3.1.1 Exchange surfaces

Question 1

Why is diffusion alone enough to supply energy for single celled organisms?

Answer 1

• Metabolic activity of a sing celled organism is usually low. So oxygen and CO2 demands are also usually low.
• the SA:V is high

Question 2

Features of effective exchange systems

Answer 2

• Increased surface area = provides the area needed for exchange and overcomes the limitations of the SA:V of larger organisms.
• Thin layers = so the distance that substances have to diffuse over is shorter, making the process faster and efficient
• Good blood supply = the steeper the conc gradient, the faster the rate of diffusion. Having a good blood supply ensures substances are constantly delivered to and removed from the exchange surface. This maintains a steep concentration gradient.
• Ventillation to maintain concentration gradient = for gases a ventillation system maintains the concentration gradient and makes the process more efficient.

Question 3

The human gaseous exchange system

Answer 3

• Mammals have small SA:V
• Mammals have high metabolic rates because they are active and maintain their body temperature independent of the environment.
• As a result they need a lot of oxygen for cellular respiration and they produce carbon dioxide which needs to be removed.
• The exchange of gas takes place in the lungs.
• Look on pp for diagram.
• Next few flashcards are the key structures in the human gaseous exchange system.

Question 4

Nasal cavity

Answer 4

• Has a large surface area with a good blood supply, which warms the air to body temperature.
• Hairy lining which secretes mucas to trap dust and bacteria, protecting lung tissue from irritation and infection.
• Moist surfaces, which increase the humidity of incoming air, reducing evapouration from the exchange surfaces.
• After entering the nasal cavitys the air enters the lung and is a similiar temperature,

Question 5

Trachea

Answer 5

• The main airway.
• Wide tube supported by incomplete rings of strong, flexible cartilage. These stop the trachea from collapsing. These rings are incomplete so food can move down the oesophagus.
• The trachea and its branches are lined with goblet cells and cilitated epithelium. Between and below the epithelial cells.
• Goblet cells secrete mucas onto the lining of the trachea, to trap dust and microorganisms that have escaped the nose lining.
• The cilia beat and move mucas, along with any trapped dirt and microorganisms, away from the lungs. Cigarette smoke stops these cilia from beating.

Question 6

Bronchus

Answer 6

• In the chest cavity the trachea divides to form the left bronchus, leading to the left lung, and the right bronchus leading to the right lung.
• They are similiar in structure to the trachea, with the supporting rings of cartilage, but they are smaller.

Question 7

Bronchioles

Answer 7

• In the lungs the bronchi divide to form many small bronchioles.
• The smaller bronchioles (diameter 1mm or less) have no cartilage rings.
• The wall of bronchioles contain smooth muscle.
• When smooth muscle contracts, the bronchioles constrict when it relaxes the bronchioles dilate. This changes the ammount of air reaching the lungs.
• Bronchioles are lined with a thin layer of flattened epithelium, making some gaseous exchange possible.

Question 8

Alveoli

Answer 8

• Tiny air sacs.
• Alveoli are unnique to mammilian lungs.
• Each alveolus are around 200-300 um and consist of layers of thin, flattened epithelial cells, along with some collagen and elastin fibres.
• Elastic tissues allow alveoli to stretch as air is drawn in. When they return to their resting size they help squeeze air out, this is called the elastic recoil of the lungs.
• They have large surface area, 300-500 million alveoli per adult lung.
• Thin layers as both alveloi and the capiliaries surrounding it have walls that are only 1 epithelial cell thick. So diffusion pathway is very short.
• Good blood supply, the alveoli are connected to a blood supply of around 280 million capillaries. This constant flow of blood brings carbon dioxide and carries off oxygen, maintaining a steep concentration gradient between the air in the alveoli and the blood in the capillaries.
• Good ventillation, breathing moves air in and out of the alveoli which maintains a steep concentration gradient.
• The inner surface of the alveoli is covered in a thin layer of solution which consists of water, salts and lung surfacent. This surfacent makes it possible for the alveoli to remain inflated.

