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Gastroenterology Year 1 > Physiology > Flashcards

Physiology Flashcards

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1
Q

What is the alimentary canal?

A

A series of hollow organs running from the mouth to the anus, separated by sphincters.

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2
Q

What are the accessory structures of the alimentary canal?

A

Salivary glands (parotid, sublingual, submandibular)
Pancreas
Liver and gall bladder

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3
Q

Name the 4 major functions of the alimentary canal

A
  1. Motility - mechanical activity mostly involving smooth muscle
  2. Secretion - for digestion, protection and lubrication
  3. Digestion - chemical breakdown by enzymatic hydrolysis of complex food to smaller, absorbable units
  4. Absorption - transfer of these absorbable units from the digestive tract to the blood
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4
Q

Name the 3 different kinds of smooth muscle responsible for motility in the GI tract

A

Circular muscle
Longitudinal muscle
Muscularis mucosae

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5
Q

What happens when the circular muscle of the GI tract contracts?

A

The lumen becomes narrower and longer

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6
Q

What happens when the longitudinal muscle of the GI tract contracts?

A

The intestine becomes shorter and larger in diameter

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7
Q

What happens when the muscular mucosae in the GI tract contracts?

A

Change in absorptive and secretory area of the mucosa due to folding

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8
Q

How are adjacent smooth muscle cells coupled in the GI tract?

A

Via gap junctions

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9
Q

What is spontaneous activity across the coupled cells in smooth muscle driven by?

A

Pacemaker cells

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10
Q

What is the definitions of a synchronous wave?

A

When many cells are depolarised and contract at the same time

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11
Q

What is the definition of a slow wave?

A

Rhythmic patterns of membrane depolarisation and repolarization caused by spontaneous electrical activity in the stomach, small intestine and large intestine

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12
Q

What are slow waves driven by?

A

Interstitial cells of Cajal (ICCs)

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13
Q

Where are interstitial cells of Cajal located?

A

Between the circular and longitudinal smooth muscle layers

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14
Q

How else are slow waves also known as?

A

Basic electrical rhythm (BER)

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15
Q

What is the parasympathetic innervation of the GI tract?

A

Pre-ganglionic fibres releasing ACh, synapse with ganglion cells within the enteric nervous system

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16
Q

What are some excitatory influences of the parasympathetic innervation of the GI tract?

A

Increased gastric, pancreatic and small intestine secretion
Increased blood flow
Increased smooth muscle contraction

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17
Q

What are some inhibitory influences of the parasympathetic innervation of the GI tract?

A

Relaxation of sphincters

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18
Q

What is the sympathetic innervation of the GI tract?

A

Pre-ganglionic fibres releasing ACh synapse in the pre-vertebral ganglia
Post-ganglionic fibres releasing noradrenaline innervate mainly enteric neurones

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19
Q

What are some excitatory influences of the sympathetic innervation of the GI tract?

A

Increased sphincter tone

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20
Q

What are some inhibitory influences of the sympathetic innervation of the GI tract?

A

Decreased motility
Decreased secretion
Decreased blood flow

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21
Q

What does the enteric nervous system consist of?

A

Sensory neurones e.g. mechanoreceptors, chemoreceptors
Interneurones
Effector neurones e.g. excitatory motor neurones, inhibitory motor neurones

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22
Q

What is peristalsis?

A

A wave of relaxation, followed by contraction that is triggered by distention of the gut wall

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23
Q

What is segmentation?

A

Rhythmic contractions of the circular muscle later that mix and divide luminal contents

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24
Q

What is colonic mass movement?

