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2nd Year > GI physiology > Flashcards

GI physiology Flashcards

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)

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2
Q

What happens in the mouth

A

Foodstuffs broken down by chewing; saliva added as lubricant

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3
Q

Whats the function of the oesophagus in digestion

A

conduit between mouth and stomach

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4
Q

What is the stomachs function in digestion

A

Digestion of proteins; foodstuffs reduced to liquid form; storage; sterilisation

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5
Q

What is the pancreas function in digestion

A

Digestive enzymes for digestion of fats, carbs and proteins

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6
Q

What is the Livers function in digestion

A

Bile salts for digestion/absorption of fats in small intestine

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7
Q

Function of gallbladder

A

Stores and concentrates bile

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8
Q

Function of small intestine in digestion

A

Final stages of chemical digestion and nutrient absorption

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9
Q

Function of the Large intestine in digestion

A

Water absorption, bacterial fermentation and formation of faeces

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10
Q

What are the 4 distinctive layers of the alimentary canal

A
  1. Mucosa: epithelium, lamina propria, muscularis mucosa
  2. Submucosa
  3. Muscularis externa
  4. Serosa/adventitia
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11
Q

What type of epithelium is present in the mouth, oesophagus, and anal canal

A

Stratified squamous

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12
Q

What type of epithelium is present in stomach, small and large intestine

A

Simple columnar

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13
Q

What is Lamina propria

A

Loose connective tissue (glands, blood/lymph vessels)

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14
Q

What is Muscularis mucosa

A

Thin smooth muscle layer

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15
Q

What is Submucosa

A

Thick, irregular connective tissue which supports mucosa

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16
Q

What is serosa / adventitia

A

Connective tissue outer layer of alimentary canal

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17
Q

What does serosa do outside the peritoneal cavity

A

Attaches oesophagus and rectum to surrounding structures

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18
Q

What does serosa do inside the peritoneal cavity

A

Surrounds stomach, small intestine and large intestine

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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)

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20
Q

Where is the myenteric plexus

A

Between circular and longitudinal muscle

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21
Q

What do the submucosal and myenteric plexus make

A

enteric nervous system (ENS) = independent control of gut function

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22
Q

Nervous control of alimentary function:
Long Parasympathetic
1.What nerve and 2.how does it affect secretion and motility

A
  1. Vagus nerve ( except salivation)

2. Increase secretion and motility

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23
Q

What are SHORT ENS reflexes

A

Just within the gut wall itself - CNS not involved in processes

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24
Q

Sympathetic control:

1. What nerve and 2. How does it affect secretion and motility

A

Inhibitory (except salivation)

  1. splanchnic nerve
  2. decreases secretion and motility
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25
Q

Arterial supply to GI tract:

Celiac trunk supplies what structures?

A

Stomach
Small intestine
Pancreas
Liver

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26
Q

Superior mesenteric artery supplies what structures?

A

Small intestine
Caecum
Ascending colon
Transverse colon

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27
Q

Inferior mesenteric artery supplies what structures

A

Descending colon
Sigmoid colon
Rectum

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28
Q

Venous drainage from GI tract:

Where does the stomach drain to

A

Gastric veins - hepatic portal vein - hepatic vein - IVC

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29
Q

Where does the pancreas drain to

A

Splenic vein - hepatic portal vein - hepatic vein - IVC

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30
Q

Where do the small intestine, caecum, ascending colon and transverse colon drain to

A

Superior mesenteric vein - hepatic portal vein - hepatic vein - IVC

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31
Q

Where do the descending colon, sigmoid colon, rectum drain to

A

Inferior mesenteric vein - hepatic portal vein - hepatic vein - IVC

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32
Q

What 2 sugars make lactose and what enzyme is involved

A

glucose and galactose

enzyme = lactase

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33
Q

What 2 sugars make sucrose and what enzyme is involved

A

glucose and fructose

enzyme = sucrase

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34
Q

What 2 sugars make maltose and what enzyme is involved

A

Glucose and Glucose

enzyme = maltase

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35
Q

What 2 sugars have a-1,4 glycosidic bonds

A

starch

glycogen

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36
Q

What sugar has B-1,4 glycosidic bonds

A

cellulose

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37
Q

Where is the brush border and what does it do

A

In the apical membrane

Increasing surface area

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38
Q

What do proteases or peptidases do

A

Enzymes which hydrolyse peptide bonds and reduce proteins or peptides to amino acids

