LECTURE 2
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Transcript of LECTURE 2
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DEVELOPMENTAL
BIOLOGY Lecture II: SPERMATOGENESIS
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SPERMATOGENESIS According to Hess
et al., 2008
Spermatogenesis is the transformation of spermatogonial cells into spermatozoa over an extended period of time within the seminiferous tubule boundaries of the testis.
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SPERM: DISCOVERY Anton van Leeuwenhoek and
Nicolas Hartsoeker
First to discover the sperm, and believe that these are “parasitic animals”
Leeuwenhoek also wrote that sperm were seeds, and that the female merely provide the nutrient soil in which seeds are planted
Hartsoeker drew the homunculus, sperm contained the entire embryonic organism
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SPERM: DISCOVERY J.L Prevost and J.B. Dumas
claimed that sperm were not parasites, but rather the active agents of fertilization.
They proposed that the sperm entered the egg and contributed materially to the next generation.
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SPERM: DISCOVERY Oscar Hertwig and Herman
Fol
In 1876, independently demonstrated sperm entry into the egg and the union of two cells’ nuclei
Hertwig repeatedly observed sperm entering the eggs and noted that only one sperm can enter each egg
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SPERM: DISCOVERY A. Von Kolliker
Described the formation of sperm formation from cells in the adult testes
Believed that sperm excited the egg to develop
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SPERM: STRUCTURE Each sperm cell consists of a haploid nucleus,
a propulsion system to move the nucleus, and a sac of enzymes that enable the nucleus to enter the egg.
Acrosome
Derived from the cell’s Golgi apparatus and contains enzymes that digest proteins and complex sugars
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SPERM: STRUCTURE The core of the
axoneme consist of 2 central microtubules surrounded by a row of 9 doublet microtubules
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SPERM: STRUCTURE Only one microtubule of
each doublet is complete, having 13 protofilaments; the other is C-shaped and has only 11 protofilaments
Profilaments ar made of dimeric protein tubulin
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SPERM: STRUCTURE
Although tubulin is the basis for the structure of the flagellum, other proteins are also critical for flagellar function. The force for sperm propulsion is provided by dynein, a protein attached to the microtubules
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SPERM: STRUCTURE Dynein is an ATPase, an enzyme that hydrolyzes ATP,
converting the released chemical energy into mechanical energy to propel the sperm.
This energy allows the active sliding of the outer doublet microtubules, causing the flagellum to bend (Ogawa et al. 1977; Shinyoji et al.1998).
The "9 + 2" microtubule arrangement with dynein arms has been conserved in axonemes throughout the eukaryotic kingdoms, suggesting that this arrangement is extremely well suited for transmitting energy for movement.
The ATP needed to whip the flagellum and propel the sperm comes from rings of mitochondria located in the midpiece of the sperm.
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SPERMATOGENESIS
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SPERMIOGENESIS The centriole produces a long
flagella at what will be the posterior end of the sperm, and the golgi apparatus forms the acrosomal vesicle at the future anterior end.
The mitocondria collect around the flagellum near the base of the haploid nucleus and become incorporated into the midiece of the sperm.
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HORMONAL FUNCTION AND CELLS INVOLVED IN TESTICULAR FUNCTION
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SERTOLI OR SUSTENTACULAR CELL Sertoli cells are supporting
cells that stretch from the lumen to the edge of the tubule
nourish the developing sperm
form a blood-testis barrier to control spermatogenesis (similar to the blood-brain barrier)
These cells also inhibit spermatogenesis before puberty and stimulate the process after puberty.
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It is activated by follicle-stimulating hormone and has FSH-receptor on its membranes.
Sertoli-Sertoli junctions divide seminiferous tubules into basal and adluminal compartments
the Sertoli cell has also been called the "mother" or "nurse" cell.
Sertoli cells also act as phagocytes, consuming the residual cytoplasm during spermatogenesis.
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LEYDIG OR INTERSTITAL CELLS
Leydig cells, also known as interstitial cells of Leydig
found adjacent to the seminiferous tubules in the testicle
They produce testosterone in the presence of luteinizing hormone (LH).
Leydig cells release a class of hormones called androgens
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stimulates Leydig cells to produce testosterone in the testes
Luteinizing Hormone
stimulates Sertoli cells to produce androgen-binding protein (ABP), thereby stimulating spermatogenesis
SH also stimulates Sertoli cells to produce inhibin, which provides negative feedback to the anterior pituitary to decrease FSH secretion
Follicle-Stimulating
Hormone
HORMONES
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gonadotropin-releasing hormoneSecreted by hypothalamusStimulates secretion of anterior pituitary secretion hormones (FSH/LH
Secreted by cells of Leydig (Interstitial cells of seminiferous tubules)
Exert negative feedback on hypothalamic and ant. pituitary hormones
Stimulates spermatogenesis by binding to ABP and development of secondary sex characteristics
GnRH
Testosterone
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is a hormone found in humans and other animals.
It is synthesized and secreted by gonadotrophs of the anterior pituitary gland.
FSH regulates the development, growth, pubertal maturation, and reproductive processes of the body.
FSH and luteinizing hormone (LH) act synergistically in reproduction.
FOLLICLE STIMULATING HORMONE
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also known as lutropin and sometimes lutrophin
is a hormone produced by gonadotroph cells in the anterior pituitary gland.
In females, an acute rise of LH ("LH surge") triggers ovulation and development of the corpus luteum.
In males, where LH had also been called interstitial cell-stimulating hormone (ICSH), it stimulates Leydig cell production of testosterone.
It acts synergistically with FSH.
LUTEINIZING HORMONE
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Temperature
The optimal temperature for spermatogenesis is 34-35 ⁰ C.
Diet
Diet must contain vitamin A, B12, folic acid and vitamin C and E which is essential for spermatogenesis.
NON-HORMONAL FACTORS