Railway Science (Biology – Excretory System)

The functions of the Kidney - produce urine every day, produce Renin hormone (regulates Blood Pressure), and help filter blood. The basic unit of the Kidney is the Nephrons.

Other substances reabsorbed are sodium, potassium, chloride, and bicarbonate. Amino acids help the body in building and repair muscle tissue. Protein helps to build muscle and fight infection.
Glucose is used in the treatment of hypoglycemia( low blood sugar). Nephron (functional unit and workhouse of the kidney) is responsible for blood filtration along with metabolite secretion and reabsorption.

Functional unit of Kidney - Nephron. Hormones produced by the kidney - Erythropoietin, Renin, Calcitriol. The functions of the Kidney - Remove waste products from the body, remove drugs from the body, balance the body's fluids, release hormones that regulate blood pressure, produce an active form of vitamin D that promotes strong, healthy bones, and controls the production of red blood cells.

Organs of excretion include the skin, liver, large intestine, lungs, and kidneys. Lungs are used in the process of gas exchange called respiration (or breathing). The Skin (the largest organ of the body) protects against germs, regulates body temperature, and enables touch (tactile) sensations.
The Small intestine is the site of complete digestion in humans and secretes intestinal juice. The Large intestine is used to absorb water and electrolytes from the undigested food and moves the waste matter toward the anus.

Transpiration - The loss of water in the form of vapor through pores present in the plant body. Diffusion is defined as the movement of individual molecules of a substance through a semipermeable barrier from an area of higher concentration to an area of lower concentration.
A storage organ - A part of a plant specifically modified for the storage of energy (generally in the form of carbohydrates) or water. Waste products in plants are oxygen, carbon dioxide, and water.

Kidneys - Bean-shaped organs that serve several essential regulatory roles in vertebrates. Besides removing urea and uric acid from the blood, the kidneys also help in maintaining the water and salt concentration in it. Nephrology (Study of Kidney). Calcium oxalate stones are the most common type of kidney stone.

Urine - 95% water , 2.5% urea and 2.5% other waste, yellowish in colour, slightly acidic. Ammonotelic - organisms generally excretes nitrogenous waste as soluble ammonia. Examples - Protozoans, fishes, larvae/tadpoles. Ureotelic - Organism generally excretes excess nitrogen as urea. Example - cartilaginous fish, human beings. Uricotelic - Excrete uric acid waste. Example - Lizards, snakes, birds.

The Glomerulus filters water and other substances from the bloodstream. Filtration membrane keeps blood cells and large proteins in the bloodstream. Reabsorption moves nutrients and water back into the bloodstream. Waste ions and hydrogen ions secreted from the blood complete the formation of urine.

Plants have no special organs for the removal of waste. The excretory products in plants are eliminated from the plant body by different mechanisms. The waste products of respiration and photosynthesis are used as raw materials for each other. Example - Oxygen gas produced as a by-product of photosynthesis is used up during respiration and carbon dioxide produced during respiration is used up during photosynthesis.

Animals excrete a variety of nitrogen waste products, but ammonia, urea and uric acid predominate. A major factor in determining the mode of nitrogen excretion is the availability of water in the environment.
Aquatic animals excrete mostly ammonia, whereas terrestrial animals excrete either urea or uric acid. Creatinine is a waste product made by the muscles as part of regular or everyday activity.