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The Kidney's Role in Homeostasis - Coggle Diagram
The Kidney's Role in Homeostasis
Wastes & Toxins Excretion
Urine Formation
Glomerular Filtration
Substances are delivered through the afferent arteriole and into the glomerulus where it is diffused in the bowman's capsule to be filtered. Small substances that were filtered are called filtrate and are moved into the proximal convoluted tubule while larger substances are moved into the the efferent arteriole.
Depending on the body's needs these substances are either reabsorbed or secreted.
Tubular Reabsorption
Substances, such as water, glucose, amino acids, sodium, and chloride, are reabsorbed back into the body via the peritubular capillaries.
From the proximal convoluted tubule, additional substances such as water, sodium, and chloride are reabsorbed in the loop of henle, and further travels to the distal convoluted tubule.
Tubular Secretion
From the distal convoluted tubule, ammonia, hydrogen ions, potassium ions and drugs are secreted, and are then called urine.
Urine travels into the collecting duct where dilution and concentration of urine occurs.
Urine travels from the collecting duct to the ureter and into the bladder where it is expelled by the body through urination.
Blood Pressure Control
A decrease in sodium, blood flow, and blood pressure will stimulate the production of the renin hormone, that is released from granular cells of the renal juxtaglomerular apparatus.
Liver produces Angiotensinogen in which the renin hormone will bind with to produce Angiotensin I which will be converted to Angiotensin II by the angiotensin converting enzyme.
Angiotensin II stimulates the adrenal cortex to produce the aldosterone hormone which reabsorbs sodium from the renal tubules, thus increasing sodium in the blood.
Sodium is very osmotic therefore it will attract water, which increases intravascular volume and that increases venous return to the heart.
Increase venous return via the frank-starling reflex, more blood is ejected from the heart, therefore cardiac output will increase thus increasing blood pressure.
Angiotensin II vasoconstrictor peripheral arterioles, thus increasing peripheral resistance, and blood pressure.
BP = CO x Peripheral Resistance
Angiotensin II affects glomerular filtration rate which has the ability to influence the amount of sodium and fluids that is retained or excreted in the body.
Regulation of Body Fluid Volume & Osmolality
Antidiuretic Hormone (ADH)
is produced in the hypothalamus and released in the posterior pituitary gland.
Osmo Receptors DETECTING the osmotic pressure of the blood and tissue fluid in the hypothalamus.
LESS ADH
= Kidneys will have greater diuresis; produce more water.
More water in the blood = decrease in osmotic potential of blood and tissue fluids, thus signalling the hypothalamus to produce LESS ADH = LESS effect on Kidneys, thus producing larger volumes of urine to be excreted from the body.
If large volumes of urine is excreted from the body then there's less water left in the blood and tissue fluids, and it's detected by the osmo receptors. Therefore fluid and osmotic balance is restored.
MORE ADH
= Kidneys will have less diuresis; less urine is produced.
Less water in the blood = increase in osmotic potential of blood and tissue fluids, thus signalling the hypothalamus to produce MORE ADH = MORE effect on the kidneys, thus producing less urine.
If smaller/less volumes of urine is produced, that urine will be more concentrated however the same amount of salt/sodium is excreted, and that lowers the osmotic potential of the tissue fluids.
Aldosterone
is mineral corticoid released by the adrenal cortex of the adrenal gland.
Low blood volume or Low BP = stimulates renin-angiotensin-aldosterone system (RAAS)
RAAS stimulates the release of aldosterone in the adrenal cortex
Aldosterone binds to a transport protein, such as albumin, or a transport protein produced by the liver.
It then travels to the distal convoluted tubule of the nephron where it results in reuptake of sodium from the nephron tubule into circulation. Water follows sodium, this there's an increase of water reabsorption as well.
Water reabsorption/retention increases fluid volume and decrease serum potassium.
Hyperkalemia, High Potassium Levels, and Low Serum Levels also stimulate aldosterone release.
