Physiology Flashcards
What is tonicity?
The effect a solution has on a cell.
How much fluid in the body is intracellular and extracellular?
Intra- 67%
Extra- 33%
What are the 4 compartments and percentages of extracellular body fluid?
Plasma- 20%
Interstitial fluid- 80%
Lymph- Negligible
Transcellular- Negligible
What tracer can be used to measure total body water?
3H2O- Ditritrium oxide/T2O
What tracer can be used to measure ECF?
Inulin
What tracer can be used to measure plasma?
Labeled albumin
What is the function of the kidneys?
Water and salt balance Acid base balance Excrete waste and drugs Maintain plasma volume and osmolarity Secrete renin and erythropoietin Activate VD
What is the primary function of the kidney?
To regulate volume, composition and osmolarity of body fluids.
What is the functional unit of the kidney?
Nephron
What are the two types of nephron?
Juxtamedullary
Cortical
What are some of the important parts of the nephron?
Blood vessels Glomerulus Proximal tubule Loop of Henle Distal tubule Collecting duct
What are the two parts of the loop of Henle?
Descending and ascending limbs
What is the glomerulus contained within?
Bowman’s capsule
What is found next to the glomerulus between the afferent and efferent arterioles?
Juxtaglomerular apparatus
What two special cell types are found in the juxtaglomerular apparatus?
Granular cells
Macula densa
What percentage of the plasma that enters the glomerulus is filtered?
20%
What two things can occur between the tubules and peritubular capillaries?
Tubular secretion and reabsorption
How do you calculate the rate of filtration?
[X]plasam x GFR
How do you calculate the rate of excretion of a substance?
[X] urine x Vu (urine flow rate)
How do you calculate the rate of reabsorption of a substance?
Rate of filtration of X - rate of excretion of X
How do you calculate the rate of secretion of a substance?
Rate of filtration of X - rate of excretion of X
What are some barriers to filtration?
Endothelium
Basement membrane
Podocytes
How do barriers to filtration work?
Physical barrier
Charge barrier
What four forces control GFR?
Glomerular capillary blood pressure (BPgc)
Bowman’s capsule oncotic pressure (COPbc)
Capillary oncotic pressure (COPgc)
Bowman’s capsule hydrostatic pressure (HPbc)
Which two forces govern fluid leaving the capillaries into the bowman’s capsule?
Glomerular capillary blood pressure (BPgc)
Bowman’s capsule oncotic pressure (COPbc)
Which two forces govern fluid leaving the bowman’s capsule into the capillaries?
Capillary oncotic pressure (COPgc)
Bowman’s capsule hydrostatic pressure (HPbc)
Under normal conditions what are the values for the four forces governing GFR?
Glomerular capillary blood pressure- 55mmHg
Bowman’s capsule oncotic pressure- 0mmHg
Capillary oncotic pressure- 30mmHg
Bowman’s capsule hydrostatic pressure-15mmHg
What is the net filtration pressure normally?
10mmHg
What is another term for the forces governing GFR?
Starling forces
What is GFR?
Rate at which protein free plasma is filtered from glomerulus into bowman’s capsule per unit time
How do you calculate GFR?
Kf (how holey the membrane is) x net filtration pressure
What is normal GFR?
125ml/min
What is an extrinsic method of regulating GFR?
Alter diameter of blood vessels to glomerulus
What are the two intrinsic/autoregulation mechanisms of regulating GFR?
Myogenic
Tubuloglomerular feedback
What does myogenic autoregulation involve?
Vascular smooth muscle into kidneys increases then automatically constricts.
What does tubuloglomerular feedback autoregulation involve?
Juxtaglomerular apparatus- mechanism unknown.
Rise in GFR leads to more NaCl in tubules causing constriction.
What do the macula densa cells in the juxtaglomerular apparatus do?
Sense NaCl
What can raise the Bowman’s capsule hydrostatic pressure (HPbc) and what effect does this have of GFR?
Renal stones. Decrease GFR.
What can raise the Capillary oncotic pressure (COPgc) and what effect does this have on GFR?
Diarrhoea. Decrease GFR.
What can drop the Capillary oncotic pressure (COPgc) and what effect does this have on GFR?
Severe burns. Increase GFR
What is plasma clearance?
How effectively the kidneys can clear the blood of a substance.
How do you calculate plasma clearance?
[X]urine x Vurine/[X]plasma
What are the units for plasma clearance?
ml/min
Clearance of what substance is GFR based on?
Inulin
Why is inulin good for calculating GFR?
Freely filtered Not reabsorbed or secreted Not metabolised my kidney Not toxic Easy to measure
What is normal clearance of inulin?
125ml/min
is glucose filtered?
Yes
If it is filtered why is glucose not normally seen in the urine?
Completely reabsorbed.
Why does urea have a clearance lower then GFR?
Freely filtered and partly reabsorbed
Why does H+ have a clearance higher than GFR?
Filtered and secreted
What is renal plasma flow?
Amount of blood flowing through the kidneys