Unit ii transport breathing mechanism
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Unit II: Transport Breathing Mechanism. Chapter 20 pp 736-759. Pulmonary Ventilation. Breathing – repeating cycle of inspiration and expiration quiet respiration – at rest forced respiration – during exercise

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Unit II: Transport Breathing Mechanism

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Unit ii transport breathing mechanism

Unit II: TransportBreathing Mechanism

Chapter 20

pp 736-759


Pulmonary ventilation

Pulmonary Ventilation

  • Breathing – repeating cycle of inspiration and expiration

    • quiet respiration – at rest

    • forced respiration – during exercise

  • Flow of air in and out of lungs requires a pressure difference between air pressure within lungs and outside body


Unit ii transport breathing mechanism

Pulmonary Ventilation

Primary Inspiratory Muscle

Accessory

Inspiratory

Muscles

External intercostal muscles

Sternocleido-

mastoid muscle

Accessory

Expiratory

Muscles

Scalene

muscles

Pectoralis

minor muscle

Internal

intercostal

muscles

Serratus

anterior muscle

Transversus

thoracis

muscle

Primary

Inspiratory

Muscle

External

oblique

muscle

Diaphragm

Rectus

abdominis

Internal

oblique

muscle


Pressure and flow

Pressure and Flow

  • Atmospheric pressure drives respiration

    • 1 atmosphere (atm) = 760 mmHg

  • Boyle’s Law:

    • pressure is inversely proportional to volume

      • for a given amount of gas, as volume , pressure  and as volume , pressure 

  • Charles’s Law:

    • Volume is directly proportional to its absolute temperature

      • for a given amount of gas, if absolute temperature is doubled, so is the volume


Inspiration

Inspiration

  • Phrenic nerves stimulate diaphragm to flatten and drop &

  • intercostal muscles cause ribs to move slightly up and out

    •  volume of thoracic cavity

  • intrapleuralpressure

  • visceral pleura clings to parietal pleura 

  • lungs expand with visceral pleura -  intrapulmonary pressure

    • net result: 757 mmHg

  • Inflation aided by warming of inhaled air

  • 500 ml of air flows with a quiet breath


Passive expiration

Passive Expiration

  • Expiration achieved by elasticity of thoracic cage

  • After inspiration, phrenic nerves continue to stimulate diaphragm to produce a braking action to elastic recoil

  • As volume of thoracic cavity ,intrapulmonary pressure  and air is expelled

    • During quiet breathing: +3mmHg

    • During forced breathing: +30mmHg


Respiratory cycle

Respiratory Cycle


Resistance to airflow

Resistance to Airflow

  • Diameter of bronchioles

  • Surface Tension

    • Thin film of water needed for gas exchange

      • creates surface tension that would collapse alveoli

    • Pulmonary surfactant (great alveolar cells)

      • an agent that disrupts the H+ bonds of water

      • decreasessurface tension


Alveolar ventilation

Alveolar Ventilation

  • Anatomical dead space

    • conducting division of airway

  • Physiological dead space

    • sum of anatomical dead space + any pathological alveolar dead space

  • Alveolar ventilation rate

    • directly relevant to ability to exchange gases


Lung volumes and capacities

Lung Volumes and Capacities


Neural control of breathing

Neural Control of Breathing

  • Breathing depends on repetitive stimuli from brain

  • Controlled at 2 levels:

  • Voluntary control provided by motor cortex

  • Neurons in medulla oblongata and pons control unconscious breathing


Respiratory control centers

Respiratory Control Centers

  • Medulla oblongata:

    • Ventral respiratory group (VRG)

      • primary generator of respiratory rhythm

    • Dorsal respiratory group (DRG)

      • modifies respiratory rhythm

      • Integrating center


Respiratory control centers1

Respiratory Control Centers

  • Pons:

    • Pontine respiratory group (PRG) or Pneumotaxic center

      • regulates shift from inspiration to exhalation

      • as frequency rises, breathe shorter and shallower


Unit ii transport breathing mechanism

Respiratory Control Centers

Forced Breathing

Quiet Breathing

INHALATION

INHALATION

(2 seconds)

Inspiratory muscles

contract, and expiratory

muscles relax. Inhalation

occurs.

Diaphragm and external

intercostal muscles

contract and inhalation

occurs.

Increased activity in the

DRG stimulates neurons of

the VRG that in turn activate

the accessory muscles

involved in inhalation. The

expiratory center of the

VRG is inhibited.

