UNIT 3: The Human Breathing System

Question 1

structure and function of: nasal and buccal cavities

Answer 1

• warm and moisten air entering lungs

- mucus and small hairs filter the air and then transport the dirt-loaded mucus to the pharynx where it is swallowed.

Question 2

structure and function of: pharynx

Answer 2

• area between oesophagus and windpipe (trachea).
• pharynx has a sphincter (epiglottis) that closes over the opening of the trachea that prevents food travelling into the trachea.

Question 3

structure and function of: glottis

Answer 3

opening to the trachea

Question 4

structure and function of:epiglottis

Answer 4

• sphincter that closes over the glottis to prevent food getting into the trachea during swallowing.
• swallowing causes the vocal chords to pull on the glottis and the larynx to be pulled upwards thereby closing the epiglottis over the glottis.

Question 5

structure and function of: larynx

Answer 5

• made of cartilage and sits on top of the trachea.
• three functions:
  1. produces sound.
  2. controls air flowing into and out of the trachea.
  3. directs food into the oesophagus.

Question 6

structure and function of: trachea

Answer 6

• directs inhaled air into the lungs.
• contains c-shaped rings of cartilage that keeps the trachea open.
• cilia and trachea carry dirt-laden mucus up the pharynx.

Question 7

structure and function of: bronchi

Answer 7

• 2 divisions of the trachea.
• directs air into respective lung.
• supported by cartilage.

Question 8

structure and function of: bronchioles

Answer 8

• tiny divisions of the bronchi.
• air passages that are less than 1mm in diametre.
• not supported by cartilage

Question 9

structure and function of: lungs

Answer 9

• composed of spongy, elastic tissue that expands easily during inhalation and recoils rapidly as exhalation occurs.

Question 10

structure and function of: pleural membranes

Answer 10

• thin pair of membranes covering and separating the lungs from other organs, such as the heart.
• the lungs are stuck to the ribcage and diaphragm by the pleural fluid

Question 11

structure and function of: rib cage

Answer 11

• composed of 12 thoracic vertebrae, 12 ribs and the sternum.
• muscles are located between each rib - called the intercostal muscles that contract causing the rib cage to move upwards and outwards, drawing air into the lungs

Question 12

structure and function of: alveoli

Answer 12

• tiny air sacs at the end of the bronchioles where gas exchange occurs.
• walls of alveoli are only 1 cell thick to maximise diffusion.
• each alveolus has rich blood supply as many capillaries surround them.
• there are ~700 million alveoli with a total surface area of 90 m^2

Question 13

essential features of the alveoli and capillaries

Answer 13

• alveoli are numerous
• alveoli have rich blood supply
• alveoli have walls only one-cell thick.
• alveoli surface is moist
• alveoli walls are elastic
• capillaries that surround each alveolus are only one-cell thick

Question 14

gas exchange

Answer 14

occurs by diffusion

Question 15

mechanism of inhalation

Answer 15

• active process where the brain sends signal to the inspiratory muscles (intercostals and disphragm) to contract.
• rib cage expands upwards and outwards and the diaphragm pulls downwards.
• the movements of the ribcage and the diaphragm reduce the pressure within the thoracic cavity and air rushes in.
• inhalation can be consciously and sub-consciously controlled.

Question 16

mechanism of exhalation

Answer 16

• passive process where there is normally no signal send to the inspiratory muscles
• can be an active process during strenuous activity when the brain sends signal to the abdominals to contract forcibly expelling air from the thoracic cavity.
• during exhalation intercostals and diaphragm relax
• rib cage moves down and inwards and the disphragm pushes upwards.
• the movements of the ribcage and the diaphragm during exhalation increase the pressure within the thoracic cavity and air rushes out.

Question 17

carbon dioxide and breathing control

Answer 17

• carbon dioxide dissolved in the blood is the most powerful stimulant for an increase in the rate of breathing.
• receptors in the brain sense the levels of carbon dioxide in the blood and respond by increasing or decreasing the rate and depth of breathing.

Question 18

effect of exercise on breathing rate

Answer 18

• exercise stimulates increased respiration which produces more carbon dioxide which diffuses into the bloodstream.
• the brain is extremely sensitive to changes in the carbon dioxide concentration within the bloodstream and acts on this by increasing breathing rate and heart rate to excrete the excess carbon dioxide.

Question 19

asthma

Answer 19

• one possible cause: immune reaction to an external allergen (e.g. pollen).
• symptoms: difficulty breathing due to constriction of airways.
• one possible preventative measure: avoid the allergen (e.g. pollen) by avoiding area where the allergen is present in high quantities.
• one possible treatment: the inhaler that has drugs in it to stimulate the airways (bronchi & bronchioles) to widen and dilate.