This unit comprises of following chapters

Respiration in Mammals
Mechanism of respiration
Transport of gases
Regulation of respiration
Respiratory disorders


Some important points

Anaerobic respiration  
also called anaerobiosis, biochemical process in living things where
substances other than oxygen are utilized to release energy.
singlequoteAnaerobicsinglequote means singlequotewithout oxygen’. So
this process does not require oxygen.

Fermentation this is
the process by which the living cell is able to obtain energy through
the breakdown of glucose and other simple sugar molecules without
requiring oxygen. Though the process is very much similar to anaerobic
respiration this term is mainly used for non-living beings.

Aerobic respiration
it is the process for which presence of oxygen is needed in this the
energy is released from glucose or from any other organic substrate

External respiration:
this simply means breathing that is the exchange of oxygen and carbon
dioxide between human being and its environment. Most animals use
specialized organs such as lungs, trachea, or gills, for the process

Transport of gases to the tissues

Internal respiration:
This means the exchange of oxygen and carbon dioxide between blood and
cells in different tissues of an animalsinglequotes body for this
process to occur oxygen is needed.

GASEOUS EXCHANGE BETWEEN BLOOD AND TISSUES.


This
process takes place at cellular level. It primarily involves oxidation
of nutrients in the cells and liberation of energy, which is utilized by
animals for their various metabolic needs.

In earthworm there
is no special respiratory organ respiration takes place through the
skin, which is highly vascular .The respiratory organ of Crustaceans are
gills and the respiratory pigment is Haemocynin

In insects
respiratory organs are trachea .they have small tubular structures
called Stigmata or Spiracles which communicate between the outside
environments and extend to the tissue inside.

In animals various pigments are present which transport the oxygen .they are as below,

Hemoglobin is the protein molecule that contains iron is found in red blood cells .
The
main function is to carry oxygen from the lungs to the bodysinglequotes
tissues and returns carbon dioxide from the tissues to the lungs.
The iron containing oxygen –transport mettalo-protein in the red cells of vertebrates and dissolved in plasma in in-vertebrates

Haemocyanin
this is also a pigment which carries oxygen in the blood of certain
molluscus and arthropods. it contains cupper and so it is blue in color.
 
Erythrocruorin
A respiratory protein from the blood of some invertebrates, such as
marine worms and certain molluscus, it resembles hemoglobin in such that
it transports oxygen.


Mammalian respiratory system consists of lungs and air passages in its course air pass through various organs and all of them compromise respiratory system.



www.cartage.org.lb/.../HumanRespiratory.htm
    

Nasal cavity
it opens to the exterior through nostrils. The entrance is marked with
external nares, small hairs are present in it through which dust and
other material is filtered the nasal cavities are separated into right
and left cavity by the nasal septum and these cavities are covered by
ciliated columnar epithelium and are highly vascular.

Pharynx
from nasal cavity air enters in the pharynx. It is common passage for
food and air both. The opening into the wind pipe is narrow slit
(glottis).which is protected by flap of tissue (Epiglottis).
This can be divided into three parts

1) Nasopharynx
2)  Oropharynx
3)  Laryngeal part.

Larynx this structure has dual purposes one it is a part of respiration and secondly it also produces sound
The larynx is composed of cartilages which are attached to each other with membranes and ligaments.

The cartilages are

Thyroid cartilage
is the most prominent C- shaped; these wings are united in midline in
front to form an angular projection also called Adam’s apple.

Cricoid cartilage lies below the thyroid cartilage, forms the lowest part of larynx and thus unites to the trachea signet ring shaped.

Arytenoid cartilages are two pyramid shaped cartilage which forms posterior wall of larynx

Epiglottis this is a leaf shaped cartilage which protects into the pharynx.
 
Inside
the larynx there is one pair of, false vocal cords which have to do
little for sound production and a pair of true vocal cords. The pitch of
sound depends upon the tension of vocal cords higher the tension more
the pitch.
 
