Respiratory System

Functions of Respiratory System

1. Provides for gas exchange

2. Regulates blood pH

3. Contains receptors for smell

4. Filters inspired air

5. Produces vocal sounds

6. Excretes small amounts of water and heat

Classification of Respiratory System Components

according to:

Structure:

• Upper Respiratory System

  • Nose

  • Nasal Cavity

  • Pharynx

• Lower Respiratory System

  • Larynx

  • Trachea

  • Bronchi

  • Lungs

Function:

• Conducting Zone

  • Nose

  • Nasal Cavity

  • Pharynx

  • Trachea

  • Bronchi

  • Bronchioles

  • Terminal Bronchioles (end point)

• Respiratory Zone

  • Respiratory Bronchioles

  • Alveolar Ducts

  • Alveolar Saccules (Sacs)

  • Pulmonary Alveoli

Note: Conducting zone filters, warms, moistens, passes air into respiratory zone; Respiratory zone is where gas exchange occurs

Related Branches of Medicine

Otorhinolaryngology:

• diagnosis and treatment of ear, nose, throat disease

• ENT

Pulmonology:

• specializes in diagnosis and treatment of lung diseases 

Nose

External Nose:

visible section of the nose

• Bony Framework

  • nasal bones + frontal bone + maxillae (upper jaw)

• Cartilaginous Framework

  • hyaline cartilage + fibrous connective tissue

• External Nares/Nostrils

Internal Nose:

nasal cavity inside skull

• Lateral Walls

  • walls formed from bone

• Nasal Cavity

  • space in skull above oral cavity

• Internal Nares

  • two openings from internal nose into pharynx

  • also called choanae

• Olfactory Epithelium

External Nose Functions

Functions of Interior Structures:

• Warming of Air

• Moistening of Air

• Filtering Incoming Air

• Detecting olfactory stimuli

• Modifying speech vibrations

  • as they pass through large, hollow, resonating chambers

Internal Nose

• a large cavity in anterior aspect of skull

• lies inferior to nasal bone

• lies superior to oral cavity

Lateral Walls:

• formed by:

  • Maxilla bone (upper jaw)

  • Ethmoid bone (at root of nose)

  • Lacrimal bone (eye socket)

  • Palatine bone (part of hard palate)

  • Inferior nasal conchae bones

Nasal Cavity:

• Vestibule

  • entrance of nasal cavity; just after nostrils

  • lined with skin w/ hair follicles, sweat glands, sebaceous glands

  • filters out large dust particles

• Nasal Septum

  • vertical partition

  • divides nose equally into left and right

  • anterior: hyaline cartilage

  • posterior: bone

• Conchae

  • different from choanae

  • also called nasal turbinates

  • three pairs of bony projections

  • superior, middle, and inferior conchae

  • increases surface area

Internal Nares:

• choanae

• posterior to nasal cavity; opens into nasopharynx

Olfactory Epithelium:

• also called olfactory receptors

• superior portion of nasal cavity

Airflow Process in Nose

1. Air enters nostrils/external nares → 

2. air passes through vestibule →

3. air is warmed by blood in capillaries as it whirls around conchae and meatuses →

4. mucus moistens air and traps dust →

5. cilia move mucus/trapped dust towards pharynx (where it can then be swallowed/spit)

Pharynx

• muscular tube-like structure

• connects nasal cavity + mouth to esophagus + larynx (voice box)

• begins at internal nares

• reaches until cricoid cartilage

Location:

• posterior to nasal + oral cavity

• superior to larynx

• anterior to cervical vertebrae

Regions:

• Nasopharynx:

  • immediately after nasal cavity; upper part

• Oropharynx

  • led into from oral cavity; middle part

  • below nasopharynx

• Laryngopharynx/Hypopharynx

  • bottom part

  • below both cavities

Pharynx Functions

• conducts air from nasal cavity + mouth to larynx and trachea (breathing)

• conducts food + liquid from oral cavity to esophagus (swallowing)

