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. Anatomy1. Connected to renal (means kidney) arteries and veins.

2. Comprised of functional groups called NEPHRONS.

NephronNephron

a. Nephrons filter fluid and produce urine.

Glomerular filtrationGlomerular filtration

+ Tubular Secretion+ 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 Toxins removed from body and secreted into body and secreted into

urineurine

Water is reabsorbedWater is reabsorbed

Proximal Convoluted Tubule

Proximal Convoluted TubuleGlomerulus

Filters blood

Proximal Convoluted Tubule

Proximal Convoluted Tubule

Afferent ArterioleEfferent Arteriole

Incoming large blood vessel. Forces high pressure blood into

small tube. Causes filtration.Outgoing small blood vessel.

Afferent ArterioleEfferent Arteriole

Proximal Convoluted Tubule

Proximal Convoluted TubuleDistal Convoluted Tubule

Proximal Convoluted Tubule

Beginning filtration tube

End of tube (before urine gets collected)

Proximal Convoluted Tubule

Proximal Convoluted Tubule

Loop of Henle

Concentrates urine

Proximal Convoluted Tubule

Proximal Convoluted Tubule

Ascending Limb

Descending LimbMoves down

Moves up

Proximal Convoluted Tubule

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 HenleWater diffuses out of the Water diffuses out of the descending limb because descending limb because

of the salty of the salty concentration inside concentration inside

kidney kidney

Only water permeable, Only water permeable, not salt permeablenot salt permeable

Descending limb

Ascending limb

H2OH2O saltsalt

salty

Doesn’t require energyDoesn’t require energy

Salt actively Salt actively pumped out pumped out

to make to make concentration concentration

gradientgradient

Only salt, not Only salt, not water, water,

permeablepermeable

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 outwardA. 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)