Senario Two - The Heart Flashcards
where is the apex of the heart
anterior point - formed by the left ventricle
where is the base of the heart
posteriorly - formed by the atria
what are the valves of the heart?
semi-lunar valves: aortic and pulmonary a/v valves: bicuspid (L) and tricuspid (R)
what is the difference in the structure of the ventricles?
left side - wall is much thicker & lumen is smaller
what is the pericardium?
membrane surrounding and protecting the heart keeps it in position within the mediastinum two parts - fibrous pericardium and serous pericardium
what is the structure of the fibrous pericardium?
Outermost layer (most superficial) Tough, dense, inelastic, irregular CT
what is the function of the fibrous pericardium?
attaches to the diaphragm and the vessels entering and leaving the heart prevents over stretching of the heart and anchors it within the mediastinum
why is the fibrous pericardium fused with the diaphragm?
fused at the central tendon, means in deep breathing it facilitates movement of blood by the heart
what is the structure of the serous pericardium
thin and delicate forms a double layer (1) outer parietal layer - fuses to fibrous pericardium (2) inner visceral layer - adheres tightly to the surface of the heart - aka epicardium lubricating pericardial fluid between the layers
what is the epicardium?
the outer layer of the heart wall
what is the structure of the epicardium?
thin outer layer of mesothelium inner layer of delicate fibroelastic tissue and adipose tissue (thickest over ventricles)
what is the function of the epicardium?
houses major cardiac vessels blood, nerve and lymph supply to myocardium smooth and slippery outer surface to the heart
what is the structure of the myocardium?
middle layer of heart wall - makes up 95% of heart cardiac muscle arranged in a spiral around the heart to facilitate strong pumping
what is the function of the myocardium?
responsible for contraction of the heart and circulation of blood
what is the endocardium?
innermost layer of thin endothelium of the heart wall
what is the structure of the endocardium
thin layer of endothelium providing a smooth lining for chambers and valves houses purkinje fibres
what is the role of the endocardium?
reduce friction as blood flows with the heart continuous with the endothelium of BVs
what is the histology of the epicardium
simple squamous epithelium
what is the cell type of the myocardium
cardiac muscle fibres and loose endomysial CT
what is the projection of the a/v valve cusps when open?
into the ventricles
what is the projection of the s/l valve cusps when open?
into lumen of the artery
what are the trabeculae carnae?
raised bundles of cardiac muscle fibres - form the papillary muscles
what are the chordae tendinae
in the ventricles attach to the outer margins of the valve, and papillary muscles when papillary muscles contract, edges of valve pulled taught = valve closes
how to the semi-lunar valves open or close?
open when pressure of the contraction forces them upwards close when pressure falls and the blood falls into the concave upper edge
how do the semi-lunar valves attach
by their convex margin to the wall of the aorta
how many cusps to semi-lunar valves
3
how many cusps to A/v valves?
mitral - 2 tricuspid - 3
what is the pathway of the cardiac conduction system
SAN –> atria –> AVN –> L & R bundle branches –> purkinje fibres –> ventricles
The conducting system: step 1
SAN spontaneously depolarises due to pacemaker potential Action potential generated and propagates through both atria - via gap junctions of intercalated discs in atrial muscle fibres Cause the atria to contract
The conducting system: step 2
AP from SAN reaches AVN in intertribal septum AP slows due to change in cell structure - allowing time for blood to empty into ventricles
The conducting system: step 3
AP enters the AV bundle (bundle of His)
The conducting system: step 4
AP travels from bundle of His to the L and R bundle branches to the apex of the heart (running through the IV septum)
The conducting system: step 5
Purkinje fibres at apex of heart conduct the AP from apex to the rest of the ventricular myocardium ventricles contract and blood is ejected through S/l valves
The cardiac cycle: step 1
Atrial contraction - due to AP reaching SAN – AV valves are open – last 20-30mls of blood flow into ventricles
The cardiac cycle: step 2
Isovolumetric Contraction of the ventricles - as AP reaches AVN – atria are relaxed – S/L and AV valves closed – pressure in ventricles rise
The cardiac cycle: step 3
Ventricular Ejection - AP reaches purkinje so ventricles fully contracted – pressure in ventricles risen higher than aortic pressure - due to isovolumetric contraction - pushes s/l valves open – blood flows from ventricle to aorta
The cardiac cycle: step 4
Isovolumetric Relaxation – Aortic pressure > ventricular pressure due to blood leaving the ventricles – causes S/l valves to close – AV valves closed
The cardiac cycle: step 5
Ventricular Filling – atria fills with blood – atria pressure > ventricular pressure so AV valves open – blood moves down concentration gradient to the ventricles - fills to 3/4 full
What does P wave represent
depolarisation of atrial fibres
What does the QRS complex reprsent
depolarisation of ventricles
what does T wave represent
repolarisation of ventricular fibres
What are the three phases of the cardiac cylce
atrial systole ventricular systole relaxation period when atria are in systole, ventricles are in diastole and vice versa
what steps of the cardiac cycle occur in atrial systole?
