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Intro Bio II Exam 3 > Digestion > Flashcards

Digestion Flashcards

1
Q

Digestion

A

The chemical and mechanical breakdown of food (breaking of COVALENT bonds)

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2
Q

Energy Reserves

A

Carbohydrates - depleted within a day
Fat - long-term major energy reserve
Protein - Broken down when fat is exhausted, BAD

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3
Q

Edema (due to malnutrition)

A

Body out of fat so breaks down protein, leading to osmotic imbalance in blood that pulls water out of plasma and into tissues - resulting in swollen belly

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4
Q

Digestive System

A

A tube that extends from mouth to anus

Mouth, esophagus, stomach, small intestine, large intestine

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5
Q

Function of Mouth (General)

A

salivary enzymes and mechanical breakdown of food

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6
Q

Function of esophagus (general)

A

Skeletal muscle toward top, transitions to smooth muscle toward bottom

Moves bolus from mouth to stomach

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7
Q

Function of stomach (general)

A

Acid, mixing, pepsin

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8
Q

Function of small intestine (general)

A

Duodenum, jejunum, ileum

Many digestive enzymes break down macromolecules and ABSORB them

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9
Q

Function of large intestine (general)

A

Water is reabsorbed

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10
Q

Digestive aids

A

Salivary glands, liver, pancreas, gallbladder

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11
Q

Bolus

A

Ball like structure of food which is pushed into esophagus when swallowed

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12
Q

Digestion in mouth (specific)

A

Softening and moistening of food by saliva to form bolus

Amylase breaks down starches, chewing increases SA, + antimicrobial enzymes in saliva

Presence of food in mouth results in feed-forward response: start secreting insulin in body

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13
Q

Salivary Glands

A

Parotid, sublingual, submandibular

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14
Q

Main functions of digestive system

A
  1. Secretion
  2. Digestion
  3. Absorption
  4. Motility
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15
Q

Are digestive processes governed by needs of organism?

A

No. All food that is eaten will be absorbed if possible, regardless of need.

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16
Q

Secretion

A

Movement of material from cells into ECF or lumen

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17
Q

Absorption

A

Movement of material from lumen into cells

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18
Q

Motility

A

Movement of material through GI tract as a result of muscle contraction

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19
Q

What separated lumen of digestive tract from blood?

A

Wall of cells

Interstitial fluid

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20
Q

Anatomy of small intestine favors…

A

Absorption, motility

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21
Q

How does SI increase absorption?

A
  1. Macro infoldings of overall tube, so it looks like an accordion
  2. Villi - finger-like projections
  3. Crypts, or invaginations between villi in the tube
  4. Microvilli - villi for your villi
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22
Q

How does SI increase motility?

A

Two layers of muscle in different directions

  1. Circular muscle
  2. Longitudinal muscle
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23
Q

What systems extend within villi?

A

Arteries, veins, lymph

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24
Q

Function of water in digestion

A

For anything to move within system, needs water: so we secrete 9 L if water and reabsorb 8.9 L

