Male Reproductive System Notes | Study Biology Class 12 - NEET

NEET: Male Reproductive System Notes | Study Biology Class 12 - NEET

The document Male Reproductive System Notes | Study Biology Class 12 - NEET is a part of the NEET Course Biology Class 12.
All you need of NEET at this link: NEET

Human Male Reproductive System

It consists of the following parts:

1. Scrotum

  • It is a pouch of deeply pigmented skin divided into two separate sacs. 
  • Each sac contains one testis. 
  • The normal temperature of the testes in the scrotum is about 20-2.5°C lower than the internal body temperature. 
  • This temperature is the ideal temperature for developing sperms. 
  • When the body is chilled, the smooth muscle contracts and brings the testes closer to the pelvic cavity. 
  • When the temperature drops, the movement towards the pelvic cavity allows the testes to absorb heat from the rest of the body so that the sperm cells do not become chilled. 
  • The scrotum remains connected with the abdomen or pelvic cavity by the inguinal canals. 
  • The spermatic cord, formed from the spermatic artery, vein and nerve bound together with connective tissue into the testis through the inguinal canal.

Male Reproductive System Notes | Study Biology Class 12 - NEETMale Reproductive system2. Testes

  • The primary sex organ in males. 
  • During early fetal life, the testis develop in the abdominal cavity but during the seventh month of the development, they descend into the scrotum through inguinal canals. 
  • There is a pair of testis that are suspended in the scrotum by the spermatic cords. 
  • A fibrous cord that extends from the caudal end of the testis to the scrotal wall is called the gubernaculum. 
  • Each testis is oval in shape with a length of about 4 to 5 cm and a width of about 2 to 3 cm. 
  • The peritoneum, called mesorchium supports the testis. 

Male Reproductive System Notes | Study Biology Class 12 - NEETLateral view of Male Testis

(i) Protective Coverings (Tunicae): The testis is surrounded by three layers. 

(a) The tunica vaginalis is the outer covering of the testis. 

(b) The tunica albuginea is a fibrous covering surrounding the testis situated under the tunica vaginalis. 

(c) The tunica vasculosa consists of a network of capillaries supported by delicate connective tissue which lines the tunica albuginea.

(ii) Testicular Lobules: Each testis has about 250 compartments called testicular lobules.

(iii) Seminiferous Tubules: 

  • Each testicular lobule of the testis contains one to three highly coiled seminiferous tubules. 
  • The Wall of each seminiferous tubule is formed of a single-layered germinal epithelium. 
  • The majority of cells in this epithelium are cuboidal called male germ cells (spermatogonia) and at certain places, there are present tall Sertoli or sustentacular cells. 
  • These cells support developing germ cells and provide them with nutrition especially spermatids. 
  • Sertoli cells secrete androgen binding protein (ABP) that concentrates testosterone in the seminiferous tubules. 
  • Sertoli cells also secrete another protein called inhibin which suppresses FSH synthesis. 
  • The cuboidal cells undergo mitosis to produce spermatogonia. 
  • Spermatogonia grow into primary spermatocytes which undergo meiosis, producing haploid cells, first secondary spermatocytes and then spermatids. 
  • The latter convert into spermatozoa (sperms). Sertoli cells provide nutrition to the developing sperms.

Anatomy of Male Reproductive OrganAnatomy of Male Reproductive Organ

(iv) Interstitial Cells or Leydig's Cells (Endocrine portion of the testis): In between the seminiferous tubules in the connective tissue, there are present small groups of rounded interstitial or Leydig's cell male sex hormones, which secrete androgens (e.g.. testosterone i.e. male sex hormone)

(v) Rete testis and efferentia: The seminiferous tubules are closed at one end but on the other side, they join to a network the rete testis from where fine ciliated ductules, the vasa efferentia arise. 

Thus testes perform two functions- production of sperms and secretion of male sex hormones.

