7 - Vascular physiology Flashcards
Propose a design for a medical device that can help compensate for a drop in blood pressure when moving from a lying to a standing position
- Passive stepping and Functional Electrical Stimulation (FES)
- Apply electrical current to cause muscle to contract, increase blood flow
Other ideas
(Stimulate muscle pump in the legs, Vasopressin, Epinephrine / sympathetic triggers, Blood volume, Compression stockings)
What are the three main factors that affect blood flow?
- Pressure gradient
- Vascular resistance
- Blood vessel radius
What are the reconditioning organs?
- Digestive organs
- Kidneys
- Skin
-> Adjust extra blood according to metabolic needs to achieve homeostasis
What’s the equation for rate of blood flow?
The flow rate is directly proportional to pressure gradient and inversely proportional to vascular resistance
What is pressure gradient?
Pressure diff between beginning and end of a vessel
What is vascular resistance? What does is depend on
A measure of the opposition of blood flow through a vessel
Depends on:
- blood viscosity, vessel length, vessel radium
Vessel’s radius has biggest impact on resistance:
What makes up the vascular tree?
- Arteries
- Arterioles (smaller branches of arteries)
- Capillaries (smaller branches of arterioles)
- Venules (smaller veins, formed when capillaries rejoin)
- Veins
What are some structural differences between veins and arteries?
Arteries:
- Thick, highly elastic walls
Veins:
- Thin-walled
Similarities: Large radii, several hundred
Arteries
What are the two functions of the arteries?
- Serve as rapid-transit passageways for blood from heart to organs (large radius = little resistance)
- Act as a pressure reservoir to provide driving force for blood when heart is relaxing
(collagen and elastin fibres give strength and elasticity)
Arteries -
What are the two kinds of arterial pressure?
- Systolic pressure
- Peak pressure exerted by ejected blood against vessel walls during cardiac systole (~120 mm Hg)
- Diastolic pressure
- Minimum pressure in arteries when blood is draining off into downstream vessles (~80 mm Hg)
Arteries -
What is Pulse pressure?
The pressure diff between systolic and diastolic pressure
ex: if blood pressure is 120/80, pulse pressure is 40 mm Hg
What is meant arterial pressure? How do you calculate mean arterial pressure?
- Average pressure driving blood forward into tissues throughout cardiac cycle
- Mean arterial pressure = diastolic pressure + 1/3 pulse pressure
ex: 120/80:
80 mm Hg + 1/3(40) = 93 mm Hg
How can you measure blood pressure?
- Using a sphygmomanometer or Korotkoff sounds
Describe this diagram.
This is showing blood pressure within different blood vessels. Left ventricle: - 0 - 120 mm Hg Large arteries: - 80 - 120 mm Hg
Pressure
Arterioles>Capillaries>Venules and veins
Arterioles
What are the main role of the Arterioles?
- Distribute cardiac output among systemic organs, depending on body’s momentary needs
- Help regulate arterial blood pressure
Arterioles
How do arterioles adjust arteriolar resistance?
- Vasoconstriction: Narrowing of a vessel
- Vasodilation: Enlargement in circumference and radius of vessel
- > Results from relaxation of smooth muscle layer (decreases resistance and increases flow)
Smooth muscle has many sympathetic nerve fibres (sensitive to many chemical changes)
What are the factors responsible for vascular tone?
(tone: degree of constriction)
1. Myogenic activity of smooth muscle (activity produced by muscle w/o any external stimulation)
2. Sympathetic stimulation
What determines the amount of CO (cardiac output) that is delivered to each organ?
- The number and vascular tone of arterioles in that area
What are the local chemical and physical influences on arteriolar radius?
(intrinsic controls)
Chemical:
- Metabolic change
- Histamine change
Physical:
- Local application of heat or cold
- Chemical response to shear stress
- Myogenic response to stretch
What extrinsic controls affect arterioles radius?
- Sympathetic stimulation of smooth muscle adjusts the total peripheral resistance, vasoconstrictor effect
- Chemical:
1. Vasopressin (maintains water balance by regulating amount of water retained by kidneys)
2. Agiotensin II (part of renin-angiotensin-aldosterine system, regulates body salt balance, have vasoconstrictor effect)
3. Epinephrine and norepinephrine (hormones that reinforce sympathetic nervous system)
**local controls override sympathetic vasoconstriction for organ-specific regulation
What are the main factors affecting arteriolar radius?
- Metabolic changes in Oxygen (Intrinsic control)
2. Sympathetic activity that affects vasoconstrictor effect (Extrinsic control)
What is the role of the medullary cardiovascular control contre?
(Located in medulla of the brain stem)
- Influence of Epinephrine and Norepinephrine (sympathetic stimulation of adrenal medulla)
- Influence of vasopressin and agiotensin II (fluid balance)
How does increased sympathetic activity affect blood pressure?
- Leads to arteriolar vasoconstriction
- When blood vessel volume is lowered, blood flow is also reduced. At the same time, the resistance or force of blood flow is raised. This causes higher blood pressure.
