LO: Describe the location of calcium in the body and its storage forms

Calcium sources

• Dairy
• Cereals
• Green vegetables

Intestinal calcium absorption

• 15-85%
• Depends on intake, active absorption, life stage, physiological state
• Vitamin D status and 1,25(OH)₂ vit D
• Bioavailability
• Gastrointestinal disorders

Calcium bodily stores

• Skeleton (99% in bones)
• Soft tissue
• Extracellular fluid

LO: Define adjusted calcium and its use

Albumin adjusted calcium

• Decreased albumin may mask hypercalcaemia
• Acidosis decreases protein binding
• Higher ionised Ca
• Alkalosis increases protein binding
• Lower ionised Ca

Functions of calcium

• Stiffness and structure
• Hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂)
• Reservoir for plasma Ca
• Neurotransmission
• Reproduction
• Hormone action
• Cellular growth
• Enzyme function

Hypocalcaemia

• Albumin adjusted Ca < 2.20 mmolL^-1
• Parasthesia - numbness, tingling
• Muscle spasm and tetany
• Cardiac abnormality
• Coma
• Renal failure
• Hypoparathyroidism - low PTH
• Vitamin D deficiency

Hypercalcaemia

• Albumin adjusted Ca > 2.60 mmolL^-1
• Nausea
• Mental disturbances
• Peptic ulcers
• Renal stones/failure
• Constipation
• Hyperparathyroidism - high PTH
• Vitamin D toxicity

Osteoporosis

• Bone mineral density - predicts fracture risk
• Osteoporosis is defined based on bone mineral density
• T-score < 2.5 $\sigma$
• Bone quality is affected, increasing risk of fracture

LO: Discuss calcium homeostasis

Calcium and phosphate metabolism

• G-coupled receptor - Calcium sensing receptor (CaSR)
• Regulates calcitonin (CT), parathyroid hormone (PTH), fibroblast growth factor 23 (FGF23)

flowchart LR

	Intestine --> A[Calcium in plasma]
	A --Mineralisation--> Bone
	A --> Kidney
	A --> Intestine
	Bone --Resorption--> A
	Kidney --> A
	
	Kidney --Excretion--> END:::hidden
	
	classDef hidden display:none;

Parathyroid hormone

• Stimulates all the arrows going into calcium in plasma so causes Ca concentration in plasma to increase

flowchart LR
	subgraph PTH["Calcium into plasma"]
		Intestine --> A[Calcium in plasma]
		A --Mineralisation--> Bone
		A --> Kidney
		A --> Intestine
		Bone --Resorption--> A
		Kidney --> A
	end
		
		Kidney --Excretion--> END:::hidden
	
	classDef hidden display:none;

Calcitonin

• Stimulates calcium plasma to bones
• Inhibits bones to plasma
• Increase in calcium stored in bones

flowchart LR
	Intestine --> A[Calcium in plasma]
	subgraph PTH["Calcium into bones"]
		A --Mineralisation--> Bone

	end
	Bone --Resorption--> A
	A --> Kidney
	A --> Intestine
	Kidney --> A
	
	Kidney --Excretion--> END:::hidden
	
	classDef hidden display:none;

1,25(OH)₂ Vitamin D

• Chondrocyte and osteoblast maturation
• Bone formation and mineralisation

Fibroblast growth factor 23 (FGF23)

• 25 Vit D stimulated to release PO₄ to be excreted