histology - respiratory system recording

Respiratory System

Peter Takizawapeter.takizawa@yale.edu

What we’ll talk about…

• Histological structures of conducting airways

• Histological structures that facilitate gas exchange

• Properties of alveoli that control ventilation

• Macrophages and handling of foreign particles

Rate of gas diffusion between air and blood is related to the surface area and thickness of the interface.

·V = kA ⋅ s

a ⋅ MW(PAir − PBlood)

Air Blood

O2O2

Water

O2

Surface Area of Barrier

Thickness of Barrier

Pressure of Gas in Air

Pressure of Gas in BloodRate of Diffusion

The respiratory system comprises conducting and gas exchange segments.

Functions of Conducting Airways• Facilitate flow of air

• Condition air

• Clear air

Trachea

The trachea connects the larynx to primary bronchi and contains cartilage rings.

Glands

Cartilage

Trachealis Muscle

The wall of the trachea contains ciliated, pseudostratifed epithelium, cartilage and glands.

Epithelium

Basement Membrane

Lamina Propria

Submucosa

Cartilage

Glands

The mucosal layer of the respiratory tract consist of epithelia, basement membrane and lamina propria.

Basement Membrane

Lamina Propria

Cilia

Mucus Cells

Epithelium

The respiratory system comprises conducting and gas exchange segments.

Bronchi contain pseudostratified epithelium and cartilage plates.

Cartilage Plate

Epithelium

Smooth Muscle

Glands

Bronchioles contain simple columnar epithelium and lack cartilage plates.

Epithelium

Smooth Muscle

Alveolus

Respiratory Airways

Respiratory bronchioles and alveoli compose the gas exchange portion of the lung.

The gas exchange portion comprises respiratory bronchioles, alveolar ducts and sacs and alveoli.

Terminal Bronchiole

Alveoli

Alveolar Sac

Respiratory Bronchioles

Alveolar Duct

Alveoli

Walls of alveoli consist of pneumocytes, capillaries and connective tissue.

Capillaries

Type II Pneumocyte

Air

Air

Type I Pneumocytes

Type I Pneumocyte

Type I pneumocytes are squamous and surround capillaries; type II pneumocytes are cuboidal.

Type II Pneumocyte

Capillary

CapillaryAir

Air

Type I Pneumocyte

Type I Pneumocyte

Lamellar Body

The gas exchange barrier comprises type I pneumocyte, basement membrane and endothelium.

Type I PneumocyteAir

Air

Blood

Basement Membrane

Basement MembraneType I Pneumocyte

Endothelial Cell

Type I and type II pneumocytes absorb fluid from the lumen via vectorial transport of sodium and chloride.

Na+K+

AQP5

Na-K Pump

Na+

K+

K Channel

H2O K+

Na+

Na-K Pump K Channel

K+

ENaC

ENaC

CFTR

CFTR

Na+

Cl-

Cl-

Type I Cell

Type II Cell

Club Cell

K+

K+

Na+

Na+

ENaC CFTR

Alveolus

Alveolar macrophages (dust cells) reside in the airway and engulf particles and microorganisms.

Capillary

Alveolar Macrophage

Air

Pulmonary Circulation

Pulmonary system delivers deoxygenated blood and bronchial system delivers oxygenated blood.

Pulmonary Artery Pulmonary Vein

Blood from right ventricle

Blood to left atrium

Bronchiole Artery

Blood from left ventricle

Alveoli

Air from trachea

Bronchus

Pulmonary arterioles have thinner walls and generate less resistance than typical arterioles.

Pulmonary Arteriole Typical Arteriole

Structural arrangement of airways and rate of ventilation

Lung section reveals bronchus, bronchioles, alveoli and blow vessels.

BronchusBronchiole

Cartilage Plate

Pulmonary Vessel

Alveoli

Pulmonary Vessel

Composition and structure of alveoli determine compliance of lung.

C =ΔVΔP

Compliance

Lung Volume Change

Intrapleural Pressure Change

Factors that Affect Compliance• Alveolar surface tension• Alveolar elastic fibers• Alveolar collagen fibers

AlveoliPleural Surface

Intrapleural Fluid

Handling Inhaled Particles

The diameter of foreign particles determines their depth of penetration into lungs.

Total

Trachea

Bronchi

Bronchioles

Alveoli

Macrophages engulf inhaled foreign particles.

Macrophage

Macrophage

Take home messages…

• Trachea and bronchi have ciliated, pseudostratified epithelium and cartilage to prevent collapse

• Bronchioles lack cartilage plates

• The gas exchange barrier consists of type I pneumocytes, endothelial cells and their shared basement membrane

• Pneumocytes facilitate fluid absorption from the airway

• Surface tension and connective tissue in alveoli resist expansion and facilitate expiration

• Macrophages (dust cells) engulf foreign particles and microorganisms