GI Flashcards
What are the functions of the stomach?
To store and mix food, dissolve and continue digestion, kill microbes, regulate flow of food, secrete proeases, secrete intrinsic factor, Lubrication.
Where is B12 absorbed?
Terminal ilium
What is chyme?
chewed up food that leaves the stomach.
What are the areas of the stomach?
cardia where the oesophagus joins, fundus at the top, body main top bit, antrum bottom main and pylorus the bit near the sphincter.
What are the key cells of the stomach?
Mucous cells, parietal cells, chief cells and enteroendocrine cells
Where are most of the mucous cells?
On the surface of the wall lining.
What are gastric pits?
The dips in the surface of the stomach. where you get parietal chief and enteroendocrine.
Where are you most likely to find parietal cells?
In the pits of the fundus and body not antrum
Where are you most likely to find chief cells?
In the pits of the antrum
What is Gastric acid?
Hydrochloric acid, about 2 litres a day, more than 150nM H+ concentration
Which cells produce gastric acid?
Parietal cells
How is gastric acid produced?
Chloride diffuses into the stomach passively to keep it electrically neutral by having potassium leaving. To increase H+ there is a hydrogen potassium pump ATP is used here. the comes from water. to replenish hydrogen ions carbonic andydrase converts CO2 into carbonic acid and the bicarbonate is released and the let into the blood by swapping with a chloride
What is an effect of vomiting ?
Low potassium
What is the turning on cephalic phase?
Initiated by the parasympathetic nervous system. this happens when we see smell or taste food. it causes Acetylcholine to be released onto parietal cells and triggers the release of gastrin and histamine which increases acid production
What is the gastric phase turning it on?
Gastric distension and the presence of pepties and amino acids stimulates release of gastrin, and this acts on parietal cells. Gastrin triggers the release of histamine which also acts on parietal cells which increase acid production
Why is histamine important?
It acts directly on parietal cells but also mediates the effects of gastrin and acetylcholine. which make this a good target for drugs
Why does protein in the stomach initiate acid release?
It is a direct stimulus for gastrin release, the protein acts as a buffer increasing pH by absorbing H+ ions, this leads to decreased somatostatin and more parietal cell activity
How is gastric acid secretion reduces in the gastric phase?
Low pH directly inhibits gastrin selection, it indirectly inhibits histamine release via gastrin and stimulates somatostatin release which inhibits parietal cell activity
How is gastric acid secretion turned off in the intestinal phase?
Distension in the duodenum, low luminal pH, hypertonic luminal contents and presenece of amino acids and fatty acids, these lead to enterogastrones being released such as secretin, which inhibits gastrin release and promotes somatostatin, it also releases choecystokinin and reduces ACh release
What type of signalling cells are gastrin, acetylcholine, histamine and somato statin?
Gastrin is a hormone, Histamin and somatostatin are paracrine chemicals, Acetylcholine is a neurotransmitter
How do the chemical act on the parietal cells?
Causes the more of the pumps to be put on the surface of the cells
What are peptic ulcers?
an ulcer is a breach in a mucosal surface.
What are the causes of peptic ulcers?
Helicobacter pylori infection, Drugs-NSAIDS, Chemical irritants alcohol and bile salts, dietary factors and gastrinoma.
What are the mechanisms of peptic ulcers?
Too much acid, or weakened mucosal defence
How is the stomach lining protected from the acid it produces?
Alkaline mucus, tight junctions between epithelial cells, replacement of damaged cells and feedback loops
How can helicobacter pylori cause an ulcer?
They live in the mucus, secreat urease splitting urea into ammonia and this can bind to hydrogen ions and proteases phospholipases and vacuolating cytotoxin A can damage the gastric epithelium and cause an inflamatory response which reduces mucus production
What are NSAIDs responsible for in the stomach?
Mucus secretion is stimulated by prostaglandins and Cyclo-oxygenase 1 needed for the synthesis of this, NSAIDS inhibit cyco-oxygenases and this reduces the mucosal defence
How can bile salts case ulcers?
Duodeno-gastric refux, regurgitated bile strips away mucus layer, reduce mucosal defence
How can Helicobacter pylori induced ulcers be treated?
Proton pump inhibitor for the acids, and two types of antibiotic to reduce numebrs of bateria
How can NSAID ulcers be treated?
Give the a proton pump inhibitor or histamine blocker, give them a prostaglandin analogue
Which cells secrete intrinsic factor?
Parietal cells
Which cells produce pepsin?
None
Which cell produces pepsinogen?
The chief cells
What is a zymogen?
An inactive form of an enzyme
What stimulates chief cells?
