Final Flashcards
Which vessels show greatest resistance to blood flow?
Arterioles
Smallest vessels in the circulation
capillaries
When the lumen of a blood vessel is suddenly expanded, the smooth muscles respond by contracting in order to restore the vessel diameter and resistance. The converse is also true. This is?
Autoregulation: Myogenic Mechanism
Proposed mechanism is stretch of vascular smooth muscle causes activation of membrane calcium channels.
The _______, located in the brainstem above the spinal cord, is the primary site in the brain for regulating ________ and __________ (vagal) outflow to the heart and blood vessels.
medulla
sympathetic
parasympathetic
Increased ICP results in increased BP until blood flows once again in the vessels of the brain. What response?
Cushing response
The _______ of each tissue continuously monitor tissue needs
microvessels
Blood flow =
pressure difference/resistance
pressure difference example: P.arterial - P.venous
greatest role of all factors in determining the rate of blood flow through a vessel
diameter/radius
Flow is Inversely proportionate to?
viscosity and length of tube
SVR is primarily determined by changes in blood vessel________.
diameters
sum of resistance vessels in a series?
totalresistanceto blood flow (Rtotal) is equal to the sum of theresistances of each vessel
R.t = R.1 + R.2 + R3, etc.
sum of resistance vessels in parallel?
1/R.t = 1/R.1 + 1/R.2 + 1/R3, etc.
(Flow through each of the parallel vesselsis determined by the pressure gradient and its ownresistance, not theresistanceof the other parallel blood vessels. However, increasing theresistanceof any of the blood vessels increases the totalvascular resistance.)
parallel arrangement permits each tissue to regulate its own blood flow, to a great extent, ___________ of flow to other tissues. Therefore, the totalresistanceis far ____ than theresistanceof any single blood vessel
independently
less
A valuable characteristic of thevascularsystem is that all blood vessels are_______.
distensible
This capability provides smooth, continuous flow of blood through the very small blood vessels of the tissues.
Distensibility/compliance
Tissue Layers of Blood Vessels:
Intima (inner most)
Media
Adventitia (outer most)
which layer of blood vessel thicker in arteries? Which is thicker in veins?
media
adventitia
arterial compliance =
Change in volume/change in pressure
Autoregulation:Metabolic Mechanism
When the pressure increases to a tissue, the flow increases, and excess oxygen and nutrients are provided to the tissues. These excess nutrients cause the blood vessels to constrict and the flow to return nearly to normal despite the increased pressure
Vasoactive substances released from endothelium lining vessels?
- nitric oxide (dilator - MOST IMPORTANT)
- prostacyclin (dilator)
- endothelin (constrictor)
-A key mechanism for long-termlocal blood flowregulation is to change the amount of vascularity of the tissues. For instance, if the metabolism in a tissue is increased for a prolonged period, vascularity increases.
-The generation of new blood vessels
Angiogenesis
When an artery or a vein is blocked, a new vascular channel usually develops around the blockage and allows at least partial resupply ofbloodto the affected tissue. Called?
Collateral Circulation
defined as theintrinsic ability of an organ to maintain a constant blood _____ despite changes in ________ pressure. What is this?
flow
perfusion
autoregulation (an intrinsic ability)
what mechanisms responsible for autoregulation? (2)
- Myogenic
- metabolic
Which vessels have the greatest surface area for exchange?
capillaries
capillaries are missing what and incapable of what?
missing smooth muscle
incapable of contraction
Mechanisms of Exchange Across The Capillary Endothelium?
- Diffusion (Oxygen, Carbon Dioxide, Lipid-Soluble Substances)
- Bulk flow (Water, Electrolytes, Small Molecules)
- Active transport (Ions, Glucose, Amino Acids)
- Vesicular transport (Proteins)
mean pressure in capillaries
25-30
which layer of vessel contains nerves and nutrient capillaries?
adventitia/externa
Higher at the arteriolar end than at the venule end. Tends to force fluid outward through the capillary membrane.
Capillary hydrostatic pressure
This is usually an outward force for fluid movement.
