Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Reproductive System  Primary sex organs (gonads)  testes in males  ovaries in females  Gonads produce sex cells called gametes and secrete sex hormones  Accessory reproductive organs – ducts, glands, and external genitalia  Sex hormones  Androgens (males),  Estrogens and progesterone (females)

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Male Reproductive System – overview of structures  The male gonads (testes) produce sperm  Sperms are delivered to the exterior through a system of ducts:  epididymis,  ductus deferens,  ejaculatory duct  urethra  Accessory sex glands:  seminal vesicles, prostate gland, and bulbourethral glands

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Male Reproductive System Figure 27.1

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Connection between testis and the body  The structures that connect the testis with the body are enclosed within a connective tissue sheath called the spermatic cord  Blood vessels  Nerve fibers  Vas deferens  Cremaster muscle

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Protection of the testis  The outermost protection is the scrotum  A sac of skin and superficial fascia that hangs outside the abdominopelvic cavity at the root of the penis  Separated by a midline septum  Its external positioning keeps the testes 3  C lower than core body temperature (needed for sperm production)  Each testis is surrounded by two tunics:  The tunica vaginalis, derived from peritoneum  The tunica albuginea, the fibrous capsule of the testis

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 27.2

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Testes protection - Testicular Thermoregulation  Sperms are not produced at core body temperature  In the scrotum, the testes are kept 2-3°C cooler than in the pelvic cavity. This is essential for sperm production.  Cooling mechanisms  The cremaster muscle contains strips of the internal abdominal oblique muscle around the spermatic cord.  It can elevate or lower the testes.  The dartos muscle is a subcutaneous layer of smooth muscle that wrinkles skin reducing surface area of scrotum. Can lifts testis upwards  The pampiniform plexus is an extensive network of veins that surround the testicular artery in the spermatic cord, keeping the testes cooler countercurrent heat exchange that cools arterial blood entering testis

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings The Testes  Divided to lobules by septa  each lobule contains 1-4 seminiferous tubules  Seminiferous tubules:  Produce the sperm

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Cells in the testes  Seminiferous tubule  lumen lined with germinal epithelium consisting of several layers of germ cells in the process of becoming sperm  Sustentacular (Sertoli) cells.  Between the seminiferous tubules are clusters of interstitial (Leydig) cells, the source of testosterone.

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings

The functions of Sertoli cells and BTB  Sustentacular cells protect the germ cells and promote their development. Tight junctions between adjacent sustentacular cells form a blood-testis barrier (BTB)  The fluid inside the tubules contains high levels of androgens, potassium and amino acids  The BTB prevents the immune system from attacking the developing spermatozoa (contain specific Ag that are not found on any other cell)  Sertoli cell supply nutrients to the developing sperms  Phagocytize cytoplasm shed by spermatids  Secrete inhibin (we will talk about this hormone later)  Secrete androgen-binding-protein (ABP) – binds testosterone inside tubules to maintain high levels

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Meiosis and production of gametes  The sequence of events that produces sperm in the seminiferous tubules of the testes  Each cell has two sets of chromosomes (one maternal, one paternal) and is said to be diploid (2n chromosomal number)  Humans have 23 pairs of homologous chromosomes  Gametes only have 23 chromosomes and are said to be haploid (n chromosomal number)  Gamete formation is by meiosis, in which the number of chromosomes is halved (from 2n to n)

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Chromosomes in Mitosis and Meiosis

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Spermatogenesis  Cells making up the walls of seminiferous tubules are in various stages of cell division  These spermatogenic cells give rise to sperm in a series of events  Mitosis of spermatogonia, forming spermatocytes  Meiosis forms spermatids from spermatocytes  Spermiogenesis – spermatids form sperm

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Mitosis of Spermatogonia  Spermatogonia – outermost cells in contact with the epithelial basal lamina  Spermatogenesis begins at puberty as each mitotic division of spermatogonia results in type A or type B daughter cells  Type A cells remain at the basement membrane and maintain the germ line  Type B cells move toward the lumen and become primary spermatocytes

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Spermatocytes to Spermatids  Primary spermatocytes undergo meiosis I, forming two haploid cells called secondary spermatocytes  Secondary spermatocytes undergo meiosis II and their daughter cells are called spermatids  Spermatids are small round cells seen close to the lumen of the tubule

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Spermatogenesis Spermatogonium (2n) Primary spermatocyte (2n) Primary spermatocyte Division – 1 st meiosis secondary spermatocyte (n) Spermatid (n) differentiation 2 nd meiosis

