control of circulation Flashcards
why do we need control (6)
- maintain blood flow
- maintain arterial pressure
- distribute blood flow
- auto-regulate / homeostasis
- function normally
- prevent catastrophe
components of circulation (5)
- anatomy
- blood
- pressure
- volume
- flow
what carries blood volume in circulation (6)
- arteries
- arterioles
- capillaries
- endothelium
- lymphatics
- veins
what are arteries
low resistance vessels that maintain blood flow to organs during diastole
structure of arteries
- Contain mainly elastic, collagen &
smooth muscle - The intima is composed of an inner
surface lining of endothelial cells & a
very small amount of collagen - The adventitia shows mainly
collagenous connective tissue - There are two elastic laminae, one at
the interface of the intima and media
and the other on the outer edge of the media
what are arterioles
smallest branch of an artery
provide the majority of resistance to blood flow
major role in determining arterial pressure
major role in distributing flow to tissues/organs
structure of arterioles
- may have an obvious media & adventitia
- smaller arterioles show only a few medial cells with a poorly defined elastic lamina
- a thin adventitia & normal intima also exist
what does TPR stand for
total peripheral resistance
what are capillaries
smallest blood vessels that connect arterioles to venules
transport blood, nutrients and oxygen to cells in your organs and body systems.
structure of capillaries
- tubes of endothelial cells (one cell thick wall - for rapid diffusion) bound to a basement membrane with co-existing pericytes (cells present at intervals along the walls of capillaries
- Pericytes have muscle fibres and may regulate blood flow
describe blood flow in capillaries
it is the slowest
- because of the high total cross-sectional
area
-this allows time for exchange of
gases and nutrients
what determines blood flow in capillaries
- arteriolar resistance
- no. of open pre capillary sphincters
what are veins
type of blood vessel that return deoxygenated blood from your organs back to your heart.
structure of veins
- compliant - because they have a thin layer of smooth muscle. A relatively small pressure must be applied to expand them.
- low resistance
- generally have collagen and little muscle & elastic with the wall & a single
internal elastic lamina - Veins contain valves for one way flow to the heart - prevent back flow
- Some veins are surrounded by skeletal muscle which contracts to increase vein
pressure and ensure blood flows back to the heart - Show variable thickness
- capacitance vessels - means they are the blood vessels that contain most of the blood and that can readily accommodate changes in the blood volume.
define lymphatic
a vessel, similar to a vein, that conveys lymph in the body.
what is the lymphatic system
network of tissues, vessels and organs that work together to move a colorless, watery fluid called lymph back into your circulatory system (your bloodstream).
functions of lymphatic system (4)
- Maintains fluid levels in your body
- Absorbs fats from the digestive tract
- Protects your body against foreign invaders
- Transports and removes waste products and abnormal cells from the lymph.
parts of the lymphatic system
- lymph
- lymph nodes
- lymphatic vessels
- collecting ducts
what helps with uni-directional flow (3)
- smooth muscle in lymphatic vessels
- skeletal muscle pump
- respiratory pump
how to calculate cardiac output (CO)
Heart Rate (HR) x Stroke Volume (SR) [typically 5 L/min]
how to calculate blood pressure
CO x Total Peripheral Resistance (TPR)
how to calculate pulse pressure
Systolic - Diastolic pressure
how to calculate mean arterial pressure (MAP)
Diastolic pressure + 1/3 PP
what is ohms law
Flow = Pressure gradient/Resistance
what is poiseuilles equation
Flow = radius to the power of 4
what 2 things are used to govern flow
ohms law and poiseuilles equation
what is the frank starling mechanism
the ability of the heart to change its force of contraction and therefore stroke volume in response to changes in venous return
(how the heart responds to volume)
explain the frank starling mechanism
- stroke volume increases as end-diastolic volume increases
- due to the length-tension relationship of muscle
- increase in EDV = increase in stretch = increase in force of contraction
- cardiac muscle at rest is not at its optimum length
- increase in venous return = increase in EDV = increase in stroke volume = increase in CO
what can stroke volume change in response to
- increasing preload
- decreasing afterload
how do you explain ventricular pressure and volume relationship
using pressure-volume loops
these are graphs, where the pressure inside the left ventricle is on the y axis and the volume of the left ventricle is on the x axis. Each loop represents one cardiac cycle, including both ventricular systole and diastole, or more simply, one heartbeat.
