Digestion n Absorption

Question 1

How is K+ absorbed in the colon

Answer 1

In general K+ reabsorption is by passive diffusion, the net movement begin determined by the potential difference between the lumen and intestinal capillaries. Note: Diarrhoea can result in severe hypokalaemia (loss of K+)

Question 2

How is Cl- absorbed in the colon

Answer 2

Cl- is actively reabsorbed in exchange for bicarbonate - resulting in the intestinal contents becoming more alkaline

Question 3

There are 2 functional states/periods the body undergoes in providing energy for cellular activities, these are

Answer 3

the absorptive & postabsorptive states

Question 4

What happens during the absorptive state

Answer 4

• During which ingested nutrients enter the blood from the GI tract
• During this state, some of the ingested nutrients provide the energy requirements of the body and the remainder is added to the body’s energy stores to be called upon during the next postabsorptive state

Question 5

What happens during the post absorptive state

Answer 5

During which the GI tract is empty of nutrients and the body’s ownstores must supply energy

Question 6

What is the average daily lipid intake

Answer 6

Average daily intake of lipid is 70 to 100 per day - most in the form of triglycerides (glycerol with three fatty acids attached)

Question 7

What are the 3 main important fatty acids we absorb

Answer 7

There are 3 main important fatty acids we absorb; Palmitic (most abundant), Stearic & Oleic acid

Question 8

what is a triglyceride

Answer 8

Triglycerides (triglycerols): A glycerol molecule with 3 fatty acids attached

Question 9

where does triglyceride digestion occur

Answer 9

Triglyceride digestion occurs to a limited extent in the mouth & stomach but it predominantly occurs in the small intestine.

Question 10

What is the main fat digestive enzyme

where is it produced
‘
how does it work

Answer 10

The major digestive enzyme is lipase (synthesised in the PANCREAS) which catalyses the splitting of bonds linking fatty acids to the 1st & 3rd carbon atomsof glycerol, producing two free fatty acids & a monoglyceride as products:

Triglyceride —> Monoglyceride + 2 Fatty acids ,
under the action of lipase

Question 11

lipids ingested in food are water insoluble so what happens to them

Answer 11

The lipids in ingested food are insoluble in water so aggregate into large lipid droplets in the upper portion of the stomach

-These lipid droplets are then converted into very small droplets (1mm in diameter) via the process of emulsification, which requires two things..

Question 12

what does the process of emulsification require

Answer 12

1. Mechanical disruption of the large droplets into smaller droplets - provided by the motility of the GI tract, in the lower portion of the stomach & in the small intestine, which grinds & mixes the luminal contents
2. An emulsifying agent - provided by the phopho-lipids in food and by bile saltssecreted in bile:

Phospho-lipds are amphipathic (both hydrophilic & phobic) molecules (containing polar or ionised groups on one end of the molecule and non-polar groups on the other) consisting of 2 non polar fatty acid chains attached to glycerol with a charged phosphate group on one end

• Bile salts are formed form cholesterol in the liver and are also amphipathic
• The non-polar portion of the phospholipids and bile salts associate with the non polar interior of the lipid droplet - leaving the polar portions exposed at the water surface - here they repel other lipid droplets that are similarly coated with these emulsifying agents thereby prevents their reaggregation into larger fat droplets

Question 13

two examples of emulsifying agents and how they work

Answer 13

• Phospholipids
• Bile salts

The non-polar portion of the phospholipids and bile salts associate with the non polar interior of the lipid droplet - leaving the polar portions exposed at the water surface - here they repel other lipid droplets that are similarly coated with these emulsifying agents thereby prevents their reaggregation into larger fat droplets

Question 14

The coating of the lipid droplets with these emulsifying agents does what to lipase

so what happens

Answer 14

impairs the accessibility of the droplet for lipase

To overcome this issue, the pancreas secretes a protein called colipase which binds to the lipid droplet surface as well as binding to lipase - thereby holding it onto the surface of the lipid droplet

