Small Intestine Anatomy & Physiology (Week 11) Flashcards
1
Q
What are the three regions of the small intestine?
A
1) duodenum
2) jejunum
3) ileum
2
Q
shortest and widest part of the small intestine, C-shaped, and closely associated with the head of the pancreas
A
duodenum
3
Q
length of duodenum
A
~ 25cm
4
Q
length of jejunum
A
~ 1m
5
Q
length of ileum
A
~ 2m
6
Q
True or False: The vast majority of the duodenum is retroperitoneal (behind the peritoneum)
A
True
7
Q
The jejunum has larger circular folds called ______________
A
plicae circulares
8
Q
The ileum has many large lymphoid nodules called ________________
A
Peyer’s patches
9
Q
The first 2/3 of the duodenum is supplied by the ___________ artery off the celiac trunk
A
hepatic
10
Q
The hepatic artery branches into the __________ and __________
A
gastroduodenal artery,
anterior superior pancreaticoduodenal artery
11
Q
The superior mesenteric artery (SMA) branches into the _____________
A
inferior pancreaticoduodenal artery
12
Q
The pancreas and duodenum receive arterial blood from both the ________ and _________
A
hepatic artery,
superor mesenteric artery (SMA)
Note: “from the top it’s from the hepatic artery and from the bottom it’s from the mesenteric artery”
13
Q
The last 1/3 of the duodenum to the ileum + first part of the large intestine up until the transverse/descending colon receives arterial blood from the ________________
A
superior mesenteric artery
14
Q
The superior mesenteric vein receives venous blood from?
A
- small intestine
- portions of the large intestine
- stomach
- pancreas
15
Q
The splenic vein receives blood from?
A
- stomach
- spleen
- pancreas
- distal large intestine
16
Q
The superior mesenteric vein and splenic vein join together to form the _____________, which drains almost all subdiaphragmatic fore-, mid-, and hindgut structures
A
hepatic portein vein
17
Q
The hepatic portal vein drains into the __________
A
liver
18
Q
Folds of mucosa and submucosa, characterized by permanent ridges about 10 mm tall that project into the lumen, encourages mixing, and enhances absorption by increasing surface area
A
plica circulares
19
Q
Finger-like projections of mucosa that are 0.5-1mm long and vastly increase surface area of epithelium
A
villi
20
Q
projections of apical membrane of absorptive cell that are 1 um long (super small), cylindrical, contain 20-30 actin filaments, and greatly increase surface area
A
microvilli
21
Q
What type of cell of the small intestine can be characterized as simple columnar epithelium with microvilli and a short life span (~ a few days)?
A
surface absorptive cell/enterocytes
22
Q
What type of cell of the small intestine can be characterized as:
- scattered among the absorptive cells
- specialized in mucus secretion
- facilitates passage of material through bowel
A
goblet cell
23
Q
What type of cell of the small intestine can be characterized as:
- typical serous-secretory appearance, with basophilic basal cytoplasm and apical secretory vesicles
- basal portion of the intestinal crypts, below the stem cells, release lyzosyme, phospholipase A2, and defensins (note: these are all immunoproteins)
- regulate the microenvironment of the intestinal crypts and innate immune response
A
paneth cell
24
Q
What type of cells in the small intestine secrete hormones?
A
1) enteroendocrine cells
2) mucosal cells
25
What do the following enteroendocrine cells in the small intestine secrete?
I cells:
S cells:
D cells:
K cells:
L cells:
Mo cells:
I cells: cholecystokinin
S cells: secretin
D cells: somatostatin
K cells: GIP
L cells: peptide YY, incretins
Mo cells: motilin
26
What do mucosal cells in the small intestine secrete
incretins (similar to L cells)
27
What is the main hormonal function of somatostatin?
Review: somatostatin is released by D cells
"turns down" the release of hormones from nearby cells
28
What is the main hormonal function of histamine?
If released from ECL --> stimulates acid secretion
If released from EC --> increased motility
29
What is the main hormonal function of gastrin?
Review: gastrin is secreted by G cells in the stomach (not small intestine)
increases secretion of stomach acid
30
What is the main hormonal function(s) of CCK (cholecystokinin)?
- pancreatic enzyme secretion*
- gallbladder contraction*
- satiety
- inhibits acid secretion
31
What is the main hormonal function of peptide YY?
- inhibits gastric secretion
- slows gastric emptying/motility
32
What is the main hormonal function of motilin?
migrating motor complex (stimulates contractions between meals)
33
What is the main hormonal function of secretin?
- bicarbonate and water secretion from pancreas
- inhibits gastric acid secretion
- slow gastric emptying
34
Stretch from chyme against intestinal wall elicits ______________ (local reflex)
concentric contractions
note: this is NOT the same as peristalsis
35
Concentric contractions in the small intestine are spaced 1 to 5cm and cause ___________
segmentation
36
Chyme propelled through the small intestine by propulsive waves that move towards the ansu is known as ____________
peristalsis
37
a powerful wave of contractile activity that travels long distances down the small intestine and is caused by intense irritation or unusual distension
peristaltic rush
38
distension in the alimentary canal causes distal parts of the canal to relax and proximal parts to contract (circular muscle)
"law of the gut"
Note: peristaltic reflex/"law of the gut" is mediated by the enteric nervous system (ENS) and various hormones
39
The hormones that enhance peristalsis include:
- gastrin
- CCK
- serotonin
40
The hormones that inhibit peristalsis include:
- secretin
- peptide YY
- epinephrine
41
What are some requirements for chyme to enter the duodenum?
