Renal Flashcards
What is the purpose of kidneys
-filtration system for the removal of wastes
->excretion in urine
-reabsorption of water, glucose and amino acids
-production of hormones
->renin0angeiotensin-aldosterone system
->calcitrol
->erythropoietin
Are kidneys located retroperitoneally
-yes
What is the hilum
-the medial indentation of each kidney
Does each kidney have an outer cortex and inner medulla
-yes
->the outer cortex features glomeruli and portions of the renal tubuli
-the inner medulla features portions of the renal tubule, loops of Henle and medullary collecting ducts
Describe renal pyramids in the medulla
-tip of each pyramid forms a renal papilla
->renal papilla drains into a minor calyx
->minor calyces form a major calyx
->guides urine into the renal pelvis
How is urine guided down the ureter
-it is guided through peristalsis
How is blood flow supplied in the kidney
-supplied by a renal artery
->artery branches successively within the kidney
->eventually branches into afferent arterioles which supply the glomerula capillaries
->glomerular capillaries drain into efferent arterioles
->efferent arterioles then supply peritubular capillaries that surround the renal tubules
What happens to the blood from the peritubular capillary
-it drains into venules
->blood passes into successively larger veins before reaching the renal vein and draining into the vena cava
What kind of nervous innervation does the kidney receive
-it receives extensive sympathetic innervation and some sensory innervation
->sympathetic activation induces renal vascular vasoconstriction decreasing renal blood flow
->innervate tubular epithelia cells to stimulate sodium reabsorption
->stimulate renin release from juxtaglomerular cells
What is the functional unit of the kidney
-they are nephrons
->each kidney features about 1 million nephrons
->nephrons cannot be regenerated
->there is the natural and gradual loss with aging
What is the structure of each nephron
-tuft of glomerular capillaries
-long tubule for conversion of filtered fluid to urine
Do glomerular capillaries have high hydrostatic pressure to other capilarries
-yes
->approximate double
What are glomerular capillaries covered in? What type of cells specifically?
-it is covered in epithelial cells
What are cortical nephrons surrounded by
-peritubular capillaries
What are juxtamedullary nephrons surrounded by
-a specialized peritubular capillary called the vasa recta
Describe the 4 key renal processes
- Filtration
->Blood comes through afferent arteriole and flows through glomerular capilarries
->fluid crosses glomerula capillaries into the Bowman’s capsule - Reabsorption
->fluid can come out of the nephron into the peritubular capillaries - Secretion
->Substances that leave the capilarries and enter the renal tubule
4.Excretion
->whatever remains in the tubules at the end is removed
How is excretion calculated
Excretion=Filtration-Reabsorption+Secretion
What has excretion rate less than filtration
-sodium and chloride
What are substances freely filtered but all reabsorbed and not excreted
-amino acids and glucose
What is an example of a substance not reabsorbed but additional parts are secreted into the peritubular capillaries
-creatinine
-uric acid
Are foreign drugs poorly reabsorbed and secreted
-yes
->because we want these things removed from the body
->we don’t want them to build up in our body
What is glomerular filtrate
-it is the fluid filtrated from glomerullar capilarries to Bowman’s capsule
->filtrate is protein free
because glomerullar capillaries are impermeable to proteins
->composition of solutes is similar to plasma
What is the difference between filtrate and the composition of solutes in the plasma?
-no proteins in the filtrate
-calcium and fatty acids are bound to plasma proteins and not freely filtered into the Bowman’s capsule
What factors determine GFR
-hydrostatic pressure(major component)
-Bowman’s capsule pressure
-Glomerular oncotic pressure
-capillary filtration coefficient
->capillary permeability
->filtering surface area(how many glomerular capillaries do we have)
What are the three major layers of the glomerular capillaries
-endothelium of the capillary
-basement of membrane
-layer of epithelial cells(podocytes)
->they surround the outer surface of the basement membrane
Why is the epithelial cells surrounding the outer surface of the basement membrane negatively charged in the glomerulus?
