6. Anatomy of the heart

Question 1

Give the structure of (each part of) the sac that surrounds the heart

Answer 1

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

Question 2

Give the function of the pericardium

Answer 2

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

Question 3

What is meant by ‘fusion’ in terms of the pericardium?

Answer 3

This refers to fluid that has entered the potential space

Question 4

State and describe the layers of the heart wall

Answer 4

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

Question 5

Describe the path of blood through the heart

Answer 5

1. Blood enters the heart through the inferior vena cava and coronary sinus into the right atrium
2. Blood then passes through the tricuspid valve into the right ventricle
3. The blood passes through the pulmonary semi-lunar valve and enters the pulmonary trunk to the lungs
4. From the lungs there are 4 pulmonary veins which the blood passes through and this leads the blood to the left atrium
5. The blood passes through the mitral valve to the left ventricle
6. Blood passes through the aortic semi-lunar valve to the ascending aorta

Question 6

What is meant by the ‘pulmonary trunk’?

Answer 6

Major vessel of the human heart originating from the right ventricle
Branches into the left and right pulmonary arteries which lead into the lungs

Question 7

Describe the external landmarks of the heart

Answer 7

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

Question 8

Describe the external sulci/grooves of the heart

Answer 8

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

Question 9

Describe the external right atrium of the heart

Answer 9

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

Question 10

Describe the external left atrium of the heart

Answer 10

Posteriorly positioned
Has a left auricle
There are four pulmonary veins emptying into this
Coronary groove separates the atrium from the ventricle

Question 11

Describe the external right ventricle of the heart

Answer 11

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

Question 12

Describe the exernal left ventricle of the heart

Answer 12

1/3 anterior and 2/3 posterior
Connects to the aorta
Makes up the inferior surface of the heart i.e. the ‘base’

Question 13

Describe the internal landmarks of the right atrium

Answer 13

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)

Question 14

Describe the internal landmarks of the right ventricle

Answer 14

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

Question 15

Describe the internal landmarks of the left atrium

Answer 15

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

Question 16

Describe the internal landmarks of the left ventricle

Answer 16

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

Question 17

Describe the left coronary artery

Answer 17

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

Question 18

Describe the right coronary artery

Answer 18

Descends down into the coronary groove

Two main branches:

• Right marginal along the right margin
• Posterior descending

Question 19

Briefly describe the coronary veins (don’t need to know much)

Answer 19

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

Question 20

Describe the fibrous skeleton of the heart

Answer 20

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

Question 21

In an image of valves, how can you distinguish between them?

Answer 21

Aortic valve is usually the only one centrally positioned

Can then work the rest out

Question 22

Describe the atriovetricular valves and how they work

Answer 22

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

Question 23

Briefly describe the papillary muscles

Answer 23

These are the most metabolically active cells in the heart

There is one muscle for every cardiac myocyte

Question 24

Describe the semi-lunar valves and how they work

Answer 24

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

Question 25

Describe conduction within the heart

Answer 25

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 (?)

Question 26

Describe conduction through the heart

Answer 26

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

Question 27

Describe the innervation of the heart

Answer 27

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

Question 28

Describe the effects of sympathetic innervation to the heart

Answer 28

Increases heart rate
Increases force of contraction
Cardio acceleratory centre

Question 29

Describe the effects of the parasympathetic innervation to the heart

Answer 29

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

Question 30

Describe the general visceral afferents (GVA)

Answer 30

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