Welcome to Zoology World

balindrakumar033@gmail.com   25/11/2017,Saturday

WELCOME TO ZOOLOGY WORLD

The science or study of animal life. Together with botany, the study of plant life, it forms the science of biology. Zoology is such a vast subject that most zoologists specialize or focus on the study of particular organisms or taxonomic groups. tion of animals.

Male reproductive system:

The male reproductive system of a scrotum,a pair of testes,vasa efferentia, a pair of epididymis,a pair of vasa deferentia,a pair of ejaculatory ducts, a urethra,a penis and certain accessory sex organs.

The male reproductive system of a scrotum,a pair of testes,vasa efferentia etc.

A spermatic cord connects testis with abdominal cavity.It consists of connective tissue that encloses an artery,a vein,a lymph vessels,a nerve,cremaster muscle and a vas deferens.A testis rests in its chamber over pad called gubernaculum. The scrotal sac of male is homologus to female's labia majora.

Variations in position of testes:

In some mammals (lion,bull,horse),the testes remain permanently in the scrotum and keep functioning throughout the year as in man.In certain seasionally breeding mammals,such as bat,otter and llama,(Insectivora, Tubulidentata and most Rodentia)the testes enlarge,become functional, and descent into the scrotum in the breeding season,but thereafter ascent into abdominal cavity,and become reduced and inactive. In a few cases (elephant,whale,seal)the testes remain permanently in the abdomen as the body temperature is low enough for sperm maturation.Scrotum is absent in such cases.Scrotum is in front of penis in Kangaroo

Human Testes:

The testes are the primary sex organs.They are about 4-5cm long,
2.5cm wide and 3cm thick.

The testes are the primary sex organs.They are about 4-5cm long, 2.5cm wide and 3cm thick.They are suspended in the scrotal sacs by spermatic cords.Each testes weighs about 10-15 gms.

Each testis has three coverings- tunica vaginalis,tunica albuginea and tunica vasculosa.Ingrowth of the tunica labuginea,called septa, divide the testis into some 200 to 300 lobules.Each testicular lobule contains 1-3 highly convoluted seminiferous tubules,blood vessels and nerve embedded in loose connective tissue.A total of about 750 seminiferous tubules occur in each testis.

A total of about 750 seminiferous tubules
occur in each testis.

Each seminiferous tubule is lined by germinal epithelium,seminiferous tubules is the site of spermatogenesis.The process occurs in waves along the length of the tubule,taking about 9 weeks(63 days) to complete in man. Seminiferous tubules contain 3 types of cells:-

(i)Germ cells:

Germ cells or primordial germ cells arise from yolk sac endoderm
and enter the testes early in development.

Germ cells or primordial germ cells arise from yolk sac endoderm and enter the testes early in development.These are spermatogenic cells,by mitotic division,produce spermatogonia into the lumen of the seminiferous tubule.The spermatogonia grow into primary spermatocytes which undergo meiosis,producing haploid cells,first secondary spermatocytes and then spermatids. Spermatids differentiate by a process of spermiogenesis into dimorphic haploid sperm(containing X or Y chromosome). Mature spermatozoa lie free in the cavity of the seminiferous tubules.

(ii)Somatic cells/Sertoli cells/Sustentacular cells/ Nurse cells:-

These are supportive nutritive and secrete a polypeptide  hormone called
inhibin and a steroid oestradiol

These are supportive nutritive and secrete a polypeptide hormone called inhibin and a steroid oestradiol which interferes with spermatogenic activity and kinetics of sperm production.

(iii)Leydig cell(Interstitial cell):-

Leydig cells are endocrine cell of testes which lie in the form of clusters or singly
in the interstitium(space between seminiferous tubules).
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  • (iii)Leydig cell(Interstitial cell):

    Leydig cells are endocrine cell of testes which lie in the form of clusters or singly
in the interstitium(space between seminiferous tubules).

    Leydig cells are endocrine cell of testes which lie in the form of clusters or singly in the interstitium(space between seminiferous tubules). These secrete a sex steroid called androgen by using cholestrol.The cell contain a rich repertoire of enzymes which faciliate formation of pathways for steroid biosynthesis and biotransformation.These enzymes are called steroid- dehydrogenases.

    Rete testis:

    This is a plexiform arrangment(Network) of space supported
by highly vascular collagenous connective tissue.

    This is a plexiform arrangment(Network) of space supported by highly vascular collagenous connective tissue.It is lined by squamous epithelial cells some of which bear flagella whose activity assists in forward migration of testicular sperm(which are immotile at this stage). The seminiferous tubules open into rete testis.

    Vasa efferentia:

    Rete testisis connected to caput epididymis by 12-12 fine tubules called
vasa efferentia or ductuli efferentes.

    Rete testisis connected to caput epididymis by 12-12 fine tubules called vasa efferentia or ductuli efferentes.Their lining epithelium is ciliated for conducting sperms.tubuli recti,rete testis and ductuli efferents constitutes an intertesticular genital duct system.The cells of vasa efferens are columnar ciliated.

    Epididymes has three parts:-

    1. Upper part(Head):
    2. Caput epididymis or globus major.

    3. Middle part:
    4. Corpus epididymis or globus normal

    5. Basal part(Tail):
    6. Cauda epididymis or globus minor.

    In epididymis the sperms are stored for a few hours to a few days till sent out through ejaculation.

    The epididymis show peristaltic and segmenting contraction at intervals to push the spermatozoa away from the testis. Testis and epididymis are together called testicles.

    Vasa deferentia(singular-vas deferens):

    The vas deferens is a continuation of the cauda epididymis.It is about 45cm.long and is slightly coiled at first but becomes straight as it enters the abdominal cavity through the inguinal canal. Vasa deferentia(ducti deferentes) conduct sperms from epididymis to urethra and is lined by pseudostratified columnar epithelia. Surgical interference(Vasectomy) of vas deferens ensure successful non-reversible male contraception.

    Difference between Vasa efferentia and Vasa deferentia:

    Vasa efferentia:-

    Arise from the rete testes.Vary from 15 to 20 in number. Are fine and convoluted.Lining bears many ciliated cells. Carry spermatozoa from rete testes to caput epididymis.

    Vasa deferentia:-

    Arise from the cauda epididymis.Are only 2 in number.
Are thick slightly coiled in the scrotum,straight in the abdomen.

    Arise from the cauda epididymis.Are only 2 in number. Are thick slightly coiled in the scrotum,straight in the abdomen. lining has sterocilia on many cells.Carry spermatozoa from cauda epididymis to ejaculatory ducts.

    6.Ejaculatory ducts:-

    They are short(2cm) straight muscular tubes each formed by union of a
vas deferens and duct fo seminal vesicle where ejaculate is formed by mixing
 of sperms with secretion of seminal vesicle.

    They are short(2cm) straight muscular tubes each formed by union of a vas deferens and duct fo seminal vesicle where ejaculate is formed by mixing of sperms with secretion of seminal vesicle.The two ejaculatory ducts join the urethra within prostate gland.

    7.Urethra:-