Male Reproductive system Introduction .
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| Male reproductive system and other organs of pelvis . |
[1]. Male Reproductive System consists of reproductive organ ,Which consist of primary sex organs and Accessory sex organs and Which help in reproductive function of male human beings .
[2]. Reproductive system ensures the continuation of species.
[3]. Gonads are the primary reproductive organs which produce the gametes (egg or ovum); a pair of testes (singular = testis) produces sperms in males and a pair of ovaries produces ovum in females.
[4]. Normally, most of the animals including humans are either definite males or definite females. However, in some organisms like earthworms and snails, both sexes may be present in the same organism and this condition is known as hermaphroditism.
[5]. In humans and most of the higher animals, reproduction occurs sexually, i.e. by mating. However, there are some species like insects which can produce offspring without mating.
Reproductive Organ .
Reproductive organs include:
1. Primary sex organs .
2. Accessory sex organs.
Primary Sex Organs .
Testes are the primary sex organs or gonads in males.
Accessory Sex Organs .
Accessory sex organs in males are:
1. Seminal vesicles .
2. Prostate gland .
3. Urethra .
4. Penis.
External and Internal Genitalia .
[1]. Reproductive organs are generally classified into two groups, namely external genitalia (genital organs) and internal genitalia.
[2]. External genital organs in males are scrotum, penis and urethra. Remaining sex organs constitute the internal genitalia.
Functional Anatomy of Testes .
[1]. Testes are the primary sex organs or gonads in males. There are two testes in almost all the species. [2]. In human beings, both the testes are ovoid or walnut-shaped bodies that are located and suspended in a sac-like structure called scrotum.
[3]. Each testis weighs about 15 to 19 g and measures about 5 × 3 cm. Testis is made up of about 900 coiled tubules known as seminiferous tubules, which produce sperms.
[4]. Seminiferous tubules continue as the vas deferens, which form the epididymis. It is continued as vas deferens. Vas deferens is also called ductus deferens, spermatic deferens or sperm duct.
[5]. From epididymis in scrotum, the vas deferens extends on its one side upwards into abdominal cavity via inguinal canal.
[6]. Terminal portion of vas deferens is called ampulla . Ampulla of vas deferens joins ducts of seminal vesicle of same side, to form ejaculatory duct. Thus, there are two ejaculatory ducts each of which receives sperm from vas deferens and secretions of seminal vesicle on its own side.
[7]. Both the ejaculatory ducts empty into a single urethra. Actually, ejaculatory ducts open into prostatic part of urethra.
Coverings of Testis .
Each testis is enclosed by three coverings.
1. Tunica Vasculosa .
[1]. Tunica Vasculosa is the innermost covering.
[2]. It is made up of connective tissue and it is rich in blood vessels
2. Tunica Albuginea .
[1]. Tunica albuginea is the middle covering.
[2]. It is a dense fibrous capsule
3. Tunica Vaginalis .
[1]. Tunica vaginalis is the outermost closed cleft like covering, formed by mesothelial cells.
[2]. It is formed by visceral and parietal layers, which glide on one another and allow free movement of testes.
[3]. Visceral layer of tunica vaginalis adheres to tunica albuginea and the parietal layer lines the inner surface of the scrotum.
[4]. Anterior and lateral surfaces of testis are covered by all the three layers. Posterior surface is covered by tunica albuginea only.
Parenchyma of Testis .
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| Structure of testis . |
Lobules of Testis .
[1]. Tunica albuginea on the posterior surface of testis is thickened to form the mediastinum testis.
[2]. From this, the connective tissue septa called septula testis radiate into testis and bind with tunica albuginea at various points.
[3]. Because of this, testis is divided into a number of pyramidal lobules, with bases directed towards the periphery and the apices towards the mediastinum .
[4]. The septula do not form complete partition so the lobules of testis anastomose with one another at many places. Each testis has about 200 to 300 lobules.
Seminiferous Tubules .
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| Pathway for the passage of sperms . |
[1]. Each lobule contains 1 to 4 coiled tubules known as the seminiferous tubules, which are surrounded and supported by interlobular connective tissue.
[2]. Seminiferous tubules do not end bluntly, but form single, double or triple arches. Limbs of an arch are not in the same lobule .
Rete Testis .
[1]. Rete testis is a network of thin-walled channels present in mediastinum.
[2]. All the seminiferous tubules open into the rete testis.
Vas Efferens .
