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1. Kidneys are essential for regulating the volume and electrolytes in the body. They filter water and electrolytes from blood; returning some to the blood and excreting some in the urine. Kidneys regulate the following electrolytes: Sodium, Potassium, Phosphate, Calcium

1.1. Sodium - reabsorbed through active transport in the Proximal tubule.

1.1.1. An increased in sodium levels stimulates the release of Atrial Natriuretic Peptide (ANP) from the cardiac atria; thereby decreasing blood pressure

1.1.2. A decrease in sodium levels activates the Renin-Angiotensin-Aldosterone System (RAAS) and Antidiuretic Hormone (ADH) in the convoluted tubule resulting to increase in BP

1.2. Potassium - filtered in the glomerulus; mostly reabsorbed in the proximal tubule and loop of Henley

1.2.1. Potassium is managed by the aldosterone

1.3. Phosphate - reabsorbed in proximal tubule if low; excreted in the urine if high

1.3.1. Maintains plasma pH in the buffer system

1.4. Calcium - reabsorbed in the renal tubule

1.4.1. A decrease in Calcium levels stimulates the parathyroid glands causing release of parathyroid hormones (PTH) that release calcium from bones and increase calcium absorption in the intestine

2. Fluid and Electrolye Balance

3. Acid-Base Balance

3.1. Kidneys control acid base balance by bicarbonate reabsorption (HCO3-) and hydrogen ion (H+) excretion.

3.1.1. Occurs in the Proximal Convoluted Tubule (PCT), Distal Tubule (DT), and Collecting Ducts.

3.1.2. A fall in pH (<7.35), body becomes acidic causing kidneys to reabsorb HCO3- and excrete H+

3.1.3. An excess HCO3- is lost in the urine and excreted

4. Erythropoietin Production

4.1. Renal Erythropoietin Producing and Oxygen Sensitive (REPOS) Cells in the cortex are sensitive to the amount of O2 flowing in to the kidneys.

4.1.1. An increase in O2 demand stimulates REPOS cells to produce erythropoietin, a hormone that stimulates process of erythropoiesis in the bone marrow and thereby, producing more erythrocytes

5. Blood Pressure Control

5.1. Renin and Secretion of Renin

5.1.1. Renin catalyzes the splitting of Angiotensin to Angiotensin I

5.1.2. Angiotensin I is converted to Angiotensin II by Angiotensin Converting Enzyme (ACE) Angiotensin II stimulates the release of Aldosterone in the Adrenal Cortex resulting in Na+ and H2O retention that will cause increased in BP Angiotensin II causes Increased Peripheral Vasoconstriction that results to increased BP

5.2. ANP Release

5.2.1. ANP in the cardiac atria acts on the medullary collecting duct, inhibiting RAAS, stimulating vasodilation resulting in decreased in blood pressure

6. Waste Excretion

6.1. Metabolic wastes; urea, creatinine, nitrogenous wastes, uric acid

6.2. Drug metabolites

6.3. Excess Ions: NA+, K, Mg, Chloride, HCO3+, H+

7. Bone Density Regulation

7.1. Released in the Juxtaglomerular apparatus in response to decreased in arterial pressure

7.2. Kidneys help regulate bone development and metabolism by regulating calcium and phosphate balance, which is essential to bone mineralization and growth.

7.2.1. Calcium and phosphate are filtered in the kidneys and are main components of bone minerals which majority of them are found in the bones and are essential for normal structure and function

7.3. Activation of Vitamin D

7.3.1. Vitamin D is essential for the absorption of calcium in the GI tract

7.3.2. Activation occurs in the liver and kidneys