3. Epididymis

  • The epididymis is a mass of long narrow closely coiled tubules which lie along the inner side of each testis. 
  • At the anterior end of the testis, it is called caput epididymis, in which the vasa efferentia opens. 
  • The middle part of the epididymis is known as corpus epididymis. 
  • The posterior end of the epididymis is called cauda epididymis
  • The epididymis stores the sperms and also secretes a fluid that is considered to nourish the sperms.

EpididymisEpididymis

4. Vasa deferentia

  • A vas deferens emerges from the cauda epididymis on each side and leaves the scrotal sac and enters the abdominal cavity through the inguinal canal. 
  • The vas deferens loops over the urinary bladder where it is joined by a duct from the seminal vesicle to form the ejaculatory duct. 
  • Vasa deferentia carry sperms.Male Reproductive System Notes | Study Biology Class 12 - NEET
    Differences between Vasa Efferentia and Vasa Deferntia
  • Rete testis, vasa efferentia, epididymis and vasa deferentia are called the male sex accessory ducts. 
  • These ducts store and transport the sperms from the testis to the outside through the urethra.

Vasa deferentiaVasa deferentia

5. Ejaculatory ducts

  • The ejaculatory ducts are two short tubes each formed by the union of the duct from a seminal vesicle and a vas deferens. 
  • They pass through the prostate gland and join the prostatic part of the urethra. 
  • The ejaculatory ducts are composed of the fibrous, muscular and columnar epithelial tissue. 
  • Ejaculatory ducts carry sperms and secretion of seminal vesicles.

Ejaculatory ductsEjaculatory ducts

6. Urethra

  • The male urethra provides a common pathway for the flow of urine called semen. 
  • It is much longer in males than in females, measuring about 20 cm. 
  • The urethra includes three parts  
    (i) The first part is surrounded by the prostate gland and is called the prostatic urethra which arises from the urinary bladder and carries urine only.
    (ii) The second part is the membranous urethra which is situated behind the lower part of the pubic symphysis. The membranous urethra is the smallest urethra.
    (iii) The third part is the penile urethra which is situated in the penis. There are two urethral sphincters. The internal sphincter consists of smooth muscle fibres situated at the neck of the bladder above the prostate gland. The external sphincter consists of striated muscle fibres surrounding the membranous part of the urethra. 
  • The membranous urethra and penile urethra carry both urine and semen. The external opening of the urethra is called the urethral meatus.

UrethraUrethra

7. Penis

  • The penis is male genitalia (male copulatory organ). 
  • At the tip of the glans penis is the slit-like opening called the external urethral orifice or urinogenital aperture. 
  • The penis in addition to conducting urine from the body transfers semen into the reproductive tract of the female during sexual intercourse. 
  • The penis contains three cylindrical masses of erectile tissue two dorsal corpora cavernosa and one ventral corpus.
  • These bodies are surrounded by fibrous tissue.
  • The corpus spongiosum contains the penile urethra, the end of the penis to form the glans penis. 
  • The penis is covered by a loose fold of skin, the prepuce or foreskin sexual arousal the three bundles of tissue in the pep become engorged with blood. 
  • The penis carries both urine and semen.

8. Male Accessory glands

Male Reproductive System Notes | Study Biology Class 12 - NEETMale Accessory Glands(i) The seminal vesicles are one pair of sac-like structures near the base of the bladder.

  • Their ducts join the vasa deferentia to form the ejaculatory ducts.
  • They produce an alkaline secretion that forms 60% of the volume of semen. 
  • The pH of seminal fluid is 7.4. 
  • The secretion of the seminal vesicles contains fructose, hormone-like prostaglandins, and clotting proteins that are different from those in blood. 
  • Fructose is a source of energy for the sperm. 
  • The prostaglandins stimulate uterine contractions and thus may help the sperm to be contractions and thus may help the sperm to be energy moved towards the female's oviducts when fertilization takes place. 
  • The clotting proteins help semen coagulate after ejaculation. 
  • The alkaline nature of the seminal fluid helps to neutralize the acidic environment of the male urethra as well as that of the female reproductive tract which otherwise would inactivate and kill sperms.

Fructose, which is produced by the seminal vesicles, is not present anywhere else in the body, provides a forensic test for rape. The presence of fructose, in females genital tract confirms sexual intercourse. 

