exchange surfaces Flashcards
1
Q
What are exchange surfaces?
A
Surfaces over which materials are
exchanged from one area to another
2
Q
What is surface area to volume
ratio (SA:V)?
A
The surface area of an organism divided by its volume As size increases.. • Surface area increases • Volume increases, more quickly than surface area • Surface area to volume ratio decreases
2
Q
What is surface area to volume
ratio (SA:V)?
A
The surface area of an organism divided by its volume As size increases.. • Surface area increases • Volume increases, more quickly than surface area • Surface area to volume ratio decreases
3
Q
Why is diffusion alone enough
to supply single-celled
organisms?
A
• Single-celled organisms have low metabolic activity, so oxygen demands are carbon dioxide production of the cell are relatively low • They have a large surface area to volume ratio (SA:V)
4
Q
Why do multicellular organisms
require specialised exchange
surfaces?
A
• Small SA:V ratio • Distance is too far for effective diffusion to take place • Diffusion is too slow for the oxygen and nutrients to diffuse across the whole organism • Surface area is no longer large enough to supply the needs of the larger volume • Multicellular organisms are also metabolically active
5
Q
List the features of effective
exchange surfaces
A
• Increased surface area • Thin layers • Good blood supply • Ventilation to maintain diffusion gradient
6
Q
Why do exchange surfaces
have increased surface area?
A
Provides the area needed for exchange and overcomes the limitations of the SA:V ratio of larger organisms • e.g. root hair cells in plants, and villi in the small intestine
7
Q
Why do exchange surfaces
have thin layers?
A
These mean the distances substances have to diffuse are short, making the process fast and efficient • e.g. alveoli in the lungs, and villi of the small intestine
8
Q
Why do exchange surfaces
have good blood supply?
A
The steeper the concentration gradient, the faster diffusion takes place • Having a good blood supply ensures substances are constantly delivered to and removed from the exchange surface • This maintains a steep concentration gradient for diffusion • e.g. the alveoli of the lungs, the gills of a fish, and the villi of the small intestine
9
Q
Why do exchange surfaces
have ventilation?
A
• For gases, a ventilation system helps maintain concentration gradients and makes the process more efficient • e.g. the alveoli, and gills of a fish where ventilation means a flow of water carrying dissolved gases
10
Q
Describe mammals
A
• Relatively big; small SA:V ratio and large volume of cells • High metabolic rate because they are active and maintain their body temperature • Therefore need lots of O2 for cellular respiration and produce CO2 which needs to be removed
11
Q
Describe the features of the
nasal cavity
A
• Large surface area with good blood supply which warms the air to body temperature • Hairy lining which secretes mucus to trap dust and bacteria • Moist surfaces which increase humidity of incoming air, reducing evaporation from the exchange surfaces
12
Q
What is the trachea?
A
The main airway, supported by
incomplete rings of cartilage, which
carries warm moist air down from
the nasal cavity into the chest
13
Q
Describe the function of
cartilage supporting the
trachea
A
Incomplete rings of strong, flexible cartilage, which stop the trachea from collapsing • Rings are incomplete so that food can move easily down the oesophagus behind the trachea
14
Q
Describe the lining of the
trachea and its branches
A
Lined with a ciliated epithelium with goblet cells between and below the epithelial cells • Goblet cells secrete mucus onto the lining of the trachea • Cilia beat and move the mucus along with anything trapped, away from the lungs • Most of it goes into the throat, is swallowed and digested • Cigarette smoke stops these cilia beating
15
Q
Describe the bronchi
A
Similar to the trachea, with the same
supporting rings of cartilage, but
they are smaller. Cartilage rings are
complete here
16
Q
Describe the bronchioles
A
• Smaller bronchioles (diameter >1mm) have no cartilage rings • Walls contain smooth muscle; contracts: the bronchioles constrict (close), relaxes: they dilate (open) • This changes amount of air reaching the lungs • Lined with a thin layer of flattened epithelium making some gas exchange possible
17
Q
What are alveoli?
A
Tiny air sacs which are the main gas exchange surfaces of the body • Unique to mammalian lungs • Each has a diameter of 200-300μm and consists of: • Thin layer of flattened epithelial cells, along with some collagen and elastic fibres (composed of elastin)
18
Q
What if the function of elastic
tissues in the alveoli?
A
• They allow the alveoli to stretch as air in drawn in • When they return to their resting size, they help squeeze the air out • This is known as the elastic recoil of the lungs
19
Q
• They allow the alveoli to stretch as air in drawn in • When they return to their resting size, they help squeeze the air out • This is known as the elastic recoil of the lungs
A
- 300-500 million alveoli per adult
lung. Alveolar surface area for
gases exchange in the 2 lungs
combined is 20-75m2 - Both alveoli and the surrounding
capillaries are only 1 epithelial
cell thick, so the diffusion
distance is very short - Surrounded by a network of 280
million capillaries. Constant flow
of blood maintains a steep
concentration grades for CO2
and O2 - breathing moves air in and out of
the alveoli, helping to maintain
steep diffusion gradients
20
Q
What is the inner surface of the
alveoli covered in?