what is the goal of control of circulation
to maintain mean systemic arterial
pressure (MAP) - the average blood pressure in the arteries during the cardiac cycle
what is mean systematic arterial pressure (MAP)
the average blood pressure in the arteries during the cardiac cycle
mainly determined by arteries and capillaries
how to calculate MAP
MAP is equal to the diastolic pressure (DP) plus one-third of the pulse pressure
(systolic pressure (SP) - DP)
MAP = DP + 1/3 (SP-DP)
MAP = CO X TPR
define blood pressure
the pressure of blood within and against the arteries
how is blood pressure measured
using 2 numbers - systolic and diastolic
what is systolic blood pressure
measures the pressure in your arteries when your heart beats.
highest when ventricles contract
(100-150mmHg)
what is diastolic blood pressure
measures the pressure in your arteries when your heart rests between beats.
lowest when ventricles relax
(60-90mmHg)
what is pulse pressure
systolic blood pressure - diastolic pressure
what instrument is used to measure bp
sphygmomanometer, which is more often referred to as a blood pressure cuff.
that cuff uses your brachial artery to measure the pressure in your arteries.
why do you use the brachial artery to measure blood pressure
because its convenient to compress
what are korotkoff sounds
are generated when a blood pressure cuff changes the flow of blood through the artery. These sounds are heard through either a stethoscope or a doppler that is placed distal to the blood pressure cuff.
they have 5 distinct phases
what is phase 1 of blood pressure sounds
a sharp tapping
provides systolic pressure reading
what is phase 2 of blood pressure sounds
A swishing/whooshing sound
the softening of the tapping sounds
as the blood flows through blood vessels as the cuff is deflated
what is phase 3 of blood pressure sounds
A thump (softer than phase 1).
Intense thumping sounds that are softer than phase 1 as the blood flows through the artery but the cuff pressure is still inflated to occlude flow during diastole
what is phase 4 of blood pressure sounds
A softer, blowing, muffled sound that fades.
Softer and muffled sounds as the cuff pressure is released.
The change from the thump of phase 3 to the muffled sound of phase 4 is known as the first diastolic reading
what is phase 5 of blood pressure sounds
silence
when the cuff pressure is released enough to allow normal blood flow
provides 2nd diastolic reading
what are the 5 components of blood pressure control
autoregulation
local mediators
humoral factors
baroreceptors
central (neural) control
what is intrinsic regulation of blood flow
when tissues and organs within the body are able to intrinsically regulate their own blood supply in order to meet their metabolic and functional needs
they regulate through specific target tissues
some mechanisms originate from within blood vessels (e.g., myogenic and endothelial factors), whereas others originate from the surrounding tissue. The tissue mechanisms are linked to tissue metabolism or other biochemical pathways
examples of intrinsic/local regulation of blood flow (3)
(myogenic) autoregulation
active hyperemia
reactive hyperemia
local mediators
what is extrinsic regulation of blood flow
regulates blood flow throughout the body
refers to control by the autonomic nervous system and endocrine system.
examples of extrinsic regulation of blood flow
- humoral factors
- baroreceptors
- neural control
examples of vasoconstricting extrinsic hormonal factors
adrenaline (alpha adrenergic receptors)
angiotensin II
Vasopressin (ADH)
examples of vasodilating extrinsic hormonal factors
AN
adrenaline (beta2 adrenergic receptors)
what is myogenic autoregulation
an arteriole regulates its own blood pressure based on how much it is stretched
1.increased blood flow
2.stretches vascular smooth muscle
3. muscle automatically constricts
4. until the diameter is normalised
or slightly reduced.
