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.
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.
3
Q
Six basic processes of digestive system
A
- Ingestion
- Secretion
- Mixing and propulsion
- Digestion (mechanical and chemical)
- Absorption
- Defection.
4
Q
Two parts of digestive system
A
Gastrointestinal (alimentary canal)
Accessory digestive organs
5
Q
Layers of the GI tract
A
- Mucosa
i. epithelium
ii. lamina propria
iii. muscularis mucosae - Submucosa
- Muscularis
- Serosa
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
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
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.
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.
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)
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
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
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.
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)
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)
16
Q
Submucosal Plexus
A
AKA Plexus of Meissner
In submucosa
Motor neuron control secretions
17
Q
Enteric Nervous System
A
Consists of:
Myenteric Plexus (muscularis)
Submucosal Plexus (submucosa)
[and subserosal - not in book]
Parasympathetic and sympathetic innervation.
18
Q
Motor neurons of ENS
A
Myenteric plexus: GI tract motility
Submucosal plexus: secretory cells of mucosal epithelium
19
Q
Interneurons of ENS
A
Interconnect Myenteric and Submucosal plexuses
20
Q
Sensory neurons of ENS
A
Supply mucosal epithelium
Contain chemo and mechanoreceptors
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
22
Q
Increased PNS:
A
Increased ENS activity –> Increased motility and secretion
23
Q
Increased SNS:
A
Decreased ENS activity –> Decreased motility and secretion
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.
25
Peritoneum
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.
26
Layers of peritoneum
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)
27
Ascites
Abnormal accumulation of serous fluid in peritoneal cavity.
Often the result of stenosis of the hepatic portal vein.
28
Retro peritoneal
Organs whose anterior surfaces only are covered by the peritoneum.
Kidneys
Ascending and descending colons.
Duodenum
Pancreas
29
5 major perintoneal folds
1. Greater omentum
2. Falciform ligament
3. Lesser omentum
4. Mesentery
5. Mesocolon
30
Greater omentum
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.
31
Falciform ligament
Attaches liver to anterior abdominal wall and diaphragm (only one to attach to anterior abdominal wall)
32
Lesser omentum
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.
33
Mesentery
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.
34
Mesocolon
Two separate peritoneal folds (transverse and sigmoid) that bind transverse colon and sigmoid colon to posterior abdominal wall.
Hold intestines loosely in place.
35
Oral cavity proper
Teeth and gums to fauces
36
Palate
Separates oral and nasal cavities.
Hard palate formed by maxilla and Palestine bone.
Soft palate separates oro- and nasopharynxes.
37
3 pairs of major salivary glands
1. Parotid
2. Submandibular
3. Sublingual
38
Parotid glands
Inferior and anterior to ears
Ducts pierce buccinator
Secretions very watery. Contain salivary amylase.
39
Submandibular glands
Floor of mouth,
Ducts open into oral cavity proper lateral to lingual frenulum
Secretes amylase and mucous cells
40
Sublingual glands
Beneath the tongue, superior to submandibular glands
Ducts open in oral cavity proper
Secrete mostly mucous and a small amount of amylase
41
Saliva: composition
99. 5% water
0. 5% solutes
Slightly acidic
42
Nervous stimulation of salivation
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)
43
What forms the floor of the oral cavity?
Tongue.
44
Lingual glands
In lamina propria of tongue.
Secretes mucous, and watery fluid that contains lingual lipase
45
Teeth
Dentes
| Accessory digestive organs located in sockets of alveolar processes of mandible and maxilla.
46
Dentin
Forms majority of tooth
Harder than bone (lots of calcium hydroxyapatite)
Covered by enamel, which is even harder.
47
Hardest substance in the body?
Enamel. Lots of hydroxyapatite.
48
Cementum
In root of tooth
Bone-like substance that attaches root to periodontal ligament.
49
Pulp cavity
Space in tooth filled with blood vessels, nerves and lymphatic vessels.
50
Salivary amylase
In saliva
Initiates breakdown of starch
(Only monosaccharides can be absorbed)
Inactivated by stomach acid
51
Lingual lipase
Secreted by lingual glands
Breaks down triglycerides into fatty acids and triglycerides.
