Lecture 17 - Kidney Flashcards
What are the dimensions of a kidney
- 6 cms in diameter
- 11 cms high in the
longest direction - 3 cms thick
How are kidneys described
Large, bean-shaped organs
What are the two sides of a kidney
- One side is concave and one side is convex
- Lateral = concave
- Medial = convex with a vertical cleft inside
What is the renal hilum
Where all your blood vessels go into the kidney and where your ureta comes out through renal pyramids
Where do ureter and renal blood supply join kidney
At Hilum
What sits on top of kidney
Adrenal gland
How can you access someones kidneys
Put someone on their front and cut open their back
Filtration, removal and drainage
- Filter blood plasma (~200 l/day) supplied by Renal Artery
- Remove excess water & waste solutes to produce urine (~2l/day), while returning ‘goodies’ to the systemic circulation
- Drained by Renal Vein
Functions of kidney - homeostasis of blood:
1) Osmoregulation, control of
total body water volume
2) Electrolyte balance
body fluid ‘osmolality’ - concentration of solutes e.g. urea, salts, KCl in blood = regulate electrolyte balance in body
3) Acid-base (pH) balance – regulate pH of blood, regulate molecules that can either make it acidic or basic e.g. urea
4) Toxic wastes Filter blood plasma (~200 L/day) supplied by Renal Artery = shows how much blood is being pumped around continuously
no alternative means of excreting metabolic wastes; urea, uric acid or creatinine = exit points for toxic wastes, some of the stuff that has been interconverted – modified by liver, put back out into blood and filtered by kidney = PROCESSES DETOXIFIED WASTES
Drugs
Other toxins
5) Produces erythropoietin & renin = regulate blood cell production & blood pressure systemically. These are hormones secreted by the kidney itself, not by the adrenal glands on top
6) Converts VitD to active form = use it throughout body
7) Starvation - metabolism and gluconeogenesis – if liver and muscles cant keep up to date with gluconeogenesis, exteme starvation, then kidney can help
What happens once liver has done its detoxification
Hepatocytes can either pump toxins into bile through bile cuniculi into bile duct into gall bladder or kick them back out into hempatic synosoids – exit into systemic circulation through central veins – go into kidneys – excreted into urine.
What is the only exit point for creatinine, urea and uric acid
Kindey
What are urea and uric acid and creatinine
- Urea and Uric acid = biproducts of protein metabolism in body, nitrogenous waste from amino acid & nucleic acid metabolism
- Creatinine = biproduct of specifically protein metabolism for skeletal muscles, muscle waste from ATP metabolism
Urinary system - organs and flow
Kidneys filter the blood and take out urine
That urine collects and goes down into ureter
Stored in bladder
Expelled through urethra when you want it
How can you regulate excretion rates of urine
Urethra has lots of sphincter muscles
Do all species have urethra
NO
Some species are continuously peeing e.g. mice
Why do we have a large bladder
Don’t continuously urinate, can selectively urinate – more socially acceptable
How does normal urine differ from filtered blood plasma
- 91-96% water content in urine & rest dissolved solutes (higher concentration than plasma) e.g. salt (Na+Cl-), other electrolytes (K+, H+, HCO3-)
- No cells, little nutrients or plasma proteins being excreted
- Slightly acidic (pH 5.5-6.0)
URINE DIFFERENT TO FILTERED BLOOD PLASMA AS IT CONTAINS NUTRIENTS AND ESSENTIALS
How much urine is produced per day by healthy adult
- 0.6L-2.6L Urine produced per day by healthy adult
- 6-8 urinations per day (~350ml bladder capacity) – depends on how much youre drinking.
