Ch 22 - Respiratory system

All body processes and ATP

• directly or indirectly require ATP (final electron acceptor)

• Most ATP synthesis requires oxygen and produces carbon dioxide

respiratory system: system of tubes

• Oxygen diffuses into the blood

• Carbon dioxide diffuses out

Respiratory and cardiovascular systems

• work together to deliver oxygen to the tissues & remove carbon dioxide

• jointly as cardiopulmonary system

Respiratory system and the urinary system

collaborate to regulate the body’s acid-base balance (as well as cardiac system)

Respiration refers to ___ of the lungs (breathing)

• ventilation

• Can also be used to refer to part of cellular metabolism

functions of respiration

• Gas exchange: O2 and CO2 exchanged between blood and air

• Communication: Speech and other vocalizations

• Olfaction: Sense of smell

• Acid-Base balance: Influences pH of body fluids by eliminating CO2

• blood pressure regulation

• blood and lymph flow

• platelet function

• blood filtration

• expulsion of abdominal contents

remember: more CO2 = ___ blood pH

decrease; more acidic

blood pressure regulation and blood & lymph flow

• helping in synthesis of angiotensin II (vasoconstrictor)

• Breathing creates pressure gradients between thorax and abdomen that promote flow of lymph and blood

platelet production and blood filtration

• More than half of platelets are made by megakaryocytes in lungs (not in bone marrow)

• lungs filter small clots

Expulsion of abdominal contents

Breath-holding assists in urination, defecation, and childbirth (Valsalva maneuver)

principal organs of respiratory system

• nose, pharynx, larynx, trachea, bronchi, lungs

• Incoming air stops in the alveoli

  • Millions of thin-walled, microscopic air sacs

  • Exchanges gases with the bloodstream through the alveolar wall, and then flows back out

Conducting zone of respiratory system

• Includes those passages that serve only for airflow; No gas exchange

• Nostrils through major bronchioles

• O/N → terminal bronchioles

respiratory zone of respiratory system

• Consists of alveoli and other gas exchange regions

• respiratory bronchi → alveolar ducts → alveoli

upper respiratory tract

in head & neck, nose through larynx

lower respiratory tract

organs of the thorax, trachea through lungs

functions of nose

• Warms, cleanses, and humidifies inhaled air

• Detects odors

• Serves as a resonating chamber that amplifies voice

anatomy of nasal region

• extends from nostrils (nares) to posterior nasal apertures (choanae)—posterior openings

• Facial part is shaped by bone and hyaline cartilage

• nasal bones & maxillae, lateral & alar cartilages, ala nasi

Nasal fossae

• R&L halves of nasal cavity

• nasal septum divides nasal cavity (composed of bone and hyaline cartilage)

• roof and floor of nasal cavity

  • ethmoid and sphenoid bones form roof

  • Hard palate forms floor

Vestibule

• Beginning of nasal cavity

• Small, dilated chamber just inside nostrils

• Lined with stratified squamous epithelium

Vibrissae

Stiff guard hairs that block insects and debris from entering nose

nasal conchae

• Chamber behind vestibule is occupied by three folds of tissue

• Superior, middle, and inferior nasal conchae (turbinates)

  • meatus: narrow air passage beneath each concha

  • Narrowness & turbulence ensure that most air contacts mucous membranes

  • Cleans, warms, and moistens the air

nasal mucosa - respiratory epithelium

• Epithelial layer in most of the mucosa

• Ciliated pseudostratified columnar epithelium

• Goblet cells produce mucus

• Cilia are motile: Propel the mucus posteriorly toward pharynx (Mucus swallowed into digestive tract)

nasal mucosa - olfactory epithelium

• Sensory—detects odors

• Immobile cilia bind odorant molecules (don’t propel mucus)

• Only covers a small area of the roof of the nasal fossa and adjacent parts of the septum and superior concha

erectile tissue (swell body)

• Extensive venous plexus in epithelium of inferior concha

• Every 30 to 60 minutes, tissue on one side swells with blood

• Restricts airflow through that fossa, so most air directed through other nostril

• Allows engorged side time to recover from drying

• Preponderant flow of air shifts between the right and left nostrils once or twice an hour

pharynx (throat)