Question 15

These small droplets are further converted into smaller droplets under the actions of what

what are these

Answer 15

under the further action of bile salts,called micelles (4-7 nm in diameter) - these consist of bile salts with fat soluble vitamins (A,D,E,K) and cholesterol, fatty acids, monoglycerides & phospholipids all clustered together with their polar ends facing outwards and their non-polar ends facing inwards

Question 16

Despite the fact that fatty acids and monoglycerides have an extremely low solubility in water what can happen

Answer 16

Despite the fact that fatty acids and monoglycerides have an extremely low solubility in water, some do exist in solution and are able to diffuse across the lipid portionof the luminal plasma membranes of the epithelial cells of the small intestine

Question 17

The micelles are in equilibrium with these free fatty acids and monoglycerides meaning

Answer 17

the micelles are continuously breaking down & reforming - as the concentration of free lipids decreases since they are diffusing through the epithelial cellsmore lipids are released into solution by the breakdown of the micelles

NOTE: it is not the micelle which is absorbed but instead the individual lipid molecules released from the micelle, thus micelles can be regarded as holding stations for lipids

Question 18

Once in the small intestine what happens to fatty acids and monoglycerides

why is this important

Answer 18

Once in the small intestine the fatty acids and monoglycerides are re-synthesised into triglycerides in the smooth endoplasmic reticulum where the enzymes for triglyceride synthesis are located.

important because …
This process decreases the cytosolic concentration of free fatty acids and monoglycerides and thus maintains a diffusion gradient for these molecules into the cell from the intestinal lumen

Question 19

The resynthesises fat does what

what does this do

Answer 19

The resynthesises fat aggregates into small droplets coated by proteins that perform an emulsifying function similar to that of bile salts

The fat droplets then pinch off the endoplasmic reticulum in vesicles where they are then processed through the golgi apparatus where they are modified into CHYLOMICRONS, they then bud off the golgi in vesicles which then fuse with the plasma membrane and enter the interstitial fluid via exocytosis

Question 20

what do chylomicrons contain

Answer 20

Chylomicrons contain not only triglycerides but other lipids such as phospholipids, cholesterol & FAT-SOLUBLE VITAMINS which have been absorbed in the same process as the fatty acids

Question 21

what do chylomicrons do after they enter the interststitial fluid

Answer 21

The chylomicrons then enter the lacteals - lymphatic vessels in the intestinal villirather than into the blood capillaries - this is due to the fact that chylomicrons cannot enter the capillaries due to the basement membrane at the outer surface of the capillaries providing a barrier to diffusion

Question 22

why cant chylomicrons enter blood capillaries

Answer 22

cannot enter the capillaries due to the basement membrane at the outer surface of the capillaries providing a barrier to diffusion

Question 23

why can chylomicrons enter lacteals

Answer 23

The lacteals have large pores between their endothelial cells which enable the chylomicrons to pass through

Question 24

what happens to the lymph from the small intestine

Answer 24

The lymph from the small intestines eventually empties into the systematic veins

Question 25

what happens once chylomicrons enters the circulation what enzyme causes this

Answer 25

Once the chylomicrons (containing triglycerides, phospholipids, cholesterol & fat soluble vitamins) have entered the circulation the processing of the triglycerides in chylomicrons in blood plasma is similar to that for VLDL’s produced by the liver The fatty acids of plasma chylomicrons are released, mainly within adipose-tissue capillaries by the action of endothelial lipoprotein lipase (since it hydrolyses the triglyceride)

Question 26

what happens to the fatty acids released from the chylomicrons in the adipose tissue capillaries

Answer 26

The released fatty acids then diffuse into adipocytes and combine with alpha-glycerol phosphate (produced from dihydroxyacetone phosphatein glycolysis), synthesised in the adipocytes from glucose metabolites to form triglycerides

Question 27

why is Glucose is ESSENTIAL for triglyceride synthesis in adipocytes

Answer 27

Glucose is ESSENTIAL for triglyceride synthesis in adipocytes due to the fact that adipocytes do not have the enzyme required for phosphorylation of glycerol to alpha glycerol, so glycerol can only be produced by reducing dihydroxyacetone phosphate (from glycolysis) and NOT from glycerol or any other fat metabolites

Question 28

In contrast to alpha glycerol there are 3 main sources of fatty acids for triglyceride synthesis; any enzymes needed?

