Flashcards in Male Reproductive Physiology Deck (46):
What do the testes consist of?
1. seminiferous tubules, where sperm are made
2. interstitial tissue, between the tubules
3. sperm transport duct system
What are the seminiferous tubules?
convoluted, hollow, fluid filled tubes that open at both ends and empty into the rete testis
What types of cells are in the seminiferous tubules?
What is on the basement membrane and lumen of the seminiferous epithelium?
basement membrane = spermatogonia (least differentiated)
lumen = spermatids (most differentiated)
What is the function of Sertoli cells?
serve to nurture the developing germ cells
(extend from basement membrane to the lumen and surround the germ cells)
Spermatogenesis consists of what?
1. cellular proliferation by repeated mitotic division
2. entry into meiosis with chromosome duplication, genetic recombination, and meiotic reduction divisions to give haploid spermatids
3. terminal differentiation of spermatids to spermatozoa
Proliferation, meiosis, and differentiation are associated with which intermediate cell types?
proliferation = spermatogonia
meiosis = spermatocytes
differentiation = spermatids
How do type A spermatogonia turn into type B spermatogonia
after going through several mitotic divisions
when spermatogonia clones enter meiosis, resting spermatogonia on basement membrane signaled to mitotically divide and new clones push previous clone closer to lumen
What happens in meiosis of spermatocytes?
Meiosis 1 - primary spermatocytes (2N4C) turn into secondary spermatocytes (1N2C)
Meiosis 2 - secondary spermatocytes (1N2C) are turned into spermatids (1N)
What happens in spermiogenesis?
long phase of terminal differentiation where the newly formed haploid round spermatid undergoes dramatic cellular changes to form the spermatozoa
Name some steps in spermiogenesis
-nucleus elongates and chromatin condenses
-Golgi apparatus produces small granules that coalesce to form acrosome
-pair of centrioles migrate to nucleus and bind to it
-axoneme elongates to form the core of the tail
-spermatid loses large amounts of cytoplasm to form the residual body
What is spermiation?
release of spermatid from its tether
(released cell is now a spermatozoa)
What is the function of apoptosis in spermatogenesis?
-keep number of germ cells to a level the Sertoli cells can support
-removal of defective sperm at quality check points
What are the functions of the Sertoli cells?
1. organize clones of germ cells in seminiferous epithelium, support the cells, and ensure their timely release
2. secrete controlling factors that regulate germ cell differentiation and maturation
3. phagocytose degenerating cells
4. produce androgen-binding protein that traps androgens for local and downstream use
5. form tight junctions that form the blood-testis barrier
6. major source of estrogen
What is the purpose of LH and FSH in males?
LH - acts on Leydig cells to increase testosterone secretion
FSH - acts on Sertoli cells and stimulates them in their supporting role, promotes seminiferous tubule growth, and androgen-binding protein production
Why is testosterone important for spermatogenesis?
testosterone helps maintain binding of Sertoli cells to developing sperm cell stages
What is the blood-testis barrier?
formed by tight junctions between adjacent SErtoli cells, divide the seminiferous epithelium into basal and adluminal compartments
What is the purpose of the blood-testis barrier?
to maintain fluid differences and provide immune compartmentalization
Why is there testicular temperature control?
reduced temperature is required for normal spermatogenesis
What are the effects of elevated temperature on spermatogenesis?
-spermatocytes and early round spermatids are very sensitive to heat, become dysfunctional
-Sertoli cells become dysfunctional
What are the 3 main regions of a spermatozoa?
2. mid piece
3. principal piece
What is the spermatozoa head made of?
What is the spermatozoa nucleus made of?
haploid DNA that is tightly condensed
What is the spermatozoa acrosome made of?
-derived from Golgi
-forms a cap over the apical 1/2 of nucleus
-contains complex array of proteins and enzymes
What is the equatorial segment?
an area where the caudal part of the acrosome thins
What are the 4 sections of the tail?
1. connecting piece
2. middle piece
3. principal piece
4. end piece
What are the major structural components of the tail?
outer dense fibers
What is the axoeneme made of?
microtubules in the classic "9+2" array, runs down the center of the entire tail
What is the mitochondrial sheath?
confined to the middle piece, the mitochondria are helically arranged around the outer dense fibers
What is the fibrous sheath?
extends the length of the principal piece and starts at the end of the mitochondrial sheath
What is the end piece?
occurs after the fibrous sheath and consists only of the tapering axoneme covered by plasma membrane
What is the sperm plasma membrane?
covers the entire sperm and is vital for normal sperm physiology and the events of fertilization
Explain the path of sperm transport
seminiferous tubule - rete testis - efferent ducts - proximal epididymis
What is the epididymis?
highly coiled structure that connects the efferent ducts to the vas deferens
What is the function of the epididymis?
transport, protect, sustain, mature, and store spermatozoa
Describe the different segments of the epididymis
initial segment = fluid resorption
middle segment = sperm maturation
terminal segment = sperm storage
What is sperm maturation?
when sperm gain fertility
Name some changes that occur in the sperm during transport
-acquisition of the potential for progressive motility
-change in cell surface electrical charge
-major alteration of plasma membrane lipid structure
-movement of the cytoplasmic droplet from the neck to the distal part of the midpiece
Why can't sperm be stored in the epididymis indefinitely?
aging sperm undergo degeneration
How is sperm quiescence maintained during storage?
1. low sodium content in the bathing fluid
2. high sperm concentration
3. secretion of viscous mucoprotein
4. secretion of cell permeating acids that diffuse into cells to keep pH low
What happens if activation of sperm occurs too early?
-incapable of reaching the site of fertilization
-incapable of fertilizing the egg
What are decapacitation factors?
proteins secreted by the epididymis that coat sperm membranes and stabilize them
What is the vas deferens?
an extension of the epididymis that runs from the cauda of the epididymis to the pelvic urethra
What are accessory sex glands?
supply the bulk of fluid in the ejaculate (seminal plasma)