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The Respiratory System

ANATOMY OF THE RESPIRATORY SYSTEM

The Respiratory Tract:

The Lungs

Alveoli

TABLE OF CONTENT

1) Respiratory Tract:Nose through bronchi 2) The lungs.

THE RESPIRATORY SYSTEM CONSISTS OF:

The respiratory tract

further divided into the upper and lower respiratory tract

The upper respiratory tract from the nose through the pharynx

The lower respiratory tract (The Bronchial Tree)

from the larynx to tertiary bronchi

The Bronchial Tree

Alveoli

The Bronchial Tree Extends to Bronchioles and Alveoli

Bronchioles and Alveoli

Cartilage Plates

No Cartilage but Smooth Muscles

Bronchioles

Cartilage Ring

asthmaattack

Cross Section Longitudinal Section

Ciliary Lining of the Lower Respiratory Tract

Cilia

Electron Micrograph of Cilia

The cilia beat upward and drive the debris-laden mucus to the pharynx, where it is swallowed.

THE LUNGS

The Lungs overlap with the respiratory tract.

Secondary Bronchi

Tertiary Bronchi

Bronchioles

Alveoli

Bronchioles

Alveoli

Primary Bronchi

Inside Lungs

THE LUNGS

- consist of the left and the right lungs

- The left lung is divided into two lobes; the right into three.

- receives the

bronchus, blood

and lymphatic

vessels, and nerves

through its hilum.

- The bronchi

extend into alveoli

ALVEOLI

~700 SF surface area

Alveoli consists of :

1) type I alveolar cells (95%), thin

2) type II alveolar cells (5%), secrete surfactant.

3) macrophages (dust cells), defense

- Each alveolus is surrounded with a basket of capillaries.

surrounded with capillaries

The respiratory membrane:

1) the wall of the alveolus

2) the endothelial wall of the capillary

3) their fused basement membranes

Alveoli contain elastic fibers which helps expiration.

Low blood pressure keeps alveoli dry.

Gas exchange occurs only in alveoli.

Dead Space

- starts from nose to terminal bronchiole

- where there is no gas exchange

- ~ 150 mlterminal bronchiole

The Respiratory Tract:

The Lungs

Alveoli

ANATOMY OF THE RESPIRATORY SYSTEM

SUMMARY

ventilation

gas exchange

transport by blood

gas exchange

MECHANICS OF VENTILATION

Driving Force for Air Flow

Resistance to Airflow

Measurements of Ventilation

Alveolar Ventilation

TABLE OF CONTENTS

Terms:

inspiration or inhalation: breathing in

expiration or exhalation: breathing out


Airflow driven by the pressure difference between atmosphere (barometric pressure) and inside the lungs (intrapulmonary pressure).

760 mmHg

atmospheric pressure = 760 mmHg

Before inspiration




Mechanism for the Change in Intrapulmonary pressure

Boyle’s Law:

Volume x Pressure = Constant

gas

P V

Volume Pressure Volume Pressure

Inspiration: Expiration:

Volume Pressure Volume Pressure

Inspiration: Expiration:

Can the lungs expand/shrink by

themselves?

1) The Diaphragm

2) External Intercostal Muscles

3) Internal Intercostal Muscles

4) The Abdominal Muscles

- the principal muscle of inspiration

- pulls the diaphragm down, increasing all three dimensions of the thoracic cage.

Major Respiratory Muscles

1) The Diaphragm


- Inspiration muscles

- increases the anteroposterior and transverse dimensions of the chest.

1) The Diaphragm



- Expiration muscles

- pulls the diaphragm up, reducing the vertical dimension of the thoracic cage.

1) The Diaphragm



4) Internal Intercostal Muscles

- Extra Expiration muscles

Coupling Between Lungs and Thoracic Cage

Visceral pleura covers the surface of each lung; parietal pleura lines the chest cavity.

- The lungs and thoracic cage are coupled by the pleurae.

pleural cavity

- The two pleurae form the pleural cavity.

- The pleural fluid serves to reduce friction during chest expansion.

