Human Heart Flashcards
What is the Pulmonary circuit?
The blood circuit which supplies and drains the lungs
What is the systemic circuit?
The blood circuit which supplies and drains the body apart from the lungs
What is unusual about blood drainage from the gut?
Blood from the small intestine first travels to the liver via the hepatic portal vein before being returned to the heart.
What proportion of blood volume is in the pulmonary circuit?
Approx. 9%
What proportion of blood is in the heart?
Approx. 7%
What proportion of blood is in the systemic circuit?
Approx. 84% (although about 3/4 of this is in the veins at any one time
What is the resistence/pressure in the pulmonary circuit?
Medium
What is the resistance/pressure in the systemic circuit?
High
What is a portal vein?
A blood vessel which moves blood from one system to another, one of which cannot be the heart
Why are inlet and outlet valves necessary?
To prevent blood from entering the heart and leaving the heart when it isn’t supposed to or in the wrong direction
Why are atria useful?
It allows blood to be being collected even while the ventricles are contracting
Why are the entrance and exit of the ventricle both on the same side?
It allows contraction to occur from 3 walls, rather than just two in a flattening motion
Why are auricles useful?
They increase the volume of blood the atria are able to hold
What blood vessels enter the right atrium?
The superior and anterior vena cava, as well as the coronary sinus
What blood vessels leave the right ventricle?
The pulmonary trunk, which then separates into the left and right pulmonary arteries
What blood vessels enter the left atrium?
The 4 pulmonary veins- two on each side
What blood vessels leave the left ventricle?
The aorta, which quickly branches into the coronary arteries and many other systemic arteries
What are the 3 sulci which envelop the heart?
The anterior and posterior interventricular sucli divide the heart into right and left
The coronary sulcus divides the heart into atria and ventricles
What is the order of the 4 major blood vessels in the heart (most ventral to most dorsal)
Most ventral: Pulmonary trunk
Aorta
Vena cava (although they are off to the side)
Pulmonary veins
Where is the mitral valve?
Between LA and LV
Where is the aortic valve?
Between LV and aorta
Where is the tricuspid valve?
Between RA and RV
Where is the pulmonary valve?
Between RV and pulmonary trunk
What are the semilunar valves?
The valves shaped a little like half moons- they are the outlet valves of the heart, between the ventricles and their arteries
How do the inlet valves work?
They have their flaps attached to chordae tendineae, which are strong, tendinous chords attached to papillary muscles in the base of the heart. When the ventricle contracts, these muscles do too, pulling the chordae tendineae against the blood trying to be released and causing the flaps to parachute up against the outflow of blood
What are the atrioventricular valves?
Valves between the atria and ventricles of the heart
What are the relative shapes of the ventricles?
The left ventricle is circular and surrounded by a thick wall of cardiac muscle. Its lumen in circular
The right ventricle is crescent shaped, as is its lumen, and is surrounded by a thinner layer of cardiac muscle. It seems to simply be on the periphery of the LV
The wall thickness ratio between the two is 3:1, while max pressure is 5:1
What are the max pressures of the 4 chambers of the heart?
RA: 5mmHg
RV: 27mmHg
LA: 8mmHg
LV: 120mmHg
How do the semilunar valves work?
They are shaped like little pockets attached to the inner wall of the artery. They don’t need chordae tendineae as they guard smaller outlets, and they support each other using the blood pressure.
When blood tries to fall back into the ventricles once the pressure in the ventricle is below that in the artery, they fill up the cups first and cause them to bulge out until they meet, resealing the entrance. When the next contraction occurs, they get pushed towards the artery wall and moved aside.
Where does the apex of the heart point?
Inferiorly, anteriorly and left
Where does most of the heart lie?
2/3rs on the left side of the body, 1/3rd on the right
What forms the right border of the heart?
The RA
What forms the inferior border of the heart?
The RV
What forms the left border of the heart?
The LV
What and where is the base of the heart?
It is the area comprised of all the large vessels coming in and out of the heart- it is located at the superior surface of the heart
What are the layers of the surrounding structures of the heart (outermost to innermost)?
Fibrous pericardium –> Parietal Pericardium –> Pericardial space –> Visceral Pericardium –> Heart wall –> Endocardium –> blood
What structures make up the pericardium?
Fibrous pericardium, parietal pericardium, pericardial space, visceral pericardium
What is the epicardium?
