Physiology Flashcards
1
Q
functions of the digestive system
A
absorption
digestion
secretion
motility
2
Q
where do nutrients primarily enter the circulatory system
A
small intestine
3
Q
how many salivary glands are there
A
3 pairs (6)
4
Q
what occurs in the mouth
A
foodstuffs broken down by chewing: saliva added as lubricant
5
Q
what is oesophagus
A
muscular conduit between stomach and mouth
6
Q
what happens in stomach
A
- digestion of proteins:
- foodstuffs reduced to liquid form
- storage
- sterilisation
7
Q
what can be found in the pancreas
A
digestive enzymes for digestion of fats, carbohydrates and proteins
8
Q
what can be found in liver
A
bile salts for digestion/ absorption of fats in the small intestine
9
Q
what happens in large intestine
A
- water absorption,
- bacterial fermentation
- formation of faeces
10
Q
what are essential for fat digestion
A
bile salts in the liver
11
Q
how long from oesophagus to rectum
A
8m ish
12
Q
4 distinctive layers of alimentary canal
A
- mucosa
- submucosa
- muscularis externa
- serosa
13
Q
2 layers of musculaisr externa
A
longitudinal
circular
14
Q
function of muscularis externa
A
provide motility
15
Q
type of epithelium in mouth, oesophagus and anal canal
A
stratified squamous
16
Q
type of epithelium in stomach, small and large intestine
A
simple columnar
17
Q
functions (3) of epithelium in GI tract
A
- barrier separating lumen of alimentary canal from body
- synthesis and secretion of digestive enzymes, hormones, mucus
- absorbs products of digestion
18
Q
components of mucosa
A
- epithelium
- lamina propria
- muscularis mucosae
19
Q
what is lamina propria
A
loose connective tissue (glands, blood/lymph vessels)
20
Q
what is muscularis mucosae
A
thin, smooth muscle layer
21
Q
what is submucosa
A
thick, irregular connective tissue
22
Q
function of submucosa
A
support mucosa
23
Q
what is contained in submucosa
A
neurons, blood and lymphatic vessels
24
Q
where are submucosal glands found
A
- oesophagus
- duodenum
25
what is the function of neurones in submucosa
form extensive network - the submucosal plexus (parasympathetic)
26
what is serosa/ adventitia
connective tissue outer layer of alimentary canal
27
function of serosa outside peritoneal cavity
adventitia attaches oesophagus and rectum to surrounding structures
28
function of serosa inside peritoneal cavity
serosa surrounds stomach, small intestine and large intestine
29
what is muscularis externa composed of
- two thick layers of muscle
```
Inner = circular
Outer = longitudinal
```
30
where is myenteric plexus located
between circular and longitudinal layers of muscularis externa
31
What makes up the enteric nervous system?
submucosal and myenteric plexuses
32
function of enteric nervous system
indépendant control of gut function
33
what enables independent control of gut function
enteric nervous system
34
what is meant by a long reflex in alimentary system
gut - CNS
35
what is meant by a short reflex in alimentary system
just in gut (gut control)
36
Parasympathetic nerve innervation of alimentary system
vagus nerve
37
sympathetic nerve innervation of alimentary system
splanchnic nerve
38
effect of parasympathetic nervous system
stimulatory
| increases secretion and motility
39
effect of sympathetic nervous system
inhibitory (reduces secretion and motility)
40
exception to stimulatory/ inhibitory rule for alimentary tract
salivation (no effect)
41
autonomic control
automatic control
| you cannot influence it
42
long vs short reflexes in the gut
long: goes to CNS
short: remains in the gut
43
foregut contents
- abdominal part of oesophagus
- liver
- pancreas
- spleen
- upper part of duodenum
- stomach
- gall bladder
44
midgut contents
- ileum
- jeudenum
- lower part of duodenum
- large intestine
- proximal 2/3 transverse colon
- appendix
- ascending colon
- caecum
45
hindgut structures
- distal 1/3 transverse colon
- descening colon
- sigmoid colon
- rectum
- upper anal canal
- urogenital sinus
46
blood supply to foregut
coeliac trunk
47
blood supply to midgut
superior mesenteric artery
48
blood supply to hindgut
inferior mesenteric artery
49
venous drainage of stomach
gastric veins
50
venous drainage of pancreas
splenic veins
51
venous drainage of midgut structures:
- small intestine
- caecum
- ascending colon
- transverse colon
superior mesenteric vein
52
venous drainage of hindgut structures:
- descending colon
- sigmoid colon
- rectum
inferior mesenteric vein
53
