session 3- the superior mediastinum and external heart

Question 1

what is contained within the mediastinum?

Answer 1

heart and pericardium, great vessels that enter and leave heart, veins that drain chest wall, trachea and main bronchi, oesophagus, nerves, lymphatics and thymus gland

Question 2

what is mediastinum divided into? what is present in each of these areas?

Answer 2

superior and inferior- split goes from sternal angle to T4/T5 vertebral junction
inferior is then divided:
anterior- anterior of sternum and anteroir of pericardial sac, contains inferior part of thymus gland in children and remanats in adults
middle- heart sat within pericardial sac, pulmonary trunk and ascending aorta
posterior- is between posterior aspect of the peroicardial sac and the vertabrae

Question 3

superior mediastinum- what is present?

Answer 3

arch of aorta and it’s three branches, superior vena cava and its tributaries (L and R brachiocephalic veins), trachea, oesophagus, phrenic nerves and vagus nerves (L and R), thoracic duct, thymus gland

Question 4

3 parts of aorta- where are they? any features? where do they go?

Answer 4

3 parts of the aorta, oxugenated blood from left ventricle:
ascending aorta- short first part, gives rise to cornary arteries
arch of aorta- curves posteriorly located in superior mediastinum and provides bramches to upper limbs, head and neck
descending aorta- through posterior mediastinum and into abdomen through diaphragm

Question 5

branches of the arch of the aoprta in superior mediastinum, names? where supplies blood to?

Answer 5

arch in superior gives rise to 3 major branches to supply the upper body:
1. brachiocephalic trunk which bifurcates into right common carotid artery (right side of head and neck inculding brain) and right subclavian (supply right upper limb)
2. left common carotid artery (supplies left side of head neck and brain)
3. left subclavian artery (supplies left upper limb)

Question 6

where are chemoreceptors found? what do they do?

Answer 6

The arch contains aortic bodies which contain chemoreceptors. They constantly montior arterial oxygen and carbon dioxide. This visceral sensory information travuls back to CNS by vagus nerve poathway and results in reflex response to regulate ventilation

Question 7

ligamentum arteriosum - what is it? where is it? what did it used to be?

Answer 7

it is a fibrous cord-like connection between pulmonary trunk and arch of aorta- remnants of ductus arteriosus (a fetal circulatory shunt, diverts mmajority of blood from pulmonary trunk directly yo aortic arch due to it being oxygenated in placenta not lungs)

Question 8

superior vena cava- purpose? location? features?

Answer 8

(carries deoxygenated blood into right atrium)
superior (from head, neck and upper limbs) vena cava
is located in superior mediastinum and is formed by the unison of the left and right brachiocephalic veins (brachium- arm, cephalic- head). Each brachiocephalic vein is formed by unison of internal jugular vein (drains head and neck) and subclavian vein (drain upper limb)

Question 9

inferior vena cava- purpose? location? features?

Answer 9

inferior (from abdomen, pelvis, lower limb) vena cava. Throcic part is very short and enters right atrium as soon as it enters thorax

Question 10

trachea- where is it? where does it go from to?

Answer 10

conducts air to and from L and R main bronchi of lungs, semi-rigid due to c-shaped rings of cartilage in walls, extends from larynx in neck into superior mediastinum and is palpable superior to the suprasternal notch, ends at sternal angle by bifurcating to L and R main bronchi (at junction known as carina)

Question 11

oesophagus- function? where it is?

Answer 11

muscular tube that extends from pharynx in neck to stomach, ‘waves’ of contraction of smooth muscle in oesophageall wall move food distally (peristalsis), located in the midline of the throax within the superior mediastinum, posterior to the trachea and descends into inferior mediastinum

Question 12

phrenic nerve- formed from what spinal nerves? type of nerve, containign what fibres? how do they enter thorax? where do they go next?

Answer 12

L and R phrenic nerves formed from the C3, C4, C5 spinal nerves innervate the diaphragm and pericardium, somatic nerves and contain motor and sensory fibres, decesnd through the neck and enter thorax through superior thoracic aperture. They then course over percardium and pierce diaphragm.

