GI physiology Flashcards
(176 cards)
1
Q
What are the 4 functions of the digestive system
A
Digestion (mechanical breakdown of food)
Secretion ( chemical breakdown)
Absorption (nutrients taken from outside your body and transferred into your body)
Motility (muscular aspect to allow everything to be pushed along)
2
Q
What happens in the mouth
A
Foodstuffs broken down by chewing; saliva added as lubricant
3
Q
Whats the function of the oesophagus in digestion
A
conduit between mouth and stomach
4
Q
What is the stomachs function in digestion
A
Digestion of proteins; foodstuffs reduced to liquid form; storage; sterilisation
5
Q
What is the pancreas function in digestion
A
Digestive enzymes for digestion of fats, carbs and proteins
6
Q
What is the Livers function in digestion
A
Bile salts for digestion/absorption of fats in small intestine
7
Q
Function of gallbladder
A
Stores and concentrates bile
8
Q
Function of small intestine in digestion
A
Final stages of chemical digestion and nutrient absorption
9
Q
Function of the Large intestine in digestion
A
Water absorption, bacterial fermentation and formation of faeces
10
Q
What are the 4 distinctive layers of the alimentary canal
A
- Mucosa: epithelium, lamina propria, muscularis mucosa
- Submucosa
- Muscularis externa
- Serosa/adventitia
11
Q
What type of epithelium is present in the mouth, oesophagus, and anal canal
A
Stratified squamous
12
Q
What type of epithelium is present in stomach, small and large intestine
A
Simple columnar
13
Q
What is Lamina propria
A
Loose connective tissue (glands, blood/lymph vessels)
14
Q
What is Muscularis mucosa
A
Thin smooth muscle layer
15
Q
What is Submucosa
A
Thick, irregular connective tissue which supports mucosa
16
Q
What is serosa / adventitia
A
Connective tissue outer layer of alimentary canal
17
Q
What does serosa do outside the peritoneal cavity
A
Attaches oesophagus and rectum to surrounding structures
18
Q
What does serosa do inside the peritoneal cavity
A
Surrounds stomach, small intestine and large intestine
19
Q
What is muscularis external
A
Two concentric thick layers of smooth muscle:
Inner layer = circular muscle (constricts lumen)
Outer layer = longitudinal muscle (shortens tube)
20
Q
Where is the myenteric plexus
A
Between circular and longitudinal muscle
21
Q
What do the submucosal and myenteric plexus make
A
enteric nervous system (ENS) = independent control of gut function
22
Q
Nervous control of alimentary function:
Long Parasympathetic
1.What nerve and 2.how does it affect secretion and motility
A
- Vagus nerve ( except salivation)
2. Increase secretion and motility
23
Q
What are SHORT ENS reflexes
A
Just within the gut wall itself - CNS not involved in processes
24
Q
Sympathetic control:
1. What nerve and 2. How does it affect secretion and motility
A
Inhibitory (except salivation)
- splanchnic nerve
- decreases secretion and motility
25
Arterial supply to GI tract:
| Celiac trunk supplies what structures?
Stomach
Small intestine
Pancreas
Liver
26
Superior mesenteric artery supplies what structures?
Small intestine
Caecum
Ascending colon
Transverse colon
27
Inferior mesenteric artery supplies what structures
Descending colon
Sigmoid colon
Rectum
28
Venous drainage from GI tract:
| Where does the stomach drain to
Gastric veins - hepatic portal vein - hepatic vein - IVC
29
Where does the pancreas drain to
Splenic vein - hepatic portal vein - hepatic vein - IVC
30
Where do the small intestine, caecum, ascending colon and transverse colon drain to
Superior mesenteric vein - hepatic portal vein - hepatic vein - IVC
31
Where do the descending colon, sigmoid colon, rectum drain to
Inferior mesenteric vein - hepatic portal vein - hepatic vein - IVC
32
What 2 sugars make lactose and what enzyme is involved
glucose and galactose
| enzyme = lactase
33
What 2 sugars make sucrose and what enzyme is involved
glucose and fructose
| enzyme = sucrase
34
What 2 sugars make maltose and what enzyme is involved
Glucose and Glucose
| enzyme = maltase
35
What 2 sugars have a-1,4 glycosidic bonds
starch
| glycogen
36
What sugar has B-1,4 glycosidic bonds
cellulose
37
Where is the brush border and what does it do
In the apical membrane
| Increasing surface area
38
What do proteases or peptidases do
Enzymes which hydrolyse peptide bonds and reduce proteins or peptides to amino acids
39
What do endopeptidase act on
The interior of the protein
40
What do exopeptidase act on
On the terminal amino acids - getting one shorter each time - can work at either end
41
What is NHE3
hydrogen and sodium exchange
| roughly 70% of protein in diet comes in this way
42
Almost all ingested fat is in the form of what
Triacylglycerol (insoluble in water)
43
All fat digestion in small intestine is by what
Pancreatic lipase
44
What is lipase
Water-soluble enzyme
45
What is emulsification
dividing large droplets into smaller droplets.
