Human Reproduction

Graafian follicle develops under influence of FSH of anterior pituitary.  Its follicular cells secrete estrogen. Rising level of estrogen decreases production of FSH, and stimulates secretion of LH. The two cause mature Graafian follicle to release the ovum.

Ovulation takes place on 14th day of cycle, concentration of LH is highest on 14th day because it has to break the Graafian follicle so as to release the ovum later if the concentration of estrogen and progesterone decrease there is lose of internal lining of uterus and menstural bleeding start.

Epimorphosis is a form of development in segmented animals in which body segmentation is completed before hatching.

Formation of sperms from small clumps of cells can not be a case of epimorphosis.

Kidney and ureter in Rana tigrina is developed from mesodermal layer.

Embryonic cells differentiate at an early stage and form an outer layer of cells, the ectoderm and an inner layer the endoderm. At the later stage, the mesoderm is formed and these three germ layers give rise to all the tissues of the developing embryo.

Both corpus luteum and macula lutea are characterised by a yellow colour. After an egg is released from the ovary, the cells that line the ovarian follicle change shape and colour to become a corpus luteum (yellow body). Macula lutea is the yellowish spot present at the posterior pole of eye. Lutein, zeaxanthin, $\mathrm{\alpha }$- carotene and $\mathrm{\beta }$- cryptoxanthin are responsible for its yellow colouration.

Sperm consists of head, neck, a middle piece and a tail.

When viewed under electron microscope, cross- section of a midpiece of sperm consists of-

(i) core of the flagellum is composed of an axoneme surrounded by 9 dense fibres.

(ii) axoneme consists of 2 singlet microtubules surrounded by 9 microtubule doublets.

(iii) mitochondria is well placed for providing the ATP required for flagellar movement.

Progesterone is a steroid hormone and main female sex hormone. It is secreted during the later half of the menstrual cycle in human females by temporary endocrine tissue, the corpus luteum. The luteinizing hormone (LH) of anterior pituitary brings about a rupture of the Graafian folllicle to release the ovum and changes the ruptured follicle into a yellow structure called corpus luteum, which secrets progesterone.

During the embryonic development in humans, cleavage division results in a hollow ball of cells called morula. Solid mass of 32 cells formed from zygote after successive mitotic division (after 3rd division of cleavage) is called morula.

The phase of menstrual cycle in humans that last for 7-8 days is ovulatory phase. During this phase, production of FSH decreases while that of LH increases which leads to ovulation on about the 14^th day. But it may range from 9^th to 16^th day (approximately).

Follicular phase begins on the first day of menstruation and ends with ovulation.

Luteal phase is the second half of cycle. It lasts for about 14 days and ends just before a menstrual period.

Oestrogen is a steroid hormone secreted by Graffian follicle. It is responsible for development of secondary sexual characters in female such as thin voice, complete development of ovary, oviduct, mammary gland, uterus and vagina. Therefore, it is a steroid sex hormone that influences secondary sex organs.