The visceral pericardium
What structures make up the heart wall?
The visceral pericardium, myocardium and the endocardium
What is the structure of the parietal and visceral pericardium?
Simple squamous mesothelium. They are continuous where the vessels enter and exit the heart.
The visceral pericardium adheres to the outside of the myocardium
The outer wall of the parietal pericardium forms a tough, non-stretchy sac called the fibrous pericardium
What is cardiac tamponade?
It occurs when a hole forms in the ventricle, and with each pump some blood is pumped into the pericardial space at high pressure. The fibrous pericardium can’t stretch, so when it pressurises the heart enough, the heart is eventually strangled.
What is aortic stenosis?
It’s the shrinking of the aortic opening
It happens in rheumatic fever. A bacteria causes the aortic valve to break down as the collagen in their leaflets is destroyed.
Fibroblasts then attempt to fix it, but end up fusing the leaflets together, creating a small aortic opening
As a result, the heart must work much harder, and the muscle increases, causing the lumen to shrink. The heart pumps less blood and so its own ability to receive oxygenated blood is diminished, eventually causing heart failure.
What and where is the fibrous skeleton of the heart?
It is fibrous rings which form around the high pressure vessels. Full rings surround the mitral and aortic valves, while a partial ring surrounds the tricuspid valve.
There is no ring surrounding the pulmonary artery.
However, there is fatty connective tissue where the fibrous skeleton is not present, meaning that there is still some support for the valves
What is the function of the fibrous skeleton?
It gives support to the valves and anchors them to the heart.
It also electrically insulates the ventricles from the atria.
What is the basic pathway of conduction within the heart?
SA node –> atrial muscle –> AV node –> AV bundle –> bundle branches –> purkinje fibres
Why are purkinje fibres good at conducting impulses throughout the ventricles?
They are not branched and are fairly insulated so they are excellent at conducting
Why are the atria poor pumps?
They have no inlet valves, so when they contract some blood returns into the veins
What is the speed and result of conduction from the SA node to the atrial muscle?
Slow (.5m/s)
It results in contraction of the atria
What is the speed and result of conduction within the AV node?
Very slow as it is a different type of cell
It results in a 100ms delay between atrial and ventricular contraction
What is the speed and result of conduction from the AV bundle to the purkinje fibres?
Fast (5m/s)
Results in even ventricular contraction
Why do we need the fibrous skeleton to insulate the ventricles from the atria?
If they were not insulated, they would all contract simultaneously, leading to poor pumping action
What is systole?
Contraction
What is diastole?
relaxation
What are the 5 phases of the cardiac cycle?
Ventricular filling Atrial contraction Isovolumetric ventricular contraction Ventricular ejection Isovolumetric ventricular relaxation
Why is the first heart sound of a lower frequency than the second?
The flaps on the atrioventricular valves are larger than the semilunar valves, meaning that they make a lower sound than the second closing does
What is involved with ventricular filling?
Blood from the atria moves into the ventricles
Ventricles are at a lower pressure than the atria
Mitral valves quietly open and blood fills ventricle to approx. 80% of its volume
Pressure in LA approx 5mmHg, pressure in ventricle is less
What is involved with atrial contraction?
SA node is fired
Left atrium contracts and completes filling of LV
Rise in atrial pressure is small as:
- Atrial muscle is thin
- There are no valves to prevent blood backflowing to the veins
What is involved with Isovolumetric ventricular contraction?
AV node is excited, and the impulse has traveled through the bundles and purkinje fibres to contract the ventricular muscle
Blood lifts back towards the atrium, causing the mitral valve to close
Ventricular pressure is above that of the atrium but less than that of the ventricle, so the blood is simply staying within the ventricle.
The closing of the mitral valves in this period is associated with the low frequency ‘lub’ sound
What is involved with ventricular ejection?
The pressure in the ventricle surpasses the pressure in the aorta, causing the aortic valve cusps to quietly open.
Blood leaves the ventricle
However: Blood leaves the ventricle faster than the aorta can take it away, causing a bolus to form and pressure in the aorta to rise steeply.
As the rate of ejection falls, ventricular pressure levels off and begins to decrease.
(pressure greater than 90mmHg)
What is involved with isovolumetric ventricular relaxation?
