Friday, December 25, 2020

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.

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