Lecture Outline - Chapter 15

15.1. Respiratory Tract (p. 270)

1. Breathing consists of inspiration (breathing in) and expiration (breathing out).
2. Air is conducted toward or away from lungs by series of cavities, tubes, and openings. (Fig. 15.1)
3. As air moves in, it is filtered, warmed, and moistened.
   • a. Hairs in nostrils and cilia from nostrils to trachea filter out dust, particles, etc.
   • b. Heat given off by surrounding blood vessels warms the air.
   • c. Air is moistened by wet surfaces of air passages.
4. As air moves out, it becomes progressively cooler and loses its moisture on the lining of the windpipe and nose; on cold days, it condenses to form a cloud.
5. The Nose: Two Cavities
   • a. Nose contains two nasal cavities separated by a bone and cartilage wall.
   • b. Inside nasal cavities are receptors for smell, openings for lacrimal glands and cranial sinuses.
   • c. Eustachian tubes lead to middle ears from nasopharynx, the upper portion of pharynx.
6. The Pharynx: Crossroads
   • a. Air is taken in through mouth or nose to throat (pharynx). (Table 15.1)
   • b. Pharynx is also common passageway for food.
   • c. Trachea lies in front of esophagus, normally closed except during swallowing.
7. The Larynx: Voice Box
   • a. Triangular box, projects in front of neck as Adam's apple.
   • b. Glottis is opening covered by epiglottis during swallowing of food.
   • c. If food, etc. passes epiglottis into larynx, reflex coughing usually expels it.
   • d. Vocal cords
     • i. Mucous membrane folds supported by elastic ligaments.
     • ii. Occur at edges of glottis. (Fig. 15.3)
     • iii. Vibrate as air is expelled past them through the glottis.
     • iv. Pitch is due to length, thickness, elasticity, and tension of vocal cords.
     • v. Intensity or loudness is due to amplitude of vibrations.
     • vi. At puberty, larynx and vocal cords grow more rapidly in males.
8. The Trachea: Windpipe
   • a. Tube held open by C-shaped cartilaginous rings.
   • b. Contains cilia projecting from epithelium of trachea to keep lungs clean by sweeping debris toward throat.
   • c. Mucus secreted to embed and transport debris.
   • d. If blocked, an incision is made to allow air in and out; operation is a tracheostomy.
9. Bronchi: Air Tubes
   • a. Trachea divides into two bronchi (sing. bronchus); cartilage rings keep tube open.
   • b. Bronchus leads to right and left lungs.
   • c. Bronchi branch into smaller units termed bronchioles; cartilage rings have diminished.
   • d. Asthma is constriction of bronchioles, which reduces or prevents air movement.
   • e. Terminate in air pockets or sacs termed alveoli.
10. Lungs: Many Alveoli
    • a. Right lung has three lobes, left lung has two lobes.
    • b. Cone-shaped lungs extend from near neck, filling chest inside ribs, with base broad and concave fitting on diaphragm.
11. Alveoli: 300 Million Air Sacs
    • a. Gas Exchange
      • i. Occurs in the alveoli.
      • ii. Passage involves crossing single layer of squamous epithelium surrounded by blood capillaries. (Fig. 15.5)
    • b. Film of lipoprotein lines inner alveolar surfaces to lower surface tension and prevent them from closing up.
    • c. Infant respiratory distress syndrome occurs in premature babies due to lack of this lipoprotein; now treated with surfactant replacement therapy.
    • d. Approximately 300 million alveoli have total cross-sectional area of 50- 70 m²; equals about 40 times surface area of the skin.

