The heart and the pericardium

Question 1

How is the mediastinum divided into and how?

Answer 1

Superior: above sternal angle
Inferior: below sternal angle
Anterior: anterior to heart in pericardial sac
Middle: pericardial sac & heart
Posterior: posterior to pericardial sac and diaphragm

Question 2

Where does the heart sit?

Answer 2

In the middle, inferior part of the mediastinum

Question 3

What surrounds the heart?

Answer 3

Pericardium – fibroserous sac – 2 components:
Fibrous – tough connective tissue. Outlines the boundaries of middle mediastinum. It blends with the outer adventitial layer of the great vessels in the superior mediastinum.
Serous – thin. Contains 2 parts:
Parietal layer – on inner surface of fibrous pericardium
Visceral layer (epicardium) – adheres to heart + forms its outer covering

Question 4

Why are pericardial sinuses important clinically?

Answer 4

Because of infection and trapping of passing blood.

2 important pericardial sinuses in the heart:

• Transverse pericardial sinus separates the arteries from the veins, that is used clinically in cardiac surgery to limit the outflow from the heart.
• oblique pericardial sinus: is where the serous pericardium visceral layer is reflecting back on itself to be the parietal layer.

Question 5

what are the chambers of the heart?

Answer 5

Right atrium
-Blood returns via superior and inferior venae cavae (body) and coronary sinus (heart)
Left atrium
-Blood returns via pulmonary veins
Right ventricle
-Outflow to the pulmonary trunk
Left ventricle
-Outflow to the ascending aorta

Question 6

What structures can be found in the right atrium?

Question 7

what does the ductus arteriousus do?

Answer 7

it is a connection between the pulmonary trunk and the aorta, which allows blood which will go to the lungs to bypass the lungs by going through this structure and to the heart.
It allows most of the blood from the right ventricle to bypass the fetus’s fluid-filled non-functioning lungs.

This closes at birth and forms the ligamentum arteriosum.

Question 8

What is the first point when the blood can bypass the lungs?

Answer 8

There is a hole in the fetus called the Foramen ovale.
This allows blood from the right atrium to go to the left atrium, and NOT go the lungs.

Closes at BIRTH.

Becomes the fossa vale after birth, it is thin

Question 9

What is a remnant of something called?

Answer 9

A fossil

Question 10

Where is the ligamentum arteriosum and when does the blood go through this

Answer 10

In the fetus, if blood doesn’t go through the foramen ovale, it will go through the ductus arteriosus.

Question 11

How many cusps in the tricuspid valve?

Answer 11

3

Anterior, septal and posterior cusp

Question 12

What is myocardial infarction?

Answer 12

Ischaemic event where the heart does not receive blood, so dies

Question 13

what is a cardiac arrest?

Answer 13

is is an arrest of the heart beat.

Electrical issue

Question 14

what type of coronary arteries are there?

Answer 14

Branches that go between the ventricles are interventricular branches
along the margin are called marginal
The ones that turn back on themselves are called circumflex

Question 15

what are some variations in the coronary arteries?

Answer 15

More common variation – right dominant coronary artery - posterior interventricular branch arises from the right coronary artery

Less common variation – left dominant coronary artery - posterior interventricular branch arises from the left coronary artery

Question 16

Describe the arrangement of the coronary veins?

Answer 16

• follow the arrangement of coronary arteries

- all of them drain into one vessel between the left atrium and the left ventricle called the CORONARY SINUS

Question 17

where are the coronary sinuses?

Answer 17

There are coronary sinuses in relation to the aortic valve, the coronary aortic valve, and another that trains into the right atrium.

Question 18

Describe the conduction system?

Answer 18

SAN= electrical activity starts here
AVN= spreads across to here
Atria contract
DELAY
ventricles contract, from the apex.
Excitation begins in sinu atrial (SA) node
Spreads across atria causing contraction
Concurrently wave stimulates atrioventricular (AV) node
Travels through the bundle of His
Then along bundle branches, through Purkinje fibres, causing ventricular contraction

Question 19

where is the bachmann’s bundle situated?

Answer 19

Inner wall of the left atrium

Question 20

what is cardiac tamponade and pericarditis

Answer 20

build-up of fluid in pericardial cavity.
Rapid accumulation of fluid in pericardial sac  pericardial effusion  cardiac tamponade  biventricular failure
A pericardial effusion is where excess fluid builds up between the parietal and visceral layers of the serous pericardium
As the fibrous pericardium is relatively fixed, it cannot expand easily, therefore the accumulation of fluid within the pericardial sac compresses the heart (cardiac tamponade)

Fibrous pericardium doesn’t stretch leading to increased pressure inside.

