Class 12 NEET Human Reproduction embryology
Human Reproduction and embryology
Sexual characteristics in human beings can be classified as follows:
Testis
The primary sex organ of a man.
Present in thin-walled skin pouches called Scrotal Sac or Scrotum.
Scrotum communicates with the abdominal cavity through the Inguinal canal.
The testis is kept extra abdominally in Scrotum in mammals because in scrotum temperature is 2-4° less than the abdomen and for spermatogenesis lower temperature is needed.
In bats, rats and others, testes descend to scrotal sacs only during the breeding season.
Whales and elephants have abdominal testes. Their body temperature is low and the cooling of testes is not required.
Histology
The outermost layer is tunica vaginalis.
Tunica albuginea is an inner white colour layer.
The seminiferous tubule is lined by germinal epithelium formed of two types of cell germ cell and Sertoli cell or nurse cell.
Rete Testis – Seminiferous tubule opens into a network of tubules called Rete testis.
Function – (i) Spermatogenesis
(ii) Secretion of Testosterone
Gubernaculum is the ligamentous connective cord (elastic cord) which connects testes to scrotal sacs posteriorly.
Gubernaculum represents mesorchium.
During embryonic life, Gubernaculum contracts and brings testis from the abdominal cavity to the scrotal sac under the influence of testosterone released from the foetal testes.
Epididymis
The epididymis is an irregular, narrow and highly convoluted tubule found on the inner surface of the testis.
The Wolffian duct of embryo gives rise to the epididymis in adults.
It is a long, highly coiled tube – with the following part :
(1) Head or Caput Epididymis or Globusmajor: It receives sperm from rete testis, by vasa efferentia, present on cranial side of testis.
(2) Body or Corpus Epididymis or Globus Normal: It stores sperm.
(3) Tail or Cauda Epididymis or Globus Minor: lower part and lies on the caudal side of testis.
Function : Storage (18 to 24 hr.), Nutrition& Physiological maturation
Vas Deferens (Seminal Duct) – long 30 cm
Vas deference or sperm duct arises from cauda epididymis. ascends to the abdomen, passes over the urinary bladder and receives the duct from seminal vesicle behind the urinary bladder forming ejaculatory duct.
Ejaculatory duct passes through the prostate to open into urethra shortly after its origin from the urinary bladder.
The urethra receives the ducts of prostate and Cowper’s gland pass through the penis and opens to outside.
Vas deferens ascend through the inguinal canal.
Penis
The penis is a copulatory organ. It has a vascular, spongy and erectile structure.
It has a glans penis at the tip covered with a fold of skin called a prepuce.
The urinogenital duct is corpus spongiosum and above it lies two corpora cavernosa.
Corpora Covernosa: two fibrous ligamentous tissues.
Corpora Spongiosa: It surrounds the urogenital canal.
The gland of Tyson: Present inside prepuce, modified oily glands.
Accessory or Secondary Sex Glands of Male
Seminal Vesicle
Seminal vesicles (uterus masculinus) are situated behind the bladder. they are narrow. long pouches with muscular tissue on their walls.
Uterus masculinus is situated at the junction of vas deference and prostate gland.
About 70% of the semen in seminal fluid is produced by seminal vesicles.
Seminal fluid has a pH of about 7.4 and contains fructose, citrate, ascorbic acid, prostaglandins and various enzymes.
The fructose is a source of energy for the spermatozoa.
Prostate Gland
Surrounds the proximal part of the urethra.
Secretion are alklaine
Also contain citric acid, some lipids & some enzymes.
Does the secretion neutralise the acidity of urethra?
Prostatic secretion contains substance important for sperm mobility notably albumin and Proteolytic enzymes fibrinolysin and fibrinogenase.
Cowpers or Bulbourethral Glands
These are also known as bulbourethral glands. situated beneath bladder and behind the urethra.
Cowper’s glands are present in male mammals.
Cowper’s glands are yellow in colour. Their secretion is slightly alkaline and is produced during sexual stimulation.
Cowper’s gland secretion acts as a lubricant for the glans penis. It also neutralizes any urine in the urethra.
Perineal Gland & Rectal Glands
These are found in rabbits, not in human beings.
Perineum refers to the space between the anus and urinogenital opening.
Perineal glands are a pair of dark elongated scent glands lying behind Cowper’s glands
They open into a hairless perineal depression on either side of the anus.
Their odorous secretion gives the rabbit its characteristic smell (its smell serves as a sexual attraction for the female).
A pair of rectal glands of unknown function is situated dorsally on the rectum.
Ejaculation
Ejaculation or seminal emission is the forceful expulsion of semen during sexual intercourse.
At an average ejection, 3 mL of semen containing about 300 million spermatozoa is emitted in men.
Cryptorchidism
Non descent of testis in scrotum.
They are present in the abdomen or Inguinal canal.
Orchidectomy
Surgical removal of testis.
Also known as castration.
Sterility
Result of – sperms is immobile, structurally abnormal or poor in number in the semen of less than 60 million.