1 Reproductive System

Gonads are primary reproductive organs which produce gametes and sex hormones.

In males, the primary sex organs are the testes.

Accessory sex organs are also present in males.

Male Reproductive Organs

Male reproductive organs are divided into:

1. Primary sex organs.
2. Accessory sex organs.

2 Testes

Functional Anatomy of Testes

There are two testes in almost all species.

These are ovoid or walnut-shaped bodies located in the scrotum.

Each testis is enclosed by three coverings.

Coverings of Testis

Parenchyma of Testis

The posterior surface of testis is thickened to form the mediastinum testis.

From the mediastinum, connective tissue septa called septula testis extend into the testis at various points.

Because of this, testis is divided into many compartments or lobules.

Each lobule contains 1 to 4 coiled seminiferous tubules.

Each testis contains about 200 to 300 lobules.

3 Seminiferous Tubules

There are about 400 to 600 seminiferous tubules in each testis.

Each seminiferous tubule is about 30 to 80 cm long and about 150 to 300 μm in diameter.

Wall of Seminiferous Tubule

Wall of seminiferous tubule is formed by three layers:

1. Outer capsule or tunica propria formed by connective tissue.
2. Thin homogeneous basement membrane.
3. Stratified epithelium.

Cells of Seminiferous Tubules

Wall of seminiferous tubule consists of two types of cells:

1. Spermatogenic cells or germ cells.
2. Sertoli cells or supporting cells.

Spermatogenic Cells

Spermatogenic cells are the precursor cells of spermatozoa.

Spermatogenic cells lie in between Sertoli cells and are attached to Sertoli cells by means of cytoplasmic connection.

In children, spermatogenic cells are in primitive form called spermatogonia.

With onset of puberty, spermatogonia develop into sperms through different stages.

Sertoli Cells

Sertoli cells or supporting cells are large and irregular columnar cells present in seminiferous tubules.

Spermatogenic cells are attached to Sertoli cells by means of cytoplasmic connections.

Functions of Sertoli Cells

1. Support and nourish the spermatogenic cells, from which spermatozoa are released.
2. Secrete the enzyme aromatase, which converts androgens into estrogen.
3. Secrete androgen-binding protein (ABP), which is essential for testosterone activity during spermatogenesis.
4. Secrete estrogen-binding protein (EBP).
5. Secrete inhibin, which inhibits the secretion of follicle-stimulating hormone (FSH) from anterior pituitary.
6. Secrete activin, which increases FSH secretion.
7. Secrete Müllerian regression factor (MRF), also called Müllerian inhibiting substance (MIS), which is responsible for regression of Müllerian duct during development.

Blood-Testis Barrier

It is formed by tight junctions between Sertoli cells near the basal membrane of seminiferous tubules.

Blood-testis barrier protects seminiferous tubules from harmful substances present in blood and prevents the entry of blood into the testis.

At the same time, it allows nutrients and other essential substances to reach spermatogenic cells.

4 Pathway of Sperm and Interstitial Cells

Pathway of Sperm

Each seminiferous lobule opens into a network of tubules called rete testis.

From rete testis, vas efferens arise.

Vas efferens join the head of epididymis and then converge to form vas deferens.

Epididymis

Duct of epididymis is an enormously coiled tube of about 4 metres in length.

It begins at the head where it receives vas efferens.

At the caudal pole of epididymis, it turns sharply upon itself and continues as vas deferens without any definite demarcation.

Interstitial Cells of Leydig

They secrete androgens, especially testosterone.

5 Accessory Sex Organs in Males

Accessory sex organs in males are:

1. Seminal vesicles.
2. Prostate gland.
3. Urethra.
4. Penis.

Seminal Vesicles

Seminal vesicles are paired glands situated in the lower abdominal region on either side of urinary bladder.

Each seminal vesicle is a hollow sac with a complexly folded mucous membrane which secretes seminal fluid.

Seminal fluid from each seminal vesicle is added to the ejaculatory duct.

The ejaculatory duct opens into the urethra.

Seminal fluid is neutral or slightly alkaline in reaction and is mucoid and viscous.

