Flashcards in Sexual reproduction in humans Deck (32):
The male reproductive system
Each testis contains thousands of coiled tubes called seminiferous tubules. The cells lining it undergo sperm formation and travel to lumen where collect in vasa efferentia (tubes taking sperm to head of epididymis). Become motile here before moving to the vas deferens, during ejaculation.
What is gametogenesis?
The production of gametes in the gonads.
Spermatogenesis is sperm formation in testis.
Oogenesis is formation of eggs in the ovary.
Start with germinal epithelial cell (2n) in outer layer of tubules, divide by mitosis producing spermatogonia. These divide by mitosis and enlarge to form primary spermatocytes (2n).
Primary spermatocytes go through meiosis 1 (reduction division; 2n to n), form 2 haploid secondary spermatocytes.
These undergo meiosis II to produce spermatids.
These differentiate or mature into spermatozoa (n), they form their mid piece and tails
What are sertoli cells?
During maturation the spermatids obtain nutrients from nearby sertoli cells. Also protect the spermatids from the male immune system.
Where is testosterone produced?
Between seminiferous tubules lie cell of Leydig (interstital cells), this is where.
Head= haploid nucleus, covered by a lysosome called the acrosome (contains enzymes for fertilisation). Mid section contains lots of mitoochondria, ATP for movement. Axial filament contains protein fibres for longitudinal rigidity.
Oogenesis; before birth?
Germinal epithelium cell divide by mitosis to produce oogonia. They divide by mitosis and enlarge to form primary oocytes. These start to divide by meiosis by stop at prophase I. GE cells divide by mitosis to form follicle cells which surround oocytes to form primary follicles. (over 400,000 in ovary).
Oogenesis; at puberty?
At puberty FSH from the pituitary gland stimulates some of the primary follicles to develop into secondary follicles.
Oogenesis; a month before ovulation
One secondary follicle each month develops into a graafian follicle. Primary oocyte inside completes meiosis I to form a haploid secondary oocyte and polar body which degenerates. Secondary oocyte begins meiosis II but stops at metaphase II.
Oogenesis; at ovulation
Graafian follicle goes through surface of ovary and ruptures it, secondary oocyte projected into oviduct; this is ovulation. Meiosis II only completed at fertilisation, only then that an ovum is formed. Graafian becomes temporary gland call Corpus Luteum producing progesterone that maintains the endometrium.
The ovulated secondary oocyte?
Haploid nucleus sits inside cell with large cytoplasm. 2nd oocyte and polar body divide unequally at end of meiosis I, oocyte gaining cytoplasm. 2nd surrounded by membrane called zona pellucida (glycoproteins). Cortical granules are present in cytoplasm, below membrane. Surrounded by follicle cells forming the corona radiata.
Journey of the sperm?
Go from epididymis, travel along vas deferens, into urethra, into top of vagina, into cervix, up an oviduct where they meet the secondary oocyte.
What is capacitation?
Where the sperm moves through the fluid in the uterus, the removal of three substances from the sperm.
Whats removed during capacitation?
Glycoprotein- outer layer added to sperm of plasma membrane in epididymis.
Plasma proteins- added to sperm plasma membrane by seminal fluid.
Cholesterol- from sperm plasma membrane, weakens membrane, Ca ions enter.
Ca ions allow acrosome membrane to fuse with sperm head plasma, enzymes can leak.
Stages of fertilisation?
Sperm cells digest through corona radiata due to enzymes.
Head with zona pellucida, causing acrosome reaction.
Membrane ruptures, enzymes released and digest zona pellucida.
1st sperm to get through meets 2nd oocyte membrane, they fuse.
Sperm nucleus enters.
Fusion starts the cortical reaction and meiosis II of 2nd oocyte to finish.
What is the cortical reaction?
Cortical granules are just below plasma membrane.
Fusion occurs, Ca ions released casuing granules to fuse with membrane, release enzymes into zona pellucida.
Enzymes expand and harden zona to prevent entry of more sperm.
Becomes fertilisation membrane.
