The Heart Flashcards
Function of cardiovascular system
To distribute oxygen and nutrients to the cells of the body, and to take away carbon dioxide and other wastes
Pulmonary circuit
Carries blood to and from the gas exchange surfaces of the lungs
Systemic circuit
Transports blood to and from the rest of the body
Flow of the pulmonary circuit
Carries oxygen-poor blood from the right ventricle, through the pulmonary arteries, to the lungs
Carries oxygen-rich blood back through the pulmonary veins to the left atrium
Flow of the systemic circuit
Carries oxygen-rich blood from the left ventricle, through the systemic arteries
Carries oxygen-poor blood through systemic veins back to the right atrium
Arteries
Carry blood away from the heart
Veins
Return blood to the heart
Great vessels
Largest veins and arteries in the body
Capillaries
Interconnect smallest arteries and smallest veins
Why do capillaries have thin walls?
To allow gas exchange and exchange of wastes between blood and surrounding tissues
Right atrium
Receives blood from systemic circuit and passes it to the right ventricle
Right ventricle
Receives blood from right atrium and passes it to pulmonary circuit
Left atrium
Receives blood from pulmonary circuit and passes it into the left ventricle
Left ventricle
Receives blood from left atrium and passes it into systemic circuit
Which chambers contract first?
Atria
Where is the heart located?
In the thoracic cavity near the anterior chest wall, directly posterior to the sternum
Where are the great vessels connected to?
The superior end of the heart at its base
In a midsagittal section, where does the base lie?
Slightly to the left of the midline
Does the heart sit in the anterior or posterior portion of the mediastinum?
Anterior
What does the mediastinum contain?
Great vessels, thymus, oesophagus, and trachea
Apex
Pointed tip of the heart
Endocardium
- Covers inner surface of heart (inc. heart valves)
- Simple squamous epithelium continuous with endothelial lining of blood vessels
- Underlying areolar tissue
Myocardium
- Middle layer
- Spiral bundles of cardiac muscle cells
Pericardium
Fibrous pericardium (dense network of collagen fibres that stabilise the position of the heart and vessels within the mediastinum) and serous pericardium
Serous pericardium
- Parietal layer
- Visceral layer (epicardium) - covers surface of heart
What separates the parietal and visceral layer of the serous pericardium?
Potential, fluid-filled pericardial cavity
Functions of the cardiac skeleton
- Anchors muscle fibres
- Supports the great vessels and heart valves
- Limits the spread of action potentials
How much pericardial fluid does the pericardial cavity normally contain?
15-50mL
What secretes pericardial fluid?
Pericardial membranes
Function of pericardial fluid
Acts as lubricant, reducing fiction between the opposing visceral and parietal surface as the heart beats
Pericarditis
Condition produced by pathogens that causes inflamed pericardial surfaces to rub against one another
Cardiac tamponade
Fluid collection in the pericardial cavity caused by increased production of pericardial fluid as a result of inflammation or traumatic injuries e.g. stab wounds
Auricle
The atriums ability to deflate and become a lumpy, wrinkled flap when not filled with blood
Coronary sulcus
A deep groove that marks the border between the atria and the ventricles
Inteventricular sulcus
- Shallow depressions that mark the boundary between the left and right ventricles
- Posterior and anterior
Name a characteristic of the coronary and inteventricular sulci
Substantial amounts of fat and arteries and veins that carry blood to and from the cardiac muscle
Visceral layer of serous pericardium (epicardium)
Consists of an:
- Exposed mesothelium
- Underlying layer of areolar connective tissue
Parietal layer of serous pericardium
Consists of an:
- Outer dense, fibrous layer
- Areolar layer
- Inner mesothelium
What are the arteries and ventricles made of?
Myocardium
Atrial myocardium
Contains muscle bundles that wrap around the atria and form figure eights that encircle the great vessels
What wraps around the ventricles?
Superficial ventricular muscles and deeper muscle layers spiral around and between the ventricles toward the apex in a figure eight pattern
What is each cardiac muscle cell wrapped in?
A strong but elastic sheath
What connects adjacent cardiac muscle cells?
Fibrous cross-links called struts
What separates the superficial and deep muscle layers?
Interwoven sheets of struts
Functions of the connective tissue fibres
- Provide physical support for the cardiac muscle fibres, blood vessels, and nerves of the myocardium
- Help distribute forces of contraction
- Add strength and prevent overexpansion of the heart
- Provide elasticity that helps return heart to its original size and shape after a contraction
Cardiac skeleton
Four dense bands of tough elastic tissue that encircle the heart valves and bases of the pulmonary trunk and aorta
Interatrial septum
Separates atria
Interventricular septum
Separates ventricles
Is the interatrial or interventricular septum thicker?
