Haemodynamics and regulation of blood pressure Flashcards
what is the pressure gradient in the pulmonary circuit
pressure in pulmonary arteries minus pressure in pulmonary veins
* Pulmonary arterial pressure = 15 mm Hg
* Pulmonary venous pressure = 0 mm Hg
* Pressure gradient = 15 – 0 = 15 mm Hg
what is the pressure gradient in the systemic circuit
pressure in aorta minus pressure in vena cava just before it empties into right atrium
Pressure in aorta - 85 mm Hg
Pressure in vena cava - 0 mm Hg
Pressure gradient 85 – 0 = 85 mm
what is the formula for mean arterial pressure
cardiac output x total peripheral resistence
what is cardiac output
This is the volume of blood the heart pumps per minute
what is the formula for cardiac output
heart rate x stroke volume
what is stroke volume
The amount of blood ejected from the heart per beat.
what factors affect total periphral resistence
- Length of vessel (Longer blood vessels create more resistance)
- Viscosity of fluid (thicker blood increases resistence)
- Radius of vessel (smaller vessels increase resistence)
how does vascoconstriction effect radius of arterioles
decrease radius (by contracting smooth
muscle) -> increase resistance -> decrease
blood flow
how does Vasodilation effect radius of arterioles
increase radius (by relaxing smooth
muscle) -> decrease resistance -> increase
blood flow
Arteriole Radius is dependent on ___
contraction state of smooth muscle in arteriole wall
what is the formula for resistence
length x viscosity
_________________
radius^4
what is Vasodilation
Widening of Blood Vessels
what is Vasoconstriction
Narrowing of Blood Vessels
name intrinstic factors effect Vasodilation
Metabolisim - low oxygen and high CO2 cause vasodilation
Locally secreted chemical messengers -cause vasodilation
Reduction in blood flow causes vasodilation
Reduced arterial pressure leads to vasodilation as smooth muscle relaxes to maintain adequate blood flow.
what Locally secreted chemical messengers cause vasodilation
nitric oxide, prostacyclin, adenosine, bradykinin
what intrinstic factors effect vasoconstriction
Locally secreted chemical messengers endothelin-1
Low CO₂ & High O₂ - vessels constrict
When blood pressure rises, smooth muscle contracts to prevent excessive blood flow and vessel damage.
what is the Most significant influence on blood flow
vessel radius
Extrinsic Factors that influence vasodilation and
vasoconstriction
The sympathetic nervous system and vasoconstrictive hormones increase blood pressure when needed, while vasodilatory hormones and parasympathetic influence help reduce it
what intrinsic factors effcet vessel radius
- low oxygen and high CO2
- Decreased pH
- Increased potassium ions
- adenosine
- Heat increases blood flow to an area by causing localised vasodilation.
- Cold causes vasoconstriction and therefore decreased blood flow.
what is central venous pressure
pressure in the large veins of the thoracic cavity that lead into the heart
how does venous return effect blood flow
Decrease in venous return –> decreases end- diastolic volume –> decreases stroke volume –>decreases cardiac output –>decreases blood flow to organs
how does cardiac output effect MAP
an increase in cardiac output leads to an increase in volume of blood contained in the aorta and an increase in mean arterial pressure
what happens when mean arterial pressure in less than normal
hypotension
inadequate blood flow to tissues
what happens when mean arterial pressure is higher than normal
hypertension
stress on heart and walls of blood vessels
what is pulse pressure at rest
40 mmHg
what is the importance of regulation of MAP on a short term basis
– Regulates cardiac output and total peripheral resistance
– Involves heart and blood vessels
– Primarily neural control
what is the importance of regulation of MAP on a long term basis
– Regulates blood volume
– Involves kidneys
– Primarily hormonal control
what is negative feedback in mean arterial pressure
controlled variable - autonomic nervous system
sensor - baroreceptors
integrator - cardiovascular centers in brainstem
effector - heart and blood vessles
what is a barorecptor
Specialised nerve endings that respond to stretch of vessel wall
Indirect response to changes in BP
where are arterial baroreceptors found
Carotid sinus
Aortic arch
where are cardiac and venous (low-pressure) barorecptors found
– Walls of large systemic veins
– Walls of the atria
what does the parasympathetic system input in the Cardiovascular system
SA node (decrease HR)
AV node
what does the sympathetic system input in the Cardiovascular system
– SA node (increase HR)
– AV node
– Ventricular myocardium (increase contractility)
– Arterioles (increase resistance)
– Veins (increase venomotor tone)
what are the types of baroreceptors
A fibres (myelinated): Low pressure (30-90 mmHg)
C fibres (unmyelinated): High pressure (70-140 mmHg)
what is an Example of the Baroreceptor Reflex in Action
A person who had been lying down stands up quickly
– Gravity causes venous pooling in the legs.
– This causes a decrease in VR, causing a decrease in
CO
– This causes a decrease in blood pressure.
– Baroreceptors sense the decrease: reflex occurs
– The reflex causes increased sympathetic and decreased
parasympathetic activity.
– CO and TPR are increased.
– Blood pressure is increased back to normal.