Answer 28

1. Glucose that enters adipose tissue and is broken down to provide building blocks for the synthesis of fatty acids 2. Glucose that is used in the liver to form VLDL triglycerides, which are transported in the blood and taken up by adipocytes 3. Ingested triglycerides transported in the blood in chylomicrons and taken up by adipocytes •2 & 3 require lipoprotein lipase to release the fatty acids from the circulating triglycerides

Question 29

Fat-soluble vitamins such as vitamin A,D,E & K follow the pathway for fat absorption mentioned above in the ILEUM •With one exception

Answer 29

water-soluble vitamins such as vitamin C & B are absorbed by diffusion or mediated transport in the JEJUNUM: •The exception is vitamin B-12, which is a very large and charged vitamin. To be absorbed B-12 must first bind to the protein intrinsic factor (secreted by parietal cells of the stomach) - intrinsic factor whit bound B-12 then binds to specific sites on the epithelial cells in the LOWER PORTION OF THE ILEUM where vitamin B-12 is absorbed via endocytosis .•Vitamin B-12 is needed for erythrocyte formationand a deficient in B-12 can lead to pernicious anaemia and is usually caused due to a deficiency in intrinsic factor

Question 30

why is vitamin B12 needed

Answer 30

Vitamin B-12 is needed for erythrocyte formationand a deficient in B-12 can lead to pernicious anaemia and is usually caused due to a deficiency in intrinsic factor

Question 31

How is Vitamin B12 absorbed

Answer 31

The exception is vitamin B-12, which is a very large and charged vitamin. To be absorbed B-12 must first bind to the protein intrinsic factor (secreted by parietal cells of the stomach) - intrinsic factor whit bound B-12 then binds to specific sites on the epithelial cells in the LOWER PORTION OF THE ILEUM where vitamin B-12 is absorbed via endocytosis

Question 32

where does the digestion and absorption of protein mainly occur

Answer 32

duodenum

Question 33

how much protein a day does a healthy adult require

Answer 33

A healthy adult only requires 40 to 50g of protein a day to supply essential amino acids and replace the nitrogen contained in amino acids that are converted to urea

Question 34

how many essential AA do we need

Answer 34

8 are essential - we cannot manufacture them

Question 35

how many AA are found in the proteins we use

Answer 35

20

Question 36

Amino acids exist as optical isomers what form is in the proteins we use

Answer 36

only the L-forms are found in the proteins we utilise

Question 37

what is a zwitterion

Answer 37

Amino acids start as very top picture but form zwitterions having bothpositive and negative groups on the same molecule

Question 38

what is the basic building block for a protein

Answer 38

The basic building block of a proteinis the peptide bond - CONH (HN-C=O)

Question 39

where does digestion of proteins begin

Answer 39

Begins in the stomach where the enzymepepsin (chief cells release pepsinogenwhich is rapidly activated by the low luminal pH) cleaves some of the peptide linkages - forming peptide fragments

Question 40

where is pepsinogen I found

Answer 40

found only in the HCl secreting region (mainly the body) of the stomach

Question 41

where is pepsinogen II found

Answer 41

found in the pyloric region

Question 42

what do pepsins do to proteins

Answer 42

Pepsins hydrolyses the bonds between an aromatic amino acid (tyrosine or phenylalanine) and a second amino acid

