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Sperm and their origin Flashcards

1
Q

When do spermatogenesis begin?

A

Spermatogenesis begins at puberty

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2
Q

What is spermatogenesis?

A

Spermatogenesis is all the events by which spermatogonia are transformed into spermatozoa.

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3
Q

What give rise to spermatogonial stem cells?

A

Primordial germ cells give rise to spermatogonial stem cells.

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4
Q

What does spermatogonial stem cells differentiate into?

A

At regular intervals, spermatogonial stem cells emerge to form type A spermatogonia, and their production marks the initiation of spermatogenesis.

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5
Q

How is type B spermatogonia produced and what do they divide into?

A

Typa A spermatogonia undergo a limited number of mitotic divisions to form clones of cells. The last cell division produces type B spermatogonia, which then divide to form primary spermatocytes.

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6
Q

What happens when the stage of primary spermatocyte is reached?

A

Primary spermatocytes then enter a prolonged prophase (22 days).

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7
Q

How are secondary spermatocytes produced?

A

Primary spermatocytes complete meiosis I and form secondary spermatocytes

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8
Q

How is spermatids produced?

A

During the second meiotic division, secondary spermatocytes form haploid spermatids.

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9
Q

Which hormone regulates spermatogenesis?

A

Spermatogenesis is regulated by luteinizing hormone produced by the pituitary gland.

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10
Q

How does luteinizing hormone regulate spermatogenesis?

A

Luteinizing hormone binds to receptors on Leydig cells and stimulates testosterone production, which in turn binds to Sertoli cells to promote spermatogenesis.

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11
Q

What is the effect of follicle-stimulating hormone in testis?

A

Follicle-stimulating hormone binds to Sertoli cells and stimulates testicular fluid production and synthesis of intracellular androgen receptor proteins.

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12
Q

What is spermiogenesis?

A

Spermiogenesis is the series of changes resulting in the transformation of spermatids into spermatozoa.

These changes include:
1. Formation of the acrosome
2. Condensation of the nucleus
3. Formation of neck, middle piece and tail
4. Shedding of most of the cytoplasm as residual bodies

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13
Q

What is the time required for a spermatogonium to develop into a mature spermatozoon?

A

Approximately 74 days

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14
Q

How man sperm cells are produced daily?

A

Approximately 300 million sperm cells are produced daily.

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15
Q

Where does the spermatozoa enter, when they are fully formed?

A

When fully formed, spermatozoa enter the lumen of seminiferous tubulus. From there, they are pushed toward the epididymis by contractile elements in the wall of the seminiferous tubules.

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16
Q

Where does the spermatozoa obtain full motility?

A

Spermatozoa obtain full motility in the epididymis

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17
Q

What are abnormal gametes in females?

A

One ovarian follicle occasionally contains two or three clearly distinguishable primary oocytes. Although these oocytes may give rise to twins or triplets, they usually degenerate before reaching maturity (A).

In rare cases, one primary oocyte contains two or even three nuclei. Such binucleated or trinucleuated oocytes die before reaching maturity (B).

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18
Q

What are abnormal gametes in males?

A

Abnormal spermatozoa are seen frequenty, and up to 10% of all spermatozoa have obserbavle defects.

The head or the tail may be abnormal, spermatozoa may be giants or dwards, and sometimes they are joined.

Sperm with morphologic abnormalities lack normal motility and probably do not fertilized oocytes.

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19
Q

Where does spermatogenesis occur?

A

Spermatogenesis occurs in the seminiferous tubulus during active sexual life as the result of stimulation by anterior pituitary gonadotropic hormones.

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20
Q

At which age does the spermatogenesis begin?

A

Spermatogenesis begins at an average age of 13 years and continues throughout most of the remainder of life but decreases markedly in old age.

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21
Q

What happens in the first stage of spermatogenesis?

A

The spermatogonia migrate among Sertoli cells toward the central lumen of the seminiferous tubule. Spermatogonia that cross the barrier into the Sertoli cell layer become progessively modified and enlarged to form large primary spermatocytes.

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22
Q

What happens in the second stage of spermatogenesis?

A

Each primary spermatocytes undergoes meiotic division to form two secondary spermatocytes.

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23
Q

What happens in the third stage of spermatogenesis?

