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Phase 1 M > GI > Flashcards

GI Flashcards

1
Q

What are the 3 components of the pharynx

A

Nasopharynx
Oropharynx
Laryngopharynx

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2
Q

What nerve stimulates the nasopharynx

A

Maxillary branch of the trigeminal nerve

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3
Q

What nerve stimulates the oropharynx

A

Glossopharyngeal

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4
Q

What nerve stimulates the laryngopharynx

A

Vagus

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5
Q

What are the three stages of swallowing

A

Voluntary
Involuntary
Involuntary

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6
Q

What happens in the first voluntary stage of swallowing?

A

Food Is compressed against the roof of the mouth and pushed towards the oropharynx by the tongue
Buccinator and supra hyoid muscles manipulate food during chewing, lift the hyoid bone and flatten the floor of the mouth

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7
Q

What happens in the secondary involuntary stage of swallowing?

A
  1. Nasopharynx is closed off by the muscles of the soft palate which tense and elevate - forms food bolus
  2. Pharynx is shortened and widened by contraction of the longitudinal muscle
  3. Impulses from the swallowing centre inhibit respiration, raise the larynx and close the glottis to stop food entering the trachea
  4. As the tongue pushes food further back into the pharynx, the epiglottis folds over the closed glottis to prevent food aspiration
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8
Q

What happens in the third involuntary stage of swallowing>

A

Sequential contraction of the pharyngeal constrictor muscles which depresses the pharynx and the hyoid bone. Before food enters the oesophagus, the Upper oesophageal sphincter relaxes then as soon as food passes through it closes, the glottis opens and breathing resumes. Once the food is in the oesophagus, peristaltic waves move it

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9
Q

Describe the innervation and location of the pharyngeal constrictor muscles

A

Innervated by the vagus nerve, 3 overlying circular muscles that form the posterior and lateral walls and contract sequentially to force food bolus into oesophagus

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10
Q

What muscles enables depression of the pharynx and hyoid bone to keep the mouth open?

A

Infra-Hyoid muscle

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11
Q

Describe the musculature of the oesophagus

A

Upper 1/3 = skeletal muscle

Lower 2/3 = Smooth muscle

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12
Q

Where are the oesophageal sphincters located?

A

Upper OS is a ring of skeletal muscle just below the pharynx

Lower OS is a ring of smooth muscle in last portion of the oesophagus

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13
Q

How long does it take for a peristaltic wave to reach the stomach?

A

9 sec

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14
Q

Describe the gag reflex and its innervation

A

Reflex elevation of the pharynx often followed by vomiting

Reflex arc of the glossopharyngeal and vagus nerves

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15
Q

What are the three main functions of saliva?

A

Lubrication for mastication
Maintain oral pH at 7.4
Digestion - alpha amylase released from the parotid gland
Defence of the oral cavity - washes away food particles which bacteria use as metabolic support

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16
Q

What is the daily secretion of saliva in adults>

A

800-1500ml

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17
Q

What is the function of serous saliva?

A

Contains alpha amylase for starch digestion

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18
Q

What is the function of mucous saliva?

A

Contains mucin components to lubricate mucosal surfaces

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19
Q

What sort of gland is the parotid gland?

A

Serous

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20
Q

What sort of gland is the submandibular gland

A

Mixed - both serous and mucous (M for Mixed)

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21
Q

What sort of gland is the sublingual gland

A

Mucous and serous but mainly mucous

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22
Q

What affects the composition and amount of saliva produced?

A 
Circadian rhythms 
Age 
Time of day 
Type and duration of the stimulus 
Diet 
Drugs 
Flow rate 
Type/size of gland
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23
Q

What are the defence systems of the oral cavity?

A

Saliva - washes food away
Mucosa - physical barrier
Palatine tonsils - acts as surveillance system for the immune system

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24
Q

What sort of gland is the minor salivary glands?

A

all are mucous except the serous glands of von Ebner

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25
Q

Which salivary glands are continuously active>

A

Submandibular, sublingual and minor glands

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26
Q

Which salivary gland dominates the unstimulated component of salivary system

A

Submandibular

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27
Q

Which salivary gland dominates the salivary system when stimulated?

A

Parotid

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28
Q

Which epithelium lines the oral cavity

A

Keratinised stratified squamous epithelium

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29
Q

What are the two main components of the salivary gland structure

A 
Acinar Cells (Functional unit)
Duct cells (Lined by acinar cells)
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30
Q

What are the two types of acini>

A

Mucous and serous

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31
Q

Describe the properties of a serous acini

A 
Dark stain
Nucleus in the basal 1/3
Small central duct 
Secrete alpha amylase and water 
Mainly found in parotid gland
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32
Q

Describe the properties of mucous acini

A 
Pale stain 
Nucleus at base 
Large central duct 
Secrete mucins, glycoproteins and water 
Mainly found in submandibular and sublingual glands
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33
Q

What are the 2 components of the interlobular duct of a salivary gland

A

Intercalated duct and the striated duct

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34
Q

Describe the function of the intercalated duct

A

Short narrow segment of cuboidal cells that connect the acini to the larger striated ducts

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35
Q

Describe the function of the striated duct

A

Major site for NaCl reabsorption and are striated at the basal end
Basal end is highly folded into microvilli to aid the active transport of HCO3 against its concentration gradient
Have mitochondria to provide the necessary energy

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36
Q

What is absorbed and what Is secreted by ducts

A

Na+ and Cl- are REABSORBED and K+ and HCO3- are SECRETED

Water is also reabsorbed

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37
Q

What is the final composition of the saliva like?

A

Hypotonic

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38
Q

What percentage of salivary flow do the major and minor salivary glands contribute respectively

A

Major = 80%

Minor = 20%

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39
Q

Where are the minor salivary glands found?

