Respiratory System Part A

OPTOMETRY · SEMESTER 1

Human Anatomy and Physiology

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RESPIRATORY SYSTEM PHYSIOLOGY

Learning Objectives

3
Mention the functions of respiratory passageways
Explain the types of respiration
Describe the mechanism of inhalation and exhalation

Describe pulmonary volumes and capacities

Learning Objectives

Explain alveolar ventilation
Describe principles of gas exchange through respiratory membranes
Describe transport of oxygen and carbon dioxide between lungs and tissues
Describe factors regulating respiration

FUNCTIONS OF RESPIRATORY PASSAGEWAYS

Introduction

The respiratory system is divided into two divisions

Upper respiratory tract

The organs are located outside of the thorax and consists of the nose, pharynx and larynx Lower respiratory tract

The organs are located within the thorax and consists of the trachea, the bronchial tree and the lungs 6

Introduction

The main role of the respiratory system is to provide gas exchange between the blood and the environment.

Primarily, oxygen is absorbed from the atmosphere into the body and carbon dioxide is expelled from the body.

The following are organs from the respiratory system
Nose
Pharynx
Larynx
Trachea
Bronchi
Lungs

The Function of the Nose

Respiration (breathing)

The nose is the first part of the respiratory system through which the inspired air passes The nose humidify, warming, filtering and cleaning of air Reception and elimination of secretions from the nasal mucosa, paranasal sinuses, and nasolacrimal ducts Olfaction (smelling)

The nose is the organ of sense of smell It aids speech- this is enhanced by the presence of paranasal sinuses, which act as resonating chambers for speech 10

Functions of the pharynx

Passageway for air and food
Warming and humidifying air
Protection
Taste

Facilitates Hearing

The pharynx is also important in vocalization and Speech

Function of larynx

Respiration filters, humidifies and warms air as it passes to the lungs.

Swallowing

The epiglottis and vestibular folds prevent swallowed material from moving into the larynx Phonation; the vocal folds are the primary source of sound production 12

TYPES OF RESPIRATION

Types of respiration

Respiration:The exchange of gases between body cells and the environment
It involves:

Breathing (pulmonary ventilation)

Ventilation is the process of moving air into the lungs (inspiration) and out of the lungs (expiration) The flow of air in and out of the lungs require pressure gradient in the opposite direction Exchange of gases in the lungs: external respiration and in the tissues: internal respiration.

External Respiration

External respiration: An exchange of gases by diffusion between the alveoli and the blood in the alveolar capillaries, across the respiratory membrane Each alveolar wall is one cell thick and is surrounded by a network of tiny capillaries (the walls of which are also only one cell thick) 16

External Respiration

Venous blood arriving at the lungs has travelled from all the tissues of the body, and contains high levels of CO2 and low levels of O2 Carbon dioxide diffuses from the blood down its concentration gradient into the alveoli until equilibrium with alveolar air is reached.

By the same process, oxygen diffuses from the alveoli into the blood

External Respiration

The PO2 within alveoli averages approximately 104mmHg, and as blood flows into the pulmonary capillaries, it has a PO2 of approximately 40mmHg.

Consequently, oxygen diffuses from the alveoli into the pulmonary capillary blood because the PO2 is greater in the alveoli than in the capillary blood.

External Respiration

The slow flow of blood through the capillaries increases the time available for gas exchange to occur.

When blood leaves the alveolar capillaries, the oxygen and carbon dioxide concentrations are in equilibrium with those of alveolar air 19

Internal Respiration

Internal respiration: An exchange of gases by diffusion between blood in the capillaries and the body cells Gaseous exchange does not occur across the walls of the arteries carrying blood from the heart to the tissues, because their walls are too thick.

P02 of blood arriving at the capillary bed is therefore the same as blood leaving the lungs 20

Internal Respiration

Blood arriving at the tissues has been cleansed of its CO2 and saturated with O2 during its passage through the lungs, and therefore has a higher P02 and a lower PC02 than the tissues.

Carbon dioxide is continually produced as a by-product of cellular respiration, and a diffusion gradient is established from tissue cells to the blood within the tissue capillaries.

Internal Respiration

The intracellular Pco2 is approximately 46mmHg, and the interstitial fluid Pco2 is approximately 45 mmHg.

At the arterial end of the tissue capillaries, the Pco2 is a close to 40 mmHg.

As blood flows through the tissue capillaries, carbon dioxide diffuses from a higher Pco2 to a lower Pco2 until equilibrium in Pco2 is established.

Internal Respiration

At the venous end of the capillaries, blood has a Pco2 of 45 mmHg.

CO2 diffuses from the cells into the extracellular fluid, then into the bloodstream towards the venous end of the capillary.

TRANSPORT OF OXYGEN AND CARBON DIOXIDE BETWEEN LUNGS AND TISSUES

Transport of Oxygen in Blood Stream

Transport of blood oxygen and carbon dioxide is essential for internal respiration to occur.

Oxygen is carried in the blood in:
Chemical combination with haemoglobin as oxyhaemoglobin (98.5%)
Solution in plasma water (1.5%).

Transport of Oxygen in Blood Stream

The amount of O2 in the blood is determined by the amount of dissolved O2, the amount of hemoglobin in the blood, and the affinity of the hemoglobin for O2.

In normal adults, most of the hemoglobin molecules contain two alpha and two beta chains Heme 26

Transport of Oxygen in Blood Stream

Each of the four iron atoms can bind reversibly one O2 molecule.

The iron stays in the ferrous state, so that the reaction is an oxygenation, not an oxidation The reaction is rapid, requiring less than 0.01 s.

The deoxygenation (reduction) of Hb4O8 is also very rapid.

Transport of Oxygen in Blood Stream

Combination of the first heme in the Hb molecule with O2 increases the affinity of the second heme for O2, and oxygenation of the second increases the affinity of the third, etc, so that the affinity of Hb for the fourth O2 molecule is many times that for the first.

When blood is equilibrated with 100% O2 (PO2 = 760 mm Hg), the normal hemoglobin becomes 100% saturated.

When fully saturated, each gram of normal hemoglobin contains 1.39 mL of O2.

Transport of Oxygen in Blood Stream

Blood normally contains small amounts of inactive hemoglobin derivative.

Oxy-haemoglobin is an unstable compound that under certain conditions readily dissociates releasing oxygen.

Factors affecting the affinity of hemoglobin for oxygen are pH and temperature and the concentration of 2,3-biphosphoglycerate.

A rise in temperature or a fall in pH shifts the curve to the right.

Oxygen-Haemoglobin Dissociation Curve

Transport of Oxygen in Blood Stream

When the curve is shifted in this direction, a higher PO2 is required for hemoglobin to bind a given amount of O2.

A fall in temperature or a rise in pH shifts the curve to the left, and a lower PO2 is required to bind a given amount of O2.

The decrease in O2 affinity of hemoglobin when the pH of blood falls is called the Bohr effect and is closely related to the fact that deoxygenated hemoglobin (deoxyhemoglobin) binds H+ more actively than does oxyhemoglobin.