Respiratory Tract Anatomy

Anatomy of the Respiratory Tract

• The respiratory passageways extend from the external nares to the alveoli of the lungs
• Key structures include:
  • External nares
  • Nasal cavity
  • Internal nares
  • Naso-, oro-, and laryngopharynx
  • Epiglottis
  • Larynx
  • Trachea
  • Carina to primary bronchi
  • Secondary bronchi
  • Tertiary bronchi
  • Bronchioles
  • Alveoli, the sites of oxygen exchange

Upper Respiratory Tract

• The upper respiratory tract is lined with pseudostratified epithelium, except for the oro- and laryngopharynx, which have stratified squamous epithelium
• The oro- and laryngopharynx serve as common passageways for both food and air

Accessory Structures in the Upper Tract

• Conchae
  • Bony projections in the nasal cavity covered with mucus membrane
  • They cause air to "swirl", increasing contact with the mucus membrane
  • This helps moisten, filter, and warm the air
• Epiglottis
  • A flap of elastic cartilage that closes off the trachea/larynx during deglutition (swallowing)

Openings in the Nasal Cavity

• There are openings in the nasal cavity that connect to the nasolacrimal duct, leading to the eye
• There are also openings to the perinasal sinuses located in the frontal, maxilla, ethmoid, and sphenoid bones
• These openings explain how a "cold" can lead to conjunctivitis or sinusitis

Auditory Tube

• The nasopharynx also connects to the auditory (Eustachian) tube, which equalizes air pressure in the middle ear
• Colds can lead to middle ear infections due to the anatomical connection between the nasopharynx and middle ear

Laryngeal Cartilages

• Important cartilages to know are:
  • Epiglottis
  • Thyroid cartilage
  • Cricoid cartilage
  • Arytenoid cartilage
  • Corniculate cartilage
  • Cuneiform cartilages
• The epiglottis, thyroid cartilage, and cricoid cartilage are single cartilages
• The cricoid cartilage forms a complete ring around the larynx

Vocal Cords

• "False vocal cords" are folds of the laryngeal wall that do not function in sound production, and they close off the airway to increase abdominal pressure
• "True vocal cords" are attached to the arytenoid and thyroid cartilages, and they have an outer layer of stratified squamous tissue covering elastic fibers

Sound Production

• True vocal cords vibrate as air is pushed through them, producing sound
• Skeletal muscles attached to the arytenoid cartilage adjust the "pull" on the vocal cords, changing tension and pitch
• The volume of voices is adjusted by changing the amount of air pushed past the vocal cords
• Sinuses act as resonance chambers, aiding in sound production

Glottis

• The glottis is defined as the space between the vocal cords
• Aspirated objects can become lodged in the vocal cords causing it impossible to breathe

Trachea Anatomy

• The trachea starts below the cricoid cartilage and ends at the carina
• It lies ventral to the esophagus, and the tracheal cartilages are open at the back to allow the esophagus to expand
• The carina has very sensitive cough receptors to prevent foreign particles from entering the primary bronchi

Trachea Physiology

• The trachea is ventral to the esophagus, which is important during intubation
• The epithelium of the trachea contains cilia that beat towards the mouth to eliminate mucus and dust particles
• This mucociliary escalator is a crucial mechanism of innate immunity

Trachea Histology

• The trachea layers include:
  • Mucosa
    • Ciliated pseudostratified epithelium
    • Lamina propria
  • Submucosa: mucus glands
  • Cartilage
    • Hyaline cartilage rings that are open at the back to allow for expansion of the esophagus
    • These rings keep the trachea from collapsing
  • Adventitia
    • Connective tissue that attaches the trachea to surrounding structures

Primary Bronchi

• There are two primary bronchi, each leading to one lung
• Clinically, the right bronchus is wider and more vertical than the left
• Aspirated objects that pass the vocal cords and carina tend to end up in the right lung
• There are 5 secondary bronchi, each supplying air to a lobe of the lung
• The right lung has 3 lobes and 3 secondary bronchi, while the left lung has 2 lobes and 2 secondary bronchi