A

Lips
Cheeks
Hard and soft palate
Tongue

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40
Q

Describe the nerve supply to the parotid gland

A

Sympathetic inhibitory innvervation from lateral horn of T1 that synapse in superior cervical ganglion an form a plexus around the external carotid artery
Parasympathetic stimulatory innervation from the inferior salivary nucleus in medulla oblongata to the glossopharyngeal nerve which gives the tympanic branch and tympanic plexus with gives the lesser petrosal nerve which synapses at the otic ganglion from which auriculotemporal branch of mandibular division of trigeminal nerve

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41
Q

What structures pass through the parotid gland?

A

Facial nerve and its branches (temporal, zygomatic, buccal, mandibular, cervical)
Retromandibular vein
External carotid artery

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42
Q

Describe the structure of the submandibular gland

A 
Consists of superficial (Larger) and deep (smaller) lobes that are separated by mylohyoid muscle 
Submandibular duct (Whartons duct) begins in the superficial lobe, wraps around the posterior border of mylohyoid and runs in to the floor of the mouth and empties at the sublingual papillae
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43
Q

Describe the sensory innervation of the submandibular gland

A

Superior salivary nucleus via the chorda tympani branch of the facial nerve that becomes part of the trigeminal lingual nerve

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44
Q

Describe the innervation of the sublingual gland

A

Parasympathetic by the chorda tympani branch of the facial nerve via the submandibular ganglion

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45
Q

What is the effect of parasympathetic innervation of the salivary system

A

Stimulates secretion

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46
Q

What is the effect of the sympathetic stimulation on the salivary system

A

Inhibits salivary secretion

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47
Q

What are the causes of xerostomia (dry mouth)

A

Cystic fibrosis or Sjorgrens syndrome (autoimmune where immune cells attack glands resulting in no saliva - mainly women)
Medication
irradiation for neck and head cancers

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48
Q

Describe where and why salivary glands can become obstructed

A

Saliva contains calcium and phosphate ions that can form salivary calculi (Stones) - most likely tp form in the submandibular gland where they block the duct at the bend around mylohyoid or at the exit at the sublingual papillae

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49
Q

What are the common causes of inflammation of the salivary gland

A

Infection secondary to obstruction

Infection caused by mumps

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50
Q

Why might salivary glands degenerate

A

Complication of irradiation from head and neck cancer

Sjorgens syndrome

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51
Q

What are the 8 functions of the stomach

A 
Store and mix food 
Dissolve food and continue digestion 
Regulate emptying into duodenum 
Kill microbes 
Secrete protease 
Secrete intrinsic factor 
Lubrication 
Mucosal protection
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52
Q

What do mucous cells produce

A

Mucous

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53
Q

What do parietal cells produce?

A

Gastric acid and intrinsic factor

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54
Q

What do chief cells produce?

A

Pepsinogen

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55
Q

What do ECL cells produce?

A

Histamine

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56
Q

What do G cells produce?

A

Gastrin

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57
Q

What do D cells produce?

A

Somatostatin

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58
Q

What is the pH of stomach acid and how much is produced a day?

A

HCL pH 2 (H+) >150mM

Approx 2L produced per day

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59
Q

Describe the difference sin the epithelium between the upper and Lower portions of the stomach

A

epithelium of stomach invaginate into mucosa
Body of stomach is thinned wall and is concerned with secretion of mucus, HCL and pepsinogen
Antrum of stomach is thicker layer of smooth muscle and is for mixing contents of stomach - glands here secrete little acid but secreted gastrin hormone instead

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60
Q

Outline how parietal cells secrete H+

A
  1. H20 in parietal cells breaks down into H+ and OH-
  2. Co2 and H20 from respiration are converted into H2CO3 by carbonic anhydrase but rapidly dissociates into HCO3- and H+
  3. HCO3 is pumped out into capillaries in exchange for CL-
  4. H+ produced can react with the OH- from H20 breakdown to reform H2O or can be pumped into the stomach lumen via the H+/K+ ATPase
  5. K+ diffused back into the stomach via K+ channels and Cl- ions enter stomach through Cl- channels
  6. In the stomach, H+ and Cl- ions combine to form HCl
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61
Q

What is the effect of increased acid stimulation?

A

Increased migration and insertion of H+/K+ ATPase channels in the membrane increasing the amount of H+ pumped into the stomach lumen

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62
Q

Describe how the cephalic phase increases gastric acid secretion

A

Triggered by the smell, sight or taste of food
Parasympathetic NS
Ahh acts indirectly on parietal cells
ACh triggers the release of gastrin from G-cells and histamine from ECL cells
These increase insertion of H+/K+ ATPase in plasma membrane of parietal cells

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63
Q

Describe how the gastric phase increases gastric acid secretion

A

Triggered by gastric distension and the presence of peptides and AA in the stomach
Causes gastrin to be released which acts directly on parietal cells
Causes Histamine to be released from ECL cells which acts directly on parietal cells
Causes increase K+/H+ ATPase insertion on the plasma membrane

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64
Q

Why is histamine a good therapeutic target in stomach acid production?

A

Because it acts directly on parietal cells but also mediates the effects of gastrin and acetylcholine

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65
Q

What is the effect of protein in the stomach?

A

Direct stimulus from gastrin release
Protein in the lumen acts as a buffer, mopping up H+ which causes the stomach pH to rise. Somatostatin secretion is subsequently inhibited and parietal cell activity increases

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66
Q

What two phases result in decreased stomach acid production

A

Gastric phase

Intestinal Phase

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67
Q

Describe the gastric phase in the decrease of stomach acid

A

Low luminal pH causes inhibition of gastrin secretion and indirect inhibition of histamine secretion
Low luminal pH stimulates the release of somatostatin which inhibits parietal cells

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68
Q

Describe the role of the intestinal phase in reducing stomach acid secretion

A

Occurs in the duodenum
Initiated by duodenal distension, low pH, hypertonic solutions and fatty acids and amino acids
Causes the release of enterogastrones including
1. Secretin –> Inhibits gastrin and promotes somatostatin
2. CCK
also triggers long and short neural pathways to reduce ACh

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69
Q

What is a peptic ulcer?