Furthermore when the smooth muscle isn’t getting stretched as much due to low blood pressure, the muscle relaxes and dilates in response.
define autoregulation of blood flow
the intrinsic ability of an organ to maintain a constant blood flow despite changes in perfusion pressure
Different organs display varying degrees of autoregulatory behaviour.
which organs show excellent autoregulation
renal
cerebral
coronary
which organs show moderate autoregulation
skeletal muscle
splanchnic
which organs show poor autoregulation
cutaneous circulation
which organs show poor autoregulation
cutaneous circulation
how are the brain and heart blood flow controlled
intrinsic control
to maintain blood flow to vital organs
how is skin blood flow controlled
extrinsic control
regulated by sympathetic vasodilation and vasoconstriction mechanisms
via hypothalamus
how is blood flow in skeletal muscle controlled
both intrinsic and extrinsic
at rest - extrinsic - vasoconstrictor tone is dominant
when exercising - intrinsic mechanisms predominate
define intrinsic autoregulation
when the arterioles either vasoconstrict or vasodilate in response to changes in resistance seemingly automatically - with the aim of maintaining constant blood flow
what are local humoral factors
factors that are transported by the circulatory system, that is, in blood
can be vasodilators or vasoconstrictors
what are local vasoconstrictor humoral factors
endothelin - 1
internal blood pressure (myogenic contraction)
what are local vasodilator humoral factors
hypoxia - only in systemic circulation
adenosine
bradykinin
NO
K+, CO2, H+
structure of endothelium
a single layer of spindle/pavement cells with tight adhesions between adjacent cells
little cytoplasm and intra-cellular organelles - but gap/adherence junctions are prominent
can be fenestrated
In some areas they may be very thin (lung) to enable rapid fluid & gas transfer
function of endothelium
releases substances that aid in blood flow so blood mvoes around body smoothly
what does it mean if the endothelium is fenestrated
have pores in them for rapid diffusion
found in the liver, kidney
glomeruli & endocrine tissues
define blood flow
the volume of blood that flows through the systemic circulation per unit of tim
units of blood flow
volume / time
define haemodynamics
the physics of blood movements
what does the movement of blood depend on
- pressure
- blood flow
- resistance
how to calculate change in pressure
change in pressure = Q x TPR
what does Q stand for
blood flow (l/min)
what does TPR stand for
total peripheral resistance
(interchangeable with Systemic Vascular Resistance (SVR)
how to calculate the velocity of blood flow
velocity = blood flow / area of a vessel (Pi r squared)
what are the 2 types of blood flow
laminar
turbulent
what is laminar blood flow
smooth, streamlined flow
what is turbulent blood flow
- disruption to laminar flow (e.g. decrease in vessel diameter)
- “bumps in the road”
- produces Korotkoff sounds
what is resistance
physical/mechanical pushback of blood
which factors affect resistance (3)
- viscosity
- vessel length
- vessel radius - main one
define hyperemia
increase in blood flow
define active hyperemia
increase in blood flow when metabolic activity is increased
define reactive hyperemia
when an organ or tissue has had its blood supply completely occluded a profound transient increase in its blood flow occurs IF blood flow is
reestablish - extreme form of autoregulation
define reactive hyperemia
when an organ or tissue has had its blood supply completely occluded a profound transient increase in its blood flow occurs IF blood flow is
reestablish - extreme form of autoregulation
how many heart sounds are there
3
describe first heart sound
low pitched lub
associated with the closure of the atrioventricular
valves
what causes first heart sound
associated with the closure of the atrioventricular
valves
describe second heart sound
a louder dub
what causes second heart sound
associated with the closure of the aortic & pulmonary valves
describe third heart sound
low-frequency, brief vibration
what causes third heart sound
sounds of blood rushing into the left ventricle
what is the medullary cardiovascular centre
located in the medulla
contains pressor region and depressor region
how does the pressor region increase blood pressure
by increasing
- vasoconstriction
- cardiac output (by increasing stroke volume and heart rate)
- contractility
what does the pressor region do
increases blood pressure
