45. Respiratory System I

What does the respiratory system consist of?

N
N
S
N
L
T
B
B
A
A

• nostrils

• nasal cavity

• sinuses

• nasopharynx

• larynx

• trachea

• bronchi

• bronchioles

• alveolar ducts

• alveoli

What aids in breathing?

diaphragm and intercostal muscles

What is the primary organ of the respiratory system?

the lung

What is the function of the lung?

facilitate O2 and CO2 exchange

What composes the conducting component of the respiratory system?

N
N
P
N
L
T
B

• nostrils

• nasal cavity

• paranasal sinuses

• nasopharynx

• larynx

• trachea

• bronchi

What is the conducting component of the respiratory system largely lined by?

pseudo-stratified, ciliated columnar cells

The conducting component has a variable proportion of what?

secretory goblet (mucous) cells

What branches from the bronchi?

bronchioles

serve as a transition zone between the conducting component (ciliated) and the air exchange (alveolar) component

transitional component

Disappearance of cilia in the transitional component is ________ ________. The ciliated cells in the proximal bronchiolar region become ________ and progressively ________, until cilia eventually ________.

not abrupt; scarce; attenuated; disappear

What do normal bronchioles lack? What do they have?

goblet cells; other types of secretory cells such as club cells (aka Clara cells) and neuroendocrine cells

Club cells contain numerous biosynthetic organelles that play an active role in what?

the detoxification of xenobiotics (foreign substances)

Clubs cells act as ________ cells in the ________ and ________ of the respiratory system.

stem; repair; remodeling

Club cells contribute to the ________ immunity of the lung by secreting ________ ________ (________) and ________ ________.

innate; protective proteins (collectins); pulmonary surfactant

What is the air exchange component of the respiratory system in all mammals formed by?

alveoli

What is the surface of the alveoli lined by?

type I and type II pneumonocytes

type of epithelial cell that covers the majority of the alveolar wall and functions in gas exchange

type I (membranous) pneumonocytes

type of epithelial cell that is larger cuboidal cells and produces surfactant

type II (granular) pneumonocytes

supports both the alveolar epithelium and alveolar capillary endothelium

interstitium

What is the blood air barrier formed from?

V
B
A

• vascular endothelium

• basement membrane

• alveolar epithelium lining cells

The alveolar walls are a ________ ________ ________.

thin delicate network

interconnecting network of interstitial stromal tissue supporting the blood and lymphatic vessels, nerves, bronchi, bronchioles. and alveoli

pulmonary interstitium

Into what compartments can the pulmonary interstitium be divided into?

1. B

2. I

3. A

1. bronchovascular interstitium

2. interlobular interstitium

3. alveolar interstitium

compartment of pulmonary interstitium where the main bronchi and pulmonary vessels are situated

bronchovascular interstitium

compartment of pulmonary interstitium separating the pulmonary lobules and supporting small blood and lymph vessels

interlobular interstitium

compartment of pulmonary interstitium supporting the alveolar walls that contain pulmonary capillaries and alveolar epithelial cells

alveolar interstitium

True or false: Pulmonary changes (edema, emphysema, and inflammation) may affect one or more of these interstitial compartments.

true

In all domestic species, what is the left lung composed of?

cranial and caudal lobes

Depending on species, what can the right lung be composed of?

cranial, middle, caudal, and accessory lobes

In what species is the right lung missing the middle lobe?

horses

What is each pulmonary lobe further subdivided by connective tissue into?

pulmonary lobules

What does the degree of lobulation determine?

the degree of air movement between the lobules

How is movement of air between the lobules in pigs and cattle described? Why?

practically absent; thick connective tissue of the interlobular septa separating individual lobules

movement of air between lobules and between adjacent alveoli

collateral ventilation

Collateral ventilation is poor in what species? It is good in what species?

cattle; dogs

single layer of mesothelial cells overlying multiple layers of connective tissue

pleurae

What lines the thoracic wall, diaphragm, and mediastinum?

parietal pleura

What lines the surface of the lungs?

visceral pleura

True or false: Between the parietal and visceral pleura is the pleural space separated by the mediastinum into left and right sides. The pleural space is minimal and under normal conditions contains only traces of clear fluid, which is a lubricant, and a few exfoliated cells.

true

In what species is the mediastinum complete? What does this mean?

cattle, goats, and pigs; no communication between the two sides

In what species are there fenestrations in the mediastinum? What does this allow?

horses and sheep; communication between these two spaces

True or false: In cats and dogs, whether the mediastinum is fenestrated or complete is controversial.

true

The microbiota (normal flora) of the respiratory system helps to do what?

prevent colonization of harmful bacteria (colonization resistance)

What is the resident microbiota present in the respiratory system of any healthy animal?

