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Human Heart. Respiratory System. Chapter 42, Campbell, 6 th edition Nancy G. Morris Volunteer State Community College. Gas Exchange In Animals. supplies O 2 for cellular respiration disposes of CO 2 (Figure 42.17)
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Respiratory System Chapter 42, Campbell, 6th edition Nancy G. Morris Volunteer State Community College
Gas Exchange In Animals • supplies O2 for cellular respiration • disposes of CO2 (Figure 42.17) • occurs between respiratory medium and organism • air is 21% oxygen but the amount of dissolved O2 in water varies due to temperature, solute concentrations, etc
Respiratory surface • place where gas exchange with respiratory medium occurs • O2 diffuses in; CO2 diffuses out • surface must be wet (gases must dissolve in water) • surface must be extensive enough to provide for the entire body
Variation of Respiratory Surfaces • entire surface – protozoa & unicellular organisms • plasma membrane of each cells contacts the outside environment – sponges, cnidarians, flatworms • moist skin over dense capillaries – earthworm and amphibians – must live in moist damp places to keep exchange surface moist
Variation of Respiratory Surfaces • most other animals lack sufficient body surface to exchange gases for the entire body • they possess a region of body surface that is extensively branched or folded • aquatic animals: gills are present & in direct contact with water • terrestrial animals: internal respiratory surfaces that open to the atmosphere through narrow tubes: lungs & insect trachea
Gills: Adaptations of Aquatic Organisms • outfoldings of the body surface specialized for gas exchange -excresence • Figure 42.18 • some have flap-like gills that extend from each segment (annelids) • localized gills on a body region where surface is subdivided to provide for large surface area (mollusks, fish)
Gills must be efficient • water has lower O2 concentration than air, SO fish expend a lot of energy to ventilate (increasing the flow of the respiratory medium over the respiratory surface) • fish possess a unique arrangement in their gills which maximizes O2 uptake from water • COUNTERCURRENT EXCHANGE – blood flows opposite to the direction in which water passes over the gills, maintaining a constant concentration gradient (Figures 42.19 & 42.20)
Adaptations of Terrestrials • air has advantages over water as respiratory medium: • higherO2 concentration • O2 and CO2 diffuse faster through air • respiratory surfaces do not have to be ventilated as thoroughly • disadvantage is that respiratory surface is continuously desiccated
Tracheal System • air enters through openings called spiracles and diffuses through small tubes extending to the surface of most cells • tubes are lines with chitin • some insects are so small they rely on diffusion to move O2 through the system; other rely on rhythmic body movements • major reason why open circulatory system works for insects.
Lungs • highly vascularized invaginations of the body surface • the circulatory system must transport oxygen from the lungs to the rest of the body • land snails use an internal mantle as a lung • spiders possess booklungs • frogs have simple balloon like w/ limited surface area • mammals have highly subdivided lungs with with a large surface area
Mammalian Respiratory Systems • lungs in thoracic cavity • surround by the plurallining – two layers held together by the surface tension of fluid between layers • air entering nostrils is filtered by cilia, warmed and moistened • travels through the pharynx, through the glottis, and into the larynx (which possesses vocal cords & a voice box)
Mammalian Respiratory Systems • enters the cartilage-lined trachea that forks into two bronchi which further branch into finer bronchioles that dead-end in alveoli • alveoli are lined with a thin layer of epithelium which serves as the respiratory surface • O2 dissolves in the moist film covering the epithelium & diffuses across the capillaries covering each alveolus • CO2 diffuses in the opposite direction
Ventilating the Lungs • vertebrates ventilate by breathing (alternate inhalation & exhalation of air) • frogs ventilate by positive air pressure – gulping air • mammals ventilate by negative air pressure • shallow inhalation results from contraction of the diaphragm (Figure 42.23)
Ventilating the Lungs • contraction of the rib muscles pulls the ribs upwards, which expands the rib cage • lung volume increases, resulting in negative pressure within the alveoli, causing air to rush in • exhalation occurs when diaphragm & rib muscles relax
Pneumatic Lungs of Birds • besides lungs, birds have 8 or 9 air sacs, which are present in the bones • functions: trims body density, act as heat sinks for heat dissipation by metabolism of flight muscles, serve as bellows, to keep air moving • air moves through the entire system in only one direction whether inhaling or exhaling thus providing a constant supply of oxygen
Breathing Control • breathing is automatic (thankfully!) • breathing control centers of the brain • 1) medulla oblongata • 2) pons • 10 – 14 times per minute • medulla’s control center also monitors blood and cerebrospinal pH • as CO2 concentrations increase, pH decreases
Respiratory Pigments • Oxygen transporting pigments: • 1) hemocyanin – arthropods & mollusks contains copper (rather than iron) which results in blue color • 2) myoglobin – a single subunit of heme found in the skeletal muscle • 3) hemoglobin – most vertebrates consists of four polypeptides with central iron-containing heme which binds O2
Cooperativity • the binding of O2 to hemoglobin is reversible • binding of O2 to one subunit of heme changes the shape which increases the affinity of the other three subunits for oxygen • the unloading of oxygen from one heme group results in conformational change that stimulates unloading from the other three
Carbon dioxide transport • CO2 is transported in three forms: • 1) dissolved CO2 in the plasma (7%) • 2) bound to the amino groups of hemoglobin (23%) • 3) as bicarbonate ions in the plasma (70%)