[1]. From rete testis, 8 to 15 tubules called vas deferens arise.
[2]. Vas Efferens join together and form the head of epididymis and then converge to form the duct of epididymis .
Epididymis .
[1]. Duct of epididymis is an enormously convoluted tubule, with a length of about 4 meter.
[2]. It begins at head, where it receives vas deferens.
Vas Deferens .
At the caudal pole of testis, epididymis turns sharply upon itself and continues as vas deferens, without any definite demarcation.
Interstitial Cells of Leydig .
Interstitial cells of Leydig are the hormone secreting cells of testis, lying in between the seminiferous tubules.
Seminiferous Tubules.
[1]. Seminiferous tubules are thread-like convoluted tubular structures which produce the spermatozoa or sperms.
[2]. There are about 400 to 600 seminiferous tubules in each testis.
[3]. Each tubule is 30 to 70 cm long with a diameter of 150 to 300 µ.
[4]. Wall of the seminiferous tubule is formed by three layers:
1. Outer capsule or tunica propria, formed by fibroelastic connective tissue .
2. Thin homogeneous basement membrane
3. Complex stratified epithelium, which consists of two types of cells :-
i. Spermatogenic cells or germ cells .
ii. Sertoli cells or supporting cells.
Spermatogenic Cells .
[1]. Spermatogenic cells or germ cells present in seminiferous tubules are precursor cells of spermatozoa.
[2]. These cells lie in between Sertoli cells and are arranged in an orderly manner in 4 to 8 layers.
[3]. In children, the testis is not fully developed. Therefore, the spermatogenic cells are in primitive stage called spermatogonia.
[4]. With the onset of puberty, spermatogonia develop into sperms through different stages.
Stages of spermatogenic cells .
Different stages of spermatogenic cells seen from periphery to the lumen of seminiferous tubules are:
1. Spermatogonium .
2. Primary spermatocyte .
3. Secondary spermatocyte .
4. Spermatid.
Sertoli Cells .
[1]. Sertoli cells are the supporting cells for spermatogenic cells in seminiferous tubules. These cells are also called sustentacular cells or nurse cells.
[2]. Sertoli cells are the large and tall irregular columnar cells, extending from basement membrane to lumen of the seminiferous tubule.
[3]. Germ cells present in seminiferous tubule are attached to Sertoli cells by means of cytoplasmic connection.
[4]. This attachment between germ cells and Sertoli cells exists till the matured spermatozoa are released into the lumen of seminiferous tubules.
Functions of Sertoli cells .
Sertoli cells provide support, protection and nourishment for the spermatogenic cells present in seminiferous tubules.
Sertoli cells:
1. Support and nourish the spermatogenic cells till the spermatozoa are released from them .
2. Secrete the enzyme aromatase, which converts androgens into estrogen .
3. Secrete androgen-binding protein (ABP), which is essential for testosterone activity, especially during spermatogenesis .
4. Secrete estrogen-binding protein (EBP) .
5. Secrete inhibin, which inhibits FSH release from anterior pituitary .
6. Secrete activin, which has opposite action of inhibin (increases FSH release) .
7. Secrete Mullerian regression factor (MRF) in fetal testes.
MRF is also called Mullerian inhibiting substance (MIS). MRF is responsible for the regression of Mullerian duct during sex differentiation in fetus.
Blood-testes Barrier .
[1]. Blood-testes barrier is a mechanical barrier that separates blood from seminiferous tubules of the testes.
[2]. It is formed by tight junctions between the adjacent Sertoli cells near the basal membrane of seminiferous tubule.
Functions of blood-testes barrier .
1. Protection of seminiferous tubules .
[1]. Blood-testes barrier protects the seminiferous tubules and spermatogenic cells by preventing the entry of toxic substances from blood and fluid of the surrounding tissues into the lumen of seminiferous tubules.
[2]. However, blood-testes barrier permits substances essential for spermatogenic cells .
[3]. Substances prevented by blood-testes barrier:
a. Large molecules including proteins, polysaccharides and cytotoxic substances .
b. Medium-sized molecules like galactose.
[4]. Substances permitted by blood-testes barrier:
a. Nutritive substances essential for spermatogenic cells .
b. Hormones necessary for spermatogenesis .
c. Water.
2. Prevention of autoimmune disorders
Blood-testes barrier also prevents the development of autoimmune disorders by inhibiting the movement of antigenic products of spermatogenesis from testis into blood.
