1. 2018 Biology2
Chapter 22. Gas Exchange

2. MECHANISMS OF GAS EXCHANGE
Respiration is the interchange of O2 and CO2 between an organism and its environment

3. 22.1 Overview: Gas exchange involves breathing, the transport of gases, and the servicing of tissue cells
Gas exchange is essential because energy metabolism requires O2 and produces CO2
There are three phases of gas exchange
The O2/CO2 gas exchange involves the respiratory system and the circulatory system.

5. 22.2 Animals exchange O2 and CO2 through moist body surfaces
O2 enters an animal and CO2 leaves by diffusion through a respiratory surface
Respiratory surface: the part of an animal where O2 diffuses into the animal and where CO2 diffuses out to the surrounding environment
Respiratory surfaces are made up of a single layer of living cells
Respiratory surfaces must be moist

6. Some animals use their entire skin as a gas-exchange organ. e. g
Some animals use their entire skin as a gas-exchange organ. e.g., earthworm, flatworm
They lack specialized gas-exchange organs

7. In most animals, specialized body parts carry out gas exchange
1. Gill: extension or outfolding of the body surface specialized for gas exchange. e.g., most aquatic animals

8. 2. Trachea in insects
Extensive system of internal tubes specialized for gas exchange
Tracheae branch throughout the body, exchanging gases directly with body cells
The circulatory system is not needed for the gas exchange

9. 3. Lungs in most terrestrial vertebrates

10. 22.3 Gills are adapted for gas exchange in aquatic environments
Gills are extensions of the body that absorb O2 dissolved in water
In fish, gill filaments bear numerous platelike lamellae
Lamellae are packed with blood vessels
They are the respiratory surfaces

11. The structure of fish gills
Four gill arches on each side of the body
Two rows of gill filaments project from each gill arch
Each filament bears many plate-like structures called lamellae
Watermouthgillwater

13. Blood flows through the lamellae in a direction opposite to water flow
This countercurrent maintains a diffusion gradient that maximizes the uptake of O2
Blood flow through lamellae
Water flow over
lamellae
Countercurrent exchange
The transfer of something from a fluid moving in one direction to another fluid moving in the opposite direction

15. 22.4 The tracheal system of insects provides direct exchange between the air and body cells
Land animals exchange gases by breathing air
Air contains more O2 and is easier to move than water
But water loss from the respiratory surfaces can be a problem

16. Tracheal system
e.g., insects
The tracheal system of insects is made up of air tubes that branch throughout the body
Air tube Trachea
Tracheole
The tiny tips of the tracheoles are closed and contain fluid
The circulatory system is not involved in transporting O2
Air sac

18. Terrestrial vertebrates have lungs
e.g., reptiles, birds, mammals, and many amphibians
In contrast to the tracheal system, lungs are restricted to one location in the body  the circulatory system is required for transporting O2
The size and complexity of lungs are correlated with an animal’s metabolic rate
e.g., the surface area of respiration: endotherm > ectotherm
Amphibians have small lungs  respiration through the skin

19. 22.6 In the human respiratory system, branching tubes convey air to lungs located in the chest cavity
In humans and other mammals, air enters through the nasal cavity
It passes through the pharynx and larynx into the trachea
The trachea forks to form two bronchi
Each bronchus branches into numerous bronchioles
Lungs are located in the chest cavity
Diaphragm: contraction of the diaphragm  inhalation

20. The human respiratory system

21. The bronchioles end in clusters of tiny sacs called alveoli
Alveoli form the respiratory surface of the lungs (the inner surface of alveoli is lined with the simple squamous epithelium)
Oxygen diffuses through the thin walls of the alveoli into the blood

22. 22.7 Connection: Smoking is a serious assault on the respiratory system
Mucus and cilia in the respiratory passages protect the lungs
Pollutants, including tobacco smoke, can destroy these protections
Smoking kills about 430,000 Americans each year

23. Smoking causes lung cancer and contributes to heart disease
Smoking also causes emphysema
Cigarette smoke makes alveoli brittle, causing them to rupture
This reduces the lungs’ capacity for gas exchange

24. 22.8 Negative pressure breathing ventilates our lungs
Breathing is the alternation of inhalation and exhalation

25. Vital capacity is the maximum volume of air we can inhale and exhale
But our lungs hold more than this amount
The alveoli do not completely collapse
A residual volume of “dead” air remains in the lungs after exhalation
Figure 22.6C
Figure 22.6B
Oxygen-rich blood
Oxygen-poor blood
Alveoli
Blood capillaries
Bronchiole
In-and-out flow of air

26. 22.9 Breathing is automatically controlled
Breathing control centers are located in the medulla oblongata (연수, 숨뇌) and pons of the brain
These automatic controls keep breathing in tune with body needs
Basic breathing rhythm

27. Cerebrum
Forebrain
Thalamus
Cerebral cortex
Hypothalamus
Pituitary gland
Midbrain
Pons
Hindbrain
Medulla oblongata
Spinal cord
Cerebellum

28. During exercise, the CO2 level in the blood rises, lowering the blood pH
Sensors in aorta and
carotid arteries
Monitor O2 and CO2 levels in the blood as well as blood pH
Increase in the breathing rate and depth

29. 22.10 Blood transports the respiratory gases
TRANSPORT OF GASES IN THE BODY
Blood transports the respiratory gases
The heart pumps oxygen-poor blood to the lungs
In the lungs it picks up O2 and drops off CO2
In the tissues, cells pick up CO2 and drop off O2
Gases diffuse down pressure gradients in the lungs and the tissues

30. Gas exchange in the body
Atrium : 혈액이 들어오는 방
Ventricle : 혈액이 나가는 방
The right part of the heart handles oxygen-poor blood
The left part of the heart handles oxygen-rich blood
The exchange of gases between capillaries and the cells around them occurs by diffusion
High partial pressue  low partial pressure

31. Hemoglobin is a protein in red blood cells
It carries most of the oxygen in the blood

33. Bohr effect
Lungs
Tissues at rest
Tissues during exercise

34. 22.11 Hemoglobin carries O2, helps transport CO2, and buffer the blood
Hemoglobin helps buffer the pH of blood and carries some CO2

35. Most CO2 in the blood combines with water to form carbonic acid
TISSUE CELL
CO2 produced
INTERSTITIAL FLUID
CO2
BLOOD PLASMA WITHIN CAPILLARY
Capillary wall
H2O
H2CO3
Carbonic acid
RED BLOOD CELL
HCO3– + H+
Hemoglobin picks up CO2 and H+
Bicarbonate
Most CO2 in the blood combines with water to form carbonic acid
The carbonic acid breaks down to form H+ ions and bicarbonate ions
These help buffer the blood
Carbonic anhydrase in RBC
Figure 22.11A

36. Most CO2 is transported to the lungs in the form of bicarbonate ions
ALVEOLAR SPACE IN LUNG
CO2
H2O
H2CO3
HCO3– + H+
Hemoglobin releases CO2 and H+
Most CO2 is transported to the lungs in the form of bicarbonate ions
7% of CO2 is dissolved in plasma
23% binds to Hb
70% is converted to bicarbonate
Figure 22.11B

37. 22.12 Connection: The human fetus exchanges gases with the mother’s bloodstream
A human fetus depends on the placenta for gas exchange
O2, CO2, nutrients, wastes

38. A network of capillaries exchanges O2 and CO2 with maternal blood that carries gases to and from the mother’s lungs
At birth, increasing CO2 in the fetal blood stimulates the fetus’s breathing control centers to initiate breathing