Ward: Small and Large Intestine II Flashcards by Megan Foggia

Three features of the small intestine that increase surface area

circular concentric Kirkring folds (3x)
villi (30x)
microvilli on villi (600x)

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The (blank) on the microvilli surface of enterocytes is the location of numerous enzymes that provide the final stages of protein and carb breakdown for absorption.

glycocaylax

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The presence of enzymes on the microvilli surface ensures that the final stages of (blank) occur at the same point where contents are (blank)

intestinal content breakdown

absorbed

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Presence of the enzymes on microvilli reduce the possibility of (blank)

osmotic diarrhea

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Each villi of the small intestine receives (blank) and has blind ended (blank) from the lymphatic system

blood supply; lacteals

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This layer contracts and relaxes in the small intestine

muscularis externa

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Blood and lymphatic supply to the villi ensure optimal removal of absorbed (blank)

peptides, AAs, sugars, fats

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To ensure maximal absorption to the small intestine, it undergoes (blank) to ensure proper mixing of the lumenal contents

segmentation

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3 major sources of carbohydrates

disaccharides
polysaccharides
other carbohydrates (amylose, glycogen...)

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Contributes to 3-5% of the hydrolysis of carbohydrates

oral amylase

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In the stomach, hydrolysis continues for up to 1 hour and results in what percentage of starches being hydrolyzed to maltose?

30-40%

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This enzyme is released following neutralization of chyme that enters the proximal duodenum (by bicarbonate secretion). Pancreatic secretion of (blank) continues the digestion of carbohydrates, producing maltose, maltotriose and a-limited dextrins

amylase

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Digestion of starch and other disacchs are further broken down by enzymes located at the (blank) of the membrane

brush border

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Final breakdown of carbs: Enzymes located near the (blank) mechanism, so free glucose goes into the enterocyte and does not cause (blank)

transport; osmotic diahrrea

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Enzymes on the brush border of the enterocytes are continually (blank)

synthesized

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Enzymes found in brush border

lactase
sucrase
maltase
a-dextrinase

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(blank) dependent carrier system takes glucose and galactose from the brush border into the cell

Na+

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Glucose and Galactose are absorbed by secondary active transport via a (blank) dependent carrier system

Na+

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Lactose intolerance exists due to a lack of membrane bound enzymes resulting in malabsorption of (blank)

carbohydrates

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Undigested lactose causes (blank) changes. (blank) is further increased by the production of lactic acid by intestinal bacteria acting on the lactose.

osmolality; osmolality

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So, essentially, lactose intolerance is a (blank) deficiency. It is popular in (blank) populations.

enzymatic; Asian

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Upon admin of lactose, a flat lactose tolerance curve or failure of blood glucose to rise indicates low (blank) activity

lactase

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These form an important addition to the bulkiness of stool and reduce the transit time of feces

dietary fibers

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Almost all proteins require (blank) before (blank). There is one exception.

digestion; absorption

newborns with gamma globulins from milk

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A second source of protein is derived from the (blank) that is continually sleuthed off into the lumen. This accounts for (blank) percent of dietary protein.

intestinal mucosa; 50%

A third source of protein are the many (blank) that are secreted into the GI tract

enzymes

T/F: Different classes of AAs are absorbed best at different concentrations

True

At the final stage of digestion of proteins, the (blank) co-transporter ultimately takes amino acids into the enterocyte and then into the bloodstream

Na+/glucose

Enterokinase, located on the brush border of duodenal enterocytes, is activated by the presence of (blank)

trypsinogen

The absorption of amino acids is coupled to the transport of (blank) similar to that described for the absorption of monosaccharides.

Na+

Gastric pepsin and pancreatic peptidases digest proteins into (blank)

di and tripeptides

T/F: there are different carrier systems for different amino acids

True

Lumenal digestion of a protein meal results in approx (blank) free AA’s and (blank) small peptides.

40%; 60%

gluten sensitive enteropathy, a specific fraction of wheat protein attacks the microvilli of the mucosa, denuding it of these cells

celiac sprue

Cystic fibrosis Hereditary Pancreatitis Cystinuria Hartnup disease

diseases associated with protein absorption

phospholipids sterols hydrocarbons waxes

dietary lipids

There is little to no absorption of fat in the stomach. (blank) slows gastric motility when fats are in the small intestine. This causes the pancreas to secrete (blank) and the gallbladder to secrete (blank)

CCK; lipase; bile

4 major events of fat absorption

(i) Secretion of bile and various lipases. (ii) Emulsification. (iii) Enzymatic hydrolysis of ester linkages. (iv) Solubilization of lipolytic products within bile salt micelles

a suspension of fat droplets, held apart by lecithin, bile salts, fatty acids and other agents

emulsification

Lipid droplets suspended in water. Micelles can be presented to the enterocyte by a passive process then enter the lacteal as (blank)

chylomicrons

Pancreatic lipase is inhibited by (blank)

bile salts

Micelles diffuse across the unstirred layer and present fatty acids and monoglycerides to the enterocytes. This is mostly a (blank) process. (blank) are not absorbed across this layer, and are recyled to form new micelles.

passive; bile salts

Two pathways involved in re-synthesis of triglycerides

1. monoglyceride acylation | 2. phosphatadic acid

Enterocytes secrete (blank) and (blank)

chylomicrons | VLDL

Fat soluble vitamins are absorbed in a (blank) process

passive

Water soluble vitamins are taken up by a (blank) process

active

Exception to vitamin absorption; requires R proteins and intrinsic factor for its absorption

B12

What percentage of the absorptive capacity of the colon is regularly utilized? Not maximized.

