Lecture 16- Urinary 1 Flashcards
Describe the anatomy of a kidney:
- Renal cortex
- Renal medulla (in it tubes)
- Renal Pelvis
- Renal artery (the blood vessel supplying and vein taking it out -large proportion of blood going to the kidney from each heartbeat)
- Renal vein
- Ureter
- the dots are glomerulus
Describe the anatomy of a nephron:
- Glomerulus=glomerulus= in cortex, round, made up of capillaries, arteriole from renal artery going onto the glomerulus then divides into capillaries then the capillaries join together and form another arteriole= the efferent one
- Afferent/efferent arterioles (around the glomerulus, start of the up and down tubules)
- Juxtaglomerular apparatus(specialised cells)
- Proximal tubule (the one closest to the glomerulus)
- Loop of Henle (special part of the tubule goes all the way deep to the medulla)
- Peritubular capillaries (vasa recta) (around the whole tubules= supplied by the afferrent arterioles, way of getting blood to the tubules and taking things away)
- Distal tubule- the one after Henle
- collecting duct (goes down from cortex to the medulla)
What does the glomerulus do?
-lining cells of the capillaries= can open and close the leakage of capillaries, depending if it is stimulated or not, so glomerulus can be very leaky or not
-filtrates
What makes up the glomerular membrane (3 components)?
- Endothelium (glomerular capillary)
- Basement membrane
- Inner layer of Bowmans capsule (podocytes)
- things have to get through these to get to the blood
podocytes= more leakage or less leakage
Which substances always leak through out of the system out of the system into the bowman’s?
-H2O, nutrients, urea and other wastes
Which substances never leak through out of the system out of the system into the bowman’s?
- blood proteins and cells= blood cells
- they can’t pass through no blood cells, too large unless there is damage in the glomerulus,
How much cardiac output goes to the kidneys?
25%
How much plasma that goes to the kidneys is filtered?
20% of plasma entering glomerulus is filtered
-not all the blood going to the kidney is being filtered at this point
What is glomerular capillary pressure?
-affects how much leakage
more pressur in the glomerular capillaries= increase in glomerular filtration
-if you get excited, sympathetic sytem= increase in blood pressure and after a while= you produce more urine= hence why people have to pee after sex9
How does afferebt arteriole pressure affect the glomerular filtration rate?
- have to consider what is happening to the afferent arteriole
- contraction= less pressure= less filtration
What is mucula densa and what does it do?
-part of the juxtaglomerular apparatus
an area of closely packed specialized cells lining the wall of the distal tubule at the point of return of the nephron to the vascular pole of its parent glomerulus
- decerase in blood pressure= lower GFR= lower concentration of Cl and Na ions in the filtrate
- The macula densa can sense this decrease and trigger an autoregulatory response to further increase reabsorption of ions and water in order to return blood pressure to normal.
- ecretes a locally active (paracrine) vasopressor which acts on the adjacent afferent arteriole to decrease glomerular filtration rate (GFR), as part of the tubuloglomerular feedback loop
What is juxtaglomerular apparatus?
- microscopic structure in the kidney, which regulates the function of each nephron.
- function in regulating renal blood flow and glomerular filtration rate. The three cellular components of the apparatus are the macula densa of the distal convoluted tubule, smooth muscle cells of the afferent arteriole and juxtaglomerular cells.
What is the tubuloglomerular feedback?
juxtagomerular apparatus
flow here will be due to the glomerular filtration rate, the cells will respond to change in flow in that area, can affect the podocytes, more leakage or not, and effect on afferent arteriole can change the filtration
so the change in flow in the tubule modifies what happens in the glomerulus
-loop of henle, starts close to the glomerulus and ends close to it
= useful, can regulate the blood flow there, depending on how much filtration is going on
What is the effect of arterial pressure on GFR?
What does podocyte contratcion do?
when they contract= more leakage, not contracted= less leakage
What is the effect of net filtration pressure on GFR?
- the net pressure depends on three components
- Capillary blood pressure
- Plasma-colloid osmotic pressure(plasma colloid- more= tends to keep the fluid in, when drops, then fluid will come out of the blood)=form of osmotic pressure exerted by proteins in a blood vessel’s plasma (blood/liquid) that usually tends to pull water into the circulatory system. It is the opposing force to hydrostatic pressure.)
- Bowmans capsule hydrostatic pressure
- in general pressure in capillaries should be greater than the bowman’s so we have easy flow, this pressure is increased by kidney stones= then urine is not able to move through but we still have fluid coming in= higher pressure! normal working kidney should have Bowman’s hydrostatic pressure= low
What is the intrinsic control of GFR?