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25
Fluid input into digestive system
Ingestion (2 L) Secretion (7 L) Secretion includes saliva, bile, gastric secretions, pancreatic secretions, and intestinal secretions Gastric secretions account for the most
26
Fluid output from digestive tract
Absorption (8.9 L) Excretion in feces (0.1 L) Most water absorption occurs in small intestine
27
which muscle is found in digestive tract
smooth muscle
28
what drives depolarization of smooth muscle in GI tract?
gastric pacemaker cells creating slow wave potentials that sum when they exceed threshold
29
smooth muscle in GI tract connected by...
gap junctions! single-unit smooth muscle
30
Definition of slow waves
Force and duration of muscle contraction directly related to amplitude and frequency of action potentials
31
Cephalic Phase Reflex
Seeing and smelling food leads to saliva secretion and gastric contraction. Stimulation of neurons in medulla oblongata leads to autonomic signaling to digestive system.
32
Gastric phase reflex
Begins when food arrives in stomach. Stretching of stomach and presence of peptides / amino acids starts short reflexes.
33
Pathway of Cephalic Reflex
Aka LONG vagal reflex: Mouth --> Brain / medulla oblongata --> pre ganglionic vagus nerve neuron --> enteric plexus --> post ganglionic parasympathetic neurons --> target cells
34
Pathway of gastric phase reflex
Aka SHORT vagal reflex: | Peptides in stomach --> enteric plexus --> post-ganglionic parasympathetic neurons --> target cells
35
Peristaltic Contractions
Responsible for forward movement Sequential contractions in different places at different times (time lag)
36
Segmental Contractions
Responsible for mixing Squeezing different segments at the same time (little / no forward movement)
37
Key anatomical features of the stomach
Surface foldings, gastric glands, circular and longitudinal muscle, ample blood supply Lymph system is NOT present in epithelium
38
Key functional unit of the stomach
Gastric mucosa
39
Cell types in the gastric mucosa
Mucous surface cell, mucous neck cell, parietal cell, enterochromaflin-like cell, chief cells, D cells, G cells
40
Mucous surface cell
Secretes: Mucous Why: physical barrier between lumen and epithelium Stimulated by: tonic secretion, irritation of mucosa
41
Mucous neck cell
Secretes: Bicarbonate Why: buffers gastric acid Stimulated by: Secreted with mucous
42
Parietal Cell
Secretes: Gastric acid (HCl) Why: activates peptide and kills bacteria Stimulated by: Ach, gastrin, histamine Secretes: Intrinsic factor Why: Complexes with vitamin B12 to permit absorption Stimulated by: Ach, gastrin, histamine
43
Enterochromaflin-like cell
Secretes: Histamine Why: stimulates gastric acid secretion Stimulated by: Ach, gastrin
44
Chief cells
Secretes: Pepsin(ogen) Why: Digest proteins Stimulated by: Ach, acid Secretes: Gastric lipase Why: Digests fat Stimulated by: Ach, acid
45
D cells
Secretes: Somatostatin Why: inhibits gastric acid Stimulated by: acid
46
G cells
Secretes: Gastrin Why: stimulates acid secretion Stimulated by: Ach, peptides, amino acids
47
How do cells survive low pH of stomach
mucous-bicarbonate barrier
48
creation of mucous bicarbonate barrier
Gastric mucous cells secrete droplets of mucous and bicarbonate, so that there is a bicarbonate mucous layer between cells and gastric juice
49
Activation of pepsin
1. HCl secreted from parietal cells activates pepsinogen secreted from chief cells 2. Already-activated pepsin activates pepsinogen
50
When are proteases activated?
After translation This way they do not cleave proteins within our cells (destructive!)
51
Formation of pH difference in stomach
1. Parietal cells react H2O with CO2 to produce H2CO3 2. Proton pumps in parietal cells pump out H+ and pump in K+ 3. HCO3- leaves cell in exchange for Cl- (chloride shift) 4. Charge is balanced (H+ and HCO3- out, Cl- and K+ in)
52
Important stomach enzymes
``` Pepsin (major) Gastric lipase (minor) ```
53
Pepsinogen
Inactive form of pepsin protease
54
How is HCl production regulated?
Four possible signals result in SECOND MESSENGERS that exocytose H+/K+ pumps to cell surface Three signals stimulate acid: Gastrin, histamine, Ach One signal inhibits acid: Somatostatin K+ leak channel maintains gradient
55
Omeprazole