46
What does emulsification require
mechanical disruption
emulsifying agent
bile salts and phospholipids
amphipathic molecules
47
What are micelles
similar to emulsion droplets but much smaller
| = bile salt + monoglycerides +fatty acids + phospholipid
48
Describe micelle breakdown
Release of small amounts of free fatty acids and monoglycerides into solution - diffusion across plasma membrane of absorbing cells
49
Dynamic equilibrium between fatty acids and monoglycerides in solution and in micelles does what?
retains most of fat digestion products in solution while constantly replenishing supply of free molecules for absorption
50
What is a chylomicron
Extracellular fat droplet - contain phospholipid, cholesterol and fat soluble vitamins.
51
How do chylomicrons travel
Pass into lacteals between endothelial cells
52
How are triacylglycerol droplets transported through the cell
In vesicles formed from Smooth endoplasmic reticulum - processed through golgi apparatus and exocytosed into extracellular fluid at serosal membrane
53
What are the fat soluble vitamins
| And how are they absorbed
A,D,E,K
| Follow same absorptive path as fat
54
What are the water soluble vitamins
| and how are they absorbed
B group, C and folic acid
| Absorbed by passive diffusion or carrier - mediated transport
55
What is Vitamin B-12 and what does it bind to in the stomach
Large charged molecule
| Binds to intrinsic factor in stomach to form complex which is absorbed via specific transport mechanism in distal ileum
56
Where is iron transported
Across brush border membrane (via DMT1) into duodenal enterocytes
57
Where is unbound iron transported
Across serosal membrane to the blood
58
What does iron in blood bind to
Transferrin
59
How is ferritin expression regulated
Body iron status
60
What is hyperaemia
Increased ferritin levels - more iron bound in enterocytes
61
What is anaemia
Decreased ferritin levels - more iron released to blood
62
Why do we chew
Prolong taste
| defence against resp failure
63
How is chewing controlled
1. Voluntary - somatic nerves - skeletal muscles of mouth and jaw
2. Reflex - contraction of jaw muscles - pressure of food against gums, hard palate and tongue - mechanoreceptors - inhibition of jaw muscles - reduced pressure - contraction...
64
Saliva is secreted by which 3 pairs of glands
Parotid
Submandibular
Sublingual
65
What is in saliva and what does each component do
1. Water - 99% of secreted fluid. Softens, moistens, dilutes particles. solvent
2. Mucins - major protein component. Mucins + water = mucus. viscous solution - lubricant function
3. a - Amylase - catalyses breakdown of polysaccharide (starch, glycogen) into disaccharide (maltose) + glucose
4. Electrolytes - tonicity / pH
5. Lysozyme - bactericida - cleaves polysaccharide component of bacterial cell wall
66
How is salivary secretion controlled - parasympathetic
Cranial nerves VII (facial) and IX (glossopharyngeal)
| stimulation - profuse watery salivary secretion
67
How is salivary secretion controlled - sympathetic
Stimulation - small vol, viscous salivary secretion high mucus content (a1 adrenoreceptors)
high amylase content (B2 adrenoreceptors)
68
How is salivary secretion controlled - Reflex control
Presence of food in mouth - chemoreceptors / pressure receptors (wall of mouth/tongue)
69
What do upper and lower oesophageal sphincters regulate
movement of material into and out of oesophagus
70
Muscularis externa is split into upper and lower - how is it split?
Upper 1/3 (superior) = skeletal muscle
| Lower 2/3 (inferior) = smooth muscle
71
Swallowing: 1.Oral phase
Voluntary
| Bolus pushed to back of mouth by tongue
72
Swallowing: 2.Pharyngeal phase
Presence of bolus - sequence of reflex contractions of pharyngeal muscles.
