Excretion and Human Excretory System

EXCRETION

      • Removal of harmful waste from the body is called excretion.
      • Many wastes are produced during Various metabolic activities.
      • These need to be removed in time because their accumulation in the body can be harmful and even lethal for an organism.

HUMAN EXCRETORY SYSTEM

      • The human excretory system is composed of a pair of kidneys. A tube; called ureter comes out where it is expelled out through urethra as and when required.

Kidney:

      • Kidney is a bean-shaped organ which lies near the vertebral column in the abdominal cavity.
      • The kidney is composed of many filtering units; called nephrons.

Nephron is called the functional unit of the kidney.

Nephron:

      • It is composed of a tangled mess of tubes and a filtering part; called glomerulus.
      • Glomerulus is a network of blood capillaries to which the renal artery is attached.
      • The artery which takes blood to the glomerulus is called afferent arteriole and the one receiving blood from the glomerulus is called efferent arteriole.
      • Glomerulus is enclosed in a capsule-like portion; called Bowman’s capsule.
      • The Bowman’s capsule extends into a fine tube which is highly coiled.

Tubes from various nephrons converge into collecting duct; which finally goes to the ureter.

Figure Human Excretory System

Filtration in Glomerulus:

      • Filtration happens because of very high pressure inside the glomerulus.
      • The lumen of efferent arterioles is smaller than that of afferent arterioles.
      • Due to this, the blood entering the glomerulus experiences very high pressure and due to this, the waste products are filtered out through the thin membrane of capillaries in the glomerulus.
      • The filtered blood is sent to the systemic circulation through efferent arterioles and the filtrate goes to the Bowman’s capsule.
      • That is how urine is formed inside the kidneys.
      • Reabsorption of water and some other filtrates takes place in the tubular part of the nephron.
      • This increases the concentration of urine.
      • The human urine is mainly composed of water and urea.

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