The internal environment of the human organism is made up of blood within the blood vessels, interstitial fluid surrounding the body cells, and lymph inside the lymph vessels.
The blood is able to pick up:
- nutrients (from the digestive tract)
- oxygen (from the lungs)
- hormones (from the endocrine glands)
- enzymes (from multiple body sites)
The blood can also act as a transportation means for disease-causing organisms. For this reason, the lymphatic system helps in picking up wastes from the interstitial fluid, cleansing them of bacteria, and returning them bacteria-free into the blood.
Physical Characteristics of the Blood
Blood Functions
1. Transportation
Blood helps in the transportation of:
- Oxygen (from the lungs to the body’s cells)
- Carbon Dioxide (from the cells to the lungs)
- Nutrients (from the digestive organs to the cells)
- Waste Products (from the cells to the kidneys, lungs, and sweat glands)
- Hormones (from the endocrine glands to the cells)
- Enzymes (to various cells)
2. Regulation
Blood helps in the regulation of:
- pH (through buffers)
- Body Temperature (through heat-absorbing and coolant properties of its water content)
- Water within the Cells (mainly through dissolved sodium ions)
3. Protection
Blood helps in protecting the body against:
- Blood Loss (through the blood clotting mechanism)
- Toxins and Foreign Microbes (through special combat-unit cells such as white blood cells)
Blood Composition
Blood is made up of 2 portions:
1. Formed Elements
- make up 45% of the total blood volume
- include Red Blood Cells, White Blood Cells (Granular – neutrophils, eosinophils & basinophils; and Agranular – lymphocytes & monocytes), and Platelets.
2. Plasma
- makes up 55% of the total blood volume
- water (91.5% of total plasma)
- proteins (7% of total plasma)
- other solutes (1.5% of total plasma)
Haematopoiesis – Blood Cell Formation
Haematopoiesis a.k.a. blood cell formation takes place within the Red Bone Marrow (myeloid tissue in the humerus, femur, sternum, ribs, vertebrae & pelvis) and Lymphoid Tissue (in the spleen, tonsils & lymph nodes).
- Red Blood Cells, Leucocytes & Platelets are produced within the Bone Marrow.
- Agranular Leucocytes (lymphocytes & monocytes) are produced by the Bone Marrow and the Lymphoid Tissue.
Red Blood Cells a.k.a. Erythrocytes
- do not contain a nucleus
- cannot reproduce
- cannot carry on extensive metabolic activities
- plasma membrane is selectively permeable
- plasma membrane encloses cytoplasm and haemoglobin
- have a biconcave shape which promotes increased surface area for diffusion purposes
- contain a lot of haemoglobin molecules which increase their capacity for oxygen transportation
- allow transportation of a small amount of carbon dioxide along with haemoglobin
Normal Haemoglobin Values
| Infants | 14-20gm/dl |
| Adult Females | 12-15gm/dl |
| Adult Males | 14-16.5gm/dl |
Erythropoiesis – Erythrocyte Production
- erythropoiesis and erythrocyte destruction usually proceed at the same pace
- if the balance between erythropoiesis and erythrocyte destruction is disrupted, a homeostatic mechanism is initiated to promote erythrocyte production
- in oxygen deficiency, particular kidney cells release the enzyme Renal Erythropoietic Factor which converts plasma protein into the hormone erythropoietin, which, when reaching the red bone marrow, stimulates haemocytoblasts to develop into red cells
NOTE: Blast is a short name for an immature WBC, such as a lymphoblast or myeloblast. In normal circumstances, less than 5% of the cells in healthy bone marrow at any one time are blasts. Within the bone marrow, normal blasts develop into mature, functioning blood cells and are then released into the bloodstream.
Haemoglobin in Erythrocytes
- erythrocyte life span is around 120 days long
- the plasma membrane of depleted cells are removed from the circulation by macrophages in the spleen, liver, and bone marrow
- haemoglobin is broken down into Haemosiderin (iron-containing pigment which is stored or used in the bone marrow for the production of new haemoglobin for new RBCs), Bilirubin (pigment secreted by the liver into bile) and Globin (protein metabolised in the liver).