Functions of Seminal Fluid

1. Nutrition to Sperms

Seminal fluid contains nutritive substances which are utilized by sperms after being ejaculated into the female genital tract.

2. Clotting of Semen

As soon as semen is ejaculated, it is clotted because of conversion of fibrinogen of seminal fluid into fibrin.

Clotting of semen is essential for holding the sperms in the female genital tract.

3. On Fertilization

Prostaglandin of seminal fluid enhances fertilization of ovum by:

1. Increasing the receptive capacity of cervical mucosa for sperms.
2. Causing reverse peristalsis in uterus and fallopian tubes. This increases the rate of transport of sperms in the female genital tract during coitus.

Oxytocin is also responsible for this process.

Prostate Gland

Prostate gland weighs about 40 g.

It is formed by 20 to 30 separate secretory glands, which open separately into the urethra.

Prostate secretes prostatic fluid.

Prostatic Fluid

Functions of Prostatic Fluid

1. Maintenance of Sperm Motility

Prostatic fluid provides optimum pH for the motility of sperms.

Generally, sperms are nonmotile at a pH of less than 6.0.

Vaginal secretions in females are highly acidic, with a pH of 3.5 to 4.0.

When semen is ejaculated into the female genital tract during coitus, sperms are initially nonmotile.

However, alkaline prostatic secretion present in semen neutralizes the acidity in vagina and maintains the pH of semen.

At a pH of 6.0 to 6.5, sperms become motile and chances of fertilization are enhanced.

2. Clotting of Semen

Clotting enzymes present in prostatic fluid convert fibrinogen from seminal vesicles into clot.

3. Lysis of Clot

The clot is dissolved by fibrinolysin of the prostatic fluid so that the sperms become motile.

Urethra

Male urethra is about 20 cm long.

After origin from urinary bladder, it traverses the prostate gland, which lies below the bladder, and then runs through the penis.

Ejaculatory duct opens into urethra.

Urethra contains mucus glands throughout its length, which are called glands of Littre.

Bilateral bulbourethral glands also open into the urethra.

Penis

Penis is made up of erectile tissue masses, including paired corpora cavernosa and an unpaired corpus spongiosum.

Corpus spongiosum surrounds the urethra and terminates to form glans penis.

6 Functions of Testes

Testes perform two functions:

1. Gametogenic function by which gametes are produced.
2. Endocrine function by which male sex hormones are secreted.

Gametogenic Function: Spermatogenesis

It takes about 74 days for the formation of sperm from a primitive germ cell.

Stages of Spermatogenesis

Spermatogenesis occurs in four stages:

1. Stage of proliferation.
2. Stage of growth.
3. Stage of maturation.
4. Stage of transformation.

Stage of Proliferation

Spermatogonia contain diploid number of chromosomes.

One member of each chromosome pair comes from the mother and the other from the father.

There are 22 pairs of autosomal chromosomes and one pair of sex chromosomes.

Sex chromosomes in males consist of one X chromosome and one Y chromosome.

During proliferative stage, spermatogonia divide repeatedly without any change in chromosomal number.

There are usually seven generations of spermatogonia.

During this stage, spermatogonia migrate and align along the cells towards the lumen of seminiferous tubules.

One generation of spermatogonia enters the stage of growth and becomes a primary spermatocyte.

Stage of Growth

During this stage, primary spermatocyte grows into a large cell.

Apart from growth, there is no other change in the primary spermatocyte during this stage.

Stage of Maturation

After attaining full size, each primary spermatocyte quickly undergoes meiotic or maturation division, which occurs in two phases.

First Phase of Maturation

In the first phase, each primary spermatocyte divides into two secondary spermatocytes.

Significance of first meiotic division is that each secondary spermatocyte receives only haploid or half the number of chromosomes.

Total of 23 chromosomes include 22 autosomes and one X or Y chromosome.

Second Phase of Maturation

During second phase, each secondary spermatocyte undergoes second meiotic division resulting in two smaller cells called spermatids.

Each spermatid has haploid number of chromosomes.

