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Human Body Systems II (BMSC 208) > Module 7: Digestive System II > Flashcards

Module 7: Digestive System II Flashcards

1
Q

__ L enter the small intestine, __ is absorbed in the first half. Where in the intestine does this absorption occur?

A

9, 7.5. In the duodenum and jejunum.

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2
Q

What in the intestine is regulated to ensure proper digestion and absorption? How is it promoted and inhibited?

A

Motility.

  • Motility promotion:
    • Parasympathetic innervation
    • Gastrin
    • Cholecystokinin
  • Motility inhibition:
    • Sympathetic innervation
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3
Q

Describe motility in the intestines in terms of contractions.

A

A combination of segmental and peristaltic contractions mix the chyme with enzymes and expose digested nutrients to mucosal epithelium for absorption.

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4
Q

_____ and _____ increase surface area in the small intestine. What do each of them do? What do crypts do?

A

Plicae (circular folds) and villi increase surface area.

  • Villi increase surface area available for absorption and secrete mucus
    • Most nutrients are absorbed into capillaries in the villi
  • ​Crypts contain hormone and fluid secretory cells + stem cells
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5
Q

What are lacteals? What is their role in the lymphatics and why is this special?

A

Lacteals are blunt ended lymphatic vessels which fats enter. This is special because most of the nutrients absorbed by the gut are done through capillaries in the villi.

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6
Q

Describe the hepatic portal system and its role.

A

Hepatic portal system: the liver acts as a biological filter, containing a variety of enzymes that metabolize drugs and xenobiotics (foreign substances) and clear them from the blood stream before it can proceed to systemic circulation. Therefore, venous blood from GI tract does not go directly to the heart.

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7
Q

What are the 5 intestinal secretions that promote digestion and what are their roles? (DIM BB)

A
  1. Digestive enzymes (intestine epithelium: brush border enzymes and pancreas)
    • Brush border enzymes: activate other enzymes
  2. Bile (liver, stored in gallbladder): helps digest fats
  3. Bicarbonate (pancreas): neutralizes acid
  4. Mucus (goblet cells): protective function
  5. Isotonic saline (crypt cells): lubricates contents of gut, driven by Cl-
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8
Q

What are the 3 primary cells of the pancreas that we discuss? (don’t say roles)

A
  1. Acinar cells
  2. Duct cells
  3. Epithelial cells
    • Endocrine secretory epithelium (islets)
    • Exocrine secretory epithelium
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9
Q

What is the role of acinar cells?

A

Secrete digestive enzymes.

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10
Q

What is the role of duct cells? What does this do? What produces this?

A

Secrete bicarbonate. This neutralizes acid entering from the stomach. Produced by carbonic anhydrase.

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11
Q

How is bicarbonate secreted from the duct cells (3 steps)? What genetic condition is widely known to interfere with this mechanism?

A
  1. CA converts water and carbon dioxide to bicarbonate and hydrogen ions
  2. Chloride enters the cells by indirect active transport (NKCC2) and leaves the apical side through a CFTR channel. Cl- then reenters in exchange for bicarbonate
  3. Leaky junctions allow paracellular movement of ions and water from basolateral to apical side

Cystic fibrosis.

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12
Q

What is the general role of epithelial cells in the pancreas? What are the roles of the two subtypes?

A

Epithelial cells release membrane-bound enterokinase (enteropeptidase), which converts trypsinogen to trypsin, which converts the inactive enzymes to active ones.

  1. Endocrine secretory epithelium (islets): insulin and glucagon (glucose metabolism)
  2. Exocrine secretory epithelium: digestive enzymes and NaHCO3
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13
Q

What are the 3 stimuli that cause secretion from exocrine secretory epithelium?

A

Stimuli for exocrine include:

  1. Distension of small intestine
  2. Neural signals
  3. Cholecystokinin (CCK)
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14
Q

What two ways are the enzymes released from the exocrine secretory epithelium?

