Lecture 13 - Epididymis, Ejaculation, Semen

Reading

• Chapter 10
• Handout on the Epididymis and Ejaculation

Lecture 13:

Spermatozoa structure

• head
  • acrosome
    • contains hydrolytic enzymes needed for fertilization
      • acrosin
      • hyaluronidase
  • nucleus
    • highly condensed with protamines replacing histones
    • crosslinking of protamines with disulfide bonds occurs in epididymis to condense sperm DNA
  • nuclear ring - formed by end of acrosome
  • postnuclear cap or region
• neck - joins head to tail
  • implantation socket
• tail
  • capitulum
    • fits into implantation socket of head
  • middle piece
    • first part has laminated columns
      • give neck flexability
    • axoneme
      • originates from distal centriole
      • microtubules - 9 pairs surround a core of 2 (9 + 2)
      • sliding of microtubules driven by ATPases to make sperm motile
    • coarse fibers
      • 9 coarse fibers surround the axoneme
    • mitochondria
      • surround coarse fibers
      • arranged in a helical pattern around axoneme
      • production of ATP via respiration for cell stability and motility
  • annulus
    • where mitochondria terminate
  • principal piece
    • composed of axoneme and associated coarse fibers
    • tough fibrous sheath surrounds the axoneme and coarse fibers
  • end piece
    • portion after end of fibrous sheath and coarse fibers
• Axoneme
  • 2 core microtubles
  • 9 outer pairs of microtubules
    • connected via radial spokes to central pair
    • nexin links connect the each of the outer pairs to each other
    • Dynein (an ATPase) located on microtuble
      • in absence of ATP dynein attached to another microtubule
      • in presence of ATP, dynein releases
      • ATP is then converted to ADP with release of energy, dynein extends, rebinds at a lower site, then dynein shortens and causes microtubules to slide past one another
      • nexin links, radial spokes, course fibers, and fiborous sheath, stretched and recoil back

Sperm metabolism

• glycolysis
  • most species can use glucose or fructose
  • sperm hexokinase can use either glucose or fructose to make Glucose-6-phosphate or Fructose-6-phosphate respectively
  • Phosphohexoisomerase converts Glucose-6-phosphate to Fructose-6-phosphate which then continues in glycolysis
  • phosphatases can convert glucose-6-phosphate back to glucose in futile subtrate cycling
• respiration
  • not always coupled to glycolysis as in other cells
  • sperm can use only glycolysis if needed
• ATP utilization
  • motility
  • futile substrate cycling
  • maintain the plasma membrane ionic gradients
  • no transcription after condensation of nucleus during spermiogenesis
• Temperature dependent so ATP dependent processes also temperature dependent
  • sperm velocity is temperature dependent

Sperm transport in the male tract

• seminiferous tubule
  • fluid flow with fluid secreted by sertoli cells
  • contractions of myoid cells
• rete testis
  • fluid flow with fluid from seminiferous tubule and secretion by rete testis cells
  • some contractions of smooth muscle in mediastinum
• vas efferentia
  • fluid flow with fluid from seminiferous tubule and rete testis
  • cilia on epithelial cells beat and move fluid along
• epididymis
  • muscle contractions
• vas deferens
  • muscle contractions
• urethra
  • muscle contractions

Epididymal Function

• maturation
  • change in fertility
  • develop motility
  • nuclear condensation
  • cytoplasmic droplet
• concentration
  • remove water
• secretion
  • testosterone converted to dihydrotestosterone (DHT)
  • energy substrates like glycerolphosphatidylcholine (GPC), free faty acids, carnitine
  • glycoproteins
  • lipids
  • enzymes
• transport
  • smooth muscle contraction
• storage
  • cauda

Hormonal control of the epididymis

• absolute requirment for androgen to function
• caput
  • tubal testosterone
• corpus
  • tubal DHT
  • vascular testosterone
• cauda
  • tubal DHT
  • vascular testosterone

Erection

• sensory and psychic input
• sympathetic nerves
  • inhibit vasoconstriction
• parasympathetic nerves
  • contraction of ischiocavernosus muscle leading to decreased venous outflow from penis
  • dilation of blood vessels in the penis leading to engorgment of corpus cavernosum
• penis becomes erect

Emission

• sensory input from glans penis
• psychic input as well
• sympathetic nerves
  • smooth muscle contraction around prostate, seminal vesicles, vas deferens, cauda epididymis
  • closure of the sphincter to the bladder
• sperm moves into urethra and is mixed with secretions from the accessory glands

Ejaculation

• sensory input from glans penis
• psychic input as well
• parasympathetic nerves
  • contraction of striated muscle in the ischiocavernosus, bulbospongiosus and pelvic urethral muscles
• forcefull contractions propels sperm with accessory gland secretions out through erect penis

Ejaculate Characteristics - Fractions

Species	Time lapse for ejaculation	Composition of Ejaculate
Bull	1 second	single fraction
Ram	1 second	single fraction
Boar	5-25 minutes	fractionated sperm-free sperm-rich coagulum
Stallion	30-60 seconds	fractionated sperm-free sperm-rich mucus
Man	10-30 seconds	single fraction but coagulated

Components of Bull Semen

• water
• semen
• substrates
  • fructose
  • sorbitol
  • inositol
  • glycerol phosphatidyl choline (GPC)
  • citric acid (not primary function)
• inorganic salts (maintain osmotic pressure)
  • sodium
  • potassium
  • calcium
  • magnesium
  • chloride
• proteins

Initial semen evaluation

• color
• volume
• concentration
• motility
• viability
• morphology

Ejaculate Characteristics - specifications

Species	Ejaculate Volume (ml)	Sperm Concentration (X 109/ml)	Total Sperm per Ejaculate (109)	% Motile	% Normal
Bull	8.0	1.5	12	75	95
Ram	1.0	3.0	3	95	95
Boar	200	.25	50	70	90
Stallion	80	.15	12	70	40 - 90
Man	2-6	.15	.9	65	30 - 70

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