HOMEOSTASIS BY THE KIDNEY FLUID AND ELECTROLYTE BALANCE Flashcards
The maintains the volume and composition of extracellular fluid, what dysfunction could arise from this
Fluid overload and metabolic derangement
The kidney does the Excretion of endogenous waste products of metabolism, what dysfunction could arise from this?
Reduction in renal excretory function (uraemia and acidosis)
The kidneys does excretion of foreign substances and their derivatives e.g. drugs and their metabolites. what dysfunction could arise from this?
Drug toxicity
The kidney produce hormones, e.g. renin, erythropoietin, and calcitriol, what dysfunction could arise from this?
Hormone function reduced
(anaemia, hypertension, etc)
What are the Functions of the Kidney?
+Volume and composition of extracellular fluid
+Excretion of endogenous
+waste products of metabolism
+Excretion of foreign substances and their derivatives e.g. drugs and their metabolites
+Synthesize prostaglandins and kinins that act within the kidney
+Production of hormones, e.g. renin, erythropoietin, and calcitriol
Which system of the body all work very closely together to maintain fluid and acid-base homeostasis (3)
The renal system, cardiovascular system and respiratory system
What can the kidney control?
Extracellular, specifically plasma, fluid volume- Effective circulating volume (ECV)
Body fluid osmolality by H2O and electrolyte control
The amount of ultrafiltrate produced in the glomeruli
The amount of H2O and electrolytes reabsorbed in the nephron and tubules
Fluid, electrolyte and H+ and HCO3- balance i.e. the amount gained minus the amount lost each day
_________ is formed at the glomerulus
Ultrafiltrate
What is the normal filtration rate?
80-120 ml/min
Does the Kidney control the extracellular or intracellular fluid volume?
Extracellular, specifically plasma, fluid volume- Effective circulating volume (ECV)
How does the kidney control the body fluid osmolality
H20 and electrolyte control
How does the kidney control the amount of urine made
controlling amount of ultrafiltrate produced in the glomeruli
controlling amount of H2O and electrolytes reabsorbed in the nephron and tubules
How much of the Ultrafiltrate formed at the glomerulus is reabsorbed back into the systemic circulation?
> 99%
Nephron controls the osmolality and volume of the urine produced through which mechanism and where?
a countercurrent mechanism in the loop of Henle
The descending limb of loop of henle are permeable to _____, but not to solutes
water
The ascending limb of loop of Henle is permeable to _____but not to water
solutes
______ is a predominantly passive process allows energy efficient ability to produce a dilute or a concentrated urine
Countercurrent Mechanism
Changes in ECV trigger which 4 effector pathways that act on the kidney
1) Renin Angiotensin Aldosterone System
(2) Sympathetic nervous system
(3) Antidiuretic Hormone (ADH) release
(4) Atrial Natriuretic Peptide (ANP) release which acts to reduce ECV
Apart from ADH, most other pathways (RAAS, SNS, ANP) use changes in ___ excretion to change effective circulating volume
Na+
How does the RAAS, Sympathetic stimulation, ADH and ANP acts on the kidneys to control effective circulating
change renal haemodynamics and Na+ transport by renal tubule cells.
_____ is group of specialised cells in distal tubule sensing sodium delivery to distal tubule
Macula densa
Central vascular receptors are blood volume receptors that detect changes in the ECV. Where are they found?
Large systemic veins
Cardiac atria
Pulmonary vasculature
Peripheral stretch receptors are baroreceptors that detect changes in ECV. Where can these be found?
Carotid sinus
Aortic arch
Renal afferent arteriole
Where are the other 2 less important baroreceptor sensors that detect changes in the ECV
CNS and liver
ADH is released by posterior pituitary gland in response to ___ and ____
hyperosmolality and volume depletion
Antidiuretic effect is mediated by _____ by acting on renal collecting ducts
V2 receptors
Which part of the Nephron is ADH most active on
Collecting ducts
In addition to ADH acting on the renal collecting ducts via V2 receptors It also increases _____ ____ mediated by ___ ___
vascular resistance
V1 receptor
Describe the regulation of ECV by ADH
reduced ECV –> peripheral baroreceptors –> hypothalamus –> ADH –> increased water reabsorption –> Increased ECV
Actions of ANP are all designed to lower ECV. True or false?
