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fluids and metabolism > digestion and absorption part 2 > Flashcards

digestion and absorption part 2 Flashcards

1
Q

why is iron important

A

its an essential element for haem synthesis
but iron is toxic in excess, high body levels of iron cause tissue damage
iron deficiency is the most common nutritional problem worldwide

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2
Q

how is iron uptake regulated

A

there is no physiological control of iron excretion
regulation of intestinal iron uptake is the only mechanism for controlling body iron content

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3
Q

how does iron homeostasis work

A
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4
Q

what affects intestinal iron absorption

A

the amount of iron ingested
diet contains haem and non haem iron 15-20mg a day
bioavailability of non haem iron
promoted by ascorbic acid (vitamin C)
gastric acid- occurs mainly in dudodenum
inhibited by certain plant components e.g phyates
efficiency of iron uptake process depends on body iron status

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5
Q

what does intestinal iron absorption increase with

A

decreased iron stores
increased erythropoietic activity
anaemia
hypoxia

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6
Q

what does intestinal iron absorption decrease with

A

increased iron stores
inflammation

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7
Q

what regulates intestinal iron absorption

A

hepcidin

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8
Q

why is calcium important

A

dietry calcium intake
1g per day
30% absorbed
duodenum- transcellular
jejunum- paracellular

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9
Q

what is calcium absorption increased with

A

calcitriol 1,25 oh2-d3 a vitamin d metabolite

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10
Q

what is calcium level in extracellular fluid regulated by

A

kidneys and skeleton

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11
Q

how is calcium homeostasis regulated

A

1,25 0h2 D and PTH regulates calcium homeostasis
during low normal dietary calcium intake 1,25(oh2)D supports calcium homeostasis by stimulating intestinal calcium transport
when intestinal calcium absorption alone does not suffice parathyroid hormone will aim to preserve serum calcium levels by acting on kidney and bone

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12
Q

what is the difference between small intestine and colonic villi

A

the crypt in colonic villi is much larger and deeper and colonic villi has no villi

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13
Q

explain key differences between small intestinal and colonic villi

A

small intestine villi are long, finger like projections whereas colon does not have villi, small intestine has large surface area due to villi and microvilli whereas colon has a smaller surface area (only crypts and microvilli). colon has deeper and numerous crypts, small intestine has fewer goblet cells compared to colon which has more goblet cells for mucous production for lubrication. small intestine contains enterocytes with microvilli and colon also has enterocytes with microvilli but specialised for water reabsorption. small intestine has paneth cells (which secrete antimicrobial peptides) whereas colon does not have paneth cells

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14
Q

what is the function of small intestine enterocytes

A

absorption of nutrients (carbs, proteins, lipids)

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15
Q

what is the function of colon enterocytes

A

absorption of water and electrolytes

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16
Q

what is the function of the colon

A

electrolyte water reabsorption
0.4-1L fluid reabsorbed per day
sodium uptake stimulated by aldosterone and is coupled to potassium secretion in the lumen
sodium uptake stimulated by short chain fatty acids (produced by colonic microflora using undigested fibre)
bicarbonate secretion/chloride uptake coupled to sodium uptake/potassium secretion
overall effect- increased transcellular nacl uptake

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17
Q

electrolyte transport across colonic epithelium

A

net movement of nacl drives water reabsorption

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18
Q

other functions of the colon

A

storage and eventual expulsion of faeces
chyme can be stored for 12-24hour
mass movement of contents into the rectum initiates defecation
nutrition- role of luminal bacteria
bacteria make up 50% faecal dry weight
synthesise small amounts of vitamins (vitamin K)
degrade many toxic products
synthesise short chain fatty acids SCFA from undigested food matter

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19
Q

what is the nutritional role of luminal bacteria in the colon

A

bacteria make up 50% of faecal dry weight
synthesises small amounts of some vitamins vitamin K
degrade many toxic products
synthesises short chain fatty acids SCFA from undigested food matter

20
Q

what do the short chain fatty acids synthesised by luminal bacteria do

A

sodium absorption
fluid absorption
mucus release
colonocyte energy source
increased motility
anti inflammatory actions
colonocyte proliferation and differentiation butyrate
retards growth of pathogens (acetate)
increased mucosal blood flow (acetate)

