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Phase 1 Medicine (JA) > GI physiology > Flashcards

GI physiology Flashcards

1
Q

Draw the basic histology of the gut (not stomach).

A

1) Mucosa (ciliated columnar epi + lamina propria + muscularis mucosae)
2) Submucosa (Dense irregular fibrous connective tissue)
3) Muscular propria (Inner circular + outer longitudinal)
4) Adventitia (Serosa/mesothelium = simple squamous)

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2
Q

Where can interstitial cells of Cajal be found and what is their function?

A

Mesenchymal cells found within the inner circular and outer longitudinal layers of the muscularis muscosae. They mediate communication between the ANS and the smooth muscle

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3
Q

Describe what slow wave potentials are and what stimulates a spike potential.

A

Slow wave potentials organise the basic motor function (resting membrane potential fluctuates between -50mv and -60mv). Mediated by Na+. Spike potentials are true action potential allowing muscle contraction. Based on an external stimulus.

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4
Q

Where can the Meissner’s and Auerbach’s plexii be found in the gut, and what are their roles?

A

Meisser’s - Submucosa (superficial). Works to regulate secretions and blood flow

Auerbach’s - between the inner circular and outer circular layers of the muscularis propria. Governs gut motility

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5
Q

Name two neurotransmitters that excite and inhibit the enteric nervous system, respectively.

A

Acetylcholine and VIP (vasoactive intestinal peptide)

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6
Q

Where is the parasympathetic nervous system found, and what effect does it have on the myenteric system?

A

Cranio-sacral divisions of the spinal cord. Consists of the Vagus nerve (CNX) and sacral divisions 2-4. Stimulates secretion of acetylcholine, attached to nicotinic acetylcholine receptors and increases Na+ and K+ permeability, leading to depolarisation of the smooth muscles cell. Cell contraction.

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7
Q

Where is the sympathetic nervous system found, and what effect does it have on the myenteric system?

A

Thoraco-lumbar region of the spinal cord. Consists of T2-L5 continuously. Has a net inhibitory effect, secretes NA, and leads to inhibition of gut smooth muscle contraction and enteric nerve function

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8
Q

Explain the routes of the sympathetic and parasympathetic motor neurones that innervate the gut (in general).

A

Para: Terminal ganglia within effector tissue. No prevertebral ganglia. Cranio-sacral nerves (Vagus [CNX] and Pelvic [S2-S4]).

Symp.: Outflow from continuous T5-L2 (Great and small small splancic) flow to the Coeliac ganglion. Coeliac ganglion goes to effector, or superior mesenteric ganglion.

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9
Q

Name the 3 types of GI reflex and what they do.

A

1) Gastrocolic relfex - reflex that controls the motility of the lower GI tract following a meal
2) Enterogastric reflex - Increased acid in the duodenum inhibits gastric secretions and motility
3) Colonileal reflex - Works with gastrocolic reflex to promote the urge to defaecate. Stimulates the opening of the ileocecal valve allowing passage of material from the Ileum to the large intestine

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10
Q

Describe the chewing/mastication reflex.

A

1) Bolus in the mouth inhibits jaw muscles from contracting, leading to lowering of the jaw
2) This leads to a stretch reflex and the jaw muscles contract
3) Jaw muscles contract and close the teeth, pushing the bolus against the surface of the mouth, repeating the cycle

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11
Q

Name four nerves involved in deglutition.

A

1) CNV (Trigeminal)
2) CNIX (Glossopharyngeal)
3) CNX (Vagus)
4) CNXII (Hypoglossal)

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12
Q

Name the three phases of deglutition.

A

1) Buccal phase (Voluntary. Tongue contracts, pushes bolus on soft palate, moves posteriorly to the oropharynx, stimulates CNIX)
2) Pharyngeal phase
3) Oesophageal phase

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13
Q

How quickly does the bolus of food move?

A

2-4 cm/s

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14
Q

What happens in phase I of deglutition?

A

Buccal phase. Voluntary contraction of the tougue pushes bolus against soft palate of the mouth, moves posteriorly to the oropharynx, stimulates CNIX.

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15
Q

What happens in phase II of deglutition?