A

breach in the mucosal surface

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70
Q

What are the causes of peptic ulcer

A

Helicobacter pylori
Drugs (NSAIDs)
Chemical Irritants (Alcohol+bile salts)
Gastrinoma

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71
Q

How does helicobacter pylori damage the mucosa?

A

Lives in the gastric mucosa
Secretes urase which splits urea into CO2 and ammonia
Ammonia combines with H+ to form ammonium
Ammonium is toxic to the gastric mucosa and reduces mucus secretion
Ammonium secreted proteases, phospholipase and vacuolated cytotoxin A damage gastric epithelium
Causes reduced mucosal defence

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72
Q

How do NSAIDs damage the gastric mucosa?

A

Mucus production is stimulated by prostaglandins but requires COX-1 for production
NSAIDs inhibit COX-1
Use prostaglandin analogues instead

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73
Q

How do chemical irritants such as alcohol and bile salts damage the mucosa?

A

Wash away the protective mucus lining
Bile salts reflux into the stomach by the duodenal-gastric reflux
Regurgitated bile strips away the mucus layer

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74
Q

What is a gastrinoma?

A

tumour of the parietal cells that causes increases gastrin release which causes increased gastric acid release which attacks the gastric mucosa causing an ulcer

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75
Q

What are the 4 ways that the gastric mucosa defends itself?

A

Alkaline mucus
Tight junctions between epithelial cells
Replacement of damaged cells
Feedback loops

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76
Q

Name 3 ways to reduce gastric acid secretion

A
  1. Proton pump inhibitors such as omeprazole block the pump that pumps H+ into the lumen but not the factors that stimulate it
  2. H2 receptor antagonists such as cimetidine block histamine receptors reducing secretion
  3. Prostaglandin analogues such as misoprostol
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77
Q

Describe the process of protease secretion

A

The zymogen pepsinogen is released from chief cells under influence of ACh release from the enteric nervous system. once in the stomach lumen, the low luminal pH causes autocatalytic conversion into pepsin. Once pepsin is released it causes positive feedback for release of more,.

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78
Q

How is pepsin inactivated?

A

HCO3- released in the duodenum irreversibly inactivates pepsin

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79
Q

What is the role of pepsin?

A

Not required as protein digestion still occurs if stomach removed but accelerates process by breaking collagen so forms chunks with larger SA
Accounts for 20% of protein digestion

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80
Q

What is the normal volume of the stomach and what is the volume after eating? why does it increase?

A

50ml normally
1.5L when eating
Increases without increase in intraluminal pressure as smooth muscle in fundus and body relax

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81
Q

How does receptive relaxation of stomach smooth muscle occur?

A

Receptive relaxation is mediated by the enteric NS which releases NO and serotonin and by the parasympathetic NS via the vagus nerve

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82
Q

Describe the process of gastric motility

A
  1. Waves in the body of the stomach are too weak for proper mixing
  2. Waves in the antrum are more powerful = mixing
  3. Pyloric sphincter closes when peristaltic wave arrives but small amount of chyme passes through into duodenum
  4. Closing of PS forces antral contents back into body for more mixing and digestion
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83
Q

Describe which cells determine the rate of peristaltic waves in the stomach

A

Interstitial pacemaker cells of Cajal in the muscularis propria give off constant waves (3/minute)
Cells undergo cycles of depolarisation and repolarisation with depolarisation travelling through gap junctions to adjacent smooth muscle

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84
Q

What factors increase the strength of peristaltic contractions in the stomach?

A

Presence of gastrin

Gastric distension mediated by mechanoreceptors

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85
Q

What factors decrease the strength of peristaltic contractions in the stomach?

A 
Duodenal distension
Increased duodenal fat content 
Increased duodenal osmolarity 
Decreased duodenal pH 
Increased sympathetic stimulation
Decreased parasympathetic stimulation
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86
Q

What is the main cause of dumping syndrome?

A

Volume of stomach is greater than the duodenum so if duodenum becomes overfilled with hypertonic solution, dumping occurs

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87
Q

What are the 8 symptoms of dumping syndrome?

A

Bloating, vomiting, diarrhoea,

Cramping, weakness, dizziness, sweating, fatigue

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88
Q

What is gastropariesis?

A

Delayed gastric emptying

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89
Q

What are the 8 causes of gastropariesis?

A

Idiopathic, autonomic neuropathies, abdominal surgery, PD, MS, scleroderma and amyloidosis

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90
Q

What are the 5 common symptoms of gastropariesis?

A

Abdominal pain/bloating, vomiting undigested food, nausea and early satiety and GORD

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91
Q

What 7 drugs are associated with causing gastropariesis?

A 
H2 receptor antagonists 
Proton pump inhibitors 
Opioid analgesics 
Diphenhydramine 
B-adrenergic receptor agonists 
Ca2+ channel blockers 
Levodopa
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92
Q

What are the 6 routes of fluid intake into the GIT and how much water do we get from each?

A 
Ingest = 2L
Saliva = 1.5L
Gastric Secretions = 2L
Pancreatic Juice = 1.5L
Bile = 0.5L
Intestinal secretion = 1.5L
TOTAL = 9L IN
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93
Q

What are the 3 routes of fluid loss from the GIT and how much water is lost at each?

A

Small intestine absorbs 7.5L
Colon absorbs <1.5L
Excreted <200ml

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94
Q

What is the most abundant substance in chyme?

