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A&P 500 > Digestive system > Flashcards

Digestive system Flashcards

1
Q

Gastrointestinal tract

A

AKA alimentary canal
Tube from mouth to anus

Mouth, most of pharynx, esophagus, stomach, small and large intestine.

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2
Q

Accessory digestive organs

A

Mostly organs that don’t contact food.
Mostly organs that produce or store secretions.

Teeth, tongue, salivary glands, liver, gall bladder, and pancreas.

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3
Q

Six basic processes of digestive system

A
  1. Ingestion
  2. Secretion
  3. Mixing and propulsion
  4. Digestion (mechanical and chemical)
  5. Absorption
  6. Defection.
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4
Q

Two parts of digestive system

A

Gastrointestinal (alimentary canal)

Accessory digestive organs

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5
Q

Layers of the GI tract

A
  1. Mucosa
    i. epithelium
    ii. lamina propria
    iii. muscularis mucosae
  2. Submucosa
  3. Muscularis
  4. Serosa
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6
Q

Mucosa

A 
Inner (closest to lumen) lining of GI tract.
3 layers:
1. epithelium
2. lamina propria
3. muscularia mucosae
  • in esophagus, near stomach, also contains mucous glands
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7
Q

Cell types of the Epithelium (mucosa)

A

Mouth, pharynx, esophagus, anal cavity: Nonkeratinized stratified squamous epithelium ( for protection)

Stomach and intestines: simple columnar epithelium (secretion and absorption), connected by tight junctions, mixed in with exocrine and enteroendocrine cells

Replaced every 5-7 days

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8
Q

Enteroendocrine cells

A

In the epithelial layer of the mucosa.
Exocrine cells located among epithelial cells that hormones
Enteroendocrine cells of the intestine the most numerous endocrine cells of the body.

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9
Q

Lamina propria

A

Middle layer of the mucosa

Areolar connective tissue
Contains lymphatic and blood vessels (through which absorbed nutrients reach the rest of the body).
Also contains the majority of MALT cells.

Connects epithelial and muscularis layers.

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10
Q

MALT

A

Mucosa-associated lymphatic tissue
Lymph nodules contain immune cells
Present mostly in lamina propria, along entire GI tract (especially tonsils, small intestine, appendix and large intestine)

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11
Q

Muscularis mucosae

A

Outermost (furthest from lumen) layer of mucosa.
Thin layer of smooth muscle fibres.

Create folds in stomach and small intestine to increase surface area for digestion and absorption

Movements ensure all absorptive cells fully exposed to contents of GI tract

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12
Q

Submucosa

A

Second layer of the GI tract (when moving away from lumen)

Areolar connective tissue that binds mucosa to musclaris
Contains many lymphatic and blood vessels that receive absorbed food

Also contains Submucosal Plexus

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13
Q

Muscularis

A

Third layer of GI tracts (from lumen).

Mouth, pharynx and superior and middle esophagus, and external anal sphincter: skeletal muscle

Remaining GI tract: smooth muscle in two sheets (inner sheet of circular fibres, and outer sheet of longitudinal fibres)

In between these two sheets is the myenteric plexus.

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14
Q

Serosa

A

Outermost (furthest from lumen) layer
In sections of GI tract suspended in abdominal cavity

AKA visceral peritoneum

Not present in esophagus (which has adventitia instead)

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15
Q

Myenteric Plexus

A

AKA Plexus of auerbach
Located between longitudinal and circular layers in smooth muscle sections of the muscularis

Mostly controls motility (specifically frequency and strength of muscular contraction)

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16
Q

Submucosal Plexus

A

AKA Plexus of Meissner

In submucosa

Motor neuron control secretions

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17
Q

Enteric Nervous System

A

Consists of:
Myenteric Plexus (muscularis)
Submucosal Plexus (submucosa)
[and subserosal - not in book]

Parasympathetic and sympathetic innervation.

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18
Q

Motor neurons of ENS

A

Myenteric plexus: GI tract motility

Submucosal plexus: secretory cells of mucosal epithelium

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19
Q

Interneurons of ENS

A

Interconnect Myenteric and Submucosal plexuses

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20
Q

Sensory neurons of ENS

A

Supply mucosal epithelium

Contain chemo and mechanoreceptors

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21
Q

ANS innervations of ENS

A

ENS nerves can function independently, but are regulated by ANS

PNS: Cranial and Sacral (lower LI only) systems
Either synapse with ENS or (maybe innervates directly)

SNS: Originate from T5-L2. Synapse with ENS

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22
Q

Increased PNS:

A

Increased ENS activity –> Increased motility and secretion

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23
Q

Increased SNS:

A

Decreased ENS activity –> Decreased motility and secretion

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24
Q

Gastrointestinal Reflex Pathways

A

Regulate GI secretion and motility in response to stimuli in the lumen.

