Heart

Question 1

Pericardium

Answer 1

heart lies in a fibrous sack lined by a layer of mesothelial cells
• outermost layer of the heart
• Layer of squamous mesothelioma cells resting on thin layer of connective tissue
• Visceral pericardium - layer on outer surface of the heart. layer is reflected at the roots of the great vessels to become the parietal pericardium, the inner of the two layers of tissue that form the pericardial sack
• parietal pericardium- layer of cells on inner surface of fibrous sack containing the heart

Question 2

Visceral pericardium

Answer 2

layer on outer surface of the heart. layer is reflected at the roots of the great vessels to become the parietal pericardium, the inner of the two layers of tissue that form the pericardial sack

Question 3

Parietal pericardium

Answer 3

layer of cells on inner surface of fibrous sack containing the heart

Question 4

Epicardium

Answer 4

layer of fatty connective tissue- underlying adipose connective tissue, vessels and nerves
• between pericardium and myocardium
• Layer contains the coronary arteries

Question 5

Myocardium

Answer 5

thickest layer of the heart
• Specialised cardiac muscle

between myocytes loose fibrous connective tissue (endomysium)- may contain small number of lymphocytes

Question 6

Myocytes

Answer 6

• striated as myofibrils are all in register
• central nuclei and a single nucleus for each cardiac muscle cell
• branching
• cells remain separate and do not form a syncitium
• intercalated discs (pale areas between adjacent myocytes when stained with H&E)- specialised connections between myocytes which join them together to form long, branching chains.
-Connect actin filaments of adjacent myocytes
-contain: gap junctions (allows flow of ions to connect cells electrochemically), adhering junctions and desmosomes (connect cells by linking intermediate cytoskeleton filaments)

Question 7

Physiology of myocytes

Answer 7

• Shorter refractory period than skeletal muscle
• Do not fatigue
- secrete hormones (ANP)

Question 8

Intercalated discs

Answer 8

specialised connections between myocytes which join them together to form long, branching chains.
-Connect actin filaments of adjacent myocytes
-contain: gap junctions (allows flow of ions to connect cells electrochemically), adhering junctions and desmosomes (connect cells by linking intermediate cytoskeleton filaments)
Only found in cardiac muscle

Question 9

Ventricular vs atrial myocytes

Answer 9

Large myocytes found in wall of left ventricle
• Atrial myocytes contain perinuclear neuroendocrine granules (atrial natriuretic peptide) located near the nuclei- hormone that is released when the cells are stretched excessively. This hormone increases the excretion of water and sodium and potassium ions by the kidney. It also inhibits renin secretion causing a lowering of blood pressure.

Question 10

Endocardium

Answer 10

innermost layer of the heart
• Thin layer of fibrous connective tissue lined on its inner surface by a single flat layer of simple squamous endothelial cells

Question 11

Valves

Answer 11

covered by endothelium
• Attach to central fibrous body that lie in the atrio-ventricular plane
• Comprise of 3 separate layers:
1. Fibrosa - dense fibrous connective tissue
2. Spongiosa - loose fibrous connective tissue
3. Ventricularis - collagen and elastin
• both sides of valve covered by vascular endothelial cells

They consist of thick collagen fibres with occasional strands of elastic tissue. Both surfaces are covered by a layer of endothelial cells.

Question 12

Fibrosa

Answer 12

dense fibrous connective tissue

Question 13

Spongiosa

Answer 13

loose fibrous connective tissue

Question 14

Ventricularis

Answer 14

collagen and elastin

Question 15

Free margins

Answer 15

The free margins of the atrio-ventricular and mitral valves are connected to papillary muscles by fibrous chordae tendinae

Question 16

Chordae tendinae

Answer 16

prevent valves everting during systole and allow papillary muscles to open the valves

Question 17

Damage to valves

Answer 17

Damage frequently takes the form of excessive collagen (scar) deposition or calcification. This results in reduced flexibility and can lead to stenosis or incompetence.

• advanced age- calcification of aortic valve
• Rheumatic fever- commonly affects aortic and mitral valve
• Infective endocarditis- destroys cardiac valves (can occur rapidly with Staphylococcus aureus infections)
• Myocardial infarction can be complicated by rupture of papillary muscles resulting in valvular incompetence

Question 18

Incompetent valves

Answer 18

cause blood to enter the preceding chamber

Question 19

Stenotic valves

Answer 19

increase afterload

Question 20

Conducting system

Answer 20

Sinoatrial node → atrial myocardium → atrioventricular node → bundle of His → Purkinje fibres (subendocardial)

Question 21

SAN and AVN

Answer 21

These nodes are composed of very small, irregularly arranged myocytes adapted for impusle conduction rather than contraction.
They are surrounded by numerous blood vessels and nerve plexuses.
• There are no clearly defined anatomical fibres linking the S.A. and A.V. nodes although large conducting fibres (Purkinje fibres) form the right and left bundle branches.

Question 22

Purkinje fibres

Answer 22

found in ventricles immediately below the endocardium - large vacillated muscle cells that contain glycogen-rich cytoplasm

Not easily seen with H&E so use PAS

Question 23

Bundle branches

Answer 23

run from the AVN through the septal myocardium beneath the endocardium towards the apex of the heart where they branch and run back up free walls of both ventricles

Question 24

Where is the SAN

Answer 24

located on the medial side of the superior vena cava at its junction with the right atrium.

Question 25

Where is the AVN

Answer 25

located at the base of the inter-atrial septum, anterior to the opening of the cardiac sinus.

Question 26

What delays the contraction of the ventricles

Answer 26

• Rings of fibrous tissue between atria and ventricles prevent them being electrically coupled other than via the AVN to delay the impulse

Question 27

Lipofuscin

Answer 27

Yellow/brown pigment that accumulates in cardiac myocytes with increasing age

Question 28

Nodules of Arantius

Answer 28

found in centre of free edges in aortic valve cusps to prevent friction when come together

Question 29

Weibel-Palade bodies

Answer 29

are small storage granules located in endothelial cells comprising the intima of the heart and blood vessels. They are found in arteries, capillaries, veins, and the endocardium, but notably not in the lymphatic vessels. Contain Von Willebrand factors and other clotting factors