physiology Flashcards
what is osmolarity?
-a concentration of osmotically active particles present in a solution
what are the units of osmolarity?
osmol/l or osmol/l
mosmol/l for body fluids as these are weak salt solutions
how can osmolarity be calculated?
It can be calculated if two factors are know:
- the molar concentration of the solution and
- the number of osmotically active particles present
what is the difference between osmolality and osmolarity?
- osmolality has units of osmol/kg of water
- osmolarity has units of osmol/l
what is the osmolarity of body fluids?
approx 300 mosmol/l
what is tonicity?
-the effect a solution has on cell volume
what is isotonic solution?
one where there is no change in cell volume if you were to insert or add a cell to the solution
what is a hypotonic solution?
a solution that causes a cell to increase in cell volume
what is a hypertonic solution?
the solution causes a decrease in cell volume
what % of body weight does total body water take up?
males= roughly 60% of body weight females= roughly 50% of body weight
this is due to women having more fat and fat has very little water
what does total body water consist of?
intracellular fluid (ICF) = 67% of total body water
extracellular fluid (ECF) = 33% of total body water
what does extracellular fluid include?
- plasma
- interstitial fluid
- lymph and transcellular fluid
what is a tracer for measuring ECF?
inulin
what is a tracer for measuring plasma?
labelled albumin
what is a tracer for measuring total body water?
3H2O
how is total body water calculated?
TBW= ECF + ICF
How is volume of distribution calculated?
how is the distribution volume of a tracer measured?
what is needed to maintain homeostasis?
input must match the output
input (s)= output (s)
what is water imbalance manifested in?
-as changes in body fluid osmolarity
what are insensible losses of water in the body?
- losses of water from the body where there are no physiological mechanisms that can stop it
- e.g. skin always losing water due to diffusion to the environment, lungs when you lose water exhaling
- skin, lungs
what are sensible losses of water in the body?
- loss of water from the body through which there are physiological mechanisms in place and can control
- e.g. sweat can be controlled by doing less exercise or changing jumper, faeces through diarrhoea, urine through dehydration decreasing urinary output or being overhydrated and increasing urinary output
- sweat, faeces, urine
how is water balance maintained?
- by increasing water ingestion
- decreased excretion of water by the kidneys alone is not enough to maintain water balance
what ions are found in ICF and ECF?
important:
- more sodium, chloride and bicarbonate ions in the ECF compared to the ICF
- more potassium ions in the ICF compared to the ECF
summary slide :0 xxx!
what is fluid shift?
-the movement of water between the ICF and ECF in response to an osmotic gradient
what occurs if the osmotic concentration of the ECF increases (the extracellular fluid would lose water but retain salt so the individual is dehydrated but no change in salt balance)?
ECF would become hypertonic compared to ICF
- this would cause movement of water from the cells into the ECF until osmotic balance has been restored
- this means cell volume would decrease and ECF would increase due to the fluid shift to try and restore osmotic balance
what occurs if the osmotic concnetration of the ECF decreases (individual is overhydrated so have too much water)?
- ECF would become hypotonic compared to ICF
- there would be movement of water from ECF to the cell to restore osmotic balance and as a result cell volume would increase and ECF volume would decrease
what are some challanges to fluid homeostasis?
-gain or loss of water changes the osmolarity with similar changes in ICF and ECF volumes
- gain or loss of NaCl will change fluid osmolarity
- Sodium is ‘excluded’ from ICF, it can only enter ECF
-gain or loss of isotonic fluid (no change in fluid osmolarity, change in ECF only)
what structure alters the composition and volume of ECF?
kidneys- this is vital for long term regulation of blood pressure
what are electrolytes?
-any substance that dissociated into free ions when dissolved
when does electrolyte balance occur?
-when rates of gain= rates of loss
whats an example of an electrolyte?
NaCl
why is electrolyte balance important?
- total electrolyte concentrations can directly affect water balance (via changes in osmolarity)
- the concnetrations of individual electrolytes can affect cell function
what role does sodium have in the ECF?
> 90% of the osmotic concentration of the ECF results from the presence of sodium salts
Na+ is a major determinent of ECF volume
Water follows salt in ECF
what does the total amount of sodium in the ECF represent?
a balance between input (dietary) and output (primarily excretion of urine)
what are the functions of the kidney?
- water balance
- salt balance
- maintenence of plasma volume
- maintenance of plasma osmolarity
- acid base balance (excretion of hydrogen and reabsorption of bicarbonate)
- excretion of metabolic waste products (e.g. bilirubin)
- excretion of exogenous foreign compounds
- secretion of renin (control ABP)
- secretion of eythropoietin (EPO, stimultes RBC production)
- conversion of vitamin D into active form (calcitrol: calcium absorption in GI tract)
what does the urinary system consists of?
