8132MED - Reproduction - Male anatomy and physiology 090924.pdf

Doctor Knowledge in Health and Illness Reproduction 1: Male anatomy and physiology Dr Christian Cobbold School of Medicine Sunshine Coast University Hospital [email protected] Learning Objectives At the end of this session you should be...

Doctor Knowledge in Health and Illness Reproduction 1: Male anatomy and physiology Dr Christian Cobbold School of Medicine Sunshine Coast University Hospital [email protected] Learning Objectives At the end of this session you should be able to… Describe the structure and function of the male human reproductive system Summarise spermatogenesis Male reproductive system: structure produces fluids - prostaglandins - smooth muscle contractions, clotting factors, semen clots in vagina fructose - nourish avoid loss alkaline to buffer against acidic environment in vagina PSA - degrade clot in vagina, release via cervix to fallopian tube fluid - mucus Lower temperature than rest of body Male reproductive system: structure encircles urethra, BPH and cancer - constrict urethra Male reproductive system What do you already know about male reproductive function? Structure Main functions Testis Spermatogenesis; Secrete testosterone stimulates spermatogenesis Epididymis & vas Sperm exit route from testis; deferens Sperm maturity site – mobility and fertility; Concentrate and store sperm Seminal vesicle Supply fructose (ejaculated sperm nourishment); Prostaglandin secretion; motility Provides majority of semen; volume Provides semen clotting factors (fibrinogen) Prostate gland Secretes alkaline fluid; neutralise acidic environemnt Secretes PSA that degrades semen clot to pass to uterus to fallopian tube Bulbourethral gland Secretes mucus for lubrication Summary of male detects molecules in the blood Hypothalamus reproductive Gonadotropin-releasing hormone at puberty pulsatile endocrinology seminiferous tubules where spermatogenesis Anterior pituitary FSH-secreting LH-secreting cells cells FSH LH Testosterone oestradiol in some tissues adipose Testes inhibit breast development 5α-reductase Sertoli Leydig in testes DHT - more potent androgen cell cell Dihydrotestosterone together LH = luteinising hormone Spermatogenesis FSH = follicle-stimulating negative feedback negative feedback hormone inhibits production Inhibin Testosterone Testosterone actions widely distributed in adipose tissue Aromatase Testosterone Oestradiol Aromatase is widely distributed in adipose tissue, which may explain some of the feminising effects observed in obese males Oestrogen receptors present in bone, testes and prostate in males Oestradiol is important for spermatogenesis also epiphyseal plate closure What is the effect of taking exogenous testosterone on the body? inject large amounts - affect endocrine Inhibit GnRH, inhibit FSH, LH - less spermatogenesis testicular atrophy - testes not stimulated aggression, depression and suicide stop - gynaecomastia - testes no longer produce more oestrogen formation clomiphene - water-bound, stops effect Review Questions Case History A 20-yr old man presented to his GP with impotence. On examination there was only sparse pubic and axillary hair, the genitalia were infantile, and muscular development poor. The following biochemical results were obtained: Testosterone 3 9-30 nmol/L LH < 1.5 2-10 U/L FSH < 1.5 2-10 U/L What is the diagnosis? Secondary hypogonadism low testosterone LH and FSH low - issue with anterior pituitary, not testes.... If primary - low testosterone, high LH/FSH Testis: structure and spermatogenesis Failure to regulate testes temperature inhibits spermatogenesis but does not affect hormone production testes drop, lover temperature Infertility Abnormal testicular metabolism and increased risk of testicular cancer to infertility What can raise the temp? Hot baths Tight fitting underwear adversely affect in longterm form mature spermatids Testis: structure and spermatogenesis Epididymis Seminiferous Vas tubule deferens seminiferous tubules Testis to epididymis - mature and pass out LH stimulate spermatogenesis FSH make up outside produce testosterone, DHT together - spermatogenesis testosterone inhibit LH, GnRH Testicular function Leydig cells release testosterone LH stimulates production of testosterone and small amounts of other steroids, eg. Oestrogen and dihydrotestosterone (DHT) Testosterone either acts on adjacent Sertoli cells or is released into the blood  actions outside the testes Testicular function Functions of testosterone and DHT Main effects Before birth Sex determination; Masculinises reproductive tract & external genitalia; Promotes descent of testes in scrotum After birth: sex- Puberty – growth and maturation of reproductive specific tissues system; Essential for spermatogenesis; Maintains reproductive tract during adulthood Other reproductive Develops sex drive related effects Controls LH and GnRH (& FSH) release negative feedback Secondary sexual Male-pattern hair growth; thickening of vocal cords characteristics Promotes muscle growth; thick skin striking in puberty Non-reproductive Protein anabolic effect; promotes