Lecture 9: Blood vessels 2 Flashcards
Describe the structure of the microcirculation:
- Arterioles (Distribution of blood)
- Terminal arterioles (SM layer)
- Metarterioles (Incomplete SM layer)
- Precapillary sphincter
What does the precap sphincter shut blood off to?
Prevents blood going to meta-arterioles or capillaries
= Travels throughfare channel to venule [Known as aterovenous anastomosis]
Describe the structure of capillary walls:
- Endothelium with basement membrane
- NO connective tissue or muscle
What are the different types of capillaries?
- Continuous (Endothelial cells form continuous sheet)
- > Closed intracellular clefts
- > Open intracellular clefts
- Fenestrated (Endothelial, perforated with small holes)
- > Closed perforations
- > Open perforations
- Sinusoids
Where are continuous endothelial cells with closed intracellular clefts found?
- CNS
- Forms impermeable BBB
Where are continuous endothelial cells with open intracellular clefts found? what can passage?
- Muscle, CT, lung etc
- Water, ions, small molecules
- NOT plasma proteins
Where are fenestrated endothelial cells with closed perforations found?
- Intestine
- Fenestrae have very thin membranous diaphragm
Where are fenestrated endothelial cells with open perforations found?
- Endocrine glands, kidney glomeruli, where water exchange is important
Whats the function of sinusoids?
- Wide bore caps
- Passage of large molecules and whole cells
Where do sinusoids occur?
- Bone marrow and spleen (RBC)
- Liver
How do sinusoids maximise exchange?
- The intracellular clefts
- Slow flow due to large lumen
Describe the structure of post cap venules?
- No smooth muscle
- Pericytes
- Accompany arteriole often.
- Drains cap bed
Whats the function of venules?
- During inflammation/allergic reaction histamine and serotonin increase leakage of blood plasma into tissue fluid (oedema)
- Also neutrophils into CT, and monocytes and lymphocytes.
Describe muscular venules?
- Up to 2 layers SM
- Thin walled in relation to lumen
- ENDOTHELIAL NUCLEI BULGE INTO LUMEN
Write some notes on veins:
- Same basic 3 layer structure
- Never well developed internal elastic lamina
- Thin walled
What are vein valves?
- Bicuspid
- Prevent backflow
- Made from folds of tunica intima
Why do legs veins have more SM?
When standing the pressure in legs can be huge thus more muscular
Why does venous thrombosis occur?
- Slow blood flow
- Increased coagulability
- Damage to epithelium
i.e surgery, childbirth, trauma, OC pill
Signs and symptoms of venous thrombosis?
- Swollen
- Red
- Painful
History
Whats the compression test for venous thrombosis?
Compress vein and then observe no flow
What is varicose veins?
- Superficial veins valves become incompetant
- Veins can become dilated, swollen and tortuous
What are the smallest lymphatic vessels?
- Lymphatic capillaries
= Blind ended endothelial tubes
Describe the structure of lymphatic caps?
- Endothelial cells
- Anchoring filaments (strands) help open clefts
How do lymphatic caps function?
- Endo tubes are tethered to surrounding CT by delicate anchoring filaments
- CT swells with fluid, anchoring filaments pull tubes open
- NO BASEMENT MEMBRANE (increases perm)
- LARGE GAPS b/w endo cells allows protein and cells to enter vessels
Describe large lymphatic vessels:
- Like veins but walls are thinner and more valves
- Lymph propelled by SM (stretch activated) and vasomotion
Are lymphatics everywhere?
No, i.e none in brain
Whats lymphoedema?
Lymphatic obstruction resulting in oedema
