Anatomy and Physiology of blood cells 1 - RBCs

Packed cell volume

It is the percentage of the packed cells (RBCs) of the total length of cells and plasma

• a) 1/3
• b) 2/3

• The species of animal
• The diet of the animal

Murky plasma indicates that it has a high lipid content e.g. the animal is eating a high fat diet.  However, some clinical conditions can cause cloudy plasma so it must be investigated.

• a) bone marrow (all bones), liver and spleen
• b) bone marrow (all bones)
• c) bone marrow (long bones - red marrow)

A pluripotent stem cell can either divide to form a lymphoid stem cell (which forms lymphocytes) or a myeloid stem cell (which forms erythrocytes, neutrophils, monocytes, eosinophils, basophils, or platelets)

Once Hb binds one O₂ molecule it is much easier to bind the second O₂ molecule, once it has bound two it is even easier to bind the third O₂ molecule and so on

The CO₂ concentration, acidity and temperature are all very low which causes Hb to have a high affinity for O₂ in the lungs

Four (as there are four haem groups present within a Hb molecule)

As Hb has a greater affinity for CO than O₂.  Hb will bind to CO in preference to O₂ - if CO is bound to Hb it cannot bind to O₂ and transport O₂ around the body.

The foetal form of Hb has a higher affinity for O₂ than adult Hb so it is able to pull O₂ off the maternal Hb.

The spleen

The autonomic, sympathetic nervous system

• Total number of RBCs
• Diameter and shape of RBCs
• Lifespan of RBCs

• Intravascular haemolysis
• Extravascular haemolysis
• Mononuclear phagocytic or macrophage systems (MPS)

This is the breakdown of RBCs within the blood vessels.  Aged cells lyse (as they are less flexible and cannot navigate through narrow capillaries), Hb binds to the plasma protein haptoglobulin and is taken to the bone marrow to be recycled, the lysed RBC is engulfed by cells of the MPS system.

This is the breakdown of RBCs outside the blood vessels.  Old RBCs are recognised as they pass through certain organ systems (most commonly the spleen which has very narrow capillaries that aged RBCs struggle to move through) and are engulfed by cells of the MPS and removed from the blood vessels to be broken down.

• Amino acids, lipids and carbohydrates
• Iron - for Hb production
• Folic acid - for DNA and RNA synthesis
• Vitamin B12 (cobalt) - maturation of erythrocytes and formation of DNA

Erythropoietin (EPO)

The kidneys stimulate EPO production by a negative feedback system.  Decreased O₂ delivery to the kidneys stimulates increased EPO production which stimulates RBC production in the bone marrow.  Increased O₂ delivery to the kidneys halts EPO production until O₂ levels within the body are back to the normal level.

Mean corpuscular volume

Mean corpuscular Hb content

Mean corpuscular Hb concentration

The general term for insufficient levels of Hb in the blood.

• Haemorrhagic
• Hypoproliferate
• Haemolytic

• Haemorrhagic - regenerative
• Hypoproliferate - non-regenerative
• Haemolytic - regenerative

Blood loss

• External/internal bleeding due to trauma/surgery
• Coagulation disorders eg warfarin, sweet clover
• Parasites eg hookworm, coccidia

• GI lesions
• Coaggulation disorders eg vit K deficiency, haemophilia
• Parasites eg ticks, lice, hookworms

Decreased erythropoiesis

• Dietary deficiencies e.g. iron (hypochromic anaemia) and Vit b12/folic acid (megaloblastic anaemia)
• Destruction of bone marrow e.g. irradiation/x-rays, certain chemicals, myeloproliferative disorders
• Bracken poisoning

Destruction of erythrocytes

• Blood parasites e.g. trypanosomiasis
• Bacterial infections eg leptospirosis
• Chemicals and drugs e.g. copper and lead poisoning
• Poisonous plants and venoms
• Immune mediated causes e.g. autoimmune haemolysis, blood transfusions

Antigens on the surface of blood cells cause blood transfusion reactions.  They also give rise to different blood groups in animals.

No.  Although animal have antigen on the surface of their red blood cells they do not have naturally occurring isoantibodies.  This means you can take blood from one animal and give it to another and it will not have the antibodies to react against the donated blood.  However, the animal will then recognise the donor cells as being foreign and it will generate immune mediate antibodies against the donor cells.  These antibodies will stay in the animal's circulation for (potentially) the rest of its life meaning if you used the same donor again for a second transfusion the animal would show an immune response - have a transfusion reaction.

Cats

As their blood is not very antigenic