Human Urinary System/Excretory System MAINTAINS HOMEOSTASIS…. Important for eliminating metabolic waste (waste produced from metabolism) Maintains the appropriate water-salt balance in the blood Maintains blood pressure Maintains Acid-base balance of blood Secretes hormones

Organs of the Urinary System Kidneys – 2 Ureters – 2 Urinary bladder -1 Urethra – 1 Lump of glandular tissue on each kidney these are the adrenal glands.

Kidneys Main organs of the Urinary System Bean shaped/reddish brown and fist sized Covered by a tough capsule of connective tissue – called the renal capsule Renal arteries bring blood to the kidneys Renal veins carry blood away from the kidneys Anytime you see the word renal – think kidneys

Ureters Extend from kidneys to bladder Peristalsis of ureters cause urine to enter the bladder

UrinaryBladder Recieves urine from the ureters Stores urine until it is expelled from the body Urine enters the bladder in spurts – 1-5 spurts per minute.

Urethra Small tube that extends from the bladder to an external opening When the urinary bladder fills to about 250 ml of urine, stretch receptors and nerve impulses cause the urinary bladder to contract, sphincters to relax -and you pee.

Anatomy of the Kidney Cortex- outer layer Medulla – middle that consists of tissue masses Pelvis – central space that is continuous with the ureter Each kidney is composed of over one million nephrons…

Nephrons (kidney tubules) Each kidney is composed of over one million microscopic nephrons Long, coiled tube with one cuplike end that fits over a mass of capillaries, the other end opens into a duct that collects urine. Cup of nephron – Glomerulus capsule or Bowman’s capsule Ball of capillaries within the cup - Glomerulus

3 Functions of the nephron Filtration Reabsorbtion Secretion

Filtration Filtration: fluid portion of the blood is forced into the glomerular capsule (filtrate) Happens in the glomerulus capsule Water, salts, nutrients (glucose, amino acids, small proteins), nitrogenous waste (urea) Blood cells and large blood proteins are NOT filtered

Reabsorption Reabsorption –absorbing again (into blood) Cells of tubules reabsorb substances needed by the body from the filtrate. happens in the proximal (close to the capsule) kidney tubules of nephron Nutrients (glucose, amino acids) and salt molecules

Secretion Secretion: Process of secreting a substance from the blood into the kidney tubules Happens between the nephron capillaries and the distal (far away from capsule) kidney tubules of the nephron (countercurrent exchange) Anything that wasn’t filtered at the glomerulus capsule or anything that was reabsorbed that shouldn’t have been H+ ions, K+ ions, creatinine and drugs

2. Substances that have undergone secretion So Urine Contains: 1. Substances that have undergone filtration but have not been reabsorbed 2. Substances that have undergone secretion Urea comes from the breakdown of amino acids.

Urea: CH4N2O is the primary Nitrogenous end product of metabolism. Amino acids broken down in the liver causing the liver to release ammonia- toxic to cells. The liver combines the ammonia with carbon dioxide to make urea – not toxic to cells and can be released in urine. Creatinine: C4H9N3O2 High energy phosphate reserve molecule in muscles Uric Acid: C5H4N4O3 From the breakdown of nucleic acids

More Kidney Functions Adrenal glands secrete the hormone Aldosterone Aldosterone regulates excretion of sodium and potassium When K+ levels are too high in the blood, aldosterone is released into the blood, stimulating the secretion of K+ ions from the blood into the tubule near the collecting duct lowering the aldosterone levels – feedback mechanism More Kidney Functions

Aldosterone Increases reabsorption of ions and water in the kidneys -- increasing blood volume… increasing blood pressure.

ADH Dehydrated – brain secretes ADH (anti-diuretic hormone) so the cell membranes of the collecting ducts become more permeable to water. Water passes from the duct to the bloodstream and water volume in the blood is restored (higher blood pressure)

More Kidney functions Removes excess salt from body – in small concentrations When humans drink high salt solutions, the body loses water b/c while trying to eliminate the excess salt, the body excretes more water than taken in.