NEET Practice Questions (MCQs) with Answers & Solutions

Menstruation is caused by the reduction of estrogen and progesterone, especially progesterone at the end of monthly ovarian cycle. The first effect is decreased stimulation of the endometrial cells by these two hormones followed rapidly by involution of the endometrium itself to : about 65% of its previous thickness.

(d) At the onset of the luteal phase, plasma gonadotropins decrease and plasma progesterone increases. A secondary rise in estrogens causes further gonadotropin suppression. Near the end of the luteal phase, progesterone and estrogen level falls, and FSH levels begin to rise to initiate the development of the next follicle.

(b) Hyaluronidase is a hydrolytic enzyme present in the acrosome of sperm (human testes). It lysis the glycosaminoglycans in the extracellular matrix holding the cell of the corona radiata together. As the coronal cells become more loosely associated, sperm cells can propel themselves inward, toward the zona pellucida by making a receptive cone or fertilization cone through the cytoplasm of the egg. Hyaluronidase may also be involved in breaking down the Zona Pellucida. Fertilizin is a chemical substance secreted from the cortical region of egg cytoplasm to attract the sperm towards the egg. Acrosin is released from the acrosome of a spermatozoa as a consequence of the acrosome reaction. It aids in the penetration of Zona Pellucida. Capacitation is the final stage in the maturation process of spermatozoa. This takes place inside the genital tract as the sperm penetrates the ovum.

(c) The activated spermatozoan on reaching the egg plasma membrane, undergoes a number of changes in its acrosomal region. All these changes are collectively described under acrosome reaction. Acrosome reaction is calcium-dependent involving massive uptake of calcium with an efflux of hydrogen generating high pH and osmotic pressure, producing negative surface charge, and
partial or total release of the acrosomal enzymes Calcium influx may activate phospholipase
resulting in accumulation of unsaturated fatty acids and fusiogenic lysophospholipids contributing to
acrosome reaction

(b) Grey crescent is the area just opposite to the site of entry of sperm into ovum. It marks the future dorsal side of the embryo. 

(a) During follicular phase (proliferative phase), follicle stimulating hormone (FSH) secreted by anterior lobe of the pituitary gland stimulates the ovarian follicle to secrete estrogens. Corpus luteum secretes large amount of progesterone in secretory phase. Both LH and FSH attain a peak level in the ovulatory phase.

(d) Humanchorionic Gonadotropin (hCG) is secreted by the placenta for maintaining corpus luteum. Its presence in urine indicates pregnancy.

(d) Atretic follicles are found in the ovary. The ovary of an adult female has about 120,000-160,000
follicles. Out of which, only one ovarian follicle matures every 28 days alternatively by the two ovaries. The rest of them degenerate at different times. These are known as atretic follicles and the degeneration process is called follicular atresia

(b) Oxytocin is released from the interior portion of pituitary gland, which induces parturition.

 During the 1970s, researcher discovered that umbilical cord blood could supply the same kinds of blood-forming (haematopoietic) stem cells as a bone marrow donor and so cord blood began to be collected and stored. Cord blood stem cells also have the potential to give rise to other cell types in the body.