Ventricle relaxes, causing pressure to drop dramatically. Flow reverses in the aorta, causing the aortic valve to close (dub sound). In addition, there is a small rise in aortic pressure after the blood begins to leave due to the return of some blood to close the ventricle (dicrotic wave)
The mitral valve remains closed as ventricular pressure is still above atrial pressure, until there is enough venous blood to open the valve and the ventricle is relaxed enough to have dropped its pressure.
What should be remembered about what causes the heart sounds?
It is not the valves themselves which cause the heart sounds, but the turbulence of the blood being stopped and rebounding against them.
What is the movement of the pressure for the LV during the cardiac cycle?
VF: Just above 0, below atrial and aortic pressure
AC: Continuous with VF
IVC: Pressure increases sharply. The start of IVC is when it passes atrial pressure and the end is when it passes aortic pressure
VE: Rises in a semicircle, maxing at approx 120
IVR: Falls steeply. The start of IVR is when it passes aortic pressure and the end is when it passes atrial pressure
VF: Just above 0, below atrial and aortic pressure
What is the movement of the pressure for the LA during the cardiac cycle?
VF: Approx 5mmHg, above ventricular pressure
AC: A spike to approx. 8mmHg, then another decrease
IVC: A small increase at the start as ventricular pressure surpasses it, causing the mitral valves to close and some blood to rebound. Then falls to near 0.
VE: begins to rise from 0 again
IVR: Continues to rise to a point of approx. 8mmHg, at which point it surpasses ventricular pressure
VF: Falls again as ventricle opens, to about 5mmHg
What is the movement of pressure in the aorta during the cardiac cycle?
VF: approx. 100mmHg, but falling slowly
AC: continues falling slowly
IVC: Falls slowly until ventricular pressure surpasses it (at approx. 80mmHg)
VE: Rises in tandem with LV pressure- a semicircle
IVR: A small spike due to the closure of the aortic valve and some blood bounding off it
VF: Continues to fall.
What is the trend in left ventricular volume during the cardiac cycle?
VF: Plateauing increase in volume to aprox. 80% of max
AC: Steeper plateauing increase to 100% max- approx. 120 mL
IVC: Constant volume
VE: Steep, plateauing decrease in volume to approx. 60mL
IVR: Constant volume
VF: Plateauing increase to 80% of max volume
What are the 6 types of blood vessels in the body?
Elastic artery Muscular artery Ateriole Capillary Venule Vein
What is the structure of an elastic artery?
Many thin sheets of elastin in its middle tunic
What is the function of an elastic artery?
During ventricular ejection, they expand to hold the bolus of blood ejected before recoiling during diastole to squeeze it forward
This occurs because the heart pumps blood to the arteries faster than the arteries can move the blood on
It is important as: You always have blood going through to the systemic circuit
It also reduces the peaks and troughs of the heart pump on the capillaries, helping to preserve them.
What is the structure of muscular arteries?
Many layers of circular smooth muscle wrapped around the middle tunic
What is the function of the muscular artery?
Distributes blood around the body at high or medium pressure
Adjusts blood flow by using its smooth muscle to vary the radius
NB flow is proportional to the fourth power of the radius- so if you halve the radius you get 1 16th of the flow
Therefore, small changes in radius have large changes for flow
The autonomic nervous system controls where blood goes- sending it to where it’s most needed
What is the structure of the arteriole?
1-3 layers of smooth muscle around the vessel
Lined with endothelial cells
What is the function of the arteriole?
It controls blood flow into capillary beds, which is why they have the most smooth muscle relative to vessel size
Biggest resistence to flow and consequent pressure drop, in order to make sure capillaries get slow moving blood. They’re the last chance to reroute the blood somewhere else before the capillaries get it
The degree of somatic arteriolar constriction determines
Total peripheral resistence
Mean arterial blood pressure
What is the structure of the capillary?
Diameter is approx the size of a red blood cell
Made up of endothelial cells with an external basement membrane
So smooth muscle or connective tissue
What is the function of the capillary?
Site of exchange of gasses, nutrients and wastes between tissues and blood
They are leaky- plasma does escape, but normally osmotic gradients drive it back inside the capillary.
What is the structure of the venule?
They have endothelium plus some connective tissues. Large ones may have some smooth muscle
What is the function of a venule?
They drain capillary beds
They are the site where white blood cells leave the blood to attack pathogens.