Same as for gastric acid
What activates pepsinogen?
Hydrochloric acid and pepsin can make it into pepsin
How is pepsinogen modified into pepsin?
it is cleaved into smaller parts
What allows for protease activation?
Low pH
How can pepsin be inactivated?
By reacting with the HCO3 in the small intestine
How much of protein digestion is the stomach responsible for?
abour 20%
What is the role of pepsin?
Not essential but accelerates protein digestion. Breaks collagen in meat
What is the volume of the stomach?
50mL
What is the maximum volume of the stomach?
1.5L
What is receptive relaxation?
Passive relaxation of the muscularis propria to increase the volume of the stomach
What helps gastric receptive relaxation?
Vagus parasympathetic innervation. NO and seretonin and enteric nerve plexuses
What is peristalsis?
Rhythmic wave like contractions in the walls of the stomach.
What are the pacemakers of the stomach?
Interstitial cells of khal also in intestines
Describe the contraction of the stomach?
Weak in fundus and body. forces food to pylorus and it closes the sphincter and squeezes food against it.
How is food let out of the stomach?
Small letting out of chyme into duodenum
How frequent is the basic electrical rhythm?
3 times per minute
How are gastricdepolarisations transmitted to other cells?
through gap junctions
How are the pacemakers able to generate action potentials?
ACh stimulus and other hormones to stimulate an action potential gastrin can do it and mechano receptors release gastrin
What duodenal factors decrease gastric motility?
increased duodenal luminal fat duodenal distension, duodenal osmolarity, decreased luminal pH
What is the importance of controlling gastric emptying?
The capacity of the duodenum is less than the capacity of the stomach
What is dumping syndrome?
When too much hypertonic solution goes into the duodenum.
What are the symptoms of dumping syndrome?
Vomiting, bloating, cramps, diarrhoes, dizziness, fatigue, weakness, sweating, dizziness, tachycardia
What is gastroparesis and its causes?
Delayed gastric emptying, no known cause, can be autonomic neuropathies, drugs, abdominal sugeries, parkinsons, MS scleroderma, amyloidosi, Female gender
What drugs can cause gastroparesis?
GI agents H2 antagonists, proton pump inhibitors, Anti cholinergic medications, Dephenhydramine, Opiod analgesics, Tricyclic antidepressants
Others Beta adregenergic agonits, calcium channek blockers, interfereon alpha
What are symptoms of gastroparesis?
Nausea, early satiety, comiting undigested food, GORD, Abdominal pain, Bloating anorexia
What is special about the circulation in the liver?
There is the normal blood supply from the hepatic artery and blood returns to the heart by the hepatic veins and the IVC. Blood also comes from the small intestine via the superior and inferior mesenteric vein.
What are some of the main functions of the liver?
Detoxification- Filters and cleans blood of waste products
Immune functions- fights infections and diseases
Synthesis- of clotting factors proteins enzymes, glycogen and fats
Production of bile- and breakdown of biirubin
Energy storage- glycogen and fat
Regulation of fat metabolism
Ability to regenerate
Describe the metabolic role of the liver
Continuous supply of energy for the body by controlling the metabolism of carbohydrates and fats
What regulates the liver metabolic activity?
Nerves and endocrine glands like the pancreas thyroid and adrenal glands
Where are lipides stored?
in adipocytes in hepatocytes and elsewhere
Which are more fluid saturated or unsaturated fatty acids?
Unsaturaes as they need more space due to their bent shape
What are the functions of lipids?
Part of cell membranes, Energy reserve, Integral to form cells, can be part of inflamatory cascades(arachadonic acid)
Hormone metabolism like sx hormones and vitamin D
Where does energy in the body come from?
The oxidation of lipids or carbohydrates. 30-40 days of lipid energy lipid reserve 100000kcal
Where is the main storage f glycogen?
In the liver
Where do lipids come from to the liver?
The portal vein hepatic artery and lymphatics
In what form are lipids brought into the liver?
As free fatty acids
How can fatty acid storage be increased?
Eat more fatty acids.
How are lipids transported in the body?
As tryglycerides or fatty acids bound to albumin or within lipoproteins. Triglycerides cant pass through membranes by fatty acids can
What are the ways that fatty acids can be taken up by the liver?
Fatty acid binding proteins, Fatty acid translocase and fatty acid transport polypeptide
What is the name of the enzyme that can convert triglycerides into free fatty acids?
Lipoprotein lipase
What enzyme releases fatty acids from adipocytes?
Hormone sensitive lipase
What does insulin do in terms of fat storage?