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39
Q

What do endopeptidase act on

A

The interior of the protein

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40
Q

What do exopeptidase act on

A

On the terminal amino acids - getting one shorter each time - can work at either end

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41
Q

What is NHE3

A

hydrogen and sodium exchange

roughly 70% of protein in diet comes in this way

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42
Q

Almost all ingested fat is in the form of what

A

Triacylglycerol (insoluble in water)

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43
Q

All fat digestion in small intestine is by what

A

Pancreatic lipase

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44
Q

What is lipase

A

Water-soluble enzyme

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45
Q

What is emulsification

A

dividing large droplets into smaller droplets.

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46
Q

What does emulsification require

A

mechanical disruption
emulsifying agent
bile salts and phospholipids
amphipathic molecules

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47
Q

What are micelles

A

similar to emulsion droplets but much smaller

= bile salt + monoglycerides +fatty acids + phospholipid

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48
Q

Describe micelle breakdown

A

Release of small amounts of free fatty acids and monoglycerides into solution - diffusion across plasma membrane of absorbing cells

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49
Q

Dynamic equilibrium between fatty acids and monoglycerides in solution and in micelles does what?

A

retains most of fat digestion products in solution while constantly replenishing supply of free molecules for absorption

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50
Q

What is a chylomicron

A

Extracellular fat droplet - contain phospholipid, cholesterol and fat soluble vitamins.

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51
Q

How do chylomicrons travel

A

Pass into lacteals between endothelial cells

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52
Q

How are triacylglycerol droplets transported through the cell

A

In vesicles formed from Smooth endoplasmic reticulum - processed through golgi apparatus and exocytosed into extracellular fluid at serosal membrane

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53
Q

What are the fat soluble vitamins

And how are they absorbed

A

A,D,E,K

Follow same absorptive path as fat

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54
Q

What are the water soluble vitamins

and how are they absorbed

A

B group, C and folic acid

Absorbed by passive diffusion or carrier - mediated transport

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55
Q

What is Vitamin B-12 and what does it bind to in the stomach

A

Large charged molecule

Binds to intrinsic factor in stomach to form complex which is absorbed via specific transport mechanism in distal ileum

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56
Q

Where is iron transported

A

Across brush border membrane (via DMT1) into duodenal enterocytes

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57
Q

Where is unbound iron transported

A

Across serosal membrane to the blood

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58
Q

What does iron in blood bind to

A

Transferrin

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59
Q

How is ferritin expression regulated

A

Body iron status

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60
Q

What is hyperaemia

A

Increased ferritin levels - more iron bound in enterocytes

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61
Q

What is anaemia

A

Decreased ferritin levels - more iron released to blood

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62
Q

Why do we chew

A

Prolong taste

defence against resp failure

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63
Q

How is chewing controlled

A
  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…
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64
Q

Saliva is secreted by which 3 pairs of glands

A

Parotid
Submandibular
Sublingual

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65
Q

What is in saliva and what does each component do

A
  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
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66
Q

How is salivary secretion controlled - parasympathetic

A

Cranial nerves VII (facial) and IX (glossopharyngeal)

stimulation - profuse watery salivary secretion

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67
Q

How is salivary secretion controlled - sympathetic

A

Stimulation - small vol, viscous salivary secretion high mucus content (a1 adrenoreceptors)
high amylase content (B2 adrenoreceptors)

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68
Q

How is salivary secretion controlled - Reflex control

A

Presence of food in mouth - chemoreceptors / pressure receptors (wall of mouth/tongue)

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69
Q

What do upper and lower oesophageal sphincters regulate

A

movement of material into and out of oesophagus

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70
Q

Muscularis externa is split into upper and lower - how is it split?

