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GI I > Physiology-Intestine Absorption and Function > Flashcards

Physiology-Intestine Absorption and Function Flashcards

1
Q

What regions of the intestinal wall are responsible for digestion and absorption?

A

Mucosa, submucosa and muscularis mucosa.

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2
Q

What regions of the intestinal wall are responsible for motility and autonomic control?

A

Muscularis externa and the enteric nervous system.

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3
Q

What structures enlarge the surface area of the intestinal wall?

A

Plicae circulares (mucosal folds) villi (epithelium and lamina propria only!) and microvilli (enterocyte brush border)

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4
Q

Goblet cell function

A

Empty mucus into the lumen to protect the epithelium from digestive enzymes

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5
Q

How much surface enlargement of the small intestine is attributed to the plicae circulares, villi and microvilli?

A

Plicae circulares by 3x, villi by 10x and microvilli by 20x

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6
Q

Why can chemotherapy cause malnutrition?

A

Enterocytes renew every 5-6 days. Chemotherapy targets rapidly reproducing cells and enterocytes get killed off.

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7
Q

What region of the small intestine is largely responsible for secretion of mucus, water and electrolytes?

A

Crypts of Lieberkuhn

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8
Q

What region of the small intestine has the highest amount of mucus secreting cells?

A

Duodenum has Brunner glands in the submucosa. These secrete lots of mucus to protect the duodenal epithelium from all the digestive enzymes that enter the duodenum.

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9
Q

What cells will you find in crypts of Lieberkuhn?

A

Goblet cells, lymphocytes, paneth cells and enteroendocrine cells.

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10
Q

Damage to what cells in your intestinal wall would result in increased bacterial infection?

A

Paneth cells. These secrete lysozyme and defensin to control bacterial growth in the small intestine.

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11
Q

Damage to what cells in your intestinal wall would result in loss of digestive regulation?

A

Enteroendocrine cells. They secrete regulatory molecules like serotonin, secretin and CCK.

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12
Q

What structures are found in the lamina propria?

A

Lactiles, veins leading to the portal system and arteries coming from the SMA.

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13
Q

What division of the enteric nervous system is responsible for shortening the villi and squishing out nutrients into the crypts and between the villi?

A

Submucosal plexus. It largely controls the muscularis mucosa.

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14
Q

What division of the enteric nervous system is responsible for peristalsis?

A

Myenteric plexus. This coordinates the contraction and relaxation of the inner and outer muscle layers of the muscularis externa.

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15
Q

What cells line the external wall of the intestine?

A

Mesothelium makes up the serosa.

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16
Q

What regions in the GI tract are not covered by serosa?

A

Esophagus, duodenum, ascending/descending colon, rectum and anal canal.

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17
Q

How do you know if you are histologically in the duodenum?

A

Brunner glands in the submucosa.

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18
Q

How do you know if you are histologically in the jejunum?

A

No Brunner glands. Some lymphatic nodules in submucosa.

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19
Q

How do you know if you are histologically in the ileum?

A

Peyer’s patches in the submucosa.

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20
Q

What chemical process is the basic reaction in breaking down carbohydrates, proteins and lipids?

A

Hydrolysis. Cleaving chemical bonds by adding water.

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21
Q

In what three locations does digestion take place?

A

Intralumenal (intestinal lumen), apical (enterocyte brush border) and intracellular.

22
Q

What makes up the majority of dietary carbohydrates?

A

60% starch, 30% glucose, 10% lactose. Of the starch, 80% is amylopectin.

23
Q

What region of the small intestine is most enzymatically active in breaking down carbohydrates?

A

Jejunum.

24
Q

What enzymes are used to break down large carbohydrates?

A

Ptyalin (saliva) and pancreatic amylase break down starch in the intestinal lumen.

25
Q

What enzymes are used to break down maltose, lactose and sucrose at the enterocyte brush border?

A

Maltase and alpha-dextrinase break down maltose to glucose. Lactase breaks down lactose to galactose and glucose. Sucrase breaks down sucrose to fructose and glucose.