A

Many pancreatic digestive enzymes released as zymogens (inactive form of enzyme that needs to be modified), while some enzymes are also secreted in the active form.

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15
Q

What is the role of the common bile duct?

A

Take bile from the gallbladder to the lumen of the intestine.

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16
Q

What is the role of the hepatic artery?

A

Bring oxygenated blood containing metabolites (bilirubin, metabolites, nutrients) to the liver

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17
Q

What is the role of the hepatic portal vein?

A

Bring blood rich in absorbed nutrients from the GI tract and hemoglobin breakdown products from the spleen to the liver.

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18
Q

What is the role of the Sphincter of Oddi?

A

Control the release of bile and pancreatic secretions into the duodenum

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19
Q

What is the primary secretion of the liver in digestion? What cell is involved in this secretion? What are the three main components of this secretion?

A

A non-enzymatic solution called bile. Hepatocytes.

  1. Bile salts (bile acid/amino acid)
  2. Bile pigments (bilirubin)
  3. Cholesterol
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20
Q

If a doctor wanted to measure the excretion of xenobiotics and/or drugs from a patient’s GI tract, what may they check?

A

Bile.

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21
Q

What is the complicating factor of the structure of fats in regards to fat digestion?

A

Fats are not very water soluble.

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22
Q

What non-enzyme molecule aids in fat digestion? How is this done?

A

Bile salts come into play and act to break down fats by coating and breaking down larger lipid droplets into smaller ones. One side of the bile molecule associates with the lipid and one side with the water. Eventually, a micelle is formed.

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23
Q

What is the role of lipase in fat digestion?

A

Digests fats (triacylglycerols) into free fatty acids and monoglyceride.

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24
Q

What is the role of colipase in fat digestion?

A

Allows lipase to target the center of lipid droplets, doesn’t do the digestion.

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25
Q

In 5 steps, describe the absorption of fats into the lacteals of the intestine.

A
  1. Bile salts from liver coat fat droplets
  2. Pancreatic lipase and colipase break down the fats into monoglycerides and fatty acids stored in micelles
  3. Monoglycerides and fatty acids move out of micelles and enter cells by diffusion. Cholesterol is transported into cells.
  4. Absorbed fats combine with cholesterol and proteins in the intestinal cells to form chylomicrons.
  5. Chylomicrons are absorbed by the lacteals.
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26
Q

What percent of the secreted bile salts are reabsorbed by the ileum? What happens to the rest?

A

95%. The other 5% is excreted in feces.

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27
Q

What are gallstones and what are they likely caused by?

A

Hardened deposits likely due to excess cholesterol or bilirubin.

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28
Q

Carbohydrates ingested include _____ and _____.

A

Starch and sucrose.

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29
Q

Glucose polymers can be broken down by _____ to produce _____ which include these 3 types.

A

Amylase, disaccharides.

  1. Maltose (glucose + glucose)
  2. Sucrose (glucose + fructose)
  3. Lactose (glucose + galactose)
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30
Q

Disaccharides are then broken down to monosaccharides by intestinal brush border enzymes known as ______.

A

Disaccharidases.

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31
Q

Most carbohydrates are brought into the cell as ______.

A

Monosaccharides.

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32
Q

Where does carbohydrate absorption occur?

A

On the villi.

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33
Q

What channels do glucose or galactose enter and exit the villi through?

A

Enters with Na+ via SGLT, exits via GLUT2.

34
Q

What channels does fructose enter or exit the cell through?

A

Enters through GLUT5, exits via GLUT2.

35
Q

Normally glucose is phosphorylated when it enters the cell, but not in enterocytes. Why?

A

Enterocytes primarily use glutamine as an energy source so glucose-6-phosphate is not formed and free glucose concentration stays high facilitating basolateral transport.

36
Q

Are all proteins equally digestible?

A

No.

37
Q

What is an enteropeptidase? What is it released as? What is the primary enteropeptidase of the stomach, and the two primary ones from the pancreas?

