Cardiovascular System - Lecture 3 Flashcards
What is blood pressure?
the force exerted by blood on the walls of blood vessels
What is the value for systemic blood pressure?
120/80 mmHg
What is the value for central venous pressure?
5-15 cm H2O (6-12 mmHg)
What region does blood move to and from?
from high pressure to low pressure
What is the formula for pressure?
Pressure = Force/Area
What kind of velocity and pressure is needed for diffusion to happen?
low velocity and low pressure
The pressure is ___ in the arteries and arterioles than in the capillaries, venules and veins.
higher
Why is the pressure in the arteries and arterioles higher than in the capillaries, venues, and veins?
because resistance is much greater in the arteries and arterioles than in the capillaries, veins and venules
What kind of resistance do arteries and arterioles have?
high resistance
What kind of resistance do veins and venules have?
low resistance
Why do arteries contract?
because they have more muscle than veins
Is pressure higher in the systemic circulation or the pulmonary circulation?
systemic circulation
Is pressure higher in systole or diastole?
systole
Which vessels have less significant pressure differences between systole and diastole?
arterioles and capillaries
Which vessels does the oscillation of pressure between systole and diastole diappear in?
venules and veins
What is the formula for perfusion pressure?
perfusion pressure = inlet pressure (arterial pressure) - outlet pressure (venous pressure)
What is perfusion pressure normally equal to?
arterial pressure
What happens to flow if there is no perfusion pressure?
there is none
What is the formula for flow?
Flow = Perfusion Pressure/Resistance
Which vessel regulates flow: arteries or veins? How?
arteries by changing the cross-sectional area, diameter and resistance
Flow is proportional to perfusion pressure, which in turn is approximately the ___ ___.
arterial pressure
What occurs between vessel walls and the blood?
friction
What happens to flow when internal surface area and resistance of a vessel doubles?
it halves
Where is the resistance greatest in a vessel?
near the surface (slowest flow)
Where is the resistance the least in a vessel?
at the center
What is laminar flow?
the entire fluid that flows in the same direction
Where is fluid speed greater in a vessel?
in the middle
What does the flow speed depend on?
the viscosity of the fluid
The greater the viscosity, the ___ the resistance to flow.
greater
In blood, what does viscosity vary depending on?
hematocrit
The more red blood cells there are, the more ___ the blood.
viscous
Why is blood viscosity generally constant?
because hematocrit varies very little under normal conditions
What is the length of blood vessels in an organism?
constant
What is resistance equal to?
8 x viscosity x length / radius
What is the main determinant of resistance variation in blood vessels?
viscosity, length of the vessel and cross-sectional area
What controls the resistance in vessels (4)?
- local metabolites
- hormones
- neurotransmitters
- endothelial cells
What happens to levels of Ca2+ in muscle cells when contraction occurs?
they increase
What happens to levels of Ca2+ in muscle cells when relaxation occurs?
they decrease
What happens to the resistance when cross-sectional area of a vessel increases?
it decreases
In a situation where the vessels are in series, the total resistance of the 2 vessels is equal to…
the sum of the resistances of vessel 1 and vessel 2
When vessels are in series, the total resistance is ___ than the resistance of each vessel taken individually.
greater
In a situation where the vessels are organized in parallel, the resistance at the entry and exit of the system is ___ than the resistance in each of the vessels.
lower
Why is the resistance inversely proportional to the radius in parallel vessels?
because the radius of the vessels at the entrance/exit is greater than the radius of each individual vessel
Which vessels have the most blood?
veins and venules
Why do veins and venules have most of the blood?
because of the high compliance they have
Why don’t arteries and arterioles have as much blood as veins?
because they have more resistance
Why are arteries able to contract very well?
because veins are able to relax very well
What does compliance depend on?
variations in vessel volume
What is the formula for compliance?
compliance = V/P
Why are veins more compliant then arteries?
because they have little smooth muscle and few elastic layers
What kind of change happens in volume when the pressure of arteries increases?
minimal change
What kind of change happens in volume when there is a slight pressure change in veins?
it increases a lot
Venous compliance is much more ___ than arterial compliance.
important
Blood pressure in the venous system is much ___ than the arterial system.
lower
Blood pressure in peripheral venules is <___ percent of that in ascending aorta.
10
What are the 2 mechanisms needed to maintain flow of blood in veins against force of gravity?
- valves
- contraction of skeletal muscles
What is the function of valves?
ensure one-way flow of blood toward heart
Valves superior to the contracting muscle ___, allowing blood to move toward the heart.
open
