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Introduction to Physiology and Parmacology > The GI system and Blood Glucose > Flashcards

The GI system and Blood Glucose Flashcards

1
Q

What is the function of the GI tract ?

A

Digestion and Absorption of nutrients.

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1
Q

What is the function of the GI tract ?

A

Digestion and Absorption of nutrients.

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2
Q

What 2 layers make up the GI tract wall ?

A

Mucosal layer
Epithelial cells
Lamina propria
Muscularis mucosae

Submucosal layer
Collagen
Elastin
Glands
Blood vessels
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3
Q

What component of GI tract wall assists motility ?

A

Circular and longitudinal muscle layers - motility
Serosa
Two main plexuses contain the ‘nervous system’ of the GI tract

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4
Q

What is the Enteric NS ?

A

ENS – collection of nerve plexuses surrounding the GI tract (inc. pancreas and biliary system)
More than 100 million neurones > spinal cord
Neurochemically very complex
1 of 3 divisions of ANS
Solely within GI tract, but modified by brain

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5
Q

How is the GI tract regulated intrinsically and extrinsically via the ANS ?

A

Extrinsic – sympathetic and parasympathetic innervation

Intrinsic - Enteric nervous system (ENS) – primary mechanism, ganglia within submucosal and myenteric plexuses

Can direct all function of GI tract even in absence of extrinsic innervation

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6
Q

How is GI activity regulated via Parasympatheric Ganglia using postganglionic neurones ?

A

Parasympathetic ganglia within plexuses coordinate information received from PNS and relay to smooth muscle, endocrine and secretory cells

Postganglionic neurones are either cholinergic (release Ach) or peptidergic (release peptides, e.g. substance P or VIP

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7
Q

How is GI activity regulated via Sympathetic Ganglia using nerve fibres ?

A

Sympathetic postganglionic nerve fibres are adrenergic (release norepinephrine)

Nerve fibres are mixed afferent and efferent, i.e. sensory and motor information is relayed between GI tract and CNS, coordinated by the plexuses

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8
Q

What are the 3 GI peptides that regulate it ?

A

Hormones – from GI endocrine cells, e.g. GIP

Paracrines – from endocrine cells, act locally, e.g. somatostatin

Neurocrines – released from neurone following action potential

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9
Q

How does the GI tract coordinate contraction ?

A

Cells electrically coupled via gap junctions - rapid spread of action potentials leading to coordinated contraction

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10
Q

What are the 2 types of GI tract contractions ?

A

Phasic – periodic contraction and relaxation (3-12/min)

Tonic – constant level of contraction/tone

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11
Q

What are slow waves and how could they generate an AP ?

A

Slow waves – subthreshold membrane depolarisation (inward Ca2+ through channel), repolarisation (outward K+)

Extension to threshold generates a true action potential

Subthreshold slow waves produce weak contraction (tonic)
Action potentials on top (phasic contractions)

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12
Q

How is the mouth involved in digestion ?

A

Teeth and tongue mechanically break down food ready for swallowing
Saliva lubricates (bolus), contains α-amylase to hydrolyse starch (genetic variation)
Mastication muscles innervated by Mandibular Nerve (V3) of Cranial Nerve 5 (CNV/Trigeminal)
Chewing involuntary (reflex) and voluntary (can override)
Mechanoreceptors - sensory information relayed to brainstem
3 phase swallowing:
Oral: Pharyngeal: Oesophageal

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13
Q

How is the Oesophagus involved in digestion ?

A

Lumen lined with stratified squamous epithelia
Swallowing reflex:
Closes upper oesophageal sphincter
Initiates primary peristaltic wave, coordinated sequential contractions
Continued distention initiates secondary peristaltic wave (by ENS)
Lower oesophageal sphincter opening mediated by vagus nerve releasing VIP neurotransmitter

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14
Q

What are the 3 phases to motility in the stomach ?

A

3 phases to motility in stomach:

  1. Receptive relaxation in thin-walled Orad stomach to receive food
  2. 3 muscular layers of Caudad region contract to mix food with gastric juice from mucosal glands (ANS control) forming chyme
    HCl
    Pepsinogen
    Intrinsic factor
    Mucus
  3. Gastric emptying through pyloric sphincter into small intestine (SI) - fat content and H+ slow emptying
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15
Q

What re the 3 sections of the small intestine ?

A

Duodenum
Jejunum
Ileum

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16
Q

How is SA increased in small intestine ?

A

Police
Villli
Microvilli

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17
Q

What is Chyme mixed with in small intestine ?

A

Mixed with digestive enzymes and pancreatic secretions.

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18
Q

How is the Pancreas an accessory organ in digestion ?

