3.1.1c Mammalian Respiratory System

Question 1

See images for labelling human gaseous exchange system

Question 2

How do gaseous exchange surfaces aid land animals that face a continual conflict between need for gaseous exchange & water

Answer 2

Gaseous exchange surfaces are moist, so oxygen dissolves in the water before diffusing into the body tissues. As a result, the conditions needed to take in oxygen successfully are also ideal for the evaporation of water.

Question 3

In what ways have mammals evolved complex exchange systems

Answer 3

They have evolved complex systems that allow them to exchange gases efficiently but minimise the amount of water lost from the body

Question 4

SA:V ratio of mammals?

Answer 4

Mammals are relatively big, so have a small SA:V ratio & a very large volume of cells

Question 5

Do mammals have a high metabolic rate

Answer 5

Yes, mammals have a high metabolic rate bc they are active & maintain their body temp independent of their environment.
As a result, they need lots of oxygen for cellular respiration & they produce CO2, which needs to be removed.

Question 6

What is the nasal cavity (human exchange system)

Answer 6

• Has a large SA w a good blood supply, which warms the air to body temp
• A hairy lining, which secrets mucus to trap dust & bacteria, protecting delicate lung tissue from irritation/infection
• Moist surfaces, which increase the humidity of the incoming air, reducing evaporation from the exchange surfaces

Question 7

What is the Trachea

Answer 7

• The main airway carrying clean, warm, moist air from the nose down into the chest.
• It is a wide tube supported by incomplete rings of strong, flexible cartilage, which stops the trachea from collapsing.
• The rings are incomplete so that food can move easily down the oesophagus behind the trachea

Question 8

Structure of the Trachea

Answer 8

• The trachea & its branches are lined w a ciliated epithelium with goblet cells between & below the epithelial cells.
• Goblet cells secrete mucus onto the lining of the trachea, to trap dust & microorganisms that have escaped w nose lining. The cilia beat & move the mucus, along w any trapped dirt & microorganisms, away from the lungs. Most of it goes into the throat & is swallowed & digested.
  (One of the effects of cigarette smoke is that it stops these cilia beating)

Question 9

see images for diagram of trachea

Question 10

What is the Bronchus

Answer 10

In the chest cavity, the trachea divides to form the left bronchus (plural bronchi), leading to the left lung, and the right bronchus leading to the right lung. They are similar in structure to the trachea, w the same supporting rings of cartilage, but they are smaller

Question 11

What are Bronchioles

Answer 11

In the lungs, the bronchi divide to form many small bronchioles. The smaller bronchioles (dia 1mm or less) have no cartilage rings.
- The walls of the bronchioles contain smooth muscle, which contracts causing the bronchioles to constrict (close up). When it relaxes, the bronchioles dilate (open up). This changes the amount of air reaching the lungs
- Lined w a thin layer of flattened epithelium, making some gaseous exchange possible

Question 12

What is the Alveoli (singular Alveolus)

Answer 12

• Tiny air sacs (200-300pm dia), which are the main gas exchange surface of the body.
• Consist of a layer of thin, flattened epithelial cells, along w some collagen & elastic fibres. (allowing the alveoli to stretch as air is drawn in, and recoil to aid exhalation). When they return to their resting size, they help squeeze the air out. This is known as the ‘elastic recoil’ of the lungs

Question 13

see diagram of gaseous exchange within an alveolus in images

Question 14

Main adaptations of the Alveoli for effective gaseous exchange

Answer 14

• Large SA
• Thin layers
• Good blood supply
• Good ventilation
• Moist
• Short diffusion pathway

Question 15

How does a large SA allow effective gaseous exchange in Alveoli

Answer 15

There are 300-500 million alveoli per adult lung. The alveolar SA for gaseous exchange in the two lungs combined is 50-75m^2. A large SA provides a large enough space for the amount of oxygen needed to diffuse into the body

Question 16

How do thin layers allow effective gaseous exchange in Alveoli

Answer 16

Both the alveoli & the capillaries surrounding them have walls that are only a single epithelial cell thick, so the diffusion distances between the air in the alveolus & the blood in the capillaries are very short

There is a short diffusion pathway due to the walls of the alveoli being one cell thick & flattened (squamous)

Question 17

How does good blood supply allow effective gaseous exchange in Alveoli

Answer 17

The millions of alveoli in each lung are supplied by a network of around 280mil capillaries.

The constant flow of blood through these capillaries brings CO2 & carries off oxygen, maintaining a steep concentration gradient for both CO2 & oxygen between the air in the alveoli & the blood in capillaries

Question 18

How does good ventilation allow effective gaseous exchange in Alveoli

Answer 18

Alveoli are ventilated, allowing effective delivery & removal of oxygen (inhalation) and CO2 (exhalation). This leads to a steep concentration gradient –> increased diffusion

Question 19

What is lung surfactant

Answer 19

The inner surface of the alveoli is covered in a thin layer of a solution of water, salts & lung surfactant. It is this surfactant that makes it possible for the alveoli to remain inflated.

