As you are aware, humans are sexually reproducing and viviparous. The reproductive events in humans include
(1)formation of gametes (gametogenesis), i.e., sperms in males and ovum in females,
(2)transfer of sperms into the female genital tract (insemination)
(3)fusion of male and female gametes (fertilisation) leading to formation of zygote.
(4) formation and development of blastocyst and
(5) attachment to the uterine wall (implantation)
(6) embryonic development (gestation)
(7) delivery of the baby (parturition).
Note-reproductive events occur after puberty. There are remarkable differences between the reproductive events in the male and in the female, for example, sperm formation continues even in old men, but formation of ovum ceases in women around the age of fifty years.
Primary sex organ: Essential organs which form the gametes. In males, the gamete forming organs are the testes.
In females, the corresponding organs are ovaries.
The male gamete is the spermatozoon. The female gamete is the ovum.
Secondary sex organ: These form the passage for the gametes to help the union of male & female gametes.
In male this includes epididymis, vas deferens, seminal vesicles, prostate, bulbourethral glands & penis.
While in female - Fallopian tube, uterus & vagina. (Breast is an accessory sex organ).
Development of Sex organ: During intra-uterine life (IUL) testis & ovary develop from mesoderm. They develop in abdominal cavity in IUL, at the time of birth, testes descend down into scrotal sac but ovaries remain in abdominal cavity.
MALE REPRODUCTIVE SYSTEM
During embryonic stage, testes develop in abdominal cavity & they descend to reach the scrotum at the time of birth. When the testes does not descend to reach the scrotum but remain in abdominal cavity at the time of birth this conditions is called undescended testes or cryptorchidism. Such testis can not develop and function properly and may develop malignancy.
Orchiopexy: When the undescended testes are brought into scrotal sac by surgical process during childhood this process called as orchiopexy.
Castration: Crushing of testes in bulls to convert them to bullocks. (This makes than more obidient due to fall in the level of testosterone).
In some animals the testis descend into the scrotum only in the breeding-season. Example: bat
Testes of some animals are permanently placed in the abdominal-cavity. Their scrotum is vestigeal-organ.
e.g. (Armadillo, Pangolin, Sloth) (Elephant) Order Cetacea
Each scrotum is connected to the abdominal cavity through a passage termed as inguinal-canal.
Spermatic cord in males passes through the inguinal canal.
Sometimes the inguinal canal may tear leading to abnormal protrusion of abdominal contents like loops of intestine into the inguinal canal. This condition is called as inguinal hernia.
Fig: Male reproductive system for humans
Internal Structure of Testis:
Testis is covered by three coats. Outer most is tunica vaginalis. Middle coat is tunica albuginea & inner most is tunica vasculosa.
Tunica vaginalis has a parietal & visceral layer. The Tunica albuginea is a dense, white fibrous coat covering the testis all around.
Tunica vasculosa is the inner most vascular coat of the testis lining testicular lobules.
Each lobules has 1 to 3 seminiferous tubules, which join together at the apices of the lobules to form a network of tubules called as rete testis.
Fig: Structure of TestesRete testis fuse to form 10 to 20 efferent ductule called as vasa efferentia.
These ductules come out from upper dorsal surface of testis & open into common tubules, which get highly coiled to form epididymis or ductus epididymis. This epididymis is responsible for functional maturation of sperm.
Total number of seminiferous tubules in each testis is about 750 to 1000.
Epididymis has 3 parts:
(i) Upper, highly coiled part- Caput epididymis
(ii) Middle part- Corpus epididymis
(iii) Basal, least coiled part-Cauda epididymis or Cauda-epididymis, enters inside the abdominal-cavity from the scrotal-sac in the form of Vas deferens or ductus deferens. Epididymis can temporarily stores the sperms for as long as one month and here the functional maturation of sperms takes place. 18 to 24 hr. after functional maturation of sperm, sperms proceed further to store in vas deferens.
The wall of epididymis is made up of 2 layers-outer circular muscle layer and inner epithelium. Wall of vas deferens is also made up of 2 layers-outer circular muscle layer and epithelium. The sperms reach the abdominal cavity due to the pulsation of the vas deferens.
Cutting of the vas deferens & tieing it by a thread is termed as vasectomy.
Cutting & tieing of the oviducts is termed as the tubectomy.
Vas deferens runs upward & enter into abdominal cavity. Both vas deferens coil around the ureter of their respective sides.
The vas deferens now forms ejaculatory duct and opens into prostatic urethra.
In human 1 pair of seminal vesicles are situated on dorsolateral side of urinary bladder which open seperately before the terminal ends of vas deferens. So terminal ends of vas deferens meet to form a single ejaculatory duct.
Accessary Reproductive Glands
The substances secreted by the accessary reproductive glands help in reproduction, these are
1. Seminal vesicle
Internally, it is lined by glandular epithelium which secretes seminal fluid, which is lubricating, transparent & jelly like substance, which makes 60–70% part of semen. It is slightly alkaline (pH 7.3). Fructose is found in seminal fluid, it act as fuel to sperm. Fibrinogen, prostaglandin, citrate, inositol and several proteins are also present in semen.
2. Prostate gland
It secretes slightly alkaline prostatic fluid which is milky, thick, sticky or jelly like. It makes about 30% part of semen and helps in sperm activation.
In the secretion of prostate-gland citric acid, Calcium and phosphate, clotting enzyme and profibrinolysin are present. The secretion of the prostate gland combines with the secretion of seminal vesicle and so the semen gets coagulated. In the coagulated semen, the mobility of sperms is reduced and so their energy is conserved. After some time due to fibrinolysins, semen again liquefies and in this semen now the sperms can move.
3. Cowper's glands
It is a pair of glands found on lateral side of urethra. It is also called as bulbourethral gland. It is situated in membranous part of urethra. It secretes transparent, slimy, jelly like fluid. it is slightly alkaline (pH is 7.2). This destroys the acidity of the urethra and cleans it for the movement of sperms.
Semen – Semen = Sperm + Accessary reproductive gland fluid
Volume = 3 to 4 ml.
Normal sperm count 20 to 120 million/ml.
Oligospermia < 20 million/ml.
Azospermia – either absence or near absence of sperms.
Penis- External genetilia
Urethra continues in a muscular & tubular organ called as penis. Terminal part of shaft of penis is bulging, it is called as Glans penis. This glans penis is covered by a movable skin called as prepuce or foreskin.
A special type of sebaceous gland is found on the prepuce called preputial gland which secretes smegma. Removal of prepuce by surgery is called is circumcision.
Seminiferous Tubules :
Each seminiferous tubule is lined on its inside by two types of cells called male germ cells (spermatogonia) and Sertoli cells . The male germ cells undergo meiotic divisions finally leading to sperm formation, while Sertoli cells provide nutrition to the germ cells.
The regions outside the seminiferous tubules called interstitial spaces, contain small blood vessels and interstitial cells or Leydig cells. Leydig cells synthesise and secrete testicular hormones called androgens. Other immunologically competent cells are also present.