Intestinal activity and motility Flashcards
1
Q
the small intstine is where
A
Most digestion and absorption takes place
- intense enzymatic activity
2
Q
what is the small intestine divided into?
A
Divided into 3 sections:
* Duodenum
* Jejunum
* Ileum
3
Q
large intesdtine function?
A
- Absorbs water and small amount of Na+ & Cl-
- Formation and temporary
storage of faeces - Microbiological activity
4
Q
the large intestineis the very final satages of
A
digestion and sborptin
5
Q
the different parts of the large intestine?
A
- Vermiform appendix
(AKA vermix,
vermiform process - Caecum (cecum)
- Colon
- Rectum
6
Q
what is segmentation?
A
Primary method of motility which
mixes and slowly propels the chyme
7
Q
segmentation is slight or absent between
A
meals
8
Q
segmentations becomes very vigorous after a meal
A
a meal
9
Q
how does segmentation tak eplace?
A
Local oscillating ring-like contractions of the
circular smooth muscle along the small
intestine’s length
* Between the contracted segments are relaxed
areas containing a small bolus of chyme
10
Q
segmentation does not
A
sweep along the length of the intestine as peristaltic waves do
11
Q
what are the functions of segmentation?
A
- To chop, churn and thoroughly mix chyme
- Move chyme through digestive tract
12
Q
how does segmentation move chyme through the digestive tract?
A
Specialised pacemaker cells which produce a Basic Electrical
Rhythm (BER) – Rhythmic pattern of spontaneous
depolarizations
13
Q
pacemaker ells spontaneously depolarise faster in the
A
upper small intestine then those in the lower intestine
14
Q
what are the function of Interstitial cells of Cajal ?
A
generate slow wave
potentials that sweep down
the stomach and Intestines
15
Q
interstitial cells of cajal are connceted via
A
gap junctions and the myenteric plexus
16
Q
Therefore, more chyme is pushed forward than
A
backwards
17
Q
Slow propulsive mechanism is advantageous as allows
A
adequate digestive and absorptive
processes. 3-5 hours for contents to move through small intestine
18
Q
In order for a contraction to occur,
A
hormone or neurocrine signal must induce the smooth
muscle cell to have an action potential.
19
Q
acetycholine increases
A
amplitude of slow wave
20
Q
norepinephrine decreases
A
amplitude of slow wave
21
Q
what modulates BER excitability?
A
Distension in the iintestine
Gastrin
Extrinsic nerve activity
22
Q
Duodenum starts to segment primarily in response to
A
local distension caused by the presence of chyme.
23
Q
Segmentation of the empty ileum is brought about by
A
gastrin secreted in response to the presence of chyme in the stomach (gastro-ileal reflex).
24
Q
Extrinsic nerves can
A
strengthen (parasympathetic) or weaken (sympathetic) contractions.
25
Once nutrients have been absorbed, intestinal segmentation contractions
reduce
26
Segmentation contractions are replaced by
weak, repetitive peristaltic waves that move a short distance
down the intestine before dying out – migrating motility complex (MMC).
27
what is migrating motility complex (MMC)?
waves of electrical activity trigger peristaltic waves during the interdigestive phase
28
Facilitate transportation of indigestible substances into the
colon
29
MMC occurs every
90-230 minutes (between meals)
30
what experience does MMC cause?
Rumbling experienced when hungry
31
MMC inhibits...
... migration of colonic bacteria into the terminal ileum
32
Digestion is finally accomplished by
pancreatic enzymes with fat digestion being
enhanced by bile secretion
33
Exocrine glands of the small intestine mucosa secrete
into the lumen 1.5 litres of aqueous salt and mucus – succus entericus
34
exocrine glands of the small intrestine provides
mucus for lubrication and protection
and plenty of water to participate in the
enzymatic digestion → hydrolysis
35
The digestive enzymes that the small intestine
synthesize are restricted to
the brush border
membrane
36
The digestive enzymes that the small intestine
synthesize are restricted to the brush border
membrane - the enzymes are embedded in...
... those microvilli of epithelial cells which completes the
digestive process
37
Fat digestion is completed in the
lumen of the small intestine
38
Protein and carbohydrate completed in
brush border
39
Brush Border Cells contain
three categories of integral membrane bound proteins that
function as enzymes and complete the digestion of carbohydrates and proteins
40
what are the three membrane bound proteins of the brush border?
- Enterokinase
- Disaccharides
- Aminopeptidases
41
enterokinase function
activates pancreatic proteolytic wenzyme trypsinogen
42
disacchrides function
(maltase, sucrose, lactase,
Limit Dextrinase/sucrose-isomaltase)
hydrolyze remaining disaccharides into their
constituent monosaccharides (carbohydrate
digestion)
43
aminopeptidases function
hydrolyze peptide fragments into their amino acid components
44
lactase function?
hydrolase involved in hydrolysis of the disaccharide lactose
into constituent galactose and glucose monomers
45
lactose intolerance?
55% to 65% adults down
regulate lactase
production
46
what is lactase persistence?
≈ 30 to 40% adults produce Lactase after weaning
47
lactase persistence most common in which populations?
Mainly Europe, some of Africa, Middle East & Southern Asia
48
Undigested Lactose
remains in
lumen
49
Accumulation of undigested lactose creates
osmotic gradient
50
1.Undigested Lactose remains in lumen
* Accumulation of undigested lactose creates osmotic
gradient
- draws in...