A

Pharyngeal phase.

1) Nasopharynx closed due to soft palate opening (levator muscle) and contraction of the uvula.
2) Glottis closes and epiglottis closure causing Trachea closure.
3) Palatoglossus and palatopharyngeus contract to only allow smallest bolus through
4) Elevation and anterior movement of the pharynx and larynx (CNX)

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16
Q

What happens in phase III of deglutition?

A

Oesophageal phase. Involuntary.

1) Moving below upper oesophageal sphincter
2) Muscles contract producing peristalsis and pushing bolus down towards the stomach. Peristaltic contraction and relaxation occurs.
3) Hyoid bone depression

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17
Q

What is primary and secondary peristalsis?

A

Primary - Swallow-induced peristalsis beginning in the pharynx and going through the oesophagus

Secondary - Elicited by oesophageal opening. Vagal afferent and efferent neurons (CNX) to and from the medulla

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18
Q

Name 3 functions of the stomach.

A

1) Stores food (1.5L capacity)
2) Breaks down food
3) Strong peristaltic contractions

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19
Q

Name the 4 parts of the stomach and their basic function.

A

1) Fundus - food reservoir
2) Body - secretions
3) Antrum - muscular
4) Pylorus - sieve, entry to duodenum

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20
Q

Name the four stages of mixing in the stomach.

A

1) Vasovagal reflex relaxes the fundus and allows food to drop in
2) Body and antrum contract
3) Pylorus contracts
4) Mixing by retropulsion

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21
Q

Name 2 ways in which stomach emptying into the duodenum is regulated.

A

1) By the stomach. a) gastric distension by the food. b) presence of Gastrin.
2) By the duodenum. Depresses pyloric pump. closes the pyloric sphincter. Excess chyme depresses the pyloric pump.

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22
Q

Name two factors that control the rate of gastric emptying from within the stomach.

A

1) Physical form of the food (Liquid empties in 20 mins and solid empties in 2 hours)
2) How full the stomach is (fuller stomachs empty quicker)

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23
Q

What is the role of segmentation?

A

Sluggish and short-lived contractions to allow mixing of chyme with bile, pancreatic enzymes, pancreatic juices, intestinal fluids, HCO3- and mucus. Increases contact time with chyme and mucosal surface and enhances absorption.

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24
Q

Describe what happens during peristalsis.

A

1) Bolus causes stretch receptors in the submucosa to fire
2) Signals to the myenteric (Auerbach’s plexus)
3) [Oral side of bolus] Ach and Sub. P causes circular muscle contraction. VIP and NO causes longitudinal muscle relaxation.
4) [Anus side of bolus] VIP and NO causes circular muscle to relax. Ach and Sub. P causes longitudinal muscle to contract
5) Bolus moves forwards and repeats

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25
Q

What is the migrating motor complex?

A

Occurs between meals in the fasting state (i.e. not affected by bolus distention). Peristaltic wave from stomach to ileum that pulls food residue, bacteria, dead cells and undigestible food material toward the anus. Regulated by motilin.

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26
Q

What is the smooth muscle that regulates transit of chyme from the ileum to the large intestine?

A

Ileocecal valve

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27
Q

Name the two reflexes that allow passage of chyme from the ileum to the caecum.

A

1) Gastrocolic - Increased stretch in the stomach releases gastrin which causes the distal portion of the ileum to contract and the ICV to relax
2) Gastroileal - passage of food into the stomach stimulates a vagovagal reflex which stimulate the dista portion of the ileum to contract, and the ICV to relax

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28
Q

Name 3 types of movement in the large intestine.

A

1) Haustral/segmentation
2) Mass
3) Peristaltic

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29
Q

What are haustral contractions?

A

Triggered by stretch, leading to contraction of Teniae Coli muscles creating segmentations. Increases contact with the mucosa to allow absorption of electrolytes and water. Primarily within the ascending and transverse colon

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30
Q

What is mass movement (peristalsis)?

A

Triggered by stretch, irritants, and the gastrocolic reflex (Increase in gastrin secretion and vasovagal stimulation for acetylcholine). Produces massive peristaltic contractions.