Interventricular septum
Atrioventricular (AV) valves
- Tricuspid and mitral
- Folds of fibrous tissue that extend into the openings between the atria and ventricles
- Permit blood flow only in one direction: atria to ventricles
Semilunar valves
- Pulmonary and aortic
- Between ventricles and their great vessels
- Ensures blood flow through the vessels
Superior vena cava
- Opens into the posterior and superior portions of the right atrium
- Delivers blood to right atrium from head, neck, upper limbs and chest
Inferior vena cava
- Opens into the posterior and inferior portion of the right atrium
- Carries blood to the right atrium from the rest of the trunk, the viscera, and the lower limbs
Are there valves between the venae cavae and the right atrium?
No
Foramen ovale
- From 5th week of embryonic development to birth
- Penetrates the interatrial septum and connects the two atria of the fetal heart
- Permits blood flow from right atrium to left atrium while lungs are developing
Fossa ovalis
A small, shallow depression that remains after the foramen ovale closes up
What is the surface of the posterior walls of the right atrium and the interatrial septum like?
Smooth
What is on the the surface of the anterior atrial wall and the inner surface of the auricle?
Prominent muscular ridges called pectinate muscles
Tricuspid valve
Contain three fibrous flaps called cusps
Chordae tendineae
Connective tissue fibres that attach to the free edge of each cusp in the tricuspid valve
Papillary muscles
- Conical muscular projections that arise from the inner surface of the right ventricle
- Chordae tednineae originate at the papillary muscles
What is on the surface of the ventricles?
Muscular ridges called trabeculae carnae
Moderator band
Muscular ridge that extends horizontally from the inferior portion of the interventricular septum and connects to the anterior papillary muscle
Conus arteriosus
Cone-shaped pouch that ends at the pulmonary valve
Pulmonary valve
Contains three semilunar cups of thick connective tissue
Pulmonary trunk
Receives blood from right ventricle and passes it on to left pulmonary arteries and the right pulmonary arteries
What forms the four pulmonary veins?
Small veins that unite
Where does the posterior wall of the left atrium receive blood from?
Two left and two right pulmonary veins
Is there a valve between the pulmonary veins and the left atrium?
No, but there’s an auricle
What guards the entrance to the left ventricle?
Mitral valve
How many cusps does the mitral valve have?
Two
Where does the mitral valve permit blood flow to?
From the left atrium into the left ventricle
What does the right ventricle have that the left ventricle doesn’t?
Moderator band
Aortic valve
Receives blood from the left ventricle and passes it to the ascending aorta
Aortic sinuses
Saclike expansions of the base of the ascending aorta that prevent individual cusps of the aortic valve from sticking to the wall of the aorta
Ascending aorta
Receives blood from the aortic valve and passes it to the aortic arch
Aortic arch
Receives blood from the ascending aorta and passes it to the descending aorta
Ligamentum arteriosum
A fibrous band that attaches the pulmonary trunk to the aortic arch
Which ventricle is larger?
The left ventricle
Why is the left ventricle larger?
It has thicker walls that allow it to push blood through the systemic circuit
Descending aorta
Receives blood from aortic arch
Function of the atria
To collect blood that is returning to the heart and convey it to the ventricles
What happens when the left ventricle contracts?
It shortens and narrows and bulges into the right ventricular cavity
Interaction between AV valves, chordae tendinae and papillary muscles
Ventricles = relaxed: chordae tendineae are loose, AV valves offer no resistance as blood flows from A to V
Ventricles = contracted: blood moving back towards atria swings the cusps together, papillary muscles tense chordae tendineae which stops cusps swinging into the atria
Regurgitation
Backflow of blood into the atria caused by cut chordae tendineae or damaged papillary muscles
3 types of valve faults
- Stenotic valve (doesn’t open)
- Regurgitant valve (doesn’t close)
- Prolapsed valve (flops backwards)
Heart murmurs
Fault valves heard through stethoscope
Why do semilunar valves not need muscular braces?
Because the arterial walls do not contract and so the cusps are stable
What prevents the individual cusps of the aortic valve from sticking to the walls of the aorta?