• provides resonating chamber for speech production

• houses tonsils

  • part of immune system, fight infections

Nasopharynx

• uppermost part of pharynx

• situated behind nasal cavity

• passageway for air only

• posterior wall contains pharyngeal tonsil

  • also called adenoid tonsil

• lined with ciliated pseudostratified columnar epithelium

  • traps and removes dust + foreign matter

• has 5 openings

  • 2 internal nares

  • 2 openings that lead into the auditory tubes

  • 1 opening into oropharynx

Functions:

• accepts air from nasal cavity

• gathers clusters of mucus with dust particles

  • cilia proper mucus downwards towards laryngopharynx

• shares some air with Eustachian Tubes (auditory tube)

  • balances air pressure between pharynx and middle ear

Oropharynx

• located behind oral cavity

• has only one opening, the fauces (opening from the mouth)

• contains palatine and lingual tonsils

• common passageway for food and air

• lined with nonkeratinized stratified squamous epithelium

  • same as GI tract because also part of GI tract

Laryngopharynx

• also called hypopharynx

• lowest part of pharynx

• situated behind the larynx (voice box)

• common pathway for food and air

• leads to esophagus, involved in swallowing process/deglutition

• lined with stratified squamous epithelium

  • protects against mechanical/chemical irritation

• begins at level of hyoid bone

• opens into esophagus (inferiorly) and larynx (anteriorly)

Larynx

• also called voice box

• short passageway, connects laryngopharynx to trachea

• pathway for air to travel when breathing

• in the middle of the neck

  • anterior to esophagus

  • anterior to C4-C6 cervical vertebrae 

• Wall is composed of 9 cartilages

  • Epiglottis

  • Thyroid

  • Cricoid

  • Arytenoid (2)

  • Cuneiform (2)

  • Corniculate (2)

Epiglottis

• primarily composed of elastic cartilage

• large, leaf-shaped

• closes the glottis

  • glottis = vocal cords + rima glottidis (the space between the cords)

• when swallowing, larynx rises which pushes the leaf portion closed

  • prevents entry of food into larynx

  • “leaf” portion is superior, broad, unattached, and free to move up and down (like flap or trap door)

Thyroid Cartilage

• also called the Adam’s Apple

• largest cartilage in larynx

• anterior region of neck, just below thyroid gland

• shield-shaped, consists of two plate-like structures (laminae)

  • meet in the midline to form front portion of larynx

• provide structural support and protection

• house and protect the vocal cords

  • role in controlling tension of vocal cords

  • crucial for speech production

Cricoid Cartilage

• ring of hyaline cartilage

• forms inferior wall of larynx 

• serves as a landmark for making an emergency airway (cricothyrotomy)

Arytenoid Cartilage

• small, triangle shaped segments of hyaline cartilage

• situated at the upper, back edge of the cricoid cartilage

• influence changes in tension and position of vocal cords

  • important for production of vocal sounds

Corniculate Cartilage

• horn-shaped pieces of elastic cartilage

• located at the apex of each arytenoid cartilage

• supporting structure for the epiglottis

Cuneiform Cartilage

• anterior to corniculate cartilage

• club-shaped elastic cartilage

• support the vocal folds

• support the lateral aspects of the epiglottis

Structures of Vocal Production

• Ventricular Folds

  • false vocal cords

  • superior to vocal folds

  • have protective function; cover the true vocal cords

  • hold breath against pressure when brought together

• Vocal Folds

  • true vocal cords

  • inferior to ventricular folds

  • thicker and longer in males (due to androgens)

  • vibrate slowly

  • bands of elastic ligament stretch within

    • when air passes through them, sound is made

• Rima Glottidis

  • space between vocal folds

• Rima Vestibuli

  • space between ventricular folds

• Laryngeal Sinus

  • lateral expansion of middle portion of laryngeal cavity

Laryngitis

• inflammation of the larynx

Common Causes:

• respiratory infection

• irritants

Hoarseness or Loss of Voice:

• potential consequence of laryngitis

• caused by inflammation of vocal cords

• can be permanent due to chronic inflammation (ex: due to smoking)

Laryngeal Cancer

• almost exclusively found in smokers

• Symptoms:

  • hoarseness

  • pain on swallowing

  • pain radiating to ear

• Treatment:

  • radiation therapy

  • surgery

  • laryngectomy

    • surgical removal of larynx

    • leaves a hole in the throat

    • patient unable to speak without device afterwards

    • patients can no longer breathe normally (epiglottis removed)

