Cell Signaling and Calcium Dynamics Quiz

Unit IV: Hormones/Signaling Molecules

• Hormones are chemical messengers secreted directly into the bloodstream.
• The bloodstream carries hormones to organs and tissues, allowing them to exert their functions.
• Many hormone types control various bodily functions and processes.
• Hormones are secreted by endocrine glands.
• Some glands also have non-endocrine regions with other functions besides hormone secretion.
  • Example: The pancreas has both exocrine (digestive enzymes) and endocrine (hormones) portions.
  • Example: The ovaries and testes produce hormones and gametes.
• Chemical messengers travel from their origin to target cells through various routes:
  • Endocrine: Hormones travel through the blood.
  • Neuroendocrine: Hormones released by nerves are carried in the blood.
  • Autocrine: Hormones bind to receptors on the same cell that released them.
  • Paracrine: Hormones diffuse to nearby target cells.
  • Neurocrine: A neuron contacts its target cell through axonal extensions, releasing the hormone into a synaptic cleft.

Hormone Classification

• Three major hormone classes:
  • Proteins and peptides: Most hormones in the body, ranging in size from small peptides (few amino acids) to proteins (almost 200 amino acids).
  • Steroids: Similar in structure to cholesterol, lipid-soluble.
  • Amines: Derivatives of tyrosine amino acid.
• Protein hormones are synthesized on the rough endoplasmic reticulum, initially as preprohormones, cleaved into prohormones in the endoplasmic reticulum and further processed in the Golgi apparatus to produce smaller, active hormones, stored in secretory vesicles and released as needed.

Steroid Hormones

• Similar in structure to cholesterol, lipid-soluble.
• Primarily produced by the adrenal cortex and gonads (testes and ovaries) and placenta during pregnancy.
• Cholesterol is a precursor for steroid hormones.

Amine Hormones

• Derivatives of the amino acid tyrosine.
• Include thyroid hormones (T4 and T3), and catecholamines (epinephrine, norepinephrine, and dopamine).
• Thyroid hormones are synthesized and stored in the thyroid gland within thyroglobulin.

Mechanisms of Action of Hormones

• Hormones usually bind to specific receptors on target cells.
• Hormone receptors are located on the cell membrane, cytoplasm, or nucleus.
• Hormone binding initiates intracellular signaling pathways. Receptors may act directly as enzymes.
• Various intracellular signaling pathways, that ultimately lead to change within the cell.
• Different types of receptors: -G protein-linked receptors: Couple with G proteins, causing a multitude of downstream effects. -Receptors that are ligand-gated ion channels: Open/close ion channels, altering membrane potential or ion concentration. -Receptors that function as enzymes: Some receptors possess intrinsic enzymatic activity. -Enzyme-linked receptors: Receptors associated with an enzyme, triggering downstream signaling after binding.

Second Messengers

• Second messengers relay signals from the cell surface to intracellular targets.
• Examples include cAMP, diacylglycerol (DAG), inositol triphosphate (IP3), and calcium ions.

Regulation of Hormone Secretion

• Hormone secretion is often regulated through feedback mechanisms.
• Examples include: increased blood glucose inhibiting glucagon secretion or the feedback of thyroid hormone on the production of TSH.

Diseases of the Thyroid

• Hyperthyroidism: Excessive thyroid hormone production.
  • Causes can be autoimmune disease (Graves' disease), or a tumor (adenoma). -Symptoms include nervousness, intolerance to heat, weight loss, and tremors.
• Hypothyroidism: Insufficient thyroid hormone production.
  • Causes include autoimmune disease (Hashimoto's), dietary iodine deficiency, or surgical removal or irradiation of the gland. -Symptoms include fatigue, weight gain, cold intolerance, and decreased metabolic rate.

Cretinism

• Caused by extreme hypothyroidism during fetal or early childhood.
  • Results in growth retardation and intellectual disability.

Insulin and Its Role

• Insulin is a hormone produced by beta cells in the pancreas.
• High blood glucose stimulates insulin release.
• Insulin promotes glucose uptake by muscle and liver cells, converting glucose into glycogen for storage and use as energy.
• Insulin also promotes fat synthesis and storage.
• Insulin enhances protein synthesis.
• Insulin inhibits glycogen breakdown, gluconeogenesis, and fat breakdown.

Glucagon and Its Role

• Glucagon is a hormone produced by alpha cells in the pancreas.
• Low blood glucose stimulates glucagon release to increase blood glucose.
• Glucagon promotes glycogenolysis (breakdown of glycogen to glucose).
• Glucagon promotes gluconeogenesis (formation of glucose from amino acids and fats).
• Glucagon promotes fat breakdown for energy.

Diabetes Mellitus

• A group of metabolic disorders characterized by high blood glucose levels.
  • Type 1: caused by lack of insulin production by beta cells in the pancreas.
  • Type 2: impaired response of tissues to insulin (insulin resistance). -Symptoms: chronic hyperglycemia (high blood sugar), glucose intolerance, high blood sugar, increased urination.