG which maintains the corpus luteum

Role of umbilical artery

Carries deoxygenated blood containing wastes away from foetus

Role of umbilical vein

Carries blood containing oxygen and nutrients to the foetus

How is concentration gradient maintained in the placenta?

Counter-current flow of maternal and foetal blood

Why is protection from the mother’s immune system necessary in the placenta?

It prevents ‘rejection’ of the foetus which will have foreign antigens

Why is protection necessary of difference in blood pressures in foetus?

So that maternal high blood pressure dosnt’t damage foetal capillaries

How is large SA and short diffusion pathway maintained in placenta?

Chorionic villi (+microvilli)

1 cell thick epithelium on chorionic villi

What change happens after 12 weeks of pregnancy?

The placenta takes over from the corpus luteum, the role of secreting hormones

2 hormones secreted by anterior pituitary gland

FSH and LH

2 hormones secreted by ovaries

Oestrogen and progesterone

Role of FSH

Travels to ovary to stimulate follicle maturation and oestrogen production

Role of oestrogen

Travels to uterus to stimulate repair of endometrium, inhibit FSH production and stimulate LH production

Role of LH

Travels to ovary to stimulate ovulation

Role of progesterone

Travel to uterus to repair and maintain the endometrium and inhibit production of FSH and LH

Ovulation

The Graafian follicle releases the secondary oocyte and becomes the corpus luteum

What happens to progesterone if implantation occurs?

HCG maintains the corpus luteum so progesterone continues to be secreted and the endometrium is maintained

What happens to progesterone if no implantation occurs?

Corpus luteum breaks down, no progesterone is produced. The endometrium is not maintained so menstruation occurs and FSH production is no longer inhibited - the cycle restarts

Roles of both oestrogen and progesterone in pregnancy

Inhibit FSH release so no new follicles mature

Inhibit prolactin release so no milk is made

Roles of oestrogen in pregnancy

Stimulates uterus and mammary gland growth

Roles of progesterone in pregnancy

Inhibits LH release so there’s no ovulation

Inhibits oxytocin release so there’s no contractions of myometrium

What is the myometrium?

Muscles in uterus wall

What happens to hormone levels just before birth?

Decrease in progesterone

Oxytocin release no longer inhibited - results in muscular contractions, releasing more (positive feedback)

What happens to prolactin levels just after birth?

Prolactin release no longer inhibited so the mammary glands can synthesise milk