Organisation of the Respiratory System

Question 1

Define Respiration.

Answer 1

The act of inhalation and exhalation in which oxygen from atmosphere is delivered to the tissue and carbon dioxide from the tissues is removed into the atmosphere.

Question 2

Stages of Respiration.

Answer 2

Ventilation Stage: Exchange of gases b/w atmosphere and pulmonary capillary blood due to pulmonary ventilation.

Transport Stage: gases are transported between lungs and tissues

Exchange Stage: gases are exchanged b/w the systemic circulation and tissues

Tissue Stage: Oxygen delivered to the tissues is utilised by the mitochondrial enzymes of the cells for oxidation during which carbon dioxide is produced.

Question 3

Components of Respiratory system.

Answer 3

URT: nose to vocal cords that include sinuses, glottis, pharynx and larynx

LRT: Trachea, airways and alveoli

respiratory apparatus also consists of thoracic cavity and associated skeletal muscle and muscles of respiration.

Question 4

Main function of URT

Answer 4

to process the inspired air so that it gets humidified and it attains body temperature by the time it reaches trachea.

Question 5

Components of URT

Answer 5

Nose, Paranasal Sinuses, Pharynx, Larynx

Question 6

Nose

Answer 6

-contains olfactory epithelium that receives smell sensation

• filters particles greater than 10 um
• secretion contains immunoglobulins and interferons that kill the organisms
• though the volume of nose is only 20 ml, the cross sectional area is greatly increased by the nasal turbinates
• offers about 50% of resistance to airflow in the respiratory system. (increases during viral infections like common cold)

Question 7

what are the Paranasal Sinuses?

Answer 7

mainly maxillary sinus, sphenoid sinus, ethmoid sinus, and frontal sinus.

Question 8

sinusitis is caused because—

Answer 8

Sinuses open into the nasal turbinates making them vulnerable to nasal infections.

Question 9

Functions of Paranasal Sinuses.

Answer 9

• Offer resonance to voice
• Lighten the skull, for which upright posture becomes easier
• provide protection to the brain during facial trauma.

Question 10

Pharynx is divided into—

Answer 10

Nasopharynx - behind the nose. extends from posterior nares to the level of soft palate. eustachian tubes and posterior nares open here

Oropharynx - behind the mouth. from soft palate to level of hyoid bone.

Laryngopharynx - from level of hyoid bone and opens into oesophagus.

infection of nasopharynx - common - URTI

Question 11

what does larynx consists of?

Answer 11

epiglottis, arytenoids, and vocal cords

Question 12

Elaborate Larynx and Glottis region

Answer 12

• epiglottis and arytenoids cover the vocal cords during deglutition - prevents aspiration of food particles into the respiratory tract
• during infections - arytenoids enlarge im children - increases resistance to air flow
• muscles of Larynx are innervated by vagal fibers
• during swallowing reflex contraction of adductor muscles closes the glottis
• unconscious and anesthetized patients - incomplete closure of glottis - food particles enter into respiratory tract - causes aspiration pneumonia
• paralysis of adductors also causes aspiration pneumonia. also causes inspiratory stridor

Question 13

lower respiratory tract consists of

Answer 13

-airway tree (trachea which bifurcates into bronchi that enter the lungs) and lungs

Question 14

explain the airway tree

Answer 14

a series of branching tubes (decreasing in diameter) constitute the airway tree.

• trachea, main airway branches into two bronchi. each bronchus enters a lung and branches many times - bronchioles - tracheobronchial tree
• trachea bronchi contain cartilages. relatively less smooth muscle content
• trachea and bronchi lined by - ciliated epithelium.
  cilia present till respiratory bronchioles. glands absent in bronchioles and terminal bronchioles.
• bronchioles and terminal bronchioles - adequate smooth muscle content,, terminal bronchioles having maximum.
• bronchioles downwards cartilages are absent

Question 15

bronchial tone.

Answer 15

tone of smooth muscles of bronchi is called bronchial tone.

contributes to the patency of bronchi and aids in Respiration.

Question 16

bronchodilation.

Answer 16

sympathetic stimulation.

Question 17

bronchoconstriction

Answer 17

• vagal stimulation.
• reflex bronchoconstriction - irritation of airways by allergens and chemicals - usually mediated by vagal cholinergic fibers
• sudden entry of cool air
• exercise (hyperventilation)

Question 18

circadian rhythm.

Answer 18

circadian rhythm for bronchial tone -

• maximum dilation - 6pm
• maximum constriction - 6am

Question 19

generation numbers

Answer 19

the progressively bifurcating airways are designated by their generation numbers.

trachea - zero generation.
left and right bronchi - first generation.

Question 20

changes occurring as generation numbers increases.