1. Respiration refers to complete process of supplying oxygen to body cells and ridding body of carbon dioxide.
2. Respiration includes following components:
   • a. Breathing: inspiration (entrance) and expiration (exit) of air in and out of lungs.
   • b. External respiration: exchange of oxygen and carbon dioxide between air and blood.
   • c. Internal respiration: exchange of gases oxygen and carbon dioxide between blood and tissue fluid.
   • d. Cellular respiration: production of ATP in cells.
3. Getting Air to the Lungs
   • a. Tidal volume is amount of air moved in and out with each breath; usually about 500 ml.
   • b. Vital capacity is maximum volume of air that can be moved in and out during a single breath. (Fig. 15.6)
   • c. Inspiratory reserve volume represents amount of air that can be taken in beyond tidal volume using forced inspiration; normally about 3,100 ml of air.
   • d. Expiratory reserve volume is amount of air that can be forced out by contracting chest and abdominal muscles beyond tidal volume; this is about 1,400 ml.
   • e. Vital capacity is sum of tidal, inspiratory reserve and expiratory reserve volumes.
   • f. Residual volume is amount of air remaining in lungs even after deepest possible expiration; averages about 1,000 ml; not useful for gas exchange purposes.
   • g. In emphysema, residual volume builds up and is no longer useful for gas exchange, reducing vital capacity.
   • h. Parts of air passageways in which inspired air never reaches the lungs (nose, trachea, etc.) and is therefore not used for gas exchange constitute dead space. (Fig. 15.1)
4. Inspiration Precedes Expiration
   • a. Air passes from atmosphere through pharynx to alveoli.
   • b. Lungs lie within a sealed-off thoracic cavity.
   • c. Rib cage forms top and sides of thoracic cavity; intercostal muscles lie between ribs.
   • d. One layer of the pleural membranes encloses lungs, second layer adheres closely to chest walls and diaphragm; they are separated by thin film of fluid; infection is called pleurisy.
   • e. The intrapleural pressure is less than atmospheric pressure by about 4 mm Hg.
5. Inspiration Is Active (p. 276)
   • a. Respiratory center located in medulla oblongata of brain consists of neuron groups that exhibit automatic rhythmic discharges to trigger respiration.
   • b. Increased amounts of CO₂ and H⁺ concentration are primary stimulus for stimulating this center.
   • c. Chemoreceptors in carotid bodies in carotid arteries and aortic bodies in aorta are mainly stimulated by changes in H+ concentration; these bodies communicate with respiratory center.
   • d. When levels of CO₂ and H⁺ rise, rate and depth of breathing increase.
   • e. Respiratory center then stimulates diaphragm and rib cage muscles to contract by nerve impulse. (Fig. 15.7)
   • f. Contraction lowers diaphragm, intercostal muscles lift rib cage upward and outward; this increases volume of thoracic cavity.
   • g. Lung expansion in turn decreases alveolar pressure.
   • h. Due to greater atmospheric pressure outside, air rushes in. (Fig. 15.8)
   • i. Therefore, humans breathe by negative pressure; creation of a partial vacuum sucks air into lungs.
6. Expiration Is Usually Passive
   • a. When respiratory center stops sending signals, diaphragm relaxes and returns to its original dome shape.
   • b. Rib cage moves down and inward.
   • c. Lungs recoil due to elastic tissue within.
   • d. Inhaling deeply expands alveoli; stretch receptors in lungs send inhibitory message to respiratory center.
   • e. Expiration therefore is usually passive process; muscle contraction is not needed.
   • f. Expiration can be active when internal intercostal muscles force rib cage downward and inward or when abdominal muscles are contracted to help expel air.

1. External respiration is exchange of gases between air in alveoli and blood in pulmonary capillaries.
2. Internal respiration is exchange of gases between blood in systemic capillaries and tissue fluid.
3. The amount of pressure each gas exerts is called its partial pressure; symbol for partial pressure of O₂ is PO₂, partial pressure of CO₂ is PCO₂.
4. Diffusion alone governs direction of gas flow.
5. External Respiration Cleanses Blood
   • a. Blood flowing into lung capillaries has a higher PCO₂ than atmospheric air; therefore, CO₂ diffuses out of blood into alveoli.
   • b. Oxygen diffuses into the capillary because there is a higher concentration of it in the alveolus.
   • c. High altitude planes pressurize cabins to maintain this gas pressure.
   • d. At the pulmonary capillary, CO₂ carried mostly as bicarbonate ions (HCO₃) begins to diffuse out:
     H⁺ + HCO₃^- --> H₂CO₃ _ H₂O + CO₂

     e. The enzyme carbonic anhydrase in red blood cells speeds up reaction; hemoglobin (HHb) releases hydrogen ions (H+) to become deoxyhemoglobin (Hb):

     Hb + O₂ --> HbO₂

     f. Hemoglobin takes up oxygen and becomes oxyhemoglobin.
6. Internal Respiration Cleanses Tissue Fluid (p. 278)
   • a. Internal respiration is exchange of gases between blood in systemic capillaries and surrounding tissue fluid.
   • b. Blood entering systemic capillaries is bright red due to oxyhemoglobin.
   • c. Oxyhemoglobin gives up oxygen which diffuses into tissues:
     HbO₂ (oxyhemoglobin, bright red) --> Hb + O₂

     d. The lower PO₂ of the tissues is due to tissues constantly using up oxygen in aerobic cellular respiration.

     e. Carbon dioxide diffuses into blood from tissues because the PCO₂of tissue fluid is higher than that of blood.

