The deficiency of vitamin A causes: MCQ with Answer and Explanation

Explanation:
The pineal gland is a small, pinecone-shaped gland located in the epithalamus, near the center of the brain. In humans, it is not a true eye, but it is photosensitive; it receives information about the light-dark cycle from the retina via the suprachiasmatic nucleus and the sympathetic nervous system, and uses this to regulate the secretion of melatonin, thus controlling circadian rhythms. In some lower vertebrates (like certain reptiles, amphibians, and fish), the pineal complex includes a parietal eye (or 'third eye'), a light-sensitive organ on the top of the head that can literally detect light and shadows, helping with camouflage and predator detection.

Explanation:
Oxytocin is a peptide hormone produced by the paraventricular nucleus of the hypothalamus and released by the posterior pituitary. In females, it has two major roles: 1) During childbirth, it stimulates powerful contractions of the uterine smooth muscle, facilitating labor and delivery (this is a positive feedback loop). 2) During lactation, it stimulates the contraction of myoepithelial cells surrounding the alveoli in the mammary glands, causing the ejection (let-down) of milk into the ducts in response to suckling. It does not produce milk; prolactin does that.

Explanation:
Approximately 97% of O₂ is transported bound to hemoglobin (as oxyhemoglobin), while only 3% is dissolved in plasma. Each hemoglobin molecule can bind four O₂ molecules cooperatively. CO₂ is mainly transported as bicarbonate (70%), carbaminohemoglobin (23%), and dissolved (7%). The affinity of hemoglobin for O₂ is influenced by pH, CO₂, and temperature (Bohr effect).