8.5 Cardiovascular system morphology

Question 1

What is the function of the atria?

Answer 1

• Receive blood from veins and allow movement into ventricles
• Right atrium receives blood from the systemic blood system/the body
• Left atrium receives blood from the pulmonary vein/circulation

Question 2

What is the function of the ventricles?

Answer 2

• Eject blood from the heart at a high pressure
• Right ventricle ejects into the pulmonary arteries/into the pulmonary system
• Left ventricle ejects into the aorta/the systemic vascular system

Question 3

What are the general features of the heart?

Answer 3

• Each compartment is separated by a valve to ensure unidirectional flow - the major valves in the heart also produce the heart sounds
• Cardiac muscle produces motor power, left ventricle wall is thicker
• Cardiac muscles has its own vascular system, the coronary arteries (first vessels off of the aortic arch) which provide oxygen and nutrition to the muscles
• Collection of pacemaker cells which initiate regular contraction
• Conducting system to allow coordinated contraction (gap junctions between cells and central cells/Purkinje fibres to allow contraction of ventricles to start at the bottom)
• Has a fibrous section to insulate the atria from the ventricles and also provides support for the valves, mostly made of fibroblasts and aligns the cardiac muscle cells

Question 4

What nervous system innervates the heart?

Answer 4

The autonomic nervous system

Question 5

What is the pericardial cavity?

Answer 5

• The gap between the two layers of serous pericardium that surrounds the heart
• The pericardium is sealed to the diaphragm and around the vessels that enter and leave this region
• Contains a small amount of serous fluid (serous = serum-like)
• Allows friction-free contact within the chest and also reduces surface tension

Question 6

How can the human cardiovascular system be summarised?

Answer 6

• Double circulation (systemic and pulmonary)
• Closed (blood is retained within the system, although there is some draining of fluid from the capillaries into the lymphatic system, as well as draining to the vascular system at certain points)

Question 7

What is the ‘major face’ of the heart?

Answer 7

• The anterior view of the heart
• Made up mostly of the right ventricle, left ventricle is more posterior (right atrium also visible more superiorly and laterally from the middle of the heart)

Question 8

What drains into the right atrium?

Answer 8

• Superior and inferior venae cavae
  
  • > azygous vein will sometimes drain directly into the right atrium, or will drain into the SVC just before entry into the atrium
• Coronary sinus (from coronary vessels)
• Some small veins from the coronary arteries also drain directly into the right atrium, known as the venae cordis minimae

Question 9

What drains into the left atrium?

Answer 9

• Oxygenated blood from the lungs via the pulmonary vein

- > there are 4x pulmonary veins

Question 10

What is the function of the right ventricle and how is it adapted for this?

Answer 10

• Ejects dioxygenated blood into the pulmonary circulation

- Lower pressure required, so muscle wall is thinner than that of the LHS

Question 11

What is the function of the left ventricle and how is it adapted for this?

Answer 11

• Ejects oxygenated blood into the aorta, into the systemic circulation
• High pressure required as must supply the rest of the body, therefore thicker muscle wall than the right ventricle

Question 12

What are the main coronary arteries and where do they go?

Answer 12

• Coronary arteries arise from the proximal artery around the level of the coronary sinus
• Penetrate into the heart muscle and perfuse it during diastole/relaxation
• Right coronary artery lies between the right atrium and the right ventricle, arises from aorta around the right aortic cusps
• RH coronary gives a marginal arch that then continues as the posterior interventricular branch
• In 60% of people, RH coronary artery provides the blood supply for the SAN, for 90% of people it supplies the AVN
• Left coronary artery arises from the aortic arch around the region of the left aortic cusp, runs down the left side of the heart
• Left is often considered dominant due to the heart’s reliance upon the LHS
• These arteries can become occluded, leading to a series of issues including ischaemia, angina and heart failure
  
  • > this is especially problematic due to the coronary arteries not having any functional anastomoses, so you can’t survive with only one side functioning

Question 13

What is the fossa ovalis?

Answer 13

• Depression in the right atria of the heart
• At the level of the interatrial septum
• Where the foramen ovale was during development (a region where oxygenated blood entering the right side of the heart was able to pass through to the other side to provide oxygenated blood to the rest of the body, acts as a shunt and allows communication)
  
  • > this sometimes will not close during development, leading to hypoxia, these need to be surgically cured

Question 14

What are the papillary muscles?

Answer 14

• Muscles found in the ventricles of the heart
• Connected by chordae tendinae (colloquial: heartstrings) to the atrioventricular valves (right: tricuspid, left: mitral)
• These muscles prevent the inversion of the valves, therefore allowing the flow of blood to be kept in one direction through the heart

Question 15

What makes up the majority of the posterior surface of the heart?

Answer 15

• Left atrium, behind the outflow tracts of the left and right ventricles
• In front of the posterior mediastinum

Question 16

What are some features of the walls of the atria?