Neurons of ENS, CNS, and ANS activate or inhibit glands or smooth muscle in response to degrees of distension.

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25
Q

Peritoneum

A

Largest serous membrane in the body
Simple squamous epithelium (mesothelium) with a layer of areolar connective tissue.

Contains folds which weave between viscera and bind organs to one another and to the walls of the abdominal cavity

Also contains VANs and lymph vessels for abdominal organs.

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26
Q

Layers of peritoneum

A

Parietal (lines wall of abdominopelvic cavity)

Peritoneal cavity (space between layers; filled with serous fluid)

Visceral layer (covers some organs in the cavity – their serosa)

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27
Q

Ascites

A

Abnormal accumulation of serous fluid in peritoneal cavity.

Often the result of stenosis of the hepatic portal vein.

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28
Q

Retro peritoneal

A

Organs whose anterior surfaces only are covered by the peritoneum.

Kidneys
Ascending and descending colons.
Duodenum
Pancreas

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29
Q

5 major perintoneal folds

A
  1. Greater omentum
  2. Falciform ligament
  3. Lesser omentum
  4. Mesentery
  5. Mesocolon
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30
Q

Greater omentum

A

Largest peritoneal fold. Apron-like

Drapes over transverse colon and small intestine.

Folds back on itself – four layers. Stomach to duodenum, then back up to transverse colon.

Contains adipose tissue.

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31
Q

Falciform ligament

A

Attaches liver to anterior abdominal wall and diaphragm (only one to attach to anterior abdominal wall)

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32
Q

Lesser omentum

A

Anterior fold in serosa of stomach and duodenum

Suspends the stomach and duodenum from liver

Contains hepatic portal vein, common hepatic artery and common bile duct.

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33
Q

Mesentery

A

Fan shaped fold of peritoneum

Extends from posterior abdominal wall; wraps around small intestine and returns (double layered)

Bonds jejunum and ileum to posterior abdominal wall.

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34
Q

Mesocolon

A

Two separate peritoneal folds (transverse and sigmoid) that bind transverse colon and sigmoid colon to posterior abdominal wall.

Hold intestines loosely in place.

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35
Q

Oral cavity proper

A

Teeth and gums to fauces

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36
Q

Palate

A

Separates oral and nasal cavities.

Hard palate formed by maxilla and Palestine bone.

Soft palate separates oro- and nasopharynxes.

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37
Q

3 pairs of major salivary glands

A
  1. Parotid
  2. Submandibular
  3. Sublingual
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38
Q

Parotid glands

A

Inferior and anterior to ears
Ducts pierce buccinator

Secretions very watery. Contain salivary amylase.

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39
Q

Submandibular glands

A

Floor of mouth,
Ducts open into oral cavity proper lateral to lingual frenulum

Secretes amylase and mucous cells

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40
Q

Sublingual glands

A

Beneath the tongue, superior to submandibular glands

Ducts open in oral cavity proper

Secrete mostly mucous and a small amount of amylase

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41
Q

Saliva: composition

A
  1. 5% water
  2. 5% solutes

Slightly acidic

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42
Q

Nervous stimulation of salivation

A

PNS promotes secretion, AND inhibits it.

Chemicals stimulate 2 salivary nuclei in brainstem (superior and inferior salivatory nuclei) which return via facial (VII) and glossopharyngeal (IX)

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43
Q

What forms the floor of the oral cavity?

A

Tongue.

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44
Q

Lingual glands

A

In lamina propria of tongue.

Secretes mucous, and watery fluid that contains lingual lipase

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45
Q

Teeth

A

Dentes

Accessory digestive organs located in sockets of alveolar processes of mandible and maxilla.

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46
Q

Dentin

A

Forms majority of tooth
Harder than bone (lots of calcium hydroxyapatite)

Covered by enamel, which is even harder.

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47
Q

Hardest substance in the body?

A

Enamel. Lots of hydroxyapatite.

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48
Q

Cementum

A

In root of tooth

Bone-like substance that attaches root to periodontal ligament.

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49
Q

Pulp cavity

A

Space in tooth filled with blood vessels, nerves and lymphatic vessels.

