Renal response to exercise (wk8) Flashcards
Describe the different fluid compartments of the body:
-Water makes up approximately 60% of our lean body weight. Our total body water is distributed within and outside our cells.
-2/3 of our total body water is located within our cells as intracellular fluid. Thus can be broken down into plasma fluid and interstitial fluid.
-The remaining 1/3 is outside the cells as extracellular fluid
-Gain water through food and metabolic activity. We lose water through sweat, urine, faeces and insensible losses.
Describe the total-body balance of sodium and water table from lecture 13/11
Describe the processes that contribute to water balance
-Water reabsorption and water moved through aquaporin channels
-Water reabsorption is by diffusion (i.e., osmosis) and is dependent upon sodium reabsorption (but not exclusively)
-Water moved through aquaporin channels. The presence of these aquaporins varies throughout the tubule segments. They are highly expressed in the proximal nephron. They are absent in the collecting ducts unless Anti-diuretic hormone (ADH) is active.
Describe the processes that contribute to water balance
-Aquaporins and ADH and urine formation
-Aquaporins (AQPs) (key summary). The regulation and function of AQP’s in the medullary-collecting-duct cells is to increase water reabsorption. ADH (aka vasopressin) initiates a cascade of event within the collecting duct cells that lead to an increased number of AQP2 channels in the luminal membrane -> this allows increased passive diffusion of water into the cell. Water exits cell through the AQP3 and AQP4, which are not vasopressin sensitive.
-ADH and urine formation -> ADH used cAMP systems to cause the insertion of aquaporins into the membranes of the principle cells of the collecting ducts. So water flows out of the collecting ducts to be reabsorbed by the body. Regulation of ADH release from posterior pituitary gland. Most important of the inputs come from osmoreceptors (primarily) and baroreceptors.
Draw the diagrams for osmoreceptor and baroreceptor control of ADH secretion:
The processes that contribute to sodium balance
-Sodium reabsorption key points
-Sodium reabsorption is an active process occurring in all tubular segments (nephron) except the descending limb of the Loop of Henle and the medullary collecting dust-Primary active sodium reabsorption key points:
* Active transport out of cells into interstitial fluid
* Transport achieved by NA+/K+ -ATPase pump
* Keeps intracellular conc. Of Na+ low to allow ‘downhill’ movement of Na+ from lumen
* Mechanism of Na+ movement across luminal membrane varies between tubule segments, whereas always via Na+/K+ -ATPase pump for basolateral membrane
* Proximal tubule (a) is responsible for co-transport/ counter-transport of organic molecules (glucose, aa)
* Cortical collecting ducts (b) are found via Na+ channels
The processes that contribute to sodium balance
-Sodium reabsorption three key factors (Aldosterone)
-Control of sodium reabsorption -> Control of absorption is more important than the control of GFR for long-term regulation of Na+ excretion. Three factors determining the rate of tubular Na+ reabsorption:
1. Aldosterone (most major) and the Renon-Angiotensin system. The release of the enzyme converts the peptide angiotensinogen to angiotensin 1. Angiotensin 1 then converted to angiotensin 2 by angiotensin-converting enzyme (ACE). Angiotensin 2 acts on angiotensin receptors located in several target tissues including the adrenal glands, kidneys, brain, and vasculature. Activation of angiotensin receptors in the adrenal glands stimulates aldosterone release from these glands, which increase Na+ and H2O reabsorption.
+ draw the renal regulation of potassium (aldosterone)
The processes that contribute to sodium balance
-Sodium reabsorption three key factors
(Atrial Natriuretic Peptide - ANP)
ANP is synthesized and sorted in atrial myocytes. ANP is released in response to stretching of the atria -> this occurs when our circulating blood volume increases. An increase in circulating levels of ANP causes an increase in Na+ excretion. It changes reabsorption in the tubules.
