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Digestive System physiology Flashcards

1
Q

What constitutes the gastrointestinal tract?

A

-Mouth
-Pharynx
-Esophagus
-Stomach
-Small intestine (duodenum, jejunum, ileum)
-Large intestine

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2
Q

What are the accessory glands of the GI tract?

A

-Teeth/tongue
-Salivary glands
-Gallbladder
-Liver
-Pancreas

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3
Q

What are the six essential activities of the digestive system?

A

-Ingestion
-Propulsion
-Mechanical digestion
-Chemical digestion
-Absorption
-Defecation

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4
Q

What are the four major tissue layers of the digestive tract? What is their defining characteristic?

A

Mucosa:
-innermost layer
-secretes mucous
-absorption
-finger-like projections

Submucosa:
-lymphatics, blood, and nerve supply

Muscularis externa:
-Circular and longitudinal muscle to increase motility

Serosa:
-Outer connective tissue later to aid in stretchiness and recoil

The same general structure from esophagus to anus

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5
Q

What are the sensory receptors in the GI tract and what do they respond to?

A

Mechanoreceptors:
-responds to stretch as food moves through
-reflex contraction

Chemoreceptors:
-responds to osmolarity and pH changes
-digestive substrates and end products

Both activate or inhibit digestive glands, and stimulate smooth muscle to mix and move lumen contents

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6
Q

Intrinsic (short reflexes) controls of the GI tract

A

-Enteric nerve plexuses (gut brain) respond to stimuli in GI tract
-Hormones from the stomach and small intestine stimulate target cells in same or different organs

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7
Q

Extrinsic controls of the GI tract

A

-Respond to stimuli inside or outside the GI tract (thought or smell of food)
-Autonomic control
-Input to the local nerve plexus into the gut
-Can receive input from the chemoreceptors, osmoreceptors, or mechanoreceptors

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8
Q

Which activity does the colon mostly do?

A

-Mostly absorption
-Small amount of secretion

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9
Q

Which activity does the small intestine mostly do?

A

-Secretion AND absorption

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10
Q

What is motility?

A

-Muscular contractions that mix and move forward the contents of the digestive tract

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11
Q

Two types of motility?

A

Peristalsis:
-Propulsive
-Alternates between no movement and movement so that you can absorb nutrients

Segmentation:
-Mixing movements
-Promotes digestion of foods
-Facilitates absorption and mixing time

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12
Q

Where are digestive enzymes secreted?

A

-Mouth
-Stomach
-Small intestine

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13
Q

Where is mucous secreted?

A

-Mouth
-Stomach
-Small intestine

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14
Q

What do hormones affect?

A

Motility and secretions

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15
Q

What do villi and microvilli do? What do they contain inside?

A

-Increase surface area for absorption
-Capillary beds and lacteals (lymphatic)

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16
Q

What is mechanical digestion?

A

-Chewing
-Chemical break-down by enzymes

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17
Q

What are the different kinds of carbohydrates?

A

-Starch: usually 2/3 of carbohydrates
-Dissaccarides: sucrose and lactose
-Monosaccarides: glucose (doesn’t need to be broken down)
-Complex carbohydrates: fibre

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18
Q

Where does amylase come from / where does it act on?

A

From salivary glands - acts in mouth

From pancreas - acts in small intestine

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19
Q

What does amylase do?

A

-breaks down starch into dissaccarides while chewing
-inactivated when swallowed by pH, so we get more from pancreas

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20
Q

Where do lactase and maltase come from / act on?

A

From mucosa and submucosa cells in SI wall - acts in SI

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21
Q

What do lactase and maltase do?

A

-break down dissaccarides into monosaccarides to be absorbed directly into blood

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22
Q

Why does gas production occur with fibre?

A

-humans lack the enzyme to completely digest complex carbs
-fibre moves to LI for E.Coli digestion
-fermentation and gas production occur

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23
Q

How many grams of protein do you need per day?

A

50-60 g

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24
Q

Where does pepsin come from / act on?

