Renal Flashcards
What is osmolarity?
An estimation of the osmolar conc. of plasma
Is proportional to the number of particles / litre of solution (mmol/l)
What is osmolality?
An estimation of the osmolar conc. of plasma
Is proportional to the number of particles / kg of solvent (mOsmol/kg)
What is tonicity?
Related to its affect on the volume of a cell
What happens to a RBC placed in a hypertonic solution?
Cell shrinkage
What happens to a RBC placed in a isotonic solution?
Nothing
What happens to a RBC placed in a hypotonic solution?
Cell lysis
Whats are RBCs very permeable to?
urea
What percentage of the weight of a male is water?
~60%
What percentage of the weight of a female is water?
~50%
How much of the total body water is Intracellular fluid?
67%
What is included in the ECF?
Plasma
Interstitial fluid (80%)
Lymph and transcellular fluid (negligible)
How can a the volume of a large body of water be calculated?
V(l) = D/C
Where V = unknown volume of water
D = dose of tracer added to water
C = concentration of dose present in a small volume of this water
What tracer can be used to obtain the total body water volume
3H20
What tracer can be used to obtain the amount of water in the ECF?
Inulin
What tracer can be used to obtain the plasma volume?
Labelled albumin
Is sodium more abundant in the ECF or ICF?
ECF
Is potassium more abundant in the ECF or ICF?
ICF
Is chloride more abundant in the ECF or ICF?
ECF
Is bicarbonate more abundant in the ECF or ICF?
ECF
What is the primary anion of the ECF?
Cl-
What are the main ions in the ICF?
Potassium, magnesium, negatively charged proteins
What organ alters the composition and volume of the ECF?
Kidney
What 2 types of nephron are found in the kidney?
Juxtamedullary (20%) - longer loops of Henle
Cortical (80%)
From deep to superficial, what are the histological layers of the glomerular capillaries?
Inner endothelial cells
Basement membrane
Podocytes face out into Bowman’s capsule
What is the juxtaglomerular apparatus?
The portion of the distal tubule which loops back very near to the glomerulus
What histologically connects the distal tubule and the glomerulus at the juxtaglomerular apparatus?
A thick macula densa of the distal tubule and granular cells in some of the arterioles
What percentage of blood that enters the glomerulus at any one time is actually filtered?
20%
How can the rate of filtration of substance X be calculated?
{X}plasma x GFR
How can the rate of excretion of substance X be calculated?
{X}urine x Vu (urine flow rate)
How can the rate of reabsorption of substance X be calculated?
rate of filtration - rate of excretion
How can the rate of secretion of substance X be calculated?
rate of excretion - rate of filtration
What barriers exist for blood filtration in the glomerulus?
Glomerular capillary endothelium (RBC barrier) Basememnt membrane (plasma protein barrier) Slit processes of podocytes (plasma protein barrier)
What barriers exist for blood filtration in the glomerulus?
Glomerular capillary endothelium (RBC barrier) Basememnt membrane (plasma protein barrier) Slit processes of podocytes (plasma protein barrier)
What is the normal GFR?
125ml/min
What is the extrinsic regulation of the GFR?
Sympathetic control via the baroceptor reflex
How is the GFR intrinsically controlled?
Myogenic mechanism and tubuloglomerular mechanism which prevent short term ABP changes affecting the GFR
How does myogenic regulation work to control the GFR?
If vascular smooth muscle is stretched (increased ABP), it contracts thus constricting the arteriole
How does the tubuloglomerular mechanism work to control the GFR?
If the GFR rises, more NaCl flows through the tubule, leading to constriction of afferent arterioles
What is plasma clearance?
A measure of hoe effectively the kidneys can clean the blood.
How can plasma clearance be calculated?
Rate of excertion/ Plasma conc.
{X}urine x Vu/ {X}plasma
How can plasma clearance be calculated?
Rate of excertion/ Plasma conc.
{X}urine x Vu/ {X}plasma
What is the rate of inulin clearance compared to the GFR?
Inulin clearance = GFR
What is the rate of clearance of glucose?
0 - it is not secreted from the body
How does the rate of urea clearance compare to the GFR?
Urea clearance less than GFR
How doe sthe rate of H+ clearance compare to the GFR?
H+ clearance > GFR
How can renal plasma flow (RPF) be calculated?
Using para-amino hippuric acid (PAH)
Why is PAH good for measuring RPF?
It is freely filtered at the glomerulus
Secreted into the tubule
Completely cleared from the plasma
What should RPF be?
~650ml/min
What is the filtration fraction?
The fraction of plasma flowing through the glomeruli that is filtered into the tubules
How can the filtration fraction be calculated?
GFR/RPF
How can the filtration fraction be calculated?
GFR/RPF
Roughly how may times per day is the plasma filtered?
65
What do the kidneys reabsorb 99-100% of in healthy individuals?
Fluid - 99
Salt - 99
Glucose
Amino acids
How much of the urea in the blood is reabsorbed by the kidneys?
50%
What percentage of creatinine is reabsorbed by the kidneys?
0%
How much filtered fluid is reabsorbed in the proximal tubule?
80ml/min
What substances are reabsorbed in the PT?
