Ions and minerals Flashcards
What is diffusion?
The net random movement of molecules from a region of high concentration to low concentration. Multicellular organisms evolve circulatory system to provide cells within their diffusion range.
What cellular structure behaves as a diffusion barrier?
Cell membrane
Which molecules can pass through the phospholipid bilayer?
Lipid soluble (Non-polar) molecules can diffuse passively with minimal resistance in comparison to water soluble (Polar molecules); phospholipid bilayer consist of hydrophobic tails repelling polar molecules.
What is osmosis?
Osmosis concerns the net movement of water across a partially permeable membrane from a region of high water potential (Hypotonic), to a region with low water potential (hypertonic).
Within isotonic solutions there is no net movement of water.
What is paracellular transport?
Molecules can pass the epithelial layer through tight junctions, and lateral intercellular spaces.
What is transcellular transport?
Transcellular transport: Transport of solutes through a cell.
What are the three membrane transport mechanisms?
Simple diffusion
Facilitated transport
Active transport
What are channel proteins?
Form aqueous pores enabling specific solute to pass cross the membrane
Faster method of transportation than carrier proteins
Channel proteins are linked with an internal hydrophilic surface in order to shield solutes from the hydrophobic fatty acid tails
What are carrier proteins?
Binds to solute and undergo conformational change to transport solute across the phospholipid bilayer into intracellular cytoplasmic space.
What are the three types of gated ion channels?
Voltage gated
Ligand gated
Mechanically gated
What is a uniporter?
A uniporter is an integral membrane protein that transports a single type of substrate species across a cell membrane
What are symporters?
Symporters are secondary active transporters that move two substances in the same direction. Example: Sodium-glucose symporter passively diffuses into the cell, resulting in the cooperative movement of glucose into the cell (Glucose has higher intracellular concentrations), as energy is supplied through passive sodium transport.
Secondary active
What is an anti-porter?
Sodium-hydrogen anti porter users energy from inward movement of sodium to move hydrogen ions extracellular (Used to maintain internal pH)
What are the two main examples of coupled transport?
Antiporters
Sympoters
What are the three main transport mechanisms?
Primary ative transporter
Secondary active transport
Facilitated transport
What is primary active transport?
Linked directly to cellular metabolism (Uses ATP to power the transporter of substrates)
What is secondary active transport?
Derives energy from the concentration gradient of another substance that is actively transported
What is facilitated transport?
Enhances the rate of a substance can flow its concentration gradient, there is a tendency to equilibrate the substance across membrane
What are the two main examples of secondary active co transporters?
SGLT-1 co transporter (Monosaccaride absorption)
HCO3/Cl- counter transporter
How are glucose and galactose molecules absorbed within enterocytes?
Secondary active transport, through SGLT-1 on enterocyte apical membrane and electrochemical gradient
What is SGLT-1?
Has the ability to transport glucose against concentration gradient, therefore effective when extracellular luminal concentrations are comparatively less than that in enterocytes
What type of transport enables fructose absorption into enterocytes?
Facilitated diffusion
Which carrier protein is involved in the fructose absorption on the apical membrane of enterocytes?
GLUT-5 glucose co-transporters
Which transporters are involved in the exist of carbohydrates from enterocytes?
GLUT-2
What is the affinity and capacity of GLUT-2?
High capacity
Low affinity
Where is the majority of water absorbed within the GI tract?
Absorbed predominantly within the jejunum
Which two hormones regulates the GI absorption of calcium?
Calcitriol
Parathyroid hormone
Which hormone regulates enterocyte absorption of iron?
Hepcidin
How much water is absorbed in the small bowel?
8L
How much water is absorbed in the large bowel?
1.4l
What is standing gradient osmosis?
Transport of sodium ions from lumen into enterocyte
Counter-transport (antiporter), hydrogen ion exchange within the duodenum
Co-transport with amino acids and monosaccarides
Co-transprot with chloride ions
Which ion are chloride ions exchanged with into the enterocytes?
bicarbonate ions
What role is performed by the basolateral enterocyte Na/K ATPae in terms of ion transport?
Chloride ion co-transported with Na+ within ileum, exchanged with HCO3- (Colon) into enterocytes. Co-transporter executed through secondary active transport on apical membrane. Symporter occurs due to active transport of Na+ into lateral intercellular spaces by Na+/K+ATPase on enterocyte basolateral membrane into lateral plasma space.
Potassium diffuse in via paracellular pathways in small intestine
Which uptake protein is responsible for the facilitated diffusion of calcium ions int the enterocyte through the apical membrane?
TRPV6 (IMcal)
How is calcium cytoplasmically transported to the basolateral membrane of enterocytes from the apical membrane?
Cytoplasmic calcium biding protein, calbindin-D permits the movement of calcium
Why is calcium intracellularly transported by calbindin-D proteins?
Prevents the action as an intracellular signal
What are the two methods of calcium absorption?
Facilitated diffusion model using IMcal
Paracellular ion channels
How are calcium ions removed from enterocyte through the basolateral membrane?
Calcium extrusion from enterocytes performed by two proteins: PMCA1 and NCXI, calcium ions are pumped across the basolateral membrane against concentration gradient into circulation
What are the two protein transporters in the basolateral membrane that enables calcium enterocyte exist?