10-25%

Water absorption is achieved by the process of (blank) transport

Na+

Progressive absorption of (blank) along the GI tract, which results in less Na+ being excreted in feces

Na+

As you move along the gut, these mechanisms help reabsorb Na+

Na+/glucose cotransport Na+/Cl- cotransport Na+/H+ cotransport

Na+ kept low inside the enterocyte due to this

Na+/K+ ATPase

In the colon, co-transport is absent, cellular junctions are less leaky, so restricted (blank) becomes very important and is under the control of (blank)

diffusion; aldosterone

Water absorption is driven by (blank) absorption and is described by the 3 compartment model

Na+

T/F: Ca+ has calcium binding proteins to control its concentration in the cell.

True

The process of Ca2+ absorption is localized in the proximal intestine and occurs in 4 major steps

(i) Entry at the brush border membrane. (ii) Regulation of intracellular Ca2+. (iii) Vitamin D affects at least one of these steps. (iv) Ca2+ exit must occur at the basolateral side of the membrane.

1,25 dihydroxyvitamin D3 inhibits calcium binding proteins and releases Ca+ in the plasma via a Ca+ ATPase. Ca+ in the plasma feeds back on (blank) to reduce the amount of 1,25 dihydroxyvitamin D3

parathyroid hormone

This disease of unregulated iron absorption leads to generalized iron overload that can eventually impair organ systems and lead to cirrhosis, diabetes, and cardiomyopathy

hemochromatosis

This creates a gradient along the small intestine with the highest frequency in the duodenum and the lowest in the terminal ileum. This gradient ensures oral to aboral movement of the contents in the lumen of the intestine

segmentation

When carbohydrates are broken down along the brush border, this allows for their products to be quickly absorbed into the enterocytes so they do not remain in the (blank) for long

intestinal lumen

How is [Na+] kept low in the enterocyte? Why is it important to keep it low?

By the Na+/K+ exchanger; important to keep it low so that Na+ will pass down its gradient from the lumen of the gut into the enterocyte and take with it glucose! This allows glucose to be reabsorbed into blood stream from the gut.

The Na+/glucose symporter is driven by high extracellular (intestinal lumen) (blank)

Na+

Lactose intolerance most common in these groups

blacks, orientals, eskimos

With lactose intolerance, there will be a build up of carbohydrates in the intestine, which will pull (blank) in, and create a watery stool.

water

Dietary fiber makes you (blank)

poop

(blank) starts a cascade of peptidase cleavage by cleaving typsinogen into trypsin

enterokinase

Proteins are digested to di and tripeptides in the gut lumen, then taken into the enterocytes by Na+ co transport. Then, they are broken down within the cell to (blank) before entering the blood.

amino acids

Di and tripeptides, as well as free AA's can enter the enterocyte, but large peptides must be acted on by brush border (blank) before entering

peptidases

Lipids enter enterocytes by a sequence of chemical and physical events that render water insoluble molecules capable of being absorbed by (blank) diffusion

passive

(blank) complexes lipase to bile salts. Once co-lipase attaches to a fat droplet, lipase will bind to the co-lipase and carry out its function.

colipase

Why are micelles important?

They solublize dietary fat and present it to the enterocytes for absorption

Do bile salts get absorbed into the enterocytes? What happens to them?

No! They are recycled to the lumen of the gut!

Within the enterocytes, fats presented by micelles become (blank) and are transported into the lacteals or they become very low density lipoproteins and enter the blood

chylomicrons

In 1 day, 7-10 L of fluid enters small intestine. How much of that enters the colon?

1-2 L

4 ways to get Na+ into enterocytes

restricted diffusion co-transport with sugars or AA's co-transport with Cl- counter-transport with bicarb

In the colon, there is no longer co-transport of Na+. So, (blank) predominates.

restricted diffusion

About 1g of calcium is taken orally, of which approximately (blank) is absorbed and is an important component in the regulation of whole body Ca2+. What vitamin is important for Ca+ transport?

40%; Vit D3

Exit of Ca+ from the enterocyte to the blood is (blank) transport, and depends primarily on a Ca+ATPase

active

Regulation of iron uptake is thought to occur at the level of brush border iron (blank) and the ratio of (blank) to transport protein

receptors; ferritin