Microanatomy of vasculature Flashcards
Organization of tubular organ
- Tunica intima (endothelium and internal elastic lamina)
- Tunica media
- Tunica externa
Tunica intima
- Endothelium (simple squamous epithelium)
- Subendotheliual layer (collagen, elastic fibers)
- Internal elastic lamina/membrane- Absent in smaller veins, inconspicuous in larger veins, avascular)
Tunica media
- Smooth muscle cell layers- allows for contraction and dilation
- Collagen
- Elastic fibers- allows for expansion and return to normal
- External elastic membrane
Tunica externa/adventitia
- Collagen and elastic fibers
- Smooth muscle cells
- Vasa vasorum- vessels of vessels
- Nervi vasorum- nerves of vessels
Macrovasculature
- Elastic and muscular arteries
- Large, medium sized veins
Microvasculature
- Arterioles
- Capillaries
- Metarterioles- connects to venule
- Venules
Flow rate and size of vasculature
- Veins are slower and have larger diameter, arteries faster and more pressure, smaller
- Arteries are thick walled to withstand flow (high pressure), veins thin walled
Artery changes as you move further from heart
More circular arranged smooth muscle cells further from heart, less elastic
- But as vessels get smaller and smaller further away, there will also be less smooth muscle
Elastic Arteries
- Tunica interna= thick
- Tunica media
o Very thick
o Concentrically arranged fenestrated elastic lamina, with smooth muscle cells and collagen
o More ground substance - Tunica externa
o More collagen fibers
Muscular arteries
Change from elastic to muscular arteries can be abrupt or gradual
Tunica interna
- Endothelium
- Thin subendothelium (collagen and elastic fibers)
- Will thin out even more as vessel decreases
- Internal elastic membrane is thick and fenestrated
Tunica media
- Very thick with smooth muscles
- Elastic and collagen fibers
- External elastic membrane present
Tunica externa
- Collagen bundles, fibroblasts and elastic fibers
Arteriole
Last of the high pressure system of the body
Tunica interna
- Endothelium
- Thin subendothelial layer and a fenestrated internal elastic membrane that disappears in smallest arterioles
Tunica media
- Less than 3 layers of smooth muscle cells
- No external elastic membrane
Capillaries
- The capillary bed density indicates metabolic activity
- 5-10 micrometers (single RBC wide)
- Lined by endothelial cells, basal lamina, pericytes and a thin layer of adventitia
- Pre-capillary sphincters are also present
- No smooth muscle
What do brain capillaries not have?
Adventitial layer
Pericytes
Capillaries and postcapillaries are basal lamina-enclosed cells. Behaves like smooth muscle cells
Types of capillaries
- Continuous capillaries
- Fenestrated capillaries
- Porous capillaries
- Sinusoids
Continuous capillaries
- Ubiquitous
- Endothelial cells with tight junctions
- Few cytoplasmic organelles
- Vesicles used to get in and out
Fenestrated capillaries
- Common in gastrointestinal tract and endocrine glands
- Large diameter
- Fenestrae (small holes)- allows for fast input and output
Porous capillaries
- Areas where you need to remove a lot of fluid because has lots of holes
- Basal lamina is still continuous. So fluid still needs to go through this layer which allows for a certain amount of control to ensure that important component stay in capillaries
- Kidney glomerulus
Sinusoids
- Very large lumen
- Maximum exchange with surrounding parenchyma because it is broken/detached. Everything including cells can get out of vessels
- Liver parenchyma and spleen
Metarterioles
- Link artery to capillary
- Has sphincter (helps control flow)
- Near side of capillary bed
Thoroughfare channel
- Connects capillary to vein
- Far side of capillary bed
Continuous flow through capillary bed
Metarteriole and thoroughfare are continuous with each other
Sphincters of capillary beds
- When sphincters relaxed, blood flows all over the capillary beds.
- When sphincters contract, blood flow will go straight through from metarterioles and thoroughfare channel
Post-capillary venules
The most leaky blood vessel in the system. Will leak fluid when inflammation present and swelling is due to the leaky blood vessels!
