6. Anatomy of the heart Flashcards
Give the structure of (each part of) the sac that surrounds the heart
Heart is surrounded by a three layered sac consisting of a serous membrane (visceral and parietal) and a fibrous membrane - this is called the ‘pericardium’
Serous pericardium - visceral and parietal
Fibrous pericardium - very thick and inflexible protective layer, attached to the great vessels and diaphragm - anchors the heart in place
Give the function of the pericardium
Fixes the heart in the mediastinum and limits it’s motion
Protects the heart from infections from other organs e.g. the lungs
Prevents excess dilation of the heart where there might be acute volume overload
MAIN FUNCTION - lubrication - allows the heart to move freely
What is meant by ‘fusion’ in terms of the pericardium?
This refers to fluid that has entered the potential space
State and describe the layers of the heart wall
Epicardium (outermost) - this is the visceral layer of the serous pericardium
Myocardium - cardiac muscle fibres are arranged in bundles - these squeeze blood out of the heart
Endocardium (innermost) - continuous with the endothelium
Describe the path of blood through the heart
- Blood enters the heart through the inferior vena cava and coronary sinus into the right atrium
- Blood then passes through the tricuspid valve into the right ventricle
- The blood passes through the pulmonary semi-lunar valve and enters the pulmonary trunk to the lungs
- From the lungs there are 4 pulmonary veins which the blood passes through and this leads the blood to the left atrium
- The blood passes through the mitral valve to the left ventricle
- Blood passes through the aortic semi-lunar valve to the ascending aorta
What is meant by the ‘pulmonary trunk’?
Major vessel of the human heart originating from the right ventricle
Branches into the left and right pulmonary arteries which lead into the lungs
Describe the external landmarks of the heart
Can see two atria
Right atrium makes up the top right hand corner of heart - can only see small part of the left atrium
Small part of the two ventricles are visible at anterior part of heart
Describe the external sulci/grooves of the heart
Atrio-ventricular groove/sulcus (aka. coronary groove) separates the atria from the ventricles - the main coronary arteries sit in this sulcus
Interventricular groove separates the two ventricles - there is an anterior one and a posterior one
Describe the external right atrium of the heart
Forms the right border of the heart
Can see the superior and inferior vena cava
Has an appendage - the right auricle which contains a slightly different type of muscle
Describe the external left atrium of the heart
Posteriorly positioned
Has a left auricle
There are four pulmonary veins emptying into this
Coronary groove separates the atrium from the ventricle
Describe the external right ventricle of the heart
2/3 on the anterior surface and 1/3 on posterior surface
Pumps blood up the pulmonary trunk
Interventricular groove separates the anterior and posterior
Describe the exernal left ventricle of the heart
1/3 anterior and 2/3 posterior
Connects to the aorta
Makes up the inferior surface of the heart i.e. the ‘base’
Describe the internal landmarks of the right atrium
Opening the right atrium reveals two different types of muscle - pectinate muscle (more on outside) and smooth muscle (more on inside) - there is a ridge between these two muscles called CRISTAE TERMINALIS where the SAN is located
Also the coronary sinus - the main vein from the coronary arteries and blood is emptied here from the coronary veins
Can see Fossa Ovalis - foetal ‘hole in the heart’ - shunts 1/2 blood from the right side to the left side - this closes at birth
DUCTUS ARTERIOSUS - this is the artery from the pulmonary trunk away from the lungs and into the aorta at birth - this is also closed at birth
Can also see AVN (both nodes positioned in the right atrium)
Describe the internal landmarks of the right ventricle
Made up of TRABECULAE CARNAE - pole/rod like muscles which form ‘bundles’ projecting from the inner surface of the ventricle into the lumen as thick ridges
Tricuspid valve - valve cusps and chordae tendinae attached to papillary muscles
Pulmonary trunk - blood pushed up here to lungs - contains pulmonary semi-lunar valve
Describe the internal landmarks of the left atrium
Posterior/base of the heart
Four pulmonary veins extend to here - two either side: superior and inferior
