Slide 7 Flashcards
How does the body sense and regulate fluid and electrolyte homeostasis?
by responding to changes in blood volume and blood pressure
Name all the receptors that sense volume and pressure.
atrial receptors, endocrine cells in the atria, carotid and aortic baroreceptors
How does the cardiovascular response differ from the kidney response?
Cardiovascular system: lower cardiac output and vasodilation
kidneys: excrete salt and H2O in urine which lowers extracellular and intracellular fluid volume
Where is urine formed?
in kidneys
What are the main structures of the urinary system from inside to the outside?
kidneys pass the urine to calyx to start the plumbing:
1- ureters (connect the kidneys to the urinary bladder)
2-urinary bladder (stores the urine)
3-urethra (which excretes urine)
What is the main functional unit of the kidney?
What are the two main regions in the nephron?
nephron!
- they have a cardiovascular and tubular component
regions:
- they consist of the renal medulla (inside) and the renal cortex (outside)
How does the passage of urine differ from female and male?
male urethras are way longer (spans across the penis)
- that’s why women are more susceptible to infections in that area because its closer to the inner parts)
Describe the glomerulus
although the vascular and tubular components are intimately related
dominant part: glomerulus
- where blood passes through and gets filtered of water and solutes
- filtered fluid is plasma-like and passes through the tubules where it gets converted to urine
Trace the nephron vascular route.
- Blood enters the kidney through the renal artery - afferent arteriole
- The blood gets filtered at the glomerulus where blood that does not enter into the tubules via efferent arteriole
- the efferent arteriole breaks down into peritubular capillaries- enveloping the tubular part of the nephron and supply blood for fluid exchange in the throughout the tubule
- peritubular capillaries join the venules which transport blood into the renal vein to exit the kidneys
Where is the glomerulus situated?
in the bowman’s capsule
Describe the route of fluid movement within the different tubules.
- glomerulus in the bowman’s capsule
- proximal tubule
- distal tubule
- descending limb of Henle
- ascending loop of Henle
- collecting tubule/ducts*
* many nephron tubules drain into a common collecting duct
Which part of the tubules are part of the cortex region?
- glomerulus
- proximal tubule
- distal tubule
Which part of the nephron is part of the medulla region?
- descending loop of Henle
- ascending loop of Henle
- collecting duct
What are the basic renal processes?
- glomerular filtration
everything in the blood is filtered EXCEPT plasma protein and RBCs
~20% - tubular reabsorption
selective movement of filtered substances from the tubular lumen back into peritubular capillaries - tubular secretion
selective movement of non filtered substances that move from the peritubular capillaries back into the tubular lumen (for excretion)
-provides a second route for substances to be excreted that were not filtered at the glomerulus ~80%
URINE is the result
“anything filtered or secreted but not absorbed is excreted”
What is the layers of glomerulus compromised of?
the afferent arteriole enters the bowman’s capsule and becomes the glomerulus
- from the lumen of the glomerular capillary: blood must pass the endothelial cells via pores between them
- they go through the acellular basement membrane
- the blood passes through to the foot processes of the podocytes in the inner lining of the Bowman’s capsule via filtration slits
What are the three forces of filtration?
- glomerular filtration
- plasma colloid osmotic pressure
- bowman’s capsule hydrostatic pressure
How does glomerular filtration allow fluid filtration?
Fluid filtered through the glomerulus into the bowman's capsule must pass through 3 layers of glomerular membrane - glomerular capillary wall - basement membrane -inner layer of bowman's capsule this becomes the ultrafiltrate
fluid moves from high pressure to low pressure
How does the plasma colloid osmotic pressure affect filtration?
it opposes filtration (fluid passing into the tubules)
this is the force due to the larger plasma protein that cannot pass through the membrane (because it is too big)
these proteins exert a colloid osmotic pressure on the filtered fluid by pulling it back from the Bowman’s capsule into the capillary
What is the effect of the bowman’s capsule hydrostatic pressure?
it also opposes filtration which can increase in the case of blockage (slightly high pressure in the bowman’s capsule)
How does the urine concentration change as it flows through the tubules?
descending loop of Henle: becomes more concentrated (hyposmotic fluid) as it is only permeable to water
Ascending loop (much thicker tubule): it become less concentrated as it moves up the loop of Henle since it is impermeable to water there it has active transport of NaCl (ion reabsorption)
distal tubule: can be acted on by hormones, permeable to water and solutes
collecting ducts: control urine osmolarity through reabsorption of water (leaves collecting duct by osmosis) and solutes (urea)
How is the osmotic gradient maintained in the medullary interstitial fluid?
descending limb: highly permeable to water but does NOT actively reabsorb Na+
Ascending limb: impermeable to water so only salt leaves WITHOUT water
Why does the medulla have a high osmolarity? How does this affect the other tubule re/absorption?
due to the NaCl+ moving out of the ascending limb (but not water)
this affects the descending limb: since water leaves descending lumb by osmosis
How does the medullary concentration change?
inner medulla > outer medulla > cortex (concentration)
Describe in detail, the action of diffusion and filtration in the descending vs. ascending loop of Henle
descending loop: only NaCl moves out but not water => medullary osmolarity is high
&
water leaves the descending limb by osmosis (as we go down the descending limb, the osmolarity increases inside the tubules)
Ascending loop: the effect of the water movement makes the filtrate (inside the tubule) very concentrated=> NaCl diffuses out of the tubules
as we go up the ascending loop, NaCl actively moves out (this part is also thicker which limits the diffusion of many molecules
=> this decrease the osolarity of the urine once in the distal tubule
Collecting ducts: urine becomes more and more concentrated as it travels down the duct due to water diffusing out in response to the osmotic gradient created by the loop of Henle, some urea also exits at the distal end
Differentiate the purpose of collecting ducts and the loop of Henle.
collecting ducts: makes urine more concentrated
loop of Henle: maintain osmotic gradient
How can we adjust the urine concentration?
water permeability of collective ducts: adjustable
higher permeability = more water reabsorption and saltier urine
this can be done by adding or removing aquaporins (mechanism of action of ADH)
How does vasopressin/anti diuretic hormone/ADH work?
