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Introduction to Healthcare Science > GI tract > Flashcards

GI tract Flashcards

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1
Q

What does the alimentary canal include?

A
  • oesophagus.
  • stomach.
  • small intestine.
  • large intestine.
  • rectum.
  • anus.
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2
Q

What are the auxiliary structures?

A
  • endocrine glands.
  • gut-associated lymphoid tissue (GALT).
  • enteric nervous system (ENS).
  • enteroendocrine cells (EEC).
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3
Q

Name the endocrine glands?

A
  • liver.
  • biliary system.
  • pancreas.
  • salivary glands.
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4
Q

What does GALT (Gut-associated lymphoid tissue) include?

A
  • follicles.
  • tonsils.
  • peyer’s patches.
  • appendix.
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5
Q

Why is the oral cavity important?

A
  • It prepares bolus for swallowing.
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6
Q

What is bolus?

A
  • a mass of food that has been chewed at the point of swallowing.
  • It then travels down the esophagus and to the stomach for digestion.
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7
Q

What is involved in bolus preparation?

A
  • biting (teeth).
  • chewing (teeth with tongue and cheeks).
  • lubrication (salivary glands).
  • taste (taste buds).
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8
Q

Are chewing and saliva needed for digestion?

A
  • No.
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9
Q

What is the purpose of the tongue?

A
  • Acts as a pestle.
  • Bolus preparation (chewing).
  • pushes the bolus back (swallowing).
  • Primary organ of taste.
  • Part of lymphatic ring.
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10
Q

What are papillae?

A
  • Small structures on the upper surface of tongue to give rough texture.
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11
Q

What are the different kinds of papillae?

A
  • circumvallate (sensory).
  • foliate (sensory).
  • fungiform (thermoregulatory and sensory): smallest.
  • filiform (mechanical): biggest.
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12
Q

What are the five basic tastes?

A
  • sweet (detection to help find energy-dense nutrients same for savoury).
  • bitter (warning against toxic food).
  • savoury.
  • sour (stops eating food that’s off).
  • salty (controls level of sodium and other ions).
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13
Q

What is interesting about the taste buds and taste receptors?

A
  • taste buds are not only found on the tongue.

- taste receptors are found not only in taste buds.

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14
Q

What is saliva?

A
  • 99.5% water and 0.5% additions.
  • additions = Electrolytes, mucus, glycoproteins, enzymes (amylase and lipase), antimicrobial compounds (secretory IgA, lysozyme and peroxidase).
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15
Q

What are the functions of saliva?

A
  • Defence against bacteria.
  • Digestive function as lubricative for mastication and swallowing and for taste perception.
  • maintanence of the ecological balance in oral cavity: wound healing, reduce microbial adherence, direct antibacterial activity, ensuring tooth integrity with salivary enzymes that break down adhered food.
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16
Q

Where are the salivary glands found?

A
  • small salivary glands: all over under the epithelial lining.
  • large salivary glands: sublingual, submandibular, parotid.
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17
Q

Describe swallowing.

A
  • Complex series of synchronised steps, involving mouth, pharynx, larynx and oesophagus.
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18
Q

What are the three phases of swallowing?

A
  • oral phase, voluntary, prepares the bolus.
  • pharyngeal phase, involuntary, shortest less than 1 sec. But most complex phase. Breathing has to stop during this phase. Involves various neuronal and musculoskeletal structures. Once bolus in pharynx all exits closed. Pharyngeal constrictor muscles contract and build up pressure.
  • oesophageal phase, involuntary, upper oesophageal sphincter muscle relaxes once pressure built up. Bolus shoots into the oesophagus and is moved down by the peristaltic wave.
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19
Q

What happens if food goes to the trachea?

A
  • this leads to inflammation and infection.
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20
Q

What is the purpose of the stomach?

A
  • Stores food and uses storage time to churn down food to paste for digestion.
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21
Q

What are the regions of the gastrointestinal tract and their functions?

