the mammilian gaseous exchange system (c,d)

Question 1

What are the conditions of the gaseous exchange?

Answer 1

• moist, so oxygen dissolves in the water before diffusing into the body tissues
• ideal for oxygen intake = evaporation of water
• allows efficient gas exchange but minimises the amount of water lost from the body
• lots of oxygen needed for cellular respiration + CO2 produced which needs to be removed

Question 2

Describe nasal cavity

Answer 2

• large SA with good blood supply - warms air to body temperature
• hairy lining - secretes mucus to trap dust + bacteria
• moist surfaces - increased humidity of incoming air, reducing evaporation from the exchange surfaces

Question 3

Describe the trachea

Answer 3

• main airway to carry clean, warm, moist air into the chest
• wide tube supported by incomplete rings of strong, flexible cartilage which stop the trachea from collapsing
• incomplete so food can move easily down the oesophagus behind the trachea
• lined with ciliated epithelium with goblet - secrete mucus onto lining of the trachea, to trap dust + microorganisms that have escaped the nose lining
• cilia beat and move the mucus away from the lungs

Question 4

Describe the bronchus

Answer 4

• similar to trachea
• some supporting rings of cartilage but smaller
• left bronchus to left lung and right bronchus to right lunch

Question 5

Describe bronchioles

Answer 5

• no cartilage rings - walls have small muscle
• when smooth muscle contracts bronchioles constrict; when it relaxes the bronchioles dilate
• alters amount of air reaching the lungs
• lined with thin layer of flattened epithelium - making some gas exchange possible

Question 6

Describe alveoli

Answer 6

• tiny air sacs - main gas exchange surface
• consists of a thin layer of flattened epithelial cells along with some collagen and elastic fibres
• they allow the alveoli to stretch as air is drawn in
• elastic recoil - when they return to resting size they help squeeze the air out

Question 7

Adaptations of alveoli

Answer 7

• large SA - needed for lots of oxygen - 500mil per lung
• thin layers for short diffusion distances between the air in the alveolus and the blood in capillaries
• good blood supply - surrounded by a network of capillaries
• good ventilation - breathing moves air in and out
• walls covered in a solution of water, salts + lung surfactant - helps alveoli remain inflated. oxygen dissolves in the water before diffusing into the blood but water can also evaporate into the air in the alveoli

Question 8

How is air moved in and out of the lungs?

Answer 8

Due to pressure changes in the thorax (chest cavity) brought about by the breathing movements. movement of air = ventilation.

Question 9

Describe the rest of the parts of the lungs

Answer 9

• ribcage - provides a semi-rigid case within which pressure can be lowered with respect to the air outside it
• diaphragm - broad, domed sheet of muscle - forming the floor of the thorax
• external and internal intercostal muscles are found between the ribs
• thorax is lined by pleural membranes which surround the lungs
• space between, the pleural cavity, is usually filled with a thin layer of lubricating fluid so the membranes slide easily over each other as you breathe

Question 10

Inspiration

Answer 10

• inhalation - energy-using
• diaphragm contracts, flattens and lowers
• external intercostal muscles contract, moving the ribs upwards and outwards
• volume of thorax increases so pressure is reduced
• pressure in thorax is lower than the atmospheric air, so air is drawn through everything into the lungs
• this equalises the pressure inside and outside the chest

Question 11

Exhalation

Answer 11

• exhalation - passive
• diaphragm muscles relax, moving up into resting domed shape
• external intercostal muscles relax so ribs move down and inwards under gravity
• elastic fibres in the alveoli return to their normal length
• these changes decrease the volume of the thorax, so the pressure is greater than the atmospheric air, so air moves out of the lungs until the pressure has equalised

Question 12

What happens when energy is used to exhale forcibly?

Answer 12

• internal intercostal muscles contract, pulling the ribs down hard and fast
• abdominal muscles contract, forcing the diaphragm up to increase pressure in the lungs rapidly