Activated by acidic environment in stomach.
52
Three parts of pharynx
Nasopharynx (respiration only)
Oropharynx
Laryngopharynx
53
Pharynx composed of
Skeletal muscle lined by mucous membrane
54
Esophagus
Collapsible, muscular tube
Posterior to trachea
Runs from laryngopharynx, goes through diaphragm at esophageal hiatus, and ends at superior stomach.
55
Hiatal hernia
When stomach proTrudes above diaphragm, through esophageal hiatus
56
Layers of esophagus
1. Mucosa
2. Submucosa
3. Muscularis
4. Adventitia
57
Esophageal muscularis
Superior 1/3 skeletal muscle
Middle 1/3 skeletal and smooth
Inferior 1/3 smooth muscle.
58
Upper esophageal sphincter
At superior eaophagus, by laryngopharynx.
Regulates movement of food from oharynx to esophagus
Skeletal muscle.
59
Lower esophageal sphincter.
Regulates movement of food from esophagus to stomach
Smooth
60
Adventitia
Outer layer of esophagus (instead of serosa)
Areolar connective tissue; merges with CT of surrounding tissue
Not covered by mesothelium
61
Two stages of deglutition
1. Voluntary (from oral cavity into oropharynx)
2. Pharyngeal stage (involuntary)
- pharynx into esophagus
3. Esophageal stage (involuntary)
- esophagus into stomach
62
Function of the stomach
Mixing chamber
Holding reservoir for food until duodenum is ready.
Digestion of starch continues
Digestion of protein and triglycerides begins.
63
Four main regions of the stomach
1. Cardia
2. Fundus
3. Body
4. Pylorus
64
Cardia
Surrounds the opening of the esophagus into the stomach
65
Fundus (stomach)
Rounded portion superior to and left of cardia
66
Body (stomach)
Large central part of stomach, inferior to fundus
67
Pylorus
Portion of stomach that connects to duodenum.
| Composed of antrum and canal
68
Pyloric antrum
Connects to stomach
69
Pyloric canal
Connects to duodenum
70
Pyloric sphincter
Between pylorus and duodenum
71
Concave medial border of stomach
Lesser curvature
72
Convex lateral border of stomac
Greater curvature
73
Gastric glands
In mucosal layer of stomach
| Columns of secretory cells formed by epithelial cells extending into lamina propria
74
Gastric pits
Narrow channels into which the gastric glands open
| Secretions flow from glands into pits then into lumen of stomach
75
Three types of exocrine cells found in Gastric Glands
1. mucous neck cells
2. parietal cells
3. chief cells
76
Mucous neck cells
In gastric glands
With surface mucous cells (which are in gastric pits), secrete mucous
77
Parietal cells
In gastric glands
Produce intrinsic factor (B12 absorption) and hydrogen + chloride
78
Chief cells
In gastric glands
Secretes pepsinogen and gastric lipase
79
Gastric Juice
Combination of the secretions of the 3 gland cells plus the G cells.
2000--3000 ml/day
80
G Cell
Enteroendocrine cell mainly located in the pyloric antrum.
Secretes gastrin
81
Muscularis of the stomach
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
82
Serosa of the stomach
Part of visceral peritoneum
At lesser curvature extends upwards to liver to become lesser omentum
At greater curvature continues downward as greater omentum
83
Mixing waves
Gentle rippling peristaltic movements that occur once food enters stomach.
Every 15-25 seconds
84
Chyme
Macerated food mixed with gastric secretions
85
Gastric emptying
Chyme forced into duodenum by mixing waves.