26
Q

What is the rate-limiting step in nutrient absorption?

A

Entry of monosaccharides into enterocytes.

27
Q

How does glucose get into your blood from the intestinal lumen?

A

Apical Na+ cotransport of glucose into cytoplasm of enterocyte. GLUT 2 pumps glucose out the basal end of the cell into the blood stream.

28
Q

What type of proteins are less digestible?

A

Plant protein

29
Q

Where do we get our endogenous proteins from?

A

Secreted enzymes, desquamated cells, etc.

30
Q

Where does digestion of protein first begin?

A

Stomach, by pepsin secreted by chief cells. This breaks down the larger protein into oligopeptides.

31
Q

Where does the majority of protein digestion occur?

A

Duodenum. The pancreas secretes trypsin, chymotrypsin, carboxypolypeptidase and proelastase. These break down the oligopeptides into di and tripeptides.

32
Q

Where is protein digestion completed?

A

In the enterocyte brush border and enterocyte cytoplasm. Peptidases convert the di and tripeptides into amino acids that can be transported into the enterocyte.

33
Q

How do amino acids get into the blood stream?

A

They are cotransported with Na+ into the enterocyte on the apical side. They are then secreted out the basal side into the blood stream.

34
Q

What is the 1st step in lipid metabolism?

A

Lingual lipases have minimal digestion of fat. Emulsification of fat by bile salts and lecithin is really the first step. This increases the surface area of fat available for digestion by pancreatic enzymes.

35
Q

How are lipids further digested after they have been emulsified?

A

Pancreatic enzymes chop them up and they are delivered to the apical enterocyte membrane by micelles. They are then remade into triglycerides, packaged into chylomicrons and released out the basal end of the enterocytes into lacteals.

36
Q

What vitamins are absorbed in the proximal intestine through micelles?

A

A,D,E and K, they are all lipid soluble.

37
Q

What are the different regions in the wall of the large intestine?

A

Mucosa -> Submucosa -> Muscularis externa (with tenia coli bands in this layer)

38
Q

Digestion of what materials can happen in the large intestine?

A

Carbohydrates and short chain fatty acids are fermented by bacteria of our normal flora. Lipids can also be digested by a few bacterial lipases.

39
Q

How do you tell histologically if you are in the large intestine vs. the small intestine?

A

No plicae, no villi, straight glands and many goblet cells.

40
Q

What histological characteristic tells you that you are in the appendix?

A

Lymphoid nodules and no tenia coli.

41
Q

What transition zone in the GI tract carries a high risk for cancer?

A

Rectum and anal canal. This is the transition from mucosa to epithelium.

42
Q

Main role of large intestine

A

Absorption of liquid and electrolytes.

43
Q

What is water reabsorption linked to in the large intestine?

A

Sodium transport.

44
Q

Who is the best at conserving sodium in the GI tract?

A

95% of Na+ entering the small bowel is reabsorbed. 50% in the jejunum, 50% in the ileum and the colon absorbs whatever else gets missed.

45
Q

What happens as a result of consuming a hypotonic meal?

A

Water flow from the intestinal lumen to the blood and nutrients flow into the lumen.

46
Q

What happens as a result of consuming a hypertonic meal?

A

Water flow from the blood to the intestinal lumen and flow of nutrients out of the lumen.

47
Q

Surgery in what region of the bowel may cause anemia?

A

Small intestine, this is where the majority of Fe is absorbed.

48
Q

What other ions are absorbed by the small intestine? What ions are poorly absorbed?

A

K+ and Cl- are well absorbed. Ca2+ and Mg2+ are poorly absorbed.

49
Q

2 mechanisms of diarrhea

A

Decreased absorption or increased secretion

50
Q

Causes of diarrhea?

A

Infection, Psychogenic (increased motility and secretion by parasympathetic stimulation), Ulcerative colitis (decreased absorption and increased motility by inflammation)

51
Q

How does cholera cause diarrhea?

A

Overactivation of cAMP increases fluid in the crypts of Lieberkuhn

GI I (47 decks)

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