histo 3

• Respiratory system

  Consists of two major components - the conductive and the respiratory parts
• Conductive portion


  Transports, cleanses and humidifies as well as cools or warms the inspired air
• Respiratory portion


  Site of the actual exchange of gases
• Regions of the nasal cavity

  • Vestibular
  • Respiratory
  • Olfactory
• Vestibular region

  • Represents the point of reflection of the skin as the mucous membrane
  • Lamina propria-t. submucosa is coarse areolar connective tissue
  • Hairs (vibrissae), sweat glands, sebaceous glands occur
  • Branched tubuloalveolar serous and mixed glands may also be present
• Respiratory region

  • Lining epithelium is pseudostratified ciliated with goblet cells
  • Muscularis mucosae is absent
  • Lamina propria-t.submucosa is areolar connective tissue
  • Glandular tissue humidifies the air
  • Engorged erectile tissue cools or warms the air
• Olfactory region

  • Specialized area for olfaction
  • Lining epithelium is pseudostratified columnar nonciliated
  • Sustentacular cells are tall with broad apices and narrow bases
  • Basal cells are cuboidal in shape
  • Olfactory cells are modified neurons
• Nasopharynx


  Portion of the pharynx above the soft plate, connects the nasal cavity with the oropharnyx
• Nasopharynx


  • Lining epithelium is pseudostratified columnar ciliated
  • No muscularis mucosae
  • Lamina propria-t. submucosa consist of loose connective tissue with numerous diffuse and nodular lymphatic tissue and tonsils
  • T. muscularis is skeletal muscle in various orientation
  • T. adventitia is continous with underlying fascia
• Larynx


  • Connects the pharynx with the trachea
  • Irregularly shaped muscular tube with cartilage support
  • Lining epithelium is either stratified squamous or pseudostratified columnar ciliated
  • No muscularis mucosae
  • Lamina propria-t. submucosa is areolar connective tissue with diffuse and nodular lymphatic tissue and branched tubuloalveolar mucous, serous and mixed glands
  • T. muscularis consist of striated muscle and cartilage
• Trachea


  • Connects the larynx and the primary bronchi
  • Lining epithelium is pseudostratified columnar ciliated with goblet cells, basal cells, brush cells, serous cells, Clara and Kultschitzky or neuroendocrine (APUD) cells
  • No muscularis mucosae
  • Lamina propria-t. submucosa is areolar c.t. and presents branched coiled tubuloalveolar mucous glands
  • T. muscularis is reduced to a transversely oriented mass of smooth muscle (trachealis muscle)
• Extrapulmonary bronchi


  • Arise at the bifurcation of the trachea and are structurally similar to it
• Lung


  Structurally is considered as a compound tubuloalveolar gland
• Types of Lung

  • Type I (Ruminants and pigs)
  • Type II (Dog, cat and monkey)
  • Type III (Horse and human)
• Type I Lung


  • With well-developed secondary lobules
  • Thick interlobular septa and thick pleura
  • Alveoli between lobules are without interalveolar pores of Kohn
  • Complete interlobular septa which extends from connective tissue of visceral pleura to c.t. surrounding major bronchi and blood vessels
• Type II Lung


  • Without secondary lobules
  • With poorly developed intraparenchymal supportive tissue strands
  • With thin visceral pleura
• Type III Lung


  • Incompletely developed secondary lobules
  • Well-defined but disorderly arrangement of interlobular septa
  • Thick visceral pleura
• Intrapulmonary bronchi

  • Same structure as the extrapulmonary bronchi except that the muscularis is present
  • Lining epithelium is pseudostratified columnar ciliated with goblet cells
  • Lamina propria is areolar
  • Muscularis mucosae is present
  • T. submucosa is areolar with branched, coiled tubuloalveolar mucous glands
• Bronchioles


  • Lining epithelium is simple columnar or simple cuboidal cells and is devoid of goblet cells
  • Lamina propria is fine collagenous and elastic fiber
  • Muscularis mucosae is present and continuous
  • Cartillage is absent
• Respiratory bronchioles


  Initial portion of lung responsible for the exchange of gases, the transition zone
• Terminal bronchiole


  The most distal conducting airway free of alveoli, lined by simple columnar or cuboidal epithelium composed of ciliated and Clara cells
• Clara cells


  Bronchiolar exocrine cells with secretory function and capable of metabolizing xenobiotic compounds
• Alveolar ducts


  • Completely lined by alveoli
  • Smooth muscle may be present along the luminal border at the apices between adjacent alveoli
  • Divide and expand peripherally into alveolar sacs or saccules which are completely lined by alveoli
• Alveoli

  • Lining epithelium consists of Type I pneumocytes (for gaseous exchange) and Type II pneumocytes (producer of alveolar fluid with pulmonary surfactant)
  • Alveolar macrophages or dust cells make up 2-9% of the cells
  • Interalveolar septa are thin sheets of tissue containing a capillary plexus and covered on both sides by a layer of epithelium and capillary endothelial cells
• Vascular supply of the lung

  • Pulmonary artery and its peripheral subdivisions
  • Bronchial arteries
• Avian respiratory system - upper respiratory tract

  • Includes the same structures as mammals with the addition of the syrinx
  • Nasal cavity lining is similar to mammals
  • Trachea has intraepithelial mucous glands, variable mucosal and submucosal glands, and complete ossified cartilage rings
  • Primary bronchi have cartilage replaced by DWFCT and smooth muscle
  • Syrinx is an inverted Y-shaped structure with a cartilaginous bar, median vocal fold, and lateral vocal folds
• Avian respiratory system - lungs

  • Extremely small compared to the thoracic cavity, not expandable
  • Air sacs aid in air movement, do not participate in gas exchange
  • Bronchioles absent, replaced by vestibulum, mesobronchus, secondary bronchi, and parabronchi
• Bronchioles which are present in the mammalian lung are absent in the avian lung
• Air sacs in birds

  • Unpaired cervical
  • Paired claviculars
  • Paired cranial thoracics
  • Paired caudal thoracics
  • Paired abdominals
• Air sacs


  • Occur free in the body cavities
  • Send diverticula into the bones (pneumatic bones e.g. humerus)
• Recurrent bronchi


  Involved in the return of air from the air sacs to the lung proper
• Mural elements of avian lung

  • Intrapulmonary bronchi
  • Vestibulum and the mesobronchus
  • Secondary bronchi
  • Parabronchi
  • Air vesicles
  • Air capillaries
• Secondary bronchi


  • Lining epithelium is simple columnar or simple cubiodal devoid of goblet cells
  • Lamina propria is loose connective tissue and usually devoid of lymphatic tissue
  • Muscularis mucosae is interrupted due to the presence of parabronchi and in some areas, air vesicles
• Parabronchi


  • Lining epithelium is interrupted by laterally projecting air vesicles
  • Between interruptions the parabronchi are lined by simple cuboidal or simple columnar epithelium
• The urinary system consists of the kidney and the urinary passages (ureter, urinary bladder and urethra)
• The urinary system is important for maintaining fluid and electrolyte balance, controlling blood pressure and eliminating waste products of metabolism
• Types of kidney in domestic animals

  • Unilobar or unipyramidal kidney
  • Multilobar kidney
• Unilobar kidney


  • Consists of only one big lobe (bean shape)
  • Presents the renal hilus, renal sinus and renal pelvis
• Multilobar kidney


  • Presents many lobes (lobulated appearance)
  • One or more pyramids may join to form a papilla
  • No renal pelvis
• Components of the uriniferous tubule

  • Nephron
  • Collecting duct system