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Phase 1 Med > Gastrointestinal > Flashcards

Gastrointestinal Flashcards

1
Q

What are the roles of the buccinator and suprahyoid muscles in swallowing?

A
  • Manipulate food when chewing
  • Elevate hyoid bone
  • In phase 1
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2
Q

What are the roles of the muscles of the palate?

A
  • Contract to cause soft palate to shut of nasopharynx
  • Also helps to form bolus
  • In phase 2
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3
Q

What are the roles of the muscles of the floor of the mouth?

A
  • Elevate hyoid bone

- In phase 2

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4
Q

What are the roles of the infrahyoid muscles of the neck?

A
  • Depress larynx

- In phase 3

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5
Q

What are the roles of the pharyngeal constrictors?

A

Contract sequentially to drive bolus down

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6
Q

Name the muscles involved in swallowing, in order of their use

A
  • Buccinator and suprahyoid
  • Palate muscles/ floor of mouth muscles
  • Infrahyoid/ pharyngeal constrictors
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7
Q

Describe phase one of swallowing. Is it voluntary or involuntary? Name the muscles used

A
  • Voluntary
  • Food compressed to roof
  • Pushed towards oropharynx
  • Buccinator and suprahyoid muscles used
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8
Q

Describe phase two of swallowing. Is it voluntary or involuntary? Name the muscles used

A
  • Involuntary
  • Soft palate closes nasopharynx
  • Pharynx shortened and widened by elevation of hyoid bone
  • Palate muscles, muscles of floor of mouth
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9
Q

Describe phase three of swallowing. Is it voluntary or involuntary? Name the muscles used

A
  • Involuntary
  • Sequential contraction of pharyngeal constrictors to drive bolus down
  • Return (depression) of hyoid bone.
  • Infrahyoid muscles, pharyngeal constrictors
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10
Q

List 4 roles of saliva

A
  • Lubricant for mastication, swallowing and speech
  • Immunty (contains antifungals etc)
  • Buffer
  • Contains solvents necessary for taste
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11
Q

What is the optimum pH of saliva

A

Around 7.2

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12
Q

What percentage of BMR is used by the liver?

A

21%

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13
Q

What percentage of BMR is used by the brain?

A

20%

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14
Q

What sources of energy does the liver use?

A

Amino acids, fatty acids, alcohol, gluscose

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15
Q

What sources of energy does the brain use?

A

Glucose and ketone bodies

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16
Q

What sources of energy do muscles use?

A

Glucose, acetate, triglycerides, branched amino acids

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17
Q

What sources of energy red blood cells use?

A

Glucose

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18
Q

What are free sugars and what are they associated with?

A
  • Mono and disaccharides

- Associated with increased blood glucose/insulin

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19
Q

What are 2 types of starch?

A

Rapidly digesting and slowly digesting (RDS and SDS)

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20
Q

What is rapidly digesting starch associated with?

A

Increased blood glucose and insulin levels

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21
Q

Name 4 functions of the stomach?

A
  • Store and mix food
  • Kill microbes
  • Secrete proteases/intrinsic factor
  • Lubrication
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22
Q

Name 4 key cells of the stomach

A
  • Parietal
  • Mucous
  • Chief
  • Enteroendocrine
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23
Q

Which cells in the stomach secrete acid, and what type of acid?

A

Parietal cells secrete HCl

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24
Q

Approximately how much acid does the stomach produce per day?

A

2L

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25
Q

What are the four phases of digestion?

A

1 - Cephalic
2 - Gastric
3 - Intestinal

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26
Q

Describe what happens in the cephalic phase of digestion

A
  • The sight, smell, taste and chewing of food causes the parasympathetic NS to release acetylcholine.
  • This therefore stimulates the release of gastrin and histamine
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27
Q

Describe what happens in the gastric phase of digestion

A
  • Gastric distension, the presence of peptides and the presence of amino acids (all due to food), cause gastrin release.
  • This therefore stimulates histamine release.
  • When pH is too high in this phase due to the acid secretion from parietal cells, somatostatin release is triggered.
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28
Q

Describe the role of proteins in the stomach in the process of digestion

A

Proteins from food acts as a buffer to mop up excess H+ ions, meaning the overall pH increases and so the stimulus for samatostatin release is removed.

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29
Q

Describe what happens in the intestinal phase of digestion

A
  • Chyme entering the duodenum, a low pH and the presence of amino acids/fatty acids leads to the release of enterogasterones.
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30
Q

Name 2 enterogasterones and their function

A
  • Secretin: decreases gastrin levels, increases somatostatin levels.
  • Cholecystokinin: CCK.
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31
Q

What is the role of acetylcholine in digestion?

