gaseous exchange
TRANSCRIPT
LUNG FUNCTION
• Humans need to get oxygen into the blood for respiration and get
rid of carbon dioxide made by respiring cells. This is where
breathing(or ventilation its sometimes called)and the lung.s come
in
LIGHT ACADEMY 3M.R.NJOROGE
Lungs are specialized organs for gaseous exchange
Fig 1.0 Lung structure
• As you breathe in the air enters the trachea (wind pipe)
• The trachea splits into two bronchi-one 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.
• The rib cage,intercostal muscles and diaphragm all work together to move air in and out.
LIGHT ACADEMYM.R.NJOROGE 4
In humans gaseous exchange happens in the
alveoli
About alveolus• Lungs contain millions of
alveoli-the gas exchange surface.
• Each alveoli is made from a single layer of thin ,flat cells called alveolar epithelium.
• Alveoli are arranged in bunches and the end of bronchioles
• They are surrounded by network of capillaries, giving each alveolus its own blood supply.
Structure of alveolus
LIGHT ACADEMYM.R.NJOROGE 6
• Oxygen diffuses out of the alveoli,across the alveolar
epithelium and the capillary endothelium.(a type of
epithelium that forms the capillary wall),and into
haemoglobin in the blood.
• Carbon dioxide diffuses into the alveoli from the blood
,crossing the capillary endothelium then the alveolar
epithelium. After entering the alveolar space its breathed
out.
LIGHT ACADEMYM.R.NJOROGE 7
Epithelial tissue is
pretty common in
the body. Its
usually found on
exchange
surfaces
ADAPTATIONS OF ALVEOLI TO GASEOUS
EXCHANGEAlveolus have features that speeds up the rate of diffusion so gases can be exchanged quickly.
• A thin exchange surface-the alveolar epithelium is only one cell thick. This means there's is a short diffusion distance.(which speeds up diffusion)
• A large surface area –the numerous alveoli means there's large surface area for gas exchange.
• Alveoli are highly vascularised to increase the rate of blood flow to and from alveoli.
LIGHT ACADEMYM.R.NJOROGE© 8
Gaseous exchange has different parts with different
functions
The respiratory system has other parts that help it to exchange gases efficiently.
• Goblet cells secrete mucus. The mucus trapsmicroorganisms and dust particles in the inhaled air stopping them from reaching the alveoli.
• Cilia on the surface of the cells beat the mucus ,which move it (plus trapped microorganisms and dust) upwards away from the alveoli towrads the throat ,where its swalloowed.thishelps prevent lung infection.
• Elastic fibres in the walls of
the trachbronchi
,bronchioles and alveoli
help in the process of
breathing out.on breathing
in ,the klungs inflate and the
elastic fibres are strethed
,then the fibres recoilto help
push the air out when
exhaling.
• Smooth muscle
LIGHT ACADEMYM.R.NJOROGE 9
Review question
LIGHT ACADEMYM.R.NJOROGE 10
1. Fig. 6.1 is a section through lung tissue showing an alveolus and its blood
supply.(a) (i) Name the type of epithelial cell shown by
label lines A and B.[1] squamous / pavement
(epithelial) ;
(ii) Describe how the elastic fibres of the alveoli
contribute to the healthy functioning of
the lungs.[2] )
stretch / expand, on inspiration and recoil on
expiration ;R contraction (stretch) to increases,
surface area / volume of air, for, diffusion / gas
exchange ;
(recoil) to help, expel air / force air out ;
A carbon dioxide A if destroyed then cannot expel
air
prevent alveoli, bursting / breaking / AW ;ref. to
emphysema if elastic fibres destroyed ; (b) The actual diameter of the alveolus along
the line X–Y is 220 micrometres (μm).
Calculate the magnification of Fig. 6.1.
Show your working and give your answer to the
nearest whole number.
answer × [2]
(c) Outline two features of a gas exchange surface
that are shown on Fig. 6.1.[2]
LIGHT ACADEMYM.R.NJOROGE 11
b) award two marks if correct answer (anything in range 336–346)
allow +/– 1 mm in reading the line (74–76 mm)
75000 μm / 220 μm = 341 ;;if answer incorrect, award one mark for
correct measurement with unit and division by 220
award one mark if correct answer given to one or more decimal
places[2]
(c) look for two ideas – follow usual rules for marking numbered
answer lines
thin, alveolar wall / epithelial lining / AW ;
Ashort diffusion distance (between air in alveolus and blood in
capillary)
Asquamous cells are thin Rthin, membrane / cell membrane R large
surface area surrounded by, capillaries
/ capillary network ;A close contact with, capillaries / blood (vessels /
cells) A many capillaries A large area of alveolus in contact with,
capillaries / blood
LIGHT ACADEMYM.R.NJOROGE 12
(d) max 3 if no ref. to diffusion
(named) gas(es), diffuse
down, pressure gradients / concentration gradient / AW ;
A from high(er) partial pressure to low(er) partial pressure
A high(er) concentration to low(er) concentration ignore
‘along a concentration gradient’
in the answers accept the following AWs
capillaries / haemoglobin for blood
lungs for alveoli body for tissues
lungs valid statement linking information in table below – 1 mark for each row
comparison in partial pressure may be ‘higher / lower’ not both or high and
low, but if not then figures have to be given
LIGHT ACADEMYM.R.NJOROGE 13
(d) Fig. 6.2 is a simplified diagram of the circulatory system of a human, showing gas
exchange in the lungs and in respiring tissue. The partial pressures of oxygen
(pO2) andcarbon dioxide (pCO2) at four locations are also shown.
With reference to Fig. 6.2, explain
how the differences in pO2 and pCO2 in the alveolus and in blood
enable gas exchange in the lungs
and respiring tissue……………………..[4]