This is due to the slow movement of blood within the venule
What is the structure of a vein?
Similar to muscular arteries, but with thinner walls (less muscle and connective tissue)
Large veins have valves, preventing backflow
Surrounding skeletal muscle contracts when you move, and pushes the blood further up, before the valves close again as the blood rushes back down
If you don’t move, it is possible for the blood to leak down (as the valves aren’t indefinitely tight, leading to fainting), or pool, leading to varicose veins.
What is the fucntion of a vein?
They drain the blood back into the atria (except portal veins, draining the blood to another system)
They stretch easily, and so act as a reservoir.
Where do the coronary arteries come from?
The ascending aorta
What is the function of the coronary artery?
Supply oxygenated blood to the heart
What happens if a coronary artery narrows to 20% of its original diameter?
The myocardium it supplies become depleted of oxygen and causes angina, and sometimes infarction.
What can the body do to compensate for a coronary artery blockage?
Use an anastomosis to provide O2 blood to the heart via a distant artery
What is the function of cardiac veins?
Drain deoxygenated blood from the heart tissue, returning it to the RA
What causes dilated cardiomyopathy?
Unclear (idiopathic)
Infected muscle fibres are attacked by lymphocytes trying to rid the body of infection.
Fibres become weaker or killed. Those remaining are longer.
The left ventricle is most affected due to the higher pressure, and it dilates as the lumen increases (as fibres are stretched
The fibrous ring supporting the mitral valve begins to stretch, moving the mitral flaps out with it
The flaps no longer meet during ventricular systole, causing mitral regurgitation.
Why is the mitral valve more affected than the aortic valve in dilated cardiomyopathy?
It’s bigger
What impact does mitral regurgitation have on the pressure curve of the cardiac cycle?
Changes:
Ventricular and aortic pressures are lower at their max due to the pressure relief of some blood regurgitating
There is a rise in atrial pressure during systole due to some blood being forced into it from both directions
What is the impact of mitral regurgitation on heart sounds?
Second heart sound is normal
First heart sound (mitral valve attempting to close) is prolonged and turbulent due to the mitral flaps attempting to parachute but flapping
Where do you need to listen to hear mitral regurgitation?
Just inferior to the inlet valves
What is the impact of mitral regurgitation on the rest of the body? (10 steps)
- LV must pump a greater volume to maintain CO
- With HR constant, EDV increases
- LA works harder to fill the LV’s increased blood demand
- LA pressure increases
- This pressure backs up into the pulmonary veins, causing PV pressure to increase
- This backs up again to the capillaries, causing their pressure to increase
- Due to higher pressure in the capillaries, more fluid is driven out into the interstitial fluid
- The lungs become heavier and wetter
- The lungs become more rigid
- Breathing requires more muscular work, causing dyspnoea, consciousness of laboured breathing.
What is the vicious circle regarding LV failure in mitral regurgitation?
- The muscle becomes dis-eased
- LV dilates
- Mitral valve stretches
- Mitral regurgitation occurs
- The LV must increase its EDV to maintain CO
- LV dilates…..
This occurs until the LV fails, causing death.
What are the similarities and differences between L&RV pressure and max volume?
Both have the same max volumes & outputs
However, LV is higher pressure than RV (120 vs 27)
Which phase of the cardiac cycle takes the longest?
Ventricular filling
What is regurgitation?
Blood flows out of the ventricle and back into its atrium during systole
What is the function of the heart?
To pump blood around the body in order to supply Oxygen, nutrients hormones etc. and to remove waste.
What is the ejection fraction?
The volume ejected by the ventricles over the total volume which was previously in the ventricles:
In other words, SV/EDV
What is the heart’s function in supply?
The more oxygen demanded by the tissues of the body, the harder the heart must work in order to supply the tissues.
What is the equation for cardiac output?
CO = SV x HR (stroke volume, heart rate)
What is cardiac output, plus units?
The amount of blood ejected by the heart per unit time. It’s normally in mL/min
What is heart rate?
Heart beats per unit time (bpm)
What is stroke volume?
The amount ejected by the left ventricle per systole- normally in mL or L.
What is venous return?
The volume of blood returning to the heart from the veins every minute. It’s linked to CO.
What is a pressure volume loop and how do you draw it?
It is a graph of left ventricular pressure by volume.
Pressure is on the y axis, with volume on the x axis.
