BIOL1421: Chapter 22 (The Respiratory System)

Pulmonary ventilation is the process of moving air in and out of the lungs.
-inhalation: air containing oxygen passes through nose and mouth → lungs
-exhalation: air containing carbon dioxide and other wastes passes from lungs → nose and mouth

External respiration is the process of gas exchange between lungs and blood.
-in the lungs, oxygen travels from tiny air sacs (alveoli) → into bloodstream
-at the same time, carbon dioxide travels from bloodstream → alveoli, for elimination

Internal respiration is the process of gas exchange between the blood and body’s cells.

The structures of the respiratory system support pulmonary ventilation, external respiration, internal respiration, olfaction, and phonation.

During pulmonary ventilation, air moves in → nasal cavity, oral cavity → through pharynx, larynx, trachea → into lungs → move back out of body again
-its structures include nasal cavity, oral cavity, pharynx, larynx, trachea, lungs

During external respiration, oxygen from inhaled hair → moves into pulmonary vessels and carbon dioxide → moves out of body, for exhalation
-its structures include lungs and pulmonary blood vessels

During internal respiration, oxygen carried by arteries → move into cells and carbon dioxide → moves into veins
-its strucutres include arteries and veins

The upper respiratory structures include nasal cavity, pharynx, and larynx,
When air enters nasal cavity, flows through passages created by superior nasal conchae, middle nasal chonchae, and inferior nasal conchae

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The respiratory system structurally consists of two parts.
1.) The upper respiratory system includes the nose, pharynx, and associated structures
2.) The lower respiratory system includes the larynx, trachea, bronchi, and lungs.

The respiratory system functionally consists of two parts.
1.) Conducting zone includes all upper and lower passageways that filter, warm, moisten and conduct air (nose to terminal bronchioles)
2.) Respiratory zones includes portions of lower respiratory system within lungs with gas exchange between air and blood (respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli)

Functions of the respiratory system include:
-regulating gas exchange (intake of O2 and elimination of CO2)
-regulating blood pH
-filtering inspired air
-excreting small amounts of water and heat
-containing receptors for the sense of smell

NOSE AND PARANASAL SINUSES
The nose is a visible external structure that is supported by cartilage and bone, with external nares.
(nasal bone, lateral nasal cartilage, septal cartilage, alar cartilage)
-nasal cavity is lined by mucous membrane, divided by nasal septum, with conchae extending into cavity from lateral walls (conchae increases surface area)
-functions of the nose include: warms moistening and filtering incoming air, detects olfactory stimuli, contributes to voice resonance

The paranasal sinuses are cavities in skull bones that open into nasal cavity.
-functions of the paranasal sinuses include: produces mucus, contributes voice resonance

PHARYNX
The pharynx is a muscular tube lined with mucus membrane. (on top of larynx)
The three regions of the pharynx include:
1.) nasopharynx - passageway to nose; has openings to auditory tube
2.) oropharynx - passageway to mouth; intermediate portion
3.) laryngopharynx - passageway to esophagus (posterior) or larynx (anterior); inferior portion

The functions of the pharynx include:
-passageway for air and food
-resonating chamber for speech sounds
-houses tonsils for immune response to inhaled or ingested pathogens

LARYNX
The larynx is the passageway connecting laryngopharynx with trachea.
-contains different types of cartilages (top thyroid cartilage, cricoid cartilage, posterior arytenoid cartilage, top of that is corniculate cartilage)

Regions of the larynx include:
1.) epiglottis opens/closes to cover larynx airway during swallowing, which helps to route food and liquids → into esophagus
2.) glottis is the opening with two mucus membrane folds, contains two mucus membrane folds
-ventricular folds, which hold breath and do not produce sound (just for protection)
-vocal folds, which vibrate to produce sound, pitch changes with change in tension

TRACHEA
The trachea is the passageway extending from larynx → primary bronchi (windpipe; anterior to esophagus)
-contains C shaped cartilage rings that give support to prevent wall from collapsing and obstructing airway
-trachealis smooth muscle and elastic connective tissue connect ends of C cartilage posteriorly
-carina is a projection of interior-most tracheal cartilage at a point where trachea divides into right and left primary bronchi, with sensitive receptors for triggering a cough reflex