Damage of blood-testes barrier .
[1]. Blood-testes barrier is commonly damaged by trauma or viral infection like mumps.
[2]. Whenever, the blood testes barrier is damaged the sperms enter the blood.
[3]. The immune system of the body is activated, resulting in the production of autoantibodies against sperms.
[4]. The antibodies destroy the germ cells, leading to consequent sterility.
Functions of Testes .
Testes performs two functions:
1. Gametogenic function: Spermatogenesis .
2. Endocrine function: Secretion of hormones.
1. Gametogenic function -Spermatogenesis .
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| Spermatogenesis. |
[1]. Spermatogenesis is the process by which the male gametes called spermatozoa (sperms) are formed from the primitive spermatogenic cells (spermatogonia) in the testis .
[2]. It takes 74 days for the formation of sperm from a primitive germ cell.
[3]. Throughout the process of spermatogenesis, the spermatogenic cells have cytoplasmic attachment with Sertoli cells.
[4]. Sertoli cells supply all the necessary materials for spermatogenesis through the cytoplasmic attachment.
Stages of Spermatogenesis .
Spermatogenesis occurs in four stages:
1. Stage of proliferation .
2. Stage of growth .
3. Stage of maturation .
4. Stage of transformation.
1. Stage of Proliferation .
[1]. Each spermatogonium contains diploid number (23 pairs) of chromosomes.
[2]. One member of each pair is from maternal origin and the other one from paternal origin.
[3]. The 23 pairs include 22 pairs of autosomal chromosomes and one pair of sex chromosomes.
[4]. Sex chromosomes are one X chromosome and one Y chromosome.
[5]. During the proliferative stage, spermatogonia divide by mitosis, without any change in chromosomal number.
[6]. In man, there are usually seven generations of spermatogonia.
[7]. The last generation enters the stage of growth as primary spermatocyte.
[8]. During this stage, the spermatogonia migrate along with Sertoli cells towards the lumen of seminiferous tubule.
2. Stage of Growth .
[1]. In this stage, the primary spermatocyte grows into a large cell.
[2]. Apart from growth, there is no other change in spermatocyte during this stage.
3. Stage of Maturation .
After reaching the full size, each primary spermatocyte quickly undergoes meiotic or maturation division, which occurs in two phases:
First phase .
[1]. In the first phase, each primary spermatocyte divides into two secondary spermatocytes.
[2]. The significance of the first meiotic division is that each secondary spermatocyte receives only the haploid or half the number of chromosomes. 23 chromosomes include 22 autosomes and a X or a Y chromosome.
Second phase .
[1]. During this phase, each secondary spermatocyte undergoes second meiotic division resulting in two smaller cells called spermatids.
[2]. Each spermatid has haploid number of chromosomes.
4. Stage of Transformation .
There is no further division. Spermatids are transformed into matured spermatozoa (sperms), by means of spermeogenesis and released by spermination.
Spermeogenesis .
Spermeogenesis is the process by which spermatids become matured spermatozoa.
Changes taking place during spermeogenesis:
1. Condensation of nuclear material .
2. Formation of acrosome, mitochondrial spiral filament and tail structures .
3. Removal of extraneous (extra volume of nonessential) cytoplasm.
Spermination .
Spermination is the process by which the matured sperms are released from Sertoli cells into the lumen of seminiferous tubules.
Factors affecting Spermatogenesis .
Spermatogenesis is influenced by:
1. Sertoli cells
2. Hormones
3. Other factors.
1. Role of Sertoli Cell in Spermatogenesis .
Sertoli cells influence spermatogenesis by:
a. Supporting and nourishing the germ cells .
b. Providing hormonal substances necessary for spermatogenesis .
c. Secreting androgen-binding protein (ABP), which is essential for testosterone activity, particularly on spermatogenesis .
d. Releasing sperms into the lumen of seminiferous tubules (spermination).
2. Role of Hormones in Spermatogenesis .
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| Role of hormones in spermatogenesis . |
[1]. Spermatogenesis is influenced by many hormones, which act either directly or indirectly .
[2]. Hormones necessary for spermatogenesis are:
a. Follicle-stimulating hormone (FSH) .
b. Testosterone .
c. Estrogen .
d. Luteinizing hormone (LH) .
e. Growth hormone (GH) .
f. Inhibin .
g. Activin .
a. Follicule-stimulating hormone .
[1]. Follicule-stimulating hormone is responsible for the initiation of spermatogenesis.
