CVS+ Flashcards
Define pulse pressure.
The difference between the systolic and diastolic blood pressure. It is measured in millimetres of mercury.
Define blood pressure.
The pressure of blood on the walls of blood vessels in the circulatory system
What is endothelin?
An amino acid peptide that is produced by vascular endothelium.
When reading blood pressure, which number is systole and which number is diastole?
Top number is systole - the highest level your blood pressure will reach when your heat beats
Bottom number is diastole - the lowest level your blood pressure will reach when your heart relaxes between beats
What is Pouseille’s Law?
Flow = radius to the power of 4
States that the flow of a fluid (Q) is related to the viscosity of the fluid (V), the pressure gradient across the tubing (P) and the length of the tube (L).
What is Ohm’s Law?
Flow = pressure gradient/resistance
What 3 factors relate to viscosity and which is the most important?
- Haematocrit (most important)
- Blood flow
- Vessel diameter
What is auto-regulation and where is it optimum?
The ability of an organ to regulate its own blood supply
Renal, cerebral and coronary systems = excellent
Splanchnic, skeletal and muscular systems = moderate
Cutaneous = poor
Which valves are classed as atrioventricular?
The mitral valve and the tricuspid valve.
What are some of the features of the atrioventricular valves?
The mitral has two cusps, the tricuspid has three.
They are between the upper chambers of the heart (atria) and the lower chambers of the heart (ventricles)
They are intrinsic parts of their ventricles
The free edge of each cusp is attached to the chordae tendineae, which are attached to the papillary muscle. The papillary muscle contracts during systole to keep the chordae tendineae taught.
Which valves are classified as the semilunar valves?
The aortic and pulmonary valve
What are some of the features of the semilunar valves?
They are intrinsic parts of their arteries (which leave the heart)
Both have three cusps
The free edge of the cusps has a thickening, which helps to shape the valve when it is closed
What are the chordae tendineae?
A group of tough, tendinous strands in the heart. Commonly referred to as the “heart strings” since they resemble small pieces of string.
Attach on one end to the edges of the tricuspid and mitral valves of the heart and on the other end to the papillary muscles
They play a vital role in holding the atrioventricular valves in place while the heart is pumping blood
At what spinal level is the arch of the aorta?
T4
What is the surface marking for the apex beat?
The 5th intercostal space in the mid-clavicular line on the left. It is in the mitral valve area.
Define apex beat.
The furthest most point inferiorly and laterally from the sternum where the cardiac impulse is still palpable.
What produces the 1st heart sound and what is the character of the sound?
The closure of the mitral valve and the sound is ‘lub’
What produces the 2nd heart sound and what is the character of the sound?
The closure of the aortic valve and the sound is ‘dub’
What is the 3rd heart sound and who may you be able to hear it in?
Normal in under 25s as heart is more elastic and you are able to hear the blood for passive filling of the ventricle
Is there a 4th heart sound? If so, when it is heard?
Usually no! If there is it is entirely PATHOLOGICAL and is caused by the atria contracting forcefully in an effort to overcome an abnormally stiff or hypertrophic ventricle. Heard just before the first heart sound (S1).
When does the aorta fill with blood?
During systole
When do the coronary arteries fill with blood?
During diastole
What is the term for when the heart is on the opposite side?
Dextrocardia. It is a congenital abnormality (it is present from birth)
How many layers make up the heart wall? What are they?
- Epicardium — protective layer mostly made of connective tissue
- Myocardium — the muscles of the heart
- Endocardium — lines the inside of the heart and protects the valves and chambers
Which chambers of the heart discharge blood?
The atria
Which chambers of the heart receive blood?
The ventricles
Which ventricle is responsible for the apex beat?
The left ventricle
From which side is the septum depolarised?
From the left side to the right side
Which coronary artery divides and what vessels does it divide into?
The left coronary artery: divides into the left anterior descending artery and the left circumflex artery
In cardiology what does dominance refer to?
Refers to the vessel that gives rise to the posterior descending artery (the right coronary artery or the left circumflex artery)
What is the usual pattern of coronary arterial dominance?
Most (70%) people are right dominant - the right coronary artery supplies the posterior descending artery
Some (20%) people are co-dominant - the right coronary artery and the left circumflex artery each help to supply the posterior descending artery
Few (10%) are left dominant - the left circumflex artery supplies the posterior descending artery
What are the three main branches at the arch of the aorta?
(Right to left) Brachiocephalic artery, left common carotid artery and the left subclavian artery.
What is unusual about the pulmonary vessels?
Arteries usually carry oxygenated blood and veins usually carry deoxygenated blood BUT…..
Pulmonary arteries: carry deoxygenated blood away from the heart to the lungs
Pulmonary veins: carry oxygenated blood back to the heart for distribution around the body.
How many pulmonary veins are there?
4
How long does a single cardiac cycle last?
0.8 seconds (systole = 0.3s + diastole = 0.5s)
How much of the blood in the ventricles is expelled with each beat?
