Respiratory System

• Gas exchange

  all cells in all organisms need to exchange gases with their surroundings regularly because gases like oxygen and carbon dioxide can't be easily stored in the body.
• Gas exchange

  Gas exchange in animals is the diffusion of oxygen from the external to the internal environment and the diffusion of carbon dioxide from the internal to external environment
• gas exchange occurs across

  alveoli (in lungs - large terrestrial animals)

  skin (amphibians)

  spiracles (insects)

  gills (fish)

  fine tubes in air sacs (birds)

  plasma membrane (parasitic jellyfish)
• What is the first requirement for the surface where gas exchange occurs?

  It needs to be moist.
• Why must the surface for gas exchange be moist?

  For gases to dissolve in the water and diffuse from one side of the membrane to the other.
• What is the second requirement for the surface where gas exchange occurs?

  It must be thin and permeable, so that gas molecules can move across quickly
• What is the third requirement for the surface where gas exchange occurs?

  It must have a large surface area in relation to the volume of the organism, to provide the gaseous requirement
• What is the fourth requirement for the surface where gas exchange occurs?

  It must have a greater concentration of required gas on one side of the membrane than the other.
• What is the fifth requirement for the surface where gas exchange occurs?

  It must be highly vascularised.
• What does it mean for a surface to be highly vascularised in the context of gas exchange?

  It means a dense network of very narrow capillaries is present.
• Why is a dense network of narrow capillaries important for gas exchange?

  It slows the movement of blood to provide enough time for gas exchange to occur.
• How do the requirements for gas exchange surfaces relate to each other?

  Each requirement ensures efficient diffusion and exchange of gases.
• respiratory surfaces are

  spiracles, gills, alveoli, and skin
• spiracles

  Spiracles have small opening found along thorax and abdomen that allow gases to pass through chitin tubes called tracheae, oxygen passes through smaller tubes called tracheoles that carry oxygen directly to into cells, body movements such as abdomen pumping speed up the rate of diffusion of gases from tracheal system into body cells, insects have water at the end of tracheoles to dissolve oxygen for diffusion.
• spiracles

  efficiency is low due to the valves that close in order to prevent water loss
• gills

  Gills in animals must have water passing through them, oxygenated water passes through the gills via the mouth and the dissolved oxygen rapidly diffuses across the surface, long thin filaments in gills increase surface area -> this is highly vascularised and uses countercurrent system, oxygen diffuses directly into the blood stream from the gills, fish constantly open their mouths and swim to allow water to pass over gills.
• Gills

  Have a very high efficiency due to countercurrent system which maximises oxygen amount that their blood can pick up
• Alveoli

  Alveoli are air sacs that are located at the end of the bronchiole in the lung, the lungs of mammals take in oxygen by inhalation and the air is warmed and moistened, air flows into alveolar sacs and then circulates into alveoli where gas exchange occurs with the capillaries that are wrapped around alveoli
• alveoli

  efficiency is high because the lining in of the alveoli is thin so gases can quickly flow through it
• Skin

  Skin is a respiratory surface that diffuses and dissolves gases across cell membranes, below the skin is a dense network of capillaries, facilitating gas exchange between the external environment and the circulatory system
• Skin

  Has moderate efficiency
• respiratory surfaces must be thin, moist, and covered in epithelial cells that allow carbon dioxide and oxygen to pass
• gas exchange in amphibians

  Amphibian skin is highly permeable with capillaries lying beneath the surface -> skin is where they exchange gases with external environment, amphibian lungs is not as effective as mammalian lung because their diaphragm is not as developed, their diaphragm muscle contracts to create a pressure gradient to force breath into their lungs, so amphibians must actively push air into lungs which is inefficient
• Gas exchange in mammals

  Most mammals are terrestrial and obtain all oxygen requirements from air, they are endothermic -> they use heat generated by metabolic activity, including respiration to keep a stable body temperature.
• Gas exchange in mammals

  aerobic cellular respiration takes place in their cells and it generates heat as a byproduct
• Gas exchange in mammals

  mammals demand for oxygen is high in order to maintain a constant body temperature
• Gas exchange in mammals

  the mammalian lung gas evolved to efficiently handle gas exchange
• alveoli

  air passes into the body through the nose and mouth -> it travels past the throat and larynx into the tracheae -> the tracheae branches into two bronchi which lead to the lungs -> each bronchus divides into smaller tubes called bronchioles once it enters the lungs, each bronchiole ends in a cluster of tiny air sacs called alveoli, there is a network of capillaries surrounding each alveolus.
• alveoli

  The thin wall of alveolus provides a boundary for the external environment, while the thin wall of the capillary provides a boundary for the internal environment, which is the blood.
• Capillaries are so narrow, red blood cells get slightly compressed into a conical shape as they pass through -> this helps slow down blood flow which gives more time for gases to be exchanged efficiently
• ventilation and breathing rate

  To help the body get oxygen from the air, we need to breathe it into the lungs, where it reaches tiny air sacs called alveoli -> this is where oxygen passes into our blood
• breathing in and out happens thanks to the movement of our ribs and a muscle called the diaphragm
• the diaphragm works together with muscles between the ribs called intercostal muscles
• when we breathe in -> diaphragm and intercostal muscles contract, which makes the chest bigger, this creates a lower pressure inside the lungs so air gets pulled in
• when we breathe out -> the diaphragm and intercostal muscles relax, making the chest smaller again, this increases the pressure inside the lungs, pushing the air out
• inhalation -> the diaphragm and intercostal muscles tighten up which causes the rib cage and chest area to expand
• exhalation -> the diaphragm and intercostal muscles relax -> makes rib cage and chest area shrink, as thoracic cavity gets smaller, the air pressure inside the lungs increase -- this higher pressure pushes air out of the lungs
• the speed at which we breathe is mainly controlled by the amount of carbon dioxide (CO2)
• our cells create CO2 during respiration which forms into bicarbonate ions which travels through the blood to the lungs, where CO2 i removed when we exhale 


  as CO2 levels drop, our brain sense that there is less need to get rid of CO2, so it signals our body to slow down and take shallower breaths -> this helps maintain balance in our body systems, making sure we dont breathe more than necessary
• Gas exchange in birds

  Birds have air capillaries and a system of air sacs that make sure air flows in one direction through their lungs -> this one way airflow allows birds to absorb oxygen more efficiently, which is important for birds as flying takes a lot of energy