A

Water

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95
Q

Which part of the small intestine absorbs the most water?

A

Jejunum

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96
Q

Why doesn’t the stomach absorb water?

A

Doesn’t have a large enough surface area and lacks solute absorbing mechanisms to create the osmotic gradient for absorbing water

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97
Q

What is the most abundant solute in chyme?

A

Na+

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98
Q

In which parts of the small intestine is Na+ actively transported?

A

Ileum and jejunum

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99
Q

Describe and draw a diagram for the process of Na+ reabsorption in the small intestine

A

Occurs by a TRANSCELLULAR ROUTE

  1. Glucose and 2Na+ are absorbed from the intestinal lumen into epithelial cell by the Na+/glucose symporter
  2. Glucose passes into the blood across the basolateral membrane of epithelial cell by GLUT2
  3. Na+ crosses into blood via Na+/K+ ATPase
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100
Q

Describe and draw a diagram for the process of Na+ reabsorption in the small intestine

A

Occurs by a TRANSCELLULAR ROUTE

  1. Glucose and 2Na+ are absorbed from the intestinal lumen into epithelial cell by the Na+/glucose symporter (SGLT1)
  2. Glucose passes into the blood across the basolateral membrane of epithelial cell by GLUT2
  3. Na+ crosses into blood via Na+/K+ ATPase
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101
Q

Describe and draw a diagram for the process of intestinal excretion

A

K+/Na+/2Cl- cotransporter moves Cl- into epithelial cells which increases cAMP which increases the secretion of Cl- into the intestinal lumen. Increasing Ca2+ levels in the cell as a result of IP3 action also increases Cl- secretion. Water follows down an osmotic gradient via a paracellular route

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102
Q

Describe the absorption of Na+/K+ and Cl- in the colon

A

Colon Is iso-osmotic with the blood so Na+ actively absorbed from lumen and water follows
K+ absorbed by passive diffusion due to concentration gradient
Cl- reabsorbed in exchange for bicarbonate causing intestinal contents to become more alkaline

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103
Q

How does the cholera toxin increase intestinal secretion?

A

Binds to intestinal cells and stimulates adenylate cyclase to produce more cAMP which causes a dramatic efflux of CL- ions which is followed by water resulting in a watery diarrhoea

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104
Q

Name the 2 functional states the body undergoes for providing the energy for cellular activities

A

Absorptive

Post absorptive

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105
Q

Define the absorptive state

A

ingested nutrients enter the blood from the GIT. Some ingested provided energy and some are added to the bodies energy store

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106
Q

Define the post-absorptive state

A

GIT is empty and bodies own stores supply the energy

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107
Q

What are the three main fatty acids we absorb?

A

Palmitic, stearic and oleic

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108
Q

Describe the structure of a triglyceride

A

A glycerol molecule with three fatty acid molecules attache d

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109
Q

Where does triglyceride digestion predominantly occur?

A

mainly in the small intestine but small amount in the mouth and the stomach

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110
Q

Describe the action of lipase on fats

A

Lipase cleaves the 1 and 3 carbon bonds producing a monoglyceride and two fatty acids

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111
Q

Describe the process of fat emulsification

A
  1. Lipids are water insoluble so aggregate into larger droplets in the upper stomach
  2. These are converted into smaller droplets in a 2 stage emulsification process
  3. Mechanical disruption occurs due to the motility of the GIT in lower stomach and intestine causing mixing
  4. Emulsification by two emulsification agents, phospholipids from food and bile salts made from cholesterol in the liver
112
Q

How to phospholipids and bile salts emulsify fat?

A 
Phospholipids are amphiphatic  molecules containing two non polar fatty acids, glycerol and a phosphate group
Bile salts (cholic) from liver are also amphiphatic 
Non polar (hydrophobic) portion of phospholipids and bile salts aggregates with the non polar interior portion of lipid droplet leaving the outer polar portion exposed which prevents the reaggregation of smaller droplets into larger ones 
Outer, hydrophilic regions help to draw the fat droplet into the intestinal chyme to allow pancreatic lipase to act
113
Q

The emulsification process impairs the action of lipase, how is this overcome?

A

Pancreas produces co-lipase that holds pancreatic lipase in place on the lipid droplets allowing breakdown to occur into FFA and monoglycerides

114
Q

What is the average daily intake of lipid

A

70-100g

115
Q

Other than emulsification, what also happens in the absorption of fat?

A

Micelles form which contain bile salts, fatty acids, phospholipids and fat soluble vitamins (A, D, E, K). Micelles are in equilibrium with free products of fat digestion this micelles are constantly breaking down and reforming.. When a micelle breaks down its contents become available to diffuse across intestinal lining. As the concentration of free lipids fall, because of diffusion, micelles break down to release more lipid

116
Q

Describe the process of fat absorption at the small intestine

A
  1. Micelles break down into fatty acids and monoglycerides which are absorbed into epithelial cells
  2. These are reformed into triglycerides in the smooth endoplasmic reticulum
  3. This decreases the cytosolic concentration of fatty acids and monoglycerides creating a concentration gradient for their entry into epithelial cells
  4. Small fat droplets reform in the rough ER and are carried in vesicles to the Golgi apparatus where they are converted to chylomicrons which are released by exocytosis
  5. Chylomicrons contain triglycerides, cholesterol, and fat soluble vitamins
  6. Chylomicrons are absorbed into the lacteals and are carried into the lymphatic system before draining into the thoracic duct
  7. Lipoprotein lipase breaks off triglycerides into FFA and monoglycerides which enter the adipose and skeletal muscle
  8. Remaining chylomicron goes to the liver to make VLDL
117
Q

How are the fat soluble vitamins A, D, E and K absorbed?

