GI Mod 3A Flashcards
1
Q
3 regions of SI + lengths
A
- duodenum (25-30cm)
- jejunum (2.5m)
- ileum (3.5m)
2
Q
where does the duodenum begin and end
A
begins - duodenal bulb
ends - ligament of Treitz
3
Q
what is the hepatopancreatic ampula in SI
A
aka Sphincter of Oddi
-allow bile and pancreatic enzyme secretions
4
Q
what are Brunner’s glands in SI
A
submucosal glands
- located in proximal duodenum
- secrete bicarbonate rich mucus to protect against acidic chyme entering the duodenum and lubricate intestinal wall
5
Q
function of duodenum
A
digestion and gastric feedback
6
Q
how does the duodenum perform enzymatic digestion/breakdown of food
A
stimulates release of digestive enzymes from pancreas and gall bladder
7
Q
the SI provides feedback to do what?
A
regulate the rate of gastric emptying
8
Q
how does the SI provide feedback for gastric emptying
A
acidic chyme (fats, partially digested protein, hyper/hypotonic fluids) entering duodenum stimulate:
- long loop reflexes
- short loop reflexes
- release hormone messengers
9
Q
what are long loop reflexes of SI feedback
A
mechanoreceptors/chemoreceptors stimulate CNS to increase sympathetic and decrease parasympathetic to stomach
10
Q
what are short loop reflexes of the SI
A
mechanoreceptors/chemoreceptors in duodenum stimulate enteric neurons in stomach to decrease stomach motility
11
Q
the SI releases hormone messengers that do what for feedback
-what hormones are involved
A
inhibit stomach motility/acid production
-secretin, VIP, CCK released from duodenum play role in inhibiting gastric motility and secretion
12
Q
hormones of the duodenum: secretin function
A
regulate pH in duodenum, inhibitory to gastric activity and facilitates digestion
13
Q
hormones of the duodenum: secretin stimulus
A
acidic (pH
14
Q
hormones of the duodenum:secretin target organ/action
A
stomach - inhibits gastric secretions (inhibits gastrin) and inhibits motility
pancreas- stimulate pancreas to secrete watery bicarb solution
liver - stimulates bile output (promote fat digestion)
brunner’s glands of duodenum - stimulate secretion of alkaline rich mucus
15
Q
hormones of the duodenum: CCK function
A
promotes bile/pancreatic enzyme release and inhibitory to gastric activity
16
Q
hormones of the duodenum: stimulus of CCK
A
fatty chyme (fats, partially digested protein) entering duodenum
17
Q
hormones of the duodenum: target tissue/action
A
stomach - inhibitory to gastric motility/secretions
pancreas - stimulate release of pancreatic enzymes
liver - stimulates bile output (promote fat digestion)
gallbladder - stimulates contraction to release stored bile
18
Q
hormones of the duodenum: GIP function
A
gastric inhibitory peptide
-relative of secretin
19
Q
hormones of the duodenum: stimulus of GIP
A
chyme entering duodenum
20
Q
hormones of the duodenum: target tissue/action of GIP
A
stomach - inhibitory to gastric motility/secretions (some resources question this role and propose secretin is stimulus)
pancreas - stimulate insulin release
21
Q
hormones of the duodenum: VIP
A
vasoactive intestinal peptide
22
Q
hormones of the duodenum: VIP stimulus
A
chyme entering duodenum
23
Q
hormones of the duodenum: VIP target tissue/action
A
stomach - inhibit gastric acid secretion
intestine - vasodilate BV, promote intestinal motility
24
Q
hormones of the duodenum: intestinal gastrin role
A
similar role as gastrin released in the antrum of stomach
25
hormones of the duodenum: stimulus of intestinal gastrin
chyme entering duodenum
26
hormones of the duodenum: target tissue/action of intestinal gastrin
stomach - stimulate gastric motility and secretions
| intestine - stimulate motility
27
hormones of the duodenum: motilin role
housekeeper of intestinal tract
28
hormones of the duodenum: stimulus of motilin
fasting or periodic release (every few hours)
29
hormones of the duodenum: target tissue/action of motilin
intestine - initiates MMC (migrating motor complex)
30
list all the hormones of the duodenum
1. secretin
2. CCK
3. GIP
4. VIP
5. intestinal gastrin
6. motilin
31
how long is the SI
5-6m
32
where does the jejunum begin and the ileum end?