A

1L exocrine pancreatic secretion into duodenum per day:
Solution rich in HCO3- secreted by centroacinar and ductal cells to neutralise H+ delivered from stomach
Enzymes secreted by acinar cells

Parasympathetic NS stimulates secretion, sympathetic inhibits

Secretion phases: cephalic; gastric and intestinal

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19
Q

How is the liver an accessory organ ?

A

Amphipathic bile salts – major constituent of bile used for emulsification and solubilisation of lipids into micelles, aiding their digestion and absorption

Liver secretes bile - produced in hepatocytes

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20
Q

What do Peristaltic contractions propel ?

A

Propel the chyme

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21
Q

What do segmentation contractions do to chyme ?

A

Segmentation contractions split and expose chyme to secretions through co-ordinated actions

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22
Q

What happens to material not absorbed by small intestine ?

A

Material not absorbed passes through Ileocaecal sphincter into the caecum of large intestine

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23
Q

What do Enterochromaffin cells release ?

A

Seretonin as a peristaltic reflex

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24
What are the 3 primary functions of the larger intestine ?
1.Absorbs water and electrolytes (Na+, Cl-, HCO3-, K+) Aldosterone increases Na+ absorption 2.Makes and absorbs vitamins K and B (1012 bacteria) 3.Forming and propelling faeces (ferments indigestible food -bacteria), to be excreted
25
What are the 2 methods of motility used by large intestines ?
Segmented contraction – caecum and proximal colon, mix contents - haustra Mass movement, 1-3/day over large distance – gastrocolic reflex
26
Give a brief overview of secretion in the GI tract
Starts in the mouth, mechanical breakdown using teeth and tongue. Salivary amylase initiates the hydrolysis of amylose and amylopeptin, deactivated by acidic conditions of stomach. Lingulil lipsase – breaks down diglycerides to fatty acids, important to infants, its actions continue into the stomach Stomach - These will initiate protein digestion, first time protein in hydrolyse. GIF secreted as it is required for absorption of B12 in ileum. Large intestine – mucus to protect the luminal lining.
27
What cells make up the oxyntic and pyloric glands in the stomach ?
Epithelial cells - HCO3- Mucous neck cells - mucus Parietal cells – HCl, intrinsic factor Chief cells - pepsinogen Antrum - pyloric glands, similar – but no parietal cells G cells – gastrin D cells - somatostatin
28
How is Gastric acid secreted in parietal cells ?
Within the intracellular fluid CO2 combines with water to make carbonic acid. It will dissociate into hydrogen ions (secreted across apical membrane with chloride following) and bicarb ion is absorbed at basolateral membrane, responsible for alkaline tide, high pH in blood, Bicarbonate ion will enter the GI tract later.
29
How is HCl secretion regulated ?
Stimulation of H+ secretion: Histamine; ACh (vagus nerve); gastrin Inhibition: low pH; somatostatin; prostaglandins
29
How is HCl secretion regulated ?
Stimulation of H+ secretion: Histamine; ACh (vagus nerve); gastrin Inhibition: low pH; somatostatin; prostaglandins
30
What does both the SI and LI absrob ?
SI and LI absorb fluid and electrolytes Na+, K+, Cl-, HCO3- via villus cells/surface epithelia respectively
31
What do Crypt epithelial cells secrete ?
Fluid and Electrolytes
32
What mechanisms are used during SI absorption ?
Apical maembrane contains chloride channels. Usually closed, open if stimulated by hormones or neurotransmitters, cAMp is activated which opens the chloride channel Basolateral has a sodium, potassium chloride transporter which brings these ions into the cell from the blood.
33
How are materials absorbed in the jejunum ?
Sugar or amino acid is cotransported with Na+ HCO3 is made from H+ in the epithelial cells
34
How are materials absorbed in the ileum ?
Same as jejunum but Cl- absorption is driven by HCO3 leaving epithelial cells
35
How does Pancreas secrete using ductal cells ?
Same as ileum but some Na+ passes through GAP junctions freely
36
How does LI (colon) absorb ?
Aldosterone drives Na+ absorption into cell and K+ leaves into lumen at same time. ATP drives Na/K pump for Na+ to move into the blood and K+ moves into blood though channel.
37
List digestive products absorbed by SI
Carbohydrases: α-amylase, α-dextrinase, maltase, sucrase, trehelase, lactase - products absorbed into villus blood Proteases: pepsin, trypsin, chymotrypsin, elastase, carboxypeptidases – product into villus blood Lipases and bile salts - products into the lacteals within villus
38
How are carbs absorbed by SI ?