atrial contraction
what steps of the cardiac cycle occur in ventricular systole?
isovolumetric contraction and ventricular contraction
what steps of the cardiac cycle occur in the relaxation period?
isovolumetric relaxation and ventricular filling
what is the effect of increased HR on the cardiac cycle
relaxation period decreases systole time only decreases slightly
What is the course of the left coronary artery
divides into anterior IV branch- supply both ventricles divides into circumflex branch - supply L atrium and L ventricle
what is the course of the right coronary artery
divides into: - posterior IV branch - supply both ventricles - marginal branch - wall of right ventricle - small atrial branches - supply the right atrium
what does the great cardiac vein drain?
blood from both ventricles and left atrium
what does the middle cardiac vein drain?
both ventricles
what does the small cardiac vein drain?
right atrium and ventricle
what does the anterior cardiac vein drain?
the right ventricle - opens directly into the right atrium
where do the great, middle and small cardiac veins go?
open into the large coronary sinus on the posterior heart - empties directly into the right atrium
What is the equation for calculating BP?
BP = CO x TPR
what effects TPR?
smooth muscle contraction or relaxation in arteriole vessels symphathetic input = vasoconstriction = smaller lumen = higher TPR = higher BP small change in TPR = large change in BP
what is cardiac output?
CO = SV x HR the amount of blood ejected from the LV per MINUTE
what is stroke volume?
the amount of blood ejected from the LV per CONTRACTION
How does blood volume effect cardiac output & blood pressure?
increased venous return –> increased stretch of muscle before contraction –> stronger contraction –> more blood ejected –> increased SV and CO –> increased BP STARLINGs LAW
what is the effect of the parasympathetic nervous system on cardiac output & blood pressure?
causes decreased heart rate means decreased CO and decreased BP no effect on SV
what is the effect of the sympathetic nervous system on cardiac output & blood pressure?
Increased TPR - due to vasoconstriction Increased heart rate Increase in contractility - due to fight or flight reflex overall increase in CO and increase in BP
What is the baroreceptor reflex
Part of the ANS response detects stretch of the heart If high amount of stretch - triggers parasymphatetics - vasodilation, decreased HR and decreased contractility If low amount of stretch - triggers symphathetics - increased HR, increase contractility, vasoconstriction
what are the two main regulators of blood pressure
Autonomic nervous system Blood volume
How does the body regulate BP through blood volume?
If there is a decrease in BP (e.g. dehydration or blood loss), then CO decreases - decreased perfusion to the kidneys Detected by baroreceptors in kidneys - cause increased renin production Renin causes Ang I to convert to Ang II - which acts to cause vasoconstriction AND aldosterone release from adrenals Aldosterone causes increased sodium and water retention blood volume increases –> SV increases –> BP increases
define BP
force exerted on the blood vessel walls
what is systolic BP and how is it effected?
left ventricular contraction effected by stroke volume
what is diasystolic BP and how is it effected?
left ventricular relaxation effected by TPR
what is a normal volume for CO?
5l/min
what is a normal volume for SV?
70ml/contraction
what is a normal volume for EDV and ESV?
EDV 120-160ml ESV 60-70ml
what is a normal HR?
60-100bpm
histology of a cardiac muscle cell - 7 points
50-100 micrometers long, 14 wide one centrally located nucleus connect to other fibres via thickenings of sacrolemma - intercalated discs discs contain desmosomes - hold fibres together discs contain gap junctions - allow AP to transmit between muscle fibres - contract as a single coordinated unit larger and more numerous mitochondria smaller SR therefore less Calcium reserves
