Cardio Respiratory - Week 1 The heart Flashcards
What are the cardiac muscles? (1)
Specialised form of striated muscles
What are the two roles of the heart? (2)
Supply oxygenated blood containing nutrients (e.g. glucose) to the major organs.
Remove waste products formed during metabolism (e.g. via the lungs and kidneys).
Where is the heart positioned in the body? (4)
Located behind sternum
Extends from the 2nd to the 5th rib
About 12-14 cm long
Weighs about 250-350 g
The circulation can be divided into three separate parallel circuits.
What are they? (3)
Pulmonary (lungs)
Coronary (heart)
Systemic (rest of body)
During coronary circulation, what is Arterial Blood Supply? (3)
Oxygenated blood is supplied to the heart muscle via the left and right coronary arteries
These arteries branch directly from the base of the aorta
During coronary circulation, what is venous drainage? (3)
Venous blood drains into the coronary sinus and then into the right atrium
From there to the lungs via the pulmonary circuit for reoxygenation
What is systemic circulation? (2)
Provides oxygenated blood for the organs and tissues of the body
The left ventricle pumps blood into the aorta which then branches into smaller arteries
What blood does the left side pump? (1)
Pumps oxygenated blood
What blood does the right side pump? (1)
Pumps deoxygenated blood
Which ventricle has a thicker wall? (1)
Left ventricle
What is the heart enclosed in? (2)
The outer layer (fibrous pericardium)
The inner, visceral, layer (serous pericardium)
What is the role of the outer layer (fibrous pericardium)? (1)
Protects, anchors and also prevents the heart overfilling with blood
What is the role of the inner, visceral, layer (serous pericardium)? (1)
Extends to cover the epicardial surface of the muscular wall of the heart.
What does the pericardial cavity contain and do? (3)
Filled with a fluid
Lubricates the serous pericardium membrane and allows the two membranes to glide over each other
Heart can stay mobile when it is pumping
What are the 4 heart valves? (4)
Right side: The atrio-ventricular (AV) valve has three cusps and is called the tricuspid valve
Left side: the AV valve has only two cusps and is called the bicuspid or Mitral valve
Semilunar valves located at the entrance of the ventricular outflow tracts - pulmonary valve and aortic valve
How many cusps do the semi lunar valves have? (1)
3
How do the valves work? (2)
They open and close in response to the pressure gradient across them
Larger pressure downstream of the value (valves close)
What are the specialised muscles in ventricles called? (2)
Papillary muscles
Attach to atrioventricular valve
What is the role of papillary muscles? (2)
Blood returning to the heart fills the atria putting pressure on the A-V valves which forces them open.
When the ventricles contract, pressure is higher in the ventricle than atrium and so the valve is forced shut.
Muscles help to create tension on atrioventricular valves to remain shut and all blood is ejected out pulmonary artery and aorta
They do not pull the valve close but prevent back flow of blood into atria.
What are the different cell types within the heart? (5)
Fibroblasts
Endothelial Cells
Smooth muscle cells
Conduction cells
Cardiomyocytes
What are fibroblasts? (3)
Contribute to the extracellular matrix
– providing mechanical support
Provide fixture for contractile cells
What are endothelial cells? (1)
Contribute to the lining of blood vessels
What are smooth muscle cells? (1)
In coronary arteries and veins
What are conduction cells? (1)
Generation and passing of electrical impulses
What are cardiomyocytes? (2)
Form the contractile apparatus of the atria and ventricles
Make up predominant mass of the heart - 70% of the mass
Describe the cellular structure of cardiac muscles (4)
Cardiac muscle appears as a latticework of cells
Ventricular myocytes ~ 120 micrometer long and approximately 30 micrometer wide
Rich in glycogen, myoglobin
Large number of mitochondria
Why does the cardiac muscles have mitochondria? (2)
Reflects the high energy demands of this tissue
Around 30% of ventricular myocytes is occupied by mitochondria
What are intercalated discs? (1)
Where one cell meets another there is a step-like cell to cell junction called the intercalated disc
What are the two roles of intercalated discs? (2)
They act to firmly bind adjacent cells together (mechanical coupling - one cell contracts and the other also pulls so they contract together ) but also to allow electrical coupling between adjacent cells - electrical signalling can pass throughout the heart
What are desmosomes? (3)
Cells are tightly adhered tighter
Occur on transverse section of intercalated discs
Involved in mechanical coupling
In mechanical coupling what are the small gaps? (1)
There is a small gap (0.02 micrometer) between the membranes of adjacent cells filled with connective tissue
What are the components in electrical coupling? (3)
Longitudinal area of close contact = nexus or gap junction
Arrays of proteins called connexins are found here
These allow the passage of ions and other small molecules between one cell and another - allow electrical signal to pass from one cell to another
What is the nexus and how does it relate to the function of the heart? (4)
The nexus provides electrical coupling between neighbouring cells
As a result ionic currents pass between neighbouring cells, evoking an action potential in the second cell.
