lecture2 endocrine

Endocrine System Overview

• Mechanisms of Communication: Key to understanding the endocrine system.

• Textbook Reference: Seeley’s Essentials of Anatomy & Physiology (11th Edition).

Learning Outcomes

• LO1: Describe hormonal control routes (stimulation & inhibition).

• LO2: Outline hormonal regulation through positive & negative feedback loops.

• LO3: Locate and describe the hypothalamus and pituitary gland's functions.

• LO4: Explain hypothalamic control of anterior vs. posterior pituitary glands.

• LO5: List anterior and posterior pituitary hormones and their target tissues.

• LO6: Describe hormone functions in main endocrine organs.

Lecture Overview

1. Hormonal Regulation: Stimulation, Inhibition, and Feedback

2. Hypothalamic-Pituitary Axis

3. Anterior Pituitary Gland

4. Posterior Pituitary Gland

5. Target Tissues & Major Endocrine Glands

Stimulation of Hormone Release

• Sources of Stimulation:

  • Humoral: Molecules in body fluids trigger hormone release (e.g., low calcium triggers parathyroid hormone).

  • Neural: Nervous system stimulation (e.g., epinephrine release during exercise).

  • Hormonal: One hormone stimulates another's release, often involving the pituitary gland.

Inhibition of Hormone Release

• Sources of Inhibition:

  • Humoral: Companion hormones inhibited by blood stimulus.

  • Neural: Inhibitory neurotransmitters.

  • Hormonal: Some hormones prevent others' secretion (e.g., aldosterone vs. companions).

Homeostatic Balance: Feedback Mechanisms

• Negative Feedback: Hormone secretion inhibited once levels reach a set point (self-limiting, e.g., body temperature regulation).

• Positive Feedback: Hormone secretion promotes further synthesis (self-propagating, e.g., labor contractions).

Hypothalamic-Pituitary Axis

• Hypothalamus: Control center of the endocrine system; communicates with the pituitary gland.

• Pituitary Gland:

  • Anterior Pituitary: Glandular tissue controlled hormonally; releases hormones to target organs.

  • Posterior Pituitary: Neural tissue regulated by the hypothalamus; hormones secreted directly into circulation.

Anterior Pituitary Hormones

1. Prolactin (PRL): Targets mammary glands; stimulates milk production.

2. Growth Hormone (GH): Targets most tissues; increases gene expression and blood glucose levels.

3. Adrenocorticotropic Hormone (ACTH): Targets adrenal glands; controls cortisol and metabolic processes.

4. Thyroid Stimulating Hormone (TSH): Targets thyroid; stimulates thyroid hormone release.

5. Luteinizing Hormone (LH): Targets gonads; promotes ovulation and testosterone synthesis.

6. Follicle Stimulating Hormone (FSH): Targets gonads; stimulates follicle maturation and sperm production.

Posterior Pituitary Hormones

1. Antidiuretic Hormone (ADH): Targets kidneys; conserves water and constricts blood vessels.

2. Oxytocin (OXT): Targets uterus and mammary glands; increases contractions and milk letdown.

Key Concepts in Hormonal Control

• Communication:

  • Anterior Pituitary: Hormonal control via hypothalamic releasing hormones.

  • Posterior Pituitary: Neural control, secreting hormones directly into blood.

Target Endocrine Organs

• Adrenal Glands:

  • Cortex: Secretes aldosterone (low BP response) & cortisol (stress response).

  • Medulla: Releases epinephrine (fight-or-flight response).

• Thyroid Gland: Secretes T3 & T4 (metabolic rate control) and calcitonin (regulates blood calcium).

• Pancreas:

  • Alpha Cells: Secrete glucagon (increase blood glucose).

  • Beta Cells: Secrete insulin (promotes glucose uptake).

Endocrine Glands, Hormones, and Corresponding Target Tissues

1. Pituitary Gland:

   • GH, ACTH, TSH, LH, FSH, PRL affecting respective tissues.

2. Thyroid: Secretes hormones for metabolic processes and calcium metabolism.

3. Adrenal Glands: Makes hormones for stress and bodily response.

4. Pancreas: Insulin and glucagon for nutrient regulation.