Lecture 17: The Heart Flashcards
What are the protections of the heart from superficial to deep?
- Fibrous pericardium
- Parietal pericardium
- Pericardial cavity with serous fluid.
- Visceral pericardium (outer surface of heart wall).
What are the layers of the heart wall from superficial to deep?
- Epicardium
- Myocardium (cardiac muscle tissue)
- Endocardium (simple squamous epithelium, exposed to blood in chambers).
How many valves are present in the heart and their names?
A. Two atrioventricular valves (right and left)
B. 2 Semilunar valves
Right side - Pulmonary semilunar valve
Left side - Aortic semilunar valve
What is the function of chordae tendineae?
Strings of collagen fibers anchored by papillary muscle. Prevents the AV valve from flapping the wrong way during ventricular contraction.
When are valves in motion (open or closed)?
AV valves: Open during ventricular relaxation (diastole) and close during ventricular contraction (systole).
Semilunar valves: Closed during diastole and open during systole.
What are the three distinct periods in the cardiac cycle?
- Diastole:
Ventricles and atria relaxed; heart is filling with blood passively. - Atria Systole:
Atria contract; ventricles still relaxed; blood ejected from atria into ventricles. - Ventricular Systole:
Ventricles contract while atria relax. Blood is ejected from the heart.
What is ventricular systole?
Rising ventricular pressure results in closing of AV valves (first heart sound). Blood is pushed up against semilunar valves, forcing them open.
Note: Pressure in ventricles must exceed the backwards pressure (afterload).
As ventricles relax, semilunar valves close.
What is early diastole?
After the heart finished pumping blood, small volume remains in ventricles called end systolic volume. Backward flow of blood cause SL valves to close (dup sound).
What is the myocardial tissue made up of?
It is made up of contractile cardiac muscle cells and pacemaker cells (1%). Pacemaker cells initiate action potentials and spread them to cardiac muscle through gap junctions.
What are the five regions of the intrinsic conduction system?
- Sinoatrial node (SA) node
- Atrioventricular node (AV)
- Atrioventricular bundle (Bundle of His)
- Bundle Branches
- Perkinje fibers
What is the function of Sinoatrial node (SA)?
Found in the superior wall of the right atrium of the heart. Has the fastest rate of spontaneous depolarization. Sets the pace for each heart beat.
What is the function of the atrioventricular node (AV)?
If the SA node is dysfunctional, the AV node take place as the pacemaker. Receives signal from the SA node and delays it slightly. Gives atria time to fully empty blood before ventricular contraction.
What is the function of AV bundle and bundle branches?
Only electrical connection between the atria and the ventricles. Depolarizing front travels down AV bundle and splits into the bundle branches.
What is the function of the perkinje fibers?
Depolarizing front through gap junctions to the myocardial cells of the ventricles causing ventricular contraction. Starts from apex and spreads superiorly.
What happens in each cycle of heart contraction?
- Atrial depolarization, initiated by SA node, causes the P wave.
- The impulse is delayed at the AV node (atria contract at this time).
- Ventricular depolarization begins at apex causing the QRS complex. (Atrial repolarization occurs).
- Ventricular depolarization is complete . (Ventricles contract at this time).
- Ventricular repolarization occurs at apex, causing the T wave.
- Ventricular repolarization is complete.
Which are three heart homeostatic imbalances?
- Ectopic Focus
- Heart Block
- Fibrillation
What is ectopic focus?
The SA node is dysfunctional which leads to the P wave being canceled and AV node slowing heart rate to 40-60 beats per minute.
What is heart block?
AV node fails to conduct some SA node impulses. As a result, there are more P waves that QRS waves.
What is Fibrillation?
Electrical activity is disorganized. Action potentials occur randomly throughout the ventricles.
What is cardiac output?
The amount of blood pumped out of the left ventricle in one minute. Measured in ml of blood per minute.
1, Heart rate (HR): number of heart beats per minute.
2. Stroke volume (SV): Volume of blood pumped out of the ventricle each beat.
CO = HR X SV
What factors influence the stroke volume?
Preload: Amount of blood that is present in the ventricle before ejection. Venous return to the heart is increased by:
1. Greater volume of blood returning
2. Increased speed of blood returning.
Where is the cardiovascular center in the brain?
Located in the medulla oblongata in the brain stem. Includes several nuclei:
1. Cardio acceleratory center
2. Cardio inhibitory center
3. Vasomotor center
Which receptors are involved in the cardiovascular center?
Baroreceptors: Detect changes in blood pressure. (Aortic arch and carotid sinuses)
Chemoreceptors: Detect changes in blood composition.
Proprioceptors: Detect increased body movement.
Difference between cardio acceleratory and inhibitory center.
Acceleratory: Sympathetic cardiac nerves in the thoracic region. Norepinephrine is released.
Inhibitory: Parasympathetic fibers in the Vagus nerve (Acetylcholine).
