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Respiratory Anatomy and physiology
anatomyThe respiratory system is made up of the organs involved in breathing and consists of the:nose pharynx larynx trachea bronchi lungs
The upper respiratory tract includes the:nose nasal cavity ethmoidal air cells frontal sinuses maxillary sinus larynx trachea
The lower respiratory tract includes the:
lungs
bronchi
alveoli
Respiration
Breathing
External respiration
Gas transport by blood
Internal respiration
Process of breathing
Breathing
Inspiration:Contraction of diaphragm / intercostal muscles
Expansion of thorax expansion of lungs Pressure in lungs ↓ Air inflow
Expiration:Relaxation of muscles Thorax / lung recoil back Pressure in lungs ↑ Air outflow
Forceful breathing
Inspiration:Contraction of accessory muscles extra expansion of thorax extra air inflow
Expiration:Contraction abdominal muscles abdominal contents move up diaphragm moves up
Abdominal muscles retract rib cage
Internal intercostal muscles retract rib cage
Lung volumes and capacities
TIDAL VOLUME (TV): Volume inspired or expired with each normal breath.
INSPIRATORY RESERVE VOLUME (IRV): Maximum volume that can be inspired over the inspiration of a tidal volume/normal breath. Used during exercise/exertion.
EXPIRATRY RESERVE VOLUME (ERV): Maximal volume that can be expired after the expiration of a tidal volume/normal breath.
RESIDUAL VOLUME (RV): Volume that remains in the lungs after a maximal expiration. CANNOT be measured by spirometry.
INSPIRATORY CAPACITY ( IC): Volume of maximal inspiration:RV + TV
FUNCTIONAL RESIDUAL CAPACITY (FRC): Volume of gas remaining in lung after normal expiration, cannot be measured by spirometry because it includes residual volume: ERV + RVVITAL CAPACITY (VC): Volume of maximal inspiration and expiration: IRV + TV + ERV = IC + ERV
TOTAL LUNG CAPACITY (TLC): The volume of the lung after maximal inspiration. The sum of all four lung volumes, cannot be measured by spirometry because it includes residual volume: IRV+ TV + ERV + RV = IC + FRC
DEAD SPACE: Volume of the respiratory apparatus that does not participate in gas exchange, approximately 300 ml in normal lungs. --ANATOMIC DEAD SPACE: Volume of the conducting airways, approximately 150 ml --PHYSIOLOGIC DEAD SPACE: The volume of the lung that does not participate in gas exchange. In normal lungs, is equal to the anatomic dead space (150 ml). May be greater in lung disease.
FORCED EXPIRATORY VOLUME in 1 SECOND (FEV1): The volume of air that can be expired in 1 second after a maximal inspiration. Is normally 80% of the forced vital capacity, expressed as FEV1/FVC. In restrictive lung disease both FEV1 and FVC decrease , thus the ratio remains greater than or equal to 0.8. In obstructive lung disease, FEV1 is reduced more than the FVC, thus the FEV1/FVC ratio is less than 0.8.
Atmospheric pressure
Free molecules
Gravity of earth
Dependent on location (height)
Normal atmospheric pressure (sea level) = 760 mm Hg
Partial pressure
Atm Pressure: 760 mm Hg
Dalton’s law
Nitrogen= 597 mm Hg
Oxygen= 159 mm Hg
Carbondioxide:
Water:
Partial pressure
Henry’s law: when a mixture of gases is in contact with a liquid, each gas will dissolve in the liquid in proportion to its partial pressure gradient
H2O H2O
Gas solubility
CO2 20 times more soluble in water than O2
N2 almost insoluble
H2O H2O H2O
Carbondioxide Oxygen Nitrogen
External respiration (in lungs)
pO2= 104 mm Hg
pCO2= 40 mm Hg
Alveoli Capillaries
pO2= 40 mm Hg
pCO2= 45 mm Hg
pO2= 104 mm Hg
pCO2= 40 mm Hg
pO2= 104 mm Hg
pCO2= 40 mm Hg
Internal respiration (in tissue)
pO2= 100 mm Hg
pCO2= 40 mm Hg
Capillaries Tissue
pO2< 40 mm Hg
pCO2> 45 mm Hg
pO2= 40 mm Hg
pCO2= 45 mm Hg
pO2= 40 mm Hg
pCO2= 45 mm Hg
Oxygen transport
1.5 % dissolved
98.5 % bound to haemoglobin
Iron in Hb binds to oxygen
4 O2 molecules per Hb molecule
Carbondioxide transport
7-10 % dissolved in plasma
22 % bound to Hb
70 % transported as HCO3-
COCO22 + H + H22OO HH22COCO33 HH++ + HCO + HCO33--
Regulation of breathing
DRG stimulates inspiratory muscles, 12-15 times / minuteVRG active in forced breathingPontine respiration centre: finetuning of breathing / inhibits DRG
Factors that influence respiration
Hypothalamus (emotions / pain)
Cortex (voluntary control)
Chemoreceptors:Central (in medulla oblongata): responds to CO2
↑CO2 passes blood brain barrier
CO2 + H2O H2CO3 H+ + HCO3-
H+ stimulates receptors breathing depth ↑ + rate ↑
Peripheral (in aortic / carotid bodies): responds when O2 < 60 mm Hg increase ventilation
Responds to pH ↓ increase ventilation
Factors that influence respiration
Marieb, Human Anatomy & Physiology, 7th edition
Overview
Breathing:Inspiration: contraction muscles thorax expansion air inflowExpiration: relaxation recoil lungs air outflow
Different lung volumes and capacitiesExternal respiration:
Gas exchange following partial pressure gradientInternal respiration
Gas exchange following partial pressure gradientGas transport
O2 mainly bound to HbCO2 mainly transported as HCO3
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Regulation of breathingRespiratory centresChemoreceptors
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