Effects of urinating too much or too less
- Too much - signs of diabetes
- Too less - not drinking enough - dehydrated
How do babies get a nappy rash
pH slightly acidic = if constantly in contact with urine – irritate skin – slightly acidic
What colour should urine be
Nice straw light yellow colour
How do kidneys regulate blood volume and salt concs and waste disposal
By excereting what your body doesn’t need in the form of urine
What is urine
Filtrate of blood plasma
Why does kidney selectively filter
Don’t want all of the nutrients and essentials in urine to just flow out and exit body – losing a lot of vital stuff
What does it show if you have plasma proteins or nutrients being excreted in your urine
Indication that something is going wrong i.e. infection in urinary system or kidney failyure. Also should not see blood in urine ( dark red )
General structure of a kidney cross section - what are the 3 key regions
- Cortex = outer region
- Medulla
- Pelvis
What is the cortex
Outer region
Light appearance
What is the medulla
Darker triangles
Dark reddish brown
Striped
Contains bundles of capillaries, blood vessels and collecting tubes
What are renal pyramids/medulla separated by
Renal columns - made of cortex
What is Pelvis
- Funnel shaped tube
- Continuous with ureter
- Fed by Calyces - major calyx
- Where urine all collects – it feeds down into ureter
What is medulla also known as
Renal pyramids
Why do regions of kidney look striated
- Due to high density of blood vessels throughout the tissue = stripey appearance
- And nephrons have long collecting tube as they go out radially and there are lots of them
What is the – main entry and exit point if larger arterioles and venules ( larger blood vessels)
Running down renal columns
What is renal hilus
Where blood vessels are coming in and renal pelvis and ureter coming out
Process of what happens in kidney
- Blood comes in through these blood vessels, gets filtered by nephron and exits again through these renal column.
- The filtrate is turned into urine and comes down collecting duct and exits first into smaller tubes – minor calyx and then into larger tubes called your major calyx – calyces – filter into larger tube – renal pelvis – it feeds down into ureter
What does nephron do
Regulate urine and blood consituents
Regions of nephron
- Bowmans capsule
- PCT
- Loop of Henle
- DCT
What is bowmans capsule
- Primary site of blood filtration
- Sits up in the cortex in kidney
What is PCT
- Comes on bowmans capsule
“ convulated “ = twists around and it’s a tube - Dives down into medulla and forms L.O.H
What is Loop Of Henle
- Has ascending ( up ) and descending ( down ) limb – in medulla
- This tube comes back up into cortex and wraps around bowmans capsule
What is DCT
- Dives back down into medulla and forms collecting duct – through medulla and opening into minor calyx
- Feeds into collecting duct which then drains into pelvis through minor calyx into ureter
What happens in nephron
- Blood filtered in bowmans capsule.
- All of that filtered plasma is running through these tubes, its changing in terms of constituents – changing water/salt levels – recapture a lot of things.
- When it gets to collecting duct, have your urine, and now the only thing that has to happen before secreted down here to ultimately go to ureter is to regulate water conc of urine
Why do you need a close relationship between nephron and blood supply
- Blood is being filtered
- Regulating components of urine that’s being created so you have to have a feedback so whatever you want to keep can get back into blood
What does renal artery cross
Pelvis/calyces
How does blood come into kidney
Through renal artery
What happens when blood comes into kidney
- Blood enters kidney through renal artery through renal hilus. It then crosses through pelvis and calyces.
- It then turns into interlobar arteries which goes in between renal pyramids into interlobular spaces
- Then it turns into smaller blood vessels known as afferent ( in )arterioles which then turn into glomerular capillaries
- Blood then exits out of these golmerualr capillaries ( whatever blood is left ) through efferent ( out )arterioles - draining glomeruli
What are glomerular capillaries
- Filtration point with bowmans capsule as nephron
- Network/bundle of capillaries that sits inside of cup of Bowmans capsule of nephron
– The interphase where you get filtration
What are Peri-tubular capillaries
- Capillaries still staying out in cortex and wrapping themselves around PCT and DCT = one way blood vessels come out
- Reclaim reabsorbed substances
What is Vasa Recta
- ‘straight vessels’ in medulla
parallel to Loop of Henle, for water/ion exchange - Blood vessels that loop around loop of henle and collecting duct
-Dives down into the medulla/renal pyramids
What are the 2 blood supplies that efferent arteriole branches off
Peri-tubular capillaries
Vasa recta
What do Peri-tubular capillaries and Vasa recta do
