Physiology- Skeletal Muscle Circulation

Question 1

Explain why under resting thermoneutral conditions blood flow per tissue mass is low

Answer 1

due to high resiting sympathetic tone causing vasoconstrition

Question 2

Skeletal muscle vascular supply characteristics

Answer 2

correlates to the metabolic and contractile characteristics of the muscle

Question 3

Skeletal muscle flow capacity

Answer 3

The maximum blood flow that can be delivered at a given perfusion pressure when the vessels are maximally vasodilated- indication of the amount that blood flow can be increased above resting levels

Question 4

Flow capacity is a function of what

Answer 4

the number, radius, and length of the blood vessels (i.e the vascular resistance) especialaly of small arteries and arterioles

Question 5

Compare the capacity of Red vs White muscle

Answer 5

In general red muscles possess a greater capacity for blood flow

Question 6

Capillary density

Answer 6

the number of capillaries per muscle cross sectional area. The GREATER the capillary density, the SMALLER the diffusion distance to the tissues

Question 7

Compare the capillary density of Red es White muscle

Answer 7

Red (slow twitch) have a high capillary density

Question 8

Purpose of torturoxity of capillaries

Answer 8

1.) increases the effective capillary surface area 2.) Provides collateral routes for flow 3.) protects capillaries from damage with lengthening

Question 9

Arteriovenous anastamoses

Answer 9

bypass the capillary bed and constitue NON-NUTRITIVE FLOW. During circulatory stress, flow appears to pass through these low resistance shunts without entering capillary circulation. May be the mechanism by which cholinergic stimulation increases muscle blood flow while actually decreasing oxygen extraction

Question 10

Compare muscle blooc flow under resting conditions to blood flow during muscular activity

Answer 10

Resting conditions: 20% of CO Muscular activity: up to 85% of cardiac output- CAPACITY TO INCREASE FLOW IS SUBSTANTIAL (UP TO 300 ML)

Question 11

Control of blood flow under resting conditions

Answer 11

Extrinsic influences predominate - Sympathetci Vasoconstriction (more HETEROGENEOUS capillary perfusion)

Question 12

Control of blood flow under muscular activity

Answer 12

Intrinsic influences predominate- local control - METABOLIC VASOREGULATION OVERRIDES THE EXTRINSIC INFLUENCES. Blood flow increases in proportion to muscle work. Increases capillary perfusion HOMOGENEITY

Question 13

Humoral control of blood flow

Answer 13

vascular smooth mucle pocesses B2 receptrs. Circulating epinephrine can cause vasodilation

Question 14

Passive Vasodilation

Answer 14

occurs when sympathetic input is decreased

Question 15

Relationship between sympathetic innervation of skeletal muscle and the Baroreflex

Answer 15

Skeletal muscle blood flow is a traget for the baroreflex- in response to hypotesion, sympathetic stimulation can markedly reduce muscle blood flow

Question 16

what is the primary mechanism of controlling muscle blood flow

Answer 16

release of lical intrinsic vasomotor factors - directly relax vascular smooth muscle (vasodilators)

Question 17

The magnitude of vasodilation and the increase in blood flow is proprotional to

Answer 17

the intensity of muscular work (oxygen consumption)

Question 18

Myogenic autoregulation

Answer 18

IMPORTANT IN INITIAL RESPONSE: causes vasoconstriction in response to sudden increases in pressure AND vasodilation in response to sudden decreases in pressure

Question 19

Endogenic regulation

Answer 19

increased flow increases the sheer stress along vessel walls which stimulates NO release (via NO synthase) resulting in vasodilation

Question 20

Role of intrinsic vasomotor nerves and gap junctions in local control

Answer 20

propagation of vasodilation and or vasoconstriction

Question 21

Exercise Hyperemia

Answer 21

Vasodilation increases muscle blood flow and results in capillary recruitement - increases the delivery of metabolic substrates and the removal of metabolic waste products

Question 22

List the mechanisms behind exercise hyperemia capillary recruitment

Answer 22

1.) more uniform (homogeneous) capillary perfuision (more capillaries have red cells flowing) 2.) Increased “effective” surface area that gets perfused 3.) Decreased diffusion distances 4.) Increased red cell flux (more red cells per unit of time)

Question 23

Describe the blood flow and the muscle pump

Answer 23

during contraction intramuscular pressure increases causing decreased blood flow (P-surround > P-in) During subsequent relaxation blood flow increases (P-in>P-surround) Muscle pump may be partially responsible for rapid increase in muscle blood flow that occurs within the first few secinds of the onset of muscle contractions