Physiology Flashcards
What are the three roles of the kidneys
Maintain balance of salt, water and pH
Endocrine function - secreting hormones
Excrete products
What is the renal blood flow
Cardiac output
Renal blood flow
Urine flow
Cardiac output approx. 5 L/min
Renal blood flow approx. 1L/min
Urine flow approx. 1 mL/min
What is the order of renal blood supply
Renal artery
Interlobar artery
Arcuate artery
Interlobar artery
Afferent arteriole
(Nephron) - glomerular capillary then peritubular capillary
What are the two capillary beds in the nephron
Glomerular capillary
Peritubular capillary
What does the passage of fluid from the blood into Bowman’s space form
Filtrate
What is the approx surface area involved in glomerular filtration
1m2
What is the distal part of the nephron responsible for
Secretion and reabsorption
What are the five determinants which effecting the movement across the filtration barrier
- Pressure
- Size of the molecule
- Charge of the molecule
- Rate of blood flow
- Binding to plasma proteins e.g. calcium, hormones such as thyroxine
What can freely pass the filtration barrier
Small molecules and ions up to 10kDa
Name examples of ions which are up to 10kDa
Glucose
Uric acid
Potassium
Creatine
What is restricted crossing the filtration barrier
Larger molecules
What cannot cross the filtration barrier
Negatively charged anions
Due to the fixed negative charge in the glomerular basement membrane repels these
What are the key features of Albumin
66kDa - molecular weight
Negatively charged
What is the protein called in urine which is produced by tubule
Tamm Horsfall protein
What is filtered fluid free from
Proteins
What is the renal blood flow ml/min
1250
What is the renal plasma flow ml/min
700ml/min
What is the glomerular filtration rate ml/min
120ml/min
What is the urine flow rate ml/min
1ml/min
What is the bodies normal pH (hydrogen ion) range
7.35-7.45
What is the bodies normal pH (hydrogen ion) range
7.35-7.45
What is the minimum urine hydrogen ion concentration (pH)
4.5
Define Base
Accepts hydrogen ions
Define acid
Donates hydrogen ions
Carbohydrates + fats =
Carbonic acid
Number the buffers involved in dietary acid load
Plasma protein
Haemoglobin
Extracellular bicarbonate
Intracellular carbonate
Phosphate
What is the name of the protein which is present in urine produced by the tubule
Tamm Horsfall
What is the renal corpuscle made up of
Glomerulus (tuft capillaries) + Bowman’s capsule
What goes is the blood flowing into the glomerulus
Afferent arteriole
What is the blood flowing out of the glomerulus
Efferent arteriole
What does the glomerulus contain
Endothelial layer
Glomerular basement membrane
What does the endothelial layer contain
Fenestrated capillaries
What is the role of fenestrated capillaries
Cannot filter formed elements e.g. blood cells
Can filter elements less than 100nm in diameter
What are the layer of the glomerular basement membrane and its role
Lamina rara interna (heparin sulphate)
Lamina Densa (type 4 collagen with laminas)
Lamina rare externa (heparin sulphate)
What is the role of the glomerular basement membrane
Negatively charged on both sides
Cannot pass negative molecules e.g. plasma proteins
Easily pass positively charged molecules e.g. sodium
Can pass (but not as well as positively charged) negatively charged molecules e.g. chloride
What is the Bowman’s capsule made up of
Parietal layer
Visceral layer (podocytes)
What is the role of podocytes
Slit diaphragm in-between made of nephrin
Only allows less than 10nm through
What can pass through the renal corpusal
Charged ions less than 10nm
What can pass through the endothelial layer
Most substances
50-100nm
What cannot pass through the glomerular basement membrane
Negative molecules repelled
What can pass through the visceral layer of the renal corpuscle
Less than 10nm
What happens in the Renal corpuscle if a macromolecule e.g. plasma protein was to get stuck in the slit diaphragm
Phagocytosed by mesangial cells
What are the role of mesangial cells
Phagocytosis
Control the amount of blood flow
Gap junctions with juxtaglomerular cells
Define glomerular filtration rate
Filtration rate per unit of time (minutes)
What percentage of blood that passes into the renal corpuscle will be filtered
20%
What happens to hydrostatic pressure along the length of the capillary
