Microanatomy Flashcards
Function of left ventricle
Pump
Mean pressure of left ventricle
95 mmHg
Structural features of left ventricle
Thick, muscular walls
Inlet and outlet valves
Large artery function
Elastic and pulsatile
Storage
Resists flow
Pushes blood forward
Mean pressure of large arteries
95 - 85 mmHg
Structural features of large arteries
Muscular walls to control diameter and connective tissue for strength
Medium artery function
Muscular
Blood distribution
Mean pressure of medium arteries
95 - 85 mmHg
Structural features of medium arteries
Muscular walls to control diameter and connective tissue for strength
Arteriole function
Microcirculation
Major method of control and fine tuning
Diverts and flushes blood
Mean pressure of arterioles
85 - 35 mmHg
Structural features of arterioles
Smooth muscle to control diameter with little connenctive tissue
Other microcirculation artery structures
Metarterioles
Precapillary sphincters
Function of capillaries
Gas exchange
No flow control
Mean pressure of capillaries
35 - 15 mmHg
Structural features of capillaries
Endothelium
No muscle or connective tissue
Function of venules
Large volume reserve
Fluid exchange
Mean pressure of venules
15 - 0 mmHg
Structural features of venules
Thin walls, large diameter
Structural features of veins
Thin walls, variable structure
Valves to assist return
Structural features of right atrium
Thin, muscular walls
Percentage of blood in venous system
70%
6 key elastic arteries
Aorta Subclavian Left carotid Brachiocephalic Pulmonary Iliacs
Tunica intima of elastic arteries
Thicker than in muscular arteries
Up to 20% of wall
Longitudinal elastin fibres in subendothelial connective tissue
Internal elastic lamina present but indistinguishable from elastic laminae
Tunica media of elastic arteries
Lamellar units made up of elastic lamina (fenestrated), smooth muscle and collagen fibres
Circular orientation around vessel
Tunica adventitia of elastic arteries
Collagen and elastin fibres
Small blood vessels (vasa vasorum)
Autonomic nerves
Tunica intima of muscular arteries
Four layers:
1) endothelium
2) basement membrane of endothelium
3) subendothelial connective tissue
4) distinctive internal elastic lamina
Tunica media of muscular arteries
Middle, thickest coat
Smooth muscle fibres control diameter
Elastin fibres give resiliency
Collagen fibres limit expansion and prevent rupture
Outer margin can include external elastic lamine - not as prominent as internal
Tunica adventitia of muscular arteries
Usually only collagen and elastic fibres
Vasa vasorum to service outer layers
4 key risk factors for arterial disease
Sedentary lifestyle
Diet high in saturated fat
Alcohol
Smoking
Berry aneurysm
Weakening of tunica media of artery
Usually in the brain
Risk increases with age and blood pressure
Atherosclerosis
Tunica intima starts to thicken, internal elastic lamina breaks down
Lipids increase
Endothelium is activated
Macrophages are recruited
Macrophages accummulate into foam cells
Foam cells aggregate into plaques
Smooth muscle activates and invades tunica intima
Atherosclerotic plaque with fatty streaks and cholesterol slits narrows lumen of vessle, causes change in flow, disrupts homeostasis
Can break off and embolise, or collagen caps can form around it making it more stable
Dissecting aneurysm
As plaque develops, tunica media thins out, causing it to rip
Common in abdominal aorta
4 key modifications in hypertension
Tunica intima thickening
Internal elastic lamina duplication
Increase in smooth muscle layers which increases peripheral resistance
Increase in density and thickness of tunica adventitia which increases collagen fibres
Arteriole key features
Less than 100 microns in diameter
Three or fewer layers of smooth muscle in tunica media
Wall thickness about equal to lumen
Intima comprised of endothelial cells overlying a basal lamina
Internal elastic lamina present in large arterioles
Thicker muscle coat in media than any other vessel
Greatest pressure drop of all vessels
Variation in diameter has pronounced effect on blood flow
The microcirculation pathway
Arteriole Terminal arteriole Splits into metarteriole and pre-capillary sphincter Continues into thoroughfare channel Capillary bed Post-capillary venule Continues into muscular venule Lymph capillaries dotted throughout
Arteriovenous anastomoses
When an arteriole leads directly to a venule without any capillaries arising from it as side branches
If their muscle coats are relaxed they allow blood to shunt directly from the arterial to the venous system
If their muscle coats contract then blood is forced into nearby metarterioles and then into capillary beds which they supply
Pre-capillary sphincter
Controls entry of blood from arteriole into capillary
When closed, blood is directed via a thoroughfare channel to a venule, bypassing the capillary bed
3 types of capillaries
Continuous
Fenestrated
Sinusoids
Continuous capillaries
Tight junctions and intercellular clefts which can be closed or open
Found in blood brain barrier, muscle, connective tissues and lungs
Allow passage of water, ions and small molecules but not plasma proteins
Fenestrated capillaries
Either closed or open perforations
Closed by thin, non-membranous diaphragms
Common in intestines, endocrine glands and kidneys
Sinusoids
Wide-bore capillaries with large gaps between edges of adjacent endothelial cells
Gaps allow easy passage of large molecules and whole cells
Found in bone marrow, spleen and liver
Postcapillary venules
Drain capillary beds
Lack smooth muscle but do have pericytes
During inflammation and allergy leak blood plasma into surrounding tissue causing oedema
Muscular venules
Large
Up to two layers of smooth muscle in tunica media
Thin wall in relation to diameter
Endothelial nuclei that bulge into the lumen
Pericytes
Contractile cells that wrap around endothelial cells in capillaries and venules
Varicose veins
Visible pooling of blood in the legs due to incompetent valves in superficial veins
Venous valves
Infoldings of tunica intima
Prevent backflow
Bicuspid
Venous thrombosis
Blood clot forms normally in deep veins of lower leg
Part of clot can break loose and embolise which is likely to pass through right heart and lodge in pulmonary arterial tree
Risk factors for venous thrombosis
Surgery Childbirth Trauma The pill Sitting still for a long time
Function of venous valves in legs
When walking, valves break up column of blood into segments with each segment experiencing only tjhe gravitational pressure proportional to its height, then bolus is pushed up by skeletal muscle compression on the veins
Lymphatic capillaries
Blind-ending endothelial tubes
Endothelial cells tethered to surrounding connective tissue by delicate anchoring filaments
No basement membrane
Large intercellular clefts
Collecting lymphatics
Larger lymphatic vessels that lymphatic capillaries drain into
Thin walls and lots of valves
Eventually enter a lymph node
Lymph enters into bloodstream via thoracic duct and right lymphatic duct