A

Second spermatocytes undergoes the second meiotic division to form spermatids.

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24
Q

What happens in the fourth stage of spermatogenesis?

A

Spermatids eventually modifies to become spermatozoa

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25
What happens in the fourth stage of spermatogenesis?
Spermatids eventually modifies to become spermatozoa
26
What is each spermatozoon composed of?
A head and a tail
27
What does the head of the spermatozoon consists of and what is the function of it?
The head comprises the condensed nucleus of the cell, with only a thin cytoplasmic and cell membrane layer around its surface. On the outside of the anterior two thirds of the head is a thick cap called the acrosome that is formed mainly from the Golgi apparatus. - The acrosome contains several enzymes similar to those found in lysosomes of the typical cell including hyaluronidase (which can digest proteoglycan filaments of tissues) and powerful proteolytic enzymes (which can digest proteins). These enzymes play important roles in allowing the sperm to enter the ovum an fertilize it.
28
What does the tail of the spermatozoon consists of and what is the function of it?
The tail of the spermatozoon, called the flagellum, has three major components: 1. a central skeleton constructed of 11 microtubules, collectively called the axoneme 2. a thin cell memebrane covering the axoneme 3. a collection of mitochondria surrounding the axoneme in the proximal portion of the tail (called the body of the tail) Back-and-forth movement of the tail (flagellar movement) provides motility for the spermatozoon. This movement results from a rhythmical longitudinal sliding motion between the anterior and posterior tubules that make up the axoneme. The energy for this process is supplied in the form of adenosinetriphosphate, which i s synthesized by the mitochondria in the body of the tail.
29
At what velocity do normal spermatozoa move?
Normal sperm move in a fliud medium at a velocity of 1-4 mm/min, which allows them to move through the female genital tract in quest of the ovum.
30
At what velocity do normal spermatozoa move?
Normal sperm move in a fliud medium at a velocity of 1-4 mm/min, which allows them to move through the female genital tract in quest of the ovum.
31
Which hormone is secreted by the Leydig cells?
Testosterone
32
Which hormone is secreted by the Leydig cells?
Testosterone
33
Which cells secretes testosterone?
Leydig cells
34
What are testosterone's role in spermatogenesis?
Testosterone is essential for growth and division of the testicular germinal cells, which is the first stage in forming sperm.
35
Which hormone stimulates the Leydig cells to secrete testosterone?
Luteinizing hormone, secreted by the anterior pituitary gland, stimulates the Leydig cells to secrete testosterone.
36
Which hormone stimulates Sertoli cells?
Follicle-stimulating hormone
37
What happens if the Sertoli cell isn't stimulated?
Without follicle-stimulating hormone the Sertoli cells wont be stimulated, and without this stimulation, the conversion of the spermatids to sperm (the process of spermiogenesis) will not occur.
38
How does growth hormone affect spermatogenesis?
Growth hormone is necessary for controlling background metabolic functions of the testes. Growth hormone specifically promotoes early division of the spermatogonia themselves; in its absence, as in pituitary dwarfs, spermatogenesis is severely deficient or absentm thus causing infertility.
39
Where does maturation of the sperm occur?
Maturation of the sperm occurs in the epididymis
40
How long is the epididymis?
6-meter-long
41
Sperm removed from the seminiferous tubules and from the early portions of the epididymis are...
Sperm removed from the seminiferous tubules and from the early portions of the epididymis are nonmotile and cannot fertilize an ovum.
42
For how long does the sperm have to be in the epididymis to develop capability of motility?
After the sperm have been in the epididymis for 18-24 hours, they develop the capability of motility, however several inhibitory proteins in the epididymal fluid prevent final motility until after ejaculation.
43
How many sperm is formed each day?
The two testes of the human adult form up to 120 million sperm each day.
44
Where are the sperm stored?
Most of the sperm are stored in the epididymis, although a small quantity is stores in ductus deferens.
45
How long can sperm live in the supressed state in the genital ducts of the testes?
Sperm can live for many weeks in the supressed state in the genital ducts of the testes
46
What is the life expectancy of ejaculated sperm in the female genital tract?
The lift expectancy of ejaculated sperm in the female genital tract is only 1 to 2 days.
47
Describe the function of the seminal vesicles
