Human reproduction

 Chapter-3 HUMAN REPRODUCTION

Events of Human Reproduction

Gametogenesis : formation of gametes.

Insemination : Transfer of sperm in female genital tract.

Fertilization : fusion of sperm and ovum.

Implantation : attachment of blastocyst with uterine wall for further development.

Gestation : Embryonic development

Parturition : Delivery of the baby. 

The Male reproductive system

1. Penis :

a. Urination

b.     Sexual intercourse

c.     Corpus cavernosum- spongy tissue that fills with blood to make penis erect

d.      Glans- the head, end of penis

e.     Foreskin

i.  Covers glans,

ii.  May be removed surgically in an operation

2.  Scrotum   

a.  Located behind penis

b.  Contains two testes

c.  Temperature sensitive (Sperm must be made in cooler conditions i.e, 2-3⁰ C lower than body temperature) 

3. Testes

a.  Sperm is produced by the seminiferous tubules due to FSH

b.  Testosterone is produced by Leydig cells due to LH

Sertoli cells : Provide nutrition to developing germ cells.

Interstitial cells / Leydig cells : Synthesize & secrete testicular hormone called androgens.

ACCESSORY DUCTS :

Epididymis:    Stores sperm until they have matured.

Vas deferens: Tube that leads from the epididymis to the urethra. Many sperm cells are stored here too.  

ACCESSORY GLANDS :

Prostate gland:     Provides an alkaline fluid that can protect sperm from harsh vaginal acids.

Seminal Vesicles:    Produce food for sperm. Food "Fructose"

Cowper's gland:      Produces clear lubricating fluid

SPERM

SEMINIFEROUS TUBULES

Head : It contains a elongated haploid nucleus, covered by acrosome. It filled with hydrolytic enzymes to dissolve the membrane of ovum for fertilization. Neck : It contains two centrioles helps in first cleavage division of zygote. Middle Piece: contains numerous mitochrondria which produce energy for movement of tail that facilitate sperm motility essential for fertilization Tail : helps in Sperm movement

Spermatogonium : it is diploid contains 46 chromosomes.   Primary Spermatocyte (2n): it complete 1st meiotic equal division (reduction) & forms 2 secondary spermatocytes.   Secondary spermatocytes : it is haploid, undergo the 2nd meiotic div to produce four equal haploid spermatids.   Spermatids : They transformed into spermatozoa (sperms) by the process called spermiogenesis with the help of FSH.   Spermiation : After spermiogenesis, sperm heads become embedded in the sertoli cells and finally released from seminiferous tubules by the process of spermiation.

The Female Reproductive System :

Ovary: i) Each ovary contains immature ova (eggs) in follicles. ii)  Females born with lifetime supply of eggs (250,000-400, 000 in each ovary) iii)  Ovaries release ovum -. Almost all ova degenerate between birth and puberty. iv)  Approx. 400 eggs will be ovulated over woman's life. v)  Egg is the largest human cell. vi)  Ovaries are located lower abdomen. 1 left and 1 on the right.   Fallopian tubes i) Two thin tubes attached to the upper sides of uterus ii)  Tubes terminate near the ovaries but are not attached iii) "Fimbriae" are finger-like structures on the end of each tube iv) Tubes conduct egg to uterus by use of small hairs called "cilia" v) Fertilization of ovum takes place in the ampullary- isthmic junction of the fallopian tubes. Egg viable for only 24-48 hours after ovulation.

Uterus: i)Pear-shaped organ located in lower abdomen. ii)Muscles(myometrium) stretch to allow baby to develop. Oxytocin starts labor contractions. iii)Lining of uterus (endometrium) thickens with blood-rich tissue due to progesterone. iv)Endometrium supports embryo/fetus during growth. v) Placenta It is the interface between baby and mother. If not pregnant, lining breaks down and is discharged from body through vagina. This is menstruation (period). vi) Cervix connects uterus to vagina. Like a door that opens during ovulation. Cervical mucous closes the door at all other times.

EXTERNAL GENITALIA:

Vagina (Birth canal) :

  ·   Menstrual blood leaves the body, Organ of intercourse , Muscular stretches to allow a baby to grow

  ·   Vaginal opening partly remains closed by thin membrane of tissue called hymen. May be stretched or torn during any physical activity or first intercourse.

Cervix:

·   Located at inner end of vagina, Opening of uterus into vagina ,

·   Mucous prevents bacteria and viruses from entering uterus, Lets sperm into uterus after ovulation

·   Where baby also passes through during vaginal birth

  Labia: Two (2) layers of skin, which fold over the opening to vagina and urethra

      ii)  Inner labia (labia minora)               iii)Outer labia (labia majora)

·   Pubic hair grows on outer labia

 Clitoris: Small organ, 5 to 10 millimeters long; Located at junction of inner labia near front of body Contains erectile tissue& sexually sensitive.

Mons pubis :Cushion like fatty tissue covered by skin and pubic hair

Gametogenesis & its hormonal regulation : 

FSH and LH from the pituitary:	FUNCTION / PRODUCTION
Hormone	In Females	In Males
FSH Controls à	Eggs + Estrogen (Follicular development)	Spermiogenesis
LH Controls à	Ovulation + Corpus Luteum	Testosterone (Spermatogenesis)

 Differentiate between: Spermatogenesis and Oogenesis :

Spermatogenesis	Oogenesis
Produces male gametes (sperm)	produces female gametes (oocytes)
–occurs in the seminiferous tubules (in testes)	–occurs in the ovaries
–occurs throughout life after puberty	occurs after puberty until menopause
may produce 3,00,00,000 per day	–humans normally produce one oocyte during each ovarian cycle
Primary spermatocyte divide equally to form two similar secondary spermatocytes	Primary otocyte divide unequally to form one large secondary oocyte and a small polar body
One spermatogonium produces 4 functional spermatozoa	An oogonium produces one functional ovum and 3 non functional polar bodies