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39 Cards in this Set
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Role of the Kidneys |
Eliminating wastes - nitrogenous waste, toxins, drugs Water Balance Regulate Blood Volume & pressure - produce enzyme Renin Produce Erythropoietin (EPO) to stimulate RBC production Maintain Ca & PO4 balance Acid-Base Balance - Controls excretion/retention of products including sodium Convert Vitamin D to active form Catabolise hormones including insulin, glucagon & PTH |
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What is the Nephron? |
Functional unit of kidney: Consists of glomerulus and associated tubule through which glomerular filtrate passes 2 types - *Cortical: short nephron-loop & glomerulus, supplies peritubular cappillaries *Juxtamedullary: long nephron-loop & glomerulus, supplies vasa recta capillaries 2 components - *Renal Corpuscle *Renal Tubule |
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What are the functional regions of the Nephron? |
Proximal Convoluted Tubule - Proximal tubule after the Bowmans Capsule. Reabsorbs glucose, Amino Acids, Na, chloride ions & water. Secretes Ammonia & Creatinine Loop of Henle - Descending: Water reabsorbed, Ascending: Na, K, Cl actively reabsorbed Distal Convoluted Tubule - Actively reabsorbed Na & Cl; Secretes Ammonion & Hydrogen ions. Permeability to water increases with ADH release. |
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How much Urine do the Kidneys produce each day? |
1.5 Litres => 62.5mls/day |
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What is Net Filtration Pressure (NFP)? |
NFP = HPg - (OPg + HPc) HPg: Glomerular Hydrostatic Pressure - Blood in glomerular capsule exerts pressure pushing substances out of blood & into filtrate OPg: Blood Colloid Osmotic (Oncotic) Pressure - Osmotic pressure exerted by proteins (notably Alb) that tends to pull water into blood. HPc: Capsular Hydrostatic Pressure - Back pressure of fluid already in the filtrate |
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How are the kidneys affected by decreased systemic blood pressure? |
Decreased GFR, decreased stretch of afferent arterioles leads to their vasodilation to allow more blood through to increase GFR. Decreased GFR, decreases filtrate and NaCl, targeting the macula densa cells of the JG Apparatus to inhibit chemical that constrict afferent arterioles. Stimulates Granular cells of JG Apparatus to release Renin that converts Angiotensinogen to Angiotensin II. Angiotensin II then stimulates Aldosterone release from Adrenal cortex increase Na & water reabsorption increasing blood volume. Angiotensin II also causes Vasoconstriction to increase blood pressure. Inhibits Baroreceptors of blood vessels, which in turn stimulates Vasoconstriction to increase blood pressure. |
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Osmolality of body fluids |
300 mOsm (300 milliosmol) |
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How is water intake regulated? |
Increased plasma osmolality decreases saliva causing dry mouth and stimulates osmoreceptors in hypothalamus. These both act on hypothalamic thirst center making a person thirsty. The person drinks and water is absorbed, decreasing plasma osmolality and thirst. Decreased Plasma volume causes decrease in blood pressure which stimulates both the hypothalamic thirst centre and the granular cells of the kidney. Granular cells stimulate the renin-angiotensin mechanism to increase Angiotensin II, also stimulating the hypothalamic thirst centre. |
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How is water output regulated? |
Increase plasma osmolality and Na concrentration stimulates hypothalamus which stimulates release of ADH from pituitary gland at base of brain. ADH increases water reabsorption by the kidneys, decreasing plasma osmolality by increasing plasma volume and producing less urine output. Increased plasma volume inhibits hypothalamus stimulating, stopping ADH release. Decreased Blood pressure & volume inhibits baroreceptors in atrium of heart & large vessels which stimulates release of ADH from pituitary, increasing kidney water reabsortion. |
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Why is tight control of fluid balance and ionic composition so important? |
? |
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How does the kidney help regulate RBC production? |
