Arterial, Venous Systems & Microcirc. Flashcards
What are the tissue layers of the blood vessels?
- intimida: inner most layer
- media: middle layer
- Adventist: outermost layer
What is the intima?
- innermost layer of the blood vessel
- can secrete chemicals to dilate or constrict vessels
- endothelial cells
- connective tissue
- intercelllular matrix
- internal elastic lamina
What is the media of a blood vessel?
Middle layer
- elastic tissue
- connective tissue
- smooth muscle *
- external elastic lamina
What is the adventitia of a blood vessel?
Outer layer
- connective tissue
- nerves
- nutrient capillaries in large vessels
Is there smooth muscle in veins?
Yes, there is much more smooth muscle in arteries but veins still have some—> large veins can contract
What are arterioles?
Small arteries
- ** bulk or resistance occurs here **
- ** “STOP COCKS” of vascular system **
- regulate distribution of blood flow to various capillary beds **
Where is the lowest pressure in systemic circulation?
RIGHT ATRIUM
Not the capillaries: capillaries must generate enough pressure to return blood to the heart
What is pulse pressure?
SBP - DBP
How do you calculate an approximate MAP?
DBP + 1/3 (SBP-DBP)
Or
(CO + SVR) + CVP
How do you calculate precise MAP?
Calculate area under arterial line tracing for 1 cardiac cycle
- requires calculus
Why is the highest BP found in the feet when supine?
SUMMATION WAVES: wave hits something and bounces back, another wave hits, and creates a bigger wave (higher pressure)
What is another name for dicrotic notch, and what does it signify?
Incisura: aortic valve closure and the beginning of diastole
What is the purpose of the vena cava?
- return blood to the heart
* ** ACT AS A BLOOD RESERVOIR: ~ 70% of blood volume resides in big veins at any time *****
What is bovine circulation?
- when left carotid comes off of the right subclavian artery (opposite side)
As vessels go further from the heart what happens?
- Delay in onset of initial pressure rise
3 major changes:
1.) the high frequency components of pulse (dicrotic notch) are damped out and eventually disappear
2.) systolic portions of pressure wave become narrowed and elevated
3.) a hump may appear on diastolic portion of wave
What does the arterial system do in terms of flow?
Converts pulsatile flow to continuous flow
- pulse dampening: aorta can expand as blood flows out of the heart
How is pulsatile flow converted to continuous flow?
Part of energy of cardiac contraction is dissipated as forward flow—> kinetic energy, the rest is stored as potential energy
- much of stroke volume is retained by stretching distensible arteries
- during diastole, elastic recoil of arterial walls converts this potential energy into capillary blood flow
- if arterial walls were rigid this would not take place- would create more work for the heart
Why is it important to convert pulsatile flow to continuous flow?
Minimized workload of the heart
More work is required to pump intermittently
What is the purpose of the arterial system?
Distribute blood supply to capillary system
What increases pulse pressure?
Decreased aortic compliance?
- age, atherosclerosis, HTN
What is the equation for compliance?
(Change in volume)/(change in pressure)
* low compliance increases SBP and decreases DBP both ** —> wider pulse pressure
Why do arteries get stiffer (less compliant) as we age?
Loss of elastic tissue
What is Ohm’s law?
Q= change in pressure/resistance
How do you calculate Cardiac output (CO)?
= (MAP - CVP)/SVR
How do you calculate SVR?
=[(MAP - CVP)/CO] x 80
What are specific blood reservoirs in the body?
Spleen Liver Heart Lungs * large abdominal veins * Venous plexus beneath the skin-> respond to temperature
Why do veins make such great reservoirs?
Distensibility: it takes a large volume of blood before you begin to see a change in venous pressure
- the volume prior to pressure change is called “unstressed volume” - during shock states you rely on unstressed volume to keep you alive
What are things that increase CVP?
- decrease in CO (blood gets backed up)
- increase in total blood volume
- venous constriction
- gravity- going from standing to supine
- arterial dilation
- respiratory activity: increased rate, and + pressure ventilation decreases venous return
- skeletal muscle pump- exercise
Is CVP a good measure of volume status?
NO
Body will try to maintain normal CVP despite substantial volume loss of unstressed reservoir
- this is done by sympathetic constriction of splanchnic venous compartment
What is something to be aware of in a tachycardic patient who has experienced large volume blood loss?
Their body is dependent on sympathetic tone to maintain BP
- if you give a med that reduces that tone, nothing will keep the BP up—> a whole stick of propofol will kill them
While standing, pressure of veins may be:?
- 90mmH in the feet
- -10mmHg in the head (Sagital veins = veins in head)
- in a sitting craniectomy: pressure in head is so low it can suck air into circulation
- ** can get air emboli anytime surgical incision is above the level of the heart ****
What are varicose veins caused by?
Incompetent valves
Caused by too much pressure or blood clots
What does spontaneous respiration do to venous return?
Decreases intra-thoracic pressure —> decreases RA pressure—> enhances venous return
What does mechanical ventilation do to venous return?
Increases intra-thoracic pressure—> increases RA pressure—> decreases venous return
What does a valsalva maneuver do to venous return?
Causes large increase in intra-thoracic pressure—> impedes venous return to RA
* if you forget to turn APL valve on after incubating it will cause a valsalva maneuver
—> patient’s BP will tank (giving all 50 psi to their lungs)
What is true regarding arterioles?
Thick smooth muscle
Give rise to metarterioles, then capillaries
What is true about metarterioles?
- precapilary sphincters regulate flow into capillaries
- local conditions in tissues regulate opening and closing of sphincters
What are some facts about capillaries?
Thin walled
Greater cross sectional area because so numerous
Greatest surface area for exchange
Devoid of smooth muscle—> CANNOT CONSTRICT
What is the intercellular cleft?
Place on capillary wall where capillaries meet
- 1 place exchange can occur
Capillary distribution varies by tissue needs. Where are the densest capillary distribution areas?
The heart
Metabolically active tissues
What is the law of la place?
Wall stress= (pressure x radius)/wall thickness
Smaller radius=smaller pressure
Larger radius=larger pressure
* this is why capillaries don’t burst *
What are the mechanisms of action across capillary endothelium?
- diffusion:
- O2, CO2, lipid soluble substances
- bulk flow:
- via intercellular clefts or “pores”
- H2O, electrolytes, small molecules
- vesicular transport
- large proteins
- active transport:
- ions, glucose, amino acids—> requires a carrier and ATP
What is vesicular transport?
Proteins are too large to go through pores of cell membrane
- they bump against the cell wall and it wraps around them creating a capsule, then releases them through the membrane and to the other side
Is the permeability of a capillary endothelial membrane the same in all body tissues?
NO
What is the difference between a continuous, fence started or discontinuous membrane?
- Continuous: no gaps in membrane, still allows for diffusion, bulk flow, vesicular and active transport
- Rene started: holes in membrane things can slip right through
- discontinuous: breaks in membrane allow things in
What tissues make up the wall of an artery?
- endothelium
- smooth muscle
- elastic fibers
- fibrous tissue
What tissues make up the wall of an arteriole?
smooth muscle and endothelium
What tissues make up the wall of a vein?
Endothelium Elastic Smooth muscle Fibrous (Same as an artery, but artery will have more smooth muscle)
What factors regulate CVP?
Venous return and right ventricular function