Trachea (windpipe)

 It is a tube of
about 4.5 inches long .with C shaped rings of hyaline cartilage in its
walls .the function of these rings is to make the trachea
non-collapsible; it is lined with cilia inside, which push the mucus
out. Its upper half is situated in the mid-line of the neck and its
lower half is situated in the superior mediastinum of the thorax
.Between trachea and the alveolar sac, the air passage divides 23 times
.The trachea is designated as generation zero.

On from the 17th generation, few alveoli can be found on the bronchioles permitting gaseous exchange called the Respiratory bronchioles.

The
16 th generation bronchioles where no exchange of gases is possible are
thus called Terminal bronchioles .The whole tracheo- bronchiole tree is
divided into two major zones

Conducting –zone   this
includes the portion of air passage where no gaseous exchange is
possible, called Dead space. This extends from nose and mouth upto
terminal bronchioles .the total capacity of this zone is 150 ml

Respiratory zone
this includes the portion of air passage where gaseous exchange takes
place .This is made up of respiratory bronchioles, alveolar ducts and
the alveloli.its volume is about 4 liters.

www.naturalhealthschool.com/bronchi_trachea.html






Alveolar lining epithelium this membrane has specialized cells which secrete surfactant Type 1) they are primary lining cells.
Type II) granular pneumocytes secrete Surfactant.

Pleura   This is a membrane which encloses lungs. It has two layers, Parietal and Visceral
Parietal pleura it is adherent to the parities’ i.e. inner side of chest wall and thoracic side of diaphragm.
Visceral pleura it is adherent to the underlying viscous i.e. the lungs.

In between the two layers there is potential space called pleural cavity filled with (approx 2 ml of fluid called pleural fluid.
In disease state sometimes fluid accumulates in between two layers of pleural membrane called pleural effusion.

Bronchi its walls are also supported by cartilaginous rings. Each bronchus divides and redivedes into smaller bronchioles.

Lungs these are the main largest organ of thoracic cavity. . Surrounded by a membrane called pleural membrane,

They can be divided into two parts the right and the left one.

Right lung is divided into three lobes and left lung into two lobes

On
examination lungs feel spongy to touch there are ample arteries and
vein supplying the lungs  Pulmonary artery has de-oxygenated blood where
as pulmonary veins has oxygenated blood.

Non- respiratory functions of respiratory system

Main function of respiratory system is gaseous exchange. But non respiratory functions include

A)    Defensive function Lung defense mechanisms  prevents foreign bodies from reaching the alveoli
B)    Bronchial secretion contains immunoglobulin that helps to reresist infection and maintain the integrity of the mucosa.
C) Metabolic and endocrine functions of lungs they secrete surfactant.

Mechanism of breathing

Thje whole process of respiration can be divided into two phases’ inspiration and expiration
And main organs involved for this purpose are intercostals muscles and diaphragm.

Inspiration
with this process the thoracic cavity is enlarged to fill up the air in
the air- spaces. This is an active process, occurs due to contraction
of external intercoastal and phrenic muscles

Expiration
this process involves making the lungs empty of air this is the passive
process occurs due to relaxation of external intercoastal and phrenic
muscles.

In forceful expiration some abdominal muscles also act.

Thoracic
breathing when we take deep breath then chest distention is brought
about by internal intercoastal muscle and the abdominal muscles this
phenomenon is called thoracic breathing.

Pulmonary air volumes:

Tidal volume (TV) volume of air inspired or expired in each breath normally, the amount is about 500ml. in an average adult man.

Inspiratory reserve volume (IRV)is
the  maximum volume of air which a person can inhale over and above
tidal volume by deepest possible voluntary inspiration .It is about
3000ml.

Expiratory reserve volume (ERV) The volume of the air which can be expired over and above the tidal volume with maximum effort .It is about 1100ml.

Residual volume (RV) The volume of the air left in the lungs after maximum forceful expiration. it is about 1200ml .

