Lesson 2 - The mammalian gaseous exchange system

Question 1

Why do we need gaseous exchange systems as mammals?

Answer 1

• Small SA:V ratio
• Very large volume of cells
• High metabolic rate, so need lots of O2 and need to dispel lots of CO2 for/from aerobic respiration

Question 2

What are all gaseous exchange systems like?

Answer 2

• Surfaces are moist so that O2 dissolves in water before diffusing into body tissues
• Conditions needed to take in O2 sufficiently are also ideal for evaporation.

Question 3

Nasal cavity: 3 features

Answer 3

1. Large surface area with good blood supply, warms the air to the temperature of the body
2. Hairy lining, which secretes mucus to trap dust and microorganisms/bacteria, protecting delicate lung tissue from irritation & infection.
3. Moist surfaces, which increase the humidity of the incoming air, reducing evaporation from the exchange surfaces

Question 4

What does the Trachea do?

Answer 4

Carries warm, moist, clean air from the nose –> chest.

Question 5

Structure of the Trachea?

Answer 5

• Wide tube supported by incomplete rings of strong, flexible hyaline cartilage. Prevent trachea from collapsing (incomplete to enable easy movement of food down the oesophagus). Incomplete as allows them to expand to larger volume and inhale/exhale when excercising.
• Trachea and branches are lined with ciliated pseudostratified columnar epithelium and goblet cells. Goblet cells secrete mucus, which trap dust and microorganisms, that escaped nose lining.
• Cillia beat and moved mucus away from lungs. Most goes to throat and are swallowed and digested.

Question 6

One effect of cigarette smoke?

Answer 6

Stops the cillia from beating

Question 7

Bronchus:

Answer 7

In the chest cavity, the trachea divides to form the left and right bronchi. The left bronchus leads to the left lung and the right bronchus leads to the right lung.
They have a similar structure to the trachea, with the same strong, flexible, supporting cartilage. They are only smaller.

Question 8

Description of the bronchioles:

Answer 8

• In the lungs the bronchi divide into many small bronchioles.
• 1mm / less in diameter
• Have no cartilage rings
• The walls of bronchioles contain smooth muscle
• Lined with thin and flattened layer of epithelium, making some gaseous exchange possible.

Question 9

Process of smooth muscle in the bronchioles?

Answer 9

• Smooth muscle contracts –> bronchioles constrict (close up)
• Smooth muscle relaxes –> bronchioles dilate (open up)

This changes the amount of air entering the lungs.

Question 10

Description of the alveoli:

Answer 10

• Tiny air sacks, which are the main gas exchange surfaces in the body
• Unique to mammalian body
• Diameter of 200 - 300 micrometers
• Consists of a flattened layer of epithelial cells, some collagen and elastic fibres (composed of elastin).
• Elastic fibres allow alveoli to stretch as air is drawn in. When they return to their resting size, they help squeeze the air out. This is known as elastic recoil of the lungs.

Question 11

Elastic recoil of the lungs:

Answer 11

Elastic fibres stretch as air is drawn in. When they return to their resting size, they help squeeze the air out.

Question 12

Adaptations of the alveoli for gaseous exchange?

Answer 12

Large Surface Area:
- 300-500 million alveoli per adult lung
- Alveoli surfaces in two lungs combined is 50-75m^2

Thin layers:
- Both the alveoli and capillaries have thin walls that are one epithelial cell thick. Diffusion distance is short.

Good blood supply:
- Alveoli are supplied by a network of 280 million capillaries
- Constant flow of blood brings in CO2 and carries away O2 maintaining a constant concentration gradient.

Good ventilation:
- breathing moves air both in and out of the alveoli.
- Help maintain steep diffusion gradient

Question 13

How does alveoli stay inflated?

Answer 13

Covered in a thin layer of water, salts and lung surfactant. Surfactant keeps the alveoli inflated.

Oxygen dissolves in water before diffusing into the blood, the water can also evaporate into the air of the alveoli.

