2.6 Histology of the heart Flashcards
Describe the pericardium…
The outermost layer of the heart. (A layer of mesothelial cells resting on a thin layer fibrous connective tissue)
Visceral and parietal layers
What does this image show and label what you can see…
The pericardium
Describe the epicardium…
Found between the pericardium and the myocardium.
The underlying adipose connective tissue, vessels and nerves.
Describe the myocardium…
The thickest layer of the heart.
It is specialised cardiac muscle.
What is this image showing and label it…
The myocardium
What is this image showing:
Intercalated discs
What is the function of intercalated discs and what do they contain?
They connect adjacent cardiac myocytes.
They contain:
Gap junctions, adhering junctions and desmosomes.
What is the endomysium?
Loose fibrous connective tissue between the muscle fibres.
What is the image showing:
Endomysium
Describe atrial myocytes
Smaller than ventricular myocytes.
They contain perinuclear neuroendocrine granules (atrial natriuretic peptide).
What is atrial natriuretic peptide and what does it do?
A hormone that is released when cells are stretched excessively.
It increases the excretion of water, sodium and potassium ions in the kidney. It also inhibits renin secretion causing a lowering of blood pressure.
What does this image show and label it…
Atrial myocyte
N - cell nucleus
M - myofibrils
G - small dark staining granules that contain ANP
How are individual myocytes joined?
By intercalated discs
What do the intercalated discs contain:
Desmosomes and adherent junctions that bind the cells together.
Gap junctions that allow the cell to become electrically coupled.
What is this image showing and what are the stains showing?
Green arrows - intercalated discs
Black stain = intercalated disc
Blue - black stain = myofibrils
Red = RBC and mitochondria
Describe the endocardium
The innermost layer of the heart.
Contains a thin layer of fibrous connective tissue and endothelial cells
Label this image:
What are specialised extensions of endocardium?
Valves
What do valves attach to?
Central fibrous body
Heart valve structure contains:
Fibrosa - dense fibrous connective tissue
Spongiosa - loose fibrous connective tissue
Ventricularis - collagen and elastin
Label this image
What layer of the heart comprises of a specialised form of involuntary striated cardiac muscle?
Myocardium
What are the 4 layers of the heart?
Pericardium
Epicardium
Myocardium
Endocardium
What is composed of fibro-elastic connective tissue?
Valves
What plane does the fibrous skeleton of the heart lie in?
The atrio-ventricular plane
What are the SAN and AVN composed of?
Small irregularly arranged myocytes adapted for impulse conduction rather than contraction.
Where is the SAN located?
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.
Describe the purkinje fibres…
Large modified muscle fibres lying beneath the endocardium in the interventricular system.
They have large vacuoles but only a few myofibrils.
They contain stores of glycogen that allows them to be easily visualised with the PAS staining procedure.
They appear pale in H&E stained sections.
What allows Purkinje fibres to be easily visualised in the PAS staining procedure?
They contain stores of glycogen
What is this image showing:
Purkinje fibres
How are the AV and mitral valves connected to papillary muscles?
By fibrous chordae tendinae
How does damage of valves occur?
Takes the form of excessive collagen deposition or calcification resulting in reduced flexibility.
Which is the outermost layer of the heart?
A. Endocardium
B. Epicardium
C. Myocardium
D. Parietal pericardium
E. Visceral pericardium
E. Visceral pericardium
From the outside, the layers of the heart are the (visceral) pericardium, epicardium, myocardium and endocardium. The parietal pericardium is a fibrous sac that contains the heart. (The cells lining the visceral and parietal layers of the pericardium are the same.)
What type of epithelium is the pericardium?
A. Pseudostratified
B. Simple columnar
C. Simple cuboidal
D. Simple squamous
E. Stratified squamous
D - simple squamous
The pericardial epithelium is a simple squamous epithelium. Because of its embryological derivation it is known as mesothelium. This is the same epithelium found in the pleura and peritoneum.
