07 Types of glands in man
1Exocrine
Structure
- Secretory cells + a duct (or system of ducts)
Secretion goes
- Through ducts to a cavity in the body or to outside
Examples
- Salivary glands, gastric glands, sweat glands, liver (bile), pancreas (juice)
2Endocrine
Structure
- Ductless
Secretion goes
- Directly into blood
Examples
- Pituitary, thyroid, parathyroids, adrenals, gonads (hormone part)
3Mixed
Structure
- Part exocrine, part endocrine
Secretion goes
- Both
Examples
- Pancreas, testes, ovaries (gametes + hormones)
- The pancreas is a mixed gland: its acini make pancreatic juice delivered through the pancreatic duct to the duodenum (exocrine), while the islets of Langerhans make insulin and glucagon released into the blood (endocrine).
- The testes and ovaries are mixed as they make gametes (exocrine-like, released through ducts) and sex hormones (endocrine).
✍️ Worked examples
Worked example 1.
- A researcher finds a gland whose secretion collects in a tube leading to the small intestine, and also finds clusters of cells within the same gland without tubes, near capillaries.
- What kind of gland, and which part makes the hormone?
- A mixed gland (pancreas); the clusters (islets of Langerhans) make the hormones.
Worked example 2.
- Why can a hormone injected into the blood only affect certain organs?
- Only the cells of the target organ have receptors that recognise that hormone.