V
B
Y
F

• viruses

• bacteria

• yeasts

• fungi

The number of organisms in microbiota are more abundant in what parts of the respiratory system?

N
P
L

• nasal cavity

• pharynx

• larynx

True or false: Some members of the nasal microbiota are pathogens that can cause important respiratory infections under some circumstances.

true

part of the bovine nasal flora but can cause pneumonia

mannheimia haemolytica

True or false: There are multiple routes to access the respiratory system. Inflammation can extend locally, regionally, or systemically. Laryngeal exudate from laryngitis can be aspirated to lungs. The large vascular bed present in the lung can allow for sepsis and septic shock.

true

What are the portals of entry into the respiratory system?

A
H
D

• aerogenous

• hematogenous

• direct extension

True or false: Hematogenous dissemination of bacteria to this serosal surface occurs commonly, often as a component of polyserositis.

true

True or false: Microbes and foreign bodies may gain access to the pleura via direct extension through the thoracic body wall in association with penetrating thoracic injury (bites, gunshot wounds, and migrating grass awns). It can include rupture of the caudal esophagus, perforation of the diaphragm, and parapneumonic spread of infectious agents as a sequela of bronchopneumonia or when a lung abscess ruptures into the pleural space.

true

What is the defense system/barrier of the conducting and transitional components of the respiratory system?

mucociliary clearance

What is the defense system/barrier of the air exchange component of the respiratory system?

phagocytosis from pulmonary alveolar macrophages

physical unidirectional movement and removal of deposited particles and gases dissolved in the mucus

mucociliary clearance

What is mucociliary clearance provided by?

mucociliary blanket (mucociliary escalator)

What is the main defense mechanism of the conducting component (nasal cavity, trachea, and bronchi)?

mucociliary clearance

What does mucus primarily act as?

barrier and vehicle

What is mucus made up of?

W
G
I
L
E

• water

• glycoproteins

• immunoglobulins

• lipids

• electrolytes

What is mucus produced by?

goblet cells, submucosal glands, and fluid from transepithelial ion and water transport

Where is serous fluid and mucus secreted? What is formed on top of cells?

onto the surface of the respiratory mucosa; a thin film of mucus

True or false: Rapid and powerful movement of cilia creates a series of synchronized waves that propels mucus, exfoliated cells, and entrapped particles to the pharynx.

true

Where does mucociliary clearance terminate at? What happens there?

the pharynx; mucus can be coughed

What will ciliary activity and mucus transport increase notably in response to?

stimuli such as in respiratory infections

Is the mucociliary apparatus available in the alveoli? Why or why not?

no; they lack ciliated and mucus-producing cells

What are the main defense mechanisms of the alveoli?

P
A

• phagocytosis provided by the pulmonary alveolar macrophages

• antimicrobial molecules of the alveolar lining fluid

Pulmonary alveolar macrophages are highly ________ cells.

phagocytic

How do pulmonary alveolar macrophages contribute to the immune system?

rapidly attaching and phagocytosing bacteria and any other particles reaching the alveolar lumens

What is the number of free macrophages in the alveolar space closely related to?

the number of inhaled particles reaching the lungs

True or false: This ability to increase, within hours, the number of available phagocytic cells is vital in protecting the distal lungs against foreign material, particularly when the inhaled particle load is high.

true

The lifespan of alveolar macrophages in the alveoli is notably ________, only a few ________. They are ________ being replaced by newly migrated blood ________.

short; days; continuously; monocytes

How do most alveolar macrophages leave the alveoli?

by migrating toward the bronchiolar (transitional) region until the mucociliary blanket is reached (via mucociliary apparatus to the pharynx)