PMCA1 & NCX1
Why does PMCA1 have a high affinity to calcium?
To maintain low intracellular concentrations
Which calcium exit transporter has a low affinity, but high capacity?
NCX1 exchanger
What would be the effect for a high intracellular concentration of calcium?
Result in activation of signalling cascade (Ca2+ is a signalling molecule)
What is the average intracellular concentration of calcium?
100nM
What is the average extracellular concentration of calcium?
1-3mM
What effect does calcitriol exhibit in terms of calcium gut absorption?
Potentiates the transcription of Calbindin-D , PMCA, andTRPV6 transports to increase calcium enterocyte absorption from lumen into circulation
Which promoter regions does Calctriol act upon?
Promoter regions VDRs -> Increases transcription
How does calcitriol increase the rate of extrusion across basolateral membrane?
Increases PMCA transporters
What are the effects of vitamin D deficiency?
Rickets
Osteporosis
Which oxidative iron state is used to form haem?
Ferrous Fe2+
What is the role of ferrous iron in haem?
Prophetic group with porphyrin ring of haemoglobin, facilitated oxygen transport
Which cytochrome does haem form within the electron transport chain?
Complex 2
What are the 3 main functions of iron?
Ferrous forms haem prophetic group within the porphyrin ring of haemoglobin - oxygen transport
Exhibits electron donor and electron acceptor properties
Essential for oxidative phosphorylation within the inner mitochondria membrane as cytochromes
How is haem iron absorbed into the enterocyte?
Absorbed into he apical membrane through haem transporter
What is the fate of ferrous iron within enterocytes?
Directly stored as mucosal ferritin (protective mechanism for overload)
Transported through the basolateral membrane via ferroportin into circulation
What happens to ferritin within enterocytes?
Shed across epithelial cells
How is ferrous iron converted into ferric iron?
Hephaestin action
Why is ferrous iron concerted into ferric iron after release from enterocyte?
In order to be associated with plasma transferrin and circulated towards liver or bone marrow
What effect does ferric iron through the liver have on hepcidin?
Increases hepcidin secretion
What effect does Hepcidin have on enterocytes?
Reduces ferrorportin integration into basolateral membrane in order to reduce systemic overload
Which cytochrome converts ferric sulphate iron into ferrous iron for entry into enterocytes?
Duodenal cytochrome B
How does ferrous iron enters into enterocytes?
Through DMT-1
Why is iron toxic in excess?
They body has no removal mechanism of actively excreting iron,
Free radicals
Which vitamin reduces Ferric iron to ferrous?
Vitamin C
What are the main insoluble ferric salts?
Hydroxide, phosphate, bicarbonate
What % of dietary iron is absorbed?
20%
Which protein potentates the absorption of haem into the apical duodenum membrane, through receptor-mediated endocytosis?
Haem carrier protein 1 (HCP1)
Which enzyme cleaves ferrous iron from erythrocytes to liberate ferrous iron?
haem oxygenate
What is the purpose of cytochrome B?
Catalyses the reduction of ferric iron to ferrous iron, in the process o iron absorption within the duodenal enterocytes
Ferrous transported into the enterocyte from divalent metal transporter H coupled co transporter
Which iron transporters enable iron exit from enterocytes?
Ferroportin ion channel
Which hormone regulates ferroportin transcription?
Hepcidin
What is Hephaestin?
Fe2+ is oxidised by transmembrane copper-dependent ferroxidase (Hephaestin) Ferric Fe3+ Bound to apotransferrin transferrin.
Which plasma protein enables the transport of ferric iron?
Transferrin
How is ferrous iron stored within enterocytes?
Fe2+ alternatively binds to cytoplasmic apoferritin forming ferritin micelle Globular protein complex (Fe2+ oxidised to Fe3+) Crystallises within protein shell. Single ferritin = 4000 iron ions. Increased dietary ion absorption Ferritin.
What is ferritin?
Ferritin: Irreversible binding of iron to ferritin in epithelial cells not available for transport into plasma. Loss in intestinal lumen and excreted into faeces Increases in cytoplasmic iron Increased ferritin synthesis.
What are the four main fat soluble vitamins?
A, D, E, and K
How are the fat soluble vitamins transported to the brush border?
As micelles
A B12 deficiency results in which type of anaemia?
Pernicious anaemia
How is B12 released within the stomach?
HCl
Which protein does B12 combiner with within the stomach?
Haptocorrin
Which factor is B12 bound to?
Intrinsic factor
Which cells synthesise intrinsic factor?
Gastric parietal cells
Which protein does B12 bind with within enterocytes?
Transcobalamin-11
Where is b12-transcobalamin-II stored?
Liver, and transported to tissues
What is intrinsic factor?
Intrinsic factor: Vit B12 binding protein secreted by parietal cells. Complex resistant do digestion Binds to cubilin receptor in distal ileum (receptor mediated endocytosis)
Which receptor does the IF-B12 complex bind onto within enterocytes?
Cubillin receptor
What are the four main causes of vitamin b12 deficiency?
Inadequate intake of sources containing the compound (Veganism)
Inadequate secretion of intrinsic factor: pernicious anaemia (an autoimmune disorder)- autoantibodies interfere.
Lack of stomach acid (achlorhydria) – after partial gastrectomy surgery.
Malabsorption- diseases in the ileum reduces B12 absorption.
