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SGUL - Physiology 1 > Introduction to Function and Control of The Alimentary Tract > Flashcards

Introduction to Function and Control of The Alimentary Tract Flashcards

1
Q

What are the digestive functions of the stomach?

A
  • Accomodation and storage
  • Mechnical and enzymatic breakdown
  • Delivery of chyme to the duodenum
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2
Q

Describe the role of the stomach during storage of digestive products.

A
  • Acts as a reservoir in which unmixed food is stored, during Stage 1 of digestion
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3
Q

How does the fundus allow large volumes of food storage?

A
  • Relaxes
  • Vagal reflex inhibits smooth muscle tone.
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4
Q

What is the purpose of the antral region of the stomach?

A

Mechanical degradation of food before mixing it with gastric secretions

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5
Q

Describe the role of the colon/rectum during storage of digestive products.

A

Storage of indigestive residues and faecal matter occur before excretion

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6
Q

Describe the storage of gastric secretions.

A

Stores 2-3 litres of gastric juice aiding in digestion and absorption of food.

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7
Q

Where are mucous gastric secretions released from and what are they needed for?

A
  • Secreted by goblet cells and mucous neck cells
  • Acts as a barrier that protects the stomach and colon and prevents trauma
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8
Q

What is the purpose of lipase gastric secretions?

A

Hydrolysis of triglycerides to fatty acids and glycerol

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9
Q

Where are pepsin gastric secretions released from and what are they needed for?

A
  • Secreted by peptic cells as pepsinogen
  • Aids protein digestion
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10
Q

Where are HCl gastric secretions released from and what are they needed for?

A
  • Secreted by parietal cells
  • Important for defence of the gut
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11
Q

Where are intrinsic factor gastric secretions released from and what are they needed for?

A
  • Secreted by parietal cells
  • Aids Vitamin B12 absorption
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12
Q

Describe the pancreatic secretions into the gut.

A
  • Secreted from cells in the mucosa
  • Chemical acts locally on adjacent cells via the interstitial fluid.
    e.g somatostatin, which inhibits gastric release in the stomach.
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13
Q

List some exocrine secretions that aid in digestion that are released from the salivary glands.

A
  • Mucous
  • Lipase
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14
Q

List some exocrine secretions that aid in digestion that are released from the gastric glands.

A
  • HCl
  • Pepsin
  • Mucous
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15
Q

List some exocrine secretions that aid in digestion that are released from the pancreas.

A
  • Bicarbonate ions
  • Enzymes (eg. amylase, lipase, carboxypeptidase)
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16
Q

List some exocrine secretions that aid in digestion that are released from the liver.

A
  • Bile salts
  • Bile acids
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17
Q

What are endocrine secretions?

A
  • Synthesised by ductless glands and enter the blood stream
  • Travel to target tissue(s) and bind to specific receptors to elicit their effects.
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18
Q

Give examples of endocrine secretions and where they are secreted from.

A
  • GASTRIN: G-cells in antrum of stomach
  • SECRETIN and PANCREOZYMIN-CHOLECYSTOKININ: duodenal mucosa
  • INSULIN: β-cells of pancreas
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19
Q

What do endocrine, exocrine and paracrine secretions allow?

A
  • Active digestion
  • Control of digestion and gastric motility
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20
Q

What is the point of absorption?

A
  • Nutrients from digestion must be transported across the intestinal epithelium into the blood (eg. glucose, amino acids, etc.) or lymph via lacteals (fats/lipids) so they can be used for physiological processes
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21
Q

Where does most fluid absorption occur?

A

Small intestine and colon

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22
Q

What causes the pathogenesis of diarrhoea?

A

Disorders of fluid secretion and absorption

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23
Q

What is motility?

A

Movements of the muscular wall (mostly smooth muscle except extreme ends of upper oesophagus/rectum)

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24
Q

What is motility needed for?

