3.Human Physiology
3.4 Excretion
Excretion
Dr V Malathi
Theexcretory systemremoves waste products and excess water from the body and helps to maintain homeostasis.
Excretion
The process of eliminating metabolic wastes and toxins from the body is called excretion.
Excretion maintains the body’s internal environment and prevents damage from toxic substances.
Some of the specific waste products that must be excreted from the body include
- carbon dioxide produced from cellular respiration,
- ammonia and urea produced from protein catabolism, and
- uric acid produced from nucleic acid catabolism.
Excretory System Organs
- Kidneys: The primary organs of the excretory system are the kidneys which are a pair of bean-shaped structures that are located just below the liver in the body cavity. They filter blood to remove urea, excess salts, and water, forming urine. There are more than a million tiny units called nephrons in each kidneys. The nephrons functions to filter blood containing the metabolic wastes from cells. All the blood in the human body is filtered about 60 times a day by the kidneys. The functions of the nephrons are : removal of wastes, concentrate them, and form urine which is collected in the bladder.
The three regions of the kidney are
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- Outer cortex: contains the nephrons—the functional unit of the kidney
- Middle medulla
- renal pelvis : collects the urine and leads to the ureter on the outside of the kidney.
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The human excretory system” by Charles Molnar and Jane Gair is licensed under CC BY 4.0
- Ureters: Tubes that carry urine from the kidneys to the bladder.
- Bladder: Stores urine until it is excreted.
- Urethra: The duct through which urine is expelled from the body.
- Liver: The liver performs a variety of important tasks, such as producing bile for fat digestion, manufacturing a large number of proteins and other molecules, storing glycogen and other materials, and secreting endocrine hormones. The liver is a vital organ for excretion in addition to doing all of these other duties. Toxins are among the numerous chemicals in the blood that the liver breaks down. For instance, the liver converts ammonia, a toxic byproduct of protein breakdown, into urea, which the kidneys remove from the blood and eliminate as urine. The protein bilirubin, which is produced when red blood cells are broken down as a result of hemoglobin catabolism, is also excreted by the liver in its bile. After passing through the small intestine, the big intestine eliminates the bile as feces.
- Skin: The skin which is a part of the integumentary system excretes sweat , produced by the sweat glands in the dermis . Sweat contains water, salts, and small amounts of urea. Though sweat functions mainly to cool the body and maintain temperature, homeostasis, it also participates in excretion by eliminating the waste
- Lungs: Lungs are in charge of eliminating gaseous waste from the body. Carbon dioxide, a waste product of cellular respiration in all body cells