Aortic sinuses
Valvular heart disease (VHD)
When valve function deteriorates to the point at which the heart cannot maintain adequate circulatory flow
Carditis
Inflammation of the heart
Rheumatic fever
Inflammatory autoimmune response to an infection by streptococcal bacteria, occurring most often in children and causing carditis
Coronary circulation
Supplies blood to muscle tissue of the heart
Where do the left and right coronary arteries originate?
At the base of the ascending aorta, at the aortic sinuses
Elastic rebound
Recoil of the aortic walls when the left ventricle relaxes, blood no longer flows into the aorta and pressure declines
Marginal arteries
Arteries that arise from right coronary artery and that extend across the surface of the right ventricle
Posterior interventricular artery
Supplies blood to the interventricular septum and adjacent portions of the ventricles
Right coronary artery
Supplies blood to:
- Right atrium
- Portions of ventricles
- Portions of electrical conducting system of heart
Left coronary artery
Supplies blood to:
- Left atrium
- Left ventricle
- Interventricular septum
Circumflex artery
Arises from left coronary artery and curves to the left around the coronary sulcus
Anterior interventricular artery
Arises from left coronary artery and swings around the pulmonary trunk, and rungs along the surface within the anterior interventricular sulcus
Arterial anastomes
Interconnections between arteries
Coronary artery disease (CAD)
Areas of partial or complete blockage of coronary circulation
Coronary ischemia
Reduced circulatory supply usually as a result from CAD
Cause of CAD
Formation of fatty deposit (atherosclerotic plaque) in the wall of a coronary vessel which narrows the passageway and reduces blood flow
Angina pectoris
First symptom of CAD - chest pain spasm
Myocardial infarction
Heart attack, when part of the coronary circulation becomes blocked, and cardiac muscle cells die from lack of oxygen
Infarct
Nonfunctional area created from death of affected tissues during myocardial infarction
Coronary thrombosis
When a vessel already narrowed by plaque formation becomes blocked by a sudden spasm in the smooth muscles of the vascular wall
Enzymes released during heart attack
Cardiac toponin T, cardiac troponin I, and CK-MB (form of creatine phosphate)
Great cardiac vein
Drains blood from region supplied by anterior interventricular artery
Where do cardiac veins return blood to?
Coronary sinus which opens into the right atrium
Posterior vein of left ventricle
Drains area served by circumflex artery
Middle cardiac vein
Drains area supplied by posterior interventricular artery
Small cardiac vein
Receives blood from posterior surfaces of right atrium and ventricle
Anterior cardiac veins
Drain the anterior surface of the right ventricle and empty directly into the right atrium
Audtorhythmicity
The hearts property of contracting on its own
Conducting system
The cells that initiate and distribute stimulus to contract
Two types of specialised cardiac muscle cells of conducting system
- Pacemaker cells - essential to heart rate
2. Conducting cells - interconnect SA and AV nodes and distribute contractile stimulus throughout myocardium
Where are pacemaker cells found?
Sinoatrial (SA) node in atrium and atrioventricular (AV) node
Where are conducting cells found?
Internodal pathways in atrial walls
Atrioventricular (AV) bundle
Bundle branches - run between ventricles
Purkinje fibres
Special characteristic of pacemaker cells of SA and AV nodes
No stable membrane resting potential (instead, pacemaker potential)
What causes pacemaker potential?
Slow inflow of Na+ without a compensating outflow of K+
Where is spontaneous depolarisation fastest?
In cells in the SA node
Pacemaker potential
Gradual depolarisation of pacemaker cells
Sinus rhythm
Heart rhythm
What establishes the sinus rhythm
The SA nodes reaching threshold first
Why is the maximum normal heart rate 230 bpm?
Because even if the SA node generates impulses at a faster rate, the ventricles will still only contract at 230 bpm
Impulse conduction - 0
SA node activity and trial activation begin
Impulse conduction - 50msec
Stimulus spreads across the atrial surfaces and reaches AV node
P wave
Impulse conduction - 150msec
Three is a 100msec delay at the AV node. Atrial contraction begins
P-R interval
Impulse conduction - 175msec
The impulse travels along the interventricular septum within the AV bundle and the bundle branches to the Purkinje fibres, and, by the moderator band, to the papillary muscles of the right ventricle
Q wave
Impulse conduction - 225msec
The impulse is distributed by Purkinje fibres and relayed throughout ventricular myocardium. Atrial contraction is completed and ventricular contraction begins
QRS complex
Why does the pacemaker cell stimulus affect only the atria?
Because the cardiac skeleton isolates the atrial myocardium from the ventricular myocardium
Why does the pacemaker impulse slow as it leaves internodal pathway and enters the AV node?
