Test 2 Phys/His

What are the basic components/layers of the nasal cavity?

• Mucosa: epithelium + lamina propria

• Submucosa beneath the mucosa

• Turbinates: trabecular bone scrolls covered by mucosa

• Epithelial type varies depending on location from rostral → caudal

How is the nasal cavity divided regionally, and what is found in each region?

• Nasal vestibule (rostral): stratified squamous epithelium continuous with skin

• Respiratory portion (middle): ciliated pseudostratified columnar epithelium + goblet cells, olfactory cells, and tubuloalveolar glands

• Olfactory portion (caudal): similar to respiratory portion but with many more olfactory cells

What is the general histologic organization of the pharynx and larynx?

• Similar to adjacent tissues

• Epithelium varies by location between ciliated pseudostratified columnar and stratified squamous

• Both contain glands

• Both have an underlying sheet of skeletal muscle

• Larynx contains cartilage for structural support

What is the primary function of the trachea?

Passage of air from the larynx → lungs

What provides structural support to the mammalian trachea?

• Hyaline cartilage arranged in tracheal rings

• Mammalian rings are generally C-shaped and open dorsally

• The open dorsal portion is lined by the trachealis muscle, which is smooth muscle

How do tracheal rings differ between mammals and non-mammals?

• Mammals: C-shaped, open rings with dorsal trachealis muscle

• Non-mammals such as reptiles and birds: rings are generally closed

What type of epithelium lines the tracheal mucosa?

• Ciliated pseudostratified columnar epithelium

• Contains goblet cells

• Forms the mucociliary apparatus/escalator

What is the mucociliary apparatus and why is it important?

• Combination of mucus produced by goblet cells and movement produced by ciliated epithelial cells

• Clears dust, dirt, inhaled particles, and pathogens from the lower respiratory

What are the major histologic layers/components of the trachea?

• Mucosa

• Submucosa — poorly defined from lamina propria

• Tracheal cartilage — C-shaped hyaline cartilage rings

• Trachealis muscle — smooth muscle dorsally

• Adventitia — loose connective tissue outer lining

• Trachea lacks a true serosa

• Glands are present

What structures make up the tracheal mucociliary apparatus?

• Goblet cells: produce mucus

• Ciliated epithelial cells: move mucus toward the pharynx

• Together they remove inhaled debris and pathogens

Where do bronchi fit into the respiratory tract?

• The trachea branches into the mainstem bronchi before entering the lung

• For purposes of this lecture, bronchi are discussed with the lung

What happens to the respiratory epithelium as you move deeper into the respiratory tract?

• Epithelium gradually transitions from tall/layered → thin/simple as you progress down the respiratory tract

What is the pleura?

• Outer lining of the lung

• Composed of loose connective tissue and some smooth muscle

What is the organization of the lung at the gross/histologic level?

• Lung is divided into lobes

• Lobes contain lobules

• Interstitium forms connective tissue framework supporting the bronchial tree and dividing/delineating lobules

• Major structures include bronchi, bronchioles, and alveoli

What are the four major histologic characteristics of a bronchus?

• Ciliated pseudostratified columnar epithelium + goblet cells

• Bronchial glands

• Cartilage

• Smooth muscle
  Also contains bronchus-associated lymphoid tissue (BALT)

How is a bronchus similar to the trachea?

Both have:

• Ciliated pseudostratified columnar epithelium

• Goblet cells

• Glands

• Cartilage

• Smooth muscle

• Respiratory air-conducting function

What is BALT and where is it found?

• Bronchus-associated lymphoid tissue (BALT)

• Lymphoid tissue associated with the bronchi

• Included as a characteristic component of the bronchus

What are the major histologic characteristics of a bronchiole?

• Similar to bronchus in having epithelium + smooth muscle

• No cartilage

• No or few glands

How does bronchiolar epithelium change toward the terminal respiratory tract

Progressively changes:
Ciliated pseudostratified columnar → ciliated columnar → ciliated cuboidal → non-ciliated cuboidal

What is the key difference between bronchi and bronchioles?