name the components of the hepatic portal vein:
- splenic vein
- inferior mesenteric artery
- superior mesenteric artery
- gastric veins
54
where does blood go after leaving GI organs (pathway)
1. portal vein tributaries
2. hepatic portal vein (goes through liver)
3. hepatic vein
4. inferior vena cava
55
what organ does all blood go through before leaving the gut
liver
56
purpose of all blood going to the liver after leaving the gut
liver screens/ purifies blood to prevent any toxins absorbed from food from entering the circulatory system
57
principle dietary constituents
- carbohydrates
- protein
- fat
- vitamins
- minerals
- water
58
monosaccharide examples:
Hexose sugars (6c)
1. glucose
2. galactose
3. fructose
59
description disaccharides
two monosaccharides linked together by glycosidic bonds
60
how are disaccharides broken down
brush border enzymes in small intestine break them down to monosaccharides
61
what is lactose broken down to
glucose and galactose
62
what breaks down lactose
lactase
63
what is sucrose broken down to
glucose and fructose
64
what breaks down sucrose
sucrase
65
what is maltose broken down to
glucose x2
66
what breaks maltose down
maltase
67
2 forms of starch
- a-amylose
| - amylopectin
68
what is a-amylose
glucose linked in straight chains
69
what is amylopectin
highly branched glucose chains
70
what type of bonds link glucose monomers in starch
a-1,4-glycosidic bonds
71
what type of reaction breaks down starch
hydrolyse
72
what enzyme is used to break down starch
amylase
73
why can vertebrates not break down cellulose by themselves
brecause they/ we don't have the enzyme cellulase which is required to break down B-1,4-glycosidic bonds
74
what is celluloses function in humans
dietary fibre
75
glycogen function
animal storage form of glucose
76
glycogen structure
glucose monomers linked by a a-1,4-glycosidic bonds
77
what are people who are lactose intolerant not have
lactase enzyme
78
texture of villi in small intestine
velvety when it doesn't have mucus
79
2 membrane types of epithelium
- apical (facing outside e.g. vein)
| - basolateral (facing inside e.g. other cells)
80
what does a brush border look like
bart simpsons hair
81
transcellular pathway
goes through the cell
82
paracellular pathway
- goes between cells through tight junctions
83
how many transporter proteins are needed to pass a molecule through a cell
at least 2 - one at apical and one at basolateral membranes respectively
84
what transporter protein is used for getting glucose into a cell
SGLT1
85
what needs to be present for getting glucose into a cell
Na, Glucose, SGLT1
86
what transporter protein gets glucose out of a cell (down the concentration gradient)
GLUT-2
87
what is a normalise blood glucose
5 mmol/l
88
what transporter protein gets fructose into a cell
GLUT-5
89
what transporter protein gets fructose out of a cell
GLUT-2
90
why does fructose transport into a cell not require any energy?
because there is no blood fructose concentration
91
what other molecules are involved in fructose transportation
NONE ahahahah fooled ya ;)
92
who is awesome
you are
93
what is a protein
polymer of amino acids linked together by peptide bonds
94
what are described as natures lego and why
proteins
| infinitely variable
95
what are enzymes that hydrolyse peptide bonds and reduce proteins/ peptides to amino acids called?
- proteases
| - peptidases
96
function of proteases and peptidases
break down proteins and peptides to form amino acids
97
endopeptidases
breaks down internal amino acids
98
exopeptidase
breaks down terminal end of amino acid (snipping at the end making it 1 shorter everytime)
99
aminopeptidases
work on amino end of protein
100
carboxypeptideases
work on carboxyl end of protein
101
how do most amino acids enter a cell
the same way as glucose; with a transporter and Na
102
how do amino acids leave a cell
using specific transporters to cross basolateral membrane
103
PepT1
protein transporter that can carry virtually any di/tripeptides into a cell using H
104
where does H come for transporting amino acids across apical membranes into a cell
acid microclimate around the surface
105
what form are almost all ingested fats found in
triglycerol
106
what enzyme digests fats in the small intestine
pancreatic lipase
107
definition of a 'lipase'
water-soluble enzyme
108
emulsification
dividing large lipid droplets into smaller droplets
109
what is required for emulsification of fats to take place?
