The Respiratory System: The Respiratory System: Movement of Air

  • The Respiratory System

    • Human life depends on the integrated functioning of the cardiovascular and respiratory systems because neither system, by itself, can supply what we need to survive.

    • The respiratory system

      • Delivers oxygen

      • Expels carbon dioxide.

      • Filters incoming air

      • Maintains blood pH.

      • Helps control fluid and thermal homeostasis.

      • Produces sound

  • The Respiratory System

    • The respiratory system has two anatomical divisions.

    • Upper respiratory tract.

      • Organs include the nose, pharynx, and larynx.

      • Warms, moistens, and filters air as it enters the body.

    • Lower respiratory tract

      • Organs include the trachea, bronchial tree (bronchi, bronchioles), and lungs.

      • Allows oxygen to enter the blood, and waste gases to leave it.

  • The Upper Respiratory Tract - “Nose”

    • Filtering

      • Coarse hairs in the nostrils filter out larger particles.

      • Mucus of the nasal passages filters incoming air by trapping small particles.

    • The epithelium in the upper respiratory tract is pseudostratified ciliated columnar epithelium.

      • Cilia move mucus (containing trapped debris) away from lungs.

      • The nasal epithelium has chemosensory neurons which provide the sense of smell.

  • The Upper Respiratory Tract - “Pharynx”

    • The pharynx has three parts

      • Nasopharynx - upper throat

        • Normally open for breathing, but it must close when we swallow.

        • The uvula, a fleshy tab of tissue that hangs down in the back of the throat, contracts when touched by solids, moving upward and closing the internal nares (that lead to the nasopharynx).

        • The Eustachian (auditory) tubes link the nasopharynx and the middle ear.

          • When your ears “pop,” these tubes open to equalize air pressure between the middle and outer ear.

      • Oropharynx - directly behind the tongue.

        • Covered by the uvula when it hangs down - all activities of the mouth.

        • The palatine and lingual tonsils are found here.

      • Laryngopharynx - the end of the laryngopharynx has two openings.

        • The anterior opening leads to the larynx and the rest of the respiratory system.

        • The posterior opening leads to the esophagus and the digestive system.

  • The Upper Respiratory Tract - “Larynx”

    • The larynx divides the upper and lower respiratory tracts.

      • Composed entirely of cartilage.

      • Holds the respiratory tract open.

      • Guards the lower tract against particulate matter.

      • Produces the sounds of speech.

    • The larynx is attached to the tongue muscles.

      • When the tongue pushes against the roof of the mouth in preparation for swallowing, the larynx moves up toward the epiglottis.

    • The larynx is called the “voice box” because it is the location of the vocal cords.

    • The larynx is composed of hyaline cartilage and consist of three parts.

      • Thyroid cartilage - in the front of the larynx.

        • Usually larger in men - testosterone stimulates its growth-thickening the vocal folds: “Adam’s apple” refers to the larger laryngeal cartilages in men.

      • Epiglottis - A leaflike flap of cartilage on the superior part of the larynx.

        • Covers the opening to the lower respiratory tract.

        • Prevents food from entering the lungs.

      • Cricoid cartilage - a complete ring of cartilage.

        • Holds the respiratory system open.

  • The Lower Respiratory Tract

    • The main function of the lower tract is to move inhaled air to the respiratory membrane.

      • Structures include the trachea, bronchial tree, lungs

    • Conducting zone

      • Physiologically, the upper tract and the first portion of the lower tract.

      • Conducts air from the atmosphere to the respiratory zone deeper in the body.

      • Includes all the structures of the upper respiratory tract, as well as the trachea, bronchi, bronchioles, and terminal bronchioles.

    • Respiratory zone

      • Lies deep within the lungs - where the actual exchange of gases takes place.

      • Includes only the respiratory bronchioles and alveoli.

  • The Lower Respiratory Tract - “Trachea”

    • The trachea connects the larynx to the bronchi.

    • Approximately 2.5 centimeters in diameter.

      • Composed of muscular walls embedded with 16 to 20 “C”-shaped pieces of hyaline cartilage.

      • The “C” rings support the trachea so it does not collapse during breathing.

