Lecture 3 - The Cardiovascular System Flashcards
What are the functions of the cardiovascular system?
Transport of O2 and CO2
Maintenance of homeostasis
Protection against infection
What are the components of the cardiovascular system?
Fluid medium - blood
System of channels - blood vessels
Pump - heart
What is the pulmonary circuit
Blood to and from the lungs
What is the systemic circuit
Blood to and from the rest of the body
What are arteries?
Away from the heart
What are the veins?
To the heart
Where is the heart located?
Thoracic cavity - near the anterior chest wall, directly posterior to sternum
Between the 2 lungs
What are the factors affecting size of the heart?
Size of person
Training status
Age
What is the general structure of the heart?
4 chambers functioning as a double pump
Two atria
Right atrium receives blood from systemic circuit
Left atrium receives blood from pulmonary circuit
Right ventricle receives blood from right atrium and pumps to pulmonary circuit
Left ventricle receives blood from left atrium and pumps to systemic circuit
Facts about the heart
Contract more than 100,000 times a day - 70 times per min
5L / min at rest
15- 20L / min during exercise
What does the heart wall consist of?
Pericardium
Pericardial fluid
Epicardium
Myocardium
Endocardium
What is the pericardium?
Fibrous tissue (collagen)
Stabilises the heart position
Physically limit on the size of the heart when taking in blood
Lubrication with the pericardial fluid
Consists of the outer fibrous layer, parietal layer (outer serous), visceral layer (inner serous/ epicardium)
What is the myocardium?
A thick muscular layer between epicardium and endocardium
Thickest in the left ventricle
Short and wide
Y shaped, branched
Large central nucleus and lots of mitochondria
Intercalated discs
Involuntary due to auto rhythmicity
What are intercalated discs?
Junction between cardiac
2 components
Gap junctions - Allows depolarisation to pass between cells, synchronising muscle contraction
Desmosomes - bind adjacent myocytes together
What is the endocardium?
Covers all inner surfaces of the heart - internal chambers and valves
Consists of epithelial tissue and continuous with the epithelium of the great vessels
What is the ventricular differences in the myocardium?
The wall of the LV is thick - cylindrical type shape
Delivers blood at pressure 80 -100 mmHg
The wall of the RV is thin - pouch like shape
Delivers blood at pressure less 15 mmHg
What are the main valves in the heart?
Tricuspid - Allows blood from atrium into right ventricle, shut when ventricles squeeze to prevent backflow
Bicuspid - Allows blood from the atrium into left ventricle
Semi lunar valves
Pulmonary valve - Allows blood flow from the right ventricle to pulmonary artery
Aortic valve - Allows blood flow from the left ventricle to the aorta
What are the chordae tendineae and papillary muscle?
Similar to tendons that attach to valves via the papillary muscle - tether valves to ventricular walls
Tight when the valves shut to prevent inversion
Outline the heartbeat and the cardiac muscle cells that cause this
A single contraction of the heart
Atria first then ventricles
Contractile - produce the contraction
Cardiac pacemaker cells - Sino atrial node , Atrio ventricular node and Purkinje fibres
Outline the cardiac cycle
- SAN node activated
- Stimulus spreads across the atria to the AV node
- There is a 100-msec delay at the AV node then atrial contraction occurs
- Impulse travels along the septum within the AV bundle to the Purkinje fibres and the by the moderator band to the papillary muscles of the right ventricle
- Impulse is distributed by the Purkinje fibres and relayed through the ventricular myocardium causing ventricular systole.
Outline the sections of an ECG
P wave - Atria depolarise
P-R interval - Conduction through AV node and AV bundle
Q wave - beginning of ventricular depolarisation (looks negative as stimulus moves away from electrode)
QRS complex - Completion of ventricular depolarisation
T wave - Ventricles repolarise
How is heart rate regulated?
Autonomic nervous system
Catecholamines
Changes in O2 / CO2 levels
Changes in blood pressure
How does the autonomic nervous system control heart rate?
Sympathetic nervous system - increases heart rate
Parasympathetic nervous system - decreases heart rate
Both innervate the SA node
Ps - rest
S - exercise
How does the catecholamine epinephrine control heart rate?
Epinephrine - (adrenalin) - released by the adrenal medulla when sympathetic nerves are stimulated during exercise, stress or anxiety
Increases heart rate and contractility (inotropy)
Binds to adrenergic receptors on the heart
How does the catecholamine Norepinephrine (Noradrenalin) control heart rate?
Initial increase of heart rate and contractility but with longer exposure heart rate and contractility decreases
Released by the adrenal medulla (20%) but mainly from spillover from sympathetic nerves innervating blood vessels
Binds to adrenergic receptors on the heart
How do chemoreceptors regulate heart rate?
Monitor blood CO2 and pH
Peripheral in the carotid bodies and aortic bodies
Central in the medulla
High CO2 - lower pH - increases heart rate
Low CO2 - higher pH - decreases heart rate
How do baroreceptors regulate heart rate?
Mechanoreceptors that sense changes in blood pressure on a beat to beat basis
Carotid sinus - senses increase and decrease
Aortic arch - increase only
Low BP = low stretch = less stretch of receptor = decreased afferent firing = increased efferent sympathetic firing and decreasing parasympathetic firing
Increased HR and contractility
Vasoconstriction
Increased BP
