NCERT Solution Class 11th Biology Chapter – 19 Excretory Products and their Elimination Notes

NCERT Solution Class 11th Biology Chapter – 19 Excretory Products and their Elimination

NCERT Solution Class 11th Biology Chapter – 19 Excretory Products and their Elimination

?Chapter – 19?

✍Excretory Products and their Elimination✍

?Notes?

Many nitrogen-containing substances, ions, CO₂, water, etc, accumulate in the body by various means, most of which have to be eliminated to keep the body in homeostasis.

The nature of nitrogenous wastes formed and their excretion vary among animals, mainly depending on the habitat (availability of water).

Ammonia, urea, and uric acid are the major nitrogenous wastes excreted.

Protonephridia, nephridia, malpighian tubules, green glands, and the kidneys are the common excretory organs in animals. They not only eliminate nitrogenous wastes but also help in the maintenance of the ionic and acid-base balance of body fluids.

In humans, the excretory system consists of one pair of kidneys, a pair of ureters, a urinary bladder, and a urethra. Each kidney has over a million tubular structures called nephrons.

The nephron is the functional unit of the kidney and has two portions glomerulus and renal tubule.

The glomerulus is a tuft of capillaries formed from afferent arterioles, fine branches of the renal artery.

The renal tubule starts with a double-walled Bowman’s capsule and is further differentiated into a proximal convoluted tubule (PCT), Henle’s loop (HL), and distal convoluted tubule (DCT).

The DCTs of many nephrons join to a common collecting duct, many of which ultimately open into the renal pelvis through the medullary pyramids.

The Bowman’s capsule encloses the glomerulus to form Malpighian or renal corpuscle.

Urine formation involves three main processes, i.e, filtration, reabsorption, and secretion.

Filtration is a non-selective process performed by the glomerulus using the glomerular capillary blood pressure.

About 1200ml of blood is filtered by the glomerulus per minute to form 125ml of filtrate in the Bowman’s capsule per minute (GFR).

JGA, a specialized portion of the nephrons plays a significant role in the regulation of GFR. Nearly 99 percent reabsorption of the filtrate takes place through different parts of the nephrons.

PCT is the major site of reabsorption and selective secretion. HI. primarily helps to maintain osmolar gradient (300m Osm/ 1 – 1200m Osm/1) within the kidney interstitium.

DCT and collecting duct allow extensive reabsorption of water and certain electrolytes, which help in osmoregulation: FT, K^+, and NH could be secreted into the filtrate by the tubules to maintain the ionic balance and pH of body fluids.

A counter current mechanism operates between the two limbs of the loop of Henle and those of the vasa recta (capillary parallel to Henle’s loop). The filtrate gets concentrated as it moves down the descending limb but is diluted by the ascending limb.

Electrolytes and urea are retained in the interstitium by this arrangement.

DCT and collecting duct concentrate the filtrate about four times i.e, from 300 mOsmoiL^-1 to 1200 mO smolL^-1, an excellent mechanism of conservation of water.

Urine is stored in the urinary bladder till a voluntary signal from CNS carries out its release through the urethra i.e. micturition.

Skin, lungs, and liver also assist in excretion.

Ureotelic – Mammals, many terrestrial amphibians, and marine fishes mainly excrete urea and are called ureotelic animals.

Uricotelic – Reptiles, birds, land snails, and insects excrete nitrog¬enous waste as uric acid in the form of a pellet or paste with a minimum loss of water and are called uricotelic animals.

Kidney – In most invertebrates, these structures are simple tubular forms whereas vertebrates have complex tubular organs called kidneys.

Renal pelvis – Inner to the hilum is a broad funnel-shaped space called the renal pelvis.

Calyces – The renal pelvis with projections called calyces.

Columns of Bertini – The cortex extends in between the medullary pyramids as a renal column. called columns of Bertini.

Nephrons – Each kidney has nearly one million complex tubular structures called nephrons, which are the functional units.

Distal convoluted tubule – The ascending limb continues as another highly coiled tubular region called the distal convoluted tubule.

Collecting duct – The DCTs of many nephrons open into a straight tube called a collecting duct.

Pertitubular capillaries – The efferent arteriole emerging from the glomerulus forms a fine capillary network around the renal tubule called the peritubular capillaries.

Glomerular Filtration – The first step in urine formation is the filtration of blood, which is carried out by the glomerulus and is called glomerular filtration.

Reabsorption – A comparison of the volume of the filtrate formed per day (180 liters/day) with that of the urine released (1.5 liters), suggests that nearly 99 percent of the filtrate has to be reabsorbed by the renal tubules. This process is called reabsorption.

Micturition reflex – The process of release of urine is called micturition and the neural mechanisms causing it is called the micturition reflex.

Uremia – Malfunctioning of kidneys can lead to accumulation of urea in blood, a condition called uremia, which is highly harmful and may lead to kidney failure.

Hemodialysis – In such patients, urea can be removed by a process called hemodialysis.