Functions of the Kidneys in Regulating Body Fluids

Study Notes

Kidney Functions

The kidneys maintain the stable internal environment necessary for cells to perform their activities by controlling the volume and electrolyte composition of body fluids.
The kidneys filter the plasma and remove substances from the filtrate at variable rates, depending on the body's needs.
The kidneys clear unwanted substances from the filtrate by excreting them in the urine and returning substances needed back to the blood.

Excretion of Waste Products

The kidneys are the primary means of eliminating waste products of metabolism, such as urea, creatinine, uric acid, and end products of hemoglobin breakdown.
The kidneys also eliminate toxins and foreign substances produced by the body or ingested, such as pesticides, drugs, and food additives.

Regulation of Body Fluids

The kidneys regulate water and electrolyte balances by matching excretion to intake precisely.
If intake exceeds excretion, the amount of the substance in the body will increase, and if intake is less than excretion, the amount will decrease.
The kidneys regulate body fluid osmolality and electrolyte concentrations.

Regulation of Other Functions

The kidneys regulate arterial pressure.
The kidneys regulate acid-base balance.
The kidneys secrete erythropoietin, which stimulates production of red blood cells by hematopoietic stem cells in the bone marrow.
The kidneys produce 1,25-dihydroxyvitamin D3 (calcitriol), the active form of vitamin D, essential for normal calcium deposition in bone and calcium reabsorption by the gastrointestinal tract.
The kidneys synthesize glucose from amino acids and other precursors during prolonged fasting, a process referred to as gluconeogenesis.

Kidney Structure and Location

The two kidneys lie on the posterior wall of the abdomen, outside the peritoneal cavity.
Each kidney weighs about 150 grams and is about the size of a clenched fist.
The medial side of each kidney contains an indented region called the hilum, which passes through the renal artery and vein, lymphatics, nerve supply, and ureter.
The kidney is surrounded by a tough fibrous capsule that protects its delicate inner structures.

Description

Explore the vital functions of the kidneys in maintaining the balance of body fluids and electrolytes. Learn how the kidneys control the volume and composition of body fluids by regulating intake and output. Dive into the significant role of kidneys in excreting waste materials and ensuring metabolic balance.