Not all of it, about 2/3rds.
Describe the pericardium.
It is the membrane enclosing the heart and consists of an outer fibrous layer and an inner double layer of serous membrane.
What are the papillary muscles?
Small muscles in the ventricles which attach to the atrioventricular valves via the chordae tendineae and help to anchor the valves in place whilst the heart beats.
What is the coronary sinus?
A collection of veins joined together to form a large vessel that collects blood from the heart muscle (myocardium). It delivers less-oxygenated blood to the right atrium, as do the superior and inferior vena cavae.
Which artery is used to measure blood pressure?
The brachial artery - it is convenient to compress and is at the level of the heart.
At rest, what percentage of its potential does the heart pump?
60%
What marks the start of ventricular systole?
Isovolumetric contraction.
What does the “atrial kick” refer to?
Atrial contraction that contributes the remaining 20-30% of ventricular filling.
How does the majority (70-80%) of ventricular filling occur?
In flow via diastole. The two atrioventricular valves, the tricuspid and mitral valves, are both open, so blood flows unimpeded from the atria and into the ventricles.
Which chamber of the heart do the pulmonary veins drain into?
The left atrium.
What is another term for preload?
End diastolic volume.
What is pulse pressure measured in?
Millimetres of mercury.
The cellular blood component of blood accounts for what percentage of the overall blood volume?
45%
What is the cellular blood component comprised of?
Platelets, white blood cells and red blood cells
The plasma component of blood accounts for what percentage of overall blood volume?
55%
What is plasma made from?
Proteins (albumin, globulins, fibrinogens)
Water
Solutes (ions, nutrients, waste products, gases)
Erythrocytes form what percentage of the blood volume?
45%
What is the name for the fraction of an anticoagulated blood sample that contains most of the white blood cells and platelets?
The buffy coat (<1% of total blood)
What is haematocrit?
Volume percentage of red blood cells in the blood
Measure of the viscosity of the blood
The level of haematocrit is related to the level of haemoglobin.
What is the total blood volume of an adult and which organ is it regulated by?
5 litres (varies depending on size, weight & muscle mass) and is regulated by the kidneys.
What is the process of creating new blood cells called?
Haematopoiesis
What is Erythropoietin?
Hormone primarily produced by the kidneys (in the renal cortex)
Plays a key role in the formation of red blood cells (erythrocytes)
Blood levels of erythropoietin are generally low unless under hypoxic stress - Erythropoietin increases the rate of production of red blood cells in response to falling levels of oxygen in the tissues
A generalised multi-potential stem cell from which all blood cells are formed is called a what?
A hemocytoblast
Where are most blood cells formed in the adult?
In the bone marrow
Which cells does the bone marrow produce?
All of the red blood cells, all of the platelets and 60-70% of the white blood cells.
Where are platelets specifically formed?
Bits of the cytoplasm of the giant cells (megakaryocytes) of the bone marrow
Where are lymphocytes produced?
The lymphatic tissues, particularly the thymus, the spleen, and the lymph nodes
Where are monocytes produced?
The reticuloendothelial tissues of the spleen, liver, lymph nodes.
What are the features of erythrocytes?
Anucleate, no mitochondria, biconcave disc shaped, 7.5 diameter, lifespan is approx. 120 days, main components are haemoglobin and glycolysis enzymes.
Produced in bone marrow and removed by liver, spleen, bone marrow or blood loss
Regulating hormone is erythropoietin
What is the name of the protein containing iron which can be found in all the red blood cells?
Haemoglobin
How many polypeptide chains is haemoglobin formed from?
Four, which in adults consist of two alpha globin chains and two beta globin chains (i.e. a2b2).
How many haem groups are there per haemoglobin molecule?
4
What is haemoglobin A2?
A normal variant of haemoglobin A that consists of two alpha and two delta chains (α2δ2) and is found at low levels in normal human blood
Describe foetal haemoglobin.
The foetus receives its blood supply via the umbilical vein from the placenta. However, by the time the blood has reached the placenta, much of its oxygen has already been used up by the mother. Consequently, foetal haemoglobin needs to be able to bind oxygen with a higher affinity than maternal blood, if enough oxygen is to reach the foetus.
At birth, approximately 50-95% of the child’s haemoglobin is foetal haemoglobin, but after six months, these levels decline and adult haemoglobin becomes predominant
Describe the normal Hb adult levels.
HbA (a2b2) = 96-98%
HbA2 (α2δ2) = 1.5-3.2%
HbF (a2Y2) = 0.5-0.8%
What is anaemia?
Deficiency/lack of red blood cells or Hb in the blood reducing the ability of the blood to carry oxygen
What type of cell can be subdivided into phagocytes and lymphocytes?
Leukocytes (white blood cells)
What is the function of white blood cells and what makes them easily distinguishable from other cells?
They are cells of the immune system that are involved in protecting the body against both infectious disease and foreign invader.