A
  • oesophagus : simple passage (squamous epithelium).
  • stomach : storage fragmentation acidification (glandular epithelium).
  • intestine : digestion (glandular epithelium).
  • anal canal : simple passage (squamous epithelium).
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22
Q

What does the alimentary system include?

A
  • oral cavity pharynx.
  • alimentary canal.
  • auxiliary structures.
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23
Q

What does the alimentary canal consist of (structure) and how are the layers separated?

A
  • an inner pipe = mucosa (digestion).
  • separated by a middle layer = submucosa (major service layer).
  • an outer pipe = muscularis (peristalsis moving food through GIT).
  • outermost layer = either adventitia or serosa (blends into the surrounding tissue/provides a clear boundary).

think cylindrical

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24
Q

When it comes to tumour staging what is the difference between solid organs and layered organs?

A
  • solid organs (breast, kidney, lung, liver) tumour staging depends on size of tumour.
  • layered organs (intestine, gall bladder, urinary bladder) tumour staging depends on the layers involved.
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25
Q

Main functions of the stomach?

A
  • ingestion takes minutes while digestion takes hours.
  • stores food until intestine ready for it.
  • grinds food down.
  • release broken down food (chyme) into intestine.
  • produces acid (denature proteins and kill microorganisms).
  • produces intrinsic factor for absorption of vitamin b12 (cobalamin).
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26
Q

What are four regions of stomach? And where is acid produced?

A
  • Fundus, corpus, cardia, pylorus.
  • 20% pop produce acid in cardia and pylorus.
  • 80% pop produce acid in fundus and corpus.
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27
Q

What are the stomachs two principal types of mucosa?

A
  • mainly muscus producing = non-oxyntic mucosa, cardia and pylorus.
  • acid and pepsinogen producing = oxyntic mucosa, corpus and fundus.
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28
Q

What is the gastric mucosa like?

A
  • Surface covered by thick mucus.
  • high glandular mucosa forming “gastric glands”.
  • strong three layered muscularis propria.
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29
Q

What are the gastric epithelial cell types?

A
  • mucous cells (45%) = alkaline mucus and bicarbonate.
  • chief/zymogenic cells (30%) = pepsinogen.
  • parietal/oxyntic cells (15%) = intrinsic factor and h+ ions for hydrochloric acid.
  • enteroendocrine cells (EEC) = secrete various gut hormones.
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30
Q

What is the role of the gastric mucosal barrier?

A
  • Protects the stomach against autodigestion and erosion by acids.
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31
Q

Why do gastric ulcers arise?

A
  • Develop almost exclusively down to infection with h.pylori and NSAIDs (e.g. Aspirin, ibuprofen).
  • We develop acid not because of too much acid but too less mucus.
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32
Q

What does the small intestine consist of?

A
  • duodenum.
  • jejunum.
  • ileum.
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33
Q

What does the large intestine consist of?

A
  • ascending, transverse and descending colon.
  • caecum appendix.
  • sigmoid.
34
Q

What is the role of the small and large intestine in digestion?

A
  • small: chyme from the stomach is turned into watery solution, mixed with digestive enzymes and buffering bicarbonate from pancreas and emulsifying bile from liver, nutrients absorbed and taken in blood to liver or in lymphatic fluid to systemic blood.
  • large: remaining bolus fermented by gut bacteria, produces vitK (comes from gut), turned into faeces by removing water.
35
Q

What are the surface foldings of the intestine and where do they take place?

A
  • microvilli (enterocyte) - most folded so give biggest surface area.
  • kerckrings folds (submucosa) - least folded up.
  • villi and crypts (lamina propria).
36
Q

What is the relevance of mucosal foldings in chronic inflammatory disease? (E.g. Coeliac disease)

A
  • There is a loss of mucosal foldings in chronic inflammatory disease.
  • the flattening of the mucosa significantly reduces the absorption of nutrients.
37
Q

What are the main interstitial epithelial cell types?