The result of this is that the heart behaves electrically as a single cell- functional syncytium
Cardiac muscle obeys the all or nothing principle - one cell contracts within the heart this signal propagest in the heart and the whole heart contracts
The heart is myogenic. What does this mean? (3)
Not neurogenic - does not rely on neuronal input to contract and generate action potential
Stimulate its own action potential
Done by specialised conductive tissue within the heart
What is the all or nothing principle of the cardiac muscles? (2)
One cell contracts within the heart this signal propagates in the heart and the whole heart contracts
What are the three properties of the heart? (3)
Excitability
Conductivity
Automaticity
What is excitability of the heart? (1)
Generate its own action potential
What is conductivity of the heart? (1)
Property of the tissue to allow to propagation the signal
What is automaticity of the heart? (1)
It doesn’t rely on an external source to product action potentials
How does the heart controls and coordinates the regular contraction of the atria and ventricles (9)
Sino atrial node sends waves/electrical activity across both atria
Both atria contract
Layer of nonconductive tissue prevents wave reaching ventricles
Wave of electrical activity reaches atrioventricular node
0.1 second delay allowing atria to empty full of blood
Wave of electrical activity sent from the atrioventricular node
Down the bundle of His to the base of the ventricles
Up the Purkinje fibres
Causing the ventricles to contract from the apex of the heart upwards
The action potential spreads rapidly away from SA node throughout the atrial muscle. This occurs via two pathways. What are these? (3)
Excitation of the atria (SAN)
(i) from cell to cell via intercalated disks
(ii) via a specialised conduction pathway: ‘The internodal tract’
Why is the conduction velocity through the AV node is very slow (~0.05 m/s) (1)
To allow the ventricles to fill with blood
How does the action potential spread throughout the rest of the ventricular muscle (1)
Via cell-to-cell coupling (rate 1 m/s) from the endocardium (inside) to the epicardium (outside)
What is the Nernst potential also known as? (1)
The equilibrium potential
What is the Nernst potential gradient? (1)
The potential gradient across the membrane to maintain concentration gradient
What is the equation for Nernst potential? (3)
Check notes - week 1
What is the potential gradient telling us? (1)
The electrical potential needed to stop on diffusion down chemical gradients
The potential difference between the inside and outside of the cell is a result of what? (1)
Result of differences in ion concentration across the membrane
How can the resting membrane potential be calculated? (1)
The resting membrane potential is a sum of different ions
Equilibrium potential * Electrical Conductance
What is the equation for resting membrane potential? (1)
Check notes - week 1
Describe the permeability of K+ at resting membrane (1)
Resting membrane had open K+ permeable channels
Describe Na+ and Ca+ channels at negative resting potentials (1)
Na+ and Ca+ channels are mostly closed at negative resting potentials
What does the electrical property of a tissue depend on? (1)
Depends on which ion channels are expressed in the membrane
What are the main channels involved in membrane excitation? (3)
Na+, K+ and Ca2+ ions
What are ion pumps? (2)
Pumps use ATP – metabolic energy Na/K
Three Na out and two K in
What are exchangers? (3)
Use energy from ion travelling down concentration to move ion in the opposite direction
(Na/H+)– pumping Na down the gradient
Minimal effect on overall charge
What are voltage gated channels? (2)
Open and close depending on voltage of cell
Allow movement of ion down concentration gradient
Describe the cardiac ion channels for Na+ (3)
Opens at negative voltages (e.g. –70 mV) -i.e. are voltage gated
Activates rapidly to allow ions to move in and then inactivates (closes) rapidly.