... water into intestinal lumen
51
Bacteria digest and
feed on lactose = production of co2 and methane gas
52
distenstion from
increased water and gases
53
lactose inteorlance symptoms
diarrhoea
cramps
bloating
nausea
chronic flatulence
54
Primary role of the small intestine is to
absorb carbohydrate, protein, electrolytes, vitamins ,
fat and water – absorbed indiscriminately.
55
Most absorption takes place in the
duodenum and jejunum – very little occurs in the ileum
56
Specialised transport mechanisms exist in
the terminal
Ileum
57
Specialised transport mechanisms exist in the terminal
Ileum for:
- vitamin b12 - intrinsic factor from stomach - secreted by parietal cells.
- bile salts (enterohepatic circulation)
58
in the small intrstine, usually only the absorption of calcium and iron are ...
...adjusted to the body’s needs
59
Thus, the more food consumed, the more
is digested and absorbed.
60
Small intestine has enormous
absorptive capacity
61
Up to ≈30% of small intestine can be
removed with little interference to overall absorption
62
Mucous lining of the small intestine is remarkably
well adapted for its special absorptive finction
63
Mucous lining of the small intestine is remarkably
well adapted for its special absorptive function for two
reasons:
1. Large surface area - Permanent
circular folds, Villi, Microvilli
2. Epithelial cells in lining have variety
of specialized transport mechanisms
64
slide 25
65
Epithelial cells in the mucosa have a variety of...
specialiszed transport mechanisms
66
epithelial cells cover
the survace of the villus
67
epithelial cells are joined at
lateral borders by tight junctions (limit the passage of luminal contents between cells
68
what do microvilli contain
contain transport carrier proteins for
absorption of specific nutrients and electrolytes
69
what do membrane bound digestive enzymes do?
complete
carbohydrate protein digestion
70
what is the connective tissue core?
lamina propria
71
what is the capillary network?
Artery enters, differentiates into a capillary network
and then rejoins as a venule that drains away
72
what is the terminal lymphatic vesseL?
central lacteal – single blinded lymphatic vessel – absorbs fats
73
central lacteal function
absorbs fats
74
In between the villi are
shallow invaginations – crypts of Lieberkühn
75
what do crypts of Lieberkühn secrete?
water
electrolytes
no digestive enzymes
76
water, electrolytes, no digestive enzymes, + mucus from specialised epithelial cells =
succus entericus
77
crypts of Lieberkühn function as...
... “nurseries”
78
crypts of Lieberkühn function as nurseries.
thet contain...
... high mitotic rate stem cells,
which create new cell which continually migrate up the villus
and push the older cells off at the tips
79
how many cells shed per minutes?
100 million cells shed per minute
80
100 million cells shed per minute; takes
3 days to migrate
81
Highly sensitive to
82
Lost cells are digested and the cell constituents
absorbed
83
paneth cells function ?
defensive function, safeguarding stem cells.
Produce lysozyme to lyse bacteria and defensins
84
the small intestine jioins the colon at the
caecum
85
what is the caecum?
The caecum is a blind-ended pouch below the junction of the small and large intestines at the ileocecal valve
86
When contents from small intestine push forward...
...they open the valve , but the folds are forcibly closed by any backward movement
87
At the bottom of the caecum is
the appendix
88
what is the appendix?
gut associated lymphoid tissu. B cell mediated immune response and extra thymus t cell
89
appendix is involved in the
maintence of gut flora
90
how much chyme does the hcolon receive each day?
500 ml of chyme from the small intesinte each day
91
The colon receives ≈ 500 ml of chyme from the small intestine
each day, most of which is ...
... indigestible and unabsorbed food residues, biliary components and water.
92
the colon extracts
more water, and electrolytes with the remainder eliminated as
faeces
93
The outer smooth muscle layer does not
completely
surround the large intestine
94
The outer smooth muscle layer does not
completely surround the large intestine
Consists of
three separate longitudinal bands
of muscle
95
The outer smooth muscle layer does not
completely surround the large intestine
Consists of three separate longitudinal bands
of muscle:
taeniae coli which run the length of the large intesrtine
96
Taeniae coli are shorter than the
underlying circular smooth muscle: the
underlying layers are gathered into pouches
called haustra
97
what are haustria?
small pouches caused by sacculation, which gives
the colon its segmented appearance.
98
Alkaline (NaHCO3) mucus is secreted from
numerous goblet cells
99
function of goblet cells?
to protect the mucosa from mechanical and chemical injury. No digestive enzymes are secreted
100
large intestine secretion of mucus is in response to ..
... mechanical and chemical stimulation of the colonic mucosa,
mediated by parasympathetic innervation.
101
NaHCO3 neutralises
acids produced by the local bacteria fermentation.
102
Majority of the time, movements of large intestine are
slow and non-propulsive (appropriate for absorptive and storage functions)
103
Contractions controlled by
autonomic smooth muscle cells at approx 30 minute intervals
104
* Majority of the time, movements of large intestine are slow and non-propulsive
(appropriate for absorptive and storage functions)
* Contractions controlled by autonomic smooth muscle cells at approx. 30 min intervals
These movements shuffle...
... the contents back and forth which exposes the
colonic contents to the absorptive mucosal surface
105
Three to four times a day (generally after meals) marked
increases in motility
106
Ascending / transverse colon contract
simultaneously
107
Ascending / transverse colon contract simultaneously; drives
faeces one third to three quarters of the length of the colon in a few seconds – Mass movement
108
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