Constant along the length
What happens to osmotic pressure along the length of the capillary
Rises along the length
What affects GFR
Net filtration rate
Surface area
Permeability of glomerulus
Define Osmolality
The concentration of a solution expressed as the total number of solute particles per kilogram
What is the volume of urine
400ml-20L in 24 hours
What is the pH of urine
4.5-8
What is the concentration of sodium in urine
100-300 mmol/24 hours
What is the concentration of potassium in urine
50-450 mmol/24 hours
What is the concentration of glucose in urine
less than 1 mmol/24 hours
What is the amount of amino acids in urine
Very little
What is the concentration of HCO3 in urine
1 mmol/24 hours
How much filtrate is there per day
180 L/day
What is the main principle of the proximal convoluted tubule
Bulk absorption (leaky)
What is the main principle of the distal convoluted tubule
Fine tubing (impermeable)
What is the order of the nephron segments
Proximal convoluted tubule
Proximal straight tubule
Thin descending limb
Loop of Henle
Thin ascending limb
Thick ascending limb
Collecting tubule
Distal convoluted tubule
Collecting
What parts of the nephron segments are in the cortex
Proximal convoluted tubule
Proximal straight tubule
Thick ascending limb
Collecting tubule
Distal convoluted tubule
What parts of the nephron segments are in the medulla
Think ascending limb
Loop of Henle
Thin ascending limb
Collecting duct
What is the functions of the proximal tubule
Bulk reabsorption of
- Na
- Cl
- Glucose
- Amino acids
- HCO3-
Secretion of organic ions
What is the functions of the Loop of Henle
More Na reabsorption
Urinary dilution
Generation of medullary hypertonicity
What is the function of the Distal convoluted tubule
Fine regulation of Na, K, CA, Pi
Separation of Na from H2O
What is the function of the collecting duct
Similar to distal tubule
More acid secretion
Regulated H2O reabsorption concentrating urine
What is bulk reabsorption in the proximal tubule driven by
Basolateral NaKATPase
Where is the majority of bulk reabsorption achieved in the proximal tubule
Mostly achieved in the first half
What permeability is the proximal convoluted tubule to H2O
Highly
What is the basolateral layer
Between the cell and the capillary
What is the apical layer
Between the cell and the lumen (of the proximal convoluted tubule)
What is secondary active transport
A molecule which is going against its concentration uses a molecule is going with its concentration gradient to move across the cell
What is the movement of potassium and sodium in ATPase
3 Na+ out
2 K+ IN
Which molecules move across the apical membrane using secondary active transport (into the cell)
2Na+ and glucose
Na+ and phosphate
Na+ and amino acids
What molecules in the proximal convoluted tubule make there way through the basal lateral membrane
Glucose
Amino acid
Lactate
What percentage of glucose, amino acids and lactate are reabsorbed into the capillary
100%
What is the process of bicarbonate filtration in the proximal convoluted tubule
In lumen
Proton (H+) reacts with bicarbonate (HCO3-) to make carbonic acid
Carbonic anhydrase breaks this into CO2 and H2O
CO2 moves into the cell and reacts with water (using carbonic anhydrase) inside the cell to form carbonic acid
Carbonic acid is not stable
Dissociates into bicarbonate and proton
Bicarbonate used sodium to move into capillary
Within the proximal convoluted tubule the reaction of bicarbonate from the lumen to capillary how many bicarbonate ions are secreted into the capillary
3
Define glucose: Tubular maximum
As plasma glucose increases at a specific amount the amount of glucose reabsorbed will stay the same and the amount of glucose excreted will increase
How does some potassium and chloride ions move across the cell in the proximal convoluted tubule
Using tight junctions between cells
How are endogenous compounds (creatinine, urate and bile salts) and drugs transported in the proximal convoluted tubule
Active transport
Uses organic cation/anion transporters
Define glomerulotubular balance
More filtered load is matched by more proximal tubular reabsorption
What does a greater filtration factor in the proximal convoluted tubule cause
Increases osmotic pressure in downstream peritubular capillaries
Sucks more back