Distinguishing factor = all white blood cells have nuclei!!!
What are phagocytes and which cells are categorised as phagocytes?
Type of cell capable of engulfing and absorbing bacteria and other small cells and particles – neutrophils, monocytes, basophils and eosinophils
What are granulocytes?
White blood cell with secretory granules in its cytoplasm = neutrophils, basophils and eosinophils
What are agranulocytes?
Also known as mononuclear leukocytes
White blood cells with a one-lobed nucleus
They are characterised by the absence of granules in their cytoplasm
= Lymphocytes and monocytes
Which is the most abundant type of leukocyte (white blood cell)?
Neutrophil = 60-70% of total WBC count
Which is the least abundant type of leukocyte (white blood cell)?
Basophil = 1% total WBC count
Name some of the features of neutrophils.
They have multilobed nucleus. Most abundant type of WBC. Forms puss, acute inflammation and phagocytic function Lifespan of 6 hours Granulocytes
Name some of the features of lymphocytes.
Have a fried egg appearance. Either B or T. B lymphocyte becomes plasma and produces antibodies T cells mediate inflammation 20-50% total WBC Agranular
Name some of the features of monocytes.
Kidney shaped nucleus
Differentiate into dendritic cells or macrophages. Adaptive immunity role
2-10% total WBC count
Agranular
Name some of the features of eosinophils.
Double lobed nucleus Acidophilic (red staining) granules Upregulated in parasitic infection 1-6% of WBCs Granular
Name some of the features of basophils.
Deep blue staining granules containing heparin, histamine, serotonin, prostaglandins –> role in allergic response.
IgE receptors
Granular
1% of WBCs
Other than the blood, where are platelets most commonly found?
In the spleen
What is another term for platelets?
Thrombocytes. Thrombocytopenia = low number Thrombocytosis = high number
Describe some of the features of platelets.
- Originate from megakaryocytes.
- Anucleate cells which circulate in an inactive state (keep the blood fluid) responsible for primary haemostasis, adhere, activate and aggregate to form a platelet thrombus
- Found in the blood and spleen
- Lifespan on 7-10 days
- Have two types of secretion vesicles: electron dense granules (calcium, ADP/ATP, serotonin) and alpha granules (platelet derived growth factor, fibrinogen, heparin antagonist, vWF)
What are platelets activated by?
Tissue factor
What are the only cells where tissue factor is NOT present?
Endothelial cells
Describe haemostasis.
Refers to the normal response of the vessel to
injury by forming a clot that serves to limit haemorrhage
Concerned with maintaining the balance of blood flow (so it is liquid in the vessels but will clot outside)
Coordinated effort between platelets and blood clotting proteins to form a blood clot and the contraction of damaged blood vessels to stop the bleed
What happens before a platelet plug begins to form?
Vasoconstriction - decreases blood flow to the area and decreases pressure in the damaged vessel. Occurs because of neural control and the release of endothelin-1 (released from endothelial cells)
Briefly describe the formation of a platelet plug.
- Endothelium disrupted exposing collagen fibres.
- Platelets adhere to Von Willebrand
factor (VWF) which is adhered to the collagen via - glycoprotein 1b receptor on platelet membrane - PLATELET ADHESION - Triggers the platelet to release platelet dense granules and thrombin via exocytosis
- Platelets change shape and become spiculated which increases their surface area - called PLATELET ACTIVATION
- Causes platelets to bind to fibrinogen enabling new platelets to adhere to the old ones - PLATELET AGGREGATION
Why doesn’t the platelet plug expand away from the damaged endothelium to invade the undamaged endothelium?
Undamaged endothelium releases:
- Prostaglandin-1 = vasodilator & inhibits aggregation
- Nitric oxide (NO) = vasodilator & inhibits platelet adhesion, activation & aggregation
When platelets change shape and become spiculated what is this process called?
Platelet activation
What is the name for the process whereby platelets bind to fibrinogen to enable new platelets to adhere to the old ones?
Platelet aggregation
Which protein polymer does a blood clot/thrombus mainly consist of?
Fibrin
What is the intrinsic pathway of the coagulation cascade?
Only uses componants from inside the blood
The pathway that generates the large amounts of thrombin needed for adequate coagulation
Begins with factor XII plasma protein - contact activation via collagen
What is the extrinsic pathway of the coagulation cascade?
Uses components from outside of the blood
Thrombin produced in this pathway is too little but triggers intrinsic pathway
Begins with tissue factor (plasma protein) that binds to factor VII
Clotting is usually initiated by extrinsic pathway but will always end up in the intrinsic path!
What is the coagulation cascade initiated by?
Activation of factor XII or the generation of the tissue factor
What is the aim of the coagulation cascade?
To form a fibrin clot
What links together the intrinsic and extrinsic pathways of the coagulation cascade?
Thrombin
What does thrombin do?
Converts the soluble fibrinogen to the insoluble fibrin which can be used to secure the blood clot and build it up
What breaks down fibrin?
