1. SODIUM: Sodium=water (the regulation of osmolarity of extracellular fluids is greatly determined by sodium, being the major solute in ECF). Changes in water volume alone will either dilute or concentrate body fluids. For example, when you become dehydrated you lose proportionately more water than solute (sodium), so the osmolarity of your bodily fluids increases. In this situation the body must conserve water but not sodium, thus stemming the rise in osmolarity. If you lose a large amount of blood from trauma or surgery, however, your loses of sodium and water are proportionate to the composition of bodily fluids. In this situation the body should conserve both water and sodium.
2. POTASSIUM: Largest proportion: stored in bones. High potassium intake = increase the extracellular K+ level twice before the kidney can excrete the extra potassium. A high plasma potassium increases secretion of aldosterone and will increase the potassium excreted to maintain homeostasis.
3. CHLORIDE: Chloride=major contributor to the osmotic pressure gradient between the intracellular fluid (ICF) and extracellular fluid (ECF). Chloride maintains hydration and keep fluids neutral. Secretion and Reabsorption of chloride ions in the renal system usually follow sodium ion paths. Hypochloremia (low blood chloride ion level) can occur because of defective renal tubular absorption. Possible causes: vomiting, diarrhea, and metabolic acidosis
4. Excretion of wastes and toxins
5. EXCRETION: Removal of unnecessary products (water or electrolytes Na, K, etc.) from our body aides in homeostasis because they affect blood pressure. Excretion removes the byproducts of our metabolism process as well (bilirubin, biliverdin, urea) as they are harmful for your kidney. If excretion doesn't occur, waste products will pile up in your body causing fluctuation in the balance in our bodies.
6. Electrolyte balance
7. DIURETICS: Diuretics may be prescribed to reduce blood volume and, thereby, reduce blood pressure. The most frequently prescribed anti-hypertensive diuretic is hydrochlorothiazide. It inhibits the Na+/ Cl– symporter in the DCT and collecting duct. The result is a loss of Na+ with water following passively by osmosis.
8. ANTI-DIURETIC HORMONE: Regulates and balance amount of water /blood water excreted by kidneys. Regulated by increased plasma osmolality. Increased ADH= fluid imbalance that can lead to seizure/cerebral edema (concentrated urine) Decreased ADH= excrete too much water, urine volume will increase leading to dehydration (decreased BP).
9. VOLUME-SENSING MECHANISMS: Blood volume cannot be directly be measured but blood pressure can. BP often reflects BV and is measured by baroreceptors in the aorta and carotid sinuses. When BP is high, these baroreceptors send more action potentials to the central nervous system and leads to a systemic dilation of veins. Included in this vasodilation are the afferent arterioles supplying the glomerulus, resulting in increased GFR, and water loss by the kidneys. If BP decreases= less action potentials travel to the central nervous system, resulting in more sympathetic stimulation-producing vasoconstriction, which will result in decreased filtration and GFR, and water loss.
10. Direct Monitoring: The kidneys also regulate blood pressure hormonally. In order to do this, the kidneys must directly monitor the blood pressure, which they do by measuring the amount of blood flow that the kidneys receive. This function is performed by special renal cells known as the juxtaglomerular cells. These cells are located in the arteries that feed into the kidneys. When blood flow to the kidney is reduced, a hormone called renin is excreted. This system can inadvertently lead to high blood pressure if the arteries leading to the kidney get narrowed because the juxtaglomerular cells will interpret this as low blood pressure even though blood pressure throughout the body is normal (or even elevated).
11. The Renin-Angiotensin Aldosterone System (RAAS): When blood volume or sodium levels in the body are low, or blood potassium is high, cells in the kidney release the enzyme, renin.Renin converts angiotensinogen, which is produced in the liver, to the hormone angiotensin I. An enzyme known as ACE or angiotensin-converting enzyme found in the lungs metabolizes angiotensin I into angiotensin II.Angiotensin II causes blood vessels to constrict and blood pressure to increase. Angiotensin II stimulates the release of the hormone aldosterone in the adrenal glands, which causes the renal tubules to retain sodium and water and excrete potassium. Together, angiotensin II and aldosterone work to raise blood volume, blood pressure and sodium levels in the blood to restore the balance of sodium, potassium, and fluids.