A
  • movement from one region to another (law of gut); mass evacuation
  • mechanical degradation (eg. gastric antrum)
  • mixing lumen contents (eg. small intestines)
  • transport of nutrients, water and of urea and electrolytes
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25
What are the different methods of excretion of drugs and other products of metabolism?
- saliva - bile - faeces - vomit
26
How are indigestible food residues excreted?
Faeces
27
How is the gut vulnerable to pathogen exposure?
- Interface with the ‘contaminated’ external environment - Intestine is the largest mucosal surface in the body and exposed to the heaviest burden of environmental antigens. - Breaches in the barrier cause toxins to enter the blood
28
What different defence mechanisms does the gut have? PART 1
- sight, smell and taste alerts to harmful food substances - vomit reflex - HCl kills most harmful bacteria
29
What different defence mechanisms does the gut have? PART 2
- mucous secretions - neutral bacterial flora prevents the colonisation of harmful bacteria - aggregation of lymphoid tissue (eg. Peyer’s patches) mount responses to food-borne antigens - analyse and response to pathogenic microbes
30
Where are Peyer's patches located?
- Lamina propria layer of the mucosa - Extend into submucosa of ileum.
31
Describe the metabolic function of the gut.
- Liver involved in carbohydrate, nitrogen and lipoprotein metabolism - Liver involved in production of bile and excretion of bilirubin.
32
What is the effect of parasympathetic innervation of the gut?
Stimulates salivation
33
What is the effect of sympathetic innervation of the gut?
- inhibits salivation - relaxes the bladder - contracts the rectum
34
Describe the three types of reflexes involved in the relaxation of the fundus.
- RECEPTIVE (mechanical stimulation of the pharynx - mechanoreceptors, sight) - ADAPTIVE (vagal innervation, {NO,VIP}, tension of the stomach) - FEEDBACK (nutrients, CCK)
35
What are receptive, adaptive and feedback-relaxation of the stomach mediated by?
- Mediated by NANC mechanisms (i.e. inhibition involving NO, VIP, etc.) - Reflex chains involving noradrenaline release
36
What happens when the stomach is ready to receive food?
- Noradrenaline is released from the sympathetic nerve fibres - Stomach relaxes
37
What is PACAP and what has it been shown to do?
- Pituitary adenylate cyclase (AC)-activating peptide - Isolated from the pituitary - Stimulates AC activity in the anterior pituitary.
38
Where is PACAP found?
- Brain - Gut (in the myenteric and submucosal ganglia).
39
What does PACAP do?
- Neuronal regulation of gastric acid secretion (contributing to intestine motility) - Relaxation of colonic smooth muscle - Stimulates pancreatic secretion (causing insulin and glucagon secretion)
40
Describe the steps of food movement through the stomach. PART 1
- Ripples of contraction move the food towards the antrum (thicker muscle layer). - Pyloric sphincter is often relaxed, but closes upon the arrival of the peristaltic wave. - Chyme repulsion causes the opening of the pyloric sphincter.
41
Describe the steps of food movement through the stomach. PART 2
- Small, partially digested material is squirted through the pyloric sphincter into the duodenum. - Repulsion of antral contents allow for mixing/grinding.
42
What are the different types of control of the alimentary tract?
- endocrine - paracrine - neural - metabolic
43
Describe the endocrine control of the alimentary tract. PART 1
- When the stomach is distended, neurons are stimulated, releasing GRP, which acts on G cells to release gastrin. - This travels through blood and affects enterochromaffin-like cells (EMF cells) and parietal cells.
44
Describe the endocrine control of the alimentary tract. PART 2
- ECL cells release histamine, which promotes acid secretion from parietal cells. - Acetylcholine also affects ECLs and parietal cells in a similar manner.
45
What do the hormones produced by the gut have in common?
They are proteins
46
Describe the paracrine control of the alimentary tract.
- Paracrine agents go to target tissues via the interstitial fluids.
47
What stimulates somatostatin release? What is its effect?
- Increased H+ stimulates D cells, which release somatostatin. - Acts on G cells to inhibit the release of gastrin.
48
Describe the neural control of the alimentary tract. PART 1 - THE VAGO-VAGAL REFLEX
- Reflex in which both the afferent (‘sensory’) and efferent (‘motor’) axons are in the vagus nerve trunk. - Reflex circuit within the GIT.
