Cardiovascular System: Capillaries And Veins

Front 1

Defining characteristics of capillaries:

Back 1

-Very small
-Very thin walls – single thin endothelial cell
-Major site of exchange with tissues (some also in venules)
-Tremendous resistance, blood flows very slowly to facilitate exchange
-All cells in the body are near a capillary, but not always in direct contact

Front 2

Precapillary Sphincter:

Back 2

-small muscle at entrance to capillary regulates blood flow at local level

Front 3

Precapillary sphincter useful for:

Back 3

Small scale, local regulation of blood distribution

Front 4

Caveat:

Back 4

only small number of capillaries in a tissue open at any given time (5%)

Front 5

Why only 5% capillaries open?

Back 5

Capillaries “take turns” opening and closing because there's not enough blood in body to fill all the capillaries if they were open

Front 6

Exchange at the capillary: Two mechanisms

Back 6

1) Diffusion
2) Bulk Flow

Front 7

1) Diffusion:

Back 7

Mechanism of exchange of nutrients, gases and metabolic wastes between blood and cells
-Lipid soluble (O2, CO2) diffuse right through thin endothelial cells
-Water soluble substances diffuse through Capillary Pores: -Intercellular Clefts and Fused-vesicle Channels

Front 8

Lipid soluble:

Back 8

(O2, CO2) diffuse right through thin endothelial cells

Front 9

Water soluble:

Back 9

substances diffuse through Capillary Pores: -Intercellular Clefts and Fused-vesicle Channels

Front 10

2) Bulk Flow:

Back 10

movement of fluid in and out of capillary to regulate extracellular fluid

Front 11

Microcirculation and intercellular clefts:

Back 11

Note: (1) intercellular clefts between endothelial cells and (2) precapillary sphincters

Front 12

Capillary cross section:

Back 12

Note: (1) intercellular clefts between endothelial cells and (2) intracellular fused-vesicle channels (fenestrations)

Front 13

Bulk flow, two ___ pressures act on ___ in and out of capillary through pores:

Back 13

opposing, movement of fluid

Front 14

Hydrostatic Pressure:

Back 14

pressure applied to blood by heart, acts to move fluid OUT of capillary through Intercellular Clefts and Fused-vesicle channels

Front 15

Osmotic Pressure:

Back 15

-Capillary wall is a semipermeable membrane with respect to plasma proteins (especially albumin)
-Higher concentration of protein in blood tends to draw fluid INTO the capillary

Front 16

Bulk Flow at the capillary, Arteriole End:
___ Hydrostatic Pressure (heart)
__ Osmotic Pressure (__ plasma)
Fluid moves __ of capillary

Back 16

High Hydrostatic Pressure (heart)
Low Osmotic Pressure (dilute plasma)
Fluid moves OUT of capillary

Front 17

Bulk flow at the capillary, Venule End:
__ Hydrostatic Pressure (__ resistance)
High Osmotic Pressure (__ concentrated as fluid __)
Fluid moves ___ capillary

Back 17

Low Hydrostatic Pressure (capillary resistance)
High Osmotic Pressure (proteins concentrated as fluid moves out)
Fluid moves INTO capillary

Front 18

Net result is:

Back 18

slow circulation of fluid around capillary:
fluid leaves at the beginning of capillary but returns at its end

Front 19

Bulk flow in capillary:
Capillary-Tissue fluid exchange

Back 19

Blood pressure equal osmotic pressure, nutrients and wastes exchanged
Arterial end- BP greater than osmotic pressure, fluid moves into tissue
Venule end- osmotic pressure greater than blood pressure, fluid moves into capillary

Front 20

Veins Lead blood __ from capillaries (___)

Back 20

Lead blood away from capillaries (portal veins)

Front 21

___ blood in systemic circuit

Back 21

deoxygenated

Front 22

___ blood in pulmonary circuit

Back 22

oxygenated

Front 23

deliver blood ___ under ___ pressure

Back 23

rapidly, low pressure

Front 24

__ walls and __ resistance

Back 24

thin, low

Front 25

Need __ to ensure blood flows in proper direction

Back 25

valves

Front 26

Venous Pressure:

Back 26

Pressure from heart lost in capillaries
How is flow maintained in veins?

Front 27

Skeletal-muscle Pump:

Back 27

contraction of skeletal muscles applies pressure to veins, valves regulate direction of flow

Front 28

Respiratory Pump:

Back 28

expansion of chest cavity provides push-pull pressure

Front 29

How does blood speed up in the veins when pressure is dropping?

Back 29

-First, remember flow is determined by difference in pressure not absolute pressure
-Second, must consider change in total cross-sectional area of the circulatory system