Na+ enters the cell down its concentration gradient- generating an inward membrane current.
What helps to move Na+ back out to the extracellular environment? (1)
Na+/K+ pump + Na+/Ca2+ exchanger
Describe the cardiac ion channels for Ca2+ (1)
2 types: T-type and L-type
What are T-type Ca2+ channels? (3)
Tiny conductance and Transient openings:
Open at -55 mV and inactivate fairly rapidly
Relatively small conductance cf. L-type
What are L-type Ca2+ channels? (3)
Large conductance and long lasting openings
Found throughout the heart
Open at –40 mV and inactivate (close) more slowly cf. T-type
Describe K+ current (2)
K+ currents are outward and make the cell more negative inside when they flow
Exert controls the resting potential and action potential duration
Describe cardiac ion channels for K+ (2)
There are many different channel types in cardiac muscle (e.g Kv)
They allow K+ current to flow at various times (e.g ik+)
Describe background K+ current (4)
Driven through inward rectifying channel (Kir)
Gives resting outward current IKir/IK1
Channels open at negative voltages
Help to set the sable negative resting membrane potential of atria and ventricular myocytes
Delayed K+ currents & Transient outward K+ currents (2)
Close at negative voltages
Membrane potential become positive - open - help to repolarise the cell after an action potential
Describe current voltage relationship for background current (3)
Look at notes for Week 1 for graph
As Em becomes more positive the channel is blocked by intracellular
- Regulation by ion channel itself
- Magnesium ions
- Polyamines
What are the two types of mixed conductance channels (2)
Background current (ib)
Funny current (if )
What is background current? (2)
Allows inward background current of Na+ ions (mostly)
Causes the cell to be slightly higher then EK
Conducts both ions so reflects the permeability of all the ions
What is funny current? (3)
Channel permeable to Na+ and K+
Activates slowly, small conductance, Erev close to -20 mV
Activated by hyperpolarisation (i.e. more inward current is generated at more negative membrane potentials)
Describe phase 4 of the ventricular myocyte action potential
Stable resting membrane potential (-85/90mV)
Describe phase 0
On initiation of action potential
Rapid
Happens around 200v/s
Describe phase 1
Initial depolarisation
Describe the ventricular myocyte action potential graph (5)
Check notes - week 1
Describe the ionic basis of ventricular action potential (11)
iK1 (iKir) These are open at negative potentials and set the resting membrane potential close to EK
The depolarisation phase (0)/ rapid upstroke, is due to the opening of voltage gated fast Na+ channels
During the upstroke, the cells are most permeable to Na+,
iNa - membrane potential depolarises towards ENa (+70 mV)
As membrane potential becomes more positive, the background K+ channels shut
ito voltage gated K+ channels transiently open, cause phase 1
When membrane potential is more positive than –40 mV, voltage gated L-type Ca2+ channels begin to open
iCa(L) Ca2+ enters the cell down its concentration gradient
This long lasting inward Ca2+ current underlies the plateau phase (2)
Repolarisation (phase 3) is brought about by the decline in the permeability to Ca2+ and an increase in permeability to K+.
iKr, iKs K+ permeability increases as the voltage-gated delayed K+ channels open
As repolarisation proceeds, and membrane potential becomes more negative, the delayed K+ channels begin to shut
When the membrane potential is close to its resting level, the background K+ channels open again to keep the resting membrane potential stable. (iK1, ib)
What initiates the cardiac action potential (1)
Specialised autorhythmic or ‘pacemaker’ cells initiate an action potential
Where is the dominant pacemaker located and what is it called? (2)
Located in the right atrium
Called the sino-atrial node
Describe the ionic basis of the SA node action potential (4)
In SA node, background K+ channels are absent.