      • While also allowing the esophagus to expand during swallowing.

    • At its lower base is the carina.

      • The mucous membrane of the carina is more sensitive to touch than any other area of the larynx or trachea.

      • This spot triggers a dramatic cough reflex when any solid object touches it.

  • The Lower Respiratory Tract - “Bronchial Tree”

    • The lower portion of the conducting zonea nd the respiratory zone are collectively referred to as the bronchial tree.

    • The trachea splits into two tubes called the primary bronchi.

      • At the level of the fifth thoracic vertebra - each leading to one lung.

    • The primary bronchi divides into the secondary bronchi - inside the lung.

      • The right bronchus divides into three secondary bronchi.

      • Left bronchus splits into two secondary bronchi.

    • This branching pattern continues getting smaller and smaller as the tubes extend farther from the primary bronchus.

      • The sequentially smaller tubes are called tertiary bronchi, bronchioles, terminal bronchioles, and respiratory bronchioles.

    • The bronchial tree undergoes two major changes as it reaches deeper into the body.

      1. The cells of the mucous membrane get smaller.

        • Pseudostratified ciliated columnar epithelium.

        • Significant mucus secretion - which cilia sweep upward.

        • Terminal bronchioles have no cilia - are lined with simple columnar epithelium.

          • If dust reaches this area - only macrophages can remove it.

      2. The composition of the walls of the bronchi and bronchioles changes.

        • Amount of cartilage decreases as the size of the bronchi and bronchioles decreases.

        • Simultaneously, amount of smooth muscle increases.

        • Without cartilage - these smaller tubes can be completely shut by contraction of the smooth muscle.

  • The lower Respiratory Tract - “Lungs”

    • The lungs are the key organs of respiration.

    • These lightweight organ extend from just above the clavicle to the twelfth thoracic vertebra and fill the rib cage.

      • The base of the lungs is the broad portion sitting on the diaphragm.

      • The apex of the lungs is the small point extending above the clavicles.

    • The lungs are paired, but they are not identical.

      • The right lung is shorter and fatter, and has three lobes.

      • The left lung is thinner and has two lobes.

        • It also has a depression for the heart, called the cardiac notch, on the medial side.

    • The lungs are covered in serous membrane called the pleura.

      • Allows that allows the lungs to expand and contract without tearing the delicate respiratory tissues.

        • The visceral pleura is snug against the lung tissue.

        • The parietal pleura lines the walls of the thoracic cavity.

        • The pleural cavity between the two pleural membranes contains serous fluid.

    • The lobes of each lung are separate sections of the lung that can be lifted away from the other lobes.

      • Air enters each lobe through one secondary bronchus.

  • The Anatomy of the Lungs

  • Gas Exchange - “Bronchopulmonary Segment”

    • Each lung has a different number of secondary bronchi.

    • Each lung has ten terminal bronchioles.

      • Each supplying one bronchopulmonary segment.

    • A bronchopulmonary segment.

      • Looks like a bunch of grapes.

  • Gas Exchange - “Alveoli”

    • Gases diffuse in the alveoli

      • Oxygen enters the bloodstream and carbon dioxide exits.

      • Alveoli have a cup-shaped membrane at the end of the terminal bronchiole.

      • Alveoli are clustered into an alveolar sac at the end of terminal bronchiole.

        • The walls of the alveolar sacs are two squamous epithelial cells “thin”.

          • One cell from the alveolar wall, one cell from the capillary wall.

          • Allowing for efficient diffusion of gases.

      • Septal cells, scattered through the lung, produce surfactant.

        • A detergent-like fluid that moistens the alveoli but prevents their walls from sticking together during exhalation.

        • Provides a moist membrane for efficient diffusion of gases.

        • Also solubilizing oxygen gas to promote uptake.

      • Alveolar macrophages patrol the alveoli.

        • These immune cells remove inhaled particles that escaped the mucus and cilia within the conducting zone.

        • No cilia in alveoli.

  • Gas Exchange

  • Gas Exchange - The Anatomy of an Alveolar Sac

    • The respiratory membrane

      • At the end of the respiratory tree.