A
  • It is a parasympathetic neurotransmitter released by enteric nuerons.
  • It acts directly on parietal cells to increase acid secretion.
  • It also stimulates the release of histamine and gastrin.
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32
Q

What is the role of gastrin in digestion?

A
  • It is a hormone

- It doesn’t act directly on parietal cells, rather stimulates the release of histamine.

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33
Q

What is the role of histamine in digestion?

A
  • It is a paracrine.

- Acts directly on parietal cells to increase acid production.

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34
Q

What is the role of somatostatin in digestion?

A
  • Acts directly on parietal cells to decrease acid production.
  • Also inhibits the production of gastrin and histamine.
  • Release is stimulated by a low pH due to excess acid release.
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35
Q

What is the definition of a peptic ulcer?

A

A breach in the gastric mucosal surface

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36
Q

What are peptic ulcers caused by?

A

Helicobacter pylori infection, drugs such as NSAIDs or chemical irritants (e.g. alcohol, bile salts)
I.e. due to a increased mucosal attack or reduced mucosal defence.

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37
Q

What are 4 gastric mucosa defences?

A
  • Alkaline mucus
  • Tight junctions
  • Replacement of damaged cells
  • Feedback loops
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38
Q

Which cells in the stomach secrete pepsinogen?

A

Chief cells

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39
Q

What is pepsinogen?

A

An inactive form of pepsin

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40
Q

What is pepsionogen mediated by?

A

ACh

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41
Q

When and how is pepsinogen converted into pepsin?

A

At pH of less than 2 by HCl

42
Q

Why is pepsiongen to pepsin conversion an example of positive feedback?

A

Because after being converted from pepsinogen into pepsin, pepsin then catalyses further conversion of pepsinogen into pepsin.

43
Q

What is the volume of an empty and full stomach?

A
  • Empty: 50mL

- Full: 1.5L

44
Q

How can the volume of a full stomach be so much greater than that of an empty stomach?

A

Because smooth muscle in the body and fundus undergoes receptive relaxation

45
Q

How is receptive relaxation achieved?

A

By the parasympathetic nervous system releasing NO and serotonin through afferent input via the Vagus nerve.

46
Q

Describe the process of peristalsis in the stomach

A

1 - Small peristaltic wave in the gastric body
2 - Larger wave in the gastric antrum. Pylorus closes as the wave reaches it.
3 - This means only a small amount of chyme passes into the duodenum. The antral contents is pushed back towards the body of the stomach i.e. to undergo mixing.

47
Q

How is the rhythm set for peristaltic waves and what at?

A
  • Set by pacemaker cells in the muscularis propria (i.e. muscular layer) at 3 per minute.
48
Q

What increases the strength of peristaltic waves?

A
  • Gastrin

- Gastric distension

49
Q

What decreases the strength of peristaltic waves?

A
  • Duodenal distension
  • Increased duodenal pH
  • Increased sympathetic action
  • Decreased parasympathetic action
50
Q

Why and how does duodenal filling occur?

A
  • The capacity of the stomach is greater than that of the duodenum.
  • If food moves too fast from the stomach to duodenum, can cause overfilling
51
Q

How is duodenal emptying prevented?

A
  • Release of enterogastrones

- Increased sympathetic and decreased parasympathetic action

52
Q

Where are the 4 different types of stomach cells found?

A
  • In gastric glands within gastric pits of the mucosal layer.
53
Q

What 2 types of enteroendocrine cells are there are what is their function?

A
  • G cells secrete gastrin

- ECL cells secrete histamine

54
Q

If water input is 9000ml, how much is ingested?

A

2000ml

55
Q

Name some ways in which water is secreted from the body?

A

Saliva, bile, via pancreas.

56
Q

Where is water reabsorbed? What percentage is reabsorbed?

A

Jejunum, ileum. colon. 98%

57
Q

How much water is there across the gastric mucosa?

A

Only little due the the high osmotic load of HCl

58
Q

Where and how is Na+ reabsorbed?

A
  • Actively pumped from lumen of ileum and jejunum

- Actively pumped into lumen of colon

59
Q

Where and how is K+ reabsorbed?

A

By passive diffusion in the jejunum, ileum and colon

60
Q

Where and how are Cl- and HCO3- reabsorbed?

A
  • Cl- actively absorbed in exchange for HCO3- in ileum and colon
61
Q

What are the two types of optical isomers of amino acids and which type are found in proteins?

A
  • D and L

- L in proteins

62
Q

What is a zwitterion?

A

A molecule which has 2 different charges within it

63
Q

Where does protein digestion begin?

A

Stomach

64
Q

What is the first part of protein digestion occurs first?

A
  • Pepsins (from pepsinogen) cleave some of the peptide bonds
65
Q

What are the 2 types of pepsinogen and where are the found?

