Which of the following is not a component saliva?

Options

A. Saliva contains electrolytes `Na^(+), K^(+), Cl^(-) and HCO_(3)^(-)` ions.
B. Ptyalin salivary amylase
C. Mucin, lysozyme and thiocyanate ions
D. Antibody IgM

Answer

To determine which of the following is not a component of saliva, we will analyze each option provided.

### Step-by-Step Solution:

1. **Understanding Saliva Composition**: Saliva is a watery fluid produced by the salivary glands in the mouth. It plays a crucial role in digestion and lubrication of food.

2. **Identifying Components of Saliva**: Saliva contains various components, including:
- **Electrolytes**: Such as sodium, potassium, chloride, and bicarbonate ions, which help in the lubrication of food.
- **Enzymes**: One of the main enzymes in saliva is salivary amylase (also known as ptyalin), which breaks down starch into simpler sugars like maltose and dextrin.
- **Mucins**: These are glycoproteins that help in the lubrication of food.
- **Lysozymes**: These enzymes have antibacterial properties and help in breaking down bacterial cell walls.
- **Thiocyanates**: These ions also contribute to the antibacterial activity of saliva.
- **Antibodies**: Saliva contains immunoglobulin A (IgA), which plays a role in the immune response.

3. **Evaluating the Options**:
- **Option 1**: Electrolytes (sodium, potassium, chloride, bicarbonate) - This is a component of saliva.
- **Option 2**: Salivary amylase (ptyalin) - This is also a component of saliva.
- **Option 3**: Mucins, lysozymes, and thiocyanates - All these are components of saliva.
- **Option 4**: Antibody IgM - This is **not** a component of saliva. Saliva contains IgA, not IgM.

4. **Conclusion**: The correct answer to the question "Which of the following is not a component of saliva?" is **Antibody IgM**.