1. Diversity… Gas exchange and Circulation

2. Structure of the Humans lungs

3. Human gas exchange. The basics.
Human Gas Exchange happens in the Alveoli.
The lungs consist of trachea that divides into 2 bronchi that then divide into many bronchiole.
Diaphragm is a sheet of muscle underneath the lungs.
Alveoli are millions of tiny air sacs at the ends of the bronchiole. These give a large surface, which are richly supplied with blood from capillaries. Alveoli walls are thin, moist and elastic.
How does it happen?
The diaphragm contracts increasing the volume of chest cavity and drawing air into the lungs.
Diaphragm relaxes reducing volume of chest cavity and forcing air out of the lungs.
Gas exchange and transport systems linked. (blood carries gasses to and from cells)
Gas exchange occurs between air and blood across alveoli walls.
The lung surface must be internal so that it remains moist for gas exchange.

4. Gas exchange happens by diffusion of gasses across the thin walls of the alveoli. The alveoli has a total surface area between 70-90m2.
The alveoli have lining which helps dissolve the gasses. These are surrounded by lots of tiny capillaries. This allows plenty of blood for the gasses to pass in and out of.
In result of gas exchange most of the oxygen and carbon dioxide in the inhaled/exhaled air changes with the air we breathe in which contains a higher percentage of oxygen and a lower percentage of carbon dioxide air that we breathe out.

5. Human Circulation Humans have a closed double circulatory system
Blood carries oxygen using red blood cells.
Closed system blood contained entirely in vessels.
Double circuit blood flows in two circuits. One carries blood to lungs and the other carries blood to tissues.
The heart has 4 chambers separated into two separate pumps. One for each circuit.
Right atrium receives deoxygenated blood from the body at low pressure and pumps it to the
Right ventricle which pumps the deoxygenated blood to the lungs at high pressure.
Left atrium receives oxygenated blood from the lungs at low pressure and pumps it to the
Left ventricle which then pumps the oxygenated blood to the body at high pressure.

6. Blood arrives at tissue at high pressure directly from heart
Blood arrives at tissue at high pressure directly from heart. This creates a high oxygen delivery rate.
Veins return blood to the heart at low pressure. Body muscles squeeze thin walled veins. Valves prevent back-flow.
Capillaries are tiny vessels penetrating tissues. Walls one cell thick allow rapid exchange of materials.
Arteries take blood away from the heart at a high pressure. These have thick elastic walls.

7. Insects Don’t Have Lungs

8. Insect Gas Exchange Insects don’t have lungs!!!
Most insects have a waterproof cuticle the cuticle water permeable and they gain required oxygen by diffusion across their cuticle.
Most insects have a respiratory system which is a system with two internal tubes called trachea.
Trachea have spiral stiffening to stop it collapsing.
Air enters from the outside through many openings called spiracles. There are two pairs of spiracles one on the thorax and the other on the abdomen.
O2 from spiracles --> tracheae --> tracheoles --> cells

9. Insect Circulation Insects have an open circulatory system.
Haemolymph does not carry oxygen no red blood cells are required.
Open system haemolymph flows freely through body cavity bathing tissues. (most haemolymph are not contained in vessels)
Dorsal vein single tube running along back of insect. Empties the haemolymph into head.
Tubular heart series of chambers separated by valves. Pumps the haemolymph back towards the head.
Wave like contractions of muscles on chambers create pumping action.
Ostia small holes which allow re-entry of the haemolymph to heart as muscles relax.
The open system is suitable for insects as they are small in size this mean shorter distance for diffusion of nutrients. This is not suitable for larger animals.

10. Gas exchange Fish

11. Fish Gas Exchange Fish extract oxygen from the water using gills.
Gill Cover protects gills and helps pump water.
Gills many thin filaments held by a bony gill bar.
Lamellae thin flaps on filaments that give a large surface richly supplied with blood from capillaries.
Breathing mouth opens with the gill cover closed to draw water into mouth cavity.
Mouth shuts as the gill cover opens forcing water over gills and out under gill cover.
Blood flows in opposite direction to water to give max oxygen and extraction.
Gas exchange and transport systems linked (blood carries gasses to and from cells)
Gas exchange occurs between water and blood across lamellae surface.

12. Fish Circulation Fish have a closed single circulatory system.
Blood carries oxygen using red blood cells.
Closed system blood contained all in vessels.
Single circuit blood flows through the gills and then through the body tissue in one single circuit.
The fish heart has three chambers connected in series acting as a single pump.
Sinus Venosus receives deoxygenated blood from the body at low pressure and pumps to the Atrium which then pumps blood to the ventricle which are thick walls and pumps blood at a high pressure to gills.
The blood loses pressure through gill capillaries before reaching the body.
There is no separate pump for oxygenated blood.
Blood arrives at tissue a low pressure from the lungs. This limits the efficient delivery of oxygen.
This is suitable for fish as their oxygen needs are lower as they are supported by water. Which means this is not suitable for land mammals as they require a higher oxygen delivery rate.