Co-ordinated by swallowing centre (medulla)
soft palate reflected backward and upward (closes off nasopharynx)
73
Swallowing: As bolus approches oesophagus
Upper oesophageal sphincter (UOS) relaxes and epiglottis covers opening to larynx (prevents food entering trachea
74
Swallowing: Once food has entered oesophagus
UOS contracts ( prevents food reflux)
75
Swallowing : 3. Oesophageal phase
Propulsion of bolus to stomach
peristaltic wave sweeps along entire oesophagus
propelled to stomach in 10secs
76
Swallowing: As bolus nears stomach
LOS relaxes - bolus enters stomach
77
Receptive relaxation of stomach
Vagal reflexes - relaxation of thin, elastic smooth muscle of gastric fundus and body.
Stomach vol - 50ml - 1500ml (no change in pressure)
78
What are the main functions of the stomach
1. Temporary store of ingested material
2. Dissolve food particles and initiate digestive process
3. Control delivery of contents to small intestine
4. Sterilise ingested material
5. Produce intrinsic factor ( Vit B 12 absorption)
79
Histology of stomach:
| What are the 3 layers of muscularis externa
Longitudinal (outer)
Circular (middle)
Oblique (inner)
80
What is present in the lumens surface
Surface mucus cells - gastric pits - gastric glands - mucus neck, parietal and chief cells
81
Submucosa and mucosa are folded when stomach is empty and what when filled?
rugae
| stretch as stomach fills
82
What is the function of the fundus of the stomach
Storage
83
What are the functions of the body of the stomach
```
Storage
Mucus
HCL
Pepsinogen
Intrinsic factor
```
84
What is the function of the antrum of the stomach
Mixing and Grinding
| Gastrin
85
What do mucous neck cells produce
Mucus
86
What do chief cells produce
pepsinogens
87
What do parietal cells produce
HCl
| intrinsic factor
88
What 3 mechanisms control gastric acid secretion
Neurocrine (vagus/local reflexes)
Endocrine (gastrin)
Paracrine (histamine)
89
What are enterogastrones and give examples
Hormones released from gland cells in duodenal mucosa
| e.g. secretin, cholecystokinin , GIP
90
When are enterogastrones released
Released in response to acid, hypertonic solutions, fatty acids or monoglycerides in duodenum
91
What do enterogastrones do
Act collectively to prevent further acid build up in duodenum
92
How do enterogastrones prevent acid build up in duodenum
Inhibit gastric acid secretion
| Reduce gastric emptying (inhibit motility/ contract of pyloric sprinter)
93
What is pepsinogen secreted by
Chief cells
94
What produces gastric mucus
Surface epithelial cells and mucus neck cells
95
What is the cytoprotective role
Protects mucosal surface from mechanical injury.
| Neutral pH protects against gastric acid corrosion and pepsin digestion
96
What is the only essential function of the stomach
Intrinsic factor
- produced by parietal cells
- required for B12 absorption
97
Where is the intrinsic factor/B12 complex absorbed from
ileum
98
Where do peristaltic wave travel
From body to antrum
99
Describe the body of the stomach in terms of muscle, contraction and mixing
Thin Muscle
Weak contraction
No mixing
100
Describe the antrum of the stomach in terms of muscle, contraction and mixing
Thick muscle
Powerful contraction
Mixing
101
What happens when the pyloric sphincter contracts
- Only small quantity of gastric content (chyme) entering duodenum
- further mixing as antral contents forced back towards body
102
What produces gastric peristaltic waves
1. peristaltic rhythm - generated by pacemaker cells (longitudinal muscle layer)
2. Slow waves - spontaneous depolarisation/repolarisation
103
Describe slow wave rhythm
Basic electrical rhythm (BER)
| Slow waves conducted through gap junctions along longitudinal muscle layer.
104
Describe depolarisation and AP of slow waves
Slow wave depolarisation sub-threshold - require further depolarisation to induce AP = contraction
Number of APs/waves determines strength of contraction
105
What happens to motility under neural/hormonal control
Gastrin = increases contraction
Distension of stomach wall - long/short reflexes - increased contraction
Fat/acid/amino acid/ hypertonicity in duodenum - inhibition of motility
106
What is responsible for neutralisation of Acid in duodenum
Bicarbonate (HCO3) secretion from brunner's gland duct cells (submucosal glands)
107
What does acid in the duodenum trigger
1. Long (vagal) and short (ENS) reflexes. HCO3 secretion
2. Release of secretin from S cells. HCO3 secretion
- secretin HCO3 secretion from pancreas and liver
- Acid neutralisation - inhibits secretin in release (negative feedback control)
108
What are the 3 parts of the pancreas.