Stage of Transformation

There is no further division.

Spermatids are transformed into mature spermatozoa (sperms).

Transformation occurs in two stages.

Spermiogenesis

Changes taking place during spermiogenesis include:

1. Formation of nuclear material.
2. Removal of unwanted quantity of cytoplasm.

Spermiogenesis is the process during which spermatids change into matured spermatozoa.

7 Role of Sertoli Cells and Hormones in Spermatogenesis

Role of Sertoli Cells in Spermatogenesis

Sertoli cells influence spermatogenesis by many ways.

Hormones Involved in Spermatogenesis

Spermatogenesis is influenced by many hormones which act either directly or indirectly.

1. Follicle-Stimulating Hormone

FSH is responsible for initiation of spermatogenesis.

It binds with Sertoli cells and spermatogonia to stimulate the proliferation of spermatogonia.

It also stimulates formation of estrogen and androgen-binding protein from Sertoli cells.

2. Luteinizing Hormone

In males this hormone is called interstitial cell stimulating hormone (ICSH).

It is essential for secretion of testosterone from Leydig cells.

3. Growth Hormone

Growth hormone is essential for general metabolic processes in testis.

It is also necessary for proliferation of spermatogonia.

In pituitary dwarfs, spermatogenesis is severely affected.

4. Testosterone

Testosterone is responsible for sequence of later stages in spermatogenesis.

It is also responsible for maintenance of spermatogenesis.

Testosterone activity is largely influenced by androgen-binding protein.

5. Estrogen

Estrogen is formed from testosterone in Sertoli cells.

It is necessary for spermiogenesis.

6. Inhibin

Inhibin is a peptide hormone and serves as a transforming growth factor.

It is secreted by Sertoli cells.

Inhibin is necessary for spermatogenesis and inhibits FSH secretion through feedback mechanism, leading to decrease in the pace of spermatogenesis.

7. Activin

Activin is also a peptide hormone secreted by Sertoli cells and Leydig cells.

Activin has opposite actions of inhibin.

It increases secretion of FSH and accelerates spermatogenesis.

Other Factors Affecting Spermatogenesis

1. Increase in body temperature: Increase in body temperature prevents spermatogenesis.
2. Cryptorchidism: Normally, temperature in scrotum is about 2°C lower than body temperature. In cryptorchidism, testes remain in abdomen where temperature is higher than that of scrotum. Increased temperature stops spermatogenesis.
3. Infectious diseases: Infectious diseases such as mumps can cause degeneration of seminiferous tubules and affect spermatogenesis.

8 Androgens and Testosterone

Androgens Secreted by Testes

1. Testosterone.
2. Dihydrotestosterone.
3. Androstenedione.

Testosterone is secreted in large quantities.

Dihydrotestosterone is more active.

Estrogen and progesterone are also found in testes.

Activin and inhibin are also secreted in testes, but these 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

In testes, androgens are secreted by the interstitial cells of Leydig, which form about 20% of the mass of testis.

Leydig cells are numerous in newborn male babies and in adult males.

Leydig cells are scanty or almost absent during childhood.

Therefore, secretion of androgens occurs in newborn babies and after puberty.

Adrenal Cortex

Androgens secreted by zona reticularis of adrenal cortex are:

• Testosterone.
• Androstenedione.
• Dehydroepiandrosterone.

Adrenal androgens do not have significant physiological actions because of their small quantity.

Chemistry

Testosterone is a C19 steroid.

Synthesis

Androgens are steroid hormones synthesized from cholesterol.

Androgens are also synthesized from acetate.

Plasma Level and Transport

Plasma level of testosterone in an adult male is between 300 and 700 ng/dL.

In adult females, testosterone level is 30 to 60 ng/dL.

Two-thirds of testosterone are transported by gonadal steroid-binding globulin.

It is also called sex steroid-binding globulin.

Remaining one-third of testosterone is transported by albumin.

Metabolism

In many target tissues, testosterone is converted into dihydrotestosterone, which is the most active form in some tissues such as adipose tissue.

