Blood vessels and hemodynamics Flashcards
Differentiate between arterioles, veins and capillaries
Arterioles = blood away from the heart
Veins = blood towards the heart
Capillaries = directly serve cells
What is the tunica intima?
Innermost layer found in both veins and arteries
Composed of:
- endothelium
- subendothelial layer → thicker in veins compared to arteries
- internal elastic membrane → present ONLY in arteries
Between veins and arteries, which contains an internal elastic membrane within the tunica intima? Why is this important?
Found only in arteries
- Arteries are stretchy at early parts where blood is pushed out ∴ this helps to allow elasticity and stetch with recoil
- This applies for the external elastic membrane found within the tunica media which is also only found within arteries
What is the tunica media?
Middle layer found in both veins and arteries
Composed of;
- smooth muscle and elastic fibers
- external elastc membrane (only found in arteries)
Smooth muscle = helps regulate diameters (for contraction/dilation)
- can also infleunce where the blood is going at any moment in time
What is the tunica externa?
Outermost layer found in both veins and arteries (outer wrapping)
Composed of;
- collagen fibers = anchoring the blood vessels
- vasa vasorum
What are some key characteristics about veins that arteries dont possess?
Veins have;
- thinner walls
- more room to accomodate blood
- larger lumens
- valves = keeps blood from backing up on itself
Recall; veins bring blood back towards the heart
What are the structures contained within a capillary?
- Basement membrane
- Endothelial cells
Very thin barrier to allow for better exchange
What are the 3 types of arterial vessels?
1) Elastic (conducting) arteries
2) Muscular (distributing) arteries
3) Arterioles
Describe elastic arteries
- Thick walled
- Large diameter arteries near heart
- highest proportion of elastin
Functions;
Smooth out pressure fluctuations, this recoil helps maintain pressure and flow of blood
Describe muscular arteries
- Smaller diameter branches
- Delivers blood to specific organs
- more smooth muscle than elastin
This is so that they can open up more when blood is needed and close more when its not needed
There is only a finite amount of blood, so choices must be made to accomodate the greatest needs of blood in the body
Describe arterioles
- Tunica media primarily smooth muscle - this is a single layer in smallest arterioles
Arterioles determine which capillary beds are flushed minute to minute
What are the 3 types of capillaries?
Walls are only a thin tunica intima as the function of capillaries is exchange
1) Continuous capillaries
2) Fenestrated capillaries
3) Sinusoidal capillaries
Describe continuous capillaries
- found in skin, muscles, brain
- endothelial cells are linked by tight junctions providing an uninterrupted lining
- except in CNS - here there are intercellular clefts that allow limited passage of fluids, small solutes (ions)
Least leaky
Describe fenestrated capillaries
- Similar to continuous but endothelial cells are riddled with pores (fenestrations) allowing for increased permeability to fluids/small solutes
- found in small intestine (digestion), endocrine organs (protein hormones), kidney (filtration and reabsorbtion)
Fenestrations = direct openings for larger molecules such as proteins
Descibe sinusoidal capillaries
- highly modified leaky capillaries
- found in liver, bone marrow (where RBCS and WBCs are made so that they can be sent out), lymphoid tissues, endocrine organs
- Have large irregular lumens and are usually fenestrated with fewer tight junctions
- large intercellular clefts for passage of proteins, RBCs
What is microcirculation?
Flow of blood from an arteriole to a venule through a capillary bed
- this flow is regulated by the diameter of the terminal arteriole
What are veins vs venules?
Venules;
Post capillary venules = just endothelium few fibroblasts
Larger venules have a couple of layers of smooth muscle and a thin tunica adventitia
Vein;
3 tunics but walls are thinner and lumers larger
Less smooth muscle in tunica media (compared to corresponding artery) and minimal elastin
Tunica adventitia is heaviest layer
Up to 65% of blood in veins at one time (at rest) = capacitance vessels (blood reservoirs)