AP BiologyAP Biology

Lab #10Physiology of

the Circulatory

System

Blood pressure is a measurement of the force applied to the walls of the arteries as the heart pumps blood throughout the body. Blood pressure is determined by the strength of contraction, amount of blood pumped into the arteries, the viscosity of the blood, and the size and flexibility of the arteries.

fluids exert fluids exert force force against against surfaces surfaces they come they come in contact in contact withwithhydrostatic pressure

fluids flow fluids flow from high from high pressure to pressure to areas of areas of low low pressurepressure

fluids fluids flow flow fasterfaster in in narrower narrower pipes… pipes…

than than wider wider pipespipes

BUT -even BUT -even though though capillaries are capillaries are

smallersmaller than than arteries; we arteries; we have have moremore capillaries capillaries

Therefore: Therefore: greater greater cross-cross-sectional sectional area of area of capillariescapillaries

ThereforeTherefore, , fluids flow fluids flow fasterfaster in in arteriesarteries than than capillariescapillaries

This is a This is a good thing, good thing, b/c gas b/c gas exchange exchange can take can take place in place in the the capillariescapillaries

Blood Blood exerts a exerts a pressure pressure against the against the

wall of wall of the vessel the vessel in which it in which it is flowing.is flowing.

At the arterial end of acapillary, blood pressure is

greater than osmotic pressure,and fluid flows out of the

capillary into the interstitial fluid.

CapillaryRedbloodcell

15 m

Tissue cell INTERSTITIAL FLUID

Capillary

Net fluidmovement out

Net fluidmovement in

Direction of blood flow

Blood pressure

Osmotic pressure

Inward flow

Outward flow

Pre

ssur

e

Arterial end of capillary Venule end

At the venule end of a capillary, blood pressure is less than osmotic pressure, and fluid flows from the interstitial fluid into the capillary.

Figure 42.14

• One type of cardiovascular disease, atherosclerosis– Is caused by the buildup of cholesterol within arteries

Figure 42.18a, b

(a) Normal artery (b) Partly clogged artery50 µm 250 µm

Smooth muscleConnective tissue Endothelium Plaque

90 or below is a normal

diastolic

reading

140 or below is a normal

systolic

reading

Cuff is wrapped around the upper arm & inflated until the pressure closes the brachial

artery

*No blood can now flow

past the cuff,

Pressure from cuff is higher than pressure in the artery

Stethoscope used to listen for the sound of blood flowing below the cuff

If artery is closed, no blood flowing… no sound.

Cuff is loosened until the blood can flow freely through the artery

You will hear the sound of blood pulsing into the artery

Pressure from blood is now greater than the pressure from the cuff

Cuff is loosened until the blood can flow freely through the artery

Sound below the cuff will disappear, pressure remaining in the artery when heart is relaxed.

Range depends on heredity, gender, environment

Range depends on heredity, gender, environment

Figure 42.9

Artery Vein

100 µm

Artery Vein

ArterioleVenule

Connectivetissue

Smoothmuscle

Endothelium

Connectivetissue

Smoothmuscle

Endothelium

Valve

Endothelium

Basementmembrane

Capillary

•All blood vessels

–Are built of similar tissues

–Have three similar layers

•Arteries have thicker

walls

–To accommodate the high pressure of

blood pumped from the

heart

• In the thinner-walled veins– Blood flows back to the heart

mainly as a result of muscle action

Figure 42.10

Direction of blood flowin vein (toward heart)

Valve (open)

Skeletal muscle

Valve (closed)