Chapter 23: The Respiratory System

Copyright 2009, John Wiley & Sons, Inc.

Respiratory System Anatomy 

Structurally 

Upper respiratory system 



Lower respiratory system 



Nose, pharynx and associated structures Larynx, trachea, bronchi and lungs

Functionally 

Conducting zone – conducts air to lungs 

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Nose, pharynx, larynx, trachea, bronchi, bronchioles and terminal bronchioles

Respiratory zone – main site of gas exchange 

Respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli

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Structures of the Respiratory System

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Nose  

External nose – portion visible on face Internal nose – large cavity beyond nasal vestibule  

 

Internal nares or choanae Ducts from paranasal sinuses and nasolacrimal ducts open into internal nose Nasal cavity divided by nasal septum Nasal conchae subdivide cavity into meatuses 



Increase surface are and prevents dehydration

Olfactory receptors in olfactory epithelium Copyright 2009, John Wiley & Sons, Inc.

Copyright 2009, John Wiley & Sons, Inc.

Pharynx 





Starts at internal nares and extends to cricoid cartilage of larynx Contraction of skeletal muscles assists in deglutition Functions   

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Passageway for air and food Resonating chamber Houses tonsils

3 anatomical regions  



Nasopharynx Oropharynx Laryngopharynx

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Larynx  

Short passageway connecting laryngopharynx with trachea Composed of 9 pieces of cartilage  

   

Thyroid cartilage or Adam’s apple Cricoid cartilage hallmark for tracheotomy

Epiglottis closes off glottis during swallowing Glottis – pair of folds of mucous membranes, vocal folds (true vocal cords, and rima glottidis (space) Cilia in upper respiratory tract move mucous and trapped particles down toward pharynx Cilia in lower respiratory tract move them up toward pharynx

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Larynx

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Structures of Voice Production 

Mucous membrane of larynx forms 

Ventricular folds (false vocal cords) – superior pair 

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Vocal folds (true vocal cords) – inferior pair 

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Function in holding breath against pressure in thoracic cavity Muscle contraction pulls elastic ligaments which stretch vocal folds out into airway Vibrate and produce sound with air Folds can move apart or together, elongate or shorten, tighter or looser

Androgens make folds thicker and longer – slower vibration and lower pitch Copyright 2009, John Wiley & Sons, Inc.

Copyright 2009, John Wiley & Sons, Inc.

Trachea 

Extends from larynx to superior border of T5 



4 layers    

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Divides into right and left primary bronchi Mucosa Submucosa Hyaline cartilage Adventitia

16-20 C-shaped rings of hyaline cartilage 

Open part faces esophagus

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Location of Trachea

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Bronchi  

Right and left primary bronchus goes to right lung Carina – internal ridge 



Divide to form bronchial tree 



Most sensitive area for triggering cough reflex

Secondary lobar bronchi (one for each lobe), tertiary (segmental) bronchi, bronchioles, terminal bronchioles

Structural changes with branching   

Mucous membrane changes Incomplete rings become plates and then disappear As cartilage decreases, smooth muscle increases  

Sympathetic ANS – relaxation/ dilation Parasympathetic ANS – contraction/ constriction

Copyright 2009, John Wiley & Sons, Inc.

Copyright 2009, John Wiley & Sons, Inc.

Lungs 

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Separated from each other by the heart and other structures in the mediastinum Each lung enclosed by double-layered pleural membrane 

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Pleural cavity is space between layers 

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Parietal pleura – lines wall of thoracic cavity Visceral pleura – covers lungs themselves Pleural fluid reduces friction, produces surface tension (stick together)

Cardiac notch – heart makes left lung 10% smaller than right

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Relationship of the Pleural Membranes to Lungs

Copyright 2009, John Wiley & Sons, Inc.

Copyright 2009, John Wiley & Sons, Inc.

