11.21 A Flashcards
In words, what is cardiac output?
the flow of blood out of the left heart and into the aorta
As an equation, cardiac output is what?
HR x stroke volume
What does MAP stand for? What is it?
- mean arterial pressure
- the average pressure in the systemic arteries
What is the hemodynamic equivalent of Ohm’s Law that applies to blood flow?
flow = (pressure differential)/resistance
What is the blood pressure in the right atrium?
negligible because it is part of the venous system
What does TPR stand for?
total peripheral resistance
What determines total peripheral resistance?
the resistance of the systemic arterioles
MAP = ???
MAP = CO x TPR = HR x SV x TPR
The baroreflex attempts to maintain what?
mean arterial pressure
The baroreflex works to maintain MAP by altering what two factors?
either cardiac output or total peripheral resistance
Changes in MAP are detected by what?
baroreceptors
What are baroreceptors?
stretch receptors in the arteries that participate in the baroreflex
What happens to baroreflex-related parasympathetic firing when MAP decreases?
it decreases
What happens to baroreflex-related sympathetic firing when MAP decreases?
it increases
When parasympathetic firing decreases as part of the baroreflex, what are the physiologic results?
decreases parasympathetic firing to the SA node, which is normally inhibitory, disinhibits firing and increases the heart rate
Parasympathetic firing to the SA node is usually (inhibitory/excitatory).
inhibitory
What portion of total body water is in the intracellular fraction?
two thirds
What portion of total body water is in the extracellular fraction?
one third
How much of the extracellular body water is interstitial?
three quarters
How much of the extracellular body water is in the plasma fraction?
one quarter
How have we determine the distribution of total body water?
by injecting a substance that has a known distribution in the fractions, taking a sample of body fluid, and using C=m/V to determine the volume
What is the most approximate way to estimate total body water?
TBW = 60% of body weight
What is the most accurate way to estimate total body water?
TBW = 72% of lean body mass = 72% of (body weight - fat weight)
How does total body water change with age?
infants have more body water and have a different ratio than adults
Where is sodium concentration high in total body water?
plasma and interstitial
Where is potassium concentration high in total body water?
in the intracellular fraction
Where is calcium concentration higher in total body water?
~ 2.5 in plasma and interstitial, 0 in intracellular
Describe protein concentration in the different fractions of total body water?
highest in intracellular (4), lowest in interstitial (0.2), plasma in the middle (1.2)
Total concentration of solutes in the three fractions of total body water are all approximately what?
290-305 mOsm
What is osmotic pressure?
the hydrostatic pressure that prevents water movement from a pure water phase into a solute phase
At normal body temp, the relationship between osmotic pressure and solute concentration is roughly what?
20 mmHg per mOsm solute difference
What is the basis for oncotic pressure?
the difference in protein concentration between the interstitial and plasma fractions and that protein is impermeant
Oncotic pressure provides the force needed for what?
re-absorption of water
What happens to capillary pressure across a capillary?
resistance increases due to narrowing of the blood vessel and so flow declines and pressure decreases
At a capillary, which is greater, the filtration volume or the reabsorption volume?
the filtration volume
What happens to the the fluid that is filtered at a capillary but isn’t reabsorbed into the venous system?
it is taken up into the lymphatic system to be returned to the vascular system
What might cause the interstitial pressure to be abnormally high and limit the force for filtration?
damage to the lymphatic system that results in fluid remaining in the interstitium
What might cause the interstitial oncotic pressure to increase?
an inflammatory response that increases vascular permeability and permits protein to leave the vessels and enter the interstitium
In the first half of a capillary, net filtration occurs because what is greater than what?
capillary pressure is greater than oncotic pressure
In the second half of a capillary, net absorbtion occurs because what is greater than what?
oncotic pressure is greater than capillary pressure
How is oncotic pressure that drives water into cells counteracted?
by a Na/K pump that changes the solute concentration gradient
What is tonicity?
the property defined by how the volume of a cell changes when the cell is placed in a solution
How does the rate of water movement compare to the rate of permeant solute movement across a semipermeable barrier?
water moves much faster than any solute
What happens to a RBC placed in an iso-osmotic but hypotonic solution of a permeant solute like urea?
it will swell until it lyses
What happens to a RBC placed in a hyperosmotic but hypotonic solution of permeant solute like urea?
the cell will initially shrink as water rapidly leave the cell but will then swell and burst as urea moves into the cell and water follows
What happens to a RBC placed in a hyperosmotic but isotonic solution?
the cell will initially shrink and then return to its original size
IV saline is ___osmotic and ____tonic.
isoosmotic and isotonic
Because saline is isoosmotic and isotonic, it will have what effects on the various body fluid fractions?
it will increase extracellular volume and not change the intracellular volume
5% dextrose will have what effects on the various body fluid fractions?
it will increase both the extracellular and intracellular volumes
