All glands, whether exocrine or endocrine in a mammal, originate from epithelial tissues.

Answer

**Step-by-Step Solution:**

1. **Understanding Glands**: Glands are specialized structures in the body that produce and secrete substances such as hormones, enzymes, or other fluids. They can be classified into two main types: exocrine and endocrine glands.

2. **Types of Glands**:
- **Exocrine Glands**: These glands have ducts and secrete their products onto epithelial surfaces or into body cavities. Examples include sweat glands, salivary glands, and digestive glands.
- **Endocrine Glands**: These glands are ductless and release their hormones directly into the bloodstream. Examples include the thyroid gland, adrenal glands, and pituitary gland.

3. **Origin of Glands**: Both exocrine and endocrine glands originate from epithelial tissues. During development, epithelial cells proliferate and differentiate to form these glands.

4. **Structure of Epithelial Tissue**: Epithelial tissues consist of closely packed cells with minimal extracellular matrix. They have a basement membrane and can form various structures, including glands.

5. **Functions of Epithelial Tissue**: Epithelial tissues serve multiple functions, including protection, secretion, absorption, excretion, filtration, diffusion, and sensory reception.

6. **Conclusion**: Since both types of glands (exocrine and endocrine) are derived from epithelial tissues, the statement "All glands, whether exocrine or endocrine in a mammal, originate from epithelial tissues" is true.

**Final Answer**: True.

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