Anatomy of Lungs 

Lobes – each lung divides by 1 or 2 fissures 

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Each lobe receives it own secondary (lobar) bronchus that branch into tertiary (segmental) bronchi

Lobules wrapped in elastic connective tissue and contains a lymphatic vessel, arteriole, venule and branch from terminal bronchiole Terminal bronchioles branch into respiratory bronchioles which divide into alveolar ducts About 25 orders of branching

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Microscopic Anatomy of Lobule of Lungs

Copyright 2009, John Wiley & Sons, Inc.

Alveoli  



Cup-shaped outpouching Alveolar sac – 2 or more alveoli sharing a common opening 2 types of alveolar epithelial cells 

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Type I alveolar cells – form nearly continuous lining, more numerous than type II, main site of gas exchange Type II alveolar cells (septal cells) – free surfaces contain microvilli, secrete alveolar fluid (surfactant reduces tendency to collapse)

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Alveolus 

Respiratory membrane   

 

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Alveolar wall – type I and type II alveolar cells Epithelial basement membrane Capillary basement membrane Capillary endothelium Very thin – only 0.5 µm thick to allow rapid diffusion of gases

Lungs receive blood from  

Pulmonary artery - deoxygenated blood Bronchial arteries – oxygenated blood to perfuse muscular walls of bronchi and bronchioles

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Components of Alveolus

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Pulmonary ventilation 

Respiration (gas exchange) steps 1.

Pulmonary ventilation/ breathing  

2.

External (pulmonary) respiration 

3.

Inhalation and exhalation Exchange of air between atmosphere and alveoli Exchange of gases between alveoli and blood

Internal (tissue) respiration 



Exchange of gases between systemic capillaries and tissue cells Supplies cellular respiration (makes ATP)

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Inhalation/ inspiration 

Pressure inside alveoli lust become lower than atmospheric pressure for air to flow into lungs 



Achieved by increasing size of lungs 

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760 millimeters of mercury (mmHg) or 1 atmosphere (1 atm) Boyle’s Law – pressure of a gas in a closed container is inversely proportional to the volume of the container

Inhalation – lungs must expand, increasing lung volume, decreasing pressure below atmospheric pressure Copyright 2009, John Wiley & Sons, Inc.

Boyle’s Law

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Inhalation 

Inhalation is active – Contraction of  Diaphragm – most important muscle of inhalation  



Flattens, lowering dome when contracted Responsible for 75% of air entering lungs during normal quiet breathing

External intercostals  

Contraction elevates ribs 25% of air entering lungs during normal quiet breathing

Accessory muscles for deep, forceful inhalation When thorax expands, parietal and visceral pleurae adhere tightly due to subatmospheric pressure and surface tension – pulled along with expanding thorax As lung volume increases, alveolar (intrapulmonic) pressure drops 





Copyright 2009, John Wiley & Sons, Inc.

Copyright 2009, John Wiley & Sons, Inc.

Exhalation/ expiration  

Pressure in lungs greater than atmospheric pressure Normally passive – muscle relax instead of contract 

 



Based on elastic recoil of chest wall and lungs from elastic fibers and surface tension of alveolar fluid Diaphragm relaxes and become dome shaped External intercostals relax and ribs drop down

Exhalation only active during forceful breathing

Copyright 2009, John Wiley & Sons, Inc.

Copyright 2009, John Wiley & Sons, Inc.

Copyright 2009, John Wiley & Sons, Inc.

Airflow  

Air pressure differences drive airflow 3 other factors affect rate of airflow and ease of pulmonary ventilation 

Surface tension of alveolar fluid   

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Lung compliance  

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Causes alveoli to assume smallest possible diameter Accounts for 2/3 of lung elastic recoil Prevents collapse of alveoli at exhalation High compliance means lungs and chest wall expand easily Related to elasticity and surface tension

Airway resistance 

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Larger diameter airway has less resistance Regulated by diameter of bronchioles & smooth muscle tone

Copyright 2009, John Wiley & Sons, Inc.