Both drain into the interlobular veins which goes out through your renal vein = exits kidney
What do efferent arterioles do
Drain glomeruli
What do afferent arterioles do
Supply GLOMERULAR CAPILLARIES
for plasma filtration at Bowmans Capsule
Which arterioles come in and out
Afferent arteriole coming in
Efferent areriole coming out
What does afferent and efferent arteriole form
Peritubular capillaries which wrap around PCT and DCT, OR have them coming out of glomerular plexus and diving down and wrapping around loop of henle = vaso recta
- Both of these are going in all nephrons at the same time
Where does filtration happen
- Between the Glomerulus / Bowman’s Capsule - Renal corpuscle
- Filtration at point where fluid coming from blood plasma into Bowmans capsule
Where does reabsorption happen and why
- At different points along PCT, loop of henle and DCT
you have reabsorption of of water and nutrients OR excretion of more water back into urine - BECAUSE whats being filtered also contains a lot of stuff you want to keep
- Happens at interphase of nephron tubules and blood vesssels = continuous exchange
How is plasma filtered
- Blood enters Glomerulus under pressure -due to afferent arteriole having a wider diameter than the efferent arteriole
(2) Glomerular endothelial wall is fenestrated
plasma (not cells) forced through the pores
(3) Bowmans Capsule, Podocytes wrap around glomerular capillaries
(4) Plasma passes through ‘filration’ slits between adjoining podocytes
To enter lumen Bowman’s capsule & then the PCT
How is plasma forced out at the beginning - what starts filtration process
Afferent arteriole that feeds into glomerular capillaries has a larger diameter than efferent arteriole that exits – all of blood inside of glomerular capillaries under higher pressure as trying to force same volume out through a smaller opening = blood plasma is under higher pressure
What makes it easier for plasma to get out of blood supply
Endothelial cells of these capillaries are fenestrated – little pores between endothelial cells
Pressure forces plasma ( no cells ) through these pores
What is each one of glomerular capillary wrapped around by
By one of these specailsied cells called podocytes – have processes that wrap themselves around capillaries
What are between podocytes
Filtration slits = gaps
All of that plasma coming out from these capillaries flows between these podocytes and enters lumen of bowmans capsule
Where does plasma flow out
Straight out through epithelium of podocytes = pure plasma in lumen of bowmans capsule - filter itself down PCT
What problems does filtration result in and what is the solution to this
- All small molecules (<8 nm = plasma proteins) enter
Bowman’s capsule, including nutrients like amino acids,
peptides, glucose, vitamins etc = DONT WANT THIS EXCRETED FROM BODY AS ITS USEFUL
(2) ~100 times more plasma is filtered through nephron each day than the
volume of urine you excrete each day that the body needs to produce = a lot of whats going into bowmans capsule is reabsorbed – back into body
SOLUTION:
- The rest of the Nephron is mainly involved in reclaiming ~98% of the initial filtrate
- Nutrients & ~66% of the water in PCT ( 98% of what you pass through bowmans capsule is actually reclaimed including a lot of water and nutrients – done by series of PCT, DCT and loop.o.h and more h20 by collecting.d = reclaim what you lost
PCT cells role
The most Active Reabsorbers of the Filtrate
Properties of PCT - Proximal convoluted tubule
- Numerous microvilli on lumenal (apical) surface = high SA for transfer and absorption
-Associated mitochondria
for active absorption nutrients & ions
-Water follows passively once change conc of electrolytes
-Mitochondria also basal region for active transport to peritubular capillaries - xs energy produced by mitochondira – active absorption of nutrients and ions
Where is water reabosrbed
By descending loop cells (which are impermeable to ions) concentrating the filtrate
Where is salts reabosrbed
By ascending loop cells (which are impermeable to water) diluting the filtrate
What is concentration of solutes in blood and what does it match
300 - match whats coming out of PCT
What happens at top of nephron
Slight reabsorption of nutrients and salts but same passive diffusion of water back in – reclaiming ( reabsorbing quite a bit )stuff in PCT but not changing conc of whats running through your duct, it remains the same ( not changing overall conc of fluid from blood ) – not good cause you want to reclaim a lot of saltse.g. NaCl /vitamins/nutrients that are left
What happens at Loop Of Henle
- Take back water from precursor of urine
- Take back salts as its gone really concentrated = active transport of salts
What is osmolality
MEASURE OF CONC = number of solute particles in 1litre of water
Are blood plasma and PCT filtrate the same
YES
Average = 300 milliOsmols (mOsm)
