The endocrinology: introduction to the endocrine system; lecture summary

Endocrinology: Introduction to the Endocrine System

🌿 Introduction to the Endocrine System
The endocrine system is a network of glands and organs that use hormones to control and
coordinate vital body functions like metabolism, growth, reproduction, and stress response.
Hormones act as chemical messengers that travel through the bloodstream to target organs.

Types of Signaling

- Endocrine: Hormones travel through the blood to distant organs.
- Paracrine: Hormones act on nearby cells (e.g., gastrin).
- Autocrine: Hormones act on the same cell that secreted them (e.g., IGF).
- Neuroendocrine: Nerves release hormones into the blood.
- Neurocrine: Communication occurs directly between neurons.


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Exocrine vs. Endocrine Glands
Feature Exocrine Glands Endocrine Glands

Definition Secrete substances onto Secrete hormones into
surfaces via ducts blood (ductless)

Ducts Present Absent

Route Through ducts to surfaces Into bloodstream

Examples Salivary, sweat, mammary Pituitary, thyroid, adrenal,
glands pancreas


⚡ Nervous System vs. Endocrine System
Feature Nervous System Endocrine System

Communication Electrical + chemical Chemical only

Response Speed Fast (milliseconds) Slower (seconds to days)

Duration Short-lived Long-lasting

Target Specific organs/cells Widespread


💡 How Hormones Work
Hormones act only on cells that have matching receptors. Cells may regulate receptor
numbers by up-regulation (increase) or down-regulation (decrease).