What are the 4 key points of a pressure volume loop?
There are 4 main ‘corners’ in the graph:
A is bottom left, at low vol and pressure. It represents the opening of the mitral valve.
B is bottom right, at high vol and low pressure. It represents the mitral valve closing (EDV)
C is top right, at high vol and pressure. It represents the aortic valve opening
D is top left, at low vol and high pressure. It represents the aortic valve closing. (ESV)
What are the four key lines of the pressure-volume loop and what do they mean?
A-B represents ventricular filling & atrial contraction
- It dips down and then up as originally there is a bit of a suction effect from the still-relaxing ventricle, and as it fills up again the pressure builds
B-C represents isovolumetric ventricular contraction
- It is a vertical, straight line as pressure increases but volume doesn’t change
C-D represents ventricular ejection
- It is an arc, but smushed to the left as the pressure continues to increase until its peak (when the aorta can’t take any more), after which the pressure decreases a little as ventricular relaxation starts
D-A represents isovolumetric ventricular relaxation
- It is also a vertical straight line as pressure drops, but volume stays identical
What can you determine from a pressure volume loop?
Strove Volume = the distance between the vertical lines
Aortic BP = the highest peak of pressure over the pressure at C as this is when the pressure in the aorta is at its lowest
How do you use a pressure-volume loop to determine whether a patient has mitral regurgitation or heart failure?
Mitral regurgitation- will see that the B-C line is slanted diagonally backward, as pressure increases during isovol contraction, but some volume escapes
Heart failure- heart is larger due to harder work, meaning volumes will be above normal, with a decreased distance between the vertical lines (decreased SV). Therefore, the loop will be thinner and shifted to the right.
What is the equation for calculating stroke volume?
SV = EDV - ESV
What is the Frank-Starling law of the heart?
The energy of ventricular contraction is a function of the initial length of the muscle fibres comprising its walls- ie, the greater the fibres are stretched (fullness of ventricle), the harder subsequent contractions will be.
What is cardiac reserve?
The difference between a person’s resting Heart Rate and max Heart Rate
What is preload?
The stretch of cardiac myocytes prior to contraction (end of diastole)
What is contractility?
The stroke volume increase when a positive intropic agent is present- ie it’s do do with how forcefully the heart contracts at a given preload due to other factors
What is afterload?
The resistance of the aorta due to its pressure- eg how hard is it for the LV to push the blood out.
Why can it be dangerous to increase your HR to max for too long?
The time for the ventricle to fill decreases, meaning that less blood is being pumped out of the heart. As a result, the tissues may not receive the Oxygen they require, and you might faint
What does the area inside the pressure-volume loop represent?
Stroke work (the total mechanical energy generated by the ventricle)
What are the features of a cardiac myocyte action potential?
Depolarization occurs rapidly due to influx of Na+ (voltage gated, fast Na+ channels open)
Plateau occurs due to Ca2+ inflow when slow voltage gated Ca2+ channels and K+ outflow when some K+ channels open
Repolarization due to closure of Ca2+ channels and K+ outflow channels, and opening of voltage-gated K+ channels
When does the refractory period occur in cardiac myocytes?
Between initial depolarisation and all through the plateau until the membrane potential is back at its original value
When does contraction occur during a cardiac myocyte AP?
From a little after the refractory pd begins until a little before it ends.
What are the 5 points of an ECG?
P
QRS
T
What does the P wave represent?
Atrial Depolarisation
What does the QRS complex represent?
Onset of ventricular depolarisation
What does the T wave represent?
Ventricular repolarization
What happens to the frequency of PQRST cycles when HR increases?
There are more cycles per unit time
What does the flat line after the P wave represent?
Atrial Contraction
What does the flat line after the S peak represent?
Ventricular contraction
What does the flat line after the T wave represent?
Ventricular relaxation
Why does the QRS complex do ‘down up down’?
The lines represent the physical direction charge is moving. When the depolarisation is passed along the heart it goes down the bundle branches, up the purkinje fibres and then down the myocytes.
What is the cardiovascular center?
The part of the medulla that regulates autonomic control of the heart, blood and vasculature
Where does the CV center get its input?
Cerebral Cortex, Limbic system and Hypothalamus
Proprioceptors, Chemoreceptors and Baroreceptors
What does the CV do in terms of output to the heart?
