The Respiratory System Allows Gas Exchange 4

Describe the structure and function of the nose.

• air enters the body through the mouth and nose

• the lining of the nose and nasal cavity is lined by mucous membranes

  • as air passes over the membranes, it is warmed and humidified

• the hairs and mucus lining the nose trap debris, preventing it from reaching the lungs

Describe the structure and function of the pharynx/throat.

• region from the nasal cavity to the top of the trachea and oesophagus

• provides a passage way for the air to travel through it before being diverted into the trachea by the epiglottis

  • epiglottis - a flap of elastic cartilage

• during inhalation, the epiglottis covers the oesophagus, guiding the air into the trachea

• during swallowing, the epiglottis covers the larynx, preventing food from entering it

Describe the structure and function of the larynx.

• a cartilage structure joining the pharynx and trachea

• contains the vocal cords, which are mucous membranes that are able to vibrate as air pass over them

• produces sound

• protects the lower respiratory tract from aspirating food into the trachea while breathing

Describe the structure and function of the trachea.

• also known as windpipe because it carries the air into and out of the lungs

• made up of C-shaped cartilage rings that hold the structure open, ensuring air can always pass through it

• at its base, the trachea splits into 2 branches, 1 branch taking air into each lung

• the epithelial lining of the trachea produces mucus, in order to trap dust and debris and prevent it from entering the lungs

• the cilia that line the trachea are able to move in a wave-like motion to take the mucus and debris up to the pharynx so that it can be swallowed and digested

Describe the structure and function of the bronchi.

• at the end of the trachea, the structure splits into 2 primary bronchi (1 for each lung)

• split further into secondary bronchi, then into tertiary bronchi, taking the air into each lobe of the lung

• made up of C-shaped cartilage rings

• as the bronchi get smaller, the cartilage is more spread out, with smooth muscle and elastin forming more of the structure

Describe the structure and function of the bronchioles.

• formed when tertiary bronchi divide to form smaller airways, which continues to split until they end in millions of terminal bronchioles

• made up of smooth muscle and elastin that allow the bronchioles to control the flow of air in the lungs, expanding when the body needs more oxygen

• cilia and mucus are also present, protecting the lungs from contaminants

Describe the structure and function of the lungs.

• 2 lungs take up the whole of the chest cavity, except for the space between them (mediastinum) that is occupied by the heart and blood vessels

• each lung is divided into lobes with the left lung having 2 lobes while the right has 3

Describe the structure and function of the pleura and pleural fluid in the lungs.

• visceral pleura covers the surface of the lungs, cushioning the lungs and parietal pleura lines the inside of the chest

• between these 2 layers of membrane is a thin layer of pleural fluid that acts as a lubricant, allowing the 2 layers to slide easily against each other

• pleura and pleural fluid work together to facilitate smooth, frictionless lung movement during breathing

Describe the structure and function of the alveoli.

• inside the lungs the smallest bronchioles open into clusters of tiny air sacs called alveoli

• 1 cell thick wall and surrounded by a network of blood capillaries

• functional units of the lungs

• alveoli are the surface for gaseous exchange, allowing a net flow of oxygen to pass from the airways into the blood and CO2 to pass from the blood into the airways

Describe the structure and function of the ribs.

• bones that form the framework of the chest

• protect the vital organs in the chest, including the heart and lungs, while also facilitating breathing by allowing the rib cage to expand and contract

Describe the structure and function of the intercostal muscles.

• muscles between the ribs

• contract to move the rib cage upwards and outwards to increase the chest volume when breathing in

Describe the structure and function of the diaphragm.

• muscles that separate the chest from the abdomen

• contract and flatten downwards to increase the chest volume when breathing in

What is ventilation?

process by which air is moved into and out of the lungs

Why does air flow into and out of the lungs?

air flows into and out of the lungs due to differences in air pressure because air flows from places of higher pressure to places of lower pressure

Describe the process of inspiration/inhalation and the structures involved.