Spiro meter is used to measure lung capacity. (Except FRC and RV)

Pulmonary capacities this is the combination of two or more pulmonary volumes

Inspiratory capacity (IC) Tidal volume +Inspiratory reserve volume .about 3500ml

Functional residual capacity (FRC) Expiratory reserve volume +Residual volume

Total lung capacity (TLC) Tidal volume +inspiratory reserve volume +residual volume +expiratory reserve volume .it is abut 5800ml.

All the pulmonary volumes and capacities are 20-25% more in males than females.

Anatomical dead space
The volume of the conducting airways of the nose, mouth, and trachea
down to the level of the alveoli, representing that portion of inspired
gas unavailable for exchange of gases with pulmonary capillary blood.

Physiological dead space is the sum of anatomical and alveolar dead space.

Factors affecting VC
A)    Physiological. More in males because of large chest size.
                                VC decreases with age due to loss of elasticity of lungs.
                                VC is more in standing posture than lying or sitting.

B)    Pathological conditions like poliomyelitis, pulmonary fibrosis. decreases  VC


Surfactant
:it is a fluid made up of protein and lipid ,and produced by alveolar
lining epithelial type II cells of the lungs and  the function is to
reduce surface tension of the alveoli which mainly contributes in
effective gaseous exchange .

Ventilation perfusion ratio V/P, It is the ratio of alveolar ventilation to pulmonary blood flow.
For example:      As alveolar ventilation is 4 L/min and pulmonary blood flow is 5L/min therefore VP ratio is 0.8

Transport of gases Distribution of oxygen in the body

                                                        Po2 (mm hg)                         02 content
Inspired air                                        158                                          21ml%
Expired air                                         116                                         16ml%
Alveolar air                                        100                                         13ml%
Arterial blood                                    98-100                                    19ml%
Venous blood                                       40                                         14ml%

Oxygen transportation it is carried in two forms,

A) In dissolved form
B) In combination with hemoglobin

In dissolved form, amount of oxygen in 0.3ml per 100ml of blood per 100mm Hg pO2.

     
in combination with  hemoglobin Each haemoglobin molecule has 4 heme
groups which have iron in ferrous form .Fe+2combines with 1 mole of O2
.Therefore ,4 moles (8 atoms) of O2 combine with one mole of hemoglobin.

 The oxygen carrying power of hemoglobin is given Oxygen Haemoglobin Dissociation Curve, which is Sigmoid shaped


 


Carriage of oxygen in the body

In the tissues

At rest tissues remove 5 ml of O₂
for each 100 ml of blood passing through them .As cardiac output is 5
ml /min, therefore approx =250 ml of O2 /min is transported from the
blood to the body tissue

In the lungs venous blood Po2 is
40 mm Hg and alveolar air Po2 is 100 mm Hg  thus because of pressure
gradient O2 rapidly diffuses from alveoli to the venous blood.


Carbon dioxide transport

There are 3 ways in which carbon dioxide is transported in the blood:

1. DISSOLVED CO₂       

•    Carbon dioxide is much more soluble in blood than oxygen
•    About 5 % of carbon dioxide is transported unchanged, simply dissolved in the plasma

2. BOUND TO HAEMOGLOBIN AND PLASMA PROTEINS

•    Carbon dioxide    +    haemoglobin to form carbamino haemoglobin.and about 10% is transported in this way.

3. BICARBONATE IONS (HCO₃- )

•    The majority of carbon dioxide is transported in this way
•   
Carbon dioxide enters red blood cells in the tissue capillaries where
it combines with water to form carbonic acid (H2CO3). This reaction is
catalyzed by the enzyme carbonic anhydrase (C.A.), which is found in the
red blood cells. Carbonic acid then dissociates to form bicarbonate
ions (HCO3-) and hydrogen ions (H+).