The processes that contribute to sodium balance
-Sodium reabsorption three key factors
(local effect of blood pressure on the tubules)
- Renal system’s role in regulating blood pressure -> Sodium and H20 are key in regulating blood pressure. The regulation of body fluid osmolarity requires separation of water excretion from Na+ excretion. It’s made possible by 2 physiological factors: Osmoreceptors and ADH dependent water reabsorption without Na+ reabsorption in the collecting ducts
- Local effect of blood pressure on the tubules -> Baroreceptor regulation of blood pressure simultaneously regulates total-body sodium. GFR is the volume of filtrate formed each minute. This is affected by the volume of surface available, filtration membrane permeability and NFP (net filtration pressure), blood pressure/ blood flow to the glomerular capillaries. GFR is directly proportional to NFP. Therefore, increases (or deceases) in systemic blood pressure causes increases (decreases) in GFR.
+High pressure also inhibits Na+ reabsorption (as well as reducing renin release)
Summary of Na+ and H20 regulation (with lecture diagram)
Pathways by which decreased plasma volume leads to increased Na+ reabsorption; via the renin-angiotensin system and aldosterone
How the renal system handles water and sodium
-Inputs controlling thirst (+diagram from lecture)
-> Because the kidney cannot create new Na+ or water, deficits must eventually be compensated for my ingestion of these substances
How the renal system handles water and sodium
-Diuretics
Diuretics are substances that promote the loss of Na+ and H20. Alcohol acts like a diuretic by inhibiting the release of vasopressin (ADH) from the pituitary gland. Diuretics can be medications use to help the body remove excess sodium and water and help control blood pressure. Example, a decrease in plasma volume through the baroreceptors makes people thirsty and is an example of a physiological thirst response. Diuretics can be a main response of effect from taking a diuretic.
* Osmotic diuretics -> Carbohydrates that are filtered but not reabsorbed e.g. Mannitol
* Loop diuretics -> Most powerful diuretic because they inhibit the formation of the medullar gradient by inhibiting Na+ reabsorption e.g. Lasix and furosemide
* Hydrochlorothiazide acts on the distal collecting duct
* Spironolactone is an aldosterone receptor antagonist. This is known as a K+ sparing diuretic. It acts because the K+ in urine is from aldosterone-driven active tubular secretion into the late DCT and collecting ducts
Key exercise-related regulatory processes involving the kidney
-Renal-function during exercise and renal blood flow
-Renal-function during exercise -> Renal blood flow decreases as soon as exercise starts. Linear relationship: increase in exercise intensity = decrease in renal flow. GFR, is only affected at exercise intensities above 50% VO2 Max. A steady decrease in GFR, down to 60% of the basal rate at maximal exercise.
-Renal blood flow -> There is a decrease in renal blood flow. There is an increase in the sympathetic nervous system activity during exercise which causes vasoconstriction of the renal arterioles. Increase in exercise intensity = increase in sympathetic nervous system activity = decrease in renal blood flow. Increased ADH release also reduced renal blood flow and ADH causes renal vasoconstriction. Despite a decrease in renal blood flow, there is an increase in work for the kidney during exercise.
Key exercise-related regulatory processes involving the kidney
-During exercise kidney function
-During exercise, the kidneys:
* Maintain pH -> Via loss of excess H+ in the urine. Kidneys remove a small amount (2%) of total lactate produced during exercise.
* Conserve body water -> Fluid regulatory hormones act to increase water and Na+ reabsorption in the kidney
* Excrete metabolites -> H+ (hydrogen), creatinine (excess created from muscle breakdown) and other proteins
Key exercise-related regulatory processes involving the kidney
-Rhabdomyolysis
A condition where skeletal muscle cell damage can cause acute renal failure and sometimes death. It is most observed with novel, strenuous and overexertion. Heat stress increases the risk and dehydration likely increases the risk (US soldiers hospitalized for serious heat illness, 25% had rhabdomyolysis and 13% had acute renal failure). When working or exercising in extreme or hot conditions, its important to: maintain hydration by drinking water, stop if you feel unwell and slow don your work rate or rest of needed.
