Chpt 14 Sec D
ARTERIES - highly elastic, large radii; low resistance; pressure reservoir
Compliance - how much a structue may be stretched
Arterial Blood Pressure avg S/D 125/75 mm Hg
Max - systolic pressure - peak ventr ejection
Min - diastolic pressure - just before ventr ejection
Magnitude of this ratio affected by -
stroke vol
speed with which stroke vol exits ventr
compliance
MAP (mean arterial pressure) driving force thruout cycle
Arterioles - contribute to MAP; regulate flow into individual organs;
have increased resistance since smaller radius
F organ = MAP / Resistance organ
Change resistance via vasoconstriction and vasodilation
Local controls for self-regulation F 39
Sensitivity to metabolites, oxygen and bl pressure-->
response is active hyperemia - incr. bl flow
(dilation) to affected organ or
tissue [ex. to muscle when exercising]
Flow autoregulation [ex. local constriction of
vessel and decreased flow to
organ result in local dilation to restore flow]
Paracrine hormones - endothelium-derived relaxing
factor; endothelin-1 are
Constrictors
Extrinsic controls - NS and hormone F 40
Summary **F 41
Organ-specific control Table 8
CAPILLARIES
Only 5% of bl vol but 90+% of function of cardiovasc syst.
Blood enter capillary beds via metarterioles; have precapillary sphincters
which control
entry to and exit of blood from cap.
Capillaries are tubes only one cell thick resting on basement membrane
Endothelium - squamous (flattened) cells
Cells may divide to produce new vessels - angiogenesis
Cells may have intercellular clefts (spaces) between them as well
as
fused-vesicle channels where endo and exocytosis occurs
fairly rapidly
D2
Flow rate of bl thru caps very slow due to enormous area; although
resistance is high in a cap, total area of cap beds compensates so that
total resistance is less than for arterioles
Materials cross endothelium via
Diffusion - nutrients, gases, metabolic by-products
water moves freely and solutes travel with it
regulated by lipid-solubility and movement thru clefts
large clefts in liver - permit passage of plasma prots
very limited in brain - receptor-mediated transport required
Vesicle transport - mostly prot transport
Bulk flow - maintenance of extracellular fluid
Magnitude of BF determined by difference between cap bl
pressure and
interstitial fluid hydrostatic pressure ** F 46
Filtration - movement out of capillary into IF
diff between cap hydrostatic pressure and IF hydrost.
pres.
hydrostatic pres varies according to organ, activity,
physiological reg.
Absorption - movement from IF into cap
diff in water conc between the 2
Net filtration pressure - algebraic sum of these 4 variables
[Starling forces]
VEINS and VENULES
Return blood to heart; valves in peripheral veins
Contain largest portion of total blood volume
Low resistance, high compliance; low pressure
Sympathetic innervation/stim of smooth muscle causes constriction,
raising pressure
and assisting flow toward heart
Venous return also assisted by skeletal-muscle pump and respiratory
pump
LYMPHATIC SYSTEM
Returns interstitial fluid to cardiovasc circ.
Lymphatic vessels with small amt of smooth musc
Sk-musc and resp pumps
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Sec E Homeostasis - Cardiovascular system
Reflex control system [Ch 7] review
1] internal variable to be maintained; 2] receptors sensitive to
changes in variable;
3] afferent pathway from receptor; 4] integrating center for
receipt and processing of
inputs and initiation of response; 5] efferent pathway to
carry response/output;
6] effector to modify variable
Purpose - CVS provides for exchange of blood constituents with body organs
Variable - mean arterial pressure (MAP) in systemic circ [**F54 summary
of reg. factors]
MAP = CO x TPR [total peripheral resistance]
Receptors - baroreceptors on carotid sinuses, aortic arch, pulmonary
vessels,
systemic veins, walls of heart
Firing rates proportional to MAP and pulse pressure
Afferent paths to brain
Integrating center - medullary cardiovascular center in medulla oblongata
Efferent paths to
parasympathetic neurons of heart
sympathetic neurons to heart and vessels
Effectors: cardiac muscle; smooth musc of vessels
**Fig 59 Ex. of regulation - loss of vol and pressure due to hemorrhage
------------------------
Sec F self-study
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Sec G Clotting
Stoppage of bleeding - hemostasis
small vessels - local constriction
Permanent closure of larger vessels requires 2 successive events
Formation of platelet plug
Clotting
Sequence of events F 69-71
Platelet plug
Rupture of endothelium exposes collagen fibers in surrounding
connective tissue
Plasma prot. (vWF) binds to collagen and then to platelets
Platelets activated to release stored chemical mediators [and to syn
and release
other mediators]
More platelets adhere to collagen and to older platelets ->
platelet plug
Plug expansion restricted by NO and PGI2 , secreted by endothelium,
which inhibit
platelet aggregation
Clotting - cascade of events, including plasma enzyme activations,
leading to
elaboration of fibrin protein which traps cells to form a
thrombus ** F 71