Peritubular interstitial cells in the kidney produce and release Erythropoietin hormone (EPO) when blood oxygen levels are low (hypoxia). EPO stimulates bone marrow stem cells to create proerythroblasts. Proerythroblasts undergo cell division to erythroblasts. They begin synthesising haemoglobin and eventually turn into reticulotytes in which Hb synthesis continues. Once the correct concentration of Hb is reached (34%), the reticulyte cells pass into the blood and 2-3 days later become Erythrocytes (RBC's). The cell division involved in Erythrocyte production relies on folate (B9) and B12 Cobalamin, so deficiency may cause megaloblastic/pernicious anemia (enlarged RBC's). |
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What is normal blood pH? |
7.4 Increased H+ => Acidity Decreased H+ => Alkalinity |
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How do the kidneys regulate acid/base balance? |
Reabsorbs Bicarbonate ions (HCO3-) and excretes Hydrogen ions (H+) to maintain blood pH. Tubule cells can create Ammonia by deaminating Amino Acids so that Hydrogen ions (H+) in filtrate can be buffered by Ammonia (NH3) to become Ammonium (NH4+). Kidney ability to maintain acid base balance is extremely important although slower acting that the respiratory centre and acid base buffer systems (dissociation & reformation of Carbonic Acid & Bicarbonate. |
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How do the Kidneys affect electrolyte balance? |
Kidneys stimulate the Adrenal Cortex to release Aldosterone hormone. When blood pressure & volume low, the JG apparatus secreted Renin, changing angiotensinogen to Angiotensin II. This constricts the blood vessels & stimulates Aldosterone release, promoting sodium & water reabsorption to increase blood volume/pressure. When blood pressure & volume high, cardiac cells are stretched, stimulating Atrial Natriuretic Hormone (ANH) by the heart atria. ANH inhibits renin and Aldosterone secretion promoting excretion of sodium (natriuresis) and water, decreasing blood volume & pressure. |
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How does alcohol contribute to dehydration? |
Alcohol inhibits secretion of Antidiuretic Hormone (ADH), causing the body to excrete sodium and water. |
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How does caffeine contribute to dehydration? |
Increases GFR and decreases sodium (Na+) reabsorption, promoting sodium and water exretion. |
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How do the kidneys affect Calcium and Phosphate balance? |
When calcium levels fall, PTH is secreted, which stimulates the kidneys to increase calcium reabsorption and decrease phosphate reabsorption. PTH also stimulates the kidney to convert Calcidiol to Active Calcitriol. Calcitriol then stimulates the gut to increase Calcium & Phosphate absorption. PTH also stimulates osteoclasts in the bone to release calcium and phosphate into the blood. When calcium levels have increase, the thyroid releases Calcitonin to inhibit bone osteoclasts. |
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How can Magnesium affect PTH? |
Mg is a cofactor used in PTH secretion, so decreased Mg may decrease PTH. Decreased PTH will decrease blood calcium levels. |
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What is Diabetic Nephropathy? |
High blood glucose damages nerves or blood vessels that bring oxygen to the nerves. Signs: tingling/numbness, shooting pains, extreme sensitivity, muscle weakness, inability to feel hot & cold, foot problems. Management: Blood glucose control, exercise |
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What is Glomerulonephritis/Nephritis? |
Damage of the glomeruli, the site of filtration. Can be acute or chronic. Will cause poor urine output, oedema of face, blood in urine, high blood pressure, foamy urine from excess protein. Treatment: Control Blood Pressure, reduced protein, salt and potassium. May require calcium supplement and/or diuretics. |
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What is Nephrotic Syndrome? |
Damage to kidneys that allows Alb to be excreted in urine. Causes Albuminuria >3g/24hr |
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What is Autosomal Dominant Polycystic Kidney Disease (ADPKD)? |
Inherited disease causing cyst growth on kidneys. Impairs kidney function and may cause kidney failure. Causes blood in urine, frequent urination, UTI's, kidney stones. Treatment: Control blood pressure, low-sodium diet, may require diuretics. |