- they kidneys (that produce the urine)
- the structures that store and carry the urine from the kidneys to the outside for elimination from the body
what is contained in the medulla of the kidneys?
-renal pyramid which contain nephrons
what is the functional unit of the kidney?
nephron (this is a picture of a cortical one)
what is the blood supply to nephrons?
the renal artery has an afferent branch which joins to the glomerulus (a knot of capillaries) and drains into an efferent arteriole and into the peritubular capillaries into a venule and a vein
where is the intitial tubular fluid formed and drains?
Bowman’s capsule
what is the juxtaglomerular apparatus?
-part of the distal tubule passes between the afferent and efferent tubules
what are the two types of nephrons?
- juxtaglomedullary (20%) (on left)
- cortical (80%) (on right)
difference between the two types of nephrons?
Juxtamedullary (20%):
- longer loop of henle is longer
- have a single capillary structure called the vasa recta
Cortical (80%):
what is the tuft of capillaries found in Bowman’s capsule called?
glomerulus
what is the inner and outer layer of Bowman’s capsule made up of?
inner= Podocytes
outer- simple squamous epithelial cells
role of glanular cells?
-produce and secrete renin
what do macula densa cell detect?
the amount of salt (sodium chloride) that is present in the tubular fluid as it passes through the juxtaglomerular apparatus
where are granular cells located?
in the juxtaglomerular apparatus
what do the kidneys require to produce urine?
- need a filtration system
- rich blood supply
- mechanisms of urine modification (reabsorption and secretion)
where does glomelura filtration start?
starts in the glomerulus
what occurs to the plasma that enters the glomerulus and is not filtered ?
it leaves through the efferent arteriole
for any substance what does the filtration (GF) + secretion (TS)= ?
Filtration (GF) + Secretion (TS) = Reabsorption (TR) + Excretion
how to figure out rate of filtration of a substance?
how to calculate rate of excretion of a substance?
what does it mean if rate of filtration> rate of excretion?
-net reabsorption of that substance has occurred
what does it mean if rate filtration < rate of excretion?
net secretion of that substance has occured
what is larger, the diameter of the afferent or efferent arterial?
afferent
what are the filtration barriers?
- glomerular capillary endothelium
- basement membrane (basal lamina)
- slit process of podocytes
what must the fluid filtered from the glomerulus into the Bowman’s capsule pass through?
-three layers that make up the glomerular membrane
what are the forces that comprise net filtration pressure?
what is GFR ?
the rate at which protein free plasma is filtered from the glomeruli into the Bowman’s capsule per unit time
how to calculate GFR using Kf and net filtration rate?
GFR= Kf x net filtration rate
what is a major determinent of GFR?
glomerular capillary flui (blood) pressure (BPgc)
what is ‘normal’ GFR?
125 ml/min
what can regulation of renal blood flow and GFR be broken into?
- Extrinsic regulation of GFR
- Autoregulation of GFR (intrinsic)
what controls extrinsic regulation of GFR?
-sympathetic control via baroreceptor reflex
what controls intrinsic regulation of GFR?
- myogenic mechanism
- tubuloglomerular feedback mechanism
what occurs to GFR if you increase arterial blood pressure?
- increase volume of blood coming in to the glomerulus
- increase glomerular capillary BP
- increase net filtration pressure
- increasing GFR
summary slide GFR and BP
what mechanisms is autoregulation made up of?
- Myogenic component (if vascular smooth muscle is stretched e.g. arterial pressure increased, it contracts this constricting the arteriole
- Tuboglomelural feedback (involves the juxtoglomelural apparatus, if GFR rises more NaCl flows through the tubule leading to constriction of afferent arterioles)
what would happen to GFR if there was a kidney stone?
it would decrease
what would happen to GFR if a patient had diarrheoa?
it would decrease
what would happen to GFR in a severely burned patient?
increase GFR
what is plasma clearance?
- a measure of how effectively the kidneys can clean the blood of a particular substance
- it equals the volume of plasma completely cleared of a particular substance per minute
- each substance that is handled by the kidney will have its own specific plasma clearance value
what is the calculation for plasma clearance?
what does measuring inulin clearance allow us to measure?
GFR
what does amount of inulin filtered per unit time =?
amount of inulin excreted per unit time
what will the clearance compared to GFR be for a substance which is filtered, secreted but not reabsorbed (e.g. H+)?
Clearance >GFR
what does para-amino hippuric acid (PAH)?
-exogenous organic anion
what is para-amino hippuric acid (PAH) used to measure?
-used clinically to measure renal plasma flow
summary slide
ideally any substance used as a clarance marker should have what properties?
- non toxic
- inert (not metabolised)
- easy to measure
how is filtration fraction measured?