A
A thin layer a solution of water, salts and lung surfactant • O2 dissolves in the water before diffusing into the blood, but water can also evaporate into the air in the alveoli • Several of the adaptations of the human gas exchange system are to reduce this loss of water
21
Q
What is lung surfactant?
A
Chemical mixture containing phospholipids and both hydrophobic and hydrophilic proteins, which coats the surfaces of the alveoli and prevents them collapsing after every breath
22
Q
Describe the following 1. Rib cage 2. Diaphragm 3. External & Internal intercostal muscles 4. Pleural membranes 5. Pleural cavity
A
• Rib cage: Provides a semi-rigid case within which pressure can be lowered with respect to the air outside it • Diaphragm: Broad, domed sheet of muscle, the floor of the thorax • External & Internal Intercostal muscles found between the ribs • Pleural membranes: line the thorax, surround the lungs • Pleural cavity: Usually filled with a thin layer of lubricating fluid so the membranes slide easily over each other as you breathe
23
Q
What happens in inspiration
(inhaling)?
A
Diaphragm contracts to move down and become flatter - this displaces the digestive system organ downwards • External intercostal muscles contract to raise the ribs • Volume of chest cavity increases • Pressure in the chest cavity drops below the atmospheric pressure • Air is moved into the lungs
24
What is expiration (exhaling)?
```
• Diaphragm relaxes and is pushed
up by the displaced organs
underneath
• External intercostal muscles
relaxed and rises falls; internal
intercostal muscles can contract
to help push air out more forcefully
(only happens during exercise, or
coughing and sneezing)
• Volume of chest cavity decreases
• Pressure in the lungs increases
and rises above pressure in the
surrounding atmosphere
• Air is moved out of the lungs
```
25
Describe 3 ways of measuring
| the capacity of the lungs
```
• Peak flow meter; device that
measure the rate at which air can
be expelled from the lungs
• Vitalographs; more sophisticated
peak flow meter, produces graph
of amount of air breathed out and
how quickly. Volume of air is called
forced expiratory volume in 1
second
• Spirometer
```
26
How does a spirometer work?
```
1. Subject should wear a nose clip
to ensure no O2 escapes from
the system and no additional air
is added
2. Subject breathes through the
mouth piece
3. As the subject inhales, O2 is
drawn from the air chamber
which therefore descends
4. As the subject exhales, the air
chamber rises again
5. Air returning to the air chamber
passes through the canister of
soda lime which absorbs CO2
6. Movements of the air chamber
are recorded by a data logger or
on a revolving drum
```
27
Define the following
```
1. Tidal volume: Volume of air that
moves into and out of the lungs
with each resting breath. About
500cm3, which uses 15% of the
vital capacity of the lungs
2. Vital capacity: Volume of air that
can be breathed in when the
strongest possible exhalation is
followed by the deepest possible
intake of breath
3. Inspiratory reserve volume:
Maximum volume of air you can
breathe in over and above a
normal inhalation
4. Expiratory reserve volume: Extra
amount of air you can force out
of your lungs over and above the
normal tidal volume of air you
breathe out
5. Residual volume: Volume of air
that is left in your lungs when
you have exhaled as hard as
possible. This can’t be measured
directly
6. Total lung capacity: The sum of
the vi
```
27
Define the following
```
1. Tidal volume: Volume of air that
moves into and out of the lungs
with each resting breath. About
500cm3, which uses 15% of the
vital capacity of the lungs
2. Vital capacity: Volume of air that
can be breathed in when the
strongest possible exhalation is
followed by the deepest possible
intake of breath
3. Inspiratory reserve volume:
Maximum volume of air you can
breathe in over and above a
normal inhalation
4. Expiratory reserve volume: Extra
amount of air you can force out
of your lungs over and above the
normal tidal volume of air you
breathe out
5. Residual volume: Volume of air
that is left in your lungs when
you have exhaled as hard as
possible. This can’t be measured
directly
6. Total lung capacity: The sum of
the vi
```
28
What is breathing rate?
The number of breaths taken per
| minute
29
What is ventilation rate?
tidal volume x breathing rate (per
| minute)
30
How is oxygen uptake
| calculated?
```
• As CO2 is removed, the total
volume in the air chamber
decreases
• the volume of O2 absorbed is
shown by the difference in height
between the last peak from the
first peak during normal breathing
• Divide this volume by time taken in
order to calculate the rate of
oxygen uptake
```
31
What happens when the
oxygen demands of the body
increase?
```
Tidal volume of air moved in and out
of the lungs with each breath can
increase from 15%- 50%. Breathing
rate also increases. Ventilation of the
lungs and so O2 uptake during
gaseous exchange can be increased
to meet demands of tissues
```
32
Describe insects
```
• Very active during parts of their life
cycles
• Land-dwelling animals with
relatively high O2 requirements
• Tough exoskeleton through which
little or no gaseous change
• Don’t usually have blood pigments
that can carry O2
• Gas exchange system delivers O2
directly to the cells and removes
CO2 in the same way
```
33
What are spiracles?