Therefore, these cells do not have a stable resting membrane potential.
Maximum diastolic potential of ~ –60 mV.
Slow depolarisation or pacemaker potential towards threshold of ~-40 mV (phase 4).
What is the pacemaker potential made up of (in terms of current) ? (5)
Made up of four over- lapping currents
Funny current (if)
T-type Ca2+ current
L-type Ca2+ current
Decay of delayed K+ channel permeability
Describe what drives phase 0 of SA node action potential (2)
At ~-40 mV, L-type Ca2+ channels open which depolarises the cells and underlies the upstroke of the SA node action potential (phase 0)
How is repolarisation induced in SA node action potential (2)
Repolarisation is induced by closure of L-type Ca2+ channels and opening of the delayed K+ channels (phase 3) (iKr, iKs )
Describe phase 4 of SA node action potential (2)
Final decay of delayed K+ current and entry of Na+ via If and background Na+ conductance generates the next pacemaker potential (phase 4).
What does pacemaker activity mean? (2)
Refers to the ‘intrinsic, spontaneous time dependent depolarisation of a cell membrane that leads to an action potential in an otherwise quiescent cell’
What are the three pacemaker tissues (3)
Sinoatrial node
Atrioventricular node
Purkinje fibres
What is the intrinsic frequency of SA node? (1)
100 beats/min
What is the intrinsic frequency of atrioventricular node? (1)
40 beats/min
What is the intrinsic frequency of Purkinje fibres ? (1)
20 beats/min
What functional pacemaker is the SA node? (1)
Primary
What functional pacemaker is the atrioventricular node? (1)
Secondary
What functional pacemaker is the Purkinje fibres? (1)
Tertiary
Describe the configuration of the action potential in various regions of the heart (5)
SA node
Atrial —> AV node
Short delay in AV node
AV node –> bundle of His –> bundle branches –> ventricles
From initiation of the AP in the SA node, it takes between 150 and 200 ms to innervate the rest of the heart.
Describe the refractory period (3)
Due to the long duration of the ventricular action potential, the absolute refractory period (ARP) is long
The ARP is almost as long as the contraction phase
This is functionally important for cardiac muscle as it means that cell can not depolarise and produce a new action potential
Draw the SA node action potential graph (4)
Check week 1 notes
Draw the ventricular action potential graph (4)
Check week 1 notes
Draw graph for the configuration of the action potential in various regions of the heart (4)
Check week 1 notes
What is dysrhythmia (1)
Disturbance of cardiac rhythm due to a change in the generation or conduction of electrical impulses
How s dysrhythmia classified? (5)
According to site of origin and type of rhythmic disturbance:
- Atria or ventricles
- Increased* or decreased rate of beating
- Regular or irregular beating rate
Give the definitions of the following:
Tachycardia
Fibrillation
Supraventricular
Ectopic beat (4)
Tachycardia – fast rate of beating
Fibrillation – irregular beating
Supraventricular – from atria or AV node (not SA node)
Ectopic beat – extra beat, not from normal SA node contro
What are the two types of Abnormal impulse generation? (2)
Automaticity (increased pacemaker activity)
Triggered activity (triggered abnormal impulses)
How do anti-dysrhythmic drugs work? (2)
Affect electrical impulse formation/propagation through effects on ion channels, receptors, ionic pumps
Which channels do these classes of anti-dysrhythmic drugs affect? (5)
Class I
Class II
Class III
Class IV
Other
Class I - Sodium channel blockers
Class II - b adrenoceptor antagonists
Class III - Potassium channel blockers
Class IV - Calcium channel blockers
Other – Cardiac glycosides (digitalis)
What are the parameters key to the generation of dysrhythmia (targets of drugs to treat dysrhythmia) (4)
How quickly the heart beats (If)
How well abnormal impulses are conducted (ICa, INa)
How quickly tissue becomes re-excitable (IK)
How easy it is to generate ectopic beats (If , ICa and [Ca2+]i)