    • must breathe through stoma (hole in neck)

Trachea

• also called windpipe

• tubular passageway for air

• anterior to esophagus

• extends from larynx to superior border of fifth thoracic vertebra (T5)

• composed of 16-20 incomplete hyaline rings (C-Shaped)

C-Shaped Rings:

• incomplete ring allows for slight expansion of esophagus into trachea when swallowing

• semi-rigid support; prevents trachea from collapsing inwards

Tracheal Wall Layers:

from deep to superficial

• mucosa

  • ciliated pseudostratified columnar epithelium

  • lamina propria of elastic and reticular fibers

• submucosa

  • areolar connective tissue

  • seromucous glands and ducts

• cartilaginous layer (hyaline)

• adventitia (areolar connective tissue)

Tracheal Obstruction

Causes:

• collapse of cartilage rings due to crushing injury to chest

• inflammation of mucus membrane

• accidental inhalation of foreign objects (ex: small toys, food particles, etc.)

• cancerous tumors that protrude into airway

Management:

Tracheostomy:

• operation, creates opening in trachea

• short, longitudinal, incision inferior to cricoid cartilage

• metal/plastic tracheal tube inserted into hole

Intubation:

• tube inserted through mouth or nose; guided downwards through larynx & trachea

• tube displaces blockages; also allows air to pass through

• mucus causing obstruction may be suctioned out using tube

Bronchi

• consists of right primary and left primary bronchi

• right bronchi is more vertical, shorter, and wider

  • as such, an inhaled object is more likely to enter and lodge in the right primary bronchus

• left and right primary bronchus enter left and right lung respectively

• also contain incomplete hyaline cartilage rings

Carina:

• also called tracheal carina

• ridge/cartilaginous projection

• point where trachea bifurcates into left and right primary bronchi

• widening/distortion of carina is indicative of carcinoma

Path from Trachea to Bronchi Composition and Histology

Note:

• approaching bronchi (downwards), cartilage decreases, smooth muscle increases

  • cartilage plates also tend to replace incomplete cartilage rings going downwards

• approaching trachea (upwards), cartilage increases, smooth muscle decreases

Pathway:

Trachea → Primary Bronchi → Secondary Bronchi → Tertiary Bronchi → Bronchioles → Terminal Bronchioles

Pathway Histology:

• From Trachea to Tertiary: ciliated pseudostratified columnar epithelium

• Large Bronchioles: ciliated simple columnar epithelium with some goblet cells

• Small Bronchioles: ciliated simple cuboidal epithelium with no goblet cells

• Terminal Bronchioles: non-ciliated simple cuboidal epithelium

Bronchi Branches

• left primary bronchi → left lung; right primary bronchi → right lung

• upon entering lungs; divide into secondary (lobar) bronchi (one for each lobe)

  • right lung = 3 lobes

  • left lung = 2 lobes

• Lobar bronchi further branch into tertiary (segmental) bronchi

  • supply specific segments within the lobes

  • 10 in each lung, despite different lobe count

• which then branch into bronchioles, which branch further repeatedly

• eventually branch into terminal bronchioles

Lungs

• paired, cone-shaped organs

• located in thoracic cavity; protected by ribcage

• pair is separated by heart and other structures in mediastinum

Right Lung:

• consists of three lobes

  • Upper/Superior

  • Middle

  • Lower/Inferior

• thicker, broader, but shorter than left lung

Left Lung:

• consists of two lobes

  • Upper/Superior

  • Lower/Inferior

  • 10% smaller than right lung

Note: if one lung collapses, the other may still function

Pleural Membrane

• a double layer of serous membrane that encloses and protects each lung

Parietal Pleura:

• superficial

• lines the walls of the thoracic cavity

Visceral Pleura:

• deep

• covers the lungs

Pleural Cavity:

• small space between the pleurae

• contains a small amount of lubricating fluid that is secreted by the membranes

Related Conditions:

Pleuritis:

• also called pleurisy

• inflammation of pleura

Pleural Effusion:

• abnormal accumulation of fluid in the pleural cavity

• may be caused by persisting inflammation

Pneumothorax:

• presence of air or gas in pleural cavity

• Causes:

  • surgical opening of chest

  • stab or gunshot wounds

• air accumulation can cause partial/complete collapse of lung

  • air takes space; presses down on lung causing collapse

Hemothorax:

• presence of blood in pleural cavity

• treatment: evacuation of blood from pleural space

Thoracentesis:

• treatment method used to remove excess fluid/air from thoracic cavity

• needle is inserted anteriorly through 7th intercostal space (space between ribs)

  • if inserted anywhere inferior to 7th, risk of accidentally hitting diaphragm 

Lungs: Surface Anatomy

Base:

• broad, concave surface

• rests on diaphragm

• extends downwards to level of the rib cage

• can be felt just above costal margin

Apex:

• rounded, superior portion

• extends above clavicle into root of neck

• can be palpated (examined by touch) just above medial third of clavicle

Cardiac Notch:

• notch on the left lung

• where the heart rests along the lung

• anterior and inferior; can be palpated along left border of the sternum

Costal Surface:

• surface of lungs that lays against the ribs

• matches round curvature of the ribs

Mediastinal (Medial) Surface:

• contains hilum

  • structure where bronchi, blood and lymph vessels, and nerves enter and exit

Fissures:

• divide the lobes

• Right Lung:

  • Oblique: separates upper and middle

  • Horizontal: separates middle and lower

• Left Lung:

  • Oblique: separates upper and lower

Lungs: Lobes and Segments

Right Lung = 3 Lobes

Left Lung = 2 Lobes

• each lobe gets its own secondary bronchus

• Right Lobe gets superior, middle, and inferior secondary bronchi

• Left Lobe gets superior and inferior secondary bronchus

Secondary Bronchi give rise to tertiary bronchi

• there are 10 in each lung, irrespective of how many lobes they have

• each tertiary bronchus supplies a bronchopulmonary segment

• branch into bronchioles

Bronchopulmonary Segments:

• also called pulmonary segments

• both a functional and anatomical unit of the lung

• supplied by a tertiary bronchus

• surrounded by connective tissue septa

• have own segmental veins that drain into the pulmonary veins

• contain small compartments called lobules

Lungs: Lobules

• small, discrete, pyramid shaped unit

• surrounded by elastic connective tissue

• contains:

  • 1 lymphatic vessel

  • 1 arteriole 

  • 1 venule

  • 1 terminal bronchiole branch

• terminal bronchioles then branch into smaller respiratory bronchioles

  • which then subdivide into several alveolar ducts

Lungs: Alveoli

Alveoli:

• tiny, ballon-like structures

• where gas exchange takes place

• around 300 million in the lungs

• provides surface area of 70 m²

Alveolar Sac:

• clusters of alveoli in the lungs

• 2 or more alveoli that share an opening

• terminal ends of the respiratory tree

• responsible for majority of gas exchange

Alveolar Ducts:

• connect respiratory bronchioles to alveolar sacs

Alveolar Wall:

• consists of two types of alveolar epithelial cells

  • Type I: 

    • extremely flat, thin

    • predominant; form most of wall

    • main site of gas exchange

  • Type II:

    • interspersed among Type I cells

    • secrete alveolar fluid

      • keeps surface between air and cells moist

    • produce surfactant

      • reduce alveolar fluid surface tension

      • reduces tendency of alveoli to collapse

      • also called septal cells

• also contain alveolar macrophages (dust cells)

  • wandering phagocytes

  • remove fine dust, particles, other debri

Alveolar Fluid:

• thin layer of fluid; lines inner surface of alveoli

• maintains proper function; facilitates gas exchange

• Composition:

  • water

  • surfactant

  • electrolytes

  • proteins

  • immune cells

Respiratory Membrane

• the membrane through which gas must diffuse in gas exchange

• allows rapid diffusion of gasses between lungs and blood

• includes alveolar and capillary walls

Consists of four layers:

• Alveolar Wall (with Type I and II cells)

• Epithelial Basement Membrane

• Capillary Basement Membrane

• Endothelial Cells of Capillaries

Aqours Third Years being Precious

Basic Respiration Processes

Pulmonary Ventilation:

• also called breathing

• the inhalation and exhalation of air

• between the alveoli and the environment

External Respiration:

• also called pulmonary respiration

• involves gas exchange between alveoli and pulmonary capillaries of the respiratory membrane

• blood is oxygenated, and loses CO₂

Internal Respiration:

• also called tissue respiration

• the exchange of gasses between systemic capillaries and tissue cells

• blood loses oxygen and gains CO₂

Pulmonary Ventilation

• air flows between atmosphere and lungs due to pressure differences

  • pressure created by contraction and relaxation of respiratory muscles

• Air moves from high to low pressure

  • into lungs when pressure is greater in atmosphere

  • out of lungs when pressure is greater in lungs

• relies on inhalation and exhalation

Inhalation

• also called breathing in or inspiration

• an active process, involving muscular contraction

• lung pressure is decreased by increasing the lung volume

  • accomplished via contraction of diaphragm and external intercostals

Diaphragm

• a dome-shaped skeletal muscle

  • while ordinarily involuntary, can be made voluntary

• forms the floor of the thoracic cavity

• most important muscle for respiration

  •  accounts for about 75% of air that enters the lungs during quiet breathing

• normally curved, but contraction flattens it

  • increases vertical volume of thoracic cavity

    • Normal Quiet Inhalation:

      • descends about 1 cm

      • generates pressure difference of 1-3 mmHg

      • inspires about 500 mL of air

    • Forceful Inhalation:

      • ex: due to physical activity

      • descends about 10 cm

      • generates pressure difference of 100 mmHg

      • inspires about 2-3 L of air

External Intercostals

• muscle between the ribs

• contraction elevates the ribs

  • increases anteroposterior and lateral diameters of the chest cavity

  • increases chest cavity volume

• responsible for about 25% of air that enters the lungs during breathing

Intrapleural and Alveolar Pressure

Intrapleural Pressure:

• as thoracic cavity expands, parietal pleura is pulled outwards

• the visceral pleura is pulled alongside it, which also pulls the lungs

Pressure between the two Pleural Layers:

• before inhalation: 756 mmHg

• after inhalation: 754 mmHg

Alveolar Pressure:

• also called intrapulmonic pressure

• as lung volume increases, the pressure within the lungs decreases

Pressure Inside Lungs:

• before inhalation: 760 mmHg

• after inhalation: 758 mmHg

Atmospheric Pressure is 760 mmHg (1 atm)

Pressure of Lungs during Exhalation:

• Intrapleural: 756 mmHg

• Alveolar: 762 mmHg

Specific numbers will not be asked for in exam

Accessory Muscles of Inhalation

• participate only during forceful inhalation

• increase the size of the thoracic cavity (by increasing diameter) 

• Sternocleidomastoid: elevate the sternum

• Scalene Muscles: elevate the first two ribs

• Pectoralis Minor Muscles: elevate the third, fourth, and fifth ribs

Exhalation

• also called breathing out or expiration

• a more passive process

• due to pressure differences, and higher pressure in lungs

• elastic recoil of muscles reduce volume of thoracic cavity

  • no muscular contraction is involved

  • simply due to natural tendency spring back after being stretched

• diaphragm relaxes = dome moves up

• external intercostals relax = ribs depressed

• resulting alveolar pressure: 762 mmHg

Forceful Breathing:

• exhalation becomes active during forceful breathing only

• requires contraction of muscles of exhalation

• Abdominal Muscles 

  • attached to the ribs

    • move inferior ribs downwards

  • compresses abdominal visceral

• Internal Intercostals

  • pulls the ribs inferiorly

Factors that Affect Pulmonary Ventilation

• Surface Tension of Alveolar Fluid

• Compliance of the Lungs

• Airway Resistance

Surface Tension of Alveolar Fluid

• due to secretions of Type II alveolar cells

  • produces thin layer of alveolar fluid

  • coats the luminal surface of the alveoli

• fluid surface tension pulls alveoli in (tries to minimize surface area)

• tension allows alveoli to assume the smallest possible diameter (without collapsing)

• in inhalation, surface tension must be overcome to expand lungs

• in exhalation, surface tensions accounts for 2/3 of the lung’s elastic recoil which decreases lung volume

Surfactant in Alveolar Fluid:

• reduces surface tension

• prevents alveolar collapse at the end of each exhalation

• reduces pressure needed for subsequent alveolar inflation

Surface Tension Related Conditions

Respiratory Distress Syndrome (RDS):

• breathing disorder in premature neonates

  • since lungs are the last organ to develop

  • since lungs are not needed as fetus

• lack of surfactant causes surface tension to increase

• leads to alveoli not remaining open

• greater effort is needed per inhalation

Symptoms:

• tachypnea (high respiratory rate)

• nasal flaring

  • harder breathing = more pressure per breath

  • causes nostrils to widen

  • a sign of use of accessory muscles

• grunting during exhalation

• blue skin color

• intercostal, subcostal, or subxiphoid retractions

  • muscles pull back farther

  • skin is also pulled towards the ribs

  • can see outline of ribs as a result

Diagnosis:

• clinical examination +

• chest radiographs +

• blood tests

Management:

• for mild: O₂ support

• for severe: intubate, give surfactant

  • surfactant available as intratracheal solution

Compliance of the Lungs

• stretchiness of lung and chest walls

  • highly compliant = can expand easily

  • low compliance = lungs resist expansion

• related to elasticity and surface tension

• lungs normally have high compliance

  • elastic fibers in lung are easily stretched

  • surfactant reduces surface tension

Conditions Where Compliance is Decreased:

• Pulmonary Tuberculosis (scarring of lung tissue)

• Pulmonary Edema

• Surfactant Deficiency

• Paralysis of Intercostal Muscles (impedes lung expansion)

Airway Resistance

airflow depends on both pressure difference and resistance

• walls of airway (bronchioles): offer some resistance to normal flow in and out of lungs

Airway Diameter:

• high determinant of resistance

• regulated by contraction/relaxation of smooth muscle in airway

• large diameter = decreased resistance

• small diameter = increased resistance

Related Conditions:

• Obstructive Lung Diseases:

  • Bronchial Asthma

    • smooth muscle constricts

    • alveolar wall is thickened and inflamed

    • fluid secretion increases

  • COPD

Breathing Patterns

Eupnea:

• normal pattern; quiet breathing

• shallow, deep, or combined shallow and deep breathing

• unlabored and effortless

Costal Breathing:

• shallow (chest) breathing

• upward & outward movement of the chest due to contraction of external intercostal muscles

Diaphragmatic Breathing:

• deep (abdominal) breathing

• outward movement of the abdomen due to contraction and descent of diaphragm 

Modified Breathing

Tidal Volume (TV)

• volume of each tide of respiration (every quiet/normal breath)

  • in one normal inhale/exhale

• around 500 mL

• 350 mL - reaches the respiratory zone

• 150 mL - only reaches the conducting zone (the anatomic dead space)

Inspiratory Reserve Volume (IRV)

• volume that can be inhaled on maximal inspiration (after tidal volume)

  • after a normal inhalation, you can inhale even more

• around 3.1 L

• deep breath = 500 mL (TV) + 3.1 L (IRV)

• note: values in textbook are based on Caucasian individuals

Expiratory Reserve Volume (ERV)

• volume that can be exhaled on maximal expiration after tidal volume

• after quiet inhalation (TV) you can exhale even more

• around 1.2 L

• note: lungs are never empty of air; not collapsed and stay patent

FEV₁ 

• test for forced expiratory volume in 1 second

• in one second, inhale as hard and blow as hard as you can into a tube

• then will check how much volume you exhaled

  • changes in obstructive diseases

• useful in COPD monitoring

Residual Volume

• even at maximum exhalation, some air is still left in

• prevents collapse of lungs; also still allows gas exchange when breathing out

• around 1.2 L

  • though tends to be slightly more than ERV

Lung Capacities

comparison of the volumes

Inspiratory Capacity (IRC):

• how much you can breathe in

• Tidal Volume + Inspiratory Reserve Volume

Functional Residual Capacity (FRC)

• total amount of air that is available for gas exchange after quiet exhalation

  • hence, functional, because it still participates in gas exchange

• Expiratory Reserve Volume + Residual Volume

Vital Capacity (VC)

• Inspiratory Reserve + Tidal Volume + Expiratory Reserve

• the total amount of air the lungs can accommodate

Total Lung Capacity:

