The Urinary System

The Urinary System

The Urinary System

The Excretory Organs Excretion: the process during which substances must pass through a membrane to leave the body Lungs: excrete carbon dioxide and water vapor in exhaled air Kidneys: excrete nitrogen waste, salts, water, and other substances in urine Skin: excretes water, salts, small amount of nitrogen wastes, and other substances in sweat

Structures of the Urinary System  Kidneys: 2 bean-shaped

kidneys the size of a clenched fist (one located behind the stomach and the other behind the liver) regulate the composition of blood (homeostasis)  Ureter: narrow-tube that leads from the kidneys to the bladder  Bladder: muscular sac that stores urine  Urethra: tube that forces urine out of the body when the bladder contracts

Function of the Kidneys Kidneys filter the blood: Kidneys eliminate nitrogenous compounds

(urea) from the breakdown of proteins  Liver removes ammonia from the blood and

converts it to urea

Excretion of water Excretion of toxins & drugs Adjustment of salt concentration

Nephrons Nephron is the filtering unit of a kidney Urineis made in the nephrons. Urine is a

liquid made of urea, water, and mineral salts

Filtration Filtration:

materials-- water, urea, glucose, vitamins, and salts--from the blood are forced out of the glomerulus—knot of capillaries and into the Bowman’s capsule In a healthy kidney,

the filtrate does not contain large

Reabsorption & Secretion  Reabsorption:

substances needed by the body are returned to the blood  Water returns to the

capillaries by osmosis  Glucose, minerals, such as sodium, potassium, and calcium are returned by active transport

 Secretion:  Wastes and toxic material pass from the blood into the filtrate

Formation of Urine The fluid that remains in the tubules is urine The urine from several renal tubules flows into a collecting duct

Elimination of Urine Urine from the collecting duct flows into the ureter Ureters lead from the kidneys to the urinary bladder, where it is stored until elimination Muscular contractions of the bladder force urine