A
  • Pepsinogen I: In HCl secreting regions

- Pepsinogen II: In pyloric region

66
Q

What happens in the second part of protein digestion and where does it occur?

A
  • In the small intestines

- Polypeptides are further fragmented by pancreatic proteases

67
Q

What are the 2 types of pancreatic proteases?

A

Endopeptidases and exopeptidases

68
Q

What happens in the final part of protein digestion and where does it occur?

A
  • Intracellular peptides break down some di/tripeptides in the lumen, brush border and within cells.
69
Q

What happens to the amino acids formed by protein digestion?

A

Pass into cells via Na 2ndary transporter, then into interstitial fluid by facilitated transporter.

70
Q

What is a lipid?

A

A fatty acid

71
Q

What is a triglyceride/triglycerol?

A

A glycerol molecule with 3 fatty acids attached

72
Q

Where does digestion of fats begin?

A

In the duodenum

73
Q

What are triglycerides hydrolysed by and how?

A
  • Pancreatic lipase
  • With the help of co-lipase
  • Hydrolyses bond 1 and 3 quickly and 2 more slowly
74
Q

What does pancreatic lipase act on specifically?

A

Emulsified fats

75
Q

How are fats emulsified?

A

Broken up into smaller droplets which are surrounded by bile salts to prevent re-association

76
Q

What happens to the fatty acids and monoglycerides after digestion?

A

They combine with bile salts and cholesterol to form micelles. This enables them to reach the brush border by diffusion, where they break down.

77
Q

What happens when fatty acids and monoglycerides reach the cell after digestion and what is the purpose of this?

A

They are esterified back into triglycerides to maintain the diffusion gradient across the cell membrane.

78
Q

What happens after monogycerides and fatty acids are esterified back into triglycerides in the cell?

A

They are packaged into chylomicrons which leave the cell by exocytosis

79
Q

What are chylomicrons?

A

Lipoproteins

80
Q

What happens to chylomicrons after they leave the cell by exocytosis?

A

They enter lacteals and circulate in the lymphatic system

81
Q

What happens to chylomicrons after they enter the lymphatic system?

A

They are delivered to cells where lipoprotein lipase hydrolyses them for use by cells

82
Q

What are monosaccharides? Give 2 examples.

A

Single sugars e.g. glucose and fructose

83
Q

What are oligosaccharides? Give 2 examples.

A

2 - 10 sugars e.g. disaccharides lactose and sucrose.

84
Q

What are polysaccharides? Give 2 examples.

A

Many sugars e.g. starch and glycogen

85
Q

What types of isomers can sugars form? Which kind are used in metabolism?

A

D and L isomers. D used in metabolism.

86
Q

Describe the structure of glycogen and starch

A
  • Glycogen: Polymer of alpha glucose. 1-4 glycosidic bonds with some 1-6 branches.
  • Starch: Same as glucose but fewer 1-6 branches.
87
Q

Where does carbohydrate/starch digestion begin?

A

In the mouth. Alpha-amylase degrades starch in saliva.

88
Q

How are starch/carbohydrates digested in small intestine?

A

Pancreatic alpha-amylase catalyses 1-4 linkages but not 1-6.

89
Q

How do hexoses and pentoses cross the intestinal mucosa?

A

Rapidly absorbed across it, into capillaries and to the portal vein

90
Q

How does glucose cross the mucosal surface?

A

By the Glucose-Na+/K+ co-transporter, hence the high Na+ on the mucosal surface

91
Q

How do you calculate BMI?

A

Weight (kg)/Height^2 (m)

92
Q

What are the categories for BMI?

A

18.5 - 25 = Normal
25 - 30 = Overweight
30 - 40 = Obese
40+ = Morbidly obese

93
Q

Define malabsorption

A

Defective absorption of nutrients across the GI tract.

94
Q

List 3 mechanisms of malabsorption

A
  • Defective digestion
  • Defective absorption
  • Abnormal transport across mucosa
95
Q

What is the main cause of malabsorption?

A

Disease of small bowel

96
Q

List 3 causes of poor weight gain

A

Insufficient calories, protein or fluid.

97
Q

Is saliva isotonic, hypertonic or hypotonic and why?

A
  • Hypotonic as striated ducts transport ions out of saliva and ensures water remains in.
98
Q

What does hypotonic mean?

A

A solution with a lower osmotic pressure than surrounding fluids. I.e. more water and fewer particles dissolved in it.

99
Q

What is somatostatin produced by?

A

D cells

100
Q

What do endo and exopeptidases do?

A

Endo: Convert large polypeptides to smaller ones.
Exo: Breakdown dipeptides and amino acids.

101
Q

What do parietal cells secrete and what is the function of the products it secretes?

A
  • HCl for digestion.

- Intrinsic factor: Aids vitamin B12 absorption.

Phase 1 Med (20 decks)

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