A

Enzymes that attack peptide bonds in the amino acid chain forming fragments (internal bonds), creating two smaller peptides. They are released as zymogens.

  1. Pepsin: stomach
  2. Trypsin: pancreas
  3. Chymotrypsin: pancreas
38
Q

What is an exopeptidase? Give the two types and what each do. Which plays a larger role?

A

Exopeptidases release single amino acids one at a time. Consist of:

  1. Aminopeptidases: cleave from amino-terminal end
    • Brush border enzyme
  2. Carboxypeptidases: cleave from carboxy-terminal end
    • Play a larger role than aminopeptidases
    • Pancreatic carboxypeptidase A1, A2, and B
39
Q

How are single amino acids absorbed?

A

Mostly enter on Na+ cotransporters (apical) and Na+ exchangers (basolateral).

40
Q

How are di and tripeptides absorbed? What mostly happens to these oligopeptides?

A

Through oligopeptide transporter (H+ cotransporter). Most oligopeptides are digested to single amino acids in the cell by peptidases and exit via Na+-AA exchanger (same as single entry)

41
Q

What happens to some peptides larger than 3 amino acids during protein absorption? What could these potentially act as and what may this cause?

A

Some peptides larger than 3 AAs are transported via transcytosis after binding to a receptor on the luminal surface. Small peptides could potentially act as antigens stimulating antibody production causing an allergic reaction. May play a role in food intolerances or allergies.

42
Q

What happens when peptide absorption is too high during infancy? What is this caused by? What may this lead to later in life?

A

The receptor mediated endocytosis is diverted to the crypts instead. The villi are too small. This leads to gluten intolerance later in life.

43
Q

How are vitamins A, D, E and K absorbed? What are these termed?

A

These are put into micelles and cross the membrane, where they are then packed into chylomicrons. These are known as fat soluble vitamins.

44
Q

How are vitamins C and B absorbed? What are these vitamins termed?

A

Mediated transport (cotransport or exchangers). These are water soluble vitamins.

45
Q

How is vitamin B12 absorbed? What process is vitamin B12 important for?

A

B12 is absorbed in the ileum after forming a complex with intrinsic factor released from parietal cells. B12 is important for DNA replication.

46
Q

How is iron absorbed? Where is iron obtained from? What is it controlled by? What would increased iron cause?

A

Free iron is brought in through a divalent metal transporter (DMT1) with H+. It is either obtained from free iron or from heme. It is controlled by hepcidin levels, which acts to remove ferroportin transporters from the basolateral membrane (decreasing Fe2+ exit from the cell).

Increased iron causes increased hepcidin, which binds the ferroportin and causes its removal, which halts the absorption of iron into the ECF

47
Q

How is calcium absorbed and how does it exit? What vitamin increases its absorption?

A

Enters through TRPV6 Ca2+ channel, exits through Na/Ca exchanger. Calcium absorption increases with increased vitamin D3.

48
Q

Where is most water absorbed in the GI tract?

A

Small intestine.

49
Q

What 4 ways is Na+ pumped into the cell? How is it pumped out?

A

In:

  1. Na+ channel
  2. Na+/Cl- cotransporter
  3. Na+/H+ exchanger
  4. Na+/organic solute (amino acid or glucose) cotransporter

Out:

  1. Na-K ATPase
50
Q

What 3 stimuli regulate the intestinal phase? What 3 mechanisms is this done through? What is the result of these stimuli?

A

Stimuli:

  1. Distension
  2. Acidity
  3. Digestive products in the small intestine

Mechanisms:

  1. Short reflexes
  2. Long reflexes
  3. Endocrine signalling

Stimuli reduce motility and secretions in the stomach, and increase them in the intestine.

51
Q

Intestinal motility is primarily regulated by _____ located in the _____.

A

ENS neurons, myenteric plexus.