Bronchi:

• Cartilage present

• Bronchial glands present

• Ciliated pseudostratified columnar epithelium

Bronchioles:

• No cartilage

• No/few glands

• Epithelium becomes progressively simpler

• Smooth muscle remains

What is an alveolus?

• Terminal outpouching of bronchioles

• Primary site of pulmonary gas exchange

• Smooth muscle is present only at the lip/junction

• Lined primarily by simple squamous epithelium

What are type I pneumocytes and what is their function?

• Simple squamous epithelial cells

• Form most of the alveolar lining

• Extremely thin

• Specialized for gas exchange

What are type II pneumocytes and what is their function?

• Cuboidal epithelial cells

• Much fewer than type I pneumocytes

• Produce surfactant

• Surfactant helps maintain alveolar function

What makes up the alveolar septum?

• A thin layer of supporting collagen

• Contains the structures associated with the alveolar capillary network

• Designed to remain thin to facilitate gas exchange

Why does alveolar structure reflect its function?

• Alveoli are the site of gas exchange

• Simple squamous type I pneumocytes create a very thin barrier

• Close association with alveolar capillaries minimizes diffusion distance

What is the overall epithelial trend from the nasal cavity to the alveoli?

Tall, layered epithelium → progressively shorter/simpler epithelium → simple squamous epithelium in alveoli, reflecting the transition from protection/air conditioning to efficient gas exchange.

What are the major components of the avian respiratory tract discussed in the lecture?

• Primary bronchi (mesobronchi): analogous to mammalian bronchi; ciliated pseudostratified columnar epithelium

• Secondary bronchi: ciliated columnar epithelium

• Tertiary bronchi (parabronchi): fenestrated cuboidal epithelium

• Atria (air vesicles) and air capillaries: analogous to mammalian alveoli and are sites of gas exchange

How do avian parabronchi compare with mammalian alveoli?

• Parabronchi are the tertiary bronchi

• Lined by fenestrated cuboidal epithelium

• Contain atria/air vesicles and air capillaries

• Air capillaries are lined by simple squamous epithelium and serve as the site of gas exchange

What is the avian respiratory sequence presented in the lecture?

Primary bronchi (mesobronchi) → secondary bronchi → tertiary bronchi (parabronchi) → atria/air vesicles → air capillaries

How is the fish respiratory system organized for gas exchange?

• Generally similar in concept to alveolar gas-exchange structures

• Respiratory surfaces are in direct contact with the aquatic environment

• Gas exchange occurs at the secondary lamellae

What specialized cells are found in fish respiratory structures, and what was noted about them?

• Chloride cells

• Pillar cells

• Other specialized cells

• Functions include ion balance, blood-flow regulation, and other functions that remain undetermined

What are these structures called

Nasal Cavity histology

What is this epithelium and where is it located

stratified squamous epithelium

Nasal cavity vestibule

epithelium continuous with skin

what is this epithelium and where is it located

ciliated pseudostratified columnar epithelium

respiratory portion of nasal cavity

identify the arrows of the trachea

left: tracheal ring (hyaline cartilage)

right: trachealis muscle (smooth muscle)

identify the layers of the trachea

top: mucosa

2nd: submucosa

3rd: tracheal cartilage

4th: Adventitia

left bottom: alveoli

top right: pleura

bottom right: bronci & bronchioles

identify the arrow

interstitium

Identify the structures of the bronchus

identify the epithelium of the bronchiole

Ciliated pesudostratified columnar

NO CARTILAGE

identify the epithelium and where it is located

simple squamous epithelium

alveolus

what animal does this belong to

Birds

identify 9 and 10 of the fish lungs

9: primary lamellae

10: secondary lamellae

What is the gas-exchange membrane (GEM), also called the respiratory-exchange membrane?

A thin layer of tissue separating the animal from the environmental medium.

How does O₂ reach and cross the gas-exchange membrane?

O₂ moves into the lungs by diffusion and/or convection and crosses the GEM by diffusion. The partial pressure of O₂ must be lower inside.

What factors determine the rate of diffusion across the GEM?

Surface area (size) of the membrane, membrane thickness, and partial-pressure differences.

