9. General principles of humoral control of the physiological functions. Telecrine and paracrine functions. Classification, synthesis, and mechanism of actions of the hormones. Control of the hormonal secretion.

General Principles of Humoral Control of Physiological Functions - whats the main point here?

• HORMONES Hormones are chemical signaling molecules that regulate:

  • Metabolism, growth, fluid balance, reproduction, stress response, etc.

• Hormones help maintain homeostasis by coordinating the function of distant organs.

• They are secreted into the bloodstream and act on target cells with specific receptors.

• The CNS influences endocrine function via:

  • Neurohormones from the hypothalamus

  • Autonomic nervous system effects on glands

Telecrine and Paracrine Functions

Telecrine function:

• Hormones secreted into bloodstream and act on distant target organs

• Most classical endocrine hormones (e.g., insulin, cortisol)

📍 Paracrine function:

• Hormones/chemicals act on neighboring or adjacent cells

• Example: Insulin secreted by β-cells inhibits glucagon release from nearby α-cells in the pancreas

Classification of Hormones

A. Amino Acid Derivatives (Water-soluble) (NAT LIKE NAT THAT BIG) (NORADRENALINE, ADRENALINEM THYROUD = NAT)

• Smallest hormones (up to 3 amino acids)

• Examples: Adrenaline, noradrenaline, thyroid hormones

B. Peptide and Protein Hormones (Water-soluble)

• Chains longer than 3 amino acids

• Examples: Insulin, glucagon, oxytocin, ADH

C. Lipid-Derived Hormones

i. Steroid hormones (from cholesterol)

• Examples: Cortisol, testosterone, oestrogen, progesterone

ii. Eicosanoids (from fatty acids)

• Examples: Prostaglandins, leukotrienes

4. Mechanism of Action of Hormones

A. Water-Soluble Hormones (cannot enter cells directly)

1. Bind to receptors on cell membrane

2. Activate G-proteins, which activate secondary messengers:

   • Adenylyl cyclase → cAMP

   • Guanylyl cyclase → cGMP

   • Phospholipase C → DAG

   • Calcium → calmodulin

3. These messengers activate enzyme pathways → physiological effects

B. Lipid-Soluble Hormones (can enter cells)

1. Diffuse through the cell membrane

2. Bind to carrier proteins in cytoplasm to form a hormone-protein complex

3. This complex enters the nucleus and binds to nuclear receptors

4. Activates DNA transcription → mRNA

5. Ribosomes produce new proteins → specific cell effects

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5. Control of Hormonal Secretion

🧠 A. Nervous system control:

• Hypothalamus produces neurohormones that regulate pituitary gland (eg somatostatin inhibits TSH and GH)

• ANS can stimulate or inhibit secretory cells (e.g., adrenal medulla)

🔁 B. Negative feedback (most common):

1. Hormone is secreted → acts on target

2. Target's response inhibits further hormone release

   • Example: High cortisol levels inhibit ACTH release

➕ C. Positive feedback (rare but important):

• Hormone action stimulates more release

• Example: Oxytocin increases uterine contractions → more oxytocin released

⚖ 6. Physiological Effects of Hormones

• Protein metabolism: Catabolic (e.g., cortisol) and anabolic (ball lickinG) (e.g., GH, insulin)

• Lipid metabolism: Control of lipid breakdown and storage

• Blood glucose regulation (normal: 2.8–6.1 mmol/L):

  • ↓ by: Insulin (only hormone that lowers glucose)

  • ↑ by: Glucagon, GH, T3/T4, catecholamines, cortisol

• Calcium-phosphate metabolism:

  • Calcium: 2.12–2.62 mmol/L (0.5 apart)

  • Phosphate: 0.7–1.7 mmol/L (1 apart)

  • Regulated by: Parathyroid hormone, calcitonin, vitamin D3

• Water-electrolyte and acid-base balance: Via ADH, aldosterone, etc.