By Gunchmaa.N

4 main stages1. Ventilation2. Diffusion

(alveoli/blood)3. Transport of O2 and

CO24. Exchange

(tissue/blood)

Non-respiratory functions• Moistens inspired air• Maintains pH• Vocalization• Modifies various materials• Enhances venous return

The Pleura• The pleura separates

each lung from the thoracic wall and other structures

• Secretes a thin intrapleural fluid which lubricates the pleural surfaces as theyslide past each other

Different Pressures

• Atmospheric pressure = 760 mm Hg • Intra-alveolar pressure - pressure within

the alveoli• Intrapleural pressure - pressure exerted

within the thoracic cavity /756 mm Hg/

Transmural Pressure Gradient

4 mm Hg difference in pressure enables lungs to expand and shrink

Basic concept• Intra-alveolar P < atmospheric P = inspiration• Intra-alveolar P > atmospheric P = expiration

Major respiratory muscles

• Diaphragm• External intercostal • Internal intercostal• Abdominal muscles

• Sternocleidomastoideous• Scalenus

Movement of rib and sternum

Pulmonary surfactant

• A complex mixture of lipids and proteins secreted by the Type II alveolar cells

• Lowers alveolar surface tension• Decreases hydrogen bonding at the alveolar

air–water interface• More crowded in small alveoli

Law of LaPlace

The smaller alveolus has a tendency(without pulmonary surfactant) to collapse and empty its air into the larger alveolus.

Surfactant avoids this!

• Surfactant proteins - synthesized in polyribosomes, modified in the ER, GA and stored in lamellar bodies before secretion.

• Surfactant phospholipids - synthesized in the ER and packaged into lamellar bodies. After exocytosis of lamellar bodies, it’s organized into tubular myelin

Alveolar interdependence

When an alveolus in a group of alveoli collapses, the surrounding alveoli are stretched. As the other alveoli recoil in resistance, they pull outward on the collapsing alveolus.

Variations in lung volume

Anatomical Dead Space

Not all the inspired air gets down tothe alveoli. Part remains in the conducting airways, where it is not available for gas exchange. The volume averages about 150 ml.

Effects of CO2 and O2

Gas transport

• Oxygen is present in the blood in two forms: physically dissolved and chemically bound to hemoglobin

• Deoxyhemoglobin/oxyhemoglobin • The saturation, measures the Hb combined

with O2 and can vary from 0% to 100%.• PO2 of the blood determines saturation

CO2 transport in blood

This reaction takes place slowly in the plasma, but it’s catalyzed by erythrocyte enzyme carbonic anhydrase.

Haldane effect

Removing O2 from Hb increases the ability ofHb to pick up CO2 and CO2-generated H ion

Components of neural control of respiration

1. Factors that generate respiratory rhythm

2. Factors that regulate the magnitude of ventilation

3. Factors that modify respiratory activity to serve other purposes.

Medullary Respiratory Center

• Dorsal respiratory group consists of inspiratory neurons. When active inspiration occurs.

• Ventral respiratory group is composed of inspiratory neurons and expiratory neurons. Activates when demands for ventilation are increased.

Pre-Bötzinger complex

A region located near the end of the medullary respiratory center. Displays pacemaker activity.

Apneustic centerPrevents the inspiratory neurons frombeing switched off.

Hering–Breuer reflex

Prevents overinflation of the lungs. Pulmonary stretch receptors’ action potentials travelthrough afferent nerve fibers to the medullary center and inhibit the inspiratory neurons.

Peripheral chemoreceptors

• Carotid/aortic bodies

• Responds to chemical changes in arterial blood

Other ventilation factors• Protective reflexes such as sneezing and

coughing• Inhalation of noxious agents triggers cessation of

ventilation.• The expression of various emotional states, such

as laughing, crying, sighing. • Hiccups• The respiratory center is reflexly inhibited during

swallowing

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