Each seminal vesicle is a tortuous, loculated tube lined with a secretory epithelium that secretes a mucoid material containing an abundance of fructose, citric acid, and other nutrient substances, as well as large quantities of prostaglandins and fibrinogen. During the process of emission and ejaculation, each seminal vesicle empties its contents into the ejaculatory duct shortly after the vas deferens empties the sperm. This action adds greatly to the bulk of the ejaculated semen, and the fructose and other substances in the seminal fluid are of considerable nutrient value for the ejaculated sperm until one of the sperm fertilizes the ovum.
48
How does prostaglandin aid fertilization?
Prostaglandins are believed to aid fertilization in two ways: 1. by reacting with the female cervical mucus to make it more repetive to sperm movement 2. by possibly causing backward, reverse peristaltic contractions in the uterus and tubae uterinae to move the ejaculated sperm towards the ovaries
49
Describe the function of the prostate gland
The prostate gland secretes a thin, milky fluid that contains calcium, citrate ion, phosphate ion, a clotting enzyme, and a profibrinolysin. - The prostatic fluid has a slightly alkaline characteristic During emission, the capsule of the prostate gland contracts simultaneously with the contractions of the vas deferens so that the thin, milky fluid of the prostate gland adds further to the bulk of the semen.
50
Describe the fluid of the vas deferens
The fluid of the vas deferens is relatively acidic owing to the presence of citric acid and metabolic end products of the sperm and, consequently, helps inhibit sperm fertility.
51
Describe the environment in the vagina and how seminal fluids contrainteracts with it
The vaginal secretions of the female are acidic (with a pH of 3,5-4,0). Sperm do not become optimally motile until the pH of the surrounding fluids rises to about 6,0-6,5. Consequently, it is probably that the slightly alkaline prostatic fluid helps neutralize the acidity of the other seminal fluids during ejaculation and this enchances the motility and fertility of the sperm.
52
What are semen composed of?
Semen is composed of the fluid and sperm from the vas deferens (about 10 percent of the total), fluid from the seminal vesicles (almost 60 percent) fluid from the prostate gland (about 30 percent), and a small amounts from the mucous glands, especially the bulbourethral glands.
53
What is the average pH of the combined semen?
7,5
54
What are the most important source of sensory nerve signals for initiating the male sexual act?
Glans penis
55
How does temperature effect spermatogenesis?
Increasing the temperature of the testes can prevent spermatogenesis by causing degeneration of most cells of the seminiferous tubules besides the spermatogonia. It has often been stated that the reason the testes are located in the dangling scrotum is to maintain the temperature of these glands below the internal temperature of the body, although usually only about 2 degrees celcius below the internal temperature.
56
What is cryptorchidism?
Cryptorchidism means failure of a testis to descend from the abdomen into the scrotum at or near the time of birth of a fetus.
57
When does the testes normally descend?
At about 3 weeks to 1 month before birth of the baby, the testes normally descend through the inguinal canals into the scrotum.
58
What happens when the descent of the testes doesnt not occur or occurs incompletely (cryptorchidism)?
Occasionally this descent does not occur or occurs incompletely, and as a result one or both testes remain in the abdomen, in the inguinal canal, or elsewhere along the route of descent.
59
What happens when the descent of the testes doesnt not occur or occurs incompletely (cryptorchidism)?
Occasionally this descent does not occur or occurs incompletely, and as a result one or both testes remain in the abdomen, in the inguinal canal, or elsewhere along the route of descent.
60
How can cryptorchidism cause sterility?
A testis that remains in the abdominal cavity throughout life is incapable of forming sperm. The tubular epithelium becomes degenerate, leavingo nly the interstitial structures of the testis. It has been claimed that even the few degrees' higher temperature in the abdoman than in the scrotum is sufficient to cause this degeneration of the tubular epithelium and, consequently, to cause sterility.
61
What are most instances of cryptorchidism caused by?
Testosterone secretion by the fetal testes is the normal stimulus that causes the testes to descend into the scrotum from the abdomen. Therefore, many, if not most, instances of cryptorchidism are caused by abnormally formed testes that are unable to secrete enough testosterone.
62
How is the sexual sensation transmitted to the central nervous system?
The slippery massaging action of intercourse on the glans stimulates the sensory end organs, and the sexual signals in turn pass through the pudendal nerve, then through the sacral plexus into the sacral portion of the spinal cord, and finally up the cord to undefined areas of the brain.
