Anemia : Introduction | Classification Of Anemia - Physiology Notes

ANEMIA TYPES & CAUSES

INTRODUCTION:

Anemia is the blood disorder, characterized by the reduction in:
1. Red blood cell(RBC) count
2. Hemoglobin Content
3. Packed cell volume (PVC)
Generally, reduction in RBC count, hemoglobin content and PCV occurs because of:
1. Decreased production of RBC
2. Increased destruction of RBC
3. Excess loss of blood from the body.
All these incidents are caused either by inherited
disorders or environmental influences such as nutritional
problem, infection and exposure to drugs or toxins.

CLASSIFICATION OF ANEMIA:

Anemia is classified by two methods:
1. Morphological classification
2. Etiological classification.

 

MORPHOLOGICAL CLASSIFICATION:

Morphological classification depends upon the size and color of RBC. Size of RBC is determined by mean corpuscular volume (MCV). Color is determined by mean corpuscular
hemoglobin concentration (MCHC). By this method, the anemia is classified into four types (Table 14.1):

morphological classification of anemia

1. Normocytic Normochromic Anemia

Size (MCV) and color (MCHC) of RBCs are normal. But the number of RBC is less.

2. Macrocytic Normochromic Anemia

RBCs are larger in size with normal color. RBC count is less.

3. Macrocytic Hypochromic Anemia

RBCs are larger in size. MCHC is less, so the cells are pale (less colored).

4. Microcytic Hypochromic Anemia

RBCs are smaller in size with less color.

ETIOLOGICAL CLASSIFICATION

On the basis of etiology (study of cause or origin), anemia is divided into five types (Table 14.2):
1. Hemorrhagic anemia
2. Hemolytic anemia
3. Nutrition deficiency anemia
4. Aplastic anemia
5. Anemia of chronic diseases.

  1. Hemorrhagic Anemia

Hemorrhage refers to excessive loss of blood (Chapter 115). Anemia due to hemorrhage is known as hemorrhagic anemia. It occurs both in acute and chronic hemorrhagic
conditions. Acute hemorrhage Acute hemorrhage refers to sudden loss of a large quantity
of blood as in the case of accident. Within about 24 hours after the hemorrhage, the plasma portion of blood
is replaced. However, the replacement of RBCs does not occur quickly and it takes at least 4 to 6 weeks. So with less number of RBCs, hemodilution occurs. However, morphologically the RBCs are normocytic and normochromic  Decreased RBC count causes hypoxia, which stimulates the bone marrow to produce more number of RBCs. So, the condition is corrected within 4 to 6 weeks.
Chronic hemorrhage It refers to loss of blood by internal or external bleeding,
over a long period of time. It occurs in conditions like peptic ulcer, purpura, hemophilia and menorrhagia.Due to continuous loss of blood, lot of iron is lost from the body causing iron deficiency. This affects the synthesis of hemoglobin resulting in less hemoglobin
content in the cells. The cells also become small. Hence the RBCs are microcytic and hypochromic

2. Hemolytic Anemia

Hemolysis means destruction of RBCs. Anemia due
to excessive hemolysis which is not compensated by
increased RBC production is called hemolytic anemia. It
is classified into two types:

• A. Extrinsic hemolytic anemia.

• B. Intrinsic hemolytic anemia.

A. Extrinsic hemolytic anemia

 It is the type of anemiacaused by destruction of RBCs by external factors.
Healthy RBCs are hemolized by factors outside the blood cells such as antibodies, chemicals and drugs. Extrinsic hemolytic anemia is also called autoimmune hemolytic anemia.
Common causes of external hemolytic anemia: 

• Liver failure 
•  Renal disorder 
• Hypersplenism 
• Infections like hepatitis, malaria and septicemia 
• Drugs such as penicillin, antimalarial drugs and sulfa Drugs 
• Poisoning by chemical substances like lead, coal and tar 
•  Presence of isoagglutinins like antiRh 

Autoimmune diseases such as rheumatoidarthritis and ulcerative colitis.

Intrinsic hemolytic anemia: 

It is the type of anemia caused by destruction of RBCs because of the defective
RBCs. There is production of unhealthy RBCs, which are short lived and are destroyed soon. Intrinsic hemolytic anemia is often inherited and it includes sickle cell anemia and thalassemia.
Because of the abnormal shape in sickle cell anemia and thalassemia, the RBCs become more fragile and susceptible for hemolysis. Sickle cell anemia Sickle cell anemia is an inherited blood disorder, characterized by sickleshaped red blood cells. It is also called hemoglobin SS disease or sickle cell disease. It is common in people of African origin. Sickle cell anemia is due to the abnormal hemoglobin called hemoglobin S (sickle cell hemoglobin). In this, alpha chains are normal and ßchains are abnormal. The molecules of hemoglobin S polymerize into long chains
and precipitate inside the cells. Because of this, the RBCs attain sickle (crescent) shape and become more fragile leading to hemolysis (Fig. 14.1). Sickle cell anemia
occurs when a person inherits two abnormal genes (one from each parent).
In children, hemolyzed sickle cells aggregate and block the blood vessels, leading to infarction (stoppage of blood supply). The infarction is common in small bones.The infarcted small bones in hand and foot results in varying length in the digits. This condition is known as hand and foot syndrome. Jaundice also occurs in these children.

Sickle cell anemia 

Sickle cell anemia is an inherited blood disorder,characterized by sickleshaped
red blood cells. It is also called hemoglobin SS disease or sickle cell disease. It
is common in people of African origin. Sickle cell anemia is due to the abnormal hemoglobin
called hemoglobin S (sickle cell hemoglobin). In this, achains are normal and ßchains
are abnormal. The molecules of hemoglobin S polymerize into long chains and precipitate inside the cells. Because of this, the RBCs attain sickle (crescent) shape and become more
fragile leading to hemolysis (Fig. 14.1). Sickle cell anemia occurs when a person inherits two abnormal genes (one  from each parent). In children, hemolyzed sickle cells aggregate and
block the blood vessels, leading to infarction (stoppage of blood supply). The infarction is common in small bones. The infarcted small bones in hand and foot results in varying length in the digits. This condition is known as hand and foot syndrome. Jaundice also occurs in these children.

Thalassemia

Thalassemia is an inherited disorder, characterized by abnormal hemoglobin. It is also known as Cooley’s anemia or Mediterranean anemia. It is more common in Thailand and to some extent in Mediterranean
countries.
Thalassemia is of two types:
i. athalassemia
ii. ßthalassemia.

The ßthalassemia
is very common among these
two.
In normal hemoglobin, number of a and ß polypeptide chains is equal. In thalassemia, the production of these chains become imbalanced because of defective
synthesis of globin genes. This causes the precipitation of the polypeptide chains in the immature RBCs, leading to disturbance in erythropoiesis. The precipitation also occurs in mature red cells, resulting in hemolysis.a-Thalassemia athalassemia occurs in fetal life or infancy. In this achains
are less, absent or abnormal. In adults, ßchains are in excess and in children, ?chains are in excess. This leads to defective erythropoiesis and hemolysis .The infants may be stillborn or may die immediately after birth. 
ß-Thalassemia In ßthalassemia,
ßchains are less in number, absent or abnormal with an excess of achains. The alpha chains precipitate causing defective erythropoiesis and hemolysis.