| About 3 ml per wave
86
In stomach, HCL:
1. kill microbes
2. partially denature proteins
3. stimulates secretion of hormones
4. activates pepsinogen --> pepsin
87
Pepsin
Only protein digesting enzyme in stomach
Secreted by chief cells
Secreted as pepsinogen, which is activated by HCL
88
Gastric Lipase
Splits small triglycerides into fatty acids and monoglycerides
Secreted by chief cells
89
Three parts of pancreas
Head, body and tail
90
Absorption in stomach
Not much,
| Aspirin, alcohol, water, ions, short chain fatty acids, some drugs
91
Location of pancreas
Retroperintoneal
Posterior to great curvature of stomach
Head lies near curve of duodenum
92
Two connections between pancreas and duodenum
```
Pancreatic duct (duct of Wirsung)
Accessory duct (duct of Santorini)
```
93
Pancreatic Duct
Duct of Wirsung
Larger of the two pancreatic ducts
Joins common bile duct
94
Hepatopancreatic ampulla
Ampulla of Vater
Where common bile duct meets duodenum
Opens at major duodenal papilla (10 cm inferior to pyloric sphincter)
95
Sphincter of the hepatopancreatic ampulla
Sphincter of Oddi
Regulates passage from common bile duct to duodenum
96
Acini cells
Clusters of exocrine cells
Make up 99% of pancreas
Secrete pancreatic juice (mixture of fluid and digestive enzymes)
97
Pancreatic Islets
Islets of Langerhans
1% of pancreatic cells (endocrine)_
Sercrete hormones (insulin, glucagons, etc.)
98
Pancreatic Juice
1200-1500 ml produced each day
| Mostly water, salts, sodium bicarbonate, enzymes.
99
Enzymes contained in Pancreatic Juice
1. pancreatic amylase
2. trypsinogen (-->trypsin)
3. chymotrypsinogen (--> chymotrypsin)
4. procarboxypeptidase (--> carboxypeptidase)
5. proelastase (--> elastase)
6. pancreatic lipase
7. ribonuclease
8. deoxyribonuclease
100
What pancreatic enzyme digests starches?
pancreatic amylase
101
Which pancreatic enzymes digests proteins?
Trypsin
Chymotrypsin
Procarboxypeptidase
Elastase
102
Which pancreatic enzyme digest lipids?
Pancreatic lipase (main fat digesting enzyme)
103
Which pancreatic enzymes digest nucleic acids?
Ribonuclease
| Deoxyribonuclease
104
Activation of protein digesting pancreatic enzymes
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
Heaviest gland in the body
Liver
106
Location of liver
Inferior to diaphragm.
| Occupies most of right hypochondriac and part of the epigastric region
107
Location of gallbladder
Depression of posterior surface of the liver
| Typically hangs from the anterior inferior margin of the liver
108
The two lobes of the liver are divided by
The falciform ligament (fold in mesentery)
109
Ligamentum teres
Round ligament
Remnant of umbilical vein
In free border of falciform ligament
110
Coronary ligaments
Right and left
Extensions of parietal peritoneum
Suspend liver from diaphragm
111
Parts of gall bladder
Broad fundus (projects inferiorly)
Body (central portion)
Neck (tapered portion)
112
Hepatocytes
Major functional cells of the liver; makes up 80% of liver
Specialized epithelial cells with 5-12 sides
Secrete bile
113
Hepatic laminae
3D structures composed of single-layer plates of hepatocytes bordered by hepatic sinusoids
114
Hepatic sinusoids
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
Blood received by hepatic sinusoid from hepatic artery
oxygen rich, (nutrient poor?)
116
Blood received by hepatic sinusoid from hepatic portal vein
oxygen poor, nutrient rich
117
Bile Canaliculi
Small ducts between hepatocytes that collect bile
118
Route of bile
```
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
Three histological components of the liver
Hepatocytes
Bile Canaliculi
Hepatic Sinusoids
120
Portal Triad
A bile duct
A branch of the hepatic artery
A branch of the hepatic portal vein
(plus lymph vessel)
121
Three ways to categorize hepatic functional units:
1. hepatic lobule
2. portal lobule
3. hepatic acinus
122
Hepatic Lobule
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
Blood flow from liver
```
Hepatic Artery and Hepatic Portal Vein
Hepatic sinusoids
Central Veins
Hepatic Veins
Inferior Vena Cava
```
124
Portal Lobule
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
Hepatic Acinus
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
Gallbladder: mucosa
simple columnar epithelium arranged in rugae (like the stomach)
127
Which layer is missing in the walls of the gallbladder?
Submucosa
128
Gallbladder: muscularis
All smooth muscle. Function to eject bile into cystic duct
129
Outer coat of gallbladder
Visceral peritoneum
130
Function of gallbladder
Store and concentrate bile produced by liver until needed by small intesting
131
How does bile get into the gallbladder?