Question 43

optimum pH for pepsin

Answer 43

The optimum pH for pepsins is around pH 1.6 - 3.2 thus action is terminated on exit from the stomach

Question 44

what is the pH in the duodenal cap

Answer 44

The pH in the duodenal cap is around pH 2 - 4

Question 45

pH in the rest of the duodenum

Answer 45

The pH in the rest of the duodenum is around pH 6.5

Question 46

what happens to peptides in the small intestine

Answer 46

In the small intestine these smaller peptides are further fragmented by enzymesproduced in the pancreas which can be divided into: Endopeptidases Exopeptidase’s

Question 47

Example of endopeptidases

Answer 47

trypsin, chymotrypsin & elastase

Question 48

example of Exopeptidase’s

Answer 48

carboxyl dipeptidases and the amino peptidases of the brush border (microvilli border)

Question 49

Some di & tripeptides are absorbed and finally broken down by intracellular peptidases meaning final digestion of peptides occurs in three locations;

Answer 49

- the intestinal lumen - the brush border - within the cell

Question 50

where does digestion and absorption of carbohydrates occur

Answer 50

occurs in duodenum

Question 51

what is a Monosaccharide

Answer 51

single sugars e.g. glucose, fructose & galactose

Question 52

What is a Oligosaccharide

Answer 52

several sugar molecules

Question 53

examples of Oligosaccharides

Answer 53

- Lactose - forms beta linkages since OH groups lies above the plane of the molecule thus it requires its own enzyme to be broken down, can’t use the same one as sucrose since it has alpha linkages. People who are lactose-intolerant do not have sufficient amounts of beta enzymes - Sucrose (most common disaccharide) - Both are disaccharides - the important dietary ones

Question 54

what is Polysaccharide

Answer 54

many sugar containing molecules

Question 55

example of polysaccharide

Answer 55

starch & glycogen

Question 56

how do sugar molecules exist which one is used in metabolism

Answer 56

Sugar molecules also exist as optical isomers - only the D-isomers are utilised in metabolism

Question 57

what is Glycogen and whats it structure

Answer 57

the principal dietary polysaccharide from animal sources, polymer of glucose molecules which are joined by alpha 1-4 glycosidic linkages and some chain branching by alpha 1-6 glycosidic linkages

Question 58

structure of starch

Answer 58

majority alpha 1-4 glycosidic linkages with some chain branching by alpha 1-6 linkages but LESS THAN IN GLYCOGEN

Question 59

structure of cellulose

Answer 59

only beta 1-4 glycosidic linkages

Question 60

how is starch initially degraded and where | what is the optimal pH of this

Answer 60

Starch is first degraded by ptyalin - the alpha amylase of saliva in the mouth only a small fraction of starch digestion occurs here The optimal pH for this is pH 6.7 and activity is terminated by gastric acidity of the stomach

Question 61

once in the small intestine how is starch degraded

Answer 61

Once in the small intestine (responsible for 95% of starch digestion), pancreatic alpha amylase catalyses alpha 1-4 linkages But NOT the alpha 1-6 linkage, the alpha 1-4 linkages next to branch points or the terminal alpha 1-4 linkages

Question 62

what are the end products of the initial digestion of starch in the small intestine

Answer 62

Thus the end products of this digestion are: • the disaccharide maltose •the trisaccharide maltotriose •larger polymers of glucose with alpha 1-4 linkages •branched polymers consisting of around 8 units called the alpha-limit dextrins

Question 63

what further digests the products of starch in the small intestine and where about what are they broken down into

Answer 63

These are further digested by the oligosaccharidases located at the outer portionof the membrane of the microvilli (the brush-border): * maltase * lactase * sucrase * alpha-limit dextrinase They are broken down into monosaccharide - glucose, galactose & fructose

Question 64

Hexoses & pentoses are rapidly absorbed across the intestinal mucosa, these then enter the capillaries which drain into what

