Respiratory System

• Ventilation is the process of moving air or water in and out of the body
• External Respiration - exchange of gases between the atmosphere and the blood
• Internal Respiration - exchange of gases between the blood and tissue cells
• Respiratory Organs

  1. Cutaneous Respiration (Skin)
  2. Gills
  3. Swim Bladder
  4. Lungs
• CUTANEOUS RESPIRATION

  The skin is an important supplementary organ for cutaneous respiration in certain organisms. It is typically thin and moist to allow the direct exchange of gases.
• The gills are respiratory organs that allow the withdrawal of oxygen in water.

  • Internal gills: associated with the pharyngeal slits and pouches
  • External gills: arise from the branchial region as filamentous capillary beds
• Swim bladder is an elongated gas-filled sac that aids in respiration. It used to function primarily as a buoyancy organ
• Lungs are the primary respiratory organs in terrestrial vertebrates. It enable the extraction of oxygen from the air and expel carbon dioxide.
• The Trachea is also known as the windpipe is formed by 16 to 20 stacked, C-shaped pieces of hyaline cartilage that are connected by dense connective tissue
• The larynx is cartilaginous structure inferior to the laryngopharynx that connects the pharynx to the trachea and helps regulate the volume of air that enters and leaves the lungs
• Swim Bladder

  • dorsal outgrowth from the pharynx
  • situated dorsal to the digestive tract
  • may be paired or unpaired
  • returning blood drains to the general systemic circulation before entering the heart
• Lungs

  • ventral outpocketing from the floor of the pharynx
  • situated ventral to the digestive tract
  • paired organ
  • venous returns to the heart separately from the generic system circulation
• Ciliary pumps facilitate respiratory exchange by ventilating surfaces.

  In early vertebrates, they allowed for the evolution of larger species and protective armor by reducing reliance on cutaneous respiration.
• Cilia: hair-like projections that line the respiratory routes

  • create water currents
  • facilitate feeding by bringing food particles to mucous traps
• Surfactants: secretion that lines the lungs and gas bladders

  • reduces surface tension at the water-air interface
  • important where there is partitioning of the interior respiratory surface
• Muscular pumps facilitate ventilation by contraction and relaxation of respiratory muscles.

  Ram ventilation is a technique by which the fish's own forward locomotion contributes to gill ventilation.
• Water Ventilation: Dual Pump

  Water-breathing fishes utilize a dual pump system comprising buccal and opercular pumps, working synchronously to create a continuous, unidirectional flow of water across the gills
• Air Ventilation: Buccal Pump

  • Air-breathing fishes and amphibians use a buccal pump for lung ventilation, expanding the mouth cavity to draw in air and compressing it to enter the lungs.
  • Two-stroke: brings air into the mouth → forces it into the lungs in the second
  • Four-stroke: transfers gas from lungs to mouth → expels air → inhalation of fresh air into the mouth → compression of fresh air into the lungs
• Air Ventilation: Aspiration Pump

  Air-breathing amniotes employ aspiration pumps to facilitate air entry or exit through suction, utilizing the rib cage and diaphragm
• Comparative Anatomy - Osteichthyes

  • Usually have 5 gill slits
  • Operculum projects backward over gill chambers
  • Interbranchial septa are very short or absent
• Comparative Anatomy - Agnathans

  • 6 - 15 pairs of gill pouches
  • pouches connected to pharynx by afferent branchial (or gill) ducts & to exterior by efferent branchial (or gill) ducts
• Comparative Anatomy - Amphibians

  • Lungs of the amphibians have 2 simple sacs; internal lining may be smooth or have simple sacculations
  • They also relies on cutaneous respiration
• Comparative Anatomy - Reptiles

  • Reptilian lungs are simple sacs in Sphenodon and snakes
  • Lizards, crocodilians, & turtles - lining is septate, with lots of chambers & sub chambers
  • air exchanged via positive-pressure ventilation
• Comparative Anatomy - Birds

  • Avian lungs are modified form of reptilian lungs
  • air sacs (diverticula of lungs) extensively distributed throughout most of the body
  • arrangement of air ducts in lungs have no passageway or a dead-end
  • air flow through lungs (parabronchi) is unidirectional
• Comparative Anatomy - Mammals

  • Mammalian lungs are multi chambered & usually divided into lobes
  • air flow is bidirectional: air exchanged via negative pressure ventilation, with
  • pressures changing due to contraction & relaxation of diaphragm intercostal muscles
• Embryonic Development

  • The development of the respiratory system begins from the primitive gut tube.
  • Respiratory diverticulum forms as an outpocketing on the proximal part of the gut tube.