Question 21

what are the branches of the aorta?

Answer 21

Ascending aorta:
Right and left coronary arteries
Aortic arch:
Brachiocephalic trunk – divides into right common carotid and right subclavian arteries
Sometimes brachiocephalic trunk (10% people) has small branch – Thyroid ima artery*
Left common carotid artery
Left subclavian artery

Question 22

where does the common carotid divide into and into what?

Answer 22

Common carotid divides into internal + external carotid arteries at around level of laryngeal prominence (C4)

Question 23

what is the pulmonary trunk

Answer 23

Arises from the right ventricle
Divides into right + left pulmonary arteries
Carries deoxygenated blood via left + right pulmonary arteries  to lungs .

Question 24

Describe the arrangement of the phrenic and vagus nerve?

Answer 24

Phrenic:
Formed in the cervical plexus from C3, 4, 5
Motor to: the diaphragm
Sensory to:
central tendon of the diaphragm
mediastinal pleura (parietal)
pericardium
peritoneum of central diaphragm

Right phrenic nerve reaches diaphragm lying on surface of:
right brachiocephalic vein
superior vena cava
right side of heart and pericardium - in front of lung root

General rule:
Phrenic nerves ANTERIOR (In front) of lung root.
Vagus nerves POSTERIOR (behind) lung roots.

Vagus:
Vagus nerves (CN X) pass posterior to lung roots and form plexus following oesophagus into abdomen, giving branches to heart and lungs on the way
Vagus nerves lateral to common carotids (*run in carotid sheaths)
Left vagus passes anterior to aortic arch
Left phrenic crosses vagus to cross aortic arch more anteriorly

Left phrenic and vagus nerves:
Cross arch of aorta
Left phrenic descends in front of lung root
Left vagus crosses behind root lung gives off left recurrent laryngeal nerve – recurs (=turns back) around ligamentum arteriosum and aortic arch
Breaks up into many branches round oesophagus

Right vagus nerve:
Lies on the trachea (on the side of it)
Crosses behind the lung root 
Recurrent laryngeal branch – recurs (turns back) around right subclavian artery
Breaks up into branches on oesophagus

Branches to chest and abdomen = parasympathetic (control smooth and cardiac muscle + glands of gut and airways)
Sensory - from gut and lungs
Note: Recurrent laryngeal nerve not parasympathetic – run back up neck to supply most skeletal muscles of larynx
*RIGHT Recurrent Laryngeal nerve HIGHER than LEFT Recurrent Laryngeal nerve. So LEFT Recurrent Laryngeal nerve is longer.

Question 25

what is the recurrent laryngeal nerve do?

Answer 25

The recurrent laryngeal nerve contributes to muscles allowing us to speak. In cardiothoracic or neck surgery damage to these nerves can contribute to loss of voice - vocal cord paresis or paralysis.

Question 26

where does the sympathetic trunk lie?

Answer 26

Sympathetic trunks lie on each side of the posterior mediastinum
Receive branches from spinal nerves T1 - L2
Distribute sympathetic nerves to smooth muscle and glands throughout body
Nerves to body wall synapse in ganglia of trunks
Nerves to internal organs (viscera) synapse in local ganglia
Also bring pain fibres back to CNS from viscera
Fibres from lower T5 - T12 reach abdomen in bundles called splanchnic nerves

Question 27

What are the reflections of the pericardium?

Answer 27

Anteriorly:
Surrounding arteries: aorta, pulmonary trunk
Posteriorly:
Surrounding the veins: SVC, IVC, pulmonary veins

These reflections form 2 sinuses (a cul de sac resulting from the reflections):
Transverse pericardial sinus
Oblique pericardial sinus.

A reflection is a point where the parietal and visceral pericardium become continuous
Transverse pericardial sinus – posterior to the ascending aorta and pulmonary artery and anterior to superior vena cava
Oblique pericardial sinus – zone of reflection around the veins is J-shaped. The sinus is posterior to the left atrium
During cardiac surgery:
When the pericardium is opened anteriorly, a finger is placed in the transverse sinus to separate the arteries from the veins. A hand placed under the apex of the heart and moved superiorly enters the oblique pericardial sinus

Question 28

what happens at T4/T5?

Answer 28

The sternal angle T4/T5 is an important landmark, it is where:
2nd costal cartilage articulates with sternum
Superior mediastinum is separated from the inferior mediastinum
The ascending aorta ends to form the aortic arch
The aortic arch ends and the thoracic (descending) aorta begins
Trachea bifurcates