Male Reproductive System 2

  1. Male Urethra
    Consists of prostatic, membranous, and spongy regions
  2. Seminal Vesicles
    • Posterior to bladder
    • Empties into ejaculatory duct
    • Forms 60% of semen
  3. Prostate Gland
    • Surround urethra and ejaculatory duct
    • Forms 30% of semen
  4. Bulbourethral Glands
    • Near bulb of penis
    • Produce clear, slippery fluid that lubricates head of penis and neutralizes acidity of urine left in penis
  5. The Penis
    • Half of the penis is an internal root, half is externally visible shaft
    • Skin over shaft loosely attached to allow expansion during erection
    • Extends over glands as prepuce (foreskin)
    • Smegma: waxy secretion of sebaceous glands in the glans and prepuce
  6. Erectile Tissue
    • Fill with blood during arousal
    • Corpus spongiosum along ventral side of penis, enclosing urethra
    • Two corpora cavernosa along dorsal side of penis
  7. Erection
    Blood fills sinuses (lacunae) of corpora cavernosa
  8. Circumcision
    • Removal of some or all of prepuce
    • Often part of religious ceremonies
    • Affects sensitivity of penis?
    • Disease prevention?
  9. Penile Arteries
    Internal pudendal artery entes root of penis and divides
  10. Dorsal Artery
    Supplies blood to skin and corpus spongiosum
  11. Deep Artery
    Supplies blood to corpora cavernosa (dilations fills lacunae for erection)
  12. Penile Vein
    Blood drains from penis through dorsal vein
  13. Penile Nerves
    • Glans has many touch and temperature receptors
    • Dorsal nerve and internal pudendal nerve converge in sacral spinal cord
    • Autonomic nerves carry information to penis
  14. Puberty
    • Reproductive system is dormant until a surge of gonadotropins from the pituitary occurs
    • First few years of adolescence, until first menstrual period or first ejaculation with viable sperm
    • Typically 12 for girls, 13 for boys
  15. Adolescence
    The period from the onset of gonadotropin secretion until person attains full adult height
  16. Endocrine Control of Puberty
    • Testes secrete lots of androgens in third trimester, but are then dormant until puberty
    • At puberty testes are controlled by secretions from hypothalamus and pituitary
    • Once hypothalamus ares to a certain extent, it produces GnRH
  17. GnRH Stimulates FSH and LH secretion
    • FSH causes Sertoli cells to initiate spermatogenesis and secrete inhibin
    • LH causes Leydig cells to produce testosterone
  18. Effects of Testosterone at Puberty
    • Enlargement of secondary sexual organs (Penis, testes, ducts, glands)
    • Generalized body growth
    • Erythropoiesis
    • Increase in basal metabolic rate
    • Pubic hair and sebaceous gland development
    • Development of sex drive
  19. Aging
    • Testosterone secretion declines with age
    • Peak secretion at age 20
    • Declines to 20% of peak by age 80
    • Fewer Leydig and Sertoli cells
    • At around 50, males experience clamacteric (andropause)
    • Can have mood changes, hot flashes
  20. Spermatogenesis
    • Process of sperm production in seminiferous tubules
    • 3 Events:
    • Reducing the chromosome number by half
    • Shuffling genes around so that new combinations exist in the sperm
    • Changing large germ cells into small, mobile sperm
  21. Meiosis
    • Germ cells go through meiosis to reduce the chromosome number by half
    • Start as diploid (two of each of the 23 chromosomes)
    • End as haploid (one of each of the 23)
    • Crossing over occurs in meiosis to shuffle genes
  22. Spermatogenesis
    • Primordial germ cells form in yolk sac of embryo
    • They migrate to gonadal ridges and become spermatogonia
    • Spermatogonia lie along seminiferous tubules and divide by mitosis
    • As they divide, one daughter cell stays in tubule wall (type A spermatogonia)
    • Type B spermatogonia migrate toward lumen and produce sperm
    • Type B spermatogonium enlarges and becomes primary spermatocyte
    • Then meiosis 2 forms secondary spermatocytes
    • Then meiosis II forms spermatids
    • Then spermiogenesis transforms them into sperm
  23. Spermiogenesis
    • Transforms spermatids into sperm
    • Excess cytoplasm is discarded and tail grows
  24. Blood Testis Barrier
    • Once a spermatocyte undergoes meiosis, it is genetically different than all other cells of the body
    • Immune system usually attacks genetically different cells, so maturing sperm must be protected
    • Sertoli cells form a tight junction so that antibodies can't get through
  25. Sperm Head
    • Nucleus: contain chromosomes
    • Acrosome: cap containing enzymes that penetrate the egg
  26. Sperm Tail
    • Midpiece: lots of mitochondria to produce ATP for flagellar movement
    • Flagellar tail
  27. Semen
    • Fluid expelled during ejaculation
    • Usually 2-5 ml
    • 60% seminal vesicle fluid, 30% prostate fluid, 10% sperm and spermatic duct secretions
    • Typically 50-120 million sperm/ml
    • Semen contains nutrients, prostaglandins that stop immune response against invading semen and initiates uterine contractions, and clotting enzymes that help entangle sperm so that they stick to vagina and cervix walls
    • Semen is alkaline to neutralize acidic vagina
  28. Male Sexual Response
    Masters and Johnson divided intercourse into four phases: Excitement, plateau, orgasm, resolution
  29. Excitement
    • Parasympathetic nervous system initiates erection in response to stimulation of penis
    • Releases nitric oxide to dilate deep arteries
    • Muscles tense
    • Increase in heart rate, blood pressure, breathing rate
    • Bulbourethral glands secrete fluid
  30. Plateau Phase
    The Seconds or minutes leading up to orgasm
  31. Orgasm
    • Short but intense reaction usually accompanied by ejaculation
    • Emission: Sympathetic nervous system induces peristalsis to propel sperm through vas deferens and beginning of urethra, glandular secretions added
    • Expulsion: Semen un urethra activates reflexes that cause muscular contractions that cause expulsion of semen
    • Internal urethral sphincter is constricted so that urine can't get into urethra and semen can't get into bladder
  32. Resolution
    • Body returns to pre-excitement stage
    • Sympathetic nervous system causes arteries to constrict
    • Penis becomes flaccid (detumescence)
    • Cardiovascular and respiratory system return to normal
    • Refractory period: period following resolution in which male cannot attain another erection
  33. Erectile Dysfunction
    • 20% of men in 60s and 50% of men in 80s have trouble maintaining erection for intercourse
    • Can be psychologically causes which responds will to placebos
    • More often cause physiologically like cardiovascular disease, low androgen, drug side affects, neurological disorders
  34. Viagra
    • Nitric oxide triggers cascade that causes vasodilation and erection
    • Viagra slows down breakdown of these intermediates to prolong erection
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Male Reproductive System 2