The Urinary System & Excretion

Detoxification of the Blood

The Urinary System

Remember!

• The liver detoxifies the blood by removing poisonous substances and detoxifying them.

• the Deamination of amino acids produces ammonia, a poison, which is then converted to urea.

• Drug metabolism – break down of toxic substances like alcohol and medicinal products like tylenol,acetominaphen.

• These products are then removed by the kidneys in the production of urine.

Functions of the Urinary System

• The kidneys produce urine that is eliminated from the body.

• Four functions occur during this production to help maintain homeostasis.

1. Excretion of Metabolic Wastes

• The most common is nitrogenous wastes.• Amino acid breakdown ends in urea production.

NH3 + CO2

• Some ammonia, NH3 is excreted as ammonium, NH4.• Creatine phosphate is a high energy reserve of

phosphates for ATP production in muscles cells. Creatinine is the metabolic waste.

• Nucleotide breakdown results in uric acid waste.

2. Maintenance of Water-Salt Balance

• The kidneys help maintain blood pressure at its set point or homeostasis. 120/80 mmHg

• Blood volume is closely linked to salt content!• Salts such as NaCl, have the ability to cause osmosis. • The more salts in the blood, the greater the blood volume,

the greater the blood pressure.• Other ion maintenance in the blood such as K+, HCO3

-, & Ca2+.

3. Maintenance of Acid-Base Balance

• Blood pH remains between the body’s set point of 7.38 and 7.4.

• If blood pH drops, becomes acidic, H+ are secreted,(excreted) and HCO3

- are reabsorbed.• If blood pH rises, the opposite occurs.• H+ + NH3 NH4, if conditions are acidic. Which

substance acts as a buffer?• Urine has a pH of ~ 6 due the acidic nature of

foods eaten.

4. Secretion of Hormones

• The kidneys aid the endocrine system with hormone production and secretion.

• Renin is produced by the juxtaglomerular apparatus and released in response to low blood pressure.

• This leads to the release of aldosterone from the adrenal cortex which promotes the reabsorption of Na+.

• Kidneys also secrete erythropoietin in response to the low oxygen carrying capacity of the blood and rbc production is increased.

• Kidneys help activate vitamin D, a hormone-like substance to promote Ca2+ absorption from the digestive tract.