Sugars Amino acids Phosphate Sulphate Lactate
What substances are secreted in the PT?
H+ Drugs and toxins Hippurates Neurotransmitters Uric acid Bile pigments
What are the 2 types of tubular reabsorption?
Transcellular
Paracellular
What are the 2 types of tubular reabsorption?
Transcellular
Paracellular
How is sodium transported into the epithelial cells of the proximal tubule?
Secondary active transport with glucose/amino acids
What is the function of the loop of Henle?
Generates a cortico-medullary solute conc. gradient
Enabling formation of hypertonic urine
What happens the the ascending limb of the loop of Henle?
Na+ and Cl- are reabsorbed
Water cannot easily permeate
What happens in the descending limb of the loop of Henle?
does NOT reabsorb NaCl
Is highly permeable to water
What ions are involved in the triple transporter?
K+
Cl-
Na+
Is fluid leaving the proximal tubule hypo, iso, or hyper tonic?
Isotonic
Is fluid entering the distal tubule hypo, iso, or hyper tonic?
Hypotonic
How does urea contribute to ~1/2 of the medullary osmolality?
Urea cycle adds solute to the interstitium
Distal tubule not permeable to urea
Urea diffuses passively into loop
How does urea contribute to ~1/2 of the medullary osmolality?
Urea cycle adds solute to the interstitium
Distal tubule not permeable to urea
Urea diffuses passively into loop
What is the purpose of countercurrent multiplication?
To concentrate the medullary ISF, enabling the kidney to produce different urine volumes and concs. according to the amounts of circulating ADH
How does ADH affect the distal tubules and the collecting ducts?
Increases water reabsorption
How does aldosterone affect the distal tubules and the collecting ducts?
Increases sodium reabsorption
Increases H+/K+ secretion
How does atrial natriuertic hormone affect the distal tubules and the collecting ducts?
Decreases Sodium reabsorption
How does PTH affect the distal tubules and the collecting ducts?
Increases Calcium reabsorption
Decreases phosphate
How does PTH affect the distal tubules and the collecting ducts?
Increases Calcium reabsorption
Decreases phosphate
What happens in the early distal tubule with ions?
Na+K+2Cl- transport
What happens the the late distal tubule with ions?
Calcium reabsorption
H+ secretion
Na+ and K+ reabsorption
What does aldosterone do in the late distal tubule?
Causes K+ secretion when the K+ secretory cells are activated
What happens in the early collecting duct?
Calcium reabsorption
H+ secretion
Na+ and K+ reabsorption
What happens in the late collecting duct?
There is low ion permeability and permeability to water is determined by ADH secretion
What happens in the late collecting duct?
There is low ion permeability and permeability to water is determined by ADH secretion
From what and where is ADH synthesised?
Octapeptide by the hypothalamus is transported down nerves where it is stored in granule form in the posterior pituitary gland
Where is ADH released into and what does it cause to happen?
Released from the posterior pituitary into the blood where APs down nerves lead to Ca2+-dependant exocytosis
What is the plasma half-life of ADH?
10-15mins
What effect does ADH have on the collecting duct membranes?
Increases their permeability to H20 by inserting aquaporins
What happens when there is maximal ADH concentration in the plasma?
Water moves from the collecting duct lumen along the osmotic gradient into the ISF thus enabling creation of hypertonic urine
How does urine travel from the kidneys to the bladder?
Propelled down the ureters by peristalic contractions
What is the micturition reflex?
Once the bladder has 250-400mls urine in it, stretch receptors in the wall of the bladder cause involuntary emptying of the bladder by bladder contraction and opening both the internal and external urethral sphincters
How can the micturition reflex be overridden?
Through voluntary control of the external sphincter
How can homeostasis of body fluid be obtained?
Monitoring and regulation of ECF osmolarity and volume
How is filtration in the kidneys regulated?
Changes in BP and the size of the filtration slits (podocytes)
What regulates the secretion/absorption in the kidneys?
Changes in solute conc.
What regulates the excretion function of the renal system?
Bladder function under neural control
How does activation of stretch receptors in the upper GI tract affect ADH?
Exerts a feed-forward inhibition of ADH
What effect does nicotine have on ADH?
Stimulates release
What effect does alcohol have on ADH?
Inhibits release
What effect does alcohol have on ADH?
Inhibits release
How does salt imbalance manifest itself?
Changes in ECFV
What regulates the amount of Na+ reabsorbed?
RAAS
In relation to ion concentrations when is aldosterone secreted?
When K+ conc rises or Na+ conc falls (or activation through RAAS)
What does aldosterone stimulate to occur in the kidney?
Na+ reabsorption
K+ secretion
How does the JGA control rennin release?
Reduced BP in the afferent arteriole stimulates rennin release
Low NaCl detected by the macula densa cells stimulates rennin release
Sympathetic activity on the granular cells, causes them to release rennin
How does the JGA control rennin release?
Reduced BP in the afferent arteriole stimulates rennin release
Low NaCl detected by the macula densa cells stimulates rennin release
Sympathetic activity on the granular cells, causes them to release rennin
What can an abnormal increase in the RAAS system cause?
Hypertension
How is hypertension caused by RAAS stimulation treated?
Low salt diet
Loop diuretics
ACEIs