Question 20

What is ventilation

Answer 20

Air is moved in & out of the lungs as a result of pressure changes in the thorax (chest cavity) brought abt by the breathing movements. This movement of air is called ventilation

Question 21

Purpose of the ribcage

Answer 21

Provides a semi-rigid case within which pressure can be lowered w respect to the air outside it

Question 22

What is the diaphragm

Answer 22

A broad, domed sheet of muscle, which forms the floor of the thorax.

Question 23

Where are the external & internal intercostal muscles

Answer 23

The external intercostal muscles & the internal intercostal muscles are found between the ribs

Question 24

What is the thorax lined by

Answer 24

The thorax is lined by the pleural membranes, which surround the lungs. The space between them (the pleural cavity) is usually filled w a thin layer of lubricating fluid so the membranes slide easily over each other as you breathe

Question 25

What is Inspiration

Answer 25

Taking air in or inhalation. It is an energy-using process

Question 26

Process of Inspiration

Answer 26

The diaphragm contracts, flattening & lowering.
The external intercostal muscles contract, moving the ribs upwards & outwards.
The volume of the thorax increases so the pressure in the thorax is reduced.
It is now lower than the pressure of the atmospheric air, so air is drawn through the nasal passages, trachea, bronchi & bronchioles into the lungs. This equalises the pressures inside & outside the chest

Question 27

What is Expiration

Answer 27

Breathing out or exhalation. It is a passive process

Question 28

Process of Expiration

Answer 28

The muscles of the diaphragm relax so it moves up into its resting domed shape.
The external intercostal muscles relax so the ribs move down & inwards under gravity.
The elastic fibres in the alveoli of the lungs return to their normal length.
The effect of all these changes is to decrease the volume of the thorax. Now 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 & out is equal again

Question 29

see images for inspiration & expiration of lungs

Question 30

What are some everyday triggers to ppl w asthma

Answer 30

House dust mites, cigarette smoke, pollen, stress

Question 31

What happens during an asthma attack

Answer 31

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

Question 32

Is there medicine for asthma

Answer 32

Asthma medicines have been developed to reduce symptoms or prevent attacks.

The drugs are delivered straight into the breathing system using an inhaler

Question 33

2 main ways to treat asthma

Answer 33

Relievers - give immediate relief from symptoms. They are chemicals similar to the hormone adrenaline. They attach to active sites on the surface membranes of smooth muscle cells in the bronchioles, making them relax & dilating the airways

Preventers - often steroids, taken everyday to reduce sensitivity of the lining of the airways

Question 34

What is special about the first breath of a newborn

Answer 34

This requires a force 15-20 times greater than normal inhalation to inflate the lungs.
The lungs are enormously stretched as the air flows in, & the elastic tissue near returns to its go length.

Question 35

What makes the first breath of a newborn possible

Answer 35

The intake of breath is only possible bc of special chemicals called lung surfactants containing phospholipids & both hydrophilic & hydrophobic proteins. The surfactant stops the alveoli collapsing & sticking tg as the baby exhales

Question 36

One reason why premature babies struggle to breathe and die

Answer 36

Babies born at full term have alveoli coated in lung surfactant all ready for breathing.

However, the cells of the alveoli do not produce enough surfactant for the lungs to work properly until around the 30th week of pregnancy

Question 37

What is being done in recent yrs to make breathing easier, help prevent lung damage & enable more babies to survive

Answer 37

Artificial lung surfactants have been produced. A tiny amount sprayed into the lungs of a premature baby coats the alveoli just like the natural surfactant, making breathing easier, help prevent lung damage & enable more babies to survive

Question 38

How does the inside of an alveoli being moist allow effective gas exchange

Answer 38

The inside lining of the alveoli is moist, meaning oxygen can dissolve into the solution and dissolve more easily. It also contains a surfactant

Question 39

How does a short diffusion pathway in alveoli allow effective gas exchange

Answer 39

The cells of the capillaries & the alveolus are connected. The capillary wall & alveolar wall are next to eachother therefore a short diffusion pathway

Question 40

What is significant about the lumen of the capillary to the alveoli

Answer 40

The lumen of the capillary is abt the same diameter of the alveolar itself

Question 41

Where is smooth muscle found

Answer 41

In the Trachea, Bronchi, Bronchioles

Question 42

What does smooth muscle do

Answer 42

Able to CONTRACT, therefore causing airways to CONSTRICT

Question 43

Where are elastic fibres found

Answer 43

In the alveoli

Question 44

What do elastic fibres do

Answer 44

They STRETCH (preventing from bursting), and RECOIL (helps forcing air out in exhalation)