A

A powerful sweeping contraction that forces faeces into the rectum

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25
What is the migrating motor complex (MMC)?
A powerful sweeping contraction that moves contents from the stomach to the terminal ileum
26
Name all the sphincters of the GI tract
1. Upper oesophageal sphincter (UOS) - skeletal muscle 2. Lower oesophageal sphincter (LOS) - smooth muscle 3. Pyloric sphincter - smooth muscle 4. Ileocaecal valve - smooth muscle 5. Internal anal sphincter - smooth muscle 6. External anal sphincter - skeletal muscle
27
How do you calculate BMI?
Weight (kg)/ Height^2 (m)
28
What are some causes/risk factors of obesity?
Increased levels of inactivity Increased consumption of high-fat foods Genetic susceptibility
29
What are some consequences of obesity?
``` Diabetes Heart disease Hypertension Sleep apnoea Non alcoholic liver disease Cancer (breast, prostate, colon) ```
30
What is the main site of control of energy intake in the brain?
The hypothalamus
31
What are some energy intake control mechanisms?
1. Satiety signalling 2. Adiposity negative feedback signalling 3. Food reward
32
What is the role of cholecystokinin (CCK) in satiation signalling?
It is released in proportion to lipids and proteins in the meal Sends satiation signals and stimulates the hindbrain directly
33
What is the role of Peptide YY in satiation signalling?
Inhibits gastric motility, slows emptying of the GI tract and reduces food intake
34
What is the role of Glucagon-like peptide 1 (GLP-1) in satiation signalling?
Inhibits gastric motility, slows emptying of the GI tract and reduces food intake
35
What is the role of oxyntomodulin (OXM) in satiation signalling?
Acts to suppress appetite
36
What is the role of ghrelin in satiation signalling?
To stimulate food intake and decrease fat utilisation hence increasing body weight
37
What is the function of leptin?
To inhibit food intake and reduce body weight
38
What are the 3 functions of the stomach?
Continue carbohydrate digestion Begin protein digestion Produce chyme
39
What are the 2 regions of the stomach known as?
``` Orad region (fundus and proximal body) Caudad region (distal body and antrum) ```
40
What is the function of the orad region of the stomach?
Storage of ingested material (for an hour min)
41
What is the function of the caudad region of the stomach?
To propel the chyme through the pyloric sphincter
42
What are the 2 gastric factors affecting stomach emptying?
Volume of chyme - distention increases motility | Consistency of chyme - thinner consistency, faster emptying
43
What is secreted in the oxyntic gastric mucosa (fundus and stomach body) of the stomach?
``` HCl - activates pepsinogen to pepsin Pepsinogen - inactive precursor of pepsin Intrinsic factor - binds to B12 Histamine - Stimulates HCl secretion Mucus- protective ```
44
Which cells secrete HCl?
Parietal cells
45
What is secreted in the pyloric gland area (pylorus and antrum) of the stomach?
Gastrin - stimulates HCl secretion Somatostatin - inhibits HCl secretion Mucus - protective
46
Which secretory substances stimulate parietal cells to produce HCl?
ACh Histamine Gastrin
47
What are the 3 phases of gastric acid secretion?
1. Cephalic phase 2. Gastric phase 3. Intestinal phase
48
Describe the cephalic phase of gastric acid secretion
Vagus nerves stimulated by the sight and smell of food stimulate enteric neurones to release ACh
49
Describe the gastric phase of gastric acid secretion
Distention of stomach activates reflects that cause acid secretion
50
Describe the intestinal phase of gastric acid secretion
Chyme entering the duodenum causes weak stimulation of acid secretion
51
What are the 3 phases of inhibition of gastric acid secretion?
1. Cephalic phase - decreased vagal activity upon cessation of eating 2. Gastric phase - pH falls which causes somatostatin release 3. Intestinal phase - enterogastrones reduce gastric secretion
52
What is the function of the small intestine?
Digestion and absorption of nutrients
53
What are some adaptations of the small intestine for absorption?
Villi and microvilli - Increase the surface area | Circular folds of Kerckring - further increase in surface area
54
What are the secretions of the small intestine?
Gastrin - stimulates HCl Secretin - promotes secretion of HCO3- Cholecystokinin -inhibits gastric emptying and stimulates pancreatic enzyme secretion Gastric inhibitory peptide - stimulates insulin release Ghrelin - stimulates appetite
55
