Week 9 - Cardiovascular system (blood vessels) Flashcards
Distinguish between he structure and function of arteries, veins and capillaries
• Arteries: Carry blood away from the heart
• Thick muscular walls to withstand high blood
pressure
• Veins: Carry blood towards the heart
• Thin muscular walls and large diameter of lumen
to decrease resistance and enhance the
drainage of blood back to the heart.
• Valves to prevent back flow of blood
• Capillaries: Involved in nutrient, gas and waste exchange
• Single layer of endothelial cells to allow for rapid
diffusion
Define blood pressure
Is the force of blood pressing against the walls of the arteries in each cardiac cycle.
Normal blood pressure is 120/80, what do these valuesre present?
- Systolic pressure - The maximum blood pressure placed on the arterial walls when the heart is contracting
- Diastolic pressure - The maximum blood pressure placed on the arterial walls when the heart is relaxing.
What is mean arterial pressure (MAP)?
Is the average arterial pressure during a single cardiac cycle.
Why is MAP considered the best indicator of blood perfusion?
It is considered the best indicator of blood perfusion as the heart spends more time relaxing than contracting
What is the calculation for MAP?
Mean arterial pressure (MAP) = diastolic + 1/3 (systolic - diastolic )
What is pulse pressure?
Systolic pressure - diastolic pressure
Don’t have to know# What are the 3 factors that influence MAP?
- Cardiac output - increases cardiac output increases MAP as there is more blood being pumped into the arterial system.
- Total peripheral resistance - vasoconstriction of blood vessels increases resistance and pressure
- Blood volume - as the cardiovascular system is a closed system increased blood volume increases pressure.
What is autoregulation?
Is the local ability for an organ or tissue to maintain constant blood flow despite changes in blood pressure.
Describe the two mechanisms that can alter blood flow
1) Diameter of blood vessels - vasoconstriction and vasodilation.
2) Precapillary sphincters - Can relax or contract to control the flow of blood into capillaries.
What organs is auto regulation particularly useful for?
Brain, kidneys and heart and constant blood flow to these areas is necessary to sustain life.
Distinguish between metabolic and myogenic regulation
Metabolic regulation occurs in response to metabolic processes, whereas myogenic regulation occurs in response to blood pressure changes.
What is the stimulus and response of metabolic regulation?
- Stimulus: Increase in metabolic wastes such as CO2 and H+ ions, and decrease in oxygen
- Response: Vasodilation of blood vessels
What is the stimulus and response of myogenic regulation?
- Stimulus: Blood pressure (blood vessel stretch)
- Response:
* Increase in blood pressure - Vasocontriction
* Decrease in blood pressure - Vasodilation
What is the purpose of the baroreceptor reflex?
It is a negative feedback mechanism that maintains stable blood pressure
What are baroreceptors and where are they found in the body?
They are stretch receptors located in the walls of the aortic arch and carotid bodies.
What nerves carry the baroreceptor signals to the brain?
- Vagus
* Glosopharyngeal
What area of the brain controls cardiac function?
Medulla oblongata
Describe the baroreceptor reflex in response to an increase in blood pressure
1) Baroreceptors detect increase stretch
2) Signals sent along cranial nerves to cardiovascular and vasomotor regulatory centres in the medulla
3) Parasympathetic activation and sympathetic inhibition decreases heart rate and stroke volume (cardiac output).
4) Vasomotor centre decreases sympathetic stimulation causing vasodilation of blood vessels
5) This results in the lowering of blood pressure
Describe the baroreceptor reflex in response to a decrease in blood pressure
1) Baroreceptors detect decrease stretch
2) Signals are transmitted to the vasomotor and cardiovascular regulatory centres in the medulla
3) Parasympathetic inhibition and sympathetic stimulation increases heart rate and stroke volume (cardiac output).
4) Vasomotor centre increases sympathetic stimulation to cause vasoconstriction of blood vessels.
5) This results in an increase in blood pressure.
What are the short and long term ways to regulate blood pressure?
- Baroreceptor reflex
* Renal blood pressure regulation
What do the kidneys regulate to provide the long term regulation of blood pressure?
Regulates blood pressure by regulating blood volume
What is the name of the long term regulation of blood pressure by the kidneys?
• Renin-angiotensin-aldosterone mechanism
What cells produce renin?
juxtaglomerular cells of the Kidneys
What organs produce angiotensinogen?
Liver
What is the function of renin?
Converts angiotensinogen to angiotensis I
What is the function of angiotensin-converting hormone?
Converts angiotensin I to angiotensin II
What is the function of angiotensin II
- It is a vasoconstrictor that decreases the diameter of blood vessels and thus increases blood pressure
- Also stimulates the release of aldosterone from the kidneys
What triggers the release of renin from the cells of the nephron?
Stimulation from the sympathetic NS in response to low BP
What organ releases angiotensin converting hormone?
Lungs
What is the function of aldosterone?
Aldosterone increases sodium re absorption in the kidney tubules and thus increases water absorption, blood volume and thus blood pressure
What cells doe the SA and AV nodes consist of?
pacemaker cells
