Sperm and their origin Flashcards
When do spermatogenesis begin?
Spermatogenesis begins at puberty
What is spermatogenesis?
Spermatogenesis is all the events by which spermatogonia are transformed into spermatozoa.
What give rise to spermatogonial stem cells?
Primordial germ cells give rise to spermatogonial stem cells.
What does spermatogonial stem cells differentiate into?
At regular intervals, spermatogonial stem cells emerge to form type A spermatogonia, and their production marks the initiation of spermatogenesis.
How is type B spermatogonia produced and what do they divide into?
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.
What happens when the stage of primary spermatocyte is reached?
Primary spermatocytes then enter a prolonged prophase (22 days).
How are secondary spermatocytes produced?
Primary spermatocytes complete meiosis I and form secondary spermatocytes
How is spermatids produced?
During the second meiotic division, secondary spermatocytes form haploid spermatids.
Which hormone regulates spermatogenesis?
Spermatogenesis is regulated by luteinizing hormone produced by the pituitary gland.
How does luteinizing hormone regulate spermatogenesis?
Luteinizing hormone binds to receptors on Leydig cells and stimulates testosterone production, which in turn binds to Sertoli cells to promote spermatogenesis.
What is the effect of follicle-stimulating hormone in testis?
Follicle-stimulating hormone binds to Sertoli cells and stimulates testicular fluid production and synthesis of intracellular androgen receptor proteins.
What is spermiogenesis?
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
What is the time required for a spermatogonium to develop into a mature spermatozoon?
Approximately 74 days
How man sperm cells are produced daily?
Approximately 300 million sperm cells are produced daily.
Where does the spermatozoa enter, when they are fully formed?
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.
Where does the spermatozoa obtain full motility?
Spermatozoa obtain full motility in the epididymis
What are abnormal gametes in females?
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).
What are abnormal gametes in males?
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.
Where does spermatogenesis occur?
Spermatogenesis occurs in the seminiferous tubulus during active sexual life as the result of stimulation by anterior pituitary gonadotropic hormones.
At which age does the spermatogenesis begin?
Spermatogenesis begins at an average age of 13 years and continues throughout most of the remainder of life but decreases markedly in old age.
What happens in the first stage of spermatogenesis?
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.
What happens in the second stage of spermatogenesis?
Each primary spermatocytes undergoes meiotic division to form two secondary spermatocytes.
What happens in the third stage of spermatogenesis?
Second spermatocytes undergoes the second meiotic division to form spermatids.
What happens in the fourth stage of spermatogenesis?
Spermatids eventually modifies to become spermatozoa
What happens in the fourth stage of spermatogenesis?
Spermatids eventually modifies to become spermatozoa
What is each spermatozoon composed of?
A head and a tail
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.
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.
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.
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.
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.
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.
What are the most important source of sensory nerve signals for initiating the male sexual act?
Glans penis
What is the first effect of male sexual stimulation?
Penile erection
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.
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.
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.
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.
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.
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.
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.
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