Answer 64

to the HEPATICPORTAL VEIN

Question 65

how is glucose transported across the intestinal mucosa

Answer 65

Glucose and Na+ SHARE the SAMETRANSPORTER - sodium-glucose cotransporter (SGLT) thus a high Na+ concentration at the mucosal surface facilitates glucose absorption

Question 66

how is galactose transported from the lumen

Answer 66

Galactose, a glucose isomer, is transported from the lumen by the SGLT

Question 67

How is fructose transported across the intestinal mucosa

Answer 67

Fructose utilises a different carrier and its absorption is independent of luminal Na+ since it is absorbed by facilitated diffusion via a glucose transporter (GLUT)

Question 68

what happens to glucose, galactose and fructose once they have been transported across the intestinal mucosa

Answer 68

- These monosaccharides then leave the epithelial cells and enter the interstitial fluid by way of facilitated diffusion via GLUT proteins in the basolateral membranes of the epithelial cells - From there, the monosaccharide diffuse into the blood through capillary pores Most ingested carbohydrates are digested & absorbed within the first 20% of the small intestine - i.e duodenum

Question 69

What happens to the monosaccharides once they have been absorbed and are now in the blood

Answer 69

After entering the hepatic portal vein and thus the liver, the liver then converts these carbohydrates into glucose

Question 70

what is the major consumer of glucose in the body

Answer 70

Skeletalmuscle make up the majority of the body and so is the major consumer of glucose, even at rest

Question 71

what does skeletal muscle do with glucose

Answer 71

Skeletal muscle not only catabolises (breaks it down into smaller units) glucose in the absorptive phase but also converts some of the glucose to the polysaccharide glycogen, which is then stored in the muscle for future use

Question 72

when is there a net uptake of glucose by the liver

Answer 72

absorptive state

Question 73

What are two things the liver can convert glucose into

Answer 73

- The LIVER also converts glucose into glycogen to be used at some point in the future - The LIVER can also convert the glucose into alpha-glycerol phosphate ( by reducing dihydroxyacetone phosphate via glycolysis) and fatty acids which are then used to synthesise triglycerides - NOTE: this process of converting glucose into alpha-glycerol phosphate (via glycolysis) and fatty acids also occurs in adipose-tissue cells (adipocytes) which can then be used to synthesise triglycerides which can be then stored in the adipocytes

Question 74

What are lipoproteins

Answer 74

Most of the fat synthesised from glucose in the liver is packaged along with specific proteins into molecular aggregates of lipids and proteins known as lipoproteins

Question 75

how do lipoproteins enter the blood

Answer 75

These aggregates are secreted by hepatocytes and enter the blood

Question 76

why are they called very-low-density lipoproteins (VLDL’s)

Answer 76

since they contain more fatthan protein and fat is less dense than protein

Question 77

What is the process of VLDL synthesis similar to

Answer 77

The synthesis of VLDL’s in hepatocytes occurs by a similar process as that ofchylomicrons by intestinal mucosa cells(see above)

Question 78

Why can't VLDL's penetrate capillary walls what happens to them instead

Answer 78

Due to their large size, VLDL’s in the blood do not readily penetrate capillary walls, instead, their triglycerides are hydrolysed mainly to monoglycerides (i.e glycerol linked to one fatty acid) and fatty acids by the enzyme lipoprotein lipase

Question 79

where is lipoprotein lipase located

Answer 79

Lipoprotein lipase is located on the on the blood-facing surface of capillary endothelial cells, especially those in adipose tissue

Question 80

why do most of the fatty acids in VLDL triglycerides originally synthesised from glucose in the liver end up being stored in triglyceride in adipose tissue

Answer 80

In adipose-tissue capillaries the fatty acids generated by the action of lipoprotein lipase diffuse from the capillaries into the adipocytes - there they combine with alpha-glycerol phosphate, supplied by glucose metabolites to form triglycerides once again. As a result, most of the fatty acids in VLDL triglycerides originally synthesised from glucose in the liver end up being stored in triglyceride in adipose tissue