- binds to membrane receptor
- receptor actives second messenger cAMP
- causes storages vesicles to insert AQP2 water pres into apical membrane
- water is absorbed by osmosis into the blood
What are factors affecting vasopressin releasing?
- INCREASED OSMOLARITY
high osmolarity = hypothalamic osmoreceptors = interneurons to hypothalamus = synthesis of vasopressing - DECREASED VOLUME
decreased atrial stretch due to low blood volume = atrial stretch receptor = sensory neuron to hypothalamus = synthesis of ADH - DECREASED PRESSURE
decreased blood pressure = carotid and aortic baroreceptors = sensory neuron to hypothalamus = synthesis of vasopressin
vasopressing released from posterioir pituitary = to collecting ducts = insert pores on APICAL membrane = increase water reabsorption to conserve water
How does plasma osmolarity and vasopressin secretion compare?
increasing plasma osmolarity positively related to plasma vasopressin release
What affects kidney filtration?
- myogenic regulation an increase in arterial pressure = stretched renal afferent artiole
vascular smooth muscle respond by contracting = increases resistance (so less blood flow to decrease pressure?)
What are granular cells and macula densa?
granular: specialised smooth muscle cells in afferent arteriole walls
macula densa: detect changes in salt level as fluid passes by them
more fluid passing = more salt detected = Macula Densa release adenosine
What is the juxtaglomerular apparatus?
located in distal tubule
positioned right between the afferent and efferent arteries (sandwiched) facing the glomerulus
What is the effect of adenosine?
paracrine regulator causes vasoconstriction at adjacent granular cells
Where is there secretion (which tubules?)
proximal tubules
distal tubules
collecting ducts
Describe the autoregulation of the tubuloglomuerular feedback.
glomeruluar filtration rate increases = flow through tubules increases = NaCl flow past macula densa increases = paracrine factor released (adenosine) = afferent arteriole constricts = more resistance in arteriole increases = hydrostatic pressure in glomerulus decreases = glomerular filtration rate decreases
What is the countercurrent exchange in the medulla of the kidney?
as fluid is being filtered = reabsorbed out of the tubules, the medullary concentration does NOT rise because the filtrate being reabsorbed Is picked up by the blood in the vasa recta (at the descending and ascending loop of Henle)
the direction of the flow is opposite to the flow in the nephron tubules
the vasa recta is actually the peritubular capillaries (when surrounding promixal and distal tubules) and vasa recta (when surrounding loop of Henle)
If afferent arterioles dilate, what happens to GFR?
it increases
secretion always refers to..
SOLUTE into nephron lumen
What are the effects of ADH on the collecting ducts?
with the presence of ADH in the collecting ducts, urine becomes more concentrated (since more water is reabsorbed) so less urine volume as well
How does sodium affect homeostatic responses?
no change in volume but increases osmolarity =
- thirst = increase water intake =
- ECF volume increases rise in blood pressure =kidneys excrete salt and water (SLOW) and osmolarity returns to normal
- blood pressure increases = cardiovascular refleces lower blood pressure (RAPID) = volume and blood pressure returns to normal - ADH released = increase renal absorption = kidneys conserve water
What happens when the body needs salt?
- aldosterone secreted from adrenal acts on principal cells in distal tubule
- aldosterone combines with cytoplasmic receptor
- hormone receptor complect initiates transcription in nucleus
- new protein channels and pumps created and upregulation of Na/K+ channels opened
- Na ATPase pump acts more quickly
- increased Na+ reabsorption and K+ secretion
What happens if there is low blood pressure?
RAAS: renin angiontensin aldosterone system
- liver prodices angiotensinogen
- decreased blood pressure stimulates granular cells in kidney to produce renin
- renin activates angiotensinogen to ANG 1 in plasma
- blood vessel endothelial cells have ACE (enzymes) to activate ANG1 to ANG 2 in plasma
- this acts on
- arterioles = vasoconstrict
- cardiovascular control in medulla oblongata = increase cardiovascular response
- hypothalamus = increase ADH and thirst
- adrenal cortex = increase aldosterone = increase Na+ reabsorption
all increase blood pressure, volume and maintain osmolarity
When is RAAS activated?
under LOW pressure
What is ANP?
atrial naturetic peptide
increase water loss and regulated blood pressure
When is ANP produced?
during HIGH pressure
How does ANP work?
ANP inhibits Na+ reabsorption
- secreted by atria in response to stretch by Na_ retention
- expansion of ECF volume and increase in arterial pressure
- release of ANP inhibits Na+ reabsorption in distal tubules which increases Na+ output in urine
- increases GFR so there’s more water loss
- inhibits renin secretion by kidneys (to stop RAAS)
- hypotensive effects help correct original stimulus that brought release of ANP
Where is ANP released (where does it act on?)
on distal tubules
What are some causes of renal failure?
- infection
- toxins
- inappropriate immune response
- obstruction of urine flow
- not enough renal blood supply
What are the kidney functions?
- maintain water balance, osmolarity, concentration of ECF ions, proper plasma volume, proper acid/base balance in body
- excretion of waste and foreign compounds
- produce erythropoietin and renin
- convert vit D to active form
If prescribed powerful aldosterone agonist what should we monitor?
blood pressure and serum potassium (high excretion due to high retention of NaCl?)
drinking large amounts of water, what hormone will be decreased?
ADH
