1. Respiration
Chapter 32
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2. Why Exchange Gases? The act of breathing is called respiration
Cellular respiration converts the energy in nutrients into the ATP used by cells, requires oxygen and generates carbon dioxide as waste
The circulatory system works in with the respiratory system
The circulatory system extracts oxygen from the air in your lungs, carries it within diffusing distance of each cell, then picks up carbon dioxide for release from the lungs
Cellular respiration depletes O2 levels, creating a concentration gradient that favors the diffusion of CO2 out of cells and the diffusion of O2 into them

3. Requirements for Diffusion
Animal respiratory systems are diverse but all meet three requirements that facilitate diffusion
Respiratory surfaces remain moist so gases can diffuse across cell membranes
Cells lining respiratory surfaces are very thin, to facilitate diffusion of gases through them
Respiratory systems have a sufficiently large area in contact with the environment to allow adequate gas exchange

4. Evolutionary Adaptations for Gas Exchange
Some animals in moist environments lack specialized respiratory structures
The outside of the body is covered by a thin, gas-permeable skin, which provides an adequate surface area for the diffusion of gases
If the body is small and elongated (microscopic roundworms) gases need to diffuse only a short distance to reach all cells
An animal’s body may be thin and flattened, (flatworms) most cells are close to the moist skin

5. Invertebrate Gas Exchange
The slow rate of gas exchange by diffusion may suffice for a larger, thicker bodied organism if energy demands are low, as sea jellies, which can be large but require little O2
Another adaptation for gas exchange involves bringing the watery environment close to each cell - Sponges circulate seawater through channels within their bodies

6. Earthworms
For O2 delivery to cells, some animals combine a large skin surface area with well-developed circulation
In earthworms, gases diffuse through moist skin and are distributed throughout the body by a circulatory system
Blood in the skin capillaries rapidly carries off O2 that has diffused through the skin, maintaining a concentration gradient that favors the inward diffusion of oxygen
The worm’s elongated shape ensures a surface area relative to its internal volume

7. Respiratory Systems Facilitate gas exchange by diffusion
Most animals have evolved specialized respiratory systems that interface with circulatory systems to exchange gases between their cells and the environment
Transfer of gases between environment and body cells usually occurs in stages that alternate between bulk flow and diffusion
During bulk flow, liquids or gases move through large spaces, from areas of higher to lower pressure
This contrasts with diffusion, where molecules move individually from higher to lower concentrations

8. Gas Exchange Occurs in Stages
For animals with well-developed respiratory systems
Air or water moves past a respiratory surface by bulk flow (down a pressure gradient), this is usually facilitated by muscular movements such as breathing
O2 and CO2 are exchanged through the respiratory surface by diffusion
O2 diffuse into the capillaries of the circulatory system
CO2 diffuses out
Gases are transported between the respiratory system and tissues by the bulk flow of blood as it is pumped throughout the body
Gases are exchanged between tissues and the circulatory system by diffusion; at the tissue level, O2 moves out of the capillaries into tissues, and CO2 moves from the tissues to the capillaries

9. Gas Exchange in Mammals
Oxygenated blood
Gases move in and out
of the lungs by breathing 1
Deoxygenated blood
CO2 O2
O2 and CO2 are
exchanged in the
lungs by diffusion 2 O2 O2
CO2 O2 O2
alveoli
(air sacs)
Gases dissolved
in the blood are
transported by the
circulatory system 3
left
atrium
right
atrium
right
ventricle
left ventricle O2
CO2
CO2
CO2
O2 and CO2
are exchanged
in the tissues
by diffusion 4
CO2
CO2

10. Gas Exchange in Aquatic Environments
Gills are the respiratory structures of some aquatic animals
The simplest gills (amphibian) are thin projections of the body surface that protrude into the surrounding water
Elaborately branched or folded to increase surface area, have dense profusion of capillaries

11. Fish Gills Protected by a bony flap or operculum
Fish create a continuous current over their gills by pumping water into their mouths and ejecting it through the operculum
Countercurrent exchange - water and blood flow in opposite directions within the gill, maintaining a concentration gradient

12. Terrestrial Animals & Internal Structures
Internal respiratory structures are used by terrestrial animals to help keep the respiratory surfaces moist
Two examples are the tracheae in insects and lungs in vertebrates

13. Insects Respire Using Tracheae
Tracheae are elaborately branched internal tubes that deliver air to the body cells
Air enters tracheae though abdominal openings or spiracles
The spiracles open into tracheae that branch into smaller tubes (tracheoles), which deliver air close to each body cell for O2 and CO2 exchange
Some insects use abdominal contractions to enhance air movements into and out of spiracles