- Intrapleural pressure: The pressure in the pleural cavity is negative.

Parietal pleura visceral pleura

Potential pleural cavity(negative intrapleural pressure)

lung

The thoracic cage is larger than the natural size of the lungs.

Generation of the negative intrapleural pressure

Parietal pleura visceral pleura

Potential pleural cavity(negative intrapleural pressure)

air

air

pneumathorax

lung

Conclusion

Lungs Thoracic Cagepleurae- pressure

Inspiration

Contraction of1) diaphragm

2) external intercostal muscles

The lungs are carried along.

Lung volume

pressure

Air flows in.

active

passive

Resting Expiration

Relaxation of1) diaphragm

2) external intercostal muscles

The lungs shrink.

Lung volume

pressure

Air flows out.

Forced Expiration

Relaxation of1) diaphragm 2) external

intercostal musclesand

Contraction ofabdominal, internal intercostal and other accessory respiratory

muscles.

Lung volume

pressure

Air flows out.

active


Atmosphere-lung pressure gradient

Major respiratory muscles

Coupling between lungs and thoracic cage

SUMMARY


TABLE OF CONTENTS Resistance

1) Alveolar Surface Tension

2) Elastic Resistance

3) Airway Resistance

Compliance

1) Alveolar Surface Tension

- generated by a thin film of liquid over the surface of alveolar epithelium,

- tends to cause a collapse of the alveoli,

- Resists against inspiration.

Alveoli

Alveolar surface tension is a resistance against inspiration.

- Surface tension is reduced by surfactant. ( type II alveolar epithelial cells)

Pre-term infants don't have enough surfactant.

type II surfactant

Resistance 1) Alveolar Surface Tension


3) Airway Resistance- Against inspiration due to elastic fibers in the lungs and chest wall,

- Increases in pulmonary fibrosis.



3) Airway Resistance- Due to friction, affected by airway caliber.

- Against inspiration and expiration!

- Increases during asthma attack (smooth muscle contraction in bronchiole.



3) Airway Resistance

Compliance

- The reciprocal of resistance,

- An indicator of ease with which the lungs expand.

Measurements of Ventilation using Spirometer

Dead Space

inspiration expiration

Alveolar ventilation rate =(tidal volume – dead space) x resp freq (/min)

Restrictive disorders - (pulmonary fibrosis)

- compliance & vital capacity.

Changes in Spirometric Measures

- No change in respiratory volumes

- FEV1.

one-second forced expiratory volume

Obstructive disorders

Changes in Spirometric Measures

MECHANICS OF VENTILATION

SUMMARY



Measurements of Ventilation

Alveolar Ventilation

NEURAL CONTROL OF VENTILATION

Rhythm?

1) inspiratory center

- stimulates inspiration muscles.

2) expiratory center

- inhibits the inspiratory center,

- stimulates expiration muscles.

Center in the medulla oblongata

The pons fine-tunes ventilation.

Afferent Connections to the Respiratory Centers

the limbic system

Hypothalamus

Chemoreceptors the lungs

Chemoreceptor-initiated Reflexes

Peripheral chemoreceptors

- aortic and carotid bodies,

- monitor O2, CO2 and pH of the blood.

Central chemoreceptors

- close to the surface of the medulla oblongata,

- monitor the pH of the cerebrospinal fluid.

O2, CO2, or pH

stimulate chemoreceptors

reflex

frequency and depth of respiration

CHEMORECEPTOR-MEDIATED REFLEX

Voluntary Control

- the motor cortex,

- bypass the brainstem

respiratory centers,

- limited voluntary control.

GAS EXCHANGE in the LUNGS

ventilation

gas exchange

transport by blood

gas exchange

- The gas exchange between

alveolar air and the blood is via

diffusion of O2 and CO2.

- Diffusion of a gas is driven

by O2 and CO2 partial

pressure gradient.

PO2 = 40 mmHgPCO2 = 46 mmHg


The partial pressure of a gas refers to the share of the total pressure generated by a mixture of gases.

