M3 Topic 2: The Heart Flashcards
(27 cards)
How big is the heart?
Approximately size of closed fist
- Weights around 250-300 grams in adults
Where is the heart located?
Located within thorax, between lungs and anterior to the vertebral column, posterior to the sternum
- Approx. 2/3 of heart’s mass on left side of midline of body
- Apex (pointed tip) of heart points downwards to the left
What are the 3 layers of the heart wall?
- Epicardium
- Myocardium
- Endocardium
Epicardium
External layer
- Also forms part of the pericardium
Myocardium
Middle layer
- Makes up majority of heart
- Primarily cardiac muscle
- Responsible for cardiac contraction and pumping action of heart
Endocardium
Innermost layer of heart
- Thin layer of squamous epithelium and connective tissue providing smooth layer lining inside of heart
What surrounds the heart?
Double-walled sac called the pericardium
Pericardium
Helps protect the heart by anchoring it to surrounding structures
- Pericardial fluid between the two layers of pericardium acts as lubricant to reduce friction as heart contracts and relaxes
How does the heart receive blood supply and nourishment?
Through the coronary circulation
- Blockages in coronary circulation deplete heart of oxygen & nutrients, causing tissue damage + potentially leading to myocardial infarction (heart attack)
Note: Although heart filled with blood inside chambers, this blood doesn’t supply heart muscle with nutrients due to thickness of myocardium
What is the wall that separates the right and left sides of the heart?
The septum
- Blood-flow in heart is one-directional
- As blood enters heart, it flows into atria before moving into ventricles, then leaving heart via arteries
- One-way flow maintained by two sets of valves
Atria structure
Small chambers with thin walls
- This is because they don’t need to generate much force to push blood to adjacent ventricle
Function of the right atrium
Receives blood from systemic circulation via the inferior and superior vena cava
- This blood passes through the tricuspid valve to the right ventricle
Function of the left atrium
Receives blood from pulmonary circulation via pulmonary veins
- This blood passes through bicuspid valve to left ventricle
Ventricle structure
Chamber with walls thicker than atria due to larger amount of force generated to pump blood
- Makes up most the mass and volume of heart
Right ventricle function
Pumps blood through pulmonary valve to pulmonary arteries
- Blood then passed through lungs, picking up oxygen, getting rid of carbon dioxide
Left ventricle function
Pumps blood through aortic valve into systemic circulation via aorta (largest artery in body)
- Vessels that branch of from aorta carry blood throughout rest of body
Blood cycle in order
- Right atrium receives deoxygenated blood from systemic circulation via the inferior and superior vena cava. This blood passes through the tricuspid valve to the right ventricle
- Right ventricle pumps blood through pulmonary valve into pulmonary arteries. Blood is then passed through lungs, picking up oxygen and getting rid of carbon dioxide
- Left atrium receives oxygenated blood from pulmonary circulation via the pulmonary veins. This blood passes through the bicuspid valve to the left ventricle
- Left ventricle pumps blood through aortic valve into systemic circulation via aorta (largest artery in body) Vessels that branch off from aorta, then carry blood throughout rest of body
Difference of wall thickness in left and right ventricles
Wall of left much thicker than wall of right
- Due to left ventricle needing to pump blood into systemic circulation, covering much greater distance than pulmonary circulation
- Thus, requires more force generated by left
Valves
Two sets of valves that ensure blood flow through heart is one-direction
- Open to let blood pass through
- Close to prevent backflow of blood
Opening and closing of valves caused by changes in pressure as chambers of heart contract and relax
Atrioventricular (AV) valves
Located between the atria and ventricles, blood flow from atria to ventricles
- Right AV has 3 cusps, thus called tricuspid valve
- Left AV has 2 cusps, thus called bicuspid valve
When does the AV valve open?
When heart relaxed…
- Cusps hang into ventricle, valve is open, allow blood flow from atria to ventricles
When does the AV valve close?
When ventricles contract…
- Increased pressure in ventricle pushes cusps upwards, closing valve, preventing backflow
Structure of cusps in AV valve
Connected to cords of connective tissue called chordae tendineae
- Cords connect valve to papillary muscles on inside of ventricular wall
- Chordae tendineae & papillary muscles act as supports to prevent AV valves from everting (opening back into atria) under high pressure
Semilunar (SL) valves
Located between ventricles and the great arteries, blood flow from ventricles to the great arteries
- Left SL valve called the aortic valve, located between left ventricle and aorta
- Right SL valve called the pulmonary valve, located between right ventricle and pulmonary artery