begins at ligament of Treitz and ends at ileocecal valve
33
where does the SI begin and end
pylori sphincter and ends at ileocecal valve
33
general function of both the jejunum and ileum
continued digestion, absorption and secretion of brush borders enzymes to assist in digestion/absorption
35
function of jejunum
major site of digested fat, carb, protein, water, and electrolyte absorption
36
function of ileum
absorb vitB12, bile salts, and remaining digested nutrients and water not absorbed in jejunum
37
function of mucosal folds of jejunum and ileum
aka plica
| physically slow the passage of food
38
function of villi in jejunum and ileum
cover mucosal folds
| considered functional unit of SI: secretion and absorption
39
composition of villi in jejunum and ileum
1. goblet cells - mucus secreting cells
| 2. absorptive columnar cells: site of absorption
40
what are microvilli in jejunum and ileum
- location
- function
located on end of each columnar cell
form the brush border of the mucosal surface
a thin layer of fluid is found along surface of brush border
function: facilitates absorption of all substances except water/electrolytes
41
what is the lamina propria layer of the jejunum and ileum
extends into each villi
| contains lacteal and central arteriole
42
function of central arteriole in jejunum and ileum
capillary transport substances directly to liver via hepatic portal vein
(carbs, proteins, and some fats to directly to liver)
43
function of lacteal in jejunum and ileum
transport fat molecules/substances (fats - mnoglycerides & fatty acids) to systemic circulation via thoracic duct
44
what are the Crypts of Lieburkuhn in jejunum and ileum
| -3 types of cells
```
at the base of villi
3 types of cells:
1. precursor cells
2. paneth cells
3. secretory cells
```
45
function of precursor cells in Crypts of Lieburkuhn of jejunum and ileum
in SI epithelium (goblet cells and columnar cells)
turnover of intestinal epithelial cells
-migrate to tip of villi, mature SI epithelial cells slough off into intestine and serve as a source of endogenous protein
-complete turnover of SI is approx 4-7 days
46
function of paneth cells in the Crypts of Lieburkuhn of jejunum and ileum
immune function - produce/secrete antibiotic peptides
47
small intestine motility - avg transit time
average transit time in SI - 1-3 hrs (with large variations of 15 min to 5+hrs)
48
stimulus of SI motility
1. small intestine hormones: secretin, CCK, gastrin, motilin
| 2. intestinal reflexes
49
three motility patterns occur in SI
1. segmentation
2. peristalsis
3. migrating motor complex (MMC)
50
what is segmentation
occurs during feeding
frequent small rhythmic contractions of circular muscle (8-12/min)
occurs more frequently than peristalsis
function: mixes chyme to allow contact with brush border
51
what is peristalsis
occurs during feeding
coordinated waves of contraction/relaxation of longitudinal muscles (short segments - 10cm)
wave of contraction moves slowly ( 1-2cm/sec) to allow for digestion/absorption
function: moves chyme toward large intestine
52
what is MMC
aka interdigestive myoelectric complex
occurs during FASTING
slow periodic waves of peristalsis that occurs every 1-2hrs
originate in stomach and pass thru small intestine
motilin plays a role in stimulus
53
function of MMC
function: "house cleaning" - sweeps out stomach/SI
- -pushes along residual chyme, nondigested substances (fiber, bone)
- -bacteria homeostasis - transport bacteria to LI, prevent reflux of bacteria from LI
54
what is the ileogastric reflex
- stimulus
- action
- result
stimulus - ileum distended
action - inhibits gastric motility
result - slows dow adding more chyme to SI to allow terminal ileum to empty contents to LI
55
what is the intestinointestinal reflex
inhibitory-protective reflex
stimulus - section of SI becomes distended
action - relaxes distal SI
result - allows chyme to be moved toward LI
56
what is gastroileal reflex
- stimulus