Question 13

vagus nerve- what spinal nerves from? types of fibres present? purpose of vagus nerve? present with? how do they eneter thorax?

Answer 13

L and R vagus nerves (CN X) arise from brainstem and contain 3 types of fibres:
somatic sensory
somatic motor
parasympathetic

decsend in the thorax posterior to root of the lung and contribute parasympatheic fibres to heart, lunmgs and oesophagus which then traverse the diaphragm to convey parasymathetic fibres to most abdominal viscera, descend through neck alongside internal carotid artery and internal jugular vein entering thorax by superior thoracic aperture

Question 14

Reccurent Langeal Nerve- from what nerve? what will this nerve do? left loops where? right loops where?

Answer 14

Each vagus nerve gives rise to a recurrent laryngeal nerve (RLN) which ascends back up into neck to innervate muscles of larynx. The left RLN loops under arch of aorta before ascending back up to left side of larynx. The righ RLN loops under right subclavian artery before ascending back up right side of neck (between trachea and oesophegus) to larynx.

Question 15

Thoracic duct- purpose? position? where it empties?

Answer 15

major channel for lymphatic drainage from most regions of the body. It ascends through posterior mediastinum then into superior mediastinum and empties into a venous system at the unsion of the left internal jugular vein and the left subclavian vein,

Question 16

Thymus gland- position? purpose?

Answer 16

is a lymphoid organ which is located anteriorly in the superior mediastinum but can extend inferiorly into anterior part of inferior mediastinum. present in children but atrohpies woth age

Question 17

pericardium - layers it consists of? gap? how is it innervated?

Answer 17

tough, fibrous sac that encloses the heart which is made of two layers:
- tough outer fibrous layer, attcahed superiorly to greater vessels and inferiorly to diaphragm
- thin inner serous layer composed of two parts: parietal layer which lines the inner aspect of the fibrous pericardium and a visceral layer that covers surface of heart (layers are continuos with each other)

the gap between this space is known as perocardial cavity and has a small amount of pericardial fluid to lubricate serous membranes allowing them to slide over each other

the L and R phrenic nerves also give rise to sensory branches that innervate the fibrous preicardium

Question 18

external features of the heart:

Answer 18

apex of heart projects towards left lung,

Question 19

surfaces of the heart-what they face?
posterior surface
inferior surface
anterior surface

Answer 19

posterior surface- face oesophagus and descending aorta
inferior surface- rest on diaphragm (also known as diaphragmatic surface)
anterior surface- faces strenum and ribs

Question 20

what parts of heart surfaces correspond to?

posterior surface
inferior/ diaphragmatic surface
anterior/sternocostal surface
left pulmonary surface
right pulmonary surface

Answer 20

posterior surface- left atrium part of right atrium
inferior/ diaphragmatic surface- left and right ventricle
anterior/sternocostal surface- right ventricle
left pulmonary surface- left ventricle
right pulmonary surface- right atrium

Question 21

where is apex formed?

Answer 21

in left venrtivle, sits in left 5th intercostal space in mid-clavincular line and epx beat is palpable here.

Question 22

borders of the heart?

Answer 22

important in discusinng X-rays,
right border- right atrium, lateral to right sternal edge, from right 3rd to 6th costal cartilage
left border- left ventricle, from left 2nd to 5th intercostal space
superior border- along line connecting 3rd costal cartilage and 2nd intercostal space
inferior border- right venrticle and part of left venrticle, along line connecting inferior end of right border with apex

Question 23

what are auricular appendages?

Answer 23

they are out pouching of the walls of L and R atria

Question 24

Clinical relevance: hoarsness of voice and lung cancer?

Answer 24

cancer at the apex of the heart can affect the recurrent langeal nerve which ruslts in results in weakness or paralysis of the ipsilateral intrinsic laryngeal muscles which move the larynx and the vocal cord causing patients voice to be hoarse

Question 25

Clinical relevance- Patent ductus arteriosus (PDA)?