- food particles must be very small (<2mm)
- small volumes of low pH fluid (large volumes of low pH/acidic fluid = damaging)
- gradual release (to allow absorption and chemical digestion)
42
The _____________ is the major organ that regulates rates of gastric emptying
duodenum
43
Both the sympathetic nervous system (@ spinal cord) and the enteric nervous system (submucosal and myenteric plexuses) will INHIBIT gastric emptying in response to what?
- increased or decreased osmolarity in the duodenum
- decreased pH (increased acidity) in the duodenum
- distention or any chemical irritation of the duodenum
- breakdown productions of proteins and fats (mostly proteins) in the duodenum
44
True or False: CCK is secreted in the small intestine, but mostly in the ileum
False
Mostly in the duodenum
45
What substances elicit CCK release?
FATS** > peptides > carbs
46
True or False: Secretin is secreted throughout both the duodenum and jejunum
True
47
What substances elicit secretin release?
low pH > fats, capsaicin, bile acids
48
a major hormone that performs the role of the "ileal brake", secreted by L cells in the distal small intestine (ileum)
peptide YY
49
What substances elicit peptide YY release?
FATS > carbs, amino acids
50
True or False: If undigested food reaches the distal small intestine (ileum), then peptide YY "slows everything down"
True
51
What is an oleate meal?
A meal that is high in fat
52
True or False: Compared to acidic and saline meals, oleate meals tend to increase the rate of gastric emptying.
False
Oleate (fatty) meals tend to slow gastric emptying, whereby there is more food remaining in the stomach after a period of time, compared to an acidic and saline meals.
53
The _______________ valve forcefully closes when excess pressure builds up in the cecum
ileocecal
54
True or False: The ileocecal sphincter usually remains mildy constricted
True
55
Digestive juices (which includes large quantities of water and electrolytes) are secreted by _____________ at a rate of about _____________ mL/day
enterocytes,
1800mL/day (1.8L)
56
True or False: intestinal juices have a pH of 7.5-8.0 and are a little more alkaline that ECF, due to the presence of more bicarbonate
True
57
The ________________ are found proximal to the sphincter of Oddi and secrete alkaline mucous in response to:
- tactile stimuli or irritating stimuli of the overlying mucosa
- vagal stimulation
- GI hormones (esp. secretin)
Brunner's Glands
Note: vagal stimulation can both increase acidic secretion in the stomach and alkaline mucous in the small intestine
58
What is the function of Brunner's Glands?
protect duodenal wall from digestion by gastric juice
59
Brunner's Glands are inhibited by ______________ (parasympathetic/sympathetic) stimulation
sympathetic
60
Chyme arrives in the duodenum via the ________ sphincter
pyloric
61
function of bile
emulsification of lipids
62
function of pancreatic enzymes
the hydrolysis of fats, proteins, and carbohydrates into smaller molecules
63
bile is secreted by the liver by the right and left _______________
hepatic ducts
64
the right and left hepatic ducts join to form the ___________________
common hepatic duct
65
the common bile duct is formed at the junction of the ___________ and _____________
cystic duct and common hepatic duct
66
the sphincter of Oddi regulates the release of bile into the _________ from the ampulla of Vater
duodenum
67
If the sphincter of Oddi is closed, then the bile is stored in the _____________
gallbladder
68
The main pancreatic duct meets the common bile duct at the __________
ampulla of Vater
69
True or False: The sphincter of Oddi regulates biliary secretions but not pancreatic secretions into the duodenum
False
The sphincter of Oddi regulate both biliary and pancreatic secretions into the duodenum
70
Enterokinase activates/cleaves trypsinogen to ____________
trypsin
71
Trypsin activates/cleaves:
chymotrypsinogen --> ?
proelastase --> ?
procarboxypeptidase --> ?
chymotrypsinogen --> chymotrypsin
proelastase --> elastase
procarboxypeptidase --> carboxypeptidase
Note: these are all enzymes relevant to PROTEIN digestion
72
What is the function of pancreatic amylase?
carbohydrate digestion (digests starch in particular)
73
What enzymes are used for lipid digestion?
- pancreatic lipase/co-lipase
- phospholipase A2
74
enzymes break macronutrients down into smaller and smaller particles through the process of hydrolysis
enzyme digestion
Note: all pancreatic, gastric, and brush border enzymes use hydrolysis as a means of breaking a macromolecule into smaller molecules
75
Food is first mixed with saliva in the mouth, which contains the enzyme __________ secreted mainly by the parotid glands
ptyalin (alpha-amylase or salivary amylase)
76
Pyalin hydrolyzes ___________ into the disaccharide maltose and other small polymers of glucose (3-9 glucose molecules, aka oligosaccharides)
starch
77
What blocks the activity of ptyalin?
the acid of gastric secretions (pH <4)
we're swallowing our saliva as we eat, so once it reaches the stomach, that's when it stops working (because it's too acidic in the stomach)
78
What enzyme do we use for digestion of carbohydrates in the small intestine?
pancreatic amylase
Note: like salivary amylase, but "much much more powerful"... "the most important enzyme for digestion of starches"
79
What are the three major enzymes that digest (hydrolyze) the major disaccharide sugars in our diet?
