human gas exchange and ventilation

image of structure of human exchange system?

what is the trachea?

• the entrance to the human gas exchange system

• when you breathe in, air flows through the trachea

• ridges of cartilage surround the front of the trachea to provide protection and structure

  • there is no cartilage at the back of the trachea so that the oesophagus is not constricted (movement)

bronchi?

• the trachea divides into 2 bronchi

• air flows along each bronchus to a lung

• the bronchi are made from cartilage and smooth muscle

bronchioles?

• each bronchus divides into smaller bronchioles

• the many bronchioles branch throughout the lungs into small air sacs called the alveoli

alveoli?

• they are sacks that fill with air when you breathe in

• oxygen in the alveoli diffuses into the bloodstream and carbon dioxide in the bloodstream diffuses into the alveoli

• there are millions of alveoli in the lungs

• the alveoli provide a large surface area for gas exchange

what is ventilation controlled by?

• ribcage, intercostal muscles and diaphragm

  • when you breathe in, these structures move to allow the lungs to fill with air

  • when you breathe out, these structures move to allow air to leave the lungs

capillaries in the alveoli?

• each alveolus is surrounded by a network of capillaries

• the many capillaries provide a large surface area for gas exchange between the alveoli and the bloodstream

alveolar epithelium?

• the epithelium is made up of a single layer of epithelial cells that line the walls of the alveoli

• the epithelium provides a very short diffusion distance from the alveoli to the capillaries, which maximises the rate of gas exchange

concentration gradient of capillaries?

• the capillaries supply carbon dioxide to the alveoli and oxygen is rapidly carried away from the alveoli

• the quick transport of gases in the bloodstream maintains a steep concentration gradient of oxygen and carbon dioxide

• the steep concentration gradient allows quick diffusion of gases into and out of the bloodstream

summary of gas exchange in alveoli?

• oxygen from the air moves down the trachea, bronchi and bronchioles, into the alveoli

• this movement happens down a pressure gradient

• once in the alveoli, the oxygen diffuses across the alveolar epithelium, then the capillary endothelium, ending up in the capillary

• this movement happens down a diffusion gradient

how is the alveoli adapted for efficient gas exchange?

• thin walls (alveolar epithelium)- short diffusion pathway

• large surface area - large number of alveoli means there’s a large surface area for gas exchange

  • the steep concentration gradient of oxygen and carbon dioxide between the alveoli and capillaries also increases the rate of diffusion

    • this is maintained by flow of blood and ventilation

• moist walls - gases dissolve in moisture before diffusing, more efficient diffusion

• permeable walls- gases dissolve freely across the membrane

what happens when you breathe in (inspiration)?

• the external intercostal muscles and diaphragm contract

• the internal intercostal muscles relax

• the diaphragm flattens

• this causes the ribcage to move upwards and outwards, increasing volume of thoracic activity

• as the volume of the thoracic activity increases, the pressure in the lungs decreases

  • air will always flow from an area of high pressure to low pressure, so air flows down trachea and into lungs

• inspiration is an active process- it requires energy

what happens when you breathe out (expiration)?

• the external intercostal muscles and diaphragm muscles relax

• the internal intercostal muscles contract

• this causes the ribcage to move down and in, causing diaphragm to be a dome shape

• the volume of the thoracic activity decreases, increasing pressure in the lungs

• air is forced down the pressure gradient and out of the lungs

• normal expiration is a passive process, so doesn’t require energy

what is tidal volume?

• volume of air in each breath

• average is between 0.4dm³ - 0.5dm³

what is ventilation rate?

• number of breaths per minute

  • average is about 15 breaths per minute

what is a spirometer?

• piece of apparatus that measure the gas exchange in the lungs

  • measures volume of air that is inspired and expired

what is forced expiratory volume?

• maximum volume of air that can be breathed out in 1 second

  • this cannot be more than total volume of gas in the lungs

  • because there is always a small amount of air that cannot be expired (residual air). the residual air ensures that the alveoli do not close

what is vital capacity?

• maximum volume of air that can be breathed in and out of the lungs

  • a spirometer can measure this

how to calculate pulmonary ventilation rate?

• PVR = tidal volume x breathing rate

common lung diseases?

• asthma

• pulmonary fibrosis

• tuberculosis

• emphysema

what causes gas exchange problems?

• when the exchange system is damaged. this could be due to:

  • decreased surface area

  • increased diffusion distance

  • decreased concentration gradient

emphysema and effects?

• emphysema is caused by smoking or air polluiton

• dirt and bacteria become trapped in the alveoli which damages their walls

• the alveoli provide a large surface area for gas exchange

• so, damage to the walls decreases the surface area and rate of gas exchange declines

asthma and effects?

• asthma increases the production of mucus by the epithelial cells

• the increased mucus increases the length of the diffusion distance

• the greater diffusion distance decreases rate of gas exchange

• an asthma attack also causes the smooth muscle in the bronchioles to contract, making it difficult to breathe

tuberculosis and effects?

• tuberculosis can affect the lungs, damaging the lung tissue

• the cells of the immune system can also damage the lungs

• the damaged lungs lead to a decreased tidal volume

what harmful chemicals does cigarette smoke contain?

• nicotine

• carbon monoxide

• carcinogens

what is bronchitis caused by?

• when smoke is breathed in, it damaged the cilia cells of the airways

• this means the cilia can not waft away the mucus produced by the goblet cells, and the mucus builds up

• this can lead to bronchitis, where the airways are partly blocked with mucus

what are cancers caused by?

• the carcinogens can cause tumours to form int he airways

  • smoking can cause mouth, throat and lung cancers

what does nicotine and carbon monoxide do to the body?

• nicotine: very addictive and puts a strain on the heart

• carbon monoxide: reduces ability of red blood cells to carry oxygen, which can also put a strain on the heart

  • both of these substances can cause heart diseases and strokes

correlation vs causation?

• correlation: a link between 2 things

• causation: a change in one variable directly causes a change in the other

  • e.g, just because there is a correlation between the number of of males who smoked and the mortality rate, doesn’t mean that one caused the other (causation)

• USE THIS WHEN INTERPRETING LUNG DISEASE DATA