But ‘Normal’ Urine is ‘Hyperosmotic’
= 500-700 mOsm – less water –mainly concentrated with waste products like urea
More concentrated due to its higher waste
(e.g. ion & urea etc) content
What happens in Counter Current Exchange
- Via difference of Osmololity Gradients in the 2 Loops of Henle
-The Driving force is the NaCl pumps of the ascending limb cells & their lack of water permeable channels - Epithelial cells are impermeable to water AND NaCl pumps – actively transferring salt across but not allowing any water transfer out of here
= creating something where you’ve taken back a lot of the salts that you want and leaving something with a high conc of H2O
-Taken some H2O back in descending limb and taking salts and stuff we don’t want to lose through ascending limb = left with solution of high conc of h20 but still has stuff like urea and uric acid in there
-Need to reclaim some h2o that is in precursor of urine by collecting and reabsorbing water as we go down collecting duct which then filters down into minor calyx
How to salts and water re enter the blood supply
Through the Vasa recta
The reabsorbed water and salt isn’t just going back into tissue of kidney, it gets pumped back into blood through vasa recta around loop.o.h
Where is initial water and mineral/ion reabsoprtion
Around PCT/DCT
Water injestion vs water excretion
SEE LECTURE SLIDES FOR FIGUIRES
A Balancing Act in kidneys depending on how much you’ve injested each day
Need to excrete the same as you injest – if too much , shrivel up, if too less, balloon up
If don’t drink much – less ingested so less excreted through urine
If taking a lot of water but if high salt diet – retain a lot of water to try and counterbalance – don’t want salt levels to accumulate in blood = body retains more water if it cant excrete salts – lot of adema - around ankles
What are extremes of urine
Very dilute or very concentrated
What happens when urine is too dilated or concentrated
Require independent regulation of water & salt urine contents
Depends on how much water and salts we need to get rid of and how much we neeed to retain
How do you get dilute urine
Excess water intake
What happens when dilute urine i.e too much water taken in
- Urine osmolality needs to be low = 100 mOsm (the same as final Henle’s Loop) = not reabsorbing water from collecting duct
- Urine volume needs to be high = 20 L/day
- No change to filtrate after Henle’s Loop and PCT - everything happens same
- No reabsorption of H20 at collecting duct
SEE LECTURE SLIDES
How do you get concentrated urine
Excess salt intake
What happens when concentrated urine i.e too much water salt in
- Urine osmolality needs to be high = 1200 mOsm (the same as the hairpin of Henle’s loop - its more cause its CONC = need more H20 to balance it)
- Urine volume needs to be low = 0.5 litres/day
- Mechanism more complex: more water must be reabsorbed from filtrate in the Collecting Ducts after Henle’s Loop
- Normally excreting 700-800, not 1200 = try to reabsorb as much H20 as possible through collecting duct = biproduct is urea = increase amount of salt conc around tissues = decrease salt reabsorption
Macula densa cells
In DCT
Monitor Nacl conc in blood
Sensory cells = in ball of DCT which makes contact with afferent and efferent arterioles entering bowmans.c.
Juxtaglomerular cells
Smooth muscle cells in space between afferent and efferent arterioles)
Monitor pressure in and out of glomerular capillaries
How is blood flow regulated throughout body:
Either a change in salt conc detected by DCT or a change in bp – change in water vol of blood can stimulate hormonal response e,g, if detect decrease in na conc in macula densa = secrete renin ( hormone ) from juxta.. Cells into bloodstream = regulates glomerular filtration rate
Effects of renin release from Juxta-glomerular cells:
It has an effect on water retention in the collecting ducts through vasopressin via pituitary gland and directly back onto kidney itself by affecting reabsorption through CT
Role of renin
- Change neural activity and direct effect on hormone arterioles around body
- Enzyme which changes angiotensinogen into active form called Angiotensin I and have secretion of another enzyme called ACE - secreted into lungs or turns A1 into A2 - picked up by adrenal glands/kidney itself/detected by pituiatry gland
SEE LECTURE SLIDES FOR NOTES
Kidney Failure
Causes:
infection, trauma, poisons (lead, solvents)
Symptoms: (severe)
oedema (water & salt retention)
cardiac arhythmia (excess K+)
azotemia (acidic blood pH)
convulsions, coma & death (brain cells swell)
Treatment: (unpleasant)
haemodialysis (artificial kidney)
organ transplant (UK waiting list 7000; 2.5-3yrs)
Haemo-Dialysis
Blood plasma cleansed via permeable tubes
Heparin given to prevent clotting
Session lasts 4-8 hours
Need 3-4 per week
Problems = haemorrhage, infection, thrombosis
= lots of filtration systems to clean it up
Tube into artery and vein, blood outt
