CVS- Types of Vessels Flashcards
What are the three things diffusion is affected by?
Area available for exchange
Movement through barrier (resistance)
Concentration gradient
How does blood exchange with tissues?
At capillaries via diffusion
How is the area available for exchange determined?
By capillary density (how many per unit volume)
Highest in metabolically active tissues.
How is resistance through a barrier determined?
Nature of the barrier (diffusion distance) and types of molecule diffusing
What type of molecules are O2 and CO2?
They are lipophilic so easily pass through capillary membrane
How is concentration gradient determined?
Affected by flow of blood
Fast flow maintains conc gradient but must be slow enough to allow exchange.
What kind of blood supply does the brain require?
A constant Hugh blood flow
0.5ml/min/g
What blood flow does the heart require at rest?
And at working hard?
At rest high 0.9ml/min/g
But at work this can increase 4x
What blood flow does the kidney require?
Constant high supply needed
3.5ml/min/g
How much blood does the CVS as a unit need to deliver to the whole body?
5-25l/min-1
What is the form of blood storage (or capacity) in the CVS
The veins
What is the distribution of blood in the CVS (as figures)
67% veins
11% arteries
5% capillaries
17% heart and lungs
What is the rate of blood flow known as?
Perfusion rate
Where is blood flow fastest?
Where total surface area is smallest
What are the features of arteries?
They carry blood away from the heart
Some are elastic, some are muscular
They have a thicker wall and narrower lumen than veins
Describe the anatomy of an elastic artery?
These are the widest artery (e.g aorta, PA)
The tunica intima - has endothelial cells with axes in parallel (to reduce friction) it also contains internal elastic lamina
The tunica media - smooth muscle cells and collagen, thin external elastic lamina
Tunica adventitia - thin layer of fibroelastic CT containing vasa vasorum (blood vessels), lymph vessels and nerves
Describe the features of muscular arteries
They are narrower than elastic ones
The tunica intima - endothelium + thick internal elastic lamella
Tunica media - 40 layers of SM. Cells connected by gap junctions to allow for coordinated contraction
Tunica adventitia - thin layer of fibroelastic CT
Explain how vasoconstriction occurs in muscular arteries
Noradrenaline realised at nerve endings diffuses through fenstratioms in external lamina into tunica media.
Depolarisation is propagated to all cells via gap junctions.
What are end arteries?
Name an example
These are the terminal arteries that supply blood directly to a body part.
E.g coronary arteries
What are arterioles?
Arteries with a diameter >0.1nm
Only 1-3 layer of SM
EEL is absent
They direct blood flow by vasoconstriction/dilation
What are metarterioles?
These supply blood to capillary bed.
Smooth muscle is not continuous
What are precapillary sphincters?
This is when the smooth muscle on the arteriole is present at the endothelium of the capillary only.
When contracted this prevents blood flow to the capillary bed.
What a capillaries?
These are narrow vessels (7-10um)
Allowing for the diffusion of metabolic substrates from blood.
What are the 3 types of capillary?
Continuous
Fenestrated
Sinusoidal
What are the features of continuous capillaries?
Most common type
Present in nervous, muscle and connective tissue
Continuous endothelial layer - cells joined by occlusion junctions
Features of fenestrated capillaries …
Little windows (interruptions) across thin parts of endothelium Bridged by a thin diaphragm Present in parts of the gut, endocrine glands etc
Features of Sinusoidal capillaries…
Larger in diameter
Caps exist in walls allowing while cells to move between blood and tissue .
Liver, spleen and bone marrow
What are venules?
These are post capillary transport vessels
As they increase in size they gain smooth muscle layer
Describe features of veins?
Small and medium veins have well developed adventitia but thin initial and media.
Large veins have thick intima and well developed longitudinal muscle in adventitia.
Superficial veins of the leg have a well defined muscular wall to resist distension caused by gravity.
What is a venae comitantes?
Deep paired veins accompanying arteries
3 vessels one sheath
