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 glandulartissue on each kidneythese 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

SecretionSecretion: 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

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

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.