Lung volumes and capacities 

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Minute ventilation (MV) = total volume of air inhaled and exhaled each minute Normal healthy adult averages 12 breaths per minute moving about 500 ml of air in and out of lungs (tidal volume) MV = 12 breaths/min x 500 ml/ breath = 6 liters/ min Copyright 2009, John Wiley & Sons, Inc.

Spirogram of Lung Volumes and Capacities

Copyright 2009, John Wiley & Sons, Inc.

Lung Volumes 

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Only about 70% of tidal volume reaches respiratory zone Other 30% remains in conducting zone Anatomic (respiratory) dead space – conducting airways with air that does not undergo respiratory gas exchange Alveolar ventilation rate – volume of air per minute that actually reaches respiratory zone Inspiratory reserve volume – taking a very deep breath

Copyright 2009, John Wiley & Sons, Inc.

Lung Volumes 

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Expiratory reserve volume – inhale normally and exhale forcefully Residual volume – air remaining after expiratory reserve volume exhaled Vital capacity = inspiratory reserve volume + tidal volume + expiratory reserve volume Total lung capacity = vital capacity + residual volume Copyright 2009, John Wiley & Sons, Inc.

Exchange of Oxygen and Carbon Dioxide 

Dalton’s Law  Each gas in a mixture of gases exerts its own pressure as if no other gases were present  Pressure of a specific gas is partial pressure Px  Total pressure is the sum of all the partial pressures  Atmospheric pressure (760 mmHg) = PN2 + PO2 + PH2O + PCO2 + Pother gases  Each gas diffuses across a permeable membrane from the are where its partial pressure is greater to the area where its partial pressure is less  The greater the difference, the faster the rate of diffusion Copyright 2009, John Wiley & Sons, Inc.

Partial Pressures of Gases in Inhaled Air PN2

=0.786

x 760mm Hg

= 597.4 mmHg

PO2

=0.209

x 760mm Hg

= 158.8 mmHg

PH2O

=0.004

x 760mm Hg

= 3.0 mmHg

PCO2

=0.0004 x 760mm Hg

= 0.3 mmHg

Pother gases

=0.0006 x 760mm Hg

= 0.5 mmHg

TOTAL Copyright 2009, John Wiley & Sons, Inc.

= 760.0 mmHg

Henry’s law 





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Quantity of a gas that will dissolve in a liquid is proportional to the partial pressures of the gas and its solubility Higher partial pressure of a gas over a liquid and higher solubility, more of the gas will stay in solution Much more CO2 is dissolved in blood than O2 because CO2 is 24 times more soluble Even though the air we breathe is mostly N2, very little dissolves in blood due to low solubility 

Decompression sickness (bends) Copyright 2009, John Wiley & Sons, Inc.

External Respiration in Lungs 

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Oxygen  Oxygen diffuses from alveolar air (PO2 105 mmHg) into blood of pulmonary capillaries (PO2 40 mmHg)  Diffusion continues until PO2 of pulmonary capillary blood matches PO2 of alveolar air  Small amount of mixing with blood from conducting portion of respiratory system drops PO2 of blood in pulmonary veins to 100 mmHg Carbon dioxide  Carbon dioxide diffuses from deoxygenated blood in pulmonary capillaries (PCO2 45 mmHg) into alveolar air (PCO2 40 mmHg)  Continues until of PCO2 blood reaches 40 mmHg

Copyright 2009, John Wiley & Sons, Inc.

Internal Respiration  

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

Internal respiration – in tissues throughout body Oxygen  Oxygen diffuses from systemic capillary blood (PO2 100 mmHg) into tissue cells (PO2 40 mmHg) – cells constantly use oxygen to make ATP  Blood drops to 40 mmHg by the time blood exits the systemic capillaries Carbon dioxide  Carbon dioxide diffuses from tissue cells (PCO2 45 mmHg) into systemic capillaries (PCO2 40 mmHg) – cells constantly make carbon dioxide  PCO2 blood reaches 45 mmHg At rest, only about 25% of the available oxygen is used  Deoxygenated blood would retain 75% of its oxygen capacity Copyright 2009, John Wiley & Sons, Inc.

