L11*-Absorption of ions and water 💦 Flashcards
(23 cards)
When is the absorption of ion and water important ?
During the postprandial state, the absorption of ions and water is enhanced in the small intestine.
Name 2 types of movement for ions and water.
- Transcellular - through the cells
-solute crosses through the cell membrane
-active transport / ATP
2.Paracellular - between cells
-solute moves passively
-between cells / via tight junctions
Too much or too little water can cause 2 things. what are they ?
Constipation
Diarrhoea
What does the movement of water depends on ?
Absorption of water depends on the absorption of ions, principally Na+ and Cl-
Describe transport of Na+ and Cl-.
-Ions move into the lateral intercellular spaces.
-Resulting high NaCl near the apical end of the intercellular space.
-Causes it to be hypertonic which causes an osmotic flow of water from the lumen.
-Via the tight junctions into the intercellular spaces.
Give general details about the absorption of Na+.
-Na+ is absorbed along the entire length of the intestine.
-3 different transport routes of entry.
-creates the gradient (basal side)
-keeps intracellular Na+ influx.
What are 3 different transport routes of entry of Na+ ?
- Na/Glucose transport or Na/Amino acid transport
- Na-H exchanger
- Parallel Na-H and Cl-HCO3 exchange (electroneutral)
Describe the 1st transport route of entry of Na+ ?
-SGLT1 (luminal side)
-Highest in jejenum
-allows Na+ to enter the cell when glucose, galactose and neutral AA’s present.
-Electrochemical gradient
Describe the 2nd transport route of entry of Na+ ?
-Na+ is exchanged for H+ (protons)
-Electrochemical gradient
-Small intestine (jejenum)
-When pH is neutral or alkaline (Secretion HCO3-)
Describe the 3rd transport route of entry of Na+ ?
- Same as before exchanged for H+ (protons)
- Electrochemical gradient
- Coupled to a Cl-HCO3 Exchanger
- Electroneutral (Na+ & H+ and Cl- & HCO3-)
- Primary method of Na+ absorption between meals (fasted state)
- Does not require glucose
- Regulated by intracellular cAMP / cGMP & Ca2
What is the clinical importance of Na+ uptake ?
-E coli food poisoning
* Enterotoxin binds to enterocytes
* Toxin is internalised (endocytosis)
* Interacts with Gs > increasing cAMP levels
* Enhanced Cl- secretion
* Blocks Na+ and Cl- uptake
Describe the absorption of Ca2+
- Dietary sources
- Intestinal secretion
- Net update
-Passive transport - paracellular route
-Active transport - trancellular route, Duodenum, VDR (Vitamin D receptor) - Nuclear receptor
Describe the uptake of Ca2+.
- TRPV6 Receptor
- Transient Receptor Potential Cation Channel Subfamily Vanilloid Member 6
- Calbindin-D9K (buffers Ca2+) > Reduces free Ca2+
- PMCA (Plasma Membrane Ca2+ ATPase)
- NCX (Na-Ca exchanger)
- Transfer calcium out of enterocyte
What does VDR do ?
VCR-Vitamin D receptor
-Binding of Vitamin D>Increases receptor transcription (apical/basal)
-Binding of vitamin D influences the expression of genes responsible for Ca2+ transport.
-Promotes the uptake from the lumen into the body.
What are the causes of deficiency of vitamin D ?
-Poor diet
-lack of sun
-demineralisation
Causes of deficiency of Vitamin D
-Hypocalcaemia
-Bone softening
-not the same as osteoporosis
Name variety of sources of iron.
-Haem iron (animal sources)
-Non-Haem iron (inorganic)
-Most of inorganic are absorbed rather than the organic
-Haem is more bioavailable
-Haem derived from myoglobin and haemoglobin
Name the role of iron in the human body.
-oxygen transport > haemoglobin >O2 carrying cell like erythrocytes and RBCs
-myoglobin
-Haematopoiesis
-Energy production in ETC
-Energy production from iron sulphur clusters
-make a component of the enzyme cytochrome (CYP450)
-also make a component of the DNA Helicase enzyme
Describe the steps for the absorption of iron.
Absorption of iron takes place in small intestine
👇
In food, Fe exists as ferritin but cant be absorbed in this form
👇
Fe3+ -> Fe2+ enzyme Ferric reductase reduce this reaction via the transporter DMT1
👇
Then in the cells, Fe2+ ->Fe3+ enzyme Hephaestin oxidise this reaction via the transporter ferroportin
👇
Fe3+ is then transported into the blood via a protein carrier called transferrin
What does Transferrin do ?
Transferrin receptor aid transport of Fe+ transferrin to 2 places.
1. transport Fe3+ to synthesis erythrocytes via erythropoiesis.
2. transport to liver to either store it as ferritin or liver can release stored Fe back to circulation through ferroportin.
What does Hepcidin do to Iron transport or regulation ?
- Hepcidin is the master regulator of Fe.
- Hepcidin inhibits ferroportin in the liver → ↓
plasma Fe concentration - Hepcidin inhibits ferroportin in the spleen too. The spleen recycles damaged/dead RBC → release Fe. Ferroportin transports these Fe to circulation.
Hepcidin action = ↓ plasma Fe concentration - Hepcidin reduce absorption of Fe from the
lumen of the small intestine.
- Fpn is in the plasma membrane of iron
exporting cells - ↓Fe levels > ↓Hepcidin > ↓inflammation
How is Fe regulated in the body ?
Stimulation of hepcidin helps to regulate plasma Fe concentration
- IL-6 (an inflammatory cytokine) stimulate hepcidin release
- ↑ plasma Fe = hepcidin stimulation
- Lipopolysaccharide from bacteria
- Haemochromatosis (HFE) protein interact with other protein to stimulate hepcidin release. Mutation of the HFE gene →
haemochromatosis (Fe overload in the tissues).
Impaired HFE protein = impaired hepcidin release = excess Fe in tissues
Overexpression of Hepcidin > Chronic anaemia (ACD) > Death
How is Haem transported in the body ?
-Haem is from Haemoglobin and myoglobin.
-Fe is removed from haem using Haem oxidase (HO-1)
-Haem – Fe = Porphyrin
-Porphyrin breakdown product is biliverdin → bilirubin (using enzyme: biliverdin reductase).
-Disorders related to this process: Hyperbilirubinemia, Haemolytic anaemia
