Kidneys: Structure and Functions

12 Questions

What is the main function of the kidney?

Maintaining electrolyte balance

Which part of the kidney divides it into lobes?

Renal impression

Where does filtration primarily occur within the kidney?

Nephrons

What happens when too much salt is absorbed from food by cells lining the small intestine?

Raises blood pressure

What separates water, salts, sugars, and other components from larger molecules in the kidney's filtration process?

Glomerulus

How are proteins and large molecules handled in the kidney's filtration process?

Return to general bloodstream via vasa recta

What can reduce blood pressure by lowering the rate of renin secretion?

Leakage of protein from damaged glomeruli

Which component of urine drainage comes after the collecting tubules?

Ureters

What controls the levels of potassium ions (K+) in the body?

Adjusting urine output

What hormone stimulates bone marrow to produce red blood cells?

Erythropoietin (EPO)

How do increased levels of renin affect blood pressure?

Increase blood pressure

Which electrolyte helps nerve impulses travel along nerves and muscles contract?

Potassium ions (K+)

Study Notes

Kidneys

The kidney is a bean-shaped organ located on either side of the vertebral column. It serves several functions, including filtration, regulation of blood pressure, excretion of waste products, maintaining electrolyte balance, and regulating red cell production.

Structure

Each kidney weighs about 150 grams and has an average length of 10 cm, width of 6 cm, and thickness of 2.5 cm. They normally lie horizontally against each other, one lying slightly higher than the other. Each kidney is usually divided into two lobes by a depression called the renal impression. This division is further split into smaller sections known as lobules, which contain numerous tubules where most of the filtration takes place.

Functions

Filtration

Filtration occurs through nephrons within the kidneys, which act like tiny filters. Blood enters the glomerulus, which separates water, salts, sugars, fatty acids, some amino acids, glycoproteins, vitamins, and hormones from larger molecules like proteins. These separated components flow out of the nephron through capillaries within the cortex of the kidney, while the proteins and large molecules return via the vasa recta back into the general bloodstream.

Regulation of Blood Pressure

When too much salt is absorbed from food by cells lining the small intestine, the excess sodium causes more fluid to enter blood vessels. As this increases the volume of plasma in the bloodstream, it also raises the blood pressure. Protein leaks from damaged glomeruli can reduce the rate of secretion of renin, thereby lowering blood pressure. Conversely, increased levels of renin increase blood pressure.

Excretion of Waste Products

Small molecules unsuitable for passage back into the bloodstream pass from the nephrons into the collecting tubules. Urine formed in these tubules drains into the ureters, urinary bladder, and eventually outside the body.

Maintaining Electrolyte Balance

Different parts of the nephron control whether various electrolytes get transported back into the bloodstream. For example, potassium ions (K+) are important because they help nerve impulses travel along nerves and muscles contract. Potassium level is controlled by adjustments in urine output. If urine doesn't seem to have enough K+, the kidney will decrease its rate of urine formation, causing less K+ to leave the body.

Regulating Red Cell Production

Erythropoietin (EPO), a hormone produced by special cells in the kidney, stimulates bone marrow to produce red blood cells. Since EPO can bind to receptors only when oxygen levels fall, the kidney plays a crucial role in detecting low oxygen levels in tissues and triggering appropriate responses.