- mechanical disruption
| - emulsifying agent
110
ampiphatic
has polar and non polar components (like phospholipid membrane)
111
how does mechanical disruption of fats in the stomach take place
muscularis externa contraction grinds and mixes lumen contents.
112
function of micelles
'vehicles' for emulsion droplets to get to the cell surface for absorption
113
components of a micelle
bile salt + monoglycerides + fatty acids + phospholipids
114
fate of micelles when they have released the fatty acid inside onto the surface of the cell
they are reused, going back to pick up more fatty acids to transport
115
how does micelle release fatty acid at cell surface
micelle destabilises in the extreme acidic microclimate immediate to the cell, releasing the fatty acids onto cell surface
116
what happens to fatty acids when they enter the cell
1. they enter the smooth endoplasmic reticulum,
2. where they are resythesised by enzymes to for triacylglycerols,
3. emulsified with amphipathic protein found in sER
4. processed through Golgi apparatus
5. exotysed into extracellular fluid at serial membrane
117
difference smooth and rough endoplasmic reticulum
smooth - no ribosomes
| rough - ribosomes
118
chylomicron
extracellular fat droplet
119
extracellular fat droplet
chylomicron
120
where do chylomicrons go
pass into lacteals between epithelial cells (cannot pass through capillary basement membrane0
121
where does fat go after leaving a cell
into lymphatic system, then circulatory system via thoracic duct/ vena cava
122
what are the 2 classes of vitamins
- fat soluble
| - water soluble
123
which vitamins are fat soluble
A,D,E,K
124
which vitamins are water soluble
B, C, Folic Acid
125
how are fat soluble vitamins absorbed
same pathway as fat
126
how are water soluble vitamins absorbed
- passive diffusion
or
- carrier mediated transport (like micelle for fat)
127
how is vitamin B12 absorbed
it binds to an intrinsic factor in the stomach to form complex which is absorbed via a specific transport mechanism in the distal ileum
128
what can occur as a result of B12 deficiency
pernicious anaemia
129
what is pernicious anaemia?
failure of red blood cell maturation
130
what causes pernicious anaemia?
B12 deficiency
131
how much of daily iron intake is absorbed into the blood?
10%
132
how is iron stored
incorporated into ferritin
133
what does iron in blood bind to
transferrin
134
what is the only nutrient that has controlled absorption?
iron
135
hyperaemia
increase ferritin levels - more iron bound in enterocytes
136
anaemia
decrease ferritin levels -more iron released into the blood
137
how is chewing controlled
VOLUNTARY
-skeletal muscles of mouth/ jaw
REFLEX
-contraction of jaw muscles ->pressure of food against gums, hard palate and tongue -> mechanoreceptors -> inhibition of jaw muscles -> reduced pressure -> contraction ... etc...
138
components of saliva
```
water
mucins
a-amylase
electrolytes
lysozyme
```
139
purpose of water in saliva
softens
moistens
dilutes particles
solvent
140
purpose of lysozyme in saliva
bactericidal (cleave polysaccharide component of bacterial cell wall)
141
purpose of electrolytes in saliva
maintains tonicity/ pH
142
exocrine duct
leads to the outside
143
endocrine duct
leads onto a surface
144
types of salivary gland
- parotid gland
- submandibular gland
- sublingual gland
145
effect of parasympathetic and sympathetic nervous system on salivary excretion
both stimulatory
146
sympathetic stimulus reaction - type of saliva
viscous, less water, more protein
147
parasympathetic stimulus reaction - type of saliva
very runny, lots of water, like a dog drooling
148
reflex control of salivary excretion - description
presence of food in mouth -> chemoreceptors/ pressure receptors
149
what type of epithelium lines oesophagus
stratified squamous epithelium
150
describe the control of muscularis externa in the oesophagus
upper 1/3 = skeletal
lower 2/3 = smooth
151
purpose oesophageal sphincters
regulate movement of material into and out of oesophagus
152
function of soft palate in mouth upon swallowing
it is reflected backwards and upwards, closing off nasopharynx to stop food coming out of the nose
153
what happens when food/ liquid approaches the oesophagus
- upper oesophageal sphincter relaxes and epiglottis covers opening to larynx (preventing food from entering the trachea)
154
what happens once food has entered the oesophagus?
