Notes – Pressure & the Body

Chapter 10, Lesson 2

What is Pressure?

• Pressure is the amount of force per unit area.• Many different units are used to measure pressure:

– mmHg (millimeters of mercury) for blood pressure– psi (pounds per square inch) for tire pressure– Pa (Pascals) for scientists and engineers

Deflated tire with very low pressure

Inflated tire with full

pressure

Changing Pressure

• Pressure increases as you increase the amount of force applied to a constant area.

Changing Pressure

• Pressure increases as you decrease the size of the area to which a constant force is applied.

Changing Pressure

• The equation for finding pressure is:

(m2)

Pressure in the Pulmonary System• When you inhale, air is pulled into your lungs, not

pushed.• The volume of the lungs is expanded, and the

pressure in the alveoli decreases.

Pressure in the Pulmonary System

Pressure in the Circulatory System• Without pressure, blood vessels would not be able

to transport blood to all tissues.

Pressure in the Circulatory System• The heart is a muscle that contracts.• When the heart contracts, the volume inside the

chamber decreases.• Blood is forced out of the chamber and the chamber

gets smaller.

Pumping in One Direction• It is important for blood to move in one direction as

the heart pumps.• The contractions of the heart muscles create areas

of greater and lesser pressure, pumping blood through the heart.

Pumping in One Direction• Valves open and close and also contribute to the

different pressures in the chambers.

Pumping in One Direction

Pumping in One Direction• The tricuspid valve separates the right atrium from

the right ventricle.

Pumping in One Direction• The bicuspid valve separates the left atrium from

the left ventricle.

Pumping in One Direction• The pulmonary valve prevents blood from flowing

back into the heart as it exits to go to the lungs.

Pumping in One Direction• The aortic valve prevents blood from flowing back

into the heart as it exits to go to the body.

Pumping in One Direction

Pumping in One Direction• Continuous surges keep the blood moving through

the arteries.

Blood Pressure• This is pressure that is exerted by the

blood against the walls of blood vessels.

• It is caused by the force with which the ventricles contract.

• Expressed as 2 numbers:

120 / 80

pressure whileventricles areclosed

pressure whileventricles relax

Problems with Blood Pressure• Hypertension is a dangerous rise in

blood pressure caused by blockages in or the hardening of blood vessels.

• Hypertension is a disease caused by genetic and environmental factors.

Normal

Atherosclerosis

Stress Inactivity

Problems with Blood Pressure• Shock is a condition in which a

large amount of blood is lost, usually in a short period of time.

• Under some circumstances such as internal bleeding, blood leaves the vessels and blood pressure decreases.

• The heart is not able to pump blood to all tissues without pressure.

How is blood pressure measured?

A millimeters of mercury

B pounds per square inch

C grams per square millimeter

D pascal

10.1 Pressure and the Body

When is air pulled into the lungs?

A when pressure in the alveoli increases

B when the pressure in the lungs is lower than atmospheric pressure

C when the chest cavity contracts

D when the diaphragm moves upward

10.1 Pressure and the Body

Which of the following does not contribute to hypertension?

A genetics

B a diet high in cholesterol

C lack of exercise

D a diet low in salt

10.1 Pressure and the Body

How have you changed the pressure on your body if you change your position from lying down to standing up?

A increase in the amount of force applied

B increase in the size of the area to which a force is applied

C decrease in the amount of force applied

D decrease in the size of the area to which a force is applied

What is shock?

A hardening of the blood vessels

B internal bleeding

C loss of blood and blood pressure

D a genetic and environmental disease

What prevents the backflow of blood?

A contractions of the heart muscle

B the atria

C valves

D constant pumping

SCI 6.j