Respiratory System

Dr. AndersonGCIT

Basic Concepts

• Surface area relative to diffusion

• Physics of Airflow

• Special ways to insure against pathogen invasion of large mucus membranes (lungs and sinuses)

Nose and Sinuses

Nose Functions

• Opening for air exchange• Moistens and warms air• Houses sensory (smell) neurons• Filters air going to lungs• Serves as resonating chamber for speech

Mucus Membranes

• Line the interior surfaces of the nasal cavity– Mucus and defensive compounds (enzymes) are

secreted to destroy trapped pathogens (E.g. defensins)

– Ciliated epithelia move mucus and trapped contaminants to the back of the throat where they are swallowed and digested in the stomach

Nasal Conchae

• Occur laterally from the lateral walls of the nasal cavity– Covered in mucosa and highly vascular– This serves to warm and moisten air and trap

particles that may be inhaled

The Pharynx

• Connects nasal cavity and mouth

• Nasopharynx – (Superior to level of the soft palate) - only serves to transport air

• Oropharynx – (Posterior to oral cavity) – both swallowed food and air pass through

• Laryngopharynx – (merging of esophagus and trachea) serves to separate food and air

Larynx - Function

• Provides a “switching” mechanism between inspiration and swallowing

• Also houses vocal cords for speech

Larynx

Cartilagenous “box” that maintains an open airway

– Needs to be rigid – why?

– Epiglottis – fold of cartilage that closes the trachea during swallowing

Voice Production

• Vocal cords are stretched on either side of the larynx, and vibrate as air passed over them from the lungs

• Air moves between these vocal cords through a space called the glottis

• Laryngeal muscles that surround the cartilage change the pitch of the voice by flexing and relaxing

Trachea (Windpipe)• Passageway for air into the lungs, from the pharynx

• Rings of cartilage prevent collapse under the negative pressure of inhalation (rigid, but flexible)

• Trachealis muscle allow the trachea to flex during inhalation, exhalation, sneezing and swallowing

• Lined with mucosa and cilia which propels particles towards the throat to be swallowed

Bronchi

• Point at which the trachea bifurcates (right bronchus is wider, shorter and more vertical)

• No cartilaginous rings, but irregular plates hold bronchi open

• Very little mucus produced, therefore pathogens and contaminants removes by WBCs (macrophages)

Bronchi• Bifurcates from trachea into lungs

- Further subdivides into secondary, (tertiary, etc. bronchi) within the lungs

- Bronchioles are 0.1 mm in diameter- Terminal bronchioles are 0.05 mm in diameter and

lead to the alveoli

Anatomy - Lungs

• Left lung – divided into 2 lobes (superior and inferior)– Also has space made to accommodate the heart

(cardiac notch)

• Right Lung – 3 lobes (superior, middle and inferior)

• Both lungs have sections called bronchopulmonary segments that are separated by connective tissue

Basic Anatomy

Alveoli (the respiratory zone)

• Respiratory bronchioles lead to alveolar ducts which lead to alveolar sacs that make up the alveoli– Roughly 300 million alveoli present for gas

exchange

Blood Supply

Alveoli - Structure

• Composed of extremely thin single layer of squamous epithelial cells, which allows rapid diffusion of O2 in and CO2 out of the blood

• Also allows the evaporation of water out of the blood

Alveolar Blood Supply

Mechanics of Breathing• Partial Pressure

• Diffusion

Atmospheric Pressure

• At sea level, air rushes towards areas of relatively lower pressure and away from areas of relatively higher pressure

• This difference in partial pressures changes in the chest cavity via muscle flexing and resultant forces in the thoracic cavity

Diaphragm• Sheet of muscle that separates the thoracic and abdominal

cavities

• Flexing the diaphragm causes it to drop (inferiorly), increasing the empty volume of the thoracic cavity

• The resulting negative pressure causes air to rush into the lungs and fill the negative space (inspiration)

• As the diaphragm relaxes, it rises and increases the pressure in the thoracic cavity, causing exhalation

Intercostal Muscles• Contraction of intercostal muscles lifts the rib

cage up (superiorly)

• This flexion serves to “open up” the rib cage and decreases the pressure inside the chest, causing air to rush in

Physics of Airflow

• Flow = Change in pressure/resistance

• Look familiar?

• Air is a fluid, just as blood is, and is therefore subject to the same physical rules

Shouldn’t lungs collapse?

• Elastic nature of lungs causes them to contract inwards

• Surface tension in alveoli (water tension) tries to collapse alveoli

• Wouldn’t this be bad?• How is this avoided?