What are some endocrine pancreatic secretions?
Insulin | Glucagon
56
What are some exocrine pancreatic secretions?
Digestive enzymes: - Trypsinogen and other proteases - Pancreatic amylase - Pancreatic lipase
57
What are the 3 phases of pancreatic secretion?
1. Cephalic phase - vagal stimulation of acinar cells 2. Gastric phase - gastric distention evokes a vagovagal reflex resulting in parasympathetic stimulation of acinar cells 3. Intestinal phase - secretion of NaHCO3- and digestive enzymes
58
What is the sequence of carbohydrate digestion?
Carbohydrates converted to oligosaccharides by a-amylase Oligosaccharides converted to monosaccharides by oligosaccharidases
59
What is the role of a-amylase?
Breaks down the a-1,4 linkages in carbohydrates
60
What is the sequence of protein digestion?
Proteins must be broken down to peptides and then oligopeptides or amino acids in order for them to be absorbed
61
Why does emulsification of lipids occur?
Increases the surface area for lipase to break down the fats
62
Name some fat soluble vitamins and explain how they are absorbed
Vitamin A, D, E and K | Incorporated into chylomicrons and distributed via the lymph
63
Name some water soluble vitamins and explain how they are absorbed
Vitamin C and B | Active transport and diffusion through the cell membrane
64
What are the structures that make up the large intestine?
Caecum and appendix Colon (ascending, transverse, descending, sigmoid) Rectum Anal canal and anus
65
What are the main functions of the colon?
1. Absorption 2. Secretion 3. Storage of colonic contents 4. Periodic elimination of faeces
66
What is haustration?
Non-propulsive segmentation in the large intestine
67
What are peristaltic propulsive movements?
Mass movement of the large intestine
68
What is defaecation?
The periodic ejection of foecal matter
69
What are the major functions of the liver?
1. Storage of fat soluble vitamins, B12, iron, copper and glycogen 2. Synthesis of proteins 3. Protection (via the Kupffer cells and the production of immune factors) 4. Detoxification
70
What are the metabolic functions of the liver?
1. Carbohydrate metabolism 2. Fat metabolism 3. Protein metabolism
71
What is the role of the liver in hormone metabolism?
Deactivation of hormones - insulin, glucagon, ADH Activation of hormones - conversion of TH to T3
72
What are some of the hepatocyte secretions?
Primary bile acids Water and electrolytes Lipids, phospholipids and cholesterol Bilirubin
73
What does enterohepatic recycling mean?
95% of bile salts are reabsorbed and recycled
74
What happens in phase I of drug metabolism?
Oxidation, reduction and hydrolysis | Makes a drug more polar and adds a chemically reactive group
75
Why is drug metabolism important?
Converts parent drugs to make more polar metabolites Converts drugs from inactive to active Convert drugs to metabolites that are less pharmacologically active than the parent compound
76
Where does drug metabolism take place?
The liver
77
What happens in phase II of drug metabolism?
Conjugation | Adds an endogenous compound, increasing polarity
78
Which monooxygenases mediate phase I reactions?
Cytochrome P450 family of monooxygenases
79
Where are CP450 monooxygenases located in?
The endoplasmic reticulum of liver hepatocytes
80
What are the 5 principle mechanisms of Na+ absorption?
1. Na+/glucose co-transport 2. Na+/amino acid co-transport 3. Na+/H+ exchange 4. Parallel Na+/H+ and Cl-/HCO3- exchange 5. Epithelial Na+ channels (ENaC)
81
How does absorption of water in the GI tract occur?
Osmosis | This is based on the transport of Na+ from the lumen of the intestines to the bloodstream
82
What are the cellular causes of diarrhoea?
1. Impaired absorption of NaCl 2. Non-absorbable/ poorly absorbable solutes in the lumen 3. Hyper-motility 4. Excessive Cl- secretion
83
What is retching?
Rhythmic reverse peristalsis of the stomach and oesophagus and forceful involuntary contraction of the abdominal muscles and diaphragm
84
What is vomiting?
The forceful expulsion of gastric/intestinal contents out of the mouth
85
Where is the vomiting centre in the brain?
Medulla Oblongata
86
Describe the pathogenesis of vomiting
1. Suspension of intestinal slow wave activity 2. Retrograde contraction from ileum to stomach 3. Suspension of breathing (closed glottis prevents aspiration) 4. Relaxation of LOS and contraction of diaphragm and abdominal muscles 5. Ejection of gastric contents through the open UOS

Gastroenterology Year 1 (8 decks)

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