Lecture 10 Flashcards
What is the organ responsible for the circulation of blood?
The heart
Where is the heart found?
In a cavity in the thorax called the pericardium
Where is the heart attached to the pericardium?
Only where the big vessels enter and leave
What is the pericardium lined by?
A layer of simple squamous epithelium called the mesothelium (forms part of the pericardial membrane)
What is the outer covering of the heart called?
The epicardium and it’s covered by a mesothelium
What do ‘Lub’ and ‘Dub’ refer to?
The two heart sounds heard when using a stethoscope
What is ‘Lub’ caused by?
The closing of the bicuspid and tricuspid valves between the left and right atria and ventricles respectively, during ventricular systole
What is ‘Dub’ caused by?
The closing of semilunar valves in the pulmonary artery and the aorta, at the beginning of ventricular diastole
What can be detected by listening to the heart sounds?
Damaged valves and heart murmurs
Layers of heart?
Endocardium-myocardium-epicardium-pericardial cavity-pericardium
Endocardium?
In direct contact with the blood
Myocardium?
The muscles in the heart
Cardiac muscle?
- Striated
- Arranged into individual cells that are separated by areas of intercalated disks (membranes with gap junctions that allow a free diffusion of ions from cell to cell)
To allow proper timing of the heart beat, cardiac muscle…?
- Is myogenic
- Functions as a syncytium
- Has a long refractory period
Myogenic?
The heart can contract rhythmically and continuously without external stimulation
Syncytium?
The action potential spreading from cell to cell
Refractory period?
A period after stimulus during which no further contraction may take place (0.25 – 0.3 sec)
What is the heart rate regulated by?
The cardiac centre
Where is the cardiac centre?
In the medulla oblongata
What does the medulla oblongata respond to?
To pressure receptors in the walls of blood vessels
Is the rate of heart beats lower in larger animals?
Yes
Discuss the adult human rate of heart beat?
- Normally contracts at about 72 beats/min
- It may rise to 195 beats/min under stress
- Trained athletes tend to have lower resting heart rates (50/min)
Where do contractions begin?
The sino-atrial node
Why does the heart have a long refractory period?
Bc it allows it to be more coordinated