A

Comes from chief cells in stomach - acts in stomach

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25
What does pepsin do?
-breaks down protein into polypeptides
26
Where do trypsin/chymotrypsin, carboxypepsidase, and aminopeptidase come from / act on?
come from pancrease - acts in SI (carbo and amino also come from the SI wall)
27
What does trypsin/chymotrypsin do?
breaks down proteins into polypeptides
28
What do carboxypepsidase and aminopeptidase do?
-breaks down polypeptides into dipeptides
29
Where does dipeptidase come from / act on?
SI - SI -brush border enzymes (SI cells)
30
What does dipeptidase do?
breaks down dipeptides into amino acids to be absorbed directly into blood
31
What role does bile play in fat digestion?
-emulsifier: binds water molecule to fat molecule to make small fat molecules -increases surface area for lipase to be more effective -does not chemically change the fat
32
Which enzymes play a role in fat digestion? Where are they made and where do they act?
-lipase from pancreas, acts in SI
33
What does lipase do?
-turns smaller fat globules into either glycerol (monoglyceride) or fatty acids -glycerol becomes sugar to be absorbed into blood -fatty acids are either turned into micelles while waiting for absorption or can enter absorptive cells -within cells, they form chylomicrons to be absorbed into the lymph lacteals
34
what do nucleases do? where do they come from / act on? what else helps them?
-digest nucleic acids from pancreas - act in SI -brush border enzymes (SI)
35
how are vitamins absorbed?
carriers
36
what function does chewing have?
-increases surface area -reduces choking -secretion of mucous (lubrication) and salivary amylase for starch digestion
37
what triggers the swallowing reflex?
-food in the pharynx -contractions coordinated by medulla
38
which sphincter or valve separates the esophagus from the stomach?
gastroesophageal
39
what causes heartburn and acid reflux?
a faulty valve in the esophagus
40
sections of the stomach
-fundus (superior portion) -body (middle portion) -antrum (distal portion
41
which sphincter separates the stomach from the duodenum?
pyloric sphincter - limits amount of food into small intestine
42
what are rugae?
-deep folds in stomach that allow for expansion
43
4 functions of the stomach
-storage -mixing -secretion -absorption
44
how much can the stomach expand? for what function?
20x (50mL to 1L) occurs in the body of stomach for storage
45
which stomach cells cause secretions? how does this process work
chief cells: releases pepsinogen for protein digestion parietal cells: releases HCl (hydrochloric acid), activates pepsinogen into pepsin
46
why is there mucous in the stomach wall and why are acid and pepsinogen secreted separately? why is there high cell replacement and tight junctions?
-to protect the wall from the acid in the gastric pits -maintains wall integrity
47
what does the stomach pH drop to?
2 - 3
48
what does pepsin break down and kill?
-connective tissue and muscle -kills pathogens
49
what does mixing and emptying create in the stomach?
chyme - moves into SI or is stored
50
which two chemicals have quick absorption but break down the mucous layer in the stomach wall?
aspirin and alcohol
51
what does gastrin do?
-it is a hormone that activates the stomach -increases HCl secretion -increases pepsinogen -increases motility
52
what stimulates gastrin release?
-parasympathetic stimulation -proteins -distension in stomach -smell
53
as stretch in the intestine increases, gastrin is _________.
decreased
54
Cephalic phase of stomach digestion
-Stimulation of taste and smell receptors inputs to hypothalamus and medulla
55
gastric phase of stomach digestion
stretch receptors are activated in stomach to increase gastrin
56
intestinal phase of stomach digestion
-presence of low pH, partially digested foods in duodenum when stomach begins to empty
57
what are some inhibitory events of stomach digestion?
-loss of appetite, depression -excessive acidity -emotional upset -distension of duodenum
58
what other hormones increase HCl secretion?
ACh Histamine Gastrin Somatostatin
59
peptic (gastric) ulcer