Plasmin
Briefly describe the fibrinolytic pathway.
Plasminogen is converted into Plasmin which breaks down fibrin and therefore breaks down the entire blood clot (thrombus).
How many blood groups are there?
4: A, B, AB and O
Group is determined by which antigen the red cells carry
Which blood group is the universal donor group?
Type O-
Has neither ABO or RhD antigens on the surface of the red cells
Which blood group is the universal recipient group?
Type AB+
Has both A and B antigens on the red blood cells but neither of the antigens are present in the plasma
Which plasma type is the universal donor?
AB because it does not carry any antibodies.
Which plasma type is the universal recipient?
O because it carries A and B antibodies
When is your blood rhesus positive?
If the RhD antigen is present
When is your blood rhesus negative?
If the RhD antigen is absent
When does Rhesus Disease/ Haemolytic Disease of the Newborn occur?
Only occurs when the mother has rhesus negative blood (RhD-) and the baby has rhesus positive blood (RhD+)
For it to occur mother must have been previously sensitised to RhD+ blood – this is probably from a previous pregnancy
Prevented using injections of anti-D immunoglobulin
Describe the distribution of total blood volume.
Veins 64%, arteries 13%, pulmonary vessels 9%, heart 7%, capillaries 5% and arterioles 2%
Describe the distribution of resistance in the circulatory system.
Arterioles 47%, capillaries 27%, large arteries 19%, veins 7%
Describe some of the features of arteries.
● Carry blood away from the heart
● High pressure
● Contain mainly elastic, collagen & smooth muscle
● Elastic arteries increase efficiency and are major distributing vessels (aorta and pulmonary arteries)
● Muscular arteries regulate blood pressure and control blood distribution (most common type of artery)
● Do not contain valves (high pressure pushes blood forwards)
● Carry oxygenated blood (apart from pulmonary arteries)
● Have a pulse
What are the histological layers of an artery?
Endothelium, basement membrane, intima, internal elastic lamina, media, external elastic lamina, adventitia..
Name some of the features of veins?
● Blood is blue-red colour
● Low pressure
● Thinner walls
● Veins generally have collagen and little muscle & elastic with the wall & a single internal elastic lamina
● Found near surface of skin
● Have valves (low pressure so need valves to keep blood flowing in the correct direction
● Carry de-oxygenated blood: apart from the pulmonary veins
● Will not have a pulse
What are the histological layers of a vein?
Endothelium, basement membrane, intima, internal elastic lamina, media, adventitia.
What are capillaries?
Composed of thin-walled endothelial cells with no surrounding muscle or connective tissue that are bound to a basement membrane with co-existing pericytes.
What are pericytes?
Contractile cells that wrap around the endothelial cells of capillaries and venules. They help to regulate flow.
What are the three types of capillary?
- Continuous - uninterrupted lining, only allowing small molecules like water and ions to diffuse through tight junctions
- Fenestrated (kidneys, small intestine) – the endothelial layer is incomplete forming windows that facilitate the movement of materials out of the circulation and into the surrounding tissue
- Discontinuous sinusoidal (liver, spleen) - special type of fenestrated capillaries with larger openings in the endothelium. Allow red and white blood cells and various serum proteins to pass through
How many systems does the circulatory system comprise of?
3 = cardiovascular, pulmonary and systemic circulation.
What are some of the features of the systemic circulation?
o Thick walled vessels with substantial muscularisation and high blood pressure
o Blood leaves the left ventricle via single large artery, the aorta.
o The arteries of the systemic circulation branch off the aorta, dividing into progressively smaller vessels.
o 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.
What are some of the features of the pulmonary circulation?
o Thin walled vessels with minor muscularisation and low blood pressure
o Blood leaves the right ventricle via a single large artery, the pulmonary trunk, which divides into the two pulmonary arteries, one supplying the right and one supply the left lung.
o In the lungs the arteries continue to branch and connect to arterioles, leading to capillaries that unite into venules and then veins.
o The blood leaves the lungs via four pulmonary veins, which empty into the left atrium
Define mean systemic arterial pressure (MAP).
MAP = diastolic pressure + 1/3 of pulse pressure (sp-dp)
The average blood pressure in the arteries during the cardiac cycle.
Define contractility.
The force in which the heart contracts with. Increasing contractility would mean the heart contracts with more strength and produces a higher pressure.
This is independent of load and reliant on sympathetic innervation and hormonal factors.
What is the term for the force of contractility of the heart?
Cardiac ianotrophy
What is the term for the rate of contraction of the heart?
Cardiac chronotrophy
Where is the pressor region and what does it do?
In the medulla oblongata.
It is the region responsible for increasing blood pressure by ↑ vasoconstriction, ↑ CO and ↑ contractility
It is sympathetic: medulla - spinal cord.
Where is the depressor region and what does it do?
