Physiology - Endocrine Control of Body Fluid Volume and Composition Flashcards
The tubular fluid leaving the ascending loop of henle is ____________
The tubular fluid leaving the asceneding loop of henle is hypo-osmotic
Where does the collecting duct originate?
Cortex
(then descends into the medulla)
Hormones such as vasopressin affect which cells in the nephron?
Those of the distal tubule and collecting duct
What are the key hormones which regulate fluid and salt regulation the the distal tubule and collecting duct?
Antidiuretic hormone
Aldosterone
Atrial natriuretic hormone
Parathyroid hormone
What affect does ADH have?
Increases water reabsorption
What affect does parathyroid hormone have?
Calcium reabsorption and phosphate excretion
What effect does atrial natriuretic hormone have?
Reduces sodium reabsorption
What effect does parathyroid hormone have?
Increases Calcium reabsorption
Decreases phosphate reabsorption
The corticomedullary gradient is set up by which two things?
Salt and urea
The distal tubule has what type of permeability to water and urea?
Low
The distal tubule has two segments, which is each responsible fore reabsorbing?
Early distal tubule: Na+/K+/2Cl- = NaCl
Late distal tubule: Ca2+, Na+, K+ (K+ is secreted under influence of aldosterone, but in the basal state, reabsorbed)
What are the two key properties of the late collecting duct?
Low ion permeability
Permeability to water and urea (influenced by ADH)
Where is ADH synthesised?
Supraoptic and paraventricular nuclei in hypothalamus
Transported down nerves to terminals where it is stored and then secreted from granules in posterior pituitary
How does vasopressin (ADH) affect the distal tubule and late collecting duct
Type 2 vasopressin receptor on basolateral membrane
Cell signalling response
Increase in cAMP
Insertion of aquaporins at apical membrane
Increases reabsorptive capability of cells to water
What happens to the aquaporins on the apical membrane of the collecting duct cells when there is no vasopressin?
They are internalised
High concentrations of ADH results in what?
Hypertonic urine
(concentrated urine, low volume)
Why does water leave the distal tubule and collecting duct?
Osmosis
In order to match the high osmolarity created by the corticomedullary gradient
(this occurs to different degrees depending on the conc of ADH)
Without ADH, the distal tubule and collecting duct are essentially ___________ to water reabsorption
Without ADH, the distal tubule and collecting duct are essentially impermeable to water reabsorption
Why can ADH only affect water reabsorption and not solute reabsorption?
Due to ADH only affecting aquaporin channel insertion into apical membranes
If there is a severe decrease in ECF (e.g. haemorrhage) which receptors can detect this?
Stretch receptors in left artria
(then increase secretion of ADH)
What is the second effect of ADH which acts only in severe decreases in ECF?
Arteriolar vasoconstriction
What are the two types of diabetes insipidus?
Central DI
Nephrogenic DI
What is the cause of central DI?
Unable to produce or secrete ADH
What is the cause of nephrogenic DI?
Failure of ADH produced to have an impact on target cells
What is the treatment for
a) Central DI
b) Nephrogenic
a) ADH replacement
b) Drugs to reduce urine output
Which drug can induce nephrogenic DI?
Lithium
(around 20% of long term users)
Nicotine will _________ ADH release and alcohol will _________ it
Nicotine will stimulate ADH release and alcohol will reduce it
When will aldosterone be secreted?
- Rising potassium or falling sodium in the blood
- Activation of RAAS system
What is the action of aldosterone?
Stimulates sodium reabsorption and potassium secretion
This raises blood pressure and blood volume as water follows sodium
An increase which ion will stimulate the adrenal cortex?
Potassium
A decrease in which ion promotes the indirect secretion of aldosterone and by which means?
Sodium
Juxtaglomerular apparatus detects low sodium levels (at macula densa)
What are the actions of angiotensin II?
Increases ADH secretion
Thirst
Arteriolar constriction
In which 3 ways is renin release controlled from granular cells in juxtaglomerular apparatus?
Reduced pressure in afferent arteriole
Macular densa cells sense amount of NaCl in distal tubule
Increase sympathetic activity as a result of reduced BP
(all of these function to increase renin secretion and increase blood pressure)
How does aldosterone impact the cells in the distal and collecting tubules?
Increases Na+/K+ATPases on basolateral membrane
Increases sodium channels on apical membrane
(this allows for a sodium gradient to be set up into the blood)
How is fluid retention related to the RAAS?
Heart failure →
Decreased BP →
RAAS stimulated →
Salt and water retention →
More pressure on failing heart
How can the issue of a failing heart and increasing RAAS activity problem be treated?
Low salt diet
Loop diuretics
ACEI
Where is atrial natriuretic peptide produced?
Heart
(stored in atrial muscle cells)
When is ANP released?
Atrial cells stretched
(due to increased circulatory volume)
What is the effect of ANP?
Increases sodium (and water) excretion
What are the four effects of ANP?
Minimises Na+ reabsorption
Decreases RAAS system activity
Decreases smooth muscle constricion of afferent arterioles (which increases GFR)
Decreases effects of sympathetic system reducing TPR
Which two mechanism govern the process of bladder emptying?
- Micturation reflex
- Voluntary control
How much fluid can the bladder hold before stretch receptors become activated?
250-400ml
(micturation reflex is then activated)
