RESPIRATORY SYSTEM



32.0, 33.0 RESPIRATORY SYSTEM

:

a) Define and use properly the following words: Respiratory system, Nasal vestibule, Stratified squamous non-keratinized epithelium, venous plexus, Olfactory epithelium, Turbinates, Olfactory cell, Bipolar neuron, Cilia chemical receptors, Sustentacular cell, Basal cell, Respiratory epithelium, Mucus membrane, Nasal glands, Vomeronasal organ, Flehmen reaction, Paranasal sinuses, Guttural pouch, Diverticulum, Nasopharynx, Soft palate, Pharyngeal tonsils, Larynx, Epiglottis, Vocal folds, Larynx Cartilages, Trachea, Cartilagineous rings, Pseudostratified ciliated columnar epithelium, Kinetic cilia, Immotile cilia syndrome, Mucous cell, Mucous granules, Neuroendocrine cell, Lamina propria/submucosa, Lymphatic aggregates, IgA, Tubuloacinar sero-mucous glands, Hyaline cartilage, Bronchus, Bronchial glands, Mast cell, Bronchiole, Bronchiolar epithelium, Bronchiolar cell, Clara cell, APUD cell, Respiratory bronchiole, Alveolar duct, Alveoli, Smooth muscle tufts, Blood-air-barrier, Endothelium, Membranous Pneumocyte, Septal cell, Lamellar bodies, Surfactant, Alveolar macrophages, Pulmonary macrophages, Intravascular macrophages, Mononuclear phagocyte system, Avian respiratory system, Syrinx, Air sacs, Parabronchi, air capillary.

b) Describe and associate basic structure/function for the following: 1) all structures listed above; 2) cell types in respiratory system that replace prior cell types; 3) cells and biochemical components of the lung that are responsible for maintaining inflation of the alveolus.

c) Identify by microscopy: Respiratory system, Nasal vestibule, Stratified squamous non-keratinized epithelium, venous plexus, Olfactory epithelium, Turbinates, Olfactory cell, Bipolar neuron, Immotile cilia, Sustentacular cell, Basal cell, Respiratory epithelium, Motile cilia, Mucus membrane, Nasal glands, Vomeronasal organ, Nasopharynx, Soft palate, Pharyngeal tonsils, Larynx, Epiglottis, Vocal folds, Larynx Cartilages, Trachea, Cartilagineous rings, Pseudostratified ciliated columnar epithelium, Kinetic cilia, Mucous cell, Mucous granules, Lamina propria/submucosa, Lymphatic aggregates, Tubuloacinar sero-mucous glands, Hyaline cartilage, Bronchus, Bronchial glands, Mast cell, Bronchiole, Bronchiolar epithelium, Bronchiolar cell, Clara cell, Respiratory bronchiole, Alveolar duct, Alveoli, Smooth muscle tufts, Blood-air-barrier, Endothelium, Membranous Pneumocyte, Septal cell (Type II), Lamellar bodies, Surfactant, Alveolar macrophages, Pulmonary macrophages, Avian respiratory system, Parabronchi, air capillary.

RESPIRATORY SYSTEM-UPPER TRACT

PRINCIPAL LAYERS (Tunics) OF A HOLLOW TUBULAR ORGAN

1. One long hollow tube.

2. Consist of four parts.

a. Mucosa

i. Epithelial lining

1. Lines the lumen of the cavity.

2. All types of epithelia found in tubular organs

ii. Lamina propria (interstitium)

1. connective tissue sheath underneath the epithelium

2. also blood vessels and nerves

iii. Muscularis mucosa

1. thin band of smooth muscle

2. below the epithelium

3. May not be present in certain regions

b. Submucosa

i. Thick layer of connective tissue underneath the mucosa.

ii. Some places may have glands present in this region

c. Muscularis externa

i. Thick muscle layer

ii. Can be smooth muscle, skeletal muscle, or combo of both

iii. Inner circular

iv. Outer longitudinal

v. Some places have cartilage

d. Adventitia or fibrosa or serosa

i. connective tissue, fat , blood vessels, and nerves

I. BASIC ORGANIZATION OF THE RESPIRATORY SYSTEM

1. Epithelia of the Respiratory System consist of a variety of cell types depending upon the specific location.

2. UPPER TRACT (Nasal cavity through the larynx -- outside the lung) functions to transport, filter, warm and humidify air. It is also responsible for the sense of smell.

3. LOWER TRACT (tracheobronchial region through alveolus -- within the lung) functions at first to conduct air and to remove particulate matter, but at the terminus functions in oxygen - carbon dioxide exchange.

