Human Respiratory System

A system that provides a large surface area for the diffusion of O2 into the

blood, and the diffusion of CO2 out of the blood.

Parts of the Respiratory System

Oral and Nasal Cavities

• Structure - openings through which air enters the system. Nasal cavity is the chamber behind the nose. It contains hairs, cilia, and mucus.

• Function - the nose and nasal cavities have the following functions:

• (A) air is cleansed by the mucus, cilia, and hair

• (B) air is heated by blood passing through a large number of capillaries just below the mucus membranes

• (C) mucus membranes moisten the air

• The cleansing, heating, and moistening of the air prevents damage to the delicate lung tissue.

Pharynx

• Structure - cavity behind the nasal cavity that is common to the respiratory and digestive systems. It contains two lymph glands: adenoids and tonsils.

• Function - transports air between the nasal cavity/mouth and the trachea.

Larynx

• Structure - consists of several pieces of cartilage. Located inside is elastic tissue known as vocal cords.

• Function - the vocal cords vibrate as air goes through them producing sound. The pitch of the sound produced depends on the length of the vocal cords.

Trachea• Structure - a tube about 10 to 17 cm long containing rings

of cartilage which prevent the tube from collapsing. At the top is located the epiglottis. It is lined with mucus membrane that is ciliated.

• Function - a connecting tube that leads air to and from the lungs.

• *Epiglottis - prevents liquids or solids from entering the lungs.

• *Mucus membrane - produces mucus that traps foreign materials that are then swept out of the trachea by the cilia. This material is carried away by food passing down the esophagus.

Bronchi

• Structure - tubes which branch from the trachea leading into the two lungs.

• Function - a connecting tube that leads air to and from the lung.

Bronchials

• Structure - small tubes that branch from the bronchi inside the lungs.

• Function - connecting tubes that lead from the bronchi to the bronchioles.

Bronchioles

• Structure - yet smaller tubes that branch from the bronchials inside the lung.

• Function - connecting tubes that lead from the bronchials to the alveoli.

Lungs• Structure:

• Protected by the ribs, sternum, and spine.

• Surrounded by two membranes called pleura. The pleura isolates the lungs and protects the delicate tissue. A lubricating fluid is found between the two layers allowing the lungs to move freely in the chest cavity during breathing.

• Function - contain a variety of tubes and chambers where gases are exchanged between the lungs and the blood.

Diaphragm

• Structure - sheet of muscle that separates the thorax (chest) and abdomen cavities.

• Function - its movement is responsible for breathing.

• Inspiration (inhale) - diaphragm contracts

• Expiration (exhale) - diaphragm relaxes

Alveoli• Structure - millions per lung, giving the lungs

a very large surface area for gas exchange. They are found at the ends of the bronchioles and are a cluster of microscopic, one cell thick, grape-like air sacs. They are moist and surrounded by capillaries.

• Function - site of gas exchange between the air in the lungs and the blood in the capillaries.

Alveoli of the Lungs

Process of Breathing• Definition - breathing is a mechanical process where

gases are exchanged between the lungs and the atmosphere. Breathing is the first step in respiration.

• Breathing occurs due to changes in the pressure in the thorax or chest cavity of the body. This pressure is controlled by changing the size of the thorax. Two structures responsible for changing the size of the thorax are: ribs and rib muscles (intercostal muscle)

diaphragm

Inhalation (Inspiration)• Definition - air enters the lungs• Process - there are six steps to the process:• (1) rib muscle and diaphragm contract• (2) ribs move up and out• (3) diaphragm moves down• (4) thorax increases in size or volume• (5) pressure decreases in the thorax due to increase in

volume. The result is lower pressure inside the thorax than outside.

• (6) air rushes into the lungs

Exhalation (Expiration)• Definition - air leaves the lungs• Process - there are six steps to the process:• (1) rib muscle and diaphragm relax• (2) ribs move down and in• (3) diaphragm moves up• (4) thorax decreases in size or volume• (5) pressure increases in the thorax due to decrease in

volume. The result is a higher pressure inside the thorax than outside.

• (6) air rushes out of the lungs

Rate of Breathing• Breathing is an involuntary response controlled

by a section of the brain called the medulla oblongata.