    • Consists of

      • Alveolar cells.

      • Epithelial basement membrane.

      • Capillary basement membrane.

      • Endothelium of the capillary.

  • Gas Movement Across the Respiratory Membrane

    • Oxygen diffuses from the alveoli to the blood in the capillary.

    • Carbon dioxide diffuses from the capillary to the alveoli.

    • Remember - The alveoli lumen (interior) is “space” that fills with air.

  • Respiration

    • Respiration involves the interplay between the respiratory and cardiovascular systems.

      • The respiratory system moves the gases in and out of the body.

      • The cardiovascular system transports the gases within the body.

    • The pulmonary capillaries exchange gases in the lungs.

    • The systemic capillaries exchange gases in the body.

    • Pulmonary ventilation

      • Is governed by Boyle’s law.

      • Which states that the volume of gas varies inversely with its pressure.

  • Inhalation/Exhalation

    • During inhalation, the diaphragm contracts, the chest expands, and the lungs are pulled outward.

      • All of these decrease pressure within the lungs, allowing air to rush in.

      • The diaphragm contracts and flattens out - causing the bottom of the thoracic cavity to drop and expand its size.

      • The intercostal muscles contract - raising the ribs and expanding the size of the ribcage.

      • The lungs also expand in size - allowing for air to enter from the environment outside.

    • During exhalation, the diaphragm and intercostal muscles relax, and the volume of the thoracic cavity and lungs decrease.

      • All of these increase the pressure within the lungs, thus forcing the air back out.

  • Muscles of Inhalation

  • Pressure Changes in Pulmonary Ventilation

  • Respiratory Rate

    • Respiratory rate is governed by the medulla oblongata and the pons in the brain stem.

      • The respiratory center in the medulla oblongata causes rhythmic contraction of the diaphragm, stimulating contraction for two seconds and allowing three seconds of rest.

      • This cycle repeats continuously unless overridden by higher brain function.

    • The body senses the levels of carbon dioxide and oxygen in the blood through chemoreceptors in the carotid artery and aorta.

      • High carbon dioxide levels immediately trigger an increase in the depth and rate of respiration.

  • Respiratory Volume

    • Different respiratory volumes describe different types of breath.

    • During “normal breathing”

      • The volume of air inhaled per minute reflects the respiratory rate and the volume of each normal breath, called the tidal volume (TV)

        • Tidal volume, approximately 500 ml.

    • During a “forced inhalation”

      • The average adult male can inhale approximately 3,300 ml of additional air, and the average adult female can force in approximately 1,900 ml.

      • This volume is called inspiratory reserve volume (IRV)

    • We can exhale much more than the 500 ml tidal volume after a normal tidal inhalation, up to about 1,000 ml for males and 700 ml for females, in the expiratory reserve volume (ERV).

      • This volume is lower than IRV because exhalation is largely passive.

    • Vital capacity (VC)

      • measures the total volume of air the lungs can inhale and exhale in one huge breath, which is essentially the maximum amount of the air the lungs can move in one respiratory cycle.

      • VC is the sum of inspiratory reserve volume, tidal volume, and expiratory reserve volume.

      • VC is between 3,100 and 4,800 ml; males generally have the larger volume.

    • The amount of air that remains in the lungs after forced expiration is called residual volume (RV).

      • The residual volume holds the alveoli open and fills the “anatomical dead spaces”

      • RV is usually between 1,100 and 1,200 ml.

  • “External Respiration”

    • External respiration is the exchange of gases between the air in the alveoli and the blood in the respiratory capillaries.

    • Oxygen enters the alveoli, and carbon dioxide leaves the alveoli.

    • The exchanges during external and internal respiration are driven by the partial pressures of oxygen and carbon dioxide.

      • In external respiration, the driving force is the difference in the partial pressures in the alveolar air and the capillary blood.

      • In nternal respiration, the driving force is the partial pressure difference in the capillary blood and the tissue fluid.

  • Dalton’s Law

    • Gases move independently down their pressure gradients.

      • From higher to lower pressure.

    • Oxygen will diffuse

      • From the air in the alveoli into the blood.

