Blood vessels Flashcards
Distinguish between micro and macrovasculature
Micro: <0.1mm e.g. arterioles, capillaries, venules
Macro: >0.1mm e.g. arteries and veins
What is meant by a portal system?
Blood carried from one capillary bed to another through
What constitutes a portal venous system?
Both capillary beds and blood vessels connecting them
2 examples of portal systems?
Hepatic portal system (GI tract to liver)
Hypothalamic pituitary system (hypothalamus to anterior pituitary)
Features of arteries?
Thick muscular walls
Branch into arterioles
Round in histological section
What is the role of the thick walls of the arteries?
Facilitate constriction and dilation to modulate blood pressure and flow
What do capillaries do?
Distribute blood from arterioles throughout tissue (important exchange unit)
What are features of capillaries?
Thin wall (one endothelial cell thick)
Don’t contract
Only have endothelium
Describe course of veins from capillary bed
Drain capillary bed as venules, these converge to form veins carrying blood to heart
What are features of veins?
Valves prevent retrograde flow/back flow
Some vascular smooth muscle (not as much as arteries)
Usually less circular/collapse in a section
Contraction of surrounding skeletal muscle aids venous return
What aids venous return to heart?
Valves prevent back flow
Contraction of surrounding skeletal muscle aids venous return
What are the 3 layers of walls of arteries and veins?
Tunica intima (endothelium)
Tunica media (muscular tissue/elastic)
Tunica adventita (connective tissue)
Which layers are more developed in arteries than veins?
Tunica intima and media
Endothelium is what sort of epithelial layer?
Squamous
What is tunica intima composed of?
Single layer of squamous epithelial cells and basal lamina
Sub endothelial layer contains connective tissue and internal elastic lamina
What separates tunica intima and media?
Internal elastic lamina of tunica intima
What layer of blood vessel is thickest?
Tunica media
What is tunica media composed of? (how is this different in large small arteries) (3)
Smooth muscle cells around lumen (in smaller arteries)
Replaced by elastic in elastic (larger) arteries
Type 3 collagen and proteoglycans dispersed within layers.
External elastic lamina
What separates tunica media and tunica adventitia?
External elastic lamina of tunica media
What is tunica adventitita composed of?
Fibroelastic connective tissue (fibroblast, type 1 collagen, elastic fibres, small blood vessels) arranged longitudinally with adipose tissue.
Blends with surrounding connective tissue
How is the fibroelastic connective tissue arranged in the tunica adventitia?
Longitudinally
True or false, external elastic lamina of tunica media is always distinguishable
False
Where are internal elastic lamina and external elastic lamina found?
Tunica intima
Tunica media
When is internal elastic lamina not visible?
Tunica media is muscular (smaller arteries)
Where is tunica media not found?
Capillaries
Post capillary venules
What is the blood supply to walls of large arteries and veins from?
Vasa vasorum
What are vasa vasorum?
Small arteries entering and branching to supply walls of large arteries and veins
What cells do vaso vasorum supply?
Tunica media and adventitia
Why are vasa vorum prevalent in veins?
Blood contains less oxygen and nutrients, less received through diffusion
Classify arteries by size (3 sizes)
Largest: Conducting arteries = elastic (elastic layers in tunica media + muscle)
Middle: distributing arteries = muscular (smooth muscle in tunica media)
Arterioles
Give examples of elastic arteries
Pulmonary artery and aorta
How do walls of aorta and pulmonary artery look, why?
Yellow, abundant elastin.
Wall has thick layer of elastic (concentric layers) occupying most of tunica media
What is benefit of elastic arterioles?
Stabilise blood flow and maintain arterial blood pressure
How does composition of arteries change the further away from heart?
Less elastin and more muscular tunica media
Give examples of muscular arteries?
Most vessels arising from aorta e.g. femoral
Are elastic or muscular arterioles thicker?
Elastic
What does muscular artery allow?
Selective distribution of blood to different organs and muscle tone to maintain blood pressure
What type of cells support microvasculature?
Smooth muscle cells around arterioles, venules and small veins (discontinuous)
Pericytes
What is the function of pericytes?
Support and stabilise arteries and veins
Regulate vascular tone
Its processes wrapped around capillary endothelium
What is unique about pericytes?
Are plastic and can differentiate to fibroblast, SMC and macrophages
Describe diameter of arterioles
<0.1mm
How many layers of SM do arterioles have?
1-2
What does arteriole control, how?
Distribution of blood to whole capillary beds, through sympathetic autonomic nerves
What are pericytes sensitive to?
Low oxygen
What are pre-capillary sphincters?
Band of SM that adjust blood flow into capillary bed
What are precapillary sphincters controlled by?
Local metabolic products
3 types of capillary
Continuous, fenestrated, discontinuous (sinusoidal)
Describe dimensions of capillary?
50 micrometer length, 8-10 micrometer diameter
Describe structure of capillaries
Squamous epithelium (endothelium) walls only one cell thick
Pericytes outside regulate blood flow
Posses no smooth muscle
Where are continuous capillaries found?
Skin, muscle, lungs, nerve tissue (i.e. where no need for protein passage)
Describe feature of continuous capillaries in terms of pores, how come?
No pores in their walls - have junctional complexes so tight control of trans endothelial transport
Describe permeability of continuous capillary
Moderate
How can substances move across continuous capillary?
Active transport, diffusion
Do capillaries exhibit vasomotor activities?
No
Describe structure of fenestrated capillaries, including size of pores.
60-80nm pores, bridged by diaphragm
What is a diaphragm (fenestrated capillary)?
Diaphragm consists of radially oriented fibrils that allows small molecules and limited amounts of protein to diffuse.
What is fenestrated capillary permeable to?
Small ions and proteins
Where are fenestrated capillaries found?
High water turnover tissue and where protein passage needed
E.g. kidney, synovial joint, intestine, pancreas, , endocrine glands, anterior eye
Describe sinusoidal capillaries structure
Discontinuous epithelial cells
Large fenestrae without diaphragm (30-40 micrometer)
Describe permeability of sinusoids
Permeable to proteins and cells (e.g. RBCs)
Where are sinusoids found?
Bone marrow, liver, spleen , lymphoid organs
What is the glycocalyx?
Structure made of GAGs that exists inside of the endothelium on the lumenal side
What forms around the gylcocalyx and why?
GAGs have many negative charges (heavily sulfated) collect Na+ ions which lowers the water potential around the calyx, leading water to gather around to form a gel like substance.
How much of the capillary lumen does the glycocalyx cover?
~1/10th
Compare the connective tissue components of arteries and veins
More pronounced in veins
Describe the boundary between tunica intima and media in veins
Not clear
Describe structure of venule walls
Similar to capillaries, thin endothelium surrounded by reticular fibres and pericytes
What forms the valve in veins?
Folds of the tunica intima
Describe structure of medium veins
<1cm
SMC of tunica media loosely organised with collagen fibres and fibroblasts
Tunica adventita is thickest layer (contains collagen and elastic)
Describe diameter of arterioles and medium vein lumen
Medium vein lumen wider
Describe structure of large veins in terms of layers
Tunica media thin
Tunica adventitia well developed
