lecture 33 - body water distribution & regulation Flashcards
What proportion of total body water is made up of Intracellular fluid?
2/3
What proportion of total body water is made up of extracellular fluid?
1/3
What are the components of Extracellular fluid?
Plasma and interstitial fluid
What proportion of ECF is plasma?
1/5
What proportion of ECF is interstitial fluid?
4/5
What factor will typically change the osmolarity of the ECF?
A change in the amount of water in the ECF
How does dehydration affect plasma osmolarity?
Decrease in water causes an increase in plasma osmolarity
How does hyper-hydration affect plasma osmolarity?
Decreases osmolarity as there is an increase in water
What happens to the balance of water in ICF and ECF if there is the loss of water only from the ECF?
The ECF will have a greater osmolarity than the ICF, so there is an osmotic gradient pushing water from the ICF to ECF, so that cells shrink
What happens to the balance of water in ICF and ECF when there is the loss of isosmotic fluid from the ECF?
The ECF will have the same osmolarity as the ICF still, so there will be no shift of water, and cells will remain the same volume
What happens to the balance of water in ICF and ECF if there is the gain of water only to the ECF?
The ECF will have a lesser osmolarity than the ICF, so there is an osmotic gradient pushing water from the ECF to ICF, so that cells swell
What happens to the balance of water in ICF and ECF when there is the gain of isosmotic fluid to the ECF?
The ECF will have the same osmolarity as the ICF still, so there will be no shift of water, and cells will remain the same volume
What are the 3 parts of the nephron where water is reabsorbed?
The proximal convoluted tubule, descending limb of the nephron loop, collecting duct
Where is the majority (67%) of water in the filtered load reabsorbed in the nephron?
Proximal convoluted tubule
What are the 2 types of reabsorption in the nephron?
Bulk and regulated reabsorption
What is bulk reabsorption?
Unregulated/obligatory/automatic reabsorption
What is regulated reabsorption?
Facultative reabsorption that is regulated by hormones, e.g. ADH
What percentage of water in the filtered load undergoes bulk reabsorption?
92%
Where does bulk reabsorption of water occur?
In the proximal convoluted tube and descending nephron loop
What type of epithelia enables bulk reabsorb on of water in the nephron?
Leaky epithelia - allow for paracellular transport
What type of absorption occurs in bulk reabsorption of water?
Trans- and para-cellular reabsorption
What regulates regulated/facultative reabsorption of water?
Anti-diuretic hormone
What type of absorption occurs in the regulated reabsorption of water?
Trans cellular reabsorption
Where does regulated water reabsorption occur in the nephron?
In the collecting duct
Where is sodium reabsorbed in the nephron?
Proximal convoluted tubule, ascending limb of the nephron loop, distal convoluted tubule, collecting duct
Where is the majority (67%) of sodium reabsorbed in the nephron?
The proximal convoluted tubule
Where does bulk sodium reabsorption occur?
In the proximal convoluted tubule and ascending nephron loop
Where does regulated sodium reabsorption occur?
The distal convoluted tubule and collecting duct
What is regulated sodium reabsorption regulated by?
Aldosterone (RAAS)
What is water reabsorption in the proximal tubule driven by?
Na+ reabsorption
How does sodium aid in glucose reabsorption in the proximal convoluted tubule?
Uses its concentration gradient to bring glucose into epithelial cells via sodium-glucose contransporter. Glucose can then diffuse out into the peritubular fluid then into capillaries. Na+ gradient maintained by Na+/K+ ATPase
How does chloride get reabsorbed in the proximal convoluted tubule?
Via the paracellular pathway, down its concentration gradient
What is the ascending nephron loop permeable to?
Sodium
What is the descending nephron loop permeable to?
Water
What are the 2 modes of reabsorption of water in the descending loop?
Transcellular - aquaporins, paracellular
What is generated inside the nephron by the reabsorption of sodium into the interstitial fluid around the ascending nephron loop?
A Hyper-Osmotic Medullary Gradient (HOMG)
What does HOMG stand for?
Hyper-Osmotic Medullary Gradient
What generates a HOMG?
The reabsorption of Na+ from the ascending nephron loop into the interstitial fluid surrounding the ascending and descending nephron loop, as well as the reabsorption of water. This leaves the bottom of the nephron loop with low water and high sodium concentration - hyper osmotic
What type of reabsorption occurs in the collecting duct during the regulated absorption of water?
Only transcellular reabsorption
What detects changes in plasma osmolarity?
Osmoreceptors in the hypothalamus
Where are osmoreceptors detecting changes in plasma osmolarity located?
The hypothalamus
What does the detection of plasma osmolarity by the hypothalamus stimulate?
Stimulates the pituitary gland to secrete more or less ADH (anti-diuretic hormone)
How doe ADH act on a cellular level to alter reabsorption of water in the kidneys?
Increases the permeability of collecting duct (CD) cells by inserting aquaporin to balance a change in TBW by retaining water via reabsorption
If total body water decreases, is ADH secretion increased or decreased?
Increased
What is released if there is an increase in ECF volume and Na+ gain?
ANP - increases sodium secretion by reducing reabsorption
What is released if there is a decrease in ECF volume and a loss of Na+?
RAAS activated and aldosterone released from the adrenal glands
What is the cellular effect of aldosterone in the kidneys?
Addition of sodium channels in the apical membrane of collecting duct cells
What is the affect of aldosterone on sodium and water absorption?
Both increase
