Chapter 9.1

Question 1

The Human Gas Exchange System

Answer 1

Gas exchange takes place in the human thorax. This is a collection of organs and tissues in the chest cavity

Question 2

Trachea

Answer 2

The airways that leads from the mouth and nose to the bronchi.

• The trachea is lined with mucus-secreting Goblet cells and cilia.
• The cilia sweep microorganisms and dust away from the lungs

Question 3

Lungs

Answer 3

Humans have two longs, both which are a central part of the respiratory system and where gas exchange takes place

Question 4

Bronchi

Answer 4

‘Bronchi” is the plural of ‘Bronchus’. The left and right bronchi are at the bottom of the trachea and are similar in structure, but narrower. The bronchi lead to bronchioles

Question 5

Bronchioles

Answer 5

These are narrow tubes(less than 1mm) which carry air from the bronchi to the alveoli.

As they are so narrow, they have no supporting cartilage and so can collapse

Question 6

Alveoli

Answer 6

The main site of gas exchange in the lungs. These are tiny sacs with many structural adaptations to enable efficient gas exchange, such as their thin walls and large surface area to volume ratio

Question 7

Capillary network

Answer 7

An extensive network of capillaries surrounds the alveoli and are an exchange surface between the lungs and the blood.

=During gas exchange, oxygen diffuses from the alveoli and into the capillaries, while carbon dioxide diffuses the other way and is exhaled

Question 8

Cartilage is a strong and flexible tissue found in various places around the body. What makes it so strong ?

Answer 8

• One place is in rings along the trachea, called Tracheal rings
• These rings help to support the trachea and ensure it stays open, while allowing it to move and flex while we breathe

Question 9

Goblet cells can be found scattered throughout the ciliated epithelium in the trachea. what are and function

Answer 9

• They are mucus-producing cells that secrete viscous mucus which traps dust, bacteria and other microorganisms and prevents them from reaching the lungs
• The mucus is then swept along by the cilia of the ciliated epithelium upwards and is swallowed
• The mucus and any microorganisms will then be destroyed by the acid in the stomach

Question 10

The alveoli have a lining of thin squamous epithelium, that allows for gas exchange why

Answer 10

The squamous epithelium forms the structure of the alveolar wall and so is very thin and permeable for the easy diffusion of gases

Question 11

Smooth muscle can be found throughout the walls of the bronchi and bronchioles why

Answer 11

It helps to regulate the flow of air into the lungs by dilating when more air is needed and constricting when less air is needed

Question 12

Each alveolus is surrounded by an extensive network of capillaries why

Answer 12

Carbon dioxide diffuses out of the capillaries and into the alveoli to be exhaled, while oxygen diffuses the other way from alveoli and into the capillaries to be carried around the body

Question 13

what ensures that there is sufficient time and opportunity for gas exchange to occur

Answer 13

capillaries which have a diameter of around 3-4µm, which is only wide enough for one red blood cell to travel through at any one time

Question 14

Ciliated epithelium is a specialised

Answer 14

tissue found along the trachea down to the bronchi. Each cell has small projections of cilia which sweep mucus, dust and bacteria upwards and away from the lungs and the epithelium itself

Question 15

Explain how the lining of the trachea, bronchus and bronchioles provide protection against pathogens

Answer 15

Cilia beat to move mucus away from the lungs and up towards the mouth.

• Mucus is produced by goblet cells and acts as a barrier to pathogens from entering the ciliated epithelium.
• The mucus also traps bacteria and microorganisms, while blood vessels bring macrophages to engulf any pathogens in phagocytosis.

Question 16

Cartilage

Answer 16

-The cartilage in the trachea has a ‘glassy’ appearance due to its translucent protoplasm -It contains no nerves or blood vessels

Question 17

Ciliated epithelium

Answer 17

• Ciliated epithelial cells are distinctive due to their narrow cell bodies and hair-like cilia located along the apical layer
• The cilia are tiny projections which greatly increase the surface area of the cell

Question 18

Goblet cells

Answer 18

• Goblet cells can be found scattered among the ciliated epithelium of the trachea and bronchi
• They are distinctive in the epithelium due to their lack of cilia (although they still have some microvilli projecting outwards)
• The nucleus is found towards the basal (bottom) layer of the cell, with a large Golgi apparatus and mucus granules found towards the apical layer

Question 19

Squamous epithelium

Answer 19

Squamous epithelium is made of thin, flat squamous cells

Question 20

Smooth muscle

Answer 20

• The cells of smooth muscle are tightly packed and are found beneath the ciliated epithelium
• Unlike skeletal muscles, they are not striated and so don’t show any cross stripes under a microscope

Question 21

Capillaries

Answer 21

-Capillaries are distinctive from other blood cells due to their tiny diameter (~4 μm) -Their walls consist of a single layer of epithelial cells

Question 22

Trachea

Answer 22

• A tracheal cross-section shows the large lumen which air has to travel through
• The innermost cells of the trachea are the ciliated epithelia with projections called cilia -The cells of the ciliated epithelium are shown here