Question 81

Some of the monoglycerides produced by the break down of triglycerides by lipoprotein lipase in the blood in adipose-tissue capillaries are also taken up by what what happens to them here

Answer 81

Some of the monoglycerides produced by the break down of triglycerides by lipoprotein lipase in the blood in adipose-tissue capillaries are also taken up by adipocytes where enzymes can then reattach fatty acids to the two available carbon atoms of the monoglyceride and thereby form a triglyceride Some of the monoglycerides travel via the blood to the liver to be metabolised

Question 82

Amino acids, triglyceride & glucose are transported to the liver for what conversion to storage molecules Then to the storage areas such as:

Answer 82

- Adipose tissue for fats | - Muscle for glycogen

Question 83

LOOK AT PHOTO FOR METHOD OF STORAGE

Answer 83

AND FOR HOW THESE FUELS ARE USED

Question 84

BMI

Answer 84

body mass index

Question 85

BMI equation

Answer 85

Weigh (Kg)/ Height2 (m)

Question 86

what is normal BMI range

Answer 86

18.5 < BMI < 25 = normal

Question 87

what is an obese BMI

Answer 87

BMI > 30 = obese

Question 88

What is underweight BMI

Answer 88

BMI < 18.5 = underweight

Question 89

what is overweight BMI

Answer 89

BMI > 25 = overweight

Question 90

Glycogen stores for a resist adult male are roughly sufficient to last Lipid stores are sufficient to last

Answer 90

12 hours 3 months

Question 91

Tissue protein as a source of energy supply only becomes significant when

Answer 91

in times of prolonged starvation

Question 92

Different tissues have very different energy requirements - the brain & liver represent about 4.6% of body weight yet consume around

Answer 92

40% of energy requirement at rest

Question 93

what fuels are used by the brain

Answer 93

glucose, ketone bodies

Question 94

what fuels are used by muscle

Answer 94

glucose, ketone bodies (in starvation), triacyglycerol & branched-chain amino acids

Question 95

what fuels are used by the liver

Answer 95

amino acids, fatty acids (including short chain acids), glucose & alcohol. NOTE: ketone bodies are not used by the liver, although they are produced herethey are then sent to extrahepatic tissue to buy used there, the liver cannot use ketone bodies for fuel due to the fact they do not have the enzyme thiolase

Question 96

why can't liver use ketone bodies as fuel

Answer 96

they do not have the enzyme thiolase

Question 97

what fuels are used by kidney

Answer 97

glucose & ketone bodies (cortex), only glucose (medulla)

Question 98

what fuels are used by small intestine

Answer 98

ketone bodies (mainly in starvation), glutamine (amino acid)

Question 99

what fuels are used by large intestine

Answer 99

short-chain fatty acids, glutamine

Question 100

what is the BMR

Answer 100

basal metabolic rate Minimum amount of energy required to keep the body alive

Question 101

how is BMR usually measured

Answer 101

Usually measured by O2 consumption in a person who is awake, restful and faster for 12 hours

Question 102

what happens to BMR with Age

Answer 102

decreases

Question 103

what units is BMR measured in

Answer 103

Measure in kcal expended/hr/m^2

Question 104

what is malabsorption

Answer 104

The inadequate absorption of nutrients from the intestines | •Failure to absorb certain vitamins, minerals, carbohydrate, proteins or fats

Question 105

what is the most common cause of malabsorption

Answer 105

Chiefly cause by disease of the small bowel

Question 106

Giardiasis

Answer 106

infection which causes the villi to atrophy thus reducingabsorption capacity

Question 107

what is Coeliac disease

Answer 107

Auto-immune condition whereby gluten is partially degraded triggering an immune response whereby the system attacks the villi & microvilli resulting in a loss of intestinal brush border surface area resulting in decreased absorption of many nutrients

