Human Reproduction | Plus 2 Zoology| Exam Capsule Notes

HUMAN REPRODUCTION: 

CHAPTER AT A GLANCE

Sequence of milk conduction in mammary glands: 

    Mammary alveoli → mammary tubules → mammary duct → mammary ampulla → lactiferous duct.

Spermatogenesis

Structure of sperm

• Acrosome: Releases lytic enzymes to penetrate the layers of ovum.
• Mitochondria: Provides energy for tail movement. 

Oogenesis

Structure of ovum (egg) 

3 membranes: 

• Plasma membrane 
• Zona pellucida 
• Corona radiata 

Sectional view of a seminiferous tubule 

Structure of ovary

• Primary sex organ. 
• Produce ovum and oestrogen & progesterone. 

MENSTRUAL CYCLE (REPRODUCTIVE CYCLE) 

Phases	Days	Main events
1.  Menstrual phase	1-5th day	Menstrual flow (bleeding).
2.  Follicular (Proliferative) phase	5-13th day	o Primary follicles → Graafian follicles. o Proliferation of ruptured uterine endometrium.
3.  Ovulatory phase	14th day	LH surge → rupture of Graafian follicle → ovulation.
4.  Secretory (Luteal) phase	15-28th day	Corpus luteum forms → progesterone → endometrium maximum vascular, thick and soft

• Menarche: The first menstruation during puberty. 
• Menopause: Permanent stopping of menstrual cycle at the age of 50. 

FERTILIZATION AND IMPLANTATION 

Zygote → cleavage → morula (8-16 blastomeres) → blastocyst → embryo 

Blastocyst 

• A. Inner cell mass: Becomes embryo. 
• B. Trophoblast: Gives nourishment to inner cell mass. Also, it is attached to endometrium. 

After attachment, blastocyst is embedded in endometrium. It is called implantation. 

PREGNANCY AND EMBRYONIC DEVELOPMENT 

Placenta: A structural & functional unit b/w foetus & uterine wall formed by interdigitation of chorionic villi & uterine tissue. 

Functions of placenta: 

• Supply O2, nutrients etc. from mother to foetus. 
• Remove CO2 and excretory wastes from foetus. 
• Acts as an endocrine gland. It secretes Human chorionic gonadotropin (hCG), human placental lactogen (hPL), oestrogens, progesterone & relaxin. 

Changes in embryo during pregnancy:

• After one month: Heart is formed.
• End of second month: Limbs and digits are developed.
• End of 12 weeks (first trimester): Major organs (limbs, external genital organs etc.)
• 5th month: Hair on the head. First movement of foetus.
• End of 24 weeks (2nd trimester): Fine body hair, eyelids separate and eye lashes are formed.
• End of 9 months: Ready for delivery.

PARTURITION AND LACTATION 

• Signals from foetus & placenta → mild uterine contractions (fetal ejection reflex) → oxytocin from pituitary → stronger uterine muscle contractions → further secretion of oxytocin → Parturition (giving birth). 
• Lactation: Production of milk from mammary glands. 
• Colostrum: Yellowish milk produced during the initial few days of lactation. It is rich in antibodies essential to develop resistance for the new born babies.