```
Small openings along the thorax and
abdomen of an insect that open and
close to control amount of air
moving in and out of the gas
exchange system, and water loss
from the exchange surfaces
• Spiracles can be opened or closed
by sphincters
• Spiracle sprinters are kept closed
as much as possible to minimise
water loss
```
34
What are the tracheae?
```
Largest tubes of insect respiratory
system
• Up to 1mm in diameter
• Carry air into the body
• Run both into and along the body
of the insect
• Tubes are lined by spirals of chitin,
which keep the open if they are
bent or pressed
• Chitin is relatively impermeable to
gases, so little gas exchange takes
place in the trachea
```
35
What are tracheoles?
```
• Minute tubes of diameter
0.6-0.8μm
• Each tracheal is a single elongated
cell with no chitin lining, so they
are freely permeable to gases
• Spread through ought the tissues
of the insect, running between
individual cells
• Where most of gas exchange
takes place between air and the
respiring cells
• Vast number gives very large
surface area for GA
• O2 dissolves on moisture on the
walls of tracheoles and diffuses
into surrounding cells
```
36
What is tracheal fluid?
```
Fluid found at the ends of the
tracheoles in insects that helps to
control the surface area available for
gas exchange and water loss.
• Gas exchange occurs between the
air in the tracheole and tracheal
fluid
```
37
How does gas exchange take
| place in insects?
```
1. Insects don’t transport O2 in
blood
2. They have an air-filled tracheal
system that supplies air directly
to all the respiring tissues
3. Air enters the system via pores
called spiracles
4. Air passes through the body in a
series of tubes called tracheae
5. These divide into smaller tubes
called tracheoles
6. The end of the tracheoles open
into tracheal fluid
7. Gas exchange occurs between
the air in the tracheole and the
tracheal fluid
```
38
What happens when oxygen
| demands build up?
```
• e.g when the insect is flying
• A lactic acid build up in the tissues
results in water moving out of the
tracheoles by osmosis
• This exposes more surface area
for gas exchange
```
39
How do larger insects increase
the level of gas exchange to
supply the extra oxygen they
need?
```
Mechanical ventilation of the
tracheal system:
• Air is actively pumped into the
system by muscular pumping
movements of the thorax/
abdomen
• Movements change the volume of
body and this changes pressure in
tracheae and tracheoles
• Air is drawn into the trachea and
tracheoles, or forced out, as the
pressure changes
Collapsible enlarged tracheae or air
sacs which act as air reservoirs:
• Used to increase the amount of air
moved through the gas exchange
system
• Usually inflate and deflated by the
ventilating movements of the
thorax and abdomen
```
40
What are the extra difficulties
fish respiratory systems have
to overcome?
```
• Water is 1000 times denser than
air
• Water is 100 times more viscous
than air
• Water has a much lower oxygen
content than air
```
41
Describe bony fish
```
e.g. trout and cod
• Relatively big, active animals that
live almost exclusively in water
• Active so have a high O2 demand
• Their SA:V ratio means that
diffusion is not enough to supply
inner cells with O2 they need
• Scaly outer covering doesn’t allow
gas exchange
```
42
What are gills?
```
The gaseous change organs of fish,
comprised of gill plates, gill
filaments and gill lamellae.
• They have the large surface area,
good blood supply, and thin layers
needed for successful gas
exchange
• Contained in a gill cavity and are
covered by protective operculum,
which is also active in maintaining
a flow of water over the gills
```
43
How are the gills adapted for
| successful gas exchange?
```
• Efferent blood vessel carries the
blood leaving the gills in the
opposite direction to the incoming
water, maintaining a steep
concentration gradient
• Each gill consists of 2 rows of gill
filaments (primary lamellae)
attached to a gill arch. Their rich
blood supply and large surface
area, are the main site of gas
exchange in the fish
• Gill filaments are very thin, and
their surface is folded into many
secondary lamellae (gill plates) and
need a flow of water to keep them
apart, exposing the large surface
area needed for gas exchange
```
44
What happens when the mouth
| is opened?
```
• Floor of buccal cavity is lowered
• Increases volume of buccal cavity
• Pressure in the cavity drops and
water moves in
• Opercular valve shuts, opercular
cavity containing gills expands
• This lowers pressure in opercular
cavity containing gills
• Floor of buccal cavity starts to
move up, increasing pressure
there so water moves from buccal
cavity over the gills
```
45
What happens when the mouth
| closes?
```
• Operculum opens and sides of
opercular cavity move inwards
• Pressure in opercular cavity
increases
• Water is forced over the gills and
out of the operculum
• Floor of buccal cavity is steadily
moved up, maintaining a flow of
water over the gills
```
46
What are 2 other adaptations
of gills that ensure most
effective gas exchange occurs
in water?
```
Tips of adjacent gill filaments
overlap
• Increases resistance to the flow of
water over the gill surfaces and
slows down movement of water
• More time for gas exchange to
take place
Countercurrent flow (water moving
over the gills and the blood in the gill
filaments flow in opposite directions)
• Steeper concentration gradients
maintained than parallel system
• Concentration gradient maintained
all along gill
• Bony fish remove 80% (CC),
Cartilaginous fish remove 50% (P)
```
