Title HUMAN REPRODUCTION.pdf ✅

 Digital www.allendigital.in [ 79 ] 1. Introduction : • To continue its own race, an organism by the process of reproduction, produces offsprings like its own. • Humans are sexually reproducing and viviparous. • In sexual reproduction the organisms produce male and female gametes which on combining, develop into a new individual. • The reproductive organs /sex organs are of two types- Primary/Essential Sex Organs : • These are the organs which form the gametes, testes in males & ovaries in females. • The male gamete is spermatozoon (pleural-spermatozoa). The female gamete is ovum. • Secondary/Accessory Sex Organs : • These organs form the passage for the gametes and help in the union of male & female gametes. • In male these include epididymis, vas deferens, seminal vesicles, prostate, bulbourethral glands, penis etc. In female these organs are fallopian tube, uterus, vagina, bartholin gland etc. Development of Sex Organ : • During intra uterine life (IUL) testis & ovary develop from mesoderm. They develop in abdominal cavity. At the time of birth, testes descend down into scrotal sac but ovaries remain in abdominal cavity. 2. The Male Reproductive System : • The male reproductive system is located in the pelvis region. It includes a pair of testes along with accessory ducts, glands and the external genitalia. • The male sex accessory ducts include tubuli recti, rete testis, vasa efferentia, epididymis, vas deferens, ejaculatory duct and urethra. These ducts store and transport the sperms from the testis to the outside through urethra. • The male accessory glands include paired seminal vesicles, a prostate and paired bulbourethral glands. 03 Human Reproduction
NEET : Biology [ 80 ] www.allendigital.in  Digital • In man, one pair testes are the main or primary reproductive organ. Size 4-5cm × 2-3cm and oval in shape • Both testes are located in a small bag like structure situated below & outside the abdominal cavity called as scrotum or scrotal sac. The temperature of scrotum is 2 – 2.5°C lesser than body temperature, necessary for spermatogenesis. • Internally, scrotum is lined by dartos muscle and spermatic fascia. Dartos muscle helps in regulation of the temperature with in the scrotum. During cold season, it becomes contracted & during warm season, it becomes relaxed. • Each testis is attached to the wall of scrotum through a group of flexible fibres collectively called as Gubernaculum or Mesorchium. • Each testis is attached to the wall of the abdominal-cavity through a cord termed as the Spermatic cord. Spermatic cord passes through the inguinal canal. This cord is made up of cremaster muscle & spermatic fascia. Cremaster muscle helps in the elevation of testes. Contents of the spermatic cord are vas deferens, gonadal veins, gonadal arteries, nerves and lymphatics. • Scrotum is connected to the abdominal cavity through a passage termed as inguinal-canal. Through this canal the testes descend down into the scrotal-sacs 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 cannot 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. (A) Internal Structure of Testis : • Testis is covered by dense covering which consist of three coats. Outer most is tunica vaginalis. Middle coat is tunica albuginea & inner most is tunica vasculosa. Tunica vaginalis has a parietal & visceral layer. It covers the whole testis except its posterior border from where the testicular vessels & nerves enter the testis. Tunica albuginea is a dense, white fibrous coat covering the testis all around. The posterior border tunica albuginea is thickened to form vertical septum called the Mediastinum testis. Tunica vasculosa is the inner most vascular coat of the testis lining testicular lobules. • Each testis has about 250 compartments called testicular lobule • Each testicular lobule has 1 to 3 seminiferous tubules (in which sperms are produced hence its called functional unit of testes), which join together at the apices of the lobules to form tubuli recti which enter the mediastinum. Here they form a network of tubules called as rete testis. Rete testis fuse to form 10 to 20 efferent ductule called as vasa efferentia. These ductules come out from upper posterior surface of testis & open into epididymis.
Human Reproduction  Digital www.allendigital.in [ 81 ] NOTE : Total number of seminiferous tubules in each testis is about 750 to 1000. • Each lobule has 1 to 3 seminiferous tubules • Total number of seminiferous tubules in each testis is about 750 to 1000. • Seminiferous tubules join together to form straight tubules or tubuli recti which enter the mediastinum. • Here they form a network of tubules called as rete testis. Rete testis fuse to form 10 to 20 efferent ductule called as vasa efferentia or ductuli efferentes. These ductules come out from upper dorsal (posterior) 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. • Liberation of sperms from testes is called semination. (B) Epididymis & Vas Deferens : • Epididymis is responsible for functional maturation of sperm and can store sperms for up to 1 month. Epididymis has 3 parts : (i) Caput epididymis - Upper, highly coiled part (ii) Corpus epididymis - Middle part (iii) Cauda epididymis -Basal, least coiled part • Vas deferens arise from cauda epididymis and enters inside the abdominal-cavity from the scrotal- sac. Terminal dilated part of vas deferens are called ampulla. • The wall of epididymis and vas deferens is made up of 2 layers - outer circular muscle layer and inner epithelium. The sperms reach the abdomen due to the pulsations/contractions of the circular muscles. • Vas deferens run upward & enter the abdominal cavity. Both vas deferens coil around the ureter of their respective sides and then dilate to form ampulla. • Ampulla of Vas deferens of each side receives the seminal vesicle of that side. The vas deferens now forms ejaculatory duct and opens into prostatic urethra. 1 pair of seminal vesicles are situated on dorso-lateral side of urinary bladder. • The urethra originates from the urinary bladder and extends through the penis to its external opening called urethral meatus.
NEET : Biology [ 82 ] www.allendigital.in  Digital (C) Accessory Reproductive Glands : • The substances secreted by the accessory reproductive glands do not form gametes but help in reproduction, these are – 1. Seminal Vesicle :- • Internally, it is lined by glandular epithelium which secretes seminal fluid. This is lubricating, transparent and jelly like substance, which makes 60–70% part of semen. It is slightly alkaline (pH 7.3). Fructose is found in seminal fluid, it acts as fuel to sperm. This fluid also contains fibrinogen, prostaglandins, etc. 2. Prostate Gland :- • This gland is located below the urinary bladder. It is unpaired and made up of 5 lobes in man. Each lobe opens into prostatic urethra through many fine apertures. 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. The secretion of prostate gland has calcium, clotting enzyme, profibrinolysin, etc. 3. Cowper's Gland :- • It is a pair of glands found on lateral sides of urethra. It is also called as bulbourethral gland. It is situated in membranous part of urethra & opens into penile urethra. It secretes transparent, slimy, jelly like fluid. It is slightly alkaline (pH 7.2). This destroys the acidity of the urethra and cleans it for the movement of sperms. It also helps in the lubrication of the penis. Semen : Semen = Sperm + Accessory reproductive gland fluid Volume = 3 to 4 ml. pH = 7.3 Normal sperm count 20 to 120 million/ml. ▪ Oligospermia sperm count & less than 20 million/ml. ▪ Azoospermia – either absence or near absence of sperms. ▪ Asthenospermia – reduced motility of sperms in semen ▪ Teratospermia – sperms with abnormal morphology Note :- The human male ejaculates about 200 to 300 million sperms during a coitus of which, for normal fertility, at least 60 per cent sperms must have normal shape and size and at least 40 per cent of them must show vigorous motility.