Heart Flashcards
Pericardium
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
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
Epicardium
layer of fatty connective tissue- underlying adipose connective tissue, vessels and nerves
• between pericardium and myocardium
• Layer contains the coronary arteries
Myocardium
thickest layer of the heart
• Specialised cardiac muscle
between myocytes loose fibrous connective tissue (endomysium)- may contain small number of lymphocytes
Myocytes
• 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)
Physiology of myocytes
• Shorter refractory period than skeletal muscle
• Do not fatigue
- secrete hormones (ANP)
Intercalated discs
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
Ventricular vs atrial myocytes
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.
Endocardium
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
Valves
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.
Fibrosa
dense fibrous connective tissue
Spongiosa
loose fibrous connective tissue
Ventricularis
collagen and elastin
Free margins
The free margins of the atrio-ventricular and mitral valves are connected to papillary muscles by fibrous chordae tendinae
Chordae tendinae
prevent valves everting during systole and allow papillary muscles to open the valves
Damage to valves
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
Incompetent valves
cause blood to enter the preceding chamber
Stenotic valves
increase afterload
Conducting system
Sinoatrial node → atrial myocardium → atrioventricular node → bundle of His → Purkinje fibres (subendocardial)
SAN and AVN
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.
Purkinje fibres
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
Bundle branches
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
Where is the SAN
located on the medial side of the superior vena cava at its junction with the right atrium.
Where is the AVN
located at the base of the inter-atrial septum, anterior to the opening of the cardiac sinus.
What delays the contraction of the ventricles
• Rings of fibrous tissue between atria and ventricles prevent them being electrically coupled other than via the AVN to delay the impulse
Lipofuscin
Yellow/brown pigment that accumulates in cardiac myocytes with increasing age
Nodules of Arantius
found in centre of free edges in aortic valve cusps to prevent friction when come together
Weibel-Palade bodies
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