A

Are absorbed in the ileum and following the same pathway as fat - are carried in micelles

118
Q

How are the water soluble vitamins except vitamin B12 absorbed?

A

Diffusion or mediated transport in the jejunum

119
Q

How is water soluble vitamin B12 absorbed?

A

Large charged vitamin so must bind to intrinsic factor first which is secreted by parietal cells.
When bound to intrinsic factor vitamin B12 binds to specific sites In the lower ileum by endocytosis

120
Q

Why is vitamin B12 required and what does an absence of intrinsic factor lead to?

A

Erythrocyte formation

Pernicious anaemia

121
Q

How much protein do we Ingest each day?

A

40-50g

122
Q

Why do we need to eat protein?

A

To supply the 8 essential amino acids and to provide nitrogen amino acids used in the urea cycle

123
Q

Describe the digestion of protein

A

Starts in stomach where pepsinogen from chief cells is converted to pepsin by low pH which cleaves the bond between aromatic amines and second amino acid forming peptide fragments
Digestion also occurs in small intestine by pancreatic enzymes trypsin and chemotrypsin (Endopeptidases)
Fragments are further digested to free AA by carboxypeptidases from the pancreas and amino peptidases on the luminal membrane of intestinal epithelial cells. These enzymes split off amino acids from the carboxy and amino ends respectively

124
Q

What are the two types of pepsinogen and where are they found>

A

Pepsinogen I found in HCl secreting region (body)

Pepsinogen II found in pyloric region

125
Q

What is the optimum pH for pepsin action =?

A

1.6-3.2 so action is terminated on exit from the stomach ie. in the duodenum when pH is 6.5

126
Q

Describe the absorption of proteins

A
  1. Free AA enter the epithelial cells y secondary active transport coupled to sodium
  2. there are multiple transporters with different specialties for 20 types of AA
  3. Short chains of two or three AA are absorbed by secondary active transport
  4. These di/tri peptides are hydrolysed to AA which enter the blood stream via facilitated diffusion carrier in basolateral membrane
127
Q

What is the daily intake of carbohydrate

A

250-300g

128
Q

Give 3 examples of monosaccharides

A

Glucose, fructose and galactose

129
Q

Give 3 examples of disaccharides

A

Sucrose and lactose and maltose

130
Q

Give 2 examples of polysaccharides

A

Starch and glycogen

131
Q

Describe the structure of glycogen

A

Glucose polymer containing alpha 1-4 glycosidic bonds and branching alpha 1-6 glycosidic bonds

132
Q

Describe the structure of starch, how is it different from glycogen?

A

Starch has alpha 1-4 glycosidic bonds and some alpha 1-6 branching chains but less than the amount found in glycogen

133
Q

Describe process of starch digestion in the oral cavity

A

Ptyalin, the salivary alpha amylase has optimal pH of 6.7 and accounts for small amount of starch digestion. Action is terminated by gastric acidity

134
Q

Describe the process of starch digestion in the small intestine

A

Accounts for 95% of starch digestion via pancreatic alpha amylase that catalyses alpha 1-4 linkages. Products of both amylases are disaccharides (maltose, sucrose and lactose) which are broken down into monosaccharides glucose, fructose and galactose by enzymes on the brush border of intestinal epithelial cells (Maltase, sucrase and lactase)

135
Q

Describe the process of monosaccharide absorption at the brush border of the small intestine

A

Hexose and pentose sugars are rapidly absorbed across the intestinal mucosa
Glucose and Na+ use the same transporter (SGLT1) thus a high conc of Na+ at mucosal surface promotes glucose uptake (Gradient in enterocytes generated by Na+/K+ ATPase on basolateral membrane
Fructose uptake is independent of Na+ and occurs by facilitated diffusion through GLUT5
From there, monosaccharides diffuse into the blood through capillary pores and GLUT2 transporters and are carried to the liver

136
Q

What digestive enzymes do salivary glands secrete

A

Amylase –> Starch

Lipase –> triglycerides

137
Q

What digestive enzymes do stomach secrete

A

Pepsin –> protein

Lipase –> Triglycerides

138
Q

What digestive enzyme does the pancreas secrete

A 
Amylase --> Starch 
Lipase and collapse --> Triglycerides 
Phospholipase --> Phospholipids
Trypsin --> Peptides 
Chmyotrypsin --> Peptides
139
Q

What digestive enzymes do the intestines secrete

A

Enterokinase - activates trypsin

Peptidases - peptides

140
Q

What are the 6 muscles/groups of muscles used in swallowing?

A
  1. Buccinator.
  2. Suprahyoids.
  3. Muscles of the palate.
  4. Muscles of the floor of the mouth.
  5. Infrahyoids.
  6. Pharyngeal constrictor muscles
141
Q

What are the 4 layers of the GIT wall from innermost to outermost

A

mucosa
submucosa
Musculares externa
Serosa

142
Q

What are the two divisions of the mucosa

A

Lamina propria

Muscularis mucosa

143
Q

What does the muscularis external contain

A

Circular muscle
Longitudinal muscle
Myenteric plexus

144
Q

What does the muscularis external contain

A

Circular muscle
Longitudinal muscle
Myenteric plexus

145
Q

What happens to amino acids i

A

Most enter cells and are used to make protein
Some enter the liver and are de-aminated to form keto-acids - removed amino groups are used to synthesise urea which enters the blood
Ketoacids enter Krebs and provide energy for liver cells

146
Q

What happens to amino acids in the liver?

A

Some are converted to ammonia then into urea
Some converted to FA
Some converted to CO2, Water and energy

147
Q

What happens to glucose that reaches the adipose tissue>

A

converted to alpha glycerol phosphate and fatty acids which then combine into triglycerides

148
Q

What happens to glucose in the brain

A

Converted to Acetyl Coa and goes through Krebs to form ATP

No storage

149
Q

What happens to glucose in the brain

A

Converted to Acetyl Coa and goes through Krebs to form ATP

No storage

150
Q

What is glycogenolysis?

