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
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Acrosome: Releases lytic enzymes to penetrate the layers of ovum.
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Mitochondria: Provides energy for tail movement.
Oogenesis
Structure of ovum (egg)
3 membranes:
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Plasma membrane
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Zona pellucida
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Corona radiata
Sectional view of a seminiferous tubule
Structure of ovary
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Primary sex organ.
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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 |
• Primary follicles → Graafian follicles. • 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 |
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Menarche: The first menstruation during puberty.
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Menopause: Permanent stopping of menstrual cycle at the age of 50.
FERTILIZATION AND IMPLANTATION
Zygote → cleavage → morula (8-16 blastomeres) → blastocyst → embryo
Blastocyst
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A. Inner cell mass: Becomes embryo.
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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:
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Supply O2, nutrients etc. from mother to foetus.
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Remove CO2 and excretory wastes from foetus.
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Acts as an endocrine gland. It secretes Human chorionic gonadotropin (hCG), human placental lactogen (hPL), oestrogens, progesterone & relaxin.
Changes in embryo during pregnancy:
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After one month: Heart is formed.
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End of second month: Limbs and digits are developed.
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End of 12 weeks (first trimester): Major organs (limbs, external genital organs etc.)
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5th month: Hair on the head. First movement of foetus.
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End of 24 weeks (2nd trimester): Fine body hair, eyelids separate and eye lashes are formed.
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End of 9 months: Ready for delivery.
PARTURITION AND LACTATION
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Signals from foetus & placenta → mild uterine contractions (fetal ejection reflex) → oxytocin from pituitary → stronger uterine muscle contractions → further secretion of oxytocin → Parturition (giving birth).
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Lactation: Production of milk from mammary glands.
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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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