63
What is the first effect of male sexual stimulation?
Penile erection
64
What can stimulate sexual sensation?
Both psychic and physical stimulation can result in sexual stimulation, and the degree of erection is proportional to the degree of stimulation.
65
Is erection caused by parasympathetic or sympathetic impulses?
Erection is caused by parasympathetic impulses that pass from the sacral portion of the spinal cord through the pelvic nerves to the penis.
66
What does the parasympathetic nerve fibers innervating the penis release?
Nitric oxide and/or vasoactive intestinal peptide
67
What is the effect of nitric oxide?
Nitric oxide activates the enzyme guanylyl cyclase, causing increased formation of cyclic guanosine monophosphate (cGMP). The cGMP especially relaxes the arteries of the penis and the trabecular meshwork of smooth muscle fibers in th erectile tissue of the corpora cavernosa and corpus spongiosum in the shaft of the penis. As the vascular smooth muscles relax, blood flow into the penis increases, causing release of nitric oxide from the vascular endothelial cells and further vasodilation.
68
Describe the phenomenon of erection
The erectile tissue of the penis consists of large cavernosous sinusoids that are normally relatively empty of blood but become dilated tremendously when arterial blood flows rapidlt into them under pressure while the venous outflow is partially occluded. Also, the erectile bodies, especially the two corpora cavernosa, are surrounded by stron fibrous coats: therefore, high pressure within the sinusoids causes ballooning of the erectile tissue to such an extent that the penis becomes hard and elongated, which is the phenomenon of erection.
69
Is lubrication caused by parasympathetic or sympathetic impulses?
Lubrication is a parasympathetic function
70
Is emission caused by parasympathetic or sympathetic impulses?
Emission is function of the sympathetic nerves
71
Is ejaculation caused by parasympathetic or sympathetic impulses?
Ejaculation is function of the sympathetic nerves
72
What is lubrication?
During sexual stimulation, the parasympathetic impulses, in addition to protmoting erection, cause the urethral glands and the bulbourethral glands (Cowper's gland) to secrete mucus. This mucus flows through the urethra during intercourse to aid the lubrication during coitus. However, most of the lubrication of coitus is provided by the female sexual organs rather than by the male organs. Without satisfactory lubrication, the male sexual act is seldom successful because unlubricated intercourse causes grating, painful sensations that inhibit rather than excite sexual sensations.
73
How are emisison and ejaculation transmitted?
When the sexual stimulus becomes extremely intense, the reflex centers of the spinal cord begin to emit sympathetic impulses that leave the cord at T12 to L2 and pass to the genital organs through the hypogastric and pelvic sympathetic nerve plexuses to initiate emission, the forerunner of ejaculation.
74
Describe the emission
Emission begins with contraction of the vas deferens and the ampulla to cause expulsion of sperm into the internal urethra. Then, contractions of the muscular coat of the prostate gland followed by contraction of the seminal vesicles expel prostatic and seminal fluid also into the urethra, forcing the sperm forward. All these fluids mix in the internal urethra with mucus already secreted by the bulbourethral glands (Cowper's glands) to form the semen. The process to this point is emission.
75
Describe the ejaculation
The filling of the internal urethra with semen elicits sensory signals that are transmitted through the pudendal nerves to the sacral regions of the cord, giving the feeling of sudden fullness in the internal genital organs. Also, these sensory signals further excite rhythmical contraction of the internal genital organs and cause contraction of the ischiocavernosus and bulbocavernosus muscles that compress the bases of the penile erectile tissue. These effects together cause rhythmical, wavelike increases in pressure in both the erectile tissue of the penis and the genital ducts and urethra, which "ejaculate" the semen from the urethra to the exterior. - This final process is called ejaculation At the same time, rhythmical contractions of the pelvic muscles and even of some of the muscles of the body trunk cause thrusting movements of the pelvis and penis, which also help propel the semen into the deepest recesses of the vagina and perhaps even slightly into the cervix of the uterus.
76
What does the male orgasm consist of?
The male orgasm consists of the period of emission and ejaculation. At its termination, the male sexual excitement disappears almost entirely within 1 to 2 minutes and erection ceases, a process called resolution

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