• process of taking air into the lungs

• for air to flow into the lungs, the pressure of air in the lungs must be less than the atmospheric pressure outside the body

• decreasing the pressure of air in the lungs is achieved by increasing the volume of the lungs, where the diaphragm and external intercostal muscles contract

• the diaphragm becomes flatter and the rib cage moves upwards and outwards, increasing the volume of the chest cavity

• as the pleura adheres to the internal wall of the chest cavity, the lungs expand with the expanding chest cavity

• increased lung volume means that the air pressure inside the lungs is slightly lower than the pressure outside

• during normal, quiet breathing, the diaphragm is mainly responsible for the changes in chest volume

Describe the process of expiration/exhalation and the structures involved.

• occurs in the opposite way to inspiration

• for air to flow out of the lungs, the pressure inside the lungs must be more than the atmospheric pressure outside the body

• achieved when diaphragm and external intercostal muscles relax, so that the diaphragm bulges more into the chest cavity and the rib cage moves downwards

• passive process when breathing quietly at rest

How does the alveoli assist lungs in their function?

• provide a large internal surface area so that large amounts of gases can be exchanged in a relatively short time

• each alveolus is well supplied with blood vessels, so that as much blood as possible is close to the air in the alveolus

  • the continuous blood flow helps the maintenance of a concentration gradient of O2 and CO2 inside and outside the lungs

• have a thin membrane that is 1 cell thick, so that gas molecules do not have far to travel when moving into or out of the blood

• the membrane should be covered by a thin layer of moisture because gases can diffuse into and out of the blood only when they are dissolved in fluid

• a slightly oily surfactant that prevents the alveolus walls from collapsing and sticking together

What are the features of lungs that assist in their function?

• positioned deep inside the body which prevents excessive evaporation from the respiratory surfaces

• lung volume can be changed by the movement of the muscles and diaphragm, so that air is made to flow into and out of the lungs

  • the constant changing of air in the alveoli helps to ensure that there is always a concentration gradient of O2 and CO2 between the air and the blood

Describe the process of gas exchange.

• the blood in the capillaries surrounding the alveoli is brought to the lungs by the pulmonary arteries

  • this blood has a lower concentration of oxygen than the air in the alveolus as it has been through the capillaries of the body, where much of the oxygen has been taken up by the body cells

  • oxygen diffuses from the higher concentration in the air in the alveolus to the lower concentration in the blood

• blood arriving at the capillaries of the alveoli has come from the body circulation where it has picked up CO2 produced from respiration in the cells

  • the concentration of CO2 in the alveolar capillaries is higher than the concentration in the air in the alveolus

  • CO2 diffuses from the higher concentration in the blood to the lower concentration in the air in the alveolus

• oxygenated blood leaves the capillaries of the alveoli and is taken to the heart in the veins from the lungs

How is a concentration gradient maintained for the diffusion of gases into and out of the blood?

• the constant flow of blood through the capillaries

  • as the blood flowing through the capillaries around each alveolus picks up O2 and loses CO2, it is replaced by more blood being pumped into the capillaries

  • the ‘new’ blood is low in O2 and high in CO2, maintaining the concentration gradient

• the movement of air into and out of the alveoli as we breathe in and out

  • the air that has picked up CO2 from, and lost oxygen to, the blood is replaced by ‘new’ air with each breath

  • the ‘new’ air is low in CO2 and high in O2

What is emphysema and how is it caused?

• disease usually caused by long-term exposure to irritating particles in the air taken into the lungs (e.g. tobacco smoke)

• people who work in high-dust conditions/live in cities with high air pollution are at greater risk

• the irritating particles cause damage to the alveoli → losing their elasticity (often replaced with fibrous tissue) and may break down, reducing the internal surface area of the lung

• because of this, the lungs are constantly inflated and breathing out no longer occurs passively but requires voluntary effort

• 2 problems:

  • inadequate surface area for gas exchange

  • difficulty in ventilating the lungs