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50
Q

Salivary amylase

A

In saliva
Initiates breakdown of starch
(Only monosaccharides can be absorbed)

Inactivated by stomach acid

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51
Q

Lingual lipase

A

Secreted by lingual glands

Breaks down triglycerides into fatty acids and triglycerides.

Activated by acidic environment in stomach.

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52
Q

Three parts of pharynx

A

Nasopharynx (respiration only)
Oropharynx
Laryngopharynx

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53
Q

Pharynx composed of

A

Skeletal muscle lined by mucous membrane

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54
Q

Esophagus

A

Collapsible, muscular tube
Posterior to trachea

Runs from laryngopharynx, goes through diaphragm at esophageal hiatus, and ends at superior stomach.

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55
Q

Hiatal hernia

A

When stomach proTrudes above diaphragm, through esophageal hiatus

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56
Q

Layers of esophagus

A
  1. Mucosa
  2. Submucosa
  3. Muscularis
  4. Adventitia
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57
Q

Esophageal muscularis

A

Superior 1/3 skeletal muscle
Middle 1/3 skeletal and smooth
Inferior 1/3 smooth muscle.

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58
Q

Upper esophageal sphincter

A

At superior eaophagus, by laryngopharynx.

Regulates movement of food from oharynx to esophagus

Skeletal muscle.

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59
Q

Lower esophageal sphincter.

A

Regulates movement of food from esophagus to stomach

Smooth

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60
Q

Adventitia

A

Outer layer of esophagus (instead of serosa)

Areolar connective tissue; merges with CT of surrounding tissue

Not covered by mesothelium

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61
Q

Two stages of deglutition

A
  1. Voluntary (from oral cavity into oropharynx)
  2. Pharyngeal stage (involuntary)
    - pharynx into esophagus
  3. Esophageal stage (involuntary)
    - esophagus into stomach
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62
Q

Function of the stomach

A

Mixing chamber
Holding reservoir for food until duodenum is ready.

Digestion of starch continues
Digestion of protein and triglycerides begins.

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63
Q

Four main regions of the stomach

A
  1. Cardia
  2. Fundus
  3. Body
  4. Pylorus
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64
Q

Cardia

A

Surrounds the opening of the esophagus into the stomach

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65
Q

Fundus (stomach)

A

Rounded portion superior to and left of cardia

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66
Q

Body (stomach)

A

Large central part of stomach, inferior to fundus

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67
Q

Pylorus

A

Portion of stomach that connects to duodenum.

Composed of antrum and canal

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68
Q

Pyloric antrum

A

Connects to stomach

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69
Q

Pyloric canal

A

Connects to duodenum

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70
Q

Pyloric sphincter

A

Between pylorus and duodenum

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71
Q

Concave medial border of stomach

A

Lesser curvature

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72
Q

Convex lateral border of stomac

A

Greater curvature

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73
Q

Gastric glands

A

In mucosal layer of stomach

Columns of secretory cells formed by epithelial cells extending into lamina propria

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74
Q

Gastric pits

A

Narrow channels into which the gastric glands open

Secretions flow from glands into pits then into lumen of stomach

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75
Q

Three types of exocrine cells found in Gastric Glands

A
  1. mucous neck cells
  2. parietal cells
  3. chief cells
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76
Q

Mucous neck cells

A

In gastric glands

With surface mucous cells (which are in gastric pits), secrete mucous

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77
Q

Parietal cells

A

In gastric glands

Produce intrinsic factor (B12 absorption) and hydrogen + chloride

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78
Q

Chief cells

A

In gastric glands

Secretes pepsinogen and gastric lipase

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79
Q

Gastric Juice

A

Combination of the secretions of the 3 gland cells plus the G cells.

2000–3000 ml/day

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80
Q

G Cell

A

Enteroendocrine cell mainly located in the pyloric antrum.

Secretes gastrin

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81
Q

Muscularis of the stomach

A

Has three layers of smooth muscle, instead of just two.
Circular, longitudinal and oblique (gives an extra dimension of movement)
Oblique mostly in body of stomach

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82
Q

Serosa of the stomach

A

Part of visceral peritoneum

At lesser curvature extends upwards to liver to become lesser omentum

At greater curvature continues downward as greater omentum

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83
Q

Mixing waves

A

Gentle rippling peristaltic movements that occur once food enters stomach.
Every 15-25 seconds

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84
Q

Chyme

A

Macerated food mixed with gastric secretions

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85
Q

Gastric emptying

A

Chyme forced into duodenum by mixing waves.

