Human Reproduction

Ovulation

Step 1: The menstrual cycle is divided into four phases — menstrual, follicular, ovulatory, and luteal. Step 2: During the ovulatory phase (around day 14), both LH and FSH reach their peak levels in the blood. Step 3: This sudden and sharp increase in LH is called the 'LH surge.' Step 4: The LH surge directly triggers the rupture of the Graafian follicle and the release of the secondary oocyte from the ovary — this is called ovulation. Step 5: After ovulation, the ruptured follicle transforms into the corpus luteum (luteal phase), which then secretes progesterone. The LH surge initiates ovulat

Corpus luteum

Step 1: After the Graafian follicle ruptures during ovulation, it does not simply disappear — the remaining cells reorganize. Step 2: The remnant of the ruptured Graafian follicle is transformed into a yellow, glandular structure called the corpus luteum. Step 3: The corpus luteum acts as a temporary endocrine gland and secretes large amounts of progesterone (and some oestrogen). Step 4: Progesterone maintains the thickened endometrium to support implantation if fertilization occurs. Step 5: If fertilization does NOT occur, the corpus luteum degenerates into a scar-like tissue called the corpu

Ampullary-isthmic junction of the fallopian tube

Step 1: After ovulation, the secondary oocyte is released into the peritoneal cavity and is picked up by the fimbriae of the fallopian tube. Step 2: The oocyte travels through the infundibulum into the ampulla of the fallopian tube. Step 3: Fertilization occurs only when the ovum and sperms are transported simultaneously to the ampullary-isthmic junction — the junction between the ampulla and the isthmus of the fallopian tube. Step 4: The uterus is where implantation occurs — not fertilization. Step 5: The infundibulum collects the ovum but fertilization does not take place there. The specific

Inner cell mass

Step 1: After fertilization, the zygote undergoes rapid mitotic divisions called cleavage, forming blastomeres. Step 2: After about 72 hours, a 16-celled berry-shaped structure called the morula is formed. Step 3: The morula continues to divide and develops into a hollow ball of about 100 cells called the blastocyst. Step 4: The blastocyst has two distinct regions: (a) Trophoblast — a single outer layer of large, flattened cells that will form the placenta, and (b) Inner Cell Mass (ICM) — a small cluster of 20-30 rounded cells on the inside. Step 5: The inner cell mass (also called embryoblast