Bronchial Tree

• The bronchial tree splits into smaller branches
• The order progresses as:
  • Primary bronchus
  • Two secondary bronchi
  • 8-10 tertiary bronchi each supplying a segment of the lung
• The tertiary bronchus still has pseudostratified epithelium and small pieces of hyaline cartilage

Bronchioles

• As branching continues, cartilage decreases, and the mucosa becomes thinner
• By the time air reaches the bronchiole: -There is no more hyaline cartilage, only a thin layer of smooth muscle
• Alveoli, at the ends of the bronchial tree, contain a layer of simple squamous cells
• Gas exchange occurs in the alveoli

Bronchiole Histology

• A bronchiole consists of a layer of epithelium that thins from pseudostratified to simple columnar to simple cuboidal
• There is no more hyaline cartilage, and the lumen diameter can change due to smooth muscle in the wall
• Bronchiole constriction increases airway resistance
• Bronchiole dilation decreases resistance
• Bronchiole diameter is controlled by the autonomic nervous system

Significance of Bronchioles

• Bronchioles constriction with mucus accumulation due to inflammation or allergies are common causes of asthma
• Epinephrine, a sympathomimetic drug, is used for acute asthma attacks to ease breathing through bronchiole dilation
• The sympathetic nervous system causes dilation of the bronchioles

Alveoli: Structure and Function

• Terminal bronchioles branch to form respiratory bronchioles alveolar ducts alveoli
• The alveolus is where gases are exchanged between capillaries and air sacs
• Alveoli are composed of simple squamous epithelium
• All respiratory tract parts other than alveoli are considered dead air space/ conducting zones

Alveoli: Capillaries

• Alveoli are surrounded by capillaries to allow for gas exchange
• The respiratory zone is where
• Oxygen moves into the blood and carbon dioxide enters the alveolus
• There are elastic fibers to help with compliance/ stretching of the lung

Alveolus

• The alveolus is lined by simple squamous cells and surrounded by capillaries
• Alveolar macrophages phagocytize debris
• Septal cells produce surfactant, a phospholipid that reduces surface tension to prevent collapsing during expiration
• Surfactant also helps inflate the alveoli quicker during inspiration
• The membrane consists of:
  • Simple squamous cell of alveolus
  • Fused basement membranes of the alveolus and capillary
  • Simple squamous cell of capillary

Alveolus Histology

• Under a microscope, the simple squamous lining can be seen
• The capillary is sandwiched between two simple squamous cells of the alveolus

Diffusion factors of gases across the Alveolar-Capillary Membrane

• The thin alveolar-capillary membrane is crucial for oxygen and carbon dioxide diffusion
• Factors that affect diffusion:
  • Membrane thickness -Thicker membranes, due to pulmonary edema, makes gas exchange difficult
  • Surface area -Compromised surface area will affect gas exchange
  • Solubility of gases -Carbon dioxide is more soluble in fat than oxygen, diffusing more readily
  • Gas concentration differences -The higher the concentration difference between the blood and alveolus, the faster the exchange

Lungs

• The right lung has three lobes; the left lung has two
• Lungs consist of mostly air spaces because they are largely formed of alveoli
• The connective tissue between these spaces is filled with elastic tissue, allowing them to stretch and recoil during breathing
• Compliance of the lung, which is this elasticity, decreases with age

Pleurae: Significance

• Visceral pleurae sit directly on each lung
• Pleurae are serous membranes that make watery fluid
• Parietal pleurae surround each lung and attach to the diaphragm and rib cage
• Pleural fluid, a thin film between these two layers, reduces friction for expansion of the lungs

Pleural Cavity

• The pleural cavity is surrounded by parietal pleurae (outer lines) and visceral pleurae (lines on the lungs)
• Fluid in the pleural space has slightly negative pressure causing the parietal and visceral pleurae to "stick" together