14. Insects Breathe Using Tracheae
body
cells
spiracles
air O2 O2
CO2
tracheoles
(a) Insect respiratory system
tracheae
tracheae
external
skeleton of
the insect
spiracle
spiracle
air
(b) Spiracle and tracheae
(c) Gas exchange pathway

15. Terrestrial Vertebrates Use Lungs
Lungs are chambers containing moist respiratory surfaces that are protected within the body, where water loss is minimized and the body wall provides support
The first lung probably developed to allow ancestral fish to survive in stagnant, oxygen-poor water
Amphibians use gills for respiration as aquatic larvae, and a simple, sac-like lung when they metamorphose into adult form

16. Reptiles and Mammals
Reptiles and mammals have relatively waterproof skin covered with scales, feathers, or fur – reducing water loss
This helps them survive in dry environments, but eliminates the skin as a respiratory organ
To compensate, the lungs of reptiles and mammals have a far larger surface area for gas exchange than do amphibians

17. Bird Lungs
Adaptations that allow exceptionally efficient gas exchange, providing O2 to support the demands of flight
Birds have 7-9 inflatable air sacs, which do not exchange gases but act as reservoirs
Bird lungs are rigid and filled with thin-walled tubes (parabronchi), that are open at both ends, allowing air to flow completely through the lungs
The parabronchi are surrounded by tissue riddled with microscopic spaces and a dense capillary network that allows gas exchange

18. Bird Lung Structure
The organization of the bird air sacs and lungs allows one-way flow of fresh, oxygenated air through the lungs, from posterior to anterior, both as the bird inhales and exhales
Inhalation inflates the air sacs, drawing fresh air to the posterior sacs via a route that bypasses the lungs
Air from the posterior air sac is pushed into the lungs, where O2 is extracted
Used air is pulled out of the lung, and as the bird exhales, the air sacs deflate, forcing the used air through the bird’s nostrils
Fresh air for the posterior sac then enters the lungs
Bird receives fresh air both when inhaling and when exhaling

19. The Bird Respiratory System

20. Human Respiratory System
Divided into two parts
Conducting portion, a series of passageways that carry air into and out of the gas-exchange portion of the respiratory system
Gas-exchange portion, where gases are exchanged with the blood in tiny sacs within the lungs

21. Conducting Portion
Carries air to the lungs and contains the apparatus that makes speaking possible
Air enters through the nose or mouth and passes through the nasal or oral cavity into the pharynx , travels to the larynx, or “voice box,”
The opening to the larynx is guarded by the epiglottis, a flap of tissue supported by cartilage which prevents food from entering the larynx when swallowing
During normal breathing, the epiglottis is tilted upward, allowing air to flow into the larynx
During swallowing, the epiglottis folds downward and covers the larynx, directing substances into the esophagus

22. The Human Respiratory System
bronchiole
pulmonary arteriole
nasal cavity
pulmonary venule
pharynx
epiglottis
oral cavity
larynx
esophagus
trachea
rings of
cartilage
bronchioles
bronchi
pulmonary veins
diaphragm
capillary
network
pulmonary artery
alveoli
(a) Human respiratory system
(b) Alveoli with capillaries

23. Don’t inhale and swallow at the same time.
The Heimlich maneuver
If an individual inhales and swallows at the same time, food can become lodged in the larynx, blocking air from entering the lungs
The use of the Heimlich maneuver clears the obstruction

24. Making Sound
Within the larynx are the vocal cords, bands of elastic tissue controlled by muscles
Muscular contractions cause the vocal cords to partially obstruct air passage through the larynx
Exhaled air causes the vocal cords to vibrate, producing the tones of speech or song
Stretching the cords changes the pitch of the tones, which can be articulated into words by movements of the tongue and lips

25. Human Respiration Structure
Inhaled air travels past the larynx into the trachea, a flexible tube with walls are reinforced with semicircular bands of stiff cartilage
Trachea splits into 2 bronchi, one leading to each lung
Inside the lung, each bronchus branches repeatedly into smaller tubes called bronchioles
Bronchioles lead to microscopic alveoli, tiny air sacs where gas exchange occurs

26. Gas Exchange Occurs in the alveoli
Alveoli cluster at the end of each bronchioles (think:grapes) , providing 1,500 square feet of surface area for diffusion
A network of capillaries covers the alveolar surface
The walls of the alveoli consist of a single thin layer of epithelial cells
The respiratory membrane, through which gases diffuse, consists of epithelial cells of the alveoli and the endothelial cells that form the wall of the capillary, across which gas exchange occurs

27. Alveoli Well adapted for gas exchange
Alveolar walls and capillary walls are only one cell thick, gases diffuse a short distance to move between the environment and blood
Alveoli are coated with a thin layer of watery fluid containing surfactant, which prevents the alveolar surfaces from sticking together and collapsing when air is exhaled
Gases dissolve in this fluid as they pass in and out of the alveolar air
Surfactant - compounds that lower the surface tension