-hole caused by inflammation and necrosis -caused in part by pepsin or helicobacter pylori (bacteria) -in stomach or duodenum -symptoms: pain, bleeding (hematemesis or melena) -treatment: reduction of inflammatory factors, antacids, surgery in severe cases
60
which secretions from the pancreas and gall bladder dump into the duodenum?
-bile (gallbladder) -amylase -trypsin -pepsidases -lipase -nucleases -bicarbonate
61
what does bicarbonate do?
neutralizes stomach pH
62
are enzymes released from the pancreas active or inactive?
inactive - were they active, they would digest the very cells that make them. -enterokinase activates them
63
what does cholecystokinin (CCK) do?
-triggered by small bolus of food entering the SI -CCK acts on the pancreas and gall bladder to increase release of enzymes and bile -chemoreceptors tell the pancreas which enzymes we need
64
triggering factors for CCK release
-stretch receptors in duodenum -fat content increases in SI
65
what does secretin do?
-released if SI is acidic -causes pancreas to release bicarbonate to neutralize acid -increases the bile formation in liver and inhibits gastric motility
66
where is CCK made?
duodenal mucosa (brush layer enzymes)
67
where is gastrin made?
stomach mucosa (G cells)
68
where is motilin made?
duodenal mucosa
69
what does motilin do?
-stimulates migrating motility complex in proximal duodenum
70
where is secretin made?
duodenal mucosa
71
how long does it take carbs and fats and proteins to digest?
carbs: 2-3 hours in first 1/2 of jejunum fats and proteins: 8-10 hours
72
how are fat-soluble vitamins absorbed?
micells
73
how are water-soluble vitamins absorbed?
carriers
74
how does water reabsorption occur?
follows solutes using osmosis
75
how is sodium absorbed?
-in duodenum -coupled with glucose and amino acids
76
how is calcium absorbed?
-regulated by vitamin D, parathyroid hormone, and calcitonin -in duodenum
77
what are the valves in the large intestine?
Ileocecal valve (between ileum and cecum)
78
what are the sphincters in the large intestine?
-external and internal anal phincter
79
Which contractions occur in the LI?
Haustral contractions: slow movements
80
What is reabsorbed in the large intestine?
Sodium and water
81
What triggers the defecation reflex?
-Distention of the rectum -Parasympathetic response: relaxes sphincters and contracts rectal walls -Can over-ride with higher brain centres
82
Total daily secretions
9 L/ day
83
How much liquid is excreted in feces a day?
100 mL / day
84
Daily absorption of small intestine and large intestine
Small intestine: 8.5 L / day Large intestine: 400 mL / day
85
Hemorrhoid
-Varicose veins in rectum either internal or external Causes: pressure in anal area, constipation, prolonged standing, pregnancy, childbirth Treatment: medications, warm baths, manual reduction, hemeroidectomy
86
What functions does the pancreas have?
Exocrine and endocrine
87
What do the duct cells of the pancreas secrete?
Bicarbonate
88
What do the acinar cells of the pancreas secrete?
Enzymes
89
What do the endocrine cells of the pancrease secrete?
Insulin and glucagon
90
Where does the liver receive blood from?
Hepatic artery and hepatic portal vein (from gut) Blood is rich in nutrients
91
What are hepatocytes? How are they arranged?
Liver cells. Sinusoids
92
Liver functions not related to digestion
-Metabolic processing of major nutrients -Detoxifying or degrading body wastes, hormones, drugs, other foreign things -Synthesizes plasma proteins -Stores glycogen, fats, iron, copper, vitamins -Makes clotting factors -Activates vitamin D -Removes bacteria and worn-out red blood cells -Excretes cholesterol and bilirubin
93
How much bile is formed per day?
900 mL per day
94
Where is bile formed between meals?
Gall bladder
95
What are the components of bile?
-Bilirubin (gives bile yellow colour) -Cholesterol -Lecithin (protein) -Bile salts (forms mycelles, derived from cholesterol) -Water
96
Where are bile salts recycled?
Recycled within gut and brought back to liver through hepatic portal vein
97
What does the gall bladder do?
-Stores and concentrates bile -Contracts with CCK release
98
Crohn's disease
* Regional enteritis * Small intestine

KNES260 (13 decks)

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