The yolk sac forms a part of the gut and is the source of the earliest blood cells and blood vessels.

The release of ovum by the rupture of the Graafian follicle is called ovulation. It occurs during ovulatory phase of menstrual cycle.

(i) The inner glandular layer of the uterus is called endometrium.
(ii) The endometrium undergoes cyclic changes during the menstrual cycle.

The accessory glands of the male reproductive system include the paired seminal vesicles and bulbourethral glands also called Cowper's gland arid a single prostate gland.

(i) Sertoli cells or nurse cell
(ii) Spermatogonic cells

Formation of specific tissues, organs and organ systems from three germ layers is called Organogenesis.

Attachment of blastocyst to the uterine wall is called Implantation.

(a) Sertoli cells or Nurse cells
(b) Spermatogonic cells or male germ cells.

Placenta during pregnancy secretes hormones such as human chorionic gonadotrophic (hcG) estrogen, progesterone and human placenta lactogen. So, placenta is regarded as an endocrine tissue.

(a) FSH - Follicular Stimulating Hormone
(b) LH - Lutinizing Hormone
(c) hCG - Human Chorionic Gonadotropin
(d) hPL - Human Placental Lactogen.

Development of female gamete is called oogenesis. Oogenesis starts at the beginning of puberty.
Development of male gamete is called spermatogenesis. Spermatogenesis starts at puberty

Spermiogenesis Spermatogenesis lt is a process of formation of sperms from immature germ cells It is a process of transformation of a non-motile spermatid into a motile
spermatozoan Number of cells increased as each spermatogonium produces four spermatids No change in number of cells as only one spermatid develops into a spermatozoa

Colostrum is the yellowish fluid produced from the mother's mammary glands during initial few days of location, after parturition.
Significance:
1. It has less lactose than milk and almost no fat, but it contains more proteins, vitamin A and minerals.
2. Colostrum is also rich in IgA antibodies.
3. This helps to protect the infant's digestive tract against bacterial infection.
4. Breast milk is the ideal food for infants as it contains all the constituents in suitable concentration and is easily digestable.
5. It is fully sufficient till about 6 months of age and all infants must be breast fed by the mother to ensure the growth of a healthy baby.

1. Polyspermy: An egg that has been fertilized by more than one sperm
2. When a sperm comes in contact with the zona pellucida layer of the ovum, it induces changes in the membrane of the ovum to block the entry of additional sperms.
3. The prevention of polyspermy ensures that only one sperm can fertilize a single ovum.