About 3 ml per wave

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86
Q

In stomach, HCL:

A
  1. kill microbes
  2. partially denature proteins
  3. stimulates secretion of hormones
  4. activates pepsinogen –> pepsin
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87
Q

Pepsin

A

Only protein digesting enzyme in stomach
Secreted by chief cells

Secreted as pepsinogen, which is activated by HCL

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88
Q

Gastric Lipase

A

Splits small triglycerides into fatty acids and monoglycerides

Secreted by chief cells

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89
Q

Three parts of pancreas

A

Head, body and tail

90
Q

Absorption in stomach

A

Not much,

Aspirin, alcohol, water, ions, short chain fatty acids, some drugs

91
Q

Location of pancreas

A

Retroperintoneal
Posterior to great curvature of stomach
Head lies near curve of duodenum

92
Q

Two connections between pancreas and duodenum

A 
Pancreatic duct (duct of Wirsung)
Accessory duct (duct of Santorini)
93
Q

Pancreatic Duct

A

Duct of Wirsung
Larger of the two pancreatic ducts

Joins common bile duct

94
Q

Hepatopancreatic ampulla

A

Ampulla of Vater

Where common bile duct meets duodenum
Opens at major duodenal papilla (10 cm inferior to pyloric sphincter)

95
Q

Sphincter of the hepatopancreatic ampulla

A

Sphincter of Oddi

Regulates passage from common bile duct to duodenum

96
Q

Acini cells

A

Clusters of exocrine cells
Make up 99% of pancreas

Secrete pancreatic juice (mixture of fluid and digestive enzymes)

97
Q

Pancreatic Islets

A

Islets of Langerhans
1% of pancreatic cells (endocrine)_

Sercrete hormones (insulin, glucagons, etc.)

98
Q

Pancreatic Juice

A

1200-1500 ml produced each day

Mostly water, salts, sodium bicarbonate, enzymes.

99
Q

Enzymes contained in Pancreatic Juice

A
  1. pancreatic amylase
  2. trypsinogen (–>trypsin)
  3. chymotrypsinogen (–> chymotrypsin)
  4. procarboxypeptidase (–> carboxypeptidase)
  5. proelastase (–> elastase)
  6. pancreatic lipase
  7. ribonuclease
  8. deoxyribonuclease
100
Q

What pancreatic enzyme digests starches?

A

pancreatic amylase

101
Q

Which pancreatic enzymes digests proteins?

A

Trypsin
Chymotrypsin
Procarboxypeptidase
Elastase

102
Q

Which pancreatic enzyme digest lipids?

A

Pancreatic lipase (main fat digesting enzyme)

103
Q

Which pancreatic enzymes digest nucleic acids?

A

Ribonuclease

Deoxyribonuclease

104
Q

Activation of protein digesting pancreatic enzymes

A

Trypsinogen (+ trypsin inhibitor) secreted by acini
In small intestine, active by enterokinase, into trypsin

Trypsin acts on chymotrypsinogen, procarboxypeptidase, proelastase to create chymotrypsin, carboxypeptidase, and elastase.

105
Q

Heaviest gland in the body

A

Liver

106
Q

Location of liver

A

Inferior to diaphragm.

Occupies most of right hypochondriac and part of the epigastric region

107
Q

Location of gallbladder

A

Depression of posterior surface of the liver

Typically hangs from the anterior inferior margin of the liver

108
Q

The two lobes of the liver are divided by

A

The falciform ligament (fold in mesentery)

109
Q

Ligamentum teres

A

Round ligament
Remnant of umbilical vein
In free border of falciform ligament

110
Q

Coronary ligaments

A

Right and left
Extensions of parietal peritoneum
Suspend liver from diaphragm

111
Q

Parts of gall bladder

A

Broad fundus (projects inferiorly)
Body (central portion)
Neck (tapered portion)

112
Q

Hepatocytes

A

Major functional cells of the liver; makes up 80% of liver
Specialized epithelial cells with 5-12 sides
Secrete bile

113
Q

Hepatic laminae

A

3D structures composed of single-layer plates of hepatocytes bordered by hepatic sinusoids

114
Q

Hepatic sinusoids

A

In Hepatic Laminae, endothelial-lined vascular spaces which border hepatocytes
Highly permeable capillaries between rows of hepatocytes. Receive blood from hepatic artery and hepatic portal vein.
Converge and deliver blood to central vein (which flows to hepatic veins, which drain into the inferior vena cava)

115
Q

Blood received by hepatic sinusoid from hepatic artery

A

oxygen rich, (nutrient poor?)