Head (located within curvature of duodenum)
Body
Tail (extends to the spleen)
109
Histology of endocrine portion of pancreas
Pancreatic islets ( islets of langerhans)
110
What do islet cells produce
Insulin
| Glucagon (control [glucose]blood) and somatostatin ( controls secretion of insulin and glucagon)
111
Histology of exocrine portion of pancreas
Acing cells and lobules
112
What is the anatomical structure of exocrine part of pancreas
Acini - Ducts - Pancreatic Duct
113
What is the function of the exocrine part of pancreas
Secretion of bicarbonate by duct cells
| Secretion of digestive enzymes by acinar cells
114
Acinar cells contain digestive enzymes stored as what and what does this prevent
Inactive zymogen granules
| Prevents auto digestion of pancreas
115
What does enterokinase do
Converts trypsinogen to trypsin
116
What does Trypsin do
Converts all other zymogens to active form
117
What do proteases do
Cleave peptide bonds
118
What do nucleases do
Hydrolyse DNA/RNA
119
What do elastases do
Collagen digestion
120
What do phospholipases do
Phospholipids to fatty acids
121
What do lipases do
Triglycerides to fatty acids + glycerol
122
What does a- amylase do
Starch to maltose + glucose
123
Bicarbonate secretion is stimulated by what
secretin
124
Secretin is released in response to what
Acid in the duodenum
125
Zymogen secretion is stimulated by what
Cholecystokinin (CCK)
126
CCK is released in response to what
Fat/ amino acids in duodenum
| - also under neural control - triggered by arrival of organic nutrients in duodenum
127
What is in the portal traid of the liver
Hepatic portal vein
Hepatic artery
Hepatic duct
128
What are hepatic cords composed of
Hepatocytes = functional cells of liver
129
What are the spaces between hepatic cords called
hepatic sinusoids
130
What lies between cells within each cord
Bile Canaliculus
131
What is the alimentary role of the liver
Production and secretion of bile
132
What are the 6 components of bile
1. Bile acids
2. Lecithin ( all these 3 synthesised in liver. solubilise fat)
3. cholesterol
4. Bile pigments ( bilirubin)
5. Toxic metals ( Detoxified in liver)
6. Bicarbonate (neutralisation of acid chyme)
133
What are the components of bile secreted by
1-5 secreted by hepatocytes (liver cells)
| HCO3 secreted by duct cells
134
What do bile pigments do
Breakdown products of haemoglobin from old/damaged erythrocytes
135
Where is bilirubin (predominant bile pigment) extracted from and what is it secreted into
Blood by hepatocytes and secreted into bile
| Yellow bile
136
What is the result of bilirubin modified by bacterial enzymes
Brown pigments
| Brown faeces
137
What does reabsorbed bilirubin excreted in urine cause
Yellow urine
138
Where are bile acids synthesised
In liver from cholesterol
139
What do bile acids do before secretion
Bile acids conjugated with glycine or taurine - bile salts
| increase solubility
140
Secreted bile salts is recycled via what
enterohepatic circulation
141
Where does the gall bladder lie
On inferior surface of liver
142
What are the 3 layers in the wall of the gallbladder
1. Mucosa (folded - rugae - expansion)
2. Muscularis (smooth muscle) - contraction
3. Serosa (connective tissue)
* Gallbladder - cystic duct - common bile duct
143
How does the sphincter of Oddi help in control of bile secretion
Controls release of bile and pancreatic juice into duodenum.
When contracted (closed) - bile forced back into gallbladder
Gallbladder concentrates bile 5-20 times (absorbs Na+ & H2O)
Fat in duodenum - release of CCK
- CCK - (A) sphincter of odds relaxes
- (B) Gallbladder contracts
Discharge of bile into duodenum - fat solubilisation
CCK - Pancreatic enzyme secretion
- Bile secretion
144
What are the 3 parts of the small intestine and what do they do
1. duodenum - gastric acid neutralisation; digestion; iron absorption
2. Jejunum - Nutrient absorption - 95%
3. Ileum - NaCl/H20 absorption - chyme dehydration
The absorptive surface area enhanced by folds, villi, microvilli
145
Intestinal Absorption and secretin: What do villi absorb
```
NaCl
monosaccharides
amino acids
peptides
fats
vitamins
minerals
Water
```
146
What do Crypts secrete
Secretes Cl and Water
147
Intestinal fluid secretion: How much water is secreted per day by the small intestine
1500ml
148
How is water secreted
Secretion comes from epithelial cells lining crypts of Lieberkuhn.
