Urinary System

Overall Functions

• Excretion – remove nitrogenous wastes from blood

• Osmoregulation – maintain proper balance of ions

• Volume regulation – maintain proper balance of water

• Regulation of pH• Detoxify superoxides, free radicals and some

types of drugs.

Why are nitrogenous wastes a problem?

• Ammonia is a moderately strong base (elevates blood pH).

• Urea is a weaker base made from ammonia and carbon dioxide in the liver – less toxic than ammonia (NH3)

• Uric Acid is a waste produced from the metabolism of nucleic acids

• Creatinine is a waste product from creatine metabolism.

The kidneys only comprise about 0.5% of the total body weight, butthey receive 1,200 mL of bloodper minute; about 20% of theTotal cardiac output.

Kidneys are constantly cleaning, balancing ions and water, and adjusting thepH of the blood.

AortaInferior Vena Cava

Renal ArteryRenal Vein

Kidney

Ureter

Urinary Bladder

Urethra

Tubule system(produces urine)

Calyx(funnel-like Structure thatCollects urine fromTubules)

Pelvis of theKidney

ureter

Cortex

Medulla

The Nephron is the Functional Unit of the Kidney

GlomerulusAfferentArteriole

EfferentArteriole

Bowman’s Capsule

Proximal Convoluted tubule

Loop of Henle

DistalConvolutedTubule

Collecting Duct

Urine is carried to Calyx,Pelvis and then the Ureter

Functions of the Nephron1. Filtration

The glomerulus is made of “fenestratedcapillaries” that are unusually permeable.

All of the following substances can easily filter out of the glomerulus and into Bowman’s capsule.

waterglucose (and other sugars)amino acidssmall organic moleculesammonia, urea, uric acidsalts, H+, HCO3

The only substances that are not usually filtered out are blood cells, proteins and larger organic molecules.

Notice that several important nutrients are filtered out of the blood duringthe filtration process.

Functions of the Nephron2. Reabsorption

Reabsorption is a process that 1. Utilizes active transport pumps 2. Occurs in the proximal and distal tubules 3. Reclaims nutrients that were lost during the filtration process. 4. Returns the nutrients to the blood

Examples of reabsorbed substances 1. glucose 2. amino acids 3. NaCl

NOTE: water is reabsorbed passively by osmosis.

Functions of the Nephron3. Tubular secretion

Secretion is a process that 1. Utilizes active transport pumps 2. Occurs in the proximal and distal tubules 3. Adds wastes from the blood that were not effectively filtered at the glomerulus. 4. Increases the concentration of wastes in the urine

Examples of secreted substances 1. Ammonia, H+ (smaller ionic) 2. histamine, creatinine (larger, organic) 3. penicillin

Glomerular Filtration RateThe two kidneys produce nearly 45 gallons (180 liters) of filtrate per day.

Glomerular Filtration Rate (GFR) depends almost completely on hydrostatic pressure in the glomerulus. * dilation or constriction of afferent and efferent arterioles. * overall blood pressure

What happens in exercise when blood pressure may increase up to 200 mm Hg or more?

During exercise, the sympathetic nervous system comes into play. Symp. Nerves stimulate the afferent arteriole and it constricts.

Regulation of Na+ ReabsorptionIf blood pressure is low for an extended period of time, the kidney reacts by releasing an enzyme called renin.

Renin is involved in a series of reactions that ultimately lead to the release of a hormone called Aldosterone from the adrenal gland.

Aldosterone is a steroid that acts on the distal convoluted tubule and increases the rate of NaCl reabsorption.

As the concentration of NaCl increases in the blood, water is reabsorbed at a faster rate (osmosis).

With more salt and water in the blood, the volume of blood goes up and blood pressure goes up.

Impact of diet and strenuous exercise . . . .

Regulation of Urine Volumecoordinate function of Loop of Henle and the Collecting Duct

Na+

Na+

Na+

Na+

Na+

Four Times SaltierThan the Blood