Chapter 27, Part 1: Male Reproductive System Flashcards
Human Reproductive Systems:
o Gonads = primary reproductive organs. o Males: (2) testes. o Females: (2) ovaries. o Function of gonads: o 1. produce gametes. o 2. secrete sex hormones. o Gametes = sex cells (haploid number of chromosomes =23). o Male: spermatozoa. o Female: ova. o Zygote = 1 spermatozoon + 1 ovum united after fertilization.
Human Chromosomes:
o Somatic cells (diploid cells)
o 23 pairs of chromosomes for a total of 46 chromosomes.
o The two chromosomes that make up each pair are homologous chromosomes since they contain similar genes in same order (but each has different information from each parent).
o One member of each pair is from each parent.
o 22 autosomes (non-sex chromosomes) & 1 sex chromosome =23.
o Sex chromosomes are either X or Y.
o Females have two X chromosomes.
o Males have an X and a smaller Y chromosome.
o Gametes (haploid cells):
o Single set of chromosomes for a total of 23.
o Produced by special type of division: meiosis (reducing).
Other Reproductive Systems:
o Accessory reproductive organs:
o Essential for reproduction.
o Include ducts, glands, and supporting structures.
o Secondary sex characteristics:
o Features not essential for reproduction, but attract sexes to each other.
o Physique, breasts, voice, scent, skin, body hair distribution, metabolic rate.
Testes:
o Paired oval glands (2” x 1”).
o Develop in utero in abdominal cavity (near kidneys)… descend thru inguinal canal at about 7th month of fetal life.
o Lie in scrotum outside abdominopelvic cavity to regulate ideal temperature for sperm production.
o Spermatogenesis requires temps 2 to 3° C below body temp.
o Controlled by cremaster muscles, dartos muscle, and pampiniform plexus.
o Exocrine function: releasing spermatozoa into ducts.
o Endocrine function: releasing hormones into blood
o Testosterone.
o Inhibin.
o Testes are regulated primarily by other hormones:
o LH from anterior pituitary stimulates secretion of testosterone.
o FSH from anterior pituitary stimulates spermatogenesis.
o LH & FSH are regulated by GnRH (gonadotropin releasing hormone) secreted by hypothalamus.
Temperature Regulation of Testes:
Pampiniform venous plexus removes heat from incoming warm blood in testicular arteries.
Descent of Testes:
o CRYPTORCHIDISM = failure of testes to descend into scrotum
o The testes develop in utero in abdominal cavity (near kidneys), and descend thru inguinal canal at about 7th month of fetal life leads to bilateral cryptorchidism can cause sterility in males and higher incidence of testicular cancer.
o 30% of premature infants.
o 80% spontaneously descend within 1st year of life.
o If do not descend, must be surgically corrected by 18 mos.
Membranes Around Testes:
o Tunica vaginalis:
o Serous membrane derived from peritoneum (remnant of testicular descent).
o Tunica albuginea:
o Forms a capsule around testes.
o Extends inward to form SEPTA that divide each testis into 200 to 300 testicular lobules.
o Each lobule contains 1 to 4 seminiferous tubules where spermatogenesis occurs.
Seminiferous Tubules:
o “Spermatozoa factories”
o 2 cell populations:
o Sertoli cells (sustentacular cells)
o Nourish & protect spermatozoa.
o Form BLOOD-TESTIS BARRIER (tight junctions between and stuff can only go through these cells).
o Secrete INHIBIN (hormone that inhibits release of FSH from anterior pituitary when spermatozoa count is high.
o INTERSTITIAL CELLS OF LEYDIG = located between the seminiferous tubules that secrete testosterone = LH affects testosterone levels…e.g., low levels of LH = low testosterone level.
o Spermatogenic cells (mitosis & meiosis):
o Spermatogonia (stem cells).
o Primary spermatocytes.
o Secondary spermatocytes.
o Spermatids.
o Spermatozoa.
Spermatogenesis:
o Spermatocytogenesis:
o Spermatogonia undergo mitosis to produce primary spermatocytes (begins at puberty).
o Meiosis I:
o Primary spermatocytes undergo Meiosis I to produce haploid number of chromosomes… Prophase I takes 22 days!
o Meiosis II:
o Secondary spermatocytes undergo Meiosis II.
o Spermiogenesis:
o Spermatids mature into spermatozoa.
Initiation of Spermatogenesis:
o Puberty!!!!
o Hypothalamus increases release of GnRH, a hormone which targets the anterior pituitary.
o Anterior pituitary increases secretion LH & FSH.
o LH stimulates Leydig cells to secrete testosterone:
o An enzyme in prostate & seminal vesicles converts testosterone into dihydrotestosterone (DHT-more potent).
o FSH stimulates spermatogenesis:
o With testosterone, stimulates SERTOLI CELLS to secrete ABP (androgen-binding protein) (keeps hormones levels high).
o Testosterone stimulates final steps spermatogenesis.
Control of Testosterone Production:
o Negative feedback system controls blood levels of testosterone.
o Receptors in hypothalamus detect increase in blood level.
o Secretion of GnRH slowed.
o Anterior pituitary (FSH & LH hormones) slowed.
o Leydig cells of testes slowed.
o Blood level returns normal.
Blood and Nerve Supply to Testes:
o Blood and lymph vessels travel within spermatic cord
o Testicular artery branches off of abdominal aorta… capillaries… testicular veins arise from pampiniform plexus.
o Both divisions of the ANS supply testes, MANY associated sensory nerves (agonizing pain if injured).
Testicular Cancer:
o Rare (1 in 20,000 males).
o Most common cancer in men ages 15 to 35 years.
o Risk factors:
o Cryptorchidism.
o Mumps virus.
o Cure rate is 90% if orchiectomy = removal of testicle(s).
Exocrine Duct System:
o Epididymis:
o 1.5 - 3” long on posterior side of testis (20 feet of coiled ductwork inside!).
o Lined with pseudostratified columnar cells with stereocilia = long microvilli for resorption of degenerated sperm.
o Temporary storage site for immature spermatozoa, may remain viable for 40 to 60 days.
o Takes 20 days minimum to reach “tail”.
o Vas Deferens = Ductus Deferens.
o Ejaculatory Duct.
o Male urethra.
Function of Epididymis:
o Epididymis absorbs 90% of fluid leaving the testis.
o Epididymis secretes substances that continue maturation of spermatozoa (to become motile with the ability to fertilize an ovum)).
o Storage of spermatozoa (40 – 60 days).
o Propulsion of sperm into ductus deferens (or vas deferens), by peristaltic contraction of smooth muscle which is innervated by the sympathetic nervous system.