• This structure sends impulses to the intercostal muscles of the ribs and diaphragm, causing them to contract which produces inspiration.

• When this impulse stops, the intercostal muscle and diaphragm relax producing expiration.

• The amount of CO2 in the blood determines the rate of breathing.

• Two sensors located in the circulatory system measure the CO2 content of the blood:

carotid artery in the neck

aorta leading from the left ventricle of the heart

CO2 Level Rate of Breathing

High Fast

Low Slow

* Breathing rates vary with age and activity.

Stages of Respiration

1. Breathing(previously discussed)

2. External Respiration

• Definition - exchange of gases between the alveoli of the lungs and the blood.

• Process - occurs by diffusion

• O2 goes into the blood from the alveoli

• CO2 goes into the alveoli from the blood

3. Gas Transport• Definition - transportation of gas between the lungs and

body cells.• Process - the gases enter the blood and combine with

the protein hemoglobin found on the red blood cell (RBC)

• lung ----> body cells : O2 enters the bloodstream and combines with the hemoglobin forming oxyhemoglobin

• body cells ----> lung : CO2 enters the bloodstream and combines with the hemoglobin forming carboxyhemoglobin

* CO2 also combines with water on the RBC and in the plasma, this forms carbonic acid.

Gas Exchange

4. Internal Respiration

• Definition - exchange of gases between the blood and the cells of the body.

• Process - occurs by diffusion

• O2 goes into the body cells from the blood

• CO2 goes into the blood from the body cells

5. Cellular Respiration

• Definition and Process both covered previously.

Diseases of the Respiratory System

Bronchitis• Definition - inflammation of the bronchial

passages. Two forms:

• Acute - severe form which involves an infection of the air passages.

• Chronic - less severe form which involves an irritation of the air passages.

• Symptoms - fever, chest pain, severe coughing and often the secretion of sputum.

Asthma• Caused by the constriction of bronchial

passages and swelling of their mucus linings. It is triggered by a hypersensitivity to various agents within an individual’s environment.

• Symptoms - attack begins with pressure in the chest, feeling of suffocation, with severe bouts of uncontrollable coughing and the secretion of a thick mucous sputum.

Pneumonia

• Caused by the infection in the alveoli resulting in the build-up of fluid in the lungs. Two major forms are bacterial and viral.

• Symptoms - fever, pain in the chest while breathing, cough, and blood-streaked sputum.

Cancer

• Cancer is the uncontrollable multiplication of cells. Cancer may occur in any part of the body, and therefore in any part of the respiratory system.

Emphysema• A progressive disease in which the tissues of

the lungs lose their elasticity, and therefore the volume of air that the lungs are able to handle continually decreases.

• The deterioration in the lungs is permanent and irreversible.

• Symptoms - severe coughing, shortness of breath, and wheezing; developing into difficulty in breathing. It sometimes results in disability and death.

Influenza

• A viral infection of the respiratory tract, especially the trachea. Commonly called flu. Reduces a person’s resistance making them susceptible to further infections such as pneumonia.

• Symptoms - sore throat, nasal discharge, fever, chills, headache, aching of muscles and joints, upset stomach

Common Cold

• A viral infection of the upper respiratory tract.

• Symptoms - sneezing, headaches, sore throat, nasal discharge

Pleurisy

• Inflammation of the pleura membranes that surrounds the lungs. Most cases are due to infections, and many are associated with pneumonia.

• Symptoms - sharp pain brought on by breathing and coughing. Patient breaths shallowly.

Carbon Monoxide Poisoning• Definition - Carbon monoxide is a chemical

compound consisting of one atom of carbon and one atom of oxygen (CO). It is an odorless and tasteless gas.

• Source - It is produced when organic compounds are burned with an insufficient air supply.

• Effects - When inhaled, it combines with the hemoglobin on the RBC, preventing absorption of oxygen.

• Symptoms - symptoms are normally mild and include nausea, headache, or fatigue. Excessive inhalation can be more serious, even fatal.

• Treatment - remove the individual from the source of CO. Perform mouth to mouth resuscitation if necessary.