Physiology of Circulation Flashcards
Arteries are under high or low pressure?
How strong are the walls?
Rapid or slow blood flow?
High pressure, strong vascular walls, rapid flow
Arterioles are what size?
What do they act as?
What is a defining characteristic of arterioles, and what are they innervated by?
Final small branches of arterial system.
Act as control conduits for blood release into capillaries.
Strong muscular walls that vasoconstrict/dilate.
Innervation by SNS only
Capillaries are what?
Defining characteristic?
How thin are the walls?
Permeable to what size substances?
Exchange site for nutrients, waste, electrolytes, fluid.
Very thin walls, (unicellular layer of endothelial cells)
Contain small capillary pores
Permeable to small molecular substances
Sickle cells have what 2 characteristics that are problematic?
Hold less hemoglobin for O2 binding, and also due to their abnormal shape can block blood cell flow in arteries.
Venules purpose is to what?
Collect blood from capillaries that merge into larger veins
Veins major function is to what?
Low pressure or high pressure?
Thin or thick walls?
can constrict or dilate?
Transport blood to heart.
Major function: serve as a blood reservoir! (64% of total blood volume)
Low pressure.
Thin walls.
Constricts/Dilates. Has muscle.
Define blood flow
Volume of blood flowing through vessel,organ or entire circulation in a given period.
Blood Pressure definition
Force per unit area exerted on a vessel wall by the contained blood mmhg.
Resistance definition
Opposes flow. Amount of friction that blood meets when passing through a vessel.
2 factors that affect blood flow
Pressure and resistance
Ohm’s Law calculates what?
Flow through a vessel as a function of pressure between both ends of a vessel and resistance.
F= change in pressure/resistance
Normal adult blood flow in liters
5 L
What are 2 descriptions of blood flow?
Laminar and Turbulent
Define conductance
Measure of blood flow through a vessel for a given pressure difference.
Reciprocal of resistance.
Small changes in diameter of a vessel impact large changes in conductance.
Poiseuille’s Law is related to what type of flow?
Laminar flow; by diameter.
How much of systemic circulation is due to arteriole resistance?
2/3
Viscosity has what kind of relationship to blood flow?
Inverse. Thickness of blood.
Hematocrit is what?
% of blood that is of red blood cells.
Average male has more hematocrit than women.
Polycythemia?
Higher amount of RBC than normal.
What controls blood flow primarily?
Needs of the tissue!
Cardiac output controlled by sum of local tissues.
What controls blood flow secondarily?
Small tissue specific vessels can dilate or constrict flow.
Mean arterial pressure definition
Average blood pressure in an individual
Pulse Pressure definition?
How does arteriosclerosis affect PP?
Difference between systolic and diastolic pressure.
PP will increase
What happens to mean arterial pressure and pulse pressure as distance from heart increases?
They decrease.
What is the average pressure at the venae cavae?
~0 mmhg
Pressure decreases steadily from capillaries–>venules –> veins –> venae cavae
What is venous distension?
Higher in veins, or arteries?
Swelling or increase in volume of blood in a vessel. Sign of high blood pressure, or obstruction.
Higher in veins!
What is vessel compliance?
Total quantity of blood stored in a given portion of the circulation of a vessel per unit of pressure rise.
Compliance = distensibility x volume
Right atrial pressure is what amount?
0 mmhg
What aids in venous return throughout the body?
Muscle pump will close one of the valves, while opening a venous valve to pump the blood towards the heart against gravity.
Name 4 blood reservoirs (that aren’t the veins)
Spleen, Liver, Heart, Lungs
What defines the acute phase of blood control?
Fast adjustments of arterioles and precapillary sphincters and other small vessels. (vasodilation/constriction)
What defines long term phase of local blood control?
Adjustment over days/weeks/months to control blood flow to tissues.
What are 3 theories of blood flow regulation?
- Vasodilator theory released from local tissues.
- Oxygen Lack theory
- Lack of other substances may also facilitate diffusion.
Large arteries upstream respond to downstream regulation by what?
Release of EDRF of nitric oxide (endothelium derived relaxing factor)
Reactive hyperemia vs Active hyperemia
Reactive: increase in blood flow following ischemia.
Active: increase in blood flow due to exercise or other metabolic activity.
Deficiency of nutrients and oxygen lead to increases of what?
Angiogenic factors –> leading to vascularization based on need
