respiratory system chapter 49 Flashcards
Gas Exchange
One of the major physiological challenges facing all multicellular animals is obtaining sufficient oxygen and disposing of excess carbon dioxide
In vertebrates, the gases diffuse into the aqueous layer covering the epithelial cells that line the respiratory organs
Diffusion is passive, driven only by the difference in O2 and CO2 concentrations on the two sides of the membranes and their relative solubilities in the plasma membrane
Rate of diffusion between two regions is governed by Fick’s Law of Diffusion
R = Rate of diffusion
D = Diffusion constant
A = Area over which diffusion takes place
Dp = Pressure difference between two sides
d = Distance over which diffusion occurs
Evolutionary changes have occurred to optimize the rate of diffusion R
Increase surface area A
Decrease distance d
Increase concentration difference Dp
Gases diffuse directly into unicellular organisms
However, most multicellular animals require system adaptations to enhance gas exchange
Amphibians respire across their skin
Echinoderms have protruding papulae
Insects have an extensive tracheal system
Fish use gills
Mammals have a large network of alveoli
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Gills
Specialized extensions of tissue that project into water
Increase surface area for diffusion
External gills are not enclosed within body structures
Found in immature fish and amphibians
Two main disadvantages
Must be constantly moved to ensure contact with oxygen-rich fresh water
Are easily damaged
Gills of bony fishes are located between the oral (buccal or mouth) cavity and the opercular cavities
Some bony fish have immobile opercula
Swim constantly to force water over gills
Ram ventilation
Most bony fish have flexible gill covers
Remora switch between ram ventilation and pumping action
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Lungs
Gills were replaced in terrestrial animals because
Air is less supportive than water
Water evaporates
The lung minimizes evaporation by moving air through a branched tubular passage
A two-way flow system
Except birds
Atmospheric pressure is a combination of
the pressures of the different gases—N, O2, CO2
Partial pressure is the pressure contributed by a particular gas to the total atmospheric pressure
Lungs of amphibians are formed as saclike outpouchings of the gut
Frogs have positive pressure breathing
Force air into their lungs by creating a positive pressure in the buccal cavity
Reptiles have negative pressure breathing
Expand rib cages by muscular contractions, creating lower pressure inside the lungs
Lungs of mammals are packed with millions of alveoli (sites of gas exchange)
Inhaled air passes through the nasal passagepharynxglottis larynx tracheabronchibronchiolesalveoli
Bifurcates into the right and left bronchi, which enter each lung and further subdivide into bronchioles
Alveoli (greatly increase surface area) are surrounded by an extensive capillary network
Lungs of birds channel air through very tiny air vessels called parabronchi
Unidirectional flow
Achieved through the action of anterior and posterior sacs (unique to birds)
When expanded during inhalation, they take in air
When compressed during exhalation, they push air in and through lungs
Respiration in birds occurs in two cycles
Cycle 1 = Inhaled air is drawn from the trachea into posterior air sacs, and exhaled into the lungs
Cycle 2 = Air is drawn from the lungs into anterior air sacs, and exhaled through the trachea
Blood flow runs 90o to the air flow
Crosscurrent flow
Not as efficient as countercurrent flow
Cycle 1—inspiration = tracheaposterior air sacs
exhalation = posterior air sacs lungs
Cycle 2—lungs anterior air sacs trachea
Gas Exchange
Gas exchange is driven by differences in partial pressures
Blood returning from the systemic circulation, depleted in oxygen, has a partial oxygen pressure (PO2) of about 40 mm Hg
By contrast, the PO2 in the alveoli is about 105 mm Hg
The blood leaving the lungs, as a result of this gas exchange, normally contains a PO2 of about 100 mm
Lung Structure and Function
Outside of each lung is covered by the visceral pleural membrane
Inner wall of the thoracic cavity is lined by the parietal pleural membrane
Space between the two membranes is called the pleural cavity
Normally very small and filled with fluid
Causes 2 membranes to adhere
Lungs move with thoracic cavity
Ventilation—movement of air in and out of the lungs
Inverse relationship between volume and pressure.
Each breath is initiated by neurons in a respiratory control center in the medulla oblongata
Stimulate external intercostal muscles and diaphragm to contract, causing inhalation
When neurons stop producing impulses, respiratory muscles relax, and exhalation occurs
Muscles of breathing usually controlled automatically
Can be voluntarily overridden – hold your breath
Neurons are sensitive to blood PCO2 changes
A rise in PCO2 causes increased production of carbonic acid (H2CO3HCO3- + H+), lowering the blood pH
Stimulates chemosensitive neurons in the aortic and carotid bodies
Send impulses to respiratory control center to increase rate of breathing
Brain also contains central chemoreceptors (in hypothalamus) that are sensitive to changes in the pH of cerebrospinal fluid (CSF)
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Respiratory Diseases
Chronic obstructive pulmonary disease (COPD)
Refers to any disorder that obstructs airflow on a long-term basis
Asthma
Allergen triggers the release of histamine, causing intense constriction of the bronchi and sometimes suffocation
Chronic obstructive pulmonary disease (COPD) (cont.)
Emphysema
Alveolar walls break down and the lung exhibits larger but fewer alveoli
Lungs become less elastic
People with emphysema become exhausted because they expend three to four times the normal amount of energy just to breathe
Eighty to 90% of emphysema deaths are caused by cigarette smoking
Lung cancer accounts for more deaths than any other form of cancer
Caused mainly by cigarette smoking
Follows or accompanies COPD
Lung cancer metastasizes (spreads) so rapidly that it has usually invaded other organs by the time it is diagnosed
Chance of recovery from metastasized lung cancer is poor, with only 3% of patients surviving for 5 years after diagnosis
