Circulatory & respiratory system

Respiration:

Intake of oxygen into the body and removal of carbon dioxide from the body

Diffusion:

Movement of something from a region of higher concentration to lower concentration.
For respiration through diffusion, a wet membrane is required.
Arthropods breathe through diffusion.
Amphibians use both diffusion and gills/lungs for respiration.

Gills:

Gills are respiratory organs present in fishes
They help in intake of oxygen dissolved in water
They have hair like tissues present that help to diffuse oxygen into the blood
The fish flap their gill cover to create a pressure difference which causes water to rush to the hair-like tissue

Lungs:

Organs that help in active intake of air.
Animals with lungs don't require moist membrane on their skin.
Large animals & warm-blooded animals need more oxygen which is provided by the lungs
Lungs are full of oxygen dissolving membranes that are kept moist with mucus
Lungs have a lot of surface areaHuman lungs have a surface area of 75² m, around half the size of a roof that help in absorbing oxygen

Working of respiratory system:

Breathe air through the nose
Air passes through and goes into the larynx which splits from the esophagus at the pharynx
Air then passes into the trachea which branches off into 2 bronchi, 1 for each lung
Air passes through the bronchi into narrow and narrower tubes called bronchioles which terminate at the alveoli
Alveoli are tiny sacs1 alveolus is 200-500 μm, there are 300 million alveoli in 1 person of thin moist membrane covered in capillaries
Oxygen dissolves through the membrane into the blood in the capillaries and the capillaries go to the heart
The reverse happens in the case of carbon dioxideFrom capillaries to alveoli to bronchi and eventually out of the nose

The thoracic diaphragm is a big flat muscle at the base of the lungs
It pushes the lungs and increases the pressure in them during exhalation and relaxes, increasing the volume of the lungs during inhalation
It is what allows us to inhale and exhale lots of air

Heart:

The heart is a muscle the size of a rat
It powers the circulatory system by pumping blood
The heart has 4 chambers in all mammals
The left and right heart is separated by the septum

Working of the circulatory system:

The left ventricle of the heart has really high pressure to help move the blood to the far reaches of the body
The left ventricle has the most muscle in all the 4 chambers
The left ventricle pumps the blood through the aortic valve into the aorta which pumps it into the arteries
Arteries are muscular and thick walled to maintain high pressure and carry blood from the heart
Arteries split into smaller arterioles and arterioles split until they form very fine little capillaries.

Capillaries form a network of blood vessels called a capillary bed
Capillary beds deliver oxygen to the cells that need it thanks to their large surface area
Capillary beds also pickup CO₂ from the cells and the bloods moves down the pressure gradient to the veins

Smaller veins combine to form larger veins and carry blood to the heart
Veins have thin walls and have valves to prevent backflow of blood
Most veins combine into 2 major veins called the superior vena cava and the inferior vena cava which are in the upper and lower parts of the body respectively

Both vena cava run into the right atrium which has the lowest pressure in the entire circulatory system
The blood then gets pumped into through the tricuspid valve into the right ventricle
The right ventricle pumps blood through the pulmonary valve into the pumlmonary artery which pumps the blood to the lungs
The blood gets oxygenated in the lungs and returns to the left atrium through the pulmonary vein
The blood then pumps through the Mitral valveBicuspid valve into the left ventricle where the cycle continues

Endotherms:

Animals which maintain a steady internal temperature
These are also called warm-blooded
Enzymes operate in a very narrow range of temperatures36° - 37° in humans
Endotherms have to eat a lot to maintain the constant temperature and have a high metabolism
Endotherms have 4 chambered hearts(except crocodiles)

Ectotherms:

Animals which don't maintain a constant temperature
They are also called cold-blooded
Ectotherms have a slow metabolism and don't need as much food as endotherms