In the medulla oblongata
Is the region responsible for lowering blood pressure by inhibiting the pressor region
Parasympathetic: medulla → vagus nerve
Where are central chemoreceptors?
In the medulla oblongata. Respond mainly to a decrease in pH as CO2 cannot diffuse across the blood brain barrier.
Where are arterial baroreceptors found?
One is found in the aortic arch (vagus nerve)
Two are found in the carotid sinus (sinus nerve → glossopharyngeal nerve)
They are stretch receptors that are stimulated by distortion of the arterial wall when pressure changes.
What type of receptors control blood pressure in the long term?
Cardiopulmonary baroreceptors that are found in the atria, ventricles and pulmonary arteries.
What is the diocrotic notch formed by?
As LV ceases contracting the pressure falls rapidly. This causes blood in the aorta to flow backwards towards the heart. This prompts the aortic valve to close, which causes a brief increase in aortic pressure = diocrotic notch.
What are the three stages of the cardiac cycle?
- Ventricular filling (ventricular filling & atrial systole) 2. Ventricular systole (isovolumetric contraction, ventricular ejection). 3. Early ventricular diastole (isovolumetric relaxation, ventricular filling)
What is normal blood pressure in the pulmonary circulation?
25/8 mmHg (millimeters of mercury)
What are the two types of cell in the heart?
Pacemaker cells and cardiac myocytes
Which type of cells make up the majority of the heart’s mass?
Cardiac myocytes. They are 100μm long and 10-25μm in diameter and make up the atria and the ventricles .
What is the function of pacemaker cells and where are they located?
Carry the impulses that are responsible for the beating of the heart – they are located throughout the heart
What are some of the unique features of cardiac muscle?
Found only in the heart
No stem cells
Contracts rhythmically
Does not fatigue like skeletal muscle because it has a lot of mitochondria, myoglobin and a good blood supply which allows continuous aerobic metabolism and the production of ATP for cardiac function
Cells are joined end to end by intercalated discs
Within the discs are desmosomes that hold the cells together and to which microfibrils attach
The desmosomes also contain gap junctions
What three types of cell junction make up intercalated discs?
Adherens junctions, gap junctions and desmosomes
At which line of the sarcomere do intercalated discs occur?
Z line
What is the function of intercalated discs?
Connect neighbouring cardio myocytes and and support the synchronised contraction of cardiac tissue, allowing it to function as a single co-ordinated unit.
Where is the sinoatrial node located?
The SA node is located in the wall (myocardium) of the right atrium, laterally to the entrance of the superior vena cava and on the crista terminalis
What is a sacromere?
The basic contractile unit for both striated and cardiac muscle and is made up of a complex mesh of thick filaments, thin filaments, and a giant protein titin
What two types of filaments does a sarcomere contain?
- Thick filaments (composed mainly of myosin)
2. Thin filaments (composed mainly of actin)
Describe myosin (thick filament).
2 heavy polypeptide chains and 4 light chains. The myosin heads have 2 binding sites; one for actin and one for ATP.
Describe actin (thin filament).
Polymerised globular protein with troponin and tropomyosin incorporated
What are elastic filaments that maintain
alignment of sarcomere?
Titin
In which part of the sarcomere is there no overlap of thick and thin filaments?
H zone (only contains thick filaments)
What is the function of Tropomyosin?
Modulates actin-myosin interaction (with troponin I)
What is the function of Troponin C?
Binds Ca+ to cause conformational change in Troponin I to allow cross bridge formation.
What is the function of Troponin T?
Binds troponin complex to thin filament
What is the function of Troponin I?
Inhibits actin-myosin interaction with tropomyosin
Name the 6 contractile proteins of the heart.
Myosin (thick), Actin (thin), Tropomyosin (thin), Troponin C (thin) Troponin I (thin) Troponin T (thin)
What effect does myocardial contraction have on the I-band and H-zone of a sarcomere?
They get shorter
What effect does myocardial contraction have on the A-band of a sarcomere?
No effect i.e. it stays the same length.
Why does the contraction of cardiac muscle last longer than skeletal muscle and how much longer is it?
Up to 15 times longer and is due to slow calcium channels
A type of signalling process that activates contractile proteins by converting an electrical stimulus (action potential) into a muscle contraction is called what?
Excitation-contraction coupling
Describe excitation-contraction coupling.
- Na+ depolarises membrane.
- A small amount of Ca2+ is released from T tubules.
- Ca2+ channels in sarcoplasmic reticulum open.
- Ca2+ binds to sarcomere and allows contraction
- After depolarisation, Ca2+ is returned to SR. K+ outflow = repolarisation.
What must the sodium channels do in order for the cell to depolarise?
Open (negative to positive charge inside the cell)
What must the sodium channels do in order for the cell to repolarise?
Close (positive to negative charge inside the cell)
What type of action potentials are “slow action potentials”?
Pacemaker action potentials
Where are pacemaker cells most commonly found?
Sinoatrial and atrioventricular nodes
Describe the channels in pacemaker action potential.