-so proteins dont cross the glomerulus into the Bowman’s capsule
What happens to glomerular filtration rate as you increase afferent arteriolar resistance
-you are reducing the glomerular filtration rate
->because you are getting less blood to the glomeruli
->reduced hydrostatic pressure in the glomeruli as well
What happens to glomerular filtration rate as you increase efferent arteriolar resistance?
-blood accumulates in glomerular capillaries and increases hydrostatic pressure, increasing the glomerular filtration rate
->but this doesn’t increase forever because you increase renal blood flow over time
->so glomerular filtration rate eventually plateaus and goes down
Why do we need a high cardiac output for the kidneys
-so we can supply enough plasma for high GFR needed to regulate body fluid volume and solute concentration
How do we regulate renal blood flow and GFR
-hormones and autacoids influence GFR
-norepinepherine, epinepherine and endothelin vasoconstrict increase afferent arteriole resistance, reducing GFR
-endothelial-derived nitric oxide and prostaglandins have a vasodilation at the afferent arteriole increasing the blood to the glomerulus increasing GFR
-angiotensin 2 can act on afferent and efferent arteriole but is preferential for efferent
->helps to preserve GFR and prevent it from falling too low
What is autoregulation
-it keeps renal blood flow and GFR constant with changing pressure
->while allowing for renal excretion and water/solutes as well
How to kidneys perform autoregulation
-they need a feedback mechanism
->that links changes to NaCl concentration at the macula densa with control of renal arteriolar resistance
-the amount of sodium chloride that reaches the distal tubule is sensed by that tubule and helps to regulare bloodflow
Describe the process that occurs in the kidneys when arterial pressure decreases
-well that leads to glomerular hydrostatic pressure and filtrate flows more slowly in the nephrons and is reabsorbed more readily
->this means less NaCl reaches the macula densula
-this less NaCl results in renin from the juxtaglomerular cells being released
->which also increases angiotensin 2 formation and increases the efferent arteriolar resistance
-as well, the afferent arteriolar resistance is increased too
What happens when arterial blood pressure increases
-increased delivery of NaCl to macula densula
->so afferent arteriolar constriction, resulting in less blood to glomerulus reducing glomerular hydrostatic pressure
What are the two steps of reabsorption
- Transport across tubular epithelial membranes into renal interstitial fluid
- Then the filtrate goes through peritubular capillary membrane back into blood
-dependant on active or passive transport mechanisms
-also dependent on transcellular route through cell membrane
-paraceulluar route is another approach as well
->through spaces between cell junctions
How are water and solutes transported from the peritubular capillaries back into the blood
-through ultrafiltration
->mediated by Starling forced
How does the Na-K ATPase work on the proximal tubular membrane to help with sodium reabsorption
-Na-K ATPase
->moves sodium out of epithelial cells into interstitial fluid and potassium back into epithelium
->water will follow sodium, just following solute
What is secondary active transport in relation to the Na-K ATPase on the tubular cells
-transport of sodium down an electrochemical gradient help another substance like glucose move against its gradient
-sodium glucose transporters carry glucose across proximal tubule cells
->then glucose transporters help diffusion of glucose out of epithelial cells into interstitial fluid
-this can be done with sodium and amino acids as well
What is secondary active secretion
-involves counter transport of a substance with sodum ions
->energy liberated from sodium moving downhill on its electrochemical gradient helps the uphill movement of a second substance towards secretion
-this can help us maintain acid base balance
Is there passive water reabsorption by osmosis coupled to sodium reabsorption?