28. Gas Exchange Between Alveoli and Capillaries
to the pulmonary vein
from the
pulmonary
artery
capillary
alveolar
membrane
respiratory
membrane
(air)
CO2 O2
surfactant
fluid
Oxygen diffuses into
the red blood cells
Carbon dioxide diffuses
into the alveolus

29. Animation: Gas Exchange in the Lungs

30. How are O2 and CO2 Transported?
Oxygen and carbon dioxide are transported in blood using different mechanisms
Blood picks up oxygen from the air in the lungs and supplies it to the body tissues, simultaneously absorbing CO2 from the tissues and releasing it into the lungs
These exchanges occur because diffusion gradients favor them
In the lungs, O2 is high and CO2 is low, whereas in body cells, CO2 is high and O2 is low

31. Oxygen Transport 90% of O2 carried by the blood, bound to hemoglobin
Each hemoglobin molecule can carry up to four O2 molecules, each bound to one of four iron-containing heme groups
As oxygen binds hemoglobin, the protein changes its shape, which alters its color
Oxygenated blood is bright cherry-red
Deoxygenated blood is maroon-red

32. Oxygen Transport surfactant fluid (air in alveolus) respiratory
membrane
red
blood
cells O2
alveolar
wall O2
hemoglobin
cells of
body tissues
(plasma)
capillary
walls O2
(extracellular
fluid)
(a) O2 transport from the lungs to the tissues

33. Animation: Oxygen Transport

34. Carbon Dioxide Transport
CO2 from cellular respiration in the body cells diffuses into nearby capillaries, then is carried in the bloodstream to the respiratory membranes of the alveoli
Alveolar capillaries have a higher CO2 concentration than that of the alveolar air
Thus, CO2 diffuses down a concentration gradient into the alveolar air, which is exhaled

35. Carbon Dioxide is Transported 3 Ways
As bicarbonate ions (70%)
Bound to hemoglobin (20%)
Dissolved in plasma as CO2 (10%)
Bicarbonate ions (HCO3–) are formed in red blood cells when CO2 combines with water, using the enzyme carbonic anhydrase
CO2 + H2O  CO2 + HCO3–

36. The reaction producing bicarbonate ions is reversed as the blood flows through capillaries surrounding the alveoli, where CO2 is low:
H+ + HCO3–  CO2 + H2O
As CO2 leaves the blood and diffuses into the alveoli, it diffuses back into red blood cells, where it recombines with H+, regenerating CO2 and H2O
The CO2 then diffuses into the air in the alveoli, which is exhaled from the lungs while the H2O remains in the blood

37. Carbon Dioxide Transport1
CO2
CO2
CO2 2
CO2
CO2
CO2 3
H2O
CO2
HCO3– + H+ 5
HCO3–
CO2
CO2 +
H2O H+
HCO3– 4
CO2
(b) CO2 transport from the tissues to the lungs

38. Animation: Carbon Dioxide Transport

39. Inhalation, Exhalation
Air is inhaled actively and exhaled passively
Breathing occurs in two stages
Inhalation, when air is drawn into the lungs
Exhalation, when air is expelled from the lungs
Inhalation occurs when the chest cavity is enlarged
The lower boundary of the chest cavity is formed by the diaphragm, which domes upward when relaxed
During inhalation, the diaphragm is contracted, which pulls it downward, and the rib muscles contract, lifting the ribs up and outward

40. Exhalation
Exhalation occurs spontaneously, when the muscles that cause inhalation are relaxed
As the diaphragm relaxes, it domes upward; at the same time, the ribs fall down and inward
These movements decrease the size of the chest cavity and force air out of the lungs

41. The Mechanics of Breathing
Air moves in
Air moves out
Rib cage
contracts
Rib cage
expands
Lungs
compress
Lungs
expand
Diaphragm
contracts downward
Diaphragm
relaxes upward
(a) Inhalation
(b) Exhalation

42. Animation: Breathing Mechanism

43. Breathing Rate Controlled by the respiratory center of the brain
Located in the medulla portion of the brain, just above the spinal cord
Nerve cells in the respiratory center generate cyclic action potentials that cause contractions (followed by passive relaxation) of respiratory muscles
The respiratory center receives input from sources and adjusts the breathing rate and volume to meet the body’s needs
Primarily modified by CO2 receptors located in the medulla that adjust the breathing rate to maintain a constant low level of CO2 in the blood, while also ensuring that O2 levels remain adequate
As a backup system, there are also O2 receptors in the aorta and carotid arteries that stimulate the respiratory center to increase the rate and depth of breathing if O2 levels in the blood drop