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The Kidney's Role in Homeostasis - Coggle Diagram
The Kidney's Role in Homeostasis
Blood Pressure Regulation
Hypertension
Secretes Renin
Activates the renin-angiotensin-aldosterone pathway and releases Antidiuretic Hormone
increased blood volume
increased cardiac output
peripheral vasoconstriction
decreased urine formation
increased tubular water reabsorption
Hypotension
Activates Atrial Natriueretic Peptide
Raised ANP = Lowers BP
peripheral vasodilation
natriuresis (increased excretion of Na+ in urine)
diuresis (increased urine output)
Blood pH regulation using Acid-Base Balance
Normal pH: 7.35-7.45
Bicarbonate Buffering System:
CO2 + H2O <-> H2CO3 <-> H+ + HCO3-
Rise in plasma pH (alkalosis)
Results from
reduced
hydrogen ion concentration in bodily fluids (hydrogen ion secretion and bicarbonate reabsorption are coupled together)
Drives the bicarbonate reaction sequence to the right to produce more H+ ions and bicarbonate ions.
Reduced bicarbonate ion concentration leads to:
Reduced lung ventilation
Leads to CO2 build-up
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Kidneys reduce the amount of H+ secretion
Fall in plasma pH (acidosis)
Results from
excess
hydrogren ions in bodily fluids
Drives the bicarbonate reaction sequence to the left, producing more CO2 and water
Kidneys excrete excess hydrogen ions through the urine
Increased respiratory rate to 'blow off' excess CO2
Waste Excretion
The kidney works as the main excretory organ to eliminate metabolic waste products, otherwise it accumulates in body tissues.
Drug Metabolites
Detoxified in the liver then excreted in urine
Excess ions
Examples: Excess sodium, potassium, magnesium ions
Metabolic Wastes
Urea
Urea is a result of protein break-down, dependent on nutritional intake.
Level: 2.5-8 mmol/L
Creatinine
It is a by-product of muscle metabolism. Raised plasma creatinine can be indicative of renal dysfunction. Level:
Less than 133 mmol/L
Electrolyte Regulation
Calcium
Important for muscle tone maintenance, nervous/muscle tissue excitability, blood clotting, neurotransmitter release, and bone density. Level: (4.5-5.5 mEq/L)
Influenced by:
Vitamin D
Undergoes metabolic conversion in liver/kidney
PTH
Stimulated by fluctuations in plasma calcium concentration (hyper/hypo-calcemia)
Potassium
Main intracellular cation. Maintains membrane potential of nerves/muscles. It is freely filtered in the glomerulus. Level: (3.5-5.0 mEq/L)
Influenced only by: Aldosterone (monitors extracellular potassium concentration and adjusts accordingly)
Hyperkalemia
Hormone is decreased to reabsorb potassium into distal tubules
Hypokalemia
Hormone is increased to excrete potassium into distal tubules
Magnesium
Important for normal neuromuscular activity, synaptic transmission and myocardial functioning. It is an important intracellular cation linked to calcium. Level: (1.3-3.1 mEq/L)
Influenced by the PTH which increases tubular reabsorption of magnesium.
Phosphate
Major component for buffer systems in maintaining plasma pH. Exists in equilibrium with calcium.
High plasma phosphate level = phosphate is excreted in urine
Low plasma phosphate level = filtered phosphate gets reabsorbed into proximal tubule
Sodium
Major solute in extracellular fluids that controls osmolarity Levels:(135-145 mEq/L)
Controlled by 3 hormones:
Aldosterone
Steroid hormone secreted by Adrenal Cortex. This directly effects the distal tubule of the nephron. More aldosterone secretion in turn absorbs more NA+.
ANP (Atrial Natriuretic Peptide)
Increases NA+ excretion and causes vasodilation
ADH (Antidiuretic hormone)
Secreted by the posterior pituitary gland in response to increased plasma osmolarity. ADH receptors are in the collecting ducts of kidney tubules.
Chloride
Controls water loss in urine. Level: (95-105 mEq/L)
Regulated by ADH, monitoring extracellular fluid.
Hormone Production
Erythropoietin
Glycoprotein that promotes proliferation and differentiation of erythrocyte precursors in bone marrow. Major component for RBC count and anemia prevention.
Erythropoietin production is stimulated by hypoxia and controlled with the negative feedback principle. The kidney then releases erythropoietin to increase the amount of Hgb to carry O2.
Aldosterone
Released by adrenal cortex with the activation of the renin-angiotensin-aldosterone system to stimulate collecting ducts to reabsorb more Na+ and Cl- and secrete more K+.
More aldosterone secretion = more sodium reabsorption
Results in more water reabsorption.
Calcitriol
Activates Vitamin D which controls calcium homeostasis
ADH
Vasopressin released by Posterior pituitary which regulates water reabsorption by raising water permeability in distal convoluted tubule and collecting duct.
Stimulated by increased osmotic pressure and decreased blood volume.
PTH
Stimulates cells in distal convoluted tubules to abosrb more Ca+. Controls phosphate reabsorption/excretion in proximal convoluted tubules.
Stimulated by hypo/hyper -calcemia.
ANP
Inhibits sodium and water reabsorption in the convoluted tubule and collecting duct.
Stimulated by atria cells.
ANP then inhibits aldosterone secretion which reduces renin release.
Reduces fluid volume by excreting Na+ and H2O.
Fluid Volume Regulation
Blood Osmolarity Regulation
Regulates water/solute loss in urine.