Because the nodal cells are smaller in diameter than the conducting cells and the interconnections between pacemaker cells are less efficient than those between conducting cells
What would happen if the atria and ventricles contracted at the same time?
The contraction of the powerful ventricles would close the AV valves and prevent blood flow from the atria to ventricles
Where is the only normal electrical connection between the atria and the ventricles?
The connection between the AV node and the AV bundle
Which bundle branch is bigger?
The left bundle branch, as it supplies the massive left ventricle
Bradychardia
Heart rate is slower than normal
Tachycardia
Heart rate is father than normal
Ectopic pacemaker
Their activity partially or completely bypasses the conducting system, disrupting the timing of the ventricular contraction
Electrocardiogram
Monitors the electrical events of the conducting system
Which components are important for in making a diagnosis with ECG?
P wave and QRS complex
Q-T inerval
The time required for the ventricles to undergo a single cycle of depolarisation and repolarisation (measured from the end of the P-R interval)
Arrhythmia
Irregularity in the normal rhythm or force of the heartbeat
Cardiac contractile cells
Form the bulk of the atrial and ventricular walls
Where do the Purkinje fibres pass the stimulus on to?
Cardiac contractile cells
What connects cardiac contractile cells to each other?
Intercalated discs
Key differences between cardiac contractile cells and skeletal muscle fibres
- Cardiac - smaller
- Cardiac - 1 nucleus
- Cardiac - branching interconnections between cells
- Cardiac - intercalated discs
How are the interlocking membranes of adjacent cells held together at intercalated discs?
By desmosomes and linked by gap junctions
Action potentital in cardiac contractile cells
- Rapid depolarisation: causes NA+ entry, ends with closure of voltage-gated fast sodium channels
- The Plateau: causes Ca2+ entry, ends with closure of slow calcium channels
- Repolaraisation: causes K+ loss, ends with closure of slow potassium channels
Refractory period
Period of time after an action potential when a cardiac contractile cell won’t respond to a second stimulus
Absolute refractory period
- The membrane cannot respons at all because the sodium ion channels are either already open or closed and inactivated
- Includes plateau and initial period of repolarisation
Relative refractory period
Voltage gated sodium ion channels are closed but can open so the membrane will respond to a stronger than normal stimulus
Cardiac cycle
Period between the start of one heart beat and the beginning of the next
Systole
The chamber contracts and pushes blood into an adjacent chamber of into an arterial trunk
Diastole
The chamber fills with blood and prepares for the next cardiac cycle
Phases of the cardiac cycle
- Atrial systole
- Atrial diastole
- Ventricular systole
- Ventricular diastole
Atrial systole
- Atrial contraction begins - already 70% filled
2. Atria ejects blood into the ventricles through open right and left AV valves - remaining 30%
Why can’t blood flow into the atria from the veins during atrial systole?
Because atrial pressure exceeds venous pressure
Ventricular systole
- AV valves close
- Ventricles contracting but no blood flow occurs as the pressure isn’t high enough to force open semilunar valves
- Ventricular ejection: semilunar valves are pushed open and blood flows into pulmonary or aortic trunk
- Semilunar valve closes and blood flows into relaxed atria
- AV valves open and passive ventricular filling occurs
Isovolumetric contraction
All the heart valves are closed, the volumes of the ventricles do not change and the ventricular pressure is rising
Heart failure
When damage to one or both ventricles can leave the heart unable to pump enough blood through peripheral tissues and organs
Cardiac output (CO)
Amount of blood pumped by the left ventricle in 1 minute
Heart rate (HR)
Number of heart beats per minute
Stroke volume (SV)
Amount of blood pumped our of a ventricle during each contraction
EDV - ESV
CO calculation
HR X SV
Cardioacceleratory center
In the medulla oblongata activates sympathetic neurons which speeds up heart rate and reduces ESV
Cardioinhibitory centre
Controls parasympathetic neurons that slow the heart rate and increases ESV
Bainbridge reflex
Accelerates heart rate when the walls of the right atrium are stretched
Venous return
Amount of blood retuning to heart through veins
Filling time
Duration of ventricular diastole
Preload
Degree of stretching in ventricular muscle cells during ventricular diastole
Afterload
Amount of tensions that the contracting ventricle must produce to force open the semilunar valve and eject blood
Frank-Straling principle
The greater the EDV, the more powerful the succeeding contraction
Cardiac reserve
Difference between resting and maximal cardiac outputs