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
Two blood supplies for the liver
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
How much bile is secreted each day?
800-1000 mL
Production increases when portal blood has an increased concentration of bile acids
134
Composition of bile
Water, bile salts, cholesterol, lecithin (phospholipid), cholesterol, bile pigments, ions
135
Bilirubin
Principle bile pigment.
Comes from breakdown of RBC
May further break down into stercobilin (= brown poo)
136
Bile is both an:
Excretory product and a digestive secretion
137
Bile salts play a role in:
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
Functions of the Liver
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
Liver: CHO metabolism
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
Liver: Lipid metabolism
Store, breakdown lipids; synthesize cholesterol to make bile salts.
141
Liver: protein metabolism
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
Liver: drug and hormone processing
Alcohol and some drugs excreted into bile.
| Chemically alters some hormones
143
Liver: storage
Glycogen, vitamins (A, B12, D, E, K), minerals (iron and copper)
144
Liver: phagocytosis
Kupffer (stellate reticuloendothelial) cells phagocytize old RBC, WBC, bacteria
145
Regions of the small intestine
Duodenum (pyloric sphinter to jejunum; shortest) 25 cm
Jejunum (duodenum to ileum) 1 m
Ileum (jejunum to ileocecal sphincter) 2 m
146
Ileocecal Sphincter
Between ileum and large intestine
147
Most digestion and absorption occurs in:
Small intestine
148
Small intestine: epithelium
```
Simple columnar cells
Absorptive cells
Goblet cells
Intestinal glands (S/CCK/K cells)
Paneth cells
```
149
Small intestine: Lamina propria
Areolar connective tissue
| MALT (solitary lymphatic nodules, aggregated lymphatic foliicles)
150
Absorptive cells
In small intestine
| Digest and absorb nutrients from chyme
151
Intestinal glands
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
Paneth cells
In the epithelial layer of the small intestine mucosa
Secrete lysozyme; regulate microbial population
153
Lysozyme
Bacterial enzyme capable of phagocytosis.
In small intestine, secreted by Paneth cells
154
Three types of enteroendocrine cells found in the small intestine
1. S cells (secretin)
2. CCK cells (CCK)
3. K cells (glucose-dependent insulinotropic peptide GIP)
155
Duodenal Glands
AKA Brunner's Glands
Only found proximal to hepatopancreatic ampulla
Secrete alkaline mucous that neutralizes gastric acid in chyme
156
Special structural features of the small intestine
1. Circular folds
2. Villi
3. Microvilli
157
Circular folds
In small intestine
Permanent ridges in mucosa and submucosa
From proximal duodenum to mid-ileum
Enhance absorption (increase surface area, spin chyme)
158
Small intestine: villi
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
Lacteal
Lymphatic capillary
160
Microvilli in small intestine
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
Intestinal juice
1-2 litres/day
Water, mucous
Slightly alkaline
Provides liquid medium to aid in absorption
162
Brush Border Enzymes
Secreted by microvilli layer of small intestine
4 carb digesting
2 protein digesting
2 nucleotide digesting
163
Carb digesting brush border enzymes
Alpha-dextrinase
Maltase
Sucrase
Lactase
Final breakdown of carbs into monosaccharides
164
Protein digesting brush border enzymes
Peptidases (aminopeptidase and dipeptidase)
165
Nucleotide digesting enzymes of the brush border
Nucleosidase
| Phosphatases
166
Two types of mechanical digestion in the small intestine
1. segmentation
2. migrating motility complex
Both regulated by myenteric plexus
167
Segmentation
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
Migrating Motility Complex
Begins in lower portion of stomach
Regular, slow, rhythmic contractions that push chyme along intestines.
169
Chyme remains in intestines for approximately
3-5 hours
170
Digestion of Carbohydrates
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
Digestion of Proteins
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
Digestion of lipids
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
Digestion of nucleic acids
Pancreatic juice contains ribonuclease and deoxyribonuclease.
Final breakdown by brush border enzymes nucleosidases and Phosphatases
Final products absorbed by active transport.