Several adaptations are designed to prevent water loss

Question 14

Chest cavity:

Answer 14

Thorax

Question 15

Ventilation?

Answer 15

Air is moved in and out o lungs as a result of pressure changes in the thorax brought about by breathing movements.

Question 16

Structure of the chest?

Answer 16

Rib cage provides a semi-rigid case within which pressure can be lowered with respect to the air outside it.

The diaphragm is broad, domed sheet of muscle, which forms the floor of the thorax.

External and internal intercostal muscles are found between the ribs.

Thorax is lined by pelural membranes, which surround the lungs. The space between them, the pelural cavity, is usually filled with a lin layer of lubricating fluid so the membranes slide easily over each other as you breath.

Question 17

Inspiration

Answer 17

Breathing in (energy-using process

1. Dome-shaped diaphragm contracts, flattening, and lowering.
2. The external intercostal muscles contract, moving the ribs upwards and outwards.
3. The volume of the thorax increases, so the pressure in the thorax is reduced. Now a lower pressure than that of the atmospheric air, so air is drawn through the nasal passages, trachea, bronchi, and bronchioles into the lungs. This equalises the pressures inside and outside the chest.

Question 18

Expiration

Answer 18

Exhalation is a passive process.

1. Muscles in the diaphgram relax so it moves up into its resting domed shape.
2. External intercostal muscles relax so the ribs move down and inwards under gravity.
3. The elastic fibres in the alveoli of the lungs return to normal length. The effect of all these changes is to decrease the volume of the thorax.
4. The pressure inside the thorax is greater than the pressure of the atmospheric air, so air moves out of the lungs until the pressure inside and out is equal again.

Question 19

Forceful exhale process:

Answer 19

Uses energy.

Internal intercostal muscles contract, pulling ribs down hard and fast, and the abdominal muscles contract forcing the diaphragm up to increase the pressure in the lungs rapidly.

Question 20

What is asthema?

Answer 20

Airways are sensitive to everyday triggers including house dust mites, cigarette smoke, pollen, and stress.

Question 21

Asthema attack?

Answer 21

Cells lining the bronchioles release histamines, chemicals that make the epithelial cells become inflamed and swollen. Histamines stimulate the goblet cells to secrete excess mucus and the smooth muscle in the bronchiole walls to contract.
As a result, the airways narrow and fill with mucus, making it difficult to breathe.

Question 22

Asthema medicines?

Answer 22

Reduce symptoms and prevent attacks.

Drugs are delivered straight into the breathing system using an inhaler.

Relievers: Immediate relief from symptoms
- Chemicals similar to the hormone adrenaline. They attach to the active sites on the surface membranes of smooth muscle cells in the bronchioles, making the relax and dialating the airways.

Preventers:
- Steroids
- Taken everyday to reduce the sensitivity of the airways

Question 23

Force of first breath

Answer 23

15-20 times more force than a normal breath.

Question 24

Why is the first breath so much harder?

Answer 24

• Lungs are stretched enormously as the air flows in, the elastic tissue never returns to its original length. This intake of breath is only possible because of special chemicals called lung surfactants, which stops the alveoli collapsing and sticking together as the baby exhales. Without it, the second breath would be as difficult as the first, and continued breathing impossible.

Question 25

What is in lung surfactants?

Answer 25

Phospholipids and both hydrophilic and hydrophobic proteins.

Question 26

Why can’t premature babies breath on their own?

Answer 26

Babies at full term have alveoli coated in lung surfactant. However, the cells of the alveoli do not produce enough surfactant for the lungs to work properly until about the 30th week of pregnancy. This means that babies can not breath on their own, as the alveoli collapse and stick together.

Question 27

How can premature babies inability to breath be combated?

Answer 27

Artificial lung surfactants. A tiny amount sprayed into the lungs of a premature baby coats the alveoli just like the natural surfactant, making breathing easier, helping to prevent lung damage and enabling babies to survive.