What happens if the deposition of inhaled mineral dust exceeds removal?

particles accumulate in the lung

What is pneumoconiosis lung disease caused by?

deposition of dust

common finding in the lungs of dogs, particularly in animals living in polluted areas or households with smokers or fireplaces

carbon (anthracosis)

What is this showing?

anthracosis

particle, microbe, or toxic gas must first gain entry to a vulnerable region of the respiratory system before it can induce an effect

aerogenous

process by which particles of various sizes and shapes are trapped within specific regions of the respiratory system

deposition

process by which deposited particles are destroyed, neutralized, or removed from the mucosal surfaces

clearance

What are the main clearance mechanisms?

S
C
M
P

• sneezing

• coughing

• mucociliary transport

• phagocytosis

What is the underlying pathogenic mechanism in many pulmonary diseases?

abnormal retention of particles resulting from increased deposition, decreased clearance, or a combination of both

True or false: Anatomic configuration of the nasal cavity and bronchi plays a unique role in preventing or reducing the penetration of noxious material into the lungs.

true

What sized microbes will lodge in the nasal passage? What happens if they are smaller than this? Smaller than what size can progress to the bronchiole and alveoli?

10 um; can progress to tracheal and bronchial bifurcations; 2 um

True or false: The anatomic features of the nasal cavity and airways provide an effective barrier, preventing the penetration of most large particles into the lungs.

true

Particles longer than ________ may also reach the lower respiratory system provided their mean diameter is less than ________.

200 um; 1 um

What is an example of a large but slender fiber that can bypass the filtrating mechanisms by traveling parallel to the airstream?

asbestos

Lungs are also susceptible to hematogenous borne microbes, toxins, or emboli why?

large vascular bed

cell responsible for the removal of circulating particles, bacteria, and endotoxins from the blood of ruminants, cats, pigs, and horses

pulmonary intravascular macrophage

In pigs, what percent of the pulmonary capillary surface is lined by pulmonary intravascular macrophages? What about ruminants?

16%; 95%

In systemic conditions, excessive release of ________ by pulmonary intravascular macrophages may result in ________ lung injury.

cytokines; acute

True or false: Existing in an oxygen-rich environment and being the site of numerous metabolic reactions means the lungs require an efficient defense mechanism against oxidant-induced cellular damage (oxidative stress).

true

What are forms of damage caused by?
I
X
F

• inhaled oxidant gases

• xenobiotic toxic metabolites

• free radicals released by phagocytic cells during inflammation

________ ________ and ________ ________ ________ (____) induce extensive pulmonary injury and impair repair.

free radicals; reactive oxygen species (ROS)

largely responsible for protecting pulmonary cells against damage

oxygen and free radical scavengers

What are examples of oxygen and free radical scavengers?

S
V

• superoxide dismutase

• vitamins E and C

Where are the scavengers present?

alveolar and bronchiolar epithelial cells and interstitium

True or false: Respiratory defense mechanisms are effective in trapping, destroying, and removing bacteria that, under normal conditions, animals can be exposed to aerosols containing massive numbers of bacteria without any ill effects. If defense mechanisms are impaired, the inhaled bacteria will colonize and multiply in bronchi, bronchioles, and alveoli, and they produce infection, which can result in fatal pneumonia. Blood borne pathogens, inhaled toxicants, or free radicals overwhelm the protective defense mechanisms, cells of the respiratory system are likely to be injured, often causing serious respiratory diseases.

true

There is ________ of viral and bacterial infections.

synergy

How long after a viral infection will the phagocytic function of pulmonary alveolar macrophages and the mucociliary clearance be impaired?

5-7 days

What viruses are known to predispose to secondary bacterial infections?

I
B
C
F

• influenza virus in pigs and horses

• bovine respiratory syncytial virus (BRSV) in cattle

• canine distemper virus

• felid herpesvirus 1 (FeHV-1) and feline calicivirus (FV)

True or false: Acquired or congenital immunodeficiencies can cause increased susceptibility to viral, bacterial, mycotic, and protozoal pneumonias, as can corticosteroids/chemotherapeutic drugs with immunosuppressive characteristics.

true