Respiratory System in Humans
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 - Openings through which air enters the system. The nasal cavity is
the chamber behind the nose that contains hair, cilia, and mucus membranes. The nose
and nasal cavity have the following functions:
- Air is cleansed by the mucus, cilia, and hair
- Air is heated by the blood passing through a large number of capillaries just
below the mucus membranes
- Mucus membranes moisten the air
Cleaning, heating, and moistening of the air prevents damage to the delicate lung tissue
Pharynx - The cavity behind the nasal cavity that is common to both the respiratory and
digestive systems. It contains two lymph glands: Adenoids & Tonsils.
It transports air between the nasal cavity and the trachea, and the mouth and the trachea
Larynx - Consists of several pieces of cartilage that contains the vocal cords. The vocal
cords vibrate as air goes through them, producing sound.
Trachea - A tube about 10-17 cm long containing rings of cartilage which prevent the tube
from collapsing and is lined with a ciliated mucus membrane. At the top is located the
epiglottis, it allows air to move to and from the lungs.
Epiglottis - a cartilaginous flap that prevents liquids or solids from entering the lungs.
Mucus membrane - produces mucus that traps foreign materials that can then be swept out of
the trachea by cilia.
Bronchi - Tubes which branch from the trachea leading into the two lungs.
Lungs - Protected by the ribs, sternum and spine and are surrounded by two membranes
called pleura. The pleura isolates and protects the delicate lung tissue with a lubricating
fluid found between the two layers allowing the lungs to move freely in the chest cavity
during breathing. Lungs contain a variety of tubes and chambers where gases are
exchanged between the lungs and the blood.
Bronchials - Small tubes that branch from the bronchi inside the lungs. Tubes that lead for
the bronchi to the bronchioles.
Bronchioles - Even smaller tubes that branch from the bronchials inside the lungs. The
connecting tubes that lead from the bronchials to the alveoli.
Alveoli - Grape-like clusters of sacs that provide a large surface area for gas exchange. Found
at the end of bronchioles, these microscopic, one-cell thick, grape-like air sacs provide a
moist surface area surrounded by capillaries that creates an ideal site for gas exchange
between the air in the lungs and the blood in the capillaries.
Diaphragm - Sheet of muscle that separates the thorax (chest) and abdominal cavities. The
movement of this muscle is chiefly responsible for creating the mechanics of breathing.
Inspiration (inhale) : Diaphragm muscle contracts
Expiration (exhale) : Diaphragm muscle relaxes
Exhalation (Expiration): Air leaves the lungs
Six steps to the process:
1. Rib muscles 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 because of the decrease in volume. This results in a
higher pressure inside the thorax than found outside the thorax.
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
Sends impulses to the intercostal muscles of the ribs and diaphragm causing them to
contract producing inspiration
When this impulse stops, the intercostal muscles and diaphragm relax producing expiration
The amount of CO2 in the blood determines the rate of breathing. There are two sensors
located in the circulatory system to measure the CO2 content of the blood:
1. Carotid artery in the neck
2.
Aorta leading from the left ventricle of the heart
When CO2 levels are high, breathing rate is fast
When CO2 levels are low, breathing rate is slow
Breathing rates vary with age and physical activity
Stages of Respiration
1. Breathing
2. External respiration
3. Internal respiration
# 2 &3 all involve gas exchange through concentration gradients
4. Cellular respiration
External Respiration
Exchange of gases between the alveoli of the lungs and the blood
Occurs by diffusion:
O2 diffuses into the blood from the alveoli
CO2 diffuses into the alveoli from the blood
Gas Transport
Transportation of gas between the lungs and body cells
Gases enters the blood and combine with the protein hemoglobin found in the RBCs
Lung to Body cells
O2 enters and combines with the hemoglobin forming oxyhemoglobin
Body cells to Lung
CO2 enters and combines with the hemoglobin forming carboxyhemoglobin
CO2 also combines with water in the RBC and in the plasma forming carbonic acid
Internal Respiration
Exchange of gases between the blood and the cells of the body
Occurs by diffusion:
O2 diffuses into the body cells from the blood
CO2 diffuses into the blood from the body cells
Cellular Respiration
Release of energy within a cell through a series of chemical reactions
Glucose is converted to ATP
Can occur aerobically or anaerobically
See previous unit for details
Diseases of the Respiratory System
Bronchitis
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
Signs and symptoms include fever, chest pain, severe coughing, and often secretion of
sputum
Asthma
Caused by the constriction of bronchial passages and swelling of their mucus linings
Triggered by hypersensitivity to various agents within an individual’s environment
Attack begins with pressure in the chest, feeling of suffocation, with severe bouts of
uncontrollable coughing and the secretion of a thick mucoid sputum
Emphysema
A progressive disease in which the tissues of the lungs lose their elasticity
The volume of air the lungs are able to handle continually decreases
Deterioration of the lungs is permanent and irreversible
Symptoms include severe coughing, shortness of breath, and wheezing
Develops into difficulty in breathing, disability, and death
Influenza
A viral infection of the respiratory tract, especially the trachea
Commonly called the flu
Reduces a person’s resistance making them susceptible to further infections such as
pneumonia
Symptoms include 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 include sneezing, headaches, sore throats, and nasal discharge
Carbon Monoxide Poisoning
Carbon monoxide is a chemical compound consisting of one atom of carbon and one atom of
oxygen (CO)
Odorless and tasteless gas
Produced when organic compounds are burned with an insufficient air supply
When inhaled it combines with the hemoglobin in the RBCs preventing absorption of oxygen
Symptoms are mild and include nausea, headache, or fatigue
Treatment involves removing the individual from the source of CO. Perform mouth to mouth
resuscitation if necessary