49
Describe the neural control of the alimentary tract. PART 2 - THE VAGO-VAGAL REFLEX
- Pathway is via the brain stem (medulla). - Refers to reflex control of responses to gut stimuli via the NTS and DMVN.
50
Describe the neural control of the alimentary tract. PART 1 - ENS/LOCAL REFLEX
Two nerve fibres are intrinsic to the gut: 1. Myenteric Plexus (Auerbach’s plexus): motor function (P + S) 2. Submucosal Plexus (Meissner’s plexus): intestinal secretions (only P) *P = Parasympathetic/ S = Sympathetic
51
Describe the neural control of the alimentary tract. PART 2 - ENS/LOCAL REFLEX
- Regulate GI functions entirely within the wall of the gut. - Connected to the CNS via the parasympathetic and the sympathetic fibres - Effects mediated by enteric nervous system
52
What is the difference between the Auerbach's plexus and Meissner's plexus?
- Auerbach’s plexus has both parasympathetic and sympathetic input - Meissner’s plexus has only parasympathetic fibres and provides secretomotor innervation to the mucosa nearest the lumen of the gut.
53
Give an example of how the innervation of the gut recognises food in the system.
- When there is food in the oesophagus, it will stimulate mechanoreceptors. - Will send impulses to the brain and back via the vagal afferent (and efferent) fibres.
54
What is the colo-colonic reflex?
- Presence of food or food products/distension of the stomach increases colon motility - Due to the stretch in the stomach and by-products of digestion in the small intestine.
55
How does stimulation of the sympathetic nervous system influence colon motility?
Decrease colon movement.
56
How does stimulation of the parasympathetic nervous system influence colon motility?
Increase contraction in the proximal colon so greater motility
57
How does stimulation of the sympathetic nervous system affect Auerbach’s plexus?
Decreased gastric motility and secretion.
58
How does stimulation of the parasympathetic nervous system affect Auerbach's plexus?
Increased gastric motility and secretion
59
Describe the metabolic control of the alimentary tract.
- Rate of emptying is dependent upon the material’s ability to be absorbed. THIS IS WHY: Carbohydrates are emptied quickly into the duodenum. Proteins are slow-emptying, while fats are even slower.
60
How do fatty acids lead to decrease in gastric emptying?
Increasing the contractility of the pyloric sphincter.
61
Describe the peristalsis of the alimentary tract.
- Wave of propulsive contractions that moves contents of the gut towards the anus. - Slower in the large intestine when compared to the small intestine.
62
Describe the regulation of movement in the alimentary tract.
- Distention initiates the contraction - Vagal inhibitory and excitatory fibres control movement.
63
What happens when peristaltic waves pass over the stomach?
Luminal material is forced into the duodenum
64
What does the vagal reflex inhibit?
→ Smooth muscle tone → Mechanoreceptors → Fundic relaxation
65
Where is the antral region?
→ Lower region of the stomach
66
How can the gut initiate its own responses?
→ It has an enteric nervous system which can initiate its own responses to gut stimuli without higher functions of the brain
67
What are the contractions initiated by?
→ Excitatory reflexes and mediated by ACh or substance P
68
What are relaxation effects mediated by?
NO/VIP
69
What are splanchnic nerves?
Sympathetic fibres
70
When does receptive relaxation occur?
→ Which happens by mechanical stimuli → Food is expected in the stomach → Sphincter relax to allow food to enter
71
Why is CCK being released?
→ Due to lipids being in the food
72
What does CCK do?
→ Decreases feeding because relaxation is occurring
73
What does CCK promote?
→ Bile secretion → Gall bladder contracting
74
What is the sieving effect?
→ Viscous and solid matter are retained in the stomach →pylorus can detect the size of food particles, 1-2mm are passed through →anything larger goes back to the antrum for grinding.
75
When is the vago-vagal reflex active?
→ during the receptive relaxation of the stomach in response to swallowing
76
What are the neurotransmitters used in the plexuses?
→ ACh, NO, NA, 5-HT, GABA and ATP
77
How does the bolus get moved along?
→ Contractions are initiated by excitatory activity mediated by substance P and AcH → The circular muscles have to relax in front and contract behind →Longitudinal muscles are contracted

SGUL - Physiology 1 (68 decks)

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