• around 6 L

Minute Ventilation:

• total amount of air inspired and expired every minute

• Normal Respiratory Rate: 12 breaths per minute (12-20 usually)

• Formula: (Breaths/Minute) x (Liter/Breath)

• or in other words: Respiratory Rate x Tidal Volume

Alveolar Ventilation:

• total amount of air reaching the respiratory zone every minute

External Respiration

• exchange of gas between alveoli and pulmonary capillaries

• Goal: convert Deoxy blood → Oxy blood

• Flow of Oxygen:

  • alveoli to pulmonary capillaries

  • 105 mmHg → 40 mmHg (alveoli has higher oxygen partial pressure)

  • flows from high to low (alveoli has higher because it just flowed in)

• Flow of Carbon Dioxide:

  • Pulmonary Capillaries → Alveoli

  • 45 mmHg → 40 mmHg

  • higher in body because it produces it

Internal Respiration

• exchange of gas between systemic capillaries and tissue cells

Flow of Oxygen:

• Systemic Caps → Tissue Cells

• 100 mmHg → 40 mmHg

Flow of CO2:

• tissue cells → Systemic Caps

• 45 mmHg → 40 mmHg

Factors Affecting Pulmonary and Systemic Gas Exchange

• difference of partial pressure of gasses

  • similar to concentration gradient in diffusion

• surface area available for gas exchange

• diffusion distance

• molecular weight and solubility of gasses

  • lower MW and more lipophilic can diffuse through membranes better

Note: partial pressure is contribution of that specific gas to the total pressure of the gas mixture

• relative to gas concentration

Partial Pressure Difference

• larger pressure difference = faster diffusion of gas

Affected by the Following:

• Altitude:

  • high altitudes decrease pressure difference due to thinner air

• Exercise

  • increases respiratory rate and decreases blood oxygen

  • increases pressure difference

• Morphine (Anesthesia)

  • decreases respiratory input

  • slow ventilation = less gas

Surface Area for Gas Exchange

• larger surface area = faster rate of diffusion

• alveoli: around 70 m² surface area

Emphysema:

• part of COPD

• destruction of alveolar walls

• decreases surface area = slower rate of gas exchange

Diffusion Distance

• higher diffusion distance = slower rate of diffusion

• respiratory membrane originally very thin; makes diffusion easy

• however conditions may increase distance:

  • Pulmonary Edema

Molecular Weight of Gas

• the lower the MW = faster rate of diffusion

• MW of O₂ is less than CO₂ 

  • as such, O₂ should diffuse faster (if only considering MW)

• O₂ diffuses across the membrane about 1.2 times faster than CO₂

Solubility of Gasses

• higher solubility = faster rate of diffusion

• Solubility of CO₂ is higher than of O₂

• solubility of CO₂ in respiratory fluids is about 24 times greater than O₂

• Net effect: net outward CO₂ is around 20x more rapid than inward O₂

Conditions:

• Emphysema: causes hypoxia and hypercapnia

Oxygen-Hemoglobin Dissociation Curve

• some gasses dissolve in the blood, but most travel via hemoglobin

• X Axis: P_O2 (partial pressure of Oxygen)

• Y Axis: Percent saturation of Hemoglobin

• As O2 increases, saturation should increase

• Follows sigmoidal curve; blunts near the end

• More linear at the center

• fully saturated hemoglobin means all hemoglobin is converted to “oxyhemoglobin”

• partially saturated means mixture of oxyhemoglobin and reduced hemoglobin

Oxygen Transport

• around 98.5% of O2 in blood is hemoglobin bound

• 1.5% dissolved in plasma

• Resting Condition: only 25% O2 unloads fro Hb and is used by tissue

  • rest is in reserve

Factors Affecting Hb affinity for O2:

• partial pressure of O2

• Acidity; Partial pressure of CO2

• Temperature

• BPG

O₂ Transport Factors

P_O2

• most important factor that determines how much O2 binds to Hb

• higher P_O2 = Higher binding

• same as the disassociation curve

Acidity:

• as acidity increases, affinity for Hgb for O2 decreases

• acidity comes from CO2 (that becomes carbonic acid)

