Physiology Of RESPIRATORY SYSTEM

Note: All the notes provided us from gcvs 

recomended book text book of veterinary physiology

Composed, Compiled and Presented by:

MUHAMMAD SAJJAD HUSSAIN

RESPIRATORY SYSTEM

Respiratory system is an important system of the body which provides O2 to each

and every cell and removes CO2 from the blood.

“A man can live without food for a week and without water for days but can live

only five minutes without O2.”

► Respiration is a voluntary action but normally it works as involuntary.

FUNCTIONS OF RESPIRATORY SYSTEM

Following are some important functions of the respiratory system.

► It provides oxygen to the tissues and removes carbon dioxide.

► It helps in phonation (Phonation means voice production).

► It helps in the maintenance of pH of the body.

► It helps in the maintenance of temperature especially in carnivores because

they do not have sweat glands, as saliva evaporates from the surface of the

tongue.

► It helps in the removal or excretion of volatile substance or other gases.

► It helps in water balance in some species of animals

COMPONENTS OF RESPIRATORY SYSTEM

The respiratory system starts from nostrils (a long passage provided with hairs),

pharynx, larynx, trachea, bronchi and bronchioles. At the end of the bronchioles

there are alveoli.

Trachea: is a windpipe made up of cartilaginous rings and in between them, smooth

muscles are there.

Alveoli: These are air sacs around them are blood capillaries. This capillary system

around the alveoli is responsible for the exchange of gases. Oxygen diffuses to these

capillaries from alveoli and carbon dioxide diffuses into the alveoli in a fraction of

seconds.

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MECHANISM OF RESPIRATION

(How Respiratory System Works?)

Respiration is of two types;

1) External Respiration:

Exchange of gases at alveolar or lungs levels is called external respiration.

2) Internal Respiration:

Exchange of gases at tissue or cellular level is called internal respiration.

The external respiration is also known as ventilation. In the ventilation, the air freely

comes into the lungs, exchange here and moves out.

The process of respiration comprises of inspiration and expiration. These two

processes collectively known as breathing.

INSPIRATION

The taking of fresh air into the lungs is called inspiration.

EXPIRATION

The taking of consumed air out from the lungs is called expiration.

Thoracic cavity (air tight) always has negative pressure and through phrenic nerve

signals come to the diaphragm. This diaphragm pushes the abdominal contents

backward or towards caudal side. Thus, air moves into the lungs from outside

because longitudinal area is increased. During expiration, abdominal contents move

upside.

During normal respiration, only diaphragm serve in inspiration and

expiration but during exercise, only diaphragm is not sufficient, so surface area of

thoracic cavity (transverse area) should also increase.

This increase in transverse area is due to movement of ribs and intercostal

muscles. That’s why arrangement of ribs is so that ends of ribs are somewhat above

than central.

When ribs move upward, the area of thoracic cavity is increased. Thus, due to

increase in surface area air comes into the lungs. Similarly when ribs move

downward the area of thoracic cavity is decreased due to which air is expelled out

from the lungs.

TYPES OF BREATHING

There are two types of breathing as follows:

1. Abdominal or Diaphragmatic Breathing

It is a quite normal breathing in which there is a movement of abdomen due to

contraction or relaxation of diaphragm.

2. Costal or Thoracic Breathing:

It is a type of breathing in which there is considerable movement of ribs.

When there is increased rate of breathing than abdominal movement is not

sufficient thus, ribs also move.

TERMINOLOGY

Eupnea: Quite normal breathing.

Dyspnea: Difficult breathing.

Apnea: No respiration. It is also known as cessation of respiration.

Hyperpnea: (Hyper: more) Increased depth or rate of respiration or both.

Polypnea: Rapid but shallow breathing

RESPIRATORY VOLUMES AND CAPACITIES

Respiratory system provides oxygen, removes carbon dioxide according to the body

requirements. Sometimes body needs less oxygen and some times (esp. during

exercise) body needs more oxygen. So, in different conditions, volume and capacities

also vary.

A) RESPIRATORY VOLUMES

Therefore, there are following four important respiratory volumes.

i) Tidal Volume

The volume of air which is inspired or expired during normal respiration or

breathing OR The volume of air which is inspired during normal inspiration

OR The volume of air which is expired during normal expiration

ii) Inspiratory Reserve Volume

The volume of air which is inspired above and beyond that is inspired during

normal inspiration.

iii) Expiratory Reserve Volume

The volume of air which is expired above and beyond that is expired during

normal expiration.

iv) Residual Volume

The volume of air which remains in lungs after maximum respiratory effort

B) RESPIRATORY CAPACITIES

There are following four respiratory capacities;

i) Vital Capicity

The maximum volume of air which is expired after maximum inspiration

ii) Functional Residual Capicity

The volume of air remaining in the lungs after normal expiration

iii) Inspiratory Capacity

It is the maximum inspiration after normal expiration. OR

It is the volume of air which is inspired maximally after normal expiration.

iv) Total Lung Capacity

It is the volume of air contained in the lungs after maximum inspiration.