true
increased ECV causes atrial stretch which leads to ANP release into circulation, ANP promotes
natriuresis (increased Na+ and H2O excretion from the kidney)
What is the overall effect on ANP in ECV regulation
inhibits actions of renin and opposes effects of Ang-II
What re the 3 specific ways ANP regulates the ECV
Natriuresis, renal vasodilation, inhibits renin through low Na
What is the only active process in the loope of Henle (upper 2/3)
Reabsorption through the NKC2 channel
auto regulation in the kidney is within what range of mean arterial pressure
80 and 180mmhg
What will be the effect of drop in mean arterial blood pressure below 80mmHg on GFR
reduced
_____ is the main solute that governs plasma osmolality (number of solutes in solution)
Sodium
What are the 2 things that stimulate renin release form the juxta glomerular cells
reduced arteriolar stretch
reduced NaCl delivery to the macular densa in the distal tubule
What are the main functions of angiotensin II in RAAS
aldosterone secretion
Renal Na reabsorption
increase systemic blood pressure (Vasoconstriction)
Plasma osmolality is sensed by ___ ___ which releases ADH to aid water reabsorption in the collecting ducts
Hypothalamic osmoreceptors
Which sensors are involved in volume regulation by sensing the circulating/vascular fluid volume
Macula densa
Baroreceptors; Atria, Carotid sinus, central veins, pulmonary vasculature, renal afferent arterioles)
Sodium and water are regulated independently
Hyponatremia= _______
Hypernatremia=__________
too much water
too little water
Does too much or too little sodium have effect on plasma concentration?
minimal or no effects
When two liquids are separated by semipermeable membrane such as cell membrane there are two opposing forces at play called _ and _
hydrostatic and osmotic pressure
pressure exerted by the volume fluid on the blood vessel that pushes water out is called
Hydrostatic pressure
The pressure exerted by the solute i.e. Na within the solution the pulls water to itself is referred to as ___
osmotic pressure
_____ is the number of ‘osmotically’ active particles in solution.
Tonicity
Larger molecules such as __ and ___ do not significantly contribute to plasma osmotic pressure (cf. plasma Tonicity) as it freely crosses the cell membrane through facilitated diffusion.
Urea and Glucose
What is the formula for calculating the plasma osmolality
2(Na + K) + Urea + Glucose
Normal Plasma osmolality
280 - 300 mosmol/kg
Why calculate difference between measured and calculated plasma osmolality?
Osmolar Gap
Identifies alcohol poisoning that might be ingested by the patient- Ethenol, Methanol, Antifreeze (Ethylene glycol)
Osmolar gap
_____ Identifies alcohol poisoning that might be ingested by the patient- Ethenol, Methanol, Antifreeze (Ethylene glycol)
_____ is the most abundant compound in the body
Water
How much of the water in the body on the ICF and ECF
ICF 2/3
ECF 1/3
If ECF effective osmolality increases, what happens to the cell and ICF?
cells shrinks (ICF↓)
If ECF effective osmolality decreases, what happens to the cells and ICF
cells swells (ICF↑)
What is the distribution of electrolytes in the intracellular and extracellular compartments
Intracellular - K+, PO4-. and Mg++
Extra cellular - NA+, Cl-, Ca2++ and HCO3-
IF a patients presents with osmolality problems with fluid compartments should we be worried about?
ECV
What is the effect is the effect of adding salt on plasma Na concentration, ECF volume, Urine Na concentration and ICF volume
plasma Na concentration - increases
ECF volume- increases
Urine Na concentration - increases
ICF volume - decreases
What is the effect of adding water on plasma Na concentration, ECF volume, Urine Na concentration and ICF volume
plasma Na concentration - decreases
ECF volume- decreases (increases initially)
Urine Na concentration - increases
ICF volume - increases
What is the effect of adding isotonic saline on plasma Na concentration, ECF volume, Urine Na concentration and ICF volume
plasma Na concentration - the same
ECF volume- increases
Urine Na concentration - increases
ICF volume -the same
What is the effect of salt loss on plasma Na concentration, ECF volume, Urine Na concentration and ICF volume
plasma Na concentration - decreases initially the balances out
ECF volume- the same initially then falls
Urine Na concentration - decreases
ICF volume -increases
___ is the commonest electrolyte imbalance/abnormality
Hyponatraemia (135-145)
What are the some causes of reduced serum osmolality
Gastrointestinal losses- eg. Diarrhoea, Vomiting
Burns
renal losses e.g. Diuretic therapy, Addison’s disease
oedematous state - HF, RF, Nephrotic syndrome
SIADH
Hypothyroidism
Psychogenic polydipsia
A 32 year old male with 3 day history of watery diarrhoea was admitted with confusion. He was hypotensive with a rapid heart rate. His serum sodium was low at 125 mmol/L (135-145 mmol/L).
What is the most common cause of hyponatraemia in clinical settings?
defect in renal water excretion
Severe hyponitraemia leads to ____
Cerebral oedema
What happens with rapid correction of hypernatremia?
cerebral oedema
How is hyponatraemia diagnosed?
Low serum sodium
Simultaneous measurement of plasma and urine osmolality for diagnosis of SIADH
How is hyponatraemia treated?
Salt replacement
Water restriction
Treatment of underlying cause
Rapid correction of (chronic) hyponatremia can lead to ________
Central Pontine Myelinosis (intracellular dehydration)
In SIADH is plasma and urine osmolality high or low?
plasma osmolality - low
urine osmolality - high
What are the causes of hypernatreamia?
Dehydration
Certain drugs eg, Lithium
Diabetes insipidus- deficiency or renal tubular resistance to ADH
