respiratory

• Respiratory system


  The primary function is to provide for the exchange of respiratory gases (oxygen and carbon dioxide) between the organism and the environment
• Conducting airways


  • Provide a series of air passages for moving air to and from the gas exchange area in the lungs
  • Serve a protective function by conditioning incoming (inspired) air
  • Conserve body heat and water by extracting them from the air during expiration
  • The mucociliary blanket traps inhaled particles and conveys them and cellular debris out of the system
  • Also functions for olfaction and phonation
• Gas exchange area

  • Includes the respiratory bronchioles, alveolar ducts, and alveolar sacs
  • Gas exchange occurs in alveoli, where only a thin blood-air barrier is present between pulmonary capillary blood and respired air
  • An extensive pulmonary capillary bed receives the entire output of the right ventricle of the heart
• Conductive portion


  Consists of the nasal cavity, nasophaynx, larynx, trachea, extra pulmonary primary bronchi, and inside the lung, the branches of the bronchial tree starting with the intrapulmonary primary bronchus and ending with the tertiary or terminal bronchiole
• Respiratory portion


  Composed of the remaining terminal branches of the bronchial tree, such as the respiratory bronchiole, alveolar duct, alveolar sac and alveolus. Part of the bronchial tree where actual exchange of gases occurs due to the presence of alveoli
• Nasal cavity


  • Separated into right and left cavities by the nasal septum
  • Lateral walls give rise to three pairs of curved plates of bone; dorsal, middle and ventral turbinates
  • Divided histologically into three distinct regions: vestibular, respiratory and olfactory regions
  • Two types of epithelium: typical respiratory epithelium and olfactory epithelium
• Vestibular region


  • A narrow region that represents the point of transition between the skin and the nasal cavity
  • Skin is typical except that it presents sinus hairs called vibrissae
  • Lining epithelium is stratified squamous nonkeratinized with pigment cell that give color to the region in most domestic species
• Respiratory region


  • Communicates with the paranasal sinuses
  • Lining epithelium is typical respiratory epithelium (TRE) of pseudostratified columnar kinociliated with goblet cells
  • The kinocilia trap inhaled dirt and bacterial particles
  • The blood sinuses in the erectile tissue transfer heat to the incoming air flow to maintain the humidity of the lung at saturation
  • The secretions of nasal glands humidify the air while the blood-engorged erectile tissue warms the air
• Olfactory region


  • The mucous membrane is highly pigmented and specialized to receive stimuli for the sense of smell (chemoreceptor)
  • The olfactory epithelium has 3 types of cells: sustentacular, basal and olfactory cells
  • Olfactory cells are bipolar neurons specialized to receive stimuli for the sense of smell
  • Olfactory glands cleanse the olfactory cell surface and ready it for reuse, and dissolve odor-producing substances
• Nasopharynx


  • The dorsal portion of the pharynx that connects with the nasal cavity
  • Separated cranially from oropharynx by the soft palate
  • Lining epithelium is TRE (pseudostratified columnar kinociliated with goblet cells)
  • Contains many diffuse and nodular lymphatic tissue and tonsils (pharyngeal tonsils) as well as branched tubuloalveolar mucous serous and mixed pharyngeal glands
• Larynx


  • A short irregularly shaped muscular tubular organ supported by hyaline and elastic cartilage
  • Phonation involves distortion of the shape so that the vocal folds at the cranial end vibrate at different rates and produce different tones
  • Connects the nasopharynx with the trachea
  • The laryngeal ventricles are lined with stratified squamous nonkeratinized epithelium in pigs and carnivores, and respiratory epithelium in horses
  • Secretions of laryngeal mucous glands help to trap dust and debris so that the beating of the ciliated cells can bring it up to the pharynx, where it is swallowed or spit out
• Trachea


  • A long, flexible, lightweight and compression-resistant tube that connects the larynx and the extrapulmonary primary bronchi
  • Supported by C-shaped hyaline cartilage rings that keep it open
  • The trachea bifurcates before entering the lung into extrapulmonary primary bronchi
  • Cilia in the TRE all beat in a coordinated manner to move the sheet of mucus upwards
  • Mucus is produced continuously so if it weren't removed, it would accumulate in deeper regions and the animal would shortly drown
  • The trachealis muscle connects the two ends of the tracheal rings and is attached to the internal surface of the tracheal cartilage in horses, pigs and ruminants, and to the external surface in carnivores
• the bronchi are tubes that branch off from the trachea into the lungs
• the trachea is the windpipe
• bronchial tree refers to all the branches of the bronchi within the lung
• Extrapulmonary Primary Bronchus