HCN channels - allow Na+ to move into the cell and for K+ to move out of the cell.
Transient calcium channels (CaT Channels) allow calcium to move into the cell
How is pacemaker action potential generated?
Na+ and Ca2+ move into the cell through HCN channels and calcium channels - depolarises cell
These channels then close and K+ flows out of the cell - repolarises cell
Briefly describe the cardiac action potential in 5 steps.
- STAGE 0 = RAPID DEPOLARISATION - Na+ channels open; influx of Na+ into cell
- STAGE 1 = PARTIAL REPOLARISATION - Na+ channels close, a small number of K+ leave the cell
- STAGE 2 = PLATEAU PERIOD - Ca2+ channels open and there is Ca2+ inflow. K+ channels are also open and there is K+ outflow.
- STAGE 3 = REPOLARISATION - Ca2+ channels close and K+ channels remain open. K+ leaves the cell
- STAGE 4 - RESTING POTENTIAL (approx -90mV). Na+ inflow, K+ outflow.
How is pacemaker action potential generated?
Na+ and Ca2+ move into the cell through HCN channels and calcium channels - depolarises cell
These channels then close and K+ flows out of the cell - repolarises cell
What is sympathetic stimulation of the heart controlled by?
Adrenaline and noradrenaline
What is the function of the refractory period?
- It prevents excessively frequent contractions - prevents muscle from tiring.
- It allows time for the atria to fill.
What effect will sympathetic stimulation have on the heart?
- Increases heart rate (positively chronotropic)
- Increases force of contraction (positively inotropic)
- Increases cardiac output
What effect will parasympathetic stimulation have on the heart?
- Decreases heart rate (negatively chronotropic)
- Decreases force of contraction (negatively inotropic)
- Decreases cardiac output
What membrane channels are responsible for the plateau period in cardiac action potential?
Voltage gated Ca2+ ‘slow’ channels.
What effect would sympathetic stimulation have on pacemaker action potential?
Adrenaline or noradrenaline binding to Beta 1 receptor causing increased Na+ permeability so that the threshold potential is reached faster
What effect would parasympathetic stimulation have on pacemaker action potential?
Parasympathetic stimulation - Acetylcholine binds to muscarinic receptors causing a decreased Na
permeability. Longer time taken to reach threshold
potential.
What are the differences between cardiac myocyte action potential and regular action potential?
Cardiac action potential has Ca2+ leaving the cell to caused a plateau
Cardiac action potential is 200-300 ms. Regular action potential in skeletal muscle cells is approximately 2-5 ms
Cardiac action potential has a longer refractory period to prevent muscle fatigue.
What is the main function of valves?
Prevent the back-flow of blood
What does it mean if a valve is not working correctly?
It is regurgitant.
Describe the arterial baroreceptor reflex in response to an increase in blood pressure.
Increased parasympathetic outflow to the heart means contractility and heart rate are reduced and so cardiac output is reduced: CO=HRxSV.
Decreased sympathetic outflow to the arterioles results in vasodilation and so TPR is reduced.
BP=COxTPR and so blood pressure is lowered.
Describe the arterial baroreceptor reflex in response to a decrease in blood pressure.
Increased sympathetic outflow to the heart means contractility and heart rate are increased and so cardiac output is increased: CO=HRxSV.
Increased sympathetic outflow to the arterioles results in vasoconstriction and so TPR is increased.
BP=COxTPR and so blood pressure is increased.
What are the main parts in the cardiac conduction system?
- Sinoatrial (SA) node
- Atrioventricular (AV) node
- Bundle of His
- Bundle branches
- Purkinje fibres
When do the SA and AV node recharge?
When the atria are filling.
What 2 channels are closed during the refractory period in a cardiac action potential?
Fast Na+ and slow Ca2+ channels
Briefly describe the electrical conduction pathway in the heart.
- The SAN generates an electrical impulse.
- This generates a wave of contraction in the atria.
- Impulse reaches AVN.
- There is a brief delay to ensure the atria have fully emptied.
- The impulse then rapidly spreads down the Bundle of His and Purkinje fibres.
- The purkinje fibres then trigger coordinated ventricular contraction.
Why is there rapid conduction in the bundle of his and purkinje fibres?
- The fibres have a large diameter.
2. There is high permeability at gap junctions.
What feature is contractility of the heart independent of?
Load
Why does cardiac muscle not tire easily?
It has many mitochondria, myoglobin and a good blood supply which allows continuous aerobic metabolism and the production of ATP for cardiac function
The myosin head contains binding sites for what two molecules?
ATP and actin
Via what mechanism does a cardiac myocyte reach its threshold potential?
Via the intercalated disc of the adjacent cardiac myocyte
Define ECG.
Electrocardiogram - process of recording the electrical activity of the heart over a period of time using electrodes placed over the skin. It is a measure of the currents generated in the EXTRACELLULAR FLUID by the changes occurring simultaneously in cardiac cells.