116
Q

Blood received by hepatic sinusoid from hepatic portal vein

A

oxygen poor, nutrient rich

117
Q

Bile Canaliculi

A

Small ducts between hepatocytes that collect bile

118
Q

Route of bile

A 
Hepatocytes
Bile canaliculi
Bile ductules
Bile ducts
[exits liver] Common Hepatic Duct
[joins Cystic Duct from gall bladder}
[forms} Common Bile Duct
Joined by Pancreatic Duct (Duct of Wirstig)
Becomes Hepatopancreatic Ampulla (Ampulla of Vater)
Passes through Sphincter of Oddi
Empties into greater duodenal papillae
119
Q

Three histological components of the liver

A

Hepatocytes
Bile Canaliculi
Hepatic Sinusoids

120
Q

Portal Triad

A

A bile duct
A branch of the hepatic artery
A branch of the hepatic portal vein
(plus lymph vessel)

121
Q

Three ways to categorize hepatic functional units:

A
  1. hepatic lobule
  2. portal lobule
  3. hepatic acinus
122
Q

Hepatic Lobule

A

One model of hepatic functional units
Each unit shaped like hexagon
Central vein surrounded by rows of hepatocytes and hepatic sinusoids
Three of six corners contain portal triad

Model works well with pigs, but not so much with people

123
Q

Blood flow from liver

A 
Hepatic Artery and Hepatic Portal Vein
Hepatic sinusoids
Central Veins
Hepatic Veins
Inferior Vena Cava
124
Q

Portal Lobule

A

One model of hepatic functional units
Emphasized exocrine (bile producing) function
Triangle connecting central veins, with Portal Triad in the middle.
Contains portions of three hepatic lobules

Not hugely popular

125
Q

Hepatic Acinus

A

Preferred model of hepatic functional units. Smallest structural and functional unity of the liver.

Oval stretching between two central veins; one long side bisected by a portal triad.
Contains portions of two neighbouring hepatic lobules

Three zones of hepatocytes, determined by proximity to branches of portal triad

126
Q

Gallbladder: mucosa

A

simple columnar epithelium arranged in rugae (like the stomach)

127
Q

Which layer is missing in the walls of the gallbladder?

A

Submucosa

128
Q

Gallbladder: muscularis

A

All smooth muscle. Function to eject bile into cystic duct

129
Q

Outer coat of gallbladder

A

Visceral peritoneum

130
Q

Function of gallbladder

A

Store and concentrate bile produced by liver until needed by small intesting

131
Q

How does bile get into the gallbladder?

A

When Sphincter of Oddi (between common bile duct and major duodenal papilla) contracts, the bile that is secreted from the liver travels up the cystic duct to be stored in the gallbladder.

132
Q

Two blood supplies for the liver

A

Hepatic artery
Hepatic portal vein

At hepatic sinusoids, oxygen, nutrients, drugs, microbes and toxins received from both sources.

Products made by hepatocytes and nutrients needed by other cells secreted back into blood

133
Q

How much bile is secreted each day?

A

800-1000 mL

Production increases when portal blood has an increased concentration of bile acids

134
Q

Composition of bile

A

Water, bile salts, cholesterol, lecithin (phospholipid), cholesterol, bile pigments, ions

135
Q

Bilirubin

A

Principle bile pigment.
Comes from breakdown of RBC
May further break down into stercobilin (= brown poo)

136
Q

Bile is both an:

A

Excretory product and a digestive secretion

137
Q

Bile salts play a role in:

A

Emulsification (breakdown of large lipid globules into a suspension of small ones, which makes the work of pancreatic lipase much more efficient)

Also help absorption of lipids following digestion

138
Q

Functions of the Liver

A
  1. Carbohydrate metabolism
  2. Lipid metabolism
  3. Protein metabolism
  4. Processing of drugs and hormones
  5. Excretion of bilirubin
  6. Synthesis of bile salts
  7. Storage
  8. Phagocytosis
  9. Activation of Vitamin D.
139
Q

Liver: CHO metabolism

A

When glucose is low, breaks down glycogen to release more. Can also convert certain amino acids and lactic acid into glucose

In times o’ plenty, stores excess glucose as glycogen and triglycerides.

140
Q

Liver: Lipid metabolism

A

Store, breakdown lipids; synthesize cholesterol to make bile salts.

