RESPIRATORY SYSTEMRESPIRATORY SYSTEM

By, Dr. Shamanthakamani

Narendran, MD

Respiration includes two processes:

Exchange of gases (oxygen and carbon-dioxide) between the blood and lungs. 

Exchange of these two gases between the blood and the cells of the body.

LUNGS

HEART

TISSUE CELLS

CARBON-DIOXIDEOXYGEN

VeinsCO2

Arteries O2

CO2O2

Exchange of O2 and CO2 between

LUNGS

BLOOD VESSELS

BLOOD VESSELS

TISSUE CELLS

A normal person breathes 12-15 times a minute. With each breath, 500 mL of air are breathed in

(inspired) and out (expired). This works out to 6-8 liters/minute. In this way, 250 mL of oxygen enter the body

each minute, while 200 mL of carbon-dioxide are breathed out.

Air normally enters through the nose, though many people also breathe through the mouth.

The nose is divided into a right left half by a septum (the nose bridge).

Each half opens to the outside through a nostril. The nose is lined with a membrane – the

mucous membrane. This lining secretes a slimy fluid, mucous,

which traps solid particles and even bacteria. This is one of the reasons why it is better to

breathe through the nose rather than the mouth. Also, the air is warmed and moistened as it

passes through the nose.

The air then enters the pharynx. The pharynx acts as a passage for food as well

as air. A thin leaf shaped flap (the epiglottis) prevents

food from passing from the pharynx into the larynx, along with the air.

The larynx is sometimes called the ‘voice box,’ and is the first part of the trachea (wind pipe).

The air enters the trachea. It is like a large cylindrical tube, which divides

in the chest into two branches called bronchi.

Each bronchus is embedded in the lung tissue. They are tiw lungs in the chest. They are made up of spongy tissue. They are roughly cone shaped. Their upper end is at the level of the first rib. Their lower surface rests on the diaphragm. The diaphragm is a dome shaped muscle, which

separates the chest from the abdomen, and plays an important part in breathing.

Both lungs are surrounded by a thin membrane called the pleura.

The pleura has two layers, separated by a thin film of fluid.

The bronchi divide into successively smaller tubes (bronchioles).

The branching resembles that of a tree. The trachea and bronchi are kept permanently

distended by firm hoops (of cartilage). The narrow bronchi have no such hoops. Hence they can collapse if the muscle lining

them contracts. Sometimes this happens in response to an

irritating or poisonous gas.

Injury is prevented, by shutting down the air passage.

Too much of this ‘shutting down’ even in response to harmless substances (perfume) occurs in asthma.

The most narrow, final bronchiole (‘terminal bronchiole’) has a number of air sacs or alveoli at its end.

There are several million alveoli. Each alveolus is surrounded by many, thin

walled blood vessels (capillaries).

THE SEQUENCE OF EVENTS THE SEQUENCE OF EVENTS DURING NORMAL RESPIRATIONDURING NORMAL RESPIRATION

The chest expands during inspiration Air enters the alveoli Oxygen passes from the alveoli to the blood

capillaries Oxygen combines with hemoglobin (the red,

iron containing pigment in the blood) The blood is now bright red – oxygenated. The blood returns to the heart. The heart pumps the oxygenated blood through

blood vessels (arteries) to the tissues.

(the tissue cells like the alveoli are also surrounded by thin walled capillaries)

The tissue cells give up carbon-dioxide, a waste product – and take oxygen from the blood.

The blood now looks dark red – deoxygenated. The blood returns to the heart through blood

vessels (veins) The heart pumps the blood to the lungs Carbon-dioxide passes from the blood (in the

capillaries) to the alveoli. When we breathe out carbon-dioxide is pushed out

from the alveoli into the atmosphere. With the next inhalation… the cycle repeats

CHEST EXPANSION DURING INSPIRATIONCHEST EXPANSION DURING INSPIRATIONbreathing inbreathing in

The expansion of the chest decreases the pressure inside the lungs, hence air gets ‘sucked into’ the nose. This expansion is because of two muscles.