BRONCHIAL TREE
The bronchial tree is a branching sequence of airways, including trachea, primary bronchi, secondary bronchi, tertiary bronchi, bronchioles, and terminal bronchioles.
Some structure changes associated with successive branching into lungs include:
-mucous membrane changes from pseudostratified → ciliated simple columnar → simple cuboidal epithelium
-cartilage incomplete rings, replaced by plates, finally disappear in distal bronchioles
-increase in smooth muscle, decrease in cartilage

branching of bronchial tree: trachea → main bronchi → lobar bronchi → segmental bronchi → bronchioles → terminal bronchioles

LUNGS
The lungs are a paired thoracic cavity organs.
-visceral pleura covers each lung
-parietal pleura lines walls and forms distinct chamber for each lung
-pleural cavity filled with serous fluid

Lobes divides by fissures
-right lung has three lobes; left lung has two lobes and cardiac notch
-each lobe is supplied by secondary (lobar) bronchus
-bronchopulmonary segments, within lobe, are supplied by tertiary bronchi
-many smaller lobules are supplied by terminal bronchiole and respiratory bronchioles with alveoli

ALVEOLI
Alveolar sac consists of two ore more cup-shaped alveoli sharing a common opening to an alveolar duct within lobule
-each lobule is wrapped in elastic connective tissue and contains lymphatic vessel, an arteriole, and a venule
-each alveolar sac is surrounded by pulmonary capillary (to help with gas exchange)

Alveoli wall around air space in lung has different kinds of cells, which include:
1.) type I alveolar cells, which are simple squamous epithelium (where gas exchange is done)
2.) type II alveolar cells (septal cells), which are rounded epithelial cells that secrete alveolar fluid with surfactant to inhibit alveolar collapse (where surfactant is produced; surfactant binds between water molecules to prevent collapsing of alveoli and lungs)
3.) alveolar macrophages, which remove dust and debris

RESPIRATORY MEMBRANE
The respiratory membrane is a site of gas exchange by diffusion.
-involves oxygen and carbon dioxide
-occurs between air space in lung and blood

The four layers of the respiratory membrane include:
1.) layer of type I and type II alveolar cells in alveolus wall
2.) epithelial basement membrane underlying alveolar wall
3.) capillary basement membrane
4.) capillary endothelium
-despite several layers, very thin to allow for rapid diffusion of gases
-two layers belong to alveoli, two layers belong to capillary

RESPIRATION
Respiration involves three basic steps to the process of gas exchange in the body.
1.) Pulmonary ventilation (breathing) is the air flow between atmosphere and alveoli due to alternating pressure differences created by contraction and relaxation of respiratory muscles
-includes inhalation and exhalation

2.) External respiration (pulmonary exchange) is the passive diffusion of gases based on gradient; gas exchange between alveoli and capillaries

3.) Internal respiration (tissue exchange) is the passive diffusion of gases based on gradient; gas exchange between capillaries and body tissue

PRESSURE CHANGES DURING PULMONARY VENTILATION
-inhalation occurs when alveolar pressure < atmospheric pressure
-exhalation occurs when alveolar pressure > atmospheric pressure
-boyle’s law: volume of gas varies inversely with its pressure
-differences in pressure. caused by changes in lung volume. force air into lungs during inhalation and out during exhalation

-alveolar pressure should always have more pressure than intrapleural pressure (to avoid from collapsing)

1.) at rest and when diaphragm is relaxed,

INHALATION
Contraction of diaphragm and external intercostal muscles increase size of the lungs
-expansion of lungs decrease alveolar pressure
-air moves down a pressure gradient from the atmosphere into the lungs
-deep, forceful inhalation involves accessory muscles that increase size of thoracic cavity further
-intrapleural pressure (pleural cavity) maintained as subatmospheric pressure helps keep alveoli slightly inflated

EXHALATION
Exhalation is the passive process during exhalation, active only with forced exhale
-relaxation of diaphragm and external intercostal results in elastic recoil of chest wall and lungs
-decreased size increases alveolar pressure
-air moves down a pressure gradient from the lungs to the atmosphere
-deep, forceful exhalation involves accessory muscles that decrease size of thoracic cavity further to force additional air out of lungs

FACTORS AFFECTING PULMONARY VENTILATION
1.) Surface tension of alveolar fluid
-alveolar fluid produces an inward force on alveoli, accounting for much of the elastic recoil of exhalation
-surfactant in alveolar fluid reduces surface tension

