Transcript Gas Exchange and Circulation

Gas Exchange and Circulation
Diversity amongst humans, fish
and insects.
Gas Exchange
Cells need energy in order to continue living. Sugars and other substances
that are broken down metabolically in cellular respiration release energy
into the cells. During this process gases need to be exchange between the
environment and the cells. CO2 and O2 are the gases exchanged in most
organisms with gas exchange surfaces in multi-cellular organisms
providing a way for gases to come into and exit the body. Some organisms
use their whole body surface as an exchange system while many
organisms have developed special gas exchange structures such as lungs
or gills.
Lung Structure
The nasal passage warms and
moistens the air that travels into
the body through the nostrils with
the nostril hairs filtering out
unwanted particles.
The air that enters the body through the
mouth mixes with the air from the
nasal passages in the pharynx.
In front of the oesophagus lies the
trachea which extends into the
thorax. C shaped bands of
cartilage strengthen it with a layer
of ciliated epithelium.
The trachea splits into two Bronchi
which are also supported by
cartilage bands.
Bronchioles stem off from the Bronchi
and continue to divide into smaller
and smaller branches. Less and
less cartilage is used on each new
branch.
Lung structure continued
Terminal Bronchiole structure
Lungs: Are internal sac-like organs which play a
major role in respiration and are where gas
exchange occurs. They are found in most
amphibians and all reptiles, birds and
mammals.
Ciliated epithelium: Ciliated, mucus secreting
epithelium lines the trachea, bronchi and
Bronchioles trapping and removing dust and
pathogens before they reach the gas
exchange surfaces.
Terminal Bronchiole: the Bronchiole end in the
terminal Bronchiole which have 2-11
alveolar ducts attached to them which in
turn have many alveoli attached to them.
This creates an extremely large surface area
(70m²) for gas exchange to take place.
Gas Exchange In Humans
In the human lung gas exchange occurs by diffusion
between the alveoli and the blood in the capillaries. Gases
move freely across the respiratory membrane which is a
junction between the alveolar cells and the cells of the
capillary. Elastic connective tissue gives the alveoli their
ability to expand and recoil. There is an estimated 300 million
alveoli which have a huge surface area for gas exchange to
take place; 70m². This gas exchange of oxygen and carbondioxide results in the reoxygenation of the blood coming from
the heart (by the pulmonary artery). This oxygenated blood
returns to the heart by the pulmonary veins and is then
distributed around the rest of the body.
Respiratory
membrane.
Gas Exchange in Fish
Fish have to obtain the oxygen they need from
water using gills. Gills are membranous structures
supported by cartilaginous or bony struts. The gills
have a big surface and as the water flows over this
the respiratory gases are exchanged between the
blood and the water. There is a far less
percentage of oxygen in water than there is in the
air. Air is 21% oxygen while the same volume of
water is 1% dissolved oxygen. An active aquatic
organism such as a fish need to extract high rates
of oxygen from the water in order to survive. This
is achieved by pumping water across the gills or
swimming continuously with the mouth open. The
gills of a fish have lots of folds which are
supported and kept apart by the water. This
creates a high surface area for gas exchange. Gas
exchange occurs by diffusion between the water
and the blood vessels inside the gill across the gill
membrane and capillaries. The operculum also
known as the gill cover allows for the exit of water
and acts as a pump drawing water past the gill
filaments. Fish gills are highly efficient and achieve
an oxygen extraction rate of 80% which is three
times our own from air.
Gas Exchange in Insects
Tracheal Systems
Insects in general are small terrestrial animals, so
they have a large surface area to volume ratio. In
terrestrial arthropods tracheal systems are the
most common type of gas exchange organs.
Most body segments of the insect have spiracles
(max 20) down their sides (the entrance/exits of the
gas exchange system). Filtering devices prevent
small particles found in the air from clogging the
respiration system and a valve controls the degree
to which a spiracle is open. Large, active insects
such as locusts tracheal systems include air sacs
which compress and expand like a bellows to aid
the movement of air through the tubules.
The air containing oxygen moves through the
spiracles down the tracheal tubes that branch off
into the tracheoles. The gases in the air move by
diffusion across the moist lining directly to and from
tissues. The end of the tubes contain small amounts
of fluid where the respiratory gases are dissolved.
The fluid gets drawn into the muscle tissue during
contraction and is released back into the tracheole
when the muscle rests. Insects make rhythmic body
movements to help move air in and out of the
tracheae.
The Circulatory System
Large complex organisms require circulatory systems to transport materials
around their bodies as diffusion would be too slow and inefficient and would
inconsistently supply the cells in the body with the materials required e.g.
oxygen. The main parts of the circulatory system are blood, a heart and
blood vessels this system transports nutrients, oxygen, carbon dioxide,
wastes and hormones. The circulatory system also maintains fluid balance,
regulates body temperature and can aid in the body’s resistance to harmful
microorganisms.