Atrial Natriuretic Peptide (ANP)
is released by the heart, specifically the atrium and ventricle. It has opposite effects of ADH and Aldosterone Hormones.
High BP and High Blood Volume = cause stretching of the heart wall which will trigger the release of ANP and BNP.
ANP and BNP inhibits the activity of the aldosterone in three ways.
By decreasing sympathetic activity that will inhibit the release of renin, thus inhibiting the RAAS.
Cause afferent vasodilation = increase GFR = signalling juxtaglomerular cells to stop releasing renin, thus inhibit RAAS.
Binds to naturally peptide receptors on vessels causing vasodilation which will lead to a reduction in peripheral resistance thus decreasing BP.
Electrolyte Balance
Potassium
High Potassium Levels = Stimulates the release of aldosterone that acts on the distal convoluted tubule to secrete excess potassium.
Low Potassium Levels = Negative feedback signals to stop the production of aldosterone, thus less potassium is secreted.
Calcium
Low Calcium Levels = Detected by the cells of the parathyroid glands which stimulates the release of parathyroid hormone (PTH) to bind to receptors on the distal convoluted tubule and the bone.
PTH signals the kidneys to increase reabsorption of calcium and decrease reabsorption of phosphate.
An increase in calcium levels signals a decrease in stimulation of PTH.
PTH converts calcidiol (form of Vitamin D produced in the liver) to calcitriol which decreases the excretion of calcium and promote reabsorption of calcium.
High Calcium Levels = Negative Feedback Loop is initiated to decrease stimulation of PTH, thus calcidiol is not converted to calcitriol, and excess calcium is excreted in the urine.
Magnesium
Low Magnesium Levels = Parathyroid Hormone (PTH) increases tubular reabsorption of magnesium in addition to calcium reabsorption.
High Magnesium Levels = Excess magnesium remain in the filtrate to be excreted by the kidneys through urination.
Phosphate
Low Phosphate Level = filtered phosphate is reabsorbed in the proximal convoluted tubule.
High Phosphate Level = Phosphate remains in the filtrate to be excreted.
An increase in PTH decreases absorption of phosphate to increase reabsorption of calcium.
Sodium
Low Sodium Levels = RAAS stimulates release of aldosterone which increases sodium and water retention.
Erythropoietin Production
Erythropoietin hormone is released by the kidneys when there is low blood volume and low oxygen (hypoxia), thus stimulating the bone marrow to produce additional red blood cells/erythrocytes in a process called erythropoiesis.
Thyroxine hormone stimulates the release of erythropoietin. The main task of this hormone is to increase the ATP production of cells and therefore more oxygen is needed from red blood cells to make ATP, thus stimulating the kidneys to produce more erythropoietin.
Red blood cells then carry oxygen that will circulate the kidney where it will detect the increased amount of oxygen. When an increased amount of oxygen is detected, the kidneys will reduce the amount of erythropoietin produced, thus reducing the stimulation of erythropoiesis.
The kidneys monitor the blood volume and oxygen content supplied by the bone marrow where red blood cells are produced.
pH Balance/Acid-Base Control
Normal Blood pH = Between 7.35 and 7.45
CO2 + H2O = H2CO3 = H+ + HCO3-
An increase in concentration of any component in one side will shift the concentration of components on that side.
Continuous supply of CO2 will drive the equilibrium to generate more hydrogen ions.
More hydrogen ions = higher acidity = lower pH
Kidneys control blood pH by adjusting the amount of hydrogen ions (H+) excreted and reabsorbed bicarbonate (HCO3-).
Reabsorption of bicarbonate is done in the proximal convoluted tubule where the amount is regulated via mechanisms in response to change in blood pH.
High plasma bicarbonate concentration = excess bicarbonate is secreted in the urine.
Low plasma bicarbonate concentration = bicarbonate ions is reserved in the blood and excess hydrogen ions is secreted in the urine.
Acidosis = excess hydrogen ions is secreted in the urine and bicarbonate ions is reabsorbed in the plasma.
Alkalosis = kidneys decrease hydrogen ions that are secreted..