bone growth at actions puberty; may induce aggressive behaviour time - reduced testosterone, androgen dificiency Testicular function Sertoli cells stimulate spermatogenesis Create seminiferous tubules (approx 300m in testes) Nourish germ cells (spermatagonium) & support spermatogenesis stimulate by LH make up seminiferous tubules Secrete inhibin negative feedback ion FSH Convert testosterone to DHT or oestradiol Testicular function: spermatogenesis Spermatagonia (46 chromosomes) are converted to spermatazoa (23 chromosomes) Division and maturation of spermatagonium takes approx 64 days At any given time, different seminiferous tubules are in different stages of spermatogenesis Thus, several hundred Spermatozoon million sperm produced Spermatid per day 2o Spermatocyte 3 stages: 1. Mitotic proliferation 1o Spermatocyte 2. Meiosis below normal temp. Spermatogonium 3. Packaging 23 chr  Testicular function: spermatogenesis Mitotic proliferation occurs in the outermost layer of the tubule Testosterone essential for mitosis and meiosis outermost layer of seminiferous tubule 46 (diploid Spermatogonium number; single strands) One daughter cell remains One daughter cell MITOSIS at the outer edge of the moves toward the seminiferous tubule to Spermatogonia lumen to produce 46 (diploid maintain the germ cell line spermatozoa number; MITOSIS single strands) Spermatogonia make more diploid, single stranded MITOSIS MITOSIS Primary 46 (diploid spermatocytes number; in resting phase one to lumen double strands) double strands together for first meiotic division primary spermatocytes Chromosomes in each cell  Testicular function: spermatogenesis During 2 meiosis rounds primary spermatocytes form 4 spermatids Spermatids have 23 single chromosomes Chromosomes No further division takes place forms 2 secondary spermatocytes in each cell with 23 double strands 46 (diploid Primary number; spermatocytes ds double strands) MEIOSIS 23 (haploid Secondary number; spermatocytes MEIOSIS double strands) 23 (haploid Spermatids number; single then spermatids, single stranded strands) Theoretically : testosterone - mitosis and meiosis 1 spermatagonium produces 4 primary spermatocytes 1 primary spermatocyte produces 4 spermatids 16 spermatids (and spermatazoa) could be produced Testicular function: spermatogenesis Extensive remodelling (packaging) of spermatids occurs under the influence of FSH Sperm are ‘stripped down’ cells with most organelles Chromosomes and cytosol removed, and then remodelled in each cell need energy - mitochondria Spermatids 23 (haploid number; single FSH - remove most cytosol strands) Spermatazoa 23 (haploid onto epididymis number; single strands) get through egg wall energy During meiosis, half the sperm receive an X chromosome and the other half a Y male sperm influence sex Spermatazoa structure and function The head has the nucleus with genetic material and an acrosome Acrosome is a modified form of a lysosome which helps penetrate the ovum aggregate vesicles Acrosomal enzymes remain inactive until sperm and egg contact drill to penetrate ovum The tail provides sperm mobility, movement of which is provided by mitochondria in the sperm midpiece Spermatazoa maturation As sperm leave the testes they are not motile or fertile Testosterone stimulates sperm maturation in the epididymis (24hrs) Sperm is concentrated 100 fold in the epididymis by absorbing fluid that enters from seminiferous tubules Defensin is released which enhances motility and defends against microorganisms Sperm are slowly moved to vas deferens by rhythmic contractions of smooth muscle, where they are stored Sperm are relatively inactive in vas deferens and are nourished by simple sugars in tubular secretions in vas deferens Accessory glands contribute most of the semen Seminal vesicles empty into the last portion of the two vas deferens most of the volume Ejaculatory duct passes from seminal vesicle entry point to the fructose prostaglandins urethra mucus Single prostate gland surrounds ejaculatory ducts and urethra Bulbourethral glands drain into the urethra Semen: accessory glands secrete fluids that support sperm viability in male and female reproductive tracts towards the egg Semen components Sperm (approx 180 million, 2.75ml) Mucus as lubricant Buffers to neutralise acid environment of vagina Nutrients (eg. Fructose) to nourish sperm Clotting factor (fibrinogen) clot in vagina Enzymes to clot semen in vagina, then liquefy the clot (PSA) Prostaglandins to stimulate smooth muscle contraction to aid sperm transport aid transport Infertility: < 20 million sperm per ejaculate to bind and enter not enough to fertilise Poor sperm quality (eg. abnormal structure or motility) What is a vasectomy? A small segment of each vas deferens is removed Blocks sperm exit, which are removed by phagocytosis Does a vasectomy affect male libido and masculinity? no testosterone activity not affected masculinity and libido not affected cannot pass out from stimulation  F - from Leydig cells and acts on Sertoli T - first stage mitosis, packaging and meiosis T several sperm T - then concentration and fluids after