section 1: exchange & transport - topic 2: gas exchange in mammals

Question 1

in mammals, what are the lungs?

Answer 1

gas exchange organs.

Question 2

what is the structure of the gaseous exchange system?

Answer 2

as you breathe in, air enters the trachea.
the trachea splits into 2 bronchi - 1 bronchus leading to each lung.
each bronchus then branches off into smaller tubes called bronchioles.
the bronchioles end in small ‘air sacs’ called alveoli - this is where gases are exchanged.

there are lots of alveoli in the lungs to provide a large surface area for diffusion.

Question 3

what are the key features of the gaseous exchange system?

Answer 3

goblet cells.
cilia.
elastic fibres.
smooth muscle.
cartilage.

Question 4

describe goblet cells.

Answer 4

goblet cells (lining the airways) secrete mucus. the mucus traps microorganisms and dust particles in the inhaled air, stopping them from reaching the alveoli.

Question 5

describe cilia.

Answer 5

the cilia are hair-like structures on the surface of epithelial cells lining the airways. they beat the mucus secreted by goblet cells. this moves the mucus upward, away from the alveoli, towards the throat, where it’s swallowed. this helps prevent lung infections.

Question 6

describe elastic fibres.

Answer 6

elastic fibres in the walls of the trachea, bronchi, bronchioles, and alveoli help the process of breathing out. on breathing in, the lungs inflate and the elastic fibres are stretched. then, the fibres recoil to help push the air out when exhaling.

Question 7

describe smooth muscle.

Answer 7

smooth muscle in the walls of the trachea, bronchi, and bronchioles (except the smallest) allows their diameter to be controlled. during exercise, the smooth muscle relaxes, making the tubes wider. this means there’s less resistance to airflow and air can move in and out of the lungs more easily.

Question 8

describe cartilage.

Answer 8

rings of cartilage in the walls of the trachea and bronchi provide support. it’s strong but flexible - it stops the trachea and bronchi collapsing when you breathe in and the pressure drops.

Question 9

what is the distribution of features in the gaseous exchange system?

Answer 9

trachea: cartilage - large c-shaped pieces, smooth muscle - yes, elastic fibres - yes, goblet cells - yes, epithelium - ciliated.

bronchi: cartilage - smaller pieces, smooth muscle - yes, elastic fibres - yes, goblet cells - yes, epithelium - ciliated.

larger bronchiole: cartilage - none, smooth muscle - yes, elastic fibres - yes, goblet cells - yes, epithelium - ciliated.

smaller bronchiole: cartilage - none, smooth muscle - yes, elastic fibres - yes, goblet cells - no, epithelium - ciliated.

smallest bronchiole: cartilage - none, smooth muscle - no, elastic fibres - yes, goblet cells - no, epithelium - no cilia.

alveoli: cartilage - none, smooth muscle - no, elastic fibres - yes, goblet cells - no, epithelium - no cilia.