174
How much absorption occurs in small intestine?
90%
175
How does absorption in small intestine occur?
Diffusion
Facilitated diffusion
Osmosis
Active transport
176
How are carbs absorbed in the small intestine?
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
How are most amino acids absorbed in the small intestine?
Most amino acids absorbed from lumen into epithelial villus cell via active transport.
From absorptive cells to capillaries: diffusion
178
How are all lipids absorbed into and out of the epithelial cells of the villus?
Simple diffusion
179
Where do absorbed lipids end up?
Small short chain fatty acids --> blood capillary
Long chain fatty acids and monoglycerides --> lacteals --> thoracic (lymphatic) duct --> left subclavian vein
180
Micelles
Amphipathic bile salts surround long chain fatty acids and monoglycerides (and fat soluble vitamins) in small intestine and transport them to brush border
181
Chylomicrons
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
Lipoprotein lipase
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
Absorption of electrolytes
Sources: GI secretions, ingested food and water.
Most sodium actively transported with glucose in GI tract
184
Absorption of Vitamins
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
Absorption of H2O
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
Functions of the Large Intestine
1. completion of absorption
2. production of certain vitamins
3. formation of feces
4. expulsion of feces
187
Major regions of the large intestine
Cecum
Colon
Rectum
Anal canal
188
What attaches the large intestine to the posterior abdominal wall?
Mesocolon (sigmoid and transverse)
189
Ileocecal sphincter
Regulates passage of chyme between ileum and cecum
Normally partially closed
Relaxed by gastrin
190
Cecum
Small pouch hanging inferior to the ileocecal valve
191
Vermiform appendix
"The" appendix
| Attached to the cecum
192
Divisions of the colon
Ascending
Transverse
Descending
Sigmoid
193
What parts of the large intestine are retroperitoneal?
Ascending and descending colon
194
Hepatic flexure
AKA Right colic flexure
| The corner between the ascending and transverse colon
195
Splenic flexure
AKA Left colic flexure
| The corner between the transverse and descending colon
196
Where does the sigmoid colon begin and end?
Begins near left iliac crest
Projects medially
Ends at rectum, around S3
197
Anal sphinters
Internal -- smooth
| External -- skeletal
198
Epithelium of the large intestine
Mostly absorptive and goblet cells
199
What structures are present in the small intestine epithelium, but absent in the large intestine?
Circular folds
Villi
(Microvilli present in both)
200
Tenaie coli
3 thickened bands of longitudinal muscle in the muscularis layer of the large intestine
Gather the colon into haustra
201
Haustra
Pouched sections of the large intestine caused by tone of the tenaie coli
202
Omental appendices
AKA epiploic appendices
Small pouches of peritoneum filled with fat, and attached to the tenaie coli
203
Gastroileal reflex
One of three extrinsic GI reflexes
| After a meal, intensifies peristalsis in ileum
204
Haustral churning
Chyme accumulates in haustra
| Haustra distends, then wall contracts and squeezes chyme to next haustra
205
Mass peristalsis
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
Gastrocolic reflex
Initiated by food in stomach; causes mass peristalsis in colon.
207
What enzymes are secreted by the large intestine?
None
208
Bacteria in large intestine
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
How long does chyme remain in the large intestine
3-10 hours
210
Defecation reflex
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
Phases of digestion
Cephalic
Gastric
Intestinal
212
Cephalic Phase
From anticipation until food reaches stomach
| Activation of Facial (VII), Glossopharyngeal (IX) and Vagus (X) nerves
213
Gastric Phase
From the moment food reaches stomach until it reaches small intestine
214
Neural regulation of gastric phase
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
Hormonal regulation of gastric phase
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
Intestinal phase
Begins once food enters small intestine
| Slows exit of chyme from stomach (preventing duodenum from becoming overloaded)
217
Neural regulation of the intestinal phase
Distension of duodenum causes enterogastric reflex
Inhibits PNS, stimulates SNS
Decreased gastric motility
Increased pyloric sphincter contraction
218
Enterogastric reflex
One of three extrinsic GI reflexes.
| Food in stomach (distension, pH) --> medulla --> decreased gastric emptying
219
CCK
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
Secretin
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
