Anatomy&Physiology Flashcards
3 layers of the heart
Endocardium
Myocardium
Epicardium
Define:
Pulmonary circulation
Systemic circulation
P- Carries blood b/w the heart and the lungs
S - carries blood b/w the heart and the rest of the body
One way blood flow of the heart is ensured by…
The coordinated action of the four heart valves: atrioventricular (mitral and tricuspid) and semilunar (pulmonary and aortic) valves.
SA node
Commonly referred to as the pacemaker of the heart.
Has a innate Rhythm, spontaneously discharged an electrical signal every .8-.9secs, generated a heart rate of ~70 bpm.
Also subject to hormonal control with adrenalin increasing HR as well as force of contraction
AV node
Acts as an electrical connection b/w the atria and the ventricles.
Located at the base of the right atrium, transmits impulses from the atria to the ventricles but only after a short delay (~0.1secs) to ensure all the blood has been pumped from the atria b4 the ventricles contract.
P-wave
Represents atrial depolarisation
The PR interval
Represents conduction through the AV node and the bundle of his.
The QRS complex
Represents depolarisation on the ventricles.
The T-wave
Represents repolarisation of the ventricles.
Describe how the autonomic nervous system affect the heart
Parasympathetic - vagus nerve, reduces HR
Sympathetic - accelerator nerve, increases HR and can also increase the force with which the atria ventricles contract.
Describe AF
Most common arrhythmia. Normal control of heart rhythm by the SA node is disrupted leading to rapid and irregular electrical signals that cause atrial quiver. Reduces efficiency of blood being pumped into the ventricles.
Consequences of AF
Pooling of blood-> blood clots (thrombus) on the wall of the atria.
Dislodge - embolism
Stroke
Pulmonary embolism
Fluid retention - peripheral and pulmonary oedema.
Heart rhythm in AF
Rapid and irregular atrial activity - 350-600bpm, causing atrial quiver rather then contract.
AV node contracts irregular and rapid - 120-189bpm.
Reduced cardiac efficiency.
Pathogenesis of AF
Atrial fibrosis is the formation of excess fibrous connective tissue in the walls of the atria.
A.fibrosis and AF go hand in hand
Fibrosis can extend to the SA and AV nodes.
Fibrotic tissue does not conduct electrical signals
Caused of atrial fibrosis
Hypertension
Congestive heart failure
Valvular disease
What is the blood made up of.
Erythrocytes - RBCs 45%
Leukocytes - WBCs and platelets <1%
Plasma - 55%
Haemostasis
Circulatory systems ability to prevent blood loss from a damaged vessel.
Primary Harmostasis
Occurs in seconds
Stimulated by exposed collagen
Bought on by activation, aggregation and adhesion of platelets to form a platelet plug
Secondary haemostasis
When damage to the endothelium exposes tissue factor (layer beneath collagen).
Activation of coagulation cascade and the production of thrombin, which converts fibrinogen into fibrin to reinforce the platelet plug
What system breaks down fibrin
Fibrinolytic system
Goal of coagulation
To transform liquid blood into a solid thrombus
A thrombus consists of…
Fibrin strands
Blood cells
Four phases of coagulation?
Stimulus- exposed collagen and tissue factor
Initiation - platelet activation : platelet plug. Thrombin amplifies
Amplification phase - large scale production of thrombin; positive feedback
Thrombin formation - conversion of fibrinogen to fibrin to form a fibrin clot
Fibrin network together with activated platelets and RBCs forms an insoluble clot.
Role of thrombin in haemostasis
- Central player in thrombus formation
- Most potent stimulus for platelet activation
- amplifies coagulation through positive feedback
- responsible for converting fibrinogen to fibrin
