Lecture 5 the respiratory system

Copyright 2010, John Wiley & Sons, Inc.

Chapter 18

The Respiratory System


Respiration: Three Major Steps1. Pulmonary ventilation

Moving air in and out of lungs

2. External respiration Gas exchange between alveoli and blood

3. Internal respiration Gas exchange between blood and cells


Organs of the Respiratory System Upper respiratory system

Nose and pharynx Lower respiratory system

Trachea, larynx, bronchi, bronchioles, and lungs “Conducting zone” consists of

All airways that carry air to lungs: Nose, pharynx, trachea, larynx, bronchi, bronchioles,

and terminal bronchioles

“Respiratory zone” Sites within lungs where gas exchange occurs

Respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli


Organs of the Respiratory System


Upper Respiratory System: Nose Structure

External nares nasal cavity internal nares Nasal septum divides nose into two sides Nasal conchae covered by mucous membrane

Functions Warm, humidify, filter/trap dust and microbes

Mucus and cilia of epithelial cells lining nose Detect olfactory stimuli Modify vocal sounds


Upper Respiratory System: Pharynx Known as the “throat” Structure

Funnel-shaped tube from internal nares to larynx 3 parts

Three regions (with tonsils in the upper two) Upper: nasopharynx; posterior to nose

Adenoids and openings of auditory (Eustachian) tubes Middle: oropharynx; posterior to mouth

Palatine and lingual tonsils are here Lower: laryngeal pharynx

Connects with both esophagus and larynx: food and air


Respiratory System: Head and Neck


Lower Respiratory System: Larynx “Voice box” Made largely of cartilage

Thyroid cartilage: V-shaped “Adam's apple”: projects more anteriorly in males Vocal cords “strung” here (and to arytenoids)

Epiglottis: leaf-shaped piece; covers airway During swallowing, larynx moves up so epiglottis covers

opening into trachea Cricoid cartilage: inferior most portion Arytenoids (paired, small) superior to cricoid


Lower Respiratory System: Larynx


Voice Production Mucous membrane of larynx forms two pairs

of folds Upper = false vocal cords Lower = true vocal cords

Contain elastic ligaments When muscles pull elastic ligaments tight, vocal

cords vibrate sounds in upper airways Pitch adjusted by tension of true vocal cords

Lower pitch of male voice Vocal cords longer and thicker; vibrate more

slowly


Lower Respiratory System: Trachea “Windpipe” Location

Anterior to esophagus and thoracic vertebrae Extends from end of larynx to primary bronchi

Structure Lined with pseudostratified ciliated mucous

membrane: traps and moves dust upward C-shaped rings of cartilage support trachea, keep

lumen open during exhalation Tracheostomy: opening in trachea for tube


Lower Respiratory System: Bronchi, Bronchioles Structure of bronchial tree

Bronchi contain cartilage rings Primary bronchi enter the lungs medially In lungs, branching secondary bronchi

One for each lobe of lung: 3 in right, 2 in left Tertiary bronchi terminal bronchioles

These smaller airways Have less cartilage, more smooth muscle. In

asthma, these airways can close. Can be bronchodilated by sympathetic nerves,

epinephrine, or related medications.


Lower Respiratory System: Lungs Two lungs: left and right

Right lung has 3 lobes Left lung has 2 lobes and cardiac notch

Lungs surrounded by pleural membrane Parietal pleura attached to diaphragm and lining

thoracic wall Visceral pleura attached to lungs Pleural cavity with little fluid between pleurae Broad bottom of lungs = base; pointy top = apex


Lung Lobes Divided into lobules fed by tertiary bronchi Further divisions terminal bronchioles Respiratory bronchioles

Lined with nonciliated epithelium Alveolar ducts Alveolar sacs Surrounded by alveoli


Lung Lobes


Lower Respiratory System: Alveoli Cup-shaped outpouchings of alveolar sacs

Alveoli: composed of three types of cells Lined with thin alveolar cells (simple squamous);

sites of gas exchange Scattered surfactant-secreting cells. Surfactant:

Lowers surface tension (keeps alveoli from collapsing) Humidifies (keeps alveoli from drying out)

Alveolar macrophages: “cleaners” Respiratory membrane: alveoli + capillary

Gases diffuse across these thin epithelial layers: air blood


Lobule of the Lung


Lobule of the Lung


Structure of an Alveolus


Respiration Step: 1. Pulmonary Ventilation Air flows: atmosphere lungs due to

difference in pressure related to lung volume Lung volume changes due to respiratory muscles

Inhalation: diaphragm + external intercostals Diaphragm contracts (moves downward) lung

volume Cohesion between parietal-visceral pleura

lung volume as thorax volume .