A
  • Enterocytes (columnar cells): secrete fluid and absorb nutrients.
  • enteroendocrine cells: secrete various hormones.
  • goblet cells: secrete alkaline mucus.
  • paneth cells: secrete antimicrobial peptides.
38
Q

How are inflammatory bowel diseases brought about?

A
  • Changes at the level of tight junctions are related to inflammatory bowel disease (crohns disease, ulcerative colitis).
39
Q

How is your digestive system regulated?

A
  • Precise timing of:
  • secretion.
  • absorption.
  • motility.
40
Q

What is extrinsic and intrinsic control of the digestive system?

A
  • Extrinsic control: input from outside the GIT.
  • Intrinsic control: self regulation inside the GIT.
  • (This is done via hormones and nerves).
41
Q

What is the trigger for the stomach to produce acid and pepsin?

A
  • When it gets full.
42
Q

How are enterocytes linked?

A
  • They are linked to each other through tight junctions.
43
Q

What is the difference between the enteric nervous system and the central nervous system?

A
  • ENS: estimated 0.5 billion neurones and > 40 neurotransmitters identified.
  • CNS: estimated 85 billion neurones >100 neurotransmitters identified.
44
Q

What are the two types of gut contractions that aid gut motility?

A
  • segmental contractions: random unorganised motor activity with peristaltic and antiperistaltic complexes, allows remixing of foods.
  • propulsive contractions: peristaltic waves allow progression of food through the intestines. The gastric pacemaker area at the junction between the body and Antrum of stomach produces electric slow waves (migrating myoelectric complexes MMC). Periodically a cluster of MMCs migrates distally.
45
Q

Name some intestinal motility disorders? (When food transmits through the digestive tract unusually).

A
  • intestinal pseudo-obstruction (ogilvie syndrome).
  • irritable bowel syndrome (ibs).
  • faecal incontinence.
  • constipation.
46
Q

What is Hirschsprung’s disease?

A
  • Congenital ananglionic megacolon, e.g. Of diseases caused by abnormalities in the enteric nervous system.
47
Q

What does absence of the enteric ganglion cells in the distal colon and rectum lead to?

A
  • it causes aganglionic bowel obstruction.

- it results in an enlargement of the proximal part of the colon.

48
Q

Describe mucosal immunity.

A
  • effector lymphocytes are scattered throughout the lamina propria and epithelium of the mucosa.
  • peyers patches (PP) and mesenteric lymph nodes (MLN) are involved in the induction of immunity and tolerance.
  • m cells transport particulate antigen across the epithelium to immune effector sites.
  • the adult gut mucosa contains about 80% of the body’s activated B cells.
49
Q

How are disorders of the alimentary system diagnosed?

A
  • medical history.
  • physical examination.
  • lab tests (faecal occult blood test, stool culture).
  • imaging tests (X-ray, CT scan, MRI scan, ultrasound).
  • endoscopic procedures (colonoscopy, sigmoidoscopy).
  • other procedures (capsule endoscopy, oesophageal ph monitoring).
50
Q

Which endoscopies are of the upper form and which are of the lower form?

A
  • Upper: oesophago-gastro-duodenoscopy.

- Lower: proctoscopy, sigmoidoscopy, colonoscopy.

51
Q

Describe the liver.

A
  • 0.5-1x10(6) lobules with diameter if 1-2 mm.
  • hepatocytes arranged in cords/strands converging towards central vein.
  • Between the lobules are connective tissue spaces = portal fields used as supply routes.
  • Venous blood leaves via the hepatic vein. Bile and lymphatics leave.
  • Arteriovenous blood goes into liver (25% via the hepatic artery and 75% via the portal vein).
52
Q

What is zonal liver injury?

A
  • Site of damage depends on whether the substance is directly toxic or after being metabolised.
  • zone 1: direct damage I.e. Ferrous sulfate, phosphorus, cocaine.
  • zone 3: indirect damage due to toxic metabolites I.e. Acetaminophen, halothane, methoxyflurane, most mushroom poisons.
53
Q

What is the most common cause of drug induced liver disease and acute liver failure worldwide?