Which of these is a feature of a ventricular cardiac myocyte?
A. Formed from multiple myoblasts
B. Fusiform cells
C. Multinucleate
D. Myofibrils in register
E. Secrete hormones
D - Myofibrils in register
Cardiac myocytes are branching cells each with a single nucleus. They do not form from the fusion multiple myoblasts (that is skeletal muscle). Their myofibrils are in register, and so they appear striated. Atrial myocytes (but not those in the ventricles) secrete a hormone (atrial natriuretic peptide).
What is the primary function of these cells?
A- Contraction
B- Store glycogen
C- Secrete atrial natriuretic peptide
D- Secrete nitric oxide
E- Transmit electrical impulses
Purkinje fibres - transmit electrical impulses (E)
These are Purkinje fibres. They are large specialised cardiac muscle cells with a cytoplasm rich in glycogen. Although rich in glycogen, their prime function is to conduct the cardiac impulse.
Where in the heart can these cells be found?
A- Beneath the endocardium
B- In the chordae tendinae
C- In the epicardium
D- In the mitral valve annulus
E- In the sinoatrial node
A- beneath the endocardium
They are found immediately below the endocardium.
How do the myocytes of the sinoatrial node differ from normal cardiac myocytes?
A- Embedded in fatty connective tissue
B- Anucleate cells
C- They are larger
D- Have no intercalated discs
E- Have no mitochondria
D- have no intercalated discs
The myocytes of the SAN are smaller than regular cardiac myocytes. Although they are joined by desmosomes, they do not have intercalated discs. The are embedded in fibrous connective tissue. All cardiac myocytes have a nucleus and mitochondria.
Which of the following cell types lines the mitral valve?
A- Cardiac myocytes
B- Endothelial cells
C- Fibroblasts
D- Mesothelial cells
E- Pericytes
B- endothelial cells
The inner surface of the heart, including the surface of the cardiac valves, is lined by vascular endothelial cells.
Where in the heart will you find the nodules of Arantius?
A- Aortic valve cusps
B- Chordae tendinae
C- Epicardium
D- Moderator band
E- Sino-atrial node
A- Aortic valve cups
The nodules of Arantius are nodules of fibroelastic tissue on the centre of the free edge of each of the valve cusps in the aortic valve and pulmonary valve. They are more prominent in the aortic valve (due to increased pressure in that side of the circulation).
What yellow/brown pigment accumulates in cardiac myocytes with increasing age?
A- Bilirubin
B- Biliverdin
C- Haemosiderin
D- Lipofuscin
E- Melanin
D- lipofuscin
Lipofuscin is a ‘wear and tear’ pigment formed by peroxidation of membrane lipids. It accumulates in cardiac myocytes with advancing age.
The coronary arteries:
A- Are muscular arteries
B- Arise from the pulmonary artery
C- Contain pericytes
D- Lack an external elastic lamina
E- Run in the endocardium
A- are muscular arteries
The coronary arteries are medium-sized muscular arteries that run in the epicardium. They do have an external elastic lamina. Pericytes are associated with capillaries and venules.
Which cells in the heart contain Weibel-Palade bodies?
A- Adipocytes
B- Cardiac myocytes
C- Endothelial cells
D- Fibroblasts
E- Purkinje cells
C- endothelial cells
Weibel-Palade bodies are storage granules found within the cytoplasm of endothelial cells (in the heart and elsewhere). They contain von Willebrand factor and other vascular mediators.
Which of the following lacks lymphatics?
A- Brain
B- Cartilage
C- Heart
D- Lung
E- Small intestine
B- cartilage
Although it was long thought that the heart and brain did not have lymphatic vessels within them, it is now known this is not the case. Almost all tissues have lymphatics, except cartilage, the eye, bone marrow and perhaps spinal cord.
What tissues do not have lymphatics?
Cartilage
Eye
Bone marrow
Perhaps spinal cord.