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Spermiogenesis spermatozoa

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Spermatozoa structure  Sperm have three major regions  Head – contains DNA and has a helmetlike acrosome containing hydrolytic enzymes that allow the sperm to penetrate and enter the egg  Midpiece – contains mitochondria spiraled around the tail filaments  Tail – a typical flagellum produced by a centriole

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Spermatic Ducts  Epididymis (head, body and tail)  6 m long coiled duct adhering to posterior of testis  site of sperm maturation and storage (fertile for 60 days)  Ductus deferens/vas deferens (peristalsis during orgasm)  muscular tube 45 cm long passing up from scrotum through inguinal canal to posterior surface of bladder  Ejaculatory duct  2 cm duct formed from ductus deferens and seminal vesicle and passing through prostate to empty into urethra  Spermatic cord – encloses PNS and SNS nerve fibers, blood vessels, and lymphatics that supply the testes

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings The Epididymis

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Epididymis functions  The epididymis functions:  The duct of the epididymis has stereocilia that:  Absorb testicular fluid  Pass nutrients to the sperm  Recycling center for damaged spermatozoa  Storage place for spermatozoa  Facilitate functional maturation preparing them for fertilization:  Plasma membrane changes, alterations in acrosomal membrane

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Urethra  Conveys both urine and semen  Consists of three regions  Prostatic – portion surrounded by the prostate  Membranous – lies in the urogenital diaphragm  Spongy, or penile – runs through the penis and opens to the outside at the external urethral orifice

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Accessory Glands: Seminal Vesicles  Lie on the posterior wall of the bladder and secrete 60% of the volume of semen  Join the ductus deferens to form the ejaculatory duct  The composition of the gland secretions include:  High concentration of fructose that is easily metabolized by spermatozoa  Prostaglandins that stimulate smooth muscle contractions in both male and female reproductive tract  Fibrinogen that forms temporary clot within the vagina after ejaculation  When the inactive sperms mix with the seminal fluid they undergo the first step of activation and the flagella start moving (in some book this is done by the help of the prostate)  The secretion of the seminal gland are discharged into the ejaculatory duct under the control of the sympathetic system

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Accessory Glands: Prostate Gland  Doughnut-shaped gland that encircles part of the urethra inferior to the bladder  Produces 20-30% of the semen volume  Contains citrate (nutrient source) and enzymes  Fluid enters the prostatic urethra during ejaculation

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Accessory Glands: Bulbourethral Glands (Cowper’s Glands)  Pea-sized glands inferior to the prostate  Produce thick, clear mucus prior to ejaculation that neutralizes traces of acidic urine in the urethra

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings The Penis  A copulatory organ designed to deliver sperm into the female reproductive tract  Erectile tissue – spongy network of connective tissue and smooth muscle with vascular spaces  Corpus spongiosum – surrounds the urethra and expands to form the glans and bulb of the penis  Corpora cavernosa – paired dorsal erectile bodies bound by fibrous tunica albuginea  Erection – during sexual excitement, the erectile tissue fills with blood causing the penis to enlarge and become rigid

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure The Penis

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings semen  The combination of sperm and the fluids secreted by the accessory glands.  The ejaculate (fluid produced during ejaculation) contains million spermatozoa/ml  The volume is about 2-5 ml

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Ejaculation  The propulsion of semen from the male duct system  At ejaculation, sympathetic nerves serving the genital organs cause:  Reproductive ducts and accessory organs to contract and empty their contents  The bladder sphincter muscle to constrict, preventing the expulsion of urine  Propulsion of semen from the urethra (peristaltic contractions)

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Hormonal Regulation of Testicular Function  The hypothalamus releases gonadotropin-releasing hormone (GnRH)  GnRH stimulates the anterior pituitary to secrete FSH and LH  FSH causes sustentacular cells to release androgen- binding protein (ABP)  LH stimulates interstitial cells to release testosterone  ABP binding of testosterone enhances spermatogenesis

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Hormones and Brain-Testicular Axis

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Testosterone  The principal androgen (male sex hormone) is testosterone.  This steroid is manufactured by the interstitial (Leydig) cells of the testes.  Secretion of testosterone increases sharply at puberty and is responsible for the development of the secondary sexual characteristics of men.  Testosterone is also essential for the production of sperm.

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Male Secondary Sex Characteristics  Male hormones make their appearance at puberty and induce changes in nonreproductive organs, including  Appearance of pubic, axillary, and facial hair  Enhanced growth of the chest and deepening of the voice  Skin thickens and becomes oily  Bones grow and increase in density  Skeletal muscles increase in size and mass  Testosterone is the basis of libido in both males and females