Human Biology and Health

Kidneys filter blood and remove metabolic wastes like urea, creatinine, and excess salts through urine formation. While kidneys also help regulate blood pressure via the renin-angiotensin system, waste removal is their primary function. Body temperature is regulated by the hypothalamus and sweat glands in the skin, not kidneys.

Hemoglobin is a protein in red blood cells that binds oxygen in the lungs and transports it to body tissues. It gives blood its red color and is essential for aerobic respiration. Hemoglobin does not destroy bacteria (that's white blood cells), prevent anemia (it actually causes anemia when deficient), or directly utilize energy.

Lachrymal glands, also called lacrimal glands, are located above each eye and secrete tears to lubricate and protect the eyes. The pituitary is the master gland regulating hormones, thyroid regulates metabolism, and pancreas produces digestive enzymes and insulin - none produce tears.

The liver is the largest internal gland and largest internal organ in the human body, weighing about 1.5 kg. It performs vital functions including detoxification, protein synthesis, and bile production. The thyroid and pancreas are much smaller endocrine glands.

The skin is the largest organ in the human body, covering about 2 square meters in adults and comprising about 16% of body weight. It provides protection, temperature regulation, and sensation. Liver, heart, and kidneys are internal organs but are much smaller than skin.

Blood group O individuals lack A and B antigens on their red blood cells, making their blood compatible with all other blood types during transfusion. O negative (lacking Rh factor) is the true universal donor. AB has both antigens, A has only A antigen, B has only B antigen.

The pituitary gland is called the master gland because it secretes hormones that control other endocrine glands, including thyroid, adrenal glands, and reproductive glands. The pancreas regulates blood sugar, thyroid regulates metabolism, and spleen is part of the immune system - none control other glands.

Newborn infants have approximately 300 bones, many of which fuse together during growth through ossification. Adults typically have 206 bones. The reduction occurs as skull bones, spine vertebrae, and pelvic bones merge. Options 206, 230, and 280 are all incorrect for newborns.

Vitamin A (retinol) is essential for healthy vision, particularly night vision, and maintaining the cornea. Deficiency causes night blindness and eventually total blindness. Vitamin B aids metabolism, Vitamin C supports immunity, and Vitamin D regulates calcium absorption - none primarily support vision.

The normal resting heart rate for adults is 60-100 beats per minute, with 72 bpm often cited as the average. A rate of 70 bpm falls within this healthy range. Rates of 50 bpm (borderline bradycardia), 80 bpm (normal but high), and 100 bpm (tachycardia threshold) are less representative of the average.

Blood group AB individuals have both A and B antigens on their red blood cells and lack anti-A and anti-B antibodies in their plasma. This allows them to receive blood from any group (A, B, AB, or O) without antibody reaction, making them universal recipients. Group O individuals are universal donors, not recipients.

Malaria is caused by Plasmodium parasites that infect and destroy red blood cells. The spleen works overtime to filter out these infected cells, leading to splenomegaly (enlarged spleen), which is a classic diagnostic feature of malaria.

Smallpox is caused by the Variola virus, making it a viral disease. Tuberculosis is caused by bacteria (Mycobacterium), malaria by protozoa (Plasmodium), and cholera by bacteria (Vibrio cholerae).

The medulla oblongata is the lowest part of the brainstem, connecting the brain to the spinal cord. It controls vital autonomic functions like breathing, heart rate, and blood pressure.

Myopia (nearsightedness) occurs when the eyeball is too long or the cornea is too curved, causing light to focus in front of the retina. This vision defect specifically affects the eyes.

Leukemia is a cancer of blood-forming tissues, primarily the bone marrow and blood cells. It involves the overproduction of abnormal white blood cells that crowd out healthy blood cells.

Myopia (nearsightedness) is corrected using concave lenses, which diverge light rays before they enter the eye. This pushes the focal point back onto the retina. Convex lenses are used for hyperopia (farsightedness).

Trachoma is a bacterial eye infection caused by Chlamydia trachomatis. It is a leading cause of infectious blindness worldwide, affecting the conjunctiva and eyelids.

Typhoid (Salmonella typhi) and cholera (Vibrio cholerae) are both transmitted through contaminated water and food. They are classic examples of water-borne diseases, not airborne infections.