– the cells are tightly packed and interspersed with goblet cells,

• The cilia are essential for sweeping bacteria and dust-filled mucus away from the lungs and up the trachea into the back of the mouth
• This mucus is then swallowed, with any pathogens hopefully destroyed by the acidic conditions in the stomach

Question 23

Bronchi

Answer 23

• Bronchi are distinctive from the trachea because their lumen is narrower; 8.7mm instead of 18mm
• However, like the trachea, they are lined by ciliated epithelium

Question 24

Bronchioles

Answer 24

• Bronchioles are approximately 1mm or less in diameter
• Smooth muscle and cuboidal epithelium are found in their walls

Question 25

Walls of the bronchus

Answer 25

Question 26

Alveoli

Answer 26

- Alveoli have a sponge-like appearance under a microscope due to their air spaces. - They are surrounded by an extensive capillary network and are lined by squamous epithelium

Question 27

Walls of the trachea

Answer 27

-The tracheal lumen is around 15 to 20 mm and is lined by ciliated epithelia -The tracheal wall is surrounded by strong and flexible cartilage which flexes during breathing -The smooth muscle of the trachea constricts and allows air to be expelled with more force

Question 28

Walls of the bronchus

Answer 28

- Like the trachea, the bronchus is lined with ciliated epithelium - The cartilage hoops provide structural support to the bronchi and the gland ducts secrete mucus in the bronchial tubes

Question 29

The Gas Exchange System: Structure & Functions

Answer 29

- Ciliated epithelial cells, goblet cells and mucous glands play vital roles in maintaining the health of the gas exchange system - Cartilage, smooth muscle, elastic fibres and squamous epithelial tissue all play important structural roles in maintaining the gas exchange system

Question 30

ciliated epithelial cells

Answer 30

These ells line the trachea to the bronchi. Each cell has tiny projections called cilia, which sweep mucus, dust, bacteria and other microorganisms up and away from the lungs to the mouth, where they are swallowed and digested by stomach acid

Question 31

goblet cells

Answer 31

they are embedded throughout the ciliated epithelium and are mucus-producing cells. The mucus they provide traps dust, bacteria, and microorganisms as mentioned above

Question 32

macous glands

Answer 32

The mucous glands work with goblet cells in the trachea and bronchi to produce mucus

Question 33

cartilage

Answer 33

Rings of cartilage line the trachea, or windpipe. Cartilage is a strong but flexible tissue and is essential for keeping the trachea open. Because of its flexibility, the cartilage is able to move and flex as we breathe

Question 34

smooth muscle

Answer 34

Smooth muscles is muscle not under conscious control and is found in the walls of the bronchi and bronchioles. It helps to regulate the flow of air into and out of the lungs by dilating and widening when more air is needed

Question 35

elastic fibres

Answer 35

- Elastic fibres are found in the squamous epithelium of the alveolar walls. - Elastic fibres are a critical component of alveoli because the allow the tiny alveoli to stretch as they fill with air and recoil to help force air out. - It is the elastic abilities of alveoli which enables them to have such a large surface area. In serious cases of COPD, such as advanced emphysema, the alveoli lose there elastic properties

Question 36

squamous epithelium

Answer 36

- The squamous epithelium consists of flat, thin cells in the walls of the alveoli. - Their thinness means that oxygen and carbon dioxide have a very short diffusion pathway during gas exchange

Question 37

Describe the cause of cystic fibrosis and explain how cystic fibrosis affects the function of the lungs

Answer 37

- Cystic fibrosis is caused by a recessive allele of the **CFTR gene**. - Cystic fibrosis affects the lungs by goblet cells producing thick, sticky and dehydrated mucus. - This mucus is much harder for cilia to sweep up the trachea and to the mouth and so mucus accumulates in the airways. - As the mucus traps bacteria but the mucus can’t be removed, this leads to frequent infections and eventually scar tissue in the lungs. - The fact that mucus obstructs the airways means that gas exchange is less efficient as it is harder for oxygen to reach the lungs and harder for carbon dioxide to be exhaled, causing breathing problems.

Question 38

Gas Exchange Processes

Answer 38

- The exchange of oxygen and dioxide occurs between the alveoli and the capillaries in the lungs - Oxygen and carbon dioxide are exchanged in a process of simple diffusion; (passive movement from high to low concentration) - The air in the alveoli contains a high concentration of oxygen. - The oxygen diffuses from the alveoli and into the blood capillaries, before being carried away to the rest of the body for aerobic respiration - The blood in the capillaries has a relatively low concentration of oxygen and a high concentration of carbon dioxide. The carbon dioxide diffuses from the blood and into the alveoli and is then exhaled

Question 39

Feature of alveoli: large surface area

Answer 39

The average human adult has around 480-500 million alveoli in their lungs. This equal a surface area of 40-75m^2. The enormous surface area increases the space available for oxygen and carbon dioxide to diffuse

Question 40

Feature of alveoli: thin walls

Answer 40

The walls of the alveoli are only one cell thick. This means that gases have a very short diffuse distance and so gas exchange is as quick and efficient as possible

Question 41

The movement of blood through the capillaries surrounding the alveoli maintains a concentration gradient to drive diffusion of oxygen into the blood

Answer 41