What is ventilation?

The creation of currents of air/water flowing to and from the gas-exchange membrane (GEM).

What is active ventilation?

Ventilation that uses energy, such as energy from muscle contraction or beating cilia, to create air/water currents to/from the GEM.

What types of pathways can active ventilation use?

Unidirectional, tidal (bidirectional), or nondirectional pathways.

How does active ventilation compare with passive ventilation?

Active ventilation is considered more reliable and controllable. Passive ventilation occurs when environmental air/water directly or indirectly induces flow to/from the GEM.

What is compliance in relation to active ventilation?

Compliance relates to the work required for inspiration/expansion of the lungs.

What provides elastic forces in the lung parenchyma?

Elastin and collagen fibers interwoven among the lung parenchyma.

What happens during inspiration regarding lung expansion?

Inspiration requires work to expand the lungs, including overcoming elastic forces.

What is the role of surface tension in the lungs?

Surface tension creates a force that must be overcome during inspiration and therefore increases the work of breathing.

What is surfactant and what does it do?

Surfactant is a surface-active agent in water that reduces surface tension.

Where is pulmonary surfactant produced?

• By Type II alveolar epithelial cells.

What is pulmonary surfactant composed of?

Phospholipid dipalmitoyl phosphatidylcholine (DPPC), surfactant apoproteins, and calcium ions.

What primarily drives expiration?

Elastic recoil of the lungs.

What is neonatal respiratory distress syndrome (RDS), and in what animals is surfactant maturation particularly relevant?

RDS occurs in pre-term animals with immature respiratory function/surfactant development. In horses, sheep, and cattle, surfactant maturation occurs late in gestation.

How is surfactant traditionally administered to animals with neonatal RDS?

Through a breathing tube/endotracheal tube connected to a ventilator.

What is Infasurf (calfactant)?

A natural surfactant extract from calf lungs containing phospholipids, neutral lipids, and hydrophobic surfactant-associated proteins SP-B and SP-C.

What is Survanta (beractant)?

A natural bovine lung extract containing phospholipids, neutral lipids, fatty acids, and surfactant-associated proteins.

What is Curosurf (poractant alfa)?

An extract of natural porcine lung surfactant.

What are the 3 components of the work of inspiration?

1) Compliance/elastic work: expanding lungs against lung and chest elastic forces. 2) Tissue resistance work: overcoming viscosity of lung/chest-wall structures. 3) Airway resistance work: resistance to movement of air into the lungs.

What are the 4 pulmonary volumes?

Tidal volume (TV), inspiratory reserve volume (IRV), expiratory reserve volume (ERV), and residual volume (RV).

What is tidal volume (TV)?

The amount of air inspired or expired at rest.

What are IRV, ERV, and RV?

IRV: extra volume that can be inspired above tidal volume. ERV: maximum extra volume that can be expired forcefully after tidal expiration. RV: volume remaining after forceful expiration.

What is inspiratory capacity (IC)?

TV + IRV = how much air can be breathed in.

What is functional residual capacity (FRC)?

ERV + RV = the amount of air in the lungs at the end of expiration.

What is vital capacity (VC)?

IRV + TV + ERV = maximum amount of air expelled after maximum inspiration.

What is total lung capacity (TLC)?

VC + RV = the maximum volume to which the lungs can be expanded.

What factors can alter pulmonary volumes and capacities, and how are they assessed?

Physical fitness, age, height, sex, and altitude can alter them. Spirometry assesses pulmonary function by monitoring airway pressures, flows, and volumes.

What are oxygen uptake, oxygen extraction efficiency, alveolar ventilation, and dead space?

O₂ uptake rate = mL gas/min = Vmedium(CInspired − CExpired), where C = concentration and V = flow rate (L/min) through the breathing organ/rate of ventilation. Oxygen utilization/extraction coefficient describes how thoroughly an animal uses O₂; examples: rainbow trout = 33%, yellowfin = 50%. Alveolar ventilation is new air entering the alveoli/min and is a major determinant of alveolar O₂ and CO₂ concentrations. Dead space is air that never reaches gas-exchange areas.