A portion of testosterone is converted into inactive forms of androgen, including androsterone and dehydroepiandrosterone.

Life of Testosterone

Testosterone is secreted in fetus by genital ridge.

Testosterone secretion continues during fetal life and starts rapidly increasing at the onset of puberty.

It remains secreted through the remaining part of life.

Secretion starts decreasing after about 40 years and becomes almost zero by the age of 90 years.

9 Functions of Testosterone in Fetal Life

Testes begin to secrete testosterone at about the 2nd to 3rd month of fetal life.

Testosterone performs three functions in fetus:

1. Sex differentiation in fetus.
2. Development of accessory sex organs.
3. Descent of the testes.

Sex Differentiation in Fetus

Testosterone is responsible for sex differentiation of fetus.

Fetus has two genital ducts:

1. Müllerian 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.

If testosterone is secreted from genital ridge of fetus at about the 7th week of intrauterine life, the Müllerian duct system disappears and male sex organs develop from Wolffian duct.

In addition to testosterone, Müllerian regression factor (MRF) secreted by Sertoli cells is also responsible for regression of Müllerian duct.

In the absence of testosterone, Wolffian duct regresses and female sex organs develop from Müllerian duct.

Development of Accessory Sex Organs and External Genitalia

Testosterone is also essential for the growth of external genitalia such as penis and scrotum and other accessory sex organs namely genital ducts and seminal vesicles.

Descent of Testes

Testes are developed in the abdominal cavity and descend into the scrotum through the inguinal canal before birth.

The process by which testes enter the scrotum is called descent of testes.

Testosterone is responsible for descent of testes.

10 Functions of Testosterone in Adult Life

1. Effect on Sex Organs

Testosterone increases the size of penis, scrotum and other male genital organs.

These organs enlarge many folds between the age of 20 years and the onset of puberty under the influence of testosterone.

Testosterone is also necessary for spermatogenesis.

It has erythropoietic action.

After puberty, testosterone causes mild increase in RBC count.

It also increases blood volume by increasing water retention and extracellular fluid volume.

2. Effect on Secondary Sexual Characters

Secondary sexual characters are the physical and behavioral characteristics that distinguish the male from female.

These characters appear at the time of puberty.

Testosterone is responsible for development of secondary sexual characters in males.

Effect on Muscular Growth

Testosterone increases muscle mass due to its anabolic effects on proteins.

It accelerates transport of amino acids into muscle cells, synthesis of proteins and storage of proteins in muscles.

Effect on Bone Growth

After puberty, testosterone increases thickness of bones by increasing matrix content and calcium deposition.

In addition to increasing the size and strength of bones, testosterone also causes early fusion of epiphyses of long bones with shaft.

If testes are removed before puberty, fusion of epiphyses is delayed and the height of the person increases.

Effect on Shoulder and Rib Cage

Testosterone causes broadening of shoulder bones and rib cage.

Effect on Pelvic Bones

Testosterone has a specific effect on pelvis which results in:

1. Lengthening of pelvis.
2. Funnel-like shape of pelvis.
3. Narrowing of pelvic outlet.

Thus, pelvis in males is different from that of females, which is broad and round or oval in shape.

Effect on Skin

Testosterone increases thickness and ruggedness of skin by increasing deposition of proteins in skin.

It also increases quantity of melanin pigment, which is responsible for deepening of skin color.

Testosterone enhances activity of sebaceous glands.

At puberty, when the body is exposed to sudden increase in testosterone secretion, excess secretion tends to cause development of acne on face.

After a few years, the skin gets adapted to testosterone secretion and acne disappears.

Effect on Hair Distribution

Testosterone causes male type of hair distribution over the body, i.e. hair growth over pubis, along alba and other parts of the body such as back and limbs.

In males, pubic hair has the base of triangle downwards whereas in females it is upwards.

Testosterone may cause baldness if there is genetic predisposition.

Effect on Voice

At the time of adolescence, boys have a cracking voice.

It is because of testosterone effect which causes:

1. Hypertrophy of laryngeal muscles.
2. Enlargement of larynx and lengthening.
3. Thickening of vocal cords.

Later, the cracking voice changes gradually into a typical adult male voice.

