Respiratory System Part B

OPTOMETRY · SEMESTER 1

Human Anatomy and Physiology

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Transport of Oxygen in Blood Stream

The pH of blood falls as its CO2 content increases, so that when the PCO2 rises, the curve shifts to the right.

In active tissues there is increased production of carbon dioxide and heat, which leads to increased release of oxygen.

In this way oxygen is available to tissues in greatest need.

When oxygen leaves the erythrocyte, the deoxygenated haemoglobin turns purplish in colour.

Transport of Oxygen in Blood Stream

The affinity of fetal hemoglobin (hemoglobin F) for O2, which is greater than that for adult hemoglobin (hemoglobin A), facilitates the movement of O2 from the mother to the fetus 3

Transport of Carbon Dioxide in Blood Stream

Carbon dioxide is one of the waste products of metabolism
It is excreted by the lungs and transported in three mechanisms

As bicarbonate ions (HC03-) in the plasma (70%) Some is carried in erythrocytes, loosely combined with haemoglobin as carbaminohaemoglobin (23 %) Some is dissolved in the plasma (7%) 4

Transport of Carbon Dioxide in Blood Stream

The solubility of CO2 in blood is about 20 times that of O2; therefore considerably more CO2 than O2 is present in simple solution at equal partial pressures The CO2 that diffuses into red blood cells is rapidly hydrated to H2CO3 because of the presence of carbonic anhydrase 5

Transport of Carbon Dioxide in Blood Stream

The H2CO3 dissociates to H+ and HCO3–, and the H+ is buffered, primarily by hemoglobin, while the HCO3– enters the plasma Some of the CO2 in the red cells reacts with the amino groups of hemoglobin and other proteins (R), forming carbamino compounds Since deoxygenated hemoglobin binds more H+ than oxyhemoglobin does and forms carbamino compounds more readily, binding of O2 to hemoglobin reduces its affinity for CO2 (This is known as Haldane effect) 6

Transport of Carbon Dioxide in Blood Stream

Venous blood carries more CO2 than arterial blood, CO2 uptake is facilitated in the tissues, and CO2 release is facilitated in the lungs About 7-11% of the CO2 added to the blood in the systemic capillaries is carried to the lungs as carbamino-CO2 In the plasma, CO2 reacts with plasma proteins to form small amounts of carbamino compounds, and small amounts of CO2 are hydrated; but the hydration reaction is slow in the absence of carbonic anhydrase 7

Transport of Carbon Dioxide in Blood Stream

Carbon dioxide from tissue diffuses into red blood cells within the capillaries Some of the carbon dioxide binds to haemoglobin, but most of it reacts with water inside the red cells to form carbonic acid, a reaction catalyzed by carbonic anhydrase The carbonic acid then dissociates to form bicarbonate and hydrogen ions 8

Transport of Carbon Dioxide in Blood Stream

Since the rise in the HCO3– content of red cells is much greater than that in plasma as the blood passes through the capillaries, about 70% of the HCO3– formed in the red cells enters the plasma The excess HCO3– leaves the red cells in exchange for Cl– This exchange is called the chloride shift 9

Transport of Carbon Dioxide in Blood Stream

Because of it, the Cl– content of the red cells in venous blood is therefore significantly greater than in arterial blood The chloride shift occurs rapidly and is essentially complete in 1 second 10

MECHANISM OF INHALATION AND EXHALATION

Breathing

Breathing (Ventilation): Breathing supply oxygen to the alveoli and eliminate carbon-dioxide Expansion of the chest during inspiration occurs as a result of muscular activity, partly involuntary and partly voluntary.

The main muscles used in normal breathing are the intercostals muscles and the diaphragm There are eleven pairs of intercostals muscles that occupy the spaces between the 12 pairs of ribs.

Breathing

The average respiratory rate is 12 to 15 breaths per minute
Each breath consists of three phases
Inspiration
Expiration
Pause

Breathing

During difficult or deep breathing, muscles of the neck, shoulders and abdomen assist in respiration.

