 Reproduction  one property of a living thing  great variety of methods  Sexual reproduction  each offspring has 2 parents and receives genetic material from both  provides genetic diversity  foundation for survival and evolution of species 27-1

 Male and female gametes (sex cells) combine their genes to form a fertilized egg (zygote)  one gamete has motility (sperm)  parent producing sperm considered male  has Y chromosome in most mammals  other gamete (egg or ovum) contains nutrients for developing zygote  parent producing eggs considered female  in mammals the female also provides shelter for the developing fetus (uterus and placenta) 27-2

 Primary sex organs  produce gametes (testes or ovaries)  Secondary sex organs  male - ducts, glands, penis deliver sperm cells  female - uterine tubes, uterus and vagina receive sperm and nourish developing fetus  Secondary sex characteristics  develop at puberty to attract a mate  pubic, axillary and facial hair, scent glands, body morphology and low-pitched voice in males 27-3

 Our cells contain 23 pairs of chromosomes  22 pairs of autosomes  1 pair of sex chromosomes (XY males: XX females)  males produce 50% Y carrying sperm and 50% X carrying  all eggs carry the X chromosome  Sex of child determined by type of sperm that fertilizes mother’s egg 27-4

 Gonads begin to develop at 6 weeks  The male and female reproductive systems have different embryological origins  mesonephric ducts develop into male reproductive system  paramesonephric ducts (müllerian ducts) develop into female reproductive tract 27-5

 SRY gene (Sex-determining Region of Y gene)  in males, codes for a protein that causes development of testes  testes secrete testosterone  testes secrete müllerian-inhibiting factor which degenerates paramesonephric ducts  In absence of hormones, fetus becomes phenotypically ‘female’ 27-6

 External genitals of both sexes begin as a  genital tubercle  becomes glans of penis or  clitoris  pair of urogenital folds  enclose urethra of male or  form labia minora  a pair of labioscrotal folds  scrotum or  labia majora 27-7

 All 8 week old fetuses have same 3 structures  by end of week 9, begin to show sexual differentiation  distinctly male or female by end of week

 Begin development near kidney  gubernaculum (cordlike structure containing muscle) extends from gonad to abdominopelvic floor  it shortens, guides testes to scrotum  Descent begins in weeks 6-10, finished by 28  3% born with undescended testes (cryptorchidism)  Location outside pelvic cavity essential for low temperatures needed for sperm production 27-9

27-10

 Impotence – Inability to sustain an erection sufficient for sexual intercourse, or inability to ejaculate  Male Sterility – Infertility caused by disorders of the male reproductive system  BPH – Benign Prostatic Hypertrophy  Cryptorchidism – Undescended testicle(s) 27-11

 Pouch holding testes  divided into 2 compartments by median septum  Spermatic cord travels up from scrotum to pass through inguinal canal  contains testicular artery, vein, nerve and lymphatics 27-12

27-13 Circumcision

 Muscular control  Cremaster muscle  Dartos muscle  Counter-current exchange  Pampiniform plexus 27-14

 Oval organs, 4 cm long x 2.5 cm in diameter  covered anteriorly by tunica vaginalis  Tunica albuginea  white fibrous capsule on testes  Septa divide testes into compartments containing seminiferous tubules  each tubule lined with a thick germinal epithelium for sperm  interstitial cells between tubules - testosterone  Rete testis  seminiferous tubules drain here 27-15

 Efferent ductules  12 small ciliated ducts collecting sperm from rete testes and transporting it to epididymis  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 (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 Vasectomy

 Regions: prostatic, membranous and penile --- totals 20 cm long 27-17

 Seminal vesicles - pair  posterior to bladder  empty into ejaculatory duct  Prostate gland - single  below bladder, surrounds urethra and ejaculatory duct  2 x 4 x 3 cm  Bulbourethral glands - pair  near bulb of penis  empty into penile urethra  lubricating fluid 27-18

 Internal root, shaft, and glans  external portion 4 in. long when flaccid  The foreskin is termed the prepuce  3 cylindrical bodies of erectile tissue  corpus spongiosum along ventral side of penis  encloses penile urethra  corpora cavernosa  diverge like arms of a Y  Erection 27-19

 Hypothalamus produces GnRH  Stimulates anterior pituitary (gonadotrope cells) to secrete  LH  stimulates interstitial cells to produce testosterone  FSH  stimulates sustentacular cells (Sertoli cells) to secrete androgen-binding protein (ABP) that interacts with testosterone to stimulate spermatogenesis 27-20

