9. Gas exchange

Question 1

Why are O2 and CO2 needed in the body?

Answer 1

O2 needed for aerobic respiration. CO2 unneeded, needs to be excreted.

Question 2

Why does gas exchange need to be able to facilitate large volumes of gas?

Answer 2

1. Humans are large multicellular organisms
2. Homeostasis - humans need to maintain constant body temperatures, therefore have high metabolic and respiratory rates

Question 3

Ventilation

Answer 3

– mechanism that moves air into (inspiration) and out of (expiration) the lungs

Question 4

Respiration

Answer 4

chemical process that produces ATP to supply energy for cells
O2 + C6H12O6 -> H2O + CO2 + ATP

Question 5

Gross structure

Answer 5

– describes the detail that you can see with the naked eye, without the help of magnifying lenses or microscopes

Question 6

Gas exchange

Answer 6

the diffusion of O2 from air in the alveolus to blood in alveolar capillaries; and diffusion of CO2 in the opposite direction

Question 7

What is the trachea?

Answer 7

A flexible airway supported by C-shaped incomplete rings of cartilage

Question 8

Why are the C-shaped rings of cartilage in the trachea incomplete?

Answer 8

Because they allow the oesophagus to expand without obstruction during swallowing, allow for flexibility.

Question 9

What is the structure of the trachea wall?

Answer 9

Smooth muscle between ends of C-shaped rings, smooth muscle

Question 10

What is the structure of the trachea lining?

Answer 10

Made of ciliated epithelium (not layered)
Ciliated epithelium consist of:
1. Goblet cells
2. Ciliated epithelial cells (contain cilia, columnar shape, attached to a basement membrane)

Question 11

What are alveoli?

Answer 11

• Tiny hollow sacs
• The site of gas exchange in mammals

Question 12

How big are alveoli?

Answer 12

• 100 um - 300 um in diameter
• 0.1 um – 0.5 um thick

Question 13

What is the structure of the alveolar wall?

Answer 13

• Very thin, large, flattened squamous epithelium cells (increase SA)
• Made of squamous epithelium connected to a basement membrane
• Some connective tissue – contains elastic fibres
• Some cells secrete surfactant (fluid that decreases surface tension during exhalation. Prevents walls from sticking to each other by cohesion)

Question 14

What is each alveolus surrounded by?

Answer 14

A network of blood capillaries.

Question 15

What is the structure of bronchi/bronchus?

Answer 15

• Similar to trachea
• Smaller diameter
• Irregular plates cartilage (NOT C-shaped)
• Wall of smooth muscle and elastic fibres
• In cross-section lining seems folded or convoluted

Question 16

What is the structure of the bronchioles?

Answer 16

• Walls thinner than bronchi
• Layer of ciliated epithelium lining seems more convoluted

Question 17

How do the bronchioles transition from bronchi?

Answer 17

• No cartilage
• Smooth muscle and elastic fibres present

Question 18

How do the bronchioles transition into the alveoli?

Answer 18

• No goblet cells
• Epithelial cells are now squamous, NOT ciliated
• Epithelial cells more cuboidal than columnar

Note: Capillary made of endothelial cells. Alveoli made of epithelial cells.

Question 20

Why is the diffusion of gases between the alveoli and blood so rapid?

Answer 20

1. Short diffusion distance
   • Walls of alveoli (single layer of epithelial cells) and capillaries (single layer of endothelial cells) 1 cell thick
   • RBCs flattened against capillary
2. Large SA:V ratio
   • Both alveoli and capillaries have very large surface areas
3. Enough time for efficient diffusion
   • Due to RBCs slowing down through pulmonary capillaries (caused by narrow capillary lumen)
4. Steep concentration gradient maintained
   Maintained through:
   • Breathing ventilating longs
   • Heart circulating blood around alveoli

Question 21

What layers will O2 molecules (in alveolar air) have to pass through to go from alveolar cavity to RBC?

Answer 21

1. From alveolar cavity through thin squamous epithelial cell
2. Through basement membrane of epithelial cell
3. Through basement membrane of endothelial cell (capillary)
4. Through endothelial cell into blood plasma
5. Through cell surface membrane of RBC
6. Binds to haemoglobin
   Note: CO2 diffuses in the opposite direction from blood to alveolus

Question 22

What are adaptations of squamous epithelium to suit function?

Answer 22

• Extremely flattened, thin (short diffusion distance)
• Small nucleus and lots of cytoplasm (little obstruction to diffusing molecules)
• Joined closely together and act as a barrier to defend against entry of pathogens into bloodstream

Question 23

How to identify cartilage in a photomicrograph?

Answer 23

• No blood vessels
• Different colour/shade of grey