A
  • Acetaminophen (paracetamol): liver damage is due to a toxic metabolite (NABQI) affecting zone 3.
54
Q

In which zone does “nutmeg liver” which is due to zonal liver damage usually occur?

A
  • Usually zone 3: centrilobar.
  • Less often zone 1: periportal.
  • Very rarely zone 2: intermediate.
55
Q

There are three zones of the liver, name them.

A
  • Zone 1 = periportal.
  • Zone 2 = intermediate.
  • Zone 3 = centrilobar.
56
Q

Name the liver cell populations.

A
  • 2/3 parenchymal (epithelial): 60% hepatocytes (in strands), 05% cholangiocytes (bile duct).
  • 1/3 non-parenchymal (non-epithelial): 25% endothelial cells (sinusoids), 10% others = these include kupffer cells which are intra-sinusoidal and lymphocytes and stellate cells which are peri-sinusoidal.
57
Q

What is the function of hepatic stellate cells?

A
  • Store 80% of the bodys retinol (VitA).
  • Produce the scaffold of the lobules (the mesh/scaffold is made up by the peri-sinusoidal cells as these allow plasma to pass through).
  • their conversion to myofibroblast like cells leads to liver fibrosis.
58
Q

What do we know about liver regeneration?

A
  • it can regenerate upto 70% depending on the Ito cells.
  • hepatocyte life span of 200-300 days, usually replaced by in situ division of other hepatocytes (liver stem cells in the cholangioles).
59
Q

What is the difference between liver regeneration and liver repair ?

A
  • if injury happens to only the cells and the ECM is still intact then proliferation of residual cells with an intact matrix will occur leading to regeneration (replication of existing cells).
  • if injury happens to both cells and matrix then the ECM scaffold is damaged you will get deposition of connective tissue, proliferation of residual cells within disrupted matrix leading to repair (scarring) (liver fibrosis).
60
Q

How can liver fibrosis come about and what happens to liver during this?

A
  • There is some fat in the liver (5% - 10% of fat = fatty liver, sign of liver disease (FLD is one of the leading causes of cirrhosis).
  • liver fibrosis (scarring) shrinks liver.
61
Q

What are the two types of fatty liver disease?

A
  • alcoholic fatty liver disease (AFLD) almost all drinkers develop this.
  • non alcoholic fatty liver disease (NAFLD) the cause of non alcoholic fatty liver disease is not clear but it is not the most common cause of chronic liver disease.
62
Q

What is the bile system of the liver?

A
  • looks like a tree, bile emulsifies fats. Bile acts as a surfactant. Bile salt anions aggregate around droplets of fat to form micelles.
  • bile 2 roles: in the liver - transporting fat soluble waste into the intestine for excretion = detoxification. In the intestine - aids digestion by emulsifying the fats in the food.
  • bile transports toxins which are not water soluble into gut/intestine.
63
Q

How does the liver secret bile and how much?

A
  • About 1 litre of bile a day.
  • Stored in gall bladder, concentrated to about 50ml.
  • Discharged into the duodenum when required.
  • 95% reabsorbed in ileum and transported back to liver via portal vein = enterohepatic circulation.
64
Q

What are the functions of the gall bladder?

A
  • storage of the continuously secreted bile.
  • 20x concentration of the stored bile (1000 to 50ml); risks stone formation.
  • secretion when needed. Presence of fatty chyme in the duodenum triggers secretion of CCK.
  • In response to CCK, the gallbladder releases its contents into the duodenum.
65
Q

What is pancreatitis?

A
  • Self digestion of pancreas.
66
Q

What is bilirubin?

A
  • Is the yellow breakdown product of normal heme catabolism, caused by the bodies clearance of aged red blood cells which contain haemoglobin.
  • Bilirubin is excreted in bile and urine, elevated levels may indicate certain diseases.
  • Responsible for yellow colour of bruising and jaundice and brown colour of faeces.
67
Q

What imaging techniques are used for imaging of bile and pancreatic ducts?