Question 9

Ventilating in the lungs

Answer 9

• Air is moved in and out of the lungs as a result of pressure changes in the thorax (chest cavity). This movement is known as air ventillation.
• The rib cage provides a semi rigid cage within which pressure can be lowered with respect to the air outside it.
• The diaphram is a broad, domed sheet of muscle, this forms the floor of the thorax.
• The external intercostal muscles and the internal intercostal muscles are found between the ribs.
• The thorax is lined by the plueral membranes, which surround the lungs.
• The space between them is called the plueral cavity and is usually filled with a thin layer of lubricating fluid which allows the membranes to easily slide over eachother as you breathe.

Question 10

Inspiration

Answer 10

• The process of taking air in.
• It is an energy using process.
• The dome shaped diaphragm contracts, flattening and lowering.
• The external intercostal muscles contract, moving the ribs upwards and outwards.
• The volume of the thorax increases so the pressure in the thorax is lowered. It is now lower than the pressure of atmospheric air, so air is drawn through nasal passages, treachea, bronchi and bronchioles into the lungs. This equalises the pressure between the inside and outside of the chest.

Question 11

Expiration

Answer 11

• Normal expiration is a passive process.
• The muscles of the diaphragm relax so it moves up into its resting dome shape.
• The external intercostal muscles relax so the ribs move down and inwards under gravity.
• The elastic fibres in the alveoli of the lungs return to their normal length.
• The effects of these changes is to decrease the volume of the thorax.
• The pressure inside the thorax is greater than the pressure of the atmoshpheric air, so air moves out of the lungs until pressure is equal again.

Question 12

Measuring the capacity of the lungs

Answer 12

• A peak flow meter is a simple device that measures the rate at which air can be expelled from the lungs. People who use athsma often use this to moniter how well their lungs are working.
• Vitalographs are more sophisticated versions of the flow meter. The patient being tested breathes out as quickly as they can using a mouthpiece and the instrument produces a graph of the ammount of air they breath out and how quickly it is breathed out.

Question 13

Spirometer

Answer 13

• Commonly used to measure different aspects of lung volume, or to investigate breathing patterns.
• They can be used to investigate the volumes of gas breathed in and out under different conditions.

Question 14

Components of lung volume

Answer 14

• Tidal volume = The volume of air which moves into and out of the lungs with each resting breathe. For adults it is around 500cm3 at rest, this uses around 15% of the lungs vital capacity.
• Vital capacity = the volume of air that can be breathed in when the strongest possible exhalation is followed by the deepest possible intake of breath.
• Inspiratory reserve volume = maximum volume of air you can breath in over and above normal exhalation.
• Expiratory reserve volume = the extra ammount of air you can force out of your lungs over and above the normal tide volume of air you breathe out.
• Residual volume = the volume of air that left in your lungs when you have exhaled as hard as possible. This cannot be measured directly.
• Total lung capacity = sum of vital capacity and the residual volume.

Look at onenote page

Question 15

Breathing rhythms

Answer 15

• The pattern and volume of breathing changes as the demands of the body changes.
• The breathing rate is the number of breaths taken per minute.
• The ventillation rate is the volume of air inhaled in 1 minute.
• Ventilation rate = tidal volume x breathing rate (per minute)
• When the oxygen demands of the body increase breathe rate increases.

Question 16

Respiratory systems in bony fish

Answer 16

• water is 1000x denser than air.
• It is 100x more viscous and has a much lower oxygen content.

Question 17

Gills

Answer 17

• A flow of water is maintained in one direction over water.
• Gills have a large surface area, good blood supply and thin layers needed for gaseous exchange.
• In bony fish they are contained in a gill cavity and covered by a protective operculum, which is also active in maintaining a flow of water over the gills.
• Bony gill arch supports the structure of the gills.
• Eferent blood vessel carries the blood leaving the gills in the opposite direction to the incoming water, maintaining a steep concentration gradient.
• Gill lamellae are the main site of gaseous exchange in fish, they have a rich blood supply and large surface area.
• Gill filaments occur is large stacks (gill plates) and need a flow of water to keep them apart, exposing the large surface area needed for gaseous exchange.

look at diagram

Question 18

Water flow over the gills

Answer 18

• When fish are swimming they can keep a current of water flowing over their gills by simply opening their mouth and operculum.
• Cartiliginous fish such as sharks often rely on continual movement to ventilate the gills, this known as ram movement.
• However bony fish do not rely on movement-generated water flow over the gills. They have evolved a sophisticated system, involving the operculum which allows them to move water over the gills at all times.

