Structure of Blood vessels Flashcards
What is the function of elastic arteries?
To store blood during ejection and recoil during diastole to squeeze blood through.
What is in the tunica intima of elastic arteries?
Endothelium, some subendothelial connective tissue (contains some longitudinal elastic fibres)
Defined by the IEL (internal elastic lamina) but isn;t very distinguishable in elastic arteries
What is in the tunica media of EA’s?
Many lamellar units which comprise of elastic lamina (fenestrated), smooth muscle cells (produce elastin and collagen) and collagen.
What is in the tunica adventitia of the EA’s?
Collagen and elastic fibres as well as vasa vasorum and autonomic nerves.
What are the layers of a MA like?
TI: endothelium, basement membrane of endothelium, the CT and a distinctive IEL
TM: elastin for resiliency and collagen to prevent rupture but primarily smooth muscle cells. Ends at external elastic lamina
TA: vasa vasorum and CT
What are the two kinds of aneurysms?
Aneurysm is when blood bleeds into the TM due to a weakened TI
Berry aneurysm: common in the brain, if rupture cause stroke.
Dissecting aneurysm: common in AAA, can be a congenital wall weakness
What is seen histologically in hypertension?
Narrow lumen; duplicated IEL; thicker TM (more SM cells); TA thicker; large vessel wall to lumen ratio
What defines an arteriole?
An overall diameter of about 100 microns or less; 3 or less layers of smooth muscle in the TM; a wall thickness equal to that of the lumen.
Note all layer are present with an IEL, no EEl. In smaller arterioles no IEL. Largest pressure drop occurs here.
Describe the microcirculation
Arterioles-> terminal arterioles (1 layer)-> meta arterioles (dispersed)-> capillary bed through pre capillary sphincters or straight to the post capillary venules through thoroughfare channels (arteriovenous shunts) May also have arterioles straight to venules as a means of shunting blood.
When would flow be increased and when would shunting occur?
During digestion, pre capillary sphincters will be relaxed in the gut or during exercise in muscles.
Shunting is a means of directing large volumes of blood to where it more needed, so in the cold, shunting occurs on the peripheries. Also invloved in erectile function.
What are the three types of capillaries?
note that capillary diameters are abut 8-10 microns
Continuous (closed and open clefts)- closed clefts by tight junctions (blood brian barrier); open clefts in muscle and CT allow passage of water, ions but no proteins.
Fenestrated (closed and open perforations)- closed ones found in intestine that allow fluids, ions and some peptides across; open fenestrations found in endocrine glands and kidney.
Sinusoids: will allow large proteins and cells through these lare gaps, found in liver, spleen and bone marrow. Also intercellular clefts.
What are the two types of venules?
Post capillary venules- lack SM, ave pericytes. Will respond to histamine and serotonin, making the leaky to fluid. Leukocytes eg neutrohils will migrate.
Muscular venules- upto two layers of smooth muscle, thin wall to lumen ration. some collagen.
What are veins like structurally?
Similar to muscular arteries however thinner layers, particulalrly tunica media. Not a well developed IEL and have valves to prevent backflow (in foldings of TI).
Whats are diseases of veins?
venous thrombosis, a blood clot often in the lower leg. Can be due to slow blood flow, intreased coagubility or endothelial damage. (eg surgery, childbirth trauma, the pill). If the clot breaks loose, an embolus can be fatal.
Varicose veins, where veins become dilated and the valve cusps do not meet. The valves are thus incompetent leaving the veins swollen and tortuous.(more likely to affect women).
What is the structure of small and large lmyphatic vessels?
Small: No/thin basement membranes, gaps due to incomplete/no tight junctions and anchoring filaments to CT so that when tissue i swollen, pulls the endothelia meaning more leaky, more fluid goes on.
Large: some SM wrapped around that contracts in response to stretch. Not found in cartilage, CNS, bone etc.