Answer 25

ductus doesn’t close immidiately after birth, some blood flows straight from aorta to pulmonary trunk, increased flow causes pulmonary hypertension causing strain on right side of heart

Question 26

where does venous blood from the coronary arteries go?

Answer 26

deoxygentaed blood goes to the coronary sinus which then enters the right atrium

Question 27

Right coronary artery (RCA)- where in the heart does it supply blood?

Answer 27

• branches of RCA suplly the sinoatrial node and the atrioventricular node
• the right marginal artery supplies the inferior border of the heart
• the posterior inter ventricular artery (PIVA) is a continuation of the right coronary artery on the inferior side of the heart and runs in the posterior interventricular sulcus supllying both ventricles

Question 28

Left coronary artery (LCA)- name of 2 large terminal branches? where each branch runs? any branches of original arteries?

Answer 28

LCA runs a short distance (here called left main stem) before it divides into 2 large terminal branches:
- anterior interventricular artery/ left anterior descending LAD
- left circumflex artery LCx

• LAD runs along anterior interventricular sulcus towards apex and supplies both ventricles
  -several diagonal branches from LAD supplying left ventricles
  -left circumflex artery runs onto inferior surface and supplies left atrium, part of right and left venrticle
  -left marginal artery arises from circumflex and supplies left ventricle (sometimes called obtuse marginal artery)

Question 29

what arteries position depends if inidividual has L or R dominant cornonary circulation? where may the artery come from in L vs R? what else can it affect?

Answer 29

the posterior interventricular artery (PIVA) may arise from left or right coronary artery and depends if an individual has left or right dominant coronary circulation.
majority of people have right dominant (both right and left venrticles supplied by PIVA). If they are left dominant PIVA arises from circumflex so LCA supplies entire left ventricle

AVN also supplied by branches of PIVA

clinical relevance- someone with left dominant, if occlusion of LCA whole left ventricle has no blood supply

Question 30

Cardiac Veins- name 2 and the artery and potion they run alongside? where do they drain?

Answer 30

• great cardiac vein which accompanies anterior intervenrticular artery (LAD) on front off heart
• middle cardiac vein which accompanies posterior interventricular artery (PIVA) on back of heart

all ultimately frain into coronary sinus which depoists black back into the right atrium

Question 31

right atrium- features?

Answer 31

• interartrial septum (sepreates atria)
• fossa ovalis- depression in the interatrial septum which is remnats of fetal foramen ovale (bypass lungs in foetus)
• crista terminalis - a muscular ridge that seperates smoothwalled posterior part of atrium from anterior which has ridged muscular walls, ridges present are pectinate muscles and extend from right auricle

Question 32

right ventricle- features?

Answer 32

interventricular septum
trabeculae carneae- muscular ridges on internal wall
papillary muscle- modified trabeculae carneae
chord tendineae- fibrous cords that connect papillary muscle to tricuspid valve
moderator band- modifed trabeculae carneae, connect interventricular septum to papillary muscle, providing an elctrical shortcut for purkinje fibres

Question 33

left atrium- features?

Answer 33

• smooth walled posterior and ridged anterior part with pectinate muscles

Question 34

do they left and right atria contract to fully empty?

Answer 34

Right- yes, Left- no

Question 35

left ventricle- features

Answer 35

• trabeculae carnaea- muscular ridges on internal wall
  -papillary muscle- modified trabeculae carneae
  -chord tendineae- fibrous cords that connect papillary muscle to mitral valve

Question 36

do the papillary muscles and schordae tendineae shut the valves?

Answer 36

no they instead prevetn them from being forced open by pressure during high pressure

Question 37

how do AV valves work?

Answer 37

when pressure increase in ventricle valve cusps of AV valve which project into venrticles close passively and when venrticles contarct so do they papillary muscles pulling the cusps and preventing them from everting into atria

Question 38

How do semilunar valves work?