- action
- result
stimulus - increased stomach (gastric motility/secretion)
action - promotes terminal ileum motility/ileocecal valve relaxation
result - empty SI so it can receive more chyme from stomach
57
ileocecal valve is regulated how and is it usually open or closed
regulated intrinsically
| usually closed
58
regulation of ileocecal valve opening
- stimulus
- action
valve opens similar to LES of esophagus and pyloric valve in stomach
stimulus - approaching peristaltic wave in the ileum
action - relaxation of the ileocecal sphincter
59
regulation of ileocecal valve closing
- stim
- action
stimulus - distension of cecum/ascending LI
| action - constriction of ileocecal valve
60
function of secretory cells of Crypts of Lieburkuhn of jejunum and ileum
secrete brush border digestive enzymes
61
total length of the large intestine
1.5 m
62
where does the LI begin and end
begin - ileocecal valve
| end - anus
63
sections of the LI
cecum, appendix, colon, rectum,anus
64
4 regions of the colon
ascending, transverse, descending, and sigmoid colon
65
LI is an unique arrangement of what 2 types of muscle
1. circular and longitudinal muscles is unique in LI
66
what are teniae coli in the LI
3 longitudinal bands if muscle along length of colon
67
what are haustra in the LI
pouches formed from circular muscle layer of intestine
68
what is O'Bierne sphincter of LI
controls passage of chyme from sigmoid colon into rectum
69
LI motility - 2 types
1. segmental
| 2. peristalsis
70
what are haustral segment contraction
occurs during fasting
individual haustra segments push contents (fecal mass) back and forth
function - maximize absorption of water and electrolytes in large intestine occurs a majority (90%) of the time
71
what is multihaustral segmentation
occurs during fasting
several haustral segments contract and relax as a single unit
function - push contents (fecal mass) a short distance forward occurs less often (10% of time)
72
what is mass movement peristalsis
promote emptying of the intestine into the sigmoid colon and rectum
73
what are the 2 intestinal reflexes of the colon
1. orthocolic reflex
| 2. gastrocolic reflex
74
what is the orthocolic reflex of the colon
- stim
- action
stimulus - standing first thing in the morning stimulates peristalsis of LI
action - peristalsis propels fecal mass into sigmoid colon and rectum
75
what is the gastrocolic reflex of the LI
stim - ingestion of food (occurs during or immediately after eating)
action - peristalsis propels fecal mass into sigmoid colon and rectum
--continuation of gastroileal reflex - increase motility of stomach promotes motility of SI
76
what is the rectal reflex of a bowel movement
stim
action
inhibition
aka defecation
stim - stretch of rectum wall
action - relaxation of internal anal sphincter and the urge to have BM
inhibited - voluntary control; cerebral cortex input/motor pathways in spinal cord: contract the external anal sphincter
77
clinical of rectal reflex - cauda equina syndrome
damage to nerve roots of lower spine
| loss of bowel control
78
digestion of carbs in the mouth
enzyme - salivary amylas
| action - starches broken into smaller molecules (dextrin and oligosaccharides)
79
digestion of carbs in SI
1. pancreatic role
enzyme - pancreatic amylase secreted from pancreas
action - further breakdown starches into major oligosaccharides (lactose, maltose, sucrose)
2. brush border
enzyme - brush border enzymes (lactase,maltase,sucrase) secreted from secretory cells of base of villi (Crypts of Lieburkuhn)
action - breakdown oligosaccharides (lactose, maltose, sucrose) into monosaccharides (galactose, glucose, and fructose)
80
absorption of carbs
location - brush border of villi
action - monosaccharides (galactose, glucose, and fructose) are absorbed by villi capillaries and transport directly to liver via hepatic portal vein
NOTE: insulin not required for intestinal uptake of glucose
81
digestion of proteins begins where?