DRG and

inspiratory

center of VRG

are inhibited.

Expiratory

center of VRG

is active.

Neurons in the VRG

become inactive. They

remain quiet for the

next 3 seconds and

allow the inspiratory

muscles to relax.

Activity in the

VRG

stimulates the

inspiratory

muscles.

After each inhalation,

active exhalation occurs

as the neurons of the

expiratory center of the

VRG stimulate the

appropriate accessory

muscles. Inspiratory

muscles relax.

Diaphragm and external

intercostal muscles relax

and passive exhalation

occurs.

EXHALATION

(3 seconds)

EXHALATION


Air water interface

Air-Water Interface

Example:

Soda is put into the can under

pressure, and the gas (carbon

dioxide) is in solution at

equilibrium.

  • Gases diffuse down their pressure gradients

  • Henry’s law

    • amount of gas that dissolves in water is determined by its solubility in water and its partial pressure in air

    • Temperature of liquid

Open the can:

internal pressure falls

gas molecules come out of solution

Volume difference is so great

that within a

half hour you are

left with “flat”

soda.


Alveolar gas exchange

External Respiration

Alveolar Gas Exchange

Alveolus

PO2 = 40

  • Exchange across the water film covering alveolar epithelium and respiratory membrane

  • Factors affecting gas exchange:

    • Pressure gradients of gases

PCO2 = 45

Respiratory

membrane

Pulmonary

circuit

Systemic

circuit

PO2 = 100

PCO2 = 40

PO2 = 100 mm Hg

Pulmonary

capillary

PCO2 = 40 mm Hg

Internal Respiration

Interstitial fluid

Systemic

circuit

PO2 = 95

PCO2 = 40

PO2 = 40

PCO2 = 45

PO2 = 40

PCO2 = 45

Systemic

capillary


Other factors affecting gas exchange

Other Factors Affecting Gas Exchange

  • Gas solubility

    • CO2 20 times as soluble as O2

  • Membrane thickness - only 0.5 m thick

  • Membrane surface area - 100 ml blood in alveolar capillaries, spread over 70 m2

  • Ventilation-perfusion coupling - areas of good ventilation need good perfusion (vasodilation)


Oxygen transport

Oxygen Transport

  • Concentration in arterial blood

    • 98.5% bound to hemoglobin

    • 1.5% dissolved

  • Binding to hemoglobin

    • each heme group of 4 globin chains may bind O2

    • oxyhemoglobin (HbO2 )

    • deoxyhemoglobin (HHb)

  • Protein subunits

    Iron ion

    Heme unit


    Oxyhemoglobin dissociation curve

    Oxyhemoglobin Dissociation Curve

    Steep slope = a large change in

    amount of oxygen associated with Hb.

    Blood entering the systemic circuit

    has a PO2 of 95 mm Hg.

    Blood leaving peripheral tissues has

    an average PO2 of 40 mm Hg.

    Oxyhemoglobin (% saturation)

    The PO2 in active muscle tissue may

    drop to 15–20 mm Hg.

    PO2 (mm Hg)


    Unit ii transport breathing mechanism

    Oxyhemoglobin Dissociation Curve

    Bohr Effect

    pH increase = curve shifts to the left

    Hemoglobin releases less oxygen.

    7.6

    7.4

    7.2

    pH decrease = curve shifts to the right

    Hemoglobin releases more oxygen.

    Oxyhemoglobin (% saturation)

    PO2 (mm Hg)


    Carbon dioxide transport

    CO2 diffuses

    into the

    bloodstream.

    Carbon Dioxide Transport

    ~7% remains

    in solution.

    93% diffuses

    into RBCs.

    ~70% is converted to

    carbonic acid by

    carbonic anhydrase

    ~23% CO2 is carried as

    Carbaminohemoglobin

    (HbCO2)

    H2CO3 H+ + HCO3–

    Hydrogen ions bind

    to hemoglobin acting as

    pH buffers.

    Bicarbonate ions move into

    the surrounding plasma in

    exchange for extracellular

    chloride ions (Cl–).

    Chloride shift


    Unit ii transport breathing mechanism

    Summary of Transport

    O2 pickup

    O2 delivery

    Pulmonary

    capillary

    Systemic

    capillary

    Plasma

    Red blood cell

    Red blood cell

    Cells in

    peripheral

    tissues

    Alveolar

    air space

    Chloride

    shift

    Alveolar

    air space

    Pulmonary

    capillary

    Systemic

    capillary

    CO2 delivery

    CO2 pickup


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