Revision: Human Anatomy and Physiology >> The Excretory System Biology (English Medium) ICSE Class 10 CISCE

The kidney while removing wastes like urea from the blood also regulates its composition, i.e., the percentage of water and salts. This function is called osmoregulation.

Micturition is the process of expelling urine out of the body through the urethra by opening the sphincter muscles and passing urine, involving the relaxation of the sphincter muscles between the urinary bladder and urethra. 

Excretion is the process that biological organisms use to expel or eliminate the waste products produced by their metabolism.

Organs which are concerned with the formation, storage and elimination of urine constitute the 'excretory system'.

The process of removal of chemical wastes (mainly nitrogenous wastes) from the body is known as 'excretion' (ex: out, crete: flow).

or

Excretion is the process of removal of harmful and unwanted nitrogenous waste products from the body.

The Malpighian capsule is the combined structure of the Bowman's capsule and glomerulus, forming the filtration unit of the nephron.

The apex of each pyramid in the medulla of the kidney that projects into the pelvis is called the papilla.

The kidney is composed of an enormous number of minute tubules called uriniferous tubules or nephrons or renal tubules or just kidney tubules. These are the structural and functional units of the kidney. 

Bowman's capsule is a thin-walled, cup-shaped structure in the nephron that surrounds the glomerulus and collects the filtrate from the blood.

The glomerulus is a knot-like network of blood capillaries located inside the Bowman's capsule, where blood filtration occurs.

The artificial process which cleans and filters the blood in a person where one or both the kidney may stop working properly is called dialysis.

Inside the kidney, there are millions of microscopic tubes called renal tubules or nephrons. It is the structural and functional unit of the kidney.

Glomerular filtration rate is the amount of glomerular filtrate formed in all the nephrons of both kidneys per minute. In a healthy individual, it is about 125 ml/minute.

The blood flows through the glomerulus under great pressure which causes the liquid part of the blood to filter out from the glomerulus into the renal tubule. This filtration under high force is called Ultrafiltration.

Ultrafiltration is the process in which blood is filtered under high pressure in the glomerulus, allowing water and small solutes to pass into the Bowman’s capsule.

Glomerular filtrate is the fluid formed after ultrafiltration that enters the renal tubule and contains water, urea, salts, glucose, and other small molecules.

Selective absorption is the process by which only useful substances like glucose, some salts, and water are absorbed from the renal tubule back into the blood, without disturbing its normal concentration.

Tubular secretion is the active transfer of certain substances, such as ions and drugs, from the blood into the renal tubule during urine formation.

Micturition is the process by which urine is expelled from the urinary bladder through the urethra by relaxation of sphincter muscles under nervous control.

The filtrate left after reabsorption and tubular secretion is called urine.

The function of the kidney that involves regulating the composition of blood, including the percentage of water and salts, while removing wastes like urea, is called osmoregulation.

An artificial kidney is a dialysis machine that removes urea and excess salts from the blood when both kidneys fail, and returns the purified blood back into the body.

Dialysis is a medical process in which nitrogenous wastes and toxic substances are removed from the blood using an artificial machine when the kidneys fail to function properly.

1. Kidneys are the main excretory organs that remove urea and other nitrogenous wastes from the blood in the form of urine.
2. Skin eliminates small amounts of urea, salts, and water through sweat, mainly for body cooling.
3. Lungs excrete carbon dioxide through exhaled air, playing a key role in gaseous waste removal.
4. Liver helps in detoxification by converting ammonia to urea and breaking down toxins like alcohol and drugs.

1. Humans have two bean-shaped kidneys, located on either side of the backbone and protected by the last two ribs.
2. The right kidney is slightly lower than the left due to the position of the liver.
3. Each kidney has a hilum where the ureter, renal artery, and renal vein are connected.
4. Internally, the kidney has an outer cortex and an inner medulla made up of conical structures called renal pyramids.
5. The kidney contains numerous nephrons (uriniferous tubules), which are the structural and functional units responsible for urine formation.

1. Each kidney contains about 2 million uriniferous tubules, each 4–5 cm long, with a total length of over 60 km aiding reabsorption.
2. The Malpighian capsule is formed by Bowman’s capsule and glomerulus, where filtration begins.
3. Proximal convoluted tubule (PCT) in the cortex is the first site of reabsorption; Loop of Henle extends into medulla and helps in water conservation.
4. Distal convoluted tubule (DCT) opens into the collecting duct, which transports urine to the pelvis.
5. Blood flows through the kidneys about 350 times a day, filtering approximately 160 litres of fluid daily, most of which is reabsorbed.
6. The kidneys produce around 1.2 litres of urine per day, and their blood supply involves afferent and efferent arterioles along with capillary networks.

1. Kidneys help maintain the balance of water and salts in the blood, a process known as osmoregulation.
2. In summer, more water is lost through sweat, so urine becomes thicker and less frequent due to increased water reabsorption.
3. In winter, water loss through sweat is less, so more urine is passed, and it is more diluted.
4. In cholera, severe water loss through vomiting and diarrhoea reduces water absorption into the blood.
5. Kidneys reabsorb almost all available water, but urea may also accumulate, leading to uremia (urea poisoning).
6. Immediate treatment includes oral rehydration solution (ORS) or glucose-saline drips to restore fluid balance.