is the pressor region sympathetic or parasympathetic
sympathetic
what does the depressor region do
decreases blood pressure
how does the pressor region decrease blood pressure
by inhibiting the pressor region
is the depressor region sympathetic or parasympathetic
parasympathetic
route of the pressor region
- Pressor region > sympathetic route > medulla > spinal cord > synapses at T1-L2 > Heart
route of the depressor region
Depressor region > medulla > vagus nerve > heart
what do central chemoreceptors in the medulla do
respond mainly to a decrease in pH (due to CO2 diffusing across the blood-brain barrier thereby reducing the pH of the CSF
what are baroreceptors
a type of mechanoreceptor allowing for the relay of information derived from blood pressure within the autonomic nervous system
2 types of baroreceptors
- high-pressure arterial baroreceptors
- low-pressure volume receptors/cardiopulmonary baroreceptors
where are arterial baroreceptors
within the carotid sinuses and the aortic arch
where are low-pressure volume receptors/cardiopulmonary baroreceptors
within the atria, ventricles, and pulmonary artery
what do arterial baroreceptors do
they are stretch receptors that only control short-term changes in blood pressure
cause some inhibition of the Renin-angiotensin & aldosterone system
how do arterial baroreceptors work
- blood pressure drops
- baroreceptors decrease discharge rate
- travels to medulla
- causing increased sympathetic activity
- Raised HR (and CO)
- Increased contractility (and CO)
- Arteriolar vasoconstriction due to innervation and raised angiotensin II (increased TPR) - causing decreased parasympathetic activity
what do cardiopulmonary baroreceptors do
control long term pressure changes
what happens when cardiopulmonary baroreceptors are stimulated eg when there is high blood pressure
- leads to the inhibition of the pressor
region/ vasoconstrictor centre in the medulla - leading to a fall in blood pressure - Also inhibits the Renin-angiotensin & aldosterone system - since angiotensin II stimulates vasoconstriction which will increase blood pressure, also aldosterone stimulates more Na+ and thus H2O reabsorption thereby increasing blood volume
and thus pressure - Also inhibits vasopressin/ADH - since it too stimulates more water reabsorption
- Thus when stimulated the cardiopulmonary baroreceptors bring about a decrease in blood pressure by promoting vasodilation & fluid loss
what is total peripheral resistance mainly dependent on and WHY
arteriole resistance
because ARTERIOLES ARE THE PRINCIPAL SITE OF RESISTANCE TO
VASCULAR FLOW
effect of endothelin -1
released by endothelium cells results in vasoconstriction
[POTENT]
what is hypoxia
when O2 supply decreases, there will be an accumulation of vasodilator
metabolites which will dilate vessels to increase local blood flow
what does nitric oxide do
released by endothelial cells - triggers vasodilation [POTENT]
what does Prostacyclin/ Prostaglandin I2 (PGI2): do
released by endotheliaal cells - triggers
vasodilation [POTENT
why can adrenaline can be
both a vasodilator & vasoconstrictor
depends on which receptors are present
what are peripheral chemoreceptors
In the aortic arch & carotid sinus (base of internal carotid artery - at the division between the internal and external carotid), stimulated by a fall in PaO2 & a rise in PaCO2 & a fall in pH causing blood pressure to increase
what is pulmonary circulation
- blood leaves the right ventricle via the pulmonary trunk
2.this divides into the two pulmonary arteries, one supplying the
right and one supply the left lung.
- In the lungs the arteries continue to branch and connect to arterioles, leading to capillaries that unite into venules and then veins.
- the blood leaves the lungs via four pulmonary veins, which empty into the left atrium
what is sytemic circulation :
- Blood leaves the left ventricle via the
aorta. - The arteries of the systemic circulation branch off the aorta, dividing into progressively smaller vessels. The smallest arteries branch into arterioles, which branch into roughly 10 billion very small vessels, the capillaries, which unite to form larger-diameter vessels known as venules.
- The arterioles, capillaries & venules
are collectively referred to as the MICROCIRCULATION. - The venules then unite to
form larger vessels, veins. - The veins from the various peripheral organs and tissues unite to produce two large veins, the inferior and superior vena cava which drain
into the right atrium