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What is Reflux Nephropathy? |
Reflux of urine back into kidneys when bladder is full, damaging the kidney. |
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What are some of the effects of Kidney Disease? |
Nausea/Vomiting Itching/Pruritus - From increased Urea and/or Phosphate Metallic Taste Increased Potassium Metabolic Acidosis (high pH) Anemia from reduced EPO Malnutrition Hypertension High TG +/- High cholesterol Increased concentrations of hormones - Insulin, glucagon, PTH |
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Stages of Chronic Kidney Disease (CKD) |
GFR Stages 1-2: >60 ml/min Stage 3: 30-59 ml/min Stage 4: 15-29 ml/min Stage 5: <15 ml/min |
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Causes of Acute Kidney Failure |
Dehydration Blood loss Sepsis drug toxicity Severe trauma/shock Muscle damage |
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Why is urine output variable in Acute Kidney Failure |
Because Urine out put is affected by both GFR and tubular reabsorption. In recovery diuretic phase, urine output increases, followed by return to normal. |
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Nutritional considerations in Acute Renal Failure |
May be hypercatabolic due to underlying cause (e.g. sepsis, trauma), leading to malnutrition. High nutritional requirements Protein 1.0 - 2.0 g/kg IBW/day May require ONS to meet needs |
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Anthropometry Assessment in Chronic Kidney Disease/Failure |
Take care to obtain "dry weigh" Assess usual body weight compared with Ideal body weight Monitor weight changes & % weight change SGA |
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Biochemistry Assessment in Chronic Kidney Disease/Failure |
Urea, Creatinine, GFR Potassium, Phosphate, Calcium Albumin Bicarbonate (Low --> acidosis) Lipids Iron status - Hb, Fe, Transferrin CRP HbA1c & BGL if diabetic |
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Clinical Assessment in Chronic Kidney Disease/Failure |
Medications
Cognition Malnutrition - muscle/fat wasting N + V Diarrhoea/Constipation Taste changes affecting intake Oedema Hypertension Residual renal function --> urine output |
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Dietary Assessment in Chronic Kidney Disease/Failure |
Appetite & appetite changes Usual food & fluid intake compared with current Usual activity & recent changes |
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Aims of treatment in Chronic Kidney Disease/Failure |
Maintain or improve nutritional status Slow progression of renal failure Control Blood Pressure and BGL's Modify protein intake as needed Treat any electrolyte imbalances Fluid restriction only if necessary (ie. cardiac issues) |
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Nutritional requirements in Chronic Kidney Disease/Failure |
Protein 0.75-1.0 g/kg IBW/day in stage 3 0.75 g/kg IBW/day in stage 4 Energy 35 kcal/kg IBW/day NAS <100 mmol/day (2300mg) (esp. if HT & oedema) K May not be required unless UO decreased or using certain blood pressure medications. 39 mg/kg IBW/day if K >6.0 PO4 May require PO4 binders Aim for <1.78 mmol/L levels Supps May require folate, Vit D (Calcitriol), Long-Chain Omega-3's |
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Differences in nutritional requirements between Haemodialysis & Peritoneal Dialysis |
Haemodialysis diet is more strict due to intermittent nature of the dialysis |
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Requirements for Haemodialysis |
Energy 30 - 35 kcal/kg IBW/day Protein 1.2 - 1.4 g/kg IBW/day Na- NAS 80-100 mmol (1840 - 2300mg) K 1 mmol/kg IBW/day (39mg) Fluid 500 ml + PDUO PO4 800 - 100 mg/day |
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What other factors can contribute to hyperkalemia? |
ACE inhibitors, Beta Blockers, K-sparing diuretics Constipation Insulin deficiency Bleeding Metabolic Acidosis Muscle breakdown Inadequate dialysis Dehydration |
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Some common Phosphate binders: |
Caltrate/Calsup (Calcium carbonate) Alutabs (Aluminium hydroxide) Renegal (Sevelamer hydrochloride) Fosrenol (Lanthanum carbonate) |
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What biochemistry should be checked when feeding Renal patients with ONS? |
Potassium and Urea |