- Myogenic mechanism(smooth muscle around the arteriole, if increase in blood pressure= vasodilation alter the flow, sudden ups and down of the pressure filtration rate isn’t the only thing affected)
- Tubuloglomerular feedback / glomerular capillaries
What is the extrinsic control of the GFR?
Sympathetic control: afferent arteriole / glomerular
capillaries
-Atrial Natriuretic peptide
What is the Atrial Natriuretic peptide?
powerful vasodilator, and a protein (polypeptide) hormone secreted by heart muscle cells.[1][2][3] It is involved in the homeostatic control of body water, sodium, potassium and fat (adipose tissue)
What three mechanisms affect the filtration/re-absorption and secretion?
three mechanisms affecting:
- leakeage in glomerulus
- some meatrial absorbed= absorption= the vasa recta. absorption important for nutrients, glucose, amino acids, salts taken from the blood get back in
- secretion, some substances can be directly secreted from the circulation into the tubule
What is absorbed in the tubular reabsorption?
- it is mainly for nutrient reabsorption
- SODIUM (Na+K + ATPase transport/ regulated: Aldosterone)=driven by ATPase transport pump= the reabsorption of sodium, the most concentrated ion in circulation, so it is in the tubule because of the concentration gradient but we don’t want to lose it= pump it out, swap sodium for potassium, sodium into circulation and potassium into tubule
- GLUCOSE/AMINO ACIDS(co-transport/ tubular maximum)=also co transports driven by the ATPase pump: they are designed to target the glucose and amino acids= if not working= problem, normal urine= low glucose level
- PO4 3 and Ca 2+ (regulated: ParaThyroid Hormone)=level of calcium and phosphate depedns on the parathyroid hormone= bones how much is stored calcium etc, if too much calcium on diet= then excreted if not then kept for bones
- CHLORIDE (main anion reabsorped)
- WATER(aquaporins/ regulated:Vasopressin)=taken up via aquaporins and depends on hormone vasopressin
- UREA-urea is waste, end product from breakdown of proteins, the nitrogen, can’t be reused so must be excreted, it is useful to be reabsorbed
- OTHER WASTES
How is Sodium reabsorbed?
sodium= pumped into the intersitial fluid and then into the capillaries= in blood once again, in circulation
only little Na lost
-driven by ATPase transport pump= the reabsorption of sodium, the most concentrated ion in circulation, so it is in the tubule because of the concentration gradient but we don’t want to lose it= pump it out, swap sodium for potassium, sodium into circulation and potassium into tubule
How is water reabsorbed?
- osmotic
- from the Na reabsorption= gradient but the aquaporines open and the gradient is decreased and water can flow out as well
- aquaporins/ regulated:Vasopressin
- taken up via aquaporins and depends on hormone vasopressin
How is urea reabsorbed?
- osmotic
- urea is reabsorped into the surrounding fluid of the loop, this increases the osmotic pressure around the tubules= useful to balance the osmotic pressure
lot of nutrients need to be reapbsorbed, this would create lot of osmotic pressure to modify that pressure, so there isn’t just wholesale reabsorption of all the sodium and all the water= urea has important the role of buffering the osmotic pressure so it’s not too great
since not all water is reabsorbed
How is glucose reabsorbed?
-lots of target sites on the tubule, glucose makes contact, then dragged back into the circulation
increase in the amount of glucose in the tubule is matched by an increase in the absorption into the circulation
we get to a point though where it can’t match up (the flattening out) the mechanism reached its limit, can’t get any more efficient
if you increase the amount of glucose going in above a certain point more of it will be excreted in the urine
=happens in diabetes, even in cats and dogs both type I and II, then they have lot of glucose in their circulation, bring is to the renal thershold= loss of glucose through urine,
What is secreted in the tubule? (taken from circulation and to the tubule directly can be done quite quickly)
- H+=can balance the pH if lot of H in blood= low pH then they’re secreted into the tubule so pH increases
- K+=Regulated: Aldosterone =K+ is in excess most of the time, pretty big issue if both Na and K are low= hard for kidneys to balance
- ORGANIC IONS=
- some need to be quickly removed=prostaglandins, histamine, adrenalin(they are not filtered, adrenalin rush= the have to get rid of it, have to turn off the effects of the rush, get rid of it by pushing the molecules into the tubules)
- some transported on plasma proteins =plasma proteins= they are not filtered either and deliver the organic ions to the tubule
- some foreign chemicals also secreted
=some foreign chemicals will go through filtration and some will go via secretion