What does efferent arteriolar constriction in the proximal convoluted tubule cause
Reduces peritubular capillary hydrostatic pressure
What are the two ways that glomerulotubular balance is achieved
Greater filtration factor
Efferent arteriolar constriction
What is the osmolality in the glomerulus compared to when entering the proximal convoluted tubule
Same
Isotonic with the blood plasma
What is the osmolality when entering the Loop of Henle
Same as the glomerulus
Isotonic with the blood plasma
Na+ and water are reabsorbed in the same amounts
Where does solute reabsorption occur within the loop of Henle
Thick ascending limb
What is the aim of countercurrent in the loop of Henle
Generate a hypertonic medullary interstitium so that H2O can be sucked out of the tubule in impermeable segments, thus concentrating the urine
What is another word for high osmolality
Hypertonic
What is another word for low osmolality
Hypotonic
How does counter current multiplier mechanism work
- Ascending limb lowers luminal osmolality and increases the medullary interstitial osmolality
- Increased interstitial osmolality draws H2O out of the descending limb, luminal osmolality increases
- Continuous flow of fluid pushes the hyperosmotic fluid from end of the thin limb to the ascending limb
What does the counter current multiplier mechanism create
Medullary interstitial osmotic gradient
What are the reasons why blood flow does not wash of the osmotic gradient achieved in the counter current multiplier mechanism
Vasa recta
Long capillaries extend into the medulla
Permeability to solute/water
What allows water to move out of the descending limb in the counter current multiplier mechanism
Aquaporin type 1 channels
Passive
Is the descending limb permeable to water
Yes
Is the descending limb permeable to solute
No
Is the ascending limb permeable to water
No
Is the ascending limb permeable to solute
Yes
How do solutes move out of the cell in the ascending limb
Na+/K+/2Cl- co-transporters
Move
Na+
K+
2Cl-
Out of the cell
What also contributes to medulla hypertonicity (Loop of Henle)
Back leak of urea out of the medullary collecting duct
What is the gradual medullary interstitial osmotic gradient
From
300
700
1000
1200
Moving down the lumen
Osmolarity
The concentration of a solution expressed as the total number of solute particles per litre
What is the role of the distal tubule
Continues the active dilution of urine by reabsorption of Na+ in water impermeable setting
What are the two divisions of the distal convoluted tubule
Early
Late
What is the late distal convoluted tubule responsive too
On hormones
What happens in the early distal convoluted tubule
Parathyroid hormone - works out how much Ca2+ is in the blood
Parathyroid actives Ca2+ transporters to get into the cell
Pumps out Ca2+ into the bloodstream
How does sodium get into the cell in the early distal convoluted tubule
Sodium chloride symporter (same direction)
Na+ and Cl-
What happens in the late distal convoluted tubule
Aldosterone responding cells
Allows the pumping of Na+ out of the cell and K+ into the cell
Is the collecting duct permeable to water
Impermeable
What is the collecting duct surrounded by
Hypertonic medullary insterstitium
What is collecting duct regulated by
Na reabsorption
K secretion
Acid secretion
Water reabsorption
What are the two types of cells found in the collecting duct
Principal cell
Intercalated cell
What is the mechanism of ADH on the collecting duct
ADH acts on receptor
Increases cAMP - kinases - vesicle shuttling
H2O enters the cell by the aquaporin 2 into the cell and leaves into the blood
What is the action of aldosterone on the collecting duct
Increases transcription (steroid receptor) of ENaC (and NaKATPase)
Increases apical Na influx
Charge movement facilitates K efflux
What does aldosterone drive in the collecting duct
Na reabsorption
K secretion
What cell does ADH (vasopressin) act on
Principal cells
What is the action of ADH in the collecting ducts
Adenylyl-cyclase coupled vasopressin receptor (V2R)
Kinase actions culminate in insertion of vesicles containing aquaporin 2 into the apical membrane
Increases water permeability
Define osmolaRity
Number of particles per litre of fluid
NUMBER of particles
Define osmolaLity
Total solute concentration within a specific volume of solute expressed in osmoles per litre (osm/L)