Name: Modes of Excretion
Uploaded: 2019-07-19
Duration: 3 min 20 s
Description: This video discusses three modes of excretion: Ammonotelism, Ureotelism, and Uricotelism. It stresses the form of nitrogenous wastes excreted in three modes of excretion and highlights the associated organisms.

Question

Describe the structure of the human excretory system with a suitable diagram. Add a note on the process of urine formation.

Accepted Answer

The human excretory system carries out the elimination of nitrogenous waste from the body in the form of urine.

Structure of the human excretory system:

In humans, the excretory system consists of a pair of kidneys, a pair of ureters, urinary bladder and urethra.

Kidneys are two bean-shaped organs lying at the back of the abdomen, one on either side of the vertebral column. Waste products from the blood and urine are removed by the kidney.

A nephron is the basic filtration unit of the kidney. It is a cluster of thin-walled blood capillaries.

The urine produced by filtering the blood is transported to the urinary bladder. This is done by a pair of ureters. Ureters are long muscular tubes.

The urinary bladder is a muscular bag-like structure that can hold urine. The urinary bladder is under the control of nerves. When the bladder is full, one gets the urge for urinating.

This urine is expelled out of the body through the urethra.

The mechanism of urine formation involves the following steps:

Glomerular Filtration: Glomerular filtration occurs in the glomerulus where blood is filtered. This process occurs across the three layers- epithelium of Bowman’s capsule, endothelium of glomerular blood vessels, and a membrane between these two layers. Blood is filtered in such a way that all the constituents of the plasma reach the Bowman’s capsule, except proteins. Therefore, this process is known as ultrafiltration.

Reabsorption: Around 99% of the filtrate obtained is reabsorbed by the renal tubules. This is achieved by active and passive transport.

Secretion: The next step in urine formation is tubular secretion. Here, tubular cells secrete substances like hydrogen ions, potassium ions, etc into the filtrate. By this process, the ionic, acid-base and the balance of other body fluids are maintained. The secreted ions combine with the filtrate and form urine. The urine passes out of the nephron tubule into a collecting duct.

Describe the structure of the human excretory system with a suitable diagram. Add a note on the process of urine formation.

Important Questions on Excretion and Osmoregulation

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