Respiratory System Histology

Question 1

Functions of the respiratory system?

Answer 1

Supplies O2 to blood, for delivery to cells in body

Removes C02 that has been accumulated in the blood from body tissues

Question 2

How does air reach the lungs?

Answer 2

Air enters via nose/mouth

Air travels via pharynx and larynx into the trachea which branches into the right and left main bronchus

Each bronchus divides into smaller bronchi, which divide into smaller bronchioles (terminate in the alveolar sacs - where gas exchange occurs)

Question 3

Function of the nasal cavity in air passage?

Answer 3

Provides extensive area for:

Warming

Moistening

Filtering …of inspired air

Also, in the roof, there is an area of specialised OLFACTORY EPITHELIUM

Question 4

Describe the lining of the nasal cavity?

Answer 4

Initial part of the nasal cavity (vestibule) - lined by KERATINISED STRATIFIED SQUAMOUS EPITHELIUM

Deeper in, keratin is lost and, deeper still, it changes again to epithelium that lines nearly all of the rest of the conducting part of the respiratory system: PSEUDOSTRATIFIED CILIATED COLUMNAR EPITHELIUM with GOBLET CELLS (AKA respiratory epithelium)

Question 5

Components of the respiratory epithelium?

Answer 5

Pseudostratified ciliated columnar epithelium

Goblet cell - surface view will show granules of mucin being secreted

Basal cell (stem cells - used to replace epithelium)

Question 6

Describe the anatomy of the nasal cavity

Answer 6

Vestibule - first part of the nasal cavity

3 conchae - inferior, middle and superior (set up turbulent air flow)

Question 7

Histology of the nasal cavity?

Answer 7

Underneath the respiratory epithelium is LAMINA PROPRIA (this connective tissue contains SEROMUCOUS GLANDS) and a RICH VENOUS PLEXUS (can engorge with blood and “block” nose)

Ducts leave the seromucous glands to the epithelium (serous cells produce a watery fluid and mucous cells produce mucous)

Question 8

Lining of the oropharynx?

Answer 8

Transmits both air and swallowed food, so must resist abrasion and is lined with NON-KERATINISED STRATIFIED SQUAMOUS EPITHELIUM

Same lining on anterior (lingual) surface and upper part of the posterior surface of the EPIGLOTTIS

Question 9

Lining of the larynx and vocal folds?

Answer 9

Walls are made up of CARTILAGE and MUSCLES with RESPIRATORY EPITHELIUM lining its surfaces

Exception is vocal folds and adjacent structures - lined with STRATIFIED SQUAMOUS EPITHELIUM (in other words, a transition has occurred)

Question 10

Structure of the trachea?

Answer 10

Contains 15-20 “C” shaped cartilages

Posterior open side of the C-shaped cartilage (towards oesophagus) is spanned by FIBROELASTIC TISSUE and SMOOTH MUSCLE (trachealis muscle)

Question 11

Lining of the trachea?

Answer 11

RESPIRATORY EPITHELIUM backed by a BASAL LAMINA, a LAMINA PROPRIA (of connection tissue with abundant elastic fibres) and a SUBMUCOSA, of loose connective tissue, that includes SEROMUCOUS GLANDS

Question 12

Structure of the 2 main bronchi?

Answer 12

“Rings” of hyaline cartilage are replaced by irregularly shaped cartilage plates (by definition, if cartilage is associated with it, the airway is a bronchus)

Question 13

Lining of 2 main bronchi?

Answer 13

Epithetlium is RESPIRATORY IN TYPE

Lamina propria contains a DISCONTINUOUS LAYER OF SMOOTH MUSCLE AND SEROMUCOUS GLANDS

Question 14

How do the cells of the conducting airways obtain O2, nutrients, etc?

Answer 14

Lung tissue itself is supplied with bronchial arteries and deoxygenated blood returns to pulmonary veins

Question 15

How do the airways differ proceeding down the respiratory tree?