Pressure Balances

• The outside of the lung (visceral pleura) is attached via pleural fluid to the parietal pleura (inside surface of the pleural cavity) keeping them from collapsing

• This keeps the lungs clinging tightly to the thoracic wall (parietal pleura), preventing their collapse

Alveolar Surfactant

• Surfactant decreases the tension between water molecules (breaks the cohesiveness between molecules)

• Reduces the force trying to pull individual alveoli together

Respiratory Volume and Pulmonary Function

• Volumes– Tidal Volume: Amount of air moved in and out

under normal resting conditions– Inspiratory Reserve Volume: amount of air that

can be inspired forcibly beyond the tidal volume– Expiratory Reserve Volume: volume that can be

forcibly expired beyond the tidal volume– Residual Volume: air left in lungs, even after

forced expiration

Gas Physics• Dalton’s Law of Partial Pressures – gases exert a

pressure in proportion to its concentration in a mixture

• Air – 78% N2, – 21% O2, – 1% Other gases (CO2, rare gases, etc.)

• Pressure of gas is proportional to its concentration in a mixture

Henry’s Law• Gas will dissolve into a liquid at a rate

proportional to its partial pressure and vice-versa– Gas liquid– Liquid gas

• This is what allows for the movement of O2 in, and CO2 out of the blood

Factors Effecting Gas Exchange Rate

• Pressure Gradients (vary with altitude, etc.)

• Ventilation-Perfusion coupling – must be an efficient match between the volume of air reaching the alveoli and the blood flow in pulmonary capillaries– This is accomplished via vasoconstriction/dilation

• Thickness and Surface area of Respiratory Membrane – Thickening of this membrane can lead to respiration issues

Oxygen Transport• O2 primarily carried by hemoglobin in blood– 4 Heme groups in hemoglobin

Deoxyhemoglobin Oxyhemoglobin

0 1 2 3 4 (Number of heme groups carrying Oxygen)

Factors Affecting Hemoglobin Saturation

• Partial Pressure of O2

• Blood pH• Temperature• BPG concentration – a metabolite that bonds

reversibly with hemoglobin

Bohr Effect

• Increasing acidity (from increasing levels of CO2) weaken the bond between hemoglobin and O2. – What does this mean? Is this a good or bad thing?

CO2 Transport

• CO2 is transported in – Plasma (7-10%)– *Bound to hemoglobin (carbaminohemoglobin) –

binds to amino acids, not the heme molecule– *as bicarbonate in plasma (via carbonic

anhydrase) and RBC’s (enzyme-mediated in BRC cytoplasm)

• CO2 loading enhances O2 release (Bohr Effect)

Control of Respiration• Neural Control – Medulla Oblongata

• Ventral Respiratory Group (VRG)– Phrenic and intercostal nerves cause diaphragm and intercostal

contraction• Dorsal Respiratory Group (DRG)

– Modulate rhythms generates by VRG due to peripheral stimulation (stretch and chemoreceptors)

• Pontine Respiratory Group (PRG)– Also modulates breathing rhythm by directing impulses to the

VRG

• Communication between all of these centers regulates breathing rhythm

Factors Influencing Breathing Rate• Chemoreceptors – monitor blood pH and O2 levels– Central (found in brain stem), monitors blood pH– Peripheral (found in aortic arch and carotid arteries),

monitors CO2, blood pH

• CO2 in blood (Hypercapnia) = blood pH = increased respiration rate

• CO2 in blood (Hypocapnia) = blood pH = decreased respiration rate

Higher Brain Respiratory Inputs

• Hypothalamus– Processes sensory input (rapid chilling and/or

heating, pain, etc.) or limbic input affect breathing rate

• Cortical Controls– Respiration rate can be consciously controlled, but

will be overridden by brain stem when CO2 gets too high

Reflexive Respiration

• Irritants can cause reflexive constriction of passageways

• Inflation reflex – stretch receptors prevent lung over-inflation (inspiring too much air)

Respiratory Adjustments

• Exercise - CO2 in blood (Hypercapnia) from muscle contractions – However, these are not the stimuli!• Psychological, cortical, and proprioreceptor input are the

cause (we think)

• Altitude– Decrease O2 pressure results in lower O2 absorption

rates• Altitude Sickness – headache, nausea, fainting, death?

Respiratory Diseases

• COPD – Chronic Obstructive Pulmonary Diseases – irreversible decrease in the ability to force air out of the lungs

– Most patients smoke (80%)– Labored breathing (dyspnea)– Coughing and infections– Hypoventilation

COPD’s• Emphysema – alveoli are enlarged and walls of alveoli are

destroyed– Harder to move air– Bronchioles open during inspiration, but collapse upon expiration,

trapping air in the lungs– Increases resistance to blood flow causing right side of heart to

increase in size

• Chronic Bronchitis – constant exposure to irritants creates stagnant mucus in lungs– Decreases air flow– Increases chance of infection

Other Respiration Disorders

• Asthma – inflammation of lung issue increases resistance to air movement– Allergies– Stress– Due to an “aseptic environment”??

• Tuberculosis – chronic bacterial infection of the lungs

• Lung Cancer– Very often metastasizes before detection