Histology of the Circulatory system Flashcards
Name the 2 division of the circulatory system
- Cardiovascular system
- Lymphatic system
List the roles of the cardiovascular system
- Transporting nutrients and oxygen to tissues
- Transporting CO2 and waste away from tissues
- Temperature regulation
- Distribution of hormones
and immune cells - Reproductive function (penile erection)
List the 3 layers of a blood vessel and describe their layering
- Tunica intima (innermost)
- Tunic media (middle)
- Tunica adventitia (outermost)
Describe the tunica intima
Innermost layer
Consists of:
- Single layer of squamous epithelial cells (endothelial cells)
- Supported by a basal lamina
- Thin layer of connective tissue (internal elastic lamina)
Describe the tunica media
Middle layer
The layers thickness varies greatly in different vessel types
Consists of:
- Mainly smooth muscle
- Some elastic fibres (external elastic lamina)
- Can have lots of elastic fibres (e.g. elastic arteries)
Describe the tunica adventitia
Outer layer
Consists of:
- supporting connective tissue
Describe the:
- Internal elastic lamina (membrane)
- External elastic lamina (membrane)
Internal elastic lamina (membrane):
- outermost bit of the tunica intima
- separates the intima from the media
External elastic lamina (membrane):
- outermost bit of the tunica media
- separates the media from the adventitia
Describe elastic arteries
The largest arteries (e.g. aorta)
- Have many sheets of elastic fibres in their tunic media
- These provide elastic recoil, maintaining MAP during diastole
Describe arterioles
Only have 1 or 2 layers of smooth muscle in their tunica media
Have almost no tunica adventitia
Describe capillaries
Consist of:
- Endothelial cells
- Basal lamina
- Pericytes
Describe a pericyte
- Connective tissue cells
- Wrap around the outside of the basal lamina
- Have contractile properties
List the 3 types of capillary
- Continuous
- Fenestrated
- Discontinuous (sinusoidal)
Describe continuous capillaries
Where are they found?
- No gaps in endothelium
- Basal lamina complete
- Found in muscle, skin, lung, nervous and connective tissues
Describe fenestrated capillaries
Where are they found?
- Small pores in endothelium
- Basal lamina complete
- Found in gut mucosa, endocrine glands, and kidney glomeruli
Describe discontinuous (sinusoidal) capillaries
Where are they found?
- Large gaps in epithelium that macromolecules (sometimes cells) can fit through
- The basal lamina is discontinuous or absent
- Found in liver, spleen, and bone marrow
Describe microvascular networks and their structure
Connect small arterioles with small venules
Made up of:
- Metarterioles
- Capillary bed
- Thoroughfare channels
Describe metarterioles and their structure
Links arterioles with capillaries
- Has no continuous tunica media
- Has a precapillary sphincter
Describe a precapillary sphincter and its structure
Individual smooth muscle cells (close together)
Found in metarterioles
Controles blood entrance to the capillary bed
Describe the thoroughfare channels found in microvascular networks
A direct channel that connects a metarteriole to a venule
- has capillaries surrounding it
Describe a postcapillary venule
Consist of:
- Endothelial lining
- Thin layer of connective tissue
- Pericytes (sometimes)
Capillary networks drain into post-capillary venules
(important site for diapedesis)
Describe venules and their structure
Consist of:
- Endothelial lining
- Thin layer of connective tissue
- Pericytes (sometimes)
- Tunica media that contains myocytes
Describe veins and their structure
Consist of:
- Tunica intima
- Tunica media (much thinner that that in arterioles)
- Tunica adventitia
Describe the tunica adventitia found in the largest veins (e.g. vena cava)
Very thick
Bundles of longitudinal smooth muscle
Describe the composition of venous valves
- In most small to medium sized veins
- Are extensions of the tunic intima
List the 3 layers of the heart
Endocardium (inner)
Myocardium (middle)
Epicardium (outer)
Describe the structure of the endocardium
Endothelium --> Basal lamina --> Thin layer of collagen fibres --> Denser layer of connective tissue
Describe the subendocardium and its structure
In some areas there is also a subendocardium
Consists of loose connective tissue containing:
- small blood vessels
- nerves
- branches of the impulse conducting system (e.g. Purkinje fibres)
Describe the structure of the myocardium
Thick central layer of heart
- Bundles and layers of contractile muscle fibres
- Individual fibres are surrounded by a collagenous connective tissue with capillaries
Describe the surroundings of individual muscle fibres
each fibre is surrounded with a delicate collagenous connective tissue
This supports a rich capillary network
Describe the nuclei found in contractile cardiac myocytes
They have a small central nucleus (sometimes 2)
Unlike skeletal myocytes
Describe the intercalated discs between cardiac myocytes
Boundary between cardiac myocytes
Have:
- Gap junctions (for transmitting impulses)
- Desmosomes (for attaching cells together)
- Zonula adherens (for attaching cells together)
Describe the contractile cardiac myocytes found in the myocardium
- Large cells
- Uninucleate (sometimes 2 nuclei)
- Some have branches
- Attached via intercalated discs
Describe the structure of the epicardium (serous visceral pericardium)
A single layer of simple squamous epithelium (mesothelium) --> basal lamina --> Fibroelastic connective tissue --> adipose tissue (in some places)
Describe the structure of the pericardium
Fibrous pericardium:
- Sac of fibrocollagenous connective tissue
Serous pericardium:
- single layer of simple squamous epithelium (mesothelium)
- ->
- basal lamina
- ->
- connective tissue
In what layer of the heart do the coronary arteries and veins flow?
Epicardium
In the adipose tissue deep to the mesothelium, basal lamina, and connective tissue
Describe the fibrous skeleton of the heart
- Made of bands of connective tissue
- Supports the valves
- Electrically insulates the atria and ventricles
- Supports myocardium
Describe the histology of the heart valves
A core lamina fibrosa:
- dense irregular connective tissue
- is continuous with the fibrous skeleton
The lamina fibrosa is covered on both sides by endothelium:
Endothelial layer --> Basal lamina --> Collagen and elastin fibres
Is there a vascular supply to the heart valves?
No
What do the chordae tendineae attach to?
on one side the papillary muscles
on the other they merge with the lamina fibrosa of the valve
List the 3 types of cardiac myocyte
- Contractile cardiac myocytes
- Pacemaker cells
- Conducting cells
Describe pacemaker cells
- Much smaller than contractile cardiac myocytes
- appear paler
- very few myofibrils
- Found in AV and SA nodes
Describe Purkinje fibres
- Larger than contractile cardiac myocytes
- In subendocardium
- No intercalated discs
- They are NOT nerves
Describe lymph vessels
- This walled
- Walls a bit like those of a vein
- drain some of the ECF and return it to circulation
- transport lymphatic fluid
- passes through lymph nodes
Describe what makes lymphatic fluid move
- Skeletal muscle movement
- pressure from incoming fluid
