Ch. 15 - Blood Flow and the Control of Blood Pressure

________ have the thickest walls.

Arteries

________ have the thinnest walls.

Capillaries

_________ have the widest lumens.

Veins

_________ have the most smooth muscle.

Arterioles

Arteries act as a...

pressure reservoir that maintains blood flow during ventricular relaxation

Veins serve as a...

expandable volume reservoir

Arterioles

site of variable resistance (because of smooth muscle); resistance changes result in flow changes

Capillaries

smallest vessels; primary site of exchange between blood and interstitial fluid; precapillary sphincters open and close to direct blood flow to capillaries or venous circulation

Venules

receive blood from capillaries; convergent pattern of flow

Veins

take blood back to the heart; contain one-way valves that prevent backward flow; more numerous than arteries and lie closer to the body surface

Angiogenesis

development of new blood vessels; necessary for normal development and wound healing; controlled by cytokines (angiogenic and antiangiogenic); regulating angiogenesis could prevent disease

Pulse Pressure

measure of the strength of the pressure wave produced by ventricular contraction; decreases over distance due to friction

Pulse pressure = systolic pressure - diastolic pressure

Venous return is aided by...

valves, skeletal muscle pump, and respiratory pump

Mean arterial pressure (MAP) is estimated as...

diastolic pressure + 1/3(systolic pressure - diastolic pressure)

If flow into arteries exceeds flow out, then arterial blood volume ____________ and MAP _____________.

increases; increases

If flow out of arteries exceeds flow in, then arterial blood volume _____________ and MAP ______________.

decreases; decreases

Blood volume is relatively ___________.

constant; some gain and loss throughout the day (if volume decreases, pressure decreases and vice versa)

Arteriolar resistance is influenced by both _______ and ______ control mechanisms.

local and systemic; local control of arterial resistance, sympathetic reflexes, and hormones (particularly those that govern water and salt excretion in the kidneys)

Myogenic Autoregulation

vascular smooth muscle has the ability to regulate its own state of contraction

In the absence of autoregulation, an increase in ______________ increases blood flow through an arteriole.

blood pressure

How does myogenic autoregulation work at the cellular level?

When vascular smooth muscle cells in arterioles are stretched, mechanically-gated Ca2+ channels in the muscle membrane open, causing a contraction

Blood distribution varies according to...

metabolic need of individual tissues; governed by local control mechanisms and homeostatic reflexes

Active Hyperemia

The process in which an increase in blood flow accompanies an increase in metabolic activity

Reactive Hyperemia

an increase in tissue blood flow following a period of low perfusion (blood flow)

Cardiovascular Control Center (CVCC)

ensures adequate blood flow to the brain and heart by maintaining sufficient mean arterial pressure

Baroreceptor Reflex

responsible for homeostatic control of blood pressure

Baroreceptors

stretch-sensitive mechanoreceptors in carotid arteries and aorta; produce continuous (tonic) action potential to brainstem; changes in pressure reflected changes in frequency of action potential

Exchange between plasma and interstitial fluid occurs by...

paracellular transport (movement between endothelial cells) and endothelial transport (movement through the cells)

Larger solutes and proteins move mostly by...

vesicular transport; in most capillaries, large molecules (including selected proteins) are transported by transcytosis

Small dissolved solutes and gases move by ___________ between or through the cells, depending on their lipid solubility and concentration gradient.

diffusion

Bulk Flow

mass movement of fluid as the result of hydrostatic or osmotic pressure gradients

Filtration

fluid movement out of capillaries; caused by hydrostatic pressure; IF hydrostatic pressure is neglible

Absorption

fluid movement into capillaries; caused by colloid osmotic pressure (also called oncotic pressure)

Net pressure determines...

direction of bulk flow; net filtration of arterial end (hydrostatic pressure > osmotic pressure); net filtration at venous end (osmotic pressure > hydrostatic pressure)

Colloid Osmotic Pressure

contribution of protein to blood osmotic pressure