             
 

Bohr`s Effect 
this explains the affinity of oxygen with hemoglobin it depends upon
the pH  A rise in Po2 or fall in pH decreases oxygen affinity of
hemoglobin,. Conversely the fall in pco2 and rise in ph increases oxygen
affinity of hemoglobin. this is called Bohr effect.

Haldane effect: It is related to CO₂
transport in the blood .It is based on the fact that Oxyhemoglobin
behaves as strong acid and releases an excess of H+ ions which bind with
bicarbonate HCO3-ions to form H2CO3 which dissociates into H₂O and CO₂ .secondly, due to increased acidity, CO₂
loses the power to combine with hemoglobin and form Carbino- hemoglobin
.effect of oxyhemoglobin formation or dissociation on CO₂ transport is called Haldane effect.

Regulation of Respiration


Normal rate of respiration is 12-16/min in adults, with a tidal volume of 500 ml
The rhythmic discharge from the brain that produces spontaneous respiration is regulated by two mechanisms

1) Nervous regulation
2) Chemical regulation
                                            
Nervous regulation      

Autonomic control of respiration.  there are two centers’ of respiration one in   Medulla and other in Pons.

Medullary centre located in medulla, Pontile center is located in lower pons this area previously known as Apneustic centre. .
An area in upper pons, called Pneumotaxic center.

                                          
CHEMICAL REGULATION OF VENTILATION

There are two types of chemo receptors

A) Peripheral Chemoreceptors   Carotid and Aortic bodies
B) Medullary chemoreceptors

Peripheral
Chemoreceptors: Carotid and Aortic bodies there is a carotid body near
the common carotid bifurcation on each side and there are usually two or
more aortic bodies near the arch of aorta

They get stimulated by

1) Hypoxia: when arterial po2 decreases
2) Vascular stasis
3) Asphyxia
4) Increase in plasma K+ levels, such as exercise.
Chemical factors affecting respiration 

A. Oxygen

1. Response as a function of Pa-O₂


 
Image taken from  www.elrinajoubert-huebner.online.de

2. Stimulus: P _a-O2
Note: not Ca-O2 because of very high chemoreceptor blood flow means that

P_a-O2 = P_c-O2

4. O2 response enhanced by P a-CO2 increase (right shift of response; hypercapnia increases sensitivity to hypoxemia
Note problem of administering high oxygen to a chronic hypercapnic patient

Respiratory disorders

Dyspnoea Means when the process of respiration becomes a conscious effort it is called dyspnoea means difficulty in breathing.

Factors causing Dyspnoea

Physiological   Severe exercise
Pathological     Bronchial asthma, emphysema.,
Even some cardiac diseases also cause difficulty in respiration.

Apnea this describes inhibition of respiration

Asphyxia it is produced by occlusion of airways, this results in hypoxia and hypercapnia.

Emphysema this is the condition when there is breaking of alveolar wall and often happens in smokers.

Tuberculosis A bacterial disease caused by Mycobacterium Tuberculosis. This causes loss of weight, loss of appetite and severe cough.

Pneumonia
infection of lungs which leads to accumulation of mucus and lymph in
alveoli, impairing gaseous exchange. Mostly happens in small children.

Asthma
when there is spasm in bronchial muscles and narrowing of bronchi. The
condition is called asthma it can be due to intrinsic and extrinsic
causes.

Cyanosis   Blueness of skin due to excessive amount of deoxygenated Hb.

Hiccups Spasmodic contraction of diaphragm due to unknown causes

Pleurisy Inflamation of pleural membrane. Which also causes dyspnoea?

Bronchitis Is the inflammation of
bronchi that is characterized by hypertrophy and hyperplasia of
sero-mucus glands and goblet cells lining the alveoli. The symptom is
recurring cough and thick greenish yellow sputum.

Occupational lung disease
is lung diseases which arise due to ones occupation because of presence
of harmful substances, such as gas, fumes, and dust present in the
environment where one works. Examples are silicosis and asbestosis.

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