Male Reproductive System

• The major function of reproduction is to pass on animal genetics and continue species survival. Homeostasis is not necessarily the goal and animal reproduction may be detrimental to survival of the parent
• Types of reproduction in animals


  • Budding or fission (asexual)
  • Parthenogenesis (asexual)
  • Sexual reproduction
• Asexual reproduction


  • Basically, cloning with little to no genetic variation from individual parent to offspring
  • Benefit: a fast way to produce offspring and pass on individual parent genetics

  
• Sexual reproduction


  • Slower riskier process involving joining of genetics from two parents
  • Benefit: greater genetic variation to overcome environmental change
• All animal cells, with the exception of germ cells, are diploid. Each cell has pairs of chromosomes (23 pairs, 46 chromosomes total in humans)
• Germ cells (egg and sperm) are haploid –each germ cell has one chromosome from each of the paired chromosomes (23 in humans)

  
• Combining the two during fertilization results in a single cell (embryo) with paired chromosomes (23 pairs, 46 chromosomes)

  
• Sexual dimorphism


  Describes a differences between males and females of the same species. Can be related to various aspects of anatomy and physiology including animal behavior and appearance such as size, color, behavior, etc.
• Development of animal young


  • Oviparous
  • Ovoviviparous
  • Viviparous
• Oviparous


  Eggs are laid, fertilized and young develop completely outside female's body. Young feed on egg contents
• Ovoviviparous


  Eggs are fertilized inside female but then laid before young hatch. Young feed on high energy egg yolk
• Viviparous


  Fertilization and development of young within the female to completion or near completion. Young feed on some egg yolk but then mother's nutrients through placenta or a rudimentary placenta
• Caring of animal young

  • Precocial
  • Altricial
• Precocial


  Hatchling or newborn needs modest parental care for survival
• Altricial


  Hatchling or newborn requires considerable parental care for survival
• Gonads and germ cells


  • Male gonads are testes (paired)
  • Female gonads are ovaries (paired)
  • Female birds have one functional gonad or ovary (left ovary)
  • Ovaries produce female germ cells (oocytes; egg or ova) by oogenesis
  • Ovaries also produce sex steroids: estradiol (E2) and progesterone (P4)
  • Testes produce male germ cells (spermatozoa/sperm) by spermatogenesis
  • Testes also produce sex steroids: testosterone (T), dihydrotestosterone (DHT) and some E2

  
• Reproductive tract


  • Function in male: sperm maturation and transport
  • Function in females: egg transport, fertilization and embryo and fetal development
  • Includes accessory sex glands with reproductive functions
• Genitalia


  • Internal mammalian genitalia: Male - testes, epididymis, vas deferens, accessory sex glands. Female - ovaries, fallopian tube or oviduct, uterus, cervix, vagina
  • External mammalian genitalia: Male - penis and scrotum. Female - vulva (includes the labia majora/minora, clitoris and vestibule)
• Male reproductive tract


  • Testis seminiferous tubules (spermatogenesis)
  • Efferent ducts
  • Epididymis
  • Vas deferens (ductus deferens)
  • Ejaculatory duct
  • Urethra and penis
• Male accessory sex glands


  • Seminal vesicles
  • Prostate
  • Bulbourethral glands
• Functions of male accessory sex glands


  • Increases pH within male urethra and female reproductive tract for sperm health
  • Supports sperm with important nutrients
  • Produces a "mating plug" in some species
• Male external genitalia


  • Penis (glans penis)
  • Scrotum
• Testes


  • During fetal development, the testes descend through the inguinal canal, an opening in the abdominal wall, into the scrotum
  • Spermatogenesis in mammals typically requires a temperature that is less than body temperature
  • The pampiniform plexus, cremaster muscle and tunica dartos help to regulate temperature in testis in animals with a scrotum
  • Cryptorchidism refers to a condition in which the testes do not descend through the inguinal canal resulting in abnormal spermatogenesis
• Spermatogenesis


  Sperm develop in waves along seminiferous tubule –different developmental stages at different points along seminiferous tubule for continuous supply of mature sperm
• Human ejaculate is approx. 2 mL and contains 150 to 600 million sperm cells. Pig ejaculate is about 250 mL contains 20-60 billion sperm cells
• It takes approximately 70 days, from start to finish, to produce a single sperm cell
• Pampiniform plexus (PP)


  Testicular artery (TA) and testicular vein (TV)
• Spermatogenesis in testis seminiferous tubules


  1. Epidydimal head (EH)

  2. Epidydimal Body (EB)

  3. Epidydimal Tail (ET)
• Epididymis


  Site of sperm storage, maturation and transport
• Sperm develop in waves along seminiferous tubule –different developmental stages at different points along seminiferous tubule for continuous supply of mature sperm
• Sertoli cells


  • Relationship to developing sperm cells
• Spermatogenesis and meiosis in males


  1. Spermatogonium

  2. Primary spermatocyte

  3. Spermatid

  
• At puberty in males, spermatogenesis and germ cell meiosis are continuous. Sperm are produced in millions or billions throughout life
• Spermatogonium, a type of stem cell, continuously divides to make primary spermatocytes

  
• During meiosis, a single primary spermatocyte makes four spermatids that become spermatozoa
• Puberty in males and females is largely influenced by nutrition, growth and age
• GnRH neurons are found in two different hypothalamic nuclei in males and females: Arcuate nucleus (ARC) and preoptic area (POA)
• ARC and POA neurons in males secrete GnRH into HH blood portal system in tonic (continuous), low amplitude pulses
• Luteinizing hormone (LH) and follicle stimulating hormone (FSH) are released by anterior pituitary gonadotrope cells into general circulation
• After puberty in males, pulses of GnRH, LH and FSH occur 4 to 8 times a day. Blood concentrations of FSH are lower but last longer because of a longer hormone half-life.