Which ventricle has the most influence on an ECG?
The left ventricle
How many leads does a normal ECG use?
12
In how many directions does an ECG provide information about the hearts electrical activity?
Three directions:
- Right ⇌ left
- Superior ⇌ inferior
- Anterior ⇌ posterior
ECG: where would you place lead 1?
Right arm (-ve) to left arm (+ve).
ECG: where would you place lead 2?
Right arm (-ve) to left leg (+ve).
ECG: where would you place lead 3?
Left arm (-ve) to left leg (+ve).
ECG: where would you place lead aVR?
Right wrist
ECG: where would you place lead aVF?
Left foot
ECG: where would you place lead aVL?
Left wrist
ECG chest leads: In which intercostal space would you place V1 and V2?
The 4th intercostal space
ECG chest leads: In which intercostal space would you place V3-V6.
The 5th intercostal space
Which part of the heart does the V4 lead represent?
The apex
What does the P wave on an ECG represent?
Atrial depolarisation. Duration is less than 0.12s
What does the QRS complex on an ECG represent?
Ventricular depolarisation. Duration is 0.08-0.1s.
What does the T wave on an ECG represent?
Ventricular re-polarisation
What might an elevated ST segment be associated with?
Myocardial infarction
What is a normal RR interval?
0.6-1 second
What does the ST segment on an ECG represent?
Period of zero potential between ventricular depolarisation and repolarisation - should be flat!
What time period does each small square on an ECG represent?
0.04 seconds
What is Einthoven’s triangle?
An imaginary formation of the 3 limb leads in a triangle shape.
Most of the cardiovascular system is derived from cells situated in which germ cell layer?
The mesoderm
Through which two processes does the circulatory system develop?
Angiogenesis and vasculogenesis
On which day of embryogenesis does angiogenesis and vasculogenesis commence?
Day 18
Why are foetal circulatory shunts needed and how many of them are there?
Vascular shunts are required to bypass the liver and non-functioning lungs
There are two separate shunts:
1) Foramen ovale - between the two atria
2) Ductus Venosus - links the distal arch of the aorta with the pulmonary trunk
Briefly describe foetal circulation.
Maternal circulation - umbilical vein (oxygenated blood) - ductus venosus - IVC - RA - LA/RV - aorta - umbilical artery (deoxygenated blood) - maternal circulation.
What does the first heart field produce?
The left ventricle.
What does the second heart field produce?
The right ventricle, atria and outflow tracts.
What are the 3 stages of heart formation?
- Formation of primitive heart tube
- Cardiac looping
- Cardiac septation
Briefly describe the formation of the primitive heart tube.
Day 19 = two endocardial tubes form which will fuse to form a single primitive heart tube
Day 22 = the heart is a single tube and it begins to beat
Describe what happens in cardiac looping.
Day 23 = heart tube begins to fold
Nodes secrete nodal, this circulates to the left due to ciliary movement. Nodal causes a cascade of transcription factors that transduce looping.
Day 28 = complete
What does the bulbus cordis form?
The right ventricle
What does the primitive ventricle form?
The left ventricle
What does the primitive atrium form?
Left atrium and anterior part of right atrium
What does the sinus venosus form?
Part of right atrium, vena cava and coronary sinus
What does the truncus arteriosus form?
The aorta and pulmonary trunk
What do the 1st and 2nd aortic arches form?
Minor vessels in the head (part of maxillary artery and stapedial artery)
What does the 3rd aortic arch form?
The common carotid arteries.
What does the left and right 4th aortic arch form?
Left = aortic arch Right = part of right subclavian artery
What does the left and right 5th aortic arch form?
There is no 5th aortic arch!!!
What does the left and right 6th aortic arch form?
Left - left pulmonary artery and ductus arteriosus.
Right - right pulmonary artery.
What does the 7th segmental aortic arch form?
Left and right subclavian arteries.
What does the left and right dorsal aortae form?
Left = descending thoracic aorta Right = part of right subclavian artery.
What pump maintains the negative resting potential of a membrane?
Na+/K+ pump.
Describe the parasympathetic innervation to the heart.
Nerve: Vagus nerve
Neurotransmitter: ACh
Receptor: muscarinic
Response: decrease heart rate
Describe the sympathetic innervation to the heart.
Nerve: spinal nerve T1-T5
Neurotransmitter: Norepinephrine
Receptor: Beta adrenergic
Response: increase heart rate
Define cardiac axis.
The average direction of the depolarisation wave spreading through the ventricles
Which artery are the SA and AV node usually supplied by?
The right coronary artery.
Which ion causes depolarisation of the nodal cells?
Ca2+
Sensory innervation of fibrous and parietal pericardium is provided by which nerves?
The phrenic nerve, the vagus nerve and the sympathetic trunk.
What are the branches of the brachiocephalic trunk?
Right common carotid (LHS). Right subclavian (RHS).
What branch does the left vagus nerve give off as it crosses the arch of the aorta?