 Reproductive system remains dormant for years after birth  surge of pituitary gonadotropins begins development  in most boys; 8-10 in most girls  Puberty  period from onset of gonadotropin secretion until first menstrual period or first ejaculation of viable sperm  Adolescence  ends when person attains full adult height

 Enlargement of secondary sexual organs  penis, testes, scrotum, ducts, glands  Development of secondary sexual characteristics  hair, scent and sebaceous glands develop  muscle mass, vocal quality  stimulates erythropoiesis and libido  During adulthood, testosterone sustains libido, spermatogenesis and reproductive tract 27-22

 Enlargement of secondary sexual organs  penis, testes, scrotum, ducts, glands  Development of secondary sexual characteristics  hair, scent and sebaceous glands develop  muscle mass, vocal quality  stimulates erythropoiesis and libido  During adulthood, testosterone sustains libido, spermatogenesis and reproductive tract 27-23

 Mitosis produces two genetically identical daughter cells (for tissue repair, embryonic growth)  Meiosis produces gametes  for sexual reproduction  2 cell divisions (only one replication of DNA)  meiosis I separates homologous chromosome pairs into 2 haploid cells  meiosis II separates duplicated sister chromatids into 4 haploid cells 27-24

 Blood-testis barrier is formed by tight junctions between and basement membrane under sustentacular cells (Sertoli cells) basal lamina, 2 spermatogonia, 3 spermatocyte 1st order, 4 spermatocyte 2nd order, 5 spermatid, 6 mature spermatid, 7 Sertoli cell, 8 tight junction (blood testis barrier)

 Spermatogonia produce 2 kinds of daughter cells  type A remain outside blood-testis barrier and produce more daughter cells until death  type B differentiate into primary spermatocytes  cells must pass through BTB to move inward toward lumen - new tight junctions form behind these cells  meiosis I  2 secondary spermatocytes  meiosis II  4 spermatids 27-26

 Changes that transform spermatids into spermatozoa  discarding excess cytoplasm and growing tails 27-27

 Head is pear-shaped front end  4 to 5 microns long structure containing the nucleus, acrosome and basal body of the tail flagella  nucleus contains haploid set of chromosomes  acrosome contains enzymes that penetrate the egg  basal body 27-28

 Tail is divided into 3 regions  midpiece contains mitochondria around axoneme of the flagella (produce ATP for flagellar movement)  principal piece is axoneme surrounded by fibers  endpiece is very narrow tip of flagella 27-29

 2-5 mL of fluid expelled during orgasm  60% seminal vesicle fluid, 30% prostatic, 10% sperm  normal sperm count million/mL  Other components of semen  fructose - energy for sperm motility  fibrinogen causes clotting  enzymes convert fibrinogen to fibrin  fibrinolysin liquefies semen within 30 minutes  prostaglandins stimulate female peristaltic contractions  spermine is a base stabilizing sperm pH at 7.2 to

27-31  Arteries of penis  dorsal and deep arteries (branches of internal pudendal)  deep artery supplies lacunae of corpora cavernosa  dilation fills lacunae causing an erection  normal penile blood supply comes from dorsal artery  Nerves of penis  abundance of tactile, pressure and temperature receptors  dorsal nerve of penis and internal pudendal nerves lead to integrating center in sacral spinal cord  both autonomic and somatic motor fibers carry impulses from integrating center to penis

27-32  Excitement is characterized by vasocongestion of genitals, myotonia, and increases in heart rate, blood pressure and pulmonary ventilation  Initiated by many different erotic stimuli  Erection of penis is due to parasympathetic triggering of nitric oxide (NO) secretion  dilation of deep arteries and filling of lacunae with blood  Erection is maintained during plateau phase

27-33  Climax (orgasm) is 15 second reaction that typically includes the discharge of semen (ejaculation)  Ejaculation has two stages  emission = sympathetic nervous system propels sperm through ducts as glandular secretions are added  expulsion = semen in urethra activates muscular contractions that lead to expulsion

27-34  Sympathetic signals constrict internal pudendal artery and reduce blood flow to penis  penis becomes soft and flaccid (detumescence)  Cardiovascular and respiratory responses return to normal  Refractory period (10 minutes to few hours)

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