    • Carbon dioxide will diffuse

      • From blood to the alveoli.

    • Each gas independently moves toward an area of lower pressure without affecting any other gas.

  • “Internal Respiration”

    • Internal respiration is the exchange of gases between body cells and blood in the systemic capillaries.

    • Oxygen enters the tissues, and carbon dioxide diffuses out of the tissues, again based on partial pressure.

      • The partial pressure of oxygen in the capillary beds of the systemic circuit is approximately 95 mmHg, whereas the partial pressure of oxygen in most tissues is about 40 mmHg.

      • This gradient allows oxygen to leave the blood and enter the respiring cells without requiring energy from the body.

    • Cellular respiration produces carbon dioxide, and the partial pressure of carbon dioxide in the tissues is about 45 mmHg.

      • blood in the capillary beds has a carbon dioxide partial pressure of 40mmHg.

      • This small gradient is still enough to cause carbon dioxide to diffuse from the cells to the blood, which carries it off to the lungs for release into the alveolar air.

  • External/Internal Respiration

  • Hemoglobin

    • Hemoglobin molecules in red blood cells carry oxygen as the blood circulates.

      • Picks up oxygen through a bond between the oxygen molecules and the iron atom of the hemoglobin’s heme complex.

    • Hemoglobin has a high affinity for oxygen under some conditions but will release it under other conditions.

    • Hemoglobin is best known for carrying oxygen, but it also conveys about 23 percent of total carbon dioxide through the bloodstream.

  • The Transport of Carbon Dioxide

    • Carbon dioxide binds to the protein portion of hemoglobin, forming carbaminohemoglobin (Hb-CO2)

      • 7 percent of the blood borne carbon dioxide is carried as dissolved CO2 gas.

      • The major share of blood-borne carbon dioxide (about 70 percent of total carbon dioxide) moves a bicarbonate ions in plasma.

    • The bicarbonate ion in the plasma then serves as a buffer, helping to maintain blood pH.

      • Without this buffering, we could not control our internal pH, and we would perish.

  • Diseases of the Upper Respiratory Tract

    • The upper respiratory tract is susceptible to infection and inflammation of the nasal passages, sinuses, and larynx.

    • One of the most common upper respiratory diseases is sinusitis.

      • An inflammation or swelling of the sinuses.

      • Acute sinusitis - usually caused by a common cold and goes away on its own within two to three weeks.

      • Chronic sinusitis - is more severe and its causes are less clear.

        • Most people who suffer from chronic sinusitis also have allergies, asthma, or a compromised immune system.

  • Diseases of the Lower Respiratory Tract

    • Diseases of the lower respiratory tract are usually either.

      • Obstructive

        • Something is obstructing the normal flow of gases through the lungs.

      • Constrictive

        • The airways have been narrowed or constricted in someway.

    • Bronchitis is a constrictive respiratory disease.

      • An inflammation of the mucous membrane lining the bronchi.

        • Acute bronchitis - caused by viruses and occasionally bacteria.

        • Chronic bronchitis - caused by smoking - lasts from months to years.

  • Asthma

    • Asthma is a constrictive pulmonary disease that can be life-threatening.

    • During an attack.

      • The smooth muscle of the bronchi contract.

      • Mucus production increases in these tubes.

      • The bronchi swell, interfering with the passage of air.

    • Asthma kills up 5,000 people every year in the United States.

  • Obstructive Pulmonary Diseases

    • The most common obstructive pulmonary disease are

      • Pneumonia, tuberculosis, emphysema, and lung cancer.

    • In all of these diseases

      • After exhalation the tubes of the airway do not spring back open because the elastic tissue is destroyed.

      • Pressure builds in the lungs as the patient tries to force air through the collapsed tubes, damaging the deliciated alveoli and reducing the respiratory surface area.

    • Pulmonary fibrosis

      • A destructive increase in collagen makes the lungs less elastic.

      • Often a result from occupational exposure to silicon or other irritants.

  • Chronic Obstructive Respiratory Disease

    • Chronic obstructive pulmonary disease (COPD) is actually two diseases.

      • Emphysema and chronic bronchitis.

      • Both obstruct airflow.