Transcript Respiration ch 33

Respiration
CHAPTER 32
PAGES
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
Requirements for Diffusion
 Animal respiratory systems are diverse but all meet
three requirements that facilitate diffusion
1.
Respiratory surfaces remain moist so gases can diffuse across
cell membranes
2.
Cells lining respiratory surfaces are very thin, to facilitate
diffusion of gases through them
3.
Respiratory systems have a sufficiently large area in contact
with the environment to allow adequate gas exchange
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
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
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
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
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
Gas Exchange in Mammals
Oxygenated blood
Deoxygenated blood
1 Gases move in and out
of the lungs by breathing
CO2
O2
O2
O2
CO2
O2
2 O2 and CO2 are
exchanged in the
lungs by diffusion
O2
alveoli
(air sacs)
3 Gases dissolved
in the blood are
transported by the
circulatory system
left
atrium
right
atrium
right
ventricle
left ventricle
O2
CO2
CO2 CO2
CO2
CO2
4 O2 and CO2
are exchanged
in the tissues
by diffusion
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
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
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
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
Insects Breathe Using Tracheae
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
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
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
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
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
The Bird Respiratory System
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
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

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
pulmonary artery
(a) Human respiratory system
capillary
network
(b) Alveoli with capillaries
alveoli
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
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
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

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
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
Gas Exchange Between Alveoli and Capillaries
to the pulmonary vein
from the
pulmonary
artery
capillary
alveolar
membrane
respiratory
membrane
surfactant
fluid
(air)
CO2
O2
Oxygen diffuses into
the red blood cells
Carbon dioxide diffuses
into the alveolus
Animation: Gas Exchange in the Lungs
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
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

Oxygen Transport
(air in
alveolus)
alveolar
wall
surfactant
fluid
respiratory
membrane
red
blood
cells
O2
O2
hemoglobin
(plasma)
capillary
walls
cells of
body tissues
O2
(extracellular
fluid)
(a) O2 transport from the lungs to the tissues
Animation: Oxygen Transport
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
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–

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
Carbon Dioxide Transport
CO2
CO2
1
2
CO2
CO2
CO2
CO2
3
H2O CO2
5 HCO3–
CO2
+
H2O
H+
HCO3–
+
H+
CO2
HCO3–
4
CO2
(b) CO2 transport from the tissues to the lungs
Animation: Carbon Dioxide Transport
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

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
The Mechanics of Breathing
Air moves in
Rib cage
expands
Air moves out
Lungs
expand
Rib cage
contracts
Diaphragm
relaxes upward
Diaphragm
contracts downward
(a) Inhalation
Lungs
compress
(b) Exhalation
Animation: Breathing Mechanism
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