A

Upper 1/3 (superior) = skeletal muscle

Lower 2/3 (inferior) = smooth muscle

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71
Q

Swallowing: 1.Oral phase

A

Voluntary

Bolus pushed to back of mouth by tongue

72
Q

Swallowing: 2.Pharyngeal phase

A

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
Q

Swallowing: As bolus approches oesophagus

A

Upper oesophageal sphincter (UOS) relaxes and epiglottis covers opening to larynx (prevents food entering trachea

74
Q

Swallowing: Once food has entered oesophagus

A

UOS contracts ( prevents food reflux)

75
Q

Swallowing : 3. Oesophageal phase

A

Propulsion of bolus to stomach
peristaltic wave sweeps along entire oesophagus
propelled to stomach in 10secs

76
Q

Swallowing: As bolus nears stomach

A

LOS relaxes - bolus enters stomach

77
Q

Receptive relaxation of stomach

A

Vagal reflexes - relaxation of thin, elastic smooth muscle of gastric fundus and body.
Stomach vol - 50ml - 1500ml (no change in pressure)

78
Q

What are the main functions of the stomach

A
  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
Q

Histology of stomach:

What are the 3 layers of muscularis externa

A

Longitudinal (outer)
Circular (middle)
Oblique (inner)

80
Q

What is present in the lumens surface

A

Surface mucus cells - gastric pits - gastric glands - mucus neck, parietal and chief cells

81
Q

Submucosa and mucosa are folded when stomach is empty and what when filled?

A

rugae

stretch as stomach fills

82
Q

What is the function of the fundus of the stomach

A

Storage

83
Q

What are the functions of the body of the stomach

A 
Storage 
Mucus 
HCL
Pepsinogen
Intrinsic factor
84
Q

What is the function of the antrum of the stomach

A

Mixing and Grinding

Gastrin

85
Q

What do mucous neck cells produce

A

Mucus

86
Q

What do chief cells produce

A

pepsinogens

87
Q

What do parietal cells produce

A

HCl

intrinsic factor

88
Q

What 3 mechanisms control gastric acid secretion

A

Neurocrine (vagus/local reflexes)
Endocrine (gastrin)
Paracrine (histamine)

89
Q

What are enterogastrones and give examples

A

Hormones released from gland cells in duodenal mucosa

e.g. secretin, cholecystokinin , GIP

90
Q

When are enterogastrones released

A

Released in response to acid, hypertonic solutions, fatty acids or monoglycerides in duodenum

91
Q

What do enterogastrones do

A

Act collectively to prevent further acid build up in duodenum

92
Q

How do enterogastrones prevent acid build up in duodenum

A

Inhibit gastric acid secretion

Reduce gastric emptying (inhibit motility/ contract of pyloric sprinter)

93
Q

What is pepsinogen secreted by

A

Chief cells

94
Q

What produces gastric mucus

A

Surface epithelial cells and mucus neck cells

95
Q

What is the cytoprotective role

A

Protects mucosal surface from mechanical injury.

Neutral pH protects against gastric acid corrosion and pepsin digestion

96
Q

What is the only essential function of the stomach

A

Intrinsic factor

  • produced by parietal cells
  • required for B12 absorption
97
Q

Where is the intrinsic factor/B12 complex absorbed from

A

ileum

98
Q

Where do peristaltic wave travel

A

From body to antrum

99
Q

Describe the body of the stomach in terms of muscle, contraction and mixing

A

Thin Muscle
Weak contraction
No mixing

100
Q

Describe the antrum of the stomach in terms of muscle, contraction and mixing

A

Thick muscle
Powerful contraction
Mixing

101
Q

What happens when the pyloric sphincter contracts

A
  • Only small quantity of gastric content (chyme) entering duodenum
  • further mixing as antral contents forced back towards body
102
Q

What produces gastric peristaltic waves

A
  1. peristaltic rhythm - generated by pacemaker cells (longitudinal muscle layer)
  2. Slow waves - spontaneous depolarisation/repolarisation
103
Q

Describe slow wave rhythm

A

Basic electrical rhythm (BER)

Slow waves conducted through gap junctions along longitudinal muscle layer.