A
  • X Ray.
  • Ultrasound.
  • MRI.
  • MRCP.
  • ERCP.
68
Q

What are the main liver functions?

A
  • processing nutrients from food (hepatocytes).
  • lipid metabolism (cholesterol) (hepatocytes).
  • sugar metabolism (hepatocytes).
  • protein synthesis (albumin,clotting factors) (hepatocytes).
  • storage (glycogen, iron, vit a) (hepatocytes and stellate cells).
  • processing of haemoglobin (hepatocytes).
  • detoxification (ammonia to urea) (hepatocytes).
  • secreting bile (hepatocytes).
  • immune defence (blood borne pathogens) (kupffer cells and lymphocytes).
  • flow of bile and blood (cholangiocytes and endothelial cells).
69
Q

How are toxins and waste removed?

A
  • All toxins and waste are excreted.

- Either into the bile and leave the body in the faeces or into the blood and are filtered out by the kidneys as urine.

70
Q

The pancreas is a mixed gland, what does this mean?

A
  • major part (98%) is an exocrine gland, secreting enzymes and chemicals into the intestine.
  • minor part (2%) is an endocrine gland, secreting hormones into the blood stream.
71
Q

What are the three classes of epithelial cell types that the pancreas contains?

A
  • ductal cells (exocrine cells).
  • acinar cells (exocrine cells).
  • islet cells (endocrine cells, organised in islets).
72
Q

How is exocrine pancreatic secretion regulated?

A
  • It is regulated by the gut hormones secretin and cholecystokinin, which are produced by the duodenum upon detection of chyme.
73
Q

What does the exocrine pancreas secrete?

A
  • an aqueous bicarbonate component from the duct cells. It neutralises gastric acid. Producing an optimum neutral-basic pH for effective enzymatic action. Triggered by secretin.
  • an enzymatic component from the acinar cells. Trypsinogen, chymotrypsinogen, elastase, lipase, carboxypeptidase and amylase. Triggered by CCK.
74
Q

What cells are present in the endocrine pancreas?

A
  • islets of langerhans (about 1x10(6) in total. About 1-3% total mass.
  • endocrine cells. 20% alpha cells (glucagon), 70% beta cells (insulin) 10% various other cells
75
Q

What do we know about insulin?

A
  • binding of insulin to its receptor triggers widespread metabolic and mitogenic effects.
  • translocation of GLUT-4 containing vesicles to the cell surface allows uptake of glucose.
  • muscles also contain a population of GLUT 4 vesicles that fuses with the cell surface during exercise, lowering blood sugar independent of the action of insulin.
76
Q

To check for liver diseases affecting hepatocyte integrity check …

A
  • Alanine aminotransferase (ALT) = (direct liver necrosis).
  • aspartate aminotransferase (AST) = (direct liver necrosis).
  • gamma glutamyl transferase (GGT) = cholestatic damage.
77
Q

To check for liver disease affecting cholangiocyte integrity check …

A
  • alkaline phosphatase (ALP) = (biliary tract disease, cholestatic liver cell damage).
  • 5’nucleotidase (5’-NT) = (biliary tract disease, cholestatic liver cell damage).
78
Q

To check for liver disease affecting bilirubin processing check …

A
  • total bilirubin (all the bilirubin in the blood).
  • conjugated bilirubin (the amount of bilirubin processed in the liver).
  • bilirubin and urobilinogen in urine (the amount of bilirubin spilling over).
79
Q

To check for liver disease affecting protein synthesis check …

A
  • albumin (the main protein made by hepatocytes).
  • total protein (albumin and all other proteins in blood).
  • prothrombin time (PT) or international normalised ratio (most clotting factors are made by hepatocytes:VitK absorption bile-dependent.
80
Q

What does the alimentary system (or GI tract) include?

A
  • oral cavity pharynx.
  • alimentary canal.
  • auxiliary structures.
81
Q

What is the principal structure of the GI tract?

A
  • it’s a tubular tract.

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