Question 108

who does coeliac disease occur in

Answer 108

Occurs in genetically disposed individuals

Question 109

What can coeliac disease cause

Answer 109

Muscular atrophy Abdominal Distention Can prevent the absorption of vitamin D which ultimately results in the decrease in calcium absorption in the GI tract - resulting is osteoporosis

Question 110

What is cystic fibrosis and what causes it

Answer 110

Caused by an autosomal recessive mutation in an epithelial channel called the cystic fibrosis transmembrane conductance regulator (CFTR). This results in problems with salt & water movement across cell membranes, which leads to thickened secretions & a high incidence of lung infection. The airways secrete a watery fluid upon which mucus can ride freely, in CF suffers the production of this fluid is impaired causing the mucous layer to become thick & dehydrated thereby obstructing the airways

Question 111

The exocrine portion of the pancreas secretes HCO3- and a number of digestive enzymes e.g how do these enter the duodenum

Answer 111

The exocrine portion of the pancreas secretes HCO3- and a number of digestive enzymes e.g. lipase, colipase & alpha amylase (see further up) into the ducts that converge into the pancreatic duct which joins the common bile duct from the liver before it enters the duodenum at the duodenal papillae.

Question 112

whats the difference between the secretion of HCO3 and the digestive enzymes

Answer 112

The enzymes are secreted by gland cells at the pancreatic end of the duct system whereas HCO3- is secreted by the epithelial cells lining the ducts.

Question 113

The pancreatic duct cells secrete HCO3- (produced from CO2 & H2O using carbonic anhydrase) into the duct lumen via what what happens to the H+ produced

Answer 113

The pancreatic duct cells secrete HCO3- (produced from CO2 & H2O using carbonic anhydrase) into the duct lumen via an apical membrane Cl-/HCO3- exchanger, while the H+ produced (from the dissociation of H2CO3) is exchangedfor extracellular Na+ on the basolateral side of the cell.

Question 114

How is HCO3- produced

Answer 114

produced from CO2 & H2O using carbonic anhydrase

Question 115

what happens to H+ when its enters the pancreatic capillaries

Answer 115

The H+ enters the pancreatic capillaries to eventually meet up in portal vein bloodwith the HCO3- produced by the stomach during the generation of luminal H+.

Question 116

the energy for the secretion of HCO3- is provided by what

Answer 116

The energy for secretion of HCO3- is provided by Na+/K+ - ATPase pumps on the basolateral membrane.

Question 117

why does Cl- no normally accumulate in the cell

Answer 117

Cl- normally does not accumulate within the cell because these ions are recycled into the lumen through the CFTR

Question 118

how do Na+ & H20 move into the ducts

Answer 118

Via a paracellular route, Na+ & H20 move into the ducts due to the electrochemical gradient established by chloride movement through the CFTR

Question 119

However in cystic fibrosis, the CFTR is faulty meaning what

Answer 119

meaning Cl- will build up in the gland cells thereby preventing the movement of HCO3- into the duct this means that less HCO3- enters the small intestine, its secreted to act as a buffer to raise the pH in the small intestine, since the contents have just been thought the low pH stomach - at low pH the digestive enzymes of the pancreas are not active - HCO3-is used as a buffer to increase intestinal pH so that the digestive enzyme can be active Thus less HCO3- in the small intestine will result in a decrease in digestion and thus absorption

Question 120

in people with cystic fibrosis the lack of normal water movement leads to

Answer 120

Furthermore the lack of normal water movement leads to a thickening of pancreatic secretions - resulting in the clogging of the pancreatic ducts and thus enzymes and HCO3- cannot be released resulting in a decrease in digestion and thus absorption. Furthermore the digestive enzymes begin clogged in the duct can result in pancreatic damage resulting in the pancreas eventually not being able to produce digestive enzymes Thus CF suffered are given pancreatic enzyme replacements to aid their digestionand thus absorption47KP