104
Q

Describe depolarisation and AP of slow waves

A

Slow wave depolarisation sub-threshold - require further depolarisation to induce AP = contraction
Number of APs/waves determines strength of contraction

105
Q

What happens to motility under neural/hormonal control

A

Gastrin = increases contraction
Distension of stomach wall - long/short reflexes - increased contraction
Fat/acid/amino acid/ hypertonicity in duodenum - inhibition of motility

106
Q

What is responsible for neutralisation of Acid in duodenum

A

Bicarbonate (HCO3) secretion from brunner’s gland duct cells (submucosal glands)

107
Q

What does acid in the duodenum trigger

A
  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
Q

What are the 3 parts of the pancreas.

A

Head (located within curvature of duodenum)
Body
Tail (extends to the spleen)

109
Q

Histology of endocrine portion of pancreas

A

Pancreatic islets ( islets of langerhans)

110
Q

What do islet cells produce

A

Insulin

Glucagon (control [glucose]blood) and somatostatin ( controls secretion of insulin and glucagon)

111
Q

Histology of exocrine portion of pancreas

A

Acing cells and lobules

112
Q

What is the anatomical structure of exocrine part of pancreas

A

Acini - Ducts - Pancreatic Duct

113
Q

What is the function of the exocrine part of pancreas

A

Secretion of bicarbonate by duct cells

Secretion of digestive enzymes by acinar cells

114
Q

Acinar cells contain digestive enzymes stored as what and what does this prevent

A

Inactive zymogen granules

Prevents auto digestion of pancreas

115
Q

What does enterokinase do

A

Converts trypsinogen to trypsin

116
Q

What does Trypsin do

A

Converts all other zymogens to active form

117
Q

What do proteases do

A

Cleave peptide bonds

118
Q

What do nucleases do

A

Hydrolyse DNA/RNA

119
Q

What do elastases do

A

Collagen digestion

120
Q

What do phospholipases do

A

Phospholipids to fatty acids

121
Q

What do lipases do

A

Triglycerides to fatty acids + glycerol

122
Q

What does a- amylase do

A

Starch to maltose + glucose

123
Q

Bicarbonate secretion is stimulated by what

A

secretin

124
Q

Secretin is released in response to what

A

Acid in the duodenum

125
Q

Zymogen secretion is stimulated by what

A

Cholecystokinin (CCK)

126
Q

CCK is released in response to what

A

Fat/ amino acids in duodenum

- also under neural control - triggered by arrival of organic nutrients in duodenum

127
Q

What is in the portal traid of the liver

A

Hepatic portal vein
Hepatic artery
Hepatic duct

128
Q

What are hepatic cords composed of

A

Hepatocytes = functional cells of liver

129
Q

What are the spaces between hepatic cords called

A

hepatic sinusoids

130
Q

What lies between cells within each cord

A

Bile Canaliculus

131
Q

What is the alimentary role of the liver

A

Production and secretion of bile

132
Q

What are the 6 components of bile

A
  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
Q

What are the components of bile secreted by

A

1-5 secreted by hepatocytes (liver cells)

HCO3 secreted by duct cells

134
Q

What do bile pigments do

A

Breakdown products of haemoglobin from old/damaged erythrocytes

135
Q

Where is bilirubin (predominant bile pigment) extracted from and what is it secreted into

