Excretory System

• The excretory system removes metabolic wastes from blood.
• The excretory system maintains chemical homeostasis in the blood and tissues of the body.
• Metabolic wastes are chemicals that are made by cells during their reactions.
• Some examples of metabolic waste are: carbon dioxide, salt, urea, and toxins.
• The excretory system also regulates the amount of water in blood which regulates blood pressure. It also regulate pH of the blood.
• Skin excretes sweat which is compose of water and salts.
• The lungs excrete carbon dioxide waste that is in blood.
• The liver excretes the breakdown products of drugs and toxic urea (from wastes made by cells).
• The kidneys filter urea from the blood, control water balance and released H+ into urine, removing H+ from blood.
• If dehydrated, the kidney can stop water filtration and less urine is formed.
• The kidneys are the major organ for processing the nitrogenous waste called urea which is made by the liver and is then secreted into the bloodstream.
• Urea is nitrogenous waste made by the liver and is toxic to cells.
• The entire blood volume (~5 liters) is filtered every 45 minutes.
• Kidneys form urine which contains mostly water, urea, and ions.
• The nephron is the filtering unit in the kidney and one kidney contains ~1 million of them.
• The actions of the nephron are filtration, reabsorption, and urine formation.
• Filtration takes place in the bowman's capsule and glomerulus.
• The bowman's capsule is a cup-like structure at the end of a nephron that fits over a cluster of capillaries called glomerulus that carry blood in from the body tissues.
• Filtrate is formed when the fluid part of blood is forced through the BC out of the capillaries.
• Filtrate is composed of water, urea, salt, and ions.
• Readsorption takes place in the tubules.
• As the filtrate passes through nephron tubules, cells adsorb some water, salt, glucose, and ions back into capillaries (not urea).
• Reabsorption happens for a variety of reason but the general concept is to restore blood concentration of excess water, salt, and ions that were first filtered.
• Urine formation takes place in the collecting ducts. Urine is the final product that enters the last portion of a nephron called the collecting duct.
• Urine contains mostly water and urea, plus a little remaining salt an some ions like Ca++ and H+.
• Hormones control how much of different materials are filtered and reabsorbed by the nephrons.
• Ex: Antidiuretic hormone (ADH) is released into the blood by the pituitary gland to regulate water volume.
• If a person is dehydrated, water volume in blood drops and blood pressure drops.
• Collecting duct cells are more permeable to water and it diffuses out of the duct and back into the blood instead of leaving with urine.
• ADH release decreases when not dehydrated.
• Maintenance of blood water homeostasis is an example of feedback regulation.
• Ureter is a tube that collects urine as it leaves each kidney to be stored in the bladder.
• The urinary bladder is a muscular organ that stores urine before release from the body.
• The urethra is a tube leading from the bladder for urine to exit the body.
• Kidney failure can occur mainly because of high blood pressure and diabetes but also physical injury or disease.
• Dialysis is a treatment used to filter a person's blood when their kidneys are failing or have failed.
• Dialysis treatments are usually preformed weekly, depending on the severity of the kidney damage.