Answer 38

the semi-lunar valves have three semicircular cusps- when ventricles contract cusps are flattend agaisnt vessel wall, when pressure in venrticles become lower than in the vessel blood flow back down and is caught by valve cusps. The sinuses fill with blood and baloon causing edges to meet and close valve

Question 39

how do coronary arteries fill with blood?

Answer 39

they arise from 2 of 3 aortic sinuses and therefore fiull during ventricular relation (diastole)

Question 40

what do we here when listening to heart?

Answer 40

when listening to heart we are listening for sound of valves closing, the sound however is transmitted in the direction of blood flow.

Question 41

where are the auscultatory areas for each valve?

Answer 41

aortic- 2nd intercostal space , right of strenum
pulmonary- 2nd intercostal space, left of sternum
tricuspid- 5th intercostal space, left of sternum
mitral- 5th intercostal space, left midclavicular line

Question 42

Sinoatrial node: purpose? location?

Answer 42

cells in sinoatrial nodegenerate electrical impulses and is located in the superior end of the crista terminalis, impulses are generated at a rate of 70 per minute, cause atria to contract

Question 43

How does AVN conduct impulse to ventricles?

Answer 43

the atrioventricular node located at the inferior end of the interatrial septum conducts impulses. Then conducting fibres form from the atrioventricular bundle (bundle of his) which divides into the L and R bundle branches which give rise to purkinje fibres that enter myocardium of L and R ventricles

Question 44

blood supply of conducting system?
- SA
-AV
-Bundle of His

Answer 44

the SA node is supplied by RCA in 60% of people and LCA in 40%
the AV node is supplied by PIVA (which in most people arises from RCA)
Bundle of His is supplied by LCA in most people

Question 45

effect of parasympatheic and sympathtic fibres on heart?

Answer 45

sympathetic and parasympathetic fibres act on SA node to eitherincrease or deacrse the rate and force of myocardial contraction

Question 46

role of visceral effernet fibvres in heart?

Answer 46

visceral afferent fibres convey sensory information from heart to CNS- majority of time doesn’t reach our concious but if myocardium ischaemic (blood flow restricted to part of body) does and is felt as pain/burning/tightness etc. It is a gerneal pain in chest, neck or arms and is what’s known as refered pain

Question 47

clinical relevance- pathology of the pericardium and cardiac tamponade

Answer 47

a pericardial effusion is when increase in volume in this space (pericarditis). This can be very dangerous when it occurs quickly as the pericardium of the heart is strong and fibrous and cannot expand under the pressure so heart is compressed and unable to fill properly (cardiac tamponade)

Question 48

clinical relevance- myocardial infarction

Answer 48

‘heart attack’, death of region of myocardium due to occlusion of coronary artery supplying it. Commonly caused by atherosclerosis. If a fatty plaque shears from vessel it may cause a clot to form in lumen occlusing blood flow

Question 49

clinical relevance- congenital cardiac anomalies

Answer 49

patent foramen ovale- typically fully shut by time infant is 1, but if not close blood can move from left and right atria. This can also occur in ventricular septal defects . Small defects can be assompomatic

Question 50

clinical relevance- valve dysfunction

Answer 50

narrowing (stenoses) or icompetent (regurgetent0 valves. Cause turbulent blood flow that produces mummurs on ausculation. Can be congenital or aquired.

Question 51

clinical relevance- conducting systems abnormality

Answer 51

myocardial infarction can cause conducting issues if coronary arteris that supply them are cut off . Some pateints will have no symptoms and only picked up by ECG. Howevere some are life-threatening but treated by pacemaker or internal cardiac defibrilator.

Question 52

clinical relevance- heart failure

Answer 52

heart is not pumping efficiently- many causes e.g. dysfunction of valves or inabiklity for myocardium to contract properly. Symptoms are tiredness, shortness of breath and leg swelling

Question 53

clinical relevance- cardiac arrest

Answer 53

cessation of cardiac contraction , sometimes electrical activity but heart is not responding. Two main causes are myocardial infarction and conducting system abnormalities, but there are many others.