O2 CO2

N2

H2O

Total = 760 mmHg

5.3%40 mmHg

13.6%104 mmHg



Oxygen and carbon dioxide cross the respiratory membrane and the air-water interface easily.

Overview of Gas Exchange in the Lungs

Factors That Affect the Efficiency of Alveolar Gas Exchange

1. partial pressure

2. solubility

3. respiratory membrane thickness/area

4. ventilation-perfusion coupling

O2

CO2

N2

O2 CO2

N2

H2O

Total = 760 mmHgTotal = 760 mmHg

Air

a) High altitudeb) Hyperbaric chamberc) Obstructive disease

PO2104 mmHgPCO2 40 mmHg

1) Partial pressure

CO2 has a higher solubility than O2.

CO2 O2

Pressure Gradient 6 mmHg 64 mmHg

PO2104 mmHgPCO2 40 mmHg

2) Solubility

PO2 40 mmHgPCO2 46 mmHg

1) Partial pressure

2) Solubility

1) Partial pressure

3) Respiratory membrane thickness/area

4) Ventilation-perfusion Coupling

- average V-P ratio = 0.8

- autoregulated by:

2) Solubility

1) Partial pressure

3) Respiratory membrane thickness/area

PO2 and PCO2

causes:1) vasoconstriction of

pulmonary arterioles2) dilation of bronchioles

summary

1) Driving force for gas exchange

2) Factors that affect the efficiency of alveolar gas exchange

Gas transport by the blood

TABLE OF CONTENT

1) Carbon Dioxide Transport

2) Oxygen Transport

7% dissolved in the blood as a gas,

23% as carbamino-hemoglobin,

70% as carbonic acid in the plasma.

Carbon Dioxide Transport

Oxygen Transport

- About 98.5% of O2 in the blood are carried by hemoglobin.

- The rest is physically dissolved in plasma.

Blood Oxygen Content

- average 20 ml/dL

- determined by:

1) saturation of hemoglobin

2) content of hemoglobin

HypoventilationCO poisoning

anemia

Hypoxemia

Carbon monoxide competes with oxygen for hemebinding with a much higher affinity.

Problem: deoxygenate hemoglobin

Treatment: hyperbaric oxygen chamber

GAS EXCHANGE in the TISSUES

1. Carbon Dioxide Loading 2. Oxygen Unloading

How to dissociate?

O2

O2

PO2 dissociation

PCO2 dissociation

pH dissociation

DPG dissociation

(2,3-diphosphoglycerate)

Temperature dissociation

Dissociation of O2 from hemoglobin (HB) is affected by:

O2High PO2, low PCO2

association with HG

favor the loading of O2

In Lungs

100% saturated

High PCO2, low PO2,

low pH, DPG

dissociation of O2

from HG

favor the unloading

O2

In tissues

High PCO2, low PO2,

low pH, DPG

dissociation of O2

from HG

favor the unloading

O2

In tissues

Utilization Coefficient

- The amount of oxygen uptake by tissue versus the arterial blood oxygen content

blood

20 ml O2/dL

cellcell

cell cell cell

Utilization Coefficient = 4.4 ml / 20 ml = 22%

15.6 ml O2/dL

4.4 ml O2/dL

Function of Oxygen ?

with oxygenwithout oxygen

glucose

2 ATP 38 ATP

Can human beings produce oxygen?

Oxygen Toxicity

- Excessive oxygen generates hydrogen peroxide and free radicals, which destroy enzymes and damage nervous tissue.

- Oxidative toxicity with aging.

Hypercapnia

- PCO2 < 37 mmHg - caused by hyperventilation

Hypocapnia

- PCO2 > 43 mmHg - caused by hypoventilation (respiratory diseases)

Summary of the Respiratory System

ventilation

gas exchange

transport by blood

gas exchange

Oxyhemoglobin Dissociation Curve

Oxygen Dissociation & Temperature

Active tissue - more O2 released

PO2 (mmHg)

Oxygen Dissociation & pH

Bohr effect: release of O2 in response to low pH

Active tissue - more O2 released