Histology Flashcards
(26 cards)
What is the tunica intima composed of?
A single layer of squamous epithelial cells called endothelial cells, supported on a basal lamina and a thin layer of connective tissue
What separates the tunica intima and tunica media?
The internal elastic membrane
What separates the tunica media and the tunica adventitia?
The external elastic membrane
Describe the tunica media and adventitia in arterioles
Tunica media -> one or two layers of smooth muscle
Tunica adventitia -> almost gone
What are capillaries composed of?
Endothelial cells and on a basal lamina
What are pericytes?
Connective tissue cells found just outside of capillaries
They have contractile and stem cell properties
What do precapillary sphincters do?
Help control blood flow through microvascular networks/anastomoses (arterioles -> capillaries -> venules)
What are post-capillary venules composed of? When do they become venules?
- Endothelial cells, a thin layer of connective tissue and occasional pericytes
- Become venules when they acquire intermittne smooth muscle cells in a tunica media layer
Post-capillary venules are important sites for…
Exchange e.g., cells moving into tissues in inflammation
When do venules become veins?
When they acquire a continuous (but still thin) tunica media
Describe the tunica adventitia of the largest veins e.g., vena cava, hepatic portal
Thick tunica adventitia incorporates bundles of smooth muscle
How can arteries and veins be told apart on a histological section?
Arteries tend to be rounder and have a thicker tunica media
Veins tend to be less round and have a thinner tunica media
What is the endocardium composed of?
- Endothelium
- Basal lamina
- Thin layer of collagen fibres
- Layer of denser connective tissue
- (some areas contain a subendocardium with branches of the impulse conducting system e.g., Purkinje fibres)
Describe the appearance of cardiac muscle
- Cardiac myocytes have a single nucleus and are relatively rounded
- Myocytes branch to form striated cardiac muscle
- Intercalated discs occur between myocytes (this is where intracellular junctions occur)
What is the epicardium composed of?
- A single layer of flattened epithelium called mesothelium
- Basal lamina
- Fibroelastic connective tissue (makes up the majority)
- Adipose tissue in areas where coronary arteries need to embed and travel around the heart
What is the epicardium also known as?
The visceral serous pericardium
Describe the fibrous pericardium
It is an outer sac of touch fibrocollagenous connective tissue that surrounds the heart
Describe the serous pericardium
- When it lines the inner surface of the fibrous pericardium, it is referred to as the parietal serous pericardium
- When it covers the surface of the heart, it is called the visceral serous pericardium (epicardium)
- The space between these layers is called the pericardial cavity
What is meant by the fibrous ‘skeleton’ of the heart?
Bands of connective tissue are found around the heart valves, between the atria and between the ventricles
What is the purpose of the fibrous skeleton of the heart?
- Supports the valves
- Provides attachment for the cardiac muscle fibres
- Electrically isolates the atria and ventricles
What are the heart valves composed of?
- Outer endothelial layer on a basal lamina
- Layer of collagen and elastin fibres
- Core of dense connective tissue called the lamina fibrosa
- There are no blood vessels in the valves
The lamina fibrosa of the heart valves is continuous with…
The fibrous skeleton of the heart
What are chordae tendinae and what do they do?
- Collagenous strands that are continuous with the lamina fibrosa of the heart valves
- They connect the heart valves to papillary muscles in the wall of the heart to prevent prolapse
What are the 3 types of cardiac muscle cells?
- Contractile cardiac myocytes (99%)
- Pacemaker cells
- Conducting cells