Diaphragm is a dome shaped muscle, which is attached to the lower part of the thoracic cage.

When it contracts it moves downwards, like a piston in a syringe.

It may move anything from 1.5 cm to 7 cm (in deep inspiration).

Contraction of the diaphragm increases the chest cavity vertically, and accounts for 75% of the total increase in the chest during quiet inspiration.

Intracostal muscles (external) pass between the ribs.

These muscles run downwards and forwards. Hence when they contract the anteroposterior

(from front to back) diameter of the chest increases.

Sometimes, when breathing is difficult, the muscles in the neck contract.

During quiet breathing exhalation (breathing out) does not involve the contraction of any muscles.

When breathing out is more forceful, abdominal muscles and muscles of the chest wall help by decreasing the chest cavity.

MOVEMENT OF GASESMOVEMENT OF GASES

Atmospheric air contains a mixture of gases. Of these nitrogen makes 78%, oxygen 20%,

carbon-dioxide 0.04%, and the remainder is made up of other gases.

These gases move easily from areas of high pressure to areas of low pressure.

This is an effortless process (no energy is needed), rather like rolling a ball down hill. This process is called diffusion.

Oxygen moves easily from the alveoli (high pressure) into the neighboring capillaries (low pressure).

Since the pressure gradients for carbon-dioxide are in the opposite direction, CO2 moves from the capillaries (high pressure) to the alveoli (low pressure).

TRANSPORT OF OXYGENTRANSPORT OF OXYGEN

Hemoglobin (Hb) is the red pigment in the blood.

It is present in the special category of cells (the red blood cells (RBCs).

Hb is made up of protein and iron. The Hb concentration in normal blood is

approximately 15 g/dL (14 g/dL in women, and 16 g/dL in men).

Oxygen binds to Hb, if the Hb is less than normal, then the amount of oxygen transported is less.

This condition is called anemia. It may be due to loss of blood (excessive

bleeding) or eating a diet which has less iron than we need.

In this context, ‘jaggery,’ green leafy vegetables, and peas or beans are good sources iron.

An anemic person thus feels tired and breathless after physical exertion.

The binding of Hb with oxygen is influenced by the body temperature and the pH (acidity) of the blood.

If there is increase in either of these factors, then O2 is freed from Hb which has less oxygen bound to it than normal.

If the reduced Hb exceeds 5 g/dL, then the tissues – particularly the lips, tongue, fingers, and nails – appear bluish. This condition is called cyanosis.

Various diseases can give rise to this condition, mainly involving the respiratory and/or the cardiovascular systems.

OXYGEN

- a ball rolling down hill

CARBON-DIOXIDE

- a ball rolling down hill

LUNGS

Capillaries (oxygenated blood)

Tissue cells

Capillaries (deoxygenated blood)

Capillaries

Tissue cells

Capillaries

LUNGS

NEURAL/NERVOUS CONTROL NEURAL/NERVOUS CONTROL OF RESPIRATIONOF RESPIRATION

The respiratory system has both voluntary and involuntary control.

In all normal individuals the voluntary control can override the involuntary.

That is why we can decide to hold our breath. This is specially relevant to people who swim

for long stretches under water. The voluntary control cannot carry on

indefinitely – a breaking point is reached – in spite of our will, we have to breathe normally.

This is because of an increase in CO2, low O2 and increased pressure in the chest.

The practice of certain yoga breath control techniques (pranayamas) has been shown to postpone the breathing point.

To the spinal cord

VOLUNTARYVOLUNTARY

BRAIN STEM

CORTEX

SPINAL CORD

TO DIAPHRAGM

INVOLUNTARYINVOLUNTARY

WHY DO WE SWITCH FROM WHY DO WE SWITCH FROM BREATHING INBREATHING IN TO TO BREATHING OUTBREATHING OUT AND SO ON? AND SO ON?