[2]. It binds with Sertoli cells and spermatogonia and induces the proliferation of spermatogonia.
[3]. It also stimulates the formation of estrogen and androgen-binding protein from Sertoli cells .
b. Testosterone .
[1]. Testosterone is responsible for the sequence of remaining stages in spermatogenesis. It is also responsible for the maintenance of spermatogenesis.
[2]. Testosterone activity is largely influenced by androgen-binding protein.
c. Estrogen .
[1]. Estrogen is formed from testosterone in Sertoli cells.
[2]. It is necessary for spermeogenesis.
d. Luteinizing Hormone .
[1]. In males, this hormone is called interstitial cell stimulating hormone.
[2]. It is essential for the secretion of testosterone from Leydig cells.
e. Growth Hormone .
[1]. Growth hormone is essential for the general metabolic processes in testis.
[2]. It is also necessary for the proliferation of spermatogonia.
[3]. In pituitary dwarfs, the spermatogenesis is severely affected.
f. Inhibin .
[1]. Inhibin is a peptide hormone and serves as a transforming growth factor. It is secreted by Sertoli cells.
[2]. In females, it is secreted by granulosa cells of ovarian follicles. Its secretion is stimulated by FSH. [3]. Inhibin plays an important role in the regulation of spermatogenesis by inhibiting FSH secretion through feedback mechanism.
[4]. FSH secreted from anterior pituitary induces spermatogenesis by stimulating Sertoli cells.
[5]. It also stimulates the secretion of inhibin from Sertoli cells. So, when the rate of spermatogenesis increases, there is a simultaneous increase in inhibin secretion also.
[6]. Inhibin in turn, acts on anterior pituitary and inhibits the secretion of FSH, leading to decrease in the pace of spermatogenesis.
[7]. It is believed that inhibin also inhibits FSH secretion indirectly by inhibiting GnRH secretion from hypothalamus.
g. Activin .
[1]. Activin is also a peptide hormone secreted in gonads along with inhibin. The exact location of its secretion in testis is not known.
[2]. It is suggested that activin is secreted by Sertoli cells and Leydig cells.
[3]. Activin has opposite actions of inhibin. It increases the secretion of FSH and accelerates spermatogenesis.
3. Role of Other Factors in Spermatogenesis .
a. Increase in body temperature .
[1]. Increase in body temperature prevents spermatogenesis.
[2]. Normally, the temperature in scrotum is about 2°C less than the body temperature. This low temperature is essential for spermatogenesis.
[3]. When the temperature increases, the spermatogenesis stops. It is very common in cryptorchidism (undescended testes).
[4]. In cryptorchidism, the testes are in the abdomen, where the temperature is always higher than that of scrotum.
[5]. High temperature in the abdomen causes degeneration of seminiferous tubules and stoppage of spermatogenesis.
b. Diseases .
Infectious diseases such as mumps cause degeneration of seminiferous tubules and stoppage of spermatogenesis.
Endocrine Functions of Testes .
Hormone Secreted by Testes .
[1]. Testes secrete male sex hormones, which are collectively called the androgens.
[2]. Androgens secreted by testes are:
1. Testosterone .
2. Dihydrotestosterone .
3. Androstenedione.
[3]. Among these three androgens, testosterone is secreted in large quantities. However, dihydrotestosterone is more active.
[4]. Female sex hormones, namely estrogen and progesterone are also found in testes.
[5]. Two more hormones activin and inhibin are also secreted in testes. However, these two hormones do not have androgenic actions.
Source of Secretion of Androgens .
Androgens are secreted in large quantities by testes and in small quantity by adrenal cortex.
Testes .
[1]. In testes, androgens are secreted by the interstitial cells of Leydig, which form 20% of mass of adult testis.
[2]. Leydig cells are numerous in newborn male baby and in adult male.
[3]. But in childhood, these cells are scanty or non-existing. So, the secretion of androgens occurs in newborn babies and after puberty.
Adrenal cortex .
[1]. Androgens secreted by zona reticularis of adrenal cortex are testosterone, androstenedione and dehydroepiandrosterone.
[2]. Adrenal androgens do not have any significant physiological actions because of their small quantity.
[3]. In abnormal conditions, the hypersecretion of adrenal androgens results in sexual disorders .
Chemistry of Testosterone .
Testosterone is a C19 steroid.
Synthesis of Androgens .
