Composition of Human Blood : The Plasma

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  • Study of blood is called haematology. Blood is a fluid connective tissue. It is bright red, slightly alkaline (pH 7.3 to 7.5),  salty viscous fluid heavier than water. pH of blood is more in arteries than that in veins. The viscosity of blood is 5 to 6 times that of water.
  • An adult has a blood volume of approximately 5 litres. It forms 6 to 10 % of the body weight.
  • Blood is the only tissue that exists in both the liquid and solid state simultaneously.


  • The figure shows separation of blood constituents on centrifuging.


  • Plasma is the straw coloured non-living, liquid part of blood. It makes up about 55 – 60% of blood’s volume and 5.5 % of body weight.
  • Blood corpuscles and platelets are suspended in it. Blood without clotting factor is called serum.

Composition of Plasma:


  • Plasma is composed of about 90 to 92% water

Plasma Proteins:

  • Plasma proteins or serum proteins constitute 6 to 8% of plasma. Important plasma-proteins are
  • Fibrinogen and prothrombin: required for blood clotting.
  • Serum albumin: These help to regulate osmotic pressure.
  • Globulins or Gamma globulins or Immunoglobins (Ig): They act as antibodies and are associated with the defence mechanism of the body.

Inorganic Salts (Minerals):

  • They form 1-2 % of plasma and includes electrolytes like chlorides, bicarbonates, phosphates of sodium, potassium and calcium.

Dissolved Nutrients:

  • Glucose, lipids, vitamins, fatty acids, amino acids and cholesterol.

Hormones and Enzymes:

  • Blood acts as the transport system for transportation of regulatory substances called hormones secreted by different glands.  Thus plasma contains hormones and enzymes.

Dissolved Gases:

  • oxygen, carbon dioxide, and nitrogen.

Excretory Substances:

  • Ammonia, urea, uric acid, creatine and creatinine.

Functions of Plasma:

Transport Nutrients:

  • Delivering nutrients to the body is another critical function of the circulatory system. Plasma of the blood is the carrier of all nutrients. After food is digested and assimilated, its component nutrients like carbohydrates, proteins, minerals, fats, and vitamins are absorbed into the bloodstream. Each of these nutrients is vital for healthy body function.

Transport of Waste Products:

  • The plasma collects metabolic waste products like urea, creatinine, and other chemical wastes and toxins and transports them to the liver, kidneys, skin, and lungs (excretory organs) for elimination from the body.

Transport of Hormones:

  • Hormones are chemical messengers produced by endocrine glands that affect distant organs. Hormones are released into the bloodstream through which they travel to target sites. The plasma collects the hormones from the endocrine glands and serves as the transportation connection between the glands and the organs or tissues.

Body Temperature Regulation:

  • Plasma Picks up excess body heat from the deep-seated heat producing organs and brings it to the skin to be excreted.
  • If body temperature drops, surface blood vessels constrict(decrease in size) to conserve body heat. Thus it  helps in regulating the body temperature

Disease Protection and Healing:

  • The immunoglobins of plasma act as antibodies and attack the foreign intruder in the body. They neutralize these harmful foreign agents. Thus plasma is responsible for the immunity of the body.
  • Fibrinogen present in the plasma is responsible for clotting of blood which is important for stopping the blood flow from the wounds.

Maintain Haemostasis and Osmoregulation:

  • Plasma supplies water to different tissues at the same time and removes excess of water produced during metabolic activities. Thus it maintains water balance in the body.

Acid-Base Buffer:

  • Plasmaproteins act as acid-base buffers and maintain blood pH within a range.

Disorders Related with Blood Plasma:

Oedema or Edema:

  • Oedema is swelling that occurs when too much fluid becomes trapped in the tissues of the body, particularly the skin. It most often occurs in the skin, especially on the hands, arms, ankles, legs, and feet. However, it can also affect the muscles, bowels, lungs, eyes, and brain. It usually starts slowly, but onset can be sudden.
  • In case of a person suffering from protein deficiency, a fall in plasma protein leads to escape of excess volume of water from the blood to tissues. Due to excess of fluid of fluid in tissues causes swelling of feet. The state is called oedema.  The condition mainly occurs in older adults and women who are pregnant.
  • Symptoms include skin that retains a dimple after being pressed for a few seconds,  puffiness of the ankles, face, or eyes, higher pulse rate and high blood pressure.
  • Diuretics are a type of medication. They help get rid of excess fluid by increasing the rate of urine production by the kidneys.


  • Cholesterol is present in plasma. Cholesterol has a tendency to deposit on the walls of blood vessels leading to the condition called atherosclerosis. The liver is responsible for producing and clearing cholesterol in the body.
  • Dietary cholesterol increases plasma total cholesterol concentrations in humans. There is a relationship between increased plasma cholesterol concentrations and cardiovascular disease risk. Dietary guidelines have consistently recommended to such person limiting food sources of cholesterol.
  • Potential sources of dietary cholesterol are limited to animal foods; eggs, dairy products and meat.
  • LDL (low-density lipoprotein) cholesterol is also called “bad” cholesterol. LDL can build up on the walls of your arteries and increase your chances of getting heart disease.
  • HDL (high-density lipoprotein) cholesterol is also called “good” cholesterol. HDL protects against heart disease by taking the bad cholesterol out of your blood and keeping it from building up in your arteries.
  • Along with cholesterol, triglycerides form plasma lipids. Excess triglycerides in plasma have been linked to the occurrence of coronary artery disease in some people.
  • Everyone over the age of 20 should get their cholesterol levels checked at least once every 5 years by a test called LIPID PROFILE. Everyone over the age of 40 should get their cholesterol levels checked at least once a year.
  • Lifestyle changes such as exercising and eating a healthy diet are the first line of defence against high cholesterol.
  • The choice of medication for high cholesterol depends on individual risk factors, age,  current health and possible side effects. Common choices include Statins, Bile-acid-binding resins, Cholesterol absorption inhibitors, Injectable medications.
  • The choice of medication for high triglycerides is Fibrates, Niacin, Omega-3 fatty acid supplements.
Science > Biology > CirculationYou are Here
Physics Chemistry  Biology  Mathematics

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