Answer 20

• airways - smaller, narrower, and shorter
• amount of cilia - dec
• no. of mucus secreting cells - dec
• quantity of submucosal glands - less
• amount of cartilage - dec
• amount of smooth muscle - inc

Question 21

function of mucus, cilia and cartilage.

Answer 21

mucus - traps small foreign particles including bacteria

cilia - beat toward pharynx. thus prevent entry of small organisms. also sweep the carpet of mucus, that is, when mucus secretion is excessive, cilia remove mucus into the pharynx from where it is either swallowed or spit outside.

cartilage - prevents the collapse of airway. present up to 10th generation (bronchi)

Question 22

airways are branched into-

Answer 22

progressively branch 23 times (i.e. 23 generations)

• conducting airways - move air by convection into the gas exchange areas of lungs (conducting zone)
• Respiratory airways - participate in gas exchange (respiratory zone)

Question 23

Conducting Zone.

Answer 23

trachea and first 16 generations

Arrangement and Functions
trachea branch out into two main bronchi which further branch out into lobar bronchi - segmental bronchi - smaller branches - terminal bronchioles- respiratory bronchioles.
The trachea, bronchi, and bronchioles have following functions:
1. warm and humidify inspired air.
2. distribute air evenly to the deeper parts of the
lungs.
3. serve as part of nonspecific defense system of the body by removing dust, bacteria, and harmful gases from the respiratory tract.

Structural Specialization
1. The considerable amount of cartilage is present in first four generations of the conducting zone - prevents collapse of these airways as they are subjected to changes in thoracic pressures. Some amount of cartilage is present up to 10th generation

2. The cartilage is absent totally in the bronchioles. Though bronchioles lack cartilage, elasticity of the lung tissue maintains their patency as they are suspended by elastic tissue of the
   lung parenchyma. However, bronchioles are susceptible to collapse especially during expiration.
3. As there is no alveoli up to 16th generation, gas exchange does not occur in the conducting zone. Therefore, the
   volume of respiratory tract starting from nose to the generation-16 airways is called anatomic dead space

Blood Supply
bronchial circulation.
fed by bronchial artery that originates from the descending aorta and
drained by pulmonary veins.

Nerve Supply
bronchi and bronchioles - innervated by ANS.

1. Vagal stimulation causes bronchoconstriction
2. Sympathetic stimulation causes bronchodilation, Activation of β2
   receptors increases bronchial secretion and α2 receptors inhibit secretion.
3. bronchodilation - non cholinergic- nonadrenergic innervation.

Question 24

Conducting Zone.

Answer 24

The trachea and first 16 generations of airway form the
conducting zone (Fig. 103.3).
Arrangement and Functions
The trachea, bronchi, and bronchioles have following
functions:
1. They warm and humidify inspired air.
2. They distribute air evenly to the deeper parts of the
lungs.
3. They also serve as part of nonspecific defense system
of the body by removing dust, bacteria, and harmful
gases from the respiratory tract.
Structural Specialization
1. The considerable amount of cartilage is present in
first four generations of the conducting zone. This
prevents collapse of these airways as they are sub-
jected to changes in thoracic pressures. Some amount
of cartilage is present up to 10th generation, up to
which the airways are referred to as bronchi (Clinical
Box 103.3).
2. The cartilage is absent totally in the bronchioles.
The smallest airways in the conducting zone are the

Question 25

Respiratory Zone.

Answer 25

• last 7 gen
• site for gaseous exchange

arrangement and functions

• respiratory bronchioles (terminal bronchioles attached with alveoli) alveolar ducts and alveoli (start budding off from 17th gen) - aka Respiratory unit or lobule
• bronchioles from 17 to 19 - respiratory bronchioles
• no of alveoli increases with each descending gen
• gen 20-22 - alveolar ducts that terminate into alveolar sac (23)

blood supply

• pulmonary circulation.
• lungs have extensive capillary network which occupies 80% of the alveolar surface area.
• capillaries surrounding each alveolus bring blood into close proximity with the air inside the alveolus. thus helping in easy diffusion

Question 26

Describe alveoli.

Answer 26

Alveolus

• functional unit of gaseous exchange
• 300 million in both lungs
• diameter - 0.2 mm
• thin walls
• total surface area - 50m2 and 100 m2. among the largest biological membranes in the body
• alveoli - capillaries - alveolar-capillary membrane - gas exchange takes place
• because of the extensiveness of the capillary plexus the flow of blood in alveolar wall has been described as a sheet of flowing blood.
• alveolar epithelium - two types of epithelial cells — Type I and Type II
• Type I epithelial cells - more - cover 95% of epithelial surface area of alveoli
• Type II cells - secrete surfactant. and play imp role in alveolar repair
• also contain pulmonary alveolar macrophages (PAMs) that cause phagocytosis
• after adolescence, alveoli only increase in size and not in nos so destruction of alveoli results in a permanent damage to the lungs as they have limited ability to repair themselves in adults.

