Functions of veins

There are three types of blood vessels:
*Arteries
*Veins
*Capillaries

Veins are a type of elastic blood vessel that return deoxygenated blood from body organs back to the heart. Arteries transport blood away from the heart while veins move blood back to the heart.

Deoxygenated blood that flows into the veins is collected within tiny blood vessels called capillaries. Capillaries are the smallest blood vessels in the body. These tiny blood vessels have thin walls. Capillaries are where oxygen and nutrients are exchanged for carbon dioxide and waste.

Veins can be categorized into four main types: pulmonary, systemic, superficial, and deep veins.
*Pulmonary veins carry oxygenated blood from the lungs to the heart
*Systemic veins return deoxygenated blood from the rest of the body to the heart.
*Superficial Veins: these veins work in unison to collect blood from skin and surrounding superficial tissues
*Deep Veins: Once blood enters these deep veins, blood is pumped to the heart as these large muscles contract, moving blood along the circulatory system

The main vein in your body is the vena cava. The superior vena cava is in the upper right part of human chest. It carries blood from head, neck, arms and chest back to the heart.

The walls of veins are made up of three different layers:
Tunica externa
Tunica media
Tunica intima
Functions of veins

What are the components of blood?

The total blood volume in an adult is about 5.5 liters. The blood consists of a fluid and formed elements.

Formed elements include:
Red blood cells
White blood cells
Platelets

Of the total volume in the human body, 50% - 60% is plasma or the liquid portion of the blood.

Various components of blood each play a role.  In humans, blood cells are produced by stem cells in the bone marrow.

Plasma is a protein-rich solution. It is the fluid portion of the blood in which electrolytes, nutrients, metabolites, vitamins, hormones, gases and parties are dissolved.

Red blood cells or erythrocytes transport O2 and play an important role in pH regulation. The cells deliver hemoglobin, which is the iron-bearing protein that makes the transportation of oxygen possible.

Hemoglobin also gives human blood and that of many other animals, its red color. The red blood cells normally make-up 40%-50% of the total blood volume.

White blood cells can be divided into neutrophilic, eosinophilic, and basophilic granulocytes, monocytes and lymphocytes.

Neutrophils play a role nonspecific immune defense, whereas monocytes and lymphocytes participate in specific immune response.

Eosinophil is an important defense against parasitic infections. It will increase in allergic states such as hay fever, asthma.

Platelets are needed for hemostasis. Platelets or thrombocytes are cell fragments without nuclei that work with blood clotting chemicals at the site of wounds.

The research has shown that platelets help fight infections by releasing proteins that kill invading bacteria and some other microorganisms.
What are the components of blood?

Atrium of the heart

The four chambers in the heart can be segregated into the left and the right side, each containing an atrium and a ventricle.

The right atrium lies anterior to the left atrium, and the right ventricle lies anterior to the left ventricle. The part of the atrium posterior to the ridge is smooth walled, whereas the interior of the auricle is roughened by bundles of muscle fibers, the musculi pectinati.

The right atrium consists of a main cavity and a small out pouching, the auricle.

The role of the right atrium and ventricle is to collect oxygen-poor blood from the body and pump it to the lungs. The role of the left atrium and ventricle is to collect oxygen-rich blood from the lungs and pump it throughout the body.

Within each side, the atrium is a site for the collection of blood, before pumping it to the ventricle.

Right atrium is larger than the left atrium but has a thinners wall and its sinus venarum between two vena cavae is separated from the atrium proper by the crista terminalis. Right atrium has at right atrial pressure that is normally slightly lower than left atrial pressure.

Left atrium is smaller and has thicker walls than the right atrium, but its wall are smooth, except for a few pectinate muscles in the auricle. The left atrium is situated behind the right atrium an forms the greater part of the base or the posterior surface of the heart.
Atrium of the heart