II. NASAL CAVITY

1. conducting, filtering, humidifying, olfaction, air warming)

2. VESTIBULAR REGION

a. EPITHELIUM:

i. Stratified squamous non-keratinized epithelium

ii. hair follicles continuous with skin (keratinized in horse, rostrally)

iii. mechanically filters large particles

b. LAMINA PROPRIA

i. capillary & venous plexuses: cools blood to the brain

ii. glandular secretions: humidify the air

3. OLFACTORY REGION

a. EPITHELIUM(olfactory):

i. Pseudostratified columnar epithelium with ciliated (olfactory) cells

ii. Plus Sustentacular cells

b. TURBINATES and nasal septum

i. Epithelial neurons

ii. send axons to olfactory bulb via 1st cranial nerve.

c. OLFACTORY CELL

i. Modified bipolar neurons

ii. long non-motile cilia (80 µm);

iii. chemical receptors

iv. basal processes are axons

i. penetrate the basal lamina, ethmoid bone,

ii. travel via 1st c.n. & synapse in the olfactory bulb of the brain.

v. Olfactory cells are clustered by specific sensitivity and fire impulses only after strong stimulus

vi. life span ~ 50 days

d. SUSTENTACULAR CELL

i. Top layer of nuclei belong to the Sustentacular cell

ii. cell provides metabolic constituents for the olfactory cells

e. BASAL CELL

i. Divides and differentiates into olfactory & sustentacular cells

f. General Information

i. with normal breathing, will bypasses olfactory region

ii. sniffing samples the air into this region

iii. chemical signals are integrated by the olfactory cells before depolarization and transmission of impulse

iv. obstruction can cause reduction in appetite in dog and most species

v. The olfactory epithelium is the only area where neurons regenerate

vi. there is a continual turnover of olfactory epithelium.

vii. Species Variation in the number of Olfactory Cells (Explains why the dog has a keen sense of smell)

Dog 280 million cells

Cat 67 million cells

human 20 million cells

4. RESPIRATORY REGION

a. EPITHELIUM:

i. Pseudostratified ciliated columnar epithelium

ii. ciliated cells with microvilli

iii. short height in the nasal cavity with rare mucous cells

iv. common to most of the tubules that conduct air to the alveoli (including ventral TURBINATES)

v. humidifies & warms air, removes noxious agents & particles

vi. “Mucus membrane" refers to the respiratory epithelium

b. NASAL GLANDS

i. found in submucosal region

ii. produce a blanket of mucous & serous fluids

iii. Submucosal large veins function to warm the air

III. VOMERONASAL ORGAN

1. paired tubes rostral to caudal at base of nasal septum

2. outpouching of the nasal cavity floor

3. contains olfactory cells (medial side) and respiratory epithelium (lateral side) & rare mucous cells

a. sample air for volatile substances

b. influences sexual behavior ...i.e., "lip curl" or "Flehmen reaction" in cattle

4. contains some serous submucosal glands

5. In cat, the tube passes from the nasal to the orgal cavity through the palatine fissure.

IV. PARANASAL SINUSES

1. consists of spaces that are continuous with the nasal cavity

2. spaces are found within cranial bone:

a. Maxillary, frontal, ethmoid and sphenoid

3. provides warm moist place for infections that can spread to the brain (sinusitis in cats)

4. Long nosed dogs (collie & setter) susceptible to tumors of nose & paranasal sinuses

5. EPITHELIUM

a. Squamous epithelium

b. may change to short respiratory with rare mucous cells

V. GUTTURAL POUCH

1. Unique to the horse (to be covered by Gross Anatomy)

2. Diverticulum of auditory tube

3. Function unknown

4. Potential site of serious infections

5. EPITHELIUM:

a. Respiratory with rare or no mucous cell

VI. NASOPHARYNX

1. located: dorsal to the soft palate

2. pharyngeal tonsils + lymphatic tissues

3. common problems include: tonsillitis, pharyngitis (gaging, yawning, swallowing are symptoms)

4. EPITHELIUM

a. Respiratory epithelium & rare mucous cells

VII. LARYNX

1. General Information

a. Connects pharynx and trachea

b. Components:

i. Epiglottis

ii. Cartilages, ligaments, skeletal muscle

iii. Vocal folds or cords

2. CARTILAGES:

a. Hyaline

i. thyroid

ii. (ventral & lateral. frames larynx)

b. elastic

i. epiglottic

ii. (attached to hyoid bone)

c. fibrous (depending upon age)

d. arytenoid hyaline & elastic (dorsal to vocal folds)

e. cricoid (completely surrounds tracheal opening)

3. EPITHELIUM

a. Stratified squamous epithelium (to the level of vocal folds)

b. Respiratory epithelium with numerous ciliated cells and

i. Species differences

1. pig & carnivore have more squamous epithelium)

c. epiglottis can have taste buds (barrel-shaped)