52
Q

Which 5 cells are primarily involved in the regulation of intestinal motility? What do each produce? Which of them are GI peptide secretors and what are these cells also known as?

A

Cells:

  1. Mo cell: motilin (migrating motor complex)
  2. S cell: secretin
  3. I cells: cholecystokinin
  4. K cells: glucose-dependent insulinotropic peptide (GIP)
  5. L cells: glucagon-like peptide 1 (GLP-1)

The last 4 (SILK) are GI peptide secretors, also known as enteroendocrine cells.

53
Q

In the fed state, what kind of contractions predominate? What cells are involved? What 3 things stimulate these cells?

A

Primarily segmental with small amounts of peristaltic contractions. Slow waves from the cells of Cajal are brought to threshold by:

  1. Distension of stomach
  2. Distension of small intestine (myoreceptors to myenteric plexus causing increased contractions
  3. Increased parasympathetic input (long reflexes)
54
Q

In the fasting state, what kind of intestinal motility is observed? What does this function to do? What cells are involved? What are they stimulated by?

A

The migrating motor complex (MMC), which functions to clean the GI tract. Brought about by Mo cells (motilin). Possibly stimulated by alkaline pH.

55
Q

Regulation of intestinal phase:

Secretions (from accessory organs) are controlled via ____\_. Broadly, these include _____ and _____.

A

Long reflexes. GI peptides and pancreatic secretions.

56
Q

Regulation of intestinal phase: S cells

  1. Secrete
  2. Stimulated by
  3. Primary role
    1. Methods (2)
A
  1. Secretin
  2. Acid entering the duodenum from the stomach
  3. Regulation of pH
    1. Stimulates bicarbonate secretion from pancreas, stimulates bile secretion from liver
    2. Inhibits gastric acid secretion by inhibiting gastric motility thus ceasing gastric emptying into SI
57
Q

Regulation of intestinal phase: I cells

  1. Secrete
  2. Stimulated by
  3. Primary roles (2)
  4. Secondary role
A
  1. Cholecystokinin (CCK)
  2. Stimulated by the presence of fatty acids and amino acids in chyme
  3. Roles:
    1. Increases pancreatic enzyme secretion
    2. Increases bile secretion
  4. Inhibits gastric acid production and emptying of the stomach
58
Q

Regulation of intestinal phase: K cells

  1. Secrete
  2. Stimulated by
  3. Primary roles (2)
  4. Endocrine/exocrine
A
  1. Glucose-dependent insulinotropic peptide (GIP)
  2. Presence of carbohydrates in GI lumen
  3. Roles:
    1. Increases insulin release, causing increased glucose uptake (glucose homeostasis)
    2. Inhibit gastric acid secretion and motility
  4. Endocrine
59
Q

Regulation of intestinal phase: L cells

  1. Secrete
  2. Stimulated by
  3. Primary roles (2)
  4. Endocrine/exocrine
A
  1. Glucagon-like peptide 1 (GLP-1)
  2. Presence of carbohydrates in the GI lumen
  3. Roles:
    1. Increase beta cell activation in pancreas, increasing insulin release (glucose homeostasis)
    2. Inhibit gastric acid secretion and motility
  4. Endocrine
60
Q

Regulation of intestinal phase: pancreatic secretions

  1. When do they begin?
  2. Stimulated by
  3. What reflex do they contribute to?
A
  1. Cephalic and gastric phases
  2. Gastrin and parasympathetic neurons
  3. Enteropancreatic reflex: increased H2O and bicarbonate release as a result of food in the stomach or just the sight, taste or smell of food.
61
Q

What is the enterogastric reflex? What 2 phases does it integrate?

A

Enterogastric reflex: acid, enzymes and digested food results in hyperosmotic chyme that inhibits gastric emptying (we don’t know which cell influences this). This reflex integrates the gastric and intestinal phases.

62
Q

What is the main role of the large intestine?

A

The main job of the LI is to store and concentrate fecal matter. Also absorbs water and electrolytes.