[1]. Androgens are steroid hormones synthesized from cholesterol.
[2]. Androgens are also synthesized directly from acetate.
Plasma Level and Transport of Androgens .
[1]. Plasma level of testosterone in an adult male varies between 300 and 700 ng/dL.
[2]. In adult female, the testosterone level is 30 to 60 mg/dL.
[3]. Two thirds of testosterone is transported in plasma by gonadal steroid-binding globulin.
[4]. It is β-globulin in nature and it is also called sex steroid-binding globulin. The remaining one third of testosterone is transported by albumin.
Metabolism of Androgens .
[1]. In many target tissues, testosterone is converted into dihydrotestosterone, which is the most active androgen.
[2]. In some of the tissues such as adipose tissue, hypothalamus and liver, testosterone is converted into estradiol.
[3]. Major portion of testosterone is degraded in liver. It is converted into inactive forms of androsterone and dehydroepiandrosterone.
[4]. These two substances are later conjugated and excreted through urine.
Testosterone Secretion in different periods of Life .
[1]. Testosterone secretion starts at 7th week of fetal life by fetal genital ridge.
[2]. Fetal testes begin to secrete testosterone at about 2nd to 4th month of fetal life.
[3]. In fetal life, testosterone secretion from testes is stimulated by human chorionic gonadotropins, secreted by placenta.
[4]. But in childhood, practically no testosterone is secreted approximately until 10 to 12 years of age. [5]. Afterwards, the testosterone secretion starts and it increases rapidly at the onset of puberty and lasts through most of the remaining part of life.
[6]. The secretion starts decreasing after 40 years and becomes almost zero by the age of 90 years .
Functions of Testosterone .
[1]. In general, testosterone is responsible for the distinguishing characters of masculine body.
[2]. It also plays an important role in fetal life.
Functions of Testosterone in Fetal Life .
Testosterone performs three functions in fetus:
1. Sex differentiation in fetus .
2. Development of accessory sex organs
3. Descent of the testes.
1. Sex differentiation in fetus .
[1]. Sex chromosomes are responsible for the determination of sex of the fetus , whereas testosterone is responsible for the sex differentiation of fetus.
[2]. Fetus has two genital ducts:
1. Mullerian duct, which gives rise to female accessory sex organs such as vagina, uterus and fallopian tube .
2. Wolffian duct, which gives rise to male accessory sex organs such as epididymis, vas deferens and seminal vesicles.
[3]. If testosterone is secreted from the genital ridge of the fetus at about 7th week of intrauterine life, the müllerian duct system disappears and male sex organs develop from Wolffian duct.
[4]. In addition to testosterone, müllerian regression factor (MRF) secreted by Sertoli cells is also responsible for regression of müllerian duct.
[5]. In the absence of testosterone, Wolffian duct regresses and female sex organs develop from müllerian duct.
2. Development of accessory sex organs and external genitalia .
Testosterone is also essential for the growth of the external genitalia, viz. penis and scrotum and other accessory sex organs, namely genital ducts, seminal vesicles and prostate.
3. Descent of testes .
[1]. Descent of testes is the process by which testes enter scrotum from abdominal cavity.
[2]. Initially, testes are developed in the abdominal cavity and are later pushed down into the scrotum through inguinal canal, just before birth.
[3]. The process by which testes enter the scrotum is called the descent of testes. Testosterone is necessary for descent of testes.
Cryptorchidism .
[1]. Cryptorchidism is a congenital disorder characterized by the failure of one or both the testes to descent from abdomen into scrotum. In such case, the testes are called undescended testes.
[2]. Males with untreated testes are prone for testicular cancer.
Treatment for Cryptorchidism .
Administration of testosterone or gonadotropic hormones (which stimulate Leydig cells) causes descent of testes, provided the inguinal canal is large enough to allow the passage of testes. Surgery is required if the inguinal canal is narrow.
Functions of Testosterone in Adult Life .
Testosterone has two important functions in adult:
1. Effect on sex organs .
2. Effect on secondary sexual characters.
1. Effect on sex organs .
[1]. Testosterone increases the size of penis, scrotum and the testes after puberty.
[2]. All these organs are enlarged at least 8 folds between the onset of puberty and the age of 20 years, under the influence of testosterone.
[3]. Testosterone is also necessary for spermatogenesis.
2. Effect on secondary sexual characters .
[1]. Secondary sexual characters are the physical and behavioral characteristics that distinguish the male from female.
