Chapter 20: The Heart Flashcards
The heart
A hollow muscular pumping organ within the thoracic cavity.
It is a dual pump:
Pulmonary circuit - the right side which pumps blood to the lungs.
Systemic circuit - the left side which pumps blood to the rest of the body.
Arteries
Vessels which take blood away from the heart
Mostly carries O2 rich blood
Veins
Vessels which take blood towards the heart.
Most carries deoxygenated blood
Capillaries
Microscopic vessels which exchanges materials between the blood and tissues.
What is the heart enclosed by
Pericardium:
- Fibrous pericardium - dense CT
- Serous pericardium - parietal (lines the cavity wall) and visceral (lines the surface of the heart)
What is visceral pericardium also referred as?
Epicardium
What are the 3 layers of the hearts wall?
- Outer epicardium - simple squamous epithelium and CT
- Middle myocardium - consists of cardiac muscle arrange in bundles
- Inner endocardium - thin layer of simple squamous cells and thin layer of CT.
What are the 4 chambers of the heart?
2 atriums - the 2 uppermost blood collecting chambers. Has thin walls.
2 ventricles - the 2 lowermost blood pumping chambers. Has thick walls.
Why is the left ventricle wall 3x as thick as the right ventricle wall?
A thicker wall means a more powerful pump, and blood has to travel further to the rest of the body from the left ventricle.
The right ventricle just pumps blood a short distance to the lungs.
Heart valves
Consists of 2 or 3 fibrous flaps of tissue (cusps) covered with endocardium.
These valves keep the one-way flow of blood (prevent back flow)
Atrioventricular (AV) valves
Located between an atrium and ventricle.
2 of them:
1. Tricuspid valve - located between the right atrium and right ventricle (contains 3 flaps)
- Bicuspid valve - located between the left atrium and left ventricle (contains 2 flaps)
Chordae tendineae
Papillary muscles which connect the edges of the AV valves to the ventricle wall
Semilunar (SL) valves
- Pulmonary SL valve - located between the right ventricle and pulmonary trunk
- Aortic SL valve - located between the left ventricle and aorta
What is the pathway of pulmonary circulation?
Right atrium -> right ventricle -> pulmonary trunk -> pulmonary arteries -> lung capillaries (blood released CO2 and picke up O2) -> pulmonary veins -> left atrium
What is the pathway of systematic circulation of blood
Left atrium -> left ventricle -> aorta -> arteries in body -> body capillaries (blood releases O2 and picks up CO2) -> veins in body -> superior or inferior vena cava -> right atrium
Coronary circulation and pathway
Functions to supply blood to the myocardium
Pathway:
Aorta -> coronary arteries -> myocardium capillaries (blood releases O2 and picks up CO2) -> coronary veins -> coronary sinus -> right atrium
What causes a heart attack?
Prolonged blockage of a coronary vessel, causing the death of a myocardium region.
Structure of cardiac muscle cells
Arranged as myofiliments with actin and myosin. Their mitochondria are larger than normal to resist fatigue.
Contain:
- myoglobin which stores O2
- Intercalated discs which have desmosomes and gap junctions
Desmosomes
Physical connection
Will anchor cells, so they don’t separate one contracting.
Gap junctions
Electrical connection
Allow ions to pass freely from cell to cell so that cells can contract as a coordinated unit.
Autorhythmic fibres
Specialized cardiac muscle cells that are self excitable and initiate an electrical impulse.
This impulse spreads to the contractile fibres to make an action potential and contract.
What is the pacemaker of the heart?
The sinoatrial node
(SA node)
Summary of what happens to noncontractile cells in the SA node
1. Cells in the SA node randomly depolarize from -60mV to the threshold -40mV (this is pacemaker potential) due to Na+ inflow.
2. A second depolarization occurs due to Ca2+ inflow, an action potential can now occur.
3. Action potential spreads to contractile cells to contract the atria.
4. Noncontractile cells repolarize once Na+ and Ca2+ channels close and K+ channels open.
Atrioventricular node
Located between the atria
Function to delay the spread of action potentials by 0.1 seconds to allow atria to finish contraction so the ventricles have time to fill with blood.
Purkinje fibres
Extend into the ventricular walls and spread an action potential throughout the ventricular myocardium so that the ventricles can contract
What is an artificial pacemaker?
A device surgically implanted to send small electrical currents to stimulate the heart and contract.
Used by those who have a damaged SA node
What is the electrical pathway through the heart?
- Sinoatrial node
- Atrioventricular node
- Bundle of His
- Left/right branches
- Purkinje fibres
Summary of what happens to contractile cells
1. Action potential from noncontractile cells open Na+ channels to depolarize membrane, then Ca2+ channels after to prolong it. (plateau phase)
2. an action potential is generated to cause muscle contraction, and it has a long refractory period.
3. Repolarization by opening K+ channels
What do the P wave, QRS complex, and T wave represent?
P wave - depolarization of the atria
QRS complex - depolarization of the ventricles
T wave - repolarization of the ventricles
Lubb
A heart sound created by the closure of the atrial ventricular valves at the start of ventricular contraction.
Dupp
A heart sound created by closure of the semi lunar valves during ventricular relaxation
