Lecture 4: Histology and Biology of the Vascular System Flashcards
What is the gradient of blood flow?
Blood flow in the vasculature flows along a pressure gradient that gradually DECREASES
Cross section of aorta = 3 cm^2 …. SMALL
Cross section of capillary bed = 3000 cm^2 … LARGE
Where is blood flow fastest? Slowest?
Aorta
Gets slower as the individual vessels become progressively smaller but cross section gets collectively bigger
What is responsible for macrocirculation?
Arteries
Veins
What is responsible for microcirculation?
Arterioles
Capillaries
Venules
What is a tunica?
Coat or layer (intima, media, adventitia)
Applies to arteries/veins but not capillaries, which only have intima
Are lymphatics a circuit?
No, they are one way
In general, what is present in the tunica intima?
- ENDOTHELIAL CELLS
- basal lamina
- subendothelial loose connective tissue
- Internal elastic lamina (arteries and veins ONLY)
In general, what is present in the tunica media?
- Smooth muscle cells
- Elastic fibers (elastic art > musc art > veins)
- collagen
In general what is present in the tunica adventitia?
- External elastic lamina (arteries only)
- Smooth muscle cells (esp. larger veins)
- Loos connective tissue
- vasa vasorum
- nerves (nervi vascularis)
What is the source of basal lamina?
Whatever cell that it is attached to (ie endothelial cells)
What is the source of the internal elastic lamina?
Smooth muscle cells
What are the similarities between arteries and veins? Differences?
Similarities
i. have similar intima
ii. predominantely differentiated by features of media
iii. lesser differences in their adventitia
Differences
Arteries tend to have THICKER walls, relative to their luminal diameter than do corresponding veins
What is the only vessel that has external elastic lamina?
Arteries
What are elastic arteries? What is it composed of?
Helps propel blood during cardiac diastole to dampen difference between systolic and diastolic arterial pressure
Example: aorta and primary branches
Elastic fibers allow aorta to expand during systole, storing energy, which can then propel arterial blood downstream during ventricular diastole
“snap” back of fibers to relaxed means closure of A-V valves
What is the vasa vasorum?
A network of small blood vessels that supply the walls of large blood vessels
Vessels of vessels
What is the function of MUSCULAR arteries?
Control regional blood flow as needed
Regulated by varying luminal diameter and resistance to flow by contraction/relaxation
Controlled by autonomic nervous system and endothelium
What are the key characteristics of small arteries/arterioles?
Major determinant of arterial RESISTANCE to blood flow and therefore arterial blood pressure
Controls flow to microvascular bed
If you want to control local blood flow and BP, you turn to the arterioles ninja
How are the small arteries/arterioles regulated?
- autonomic nervous system
- angiotensin II
- endothelial factors
i. NO
ii. endothelin
iii. Prostacyclin - chemical environment including O2, CO2, pH, etc.
At what point do the vessels stop having 3 layers?
Capillaries
What are the characteristics of the capillaries?
Responsible for fluid, gas, electrolyte and small molecule exchange between blood and tissues
Comprised of very thin endothelial cells with a basal lamina
Pericytes may surround capillaries
Lacks media and adventitia!
What are pericytes?
Contractile cells that wrap around endothelial cells of capillaries
Aka Rouget or mural cells
What are the mechanisms of exchange between capillary lumen and extravascular space?
- Passive diffusion across the membranes and cytoplasm
- Active transport across membranes via pinocytic vesicles (w/ or w/o receptors)
- Passage between adjacent endothelial cells
What is the function of venules?
Controls permeability and leukocyte emigration
What are the key characteristics of venules?
Capacitance vessels readily distend and can store variable volume of blood
Site of egress of inflammatory cells from blood to tissues
What are the function of venous valves?
Endothelial covered semi-lunar flaps of INTIMA that protrude into venous lumen in direction of forward flow
What are the key characteristics of veins?
Tend to have thinner walls, esp media, and larger lumen compared to arteries
Have less muscle and elastic fibers in media
More easily stretched so can be capacitance (or
Storage) vessels for blood volume
have SEMILUNAR valves that prevent backflow
What are the three kinds of capillaries?
- Continuous capillaries
- Fenestrated capillaries
- Discontinuous capillaries