141
Q

Liver: protein metabolism

A

Deaminate amino acids (remove amino group – NH2).
Amino acids used for ATP or converted to carbs or fats.
Remaining NH3 (toxic ammonia) converted to nicer form and excreted in urine

142
Q

Liver: drug and hormone processing

A

Alcohol and some drugs excreted into bile.

Chemically alters some hormones

143
Q

Liver: storage

A

Glycogen, vitamins (A, B12, D, E, K), minerals (iron and copper)

144
Q

Liver: phagocytosis

A

Kupffer (stellate reticuloendothelial) cells phagocytize old RBC, WBC, bacteria

145
Q

Regions of the small intestine

A

Duodenum (pyloric sphinter to jejunum; shortest) 25 cm
Jejunum (duodenum to ileum) 1 m
Ileum (jejunum to ileocecal sphincter) 2 m

146
Q

Ileocecal Sphincter

A

Between ileum and large intestine

147
Q

Most digestion and absorption occurs in:

A

Small intestine

148
Q

Small intestine: epithelium

A 
Simple columnar cells
Absorptive cells
Goblet cells
Intestinal glands (S/CCK/K cells)
Paneth cells
149
Q

Small intestine: Lamina propria

A

Areolar connective tissue

MALT (solitary lymphatic nodules, aggregated lymphatic foliicles)

150
Q

Absorptive cells

A

In small intestine

Digest and absorb nutrients from chyme

151
Q

Intestinal glands

A

Cells lining deep crevasses in the mucosa of the small intestine
AKA crypts of Lieberkuhn

Secrete intestinal juice

Include absorptive, Paneth, enteroendocrine and goblet cells

152
Q

Paneth cells

A

In the epithelial layer of the small intestine mucosa

Secrete lysozyme; regulate microbial population

153
Q

Lysozyme

A

Bacterial enzyme capable of phagocytosis.

In small intestine, secreted by Paneth cells

154
Q

Three types of enteroendocrine cells found in the small intestine

A
  1. S cells (secretin)
  2. CCK cells (CCK)
  3. K cells (glucose-dependent insulinotropic peptide GIP)
155
Q

Duodenal Glands

A

AKA Brunner’s Glands
Only found proximal to hepatopancreatic ampulla

Secrete alkaline mucous that neutralizes gastric acid in chyme

156
Q

Special structural features of the small intestine

A
  1. Circular folds
  2. Villi
  3. Microvilli
157
Q

Circular folds

A

In small intestine
Permanent ridges in mucosa and submucosa

From proximal duodenum to mid-ileum

Enhance absorption (increase surface area, spin chyme)

158
Q

Small intestine: villi

A

Finger like projections of mucosa
.5-1 mm
Each on covered by epithelium, and with a core containing an arteriole, a blood capillary network, and a lacteal

Increases surface area for absorption and digestion.

Gives velvety appearance to mucosa

159
Q

Lacteal

A

Lymphatic capillary

160
Q

Microvilli in small intestine

A

Projections of apical membrane of absorptive cells

Too small to be seen individually by microscope. Appear as fuzzy Brush Border

Increase surface area, contains brush border enzymes

161
Q

Intestinal juice

A

1-2 litres/day
Water, mucous
Slightly alkaline
Provides liquid medium to aid in absorption

162
Q

Brush Border Enzymes

A

Secreted by microvilli layer of small intestine

4 carb digesting
2 protein digesting
2 nucleotide digesting

163
Q

Carb digesting brush border enzymes

A

Alpha-dextrinase
Maltase
Sucrase
Lactase

Final breakdown of carbs into monosaccharides

164
Q

Protein digesting brush border enzymes

A

Peptidases (aminopeptidase and dipeptidase)

165
Q

Nucleotide digesting enzymes of the brush border

A

Nucleosidase

Phosphatases

166
Q

Two types of mechanical digestion in the small intestine

A
  1. segmentation
  2. migrating motility complex

Both regulated by myenteric plexus

167
Q

Segmentation

A

Localized, mixing contractions that occur in portions of intestine distended by large volumes of chyme

More frequently in duodenum; slows by ileum.

Chyme sloshed back a forth until most of the chyme absorbed.

168
Q

Migrating Motility Complex

A

Begins in lower portion of stomach

Regular, slow, rhythmic contractions that push chyme along intestines.

