Urinary System

A. Functions - regulates volume, composition, and pH of body fluids; excretes N and S wastes; controls red blood cell production; regulates blood pressure I. Organs - 2 kidneys, 2 URETERS, URINARY BLADDER, URETHRA. II. The kidney B. Anatomy 1. Connected to renal (means kidney) arteries and veins.

2. Comprised of functional groups called NEPHRONS. Nephron

a. Nephrons filter fluid and produce urine. Glomerular filtration Glomerular filtration + Tubular Secretion - Tubular reabsorption - Tubular reabsorption_________________________ = Urinary Excretion = Urinary Excretion In other words: The amount of urine is equal to the amount of liquid the nephrons filter + the amount of substances the tubes secrete into the urine - the amount of liquid the tubes reabsorb from the urine. Toxins removed from body and secreted into urine Water is reabsorbed

Proximal Convoluted Tubule

Glomerulus Filters blood

Proximal Convoluted Tubule

Afferent Arteriole Efferent Arteriole Incoming large blood vessel. Forces high pressure blood into small tube. Causes filtration. Outgoing small blood vessel. Afferent Arteriole Efferent Arteriole

Proximal Convoluted Tubule

Distal Convoluted Tubule Proximal Convoluted Tubule Beginning filtration tube End of tube (before urine gets collected)

Proximal Convoluted Tubule

Loop of Henle Concentrates urine

Proximal Convoluted Tubule

Ascending Limb Descending Limb Moves down Moves up

Proximal Convoluted Tubule

Collecting duct Multiple distal convoluted tubules join up with one collecting duct

III. How filtration/urine concentration works A. Proximal convoluted tubule does selective reabsorption - nutrients reabsorbed by the body (active transport) and wastes left behind. B. Loop of Henle - conserves water and concentrates urine.

Loop of Henle Water diffuses out of the descending limb because of the salty concentration inside kidney Only water permeable, not salt permeable Descending limb Ascending limb H2Osalt salty Doesn’t require energy Salt actively pumped out to make concentration gradient Only salt, not water, permeable

C. Collecting duct - passes through salty area. Its permeability is controlled by hormones. Sometimes it is water permeable, other times it is not. IV. Hormones A. Antidiuretic hormone - Activated if blood becomes too salty. 1. Makes collecting duct water permeable and concentrates urine.

B. Aldosterone - Made by kidney when blood pressure falls. Causes body to retain sodium and water and excrete potassium. C. Atrial Natriuretic Hormone - secreted by atria of the heart when pressure is too high. It decreases water concentration in the blood.

IV. Onward and outward A. Urine moves through peristalsis from the kidneys to the bladder through a long tube called a ureter. B. In the bladder, a sphincter prevents emptying. 1. Filling of the bladder stimulates the urination urge by signaling the stretch receptors. 2. The external urethral sphincter relaxes (it is under voluntary control).

C. Urine exits the body through the urethra (about 2.5 cm long in females and 19.5 cm long in males. In males, the urethra is also a channel for semen)