     f. Small amount of CO₂ is taken up by hemoglobin, forming carbaminohemoglobin.

     g. Most CO₂ combines with water forming carbonic acid which dissociates to hydrogen ions and bicarbonate ions:

     CO₂ + H₂O --> H₂CO₃ (carbonic acid) --> H⁺ + HCO₃^-

     h. Enzyme carbonic anhydrase in RBCs speeds up the reaction.

     i. Globin part of hemoglobin combines with excess hydrogen ions to form HHb, called reduced hemoglobin; HHb is purple in color.

     j. Bicarbonate ions diffuse out of RBCs to be carried by plasma as major transport mechanism.
7. External and Internal Respiration Revisited
   • a. PO₂ of air entering lungs is about 100 mm Hg, sufficient to cause hemoglobin to become saturated with oxygen.
   • b. Lower PO₂ in tissues causes hemoglobin to release its oxygen.
   • c. Lungs have a lower temperature and higher pH than the tissues; this assists in transfer of oxygen from lungs to blood and blood to tissues. (Fig. 15.10)
   • d. Hemoglobin is about 98- 100% saturated in lungs; about 60- 70% saturated in tissues.

1. Respiratory Tract Infections
   • a. The respiratory system with bacteria and viruses in mucous is source of cross infection for humans.
   • b. Many microbes are spread by droplets in a sneeze.
   • c. Cold and flu viruses penetrate mucous membrane defenses when numbers are large or resistance is low.
2. Bronchitis: Acute and Chronic
   • a. Viral infections spread to:
     - sinuses (sinusitis).
     - middle ears (otitis media).
     - larynx (laryngitis).
     - bronchi (bronchitis).

     b. Acute bronchitis: (Fig. 15.11)

     - is usually caused by secondary bacterial infection of bronchi.

     - results in heavy mucus discharge with much coughing.

     - responds to antibiotics.

     c. Chronic bronchitis:

     - may not be due to infection.

     - is often caused by constant irritation of bronchi, as in smoking, causing degeneration, loss of cilia, etc.

     - increases susceptibility to other respiratory infections.
3. Strep Throat: Risks Rheumatic Fever
   • a. Severe throat infection due to the Streptococcus pyogenes.
   • b. Swallowing is difficult.
   • c. Fever present.
   • d. If not treated with antibiotics, it may lead to rheumatic fever which can damage heart valves.
4. Lung Disorders
   • a. Pneumonia: Lobules Fill and Breathing Ceases
     • i. Most forms caused by bacteria or viruses.
     • ii. AIDS patients may have pneumonia due to protozoan Pneumocystis carinii.
   • b. Pulmonary Tuberculosis: Past and Recent Threat (p. 282)
     • i. Caused by tubercle bacilli that invade lung tissue.
     • ii. Surrounding cells build up protective capsule (tubercle) that can be seen on a chest X ray.
     • iii. Skin test detects immunity developed due to previous exposure.
     • iv. Historically a serious widespread disease; controlled by antibiotics.
     • v. Again on rise with some strains resistant to antibiotics.
   • c. Emphysema: Bronchioles Collapse and Alveoli Burst (p. 282)
     • i. Lung tissue is destroyed due to break down and collapse of bronchioles.
     • ii. Air is trapped in alveoli which often causes rupturing of alveolar walls. (Fig. 15.11).
     • iii. Surface area for gas exchange is decreased; this in turn forces the heart to work harder to get oxygenated blood and may lead to a heart condition.
     • iv. Lack of oxygen to brain causes depression, irritability, etc.
   • d. Pulmonary Fibrosis: Inhaling Particles
     • i. Inhaling silica, coal dust, and asbestos leads to this condition. (Fig. 15.11)
     • ii. Fibrous connective tissue builds up in lungs.
     • iii. Breathing is impaired, and the development of cancer is common.
   • e. Lung Cancer: Women Catch Up
     • i. Increased lung cancer in women is linked to increased numbers of women who smoke; has surpassed breast cancer as leading cancer.
     • ii. Callused cells thicken to block bronchi.
     • iii. Cilia are lost and protection decreases.
     • iv. Cells with atypical nuclei appear.
     • v. Disordered cells grow in situ, then break loose and spread (metastasis).
     • vi. Tumor may grow until bronchus is blocked, lung collapses, fluid is trapped inside, and pneumonia may result.
     • vii. Removal of lung is termed pneumonectomy.
     • viii. Involuntary smoking, breathing in air containing smoke, can also cause lung cancer.
     • ix. Stopping smoking or exposure helps return tissues to normal over time.