Respiratory System II:

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Respiratory System II
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Bronchioles

• Function- same as bronchi with added involvement
  in gas exchange
• Types
• Bronchioles
• Terminal bronchioles
• Respiratory bronchioles

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Bronchioles

• Bronchioles-
• less than one millimeter in diameter
• Mucosa
• Ciliated simple columnar w/Goblet cells
• Lamina propria
• Thin elastic fibroconnective tissue.
• Submucosa
• smooth muscle
• No mucosal glands

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Bronchioles

• Terminal bronchioles
• Mucosa
• ciliated simple columnar to ciliated cuboidal to
  non-ciliated cuboidal
• Lacks goblet cells
• Clara cells
• Lamina propria
• Very thin elastic fibroconnective tissue
• Submucosa - same as bronchioles

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Bronchioles

• Respiratory bronchioles
• Mucosa
• Cuboidal to flattened squamous epithelium.
• discontinuous smooth muscle in the lamina propria
• Terminate in the alveolar ducts

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Terminal airways

• Alveolar ducts
• Small alveoli open up from thin walls of these
  ducts
• Terminate in alveolar sacs
• Smooth muscle at opening into the alveolar sacs

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Lungs

• Alveoli- constitute the majority of the lung
  parenchyma
• Air exchange
• Squamous epithelium
• Type I alveolar cell (pneumocyte)
• Forms wall of the alveoli
• Basement membranes fused with basement membrane
  of capillaries in septa

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Lungs

• Type II alveolar cell (pneumocyte)
• Cuboidal rather than squamous
• Primary function is the production of surfactant
• Act as reserve cells- can differentiate into type
  I alveolar cell if needed

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Lungs

• Alveolar macrophages (dust cells)- derived from
  blood monocytes, clean up debris

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Lungs

• Septa
• Composed of capillaries supported by a fine
  fibrous stroma
• No smooth muscle
• Alveolar pores- equalize pressure and provide
  collateral air circulation when bronchi leading
  to the alveoli are blocked

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Pleura

• Visceral pleura
• Thick in large animals (cattle, horses)
• Thin in carnivores
• Consists
• Mesothelium superficial layer of squamous
  epithelial cells
• Elastic fibrous connective tissue and some smooth
  muscle
• Divides lungs into lobules
• prominent in ruminants.
• Sparse in carnivores

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Circulatory system

• Vasculature
• Dual system
• Pulmonary arterial system (primary blood supply)
• Bronchial system

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Pulmonary Circulation

• Pulmonary system
• Relatively thin walled and large caliber
• Usually about the same size as accompanying
  airway
• Are elastic arteries not muscular
• Maintain pressure at a constant through out the
  cardiac cycle, (expand and recoil)

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Bronchial Circulation

• Bronchial system.
• Small branches off the aorta.
• Supply the walls of the airways and the pleura
• Venous return
• Majority returns to the left atrium via the
  pulmonary veins
• A portion from the bronchial system returns to
  the right heart via the azygos system

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Pulmonary Blood Flow

• Control of blood flow in capillaries.
• Matches blood flow (perfusion) to oxygenation
• Controlled by partial pressures of gases in
  alveoli
• High pO2 and low pCO2- vasodilation- increases
  blood flow to alveolar system
• Low pO2 and high pCO2- vasoconstriction-
  decreases blood flow to alveolar system

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Respiratory System

• Lymphatics
• Associated with pulmonary blood vessels and
  airways.
• Drain into thoracic duct at lung hilus
• No lymphatics are found in the alveolar septa

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Respiratory System

• Avian Respiratory System
• Trachea
• Overlapping complete cartilaginous rings
• Epithelium of anterior segment- many mucus glands
• Epithelium of the posterior segment- glands are
  replaced by goblet cells
• Submucosa has very high elastic fiber component

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Respiratory System

• Syrinx- phonation, located at tracheal
  bifurcation
• Bronchi
• Extrapulmonary primary bronchi (mesobronchus)
• Ciliated pseudostratified columnar epithelium
  with goblet cells and mucous glands
• Hyaline C-shaped cartilage.
• Smooth muscle
• Elastic fibers

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Respiratory System

• Intrapulmonary primary bronchus (mesobronchus)
• Ciliated pseudostratified columnar epithelium
  with goblet cells and mucous glands
• Cartilage plates- number decreases as the
  diameter of the bronchus decreases
• Smooth muscle
• Elastic fibers
• Connects to the caudal air sacs

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Respiratory System

• Secondary bronchi
• Ciliated columnar epithelium with mucus cells
• Numerous parabronchi branch from wall

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Respiratory System

• Tertiary bronchi (parabronchi)- form anastomoses
  with air capillaries
• Cuboidal epithelium
• Smooth muscle
• Lead to atrium - cuboidal to squamous epithelium

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Respiratory System

• Atrium
• opens into multiple air capillaries lined by
  squamous epithelium
• Vascular capillaries for gas exchange surround
  air capillaries
• Flow of air and blood is a counter-current system

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Respiratory System

• Air Sacs
• Connect to lungs by mesobronchi
• May extend into hollow bones
• Variable epithelial lining- squamous, ciliated
  columnar, ciliated cuboidal
• Elastic fibers in stroma
• Do not participate in gas exchange
• Act as air pumps to move air by distension and
  compression

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Respiratory System

• Respiration is circular (one-way) verses the
  in-out pattern of mammalian respiration
• Much more efficient- extracts more Oxygen per
  respiratory cycle