Histology Flashcards
Roles of the circulatory system (5)
- Transport oxygen and nutrients to the tissues
- Transport CO2 and other metabolic waste away from tissues
- Temperature regulation
- Distribution of hormones and immune cells
- Reproductive function in males (penile erection)
3 layers of blood vessels, from inner layer to outer layer
Tunica intima, tunica media, tunica adventitia
Tunica intima:
- What does it consist of?
- What is it separated from the tunica media by?
- Consists of single layer of squamous epithelial cells (endothelial cells) supported by a basal lamina and thin layer of connective tissue
- Layer of elastic tissue called internal elastic membrane
Tunica media:
- What is it made up of?
- What is it separated from the tunica adventitia by?
- Made up predominantly of smooth muscle, of which the thickness varies
- Layer of elastic tissue called external elastic membrane
Tunica adventitia:
- What is it made up of?
Supporting connective tissues separated by elastic lamina
Why are the largest arteries called elastic arteries?
They have many sheets of elastic fibres in their tunica media to provide elastic recoil
Arterioles:
- Describe tunica media and adventitia in arterioles
- Typical diameter
- Only one or two layers of smooth muscle in tunica media and almost no adventitia
- 30-200 microns
Capillaries:
- What are they composed of?
- Typical diameter
- Endothelial cells and basal lamina
- 4-8 microns
Pericytes in capillaries
Connective tissue cells that have contractile properties found at intervals just outside the basal lamina
3 types of capillaries
Continuous capillaries (more common), fenestrated capillaries, sinusoidal or discontinuous capillaries
Continuous capillaries:
- Where are they found?
Muscle, connective tissue, lung, skin, nerve
Fenestrated capillaries:
- What do they contain in their wall?
- Where are the found?
- 50nm pores in the wall
- Mucosa of the gut, endocrine glands, glomeruli of the kidneys
Sinusoidal/discontinuous capillaries:
- What do they contain?
- Describe the basal lamina
- Where are they found?
- Large gaps through which macromolecules and sometimes even cells can pass
- Discontinuous or absent basal lamina
- Found in the liver, spleen and bone marrow
What do capillary networks drain into and what size are these?
Post-capillary venules which are about 10-30 microns
Structure of post-capillary venules
Endothelial lined with a thin layer of connective tissue and occasional pericytes
When do post-capillary venules become venules?
Once the vessel begins to acquire intermittent smooth muscle cells in a tunica media layer
Size of venules
generally >50 microns
Describe tunica media in veins
Relatively thin but continuous tunica media, typically consisting of a few layers of smooth muscle
What are valves?
Inward extensions of the tunica intima
Tunica media in arteries compared to veins
It is much thicker
3 layers of the heart inner to outer
Endocardium, myocardium, epicardium
Endocardium:
- What does it consist of??
- Where is it present?
- Consists of a layer of endothelial cells backed by connective tissue
- Lines the entire surface of the heart including the valves
Myocardium:
- What does it consist of?
Thick coat of muscle cells and bundles of layers of contractile cardiac muscle fibres
What are individual muscle fibres in the myocardium surrounded by?
Delicate, collagenous connective tissue with a rich network of capillaries
Epicardium:
- What does it consist of?
- Where is it?
- A single layer of flattened epithelium called mesothelium, basal lamina, fibroelastic connective tissue and in some places, connective tissue
- On the surface of the heart
2 parts of the pericardium
Fibrous pericardium and serous pericardium
Fibrous pericardium
Sac of touch fibrocollagenous connective tissue
Serous pericardium
Simple layer of simple squamous epithelium backed by basal lamina and connective tissue
2 types of serous pericardium and what they cover
Parietal serous pericardium - lines inner surface of fibrous pericardium
Visceral serous pericardium - covers the surface of the heart
Fibrous skeleton of the heart:
- What is it formed by?
- Where is it?
- What does it do?
- Formed by thick bands of fibrous connective tissue
- Around the heart valves, between the atria and between the ventricles
- Supports the valves and provides attachment for the cardiac muscle fibres
Heart valves:
- Outer layer, middle layer and core
- Outer layer endothelial layer with basal lamina
- Layer of collagen and elastic fibres
- Core of dense connective tissue called lamina fibrosa that is in continuity with the fibrous skeleton
3 types of cardiac muscle cells
Contractile cells, pacemaker cells, conducting cells
What percentage of cardiac muscle cells are contractile cells?
99%
Functions of the fibrous skeleton
Provides physical support to the heart and electrically isolates the atria from the ventricles
Where are purkinje fibres found?
Subendocardial layer just deep to the endocardium
What do purkinje fibres contain?
Abundant glycogen, sparse actin and myosin filaments which tend to be found at the periphery of cell
What do purkinje fibres do?
Distribute excitatory activity such that ventricular contraction generally occurs from inferior to superior
Function of the lymphatic system
Drains excess interstitial fluid into the bloodstream
What does interstitial fluid contain?
Ions, lipids, protein and occasional cells
How is flow produced in lymphatic vessels?
Hydrostatic pressure within the tissue and compression of the tissue by voluntary muscle, combined with valves in the vessels, produce flow
