Lecture 17- Urinary 2 Flashcards Preview

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How do you calculate plasma clearance?

plasma changed by going through the kidney, so some amount will be filtered, some reabsorbed and some may be secreted= so a combination of these will determine how much is cleared clearance= filtered- reabsorbed+secreted


How do you calculate the plasma clearance rate?

[urine] x urine flow rate( how many mls per minute)/[plasma] -plasma conc= from blood sample, -urine conc=from urine sample, clearance rate=being cleared per minute, how much plasma is going through that process


When does clearance rate of a substance equal GFR?

-if substance is going to be completely filtered then it is cleared at the glomerular filtration rate -can work out the GFR if we have someting that is filtered and it's not reabsorbed and not secreted


Which substances can we use to estimate GFR?

-insulin -creatinine


How do we get GFR using insulin?

so inject inulin, know how much in the blood and see how much is in urine using the formula above and then get GFR


How do we get GFR using creatinine?

-so we don't have to inject, this we can know approx how much in the body, assume it's coming in at a constant rate so can get an approximation of GFR, more practical


Which substances have clearance rate lower than GFR?

-less than GFR, expect little glucose! we can check what is small by calculating the clearance rate! since it has the conc of blood and urine glucose= filtered+ reabsorbed -urea 50% reabsorbed


Which substances have clearance rate higher than GFR?

-H+=greater than GFR for those that are secreted -important for pH regulation. -Para-aminohippuric acid (PAH)=inject this into the animal it is filtered and secreted but not reabsorbed so if we know know the clearanc rate we can work out the renal plasma flow= filtered+ secreted not reabsorbed


How can tonicity of the tubular liquid change?

-Urine: isotonic / hypertonic / hypotonic -Proximal tubule: Unregulated reabsorption /isotonic -Loop of Henle: counter-current system / hypotonic -Distal and Collecting ducts: regulated absorption /hypertonic/ hypotonic / isotonic


What is the descending Loop of Henle permeable to?

-H20 permeable, no Na+ absorption


What is the ascending loop of Henle permeable to ?

-non- permeable to H20 , Na+ absorption


How is Na+ reabsorbed?

-in the descending= lot of water is pumped out of the tube= creates a concentration gradient in the ascending loop for Na+ to leave, then aldosterone is important in the collecting duct where the fine tuning happens -osomsis= osmotic gradient -usually about 99% of Na+ is reabsorbed, aldosterone makes up the tiny differences -aldosterone saves salt= more kept in the body


Where is the osmolarity of urine decided?

the osmolarity of the outcoming urine is not controlled in the loop of henle it is later


What is the role of vasopressin in water reabsorption?

-if aquaporines opened up then the water goes out quite quickly, the opening of aquaporines is controlled by hormone vasopressin the concentration set up in loop of henle makes it possible for the water to come out in the end bit -water lost there depends on how much in the body, imoprtant to control otherwise= dehydration -vasopressin "opens" the aquaporines= malakes them expressed on the membrane so more water can come back into the body


What would happen if there were no vasopressin present in the loop of Henle?

-no vasopressin= no aquaporines open then izt'll be isotonic and lot of water lost


Where is most of the water reabsorbed?

-lot of the water (20%) is in fact reabsorbed in the proximal and distal tubule the bits before the end due to Na+ pumping and the water follows it the 20% here important for balancing water in the body depnding on the need


What is the Renin-Angiotensin-Aldosterone System?

Aldosterone secretion is stimulated by angiotensin II. Recall that the limiting step for the formation of angiotensin II is the hormone renin, which is released by the juxtaglomerular cells located in the afferent arteriole of the kidney. The juxtaglomerular cells are stimulated to secrete renin by three mechanisms, all of which are activated in response to decreased ECF volume. -The sympathetic nervous system innervates the juxtaglomerular cells. A decrease in ECF volume will cause a drop in mean arterial pressure (MAP). Decreased MAP is detected by the carotid baroreceptors, which activate these sympathetic nervous system inputs to cause renin secretion. The juxtaglomerular cells act as baroreceptors. A drop in MAP means less pressure in the afferent arteriole, with less stretch of the juxtaglomerular cells. Less stretch of the juxtaglomerular cells activates renin secretion. Less Na+ delivered to the distal tubule activates the juxtaglomerular cells via the juxtaglomerular apparatus.


