CASE 3 Flashcards
Blood vessels
three major types
- arteries
- capillaries
- veins
Arterioles
smallest branch of arteries, which feed into the capillary beds of body organs and tissues
venules
blood drains from the capillaries into the venules, smallest veins
wall has three layers (tunics)
- tunica intima
- tunica media
- tunica externa
the vessel lumen
central blood-containing space
tunica intima
- closest to lumen
- contains endothelium
- minimizes friction as blood moves through the lumen
tunica media
- middle tunic
- mostly smooth muscle and sheets of elastin
- can cause vasoconstriction of vasodilation, maintain blood pressure and circulation
tunica externa
- loosely woven collagen fibers, protect and strengthen and anchor it to surrounding structures
- contains nerve fibers, lymphatic vessels (and elastic fibers in bigger vessels)
vasa vasorum
- tunica externa of bigger vessels contain the vasa vasorum
- system of tiny blood vessels
- nourish the tunica externa
Three types of arteries
- Elastic arteries
- Muscular arteries
- Arterioles
Elastic arteries
- thick-walled near the heart
- also called conducting arteries
- inactive in vasoconstriction
- expand and recoil as the heart ejects blood
- blood flows continuously
muscular arteries
- elastic arteries turn into muscular arteries
- deliver blood to specific organs, also called distributing arteries
- thickest tunica media
- active in vasoconstriction and less capable of stretching
arterioles
- very small ones contain one layer of smooth muscle cells
- constrict: tissues served are largely bypassed
- dilate: blood flow into the local capillaries increases dramatically
Three types of capillaries
- continuous capillaries
- fenestrated capillaries
- sinusoid capillaries
Capillaries
- smallest blood vessels
- thin layer of tunica intima
pericytes
- smooth muscle- like cells that stabilize the capillary wall and help control capillary permeability
continuous capillaries
- abundant in skin and muscle
- their endothelial cells are joined by tight junctions
- gaps of unjoined membrane: intercellular clefts, allow limited passage of fluids and small solutes
fenestrated capillaries
- endothelial cells are riddles with oval pores, fenestrations
- more permeable to fluids and small solutes
- they are found wherever active capillary absorption on filtration occurs
sinusoid capillaries
- most leaky capillaries
- found in liver, bone marrow, spleen and adrenal medulla
- fewer tight junctions, larger intercellular clefts
- allow blood cells to go out of the membrane
capillary beds
capillaries work in networks called capillary beds.
- consist of two types of vessels
1. vascular shunt
2. true capillaries
microcirculation
flow of blood from arteriole to venule, through capillary beds
vascular shunt
directly connects arteriole and venule at opposite ends of the bed
a. metarteriole: from terminal arteriole to middle of capillary bed
b. thoroughfare channel: from the middle of the capillary bed to the postcapillary venule
true capillaries
- exchange vessels
- branch of the metarteriole and return to the thoroughfare channel.
- precapillary sphincter, a cuff of smooth muscle fibers, acts as a valve to regulate blood flow into the capillary
Venous system
- carry blood from capillary beds to heart
- diameter increases and walls thicken along the way
Venules
- postcapillary venules consist of endothelium around which pericytes gather.
- PC venules are porous; fluid and leukocytes can move easily
- larger venules have one or two layers of smooth muscle cells and a thin tunica externa as well
Veins
- venules join to form veins
- have 3 distinct tunics
- tunica media has little smooth muscle and elastin
- tunica externa, has collagen fibers and elastin networks.
- hold up to 65% of blood supply at any time.
- blood pressure is low to ensure that blood enters the heart at the same rate it was pumped out
venous valves
- formed from folds of tunica intima
- prevent blood from flowing backwards
venous sinuses
- flattened veins with extremely thin walls composed of only endothelium
vascular anastomoses
- special interconnections
- arteries supplying the same territory merge forming arterial anastomoses.
- collateral channels for blood to reach a given body region that can be used when one branch is cut or blocked.
Blood distribution
- nervous system can alter blood flow to organs
- varies according to metabolic needs of organs
Flow through individual arterioles
depends on their resistance and pressure difference. The higher the resistance in arteriole, the lower the blood flow.
- The higher the difference in pressure, the higher the fluid flow
- The lower the resistance, the higher the fluid flow
this is ohm’s law
cardiovascular control center
- The CNS coordinates the reflex control of blood pressure and distribution of blood to tissues, regulated by medulla oblongata
- ensure sufficient blood flow to the brain and heart by maintaining arterial pressure
Cardiovascular function is regulated by
- baroreceptors: maintain arterial blood pressure
- chemoreceptors : increase cardiac output and breathing rate
exercise on pressure volume loop
- small increase in end-diastolic volume because increased venous return to the heart
- decrease end-systolic volume, because of sympathetic activation of the heart which increases ventricular contration
Pulse pressure
difference between diastolic and systolic pressure
mean arterial pressure (MAP)
pressure that propels blood to the tissues
Three adaptations for venous pressure
- muscular pump
- respiratory pump
- sympathetic venoconstriction
muscular pump
- skeletal muscle, during movement, pushes blood in the desired direction
respiratory pump
- moves blood towards heart as pressure changes in ventral body cavity during breathing
sympathetic venoconstriction
- reduces the volume of blood in veins
Short term regulation blood pressure
by nervous system and bloodborne hormones alter by changing peripheral resistance and cardiac output
long term regulation blood pressure
alters blood volume via the kidneys
