Sexual reproduction in humans Flashcards
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.
Spermatogenesis
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.
Sperm structure?
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.
