Communication: The Key to Life

The better the communication, the more sophisticated the animal.
- Compare animals: jellyfish vs. giraffe.
Better communication means that the animal or society can do more sophisticated and complicated things.

Two Communication Systems in Animals: Endocrine and Nervous

Endocrine System
- The slower of the two communication systems
- Analogous to regular mail
- It shares common infrastructure with other systems.
  - Mail system uses roads.
  - Endocrine system uses circulatory system.
- Three parts of the system
  - Endocrine cells: produce and release chemical messages called hormones.
  - Circulatory system: a pathway to carry the signal to other cells
  - Target cells: these cells have receptors for the hormone; only they respond, because only they have the proper receptors!
Nervous system
- The faster of the two communication systems
- Analogous to the telephone system
- It has its own special infrastructure.
  - Telephone system has its own special wires, switching stations, etc.
  - Nervous system has its own special system of neurons, ganglia, etc.
- Three parts of the system
  - Nerve cell (output): produces and releases a chemical message called a neurotransmitter.
  - Synapse: a narrow space between one nerve cell and the next nerve cell
  - Nerve cell (input): have receptors to the neurotransmitters, and respond to them.

Demonstrates how nerve cells pass signals between each other across synapses using neurotransmitters.

Demonstrates how hormones are emitted from endocrine cells, travel throughout the bloodstream, and end up at the target cell.

Figures 11.3(b) and part of 11.3(a), page 190, Campbell's Biology, 5th Edition

The Endocrine System's Chemical Messengers: Hormones

The endocrine system employs three families of hormones.

Polypeptides (proteins)
- Not lipid soluble
- Bind to receptors on cell surface
Amino acids and amino acid derivatives
- Not lipid soluble (most)
- Bind to receptors on cell surface
Steroids
- Lipid soluble
- Bind to receptors inside target cell

Shows the three families of hormones and how they interact with the target cell.

Unknown source

Endocrine System Overview

The endocrine system consists of a diverse group of endocrine glands located throughout the body.
At one time it was believed there was no relationship between these glands.
It was thought that each gland individually produced a particular hormone, which when released influenced one particular “target tissue” that had the appropriate receptor molecules.

Shows the location of many different human endocrine glands.

Figure 45.6, page 898, Campbell's Biology, 5th Edition

The “Master Gland”

By the 1950s, it was determined that the pituitary gland produced hormones that influenced many other endocrine glands and tissues in the body.
For this reason, it was called the “master gland.”
By the late 1960s and early 1970s, it was shown that the pituitary gland was actually under control of the hypothalamus, a region of the brain.
This research shows the strong linkage between the nervous system and endocrine system; they “talk” to one another.

Demonstrates how the hypothalmus directs the pituitary, which in turn influences many other glands.

Via Domenic Denicola's mad Visio skills

Posterior Lobe

The posterior lobe of the pituitary gland is really an extension of the brain into the pituitary gland.
The cells that produce and release the hormones are called neurosecretory cells.
- They grow down from the hypothalamus into the posterior lobe of the pituitary gland.
- They release two hormones:
  - ADH (antidiuretic hormone): acts on the collecting ducts in the kidneys to help increase water retention.
  - Oxytocin: causes the smooth muscles of the uterus and mammary glands to contract; important in labor and nursing.

Shows the posterior pituitary, including its structure and what hormones it uses to affect what target cells.

Figure 45.7(a), page 901, Campbell's Biology, 5th Edition

Anterior Lobe

Neurosecretory cells in the hypothalamus release hormones that travel through a portal system to the anterior lobe of the pituitary, where they either inhibit or encourage the release of a wide range of hormones from the pituitary.

Shows the anterior pituitary, including its structure and what hormones it uses to affect what target cells.

Figure 45.7(b), page 901, Campbell's Biology, 5th Edition

Four Tropic Hormones

A tropic hormone has another endocrine gland as a target. Therefore, for each tropic hormone, ask which endocrine gland it affects.

Gonadatropins: influence the release of hormones from the gonads.
- FSH (follicle stimulating hormone)
- LH (luteinizing hormone)
TSH (thyroid stimulating hormone): regulates the release of thyroid hormone from the thyroid.
ACTH (adrenalcorticotropic hormone): stimulates the production and secretion of steroid hormones from the adrenal cortex.

Four Nontropic Hormones

GH (growth hormone): stimulates the liver to produce insulinlike growth factors (IGFs).
PRL (prolactin): causes milk production.
MSH (melanocyte stimulating hormone):
- Causes a dramatic darkening of skin in fish, amphibians, and reptiles by increasing the production of the dark pigment melanin in skins cells called melanocytes.
  - In humans, melanocytes are responsible for moles, freckles, and suntan.
  - Cancer of melanocytes is called melanoma.
- MSH seems to have some effect on appetite suppression in humans, although the details are not yet clear.
Endorphins
- Influence pain receptors in the brain.
- Inhibit pain from these receptors.
- Are known as natural opiates.
- May be the cause of “runner's high.”

Endocrine System—Part 1