169
Q

Chyme remains in intestines for approximately

A

3-5 hours

170
Q

Digestion of Carbohydrates

A

Starts in mouth: salivary amylase
Salivary amylase deactivated by stomach acids
In small intestines, pancreatic amylase joins party, acting on glycogen and starches, splitting them into smaller fragments.
Alpha-dextrinase breaks down alpha-dextrins further
The other brush border enzymes reduce everything into monosaccharides, which the digestive system can absorb

sucrose –(sucrase)–> glucose and fructose
lactose –(lactase)–>glucose and galactose
maltose/maltotriose –(maltase)–> glucose

171
Q

Digestion of Proteins

A

Starts in stomach with pepsin

Pancreatic enzymes continue the process (trypsin, chymotrypsin, carboxypeptidase, elastase) continue to break proteins into peptides

Process completed by brush border enzymes, amniopeptidase (cleaves amino acids at amino end of peptide) and dipeptidase (spites dipeptides into single amino acids)

about half digested amino acids bio-recycling

172
Q

Digestion of lipids

A

Starts in stomach (lingual and gastric lipase)
Most occurs in small intestine because of pancreatic lipase, which breaks fats into glycerol and fatty acids.

Bile salts emulsify large lipid globules, breaking them into small globules

173
Q

Digestion of nucleic acids

A

Pancreatic juice contains ribonuclease and deoxyribonuclease.

Final breakdown by brush border enzymes nucleosidases and Phosphatases

Final products absorbed by active transport.

174
Q

How much absorption occurs in small intestine?

A

90%

175
Q

How does absorption in small intestine occur?

A

Diffusion
Facilitated diffusion
Osmosis
Active transport

176
Q

How are carbs absorbed in the small intestine?

A

From lumen through apical membrane of villus:
Facilitated diffusion: fructose
(Secondary) active transport: glucose and galactose (glucose coupled with sodium)

All monosaccharides move from absorptive cells to capillaries via facilitated diffusion.

177
Q

How are most amino acids absorbed in the small intestine?

A

Most amino acids absorbed from lumen into epithelial villus cell via active transport.
From absorptive cells to capillaries: diffusion

178
Q

How are all lipids absorbed into and out of the epithelial cells of the villus?

A

Simple diffusion

179
Q

Where do absorbed lipids end up?

A

Small short chain fatty acids –> blood capillary

Long chain fatty acids and monoglycerides –> lacteals –> thoracic (lymphatic) duct –> left subclavian vein

180
Q

Micelles

A

Amphipathic bile salts surround long chain fatty acids and monoglycerides (and fat soluble vitamins) in small intestine and transport them to brush border

181
Q

Chylomicrons

A

Protein-coated triglycerides formed by long chain fatty acids and monoglycerides once they enter the absorptive cell.

Exocytose into lacteals because they are too large for regular capillary pores. Join thoracic duct and drain into blood stream at left subclavian vein

Disappear within 2-3 hours of eating.

182
Q

Lipoprotein lipase

A

Enzyme attached to apical surface of capillary endothelial cells. Break down triglycerides in chylomicrons into fatty acids and glycerol, which are absorbed in hepatic and adipose cells.

183
Q

Absorption of electrolytes

A

Sources: GI secretions, ingested food and water.

Most sodium actively transported with glucose in GI tract

184
Q

Absorption of Vitamins

A

Fat soluble vitamins (ADEK) transported by micelles and absorbed via simple diffusion

Most water soluble vitamins absorbed via simple diffusion

B12 combines with intrinsic factor in stomach and absorbed in ileum

185
Q

Absorption of H2O

A

Roughly 9.3L enters small intestine, and all but one litre is absorbed before getting to the large intestine.

Osmosis from lumen into absorptive cells and into the capillaries

(of the remaining 1 litre, .9 is absorbed in large intestine)

186
Q

Functions of the Large Intestine

A
  1. completion of absorption
  2. production of certain vitamins
  3. formation of feces
  4. expulsion of feces
187
Q

Major regions of the large intestine

A

Cecum
Colon
Rectum
Anal canal

188
Q

What attaches the large intestine to the posterior abdominal wall?

A

Mesocolon (sigmoid and transverse)

189
Q

Ileocecal sphincter

A

Regulates passage of chyme between ileum and cecum
Normally partially closed
Relaxed by gastrin

190
Q

Cecum

A

Small pouch hanging inferior to the ileocecal valve

191
Q

Vermiform appendix

A

“The” appendix

Attached to the cecum

192
Q

Divisions of the colon

A

Ascending
Transverse
Descending
Sigmoid

193
Q

What parts of the large intestine are retroperitoneal?