Interstitial fluid hydrostatic pressure
What are the Starling Forces with regards to capillary filtration/reabsorption? (4)
- Capillary hydrostatic pressure (P.c)
- Interstitial fluid hydrostatic pressure (P.if)
- plasma colloid osmotic pressure (Pie.p)
- interstitial fluid osmotic pressure (Pie.if)
What is capillary reabsorption?
net movement of water from the interstitial space to the capillary
(net driving force < 0)
What is capillary filtration?
net movement of water from the capillary to the interstitial space
(net driving force > 0)
If Net Driving Forces are positive, does it favor capillary filtration or reabsorption?
Filtration
Are hydrostatic pressures within the capillary equal at the arteriolar end and the venous end?
No, pressures higher on arteriole side
Under normal circumstances, what Net Driving Force favors fluid movement INTO the capillary?
plasma colloid osmotic pressure a.k.a. plasma oncotic pressure (reabsorption)
What is the function of the lymphatic system? and what does it return to circulation? (4)
an accessory route through which fluid can flow from the interstitial spaces into the blood
Returns to circulation:
- Protein (Albumin)
- Bacteria
- Fat
- Excess fluid
How is plasma filtrate returned to the circulation by the lymphatic system? (4)
- Lymphatic vessel contraction
- Intermittent skeletal muscle activity
- System of one-way valves
- Tissue pressure
which of the two oncotic pressures have a greater force?
capillary plasma oncotic pressure (forcing reabsorption)
what does the increased concentration of protein along the capillary do? (2)
- increases capillary plasma oncotic pressure
- Decreases NDF (net driving force)
Effect causing extra force in plasma protein?
Gibbs-Donnan Effect - cations in plasma creating extra pressure (9mmHg)
on which sides does filtration/reabsorption occur?
Fitration - Arteriole side
Absorption - Venule side
What does a decreased capillary hydrostatic pressure and increased oncotic pressure reveal?
Dehydration
Lower NDF and longer Reabsorption period
Capillary hydrostatic pressure (P.c) in Arterioles vs Venules? and net driving forces?
30mmHg vs 10mmHg
15mmHg vs (-)5mmHg
What is the formula for coronary perfusion pressure?
Diastolic BP – LVEDP (or PCWP)
Does the majority of coronary blood flow occur during systole or diastole in the left ventricle? Why?
Diastole
Extravascular compression during systole markedly affects coronary flow
What is coronary flow reserve? how much max vs resting?
Difference between resting/baseline blood flow and maximal flow
maximal flow is 4 – 5 times as great as at rest
Do the major epicardial arteries contribute significantly to coronary vascular resistance?
no, myocardial vessels do
What are the major determinants of myocardial oxygen demand?
HR
Contractility
Systolic wall tension
What are the major determinants of myocardial oxygen supply?
Coronary blood flow
O2 carrying capacity
Which layer of the myocardium is at greatest risk for ischemia? Why?
subendocardium
Epicardial coronary stenoses are associated with reductions in the subendocardial to subepicardial flow ratio
Which of the following places a greater oxygen cost on the heart? Pressure work versus volume work.
Pressures work
increasing arterial pressure at a constant cardiac output harder on heart
How stenotic do coronary vessels have to be before there is a significant decrease in flow?
60% occluded or 40% max Radius
What controls coronary blood flow?
Vascular resistance
What controls vascular resistance?
Neural control Metabolic control Endothelial control Autoregulation Extravascular compressive forces
Blood flow through thecoronarysystem is regulated mostly by __________ ?
local arteriolar vasodilation
normal coronary blood flow?
- 70 ml/min/100 g of heart weight,
- 225 ml/min
- 4 to 5 percent of the total cardiac output
What of the heart is the most important physiological mechanism regulating coronary vascular resistance
Metabolic activity
what mechanisms are responsible for metabolic control of the heart?
Nitric oxide
Adenosine
Prostaglandins
K+ATP channels
(causes increased blood flow and vasodilation)
Definition: conduction velocity
Dromotropy
What is the Baroreceptor Reflex? Where are the receptors for this reflex located?
- Reflex responsible for rapid changes in BP
- Carotid sinus (and aortic arch)