Functions of the kidneys

Functions of the kidneys (LeMone)

1. water & electrolyte regulation

a. Bowman's capsule (ultrafiltrate) process by which the fluid part of urine is formed,

comes from plasma & flows into proxima convoluted tubule

b. Moves to the proximal convoluted tubule where most of the H2O, Na⁺ , Ca⁺⁺ , Cl⁺ , &

HCO₃ that were filtered out in capsule are resorbed into blood

c. Finally their concentration is adjusted in the distal nephron by hormones:

aldosterone produced by adrenal cortex

ADH (vasopressin) produced by hypothalamus & stored in pituitary. ADH released

when pt is bleeding or not taking in enough fluid.

d. Body waste products such as hydrogen ions, phosphate, & drugs & their metabolites are

secreted from blood in proximal tubules

2. Maintenance of Acid-Base balance

a. The respiratory system & kidneys work together to maintain ratio

b. The lungs vary the CO₂ content of the blood & kidneys principally secrete or retain

bicarb or H⁺ ions in response to blood pH

c. These two substances must move in or out of the blood at precisely the right time for

pH to remain stable

d. The exchange is accomplished in the proximal tubes & collecting ducts of the nephron

3. Erythropoiesis - kidney plays crucial role in RBC production

a. decreased tissue oxygenation stimulates special cells (peritubular capillaries) in kidneys

to produce 90% of body's erythropoietin

b. Erythropoietin stimulates the bone marrow to produce pro-erythroblasts which develop

into erythrocytes

c. Hypoxia & anemia generally trigger an ↑in production of erythrocytes

d. If a person has anemia secondary to chronic kidney failure then pt can receive

erythropoeitin "Epigen" or "Procrit" transfusion which can improve hematocrit & ↓

need for blood transfusion

4. Calcium & phosphorus regulation one of kidney's important functions

a. The kidneys influence reciprocal calcium & phosphorus balance by converting inactive

form of Vit. D. that is absorbed from gut to active form.

b. Parathyroid gland secretion of parathyroid hormone regulated by this form

of Vit. D & [Ca₂]

c. Under the influence of the parathyroid hormone, Ca₂ resorption ↑, phosphate

resorption ↓

5. Blood pressure regulation the kidneys play an active role in the regulation of BP,

primarily by plasma volume & vascular tone

a. blood pressure is manipulated through the kidney's response to several mechanisms that

alter total blood volume in circulatory system

b. These mechanisms include ADH response, the renin-angiotensin system, and aldosterone

response.

c. ADH release by the pituitary causes the kidneys to reabsorb water which is going to↑ BP

d. The renin-angiotensis & aldosterone response also influence regulation of BP

e. Renin is a hormone released by the juxtaglomerular apparatus of the nephron, in

response to Na & K depletion, a drop in renal artery BP or sympathetic stimulation

1. Renin stimulates the conversion of angiontensinogen (from liver) to angiotensin I

2. Conversion of angiotensin I to angiotensin II by angiotensin-converting enzyme from

lungs & produces powerful vasoconstriction & release of aldosterone result in ↑BP

3. Aldosterone is released from the adrenal glands & acts on kidney to resorb Na & H₂O

increasing circulatory blood volume & pressure

f. Prostaglandin & bradykinin, hormones produced by the kidney & other tissues, help

elevate BP & increase renal blood flow

1. they are released in response to renal ischemia, presence of ADH, Angio. II, &

sympathetic stimulation, they provide an immediate mechanism for improving blood

flow

g. Angiotensin-Converting Enzyme inhibitors angiotensin converting enzyme is blocked