- Cardiac accelerator nerves (Sympathetic, Uses NE on B receptors). These increase the rate of spontaneous depolarization in both the SA and AV node and increase heart rate. They also increase the contractility of the atria and ventricles, increasing stroke volume at a given preload.
- Vagus (X) nerve (Parasympathetic, uses ACh): This decreases the rate of spontaneous depolarization in the SA and AV node, to decrease heart rate
What two factors increase CO?
Increased SV
Increased HR
What factors increase HR?
- Nervous system (More symp. stimulation, less parasymp. stimulation)
- Chemicals (Catecholamine or thyroid hormones- promote increase in Ca2+)
- Other factors (age, fitness, body temp)
What factors increase SV?
Increased preload (due to increased EDV- fibres contract more forcefully) Increased contractility- (caused by positive ionotropic agents (eg. catecholamines). Leads to increased contraction regardless of stretch) Decreased afterload (due to decreased diastolic arterial BP, allows semilunar valves to open sooner as LV pressure must reach a lower threshold)
Define Chronotropy
An effect acting on the SA node’s conduction system, resulting in a change in heart rate. Positive chronotropy increases heart rate, negative decreases it..
What is the method of myocyte contraction?
- It is depolarized by a nerve, causing Na+ to flood in and depolarize it. This is co-transported with Ca2+
- Ca2+ activates ligand gated channels in the SR, causing another influx of Ca2+, called CICR
- Calcium is reabsorbed into the SR and removed from the cytoplasm, and the cell depolarizes due to the exit of K+
What happens when blood pressure is too high?
It can cause damage to bodily structures
What happens when blood pressure is too low?
It can deprive organs of nutrients and sufficient oxygen
What is blood flow?
The movement of blood through the vasculature
How is blood flow calculated, and what does this mean when changing the variables?
BF = (Pressure diff between 2 areas) / Resistence
So: When the pressure gradient gets larger, flow increases
At higher resistence, flow does not increase as much per increase in pressure gradient (Ie if graphed, the slope showing the relationship between the two would be flatter)
What are the pressure gradients which determine capillary exchange?
BHP- Blood Hydrostatic Pressure
BCOP- Blood Colloid Osmotic Pressure
IFOP- Interstitial Fluid Osmotic Pressure
IFHP- Interstitial Fluid Hydrostatic Pressure
(NFP)- Net Filtration Pressure
Which direction does BHP push?
Into the IF
Which direction does BCOP push?
Into the vessel
Which direction does IFOP push?
Into the IF
Which direction does IFHP push?
Into the vessel
Which pressures are present at the arteriole end of the vessel?
BHP, BCOP and IFOP
Which pressures are present at the venule end of the vessel?
BHP, BCOP and IFHP
How does BHP change across the capillary?
It decreases
How does BCOP change across the capillary?
It stays the same
How do you calculate NFP?
(BHP + IFOP) - (BCOP + IFHP)
Pressures going out minus those going in
What happens if NFP is positive?
A net filtration is occurring
What happens if NFP is negative?
A net reabsorption is occurring
Why does BCOP stay the same between different ends of the capillary?
The BCOP’s attempts to draw in fluid fail due to the High BP of the arteriolar end, so must remain until the venule end
What is starling’s law of the capillaries?
Fluid absorbed at the venous end of the capillary is nearly equal to the volume filtered at the arteriolar end
Where does the fluid not reabsorbed go?
Into the lymph system
What causes edema?
A large net filtration, with insufficient reabsorption
What is the relationship between velocity of blood flow and x-sectional area of blood vessels?
The larger the cross sectional area, the slower the blood flow.
HOWever, remember that this refers to their total x sectional areas- so capillaries have the highest area as there are the most of them.
What happens when you contract the precapillary sphincters (control whether blood goes from arteriole to capillaries or not)
FIND OUT THE ANSWER
What is blood pressure?
BP = CO x TPR
What hormones influence CO and what do they do?
Norepinephrine and epinephrine increase HR and therefore blood pressure
What hormones influence vascular resistance and what do they do?
Angiotensin II, ADH, norepinephrine (a receptors @ skin/abdomen) and epinephrine (b receptors at cardiac/skeletal) constrict the blood vessels, increasing BP
ANP, Epinephrine and NO dilate the blood vessels, decreasing BP
What hormones influence blood volume and what do they do?