Water secreted passively as a consequence of active secretion of chloride into intestinal lumen.
Normally water secreted by crypts reabsorbed by villi
149
Water secretion important for which normal digestive processes
A - Maintains lumens contents in liquid state
B - Promotes mixing of nutrients with digestive enzymes
C - Acids nutrient presentation to absorbing surface
D - Dilutes and washes away potentially injurious substances
150
Intestinal motility:
| What are the two distinct types of movement
Segmentation
| Peristalsis
151
Describe segmentation:
1. Most common during meal
2. contraction relaxation of short intestinal segments
- Contraction (few seconds) moves chyme (up and down) into adjacent area of relaxation
3. relaxed areas then contract and push chyme back
- Provides through mixing of contents with digestive enzymes
- bring chyme into contact with absorbing surface
152
How is the generation of segmentation contractions initiated
By depolarisation generated by pacemaker cells in longitudinal muscle layer
153
What determines the frequency of the segmentation
The basic electrical rhythm
| BER decreases as move down intestine - rectum
154
What effect does the parasympathetic NS have on contraction
Increases contraction
155
What effect does the sympathetic NS have on contraction
Decreases contraction
156
Describe peristalsis
Migrating motility complex (MMC)
- Pattern of peristaltic activity travelling down small intestine (starts in gastric antrum)
- As on MMC ends (terminal ileum) another begins
- Arrival of food in stomach - cessation of MMC and initiation of segmentation
157
What does Migrating motility Complex do
Move undigested material into large intestine
| Limit bacterial colonisation of small intestine.
158
What is the hormone involved in initiating MMC
Motilin
159
What is the law of the intestine
If intestinal smooth muscle is distended
Muscle on oral side of bolus contracts - muscle on anal side of bolus relaxes - Bolus is moved into area of relaxation towards colon.
Mediated by neurones in myenteric plexus
160
What is the gastroileal reflex
Gastric emptying - increases segmentation activity in ileum.
- opening of ileocaecal valve (sphincter)
- entry of chyme into large intestine
- distension of colon
- reflex contraction of ileocaecal sphincter (prevents back flux into small intestine)
161
What are the 4 parts of the large intestine
Ascending, transverse, descending and sigmoid
162
What do large, straight crypts lined with and what do they do
Lined with large number of goblet cells
| They are there for lubrication for movement of faeces
163
Where is the rectum located
Straight, muscular tube - between end of sigmoid colon and anal canal
164
What is the muscularis externa like in the rectum
Thick compared to other regions of alimentary canal
165
Where is the anal canal
2-3 cm between distal rectum and anus
166
Describe the 1. Muscularis
| 2. Sphincter and 3. Epithelium of the anal canal
1. Muscularis thicker than rectum - internal anal sphincter
2. External anal sphincter = skeletal muscle
3. Epithelium: simple columnar - stratified squamous
167
What happens in the colon
Actively transports sodium from lumen into blood - osmotic absorption of water - dehydration of chyme - solid faecal pellets
168
Defaecation following a meal
Wave of intense contraction (Mass movement contraction) - colon --> rectum.
Distension of rectal wall produced by mass movement of faecal material into rectum --> mechanoreceptors --> defaecation reflex --> urge to defaecate
169
What is the Defaecation Reflex
Under parasympathetic control - via pelvic splanchnic nerves
1. Contraction of rectum
2. Relaxation of internal and contraction of external anal sphincters
3. Increased peristaltic activity in colon
- increases pressure on external anal sphincter - relaxes under voluntary control = expulsion of faeces
170
What causes constipation
No absorption of toxins from faecal material following long periods of retention.
171
What are some symptoms associated with constipation
Headaches
Nausea
Loss of appetite
Abdominal distension
172
What is diarrhoea
Too frequent passage of faeces which are too liquid
173
What are the causes of diarrhoea
```
Pathogenic bacteria
Protozoans
viruses
toxins
food
```
174
What do enterotoxigenic bacteria do
Produce protein enterotoxins which maximally turn on intestinal chloride secretion from crypt cells.
Increases water secretion
- Elevate intracellular second messengers
175
How do you treat secretory diarrhoea
Give sodium/glucose solution
- drive water absorption - rehydration
- secretion still going --> wash away infection
- Oral rehydration therapy
176
What does secreting help regulate and how?
pH of duodenum by:
1) inhibiting secretion of gastric acid from parietal cells.
2) stimulating production of bicarbonate from ductal cells of the pancreas