A

Ascending and descending colon

194
Q

Hepatic flexure

A

AKA Right colic flexure

The corner between the ascending and transverse colon

195
Q

Splenic flexure

A

AKA Left colic flexure

The corner between the transverse and descending colon

196
Q

Where does the sigmoid colon begin and end?

A

Begins near left iliac crest
Projects medially
Ends at rectum, around S3

197
Q

Anal sphinters

A

Internal – smooth

External – skeletal

198
Q

Epithelium of the large intestine

A

Mostly absorptive and goblet cells

199
Q

What structures are present in the small intestine epithelium, but absent in the large intestine?

A

Circular folds
Villi
(Microvilli present in both)

200
Q

Tenaie coli

A

3 thickened bands of longitudinal muscle in the muscularis layer of the large intestine

Gather the colon into haustra

201
Q

Haustra

A

Pouched sections of the large intestine caused by tone of the tenaie coli

202
Q

Omental appendices

A

AKA epiploic appendices

Small pouches of peritoneum filled with fat, and attached to the tenaie coli

203
Q

Gastroileal reflex

A

One of three extrinsic GI reflexes

After a meal, intensifies peristalsis in ileum

204
Q

Haustral churning

A

Chyme accumulates in haustra

Haustra distends, then wall contracts and squeezes chyme to next haustra

205
Q

Mass peristalsis

A

Strong peristaltic waves that begin in the middle of the transverse colon and drives contents into rectum.
Initiated by gastrocolic reflex

Occurs 3-4 x day

206
Q

Gastrocolic reflex

A

Initiated by food in stomach; causes mass peristalsis in colon.

207
Q

What enzymes are secreted by the large intestine?

A

None

208
Q

Bacteria in large intestine

A

Ferment carbs (releasing H, CO2, methane)
Convert remaining proteins to amino acids, and which are broken down further (and then excreted or sent to liver)
Convert bilirubin to sterocobilin
Produce Vitamin K and B6

209
Q

How long does chyme remain in the large intestine

A

3-10 hours

210
Q

Defecation reflex

A

Initiated by distension of the rectum
Sensory signal to sacral spinal cord
Motor signal back to colon, rectum and anus
Contraction of longitudinal muscles shortens intestine

211
Q

Phases of digestion

A

Cephalic
Gastric
Intestinal

212
Q

Cephalic Phase

A

From anticipation until food reaches stomach

Activation of Facial (VII), Glossopharyngeal (IX) and Vagus (X) nerves

213
Q

Gastric Phase

A

From the moment food reaches stomach until it reaches small intestine

214
Q

Neural regulation of gastric phase

A

Distension and increasing pH –>
Submucosal plexus activates parasympathetic and enteric nervous systems –>
peristalsis and flow of gastric juice –>
Food exits stomach, distension and pH drop –>
NEGATIVE FEEDBACK no more gastric juices

215
Q

Hormonal regulation of gastric phase

A

G cells release Gastrin (response to distension, presence of proteins, high pH, and caffeine and ACh in chyme)

Gastrin:

  • stimulates glands to secrete gastric juice
  • strengthens contraction of lower esophageal sphincter
  • increases motility of the stomach
  • relaxes pyloric and ileocecal sphincter
216
Q

Intestinal phase

A

Begins once food enters small intestine

Slows exit of chyme from stomach (preventing duodenum from becoming overloaded)

217
Q

Neural regulation of the intestinal phase

A

Distension of duodenum causes enterogastric reflex
Inhibits PNS, stimulates SNS
Decreased gastric motility
Increased pyloric sphincter contraction

218
Q

Enterogastric reflex

A

One of three extrinsic GI reflexes.

Food in stomach (distension, pH) –> medulla –> decreased gastric emptying

219
Q

CCK

A

Cholecystokinin
Secreted by CCK cells in small intestine
- Stimulates secretion of pancreatic juice
- causes contraction of gallbladder to release bile
- causes relaxation of the Sphincter of Oddi to allow more pancreatic juice and bile into duodenum
- slows gastric emptying

220
Q

Secretin

A

Secreted by S cells in small intestine in response to acidic chyme entering duodenum

  • stimulates release of bicarbonate-rich pancreatic juice
  • inhibits secretion of gastric juice (decreases pH)
  • promotes normal growth and maintenance of pancreas
  • enhances effects of CCK

A&P 500 (3 decks)

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