Chapter 7 Exchange Surfaces and Breathing Flashcards
What is the need for exchange surfaces?
Diffusion isn’t enough alone to supply the needs of single celled organisms because - 1. Metabolic activity of single cell is low
2. SA:V of an organism is large.
How does SA:V change?
As organisms get bigger the surface area to volume ratio decreases.
What features of large organisms are specific for specialised exchange surfaces?
Increased surface area - gives the area needed to overcome the limits of low SA:V
Thin layers - less distance for substances to travel through
Good blood supply - keeps the concentration gradient is steep always
Ventilation to maintain diffusion gradient - helps maintain concentration gradient
The human gas exchange system explained
Mammals are big - small SA:V, large number of cells
also have a high metabolic rate
they need lots of oxygen for cellular respiration and they produce carbon dioxide which needs to be removed.
Exchange takes place in the lungs.
Nasal Cavity features and functions
large surface area with a good blood supply, which warms the air to body temperature
a hairy lining - secretes mucus to trap dust and bacteria
moist surfaces - increase the humidity of incoming air reducing evaporation from the exchange surfaces.
Trachea
The main airway - a wide tube supported by strong flexible cartilage, which stop it from collapsing. incomplete rings so food can move down oesophagous easily.
Trachea lined with ciliated epithelium with goblet cells. Cigarette smoke stops these cilia beating.
Bronchus
Similar structure to trachea but smaller.
They divide into two leading to each lung.
left bronchus and right bronchus.
Bonchioles
small with 1mm diameter. no cartilage
made of smooth muscle.
when smooth muscle contracts the bronchioles constrict.
This changes the amount of air reaching the lungs.
They have a thing layer of flattened epithelium making some gas exchange possible.
What are the alveoli
tiny air sacs.
0.2mm in diamter
has a layer of epithelial cells, along with some collagen and elastic fibres
elastic tissues allow it stretch when air is drawn in.
This is known as elastic recoil of the lungs
Adaptations of the alveoli
large surface area - 300 million alveoli per adult lung.
thin layers - one cell thick
good blood supply - keeps steep concentration gradient
good ventilation - breathing keeps high concentration gradient.
Ventilation
Ventilation is the movement of air caused by pressure changes in the lungs
What are the following:
- rib cage
- the diaphragm
- the external/ internal intercostal muscles
- the thorax
rib cage - provides a semi-rigid case
diaphragm - domed sheet muscle, forms the floor of the thorax
external / internal intercostal - found between the ribs
thorax - lined bey the pleural membranes, which surround the lungs.
pleural cavity is filled with a thin layer of lubricating fluid so membranes can slide over each other.
Inspiration
it is when you take in air or inhale and uses energy
the diaphragm contracts causing it to lower.
external intercostal muscles contract, moving the ribs upward and outward. the volume of the thorax increases, so pressure is reduced until it is lower than the pressure of the air. so air is drawn in through the nasal passages, trachea, bronchi, and bronchioles into the lungs. Equalises pressure.
Expiration
breathing out or exhaling - passive process.
diaphragm relaxes
external intercostal muscles relax
elastic fibres in alveoli return to normal length.
decreases the volume of the thorax.
pressure in thorax is greater than air, so air move out of the lungs until the pressure inside and out is equal again.
Forced expiration
uses energy
internal intercostal muscles contract, and abdominal muscles contract, diaphragm goes up increasing pressure in lungs rapidly.
Measuring the capacity of the lungs methods
a peak flow meter is a simple device that meausres the rate at which air can be expelled from the lungs.
vitalographs - sophisticated versions of peak flow
A spirometer - used to measure different aspects of lung volume, or breathing patterns.
Components of lung volume
Tidal volume - the volume of air that moves into and out of the lungs with each resting breather. uses 15% of vital capacity.
Vital capacity - the volume of air that can be exhaled when the deepest possible intake of breath is followed by the strongest possible exhalation
Inspiratory reserve volume - maximum volume of air you can breathe in over and above a normal inhalation
Expiratory reserve volume - the extra amount of air you can force out of your lungs over and above the normal tidal volume of air your breath out.
Residual volume - the volume of air that is left in your lungs when you have exhaled as hard as possible. Cant be measured directly.
Total lung capacity - the sum of the ital capacity + residual volume
Breathing rhythms
The pattern and volume of breathing changes as the demands of the body change. The breathing rate is the number of breathes taken per minute. The ventilation rate is the total volume of air inhaled in one minute.
Ventilation rate = tidal volume x breathing rate
How does gas exchange take place in insects?
Along the thorax and abdomen there are spiracles where air enters and leaves along with water loss. To control opening and closing of spiracles there are sphincters.
From the spiracle it goes to the trachea.
Trachea branch into tracheoles.
Air moves by diffusion down the trachea and tracheoles
Towards the end of tracheoles there is tracheal fluid which limits the penetration of air for diffusion
No gas exchange in trachea
Gas exchange in tracheoles
Adaptations of the trachea in insects
1mm diameter
spirals of chitin to keep them open from any bending or pressing.
Chiting is impermeable so no gas exchange takes place
Adaptations of tracheoles in insects
0.6-0.8um diameter
each tracheole is a single, elongated cell with no chitin lining so they are freely permeable to gases.
They run between individual cells allowing gas exchange
Mechanisms of larger insects like beatles, locusts and how they meet their high energy demands.
air is actively pumped into the system by muscular pumping of the thorax and abdomen. This will change the volume and pressure in the trachea and tracheoles so air is drawn in or forced out.
Collapsible enlarged trachea or air sacs, which act as air reservoirs - these are used to increase the amount of air moved through the gas exchange system. They are usually inflated and deflated by ventilating movements of the thorax and abdomen.
Issues that marine animals have when doing gas exchange
Water is 1000x denser than air
It is 100x more viscous and has much lower oxygen content. To cope fish have specialised respiratory systems.
It would use up far too much energy to move dense, viscous water in and out of lung-like respiratory organs. Moving water in one direction is more efficient in terms of energy.
Why is there a need for gills
Bony fish are relatively big and are very active so high oxygen demands. SA:V is small so not enough for diffusion, and scaly outer covering prevents gaseous exchange on the surface.
So they use gills, which is maintained by a flow of water one direction over the gill.
Gills have large SA, good blood supply and thin layers for gas exchange
They are covered by a operculum for protection.
Water flow over gills
Fish can get water flowing over the gills by opening their mouth and operculum. When a fish stops moving the water flow also stops.
The mouth is opened and the floor of the buccal cavity is lowered. This increases volume of buccal cavity. Pressure in the cavity drops and water moves in. At the same time the opercular valve is shut and the opercular cavity containg the gils expands. This lowers pressure in the opercular cavity containing the gills. The buccal cavity floor moves up increasing pressure. So water moves from the buccal cavity over the gills. The mouth closes, the operculum opens and the sides of the opercular cavity move inwards. All of these actions increase the pressure in the opercular cavity and force water over the gills and out of the operculum. The floor of hte buccal cavity is steadily moved up, maintaining a flow of water over the gills.
Adaptations for effective gas exchange in water
Large surface and good blood supply, thing layers for gills.
The tips of adjacent gill filaments overlap. This increases the resistance to the flow of water over the gill surfaces and slows down the movement of the water. As a result there is more time for gas exchange to take place.
Water moves over the gills in the opposite direction that the blood moves through the gills. This keeps a steep conc. gradient.
Countercurrent exchange system
