Overview
This lecture covers how hormone production is regulated in the body, focusing on negative feedback mechanisms and three types of stimuli that control hormone release.
Negative Feedback and Hormone Regulation
- Most hormone production is controlled through negative feedback systems that maintain hormone levels within narrow limits.
- In negative feedback, high levels of a hormone signal endocrine organs to reduce or stop production.
- Example: The anterior pituitary releases TSH to stimulate the thyroid; increased T3 and T4 inhibit further pituitary and hypothalamus stimulation.
Types of Hormone Stimuli
- Endocrine glands can be stimulated to release hormones by humoral, hormonal, or neural stimuli.
Humoral Stimuli
- Humoral stimuli involve hormone release in response to changes in bodily fluid composition, such as ion or nutrient levels.
- Example: High blood glucose triggers insulin release; insulin lowers glucose, signaling the pancreas to stop production.
Hormonal Stimuli
- Hormonal stimuli occur when one hormone stimulates the release of another hormone from a different gland.
- Example: Hypothalamus releases hormones that stimulate the anterior pituitary, which then releases hormones that prompt other glands (e.g., TSH stimulates thyroid).
Neural Stimuli
- Neural stimuli involve direct nerve signals that trigger hormone release from endocrine glands.
- Example: Stress signals from the sympathetic nervous system cause the adrenal medulla to release epinephrine and norepinephrine.
Clinical Application: Thyroid Disorders
- Hypothyroidism symptoms: weight gain, cold sensitivity, fatigue, and low heart rate (Patient A).
- Hyperthyroidism symptoms: weight loss, sweating, high heart rate, and sleeping difficulties (Patient B).
Key Terms & Definitions
- Negative feedback — a process where increased hormone levels inhibit further hormone release.
- Humoral stimulus — hormone release triggered by changes in body fluid composition.
- Hormonal stimulus — hormone release triggered by another hormone.
- Neural stimulus — hormone release triggered by direct nerve stimulation.
- TSH (Thyroid-stimulating hormone) — hormone that prompts the thyroid to release thyroid hormones.
- T3/T4 — thyroid hormones that regulate metabolism.
- Hypothyroidism — underactive thyroid gland.
- Hyperthyroidism — overactive thyroid gland.
Action Items / Next Steps
- Review the feedback mechanisms for other endocrine glands.
- Be prepared to identify types of stimuli in hormone regulation on assessments.