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Intro Bio II Exam 3 > Digestion > Flashcards

Digestion Flashcards

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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
Q

Fluid input into digestive system

A

Ingestion (2 L)
Secretion (7 L)

Secretion includes saliva, bile, gastric secretions, pancreatic secretions, and intestinal secretions

Gastric secretions account for the most

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26
Q

Fluid output from digestive tract

A

Absorption (8.9 L)
Excretion in feces (0.1 L)

Most water absorption occurs in small intestine

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27
Q

which muscle is found in digestive tract

A

smooth muscle

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28
Q

what drives depolarization of smooth muscle in GI tract?

A

gastric pacemaker cells creating slow wave potentials that sum when they exceed threshold

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29
Q

smooth muscle in GI tract connected by…

A

gap junctions! single-unit smooth muscle

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30
Q

Definition of slow waves

A

Force and duration of muscle contraction directly related to amplitude and frequency of action potentials

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31
Q

Cephalic Phase Reflex

A

Seeing and smelling food leads to saliva secretion and gastric contraction. Stimulation of neurons in medulla oblongata leads to autonomic signaling to digestive system.

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32
Q

Gastric phase reflex

A

Begins when food arrives in stomach. Stretching of stomach and presence of peptides / amino acids starts short reflexes.

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33
Q

Pathway of Cephalic Reflex

A

Aka LONG vagal reflex:
Mouth –> Brain / medulla oblongata –> pre ganglionic vagus nerve neuron –> enteric plexus –> post ganglionic parasympathetic neurons –> target cells

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34
Q

Pathway of gastric phase reflex

A

Aka SHORT vagal reflex:

Peptides in stomach –> enteric plexus –> post-ganglionic parasympathetic neurons –> target cells

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35
Q

Peristaltic Contractions

A

Responsible for forward movement

Sequential contractions in different places at different times (time lag)

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36
Q

Segmental Contractions

A

Responsible for mixing

Squeezing different segments at the same time (little / no forward movement)

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37
Q

Key anatomical features of the stomach

A

Surface foldings, gastric glands, circular and longitudinal muscle, ample blood supply

Lymph system is NOT present in epithelium

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38
Q

Key functional unit of the stomach

A

Gastric mucosa

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39
Q

Cell types in the gastric mucosa

A

Mucous surface cell, mucous neck cell, parietal cell, enterochromaflin-like cell, chief cells, D cells, G cells

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40
Q

Mucous surface cell

A

Secretes: Mucous
Why: physical barrier between lumen and epithelium
Stimulated by: tonic secretion, irritation of mucosa

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41
Q

Mucous neck cell

A

Secretes: Bicarbonate
Why: buffers gastric acid
Stimulated by: Secreted with mucous

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42
Q

Parietal Cell

A

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

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43
Q

Enterochromaflin-like cell

A

Secretes: Histamine
Why: stimulates gastric acid secretion
Stimulated by: Ach, gastrin

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44
Q

Chief cells

A

Secretes: Pepsin(ogen)
Why: Digest proteins
Stimulated by: Ach, acid

Secretes: Gastric lipase
Why: Digests fat
Stimulated by: Ach, acid

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45
Q

D cells

A

Secretes: Somatostatin
Why: inhibits gastric acid
Stimulated by: acid

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46
Q

G cells

A

Secretes: Gastrin
Why: stimulates acid secretion
Stimulated by: Ach, peptides, amino acids

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47
Q

How do cells survive low pH of stomach

A

mucous-bicarbonate barrier

48
Q

creation of mucous bicarbonate barrier

A

Gastric mucous cells secrete droplets of mucous and bicarbonate, so that there is a bicarbonate mucous layer between cells and gastric juice

49
Q

Activation of pepsin

A
  1. HCl secreted from parietal cells activates pepsinogen secreted from chief cells
  2. Already-activated pepsin activates pepsinogen
50
Q

When are proteases activated?

A

After translation

This way they do not cleave proteins within our cells (destructive!)

51
Q

Formation of pH difference in stomach

A
  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
Q

Important stomach enzymes

A 
Pepsin (major)
Gastric lipase (minor)
53
Q

Pepsinogen

A

Inactive form of pepsin protease

54
Q

How is HCl production regulated?

A

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
Q

Omeprazole

A

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
Q

What causes ulcers?

A

H. pylori infection
NOT ACID!

Proven by Marshall and Warren; cured with antibiotics

57
Q

Koch’s Postulates

A

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
Q

Hepatic Portal System

A

Blood leaving digestive tract (stomach, intestines, pancreas, spleen) travels to liver for detoxification

This is technically VENOUS blood : deoxygenated

59
Q

Blood inputs to liver

A
  1. From hepatic portal system (venous blood, deoxygenated)

2. From hepatic artery (arterial blood, oxygenated)

60
Q

Brush border

A

The microvilli of the SI : creates a hairy border between cells (apical membrane) and lumen

61
Q

What is absorbed in SI?