Irreversibly inhibits proton pumps in stomach by covalently binding to them HOWEVER must be taken over and over again, because so many proton pumps are constantly produced!
56
What causes ulcers?
H. pylori infection NOT ACID! Proven by Marshall and Warren; cured with antibiotics
57
Koch's Postulates
Method of proving that a microorganism is the cause of a disease 1. Microorganism must be present in every case 2. Microorganism must be cultured from sick host 3. Isolated bacteria must cause disease in second host 4. That bacteria must be cultured AGAIN from the second host post-infection / disease
58
Hepatic Portal System
Blood leaving digestive tract (stomach, intestines, pancreas, spleen) travels to liver for detoxification This is technically VENOUS blood : deoxygenated
59
Blood inputs to liver
1. From hepatic portal system (venous blood, deoxygenated) | 2. From hepatic artery (arterial blood, oxygenated)
60
Brush border
The microvilli of the SI : creates a hairy border between cells (apical membrane) and lumen
61
What is absorbed in SI?
Monosaccharides Amino acids, small peptides Triglycerides, glycerol Ions
62
Cells of the SI
``` Enterocytes - absorb nutrients, ions goblet cells - secrete mucous stem cells - replaced damaged cells crypt cells - secrete ions and water endocrine cells - secrete hormones ```
63
Lacteal
Vessel of lymph system that projects into villi of SI, transports most fats to the lymph
64
Denaturing of Proteins
Break nonvcovalent bonds (H-bonds, electrostatic attractions) of folded protein to return to primary structure, aka the pure amino acid sequence Disulfide bonds may or may not be reduced in this process...? (TBD)
65
What is secreted in SI?
Water, ions | BICARBONATE!
66
Endocrine Pancreas
Blood glucose homeostasis | Glucagon, insulin
67
Exocrine Pancreas
Digestion | Pancreatic enzymes, bicarbonate
68
Pancreatic Islet Cells
Secrete hormones (glucagon, insulin) into capillaries
69
Pancreatic acini cels
Secrete digestive enzymes into lumen of pancreatic duct
70
Duct cells of pancreas
Secrete NaHCO3 into lumen of pancreatic duct
71
Zymogens
Digestive enzymes of pancreas in INACTIVE form Need to be inactive so do not digest things within the cell itself Examples: Chymotrypsinogen, procarboxypeptidase, procolipase, prophospholipase
72
Trypsinogen
Inactive form of the pancreatic zymogen that activates other zymogens
73
Trypsin
Activated zymogen that activates digestive enzymes
74
Enteropeptidase
Enzyme in brush border that activates trypsinogen to trypsin
75
Pathway and activation of zymogens
1. Zymogens secreted by acinar cells into pancreatic duct 2. Ducts flushes enzymes out into lumen of SI 3. Brush border epithelial cell enzyme, enteropeptidase, activates trypsinogen to trypsin 4. Trypsin activates the 4 pancreatic digestive zymogens 5. Digestion!
76
What is the only pancreatic enzyme NOT secreted as a zymogen?
Amylase We do not have starch in our cells!
77
Isotonic Saline
mixes with mucous and lubricates the SI to increase motility
78
Secretion of isotonic saline (step-by-step)
1. NKCC cotransporter moves Na+, Cl-, K+ into intestinal cell 2. CFTR moves Cl- cell into lumen of SI 3. Na+ is reabsorbed via Na+/K+ pump 4. Na+ follows Cl- into lumen via paracellular pathway; water follows solute
79
What secretes bicarbonate in the gut
Pancreas, duodenum
80
Secretion of bicarb in gut (step by step)
1. Cells that produce bicarb have LOTS of carbonic anhydrase 2. Cl- enters cells via NKCC, then Cl- exits cell via CFTR 3. THEN Cl-/HCO3- exchange protein brings Cl- into cell in exchange for HCO3- (chloride shift!) 4. Leaky junctions allow paracellular movement of ions (Na+) and water
81
Chyme
Acidic mixture of food and secretions in the stomach that is then squeezed through pyloric sphincter into duodenum of SI
82
What if pH in the duodenum is too low?
Cells damaged, ulcer
83
Where does bulk of digestion and absorption take place?
Duodenum of SI
84
Gallbladder
Stores bile
85
What produces bile?
Liver
86
Common Hepatic Duct
Transports bile from liver to gallbladder
87
Common Bile Duct
Take bile from gallbladder to lumen of small intestine
88
Sphincter of Oddi
Sphincter that seals off the common bile duct and pancreatic duct, opening allows for bile salt / pancreatic enzyme secretion into duodenum
89
Bile salts