A

Blood by hepatocytes and secreted into bile

Yellow bile

136
Q

What is the result of bilirubin modified by bacterial enzymes

A

Brown pigments

Brown faeces

137
Q

What does reabsorbed bilirubin excreted in urine cause

A

Yellow urine

138
Q

Where are bile acids synthesised

A

In liver from cholesterol

139
Q

What do bile acids do before secretion

A

Bile acids conjugated with glycine or taurine - bile salts

increase solubility

140
Q

Secreted bile salts is recycled via what

A

enterohepatic circulation

141
Q

Where does the gall bladder lie

A

On inferior surface of liver

142
Q

What are the 3 layers in the wall of the gallbladder

A
  1. Mucosa (folded - rugae - expansion)
  2. Muscularis (smooth muscle) - contraction
  3. Serosa (connective tissue)
    * Gallbladder - cystic duct - common bile duct
143
Q

How does the sphincter of Oddi help in control of bile secretion

A

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
Q

What are the 3 parts of the small intestine and what do they do

A
  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
Q

Intestinal Absorption and secretin: What do villi absorb

A 
NaCl
monosaccharides 
amino acids 
peptides
fats
vitamins 
minerals 
Water
146
Q

What do Crypts secrete

A

Secretes Cl and Water

147
Q

Intestinal fluid secretion: How much water is secreted per day by the small intestine

A

1500ml

148
Q

How is water secreted

A

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
Q

Water secretion important for which normal digestive processes

A

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
Q

Intestinal motility:

What are the two distinct types of movement

A

Segmentation

Peristalsis

151
Q

Describe segmentation:

A
  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
Q

How is the generation of segmentation contractions initiated

A

By depolarisation generated by pacemaker cells in longitudinal muscle layer

153
Q

What determines the frequency of the segmentation

A

The basic electrical rhythm

BER decreases as move down intestine - rectum

154
Q

What effect does the parasympathetic NS have on contraction

A

Increases contraction

155
Q

What effect does the sympathetic NS have on contraction

A

Decreases contraction

156
Q

Describe peristalsis

A

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
Q

What does Migrating motility Complex do

A

Move undigested material into large intestine

Limit bacterial colonisation of small intestine.

158
Q

What is the hormone involved in initiating MMC

A

Motilin

159
Q

What is the law of the intestine

A

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
Q

What is the gastroileal reflex

A

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
Q

What are the 4 parts of the large intestine

A

Ascending, transverse, descending and sigmoid

162
Q

What do large, straight crypts lined with and what do they do

A

Lined with large number of goblet cells

They are there for lubrication for movement of faeces

163
Q

Where is the rectum located

A

Straight, muscular tube - between end of sigmoid colon and anal canal

164
Q

What is the muscularis externa like in the rectum

A

Thick compared to other regions of alimentary canal

165
Q

Where is the anal canal

A

2-3 cm between distal rectum and anus

166
Q

Describe the 1. Muscularis

2. Sphincter and 3. Epithelium of the anal canal

A
  1. Muscularis thicker than rectum - internal anal sphincter
  2. External anal sphincter = skeletal muscle
  3. Epithelium: simple columnar - stratified squamous
167
Q

What happens in the colon

A

Actively transports sodium from lumen into blood - osmotic absorption of water - dehydration of chyme - solid faecal pellets

168
Q

Defaecation following a meal

A

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
Q

What is the Defaecation Reflex

A

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
Q

What causes constipation

A

No absorption of toxins from faecal material following long periods of retention.

171
Q

What are some symptoms associated with constipation

A

Headaches
Nausea
Loss of appetite
Abdominal distension

172
Q

What is diarrhoea

A

Too frequent passage of faeces which are too liquid

173
Q

What are the causes of diarrhoea

A 
Pathogenic bacteria 
Protozoans
viruses 
toxins
food
174
Q

What do enterotoxigenic bacteria do

A

Produce protein enterotoxins which maximally turn on intestinal chloride secretion from crypt cells.
Increases water secretion
- Elevate intracellular second messengers

175
Q

How do you treat secretory diarrhoea

A

Give sodium/glucose solution

  • drive water absorption - rehydration
  • secretion still going –> wash away infection
  • Oral rehydration therapy
176
Q

What does secreting help regulate and how?

A

pH of duodenum by:

1) inhibiting secretion of gastric acid from parietal cells.
2) stimulating production of bicarbonate from ductal cells of the pancreas

2nd Year (27 decks)

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