Lecture 8: Heart (continued) Flashcards
Describe the orientation of the Heart in the body - where can I find it
2/3 of heart mass lies to the left of the midline with 1/3 lying to the right of the midline. The apex of the heart - formed by the tip of the left ventricle and rests of the diaphragm, pointing anteriorly, inferiorly and to the left. The base of the heart is opposite the apex and is formed by the atria.
Describe the borders of the heart : right, inferior, left, superior
Right border: formed by right atrium which has vertical orientation.
Inferior border: formed by right ventricle
Left border: left ventricle
Superior border: blood vessels= base
What are four kind of layers considered part of the Pericardium from inside to outside
Visceral pericardium/Epicardium, Periocardial space filled with pericardial fluid, Parietal Pericardium. Fibrous Pericardium.
What is the structure and function of the Serous Pericardium
Delicate membranous sack made of squamous mesothelial cells that secrete serous fluid inside the pericardial cavity to help reduce friction between the parietal and visceral layers as the heart moves
What is the structure and function of the Fibrous Pericardium
It is a layer of of touch, inelastic dense irregular connective tissue that partially fused to the central tendon of the diaphragm. Therefore it helps to prevent overstretching of the heart, provides protection and anchors the heart in the mediastinum.
Describe the structure of Fibrous skeleton of the Heart
Fibrous skeleton is made of dense connective tissue that forms a tricuspid ring around the valves of the heart. There is a complete ring around the Mitral valve (pulmonary to LV) and Aortic valve (LV to systemic) while the Tricuspid (systemic to RV) ring is incomplete and Pulmonary valve (RV to pulmonary) has none. Instead they have Fatty connective tissue in areas where the fibrous skeleton is incomplete.
Describe the mechanical and electrical purpose of Fibrous skeleton of the Heart
They form a structural foundation for the heart valves, preventing overstretching of the valves as blood passes through them. They also serve as a point of insertion for bundles of cardiac muscle fibres and acts as an electrical insulator between the atria and ventricles.
List the 3 stages of conduction system of the heart
- SA node to the atrial muscle
- Atrioventriucular node
- Atrioventricular bundle to Purkinje fibres
Describe the speed and result of 1st stage of conduction from the heart
Cardiac excitation occurs at the SA located in the right atrial wall. These are autorhythmic cells that spontaneously depolarise to threshold- acting as a pacemaker. The action potentials triggered from this propogate through both atria through gap junctions in intercalated discs of muscle fibres.
Result : This makes the atria uniform contract at the same time.
Speed: slow
Describe the speed and result of 2nd stage of conduction from the heart
The action potential reaches the AV node located in the interatrial septum and here it slows down because of differences in AV node cell structures. Fibrous skeleton insulates the Action potential elsewhere
Result: 100 m/s delay allowing time for Atria to fill up to the ventricle
Speed: very slow 10x slower than 1st
Describe the speed and result of 3rd stage of conduction from the heart
The action potential goes to the AV bundle located in the interventricular septum, entering the left and right bundles and then to large diameter Purkinje fibres which conduct the action potential from the apex to remaining ventricular myocardium.
Result: Complete and even contraction of ventricles, pushing blood upwards into the arteries (systole)
Speed: Fast 10x 1st
Name the 5 phases of the cardiac cycle in order starting from ventricular filling
Ventricular filling, Atrial contraction, Isovolumetric ventricular contraction, Ventricular ejection, Isovolumetric ventricular relaxation.
Describe the ventricular filling phase of the cardiac cycle:
- Is is there a systole involved- if so wheres the AP
- What is the relative pressure of the artery and atrium attached to the & ventricle, and therefore which valve is open: inlet or outlet
- What is happening to the volume of blood in the ventricle
- What is the relative time (if applicable
Ventricular has no systole involved. The ventricle is relaxed, arterial pressure is still very high but outlet valve is closed. Atrium pressure is relatively low and Ventricular pressure is just below the atrium pressure so this causes the inlet valve to open and blood volume to increase to 80% of capacity passively.
Describe the Atrial contraction phase of the cardiac cycle:
- Is is there a systole involved- if so wheres the AP
- What is the relative pressure of the artery and atrium attached to the & ventricle, and therefore which valve is open: inlet or outlet
- What is happening to the volume of blood in the ventricle
- What is the relative time (if applicable
SA node depolarises causing Atrial systole. AP goes to the AV node where it is delayed for 100m/s. The pressure in the arteries as slightly decreased and the outlet valve is still closed. The pressure in the atrium has only slightly increased because it has only thin muscular layer and there are no valves to prevent backflow into the veins. This is still sufficient to top up the remaining 20% of blood volume in the ventricle
Describe the Isovolumetric Ventricular contraction phase of the cardiac cycle:
- Is is there a systole involved- if so wheres the AP
- What is the relative pressure of the artery and atrium attached to the & ventricle, and therefore which valve is open: inlet or outlet
- What is happening to the volume of blood in the ventricle
- What is the relative time (if applicable
AP goes from AV bundle to Purkinje fibres causing Ventricular systole to start. The ventricular pressure rises rapidly for 0.05 s. As the pressure rises past the atrial pressure but not above the arterial pressure, both of the inlet and outlet valves are closed and the volume doesn’t change.