stomach
82
digestion of protein in stomach
enzyme: pepsin
NOTE: pepsinogen released from chief cells is converted into pepsin when combined with gastric acids (HCl)
action: break down protein into smaller protein molecules (proteoses, peptones)
NOTE: this site of protein digestion is not essential...SI is primary site
83
digestion of protein in SI
1. pancreatic role:
enzyme: pancreatic enzymes (trypsin, chymotrypsin, carboxpeptidase) secreted by pancreas into duodenum
action: breakdown protein molecules into smaller peptides (polypeptides and dipeptides)
2. brush border role
enzyme: brush border enzymes (aminopeptidases/dipeptidase) are secreted from secretory cells of base of villi (Crypts of Lieburkuhn)
action: breakdown smaller peptides (polypeptides and dipeptides) into amino acids
84
absorption of proteins
location - villi in SI
| action - amino acids are absorbed by villia capillaries and transported directly to liver (via hepatic portal vein)
85
digestion of fats requires what
emulsification
86
emulsifying agents in GI
fatty acids, monoglycerides, lecithin, cholesterol, protein, bile salts
87
what do emulsifying agents do
surround small fat articles and prevent them from reforming into larger fat droplets
emulsification reduces the surface tension and separates the molecules
88
digestion of fats starts where
stomach
89
digestion of fats in stomach
enzyme: gastric lipase
action: initiate breakdown of fats
90
digestion of fat in SI
1. emulsification of fat droplets
action - smaller fat droplets are formed in the presence of emulsifying agents
2. lypolysis
enzymes: lipase, phospholipase, hydrolipase secreted from pancreas
action - emulsified fat molecules are broken down into diglycerides, monoglycerides, FFAs, glycerol
91
absorption of fats
fast molecule must be made water soluble to reach intestinal epithelium
--accomplished by formation of micelles (water soluble molecule)
92
steps in fat absorption
1. Micelles formation
2. Transport of fats into columnar epithelial cell of SI
3. transport of fats into lacteals
93
what happens in Micelles formation
bile salts, fat molecules, cholesterol, fat soluble vitamins (A,D,E,K) combine to form a micelle
94
what happens in the transport of fats into the columnar epithelial cell of SI
- micelle can pass thru aqueous brush border fluid and contact epithelial cell
- fat contents of micelle then diffuse into epithelial cell
- left over bile salts from micelle remain in intestine and are reabsorbed in the distal ileum
95
what happens during transport of fats into lacteals
- inside the epithelial cells the fat molecules are resynthesized into triglycerides and phosphoplipids
- these new fat particles are called chylomicrons
- the chylomicrons exit the intestinal wall (epithelial cell) into lacteals of villi and are transported to heart and systemic circulation
- NOTE: most fats are absorbed via lacteals however some fat(glycerol and fatty acids) are absorbed directly into capillary system
96
chylomicrons exit the cell via what process in the transport of fats into lacteals
CHYLOMICRONS EXIT the cell via exocytosis
97
fluid is ingested or secreted into GI tract thruout which regions of GI
all regions
98
total ingested/secreted fluid into GI tract
7.5-8L/day
99
which part of GI will absorb most fluid back into blood stream
SI - approx 85-90% reabsorbed in SI
100
what will secrete and absorb the final fluid balance
LI - driven by electrolyte balance
| --fine tunes fluid and electrolyte homeostasis
101
how much fluid is excreted in stool in normal BM
100ml (1/10L)
102
normal renal excretion of fluid
renal excretion = 1-2L/day
103
vit b12 absorption
occurs in terminal ileum
| absorption requries B12 to bind with IF - which is secreted by gastric parietal cells
104
lack of B12 causes
```
pernicious anemia (macrocytic anemia) - poor RBC formation
liver and kidneys store enough B12 to last for years
```