Effect on Basal Metabolic Rate

At the time of puberty and earlier part of adult life, testosterone increases basal metabolic rate to about 5 to 10% by its anabolic effects on protein metabolism.

Effect on Electrolyte and Water Balance

Testosterone increases sodium reabsorption from renal tubules along with water.

It leads to increase in extracellular fluid volume.

Effect on Blood

Testosterone has erythropoietic action.

After puberty, testosterone causes mild increase in RBC count.

It also increases blood volume by increasing water retention and extracellular fluid volume.

11 Regulation of Testosterone Secretion

In Fetus

During fetal life, testosterone secretion from testes is stimulated by human chorionic gonadotropin (HCG), which has the properties of luteinizing hormone.

HCG stimulates the development of Leydig cells in fetal testes and promotes testosterone secretion.

In Adult

Interstitial cell stimulating hormone (ICSH) or luteinizing hormone (LH) stimulates Leydig cells and secretion of testosterone is directly proportional to the amount of LH available.

Feedback Control

Testosterone regulates its own secretion through feedback mechanism.

It acts on hypothalamus and inhibits the secretion of luteinizing hormone-releasing hormone (LHRH).

When LHRH is inhibited, LH is not released from anterior pituitary, resulting in stoppage of testosterone secretion.

On the other hand, when testosterone level in blood is low, lack of inhibition of hypothalamus increases secretion of testosterone through LHRH and LH.

12 Semen

Semen is discharged during sexual act and the discharge of semen is called ejaculation.

Testes contribute sperms.

Prostatic secretion gives milky appearance to semen.

Secretions of seminal vesicles and bulbourethral glands provide consistency to semen.

At the time of ejaculation, human semen is alkaline in nature.

Immediately, it coagulates and after some time becomes liquid again.

Fibrinogen secreted from seminal vesicle is converted into a weak coagulum by clotting enzymes secreted from prostate gland.

Coagulum is liquefied by fibrinolysin of the prostatic fluid.

Properties of Semen

• Volume: about 2 to 6 mL per ejaculation.
• It is alkaline with a pH of about 7.5.
• It contains sperms and seminal plasma.

Composition of Semen

Semen contains about 10% sperms and 90% seminal plasma.

Seminal plasma contains secretions from seminal vesicle and prostate gland.

It also has a small quantity of secretions from other glands, particularly the bulbourethral glands.

Sperm Count

Normal sperm count is about 15 to 300 million/mL of semen.

Sterility occurs when the sperm count falls below 15 million/mL.

Survival Time of Sperm

Though sperms can be stored in male genital tract for long periods, after ejaculation the survival time is limited.

Sperms survive in the female genital tract for about 24 to 48 hours at a temperature equivalent to body temperature.

After sexual intercourse, sperms reach the fallopian tube in about 30 to 60 minutes.

Uterine contractions facilitate movement of sperms.

13 Sperm

Matured sperm develops from germ cells in the testis.

Structure of Sperm

Each sperm consists of four parts:

1. Head.
2. Neck.
3. Body.
4. Tail.

1. Head

Sperm is oval in shape in front view, with a length of about 3 to 5 μm and width of up to 3 μm.

The anterior portion of head is thin.

Head is formed by thin cytoplasm with a condensed nucleus and is covered by a thin cell membrane.

Anterior two-thirds of the head appear like a thick cap and is called acrosome.

Acrosome develops from Golgi apparatus.

It is made up of mucopolysaccharide and acid phosphatase.

It also contains hyaluronidase and proteolytic enzymes which are essential for the sperm to fertilize the ovum.

2. Neck

Head is connected to the body by a short neck.

Anterior end of the neck is formed by a thick disk-shaped anterior end knob, also called the proximal centriole.

Posterior end of neck is formed by another similar structure known as the posterior end knob.

Posterior end knob gives rise to the axial filament of the body.

Often, neck and body of sperm are together called the midpiece.

3. Body

Body of sperm is cylindrical with a length of 5 to 9 μm and thickness of about 1 μm.