Exhalation Exhalation is normally passive process due

to muscle relaxation Diaphragm relaxes and rises lung volume External intercostals relax lung volume

Active exhalation: exhale forcefully Example: playing wind instrument Uses additional muscles: internal intercostals,

abdominal muscles


Muscles of Inhalation and Exhalation


Muscles of Inhalation and Exhalation


Volume-Pressure Changes in Lungs Volume and pressure are inversely related

As lung volume alveolar pressure As lung volume alveolar pressure

Contraction of diaphragm lowers diaphragm lung volume alveolar pressure so it is < atmospheric pressure air enters lungs = inhalation

Relaxation of diaphragm raises diaphragm lung volume alveolar pressure so it is > atmospheric pressure air leaves lungs = exhalation


Volume-Pressure Changes in Lungs


Air Flow Terms Frequency = breaths/min; normal: 12 Tidal volume (TV) = volume moved in one

breath. Normal ~ 500 ml About 70% of TV reaches alveoli (350 ml) Only this amount is involved in gas exchange 30% in airways = anatomic dead space

Minute ventilation (MV) = f x TV = 6000 mL/min


Lung Volumes Measured by spirometer

Inspiratory reserve volume (ERV) = volume of air that can be inhaled beyond tidal volume (TV)

Expiratory reserve volume (IRV) = volume of air that can be exhaled beyond TV

Air remaining in lungs after a maximum expiration = residual volume (RV)


Lung Capacities Inspiratory capacity = TV + IRV Functional residual capacity (FRC) =

RV + ERV Vital capacity (VC) = IRV + TV + ERV Total lung capacity (TLC) = VC + RV


Lung Capacities


Breathing Patterns Eupnea = normal breathing

Highly variable in pattern Costal breathing: shallow with rib movements Diaphragmatic breathing: deep breathing

Special modifications for speech and emotional responses

Also variations for coughing and sneezing to clear airways See Table 18.1


Nature of Air Mixture of gases (N2, O2,, CO2, H2O, and

others) Each gas has own partial pressure, such as

PO2 or PN2

Sum of all partial pressures = atmospheric pressure

Each gas diffuses down its partial pressure gradient


Respiration Step 2: Pulmonary Gas Exchange: External Respiration Diffusion across alveolar-capillary membrane

O2 diffuses from air (PO2 ~105 mm Hg) to pulmonary artery (“blue”) blood (PO2 ~40 mm Hg). (Partial pressure gradient = 65 mm Hg)

Continues until equilibrium (PO2 ~100-105 mm Hg)

Meanwhile “blue” blood (PCO2 ~45) diffuses to alveolar air (PCO2 ~40) (Partial pressure gradient = 5 mm Hg)


Respiration Step 3: Systemic Gas Exchange: Internal Respiration Occurs throughout body O2 diffuses from blood to cells: down partial

pressure gradient PO2 lower in cells than in blood because O2

used in cellular metabolism Meanwhile CO2 diffuses in opposite direction:

cells blood


Internal and External Respiration


Transport of Oxygen within Blood 98.5% of O2 is transported bound to

hemoglobin in RBCs Binding depends on PO2

High PO2 in lung and lower in tissues O2 dissolves poorly in plasma so only 1.5% is

transported in plasma Tissue release of O2 to cells is increased by

factors present during exercise: High CO2 (from active muscles) Acidity (lactic acid from active muscles) Higher temperatures (during exercise)


Transport of Carbon Dioxide CO2 diffuses from tissues into blood

CO2 carried in blood: Some dissolved in plasma (7%) Bound to proteins including hemoglobin (23%) Mostly as part of bicarbonate ions (70%)

CO2 + H2O H+ + HCO3-

Process reverses in lungs as CO2 diffuses from blood into alveolar air exhaled


Transport of Oxygen and Carbon Dioxide


Control of Respiration Medullary rhythmicity area in medulla

Contains both inspiratory and expiratory areas Quiet breathing

Inspiratory area nerve signals to inspiratory muscles for ~2 sec

Inspiration Inspiration ends and muscles relax Expiration Expiratory center active only during forceful

breathing Two areas in pons adjust length of inspiratory

stimulation


Control of Respiration


Control of Respiration


Regulation of Respiratory Center Cortical input: voluntary adjustment of

patterns For talking or cessation of breathing while

swimming Chemoreceptor input will override breath-holding


Regulation of Respiratory Center Chemoreceptor input to increase

ventilation Central receptors in medulla: sensitive to H+ or

PCO2 in CSF

Peripheral receptors in arch of aorta + common carotids: respond to PO2 as well as H+ or PCO2 in blood

Blood and brain pH can be maintained by these negative feedback mechanisms


Regulation of Respiratory Center


Other Regulatory Factors of Respiration Respiration can be stimulated by

Limbic system: anticipation of activity, emotion Proprioception as activity is started Increase of body temperature

Sudden pain can apnea: stop breathing Prolonged somatic pain can increase rate

Airway irritation cough or sneeze Inflation reflex

Bronchi wall stretch receptors inhibit inspiration Prevents overinflation


Aging and the Respiratory System Lungs lose elasticity/ability to recoil more

rigid; leads to Decrease in vital capacity Decreased blood PO2 level Decreased exercise capacity

Decreased macrophage activity and ciliary action Increased susceptibility to pneumonia, bronchitis

and other disorders


End of Chapter 18

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Lecture 5 the respiratory system