upper oesophageal sphincter contracts preventing food reflux
155
how long does it take to get food from mouth to stomach
about 10 seconds
156
what happens as food nears the stomach
lower oesophageal sphincter relaxes - food enters the stomach
157
describe the change in pressure of the stomach when food enters (up to 1.5l)
there is no change in pressure due to Rugae (folds in the stomach lining) moving out
158
5 functions of the stomach
- store food temporarily
- sterilise ingested material
- dissolve food particles and initiate digestive process
- control delivery of contents to the small intestine
- produce intrinsic factor needed for vitamin B absorption
159
what is the only non-compensatable function of the stomach
producing the intrinsic factor that enables vitamin B12 absorption
160
what is serosa
connective tissue outer layer
161
what type of cells are found in gastric glands
- surface mucous cell
- mucous neck cell
- parietal cell
- chief cell
162
where are gastric glands found
stomach
163
what is produced in the body of the stomach
mucous
HCL
Pepsinogen
Intrinsic Factor
164
what is a fundus
hollow part of an organ
165
what is the purpose of the fundus in the stomach
food storage
166
function of the antrum of the stomach
- mixing/ grinding food
| - producing gastrin
167
explain pepsin storage in stomach
pepsin digests protein, so if left by itself in the stomach it would digest the stomach. it is therefore stores in an inactive precursor form; pepsinogen.
168
what produced gastrin
G-cells
169
function mucous neck cells
produce mucous
170
function chief cells
produce, store and secrete pepsinogens
171
function parietal cells
- secrete HCl
| - secrete intrinsic factor
172
what happens to the cells as you go further down a gastric gland?
they become more specialised
173
describe the journey of gastrin
produced in the antrum of the stomach, travels all the way round the circulatory system only to end up 1cm above where it started in the stomach
174
what 3 regulatory molecules stimulate acid secretion in the stomach?
gastrin
histamine
acetylcholine
175
what do these 3 molecules have in common?
- gastrin
- acetylcholine
- histamine
they all stimulate acid secretion in the stomach
176
function of prostaglandins in the stomach?
inhibit acid secretion
177
what molecule inhibits acid secretion in the stomach
prostaglandins
178
what molecule is a lot of produces when stimulating acid production? (and not the acid itself)
Ca
179
what 3 mechanisms is gastric acid secretion controlled by
neurocrine
endocrine
paracrine
180
how does neurocrine control gastric acid secretion
vagus/ local reflexes
181
how does endocrine control gastric acid secretion
gastrin (hormone)
182
how does paracrine control gastric acid secretion
histamine
183
explain paracrine
hormone which only has an effect on the vicinity of the gland secreting it - it doesn't travel anywhere else
184
what happens when we see/ smell/ taste food?
vagus nerve is stimulates, causing an increase in production of ACh and gastrin, which stimulates parietal cells resulting in an increased production of gastric acid
185
what happens when there is a large amount of gastrin/ ACh
- stimulates parietal cells
| - activates ECL cells, which release histamine, again stimulates parietal cells
186
Cephalic Stimuli for Parietal cells
- smell/ sight/ taste of food
187
Gastric stimuli of parietal cells
- distension of stomach (arrival of food)
- peptides in lumen
- gastrin/ ACh
188
what happens upon distension of stomach (arrival of food)
vagal/ enteric reflexes activated producing ACh, which activates parietal cells
189
what happens when there are peptides in the lumen
G Cells activated, gastrin produced activating parietal cells
190
cephalic mechanisms inhibiting gastric acid secretion
stopping eating = decrease in vagal activity
191
gastric mechanisms inhibiting gastric acid secretion
decrease in pH = increase in HCl = decrease in gastrin
192
intestinal mechanisms inhibiting gastric acid secretion
acid shouldn't be in the duodenum cause that means theres an excess thats not being used; therefore if any appears here this inhibits it
193
different areas for inhibition of gastric acid secretion
- intesine (duodenum)
- cephalic (head)
- gastric (stomach)
194
enterogastrones
hormones released from gland cells in duodenal mucosa
195
why are enterogastrones released
in response to acid, hypertonic solutions, fatty acids or monoglycerides in duodenum.
196
what do enterogastrones do
act collectively to prevent further acid build up in duodenum
197
what 2 strategies do enterogastrones employ to prevent acid build up in duodenum?