Formation of a zygote?
Fusion of plasma stimulates meiosis II by 2nd oocyte. 2nd polar body formed. Chromosomes line up during metaphase, fertilised oocyte is now a zygote (2n), when division complete 2 embryos formed.
Implantation of the blastocyst?
2 cells divide, form a hollow ball of cells= blastocyst.
Division cells= cleavage.
Blastocyst reaches uterus, embeds into endometrium= implantation.
Blastocyst= outer layer is trophoblast, large group of cells is inner mass, fluid filled space= blastocoele.
Trophoblast develop villi which penetrate endometrium.
Trophoblast develops into chorion (mem surrounding embryo).
What is the amnion?
Outer cells of embryo form a membrane called amnion, which forms a fluid filled sac surrounding foetus called amniotic fluid.
What are the functions of the amniotic fluid?
Acts as shock and protects foetus during development.
Maintains foetus temperature.
Contributes to lung development.
Allows movement so muscle and bones function before birth.
What are the functions of the placenta (hormones)
HCG in blood maintains corpus luteum.
C.L maintains production of hormones.
Progesterone= prevents uterine contraction.
Oestrogen= stimulates growth of uterus to accommodate for foetus.
Within 2 months, placenta produces these hormones.
Overall functions of placenta?
Endocrine organ (hormones).
Exchange between mothers and foetus blood.
Physical barrier between foetus and maternal circulation; protects fragile capillaries of foetus from high BP of mother.
Provides passive immunity (antibodies) from mum to foe.
Protects foetus from mum immune system (WBC cannot get through).
What is the placenta made of?
It is made of foetal and maternal tissue.
Trophoblast into chorion, secretes HCG.
Chorion develops chorionic villi with blood capillaries to umbilical artery and vein.
Villi has microvilli for larger surface area.
Endometrium forms projections.
Between projections are spaces= lacunae, supplied with blood from mother.
More on the placenta?
Embryo and mothers blood does not make contact.
Villi and lacunae is 5um.
Conc gradient is maintained by counter-current flow.
Umbilical cord develops from chorion, transfers blood to placenta in 2 umbilical arteries (low nut+O). Blood returns in umbilical vein (high in nut+O).
The placenta as an endocrine gland?
Placenta steadily increases conc of O+P in plasma until end of pregnancy.
Hormones that inhibit:
FSH so that no more follicles mature.
LH so no ovulation occurs.
Prolactin so that milk not produced.
Progesterone also inhibits oxytocin, a hormone that causes uterus wall (myometrium) to contract.
Hormones at birth?
39 weeks, foetal hormones decrease conc of progesterone, no longer inhibits oxytocin and prolactin
Oxytocin= causes contraction of myometrium, mild contractions, increase production.
Prolactin= causes glandular tissue in mammary glands to make milk.
Problems with the placenta?
Spontaneous abortions, same as rejection of transplanted organ.
Abnormal immune response towards placenta can cause pre-eclampsia.
Rhesus disease in foetus due to RID of foetus BC by antibodies made my - mother.
Transfer across placenta; drugs, nicotine, small viruses like rubella.
The menstrual cycle?
Where hormonal and uterine changes occur. Absence of embryo, endometrium sheds through menstruation. Menstrual cycle involves - and + feedback in brain, ovaries and uterus.
What are the four main hormones involved?
Follicle stimulating hormone (FSH).
Luteinising hormone (LH).
Menstrual cycle: Days 0-14?
Day 0 is first day of period, 4 hormones are low, gonadotrophic releasing hormone (GnHR) secreted stimulating P.gland to secrete FSH and LH.
FSH= stimulates primary follicles, develop into graafian follicle, produce oestrogen.
Oestrogen causes rebuilding of endometrium.
It inhibits FSH (-ve), stimulates LH (+ve), reaches peak causes surge of LH 12-14.
The menstrual cycle: Day 14 (ovulation)?
LH induces ovulation.
Its surge at day 14 causes graffian follicle (at surface) to release 2nd oocyte.
LH surge stimulates FSH surge.