Answer 15

Respiratory epithelium gets shorter (columnar epithelium not as tall) and goblet cells become less frequent moving down

Cartilage begins to disappear and smooth muscle increases

Question 16

Structure of bronchioles?

Answer 16

Less than 1 mm in diameter and LACK CARTILAGE AND GLANDS, but may

contain a few goblet cells in initial portion Epithelium decreases in height, FROM COLUMNAR TO CUBOIDAL, progressing to smallest bronchioles

Lamina propria is composed of SMOOTH MUSCLE, elastic and collagenous fibres

Question 17

Describe the smooth muscle of the bronchioles

Answer 17

Responds to PARASYMPATHETIC innervation, HISTAMINE and other factors by contracting, and thus constricting the bronchiole diameter.

Mechanism plays a significant role in asthma attacks and allergic regulation

Question 18

What are the terminal bronchioles?

Answer 18

Not the last bronchioles in the respiratory tree but are the last conducting airways

Question 19

Lining of terminal bronchioles?

Answer 19

Lined with CUBOOIDAL CILIATED EPITHELIUM and contain non-ciliated CLUB CELLS (clara cells), that project above the level of adjacent ciliated cells

Question 20

Functions of club cells?

Answer 20

Stem cells

Detoxification

Immune modulation

Begin surfactant production

Question 21

Difference between the terminal and respiratory bronchioles?

Answer 21

ALVEOLI interrupt the RESPIRATORY BRONCHIOLES and the low cuboidal epithelium is replaced by discontinuous squamous Type I alveolar cells

Question 22

Two parts of the lower respiratory system?

Answer 22

Conducting portion (includes trachea, main bronchi, secondary bronchi, secondary bronchi, bronchioles and terminal bronchioles)

Non-conducting portion (includes respiratory bronchioles, alveolar ducts and alveolar sacs)

Question 23

Describe progress along the respiratory tree, from terminal bronchioles

Answer 23

Terminal bronchioles branch into the respiratory bronchioles, which proceed to the alveolar ducts and then to the alveolar sacs (termination of alveolar ducts)

Question 24

Describe the alveoli

Answer 24

Terminal portions of the bronchial tree

Responsible for spongy nature of lungs; resemble pockets similar to honeycombs

Function in O2 and CO2 exchange across air-blood barrier

Question 25

Two types of alveoli?

Answer 25

Type I alveolar cells

Type II alveolar cells

Alveolar cells, AKA pneumocytes

Question 26

Structure and function of type I alveolar cells?

Answer 26

Types I cells are SIMPLE SQUAMOUS EPITHELIUM that line alveolar surfaces, covering over 90% of the alveolar surface

Provide a barrier of minimal thickness (permeable to gases)

Question 27

Structure type II alveolar cells

Answer 27

Polygonal in shape

Free surface covered by microvilli and cytoplasm displays dense membrane-bound LAMELLAR BODIES

Often found at the corner of alveoli (not always)

Question 28

Function of type II alveolar cells?

Answer 28

Produce surfactin (released by exocytosis), contained within the LAMELLAR BODIES

Surfactin spreads over the pulmonary surface to REDUCE SURFACE TENSION, at the air-fluid interface (reduces tendency for alveoli to collapse at the end of expiration)

Question 29

Function of alveolar pores?

Answer 29

Allows airflow to equalise across alveoli

Question 30

Immune defence of alveoli?

Answer 30

Also present in alveoli are ALVEOLAR MACROPHAGES (DUST CELLS) - free cells in the septa/migrating over the luminal surfaces of the alveoli

Function - phagocytose inhaled particles that may have escaped entrapment by mucous lining of the airway

Typically migrate up bronchial tree, transported by ciliary action (mucociliary escalator) to the pharynx where they are swallowed OR they migrate to lymph nodes

Question 31

Structure of the alveolar wall (air-blood barrier)?

Answer 31

Consists of Type I alveolar cells, endothelial cells and the basal lamina of each

Allows easy gas exchange

Question 32

How to differentiate arteries and airways?

Answer 32

Arteries contains rbcs

Arteries have simple squamous epithelium

Airways have tall columnar epithelium