Anatomy & Physiology of the Male Reproductive System PDF

Anatomy & Physiology of the Male Reproductive Tract RIZVI, Fahad PHAS5001 LEARNING OUTCOMES Describe the main anatomical features of the male reproductive tract Relate male anatomy to common clinical problems Describe the main physiological functions of the male reprodu...

Anatomy & Physiology of the Male Reproductive Tract RIZVI, Fahad PHAS5001 LEARNING OUTCOMES Describe the main anatomical features of the male reproductive tract Relate male anatomy to common clinical problems Describe the main physiological functions of the male reproductive system, including: Hormonal regulation Spermatogenesis Male sexual response  Why have a reproductive system? In order to pass genetic information from generation to generation. The only body system not required to keep the BODY alive, but required to keep the SPECIES alive. Reproduction… Is the process in which organisms produce offspring by means of germ cells called Gametes The Gonads produce gametes and secrete the reproductive hormones. Female vs Male Anatomy Development of the testis and ovaries SRY gene encodes Testis Determining Factor (TDF) In the presence of TDF testis will develop, and testosterone from the developing testis will promote the development of male external genitals. In the absence of TDF, ovaries will develop and female genitals. Development of the testis and ovaries Males – Paramesonephric tube will degenerate due to Anti- mullerian hormone Female – mesonephric will degenerate and paramesonephric remains https://www.youtube.com/watch?v=hzjKRCU5Tq4 Development of the external genitals  Neural Control of the sexual act (Erection and ejaculation) Sexual behaviour (in part) Control of the reproductive system Male Anatomy and Physiology Sagital Section  Testes Paired oval-shaped glands Usually 4cm long and 2.5 cm Wide Covered in a fibrous capsule tunica albuginea Outer layer is double layered tunica vaginalis Functional units are the seminiferous tubules – found withing the lobules. In the adult male, each testis may contain 300-900 m of tubule... It’s 1000 m from here to the train station! - Epithelial cells, columnar cells and smooth muscle like myoid cells Storage and maturation area (epididymis) Testicles = Testes + epididymis + spermatic chord Gross anatomy  Histology Tunica albuginea Epididymis Storage area Fibroblasts Myofibroblasts Fibrous septa Seminiferous tubules Sperm production Rete testis Entrance to epididymis Sagittal section Van Gieson (collagen red) x3 Mag. Histology BV Septa Transverse section, X 65 H&E (connective pink, nuclei purple) ST TA Ross & Pawlina; Histology, 5th Ed. Epididymis: Highly coiled. Nonmotile sperms are released into the epididymis as move along the duct with fluid. Journey takes 20 days to become motile. Sperm are ejaculated from here, if not, can be stored for several months. Epithelial cells phagocytise the cells. Ductus Deferens/Vas Deference: Is approx. 45 cm long. Runs upwards from the epididymis to the pelvic cavity as part of the spermatic cord. Has thick layer of stratified epithelium. It joins with the seminal gland and makes… Ejaculatory Duct: Enters the prostate and empties into the Urethra Urethra: Terminal part that can carry both semen and urine – (not together). Spongy urethra = 15 cm and accounts for ¾ of the urethra – Secreted mucus before ejaculation Sagital Section  Ductus (Vas) Deferens Runs from tail of epididymis to ejaculatory duct Smooth muscle - peristalsis Vasectomy – ductus is ligated just distal to superficial inguinal ring Seminal gland: Found on the surface of the bladder. The thick fibrous capsule layer encloses smooth muscle cells that contact during ejaculation. Seminal fluid + sperm → Ejaculatory duct → Urethra. Seminal fluid contains fructose, citric acid, coagulating enzymes, prostaglandins + other substance to enhance sperm motility. Prostate: Smooth muscle cells that contract during ejaculation and force the prostatic secretions into the urethra. Fluid is a milky colour and allows activation of sperms. Bulbo-urethral glands: Pea sized gland located inferior to the prostate. Produces thick mucus which drains into the urethra which neutralises residual acidic urine and lubricates