Circulatory Systems
There are two basic types of circulatory systems that have evolved in
animals; open circulatory systems and closed circulatory systems. Many
invertebrates such the arthropods have open circulatory systems which
are not only used as transport systems but are important to hydraulic
movements of the whole body. Humans and other vertebrates have
closed circulatory systems also known as cardiovascular systems
because they contain a heart and a network of tube-like vessels. Closed
circulatory systems can be can be single circuit systems or double
circuit systems.
Open Circulation system
Arthropods and most molluscs except for squid and octopus all have open
circulatory systems. These organisms all have tube or sac-like hearts. The
heart pumps blood through short vessels into the sizable spaces in the
body cavity. The organisms cells are then soaked in the blood before the
blood reenters the heart through holes called ostia. The circulation of the
blood is aided by muscle movements.
Insects have open circulatory systems
Ostium are holes
for the uptake of
blood
The tubular heart is stretched across the
top (dorsal surface) of the animal and
circulating fluids get pumped towards the
head.
One way valves in the heart ensure the
blood moves in a forward circulation.
Body fluids flow freely within the body cavity.
Closed, Single Circuit Systems
Oxygen moves
into the blood
Deoxygenated blood
oxygenated blood
Blood in closed circulation systems are held
in blood vessels and the blood is returned to
the heart after every circulation of the body.
The fluids which bath the cells exchange
substances with the blood by diffusion across
capillaries. In fish the blood goes directly from
the gills to the body with the blood losing
pressure at the gills and flowing at low
pressure around the body.
Oxygen moves
into the tissues
Fish have closed single circuit systems
oxygenated blood
Deoxygenated blood
Closed, Double Circuit Systems
All vertebrates besides fish have
closed double circuit systems. The
blood gets pumped through a
pulmonary circuit to the lungs where
it is oxygenated the blood then
returns to the heart which pumps the
oxygenated blood through a
systematic circuit through the body.
In amphibians and most reptiles
there is some mixing of oxygenated
and deoxygenated blood in the heart
as it is not completely divided. In
birds and mammals there is no
mixing.
The Heart
The heart is the centre of the cardiovascular system. Insects have a tubular heart
(see the open circulatory system slide), fish have linear hearts and humans and
mammals have fully partitioned hearts.
The human Heart
The human heart is a hollow muscular
organ, it beats over 100 000 times a
day to pump 3780 litres of blood
through our 100 000km of blood
vessels. The heart is made up of four
muscular chambers which alternate
between filling and emptying of blood
and act as a double pump. The left
side pumps oxygenated blood to the
body tissues while the right pumps
deoxygenated blood to the lungs. The
upper chambers are the atria (right
and left) and the lower chambers are
the ventricles (right and left). Both
upper and lower chambers are
separated by a partition or septum.
Coronary arteries branch off from the
aorta and provide circulation for the
heart muscle itself.
The Fish Heart
Fish have linear hearts, which are
made up of a sequence of three
chambers in a series. (in some cases
the conus/bulbus arteriosus may be
included as a fourth chamber.) Blood
from the fishes’ body enters the heart
through its sinus venosus, then passes
into the atrium and the ventricle. A
series of one way valves situated
between the chambers prevents blood
from flowing in reverse.
Bibliography
Slide 3:
http://www.cartage.org.lb/en/themes/Sciences/LifeScience/GeneralBiology/Physiology/RespiratorySystem/Human
Respiratory/humrespsys_1.gif
Slide 4:
http://content.answers.com/main/content/wp/en/thumb/1/19/300px-Alveoli_diagram.png
Slide 5:
http://www.healthandage.com/html/res/primer/pics/l3.gif
http://upload.wikimedia.org/wikipedia/commons/thumb/8/8b/Alveoli.svg/300px-Alveoli.svg.png
Slide 6:
http://www.examstutor.com/biology/resources/studyroom/organs_and_systems/gas_exchange/pictures/fig144b_s
maller.gif
Slide 7:
http://www.dwm.ks.edu.tw/bio/activelearner/44/images/ch44c3.jpg
Slide 10:
http://blood-system-atlas.net/types/im2.gif
Slide 11:
http://www.biosci.uga.edu/almanac/bio_104/notes/may_7.html.
Slide 12:
http://www.mikalac.com/tech/sci/pho/circulatorysystem.gif
Slide 14:
http://cache.eb.com/eb/image?id=72171&rendTypeId=35
Slide 15:
http://www.cartage.org.lb/en/themes/sciences/zoology/ClassesFish/ClassesFish/fishheart.gif
Helpful books: Year 12 Biology Biozone 2008