Lecture on the Endocrine System

Introduction to the Endocrine System

Definition: A system of hormones controlling cellular processes.
Communication Types: Different methods cells use to communicate:
- Direct contact
- Synaptic signaling
- Pheromone signaling
- Endocrine signaling
- Paracrine signaling

Direct Contact
- Cells in physical contact can exchange compounds.
- Example: Gap junctions in animals.
Synaptic Signaling
- Used in the nervous system.
- Neurons communicate chemically with adjacent cells via neurotransmitters.
Pheromone Signaling
- Chemicals released by one individual affect another.
- Example: Male goat releasing pheromones affecting female goats.
Paracrine Signaling
- Affects nearby cells.
- Chemicals released affect cells in close proximity.
Endocrine Signaling
- Hormones released into the bloodstream.
- Affect cells throughout the body.
- Example: Hormones like corticosterone traveling and affecting specific tissues with receptors.

Lipophilic Hormones
- Fat-soluble.
- Examples: Steroid hormones like testosterone, estrogen, cortisol.
Hydrophilic Hormones
- Water-soluble.
- Types:
  - Large proteins, peptides, polypeptides (e.g., oxytocin, prolactin).
  - Amino acid derived (e.g., epinephrine).

Lipophilic Hormones
- Transport needs a protein carrier in the bloodstream.
- Dissolve easily in cell membranes; receptor inside the cell.
Hydrophilic Hormones
- Dissolve well in blood.
- Cannot penetrate cell membrane; receptor is on the membrane's exterior.

Negative Feedback
- Common in hormone regulation.
- Hormone presence inhibits further hormone production.
- Example: Stress-induced hormone production.
Positive Feedback
- Less common.
- Hormone presence amplifies further production.
- Example: Oxytocin during labor increasing contractions.

This concludes the lecture on hormones and the endocrine system.