Lecture 23 Cardio 3 (2) Flashcards Preview

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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

If TPR decreases

CO increases to maintain MAP