2.) Compliance of lung tissue
-amount of effort required to stretch the lungs
-typically high compliance (expand easily) due to elastic fibers

3.) Airway resistance
-walls of airway offer resistance to flow of air in lumen
-anything that narrows or obstructs airways increases resistance

MODIFIED RESPIRATORY MOVEMENTS
Respiratory movements are also modified and controlled during speech.
-others are reflexes to express emotion or expel foreign matter from lower airways (some can be initiated voluntarily)
-eg. coughing, sneezing, sighing, yawning, crying, laughing, hiccupping, valsalva maneuver, pressurizing middle ear

LUNG VOLUMES AND CAPACITIES
Spirometer measures the volume of air exchanged during breathing, and measures the respiratory rate.
-anatomic dead space: 70% of air in single breath reaches respiratory zone for external respiration, remaining 30% moves to conducting zone and known as anatomic dead space
-capacities are combinations of specific lung volumes

LUNG VOLUMES
-tidal volume: volume of air in one breath
-inspiratory reserve volume: additional air during forced inspiration
-expiratory reserve volume: additional air during forced exhalation
-residual volume: volume of air remaining in alveoli and airways after forced exhalation
-minute ventilation (MV): breathing rate x tidal volume

LUNG CAPACITIES
-inspiratory capacity: tidal volume + inspiratory reserve volume
-functional residual capacity: residual volume + expiratory reserve volume
-vital capacity: sum of inspiratory reserve volume, tidal volume, and expiratory reserve volume
-total lung capacity: vital capacity + residual volume

DIFFUSION OF GASES
Partial pressure of a gas is the pressure exerted by the gas in a mixture of gases.
-passive diffusion of gases is based on partial pressure gradients and solubility

Dalton’s Law
-each gas in a mixture exerts its own pressure as if the other gases were not present
-each gas diffuses across a membrane by moving down its partial pressure gradient

Henry’s Law
-the quantity of a gas that will diffuse into a liquid is proportional to its partial pressure and solubility in water
(higher pressures will move to lower pressures)

EXTERNAL AND INTERNAL RESPIRATION
External respiration = net pulmonary gas exchange
-diffusion of O2 from alveoli → blood in pulmonary capillaries
-diffusion of CO2 from pulmonary capillary blood → air
-converts oxygen-poor blood from right ventricle into oxygen-rich blood → returns to left atrium

Internal respiration = net tissue gas exchange
-diffusion of O2 from systemic capillary blood → cell
-diffusion of CO2 from cell → systemic capillary blood
-converts oxygen-rich blood from left ventricle into oxygen-poor blood that returns to right atrium

Direction of exchange depends on partial pressure gradient across membranes.

EXTERNAL AND INTERNAL RESPIRATION RATE
Rate of exchange varies depending on several factors
1.) partial pressure differences of the gases
-larger differences accelerates rates of diffusion

2.) surface area available for gas exchange
-any decrease in functional surface area slows diffusion

3.) diffusion distance
-buildup of interstitial fluid increases distance and slows diffusion

4.) molecular weight and solubility of the gases
-CO2 net diffusion > O2 net diffusion

OXYGEN TRANSPORT
Most oxygen transported in blood bound temporarily to iron of hemoglobin in RBCS.
-small amount of O2 is dissolved in blood plasma
-reversible reaction: oxhemoglobin/deoxyhemoglobin

Amount bound depends on partial pressure of oxygen (P O2)
-higher

CARBON DIOXIDE TRANSPORT
-CO2 attaches to the globin part in hemoglobin
-carbon dioxide reacts with water to produce H2CO3, breaks into H+ and

As affinity (tightness of hemoglobin-oxygen bond) changes, O2 is released from hemoglobin (unloaded), providing more O2 to metabolically active cells

CARBON DIOXIDE TRANSPORT
CO2 is transported from cells → back to lungs in three main forms
1.) dissolved in blood plasma (7%)

2.) bound to hemoglobin (23%)

3.) bicarbonate ions (70%)

CONTROL OF RESPIRATION
Respiratory center, in the brain stem, sends impulses → respiratory muscles, that alter size of thorax for ventilation

The medullary rhythmicity area is the medulla oblongata.

The upper pons is the pneumotaxic area.
-inhibits inspiratory area before the lungs become too full

The lower pons is the apneustic area.
-stimulates inspiratory area to prolong inhalation