• Muscular funnel extending about 5 in. from choanae to larynx

• Muscles of the pharynx assist in swallowing and speech

• Three regions of pharynx: Nasopharynx, Oropharynx, Laryngopharynx

nasopharynx

• Posterior to nasal apertures and above soft palate

• Receives auditory tubes and contains pharyngeal tonsil

• 90 degrees downward turn traps large particles

• passes only air & lined by pseudostratified columnar epithelium

Oropharynx

• Space between soft palate and epiglottis

• Contains palatine tonsils

• pass air, food, and drink and are lined by stratified squamous epithelium

Laryngopharynx

• Epiglottis to cricoid cartilage

• Esophagus begins at that point

• pass air, food, and drink and are lined by stratified squamous epithelium

larynx

• Cartilaginous chamber about 4 cm (1.5 in.) long

• Primary function is to keep food and drink out of airway

• Voice box; In several animals, it has evolved the additional role of phonation—the production of sound

Epiglottis

• Flap of tissue that guards superior opening of larynx

• At rest, stands almost vertically

• during swallowing, extrinsic muscles pull larynx upward

• Tongue pushes epiglottis down to meet it

• Closes airway and directs food to esophagus behind it

• Vestibular folds of the larynx play greater role in keeping food and drink out of the airway

larynx 9 cartilages

• solitary & relatively large: Epiglottic, Thyroid, Cricoid cartilage

• smaller, paired: Arytenoid, Corniculate, Cuneiform

3 ligaments of larynx

• suspend larynx from hyoid and hold it together

• Thyrohyoid (suspends it from hyoid)

• Cricotracheal (suspends trachea from larynx)

• Intrinsic (hold laryngeal cartilages together)

larynx interior wall has vocal cords & 2 folds

• superior vestibular folds

  • no role in speech; close to larynx during swallowing

• inferior vocal cords

  • produce sound when air passes between; contain vocal ligaments

  • covered in stratified squamous epithelium (endure vibration & contact)

  • glottis - vocal cords & opening between them

walls of larynx (muscles)

• deep intrinsic muscles operate vocal cords

• superior extrinsic muscles connect larynx to hyoid bone

  • elevate larynx during swallowing; infrahyoid group

intrinsic muscles control ___ ( & mechanism?)

• vocal cords

• Pull on corniculate and arytenoid cartilages causing cartilages to pivot

• Abduct or adduct vocal cords, depending on direction of rotation

• Air forced between adducted vocal cords vibrates them producing high-pitched sound when cords are taut

  • Produces lower-pitched sound when cords are more slack

vocal cords (adult male vs female, loudness…)

• male: usually longer & thicker, vibrate more slowly, produce lower-pitch sound

• loudness: determined by force of air passing between vocal cords

• produce crude sounds that are formed into words by actions of pharynx, oral cavity, tongue, and lips

trachea (windpipe)

• ridged tube; anterior to esophogus

• 16 to 20 C-shaped rings of hyaline cartilage

  • Reinforce trachea and prevent collapse during inhalation

  • Opening in C-rings faces posteriorly toward esophagus

    • Allows esophagus to expand

  • Trachealis muscle spans opening in rings

    • Contracts or relaxes to adjust airflow

trachea lining

• lined by ciliated pseudostratified columnar epithelium

• Mucus-secreting cells, ciliated cells, and stem cells

• Mucociliary escalator, Middle tracheal layer, Adventitia

Mucociliary escalator and middle tracheal layer

• Mechanism for debris removal: Mucus traps inhaled particles; Upward beating cilia moves mucus to pharynx to be swallowed

• Connective tissue beneath the tracheal epithelium

  • Contains lymphatic nodules, mucous and serous glands, and the tracheal cartilages

adventitia

• Outermost layer of trachea

• Fibrous connective tissue that blends into adventitia of other organs of mediastinum

R&L main bronchi (trachea)

• trachea forks at level of sternal angle

• carina - internal medial ridge in lowermost tracheal cartilage; directs airflow to R&L

Tracheotomy (& potential problems)

• make a temporary opening in the trachea and insert a tube to allow airflow (permanent opening is called a tracheostomy)

• Prevents asphyxiation due to upper airway obstruction

• Potential problems include:

  • Inhaled air bypasses the nasal cavity (hot humidified) → dry out mucous membranes → tract becomes encrusted → promoting infection

intubation

• Patient is on a ventilator, air introduced directly into trachea

• Air must be filtered and humidified

lung anatomy

• base: broad concave portion resting on diaphragm

• apex: tip that projects just above clavicle

• costal surface: pressed against ribcage

• mediastinal surface: faces medially toward heart

mediastinal surface (lung)

• faces medially toward heart

• hilum: slit though which lung receives main bronchus, blood vessels, lymphatics, nerves