A

Breakdown of glycogen into glucose-6-phosphate monomers occurring in liver an skeletal muscle via the action of glucagon

151
Q

What is glycogenolysis?

A

Breakdown of glycogen into glucose via the action of glucagon

152
Q

How is glucose produced following a short fast?

A

Glycogenolysis

153
Q

What is gluconeogenesis

A

Production of glucose from non glycogen sources
ie. AA from muscles
Lactate from RBCs
Glycerol from adipocytes

154
Q

what happens to triglycerides produced from glucose in the liver?

A

Some are stored but most triglycerides are packaged into aggregates with lipids and proteins into lipoproteins (VLDL) and enter the blood

155
Q

Describe the function and location of lipoprotein lipase

A

Found on the blood facing surface of capillary endothelial cells, especially in adipose cells which breaks down VLDL into monoglycerides and fatty acids

156
Q

Describe the function and location of lipoprotein lipase

A

Found on the blood facing surface of capillary endothelial cells, especially in adipose cells which breaks down VLDL into monoglycerides and fatty acids

157
Q

What sort of hormone is a insulin and how does it work

A

Peptide hormone that binds to specific receptors on the plasma membrane of target cells triggering transduction pathways that influence plasma membrane transport proteins

158
Q

What sort of hormone is a insulin and how does it work

A

Peptide hormone that binds to specific receptors on the plasma membrane of target cells triggering transduction pathways that influence plasma membrane transport proteins

159
Q

What are the effects of increased plasma insulin on muscle?

A

Increased glucose uptake and utilisation
Net glycogen synthesis
Net AA uptake
Net protein synthesis

160
Q

What are the effects of increased plasma insulin on adipocytes?

A

Increased glucose uptake and utilisation

net triglyceride synthesis

161
Q

What are the effects of increased plasma insulin on the liver?

A

Increased glucose uptake
Net glycogen synthesis
Net triglyceride synthesis
No ketone synthesis

162
Q

What are the effects of decreased plasma insulin on muscle

A 
decreased glucose uptake and utilisation 
Net glycogen catabolism 
net protein catabolism 
net AA release 
FA uptake and utilisation
163
Q

What are the effects of decreased plasma insulin on liver?

A

Increased glucose release due to glycogen catabolism and gluconeogenesis
Increased ketone synthesis

164
Q

What are the effects of decreased plasma insulin on liver?

A

Increased glucose release due to glycogen catabolism and gluconeogenesis
Increased ketone synthesis

165
Q

What are the effects of cortisol on fuel metabolism and where is it produced?

A 
Produced in the adrenal glands and prepares for stress response 
Lipolysis 
Protein breakdown 
Gluconeogenesis 
Glycogen storage
166
Q

What disease does long term increase in cortisol cause?

A

Cushings disease

167
Q

What are the effects of adrenaline on fuel metabolism

A

Causes flight or fight
Glycogenolysis
Gluconeogenesis
Lipolysis

168
Q

Effects of thyroxine on fuel metabolism

A 
Glycolysis 
Cholsterol synthesis 
Glucose uptake 
Protein synthesis 
Sensitises tissue to adrenaline
169
Q

What are the effects of growth hormone on fuel metabolism

A

Gluconeogenesis
Glycogen synthesis
Lipolysis
Protein synthesis

170
Q

What are the effects of grehlin

A

Stimulates appetite

171
Q

What are the effects of grehlin

A

Stimulates appetite

172
Q

What are the functions of the liver?

A 
Carbohydrate metabolism 
Fat metabolism 
Protein metabolism 
Hormone metabolism 
Toxin/drug metabolism 
Storage 
Bilirubin and excretion
173
Q

What protein is responsible for iron storage

A

Ferritin

174
Q

What are the functions of vitamins

A

Gene activators
Free-radical scavengers
Co-enzymes/co-cofactors in metabolic reactions

175
Q

Which vitamins are water soluble

A

B and C

176
Q

Which vitamins are fat soluble

A

A, D, E and K

177
Q

Where is vitamin A stored

A

Ito cells and spaces of Disse in the liver

178
Q

What are the functions of vitamin A (Retinoids)

A 
Vision
cellular growth and differentiation 
Reproduction 
Lymphocyte production
Embryological development 
Stabilisation of cellular membranes
179
Q

What are the sources of vitamin A?

A

Retinols come from liver, oily fish, dairy and margarine

Carotenoids come from carrots, spinach, sweet potato and tomatoes

180
Q

What is the function of vitamin B?

A

Important in cell metabolism & energy production

181
Q

What is the function of vitamin B?

A

Important in cell metabolism & energy production

182
Q

What are the sources of vitamin B?

A

Main one is B-12: found in fish, poultry, meat & eggs

183
Q

What disease results from a deficiency of vitamin B

A

pernicious anaemia - reduced production of RBC

184
Q

What are the functions of vitamin D?

A

Increased intestinal absorption of calcium
Resorption and formation of bone
Reduced renal excretion of calcium

185
Q

What are the sources of vitamin D?

A

Vitamin D3 is formed by UV light

Vitamin D2 comes from plants

186
Q

What are the sources of vitamin D?

A

Vitamin D3 is formed by UV light

Vitamin D2 comes from plants

187
Q

What is the main function of vitamin E?

A

Anti-oxidant

188
Q

What are the main sources of vitamin E?

A

Oils
Carrots
Spinach
Avacado

189
Q

What does a deficiency in vitamin E cause?

A

Fat malabsorption
premature infants
Abetalipoproteinaemia

190
Q

What does a deficiency in vitamin E cause?

