Vessel I Flashcards
What do arterial vessels do and what do they lead to?
Carry blood away from the heart
Aorta -> Arteries of decreasing size -> arterioles
What is microcirculation and what is its path?
Regulates blood flow in and out of capillary beds - metarterioles and postcapillary venules
2-way fluid exchange with tissues - capillaries
Metarterioles -> capillaries -> tissue -> postcapillary venules
What do venous vessels do and what is their path?
Carry blood towards the heart
Venules -> veins of increasing size -> SVC/IVC
What are the 3 layers of blood vessels?
Tunica intima
Tunia media
Tunica externa
What is the function and structure of tunica intima?
Endothelium lines vessels - interface in direct contact with bloodstream
Subendothelial CT anchors endothelium to rest of vessel
Internal elastic lamina
What is the structure and function of the tunica media?
Middle, muscular layer
Smooth muscle and elastic CT allow the vessel to change its lumen diameter in order to restrict or accommodate volume of blood flowing through it
External elastic lamina
What is the structure and function of the tunica externa?
Outer layer or tunica adventitia
Connects/anchors vessels to surrounding tissues
Protective pathway for smaller vessels and nerves that supply the vessel wall
CT with collagen and elastic fibers
Blood vessels and nerves that supply the vessel wall run in this layer
What forces occur to vessels and affect their structure?
Distance from heart
Blood pressure
Blood flow (speed and direction)
What are the components of the tunica externa?
CT layer - mostly collagen I fibers, elastic fibers, fibroblasts, white fat cells
Blood vessels and nerves - present in all arteries/veins > 1mm diameter, vasa vasorum, nervi vasorum
Merges with loose CT surrounding vessels
What are the components of the tunica media?
Mostly smooth muscle cells in concentric layers - lumen diameter changes when smooth muscle cells in the media contract or relax
Variable # of elastic lamellae (concentric sheets of elastin) and elastic fibers
External elastic lamina (EEL) - thicker sheet of elastin outside the tunica media, fenestrated that allow nervi and vasa vasorum to contact media
What are the components of the tunica intima?
Endothelium - simple squamous epithelium + BM
Subendothelium - mostly loose CT fibroblasts, few smooth muscle cells
Internal elastic lamina (IEL) - thicker sheet of elastic outside tunica intima, fenestrated so aids in diffusion from lumen to tunica media and allows endothelial cells to contact smooth muscle cells in tunica media
What lines the lumen in all blood vessels?
Simple squamous epithelium called the endothelium - endothelial cells and tunica intima
What is the benefit of the long axis of endothelial cells being parallel with the direction of blood flow?
Streamlining reduces the amount of shear stress experienced by endothelial cells as blood flows over them
What are the functions of the endothelium?
Maintain structural integrity of the endothelium
Coordinate endothelial cell activities
Maintain a selectively permeable barrier
Regulate inflammatory and immune cell traffic
Regulate vessel formation during angiogenesis
Modulate smooth muscle activity, which determine vessel diameter and vascular resistance to blood pressure/flow
Regulates thrombus function
How does the endothelium maintain structural integrity?
Junctional complexes
Hemidesmosomes and focal adhesions
How does the endothelium coordinate endothelial cell activities?
Gap junctions
How does the endothelium maintain a selectively permeable barrier?
Regulate access to paracellular pathway
Exchange of gas and nutrients across the endothelium via pinocytotic vesicles, receptor mediated endocytosis, active transport, and diffusion
Surface receptors - for histamines, LDL, insulin
How does the endothelium regulate inflammatory and immune cell traffic?
Endothelial cells extend cell adhesion molecules that can bind specific WBCs
WBCs then work with endothelial cells to unlock cell junctions
How do WBCs get access to underlying tissues?
- Macrophages release cytokines in response to stimulus
- Endothelial cells extend CAMs
- Circulating neutrophil binds CAMs, rolls along endothelium surface
- Neutrophil expresses integrins
- Integrins bind receptors in endothelium and junctions unlock
- Neutrophil enters underlying CT between endothelial cells
How do endothelium modulate smooth muscle activity?
Myoendothelial junctions
Secreting chemicals that promote vasoconstriction
Secreting chemical that promote vasodilation
What is secreted to promote vasoconstriction?
Endothelins - promote smooth muscle contraction
What is secreted to promote vasodilation?
NO and prostacyclin both promote smooth muscle relaxation
What is the myoendothelial junction?
Physical connection between an endothelial cell (intima) and a smooth muscle cell (media)
Endothelial cell extends a cellular process through BM and IEL (fenestrated)
Myoendothelial junctions contain many many gap junctions
What does increased shear stress also stimulate besides vasodilation?
NO production by endothelial cells
How does the endothelium regulate thrombus formation?
Thrombus - clot that forms in a vessel and stays there
Release anticoagulants - prevent fibrinogen from being converted into fibrin
Release antithrombogenic substances - interfere with platelet aggregation (prostacyclin)
Release thrombolytic substances - break down clots (tissue plasminogen activator)
What is released when a vessel is torn?
Endothelial cells release prothrombogenic substances that promote formation of protective clots, which seal tears and prevent blood loss (von Willebrand factor and other clotting factors)
What are Weibel-Palade bodies?
Membrane-bound organelles unique to endothelial cells
Store von Willebrand factor and some proteins that mediate immune/inflammatory responses
After vessel injury, fuse with cell membrane and secrete that factor
What is von Willebrand factor?
Prothrombogenic glycoprotein that promotes platelet adhesion
What is different between arteries and veins in regards to walls and lumens?
Arteries have thicker walls and smaller lumens vs veins of same external diameter
Arteries need thicker walls to deal with high BP and need more smooth muscle to control blood flow and resist pressure of blood on arterial walls
List the arteries in order from largest diameter to smallest diameter.
Elastic (large) arteries
Muscular (medium) arteries
Small arteries
Arterioles
Metarterioles
Capillaries
What are the elastic arteries and their function?
Aorta and its main branches
Transport large volumes of blood away from the heart
Ability to stretch accomodates large changes in blood volume and BP between systole and diastole
What is the structure of elastic arteries?
Subendothelium - some smooth muscle cells
Tunica media - alternating layers of smooth muscle and elastic lamella
Tunica externa - type I collagen
What are muscular arteries?
Distributing arteries that control the distribution of blood to major body regions
What is the structure of muscular arteries?
Subendothelium - few smooth muscle cells, IEL prominent
Tunica media - elastic lamellae less prominent, EEL often prominent
Tunica externa - relatively thick
What are small arteries?
Smaller distributing arteries that control the distribution of blood to smaller body regions
What is the structure of small arteries?
Subendothelium - IEL usually present
Tunica media - 3-10 layers of smooth muscle, no elastic lamellae, EEL not usually visible
Tunica externa - thin, no vasa or nervi vasorum
What are arterioles?
Main resistance vessels in circulation
Very vasoactive - constantly dilating or constricting
Greatly influence volume of flow to a localized area
What is the structure of arterioles?
Subendothelium - very little
Tunica media - 1-2 complete layers of smooth muscle
Tunica externa - functionally absent, no vasa or nervi vasorum
Where does most vasoconstriction occur?
Happens in Arterioles
Vasoconstriction
Of Arterioles is stimulated by sympathetic (vasomotor) nerve fibers that discharge norepinephrine
Diffuses to smooth muscle in tunica media and causes contraction
Vasodilation
Parasympathetic nerve fibers stimulate the arteriole’s endothelium to release NO
Diffuses to smooth muscle in tunica media and induces relaxation