  • structures near hilum constitute root of lung

right lung

• shorter than left because liver rises higher on right

• has 3 lobes separated by horizontal & oblique fissure

left lung

• tall & narrow b/c heart tilts towards left and occupies more space on this side of mediastium

• has indentation (cardiac impression)

• has 2 lobes separated by single oblique fissure

bronchial tree

branching system of air tubes in each lung (from main bronchus to 65k terminal bronchioles)

main (primary) bronchi

• from fork of trachea

• supported by C-shaped hyaline cartilage rings

• R main bronchus wider and more vertical than L

• aspirated foreign objects lodge in R main bronchus more often than L

lobar (secondary) bronchi

• supported by crescent-shaped cartilage plates

• 3 R lobar bronchi: superior, middle, inferior (1 to each lobe)

• 2 L lobar bronchi: superior, inferior (1 to each lobe)

segmental (tertiary) bronchi

• supported by crescent-shaped cartilage plates

• 10 on right, 8 on left

• bronchopulmonary segment (functionally independent unit of lung tissue)

bronchi lined with ___ epithelium

• ciliated pseudostratified columnar epithelium

• lamina propria has abundance of mucous glands and lymphocyte nodules (mucosa-associated lymphoid tissue, MALT)

  • intercept inhaled pathogens

• all divisions of bronchial tree have large amount of elastic connective tissue (recoil that expels air from lungs)

mucosa has well-developed layer of ___ muscle

• smooth muscle

• muscularis mucosae contracts or relaxes to constrict or dilate airway, regulating airflow

pulmonary and bronchial artery related to bronchial tree

• pulmonary artery branches closely follow bronchial tree in way to alveoli

• bronchial artery services bronchial tree with systemic blood (arises from aorta)

bronchioles

• 1 mm or less in diameter (mucous sensitive → obstruction)

• pulmonary lobule: portion of lung ventilated by 1 bronchiole

• have ciliated cuboidal epithelium; have layer of smooth muscle

• Divides into 50 to 80 terminal bronchioles

  • final branches of conducting zone

  • have no mucous glands or goblet cells

  • Have cilia that move mucus draining into them back by mucociliary escalator

  • Each terminal bronchiole gives off 2 or more smaller respiratory bronchioles

respiratory bronchioles

• Have alveoli budding from their walls

• Considered the beginning of the respiratory zone since alveoli participate in gas exchange

• Divide into 2 to 10 alveolar ducts

  • End in alveolar sacs (Clusters of alveoli around a central space (atrium))

cells of alveolus

• Squamous (type I) alveolar cells

• Great (type II) alveolar cells

• Alveolar macrophages (dust cells)

Squamous alveolar cells (type 1; pneumocytes)

• Thin cells allow rapid gas diffusion between air and blood

• Cover 95% of alveolus surface area

• also called pneumocytes (do gas exchange)

Great (type II) alveolar cells

• Round to cuboidal cells that cover the remaining 5% of alveolar surface

• Repair the alveolar epithelium when the squamous (type I) cells are damaged

• Secrete pulmonary surfactant

  • A mixture of phospholipids and proteins that coats the alveoli and prevents them from collapsing during exhalation

  • CO2, O2 gas exchange more effective and quicker

  • prevent collapse when exhale; easier to inhale

Alveolar macrophages (dust cells)

• most numerous of all cells in lung

• Wander lumens of alveoli and connective tissue between them

• Keep alveoli free from debris by phagocytizing dust particles

• dust cells die each day as they ride up the mucociliary escalator to be swallowed and digested with their load of debris

  • ineffective to geometric solids → dump into lung tissue → fibrosis

  • TB live in cells and replicate

alveoli anatomy

• each alveolus surrounded by a basket of capillaries supplied by the pulmonary artery

• Respiratory membrane: thin barrier b/w alveolar air and blood

  • consists of 3 layers:

    • Squamous alveolar cells

    • Endothelial cells of blood capillary

    • Their shared basement membrane

fluid in the lungs can be ___

• fatal

• Gases diffuse too slowly through liquid to sufficiently aerate the blood

prevent fluid accumulation in alveoli

• Alveoli are kept dry by low blood pressure in capillaries

• Reabsorption (osmotic uptake of water) overrides filtration and keeps the alveoli free of excess fluid

  • increased osmotic pressure, decrease hydropressure

  • low capillary blood pressure prevents rupture of the delicate respiratory membrane

• Lungs have more extensive lymphatic drainage than any other organ

pleurae layers and pressure of lungs

• visceral pleura (serious membrane that covers lungs)