A

Monosaccharides
Amino acids, small peptides
Triglycerides, glycerol
Ions

62
Q

Cells of the SI

A 
Enterocytes - absorb nutrients, ions 
goblet cells - secrete mucous 
stem cells - replaced damaged cells 
crypt cells - secrete ions and water 
endocrine cells - secrete hormones
63
Q

Lacteal

A

Vessel of lymph system that projects into villi of SI, transports most fats to the lymph

64
Q

Denaturing of Proteins

A

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
Q

What is secreted in SI?

A

Water, ions

BICARBONATE!

66
Q

Endocrine Pancreas

A

Blood glucose homeostasis

Glucagon, insulin

67
Q

Exocrine Pancreas

A

Digestion

Pancreatic enzymes, bicarbonate

68
Q

Pancreatic Islet Cells

A

Secrete hormones (glucagon, insulin) into capillaries

69
Q

Pancreatic acini cels

A

Secrete digestive enzymes into lumen of pancreatic duct

70
Q

Duct cells of pancreas

A

Secrete NaHCO3 into lumen of pancreatic duct

71
Q

Zymogens

A

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
Q

Trypsinogen

A

Inactive form of the pancreatic zymogen that activates other zymogens

73
Q

Trypsin

A

Activated zymogen that activates digestive enzymes

74
Q

Enteropeptidase

A

Enzyme in brush border that activates trypsinogen to trypsin

75
Q

Pathway and activation of zymogens

A
  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
Q

What is the only pancreatic enzyme NOT secreted as a zymogen?

A

Amylase

We do not have starch in our cells!

77
Q

Isotonic Saline

A

mixes with mucous and lubricates the SI to increase motility

78
Q

Secretion of isotonic saline (step-by-step)

A
  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
Q

What secretes bicarbonate in the gut

A

Pancreas, duodenum

80
Q

Secretion of bicarb in gut (step by step)

A
  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
Q

Chyme

A

Acidic mixture of food and secretions in the stomach that is then squeezed through pyloric sphincter into duodenum of SI

82
Q

What if pH in the duodenum is too low?

A

Cells damaged, ulcer

83
Q

Where does bulk of digestion and absorption take place?

A

Duodenum of SI

84
Q

Gallbladder

A

Stores bile

85
Q

What produces bile?

A

Liver

86
Q

Common Hepatic Duct

A

Transports bile from liver to gallbladder

87
Q

Common Bile Duct

A

Take bile from gallbladder to lumen of small intestine

88
Q

Sphincter of Oddi

A

Sphincter that seals off the common bile duct and pancreatic duct, opening allows for bile salt / pancreatic enzyme secretion into duodenum

89
Q

Bile salts

A

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
Q

Bile acids

A

Made from cholesterol

If add amino acid, become bile salt

91
Q

Bile

A

Bile salt, bile pigments, cholesterol

Bile salts are recycled, pigments and cholesterol excreted

92
Q

Micelles from Bile Salts

A

Small disks with bile salts, phospholipids, fatty acids, cholesterol, and mono- and di-glycerides

93
Q

Lipase and Colipase

A

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
Q

Role of Bile Salts in Digestion (step by step)

A
  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
Q

Emulsions vs Micelles

A

Emulsions are bigger, micelles smaller (in micelles hydrophobic tails should be touching)

96
Q

Why do chylomicrons travel through lymph system?

A

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
Q

Enzymes that break down carbohydrates

A
  1. Amylase (in mouth, intestines)
  2. Sucrase, maltase, lactase
    Found on brush border
98
Q

Mechanism by which carbs are absorbed in SI

A

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
Q

Protein Digestion Enzymes

A

Proteases, peptidases

Peptidases made in ACTIVE form because no naturally occurring peptides in the cell

100
Q

Endopeptidase

A

digests internal peptide bonds

e.g. pepsin, trypsin

101
Q

Exopeptidase

A

digest terminal peptide bond to release individual amino acids
e.g. carboxy- or aminopeptidase

102
Q

Methods of transporting amino acids

A
  1. secondary active transport
    Di/tri-peptides cotransported with H+ on PepT1
    Amino acids cotransported with Na+
  2. transcytosis
103
Q

Divalent Cations absorbed in SI

A

Iron, calcium

104
Q

Iron Absorption SI

A
  1. Heme transported in, separated into porphyrin and Fe2+
  2. Fe2+ cotransported with H+ by DMT1
  3. Ferroportin moves Fe2+ into ECF
105
Q

Calcium Absorption SI

A
  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
Q

Absorption of ions and water in SI

A
  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
Q

Alexis St Martin

A

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
Q

Is digestion always on?

A

No! Need food intake to turn digestion on

109
Q

Chyme moving into duodenum triggers…

A
  1. Enzyme and bicarb secretion
  2. Feed back to slow gastric digestion and emptying
  3. Feed forward to start insulin secretion
110
Q

Food moving into stomach triggers…

A
  1. Acid secretion
  2. Pepsin and lipase secretion
  3. Gastric motility
111
Q

Carbohydrates in SI signal for…

A

GIP, GLP-1

These signal for insulin

112
Q

Fats, proteins in SI signal for…

A

CCK

Stimulates pancreatic enzyme secretion

113
Q

Acid signals for…

A

Secretin

Signals for bicarb

114
Q

CCK

A

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
Q

Why is the liver so special??

A

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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