63
Q

Approximately ___ L of chyme proceed through the ileocecal valve.

A

1.5

64
Q

What is the gastroileal reflex?

A

Food in stomach causes contraction of ileum and relaxation of ileocecal valve.

65
Q

The large intestine (contains/lacks) villi

A

Lacks

66
Q

_____ cells in the LI produce mucus

A

Goblet.

67
Q

By the end of digestion, ___ L of ions and water is excreted through the feces

A

0.1.

68
Q

Secretions in the large intestine are minimal and primarily consist of _____.

A

Mucus

69
Q

Does digestion occur in the large intestine? How?

A

Yes. This is done by the use of bacteria which break down indigestible complex carbohydrates, fats and proteins.

70
Q

What 3 products do bacteria in the LI produce? (LAG)

A
  1. Lactate and short chain FA’s used by colonocytes for energy production
  2. Absorbable vitamins (Vit K)
  3. Gases
71
Q

How long does the entire digestional process take? Break down each sector.

A

40 hours.

  1. Mouth to stomach: rapid
  2. Stomach: 5 hours
  3. SI: 5 hours
  4. LI: 18-24 hours
72
Q

What are the 3 forms of motility in the large intestine? Describe each.

A
  1. Slow segmental contractions
  2. Haustral rolling or churning
    • Thickened bands of longitudinal muscle layer taenia coli
      • Create pouches called haustra
  3. Mass peristalsis
    • Gastrocolic reflex, stimulated by food in stomach
    • 2-3 times/day
    • Forceful and faster contractions
73
Q

Defecation comes as a result of 2 reflexes initiated by distension of the _____. Describe both reflexes.

A

Rectum.

  1. Short reflex
    • Local peristaltic waves
    • Relaxation of internal sphincter (smooth muscle)
  2. Long reflex
    • More forceful peristaltic contractions from parasympathetic input
74
Q

Defecation is completed by voluntary relaxation of _____, and aided by _____.

A

Voluntary relaxation of external sphincter, abdominal contractions.

75
Q

Define diarrhea. What are the 4 types?

A

An increase in the frequency, volume and fluid content of the feces due to increased secretion, reduced absorption or increased motility.

  1. Osmotic
  2. Secretory
  3. Inflammatory
  4. Motility induced
76
Q

How does cholera cause diarrhea? What type is it?

A

Cholera releases a toxin causing stimulation of cAMP pathway leading to increased opening of CFTR channels, leading to massive flux of Cl- into the lumen, causing a massive amount of water and Na+ to follow as well. It is a type of secretory diarrhea.

77
Q

Use of penicillin-based antibiotics can alter the normal bacterial flora. What can this cause? How can this be treated?

A

The remaining bacteria have reduced competition for space and nutrients, which leaves you prone to infection by C. difficile, which can cause colitis. Can be treated using a fecal transplant via colonoscopy or by the “poo-pill”

78
Q

What two zones control vomiting? What are the 3 primary responses to stimulation of these?

A

Control:

  1. Vomiting center in medulla
  2. Chemoreceptor trigger zone (CTZ)

Primary responses:

  1. Retrograde (reverse) peristaltic contractions in the small intestine and stomach
  2. Contraction of abdominal and inspiratory muscles (diaphragm) increases gastric pressure
  3. Relaxation of esophageal sphincters
79
Q

_____ contains 80% of lymphocytes located in the gut.

A

Gut-associated lymphoid tissue (GALT).

80
Q

Which cells play big roles in immune responses? What 3 things do they do?

A

M cells

  1. Sample lumen contents through receptor mediated endocytosis
  2. Transport antigens to macrophages, lymphocytes, and dendritic cells
  3. Release cytokines to attract more immune cells and trigger increased Cl- secretion (diarrhea) to flush out pathogens
81
Q

What is the Payer’s patch?

A

Region in GI tract with high immune cell concentration

Human Body Systems II (BMSC 208) (11 decks)

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