Aldosterone and ADH increase blood volume (by retaining water etc), increasing BP
ANP decreases blood volume, decreasing BP
What is the acronym for the negative feedback regulation of BP using baroreceptors?
CRCER (read: syr syr) Controlled condition Receptors Control Centers Effectors Response
What is an example of the CRCER process for low blood pressure?
- C: Controlled Condition: Blood pressure decreases
- R: Receptors: Baroreceptors in the carotid sinus & aorta stretch less, which decreases their rate of nerve impulses
- C: Control Center: In the CV Center, there is increased symp. response and decreased parasymp. response.
Adrenal Medulla: Increased epi and norepi
4: E: Effectors: In the heart, SV and HR increase, leading to increased CO.
In the blood vessels, constriction occurs, increasing resistence. - R: Response: Increased BP
What can lead to increased venous return?
- Increased blood volume
- Skeletal muscle pump (veins)
- Respiratory pump
- Venoconstriction
what can lead to increased SV?
- Increased venous return
- Increased symp impulses and hormones
What can lead to increased HR
- Increased symp impulses and hormones
- Decreased parasymp impulses
What can lead to greater CO?
- Higher HR
- Higher SV
What can lead to increased blood viscosity?
Increased RBCs (like polycythemia)
What can lead to increased total blood vessel length?
Increased body size (obesity)
What can lead to increased systemic vascular resistence?
Increased blood viscosity
Increased total blood vessel length
Decreased blood vessel radius
What leads to increased MAP?
Higher TPR and CO
What does increased blood volume lead to?
Increased venous return
What does increased skeletal muscle pumping do?
Increase venous return
What does the respiratory pump do?
Increases venous return
What does venoconstriction do?
Increased venous return
What does dec. parasymp do?
Increased HR
What does increased symp. do?
Increased HR
Increased SV
What does increased venous return do?
Increased SV
What does increased RBCs do?
Increased blood viscosity
What does increased body size do?
increased total blood vessel length
What does increased blood viscosity do?
Increased TPR
What does increased total blood vessel length do?
Increased TPR
What does increased vasoconstriction do?
Increased TPR
What does higher CO and SVR do?
Increased MAP
How do carotid and aortic baroreceptors work?
The more signals they send, the more the CV centre inhibits symp and increases parasymp stimulation, and vice versa
How do renal baroreceptors (juxtaglomerular cells) work?
Low BP = higher secretion of renin (to be made into a sympathetic hormone)
How does the CV centre work to control BP?
Fewer impulses from carotid baroreceptors = decreased symp and increased parasymp
How does the hympothalamus/pituitary gland control BP?
Decreased BP = higher ADH in blood
How do the liver/lungs control BP?
They modify renin into angiotensin II
What does increased symp/decreased parasymp do?
increased HR and contractility
Constriction of vessels
What does ADH do?
Causes kidneys to conserve salt & water
Blood vessels constrict
What does Angiotensin II do?
Encourages adrenal medulla to produce aldosterone (which conserves salt & water), constricts blood vessels
How does the heart act as an effector?
Its contractility, heart rate and SV may be changed
How does the adrenal medulla act as an effector?
It can produce aldosterone
How do the blood vessels act as effectors?
Can constrict and dilate
How do the kidneys act as effectors?
They can conserve or release salt and water
What is tachycardia?
A faster heart rate than normal
What is bradycardia?
A slower heart rate than normal
What is poiseuille’s law?
The resistence of a vessel is a function of the 4th power of its radius
What is haemorrhage?
The escape of blood from a blood vessel
How is angiotensin II formed?
- BP decrease registered in juxtaglomerular cells of kidney
- Kidneys release renin (RDS)
- Liver releases angiotensinogen
- Angiotensin I produced with enough renin
- Angiotensin I converted to II via ACE in the lungs
What does angiotensin II do?
Constricts blood vessels to raise BP (most potent known vasoconstrictor)
Causes kidneys to retain Na and H2O
Increases sympathetic drive
What happens when you get shot and start bleeding out?
- Blood pressure drops
- Baroreceptors fire less frequently
- CV centre detects this and inhibits parasymp and increases symp activity
- HR, SV, vasoconstriction and retention of water increase
However, you’re losing blood so:
- Decrease venous return
- Decrease SV
- Decrease BP
- Baroreceptors fire less frequently…