- inhibit gastric secretion
| - reduce gastric emptying (inhibit motility/ contract pyloric sphincter)
198
what is pepsinogen secreted by?
chief cells in gastric glands
199
what happens to pepsin below pH 3
becomes pepsinogen
200
what happens to pepsins at neutral pH?
inactivated
201
what produces gastric mucus
- surface epithelial cells
| - mucous neck cells
202
cytoprotective role of gastric mucous?
- protects mucosal surface from mechanical injury
| - neutral pH - protects against gastric acid corrosion and pepsin digestion
203
what is produced by parietal cells other than gastric acid?
intrinsic factor required for vitamin B12 absorption
204
2 major lobes of the liver
right> left
205
2 minor lobes of the liver
caudate, quadrate
206
where is the entry/ exit point of blood and lymphatic vessels, and nerves in the liver
Porta
207
what is the porta
the entry/ exit point of blood and lymphatic vessels, and nerves in the liver
208
Sphincter of Oddi
Mucular valve that controls the release of digestive juices (pancreatic enzymes and bile) from the first part of the duodenum into the second.
209
falciform ligament
separates right and left lobes of the liver, but also keeps them attached
210
which part of the liver attaches to the under side of the diaphragm?
Caudate
211
septa meaning
walls
212
what is the liver covered by?
connective tissue capsule and visceral peritoneum except for the bare area
213
how is the liver divided and by what
into hexagonal lobules and by septa
214
what is portal triad composed of?
- hepatic portal vein
- hepatic artery
- hepatic duct
215
where are portal triads located
at each corner of hexagonal lobule
216
what are the functional units of the liver
lobules
217
what are hepatic cords composed of?
hepatocytes
218
function of hepaocytes
functional cells of the liver: remove rubbish and dump into canaliculus.
219
where does clean blood from the liver go to
hepatic sinusoids
220
what are the spaces between hepatic cords known as
hepatic sinusoids
221
where do toxins go once they have been thrown out of your liver?
intestine then out of body
222
six components of bile
1) bile acids
2) lecithin
3) cholesterol
4) bile pigments
5) toxic metals
6) bicarbonate
223
what is the only bile component not secreted by hepatocytes?
bicarbonate (HCO3)
224
how is HCO3 produced?
secreted by duct cells
225
how do bile pigments occur?
breakdown products of haemoglobin from old/damaged erythrocytes
226
what is the predominant bile pigment
bilirubin
227
what colour does bilirubin turn bile
yellow
228
what causes bilirubin to turn brown
modification by bacterial enzymes
229
what happens to reabsorbed bilirubin and what is it's effect
excreted in urine - turns urine yellow
230
how much bile acid has to be synthesised every day to replace lost volume
0.5g/day
231
what is bile acid synthesised from?
cholesterol
232
what happens to bile acids before secretion?
they are conjugates with glycine or taurine to make bile salts
233
purpose of turning bile acids to bile salts?
increase solubility
234
how are secreted bile salts recycled
via enterohepatic circulation
235
describe the shape/ location of the gallbladder
saclike structure on inferior surface of the liver
236
3 layers in the gallbladder wall
- mucosa
- muscularis
- serosa
237
what happens when the sphincter of Oddi is closed?
bile is forced back into the gall bladder
238
what effects does the gallbladder have on bile concentration?
increases it 5-20x (dependent on how long its in there)
239
what happens when there is fat in the duodenum?
CCK is released, the sphincter of oddi relaxes and the gallbladder contracts, releasing bile
240
over what area do peristaltic waves occur?
body --> antrum of stomach
241
describe motility of the body of the stomach
thin muscle
weak contraction
no mixing
242
describe motility of the antrum of the stomach
thick muscle
powerful contraction
mixing
243
describe the effects of peristaltic waves on movement of stomach contents to duodenum
cause contraction of pyloric sphincter, squeezing a small quantity of gastric contents into the duodenum
244
what produces and, conducts gastric peristaltic waves?
pacemaker cells in the longitudinal muscle layer. conducted through gap junctions along longitudinal muscle layer
245
how many gastric peristaltic waves are there per minute
3ish
246
what causes the slow wave rhythm of gastric peristaltic wave?
BER/ Basic Electrical Rhythm
247
what determines the strength of contraction of a peristaltic wave?
number of action potentials per wave
248
what can cause an increase in strength of contraction of peristaltic wave?
- gastrin
| - distension of stomach wall (when it fills with food)
249
what can cause an decrease in strength of contraction of peristaltic wave?