A

Fat malabsorption
premature infants
Abetalipoproteinaemia

191
Q

What are the functions of vitamin K?

A

Responsible for the activation of some blood clotting factors
necessary for liver synthesis of plasma clotting factors II, VII, IX and X

192
Q

What are the four sources of vitamin K

A

VK1 = Phylloquinone (Synthesised in plants and food)
VK2 = Menaquinone (Synthesised in intestinal bacteria)
Synthetic vitamin K’s
K3 (Menadione)
K4 (Menadiol)

193
Q

What does a deficiency in vitamin K result in?

A

Haemorrhagic disease of the newborn

194
Q

What are the sources of vitamin C

A

Fresh fruit and vegetables

195
Q

What are the functions of vitamin C

A

Collagen synthesis
Antioxidant
Iron absorption

196
Q

What does a deficiency in vitamin C causes ?

A

Easy bruising and bleeding
Teeth and gum disease
Hair loss

197
Q

Where is folate found?

A

Foods high in folic acid

198
Q

What does a deficiency in folate cause?

A

Macrolytic anaemia
High homocysteine levels
Foetal development abnormalities

199
Q

What does a deficiency in folate cause?

A

Macrolytic anaemia
High homocysteine levels
Foetal development abnormalities

200
Q

Describe the length of the foregut?

A

Runs from the mouth to the common bile duct

201
Q

Describe the length of the midgut?

A

Runs from the common bile duct to 2/3 transverse colon

202
Q

Describe the length of the hindgut

A

Runs from the 2/3 transverse Colon to the anal canal

203
Q

What is the blood supply of the foregut?

A

coeliac artery

204
Q

what is the blood supply of the midgut?

A

superior mesenteric artery

205
Q

What is the blood supply of the hindgut?

A

Inferior mesenteric artery

206
Q

What are the components of the foregut?

A

pharynx, oesophagus, stomach, proximal half of duodenum

207
Q

What are the components of the midgut?

A 
Distal half of the duodenum
jejunum
Ileum
Caecum
Appendix
Ascending colon
right 2/3 of transverse colon
208
Q

What are the components of the hindgut?

A 
Left 1/3 of the transverse Colon
Descending colon 
sigmoid colon
rectum 
Anal canal
209
Q

At what point does embryonic folding begin?

A

4th week

210
Q

In what two planes does embryological folding occur?

A

Horizontal

Medial

211
Q

What does embryological folding in the horizontal plane form

A

two lateral body folds

212
Q

What does embryological folding in the medial plane form

A

A cranial and caudal fold

213
Q

How is the primitive gut tube formed?

A

Endoderm folds towards the midline and fuses incoporating the yolk sac to form a tube

214
Q

How is the primitive gut tube formed?

A

Endoderm folds towards the midline and fuses incoporating the yolk sac to form a tube

215
Q

What is the primitive gut tube derived from

A

Endoderm and visceral mesoderm

216
Q

What does the endoderm give rise to in the gut?

A

Epithelial lining of GIT
Hepatocytes
Endo/Exocrine cells of pancreas

217
Q

What does the visceral mesoderm give rise to in the gut?

A

Muscle, connective tissue and peritoneal components of the gut wall
Gland connective tissue

218
Q

How and when does the mouth form?

A

Foregut at cranial end closed by oropharyngeal membrane which ruptures at 4th week to form mouth

219
Q

How and when does the anus form?

A

Hindgut lies at the caudal end and is closed by the cloacal membrane which ruptures at 7th week forming anus

220
Q

What is the nerve supply of the foregut?

A

Greater splanchnic nerve T5-T9

221
Q

What is the nerve supply of the hindgut?

A

Least splanchnic nerve T12-L1

222
Q

What is the nerve supply of the hindgut?

A

Least splanchnic nerve T12-L1

223
Q

How is the primary intestinal loop connected to the yolk sac?

A

By the vitelline loop

224
Q

What does the cephalic portion of the primary intestinal loop form?

A

distal duodenum
Ileum
Jejunum

225
Q

What odes the caudal portion of the primary intestinal loop form?

A 
Lower Ileum
Caecum
Appendix 
Ascending Colon
Proximal 2/3 transverse colon
226
Q

Name the 5 stages of midgut formation

A

1 and 2 = Elongation and herniation

  1. Rotation
  2. Retraction of herniated loops
  3. Fixation
227
Q

What happens in stage 1 and 2 of midgut formation

A

Elongation and herniation
Elongation of cephalic limb of primary intestinal loop
Intestine herniates into extra embryonic cavity due to expansion of liver making the abdominal cavity too small

228
Q

What happens in stage 4 of midgut formation?

A

Retraction of herniated loops occurs in 10th week due to regression of mesonephric kidney, reduced liver growth and expansion of abdominal cavity
Proximal jejunum returns first
Caecal bud returns last and lies in upper right quadrant before descending into right iliac fossa placing ascending colon and hepatic flexure

229
Q

What happens in stage 4 of midgut formation?

A

Retraction of herniated loops occurs in 10th week due to regression of mesonephric kidney, reduced liver growth and expansion of abdominal cavity
Proximal jejunum returns first
Caecal bud returns last and lies in upper right quadrant before descending into right iliac fossa placing ascending colon and hepatic flexure

230
Q

What happens during stage 5 of midgut formation?

A

Fixation
Ascending and descending colon reach definitive positions and their mesenteries press against peritoneum and fuse so become anchored retroperitoneally
Appendix, lower caecum and sigmoid colon retain their free mesenteries and flexibility
Transverse colon fuses with posterior wall greater omentum and maintains flexibility

231
Q

What component of the abdominal cavity are mobile?

A 
Stomach
Jejunum
Ileum
Appendix 
Transverse colon 
Sigmoid colon
232
Q

What component of the abdominal cavity are mobile?