What controls the distal tubule and the collecting duct?

-20% water reabsorbed here -vasopressin= -Posterior pituitary -Opens aquaporins -Stimulated by Angiotensin II 8% Na+ reabsorption (most happens in the proximal tubule) -Aldosterone= -Adrenal cortex - Na+K+ATPase pump -Stimulated by Renin / Angiotensin system =also angiotensin= so connection of the Na and H20 system


How does camel survive with so little water?

-medulla is much thicker than the cortex in comparison to he ones before so greater gradients can be established and concentration of urine can be even greater as the medulla has longer tubes -High medulla:cortex ratio -Rapid increase in GFR when drinking -can turn on the kidney more efficinet when there is water and so there is decreased GFR at other times= cost= waste removal not as good but when water available= very fast waste removal


What is idiopathic thirst?

-some horses hav ethis behavioural thing: when can get water they'll drink more than seems necessary for their water balance if you drink too much water= excess water in curculation= damping down of the release of vasopressin, extra urine is produced= hypertonic urine lots of it= so net loss of Na lost as there is so much urime produced, so it's depleting the Na in horses= so lowered level of ECF due to the sodium loss then become dehydrated


What are the hormones controlling urine flow?

-renin -angiotensin converting enzyme -angiotensin II -renin is secreted in the juxtaglomerulal apparatus


What are the three main things the renin angiotensin aldosterone system does?

(1) to maintain a proper blood pressure/blood flow, (2) to maintain the right concentration of sodium (Na+) in the blood (3) to maintain the right amount of water in the blood.


Describe the pic of the renin-angitensin-aldosterone system:



How is fluid regulated, when there is a decrease in Na+, or ECF volume, and or arterial pressure?

-increase in renin -leads to increase in Angiotensin I and then II -which leads to increase in aldosterone(also caused by increase in plasma K+) -and aldosterone increases tubular K+ secretion and urinary K+ secretion and tubular Na+ reabsorption -and thus it decreases=Urinary Na+ excretion


Which 3 things lead to the release of atrial natriuretic peptide?

-increase in NaCl, ECF volume and arterial blood pressure


What does atrial natriuretic peptide do?

-atrial natriuretic peptide= can increase ECF even if no rise in blood pressure comes from the atria -so when more ECF then more blood coming in strecthed and NAP released decreases= Na+ reabsorption by kidney tubules, salt conserving renin-angitoensin-aldosterone system, smooth muscle of afferent arterioles and sympathetic nervous system


What is chronic renal disease?

-a progressive loss in renal function over a period of months or years -common in cats -leads to increase in urea (Blood urea nitrogen=BUN)levels -blood has more urea in blood= so breath like ammonia plus depression -rise and rise, measure the creatine level high= kidneys bad= high creatinine levels -toxicity -dehydration -acidosis -weight loss


What is the latch mechanism in the bladder?

-Bladder: adapting smooth muscle -latch mechanism, increases in volume and then adapts, reataches at the new level until full bladder


Is urination voluntary?

-yes when everything ok


What is the Reflex micturition?

-when too much it bursts,


What is bladder protein secretion?

-normally bad -means something wrong -sometimes crystalisation of salts= sharp can damage to the urehra (especially horses= they relrase a protein that coats the crystals= special case when proetin is ok in urine white froth in horse urine= protein letherin identical to sweat protein= the white sweat on exercising horses also produced in saliva= frothy protein


What does the bladder have?

-Stretch receptors - External sphincter: skeletal muscle -comb of two sphincter external and skeketal muscle sphincter


How is urination controlled?

-normally bladders fills =+stretch receptors =+ parasympathetic nerve =+bladder =bladder contracts (when go and pee) =internal urethral sphincter mechanically opens when bladder contracts= urination -but also input from the cerebral cortex =+Motor neuron to external sphincter =External urethral sphincter remains closed when motor neuron is stimulated =no urination -and also the reflex=too strechted -stretch receptors inhibit the =- Motor neuron to external sphincter =External urethral sphincter opens when motor neuron is inhibited =urination