Mineral Bioavailability/Absorption

Calcium

Found in dairy products (no oxalates or phytates), leafy greens, tofu, canned fish with bones

Absorption: active transport (requires vitamin D and calbindin) and passive transport (gradient dependent)

Calbindin —>  calcium binding protein in intestinal cells that transports calcium across the cell, stimulated by vitamin D (calcitriol)

Bioavailability: fraction decreases as calcium intake increases (body adpts by reducing absorption efficiency)

Inhibitors: oxalates (green veggies, tea, cocoa)  and phytates (whole grain, nuts) interfere
Increasing absorption: vitamin D (calcitriol) increases absorption

Phosphorus

Found in meat, poultry, fish, dairy, eggs, nuts, legumes, seafood (no phytates, better than plant sources)

Vitamin D promotes phosphorous absorption
Inhibitors: phytates (whole grain, nuts) interfere NOT OXYLATES
Increasing absorption: vitamin D (calcitriol) increases absorption

General mineral availability

animal sources have more than plant sources, environmental influences (amount in soil, feed, etc), affected by food processing (whole vs white bread)

Ex: selenium deficiency in California soil causing selenium deficiency in livestock

white vs whole bread

whole wheat bread has higher mineral content than white bread because it retains the bran and germ, which are rich in minerals.

intestinal absorption of nutrients pathway

stomach —> duodenum —> jejunum —> illeum —> colon

intestinal absorption of nutrients absorption

Active transport
    - membrane transport protein, requires energy, affected by other components of foods
Passive transport (diffusion/osmosis)
    - no energy, transport protein
     - through intestinal wall (transcellular) or between cells (interstital, paracellular)

bioavailability

percentage of a nutrient in a food or supplement that is absorbed and available to be used by the body

Sodium and Chloride Absorption

SOURCES:
High —> salt, processed
Moderate —> meats, dairy, seafood
Low —> fruits, vegetables

Absorption
absorbed in small intestine. sodium uptake occurs thorugh active transport, coupled with glucose via the soidum-glucose cotransporter. chloride follows sodium passively (electrical neutrality). --> COLON, sodium and chloride and absorbed through passive diffusion. HIGH BIOAVAILABITY

Sodium and Chloride Homeostasis

when low BP, kidneys trigger sodium and chloride reabsorption via active transport (increasing water retention). This raises BP in blood. Liver regulates sodium retention through system, supporting electrolyte balance. Colon also absords sodium and chloride by passive diffusion (colon --> fine tuner for homeostasis)

Low BP —> extracellular fluid (ECF) decreasing. Kidney increase s/c reabsoprtion, aided by renin-angiotensin-aldosterone system (retainin water and raising BP). 
Antidiruetic hormone (ADH) —> promotes water absorption (concentrating ECF)

then… natriuretic peptides are released when BP is high to promote sodium/chloride exccretion

Potassium absorption and bioavailabity

Found in fruits, vegetables, legumes

Absorption: absorbed mainly in small intestine through passive diffusion.

moves 1 sodium, 1 potassium, and 2 chloride ions from the filtrate into the cell using the sodium gradient maintained by the Na⁺/K⁺ pump, helping reabsorb electrolytes and dilute urine.

Potassium homeostasis

when plasma K+ rises, the adrenal cortext secretes aldosterone (increases renal K+ execretion and Na+absorption) in liver. restores plasma K+ to normal.

when K+ decreases, aldosterone is decreased, cosnerving K+.

Magnesium  absorption and bioavailabity

found in spinach, almonds, cocoa, brazil nuts

Absorption
in small intestine. sodium potassium gradeint across intestine cells.
Magnesium is absorbed mainly in the small intestine, partly via passive diffusion, and partly via active transport that can be linked to sodium and potassium gradients across the intestinal cells. keeps low sodium and high potassium inside the cell, and this difference helps pull magnesium into the cell for absorption.

phyates (nuts, seeds) chelate (bind) magnesium absorption

Magnesium homoeostasis

GI Tract --> blood while kidneys conserve ions to maintain extracellular fluid balance. When plasma levels are high, kidneys excrete the rest.

no known hormons or enzymes that directly regular magnesium balace but likely similar to ca and P