Glucose and Galactose - cotransport via SGLT1 using Na+ Fructose - no cotransport via GLUT5
39
How is protein absorbed in SI ?
Amino acids and H+ cotransported with Na+ Di and Tripeptides made in epithelial cell then transported out.
40
What are the products of lipid digestion ?
Products of lipid digestion: cholesterol, lysophospolipids, monoglycerides and free fatty acid solubilised in mixed micelles (glycerol H2O soluble) Digestive products modified and absorbed into lacteal
41
How are lipid products packaged of re-esterified ?
Products re-esterified with free fatty acids in SER Packaged into chylomicrons
42
What are the Islets of Langerhans main secretory cells ?
β (65%) α (20%) δ (10%)
43
What are the other single/grouped endocrine cells in the islet cells ?
F (PP/γ) cells ε cells Enterochromaffin cells
44
What are the endocrine tissue secretory products ?
``` β cells – insulin, proinsulin, C peptide, amylin (IAPP) α cells – glucagon δ cells – somatostatin F (PP) cells – pancreatic polypeptide ε cells – Ghrelin protein (Enterochromaffin cells – substance P) ```
45
How do Islet cells communicate and control ?
Gap junctions between β and α cells | Delta cells send dendrite-like processes to beta cells
46
What neurones innervate Islet cells ?
Adrenergic Cholinergic Peptidergic
47
How is insulin secretion regulated via Islet beta cell receptors ?
High blood glucose stimulates synthesis and secretion, low levels inhibit
48
How do Sympathetic and Parasympathetic neurones regulate insulin secretion ?
Sympathetic : β -adrenergic stimulation increases secretion α-adrenergic stimulation inhibits secretion Parasympathetic stimulation via vagus nerve releases ACh - increases insulin release
49
What humoral factors can regulate insulin secretion ?
Humoral factors, GIP, Amylin, Somatostatin
50
What drugs can regulate insulin secretion ?
Drugs, e.g. Sulphonylureas acting on KATP channels increasing secretion of insulin
51
How does insulin act ?
Via a hertotramer receptor 2 extracellular α chains, 2 membrane-spanning β chains
52
What happens when insulin binds to an insulin receptor ?
2 Dif signalling pathways 1. Cell growth, proliferation, gene expression 2. Synthesis of lipids, proteins, glycogen
53
What does insulin do to Blood glucose ?
Decreases blood glucose concentration Increased glucose transport into target cells by insertion of GLUT4 Promotes conversion of glucose to glycogen in liver and muscle (glycogenesis) When glycogen stores replenished, excess glucose converted into fat (lipogenesis)
54
What does insulin do in the liver ?
Promotes formation of glycogen from glucose (glycogenesis) Inhibits glycogenolysis Inhibits gluconeogenesis Reduces blood glucose levels
55
What does insulin do in Muscles ?
Decreases blood amino acid concentration Anabolic effect Increasing uptake of amino acids and protein Stimulation of protein synthesis and inhibition of degradation
56
What does insulin do in adipocyte cells ?
It increases GLUT4 transporters expression for rapid glucose uptake. glucose then converted into Fatty acids, stored as triglycerides - driven by increased lipoprotein lipase conc Insulin inhibits lipolysis
56
What does insulin do in adipocyte cells ?
It increases GLUT4 transporters expression for rapid glucose uptake. glucose then converted into Fatty acids, stored as triglycerides - driven by increased lipoprotein lipase conc Insulin inhibits lipolysis
57
How does insulin effect K+ uptake ?
Promotes K+ uptake into cells through increased activity of N+-K+ ATPase Direct effect on hypothalamic satiety centre
58
Whats the cause of type 1 diabetes ?
Type I diabetes mellitus (DM) results from autoimmune destruction of Pancreatic Islet β cells Not enough insulin secreted
59
What is Diabetes Mellitus ?
High blood sugar conc for a long time
60
What causes Type 2 DM ?
Low insulin production Peripheral insulin resistance Obesity Down regulation of insulin receptors in target tissue and insulin resistance Blood glucose elevated postprandial and fasting at normal levels of insulin
61
What are the results of Type 1 DM ?
Hyperglycaemia resulting from decreased uptake into cells Increased blood fatty acid and ketoacid concentration- increased lipolysis Increased blood amino acid concentration Osmotic diuresis Polyuria Hypotension K+ movement out of cells – hyperkalaemia
62
What are the symptoms of Type 1 and 2 DM that lead to diagnosis ?
``` increased thirst and urination hunger weight loss fatigue irritability fruity smell on the breath Diabetic ketoacidosis (DKA) blurred vision ```
63
How to treat Type 1 DM ?
Insulin replacement therapy
64
How to treat Type 2 DM ?
Sulphonyurea drugs (e.g. tolbutamide) stimulate insulin secretion Biguanide drugs (e.g. metformin) upregulate receptors on target tissues Calorie restriction/weight reduction

Introduction to Physiology and Parmacology (7 decks)

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