The left recurrent laryngeal nerve
What structures form the left border of the heart?
- Left pulmonary artery.
- Left auricular appendage.
- Left ventricle.
What forms the right border of the heart?
The right sternal edge.
On what aspect of the heart would you find the left atrium?
The posterior aspect.
Name the 2 main branches of the LCA.
- Circumflex.
2. Left anterior descending (LAD).
Name the artery that supplies:
a) The SAN
b) The AVN
a) Sino-atrial nodal branch of RCA.
b) Posterior inter-ventricular branch, usually RCA.
At what phase of the cardiac cycle do the coronary arteries fill?
Diastole; when the ventricles are relaxed.
How do the mitral and tricuspid valves work?
They open passively when the atria contract and then close afterwards to prevent backflow. The papillary muscles and chordae tendinae work to keep the valves closed during ventricular contraction.
How do the atrial and pulmonary valves work?
They open passively when the ventricles contract. Towards the end of systole they close to prevent the back flow of blood. The pressure of blood on the valves keeps them closed.
How would you know if the atrial and pulmonary valves were incompetent?
You would get regurgitation of blood into the ventricles. This could be heard as a diastolic murmur.
Where can you hear the pulmonary valve?
Left of the sternum, 2nd intercostal space.
Where can you hear the aortic valve?
Right of the sternum, 2nd intercostal space.
Where on the heart would you find the left ventricle?
At the apex
On what border of the heart would you find the right ventricle?
On the inferior border.
What is the inner layer of the heart called?
Endocardium
Which is the most important class of immunoglobulins?
IgG
Which class of immunoglobulins do all immunoglobulins start as?
IgM
Which Ig is first produces in infection?
IgM
What is the most abundant Ig in circulation?
IgG
Which type of cell produces immunoglobulin?
B lymphocytes
Which property of immunity does vaccination use?
Immunological memory
Where are B-lymphocytes made and stored?
Made in bone marrow mature but are stored in secondary lymphoid organs e.g. lymph nodes etc
Which type of Ig are made to things that we are allergic to?
IgE
Why is there no change in hematocrit during blood loss?
Because the hematocrit is a percentage of red blood cells, as compared to the total volume of blood. As plasma and red blood cells are lost in equal proportions there will be no change.
Give examples of hormonal vasoconstrictors.
Adrenaline, angiotensin II, ADH (vasopressin)
Give examples of hormonal vasodilators.
Atrial natriuretic peptide, adrenaline.
Explain neural control factor.
Blood pessure deviates from norm
Baroreceptors detect change in BP
Baroreceptors send impulse to brainstem
Brainstem causes change to cardiac output and vessel diameter
Give examples of local vasoconstrictors.
Blood pressure – myogenic autoregulation
Endothelin 1 – stimulated by angiotensin and ADH -> released from endothelial cell -> binds to smooth muscle receptors and causes calcium release
Give examples of local vasodilators.
Hypoxia
Nitrous oxide
Decrease in ph (increase in hydrogen ions and CO2)
What is the function of the right atrium?
Receives deoxygenated blood from superior and inferior vena cava
Smooth (sinus venosus) and trabeculated (muscle bundles) parts separated by cristae terminalis
Pumps blood through tricuspid valve into right ventricle
What is the function of the right ventricle?
Thinner muscular wall (pulmonary ventricle)
Trabeculae carnae gives ventricle sponge like appearance
Pumps deoxygenated blood through pulmonary valve to pulmonary artery
What is the function of the left atrium?
Receives oxygenated blood from four pulmonary veins
Pumps blood through mitral valve into left ventricle
What is the function of the left ventricle?
Thicker muscular wall (systemic ventricle) trabeculae carnea gives ventricle sponge like appearance
Pumps oxygenated blood through aortic valve to aorta
What is the name of the non-smooth muscle bundles in the heart that are separated from the smooth muscle parts (sinus venosus) in the right atrium and give the ventricles their spongy appearance?
Trabeculae carnea
What is end systolic volume?
The volume of blood remaining in the ventricles following systole.
Define preload
The volume of blood in the ventricles just before contraction occurs.
Define afterload
The pressure resistance that the ventricles must overcome in order to eject blood in systole
Define elasticity
The heart’s ability to revert back to its orginal shape following systolic stress.
Define compliance
How easily a chamber of the heart expands when it is filled with blood.
Define diastolic distensibility
The pressure required to fill the ventricle to the same diastolic volume.
What is the basic principle of Starling’s law of the heart?
The greater the EDV the greater the SV
Explain Starling’s Law.
The greater the end-diastolic volume the greater the sarcomeres are stretched and the more forceful the contractions.
What is the equation for stroke volume?
SV = EDV-ESV
Stroke volume = end diastolic volume - end systolic volume
Define cardiac output and give the equation.
The volume of blood that each ventricle pumps per unit of time. CO = HR x SV
How is blood pressure calculated?
BP = CO x TPR