Amphipathic molecules that act as detergents to coat lipids to make emulsions, facilitating cleavage of triglycerides Made in liver via addition of amino acid to bile acid Most bile salts are reabsorbed in ileum and recycled over course of single meal
90
Bile acids
Made from cholesterol If add amino acid, become bile salt
91
Bile
Bile salt, bile pigments, cholesterol Bile salts are recycled, pigments and cholesterol excreted
92
Micelles from Bile Salts
Small disks with bile salts, phospholipids, fatty acids, cholesterol, and mono- and di-glycerides
93
Lipase and Colipase
Enzymes that digest triglycerides; act at lipid-aqueous interface, more efficient when given more SA to work on So wants SMALLER micelles so more SA to volume
94
Role of Bile Salts in Digestion (step by step)
1. Bile salts from liver coat fat droplets 2. Lipase nad collapse from pancreas break down lipids and fatty acids in micelles 3. Monoglycerides and fatty acids enter cells by diffusion; cholesterol transported 4. Fats recombine with cholesterol, proteins to form chylomicrons 5. Chylomicrons go to lacteal, transported to lymphatic system
95
Emulsions vs Micelles
Emulsions are bigger, micelles smaller (in micelles hydrophobic tails should be touching)
96
Why do chylomicrons travel through lymph system?
Huge! Can't actually make it through the capillaries of hepatic portal system Need to go to fenestrated capillaries where openings are more porous to enter the body
97
Enzymes that break down carbohydrates
1. Amylase (in mouth, intestines) 2. Sucrase, maltase, lactase Found on brush border
98
Mechanism by which carbs are absorbed in SI
Glucose / galactose enter via SGLT, exit via GLUT2 Active transport in, facilitated diffusion out Fructose enters via GLUT5, exits via GLUT2 Diffusion in, diffusion out Fructose is source of energy for epithelial cells!
99
Protein Digestion Enzymes
Proteases, peptidases Peptidases made in ACTIVE form because no naturally occurring peptides in the cell
100
Endopeptidase
digests internal peptide bonds | e.g. pepsin, trypsin
101
Exopeptidase
digest terminal peptide bond to release individual amino acids e.g. carboxy- or aminopeptidase
102
Methods of transporting amino acids
1. secondary active transport Di/tri-peptides cotransported with H+ on PepT1 Amino acids cotransported with Na+ 2. transcytosis
103
Divalent Cations absorbed in SI
Iron, calcium
104
Iron Absorption SI
1. Heme transported in, separated into porphyrin and Fe2+ 2. Fe2+ cotransported with H+ by DMT1 3. Ferroportin moves Fe2+ into ECF
105
Calcium Absorption SI
1. Paracellular absorption into ECF 2. Ca2+ channel allow Ca2+ into cell 3. Transcellular transport regulated by Vitamin D3: some pumped out, some exchanged with Na+
106
Absorption of ions and water in SI
1. Na+ enters cells by multiple paths (cotransported, channels, H+ pumps) 2. Na+/K+ ATPase pumps Na+ out of cell again 3. Water and K+ move via paracellular pathway into ECF
107
Alexis St Martin
Man with exposed stomach that never became infected Beaumont performed experiments to time digestion of different substances Gastric juice observed to coagulate egg white (denaturing), heal sores (antimicrobial), react with alkali (acidic)
108
Is digestion always on?
No! Need food intake to turn digestion on
109
Chyme moving into duodenum triggers...
1. Enzyme and bicarb secretion 2. Feed back to slow gastric digestion and emptying 3. Feed forward to start insulin secretion
110
Food moving into stomach triggers...
1. Acid secretion 2. Pepsin and lipase secretion 3. Gastric motility
111
Carbohydrates in SI signal for...
GIP, GLP-1 These signal for insulin
112
Fats, proteins in SI signal for...
CCK Stimulates pancreatic enzyme secretion
113
Acid signals for...
Secretin Signals for bicarb
114
CCK
Stimulated by fats, proteins Targets gallbladder, pancreas, stomach Stimulates gallbladder contraction, pancreatic enzyme secretion, opening of sphincter of odd Inhibits gastric emptying and acid secretion: so FATS = satiety! stomach is fuller for longer!
115
Why is the liver so special??
Second largest organ in the body Manufactures essential proteins for osmotic pressure in blood, transport proteins, blood clotting factors, and detoxifies blood, regulates vitamins Diseases caused by hepatitis, build up of fats

Intro Bio II Exam 3 (8 decks)

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