21
Q

what mechanism do luminal bacteria make short chain fatty acids by

A

microbial fermentation of undigested dietary polysaccharides

22
Q

what is the weight of the gut microbiome

23
Q

what bacteria make up the microbiome in the stomach

A

lactobacillus
candida
helicobacter pylori
streptococcus
peptosstreptococcus

24
Q

what bacteria are found in the colon

A

bacteroides
clostridium groups
bifidobacterium
enterobacteriacae

25
what natural bacteria are found in the jejunum
streptococcus lactobacillus
26
what natural bacteria are found in the duodenum
streptoccocus lactobacillus
27
what natural bacteria are found in the proximal ileum
streptococcus lactobacillus
28
what natural bacteria are found in the distal ileum
clostridium streptococcus bacteroides actinomycinae corynebacteria
29
what diseases can lead to gut diysbiosis
cardiovascular disease- atherosclerosis hypothyroidism sarcopenia rheumatoid arthritis inflammatory bowel disease obesity type 2 diabetes
30
what dna sequencing is used to investigate the faecal microbiome
metagenomic dna
31
where does most of the evidence of the gut microbiome come from
rodent studies
32
what is the key to a healthy gut microbiome
diversity rural indigenous populations have diversity in their gut microbiomes includes novel microbes not found in industrialised populations loss of diversity has been linked to rise of chronic diseases
33
what two factors determine diversity needed for healthy gut microbiome
diet geographicla environment metagenomic sequencing was used to investigate faceal microbiome migration from a non western country to the united states is associated with immediate loss of gut microbiome diversity and function these effects increase with duration of us residence
34
what are dietary modifications of the microbiome
probiotics and prebiotics probiotics- live microorganisms, bacteria or yeast . in food that contains live cultures such as yoghurt, coconut water, aged cheese, pickles probiotics support treatment of diarrhoea ibs and can reduce severity of colds and flu or aid digestion prebiotics-non living non digestible by carbohydrates
35
list some examples of pre biotics
yoghurt kimchi cheese pickles
36
list examples of probiotics
yeast asparagus wheat banana
37
how do you modify microbiome surgically
faecal transplant
38
how does fecal transplantation work
in a fecal transplant, stool from a healthy donor is used to replace a patient's gut microbial flora 2) the stool blended with saline and put through strainer, it can be frozen before use 3) stool can be applied into the small intestine via a tube through mouth or nose. enemas are popular for at home treatments but they only reach the lower end of the colon 4)scientists hope to replace fecal transplants with an odorless mix of bacterial strains derived from human stool, grown in the lab it could be applied using using existing methods into capsules
39
how does iron homeostasis work
iron is toxic in excess, around 3mg, bound to transferrin (iron binding protein) transferrin prevents iron from causing cellular damage. 1g of iron in liver and 400mg in other cell nd tissues- responsible for short term delivery of iron into circulation erythrocytes- 1.8g of iron sequested in rbcs red blood cells are turned over every 120 days, reticuloendothelial macrophages break down erythrocytes and release iron into circulation iron reused recirculted to make new red blood cells dudodenum only absorbs around 1-2mg per day of iron and 1-2mg of iron is also loss into faeces to keep serum iron level normal
40
how does duodenal iron uptake work
iron is consumed in two forms haem iron 9from animals) and non haem iron (from plants) non haem iron fe3+ is the most common type but less efficiently absorbed non haem iron fe3+ is reduced to fe2+ by duodenal cytochrome B DCYTB ferric reductase divalent metal transporter 1 dmt1 absorbs fe2+ into intestinal cells haem iron is transported via a heme transporter and broken down by heme oxygenase to release fe2+ some fe2+ is stored as mucosal ferritin in intestinal cells the rest is transported into the bloodstream via ferroportin 1 fe2+ is oxidised to fe3+ by haephestin (ferroxoidase) and binds to plasma transferrin for transport to tissues like erythroid marrow for rbc production hepcidin regulates iron levels by inhibiting ferropotin when iron levels are high hepcidin increases blocking ferropotin and decreasing iron absorption when iron levels are low hepcidin decreases allowing iron absorption iron can be lost through epithelial shedding
41
how does body calcium homeostasis work
daily dietry calcium intake 1g absorption in the intestine 0.3g enters the ecf secretion back into intestines 0.1g calcium lost in faeces 0.8g calcium in the body ecf holds about 1g calcium exchangeable pool of 4g of calcium skeletal calcium storage is around 1000g of calcium bone remodelling-0.5g per day is deposited into bones from ecf 0.5g of calcium released fromb ones into ecf maintains bone health and blood calcium levels renal regulation- kidneys filtration and reabsorption-99% of filtered calcium is reabsorbed 0.2g of calcium is lost daily maintaining bone strength nerve function muscle contraction intestines bones and kidneys involved in calcium homeostasis
42
what two ways does intestine absorb calcium
low calcium diets active transcellular absorption high calcium diets passive paracellular absorption
43
how does transcellular absorption work for low calcium diets
active vitamin d pathway TRPV6 channel calcium enters enterocytes from the lumen via transient receptor potential vanilloid 6 channels calbindin D inside the enterocyte binds to calcium and is a calcium transporting protein that helps calcium transport across cytoplasm pmca1b pump calcium is actively transported into the bloodstream by calcium atp ase vitamin d receptor activates gene expression for the transient receptor potential vanilloid channel, the calbindin d, and the calcium atp ase pump to enhance active transcellular transport compensating for low dietry calcium
43
what regulates calcium homeostasis
pth calcitonin vitamin d
44
how does passive paracellular calcium absorption take place for high calcium diets include the calcium concentrations
when dietry calcium is high, most absorption occurs passively via diffusion paraceullarly between the enterocytes calcium moves down its concentration gradient through tight junctions between intestinal cells process does not require vitamin d or any active transport proteins in the lumen of intestine 1mM in blood- calcium is 1.2mM so theres a gradient favouring absorption
45
what is vitamin D 1,25 (oh)2D3 essential for
transcellular active absorption activates gene expression of Transient receptor potential vanilloid 6 receptor channel, calbindin D and calcium atp ase

fluids and metabolism (16 decks)

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