(ii) The prostate gland is a single large gland that surrounds the urethra. 

  • It produces a milky secretion with pH 6.5 which forms 25% of the volume of semen.
  • This secretion contains citric acid (a sperm nutrient) and enzymes (acid phosphatase, amylase, pepsinogen) and prostaglandins. 
  • Due to the presence of citric acid, it is slightly acid. 
  • A number of small ducts carry fluid from the prostate to the urethra. 
  • Secretion of the prostate gland nourishes and activates the spermatozoa to swim.

(iii) A pair of bulbourethral glands or Cowper's glands are present on either side of the membranous urethra. 

  • These glands secrete an alkaline fluid. 
  • Their ducts open into the membranous urethra carrying the fluid that neutralizes acids from urine in the urethra. 
  • They also secrete mucus that lubricates the end of the penis and the lining of the urethra. 
  • This decreases the number of sperm damaged during ejaculation.

Secretions of these glands constitute the seminal plasma which is rich in fructose, calcium and certain enzymes as mentioned above. The secretion of bulbourethral glands also helps in the lubrication of the penis.

Secretion of bulbourethral glands carries some spermatozoa (sperms) released before ejaculation. This is one of the reasons for the high failure rate of the withdrawal method of birth control.

Functions of Male Reproductive System 

1. Spermatogenesis. The germinal epithelial cells of seminiferous tubules produce sperms. 

2. Male Sex hormones. Leydig's cells (interstitial cells) produce male sex hormones

(e.g., testosterone). 

3. Transfer of Sperms. The copulatory organ (e.g.. penis) transfers sperms into the vagina of the female during copulation.


Semen

SemenSemen

  • Semen is a collection of secretions from the seminal vesicles, prostate gland and Cowper's glands and sperms from testes.
  • Semen is ejected from the penis during ejaculation. A single ejaculation may contain 200 to 300 million spermatozoa (sperms) of which at least 60% of sperms must have normal shape and size and at least 40% of them must show vigorous motility for normal fertility. 
  • Semen has a pH of 7.35 to 7.50; its alkalinity helps to neutralize the acidity of the urethra left from the passage of urine and protects the sperms from the acidity of the vagina. In fact, the fluid part of semen is called seminal plasma.

Hormonal Control of Male Reproductive System

  • The growth, maintenance and functions of the male reproductive organs are under hormonal control as described below. 
  • GnRH is secreted by the hypothalamus. It stimulates the anterior lobe of the pituitary gland to secrete LH and FSH. 
  • In males, LH is called interstitial cells stimulating hormone (ICSH) because it stimulates interstitial cells. (Leydig's cells) of the testes to secrete androgens.
  • Testosterone is the principal androgen, FSH stimulates Sertoli cells of the testes to secrete an androgen-bind ing protein (ABP) that concentrates testosterone in the seminiferous tubules. 
  • Sertoli cells also secrete a protein hormone called inhibin which suppresses FSH synthesis. 
  • FSH acts directly on spermatogonia to stimulate sperm production. 

Male Reproductive System Notes | Study Biology Class 12 - NEET

The onset of Puberty in Human Male Puberty

Male Reproductive System Notes | Study Biology Class 12 - NEET

  • Puberty is a period when reproductive organs start functioning. 
  • Puberty in human males is attained between 13-16 years. 
  • The hormone testosterone plays a significant role in the onset of puberty.
  • Gonadotropin-releasing hormone (GnRH) is secreted by the hypothalamus, which stimulates the anterior lobe of the pituitary gland to secrete luteinizing hormone (LH) and follicle-stimulating hormone (FSH). 
  • In males, LH may be called interstitial cells stimulating hormone (ICSH) because it stimulates the interstitial cells (Leydig's cells) of the seminiferous tubules of the testes to secrete androgens. 
  • Testosterone is the principal androgen that brings about the growth of the secondary sex organs and the development of secondary sexual characters. This is the onset of puberty in human males.
The document Male Reproductive System Notes | Study Biology Class 12 - NEET is a part of the NEET Course Biology Class 12.
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