Mitral/bicuspid valve empties into the left ventricle
Smooth muscle walls
Pectinate muscle in the left auricle
Fossa ovalis
Describe the internal landmarks of the left ventricle
Mitral valve - chordae tendineae, papillary muscles
Ascending aorta - aortic semi-lunar valve
THICK wall - much thicker myocardium than in the right ventricle
The right ventricle kind of wraps around the left ventricle
Describe the left coronary artery
Known as the ‘left main stem’
Emerges from the aorta
Positioned just behind the pulmonary trunk and the auricle
Splits into two main branches and one other branch SO three in total:
- Anterior interventricular branch of the main coronary artery/Left anterior descending (LAD) - crucial part of the heart and supplies majority of the conducting system
- Circumflex
- Marginal
Describe the right coronary artery
Descends down into the coronary groove
Two main branches:
- Right marginal along the right margin
- Posterior descending
Briefly describe the coronary veins (don’t need to know much)
Collect waste from the cardiac muscle
Drain into large sinus which empties into right atrium SO right atrium has three sources of deoxygenated blood - SVC IVC and coronary sinus
Describe the fibrous skeleton of the heart
Valves sit on a plane formed by the fibrous skeleton of the heart - fibrous rings surround all valves and are continuous with the septum (partition between the two chambers)
The rings: Anchor and support the valves Separate the atria and the ventricles Provide attachment for muscle fibres Support valves and prevent stretching From basis of electrical discontinuity - action potential passes through here when passing from atria to ventricles
In an image of valves, how can you distinguish between them?
Aortic valve is usually the only one centrally positioned
Can then work the rest out
Describe the atriovetricular valves and how they work
Tricuspid and bicuspid/mitral valves
During systole, blood pushes back towards the valves and causes them to close
The inflexible cornae tendineae anchor the valves - papillary muscles contract and pull the cusps so they don’t collapse
Briefly describe the papillary muscles
These are the most metabolically active cells in the heart
There is one muscle for every cardiac myocyte
Describe the semi-lunar valves and how they work
Three cusps
Prevent back-flow from aorta and pulmonary trunk into the ventricles
Passive action - work in a similar way to valves in the veins
Just above the valves are two coronary arteries so when the valves close and the blood is on top of them and not moving, it is diverted into the coronary arteries
Describe conduction within the heart
Conducting system of the heart is through two different networks separated by fibrous skeleton - atrial network and ventricular network - these are formed via gap junctions at intercalated disks (?)
Describe conduction through the heart
SAN generates the action potential - this triggers the contraction of the atria and sends the action potential along the intermodal path
The AVN triggers ventricular contraction - this relays the action potential to the atrioventricular bundle i.e. purkinje fibres on the right and left side near the apex
The purkinje fibres take the action potential down the interventricular septum and then cause the contraction to move around to the myocytes
Describe the innervation of the heart
Heart is supplied by the cardiac plexus of the nerves
Lies anterior to the bifurcation of the trachea (carina) and posterior to the arch of the aorta
Contains parasympathetic (vagus), sympathetic (sympathetic trunk) and visceral general afferents (GVA)
Fibres extend from the plexus to the coronary arteries and SAN and AVN
Describe the effects of sympathetic innervation to the heart
Increases heart rate
Increases force of contraction
Cardio acceleratory centre
Describe the effects of the parasympathetic innervation to the heart
Slows the heart rate
Comes from the same centre as the sympathetic and then goes to the vagus nerve (CNX) which starts in the medulla
Synapse on/near the target organ
Describe the general visceral afferents (GVA)
Enters the spinal cord through the sympathetic trunk
Enters through the sensory dorsal root at the same level as the normal somatic afference
This can result in referred pain - not felt by the arm but felt further down e.g. the arm - generally referred to skin supplied by T1-T4
