Menstrual disorders include:
1. Dysmenorrhea refers to painful cramps during menstruation.
2. Premenstrual syndrome refers to physical and psychological symptoms occurring prior to menstruation.
3. Menorrhagia is heavy bleeding, including prolonged menstrual periods or excessive bleeding during a normal-length period.
4. Metrorrhagia is bleeding at irregular intervals, particularly between expected menstrual periods.
5. Amenorrhea is the absence of menstruation.
6. Oligomenorrhea refers to infrequent menstrual periods. Hypomenorrhea refers to light periods.

Human Ovum
a - Vitelline membrane
b - Nucleus
c - Zona Pellucida
d - Corona radiata

Relaxin  
(i) It is a hormone secreted by the placenta and also by the corpus luteum during pregnancy.
(ii) It promotes parturition by relaxing the pelvic joints and by dilation of cervical ligaments with continued powerful contractions.
Oxytocin:
(i) It causes the "Let-Down" reflex.
(ii) The actual ejection of milk from the alveoli of the mammary glands.
(iii) During lactation, oxytocin also stimulates the recently emptied uterus to contract, helping it to return to pre-pregnancy size..

(i) Human ovum is non-cleidoic, alecithal and microscopic in nature.
(ii) Its cytoplasm called ooplasm contains a large nucleus called the germinal vesicle.
(iii) The ovum is surrounded by three coverings namely an inner thin transparent vitelline membrane, middle thick zona pellucida and outer thick coat of follicular cells called corona radiata.
(iv) Between the vitelline membrane and zona pellucida is a narrow perivitelline space.

Semen or seminal fluid is a milky white fluid which contains sperms and the seminal plasma, which is secreted from the seminal vesicles, prostate glands and bulbo urethal glands or Cowper's gland.
The semen comprises of Fructose, ascorbic acid, zinc, cholesterol, protein, calcium, chlorine, blood group antigens, citric acid, DNA, magnesium, Vitamin B12, phosphorous, sodium, potassium, uric acid,lactic acid, nitrogen, and other nutrients for the sperms.

1. Testes are the primary male sex organs.
2. They are a pair of ovoid bodies lying in the scrotum.
3. The scrotum is a sac of skin that hangs outside the abdominal cavity.
4. Since viable sperms cannot be produced at normal body temperature, the scrotum is placed outside the abdominal cavity to provide a temperature 2-3°C lower than the normal internal body temperature.
5. Thus, the scrotum acts as a thermoregulator for spermatogenesis.

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.