the penis during ejaculation. Sagital Section Seminal Vesicles 2 x Accessory gland (~5cm long) Develops as outgrowth of ductus deferens Smooth muscle Lies between bladder and rectum Duct of seminal vesicle combines to join ductus deferens to form: Ejaculatory duct Seminal vesicles do not store sperm –they produce alkaline fluid (~70-80% of ejaculate volume)  Prostate Fibromuscular(1/3) & glandular (2/3) ~ 20% seminal fluid Surrounds urethra Lies between bladder and levator ani Closely related to the rectum Prostatic utricle (Digital Rectal Examination) Fibrous Lymphatic drainage towards spine capsule Ejaculatory ducts x 2 Prostatic Urethral crest Peripheral (PZ) ductules and sinus Central (CZ) Transitional (TZ) Semen Semen is a viscid whitish fluid of the male reproductive tract consisting of spermatozoa suspended in secretions of accessory glands It consists of secretions from: Spermatozoa from the Seminiferous tubules Seminal vesicle fluid (50-70% volume) Prostate fluid (20-30% volume) Bulbourethral gland fluid (Cowper’s gland) Normal ejaculation: 2-5ml  Semen It consists of secretions from: Seminal vesicle fluid (50-70% volume) Fructose for sperm to generate ATP for movement Prostaglandins uterine contractility Alkaline combat acid environment of FGT Prostate fluid (20-30% volume) PSA Zinc Citric acid and proteases to break down semen clots First coagulate and then decoagulate the semen following ejaculation - temporary thickening of semen helps retain it within the female reproductive tract Bulbourethral gland fluid (Cowper’s gland) Pre ejaculate - lubricant, Clearing traces of acidic urine before ejaculation Glands and ducts… sperms journey Sagital Section Spermatic Cord Content and covering of the cord described in 3’s: 1.Pampiniform plexus 2.Ductus deferens 3.Lymphatics 1.Testicular artery 2.Ductus deferens artery 3.Cremasteric artery 1.Genital nerve 2.Autonomic nerves 3.(Ilioinguinal nerve) Testicle development The testicle develops in a retroperitoneal position Gubernaculum -Testicle descends on this fibrous cord Processus vaginalis – fold of parietal peritoneum. The processus vaginalis is a potential weak spot and is the route taken by indirect inguinal hernias Inguinal Hernias Indirect Direct  Varicocele https://www.ncbi.nlm.nih.gov/pubmed/28675168 Enlargement of testicular venous pampiniform plexus Increased testicular temp. & oxidative stress May impact on semen quality Some evidence that surgical treatment can restore fertility https://commons.wikimedia.org/wiki/File:Varicocele.png Penis Corpus cavernosum Thin, relatively hairless skin Corona 2 x corpus cavernosum EUM 1 x corpus spongiosum Glans Root = attached parts Corpus spongiosum Bulb Hypospadias - Congenital defect  Sexual stimuli: Touch/ sound / smell / emotional or mental activity Erection CNS responds by activating the parasympathetic nervous system - Enlargement and stiffening of the penis - Penis is flaccid when a male is not sexually aroused → arterioles supplying to the erectile tissue are constricted Erection of the penis is mediated through the parasympathetic nervous system, and release of Nitric Oxide – a vasodilator NO → relax SMC → blood vessel dilated→ erectile bodies fill with blood Corpus cavernosa and spongiosum fills with blood, restricting veins.  Ejaculation Ejaculation is mediated by the sympathetic nervous system via a mass spinal reflex causing: Constriction of the bladder sphincters muscle - preventing expulsion of urine or reflux of semen into the bladder Contraction of the ducts and glands – emptying substances into the urethra Contraction of the penis muscles to ‘shoot forth’ semen – speed up to 500 cm/s Event or climax or orgasm → Resolution period (relaxation) – Unable to achieve another orgasms for mintes during the latent or refractory period.  