FRACTIONS OF INSPIRED AND EXPIRED AIR

Activity O2 CO2 N2

Inspired Air 20.93 % 0.03 % 79.04 %

Expired Air 16.29 % 4.21 % 79.5 %

PRESSURE RELATIONSHIPS

Intrapulmonic Pressure

The pressure inside the lungs is called intrapulmonic pressure.

► This pressure is 760 mmHg. This pressure may vary from -70 to +100 mmHg.

Intrapleural Pressure

The pressure outside the lungs (in the pleural cavities) is called intrapleural

pressure.

► This pressure is always negative and ranges from -2 to -10 mmHg, because

pleural cavity has always –ve pressure in contrast to atmospheric pressure.

This is very necessary to prevent the lungs from collapse.

FORCED INSPIRATION

Inspiratory effort with closed glottis helps in:

i) Return of blood to the thoracic vena cava.

ii) Return of lymph to the thoracic cavity

iii) Helps for vomition, eructation ( ), belching ( ), and

regurgitation in ruminants.

FORCED EXPIRATION

Expiratory effort with closed glottis helps in:

i) Micturation or urination ( )

ii) Defecation (to pass through fecal material)

iii) Expulsion of fetus to birth canal.

ARTIFICIAL RESPIRATION

Sometime there is need of artificial respiration in human being as well as in animals.

It may be due to apnea (cessation of respiration). This condition may be very serious

and lead to death.

Q. When an individual have a need of Artificial Breathing?

This need may be due to;

► Opening of thoracic cavity

► Electric shock, accident and surgery may be the causes for a need of art.

Breathing.

► Blow on belly

► Depression of nervous system (esp. of medulla where respiratory center is

located)

► During anaesthesia

All these causes may lead to apnea thus these condition may acquire artificial

breathing.

Methods of Artificial Breathing

Following are some methods of artificial breathing in animals and humans as well.

 Put the animal (e.g. dog) on lateral recumbency (have flexible thoracic cavity)

 Open the mouth of animal and keep the tongue on as side.

 Compress and relax the thoracic cavity according to the need.

 Repeat this process four or five times

Arm Chest Lift Method (for human being)

 Put the person on ventral recumbency and put his hand beneath his/her chest.

 Come on victim and lift him up with his arm because thoracic cavity has

negative (-ve) pressure thus air will move into thoracic cavity or lungs.

 Put the victim back, it leads to expiration. Thus, respiration of victim will

restart.

Mouth to Mouth Respiration Method (Kiss to Life Method)

 Put the person on dorsal recumbency.

 Raise the chin, close the nose and open the mouth

 Inflate your own lungs maximally and blow into the mouth of that person.

 Then, suck back (forced expiration) from the mouth of that person.

 Repeat this process again and again to restore normal respiration.

This method is very effective in man, dog, cat, and small animals but not applicable

in large animals.

EXCHANGE OF GASES

Gases obey all the laws while exchange in the body. This exchange is either at

alveolar level or tissue level. Blood unloaded the oxygen and it diffuses into the

tissues. This diffusion takes place in fraction of seconds and is usually due to

difference of partial pressure of gases at the exchange sites. From alveoli O2 diffuses

into the blood and CO2 from blood to alveoli.

The gases at the alveolar level have to cross the respiratory membrane.

Components of Alveolar Membrane

The respiratory membrane comprises of following six structures;

i) Endothelial lining

ii) Capillary basement membrane

iii) Interstitial fluid

iv) Alveolar fluid

v) Alveolar epithelium

vi) A layer of alveolar surfactants (surfactants break the surface tension)

Factors Responsible for Gaseous Exchange

Following are some factors which are responsible for gaseous exchange;

► Permeability of respiratory membrane

► Area of surface in contact

► Partial pressure of gases

► Volume of blood exposed

Loading and Unloading of Oxygen

There are some factors which favours the leading the loading and unloading of O2 to

the hemoglobin. The loading and unloading may be affected by:

1) Partial pressure of O2 and CO2

2) Blood pH

3) Amount of 2,3 diphospho-glycerate (2,3 DPG)

4) Temperature

Partial Pressure of O2 and CO2

If partial pressure of O2 is higher in alveoli than that of blood, it will favour

unloading of O2 to Hb. If partial pressure of CO2 is higher in blood than that of

alveoli then, it will favour diffusion of CO2 to alveoli.

2) Blood pH

If the pH of blood is low (acidosis) it will decrease the effect of unloading of

O2. It means low pH favours unloading of O2

3) Temperature

Higher temperature favours the unloading of O2 to Hb.

4) Acidity

Acidity will favour the unloading of O2 at tissue level. At alveolar level, it will

favour the loading of O2.

5) 2,3, DPG

More the concentration of 2,3 DPG will favours the unloading of O2 at tissue

level. At alveolar level, its more concentration will favour the loading

phenomenon.

6) Bohr’s Effect

It states as “Higher the concentration of CO2 decreases the pH or acidity of the

blood”. This effect favours the unloading of O2.