Question 27

pleura of lungs

Answer 27

• lungs are covered by pleura
• two layers : parietal and visceral
• parietal pleura : outer layer of pleural sac that contains blood vessels
• visceral pleura: lies directly on the lung
• parietal pleura produces - pleural fluid (ultrafiltrate of plasma)
• space between these pleura - pleural cavity - filled with 10 - 20 ml of pleural fluid
• viscous pleural fluid forms a lining of about 10 um thick b/w the two layers which functions as a lubricant so that lungs can slide against the chest wall.
• pleural fluid facilitates the change in size and shape of lungs during Respiration
• also protects lungs from external damage.

Question 28

pleural effusion

Answer 28

accumulation of pleural fluid in excess in the pleural cavity is called pleural effusion.
significant pleural effusion limits lung expansion and dec gas exchange.

• entry of air into the pleural cavity that occurs either due to trauma or rupture of alveoli results in pneumothorax
• and entry of blood - hemothorax

Question 29

lobes of lungs

Answer 29

three lobes in right lung (upper, middle and lower) and two lobes in left lung (upper and lower)

right mein tv left mein bv

-right lung constitutes 55% of total lung mass and function.

Question 30

functions of respiratory system

Answer 30

Respiratory Functions:
1. Gas exchange - lungs are the central structures in Respiration. inhalation of oxygen and removal of carbon dioxide from the body takes place through lungs.

Non Respiratory Functions:
1. Left Ventricular reservoir - the entire cardiac output from right ventricle is pumped into pulmonary circulation. due to their high compliance, pulmonary vessels normally accomodate about 0.5 liter of blood at any given time. this serves as reservoir for left ventricular filling.

2. Filtering small emboli from blood - venous blood - microemboli of blood clots, fats or air bubbles. if they escape - tissue damage. pulmonary vasculature traps and removes these emboli before they get the chance to enter into systemic circulation.
3. Processing of inhaled air - filtration of inhaled air. prevents entry of toxic substances and infective organisms into the body.
   - hairs
   - turbulent precipitation - conchae, the septum, and the pharyngeal wall.
   › so effective no particle larger than 6 um enters the lungs.
   › particles between 1 to 5 um settle in smaller bronchioles due to gravitational precipitation. eg. terminal bronchiolar disease in coal miners.
   › smaller than 1 - diffuse and adhere to the alveolar fluid
   › smaller than 0.5 um - remain suspended and exhaled.
   warming and moisturizing of inhaled air by the conducting pathway - help prevent alveolar damage.
4. immune functions :
   i) organisms that enter lungs are phagocytosed by PAMs (dust cells) or interstitial macrophages. thus lungs play an imp role in nonspecific defense.
   - particles less than 2 um - phagocytosed by alveolar macrophages.
   - particles with 2-10um - removed by conducting airways.
   - remaining particles are carried away by the lung lymphatics

ii) immunoglobulin A - present in bronchial secretion- resistance to infections. also maintains integrity of mucosal lining.
iii) epithelium of lungs contain protease activated receptors - on activation release PGE2 which in turn protects pulmonary epithelial cells.

5. metabolic functions-
   i) synthesis- synthesize surfactant
   ii) lysis - lyse clot (local fibrinolytic system)
   iii) synthesis and release- histamine, kallikrein, prostaglandins, angiotensin I is activated to angiotensin II.
   iv) removal from blood - lungs partially remove prostaglandins, bradykinin, adenosine, serotonin, acetylcholine, and norepinephrine.
6. Phonation - achieved by Larynx. acts as a vibrator and vibrating elements vocal folds.
   during phonation, vocal cords move together so that passage of air between them will cause vibration. movement of air in the respiratory passage helps in the improvement of voice. therefore voice becomes thick with nasal intonation in nasopharyngitis and nasal obstruction.
7. Acid Base Balance - by controlling co2 output from the body, lungs control plasma bicarbonate concentration. therefore, lungs play an imp role in acid-base balance.
8. biochemical functions - many chemical substances are removed in the lungs. lungs decide which chemical substance should reach systemic circulation.
   eg- PGE1, 2, 2a, leukotrienes, serotonin and bradykinin.
9. olfactory function - breathing is essential for delivering odorants from the environment to the olfactory epithelium.
10. route for administration of anesthesia - general anesthesia is usually administered via Respiratory route.

Question 31

enumerate muscles of normal tidal Respiration.

Answer 31

• diaphragm

* external inter coastal muscles

Question 32

Name accessory muscles of inspiration.

Answer 32

• Scalene.
• Sternomastoid.
• Serratus anterior and alae nasi.

Question 33

Name the muscles.of expiration

Answer 33

Abdominal muscles.
• Abdominal recti muscles.
• Transverse abdominis muscles.
• Internal oblique muscles.
• External oblique muscles.

Internal intercostal muscles