Answer 16

• Left atrium has a region of smooth interior wall formed by incorporation of primitive pulmonary veins during development
• Also has an auricle region which is rough-walled, formed from the primitive atrium
• The right atrium has a rough region of terminal crest pectinate muscles, derived from the primitive atrium, and also a smooth walled section derived from incorporating the sinus venosus and interatrial septum during development

Question 17

What are the right and left auricles (aka appendages)?

Answer 17

• Flap-like structures within the atria of the heart (name comes from the Latin for ear, this is due to their resemblance to floppy dog ears)
• Extend the surface of the heart (around the root of the aorta on the right and up to the pulmonary trunk on the left)
• Have muscular walls so are involved in the active transfer of blood from the atria to the ventricles

Question 18

What are the four valves within the heart and where do they lie? What are the general features?

Answer 18

• Tricuspid valve, from the right atrium to the right ventricle
• Pulmonary/semilunar valve from the right ventricle to the pulmonary trunk
• Mitral valve, from the left atrium to the left ventricle, bicuspid
• Aortic/semilunar valve from the left ventricle to the trunk of the aorta

General features:

• AV valves are flattened sheets, held by chordae tendineae and papillary muscles which prevent reflux
• Valves between ventricles and circulation are tricuspid (although bicuspid and 4-flapped variants are also seen with some frequency), backflow is prevented through blood causing the cusps to bulge and shut
• Supported by the fibrous skeleton of the heart (which also provides electrical insulation between the different compartments of the heart)
  
  • > fibrous skeleton connects to the outflow valves during heart folding of development

Question 19

• What can be a negative effect of hypertrophy?

Answer 19

Often in the left ventricle as a result of stenosis (aortic valve stiffening/narrowing), can lead to arrhythmia throughout the heart and therefore cardiac arrest
-> pacemaker needs to be inserted

Question 20

What are the features of the pacemaker and conducting system of the heart?

Answer 20

• Main pacemaker is the sino-atrial node (SAN)
• Impulses arise from here and spread throughout the atrial muscle until it reaches the atrio-ventricular node (AVN)
• Fibrous skeleton insulates between the atria and ventricles, preventing transmission between the two
• AVN delays the impulse for approximately 0.09s before transmitting it to the AV-bundle of His
  
  • > these conducting fibres pass through the fibrous skeleton and membranous part of the septum until the Purkinje fibres are reached
  • > here, the impulse splits and innervates the muscles of the left and right ventricles to initiate contraction

Question 21

What is the cardiac plexus?

Answer 21

• Nervous plexus that innervates the heart
• Receives nerves from both the sympathetic (sympathetic trunk) and parasympathetic (vagus nerve) systems
• Located beneath the aortic arch
• Due to the heart developing further up in the neck, many of the nerves in the cardiac plexus arise from further up in the neck

Question 22

What is the function of sympathetic innervation of the heart?

Answer 22

• Innervates the SAN and the AVN

- Causes an increase in heart rate and in force of contraction

Question 23

What is the function of parasympathetic innervation of the heart?

Answer 23

• Primarily innervates the SAN
• Causes a slowing in heart rate
• Parasympathetic innervation will always take preference over sympathetic/parasympathetic effects are dominant

Question 24

Look at imaging of the heart and do some labelling

Answer 24

Do it!

Question 25

What is situs inversus?

Answer 25

This is where all of the organs in the abdomen lie on the opposite side of where they should, results in dextrocardia (where the apex of the heart points to the right rather than the left)

Question 26

• What is heterotaxia?

Answer 26

This is where some of the organs in the abdomen are flipped symmetrically but not all, resulting in some serious complications

Question 27

What are the major veins running through the mediastinum?

Answer 27

• Superior vena cava, drains into right atrium carrying blood from the upper limb, head and neck
  
  • > this is formed from the right and left brachiocephalic veins, azygous vein will also sometimes drain into it if not draining directly into the right atrium
  • > brachiocephalic vein is formed from the internal jugular vein joining with the subclavian
• Inferior vena cava will also drain into the right atrium, carrying blood from the lower half of the body

Question 28

Where does the aorta lie within the different sections of the mediastinum?

Answer 28

• Ascending aorta passes up and right into the superior mediastinum, forming the aortic arch
  
  • > major branches coming off of the aortic arch are the brachiocephalic, left common carotid and left subclavian arteries
• This then passes to the left and moves down, continuous with the descending aorta
  
  • > this passes through the posterior mediastinum

Question 29

How are the sinuses in the pericardial sac defined?

Answer 29

By the major vessels within the mediastinum

• Transverse sinus lies between the aorta and the pulmonary trunk anteriorly and the SVC and pulmonary veins behind
  
  • > this is formed during development when the dorsal mesocardium breaks down during development
• The oblique sinus is an extension of the pericardial sac between the four pulmonary veins, allowing the left atrium to move on the pericardium and therefore the posterior mediastinum