Pulmonary Ventilation: Inspiration

• Two main factors when inspiring:
  • Diaphragm contracts/ moves downward
  • External intercostal muscles contract/ chest cavity moves outward
• Parietal pleurae attach to the diaphragm and the wall of the thoracic cage
• As the diaphragm contracts downwards, so do the parietal pleurae
• Visceral pleurae are then "stuck" essentially along with the parietal and therefore follow
• Increase in volume decreases pressure in the lungs
• Air flows from high to low pressure
• Boyle's Law states that when the volume of a cylinder (the lungs) increases, pressure will decrease

Pulmonary Ventilation: Expiration

• Boyle's Gas Law states when volume in the lungs increase (during inspiration), intrapulmonary pressure will decrease
• During expiration:
  • Diaphragm relaxes upward
  • Parietal pleurae also push up, pushing up the visceral pleurae, which makes the lungs smaller
  • The internal intercostal muscles contract which creates less diameter in the thoracic cage
• Because the pressure in the lungs is now greater than the outside air, air is pushed out
  • Pulmonary ventilation relies on intact pleurae and lung elasticity
    • 80% relies on contraction of the diaphragm

Respiratory Muscles: Inspiration

• Good muscles for inspiration:
  • Diaphragm
  • External intercostals
  • Scalenes
  • Sternocleidomastoid
  • Pectoralis minor, innervated by two phrenic nerves of the cervical plexus

Respiratory Muscles: Expiration

• Good muscles for expiration:
  • Diaphragm
  • Internal intercostals
  • Rectus abdominis
  • External obliques

Ventilation issues can be as a result of

• Skeletal muscle problems -All voluntary muscles of the diaphragm and intercostal -Muscular Dystrophy
• Issues with the phrenic nerve -No action potential occurs, so paralysis, and is unable to breathe
• There are issues with the pleurae -Essential for optimal ventilation -Intrapleural can cause issues of the lung to collapse i.e. Atelectasis
• Medulla/Pons -This begins rhythm
• The elasticity of the lung can also effect ventilation

Lung Volumes

• Know the lung volumes and capacities
  • The Volume of normal breath = 500mL Tidal Volume
  • Total amount of exchangeable air of the lung measured by max inhale and fully exhaling =4800mL (Vital Capacity)
• You never get rid of all the air in your lungs, what you dont get rid of is the residual volume.

Pulmonary Function

• Pulmonary function is measured by what degree one testing their lung volumes
  • One such test is the force one can breath after a second -FEV1 or force expiatory volume in one second -Those with the diagnosis of asthma it is harder to force air our

Minute volume Respiration

• MVR = 500mlx12breath/min=6L/MIN

Respiratory Physiology

• Three major steps - Pulmonary Ventilation -By which we inhale and exhale largely dues to the pleurae -External Ventilation -O2 and CO2 exchange between the aveoli of Capillaries of the lungs via diffusion as both are soluble gasses -Internal Ventilation - Gasses again exchanged via diffusion -Occurs between the capillaries of the tissues
  • The gases more from low to high concentration

Partial pressure

• Carbon Dioxide and Oxygen is known to be lipid soluble so easily diffused
• To measure gasses based in the setting it measures based on the partial pressure.
• Partial Pressure
  • The pressure by one gas in a mixed gas
  • P= 760mmHG If air is 80% nitrogen 20% oxygen in 760mmHG then:
  • N=.80x760= 600mmhg
  • 02= .20x760= 160mmHG
• Therefore the greater the concentration of gas in a mixture the greater will be the pressure

Alevolus

• You should learn the numbers of normal alveolus, oxygenized and deoxygenated blood - PCO2 Alveolus or oxygenated blood = 40 mm HG - PCO2 deoxygenated blood = 45mmHG - PO2 Alveolus or oxygenated blood = 105 mmHG - PO2 deoxygenated blood = 40mmHG
• The numbers are average and will always use in class -Notice that the alveolar concentrations are identical to those in oxygen blood

How does Alveolar PO2 reach 105 if atomospheric Po2 is 160mmhg?

