Calcium Homeostasis Bio PDF, RCSI 2024/25

Calcium Homeostasis Course DEM2 Year 2024/25 Module Endocrine Breast (ENDOB) Lecturer Dr Damir Varešlija Email: [email protected]  Lear ning Ou tcomes 1. Outline the factors effecting calcium homeostasis 2. Describe vitamin D metabolism 3. Outline the role of P...

Calcium Homeostasis Course DEM2 Year 2024/25 Module Endocrine Breast (ENDOB) Lecturer Dr Damir Varešlija Email: [email protected]  Lear ning Ou tcomes 1. Outline the factors effecting calcium homeostasis 2. Describe vitamin D metabolism 3. Outline the role of PTH, PTHrP and calcitonin 4. Describe bone turn-over and appreciate different forms of metabolic bone disease 5. Describe some of the clinical features of hyper- and hypocalcaemia  What is calcium? LO1 Essential Mineral: Calcium cannot be synthesized by the body and must be Most abundant mineral in the human obtained through diet. body. A macromineral, required in amounts >100 mg/day, like phosphorus (inorganic phosphate). Disorders of phosphate and magnesium often coexist with calcium Functions: imbalances. A key component of hydroxylapatite (Ca₅[PO₄]₃OH) in bones and teeth. Supports structural integrity and acts as a reservoir for calcium. Distribution in the Body: ~98% stored in bone. ~1% in extracellular fluid and blood. Small amounts in cells for signaling.  LO1 Essential Functions of Calcium in the Human Body 1. Muscle Contraction & Nerve Excitability: Required for muscle fibre contraction. Regulates nerve impulse transmission. Deficit (low Ca²⁺): Hyperexcitability of cells. Excess (high Ca²⁺): Increased contractility. 2. Neurotransmitter & Hormonal Release: Facilitates neurotransmitter release at synapses. Plays a role in hormone secretion from endocrine glands. 3. Enzyme Function: Acts as a cofactor for various enzymes, modulating their activity. 4. Blood Coagulation: Essential for activation of several clotting factors. Vital for the blood coagulation process. 5. Structural Support: Provides strength and rigidity to bones and teeth. 6. Membrane Integrity & Permeability: Maintains cell membrane stability. Regulates membrane permeability and signalling pathways.  Calcium Regulation LO1 Bone Bone acts as a calcium reservoir, and if other mechanisms fail, calcium is mobilized from bone at the expense of calcification. Dietary calcium The only “in” Hormonal regulation Parathyroid Hormone (PTH): Increases plasma calcium Intake: Dietary calcium. BLOOD CALCIUM Calcitriol (1,25-VitD): Increases plasma calcium Extracellular Calcium Levels: Tightly regulated between 2.2–2.6 mmol/L Calcitonin: Lowers plasma calcium Intestinal absorption Absorbs dietary calcium. Kidneys Filter and reabsorb calcium. Urine The principal “out” Calcium Regulation LO1 Intake: ~200 mg of dietary calcium is absorbed daily. Occurs in the small intestine. Requires active vitamin D for efficient absorption. Calcium Regulation LO1 Intake: ~200 mg of dietary calcium is absorbed daily. Occurs in the small intestine. Requires active vitamin D for efficient absorption. Storage: Calcium is stored in the bone reservoir. Regulated by: Calcitonin: Promotes calcium deposition in bones. Parathyroid Hormone (PTH): Mobilizes calcium from bones into the bloodstream. Calcium Regulation LO1 Intake: ~200 mg of dietary calcium is absorbed daily. Occurs in the small intestine. Requires active vitamin D for efficient absorption. Storage: Calcium is stored in the bone reservoir. Regulated by: Calcitonin: Promotes calcium deposition in bones. Parathyroid Hormone (PTH): Mobilizes calcium from bones into the bloodstream. Excretion: The kidneys are the primary site for calcium excretion. Regulated by: Calcitonin: Increases urinary excretion of calcium. PTH: Reduces calcium excretion by enhancing reabsorption in renal tubules.  Calcium Homeostasis LO1 Absorption Plasma Excretion Regulation Diet Soft Tissue Digestive tract Absorption Filtration Plasma [Ca2+] Kidney Reabsorption Calcification Resorption Urine Bone Faeces  LO1 Intestinal Calciu m Absor ption Two separate Mechanisms of Absorption: 1.Passive Absorption: Occurs throughout the entire small intestine. Proportional to the intraluminal calcium concentration. 2.Active Transport: Localized to the small intestine (mainly duodenum). Requires active vitamin D metabolite (1,25- dihydroxyvitamin D: “calcitriol”). Colonic Calcium Exchange: Minimal contribution to overall calcium absorption. Net Calcium Absorption: Depends on dietary intake. Typically,