- fat/ acid/ amino acid/ hypertonicity in duodenum (means too much stuff is going through too quickly)
250
where is bicarbonate (HCO3) produced?
Brunner's gland duct cells (submucosal)
251
what is triggered by acid in the duodenum that results in HCO3 secretion
- long (vagal) and short (ENS) reflexes
| - release of secretin from S Cells
252
explain the pathway of secretin and HCO3
secretin released from S Cells -> HCO3 secreted from pancreas and liver -> acid neutralisation -> inhibits secretin release
negative feedback control pathway
253
4 sections of pancreas
head (located within curvature of duodenum)
neck
body
tail
254
explain endocrine portion of pancreas
there are pancreatic islets which produce hormones
255
what hormones are produced by the endocrine portion of the pancreas
- insulin
- glucagon
- somatostatin
256
what does somatostatin do?
controls secretion of insulin and glucagon in the pancreas
257
explain exocrine portion of the pancreas
acinar cells produces enzymes which are secreted into the duodenum via ducts
responsible for digestive function of the pancreas
258
What proportion of the duodenum is taken up by exocrine-ness
80-85%
259
function of exocrine pancreas
- secretion of bicarbonate by duct cells
| - secretion of digestive enzymes by acinar cells
260
where is sphincter of oddi located?
between pancreas and duodenum
261
function of Islet of Langerhans
secrete insulin
262
what do acinar cells contain
digestive enzymes stored as inactive zymogen granules
263
what prevents auto digestion of the pancreas?
the ability of acinar cells to store digestive enzymes inactively as zymogen granules
264
function enterokinase
converts trypsinogen to trypsin
265
location enterokinase
bound to brush border of duodenal enterocytes
266
function trypsin
converts all other zymogens to active forms
267
different categories of pancreatic enzymes (6)
```
proteases
nucleases
elastase
phospholipases
lipases
a-amylase
```
268
proteases
cleave peptide bonds
269
nucleases
hydrolyse DNA/RNA
270
elastases
collagen digestion
271
phospholipases
phospholipids -> fatty acids
272
lipases
triglycerides -> fatty acids and glycerol
273
a-amylases
starch -> maltose and glucose
274
what stimulates zymogen secretion
cholecystokinin (CCK)
275
what causes CCK (cholecystokinin) to be released?
- Fat/ amino acids in duodenum
| - organic nutrients in duodenum (local reflexes due to distension)
276
approximate length small intestine
6m
277
approximate lengths of parts of small intestine
1. duodenum = 25cm
2. jejunum = 250cm
3. ileum =. 350cm
278
functions duodenum
- gastric acid neutralisation
- digestion
- iron absorption
279
functions jejunum
- 95% nutrient absorption
280
functions ileum
- NaCl/ H2O absorption (chyme dehydration)
281
chyme
gastric contents coming out of stomach
282
how is the absorptive surface area of the small intestine increased
folds
villi
microvilli
283
name of folds inside small intestine
plicae
284
difference in appearance of villi in vegetarians
flatter than meat eaters
285
how often are small intestinal cells replaced
every 5 days
286
consequences of rapid dividing time of small intestinal cells
they can be affected by drugs targeting rapidly dividing cells e.g. cancer treatment
287
explain cell movement on villi
cells start at the bottom and migrate upwards, specialising as they go
288
what is secreted/ absorbed by crypts in small intestine
H2O + Cl secreted, nothing absorbed
289
explain crypts in terms of someone with cystic fibrosis
they don't secrete water, meaning that mucous layer on top of villi begins to build up and nutrients cannot be absorbed
290
what is absorbed by a villus cell in small intestine
```
NaCl
Monosaccharides
Amino Acids
Peptides
Fats
Vitamins
Minerals
Water
```
291
how much fluid does the small intestine secrete per day
1500ml ish
292
how does H2O secretion in small intestine occur
passively, along osmotic gradient cause theres a high amount of choride in intestinal lumen
293
why is H20 secretion in the small intestine important for normal digestive process
- maintains lumen contents in liquid state
- promotes mixing of nutrients with digestive enzymes
- aids nutrient presentation to absorbing surface
- dilutes and washes away potentially injurous substances (protective function)
294
what are the 2 distinct types of intestinal movement
1. segmentation
| 2. peristalsis
295
explain segementation in the small intestine
- most common during a meal
- contraction/ relaxation of small segments
- chyme moves up and down from contracted areas to relaxed areas, then these switch
296
benefits of the segmentation movement
- provides a thorough mixing of contents
| - brings chyme into contact with absorbing surface
297
difference between gastric peristaltic wave creation and intestinal segmentation contractions
whereas the rate of contraction in the stomach remains the same throughout its length, the BER decreases slowly as it moves from intestine -> rectum
298
reasoning for change of rate of contraction. throughout the intestine
more is being squeezed down from the top than up from the bottom
299
can we conciously influence rate of contraction of intestine, stomach etc.
