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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