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31
Q

Name the 6 steps that lead to defaecation.

A

1) Stretch - afferent sensory fibres (pelvic nerve) go to S2-S4
2) Efferent motor neurones (pelvic) nerve stimulate the Auerbach’s plexus, increases contraction in the sigmoid colon and rectum
3) The internal anal sphincter relaxes (Smooth muscle)
4) The external anal sphincter is under voluntary control. Innervated by the pudendal nerve.
5) Pudendal nerve also acts on the levator ani to lift the rectum up
6) Valsavas manoeuvre - closure of the glottis, leads to increased intrabdominal pressure and increases force for faeces

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32
Q

What is the valsavas manoevre?

A

Closure of the glottis to increase intraabdominal pressure and increase the force of the faeces expulsion. Abdominals are also involved in this

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33
Q

Name the steps of the vomiting reflex.

A

1) Initiated by the vomiting centre on the medulla oblongata, which can be stimulated by the chemoreceptor trigger zone (by 5HT receptors)
2) Leads to opening of the oesophagus
3) Contraction of the diaphragm and abs, which increases intrathoracic pressure
4) Reverse retrograde peristalsis occurs
5) Epiglottis closes

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34
Q

Name 2 causes of vomiting, and how this can be treated?

A

Motion sickness, opioids, chemotherapy. Treated with anti-emetics such as ondansetron (5HT receptor antagonist)

35
Q

Name the 3 phases of gastric secretion.

A

1) Cephalic
2) Gastric
3) Intestinal

36
Q

Name the four stimulants of the cephalic phase of gastric secretion.

A

Sight, smell, thought, taste (all before food has entered the stomach)

37
Q

What is the neural pathway of the cephalic phase of gastric secretion?

A

Parasympathetic (craniosacral) CNX, S2-S4

1) Cerebral cortex
2) Hypothalamus
3) D.N.V (dorsal nucleus of vagus)
4) Vagus nerve to the stomach
5) Stimulates parietal and chief cells

38
Q

What inhibits the cephalic phase of gastric secretion?

A

Sympathetic nervous system. Stress, emotional upset. Stimulates the thoracolumbar region. Great and small splancic nerves to the coeliac and superior mesenteric ganglion will inhibit secretions of the parietal and chief cells.

39
Q

What stimulates the gastric phase of secretion?

A

Distension of the stomach, partially digested proteins

40
Q

Name two ways in which distention of the stomach acts to promote the secretions of the stomach?

A

1) Long reflex arc - Stretch receptors in the stomach stimulate the afferent vagus nerve. This stimulates the efferent vagus nerve to the stomach to promote secretions. A vagovagal reflex.
2) Short reflex arc - Stretch receptors in the stomach stimulate the afferent vagus nerve. This stimulates the submucosal plexus (Meissner’s plexus) to stimulate blood flow and secretions.

41
Q

Where are pyloric glands found and what cells do they contain?

A

Antrum of the stomach. Upper aspect contain mucus secreting cells. Lower aspect contain G cells which secrete gastrin.

42
Q

How do partially digested proteins stimulate the gastric secretions?

A

1) Partially digested proteins stimulates gastrin secretion from G cells of the pyloric gland of the antrum
2) Gastrin is a hormone which stimulates parietal cell (oxyntic gland) to secrete hydrochloric acid
3) Gastrin also stimulates chief cells (oxyntic gland) to secrete pepsinogen, which is converted into pepsin via acidity.

43
Q

Which glands can parietal cells be found in, and what do they secrete?

A

Found in the oxyntic glands. Secrete HCL.

44
Q

What cells do the oxyntic glands contains?

A

Upper aspect, mucus secreting glands. Lower aspect, parietal cells, chief cells and enterochromaffin-like cells (ECL).

45
Q

What are the inhibitors of the gastric phase of secretion?

A

1) Sympathetic nervous system

2) Somatostatin (when pH is too low)

46
Q

What is the alkaline tide?

A

The ejection of HCO3- from parietal cells into the gastric veins. Will allow the influx of Cl- into the cell.

47
Q

How do parietal cells secrete HCL?