White Blood Cells a.k.a. Leucocytes
- there is a much lesser amount of WBCs than RBCs in the human body: 700 RBCs per 1 WBC
- leucocytes contain nuclei
- leucocytes do NOT contain haemoglobin
- leucocytes have surface proteins called Human Leucocyte Associated Antigens (HLA) which are unique to each and every person
There are 2 types of WBCs:
GRANULAR LEUCOCYTES:
- NEUTROPHILS (POLYMORPHS) – make up the biggest amount of total leucocytes; involved in phagocytosis of bacterial pathogens and the release of antimicrobial chemicals
- EOSINOPHILS – involved in phagocytosis of antigen-antibody complexes, allergens and inflammatory chemicals, and the release of enzymes which help weaken or destroy parasites
- BASOPHILS – involved in the secretion of histamine which promotes blood flow to a particular tissue, and the secretion of heparin which promotes mobility of other WBCs by clotting prevention
- develop from red bone marrow
- have granules in the cytoplasm
- have a lobed nuclei
AGRANULAR LEUCOCYTES:
- MONOCYTES – turn into macrophages; phagocytise pathogens, dead neutrophils, and dead cells debris; and present antigens that activate other cells within the immune system
- LYMPHOCYTES – assist with immune memory, secrete antibodies, present antigens for the activation of other cells within the immune system, and help in destroying cancer cells, virus-infected cells, and foreign cells
- develop from lymphoid and myeloid tissue
- do not have granules in the cytoplasm
Differential Blood Count
| Type of White Blood Cell | Normal Differential Count | High WBC Count Implication |
| Neutrophils | 60% – 70% | damage caused by invading bacteria |
| Eosinophils | 2% – 4% | allergic reaction |
| Basophils | 0.5% – 1% | allergic reaction |
| Lymphocytes | 20% – 25% | antigen-antibody reaction |
| Monocytes | 3% – 8% | chronic infection |
Life Span of Leucocytes
- leucocytes can live from just a few days to a few months, depending on what type of leucocytes they are
- during infection, white blood cells become very active, usually living for only a few hours
Platelets
- platelets contain no nucleus
- platelets have a life span of between 5 to 9 days
- platelets help prevent fluid loss through a chain of reaction leading in blood clotting
- stem cell development from haemocytoblast to platelets takes place in the red bone marrow
Plasma
Plasma is made up of:
- WATER – 90% of total amount of water in plasma is derived from the GI tract; 10% is derived from cellular respiration; water absorbs heat and acts as a solvent and suspending medium for the blood’s solid components
- SOLUTES – makes up 8.5% of the total plasma volume
- PROTEINS – ALBUMINS (55% of plasma proteins) are produced by the liver; provide viscosity in the blood which helps maintain blood pressure; exert osmotic pressure to help in maintaining water balance between the blood and the tissues; help regulate blood volume; GLOBULINS (38% of plasma proteins) a.k.a. antibodies; FIBRINOGEN (7% of plasma proteins) is produced by the liver; it helps in the blood clotting process
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Claire Galea is a mum of three currently in her final year following a Degree in Nursing at the Faculty of Health Sciences, University of Malta, as a mature student.
Claire is keen about public education on health-related subjects as well as holistic patient-centered care. She is also passionate about spreading awareness on the negative effects that domestic abuse leaves on its victims’ mental, emotional, social and physical wellbeing.
Claire aspires to continue studying following completion of her Nursing Degree, because she truly believes in lifelong education.
Claire is keen about public education on health-related subjects as well as holistic patient-centered care. She is also passionate about spreading awareness on the negative effects that domestic abuse leaves on its victims’ mental, emotional, social and physical wellbeing.
Claire aspires to continue studying following completion of her Nursing Degree, because she truly believes in lifelong education.
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