THE HUMAN GAS EXCHANGE SYSTEM, Distribution of Tissues in the Gas exchange system, Gas exchange processes, Features of the alveoli:, Structure & functions. This contains extensive information that got me an A in paper 1 and paper 2.
TOPIC 9: THE GAS EXCHANGE SYSTEM
THE HUMAN GAS EXCHANGE SYSTEM
- Gas exchange takes place in the human thorax. This is a collection of organs
and tissues in the chest cavity.
- Trachea: the airway that leads from the mouth and nose to the bronchi. The
trachea is lined with mucus - secreting Goblet cells and cilia. The cilia sweep
microorganisms and dust away from the lungs
- Lungs: humans have two lungs, both which are a central part of the
respiratory system and where gas exchange takes place.
- Bronchi: the left and right bronchi are at the bottom of the trachea and are
similar in structure, but narrower. The bronchi lead to bronchioles
- Bronchioles: these are narrow tubes (less than 1mm) which carry air from the
bronchi to the alveoli. As they are so narrow, they have no supporting
cartilage and so can collapse.
- Alveoli: the main site of gas exchange in the lungs. These are tiny sacs with
many structural adaptations to enable efficient gas exchange, such as their
thin walls and large surface area to volume ratio.
- Capillary network: an extensive network of capillaries surrounds the alveoli
and are an exchange surface between the lungs and the blood. During gas
exchange, oxygen diffuses from the alveoli and into the capillaries, while
carbon dioxide diffuses the other way and is exhaled.
, Distribution of Tissues in the Gas exchange system
- Cartilage is a strong and flexible tissue found in various places around the
body. One place is in rings along the trachea, called Tracheal rings. These
rings help to support the trachea and ensure it stays open, while allowing it to
move and flex while we breathe.
- Ciliated epithelium is a specialised tissue found along the trachea down to the
bronchi. Each cell has small projections of cilia which sweep mucus, dust and
bacteria upwards and away from the lungs and the epithelium itself.
- Goblet cells can be found scattered throughout the ciliated epithelium in the
trachea. They are mucus - producing cells that secrete viscous mucus which
traps dust, bacteria and other microorganisms and prevents them from
reaching the lungs. The mucus is then swept along by the cilia of the ciliated
epithelium upwards and swallowed. The mucus and any microorganisms will
then be destroyed by the acid in the stomach.
- The alveoli have a lining of thin squamous epithelium that allows for gas
exchange, the squamous epithelium forms the structure of the alveolar wall
and so is very thin and permeabel for the easy diffusion of gases.
- Smooth muscle can be found throughout the walls of the bronchi and
bronchioles. It helps to regulate the flow of air into the lungs by dilating when
more air is needed and constricting when less air is needed.
- Each alveolus is surrounded by an extensive network of capillaries. Carbon
dioxide diffuses out of the capillaries and into the alveoli to be exhaled, while
oxygen diffuses the other way from alveoli and into the capillaries to be
carried around the body.
- These capillaries have a diameter of around 3-4μm, which is only wide
enough for one red blood cell to travel through at any one time, ensuring that
there is sufficient time and opportunity for gas exchange to occur.
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