[2]. These characters appear at the time of puberty in humans.
[3]. Testosterone is responsible for the development of secondary sexual characters in males.
Secondary sexual characters in males .
a. Effect on muscular growth .
[1]. One of the most important male sexual characters is the development of musculature after puberty. [2]. Muscle mass increases by about 50%, due to the anabolic effect of testosterone on proteins.
[3]. Testosterone accelerates the transport of amino acids into the muscle cells, synthesis of proteins and storage of proteins.
[4]. Testosterone also decreases the breakdown of proteins.
b. Effect on bone growth .
[1]. After puberty, testosterone increases the thickness of bones by increasing the bone matrix and deposition of calcium.
[2]. It is because of the protein anabolic activity of testosterone.
[3]. Deposition of calcium is secondary to the increase in bone matrix.
[4]. In addition to increase in the size and strength of bones, testosterone also causes early fusion of epiphyses of long bones with shaft.
[5]. So, if testes are removed before puberty, the fusion of epiphyses is delayed and the height of the person increases.
c. Effect on shoulder and pelvic bones .
Testosterone causes broadening of shoulders and it has a specific effect on pelvis, which results in:
a. Lengthening of pelvis .
b. Funnel-like shape of pelvis.
c. Narrowing of pelvic outlet.
Thus, pelvis in males is different from that of females, which is broad and round or oval in shape.
d. Effect on skin .
[1]. Testosterone increases the thickness of skin and ruggedness of subcutaneous tissue.
[2]. These changes in skin are due to the deposition of proteins in skin.
[3]. It also increases the quantity of melanin pigment, which is responsible for the deepening of the skin color.
[4]. Testosterone enhances the secretory activity of sebaceous glands.
[5]. So, at the time of puberty, when the body is exposed to sudden increase in testosterone secretion, the excess secretion of sebum leads to development of acne on the face.
[6]. After few years, the skin gets adapted to testosterone secretion and the acne disappears.
e. Effect on hair distribution .
[1]. Testosterone causes male type of hair distribution on the body, i.e. hair growth over the pubis, along linea alba up to umbilicus, on face, chest and other parts of the body such as back and limbs.
[2]. In males, the pubic hair has the base of the triangle downwards where as in females it is upwards. [3]. Testosterone decreases the hair growth on the head and may cause baldness, if there is genetic background.
f. Effect on voice .
[1]. At the time of adolescence, the boys have a cracking voice.
[2]. It is because of the testosterone effect, which causes:
a. Hypertrophy of laryngeal muscles .
b. Enlargement of larynx and lengthening .
c. Thickening of vocal cords.
Later, the cracking voice changes gradually into a typical adult male voice with a bossing sound.
g. Effect on basal metabolic rate .
At the time of puberty and earlier part of adult life, the testosterone increases the basal metabolic rate to about 5% to 10% by its anabolic effects on protein metabolism.
h. Effect on electrolyte and water balance .
[1]. Testosterone increases the sodium reabsorption from renal tubules, along with water reabsorption.
[2]. It leads to increase in ECF volume.
i. Effect on blood .
[1]. Testosterone has got erythropoietic action. So, after puberty, testosterone causes mild increase in RBC count.
[2]. It also increases the blood volume by increasing the water retention and ECF volume.
Mode of Action of Testosterone .
[1]. Testosterone combines with receptor proteins.
[2]. The testosterone-receptor complex migrates to nucleus, binds with a nuclear protein and induces the DNA-RNA transcription process.
[3]. In 30 minutes, the RNA polymer is activated and the concentration of RNA increases.
[4]. The quantity of DNA also increases. So, the testosterone primarily stimulates the protein synthesis in the target cells, which are responsible for the development of secondary sexual characters.
[5]. Testosterone is converted into dihydrotestosterone (DHT) in the target cells of some accessory sex organs such as epididymis and penis.
[6]. DHT combines with receptor proteins and the DHT-receptor complex induces the DNA-RNA transcription process.
[7]. DHT receptor complex is more stable than testosterone receptor complex. In brain, testosterone is converted into estrogen (estradiol).
Regulation of Testosterone Secretion .
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| Regulation of testosterone secretion . |
In Fetus .
[1]. During fetal life, the testosterone secretion from testes is stimulated by human chorionic gonadotropin, which has the properties similar to those of luteinizing hormone.
[2]. Human chorionic gonadotropin stimulates the development of Leydig cells in the fetal testes and promotes testosterone secretion.
