Renal Physiology – General Concepts

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Kidneys perform following categories of functions:

  • Homeostasis
  • Urine Formation
  • Hormone Secretion


Kidney play a critical role to maintain healthy serum, interstitial, and intracellular  environments. Here are the some of the homeostatic functions that kidneys perform:

  • Acid-base balances (Davenport diagram is a must for medical students to understand.)
  • Serum electrolyte concentrations in varying external and internal situations. (Knowing kidney’s role to maintain Na+, K+, Ca++, H+, PO4, NH3, etc. is critical.)
  • Total body fluid and its distribution in various compartments is influenced by the kidneys.
  • Body fluid osmolarity

Urine Formation

Kidney has a number of functions that help with the homeostasis. One result of this is to excrete extra water, electrolytes, and waste products.

Following renal Processes are used for Homeostasis

  • Filtration. Passive movement of the water and electrolytes from the serum into the nephron (glomerular capsule).
  • Reabsorption. Active and passive movement of the filtrate back into the interstitium and blood compartment.
  • Secretion. Active movement of the substances from the serum to the nephron at any point other than the glomerulus.
  • Excretion. discarding the waste products to the bladder and eventually out of the body.

Hormone Secretion

Kidneys make and release following hormones in the blood:

  • Vitamin D conversion to its active form.
  • Renin secretion helps with blood pressure and blood volume.
  • Erythropoietin helps with the RBC concentration (hematocrit).

Hormones Acting on the Kidneys

Following hormones influence kidney’s function:

  • Antidiuretic Hormone (ADH).
  • Atrial Natriuretic Hormone (ANH).
  • Renin-Angiotensin-Aldosterone System.


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