Partial pressure of O2:

At alveolar level: 104mmHg

In arterial blood: 95 mmHg

At cellular or tissue level: 40 mmHg

Partial pressure of CO2

At alveolar level: 40 mmHg

In venous blood: 40 mmHg

At cellular/tissue level: 45 mmHg

ROLE OF HEMOGLOBIN IN BLOOD

The amount of hemoglobin (Hb) in the blood is 16 g/100ml of blood.

One gram of hemoglobin can carry 1.34 ml of O2. Thus, 100ml will carry 19.6ml of O2.

► If Hb will not be responsible to carry O2 then 70 times more water will be

required to transport the same amount of O2.

Transport of Oxygen

O2 is transported 97% by hemoglobin (Hb) and only 3% by dissolving in H2O.

Transport of Carbon Dioxide

CO2 is transported in three forms in the body as follows;

i) In the form of CO3-2 ions

ii) In the form of H2CO3

iv) In the form of carbonamino hemoglobin.

► Hb has 210 times more affinity for Carbon Monoxide (CO) than oxygen (O2), thus

when Hb combines with CO it leads to suffocation.

PATHOPHYSIOLOGY OF RESPIRATORY SYSTEM

When a person or animal suffers from some disease of respiratory system, then that

is the pathophysiology of respiratory system.

Some serious problems of respiratory system are; TB, Asthma, Pneumonia

Following terms are frequently used in pathophysiology of respiratory system.

Auscultation

“Listening of sound is called auscultation”. The sound of the lungs can be listen and

auscultation is used to differentiate between the normal and abnormal sound of

lungs.

► Now a days, Stethoscope is commonly used for this purpose.

► If a person is suffering from cough, the sound of the lungs will be like air

flowing over dry leaves. If there is sputum in the respiratory tract, the sound

will be dull.

Percussion

“It is the listening of sound by striking any organ or tissue”. If there is no gas in the

lungs, sound will be dull but if there is gas, then the sound will be like drum beat.

Laryngioscopy

“Checking of respiratory tract with the help of instrument”. In this case, a tube is

inserted into the tract with a camera.

PROBLEMS RELATED TO RESPIRATORY SYSTEM

Following are some common problems related to respiratory system.

EPISTAXIS

“The nose bleeding is called epistaxis”. The innerside of the nasal cavity is highly

vascular. Due to high blood pressure, these delicate capillaries are ruptured and

bleeding occur. This problem is very common in race horses.

Causes

i) Blow on the nose

ii) High blood pressure

iii) This may occur in response to: Inflammation, irritation, deficiency of vitamin K.

Vitamin K is very necessary for prothrombin (clotting factor) production in the liver.

Treatment

► Cool down the nose with ice gauze

► Cool down the head

► Take vitamin K in diet

RHINITIS

“Inflammaion of nasal cavity (esp. nasal lining) is called rhinitis.”

There is inflammation and sloughing of nasal lining. This is commonly observed in

pigs because of bacterial infection.

Causes

It may be in response to bacterial or viral infection. This is known as infectious

rhinitis.

It may be due to any irritating substances or allergens. This is known as allergic

rhinitis.

PHARYNGITIS

“Inflammation of pharynx is called pharyngitis”. It is also termed as “sore throat”.

Symptoms

i) Swelling ii) Redness iii) Pain iv) Irritation v) Difficulty in swallowing and drinking.

TONSILITIS

”Inflammation of tonsils is called tonsilitis”.

Causes

Bacterial, viral or fungal infection or bacterial toxins

Symptoms

i) irritation ii) Redness iii) Pain iv) Swelling v) Difficulty in swallowing and drinking.

It this problem persists for a longer time, pus formation may be seen there.

LARYNGITIS

“Inflammation of Larynx is called Laryngitis”.

Causes and Symptoms

 It may be in response to bacterial, viral or fungal infection.

 If it persists then, there is difficulty in breathing or no breathing.

 Diphtheria may lead to these symptoms.

TRACHITIS

“Inflammation of trachea is known as trachitis”.

Symptoms

i) Redness ii) Irritation iii) Pain iv) Swelling v) Difficulty in breathing and drinking

BRONCHITIS

“Inflammation of bronchi or bronchiole is known as bronchitis.”

Symptoms

i) Irritation ii) Coughing and difficulty in breathing iv) Particularly expiration is

difficult iv) Abnormal sound in breathing

Causes

i) Allergic substances ii) Asthma

PNEUMONIA

“Inflammation of alveoli (air sac) of the lungs”

Causes and Symptoms

i) Bacterial, viral or fungal infections

“Aspiration Pneumonia”

If any fluid or food particle goes in to the respiratory tract or ultimately to the lungs,

it leads to aspiration pneumonia.

PLEURITIS

“Inflammation of pleura or lungs covering is called pleuritis”.

In response to this infection, there is an Increase in serous fluid is known as

Hydrothorax. Thus, it leads to infectious pleuritis.

EMPHYSEMA

Air in subcutaneous tissues or in between alveoli leads to emphysema.

When air enters in between alveoli, it ruptures the alveoli. Due to rupturing of alveoli

and escaping of air (observed in equines), a sound is produced which is known as

“Heaves”.

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