A

(draw diagram)

1) Mitochondria create CO2 which is converted into H+ and HCO3-
2) Na+/K+ ATPase is ejected 3Na+ and bringing in 2K+ to create a concentration gradient
3) HCO3- is removed from the cell into the blood (alkaline tide) and brings in CL- in return. CL- is then passed into the lumen via a Cl- pump
4) H+ is ejected from the cell into the lumen in return for K+ (where omeprazole works)
5) H+ also ejected into the veins in return for the Na+ that was pumped out

48
Q

How does somatostatin work?

A

Inhibits gastric phase secretions. D-cells in the pyloric gland of the antrum secrete somatostatin in response to low pH. Paracrine action on G-cell to stop gastrin secretion.

49
Q

Which cells secrete histamines, and what does histamine do?

A

Enterochromaffin-like cells (oxyntic gland). Secretes histamine in response to gastrin and Ach. Histamine stimulates parietal and chief cells (pyloric gland in antrum) to release H+ and pepsinogen.

50
Q

Which cell secretes intrinsic factor?

A

Parietal cells. Intrinsic factor is used to absorb Vitamin B12 in the ileum. (think pernicious anaemia). Alcoholics destroy their oxyntic glands and chief cells and often develop pernicious anaemia

51
Q

Which hormone do S cells secrete, and what is their stimulus?

A

Secretin. Found in the duodenum. Stimulated by high H+ ions and high fats in the chyme.

52
Q

What 4 things does secretin do?

A

1) Acts in an endocrine fashion to the stomach. Inhibits G cells in the pyloric gland in the antrum, will not secrete gastrin
2) Acts on the liver, stimulates the conversion of cholesterol to bile
3) Acts of pancreatic cells to secrete bicarbonate HCO3- into the main pancreatic duct
4) Stimulates chief cells to secrete pepsinogen

53
Q

Which hormone do I cells secrete, and to what stimulus?

A

CCK (cholecystokinin). Released in response to high fats, high peptones, and high oligosaccharides

54
Q

What 5 things does CCK do?

A

1) Will inhibit the secretion of H+ from parietal cells
2) Enhances the action of secretin at the liver - increased bile release
3) Will act on the gall bladder to promote concentrated bile secretion out of the cystic duct into the common bile duct
4) Will act to relax the sphincter of oddi to allow passage of bile into the duodenum
5) Stimulates acinar cells in the exocrine pancrease to secrete zymogen granules

55
Q

What do K cells secrete, and what is the stimulus?

A

GIP (Gastric inhibitory peptide). Secreted in response to high fats and high oligosaccharides in the chyme

56
Q

What 2 things does GIP do?

A

1) Inhibits parietal cells from secreting H+

2) Stimulates beta cells in the endocrine pancreas to release insulin.

57
Q

What are acinar cells, and what do they look like histologically?

A

Acinar cells are the main cell of the acinii of the exocrine pancreas. They contain a single nucleus basally, along with many mitochondria, and rER. Contains zymogen granules apically.

58
Q

Intestinal villus consist of which layers of the small intestine?

A

Mucosa. Simple ciliated columnar epithelium, lamina propria, and muscularis mucosae.

59
Q

What cells are found within the crypts of Lieberkuhn?

A

1) Intestinal stem cells
2) Paneth cells
3) Transit amplifying cell

60
Q

What do Paneth cells do?

A

Rich in antimicrobial peptides (lysozymes, alpha-defensins, cryptidins), immune modulators and trophic factors. Functionally similar to neutrophils.

61
Q

What is the principle secretions of the crypts of lieberkuhn?

A

Fluid similar to ECF. This will make the chyme less viscous. Causes osmotic drag.

62
Q

Where can Brunner’s glands be found?

A

Duodenum. Distinguish the duodenum from the jejunum and ileum.

63
Q

What do Brunner’s glands do?

A

1) Lubricate - with mucins
2) Buffer - with alkaline mucus
3) Protect - from acidic chyme

64
Q

Draw a simple diagram of carbohydrate absorption in the intestine.