There is a switch like mechanism in the brainstem.

The nerve cells in the brainstem, which are concentrated with inspiration are active. (we breathe in)

Simultaneously they activate another nerve cell. This (other) nerve cell inhibits the brainstem

nerve cells (we breathe out). After a period of being inhibited, the nerve cell

shows REBOUND EXCITATION (we breathe in, again)

The respiratory center in the brainstem is strongly stimulated by

CO2 acid(H+) also O2

Pain, Stress, Anxiety The respiratory centre receives information from

special receptors which are situated close to the important arteries like the aorta and the carotid artery which supplies the brain.

These special receptors sense changes in blood gases (ie an increase in CO2, increase in H+ or a decrease in O2).

These changes are signals to the respiratory center to increase respiration.

SNEEZING and COUGH are protective reflexes.

The centre for these reflexes is in the brainstem. Irritants are removed by these reflexes. However, nasal allergy is an example of too

much of a good thing. The lining of the nose is over sensitive and sends

messages (“this is an irritant”) to the brain. This happens even when the substance is

harmless (eg dust or cool air). Certain yoga cleansing techniques (;kriyas’ or

cleansing techniques) are supposed to reduce this over sensitivity.

RESPIRATORY ADJUSTMENTS TO EXERCISERESPIRATORY ADJUSTMENTS TO EXERCISE

During exercise there is an increase in depth of breathing.

Later on, the rate of respiration increases. Active cells use up more oxygen. Since body temperature increases and blood

gets more acidic (more CO2), O2 is freed easily from Hb.

Upto a particular point energy needs are met by processes which use O2.

If the energy needs are still more, then other processes are used to produce energy.

These other processes do nor require O2. They produce waste products (lactic acid) and

cannot go on for long. To remove the waste products, after exercise is

over, additional O2 is needed. This is called an oxygen debt.

SOUND PRODUCTIONSOUND PRODUCTION As described earlier, the brain controls speech. It decides what has to be said, how it should be

said (very pleasantly, very rudely) and then sends messages to the concerned muscles.

The ‘sound box’ or larynx lies in the throat. The vocal cords are small muscles which are

attached to three sets of cartilage. (cartilage = a firm tissue, not as hard as bone.)

One of these cartilages is the thyroid cartilage. It is V shaped, and the pointed end faces

forward.

In men, it is more prominent than in women, and is called ‘Adam’s apple.’

Two other sets of cartilage lie lower down. During inhalation, the vocal cords move apart. During exhalation they come together. They also come towards the midline when we

speak.

OTHER FACTORS WHICH INFLUENCE OTHER FACTORS WHICH INFLUENCE OUR VOICE/SOUND PRODUCTIONOUR VOICE/SOUND PRODUCTION

The force of exhalation. The degree of tension of the vocal cords. The movement of tongue and lips.

The main job of the respiratory system is to get oxygen into the body and waste gases out of the body.  It is the function of the respiratory system to transport gases to and from the circulatory system.

Respiration is a vital function of all living organisms.

Respiration occurs at TWO DIFFERENT LEVELS: The level of the CELL & ORGANISM

FLOW OF AIR

The nose will do three things to the air we breathe in:

a. Filter the air

b. Warm the air

c. Provide moisture (water vapor or humidity) to the air.

Right and Left BRONCHI

ALVEOLI

The Alveoli consist of thin, flexible membranes that contain an extensive network of Capillaries. The Membranes separate a gas from liquid.  The gas is the air we take in through our Respiratory System, and the liquid is BLOOD.

VENTILATION movement of air to and from the Alveoli.

INHALATION - air is pulled into the LUNGS.

EXHALATION - air is pushed out of the Lungs.

MECHANISM OF BREATHING

THINGS HAPPEN TO THE AIR WE INHALE

a. Oxygen is removed

b. Carbon dioxide is added

c. Water vapor is added.

Blood contains a large amount of CO2 and Little O2.

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