Copyright 2009, John Wiley & Sons, Inc.

Rate of Pulmonary and Systemic Gas Exchange 

Depends on 

Partial pressures of gases 

  

Alveolar PO2 must be higher than blood PO2 for diffusion to occur – problem with increasing altitude

Surface area available for gas exchange Diffusion distance Molecular weight and solubility of gases 

O2 has a lower molecular weight and should diffuse faster than CO2 except for its low solubility - when diffusion is slow, hypoxia occurs before hypercapnia

Copyright 2009, John Wiley & Sons, Inc.

Transport of Oxygen and Carbon Dioxide 

Oxygen transport  

Only about 1.5% dissolved in plasma 98.5% bound to hemoglobin in red blood cells 

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 

Heme portion of hemoglobin contains 4 iron atoms – each can bind one O2 molecule Oxyhemoglobin Only dissolved portion can diffuse out of blood into cells Oxygen must be able to bind and dissociate from heme

Copyright 2009, John Wiley & Sons, Inc.

Copyright 2009, John Wiley & Sons, Inc.

Relationship between Hemoglobin and Oxygen Partial Pressure   



Higher the PO2, More O2 combines with Hb Fully saturated – completely converted to oxyhemoglobin Percent saturation expresses average saturation of hemoglobin with oxygen Oxygen-hemoglobin dissociation curve  

In pulmonary capillaries, O2 loads onto Hb In tissues, O2 is not held and unloaded 

75% may still remain in deoxygenated blood (reserve)

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Oxygen-hemoglobin Dissociation Curve

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Hemoglobin and Oxygen 

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Other factors affecting affinity of Hemoglobin for oxygen Each makes sense if you keep in mind that metabolically active tissues need O2, and produce acids, CO2, and heat as wastes 

 

Acidity PCO2 Temperature

Copyright 2009, John Wiley & Sons, Inc.

Bohr Effect 

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As acidity increases (pH decreases), affinity of Hb for O2 decreases Increasing acidity enhances unloading Shifts curve to right

PCO2  Also shifts curve to right  As PCO2 rises, Hb unloads oxygen more easily  Low blood pH can result from high PCO2 Copyright 2009, John Wiley & Sons, Inc.

Temperature Changes Within limits, as temperature increases, more oxygen is released from Hb  During hypothermia, more oxygen remains bound 2,3-bisphosphoglycerate  BPG formed by red blood cells during glycolysis  Helps unload oxygen by binding with Hb 



Copyright 2009, John Wiley & Sons, Inc.

Fetal and Maternal Hemoglobin 

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

Fetal hemoglobin has a higher affinity for oxygen than adult hemoglobin Hb-F can carry up to 30% more oxygen Maternal blood’s oxygen readily transferred to fetal blood

Copyright 2009, John Wiley & Sons, Inc.

Carbon Dioxide Transport 

Dissolved CO2 



Carbamino compounds  

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Smallest amount, about 7% About 23% combines with amino acids including those in Hb Carbaminohemoglobin

Bicarbonate ions 

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70% transported in plasma as HCO3Enzyme carbonic anhydrase forms carbonic acid (H2CO3) which dissociates into H+ and HCO3-

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CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3

Chloride shift 

 

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HCO3- accumulates inside RBCs as they pick up carbon dioxide Some diffuses out into plasma To balance the loss of negative ions, chloride (Cl-) moves into RBCs from plasma Reverse happens in lungs – Cl- moves out as moves back into RBCs

Copyright 2009, John Wiley & Sons, Inc.

Copyright 2009, John Wiley & Sons, Inc.

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