Question 19

Inspiration in bony fish

Answer 19

• Mouth is open.
• Floor of bucal cavity is lowered.
• Volume of buccal cavity increases.
• Water is drawn due to pressure gradient.
• Operculum (covering of gills) is closed.
• The cavity is filled with water.
• Operculum moves outwards while closed which increases the volume and helps pull in more water.

Question 20

Expiration in bony fish

Answer 20

• Mouth is closed.
• Floor of buccal cavity is raised.
• Volume in buccal cavity decreases.
• Preasure increases.
• Operculum is open.
• water flows over gill lamellae and out of operculum due to pressure gradient.
• Maximum gas exchange occurs between water and blood flowing through the gills because of the countercurrent mechanism.

Question 21

Why are gills effective for gaseous exchange under water?

Answer 21

• Rich blood supply to maintain steep concentration gradient for diffusion, thin layers so short diffusion pathway, large surface area.
• The tips of adjacent filaments overlap, this increases the resistance to the flow of water over the gill surfaces and slows down the movemnt of water. As a result there is more time for gaseous exchange to take place.
• The water moving over the gills and the blood in the gill filaments flow in different directions. Because blood and water flow in opposite directions a countercurrent system is set up. This adaption ensures that steeper concentration gradients are maintained than if water and blood flowed in the same direction. The bony fish remove about 80% of oxygen from the water around them with the countercurrent system. Compared to cartilaginous fish with parallel systems that only extract around 50% of oxygen from the water around them.

Question 22

Parallel system

Answer 22

• Blood in the gills and water flowing over the gills travel in the same direction, this gives an original steep concentration gradient between blood and water.
• Diffusion takes place until the oxygen concentration of the blood and water are in eqilibrium, then no net movement of oxygen into the blood occurs.

Question 23

Countercurrent system

Answer 23

• Blood and water flow in opposite directions so an oxygen concentration gradient between the blood and water is maintained all along the gill.
• Oxygen continues to diffuse down the concentration gradient so a much higher level of oxygen saturation of the blood is acheived.

Question 24

Gas exchange in insects

Answer 24

• Insect bodies are covered by exoskeleton made from chitin and the waxy cuticle. To reduce water loss.
• Pores called spiracles that line the length of the body allow entry of air into the gas exchange (tracheal) system.

Question 25

How does gas exchange take place along insects?

Answer 25

- Along the thorax and abdomen are small openings known as spiracles. Air enters and leaves the system through spiracles, but water is also lost. - When an insect is inactive and oxygen demands are very low, the spiracles will all be closed most of the time. - Leading away from the spiacles are the tracheae. These are the largest tubes of the insect system, and are up to 1mm in diameter, and they carry air into the body. The tubes are lined by spirals of chitin, which keep them open if they are bent or pressed, chitin is relatively impermeable so little gas exchange takes place in the tracheae. - The tracheae then divide into the tracheoles, these tubes have a diameter of 0.6-0.6 um. Each tracheole is is a single, greatly elongated cell with no chitin lining so they are freely permeable to gases. - Towards the end of the tracheoles there is tracheal fluid, which limts the penetration of air for diffusion. However when oxygen builds up, a lactic acid build up in the tissues results in water moving out of the tracheoles via osmosis. This exposes more surface area for gaseous exchange. Spiracle > main trachea > branching of tracheae > tracheoles > all respiring cells

Question 26

How do insects with high oxygen demands get the supply of extra oxygen they need?

Answer 26

- Mechanical ventillation of the tracheal system = air is actively pumped into the system by muscular pumping movements of the thorax and/or the abodomen. These movements change the volume of the body and changes the pressure in the trachea and the tracheoles so air is either drawn in or out. - Collapsible enlarged tracheae or air sacs = these are used to increased the ammount of air moved through the gas exchange system.