Respiratory System

The respiratory system includes tubes that remove particles from incoming air and transports air to and from the lungs and the air sacs where gases are exchanged.

Respiration is the entire process of gas exchange between the atmosphere and body cells.

Organs of the Respiratory System Outside the Thorax

Nose1. Bone and cartilage support the nose2. The nostrils are opening for air.3. Many internal hairs guard the nostrils, preventing

entry of large particles carried in the airNasal Cavity1. Nasal conchae divide the nasal cavity into

passageways and help increase the surface area of the mucous membrane.

2. The mucous membrane filters, warms, and moistens incoming air.

3. Ciliary action carries particles trapped in mucus to the pharynx, where they are swallowed.

Paranasal Sinuses

1. The paranasal sinuses are spaces in the bone of the skull that open into the nasal cavity.

2. Mucous membrane lines the sinuses

Pharynx1. The pharynx is behind the oral cavity and between the

nasal cavity and the larynx.2. It is a passageway for air and food.

Larynx1. The larynx conducts air and helps prevent foreign

objects from entering the trachea.2. It is composed of muscles and cartilages and is lined

with mucous membrane.3. It contains the vocal cords, which vibrate from side to

side and produce sounds when air passes between them.

4. The glottis and epiglottis help prevent foods and liquids from entering the trachea.

Organs of the Respiratory System Inside the Thorax

Trachea1. Extends into the thoracic cavity in front of the

esophagus.2. Divides into right and left bronchi.

Bronchial Tree1. The bronchial tree consists of branched air passages

(primary bronchi, bronchioles, and alveolar ducts) that lead from the trachea to the air sacs.

2. Alveoli are at the distal ends of the narrowest tubes, the alveolar ducts.

Alveoli1. Alveoli provide a large surface area of thin simple

squamous epithelial cells through which gases can easily be exchanged.

2. Oxygen diffuses through alveolar walls and enters blood in the nearby capillaries, and carbon dioxide diffuses from blood through the walls and enters alveoli.

3. An adult lung has about 300 million alveoli, providing a total surface area half the size of a tennis court.

Lungs1. The mediastinum separates the left and right lungs,

and the diaphragm and thoracic cage enclose them.2. The visceral pleura attaches to the surface of the

lungs. The parietal pleura lines the thoracic cavity.3. Each lobe of the lungs is composed of alveoli, blood

vessels, and supporting tissue.

Breathing MechanismChanges in the size of the thoracic cavity accompany

inspiration and expiration.

Inspiration1. Atmospheric pressure due to the weight of air is the

force that moves air into the lungs. Normal air pressure is equal to 760mm of mercury (Hg).

2. If the pressure inside the lungs and alveoli decreases, atmospheric pressure will push outside air into the airways.

3. Impulses carried on the phrenic nerves stimulate muscle fibers in the dome-shaped diaphragm below the lungs to contract, moving it downward. The thoracic cavity enlarges, and the pressure within the alveoli falls to about 2mm Hg below that of atmospheric pressure

4. The external (inspiratory) intercostal muscles between the ribs may be stimulated to contract, raising the ribs and elevating the sternum, enlarging the thoracic cavity even more, resulting in further reduction of pressure.

5. The water molecules in the serous fluid greatly attract one another, creating a force called surface tension that holds the moist surfaces of the pleural membranes tightly together. When the intercostal muscles move the thoracic wall upward and outward, the parietal pleura moves, the visceral pleura follows it, helping to expand the lungs in all directions

6. Certain alveolar cells synthesize a mixture of lipoproteins called surfactant, which is secreted continuously into alveolar air spaces, reducing surface tension and decreasing alveoli’s tendency to collapse when lung volume is low.

7. Additional muscle, such as the pectoralis minors and sternocleidomastoids, can also pull the thoracic cage farther upward and outward, enlarging the cavity and decreasing internal pressure.

Exhalation1. The forces responsible for normal expiration come

from the elastic recoil of tissues and from surface tension.

2. Similarly, the abdominal organs spring back into their previous shapes, pushing the diaphragm upward.

3. At the same time, the surface tension that develops between the moist surfaces of the alveolar linings decreases the diameter of the alveoli.

4. Each of these factors increases aveolar pressure about 1mm HG above atmospheric pressure, so the air inside the lungs is forced out through respiratory passages.

5. If a person needs to exhale more air than normal, the posterior internal (expiratory) intercostal muscles can be contracted to pull the ribs and sternum downward and inward, increasing the pressure in the lungs. Also, the abdominal wall muscles can squeeze the abdominal organs inward, which will increase pressure in the abdominal cavity and force the diaphragm still higher against the lungs

Respiratory Air Volumes and Capacities

1. The amount of air that enters the lungs during inspiration (about 500mL at rest) is approximately the same amount that leaves during normal expiration. One inspiration followed by an expiration is called a respiratory cycle.

2. The volume of air that enters (or leaves) during a single respiratory cycle is termed tidal volume.

3. During forced inspiration, air in addition to the resting tidal volume enters the lungs. This extra volume is inspiratory reserve volume, and at maximum, it equals about 3,000mL.

