Muscle and skin blood flow

Question 1

Skeletal muscle - special tasks

Answer 1

Enhanced flow during exercise

Modulation of artetial pressure

Question 2

Skeletal muscle - structural adaptations

Answer 2

Type I red fibres - slow oxidative fatigue resistant fibres.
Type IIa red fibres - fast oxidative fatigue resistant fibres
Both contain large amounts of myoglobin, many mitochondria, many blood capillaries, found largely in postural muscles.
Type IIx/IIb white fibres - phasic, fast twitch, fatiguable
Contain low myoglobin, few mitochondria and few capillaries.

Question 3

Skeletal muscle - functional adaptations

Answer 3

Arterioles are richly innervated by sympathetic vasoconstrictor fibres, constituitively active.
Flow rises almost linearly with metabolic rate.
Variable oxygen extraction.
Skeletal muscle pump.

Question 4

Skeletal muscle - special problems

Answer 4

Mechanical interference - muscular contraction impairs blood flow by compressing intramuscular vessels.
Increased capilary function during exercise - loss of plasma volume and Can affect BP.

Question 5

Cutaneous circulation - special tasks

Answer 5

Temperature regulation
Key factor in control of heat loss and production.
Role in regukation of bp - as it is involved in many cv reflexes.

Question 6

Cutaneous circulation - structural adaptations

Answer 6

Arterioles - some basal tone, autoregulate

Arterio-venous anastomoses in acral skin, sympathetic innervation, no autoregulation.

Question 7

Cutaneous circulation - functional adaptations

Answer 7

Sensitivity to ambient temperature - local heating of skin causes dilation of cutaneous blood vessels, skin reddens due to infrease of oxigenated blood in dermal venular plexus, heat loss is enhanced.
Local cooling causes vaso/venoconstriction
Mechanism - decreased temp = increased alpha2 affinity for NA causing vasoconstriction.

Question 8

Paradox of cold induced vasodilation

Answer 8

Initial cold induced vasoconstriction gives way to vasodilation after 5-10mins, occurs in regions rich in AVAs. Thought to be due to temporary impairment of NA transmission and release of vasodilators to prevent skin damage jn prolonged exposure to cold.

Question 9

Regulation of cutaneous perfusion by the hypothalamic temperature regulating centre (HTRC)

Answer 9

Hypothalamic neurones regulate brainstem neurones that control sympathetic vasomotor discharge to the skin (blood vessels / sweat glands)

Question 10

Cutaneous perfusion - special problems

Answer 10

Compression when weight bearing -impedes flow leading to ischemia, most ischemic damage prevented by high tolerence of skin to hypoxia.
Hot weather - cutaneous vasodilation increases local capillary filtration, local oedema.