Male sexual response Main phases of male sexual response Erection Ejaculation Erectile Dysfunction Failure to achieve or maintain an erection Very common, ~50% men between 40-70 years old Physical or psychological Testosterone deficiency Diabetes & Cardiovascular disease Stress, performance anxiety Certain drugs, e.g. SSRIs, antihypertensives, recreational drugs Sildenafil initially developed as a drug for angina Relaxation of coronary arteries → increased blood flow → pain relief Spermatogenesis Spermatogenesis Sequence of events in the seminiferous tubules of the testes that produces male gametes (sperm) Begins around the age of 14 and continues throughout life Healthy adult male produces ~400 million sperm/day Gamete formation involves meiosis Unique type of nuclear formation that only occurs in the gonads Rate of spermatogenesis is determined by hormones testosterone and FSH Spermatogenesis Spermatogenic cells Epithelial cells Tortora et al Mitosis of Spermatogonia: Outer most cells in contact with basal lamina are spermatogonia stem cells. Divide by mitosis until puberty. Mitosis after puberty results in Type A and Type B daughter cells. Type A stays in the basal lamina and Type B (makes 4 spem cells) become primary spermatocyte at the lumen. Meiosis of spermatocytes produces spermatids. Primary spermatocyte undergoes meiosis to make haploid secondary spermatocytes which produced spermatids by meoisis II. Spermiogenesis: Elongation, shedding cytoplasmic baggage and tail formation for spermatids to produce sperm cells/spermatazoa.  Spermatogenesis Cytoplasmic Bridges Ensure sperm develop at the same rate. Tight Junctions Stops immune system attacking genetically different sperm Sertoli Cells Sperm development takes place moving through the sertoli cells – produce Inhibin and Androgen Binding Protein Hormones Steroid Hormone Release is Regulated by Negative Feedback Hypothalamus GnRH Ant. Pituitary Gonadotrophs (FSH) LH Oestrogen Gonad Testosterone The principle is the hypothalamus – pituitary – gonad axis is controlled by negative feedback  The Hypothalamus–Pituitary Axis Regulates Spermatogenesis Hypothalamus GnRH GnRH Conc. Ant Pituitray 60-90 min Gonadotrophs FSH LH GnRH is released in pulses every 60-90 min, throughout the day, every day... (unlike women) Testis Testosterone This means that LH and FSH are also released in pulses. Spermatogenesis Appears to be critical in spermatogenesis – no pulses, no sperm  Gonadotropin- releasing-hormone (GnRH) released by the hypothalamus --> anterior pituitary cells GnRh controls the relase of Follicle stimulating hormone (FSH) and luteinizing hormone (LH) FSH ad LH secreted into the blood FSH causes the release of androgen binding protein (ABP) from sustentocytes. ABP has a role to maintaining a high testostrone level around the spermatogenic cells. LH causes further secretion of testosterone Testosterone – enters the blood and allows development of sex organs. Increased level of testosterone brings about a feedback look which inhibits GnRH release from the hypothalamus. Inhibin: protein hormone produced by sustentocytes. Act as a baroreceptor – when sperm count is high, more inhibin released – inhibiting the pituitary gland releasing FSH and hypothalamus releasing GnRH. Tortora: Principles of human anatomy and physiology. 11th Edition  Inhibin Inhibits FSH Release A peptide hormone released by Sertoli cells Hypothalamus Sperm maturation is sufficient Sertoli cells release inhibin GnRH inhibits FSH secretion by the anterior pituitary decreases sperm production Ant Pituitray Gonadotrophs Sperm maturation is proceeding too slowly less inhibin is released by Sertoli cells FSH LH more FSH will be secreted sperm production will be increased Inhibin Testis Testosterone Spermatogenesis 44 Endocrine Regulation of Testis Function Testes are responsible for spermatogenesis and steroidgenesis. FSH is critical for the initiation and first stages of spermatogenesis Testosterone is critical for spermatozoa maturation in epididymis mediated via Sertoli cell secretion of Androgen Binding Protein (ABP) Androgens: Testosterone and Dihydrotestosterone produced by Leydig cells Ligands of the Androgen nuclear hormone receptor (AR) Responsible for Sexual differentiation and development (in utero) Sexual maturation (puberty) Maintenance of spermatogenesis (adulthood) Effects of testosterone Development of male primary and secondary sexual characteristics Primary: Secondary: Enlargement / Hair growth and differentiation of the distribution male genitalia Skin texture Ability to produce Changes in the larynx sperm cells Increased metabolism Skeletal muscle and bone development