In Adults .
[1]. Luteinizing hormone (LH) or interstitial cell stimulating hormone (ICSH) stimulates the Leydig cells and the quantity of testosterone secreted is directly proportional to the amount of LH available. [2]. Secretion of LH from anterior pituitary gland is stimulated by luteinizing hormone releasing hormone (LHRH) from hypothalamus.
Feedback Control .
[1]. Testosterone regulates its own secretion by negative feedback mechanism.
[2]. It acts on hypothalamus and inhibits the secretion of LHRH.
[3]. When LHRH secretion is inhibited, LH is not released from anterior pituitary, resulting in stoppage of testosterone secretion from testes.
[4]. On the other hand, when testosterone production is low, lack of inhibition of hypothalamus leads to secretion of testosterone through LHRH and LH .
Anabolic Steroids .
[1]. Anabolic steroids are the synthetic forms of testosterone, which are used to increase the growth of muscles and bones.
[2]. Like androgens, these steroids also increase the growth of muscles and bones by accelerating protein synthesis (anabolic effect). These drugs are also called anabolic-androgenic steroids (AAS).
Therapeutic Uses of Anabolic Steroids .
1. Growth stimulation .
2. Bone marrow stimulation .
3. Hormone replacement therapy .
4. Induction of puberty in males.
Abuse of Anabolic Steroids .
[1]. Anabolic steroids are commonly used by athletes to improve their performances during competitions, particularly in professional sports.
[2]. Organizations of many sports have banned the use of anabolic steroids by their athletes.
Production of female Sex Hormones in Males .
Estrogen .
[1]. Small amount of estrogen is produced in males.
[2]. Estrogen level in plasma of normal adult male is 12 to 34 pg/mL.
[3]. Estrogens have three sources of production in males.
1. Adrenal Cortex .
Adrenal cortex secretes small quantity of estrogen.
2. Testes .
[1]. Up to 20% of estrogen in males is produced in testes.
[2]. Estrogen is formed from androgens in Sertoli cells of testes, by the influence of the enzyme aromatase.
3. Other Organs .
About 80% of estrogen is formed from androgens in other organs, particularly liver.
Progesterone .
[1]. Progesterone is also produced from androgens in males though the quantity is very less.
[2]. Plasma progesterone level in normal adult male is 0.3 ng/mL.
Male Andropause or Climacteric .
[1]. Male andropause or climacteric is the condition in men, characterized by emotional and physical changes in the body, due to low androgen level with aging. It is also called viropause.
[2]. After the age of 50, testosterone secretion starts declining.
[3]. It is accompanied by decrease in number and secretory activity of Leydig cells.
[4]. Low level of testosterone increases the secretion of FSH and LH, which leads to some changes in the body.
[5]. It does not affect most of the men. But some men develop symptoms similar to those of female menopausal syndrome .
[6]. Common symptoms are hot flashes, illusions of suffocation and mood changes.
Accessory Sex organs in Males .
Seminal Vesicles .
[1]. Seminal vesicles are the paired glands situated in lower abdomen on either side of prostate gland behind urinary bladder.
[2]. Each seminal vesicle is a hollow sac of irregular shape and is lined by complexly folded mucous membrane.
[3]. Epithelial cells of the mucous membrane are secretory in nature and secrete seminal fluid.
[4]. Duct of seminal vesicle from each side joins with ampulla of vas deferens to form ejactulatory duct. Thus seminal fluid is emptied into ejaculatory ducts, which open into urethra.
Prostate gland .
[1]. Human prostate gland weighs about 40 g. It consists of 20 to 30 separate glands, which open separately into the urethra. These glands are tubuloalveolar in nature.
[2]. Epithelial lining of these glands is made up of columnar cells.
[3]. Prostate secretes prostatic fluid, which is emptied into prostatic urethra through prostatic sinuses
Urethra .
[1], Urethra in male has both reproductive and urinary functions.
[2]. Urethra contains mucus glands throughout its length, which are called glands of Littre.
[3]. The bilateral bulbourethral glands or Cowper glands also open into the urethra.
Penis .
[1]. Penis is the male genital organ. Urethra passes through penis and opens to the exterior.
[2]. Penis is formed by three erectile tissue masses, i.e. a paired corpora cavernosa and an unpaired corpus spongiosum.
[3]. Corpus spongiosum surrounds the urethra and terminates distally to form glans penis.
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