Biology 115 Lecture 7
T. Irving 01/07/98; revised A.Howard 02/07/00
Respiratory System

Objectives:

Students should be able to:

State & define the four processes involved in respiration

Describe the path of air in the body and describe generally the structure & function of organs involved.

Describe the mechanism of breathing

Describe the events of internal and external respiration

Show how hemoglobin is suited for its role as a respiratory pigment.

Describe various infections of the respiratory tract.

Describe the effects of smoking on the respiratory tract & on overall health.

Respiratory tract:

Main functions of initial air passages are to warm, filter and moisten incoming air

• Nose

  • Nose hairs and cilia filter air
  • Nose contains odor receptors, ciliated cells upper part nasal cavity

• Pharynx

  • Connects oral cavity, nasal cavity and larynx
  • upper part called the nasopharynx from which Eustachian tubes lead to middle ears (pressure equalization)

• Larynx

  • Bound on the top by the epiglottis, which covers the opening during swallowing
  • Vocal cords are mucus membranes supported by ligaments surrounding the opening called the glottis;
    these vibrate to produce sound as air passes by them
  • Volume of sound depends on volume of air expelled
  • Pitch of sound can be varied by varying tension on the cords;
    The pitch of an individual's voice depends on length and elasticity of his or her vocal cords.

• Trachea

  • Cartilaginous rings keep it open
  • Cilia beat upwards carrying mucus, dust upwards to pharynx
  • Tracheotomy - surgical process of inserting a hole into the trachea in case of blockage
  • Trachea branches into 2 bronchi which in turn branch into many bronchioles

• Bronchi and Bronchioles

  • Bronchioles terminate in small air sacs called alveoli which make up the lungs
  • Bronchi structured like trachea but get thinner as they branch further
  • Smaller ones lack small rings of cartilage

• Alveoli

  • Small membrane bound sacs consisting of simple squamous epithelium surrounded by blood capillaries
  • Lined with a lipoprotein surfactant layer
    which prevents them from collapsing due to surface tension

• Lungs

  • There is a right & left lung consisting of all the alveoli surrounded by the inner pleural membrane
  • There is another outer pleural membrane attached to the rib cage
  • The lungs are contained in the thoracic cavity which is bounded on the top and sides by the rib cage and the bottom by the diaphragm
  • The diaphragm is a sheet of striated muscle , normally dome shaped

Inspiration is an Active Process

• Begins with respiratory center in medulla oblongata
• Activity regulated by levels of CO₂ and H⁺ in the blood but not by O₂
• Excitatory nerve impulses are sent to the diaphragm and muscles of rib cage
• As they contract, diaphragm lowers and rib cage moves upwards and outwards
• Lungs expand, creating a partial vacuum which causes air to rush in

Expiration

• Excitatory impulse stop and diaphragm & rib muscles relax causing the thoracic cavity to shrink in size.
• Lungs' elasticity recoil pushing air out
• This is normally a passive process, but contraction of the internal intercostal muscles can force air out deep and/or rapid breathing

Some Physiological Terms:

Exercise and other physiologists are often interested in the following quantities:

• Tidal volume:
  This is the amount of air moved in and out in each breath-- typically about 500 ml
• Vital capacity:
  
  • Maximum amount that can be moved in and out, typically ~4800 mL

  • Equals sum of tidal volume, inspiratory reserve volume, expiratory reserve volume (see below).

• Residual volume:
  About 1 liter; always stays in the lung and is not available for gas exchange
• Dead space:
  Air that fills bronchioles etc. said to be dead space since not used for gas exchange

Gas Exchange

• Carbon dioxide is carried in the blood as the bicarbonate ion (HCO₃^-)
• Equilibrium: H⁺ + HCO₃^- <====> H₂CO₃ <===> CO₂ + H₂O

• Right-hand reaction can be accelerated by the enzyme carbonic anhydrase
• Hemoglobin in the absence of oxygen combines with H⁺ ions to become protonated hemoglobin (HHb)
• In the lungs HHb supplies protons for bicarbonate reaction
• Oxygen can then combine with hemoglobin to become oxyhemoglobin (HbO₂).

External Respiration

• Process by which oxygen enters blood and carbon dioxide leaves blood in the alveoli
• Gases exchange across the alveoli walls by passive diffusion
• Hb takes up oxygen readily relatively cool temperature of lungs and neutral pH

Internal Respiration

• Process by which oxygen leaves the blood and carbon dioxide enters blood in the tissues
• HbO₂ ---> Hb + O₂
• Process potentiated by warmer temperature and more acidic pH of tissues
• CO₂ <====> H₂CO₃ <===> H⁺ + HCO₃^-
• Hemoglobin recombines with H⁺ ions to become protonated hemoglobin (HHb) (see fig. 8.10)

Upper Respiratory tract ailments:

• Mucus covering of respiratory tract normally protects us from infectious agents

• Sneezing very effective way of transmitting bacteria and viruses. If resistance is lowered, flu, colds, and more serious ailments may result

• Colds and influenza:

  • Caused by viruses (rhinovirus, influenza)
  • Molecular structures of viral proteins determined by crystallography in 1980's:
    rhinovirus: M.Rossmann @ Purdue;
    influenza: D. Wiley @ Harvard and others)
  • Viral proteins mutate very fast, thwarting attempts to design drugs to combat them
  • Still not much you can do about treating a cold or flu (but better days may be before us)

• Bronchitis:

  • Secondary bacterial infections associated with colds may cause infection of the bronchi responds to antibiotic treatment
  • Chronic bronchitis may be due to long term degeneration caused by smoking or air pollution

• Strep throat:

  
  
  • Throat infection caused by Streptococcus pyogenes; Very sore throat and fever
  • May lead to Rheumatic fever - damages heart valves

Lung disorders

• Pneumonia

  • Caused by bacterial or viral infections of the lungs
  • Alveoli become nonfunctional as they fill with mucus and pus

• Tuberculosis

  • Caused by tubercle bacillus
  • Alveoli burst and replaced connective tissue
  • Bacilli protect themselves with a capsule caused a tubercle.
  • Antibiotic resistant strains of TB are a grave concern

• Emphysema

  • Bronchioles become damaged and collapse;
    simplification of the highly convoluted structure of lung
  • Air is trapped, alveoli may rupture
  • Symptoms are breathlessness (apnea) and coughing
  • Oxygen to blood stream is reduced leading to mental disabilities
  • Heart works harder to pump more blood through pulmonary capillaries to compensate, may lead to heart problems

• Lung Cancer

  • Smoking major cause of lung cancer
  • Cells lining the bronchi thicken "callus"
  • Cilia gradually disappear
  • Tar (hydrocarbons, other complex organics) and other substances settle in lungs
  • Individual cells may eventually develop abnormal nuclei - "transformed"
  • Cancer cells proliferate, tumors develop
  • Individual cells may break loose and invade other tissues;
    process is called metastasis