Venules
- First venous channel that collect tissue fluid
- Incomplete tight junctions; leaky; important during inflammation, can have valves
Different Venules
- Post capillary veins (smallest)
- Pericytic venules
- Muscular venules
Small veins
Tunica media: 2-4 layers of circular smooth muscle layers
Medium veins
Satellite to muscular arteries
Tunica interna
- Endothelium
- Can have valves
- Very thin subendothelial layer of collagen and elastic fibers
- Internal elastic membrane may be present in larger veins
Tunica media
- Many layers of circular and some longitudinal smooth muscle cells
Tunica externa
- Predominantly collagenous
- Some longitudinal elastic fibers
Large veins
Structure similar to medium veins
Tunica media
- Thin compared to size of vessel
- Smooth muscle cells
- Collagen and elastic fibers
Tunica externa
- Thick
- Longitudinal/spiral smooth muscle bundles
- Collagen and elastic fibers
Specialized blood vessels
Special structures for specific functions
Thick walled (NO needed to open up)
- Teat (artery and vein)
- Veins in glans penis
- Coronary arteries
Decreased thickness
- Arteries of brain, bone and lungs
Circular sphincter like thickenings in tunica media
- Veins of large intestine, liver, and skin
Sensory receptors affecting vessels
Carotid body and carotid sinus have sensory cells that detect changes in blood vessels CO2 and O2 levels
Lymphatics
- Lymph capillaries
- Small and medium sized lymph vessels
- Large lymph vessels
- valves
Lymph capillaries
- Very thin endothelium
- Mainly present in loose connective tissue
- Junctional complexes are very weak and can create gaps allowing for easy entrance of fluids
- Outer surface of endothelium is connected to collagen and elastic fibers which helps keep the lumen open
- Absent in CNS, eyeball, bone marrow red pulp of spleen, liver lobule and tonsils
Small and medium sized lymph vessels
- Large diameter
- One or two layers of smooth muscle cells and elastic fibers
- Tunica externa is not distinguishable from surrounding connective tissue
Large lymph vessels
- Have tunica interna, tunica media, and tunica externa but they are not well delineated
- No internal elastic membrane
Lymphatic valves
- Present in all lymph vessels (but capillaries may not have them)
- Endothelial fold with very little connective tissue core
Layers of heart
- Endocardium
- Myocardium
- Epicardium
Endocardium
Lining of the inside of the heart
Composed of 3 layers
- Endothelium
- Inner subendothelial layer (dense CT with collagen and elastic fibers, some smooth muscle)
- Outer subendothelial layer (loose collagen, and elastic fibers, purkinje fibers, adipose tissue, lymph and blood supply)
Atrioventricular valves
- Collagen fibers predominate and connect with fibrous rings and chordae tendineae
- Central layer has elastic fibers
Semilunar valves
- Connective tissue fibers are circularly arranged
- Elastic fibers are thin towards the blood vessels and thick towards the ventricular surface
- Presence of loose connective tissue and cartilage makes the free edge thick
Impulse generation
Occurs at the sinoatrial (SA) node and atrioventricular node (AV)
SA node
- Network of thin branching nodal muscle cells, scarce muscle fibers, no intercalated disks
- Cardiac muscle
- Many autonomic nerve fibers
AV node
- Similar to SA node
- Nodal muscle fibers continuous with atrial myocardial fibers and impulse conducting cardiac fibers forming atrioventricular bundle
Myocardium
- Thickest layer of the heart
- Includes cardiac muscle, impulse conducting system, and cardiac muscle skeleton
Epicardium
- Covered externally by visceral pericardium
- Many elastic fibers that protect blood vessels and nerves
Pericardium
- Consists of thick layer of collagen bundles and elastic fibers covered with inner and outer mesothelial layers
- Space between visceral and parietal layers is pericardial cavity which contains serous fluid for easy movement of the heart