• parietal pleura (adheres to mediastinum, inner surface of the rib cage, and superior surface of the diaphragm)

• pleural cavity (potential space b/w pleurae)

pleural cavity

• negative intrapleural pressure: -4 to -6 mm Hg (prevent collapsing)

• contains film of slippery pleural fluid

  • pleural effusion: pathological seepage of fluid into pleural cavity

functions of pleurae and pleural fluid

• reduction of friction

• creation of pressure gradient (lower pressure than atmospheric pressure (atm); assists lung inflation)

• compartmentalization (prevents spread of infection from 1 organ in mediastium to others)

pulmonary ventilation (breathing cycles)

• repetitive cycle (inspiration, expiration)

• respiratory cycle (one complete inspiration and expiration)

• quiet respiration (breathing at rest, effortless, automatic)

• forced respiration (deep, rapid breathing, during exercise)

Flow of air in and out of lung depends on a ___ between air within lungs and outside body

• pressure difference

• Respiratory muscles change lung volumes and create differences in pressure relative to the atmosphere

diaphram

• Phrenic nerve: C3 to C5 in spine

• prime mover of respiration; Accounts for 2/3 of airflow

• Contraction flattens diaphragm, enlarging thoracic cavity and pulling air into lungs

• Relaxation allows diaphragm to bulge upward again, compressing the lungs and expelling air

Internal and external intercostal muscles

• Synergists to diaphragm; Located between ribs

• Stiffen the thoracic cage during respiration

• Prevent it from caving inward when diaphragm descends

• Contribute to enlargement and contraction of thoracic cage

• internal: posterior of ribs; down and in; air out

• external: anterior surface of ribs

scalenes

• Synergist to diaphragm

• Fix or elevate ribs 1 and 2; pull up → more air

Accessory muscles of respiration act mainly in forced respiration

• Erector spinae, sternocleidomastoid, pectoralis major, pectoralis minor, and serratus anterior muscles and scalenes

• Greatly increase thoracic volume

normal quiet expiration

• Energy-saving passive process achieved by the elasticity of the lungs and thoracic cage

• As muscles relax, structures recoil to original shape and original size of thoracic cavity

  • Results in airflow out of lungs

forced expiration

• Rectus abdominis, internal intercostals, and other lumbar, abdominal, and pelvic muscles

• Greatly increased abdominal pressure pushes viscera up against diaphragm increasing thoracic pressure, forcing air out

• Important for “abdominal breathing”

Valsalva maneuver

• Breathing technique used to help expel contents of certain abdominal organs

• Depression of the diaphragm raises abdominal pressure

• Consists of taking a deep breath, holding it by closing the glottis, and then contracting the abdominal muscles

  • Aids in childbirth, urination, defecation, vomiting

neutral control of breathing

• No autorhythmic pacemaker cells for respiration, as in the heart

• Breathing depends on repetitive stimulation of skeletal muscles from brain and will cease if spinal cord is severed high in neck

  • Skeletal muscles require nervous stimulation

  • Multiple respiratory muscles require coordination

• breathing controlled at 2 levels of brain: 1 is cerebral and conscious, Other is unconscious and automatic

brainstem respiratory centers

• Automatic, unconscious breathing is controlled by respiratory centers in reticular formation (medulla oblongata and pons)

• 2 pairs in medulla: Ventral respiratory group (VRG), Dorsal respiratory group (DRG)

• 1 pair in pons: Pontine respiratory group (PRG)

Ventral respiratory group (VRG)

• pair in medulla

• Primary generator of the respiratory rhythm

• Produces a respiratory rhythm of 12 breaths per minute

• In quiet breathing (eupnea), inspiratory neurons fire for about 2 sec, expiratory neurons fire for about 3 sec

Dorsal respiratory group (DRG)

• pair in medulla

• Modifies the rate and depth of breathing

• Receives influences from external sources

Pontine respiratory group (PRG)

• pair in pons

• Modifies rhythm of VRG by outputs to both VRG and DRG

• Adapts breathing to special circumstances such as sleep, exercise, vocalization, and emotional responses

hyperventilation

• Anxiety-triggered state → breathing is so rapid that it expels CO2 from the body faster than it is produced (more than medibolically required)

  • As blood CO2 levels drop, the pH (alkaline) rises causing the cerebral arteries to constrict

