Human Respiratory System
Exchange:
- Oxygen and carbon dioxide are being exchanged because oxygen is needed for respiration, and we produce carbon dioxide from respiration.
- Gas exchange requires concentration gradients for diffusion entry and exit.
Functions:
- Lungs: Major organs containing the gas exchange surfaces.
- Pleural membranes: Allow lungs to move easily during ventilation by reducing friction.
- Trachea: The windpipe leads from the nasopharynx to the two bronchi.
- Bronchiole: Smaller tubes inside the lungs leading from the bronchus to the alveoli.
- Intercostal muscles: Allow the ribcage to change in volume for ventilation.
- Bronchus: Tubes leading from the bronchi to the alveoli.
- Diaphragm: Muscle working with the intercostal muscles to allow ventilation to happen.
- Alveoli: Tiny air sacs at the end of bronchioles where gas exchange occurs.
- Ribs: Provide a moveable cage to enclose and protect the lungs.
Alveoli
- Alveoli are tiny air sacs that are the site of gas exchange.
- Each lung contains millions of alveoli, facilitating faster gas exchange and providing a large surface area for gas exchange.
- The walls of the alveoli are thin, measuring only 1 cell thick, which allows for a shorter diffusion distance, thereby speeding up gas exchange.
- The alveoli have a good blood supply to maintain a steep concentration gradient. You want to constantly have oxygen in your lungs. Blood carries away oxygen so more can enter.
- The alveolar surfaces are moist because gases must dissolve (solve) in your blood to be present.
Human Respiratory System
Inhalation:
- The intercostal muscles between the ribs contract.
- This action raises and extends the ribs.
- At the same time, the diaphragm muscle contracts and moves downwards.
- This decreases the pressure inside the chest. The air pressure outside the chest is higher, so air enters the lungs.
- The volume of air inside the chest increases.
Exhalation:
- The intercostal muscles relax.
- The ribs move inward and downward.
- At the same time, the diaphragm muscle relaxes and moves up.
- This increases the pressure inside the chest. The air pressure outside the chest is now lower, so air leaves the lungs.
- The volume of the chest decreases.
- We measure breathing with a spirometer.
The Heart
- Animals need a heart to pump blood around the body.
- Large objects require a heart. The larger the mass, the larger the heart.
- Cardiac muscle makes up the heart.
- The heart beats 60-80 times a minute (avg. resting heart rate for an adult).
- There are four chambers in the heart:
1. Two atria (also known as s.g. atrium) receive blood from veins.
2. Two ventricles work together to pump blood into the arteries.
- Blood always flows from high to low pressure. The steeper the pressure gradient, the faster the blood will flow.
- The muscle contracts to generate the pressure.
- The walls of the ventricles are thicker than those of the atria due to their need to pump blood further. The left ventricle has to pump blood even further than the right, so it has an even thicker wall.
- The aorta is the main and largest artery that carries oxygenated blood to your whole body. The PA carries deoxygenated blood to the lungs.
- The vena cava is a large vein that carries deoxygenated blood to the right atrium.
- The right atrium receives oxygen-poor blood from the body and pumps it to the right ventricle. The RV pumps the oxygen-poor blood to the lungs. The left atrium receives oxygen-rich blood from the lungs and pumps it to the left ventricle.
Double Circulatory System
- Humans have a double circulatory system.
- Blood passes through the heart twice on each complete circuit of the body. Double pump.
→ The right side pumps blood to the lungs.
→ The left side pumps blood to the body.
Advantages:
- The body can pump blood at a higher pressure than the lungs. If the pressure was too high, it would destroy the alveoli.
- This means blood can flow faster to the body.
- Additionally, it is more efficient to keep oxygenated and deoxygenated blood separate.
- If the heart had a hole, the oxygenated and deoxygenated blood would mix, leading to fatigue.
Other Systems
Fish:
- Fish have a single circulatory system, which is not as efficient as other animals.
- Blood passes through the heart once on a complete circuit.
- Fish don't need as much energy as they're cold-blooded.
- The blood goes from the heart to the gills and then to the body.
Insects:
- Insects have an open circulatory system. It has more than one heart.
- The blood isn't in blood vessels.
- Blood is squirted around the body. Then it collects at the bottom and is pumped to the top again to be squirted.
- Because O₂ isn't in the blood, it functions slowly and is therefore less efficient.
Blood
In a blood smear, there is:
- Red blood cells
- White blood cells
- Blood plasma
- Platelets (involved in blood clotting) → Allows blood to clot. → This stops bleeding and protects you from pathogens.
Plasma:
- Transports many substances:
1) CO₂
2) Hormones
3) Vitamins
4) Antibodies
5) Amino acids
6) Water
7) Glucose
8) Waste products
- Most CO₂ is carried here.
Red Blood Cell:
- Tiny 7 μm can pass through blood vessels and capillaries.
- The biconcave disc shape increases the SA:V ratio for faster O₂ diffusion.
- Haemoglobin, which carries oxygen, lacks a nucleus to create additional space.
- When haemoglobin picks up O₂ in the lungs, it becomes oxyhaemoglobin, a bright red. This happens in reverse when red blood cells flow past respiring tissues.
Other Structures
Arteries:
- Carries blood away from the heart.
- Thick, muscular, and elastic walls.
→ It helps the artery to withstand high pressure and not burst.
→ Maintaining high pressure as it presses against the blood results in elasticity and elastic recoil.
Veins:
- Carry blood to the heart.
- Blood is under low pressure.
- Veins have a large lumen to reduce resistance to blood flow.
- Veins frequently exist between muscles to assist in returning blood to the heart.
- Veins also contain valves.
- Their sole responsibility is to stop blood from flowing backward due to low blood pressure.
Capillaries
- Joins arteries to veins
- Site of exchange
- Very small
- Thin and permeable walls
Blood Vessels
- The blood pressure exerted against the artery walls causes the blood to flow along the arteries. Heart pumping.
- Veins must work against gravity to return the blood to the heart. Veins have a large lumen to reduce resistance to blood flow. Since low-pressure veins contain valves to stop the backflow of blood.