Human Excretion and Kidney Physiology

Both options 2 and 3 are correct.

Urea cycle disorders lead to buildup of ammonia. The mainstay of current treatment is to use substances such as sodium benzoate and sodium phenylacetate to complex with ammonia, forming water soluble compounds that can be excreted in the urine.

Commonly, the dose of a drug is reduced when there is renal impairment to prevent the accumulation of the drug. It is also common to reduce the frequency of the doses.

ANP stands for atrial natriuretic peptide. It is made in the atrial cells in the heart and in some cells in the kidney. It can increase sodium excretion by inhibiting collecting duct sodium reabsorption. However, it probably does not play an important role in the normal regulation of sodium excretion.

In particular, there can be a failure of reabsorption of sodium in the proximal tubule. This results in excess sodium reaching the collecting ducts where some of it is exchanged for potassium, causing excess potassium loss and a low plasma potassium level. Hence, there is a loss of bicarbonate .

Body osmolality is sensed in the hypothalamus by osmoreceptors which influence thirst (water intake) and ADH (anti-diuretic hormone or vasopressin) secretion (which influences water output by the kidneys). 

ADH (Anti diuretic hormone) has this function which gives it its name.

The cup-shaped part of nephron which receives the glomerular filtrate is called Bowman’s capsule.

The blood in kidneys is filtered by nephrons, the functional units of the kidney. Each nephron begins in a renal corpuscle, which is composed of a glomerulus enclosed in a Bowman's capsule.

Several collecting ducts unite to form larger ducts that empty urine into a calyx at the tip of the renal pyramid. 

The outlet of urine from the body is through urethra. Urine produced in the kidneys passes through the ureters into the urinary bladder where it is released through the urethra. Ureters are the long tubes, which connect the kidneys with the urinary bladder. Urinary bladder is muscular sac where urine is stored until the pressure of the expanded bladder leads to urge to pass it out through the urethra. Anus is the excretory opening at the end of the digestive tract, it controls the excretion of faeces produced during digestion.

Nitrogenous waste substances such as ammonia, urea and uric acid are produced during protein metabolism according to the species. Amino acids are the breakdown products of proteins in the body. Ammonia is the most toxic and requires large amount of water for its excretion. It is excreted as waste product in protozoans, e.g. amoeba, paramecium, sponges, hydra, liver fluke, earthworm, etc. Uric acid is also excreted as waste product by the most insects (e.g. cockroach), land snails (e.g. helix), land reptiles (e.g. lizards), snakes and birds. 

Nephron is the basic functional unit of kidneys. Each human kidney possesses about one million structural and functional units called nephrons.

Along with the removal of waste, kidneys also maintain constant blood pressure. One of the major roles of the kidneys is maintaining the proper levels of electrolytes (such as sodium and potassium) in the body. The amount of electrolytes in the body influences the amount of fluid in the body. When electrolyte levels are high, the body retains more water, which in turn increases the volume of the blood. More blood volume results in higher blood pressure. Thus, the kidneys maintain blood pressure by indirectly controlling the amount of blood in the body. 

Kidneys are multicellular organs. They filter approximately 1100-1200 ml of blood per minute. The amount of filtrate formed by the kidney per minute is called Glomerular filtrate rate (GFR). GFR, in healthy individual, is approximately 125 ml per minute, i.e. 180 litres per day. Thus, kidney needs to have million nephrons.