A

1) Na+/k+ ATPase generates Na+ gradient internally. (2K+ internal, 3NA+ external)
2) Na+/glucose(or galactose) cotransporter brings in glucose and galactose (SGLT1)
3) GLUT5 transport brings in fructose
4) GLUT2 transport on the basal membrane pushes glucose into the ECF
5) H20 and Cl- follow Na+ flow.

65
Q

Draw a simple diagram of protein absorption in the intestine

A

1) Na+/k+ ATPase generates Na+ gradient internally. (2K+ internal, 3NA+ external)
2) H+/AA cotransporter brings in amino acids <=3 amino acids long
3) Na+/H+ antiporter keeps pH regulated internally
4) AAT (amino acid transporter) transports AAs into the ECF

66
Q

Draw a simple diagram of lipid absorption.

A

1) Bile emulsifies fats in the small intestine and breaks them down
2) Forms micelles
3) Micelle cross the apical membrane and are processes by sER and rER
4) Forms a chylomicron
5) To big for veins, so transported into lacteals (like fenestrated sinosoids) - transported into the lymphatics

67
Q

What do the salivary glands do?

A

1) Lubrication
2) Hydration
3) Oral hygiene
4) Digestion

68
Q

Name 3 extrinsic and intrinsic salivary glands, and what is their distinction.

A

Extrinsic: Parotid, submandibular, sublingual (stimulated to secrete saliva)
Intrinsic: Buccal, Labial (constantly secrete saliva)

69
Q

Where do the extrinsic salivary glands open in the oral cavity?

A

1) Parotid - upper 2nd molar (via parotid duct)
2) Submandibular - lingual frenulum (via Stensons duct)
3) Sublingual - floor (Wartons’ duct)

70
Q

Which type of cells make up the extrinsic salivary glands?

A

Parotid - serous
Submandibular - Mixed
Sublingual - Mucus

71
Q

What innervates the submandibular and sublingual salivary gland?

A

Superior salivatory nucleus (pons) > Facial nerve (CNVII) > Lingual nerve.

72
Q

What innervates the parotid gland?

A

Inferior salivatory nucleus (pons) > Glossopharyngeal nerve (CNIX) > Otic ganglion.

73
Q

Name the 5 main ions found in the primary secretion.

A

Na+, K+, Cl-, H2O, HCO3-

74
Q

Is primary secretion isotonic, hypertonic or hypotonic to blood plasma?

A

Isotonic. Na+ and Cl- = H2O

75
Q

What is the difference between primary and secondary secretions?

A

Less Na+ and Cl- in secondary secretion. Modifies the secondary secretion to bring in HCO3- and H+ ions.

76
Q

Is secondary secretion isotonic, hypertonic or hypotonic compared with blood plasma?

A

Hypotonic. Na+ and Cl- < H2O

77
Q

Where is haemoglobin metabolised?

A

Macrophages of the spleen

78
Q

What is unconjugated bilirubin?

A

Bilirubin bound with albumin

79
Q

Describe the haemoglobin metabolism process.

A

1) Haemoglobin > Haem + Globin
2) Globin > AAs
3) Haem > Bilivirdin (Haemoxigenase)
4) Biliverdin > Bilirubin (Bilivirdin reductase) + Fe++
5) Bilirubin > Unconjugated bilirubin via addition of albumin
6) Unconjugated bilirubin to conjugated bilirubin via addition of glucuronate (via UDP-glucuronyltransferase)

80
Q

What is conjugated bilirubin?

A

Bilirubin bound to glucuronate (via UDP-glucuronyltransferase)

81
Q

Name 3 different types of jaundice.

A

1) Haemolytic jaundice (excessive RBC lysis)
2) Hepatocellular jaundice (damage to the liver)
3) Cholestatic (obstruction of the bile flow, fibrosis, tumours, gall stones)

82
Q

Name the 4 muscles that depress the mandible.

A

1) Lateral pterygoid (CN5 innervation)
2) Digastric anterior belly
3) Mylohyoid
4) Genial hyoid

83
Q

Name the 3 muscles that elevate the mandible.

A

1) Masseter
2) Temporalis
3) Medial pterygoid

84
Q

Where is albumin formed?

A

The liver

Phase 1 Medicine (JA) (8 decks)

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