nah xox
300
what happens following the absorption of nutrients in the small intestine
peristalsis movement replaces segmentation
301
what is the MMC (Migrating Motility Complex)
pattern of peristaltic activity travelling down small intestine (starts in gastric antrum)
302
what causes the cessation of MMC and the initiation of segmentation
arrival of food in stomach
303
functions MMC
- move undigested material to large intestine
| - limit bacterial colonisation of small intestine
304
what hormone is involved in MMC?
motilin
305
difference between peristalsis and segmentation
peristalsis only squishes food one way - no reverse peristalsis
306
law of small intestine
if intestinal smooth muscle is distended (e.g. by bolus of chyme), muscle on oral side contracts, muscle on anal side relaxes.
307
gastroilieal reflex - explain
1. opening of ileocaecal valce
2. entry of chyme into large intestine
3. distension of colon
4. reflex contraction of ileocecal sphincter (prevents reflux back into small intestine)
308
how long is colon/ large intestine
1.5-1.8m
309
4 parts of large intestine
ascending
transverse
descending
sigmoid
310
describe muscle layers colon
circular complete, longitudinal incomplete - hence puffs jacket look because circular pops through
311
what happens upon contractions of tiniae coli in large intestine
pouches (puffa jacket appearance)
312
what are pouches in large intestine called
haustra
313
surface of mucosa in large intestine:
large, straight crypts lines with a large number of goblet cells (lubrication for movement of faeces)
314
describe rectum
straight, muscular tube between sigmoid colon and anal canal
315
describe epithelium mucosa of rectum and large intestine
similar columnar epithelium
316
describe muscularis externa of rectum
thick compared to other regions of alimentary canal
317
describe anal canal
2-3cm between distal rectum and anus
318
describe muscularis externa of anal canal
thicker than rectum
319
what is the external anal sphincter made of
skeletal muscle (we have voluntary control over it)
320
epithelium anal canal
stratified squamous
321
purpose of colon
actively transports Na from lumen to blood -> osmotic absorption of water -> dehydration of chyme -> solid faecal pellets
322
describe presence of bacteria in colon
around 10^14 - about 1kg of colonic microflora
323
purpose of bacteria in colon
fermentate undigested carbohydrate into short chain fatty acids, vitamin K and gas (flatus/pops)
324
problems associated with not having bacteria in your colon when you're born
you can't fermentate the undigested bacteria, and therefore can't make vitamin K, so are at risk of bleeding
325
function of vitamin K
blood clotting
326
what happens following a meal with regards to MMC and defaecation
wave of intense contraction resulting in distension of rectal wall as a mass movement of faecal material into the rectum occurs, initiating a defaecation reflex and an urge to defaecate.
327
what nerve supply controls defaecation
pelvic splanchnic nerves (parasympathetic)
328
3 stages of defaecation
1. contraction of rectum
2. relaxation of internal and contraction of external anal sphincters
3. increased peristaltic activity in colon
4. an increase in pressure on external sphincter, which relaxes under voluntary control
5. expulsion of faeces
329
why do children under 2ish have to wear nappies
because voluntary delay of defaeciation has to be learned
330
symptoms of constipation
headaches
nausea
loss of appetite
abdominal distension
331
what causes constipation
distension of rectum
332
causes of diarrhoea
```
pathogenic bacteria
protozoans
viruses
toxins
food
nervousness
```
333
type of bacteria causing diarrhoea and examples
enterotoxigenic bacteria
e. g.
- vibrio cholerae
- e. coli
334
effect bacteria have that causes diarrhoea
they turn on intestinal chloride solution, which in turn increases H2O secretion. large intestine doesn't have a large surface area, so can't absorb the water efficiently- hence the diarrhoea
dont damage villi
335
treatment of secretory diarrhoea
- give sodium/glucose solution cause this drives H2O absorption, rehydrating
