Endocrine System Notes(Exam 5)

Chemical Signaling in Animals

Animals use 6 types of chemical signals:

1. Autocrine – Acts on the same cell that secretes it.

2. Paracrine – Local signaling (e.g., inflammation, clotting).

3. Endocrine – Hormones travel via bloodstream.

4. Neural Signals – Neurotransmitters (synaptic communication).

5. Neuroendocrine – Neurotransmitters released into blood (e.g., oxytocin).

6. Pheromones – Signals between individuals (e.g., mating, alarm).

Pheromones

- Common in insects (trail, sex, alarm pheromones).

- Detected by the vomeronasal organ (VNO) in vertebrates.

- Humans: Lack VNO but may detect immune-related chemicals (mate selection).

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Hormones & Endocrine Glands

Types of Hormones

| Type | Examples | Solubility & Mechanism |

|————————————|—————————————|——————————————————————|

| Polypeptides | Growth hormone, oxytocin | Water-soluble; bind surface receptors. |

| Amino Acid Derivatives | Adrenaline, thyroxine | Some lipid-soluble (thyroxine enters cells). |

| Steroids | Testosterone, estrogen | Lipid-soluble; enter cells, alter gene expression. |

Key Endocrine Glands & Hormones

| Gland | Hormones Produced | Functions |

|————————|—————————————————————|———————————————————|

| Hypothalamus | ADH, oxytocin (released by posterior pituitary) | Regulates thirst, bonding, childbirth. |

| Anterior Pituitary| Growth hormone (GH), ACTH, TSH | "Master gland"; controls other glands. |

| Thyroid | Thyroxine (T4), triiodothyronine (T3) | Sets metabolic rate; needs iodine (deficiency → goiter). |

| Adrenal Medulla | Epinephrine, norepinephrine | "Fight or flight" response. |

| Adrenal Cortex | Cortisol, aldosterone | Stress response; regulates Na+/K+. |

| Pancreas | Insulin, glucagon | Regulates blood glucose. |

| Gonads | Testosterone (testes), estrogen/progesterone (ovaries) | Secondary sexual characteristics. |

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Regulation & Feedback

Hypothalamus-Pituitary Axis

- Posterior Pituitary: Stores/releases hormones made in hypothalamus (ADH, oxytocin).

- Alcohol inhibits ADH → dehydration.

- Anterior Pituitary: Produces hormones (e.g., GH) that stimulate other glands.

- Excess GH → gigantism (Robert Wadlow: 8’11”).

Thyroid & Development

- Metamorphosis (e.g., tadpoles → frogs) driven by thyroid hormones (T3/T4).

- Iodine deficiency → enlarged thyroid (**goiter**).

Adrenal Glands & Stress

- Short-term stress: Adrenaline (medulla) → rapid energy mobilization.

- Long-term stress: Cortisol (cortex) → increases blood sugar, suppresses immunity.

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Hormonal Control in Animals

- Insects:

- Ecdysone triggers molting.

- Juvenile hormone levels determine larval vs. adult forms.

- Vertebrates:

- Testosterone implants in birds increase courtship but reduce parental care.

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Endocrine Disruptors

Chemicals that interfere with hormone function:

- Agonists (mimic hormones): BPA, zeranol.

- Antagonists (block hormones): Atrazine, DDT.

- Effects: Developmental disorders, reproductive issues.

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Key Takeaways

1. Hormones regulate growth, metabolism, stress, and reproduction.

2. Pituitary is the "master gland," controlled by the hypothalamus.

3. Steroid hormones (e.g., testosterone) alter gene expression; peptide hormones (e.g., insulin) use surface receptors.

4. Endocrine disruptors (e.g., BPA) mimic or block natural hormones.

Visual Summary:

- Hypothalamus → Pituitary → Target Glands → Hormone Release → Physiological Effects.

- Negative Feedback Loops maintain homeostasis (e.g., high cortisol inhibits ACTH).