A 
Stomach
Jejunum
Ileum
Appendix 
Transverse colon 
Sigmoid colon
233
Q

What are the three main substrates for gluconeogenesis?

A

Lactic acid
AA
Glycerol

234
Q

What does the dorsal mesogastrium become?

A

Greater omentum

235
Q

What does the dorsal mesogastrium become?

A

Greater omentum

236
Q

Describe the composition of the primary secretion

A

Amount of Na+ and Cl- is equal to water so is Isotonic compared to blood plasma

237
Q

Describe the composition of the secondary secretion

A

Na+ and Cl- have been removed so are less than water content so is HYPOTONIC compared to blood plasma

238
Q

How does the submandibular gland enter the oral cavity?

A

Through the submandibular duct (Wharton’s Duct) which attaches to the lingual frenulum

239
Q

Which cranial nerve supplies the parotid gland innervation

A

Glossopharyngeal

240
Q

Which cranial nerve supplies the submandibular and sublingual innervation

A

Facial

241
Q

Which salivary glands does the superior salivary centre innervate?

A

Submandibular and sublingual

242
Q

Which salivary gland does the inferior salivary centre innervate

A

Parotid

243
Q

Describe the course of the nerve supply of the parotid gland

A

Inferior salivary centre to glossopharyngeal to jugular foramen to middle ear cavity to lesser petrosal nerve to lesser petrosal foramen to otic ganglion to the parotid

244
Q

Describe the course of the nerve supply of the parotid gland

A

Inferior salivary centre to glossopharyngeal to jugular foramen to middle ear cavity to lesser petrosal nerve to lesser petrosal formamen to otic ganglion to the parotid

245
Q

What is the anterior border of the oral cavity?

A

Oral vestibule (Gap between the teeth and lips

246
Q

What is the posterior border of the oral cavity?

A

Palatoglossal arch

247
Q

Which 4 muscles depress the mandible?

A

Lateral pteygoid
Digastric anterior belly
Mylohyoid
Geniohyoid

248
Q

What is the innervation of lateral pytergoid muscle

A

Mandibular division of trigeminal nerve

249
Q

What is the innervation of the digastric anterior belly

A

Mandibular division of trigeminal nerve

250
Q

What is the innervation of myelohyoid

A

Mandibular division of trigeminal nerve

251
Q

What is the innervation of geniohyoid

A

Cervical Plexus (Mainly C1)

252
Q

What are the three mandibular elevators and what is their innervation?

A

Masseter
Temporalis
Medial Pterygoid
All innervated by mandibular division of trigeminal nerve

253
Q

What is the role of the intrinsic muscles of the tongue in the oral phase of swallowing

A

Creates central trough on tongue for bolus to slide down

254
Q

What is the role of the extrinsic muscles of the tongue in the oral phase of swallowing

A

Elevate the tongue so the tip touches the hard palate

255
Q

What cranial nerve innervates the intrinsic and extrinsic muscles of the tongue

A

Hypoglossal nerve

256
Q

What are the two arches of the oral cavity and which is more anterior? what is the space between the arches called?

A

Palatopharyngeus
Palatohypoglossus
Space between is tonsilar fossa
Palatoglossal is more anterior

257
Q

Which cranial nerve stimulates the uvula to contract and close off the nasopharynx during swallowing?

A

Vagus nerve

258
Q

What are the two muscles that elevate the soft palate

A

Levator veli palatini

Tensor veli palatini

259
Q

What is the innnervation of Levator veli palatini?

A

Vagus nerve

260
Q

What 3 processes occur to stop the food bolus entering the larynx?

A

The true vocal cords adduct the glottis
Epiglottis retroverts to cover larynx
Suprahyoids contract to elevate the larynx and pull it anteriorly

261
Q

What muscles contract to help the bolus enter the pharynx?

A

Palatoglossus

Palatopharyngeus

262
Q

Which muscles contract to elevate the pharynx and the larynx

A

Outer longitudinal muscles including stylopharyngeus, salpingopharyngeus and palatopharyngeus

263
Q

Which nerve innervates stylopharyngeus

A

Glossopharyngeal

264
Q

Which nerve innervates salpingopharyngeus and palatopharyngeus

A

Vagus

265
Q

Which muscles enable pharyngeal peristalsis to occur?

A

Superior, middle and inferior pharyngeal constrictors (Inner circular muscles)

266
Q

Which muscle makes up the upper oesophageal sphincter?

A

Cricopharyngeus which is part of the inferior pharyngeal constrictor

267
Q

What are the two major carbohydrates in food and describe their structure

A

Amylopectin (Branched) contains alpha 1,4 and alpha 1,6 glycosidic bonds
Amylose (Linear) only contains alpha 1,4

268
Q

What bonds does salivary and pancreatic alpha amylase break

A

Alpha 1,4 glycosidic bonds

269
Q

What does alpha amylase break amylopectin and amylose into?

A

Maltose, Maltriose, alpha limit dextrin, lactose, sucrose

270
Q

What are the 4 brush border enzymes in carbohydrate digestion?

A

Lactase, maltase, sucrase, isomaltase (Breaks down alpha limit dextrin

271
Q

What are the three types of lipase that act in fat digestion?

A

Lingual lipase
Gastric lipase (From chief cells)
Pancreatic lipase

272
Q

What does bile contain that is important in the emulsification of fats

A 
Bile salts (Cholic, chendooxycholic acid 
Phospholipids (Lecithin)
273
Q

What enzymes does the pancreas release to aid fat digestion

A

pancreatic lipase
Phospholipase A2
Cholesterol ester hydrolase

274
Q

What does cholic acid react with to form a bile salt?

A

Taurine

275
Q

What does chendeoxycholic acid react with to form a bile salt

A

Glycine

Phase 1 M (11 decks)

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