Human Circulatory System

It prevents the artery from collapsing. It is the middle thick coat of circularly disposed, smooth or unstriped muscle fibres and elastic connective fibres. The thick coat prevents arteries from collapsing.

This layer carries small vessels and nerves to nourish the arterial wall.

Arterioles are the smallest tubes of the arterial system.

Blood is classified as a connective tissue in biological terms because it consists of cells suspended in a liquid matrix (plasma). Liver, skin, and heart are organs.

At each heart beat ventricles pump about 70 ml of blood. This volume is called stroke volume.

The azygos venous system returns blood from the posterior walls of the thorax and the abdomen and dumps into the superior vena cava. The superior vena cava then takes the blood to the right auricle.

The right auricle receives deoxygenated blood from superior and inferior vena cava.

This is the right course. RA receives deoxygenated from body. Deoxygenated blood then passes to RV from where it goes to the lungs for oxygenation. The oxygenated blood comes to LA from the lungs, from where it goes to LV to be supplied to the whole body.

The left auricle receives oxygenated blood from the lungs by  the four pulmonary veins.

The aorta artery supplies blood to the whole body.

Semilunar valves prevent the backflow of blood from the arteries to the ventricles.

In hydra, internal circulatory fluid is absent. Thus, it uses external medium (water) as circulatory fluid.

Food transport takes place with the help of pseudocoelomic fluid.

In open blood vascular system, the blood vessels do not divide into capillaries and open in a wide space called sinuses in the body cavity. The blood fills the cavity and bathes the organs.

The heart is the muscular organ responsible for pumping blood throughout the circulatory system to deliver oxygen and nutrients to tissues.