The Reproductive System: Part I Anatomy and Physiology of the Male Reproductive System

Reproductive System: Functions Gonads produce gametes (sex cells) Ovaries produce oocytes (egg cells) Testes produce spermatocytes (sperm cells) Sustain and transfer spermatocytes/Receive spermatocytes

Reproductive System: Functions Sexual reproduction produces new individuals Fertilization produces one cell (a zygote)with one set of chromosomes from each parent Creates genetic variation Gonads secrete sex hormones

Reproductive System Overlaps with Endocrine System Gonadotropin Releasing Hormone (GnRH)produced by Hypothalamus Follicle-stimulating hormone and luteinizing hormones produced by Pituitary Gland Hormones in bold Glands in italics

Sexual Development During the seventh week of development, male and female embryos start to develop differently.

Hormones Puberty Anatomy Male Reproductive System

Figure 19.2 page 547

Male Hormones Gonadotropin-releasing hormone (GnRH) Released by hypothalamus, triggers LH,FSH Lutenizing hormone (LH) Released by anterior pituitary gland Binds to interstitial cells in testes Causes secretion of testosterone Follicle-stimulating hormone (FSH) Released by anterior pituitary gland Binds to Sertoli cells in seminiferous tubules to promote sperm development Increases secretion of inhibitin (neg. feedback FSH)

Male Hormones Testosterone Released by interstitial cells of testes Enlargement and differentiation male genitals and reproductive duct system Spermatogenesis (production of sperm) Development of secondary sexual characteristics Hair distribution/growth Skin texture, fat distribution Skeletal muscle growth Changes in larynx Influences brain function (hypothalamus)

Puberty Period of rapid growth and sexual maturation during which the reproductive system becomes fully functional -male age (done 18) -female age (done 16)

Puberty Estrogens and testosterone are steroid hormones. These hormones act on cells and tissues to produce many male/female physical characteristics.

Male Reproductive System When puberty is complete, the reproductive system is fully functional: the male can produce and release active sperm.

Male Reproductive System Penis Ductus deferens-sperm duct Testis-sperm formation Epididymis-sperm maturation Scrotum-cools testis Prostate-semen Seminal vesicle-semen Urethra-urine

Male Reproductive System Just before birth (or just after), the testes descend from the abdomen into an external sac called the scrotum.

Cryptorchidism Failure of testes to descend: causes infertility because testes remain too warm to correctly develop sperm 3% of full-term newborn males have cryptorchidism; within the first year, number drops to 1% Fixed by surgery (orchioplexy)

Scrotum Saclike structure containing testes Sac of loose skin, fascia & smooth muscle (Dartos muscle) divided into two pouches by a septum

Scrotum Temperature regulation of testes Sperm survival requires 2-3 degrees lower temperature than core body temperature Muscle in scrotum (Dartos muscle) Contracts & elevates testes on exposure to cold & during arousal Warmth reverses the process

Testes Seminiferous tubule Lobule Septum Oval organs about 4-5 cm long 250 cone-shaped lobules Contain seminiferous tubules and Leydig cells (interstitial). SRY gene

Seminiferous Tubules Clusters of hundreds of tiny tubules within testes. Location of meiosis Diploid germ cell divides twice to form haploid gametes Human sperm should have 23 chromosomes Nondisjunction: failure of chromosome pairs to separate results in trisomy or monosomy

Seminiferous Tubules Germ cells: sperm producing cells Sertoli cells: nourish sperm, produce hormones Interstitial (Leydig) cells: in between tubules secrete testosterone

Sertoli Cells Sertoli cells -- extend from basement membrane to lumen form blood-testis barrier support developing sperm cells produce fluid & control release of sperm into lumen secrete inhibin which slows sperm production

Spermatogenesis Formation of sperm cells Epididymis: Spermatids are moved here after production and are stored as they mature. 2-3 months to fully mature

Spermatogenesis Sperm forming cells go through two meiotic divisions Each of four spermatids develop into a sperm Second meiosis division give four spermatids,each with 23 single stranded chromosomes First meiosis division give two secondary spermatocytes, each with 23 chromosomes that become double stranded. Primary spermatocyte with 2n=46 chromosomes Spermatogonium with 2n=46 chromosomes multiply by mitosis.

Vas Deferens From the epididymis, some sperm are moved into a tube called the vas deferens, which extends upward from the scrotum and merges with the urethra.

Seminal Fluid Glands lining the reproductive tract produce a nutrient-rich fluid called seminal fluid. The seminal fluid nourishes the sperm and protects them from the acidity of the female reproductive tract. Bulbourethral Prostate Seminal Vesicle

Male Glands Seminal Vesicles Secrete 60% of clear, alkaline seminal fluid, with fructose sugar, ATP and prostaglandins for normal sperm nutrition & function Chemicals for coagulation of semen Prostate Secretes 30% of milky, slightly acidic seminal fluid with an antibiotic to kill bacteria Bulbourethral Glands Secrete clear, alkaline mucus to buffer and lubricate urethra

Semen Mixture of sperms and seminal fluid 60% from seminal vesicles, 30% from prostate Slightly alkaline, milky appearance and sticky Contains nutrients, clotting proteins & an antibiotic to protect the sperms Typical ejaculate is 2.5 to 5 ml in volume Normal sperm count is 50 to 150 millions/mL Actions of many sperm are needed for one to enter If less than 20 millions/mL sterile

Sperm Morphology A mature sperm cell consists of a head, which contains a highly condensed nucleus; a midpiece, which is packed with energy- releasing mitochondria; a tail, or flagellum, which propels the cell forward.

Sperm Morphology Adapted for reaching and fertilizing the egg Head contains DNA contains acrosome Holds enzymes for penetrating the egg

Hormonal Control of Male Physiology Hypothalamus secretes gonadotropin releasing hormone (GnRH) Anterior pituitary secretes FSH and LH FSH causes Sertoli cells to secrete ABP and inhibin LH causes interstitial cells to secrete testosterone ABP and testosterone stimulate spermatogenesis Control is Negative FB by  testosterone and inhibin Hypothalamus GnRh Anterior Pituitary Follicle Stimulating Hormone Luteinizing Hormone Sertoli CellsInterstitial Cells TestosteroneAndrogen Binding Protein Spermatogenesis