  Short paired flexible tube between the trachea and the lung. Each bronchus enters the lung.
• Extrapulmonary Primary Bronchus


  • In pigs, the right extrapulmonary bronchus gives off a branch to the apical lobe of the right lung
  • Microscopic structure is similar to that of the trachea: flexible tube with stiffening walls of hyaline cartilage
• Lung


  Expandable structure encapsulated with the visceral pleura, a serous membrane (DWFCT covered by mesothelium). Divided into lobes covered by serous membranes; each lobe is divided into lobules by thin connective tissue septa rich in elastic fibers.
• Lung


  • Presents thin interalveolar CT septa (fine collagen and elastic fibers and fibroblasts that support individual alveoli)
  • Parenchyma consists of an immense network of blood capillaries and tubular structures that branch and re-branch to form a bronchial tree
• Lungs of calf, sheep, goat, cat and pig

  • Clusters of lymphocytes and lymphoid nodules are found in the walls of the airways and in association with blood vessels, referred to as BALT (bronchus-associated lymphoid tissue)
• Ruminants and pig


  • Pulmonary interstitial tissue is prominent
• Horse and carnivores


  • Pulmonary interstitium is relatively sparse
• Branches of the bronchial tree from the largest to the smallest

  1. Intrapulmonary Primary Bronchus

  2. Secondary Bronchus

  3. Tertiary Bronchus

  4. Primary Bronchiole
• Intrapulmonary Primary Bronchus


  • Gives off several secondary bronchi
  • Mucosa is folded, unlike the smooth surface of extrapulmonary primary bronchus and trachea
  • Folds are an adaptation to expansion as the lungs inflate and give the bronchus a "scalloped" appearance
  • Lamina epithelialis - typical with occasional DLT and NLT
  • Lamina propria - typical with occasional DLT and NLT
  • Muscularis mucosae - present and completely encircles the bronchial lumen; the spiral arrangement accounts for folding of the t. mucosa
  • Submucosa - typical with branched, coiled tubuloalveolar mucous glands, glands decrease in number toward the tertiary bronchi, in cats glands may extend into the primary bronchioles
  • Muscularis - replaced by hyaline cartilage plates that appears in cross section as two or more overlapping irregular half-moon or oval plates
  • Adventitia - typical and blends with lung stroma
• Secondary Bronchus


  • Same structure as the intrapulmonary primary bronchus except that it has a smaller diameter and the cartilage in t. muscularis is reduced to several large plates separated by gaps filled with loose CT and smooth muscle
• Tertiary Bronchus


  • Same structure as the secondary bronchus except that it has a much smaller diameter and the cartilage plates are smaller and fewer
• Primary Bronchiole


  • Part of the bronchial tree without cartilage in its wall
  • Cartilage is not necessary in bronchioles because they are small (diameter is below 0.5 mm) and the smooth muscle (muscularis mucosae) has sufficient tone to resist their collapse when the lung expands
  • Reinforcement by cartilage is therefore not needed in bronchioles
• the trachea is made of cartilage rings which support its structure
• the trachea branches into the left and right mainstem bronchus
• tertiary bronchi are the third branches of secondary bronchi
• secondary bronchi are the second branches of the primary bronchi
• primary bronchi are the first branches of the trachea
• the left mainstem bronchus goes directly down towards the heart while the right mainstem bronchus angles more sharply towards the back
• Wall of bronchiole


  • T. mucosa - folded like that in tertiary bronchus
  • LE - simple columnar or simple cuboidal ciliated without goblet cells
  • LP - thin loose CT without glands
  • MM - folded and continuous
  • T. submucosa - thin loose connective tissue
  • T. muscularis - absent and cartilage is also absent
  • T. adventitia - absent
• Secondary Bronchiole


  The same structure as the primary bronchiole except that it has a smaller diameter
• Secondary Bronchiole


  Gives off several tertiary bronchioles
• Tertiary or Terminal Bronchiole


  The same structure as secondary bronchiole except that it has a smaller diameter and its lining epithelium is nonciliated
• Tertiary or Terminal Bronchiole


  Gives off several respiratory bronchioles
• Respiratory Bronchiole


  Initial structure of the respiratory portion
• Respiratory Bronchiole


  • Rarely observed in ruminant and swine, few in horse and man, extensive in carnivores and monkeys and absent in mouse
  • Where the respiratory bronchiole is absent the terminal bronchiole connects directly with the alveolar duct