Heart Flashcards
(40 cards)
What is the pericardium?
The pericardium is the membrane that surrounds and protects the heart. It has two parts - the fibrous pericardium and the serous pericardium.
The fibrous pericardium protects the heart and anchors it to the mediastinum. What is the fibrous pericardium made of?
The fibrous pericardium is the superficial layer of the pericardium and is composed of rough inelastic dense irregular connective tissue. Fused with connective tissue of the blood vessels that enter and leave the heart.
The serous pericardium is a thinner more delicate membrane which forms a double layer around the heart. What are these layers called?
The outer parietal layer of the serous pericardium is fused to the fibrous pericardium.
The inner visceral layer of the serous pericardium is also called the epicardium. Pericardial fluid between two layers reduces friction as the heart moves.
What are the four chambers of the heart?
The right atrium, the right ventricle, the left atrium, the left ventricle.
Is the left atrium the same thickness as the right atrium?
Yes the left and right atrium are the same thickness and they form the base of the heart.
What is the thickest chamber of the heart?
The left ventricle is the thickest chamber of the heart as it forms the apex of the heart. The left ventricle pumps blood from the heart into the aorta and out arteries into circulation.
What veins does the right atrium receive blood from?
The right atrium receives blood from the superior vena cava, inferior vena cava and coronary sinus.
What is the tricuspid valve?
Blood passes from the right atrium, through the tricuspid valve, into the right ventricle. The tricuspid valve is also called the right atrioventricular valve.
Where does blood go after it leaves the right ventricle?
Deoxygenated blood leaves the right ventricle through the pulmonary valve to the pulmonary trunk and arteries, and enters the lungs (where it is oxygenated).
What happens in the pulmonary capillaries?
Blood loses carbon dioxide and gains oxygen through the pulmonary capillaries and lungs. The blood then returns to the heart, entering the left atrium through the pulmonary veins.
What is the valve called between the left atrium and the left ventricle?
Oxygenated blood passes from the left atrium, through the bicuspid valve, to the left ventricle (going on to exit the heart through the aorta). The bicuspid valve is also called the left atrioventricular valve.
What is the histology of cardiac muscle?
- Centrally located nucleus
- Intercalated discs connect adjacent muscle fibers and contain
- Desmosomes
- Gap junctions
- Large & numerous mitochondria
What is the conduction system?
- The conduction system is formed by network of autorhythmic fibers
(rare & specialised cardiac muscle cells,
self-excitable, generate action potentials that trigger heart contraction. - Autorhythmic fibres act as pacemaker
(setting rhythm of electrical excitation that causes contractions). - Autorhythmic fibres form the conduction system and provide excitation pathways throughout the heart to ensure coordinated contractions of cardiac chambers.
- Cardiac excitation begins in the sinoatrial (SA) node
- Action potential initiated by the SA node (autorhythmic fibers) spreads out and excites “working” atrial and ventricular muscle fibers called contractile fibers.
What is the conduction system sequence?
- Impulses generated at SA node (sinoatrial) – heart’s internal pacemaker -> Atrial Contraction
- Distributed along atria to the AV node (atrioventricular) via internodal pathways
- Enters the AV bundle (bundle of HIS) (centre of heart – between L & R side). This is the only site where action potentials can conduct from the atria to the ventricles
- Action potential propagates along the AV bundle and enters both the left and right bundle branches. -> extend through the interventricular septum towards the apex.
- Finally, large diameter Purkinje fibers rapidly conduct the action potential from the apex upward to the remainder of the ventricular myocardium.
- > Ventricles contract
Action potential (AP) or impulse has two main phases. What are they?
- Depolarising phase – MP becomes less negative
- Repolarising phase – MP restored back to resting state
Where is the heart located?
The heart is located in the mediastinum.
What is the heart shaped like?
The heart is shaped like a cone lying on its side.
Apex is the pointed inferior part
Base is the broad superior part
What does the heart wall consist of?
Wall consists of three layers
- Epicardium: Also called visceral layer of the serous membrane, composed of mesothelium & connective tissue
- Myocardium: Cardiac muscle tissue, makes up 95% of heart
- Endocardium: Thin layer continuous with endothelial lining of large vessels attached to heart.
The pericardium surround the epicardium, myocardium and endocardium (in that order superficial to deep).
There are four hearts valves:
Atrioventricular valves – tricuspid & bicuspid
Semilunar valves – aortic & pulmonary
What are features of heart valves?
Heart valves open & close in response to pressure changes as heart contracts & relaxes.
Heart valves ensure the one way flow of blood - open to let blood flow through & close to prevent backflow.
When ventricles are relaxed, the atrioventricular valves are open.
How do the semilunar vales (aortic and pulmonary) work?
Aortic & pulmonary:
Allow ejection of blood from heart to arteries but prevent backflow
When ventricles contract the semilunar valves open
When ventricles relax the semilunar valves close
What is systemic circulation?
Circulation of blood throughout body except for air sacs in the lung
- Left side of heart is its pump
- LV ejects oxygenated blood into aorta > systemic arteries> arterioles> capillaries (oxygen drawn into tissues) > venules> veins which carry blood back to RA
What is pulmonary circulation?
Circulation of blood through lungs
- Right side of heart is its pump
- RV ejects blood into pulmonary trunk> pulmonary arteries > pulmonary capillaries> pulmonary veins which carry oxygenated blood back to LA
What are phases of an action potential?
- Depolarisation
Voltage gated fast. Na+ channels open in response to action potential of neighbouring cell > inflow of Na+ down electrochemical gradient - Plateau
Period of maintained depolarisation due to voltage gated slow. Ca2+ channels > increased Ca2+ concentration in the cytosol > contraction. - Repolarization
Recovery of the resting membrane potential of -90mV. After a delay additional voltage gated K+ channels open > restoring negative resting membrane potential
What is an Electrocardiogram (ECG)?
As action potentials propogate throughout the heart, they generate electrical currents that can be detected at the surface of the body.
An ECG is a recording of these signals
