ENDOCRINE-PPT

ENDOCRINE SYSTEM

  • Endocrine glands secrete hormones into interstitial fluid.

  • Hormones diffuse into blood to target tissues.

  • The term "endocrine" comes from Greek: "endo" (within), "krino" (to secrete).

  • Endocrinology studies the endocrine system.

ENDOCRINE GLANDS

  • Major glands include: hypothalamus, pineal gland, pituitary gland, thyroid, parathyroid, thymus, adrenals, pancreas, ovaries (female), testes (male).

COMPARISON OF ENDOCRINE AND NERVOUS SYSTEM

Similarities:

  1. Both utilize brain structures.

  2. Hypothalamus integrates nervous and hormonal functions.

  3. Neurons can secrete hormones like ADH and oxytocin.

  4. Both systems regulate critical physiology and engage receptors for action.

Differences:

  1. Mode of transport (blood vs. synapse).

  2. Response speed.

  3. Duration of effects.

CHEMICAL MESSENGERS

  • Classifications:

    • Autocrine: Affects the same cell (e.g., eicosanoids).

    • Paracrine: Affects neighboring tissues (e.g., histamine).

    • Neurotransmitter: Neuron-released, travels short distances (e.g., acetylcholine).

    • Endocrine Hormones: Travels via blood to distal targets (e.g., insulin).

HORMONES

  • Defined as bodily chemical messengers.

  • Two categories:

    1. Lipid-soluble: Steroid and thyroid hormones (requires transport proteins).

    2. Water-soluble: Peptide and amino-acid derived hormones (often free in plasma).

HORMONE SECRETION PATTERNS

  1. Chronic: Constant blood levels (e.g., thyroid hormones).

  2. Acute: Sudden, irregular changes.

  3. Episodic: Predictable intervals (e.g., reproductive hormones).

REGULATION OF HORMONE LEVELS

  • Negative feedback: Most common regulation method.

  • Positive feedback: Some hormones reinforce their own production.

HORMONE RECEPTORS

  • Hormones act by binding to specific receptors on target cells.

  • Agonist: Activates a receptor; Antagonist: Inhibits a receptor.

PITUITARY GLAND

Overview:

  • Secretes nine key hormones.

  • Divided into anterior and posterior lobes.

Anterior Pituitary:

  • Hormones include GH, TSH, ACTH, LH, FSH, PRL.

  • Regulated by hypothalamic hormones.

Posterior Pituitary:

  • Stores and releases ADH and oxytocin (neurohormones).

THYROID GLAND

  • Secretes T3, T4, calcitonin.

  • Regulates metabolic rate and calcium levels.

PARATHYROID GLAND

  • Regulates calcium through PTH secretion.

ADRENAL GLAND

  • Composed of medulla (produces epinephrine and norepinephrine) and cortex (produces steroid hormones).

PANCREAS

  • Functions as both exocrine and endocrine gland.

  • Controls glucose levels via insulin and glucagon.

REPRODUCTIVE HORMONES

  • Testes: Produce testosterone; Ovaries: Produce estrogen and progesterone.

PINEAL GLAND

  • Regulates reproductive functions through melatonin secretion.

THYMUS

  • Important for immune development; secretes thymosin.

ENDOCRINE DISORDERS

  • Conditions like diabetes insipidus, Hashimoto thyroiditis, Addison disease, etc.

EFFECTS OF AGING

  • Hormone secretion generally declines with age.

PITUITARY GLAND

Overview: Secretes nine key hormones. Divided into anterior and posterior lobes.

Anterior Pituitary Hormones:

  1. Growth Hormone (GH): Stimulates growth and cell reproduction by promoting protein synthesis and the utilization of fat.

  2. Thyroid Stimulating Hormone (TSH): Stimulates the thyroid gland to produce thyroid hormones (T3 and T4), which regulate metabolism.

  3. Adrenocorticotropic Hormone (ACTH): Stimulates the adrenal cortex to release glucocorticoids, important for stress response and metabolism regulation.

  4. Luteinizing Hormone (LH): Triggers ovulation in females and stimulates testosterone production in males.

  5. Follicle Stimulating Hormone (FSH): Stimulates follicle development in ovaries and sperm production in testes.

  6. Prolactin (PRL): Promotes milk production in breastfeeding females and may influence reproductive functions in both sexes.

Posterior Pituitary: Stores and releases ADH and oxytocin (neurohormones).