It consists of a central core called axial filament covered by a thin cytoplasmic capsule.

Axial filament starts from posterior end knob of the neck.

It passes through the body and a perforated disk called end disk or end ring centriole.

Finally, axial filament reaches the tail as axial thread.

In the body, axial filament is surrounded by a closely wound spiral filament consisting of mitochondria.

4. Tail

Tail of sperm consists of two segments:

1. Chief or main piece of tail: enclosed by cytoplasmic capsule and has an axial thread. It is about 40 to 50 μm long.
2. Terminal or end piece of tail: has only the axial thread.

Motility of Sperm

Rate of motility of sperm in female genital tract is about 3 mm/minute.

The sperm moves through the female genital tract and reaches the fallopian tube.

Uterine contractions facilitate movement of sperms.

14 Male Climacteric

After the age of about 40 years, androgen secretion starts declining because of decreased secretory activity of Leydig cells.

15 Applied Physiology

Effects of Extirpation of Testes

Removal of testes is called castration.

Effects of removal of testes depend upon the age when testes are removed.

1. Effects of Extirpation of Testes Before Puberty

Eunuchism

If a boy loses testes before puberty, he develops infantile sexual characteristics throughout life.

This condition is called eunuchism.

• Height is slightly more.
• Bones are weak.
• Muscles and shoulder remain thin.
• Sex organs do not increase in size.
• Secondary sexual characters do not develop.
• Voice remains like that of a child.
• There is abnormal deposition of fat on buttocks, pubis and breasts.
• The fat distribution resembles the feminine pattern.

2. Effects of Extirpation of Testes Immediately After Puberty

If testes are removed after puberty, some of the secondary sexual characters revert to those of childhood, whereas other masculine characters are retained.

• Functions of sex organs are suppressed.
• Seminal vesicles and prostate undergo atrophy.
• Penis becomes smaller.
• Voice remains mostly masculine.
• Masculine distribution, musculature and thickness of bones are lost.
• There may be loss of sexual desire and sexual activities.

3. Effects of Extirpation of Testes in Adults

Removal of testes in adults does not cause loss of secondary sexual characters.

But accessory sex organs start degenerating.

Sexual desire is not totally lost.

Erection occurs but ejaculation is rare because of degeneration of accessory sex organs and lack of sperms.

Hypergonadism in Males

Cause of Hypergonadism

Hypergonadism in males is mainly due to increased activity of Leydig cells.

It is common in prepubertal boys and may develop precocious puberty.

Symptoms of Hypergonadism

• Rapid growth of musculature and bones.
• Development of early secondary sexual characters.
• Excess development of male sexual characters.
• Growth of the person may be less because of early fusion of epiphyses.
• Excess estrogenic effect may cause gynecomastia.

Hypogonadism in Males

Causes of Hypogonadism

1. Congenital non-functioning of testes.
2. Undeveloped testes due to absence of human chorionic gonadotropins in fetal life.
3. Cryptorchidism associated with partial or total failure of descent of testes.
4. Mutation of androgen receptors in testes.
5. Destruction of gonadotrophs, the cells secreting gonadotropins, in anterior pituitary.
6. Hypothalamic disorder.

Signs and Symptoms of Hypogonadism

Clinical picture of male hypogonadism depends upon whether the testicular deficiency develops before or after puberty.

Before Puberty

Features of hypogonadism are similar to those developed due to extirpation of testes before puberty.

After Puberty

Symptoms are similar to those developed due to extirpation of testes after puberty.

In Adults

Same symptoms, which develop after extirpation of testes, occur in this condition.

Hypergonadotropic Hypogonadism

Hypogonadism caused by testicular disorders increases gonadotropin secretion and the condition is called hypergonadotropic hypogonadism.

Hypogonadotropic Hypogonadism

Hypogonadism that occurs due to deficiency of gonadotropins caused by pituitary or hypothalamic disorder is called hypogonadotropic hypogonadism.

Dystrophia Adiposogenitalis

It is also called Fröhlich’s syndrome or hypothalamic eunuchism.