Flashcards in Lecture 23 Cardio 3 (2) Deck (20)
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1
Control of blood flow to the tissues
Intrinsic control - metabolic
Extrinsic control -autonomic & hormones
2
Intrinsic Control
metabolic control - repsonse of vascular smooth muscle to local chemical changes due to metabolism
hyperemia and ischemia
3
Hyperemia
increase in blood flow to tissue in response to increase metabolic demand
4
Ischemia
insufficient (reduction) blood flow to tissue
5
Perfusion
blood flow to tissue or organ
6
Extrinsic control
Autonomic NS
sympathetic NS: NE -> a1 adrenergic receptors -> vasoconstriction in most tissues
this reduces blood flow
no dual innervation
7
Extrinsic control
Hormones
Epi -> B2 adrenergic receptors -> vasodilation in skeletal muscles
ADH (vasopressin) -> vasoconstriction in most tissues
Paracrine regulators:
nitric oxide (NO) -> vasodilation
Prostaglandins -> vasodilation or vasoconstriction
8
Capillary Circulation (Microcirculation)
Flow through capillary beds
Exchange across capillary walls
Filtration and reabsorption
9
Flow through capillary beds
blood flow (perfusion) through capillaries is highly variable
regulated by: arteriolar smooth muscle (vasoconstiction/vasodilation), precapillary sphincters
10
Exchange across capillary walls
capillaries interstitial fluid
fluid and substance exchanged across endothelium via diffusion, transcytosis, and bulk flow
11
Bulk flow across capillary walls - Filtration
filtration out of a capillary - driven mostly by blood pressure in the capillary bed (BPcap)
12
Bulk flow across capillary walls - Reabsorption
reabsorption back into capillary - driven mostly by colloid osmotic pressure (COP)
(oncotic pressure) which is due to plasma proteins (albumin) that stay in capillaries
COP = 25 mmHg
13
Filtration and reasborption is determined by
the balance between BP and COP in the capillary
14
Net filtration pressure
arteriole end vs venule end
NFP = BPcap - COP
at arteriole end: BPcap > COP -> NFP is positive -> filtration
at venule end: BPcap < COP -> NFP is negative -> reabsorption
total filtration exceeds reabsorption by approx. 2-3 L/day
excess interstitial fluid is collected by the lymphatic system and returned to veins
15
Edema
results when filtration >> reabsorption
16
Histamine
local vasodilator
increases capillary permeability, plasma proteins leak out
17
high arterial BP
can increase BPcap slightly, regualted by local vasoconstriction
18
high venous BP (back pressure)
increases BPcap, hard to regulate
e.g. venous obstruction, congestive heart failure
19
Atherosclerosis
fatty deposits in arterial wall
carried by LDL
20
