ions vitamins and minerals Flashcards
what are the two main types of transport?
- para cellular
- transcellular
what are the methods via transcellular transport?
what do these also involve?
- facilitated diffusion
- simple diffusion
- active transport
carrier proteins
what is paracellular transport?
when things don’t go through the cells they travel around the cells
what are the two types of channel proteins?
Channel proteins :
channel proteins form aqueous pores allowing specific solutes to pass across the membrane
(much faster)
Carrier proteins:
carrier proteins bind to the solute and undergo an conformational change to transport it across the membrane
what are the two ways of active transport?
- primary
linked directly to cellular metabolism - secondary
derives energy from concentration gradient of another substance actively transported
example of secondary active transport?
- enterocytes absorb GLUCOSE & GALACTOSE via 2nd active transport
- glucose transporter
example of facilitated diffusion?
Exit of glucose then via facilitated diffusion (GLUT-2)
absorption of fructose
example of primary active transport?
sodium potassium ATPase
where does water absorption happen ?
how much water is absorbed?
99% of water is absorbed by GI tract
- Most water is absorbed in the small intestine
mainly jejunem
how are ions absorbed?
- Many ions absorbed slowly by passive diffusion
- Ca2+
and iron are incompletely absorbed
how much water does the small intestine absorb?
8 litres
how much water does the colon absorb?
1.4 litres
where does the water come from?
Ingestion (2L) saliva (1.2L). Gastric secretions (2L) bile (0.7L). The pancreas (1.2L) intestine (2.4L).
what is the name of the process by which the water is absorbed?
- standing gradient osmosis
- is driven by absorption of the sodium ion
how does sodium get into cells in different placed enterocytes?
- proximal bowel - counter transport of Na+ for H+
- jejunum - co-transport with amino acid, monosaccharides
- ileum - co transport with Cl-
- colon - restricted movement through the ion channels
how are chloride ions moved?
Cl- is co-transported with Na+
in the ILEUM and
exchanged with HCO3- in the COLON.
how is potassium chlorides transported?
Cl- is co-transported with Na+
in the ILEUM and
exchanged with HCO3-in the COLON.
so we get potassium in faeces
what happens with high sodium in the cell?
- sodium is pumped into lateral intracellular spaces by Na/K ATPase
- this increases the electrochemical gradient to positive
- so negative ions move Cl- and HCO3
- the solution is hypertonic
- so this drives the absorbtion of water
where is the calcium absorbed?
Most absorption of calcium occurs in the duodenum and ileum.
what stimulates the absorption of calcium?
- calcium deficiency increases the absorbtion
- Vitamin D and parathormone stimulate the absorption of calcium
how much calcium do we ingest
how much calcium do we absorb?
1-6g of calcium a day
we only absorb 0.7g of it
by which transporters is the calcium carried across by?
- intestinal calcium binding protein (IMcal)
- ion channel
what is the issue with absorbing calcium
calcium acts as a secondary transporter
- we need to keep it inactive so we bind it to calbindin to make it inactive
how do we ship the calcium across the cell into the blood stream ?
actively transport it
- using Ca2+ATPase (PMCA).
- HIGH affinity but LOW capacity.
Na+/Ca2+ exchanger.
low affinity but high capacity