4. LAMINA PROPRIA – SUBMUCOSA

a. elastic fibers with collagen

b. lymphatic aggregates

i. paraepiglottic tonsils (pig, cat, & some ruminants)

c. mixed tubuloacinar glands (mostly mucous)

RESPIRATORY SYSTEM-LOWER TRACT

I. TRACHEA

1. General Information

a. Continuously open

b. incomplete hyaline cartilagineous rings and inter-annular ligaments provide support

c. tracheal collapse is detected by palpation

i. common in chihuahuas, toy poodles, & terriers

d. Carina is the bifurcation of the trachea into paired bronchi external to the lung

2. EPITHELIUM:

a. General Information

i. Pseudostratified ciliated columnar epithelium with mucous cells (respiratory epithelium)

ii. can find some stratified squamous, particularly with prolonged irritation)

iii. taller in large mammals and taller than in the nasal cavity

iv. easily irritated which causes hypertrophy of goblet cells

v. prolonged irritation induces squamous metaplasia

b. CILIATED CELL

i. centrally located nucleus

ii. 300 cilia/cell with small microvilli between

iii. synchronized beat toward pharynx

iv. Clinical significance

1. Kartagener's Disease (Immotile cilia syndrome)

2. congenital inhibition of ciliary beat causes chronic bronchitis, sinusitis, sometimes infertility

c. MUCOUS CELL

i. similar to the goblet cell of intestine but different secretion

ii. granules (PAS+ glycolipoproteins)

1. membrane-bound granules released by merocrine secretion

2. mucus (from epithelial mucous cells & glands)

3. traps bacteria, particles & noxious chemicals.

4. Cilia move trapped material toward the pharynx

d. BASAL CELL

i. small cell, nucleus near basal lamina

ii. differentiates into the other cell types

e. NEUROENDOCRINE CELL (SMALL GRANULE CELL)

i. very rare, but could be involved in certain tumors

3. LAMINA PROPRIA – SUBMUCOSA

a. lymphocytes : abundant aggregates or nodules

b. first line of immune defense to foreign antigens

c. IgA secreted and released into the lumen

d. elastic fibers

e. tubuloacinar sero-mucous glands

i. extend into submucosa

ii. tubules contain mucous cells,

iii. acini contain serous cells

iv. ducts and tubules also contain ciliated cells and some serous cells

4. MUSCULARIS EXTERNA

a. Cartilage

i. incomplete hyaline rings

b. smooth muscle

i. trachealis m.

ii. connects the ends of cartilage rings dorsally on the esophagus side

II. ORGANIZATION OF LUNG

1. BRONCHUS -- BRONCHIOLE -- ALVEOLAR DUCT – ALVEOLUS

2. Transitional changes:

a. As the trachea becomes bronchus and the respiratory tract makes its way to the alveolus, the following changes take place:

i. gradual decrease in diameter of tubules

ii. epithelial height is reduced

iii. glands, mucous cells, and cilia are lost

iv. gradual loss of submucosa

v. cartilage is replaced by smooth muscle

vi. increased smooth muscle from trachea to bronchioles, then decreased smooth from bronchioles to alveoli

b. CONDUCTION of air

i. takes place in the trachea through the terminal bronchioles.

c. EXCHANGE of air

i. O2 and CO2 exchange begins in the Respiratory bronchioles

3. The Pleura

a. an outer CT covering of the lung; a squamous mesothelium

III. BRONCHUS

1. EPITHELIUM

a. RESPIRATORY (With ciliated & mucous cells):

i. gradual decrease in goblet cells

ii. mucosa is folded (due to smooth muscle contraction during fixation)

2. LAMINA PROPRIA – SUBMUCOSA

a. submucosa only in bronchus

b. loose CT layer with numerous Mast cells (which cause the airways to contract after the release of histamine)

c. lymphocytes

d. elastic fiber lamina

e. BRONCHIAL GLANDS

i. carnivores, ruminants, horse, pig: Mixed tubuloacinar

ii. mucous

1. Alcian blue+ (stains acidic polysaccharides)

iii. serous

1. PAS+ (glycoproteins and water from the blood are passed into the secretory fluids and released into the bronchus lumen.)

