GAS EXCHANGEIN HUMANS

The Human Respiratory System

The human respiratory system is made up of lungs and a system of air tubes that carry air to and from the lungs.

LUNGS are the gas exchange organs in air-breathing vertebrates and in some other animals.

DIAPHRAGM is a muscle that forms the floor of the chest cavity

PLEURA each lung is covered with a two-layered membrane called pleura.

The Human Respiratory System

Air passes through;

The nose Pharynx Larynx Trachea

Bronchi

Bronchial tubes

Bronchioles

Alveoli

THE NOSE:

•air enters through nostrils

• the spaces in the nose are called nasal passages

• hairs stop foreign substances from entering

• the wall of the nasal passages are covered with;

Mucous membrane Cells that have cilia

moistens air They both trap bacteria, dust, and particles

The Human Respiratory System

THE PHARYNX:

• from the nasal passages, air travels through the pharynx (throat)

• it connects the nasal cavity and oral cavity to larynx

• tonsils form a protective barrier at the junction of pharynx and oral cavity

The Human Respiratory System

THE LARYNX: (VOICEBOX)

• it is mainly made up of cartilage

• vocal cords are two pairs of membranes streched across the inside of the larynx

• as air is breathed out, the vocal cords vibrate

The Human Respiratory System

Epiglottis:

To prevent chocking during swallowing food and liquids are blocked from entering the opening of the larynx by the epiglottis.

The Human Respiratory System

TRACHEA:

• is made up of smooth muscle, cartilage and mucous membrane

• it’s always open by cartilage rings

• inside of it is lined with ciliated mucous membrane

The Human Respiratory System

BRONCHI:

• in the middle of the chest cavity, trachea branches into two bronchi.

• they are made up of cartilage and lined with ciliated cells.

• when they enter the lungs, they form the bronchial tubes

BRONCHIOLES:

• the bronchial tubes divide and subdivide, finally they become a group of tiny tubes called bronchioles

The Human Respiratory System

ALVEOLI:

• each bronchiole ends in a tiny air chamber that looks like a cluster of grapes

• each chamber contains several cup-shaped cavities called alveoli

• the walls of the alveoli is only one cell-thick and they are the respiratory surface

• they are moist and surrounded by large no. of capillaries

• the exchange of O2 and CO2 between air and blood takes place through the capillaries.

The Human Respiratory System

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Gas Exchange in Humans

Gas exchange in humans can be divided into 4 stages;

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

*External respiration is the exchange of O2 and CO2 between the air and the blood

in the lungs

*Internal respiration is the exchange of O2 and CO2 between the blood and the body cells

*O2 and CO2 transport is the movement of gases between the lungs and other body parts

DURING INHALATION (INSPIRATION)DURING EXHALATION

(EXPIRATION)

The diaphragm muscles contract and pull it downThe diaphragm muscles relax, allowing the diaphragm to return to its domed shape (upward-arched)

The intercostal (rib) muscles contract and pull the rib cage up and out.

The intercostal (rib) muscles relax, allowing the ribs to move downwards under their own weight.

Chest (thoracic) cavity volume increases Chest (thoracic) cavity volume decreases

Pressure in the cavity decreases as (compared to atmosphere)

Pressure in the cavity increases (as compared to atmosphere)

Air is sucked into the respiratory tract & lungs Air is forced out through the system.

AN ACTIVE PROCESS A PASSIVE PROCESS

Control of Breathing

Breathing is mostly involuntary and it’s controlled by respiratory center in the brain.

When [CO2 ] increases in blood

Chemoreceptors on aorta and some arteries detect changes

Respiratory center in the brain is stimulated

Nerves carry impulses to

Diaphragm and chest muscles

The rate and depth of

breathing is increased

[CO2 ] is lowered in the blood

Control of Breathing

***CO2 and lactic acid that is formed during heavy exercise increases the acidity of blood and stimulates respiratory center to increase breathing.

Control of Breathing

External and Internal Breathing

External Respiration is the exchange of O2 and CO2 between the air and the blood in the lungs.

After inhalation, the amount of O2 in the alveoli is higher than in the blood

So O2 dissolves into moist lining of alveoli

Then diffuses into blood that is the region where [O2] is lower

As the blood is pumped from heart, O2 rich blood from lungs is carried to body tissues

External and Internal Breathing

Blood that is rich in CO2 from body tissues is returned to lungs

Then diffuses into blood that is the region where [O2]

In the lungs, the amount of CO2 in the blood is higher than the CO2 in the alveoli

CO2 diffuses out of the blood into the alveoli

External and Internal Breathing

Internal Respiration is the exchange of O2 and CO2 between the blood and the body cells.

In the capillaries of the body tissues, O2

diffuses from blood the body cells.

CO2 diffuses out of the cells into the blood.

***Each gas diffuses down a concentration gradient, that is each gas diffuses from a high concentration area to a low concentration area.

O2 and CO2 Transport

Oxygen Transport

1.98% of oxygen is carried from lungs to body tissues by the hemoglobin in RBCs. (Hemoglobin holds O2 loosely)

Hb + O2 HbO 2

(Hemoglobin) (Oxyhemoglobin)

2. 2% of oxygen is transported by blood plasma as dissolved O2

O2 and CO2 Transport

** The amount of oxygen in the surrounding tissues determines whether hemoglobin will combine with oxygen or will release oxygen.

In the lungs there is large amount of O2

Hemoglobin combines with O2 to form oxyhemoglobin

When blood reaches to body cells, amount of O2 in the surrounding is low

Oxyhemoglobin breaks down into oxygen and hemoglobin

O2 and CO2 Transport

O2 and CO2 Transport

O2 and CO2 Transport

Carbondioxide Transport

1.70% of CO2 is transported in blood is carried in blood plasma.

CO2 + H2O H2CO3

Carbonic anhydrase

H2CO3 quickly breaks down into H+ ions and HCO3

H2CO3 H+ + HCO3-

(is held by (bicarbonate ions

hemoglobin) diffuses into plasma)

forms quickly by the enzyme found in RBCs

O2 and CO2 Transport

2. 20% of carbondioxide is transported by RBCs as carboxyhemoglobin.

CO2 + Hb HbCO2 (carboxyhemoglobin)

3. 10% of carbondioxide that diffuses into blood is transported by blood plasma as dissolved CO2.

O2 and CO2 Transport

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