4. During forced expiration, the lungs can expel up to 1,100mL of air beyond the resting tidal volume. This quantity is called expiratory reserve volume.

5. Even after the most forceful expiration, about 1,200mL of air remains in the lungs. This is called the residual volume.

6. Residual air remains in the lungs at all time. This prevents oxygen and carbon dioxide concentrations in the lungs from fluctuating greatly with each breath.

7. Combining 2 or more of the respiratory volumes yields four respiratory capacities.

a. vital capacity (4,600mL) – IRV +TV+ERV; the maximum amount of air a person can exhale after taking the deepest breath possibleb. inspiratory capacity (3,500mL) – TV+IRV;

maximum amount of air a person can inhale following a resting expirationc. functional residual capacity (2,300mL) – ERV+RV; volume of air that remains in the lungs following a resting inspirationd. total lung capacity (5,800mL) – VC+RV

8. Some of the air that enters the respiratory tract during breathing does not reach the alveoli. This volume (about 150mL) remains in passageways of the trachea, bronchi, and bronchioles. Because gas is not exchanged through the walls of these passages, the air is said to occupy anatomic dead space.

Control of BreathingNormal breathing is a rhythmic, involuntary act that continues even

when a person is unconscious. The respiratory muscles, however, are under voluntary control.

Respiratory Center – located in the brain stem, and includes the pons and medulla oblongata1. Medullary Rhythmic Area

a. dorsal respiratory group – neurons that control the basic rhythm of breathingb. ventral respiratory group – quiet during normal breathing; generate impulses that increase inspiratory movements when more forceful breathing is required;

other neurons in the group activate muscles associated with forceful expiration

2. Pneumotaxic Area – control breathing rate by continuously transmitting impulses to the dorsal respiratory group; when signals are strong, the inspiratory burst are shorter, and breathing rate increases; when signals are weak, the inspiratory burst are longer, and the breathing rate decreases

Factors Affecting Breathing1. Chemosensitive areas (central chemoreceptors) that

are associated with the respiratory centera. Blood concentrations of carbon dioxide and hydrogen ions influence these receptors to signal the respiratory center, so that respiratory rate and tidal volume will increase

2. Peripheral chemoreceptors are in the walls of certain arteriesa. These receptors sense low oxygen concentrations and increase breathing rate.

3. Overstretching lung tissues triggers an inflation reflexa. helps regulate depth of breathing by shortening the duration of inspiratory movementsb. prevents overinflation of the lungs during forceful breathing

4. Hyperventilation – decreases blood carbon dioxide concentrations; but is very dangerous when done before swimming underwater

Alveolar Gas Exchange1. Alveoli – microscopic air sacs clustered at the distal

ends of the narrowest respiratory tubes, the alveolar ducts. They carry on vital processes of exchanging gases between air and blood.

2. Respiratory membrane – two thicknesses of simple squamous epithlial cells and a layer of fused basement membranes separate the air in the alveolus from blood in the capillaries

3. Diffusion across the Respiratory Membranea. The parietal pressure of a gas is proportional to the

concentration of that gas in a mixture or the concentration dissolved in a liquid.b. Gases diffuse from regions of higher partial pressure toward regions of lower partial pressure.c. Oxygen diffuses from alveolar air into blood. Carbon

dioxide diffuses from blood into alveolar air.

Gas Transport

Oxygen transport

1. Blood mainly transports oxygen in combination with hemoglobin molecules.

2. The resulting oxyhemoglobin is unstable and releases its oxygen in regions where the oxygen is low due to cellular respiration

3. More oxygen is released as the blood becomes more acidic, and blood temperature increases

Gas Transport cont…Carbon Dioxide Transport

1. Carbon dioxide may be carried in solutions, bound to hemoglobin (the globin part), or as a bicarbonate

ion.2. Most carbon dioxide is transported in the from of bicarbonate ions.3. The enzyme carbonic anhydrase speeds the reaction

between carbon dioxide and water to form carbonic acid.4. Carbonic acid dissociates to release hydrogen ions and bicarbonate ions.5. The bicarbonate ions diffuse out of red blood cells and

enter the plasma. Nearly 70% of the carbon dioxide that blood transports is in this form and the other 30% is given off when we exhale.

Surfactant Production

Babies are considered premature if they are born before 37 weeks gestation.

Fetuses begin to produce surfactant between weeks 24 and 28. By about 35 weeks, most babies have enough naturally produced surfactant to keep the alveoli from collapsing.

Babies born before 35 weeks, especially those born very prematurely (before 30 weeks), are likely to need surfactant replacement therapy. Over half the babies born before 28 weeks gestation need this treatment, while about one-third born between 32 and 36 weeks need supplemental surfactant.

COPD(Chronic Obstructive Pulmonary Disease)

Exemplified by:

Chronic bronchitis

Emphysema

Features of these 2 diseases:

1.History of smoking

2.Dyspnea (difficult or labored breathing)

3.Coughing and frequent infections

4.Hypoxic (retain CO2and have respiratory acidosis)

Lung Cancer