These muscles are:
sternocleidomastoid
and scaleneus muscles- anterior, middle and posterior

Thoracic diaphragm

The diaphragm is a dome-shaped musculo-fibrous septum which separates the thoracic cavity from the abdominal cavity, its convex upper surface forming the floor of the former, and its concave under surface the roof of the latter.

The diaphragm is pierced by a series of apertures to permit of the passage of structures between the thorax and abdomen.

Thoracic diaphragm

There are three large openings (diaphragmatic hiatus):
the aortic
the esophageal

and the vena cava openings

The clinical importance of oesophageal opening is that; weakness can occur and this can cause the development of hiatus hernia The diaphragm is crucial for breathing and respiration The diaphragm is innervated by the phrenic nerve 16

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Inspiration(0)

Inspiration(1)

During inspiration, the diaphragm contracts and moves downwards while the external intercostals muscles contracts raising the ribs and elevate the sternum, increasing the size of the thoracic cavity even more This causes expansion of the lungs, as a result, the intra-alveolar pressure falls and the atmospheric pressure forces more air into the airways 18

Inspiration(2)

The process of inspiration is active, as it needs energy for muscle contraction.
This process is enhanced by the following:

Compliance; ability of pulmonary tissue to stretch, making inspiration possible The pressure between parietal and visceral pleura is always less than atmospheric pressure.

Elastic coil – tendency of pulmonary tissue to return to a smaller size after having been stretched, passively during expiration 19

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Expiration(0)

Expiration(1)

During expiration, the diaphragm and intercostals muscles relax, causing the lungs to recoil, and return to the original shape.

This increases the intra-alveolar pressure above the atmospheric pressure, so the air inside the lungs is forced out through the respiratory passages.

Because normal resting expiration occurs without the contraction of muscles, it is considered a passive process.

Expiration(2)

At rest, expiration lasts about 3 seconds and after expiration there is a pause before the next cycle begins Expiration is a passive process that begins when the inspiratory muscles are relaxed, decreasing the size of the thorax and increasing intra-pleural pressure 22

Expiration(3)

During expiration, relaxation of the intercostal muscles and the diaphragm results in downward and inward movement of the rib cage and elastic recoil of the lungs.

As this occurs, pressure inside the lungs exceeds that in atmosphere and so air is expelled from the respiratory tract.

The lungs still contain some air, and are prevented from complete collapse by the intact pleura This process is passive as it does not require the expenditure of energy 23

PULMONARY VOLUMES AND CAPACITIES

A Spirometer

Spirometry

Spirometry is the process of measuring volumes of air that move into and out of the respiratory system.

Spirometer is a device used to measure these pulmonary volumes.
Pulmonary volumes are the amount of air moved in and out.
These are important for normal exchange of oxygen and carbon dioxide to take place.

Pulmonary Volumes

There are four volumes:

Tidal volume (TV) – amount of air exhaled or inhaled after normal inspiration or expiration is approximately 500mls Expiratory reserve volume (ERV)– Maximum volume of air that can be forcibly exhaled after a normal expiration (normal tidal volume) is approximately between 1.0 and 1.2 litres Inspiratory reserve volume (IRV)– Maximum amount of air that can be forcibly inhaled after normal inspiration (normal IRV is 3 – 3.3 litres) Residual volume amount of air that cannot be forcibly exhaled (1.2 litres) i.e. the amount of air that remain in the lungs after the most forceful expiration 28

Pulmonary Capacities

Pulmonary capacities are the sum of two or more pulmonary volumes.
There are 4 lung capacities:
Vital capacity
Functional residual capacity
Total lung capacity
Inspiratory capacity

Vital capacity

Vital capacity is the maximum volume of air that a person can exhale after maximum inhalation It can also be the maximum volume of air that a person can inhale after maximum exhalation.

Therefore; it equals the inspiratory reserve volume plus the tidal volume plus the expiratory reserve volume; it is about 4600 millilitres. (IRV + TV + ERV it is 4.6 litres) 30

Vital capacity

A person’s vital capacity depends on many factors, including the size of the thoracic cavity and posture so with other physiological measurements, the vital capacity can help make a diagnosis of underlying lung disease.