• that way, oxygen releases when and where CO2 is high

• called the Bohr Effect

  • increase in H+ can cause O2 to unload

  • binding of O2 can cause H+ to unload from Hgb

  • Hemoglobin also acts as a blood buffer

Partial Pressure of CO2:

• high CO2 decreases affinity of Hgb for O2

  • this is in addition to the H+ effects

• related to H+ levels

2,3-Bisphosphoglycerate (BPG)

• decreases affinity of Hgb for O2

• a product of metabolism

• helps unloading of O2 in target tissues

• important factor in maternal-fetal circulation

Fetal Hemoglobin (Hb-F)

• higher affinity for O2 than any other hemoglobin

• can carry up to 30% more O2 than adult Hgb

CO2 Transport

Dissolved CO2:

• around 7%

• diffuses out of blood into alveoli (because it is more lipophilic)

Carbamino Compounds

• CO2 + Hgb → Reversible binding (Carbaminohemoglobin)

• accounts for 23% of CO2

Bicarbonate:

• 70% of CO2

• produced by action of carbonic anhydrase

• Movement of HCO3 into blood plasma from RBC causes chloride shift

Haldane Effect:

• lower amount of Hb-O2, the higher amount of CO2-carrying capacity of blood

  • as O2 leaves; frees up space for CO2

  • allows it to be picked up and carried out of the body

Respiratory Center

• group of neurons that send the impulse for respiratory muscle contraction

2 principal areas

• Medullary Respiratory Center

• Pontine Respiratory Center

Medullary Respiratory Center

has two groups:

• Dorsal Respiratory Group

  • important for normal/quiet respiration

• Ventral Respiratory Group

  • pre-Botzinger complex (pacemaker of normal respiration)

  • important for forceful respiration

Pathway:

DRG activates VRG; which activates forceful respiration

• accessory muscles of inhalation contract

or DRG triggers diaphragph

• follow rest from ppt later

Pontine Respiratory Group

• in midbrain

• formerly called the pneumotaxic area

• active during inhalation and exhalation

• modifies basic rhythm generated by VRG for 

Cerebral Cortex in breathing

• breathing can be made voluntary

• enables activities like holding breath, swimming, avoiding irritating gasses

• holding breath eventually limited by buildup of CO2 and H+

  • when high enough, DRG takes over

  • instinct will force breathing

  • if fought against, you will pass out

  • fainting → loss of conscious control → DRG will still take over

• hypothalamic impulses can also alter breathing pattern

  • ex: crying, laughing

• note: this is also how drowning works; DRG kicks in while still underwater

Chemoreceptor Regulation

• chemoreceptors for CO2, H+, and O2

• provides input to respiratory center

Central Chemoreceptors:

• present in medulla oblongata

• are sensitive to H+ and P_CO2

• vigorous response to even slight increase in P_CO2 

Peripheral Chemoreceptors:

• in aortic bodies or carotid arteries

• more sensitive to P_O2, H+ and P_CO2

• uniquely sensitive to O2, activates when PO2 is less than 00 mmHg

Brain concerned with CO2, body concerned with O2 I guess

Negative Feedback:

• Decreased PO2 → DRG activation → Hyperventilation

• Hypocapnia/Hypocarbia → DRG activation → sets moderate pace of breathing

Breathing into a bag

• during hyperventilation = excess CO2 exhalation = alkalinity

• breathing into bag recycles some CO2

• effective for mild cases

• if caused by more serious case (ex: renal disease) though probably won’t be enough

Hypoxia

• deficiency of O2 at the tissue level

Hypoxic Hypoxia:

• caused by low PO2 in arterial blood

• ex: due to high altitude, obstruction, fluid in lungs

Anemic Hypoxia:

• due to too little functioning hemoglobin; causes decreased O2 transport → insufficient O2

• ex: due to hemorrhage, anemia, carbon monoxide poisoning, etc.

Ischemic Hypoxia:

• blood flow to tissue is reduced (due to block, usually)

• despite PO2 and oxyhemoglobin levels being normal

Histotoxic Hypoxia:

• blood delivers normal O2 to tissues, but they are unable to use it

• due to some toxic agent

• ex: cyanide poisoning