Body Fluid and Immune Mechanism — the first-year Physiology chapter on blood, lymph and defence

A drop of blood looks simple. It is red, it is wet, and it clots when you cut your finger. This chapter shows how much is going on inside that drop.

The NCH syllabus gives “Body Fluid & Immune Mechanism” chapter four of Physiology and Biochemistry (HomUG-PB). The sheet lists nineteen topics. Most of them are about blood. The last few move out into lymph and the fluid around cells. This piece sorts the nineteen into six groups and explains the harder words.

Group one: blood and plasma

• Blood
• Plasma proteins
• Blood volume

Blood has a liquid part, called plasma, and cells that float in it. Plasma proteins are the proteins carried in that liquid. Blood volume is the total amount of blood in the body. Your textbook will give the figures and the ways it is measured.

Group two: the red cells

• Red blood cells
• Erythropoiesis
• Haemoglobin and iron metabolism
• Erythrocyte sedimentation rate
• Packed cell volume and blood indices
• Haemolysis and fragility of red blood cells

“Erythro” means red. An erythrocyte is a red blood cell. Erythropoiesis is how red cells are made.

Haemoglobin is the substance inside red cells that carries oxygen. It needs iron, so the sheet pairs it with iron metabolism: how the body takes in, uses and stores iron.

The next three lines are about measuring red cells. The erythrocyte sedimentation rate (ESR) is how fast red cells settle in a tube of blood. Packed cell volume (PCV) is the share of blood made up of red cells. Blood indices are simple calculations about the size and haemoglobin of red cells. Haemolysis is the breaking of red cells. Fragility is how easily they break.

This group has six lines, so give it time. A good method is a one-page summary: what red cells are, how they are made, what they carry, and how they are measured.

Group three: white cells and immunity

• White blood cell
• Immunity
• Reticulo-endothelial system and tissue macrophage

White blood cells are part of the body’s defence. Immunity is the body’s ability to defend itself. The reticulo-endothelial system is a network of cells spread through the body. Macrophages, which live in tissues, are among them. “Macro” means large, and “phage” means eater. These cells take in and break down unwanted material.

A careful note. This is a physiology topic about how the normal body defends itself. It is not about any medicine, and it says nothing about what any treatment can or cannot do.

Group four: platelets and clotting

• Platelets
• Haemostasis
• Coagulation of blood

Platelets are small cell fragments in the blood. Haemostasis means stopping bleeding. Coagulation is clotting, the process by which blood turns from liquid to a gel at a wound.

Clotting happens in steps, one after another. Your textbook will set them out. Draw them as a flow chart. It is much easier to learn a chain of steps as a picture than as a paragraph.

Group five: blood groups and transfusion

• Blood groups
• Blood transfusion

People have different blood groups. Your textbook will explain the systems used to name them. Transfusion is giving blood from one person to another. The two topics sit together because matching blood groups is part of safe transfusion.

Group six: beyond the blood vessels

• Lymphatic system and lymph
• Tissue fluid and oedema

Tissue fluid is the fluid that bathes the cells, outside the blood vessels. Lymph is fluid that has been gathered into lymph vessels. Oedema is swelling caused by extra fluid in the tissues. The sheet asks how these fluids form and move.

These topics link back to chapter one, General Physiology, and its line on body fluid compartments. First-year Anatomy lists the lymphatic system in General Anatomy too.

How the chapter sits in the year

This is one of the longer chapters of first-year Physiology. It comes after General Physiology, Bio-Physical Sciences and Skin, and before Nerve Muscle Physiology. Ideas from the earlier chapters return here. Osmosis and filtration help explain tissue fluid. Homeostasis helps explain why blood volume is held steady.

What to take from it

1. See the chapter as six groups, not nineteen loose lines.
2. Know the plain meaning of erythropoiesis, haemolysis, haemostasis and coagulation.
3. Make a one-page summary of red cells.
4. Draw the clotting steps as a flow chart.
5. Link tissue fluid and lymph back to body fluid compartments.

The sheet gives topic names only. Normal values, test methods and exam depth come from your textbook, your practical classes and your teachers.

Where to go next on the platform

This piece belongs to the first-year Physiology and Biochemistry room. “General Physiology — the first-year Physiology chapter on how a cell lives” explains the body fluid compartments this chapter builds on. “Bio-Physical Sciences — the first-year Physiology chapter on the physics inside the body” gives the processes, like osmosis, behind tissue fluid.