2. The fluid contains serum proteins, secretory IgA, IgM, and a bacteriostatic agent

iv. stimulated by parasympathetic nervous system

3. MUSCULARIS EXTERNA of bronchus

a. Hyaline cartilage

b. smooth muscle layer

c. smooth muscle contracts during fixation

IV. BRONCHIOLES (primary, secondary & terminal)

1. General Information

a. smooth muscle layer: causes folded epithelium

b. NO cartilage

c. EPITHELIUM: CILIATED COLUMNAR EPITHELIUM changes to BRONCHIOLAR

i. becomes simple cuboidal bronchiolar cells +/- cilia

ii. gradual increase in number of bronchiolar cells

iii. decrease in number of goblet cells (+/-) until lost

d. mucosa heavily folded except in the terminal region

e. terminal bronchiole is main site of obstruction especially if mucous moves into this region

f. Clinical significance

i. chronic bronchitis will result from the obstruction

ii. terminal bronchiole is poorly developed in cat & dog

iii. In Kartagener's disease the cilia can be immotile ("Immotile Cilia Syndrome")

iv. so, mucous from the bronchi lodges in the contracted areas of the terminal bronchioles

v. Bronchiolar asthma (respiratory system becomes stressed by infection)

2. BRONCHIOLAR EPITHELIUM

a. BRONCHIOLAR CELL

i. called "Clara cell"

1. cuboidal & non-ciliated

2. invaginated nucleus

3. serous secretion releases proteolytic and mucolytic enzymes

ii. replaces mucous cell (goblet)...distal

iii. purpose is to wash the mucous out of bronchioles

iv. lots of SER (possibly to detoxify chemicals)

b. CILIATED CELL

i. Few in number

c. NEUROENDOCRINE CELL

i. APUD cell (Amine Precursor Uptake Decarboxylation)

V. RESPIRATORY BRONCHIOLE

1. EPITHELIUM

a. The wall is interrupted by invaginations of the alveoli

b. CUBOIDAL WITH FEW OR NO CILIATED CELLS

c. Bronchiolar cells are the major cell type

d. smooth muscle bundles lie beneath

e. Species differences

i. absent or reduced (horse, swine, ruminant, man)

ii. present (carnivore, monkey, rat)

VI. ALVEOLAR DUCT

1. wide lumen with balls (tufts) of smooth muscle

2. near the opening of alveoli

3. EPITHELIUM

a. squamous

VII. ALVEOLUS

1. General Information

a. Numerous air-exchange units

i. lined by squamous epithelium and network of capillaries

ii. 300 million in human size lung

iii. 200 µ diameter

iv. pores (holes) between alveoli

b. septal space contains

i. capillaries, macrophages, mast cells and some other CT cells

c. BLOOD-AIR BARRIER

i. Epithelial cell

ii. basal lamina from both cells

iii. Endothelium

2. EPITHELIUM

a. Membranous Pneumocyte (Type I Pneumocyte)

i. Squamous (attenuated, long cytoplasm)

ii. primary lining cell

iii. back to back with the basal lamina of capillary endothelium

b. Septal cell (Type II cell)

i. projects into lumen; cuboidal cell

ii. produces surfactant

1. Phospholipid) extracted by embedding solvents (foamy cytoplasm)

2. Lamellar bodies (EM level only)

iii. proliferates in response to injury to replace the Type I cells

3. Alveolar macrophages

a. The Alveolar macrophage migrates over the alveolar surface and through pores

b. can also be wash into bronchi into trachea and be swallowed.

4. Pulmonary macrophages

a. Interstitial macrophage is stationary in the lamina propria between alveoli.

b. The cell can remain in lamina propria filled with debris for years

c. There is also an Intravascular macrophage that adheres to the endothelium of alveolar capillaries to phagocytize bacteria & viruses in the blood (only in ruminants, swine, horse, cats)

d. derived from the mononuclear phagocyte system

e. these are scavenger cells that phagocytize foreign material

VIII. BLOOD VESSELS, LYMPHATICS, NERVES

1. Pulmonary arteries

a. give rise alveolar capillaries that are involved in gas exchange

2. Bronchiolar arteries

a. Provide O2 for bronchus and associated lung structures

IX. AVIAN RESPIRATORY SYSTEM

1. For those wanting a more detailed description of the avian system the following are recommended:

a. pages 404-407 of Applied Veterinary Histology by Banks

b. Fedde, 1980 in Poultry Science 59: 2642-2653.

2. Upper respiratory

a. Histologically similar to the mammal (except, cartilage rings ossify with age)

b. Syrinx is a junction between the trachea and bronchi, unique to the bird.

c. It has 2 lateral folds and is highly developed in singing birds

3. Lung

a. Completely different from mammal

b. Lungs are small and do not expand;

c. instead they are connected to air sacs.

d. Air sacs serve as bellows and become easy targets for infection

e. air sacs are located throughout the body and connect to large bronchi and parabronchi

f. Gas exchange occurs during inspiration and expiration as air passes through air capillaries.

g. Epithelium is pseudostratified ciliated columnar with goblet cells and mucous glands which become columnar to cuboidal and then squamous

h. Air flow: Trachea to bronchus to parabronchus to air capillaries (alveoli) to parabronchus

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