Anatomy and Physiology Biology 2401 Chapter-28 The Reproductive System

Introduction Male and female reproductive systems are made of: Gonads – produce gametes and hormones Ducts – transport gametes and/or developing embryo Accessory structures – secrete fluid, support embryo/newborn

Male Reproductive System Made of: Gonads - Testes – produce sperms and hormones Ducts – Epididymis , Vas deferens, Ejaculatory duct & Urethra – ducts that transports semen (sperms + seminal fluid) Accessory Structures - Seminal vesicle, prostate, and bulbourethral glands – produce seminal fluid to support the sperms

Male Reproductive System Scrotum: Pouch formed by the abdominal wall divided into two sacs by a septum Skin with dartos muscle  contraction during sexual arousal  causes tightening and wrinkling of the skin Closer to birth  testes descend into the scrotum through the inguinal canal  inguinal canal then closes  testes are suspended in the scrotal sac by a spermatic cord and cremaster muscles Cryptorchidism: Testes fail to descend into the scrotum  testes remain in the abdomen  temperature same as the body temperature  no sperms are formed and greater risk of testicular cancer

Male Reproductive System Temperature regulation of testes: Sperm formation requires a temperature 2-3° lower than the body temperature Testicular temperature drops  cremaster muscles contract  testes are pulled closer to the abdomen  testes temperature rises Testicular temperature rises  cremaster muscles relax  testes are pulled away from the abdomen  testes temperature drops

Male Reproductive System Testes: Tunica vaginalis – parietal and visceral layer. Tunica albuginea - a dense connective tissue capsule surrounding the testes Seminiferous tubules – long, coiled tubes packed inside the testes where spermatogenesis (sperm formation) takes place

Male Reproductive System

Male Reproductive System Seminiferous tubules has Developing germ cells - begin their development near the periphery of the tubules - get released as spermatozoa in the lumen of the tubule Sertoli or sustentacular or nurse cells that - support developing germ cells- nourish, protect - phagocytize germ cell debris - secrete hormone (inhibin) to regulate FSH release - secrete androgen binding protein (ABP) that concentrates testosterone Between seminiferous tubules are Leydig or interstitial cells - endocrine cells  secrete hormones  help regulate spermatogenesis

Male Reproductive System 44XY 44XY 44XY 22X 22Y Spermatogenesis: sperm formation Diploid spermatogonia in the periphery of seminiferous tubules  divide by mitosis to form diploid primary spermatocytes  divide by meiosis to form 4 haploid spermatids Spermiogenesis: Spermatids transform  spermatozoa/sperm Spermiation: Release of spermatozoa in the lumen of seminiferous tubules 22X 22X 22Y 22Y 22X 22X 22Y 22Y

Male Reproductive System Sperms Consist of: Head – has the haploid nucleus (with 22X or 22Y chromosomes) – has a membrane sac containing hydrolytic enzymes that aid fertilization Midpiece – contains mitochondria that provide ATP for motility of the sperm Tail – is the flagellum that provides movement to the sperm

Male Reproductive System Sperms About 300 million sperms are produced per day. Sperms are made in seminiferous tubules in the testes  released and mature in epididymis  as they are released, they are mixed with seminal fluid, secretions from 3 exocrine glands: Seminal vesicle Prostate gland Bulbourethral / Cowper’s gland Semen: sperms + seminal fluid : 2.5 – 5.0 ml per ejaculate : Slightly alkaline – pH 7.2 – 7.7 : About 50 – 150 million sperms/ml : Less than 20 million sperms/ml may be a cause for infertility

Epididymis Sperms are made in the seminiferous tubule --> travel through the rete tesis --> efferent ductules in the testes --> reach the epididymis. Epididymis is a coiled tube on the posterior side of testes.   Three Functions of the Epididymis Monitors and adjusts fluid produced by seminiferous tubules Recycles damaged spermatozoa Stores and protects spermatozoa Facilitates functional maturation Sperms remain in epididymis for 10-14 days, mature (gain motility, ability to fertilize - in a process called capacitation) if not ejaculated: sperms break down and get reabsorbed by the body if ejaculated: sperms move towards the next part of the male reproductive structure.

Male Reproductive System  if ejaculated: sperms move with the help of peristalsis  to vas deferens that goes through the spermatic cord and enters the abdomen  to the ampula of the vas deferens  mix with the secretion of seminal vesicle  enter ejaculatory duct that passes through the prostate gland  released into the prostatic urethra  mix with the secretion of prostate gland  pass through the membranous urethra  enter spongy urethra  mix with the secretion of Cowper’s gland  pass through the spongy urethra of the penis  ejaculated at the urethral orifice

The Accessory Glands Produce semen, which is a mixture of secretions from many glands Each with distinctive biochemical characteristics Important glands include: Seminal glands Prostate gland Bulbo-urethral glands

28-2 Male Reproductive Functions Four Major Functions of Male Glands Activating spermatozoa - capacitation Providing nutrients spermatozoa need for motility Propelling spermatozoa and fluids along reproductive tract Mainly by peristaltic contractions Producing buffers To counteract acidity of urethral and vaginal environments

Male Reproductive System Penis Common passage for urine and semen Has corpus spongiosum – a mid-ventral, sinus rich tissue surrounding the spongy urethra: Expands at the tip of the penis to form glans penis (which is surrounded by prepuce- the foreskin) Forms the bulb to anchor the penis to the abdomen Has corpora cavernosa - two dorso-lateral, sinus-rich masses of tissues

Male Reproductive System Erection: Sexual arousal  nerve impulses to blood sinuses in erectile tissue (corpora cavernosa and corpus spongiosum)  dilatation  blood fills in the sinuses  penis expands Ejaculation: Peristalsis in vas deferens and urethra  sperms ejected : Closing of smooth muscle sphincter at the base of urinary bladder  preventing the release of urine

Male Reproductive System – Hormonal Control

Male Reproductive System – Hormonal Control Hypothalamus secretes gonadotropin releasing hormone (GnRH)  stimulates anterior pituitary to secrete: A. Follicle stimulating hormone (FSH) that stimulates Sertoli/sustentacular cells to make - Androgen binding protein (ABP), for concentrating testosterone for germ cells - Inhibin, a hormone that inhibits hypothalamus and anterior pituitary to inhibit LH and FSH secretion - Activin, a hormone that activates hypothalamus and anterior pituitary to activate LH and FSH secretion B. Luteinizing hormone (LH) stimulates Leydig cells  secrete testosterone (T)  stimulates spermatogenesis, development of secondary male characteristics, metabolism and bone and muscle growth

Male Reproductive System - Disorder Circumcision: Surgical removal of prepuce Erectile dysfunction: Inability to maintain erection : Due to - Reduced testosterone level (hypothalamus, pituitary or testes disorder) - Nerve disorder (unable to stimulate blood sinuses in erectile tissue) - Blood vessel disorder (nerve impulses  stimulate endothelial cells  release of nitric oxide – *Viagra increases NO levels  relaxation of smooth muscle in the wall of blood sinuses  vasodilation  erection) Prostate enlargement and cancer: Enlargement  causes constriction of urethra  difficulty in urination : Cancer  PSA levels increase in blood Inguinal hernia: Due to sudden stress (lifting weight)  a portion of small intestine gets pushed into the inguinal canal  swelling, severe pain and affect on digestive and reproductive functions

Male Reproductive System – Aging After 50 years of age Gradual decrease in the size of the testes and number of Leydig cells  gradual decrease in T levels  decreased sperm production and muscles Increased chances of prostate enlargement and cancer Increased fibrous connective tissue development in the erectile tissue of penis  decreased capacity to develop and maintain for erection