-yes
->this happens mostly through tight junctions between epithelia cells and through cells themselves
How does water and solutes enter the peritubular capillaries by bulf flow? Talk about Starling forces
-lower peritubular capillary hydrostatic pressure and much higher oncotic pressure drives net reabsorption into capillaries
What is pressure natriuresis(salt loss) and pressure diuresis(water loss)
-it happens because of increased blood pressure, increasing urine excretion
-also slight increase in peritubular capillary hydrostatic pressure, especially in vasa recta
->this leads to subsequent increase in renal interstitial fluid hydrostatic pressure
Describe the reabsorption in the proximal tubule
-bulk of water and sodium reabsorption(65%)
-epithelia cells are highly metabolic, supporting active transport processes(large amount of mitochondria)
-extensive luminal brush border
-large surface area on luminal and basolateral epithelia
-loaded with protein carrier molecules
Does the concentration of sodium change in the proximal tubule due to water loss
-no because water follows sodium
-so yes you lose sodium, but you also lose water balancing out that concentration of sodium and keeping it consistent
Is there secretion of organic acids and bases into the proximal tubule?
-yes
Describe the thin descending/ascending loop of henle in terms of reabsorption. As well you can mention the thick ascending portion as well
-thin epithelial membranes, no brush borders, few mitochondria, minimal metabolic activity
-the thin descending specifically have high permeability to water
->moderate permeability to most solutes
->20% of filtered water is reabsorbed in Loop of Henle, mostly in the thin descending portion
-the thin ascending/thick ascending are virtually impermeable to water
->filtrate becomes hypotonic because water can’t leave
Describe the thick ascending loop of henle transport mechanisms
-we have the Na-K ATPase
->this can be used to drive Cl and K transport
-drugs(loop)direutics target Na-K ATPase transporters
->accumulate ions in filtrate and water is not reabsorbed
-there is also paracellular diffusion of other solutes such as magnesium, calcium, sodium and potassium
->because potassium can accumullate in the filtrate due to leak channels
-there are also potassium leak channels
Describe the reabsorption processes of the early distal tubule
-the first portion of the macula densa
-similar reabsorptive characteristics of the thick ascending limb of loop of Henle
-very permeable to solutes but not water so filtrate becomes diluted
Why would Na-Cl co-transporters be inhibited in the distal tubules
-to help treat hypertension
Describe the reabsorption process of the late distal tubule and collecting tubule
Two cell types
-principal cells which help reabsorb Na and water from the lumen and secrete K into lumen
->site of action of aldosterone for Na reabsorption
-intercalated cells
->help reabsorb K and secrete hydrogen into tubular lumen
->contribute to acid-base balance
How is the water permeability of the late distal tubule and cortical collecting duct controlled
-by ADH
->if we are volume depleted, we can help reabsorb the water back into the blood
Why are principal cells important
-because of sodium reabsorption and potassium secretion
-low intracellular Na favors sodium diffusion into cell from lumen through sodium channels
-potassium secretion happens in two steps
->first potassium enters cell due to Na-K ATPase action
->resulting in high intracellular potassium
->once in cell, potassium diffused down the concentration gradient into a tubular fluid
What are aldosterone antagonists and sodium channel blockers(potassium-sparing direutics)
-they block sodium reabsorption and water reabsorption
->as well they decrease K transport into cells and reduces K secretion into tubules
Describe the reabsorption process in the medullary collecting duct
-reabsorbs less than 10% of filtered water and sodium
-final site for processing urine
-epithelial cells feature few mitochondria
-permeability to water controlled by ADH
-permeable to urea and urea transporters present
->raises osmolarity in medullary intestitium helping form concentrated urine
What happens with excessive water consumption
-osmolarity of renal medullary interstitium is decreased
->ability to concentrate urine is impaired
What converts angiotensin 1 into angiotensin 2
-in the lungs through ACE enzymes
What does angiotensin 2 do?
-blood vessel vasoconstriction, which increased total peripheral resistance
->result in increased blood pressure
-increased release of aldosterone which acts on principal cells
->helps with sodium reabsorption
-acts on brain and helps release AVP or ADH, increase permeability of latter tubules to water
->increasing reabsorption here as well
-as well, thirst increases too
What happens when there is volume overload
-there is an atrial stretch at the heart
->there is release of atrial natriuretic peptide(ANP)
ANP has multiple effects
->works to oppose aldosterone release
->vasodilates blood vessels and reduces pressure
->opposes the release of renin and angiotensin 2 as well
-ANP increases total urine output, resulting in naturasis and direusis
