The reproductive system

• Male gametogenesis begins at puberty. Men are continuously fertile. Around 1500 mature sperm produced per second.
• Before birth, multiplication of oogonia, forms primary oocytes within ovarian follicles which begin meiosis (halted in prophase). Some primordial follicles degenerate (atresia). Further atresia occurs and by puberty half a mill eggs per ovary.
• Testes produce sperm. They are suspended in the scrotum to keep temperature 2-3 degrees lower than the rest of the body. If the temperature is any higher then sperm production ceases.
• The testes have approximately 300 lobules each with 1-4 seminiferous tubules which have closed loops and drain into rete testis then epididymis for storage then vas deferens
• The three layers of the testes are tunica vasculosa (contains blood vessels), tunica albuginea (thick layer forming the septa that divides testis into lobules) and tunica vaginalis (covering testis and epididymis)
• The arterial blood supply of the testes comes from testicular arteries from the aorta via spermatic cord.
• The lymphatic drainage of the testes occurs through para-aortic lymph nodes
• Vas deferens allows male sterilisation by being cut as it is palpable
• The epididymis is a single tightly coiled tube. It stores and transports spermatozoa produced in the testes. It matures the sperm and if they're not ejaculated, then they're broken down within the epididymis.
• The vas deferens transports the sperm to the penis.
• The prostate and seminal vesicles secrete seminal fluid to support ejaculated sperm.
• Seminal fluid is made of fructose, citric acid nutrient, bicarbonate (to neutralise vaginal acidity), fibrinogen (thickener) and fibrinolytic enzymes
• The penis deposits sperm in vagina. It is made up of two corpus cavernous and one corpus spongiosum.
• Parasympathetic stimulation due to arterial relaxation leading to increasing pressure obstructing venous drainage leads to erection. Sympathetic stimulation leads to ejaculation.
• Bulbo urethral glands secrete sugar rich mucus into urethra for lubrication and contribute to pre-ejaculatory emission from penis.
• Spermatic cord is formed at the deep inguinal ring. It contains the testicular artery, pampiniform plexus of veins, autonomic and GF nerves, lymph vessels, vas deferens.
• Spermatogonium (diploid) --> Primary spermatocyte (diploid) --> Secondary spermatocyte (haploid) --> spermatids (haploid) --> spermatozoa (haploid)
• Spermatogenesis occurs in intratubular compartment of seminiferous tubules. Seminiferous tubules are made of tunica propria which are several layers of flattened cells forming a basement membrane next to which spermatogonia lie
• Spermatogonia next to tunica propria mature and move inwards forming primary and secondary spermatocytes (latter is rarely seen) and ultimately spermatids that are released into duct. Continuous fertility is achieved as spermatogenesis at different stages in different parts of tubule.
• The hormones that are released by the testes are androgens (testosterone, DHT, androstenedione), inhibin and actin (for FSH production regulation) and oestrogens
• Oestrogen is produced from androgen aromatisation by action of aromatase enzyme
• Sertolli cells have FSH receptors and are found within seminiferous tubules. They synthesis inhibin and activin (feedback on FSH secretion from anterior pituitary), anti-mullerian hormone, androgen binding protein.
• Anti-mullerian hormone aids regression of mullerian ducts in male sex development
• Androgen Binding Protein helps to direct testosterone from the Leydig cells to the germ cells. Its release is stimulated by germ cells.
• Sertoli cells support developing germ cells in three ways: assist in movement of germ cells to tubular lumen, transfer nutrients from capillaries to developing germ cells and phagocytosis of damaged germ cells.
• Leydig cells are found between seminiferous tubules and have LH receptors. They have pale cytoplasm because they are cholesterol-rich. Upon LH stimulation Leydig cells secrete testosterone (oestrogens), androstenedione, DHEA.
• Semen is made up of spermatozoa, seminal fluid, leukocytes, potentially viruses like hep B, HIV
• Seminal fluid comes from mainly accessory sex glands- seminal vesicles, prostate, bulbourerethral glands. Small contribution from epididymis/ testis
• After the testis, spermatozoa go into the efferent ducts where tubular fluid is reabsorbed resulting in concentrated fluid, induced by oestrogen. Then enter epididymis where nutrients (e.g. fructose for energy for sperm journey) and glycoproteins (protective coating for sperm) are secreted into epidydimal fluid, induced by androgens.
• Ovaries are in the peritoneal cavity and everything else is outside.
• Fallopian tubes are lined by cilia and have spiral muscle. Through peristalsis and wafting of the cilia the oocyte gets moved down the tube. If this motility is slow then susceptible to ectopic pregnancy
• Fertilisation usually occurs in the widest section of the Fallopian tube known as the ampulla
• The tone of pelvic floor- elevator ani and coccyges muscles and ligaments are what support the uterus to stop it prolapsing out of the vagina.
• The uterus is lined by the endometrium
• The 3 layers of the uterus are the perimetric (external), myometrium (thick smooth muscle layer sensitive to hormones) and the endometrium (specialised epithelium).
• During menstruation the endometrium sheds. Progesterone levels fall which leads to vasoconstriction of the arterioles in endometrium. Ischaemia/ necrosis cause shedding and haemorrhage of menstruation.
• The ureter is 1cm lateral to the cervix on either side. This is important when considering cervical cancer.
• Sterility is maintained in the areas above the cervix by shedding of endometrium, thick cervical mucus, narrow external os and low pH due to lactic acid (oestrogen stimulates vaginal epithelium to secrete glycogen which the lactobacillus vaginalis digest producing lactic acid which lowers pH to kill other pathogens). Antibiotics can disrupt this causing overgrowth and infections like candidiasis.
• Oogonium (diploid) --> Primary oocyte (diploid) --> Secondary oocyte (haploid) --> ootids (haploid) --> ova (haploid)
• Polar bodies are small haploid cells with virtually no cytoplasm as oocyte cytoplasm doesn't divide evenly- they undergo apoptosis.