Lesson 3: Gas Exchange

Question 1

Gas
Exchange in
Humans

Answer 1

Gas exchange is divided into 4 stages:

Breathing

External Respiration

Internal Respiration

Oxygen and Carbon Dioxide
Transport

Question 2

Breathing

Answer 2

Breathing is the movement of air into and out
of the lungs

Breathing occurs in two phases:

Inhalation – the ribs are pulled up and out and the diaphragm is pulled
downward. The pressure within the chest cavity is reduced, forcing air to
rush down the passageway into the lungs, forcing the lungs to expand.

Exhalation – the diaphragm and rib muscles relax causing the ribs to drop,
making the chest cavity smaller. The pressure becomes greater, squeezing
the air out of the lungs.
Breathing is controlled by the respiratory center in the brain.

Chemoreceptors in the aorta and other large arteries sense the amount of
oxygen and carbon dioxide in the blood and send signals to the
respiratory centre

When carbon dioxide in the blood increases the chemoreceptors send
messages to the brain and the brain sends impulses to the diaphragm
and chest muscles to raise the rate and depth of breathing.

Question 3

External Respiration

Answer 3

External respiration is the exchange of oxygen
and carbon dioxide in the air and blood in the
lungs.

After inhalation the amount of oxygen in
the alveoli is higher than the amount of
oxygen in the blood

Oxygen dissolves in the walls of the
alveoli and diffuses from an area of
high concentration to an area of low
concentration.

Blood rich in carbon dioxide returns to the
lungs from the heart, the amount of carbon
dioxide in the blood is greater than the
amount of carbon dioxide in the alveoli and
diffusion occurs.

Question 4

Internal Respiration

Answer 4

Internal respiration is the exchange of oxygen and carbon dioxide between the blood in the capillaries and the body cells.

Oxygen diffuses from the blood through the
intercellular fluid into the body cells

Carbon dioxide diffuses form the body cells through
the intercellular fluid into the blood

Question 5

Oxygen Transport

Answer 5

Oxygen is carried from the lungs to the
body tissues by hemoglobin in the red
blood cells.

Hemoglobin (Hb) is a red, iron – containing
pigment that combines easily with oxygen.

In the lungs, Hb combines with oxygen
to form oxyhemoglobin. Oxygen rich
blood is red due to oxyhemoglobin.

When blood reaches the body tissues,
the oxyhemoglobin breaks into oxygen
and Hb. The blood is now low in oxygen
and is dark red or purple in colour.

Question 6

Carbon Dioxide
Transport

Answer 6

Carbon dioxide is carried in the blood to the lungs in 3 ways:

Most of the carbon dioxide that diffuses into the blood combines with water to form carbonic acid. The carbonic acid quickly breaks down into H+ ions and bicarbonate ions. These bicarbonate ions are
what is carried away in the plasma.

Some of the carbon dioxide that diffuses into the blood combines with Hb to form carboxyhemoglobin

A little of the carbon dioxide that diffuses into the blood is dissolved in the plasma

Question 7

Diseases of the
Respiratory System

Answer 7

Asthma – severe allergic reaction causing the
bronchioles to spasm

Bronchitis – bronchial tubes become swollen.

Emphysema – lungs loose elasticity – caused by
smoking

Pneumonia – alveoli fill with fluid

Lung cancer – tumors form on the lungs – caused
by smoking