2. The heart Flashcards
How heavy is the heart?
250 - 350 grams
Where is the heart located?
2/3 offset left of the midline of the sternum
Where is the heart within?
The mediastinum
What encloses the heart?
The pericardium
What is a function of the pericardium?
Attaches heart to surrounding tissues
What is the pericardium?
A tough double layered membranous sac
What are the two layers of the pericardium and where are they present?
- Visceral layer (attached to heart surface)
2. Parietal layer (outer pericardial layer)
What is the function of the lubricating fluid between pericardial layers?
Reduces friction during movement of heart with contraction
Left circuit
Systemic circuit
Right circuit
Pulmonary circuit
Why are there no valves between the atria and veins?
As back flow isn’t a significant problem here
Describe the fibrous skeleton of the valves
Four interconnecting rings of dense connective tissue of the heart surround and support the four heart valves
What happens when pressure is greater behind the valve?
It opens
What happens when there is greater pressure in front of the valve?
It closes
Where does the heart receive most of its blood supply?
Through the coronary circulation during diastole
Why is coronary blood flow adjusted?
In response to changes in the heart’s O2 requirements.
What are cardiac muscles connected by?
Intercalated discs.
Cardiac muscle automaticity:
The heart contracts rhythmically as a result of action potentials that it generates by itself
What makes up 99% of cardiac cells?
Contractile cells
What is the function of autorhythmic cells?
Initiate and conduct the action potentials responsible for contraction of working cells
What are the specialised pacemaker areas?
‒ Sinoatrial node (SA node)
‒ Atrioventricular node (AV node)
‒ Bundle of His
‒ Purkinje fibres
What is the rate of cardiac muscle controlled by and what does it control?
ANS:
‒ Sympathetic & parasympathetic
‒ Control of rate & contractile strength
Central output to: (nervous system)
- Parasympathetic NS (vagus nerve)
- Sympathetic NS via rostral ventrolateral medulla
- Sympathetic chain
x 7 properties of an effective heart
- Regular contractions at appropriate rate for metabolism
- Guaranteed time for ventricular filling after atrial & ventricular contractions
- Contraction duration long enough for physical movement of fluid
- Contractile strength sufficient to generate appropriate pressures
- Ventricular pressure directed towards exit valves
- Coordination of left & right, and atrial & ventricular contractions
- Matched volumes of emptying & filling
