8 Endocrine System 1.pptx

Overview of the Endocrine System

• Course subject presented by Dr. Elita Partosoedarso.

• Recording available for review.

• Slides can be modified (resize, delete, reorganize).

• Google slides/docs are "View Only." To edit, sign in, download, or make a copy.

• Treat recording like an in-person lecture: complete in original duration to enhance learning.

Endocrine System Signaling Overview

• Types of Signaling:

  • Endocrine vs Nervous signaling

• Classification of Hormones:

  • Functional and structural classification

  • Basic hormone action defined.

• Factors Affecting Target Cell Response:

  • Regulation and combined effects.

• Hypothalamus-Pituitary Axis (HPA):

  • Connection and functioning of hypothalamus and pituitary glands.

  • Hormone production, storage, and regulation.

Types of Chemical Signaling

1. Autocrine Signaling:

   • Cell acts on itself (e.g., pain regulation).

2. Direct Signaling Across Gap Junctions:

   • Communication through gap junctions between adjacent cells.

3. Paracrine Signaling:

   • Chemical mediators (e.g., neurotransmitters) act on nearby cells.

4. Endocrine Signaling:

   • Mediators (hormones) released into bloodstream to distant targets.

Overview of the Endocrine System

1. Works alongside the nervous system.

2. Scattered endocrine glands throughout the body.

3. Some glands (e.g., hypothalamus, adrenal medulla) are neurosecretory.

4. Ductless Glands:

   • Composed of glandular epithelium, releasing hormones directly into the blood.

5. Endocrine glands produce excess hormone molecules; unused hormones are broken down or excreted.

General Principles of Hormone Action

• Similarities between endocrine and nervous systems:

  1. Hormones regulate target cells; this is the primary function.

  2. Hormones bind to specific receptors in a "lock-and-key" mechanism.

  3. Multiple receptors can exist on one cell, targeting different hormones.

  4. Diverse hormone-receptor interactions lead to various regulatory changes.

  5. Hormones may be released in response to other hormones.

  6. Neural stimuli can prompt hormone release (e.g., epinephrine).

  7. Endocrine glands respond to physiological changes from target cells.

  8. Sensitivity of target cells can be altered by factors affecting signal transduction or gene transcription.

Neural vs. Endocrine Signaling

Classification of Hormones

According to Function:

1. Tropic Hormones: Target other endocrine glands to stimulate growth and secretion.

2. Sex Hormones: Target reproductive tissues.

3. Anabolic Hormones: Stimulate production of complex molecules in target cells.

According to Chemical Structure:

• Non-Steroid Hormones: Hydrophilic, synthesized mainly from amino acids.

• Steroid Hormones: Lipophilic, synthesized from cholesterol.

Mechanisms of Action

Non-Steroid Hormone:

1. Bind to specific receptors on cell's plasma membrane.

2. Activate a cascade - e.g., cyclic AMP (cAMP) pathway.

3. Faster response (minutes, not involving transcription).

Steroid Hormone:

1. Binds to cytoplasmic or nuclear receptor to form hormone-receptor complex.

2. Activates DNA for protein synthesis.

3. Response time: 45 minutes to several days.

Factors Affecting Target Cell Response

1. Upregulation: Occurs with decreased hormone levels, increasing receptor sensitivity.

2. Downregulation: Occurs with increased hormone levels, decreasing receptor sensitivity.

Combined Effects of Hormones

1. Synergism: Combined effect greater than individual effects; e.g., FSH/testosterone.

2. Permissiveness: A small amount of one hormone allows a second to have full effect; e.g., cortisol/GH.

3. Antagonism: One hormone opposes another; e.g., insulin/glucagon.

Regulation of Hormone Secretion: Feedback Loops

1. Positive Feedback: Amplifies changes; swift completion (e.g., oxytocin during childbirth).

2. Negative Feedback: Inhibits changes; maintains homeostasis (e.g., glucocorticoids).

Hypothalamus-Pituitary Axis (HPA)

• Command center of endocrine system.

• Coordinates messages between endocrine and nervous systems.

• Hypothalamus: Anterior-inferior to thalamus; oversees both neural and endocrine functions.

• Pituitary Gland: Located in the sella turcica; divided into anterior and posterior lobes.

Functions of the Hypothalamus

1. Links the nervous system to endocrine functions.

2. Regulates homeostasis (water balance, temperature).

3. Involvement in memory and emotion regulation.

4. Relay station between cerebral cortex & autonomic centers.

5. Key role in waking state maintenance.

The Pituitary Glands

1. Neurohypophysis (Posterior Pituitary): Stores/releases ADH and OT.

   • Regulated by hypothalamic signals.

2. Adenohypophysis (Anterior Pituitary): Synthesizes hormones.

   • Regulated by hypothalamic releasing hormones via hypophyseal portal system.

Hypothalamic and Anterior Pituitary Hormones

• Governed by hypothalamic hormones that travel directly to the anterior pituitary via hypophyseal portal.

  1. GnRH: Stimulates FSH and LH.

  2. TRH: Stimulates TSH.

  3. GHRH/GHIH: Regulates GH.

  4. PRH/PIH: Manages prolactin.

  5. CRH: Directs ACTH secretion.

Regulation of Anterior Pituitary Hormones

• Anterior pituitary hormones exert effects on targeted organs, often referred to as tropic hormones.

• Feedback loops maintain hormone levels within their normal ranges.

Neurohypophysis Hormones

1. Oxytocin (OT): Produced by the paraventricular nucleus; regulated by positive feedback.

   • Functions include uterine contractions and lactation support.

2. ADH/Vasopressin: Produced by the supraoptic nucleus; regulated by negative feedback.

   • Functions in water reabsorption and blood pressure regulation.

Homeostasis Restoration with ADH

• Achieved when there is a change in plasma volume or osmolarity, stimulating the release of ADH which minimizes urine production, increases blood pressure, and promotes hydration.

Oxytocin Functions

• Exerts effects via positive feedback during childbirth and breastfeeding, facilitating uterine contractions and milk ejection.