Circulation in Animals

What truly is the point of Circulation? Why build such a complex system stretching through out the entire body? Below these questions shall be answered.

Exchange of Materials

The true point of the Circulatory system is to exchange, and transport materials from cells, and to cell, and to other parts of the body. This includes:
Needs

• Oxygen
• nutrients
• Sugars, proteins, etc.
• Water
• Protective Agents(White blood cells, antibodies, platelet's, etc.)
  
• Hormones

Wastes

• Carbon Dioxide
• Urea
• Water

Multicellular Animals need these essential materials, and to get ride of waste, but unlike unicellular organisms cant obtain it through diffusion alone, for this reason they need the Circulatory system, this network or highway for transport.

Types of Circulatory Systems

All Animals have some characteristics in common for their mode of circulation. The all contain blood vessels, a heart, and some type of fluid to transport materials in (blood for humans).
Open

• Invertebrates( insects, mollusk, anthropods) contain an open circulatory system which means they have no separation between blood, and interstitial fluid, instead they have hemolymph. This is a fluid that runs through their entire body touching the organs, and giving them nutrients.

Closed

• Invertebrates( Octopie, earthworms, squid ) have separate blood from interstitial fluid. They have at least one heart, complex blood vessels, exchanging of materials between the blood, and the outside interstitial fluid.
• Vertebrates( humans, clownfish , macaques ) also have a closed circulatory system. They have seperate blood from interstitial fluid, and complex blood vessels. The characteristics of vertebrates differ greatly through different evolutionary stages.

Evolution of heart chambers

The number of heart chambers differs greatly ranging from 2-4 in vertebrates. Having more chambers was a selective value because it is more efficient system, separating oxygen rich, and oxygen poor blood giving cells a fresh supply of concentrated oxygen. Having only 2 chambers, like a fish mixes the oxygen rich, and oxygen poor blood giving less overall oxygen to the cells. Since mammals, and birds are endothermic they also had a selective force to heave 4 chambered hearts so they could supply they needs of making heat by getting the supplies around faster, and with what is truely needed.

Blood Vessels

There are 3 main types of Blood Vessels found in the circulatory system of vertebrates.
Arteries

• Arteries are the blood vessels that carry blood away from the heart.
  
• They are thicker than veins so that they can be able to make high pressure pumping of blood. Since it is pumping blood to the body it ne eds pressure to force the blood to move to the different parts of the body.
• Has a narrow diameter to help keep high pressure within the vessels.
  

Veins

• Veins are the blood vessels that carry blood towards, or back to the heart.
• Low pressure so that skeletal muscle contractions are able to move the blood flow more easily towards the heart.
• Wider diameter so there is less pressure.
• Thinner walls for less pressure.
• Valves in some of the larger veins help to direct blood flow by opening and closing leading blood to the heart.

Capillaries

• Very small blood vessels that branch from the larger veins, and arteries but connected to the arterioles, and venules.
  
• Very thin, only one layer of cells, endothelium.
• Very permeable from thinness allowing the diffusions of molecules such as oxygen, and urea, and making for the connection for the transp ort of materials between cells, and the circulatory system.

The blood flow in capillaries can be controlled through the pre-capillary sphincters. They can retrict or allow blood flow through capillaries by either closing, or opening up. This is useful for when certain body parts are in need of blood, open, an d to close them when the part is in no need of blood.
The capillaries also exchange fluids, and solutes into the interstitial fluid through "bulk flow" or having a high pressure gradient. The interstitial fluid also flows into the capillaries through osmosis.

Lymphatic System

The Lymph system very much like the circulatory system and is parallel with it. The Lymph system is an open system, and helps collect, and return interstitial fluid to the blood. It also helps the bodies immune system greatly. It aids in the production of lymphocytes, and anti-bodies, also transporting these throughout the whole body as well as white blood cells to aid wherever they are needed. The system drops its load into the circulatory system near the vena cava, and right atrium.

Mammalian heart

The heart of your typical mammal is very similar, as we saw in the cow heart dissection. It consists of Pulmonary arteries, and veins which pump blood to and out the capillaries of the lungs, and the Aorta which is an artery that pumps blood throughout the body. The Coronary arteries give a supply of blood to the heart giving fresh supplies of oxygen. Many times this is blocked by buildup of cholesterol, and can cause a heart attack which can lead to needing bypass surgery, in which a alternate pathway from the aorta is made to the heart so it can get its supply of blood and not fail to pump.
The heart is made of up 4 chambers, the left and right Ventricle, and the left and right Atrium. These chambers are separated by four valves, made up of connective tissue that prevent back flow keeping the blood pumping in the direction it is needed. The sounds "Lub" and "dub" are produced from these valves closing, and opening. The Atrioventricular valves (AV) are between the atrium, and ventricle, and prevents blood from flowing in the atria when the ventricles contract. The Semi lunar valves are between the ventricles, and arteries and prevent blood from flowing into the ventricles from the arteries when the heart is relaxing.
A Cardiac cycle is one complete cycle of the hear pumping. This is when the heart contracts, and pumps, then relaxes and refills with blood. The contraction phase is called systole, and the relaxation phase is called diastole. This is the way someones blood pressure is measured to check if they have hypertension. The top number is systolic pumping(a higher number), and the bottom number is the diastolic pumping(lower number).