• Lower in avelous due to -Addition of water being humified as it enters the lungs -Addition of the presence CO2 addition -Movement of some oxygen into the blood

Difussion Gradient

• Magnitude difference between 02 and C02 at the Alveolar and Pulmonary interface
  • PO2 Alveolus is 105mmHG and DEOXYGENATED Blood is 40MMhg PO2 diff gradient is 65mmhG -CO2 Alevolus is 40mmhG and DEOXYGENATED Blood is 45MMhg C02 diff gradient is 5mmhG

Gas Exchange; external respiration

• External ventilation is the exchange of gasses between alveolus and blood In the alveolus 02 concentration maintained at the high 105 normal circumstances
• As the blood is flowed, oxygen will move by defusion until concentration equiliorates with the alveolus.
• The oxygen in the alveolus is always replacing itself, the concentration remains constant -Carbon Dioxide will move in the opposite direction -under normal terms
• Carbon dioxide levels in the avelous is lower than blood -Pulmonary venous blood -will leave the avelous and will have the same carbon dioxide concentration as the avelous.

Internal Repsiration Factors

-Driven by the concentration difference from capillary blood and alveolus concentration -Gradient for oxygen is 65 mmHG - Carbon gradient is 500mHG

• Carbon Dioxide is much more soluble than lipid therefore the gradient(though small) is suffincent
  • Concentration of oxygen if there is lack of a normal, then the volume of oxygen cannot go to high enough volumes -Avelolar Cap Membrane -Difussion is facilitated by the facts they are thin, if not then defusion is impaired. -Surface Area -If less then area their will be poor gas exchange -Pulmoary Blood Flow is a major determinant. If blood flow is contricted then poor gas exchange will result.

Gas Exhcange: Internal Ventilation

• internal ventilation is the gas exchange between cap blood and tiss -02 in the alvelours is 100 Mmhg but may be differnt in systemic tissues
  • In cappilaries --02 leaves blood and flows into the tiss b/c P02 is lower thn concentration in blood
  • carbon dioxde flows for the other directions as it is concentrated high in tiss ( being made during Krebs) -

Influencing factors Internal Vent

• The concentration of 02 and c02 -Poor blood flow -Nicotine -arterial sclerosis -Poor oxygen exchange throughout the tissues

Average and Numbers

• tissue P02 40 mmHG and PCO2 45 mmHG just for tiss
• The more Active the tissue the lower the 02 (tissue being a consumer)

Overview

• Alveoli PO2(105) PCO2(40) this is a constant because we breath Blood leaving is aPO2 and aPCO2 will equal the same

Oxygen transport

• 97 Percent is carried by hemoglobin
• called oxyghemoglobin -non polar so less than 3 percent dissolves in bloodstream
• attached to iron on the hemogiblin
• 250,000,0000 are on a sing red blood cell
• Affected a lot with tissue conditions for what is more or less bound

02 hemoglobin sat curve

• Y axis amount of hemoglobin x axis PO2 amount Curve increases at a higher rate and then plateaus -High PO2 more is attached that would make since
• PO 2 in the lungs hemoglobin is nearly saturdated % of hemoglobin is called O2stat
• Means that there is a huge difference in 012stat level. If you can get close to 75 percent you are good

Curve

• Tell us two reasons
  • in the lungs -Small change still leads to more saturation w o2 In the tiss Small change drastly increases and allows them to go to more tiss needing

Factors

• Can shift one way or the other making it easy or harder by the 02 state

Bicarbonate and Carbon dioxide

• Small percentage goes hemoglobin-23
• Small percentage goes to dissolve-7
• Most goes to bicarbonate-70 Equation-co2 and h20-h203-03

HCo (plasma)

• shifts on way or the other to work things down to the tissues and lungs accordingly