Histology of the Respiratory System

Question 1

What are the two main processes in respiration?

Answer 1

physical process- ventilation which involves inspiratory and expiratory movement of chest wall

chemical process- exchange of gases between air and blood takes place at the cellular level

Question 2

What are the two portions that the respiratory system can be divided into?

Answer 2

conducting portion- no gaseous exchange takes place here with the bloodstream
(includes nose, pharynx, larynx, trachea, bronchi and bronchioles)

Respiratory portion- gaseous exchange takes place here with the blood stream (Respiratory bronchioles, alveolar ducts, alveolar sacs. alveoli)

Question 3

Where does the exchange of gases occur?

Answer 3

at the alveolar capillary barrier

Question 4

What is the total thickness in order for gas to be exchanged?

Answer 4

0.2 micron

Question 5

What are the 4 layers of the tracheobronchial tree?

Answer 5

mucosa (epithelium and supporting lamina propria)
sub-mucosa (seromucous glands)
cartilage and/ or muscle layer
adventitia- connective tissue which covers the tree

Question 6

Describe the trachea shape and length and diameter ?

Answer 6

wide flexible tube

15-20cm long and 2-3 cm in diameter

Question 7

Describe where the trachea is?

Answer 7

situated between the larynx and a cartilage called carina

Question 8

How many C-shaped tracheal cartilages are there?

Answer 8

has 16-20 C-shaped cartilage on the anterolateral aspect

Question 9

What are the gaps between rings of cartilage?

Answer 9

at the back- the gaps between rings of cartillage filled up with the muscle called trachealis and fibroelastic tissue

Question 10

What is function of respiratory mucosa and submucosa?

Answer 10

respiratory mucosa and submucosa are adapted to warm and moisten the air
and to trap the foreign particles in the mucous.

Question 11

What is found in sub mucosa?

Answer 11

mixed sero-mucous glands:
the watery secretions from the serous glands humidify the inspired air.
The mucus, together with mucus from the goblet cells traps particles from the air which are transported upwards towards the pharynx by the cilia on the epithelium. This helps to keep the lungs free of particles and bacteria.

Question 12

What is the innermost layer of trachea and what does it consist of?

Answer 12

mucosa

epithelium: ciliated pseudostratified columnar epithelium with goblet cells

lamina propria: underneath the epithelium contains elastin blood vessels

Question 13

What is adventitia?

Answer 13

connects and supports trachea to surrounding tissue e.g. thyroid and oesophagus
contains nerves, vessels and adipose tissue

Question 14

What are basal cells?

Answer 14

stem cells which can regenerate the columnar cells if these are damaged or renewal is needed

Question 15

Where are the basal and columnar cells attached?

Answer 15

at one single basement membrane

Question 16

What does the lamina propria contain?

Answer 16

areolar connective tissue where you have elastin and also blood vessels.
Possibly also some macrophages or immune cells.

Question 17

Where does respiratory epithelium begin and end?

Answer 17

starts from nose and goes up to the level of the terminal bronchiole where it starts to become non-ciliated columnar single layer.

Question 18

What’s the difference between extrapulmonary bronchi and intrapulmonary bronchi?

Answer 18

Extrapulmonary- primary bronchi which does not enter the lung tissue.
And closely resemble the trachea histologically.

Intrapulmonary- less cartilage and does not completely encircle the lumen.
Includes secondary, tertiary and their consecutive divisions.
Gaps in the cartillage
Contains layers of smooth muscle between mucosa and submucosa.

Question 19

What is the difference between bronchi and bronchioles?

Answer 19

bronchioles- 1mm diameter or less
it is covered with ciliated columnar epithelium
(however non-ciliated in smaller bronchioles, e.g. terminal bronchioles)
smooth muscle thicker than bronchi
non ciliated clara cells are present :secretes surfactant
no goblet cells
non-ciliated cells
no submucosal glands
no cartilage
no glands in lamina propria

Question 20

What do respiratory tubes contain?

Answer 20

respiratory bronchioles- ciliated cuboidal epithelium

alveolar ducts - surrounded by smooth muscle, elastin and collagen

alveolar sacs- surrounded by blood vessels/ pulmonary capillaries

alveoli- surrounded by blood vessels/ pulmonary capillaries (0.2 micro m blood-alveoli barrier). Gaseous exchange between blood and air occurs.

Question 21

What are the main types of cells found in epithelium of the alveoli?

Answer 21

type 1 pneumocytes -large flattened cells- (95% of the total alveolar area) which present a very thin diffusion barrier for gases

type 2 pneumocytes- (making up 5 % of the total alveolar area, but 60% of total cells). These cells secrete ‘surfactant’ which decreases alveolar surface tension and stops alveoli collapsing when we breathe out

macrophages(dust cell)- are also present in the walls. These , when found in the lumen of the alveolus , are also known as “dust cells” due to their brownish appearance. Keeps respiratory system clean as we inhale dust and any foreign particles

Question 22

Where does gaseous exchange take place?

Answer 22

through the endothelial cell of the capillary, basement membrane and type I pneumocyte

the wall of the capillary endothelial cell is fused to that of the alveolar cell, and there is only a very thin basement membrane between these two cells.

Question 23

When do goblet cells dissapear?

Answer 23

At bronchus level, no goblet cells in bronchioles

Question 24

When do clara cells appear?

Answer 24

from lobar bronchus to terminal bronchioles

Question 25

Where are ciliated cells reduced?

Answer 25

where respiratory bronchiole starts
as the mucosa has simple cuboidal epithelium.
Onwards becomes squamous.

Question 26

Where does seromucous gland in submucosa disappear?

Answer 26

at bronchus level

Question 27

Where does hyaline cartilage disapear?

Answer 27

at bronchus level

Question 28

Where does smooth muscle dissappear?

Answer 28

stays up to resp bronchiole then the thickness gets reduced for gas exchange

Question 29

Where do elastic fibres disapear?

Answer 29

stay throughout the tracheobronchial tree as important for recoil of lung

Question 30

What is function of club cell?

Answer 30

same as clara cell
protects airways
regenerates bronchiolar epithelium
produces surfactant

Question 31

How is conducting portion characterized?

Answer 31

pseudostratified columnar epithelium with cilia
goblet cells
gland tissue
hyaline cartilage

Question 32

How is respiratory portion characterized?

Answer 32

respiratory portion begins with the first branches of the respiratory bronchioles

epithelium gradual transition from cuboidal to simple squamous

cartilage ends

abundant smooth muscle, elastic fibres, reticular fibres

Question 33

What are the three parts of the nasal cavity?

Answer 33

vestibule, respiratory part and olfactory

Question 34

What is the vestibule outer layer and inner layer lined by?

Answer 34

outer:
stratified squamous - keratinised

inner:
stratified squamous- non keratinised

Question 35

What is the respiratory part covered by?

Answer 35

respiratory epithelium

Question 36

What is the olfactory part covered by?

Answer 36

olfactory epithelium .

Question 37

What are the parts of the pharynx?

Answer 37

nasal part - respiratory epithelium
oral part - stratified squamous which is non keratinised

Question 38

What is the surface of the epiglottis?

Answer 38

top surface covered with stratified squamous up to the vocal fold of the larynx.
Below vocal fold of the larynx we have respiratory epithelia