1) lactase
2) maltase (isomaltase)
3) sucrase
80
glucose + galactose = ?
lactose
81
glucose + glucose = ?
maltose
82
fructose + glucose = ?
sucrose
83
Pepsin is most active between pH _________
1.5-3.5
84
True or False: In the mouth, there is only mechanical digestion of protein and no enzymatic digestion
True
85
True or False: In the stomach, HCL denatures protein but is not involved in hydrolysis
True
Note: denaturation improves the "exposure" of peptide bonds to digestive enzymes
86
Where does most protein digestion occur?
duodenum and upper jejunum
87
Upon entering the small intestine, polypeptides (protein) are attacked by the following enzymes: trypsin, chymotrypsin, carboxypolypeptidases, and proelastase
Which of these four enzymes activates the others?
trypsin
88
33% of protein is absorbed as ___________ and 67% is absorbed as ____________
free amino acids,
peptides
89
Why is the digestion of fats challenging?
not very water soluble (therefore tends to accumulate in large droplets) --> reduces surface area --> poor water solubility --> impairs the process of chemical digestion and absorption
90
How do we improve the digestion of fats?
emulsify the fat droplets into very small droplets that have an amphipathic molecule on the outside (formation of micelles)
Note: this increases surface area which improves interaction with water
91
________ contains a variety of amphipathic molecules that help with the formation of micelles...
- lecithins
- bile salts
- cholesterol
Bile
92
Outside of the micelle is ____________ (hydrophobic/hydrophilic)
hydrophilic
93
Inside the micelle is _____________ (hydrophobic/hydrophilic)
hydrophobic
94
Once micelles have been formed, _____________ acts on the triglycerides inside the micelle
pancreatic lipase
95
True or False: Pancreatic lipase works alone to digest lipids
False
Usually requires colipase to help it insert into the micelle and activate it
96
What does pancreatic lipase break triglycerides into?
2 free fatty acids and 2-monoacyl glycerol
97
When free fatty acids and 2-monoacyl glycerol diffuse across the brush border of the enterocyte, they reassemble into _______________
triglycerides
98
Phospholipase works similar to pancreatic lipase, except it breaks down _____________ into fatty acids and other components
phospholipids
99
After triglycerides are reassembled into the enterocyte, they are inserted into ________________
chylomicrons
100
a spherical lipoprotein, with a phospholipid bilayer and proteins on the outside and that absorbs triglycerides and cholesterol in the inside
chylomicron
Note: chylomicrons are necessary for transporting triglycerides and cholesterol esters (big molecules) throughout our circulation
101
Chylomicrons are secreted into the ____________ and eventually transported into the _____________, to join the venous blood
lymphatic vessels,
thoracic duct
102
True or False: Carbohydrates, amino acids, and small free fatty acids can diffuse across the basement membrane of the enterocyte, into the capillary loops within the villus, but larger lipids need to be carried by chylomicrons, which enter via openings of the lacteals (lymphatic capillaries within the villi)
True
103
When absorption at the small intestine is unsuccessful, nutreints remain int he lumen of the intestine, potentially leading to what?
- diarrhea
- micronutrient and macronutrient deficiencies
104
What are four major malabsorption problems that can occur?
1) disturbances in intraluminal digestion
2) disturbances in terminal digestion
3) disturbances in transepithelial transport
4) disturbances in lymphatic transport
105
when enzymes/bile secreted into the lumen are inadequate for the near-complete breakdown of proteins, carbs, or fats
disturbances in intraluminal digestion
106
when the brush border enzymes cannot break down small peptides or disaccharides
disturbances in terminal digestion
107
when nutrient, fluid, and/or electrolyte transport are disordered
disturbances in transepithelial transport
108
when lipid transport is impaired
disturbances in lymphatic transport
109
pathogenesis of celiac disease
damage to the villi and microvilli resulting in loss of surface area and overall absorptive enterocyte function
characterized by disturbances in:
- terminal digestion
- transepithelial transport
110
pathogenesis of chronic pancreatitis
lack of major digestive enzymes from the pancreas leads to major impairment in absorption, diarrhea, and nutrient deficiencies
characterized by disturbances in:
- intraluminal digestion
111
pathogenesis of disaccharidase deficiencies (e.g., lactose intolerance)
lack of disaccharide [digestion?] results in unabsorbed sugar in the lumen --> results in bacterial gas production and osmotic diarrhea
characterized by disturbances in:
- terminal digestion
112
pathogenesis of gastroenteritis (e.g., bacterial, viral, parasitic)
damage to the brush border or dysregulation of electrolyte transport results in impaired ability to absorb nutrients
characterized by disturbances in:
- terminal digestion
- transepithelial transport