  • This reduces cerebral perfusion which may cause dizziness or fainting

• Can be brought under control by having the person rebreathe the expired CO2 from a paper bag

central chemoreceptors

• Brainstem neurons that respond to changes in pH of CSF

• pH of CSF reflects the CO2 level in the blood

• Regulate respiration to maintain stable pH

• Ensures stable CO2 level in blood

• medulla → CNS

peripheral chemoreceptors

• Carotid and aortic bodies

• Respond to the O2 and CO2 content and the pH of blood

stretch receptors

• Found in the smooth muscles of bronchi and bronchioles, and in the visceral pleura

• Respond to inflation of the lungs

• Inflation (Hering–Breuer) reflex: triggered by excessive inflation

  • Protective reflex that inhibits inspiratory neurons and stops

    inspiration

irritant receptors

• Nerve endings amid the epithelial cells of the airway

• Respond to smoke, dust, pollen, chemical fumes, cold air, and excess mucus

• Trigger protective reflexes such as bronchoconstriction, shallower breathing, breath-holding (apnea), or coughing

Voluntary control over breathing originates in the ___ of the cerebrum

• motor cortex of frontal lobe

• Sends impulses down corticospinal tracts to respiratory neurons in spinal cord, bypassing brainstem

• limits to voluntary control

  • Breaking point: when CO2 levels rise to a point where automatic controls override one’s will

Respiratory airflow is governed by the same principles of ___ as blood flow

• flow, pressure, and resistance

• The flow of a fluid is directly proportional to the pressure difference

• The flow of a fluid is inversely proportional to the resistance

• atm drives respiration (Lower at higher elevations)

Boyle’s law

• at constant temperature, the pressure of a gas is inversely proportional to its volume

• Describes air flow in and out of lungs during ventilation

• lung volume increases, internal pressure (intrapulmonary pressure) decreases

• pressure falls below atm, air moves into lungs

inspiration and intrapleural pressure

• slightly negative pressure between 2 pleural layers (-4 to -6 mm Hg)

• Recoil of lung tissue & tissues of thoracic cage causes lungs and chest wall to be pulling in opposite directions

• The small space between the parietal and visceral pleura is filled with watery fluid, and so these layers stay together

2 pleural layers cling together due to the ___ of water (during inspiration)

• cohesion

• When the ribs swing upward and outward during inspiration, the parietal pleura follows them

• The visceral pleura clings to it by the cohesion of water and it follows the parietal pleura

• It stretches the alveoli within the lungs; entire lung expands along the thoracic cage

• As it increases in volume, its internal pressure drops, and air flows in

Charles’ Law

• Volume of a gas is directly proportional to its absolute temperature

• Affects expansion of lungs

  • On a cool day, air will increase its temperature during inspiration

  • Inhaled air is warmed by the time it reaches the alveoli

  • Inhaled volume of 500 mL will expand to 536 mL and this thermal expansion will contribute to the inflation of the lungs

relaxed breathing and expiration

• Passive process achieved mainly by elastic recoil of thoracic cage

• Recoil compresses the lungs

• Volume of thoracic cavity decreases; Raises intrapulmonary pressure

• Air flows down the pressure gradient and out of the lungs

forced breathing and expiraton

Accessory muscles raise intrapulmonary pressure as high as +40 cm H2O

Pneumothorax

• Presence of air in pleural cavity

• Thoracic wall is punctured

• Inspiration sucks air through the wound into the pleural cavity

• Potential space becomes an air-filled cavity

• Loss of negative intrapleural pressure allows lungs to recoil and collapse

Atelectasis

• Collapse of part or all of a lung

• Can also result from an airway obstruction as blood absorbs gases from blood

resistance to airflow (factors)

• Increasing resistance decreases airflow

• Two factors influence airway resistance: bronchiole diameter & pulmonary compliance

bronchodilation

• increase in diameter of bronchioles → Increase airflow

• Epinephrine and sympathetic stimulation

• beta receptor → dilation

bronchoconstriction (bronchospasm)

• decrease in diameter → Decrease airflow

• Histamine, parasympathetic nerves, cold air, and chemical irritants

• Suffocation can occur from extreme bronchoconstriction brought about by anaphylactic shock and asthma

• alpha receptor & ACh → constriction

pulmonary compliance (reducing and limits)

• stretch vs non-stretch of lungs

• Compliance is reduced by degenerative lung diseases in which the lungs are stiffened by scar tissue

• Compliance is limited by the surface tension of the water film inside alveoli

  • Surfactant secreted by great cells of alveoli disrupts hydrogen

    bonds between water molecules → reduces the surface tension & prevent collapse

Infant respiratory distress syndrome (IRDS)

premature babies lacking surfactant are treated with artificial surfactant until they can make their own