Fat storage in adipocytes, stimulates lipoprotein lipase to break down TG to release FFA to be stored in the adipocytes. it reduces the activity of HSL so there is reduced export of lipids from the adipocytes
What are the effects of insulin resistance on fats?
Increased lipolysis in adipocytes leading to lots of TG in circulation, Increased offer of fatty acids to the liver so their uptake increases. increased glucose levels in blood mean less demand for lipids so used to store energy.
What is de novo lipogenesis?
Happens in the liver and is the sequential extension of an alkaoic chain starting from Acetyl-CoA via seria decarboxylative condensation reactions.
What is the rate limiting step of de novo lipogenesis?
Aecetyl-CoA to Malonyl-CoA catalysed by Acetyl-CoA carboxylase
What affects the rate of de novo lipogenesis?
Rate is related to Fatty acid sythetase which is activated by insulin and inactivated by catecholamines and glucagon, it has negative feedback on itself
What are lipoproteins?
A core of triglycerides and cholesterol-esters and a surface monolayer of phospholipids colesteral and specific proteins(apoproteins)
What determines the type of lipoprotein?
the ratio of protein to lipid defined by their density LDL HDL VLDL and chylomicrons
What do chylomicrons do?
Carry lipids from the gut to muscle and adipose tissue
What happens to chylomicron remnants?
They are taken up in the liver
What percentage of cholesterol comes from food?
10%
Where is cholesterol processed?
In the liver
How is cholesterol excreted?
Through the bile. it taken by lipoproteins in the circulation to the liver
How is fats and cholesterol exported from the liver?
As bile acids and VLDL
What is the process to export a fatty acid?
Apoprotein B100 is synthesised in the rER the lipid compnent is synthesised in the sER they are atted by TAG proteinsto ApoB. They are sent to the Golgi apparatus where ApoB is glycoosylated and then migrates to the sinusoidal membrane and exocytosed as a VLDL
What affects Fatty acid oxidation?
Periperal fatty acid availablility increased by glucagon and decreased by insulin.
What are the 3 locations for oxidation of fatty acids in the liver?
Peroxysomal Beta oxidation
Mitochondrial beta oxidation and ER omega oxidation CYP4a catalysed
What is mitochondrial beta oxidation?
Multistep progressive reduction in chain length which leads to ketone bodies. It is regulated CPT carnitine palmitosyl transferase and carnitine concentration and malonyla CoA which inhibist CPT. genetic disorders can affect it and alcohol
What is peroxisomal beta oxidation?
Main role is detoxification of
very long chains, 2 methyl branched FA, dicarbolic acid which inhibit mitochondira, prostanoids, C-27 bile acid intermediaroes
It is 4 step and each step can be done by 2 enzymes,. if it goes wrond leats to microvesicular steatosis
What is steatosis?
Fat gathering in the liver cells
What is microsomal omega oxidation?
Important in overload, CYP4A enzyes oxidise saturated and unsaturated fatty acids, hydroxylation in ER folloed by decarboxylation to enter beta oxuadation.
How are Fatty acids able to regulate actions?
Gene expresson by controlling transcription factors. the control metabolic machinary for metabolic machinery for fatty acid metabolism
What are PPAR?
Receptors for lipids, all involved in lipid homeostasis, only gamma is energy storage alpha is gene transcription
What happens in defective metabolism?
Less oxidation(or is overloaded) microsomal oxidation increases causein more dicarboxyl acids which inhibit other pathways ofoxidation and leat to lipotoxicity and steatohepatitis
What are the deaseases reated to fat in the liver?
NAFLD non-alcoholic fattty liver diseas and NASH non-alcoholic steatohepatitis.
What are the stages of liver damage?
Fatty liver (deposits of fat cause enlargement), liver fibrosis (scar tissue forms) and cirrhosis ( growth of connective tissue destroys liver structure .
What causes fatty liver?
Increased TG in plasma from excess diarary intake and caloric intake. Also increased flux of FA increase releae of FA and uptake by hepatocytes. Decreased FA oxidation which decreased demand for lipids and increases storage.
What is steathepatitis?
Too much fat in the liver. Leads to large release of TG and FA overload increase Reactive Oxygen species production, It causes inflamation from kupffercells ad ethanol can activate stellate cells for fibrogeneseis. lipidperoxidation products cause inflamation
How do you manage fatty liver diseas?
Reduce calories, increase demant for consumption. usually will burn the fat off
How does alcohol cause fatty liver?
The high calorific values cause fat storage.
How does alcochol get procesed?
Increases loads PPAR aloha is inhibited and so is fat oxidation and FAS increases lipogenesis. causes dammge to organells and causes fibrosis
Which of the layers in the trilamina disk form the mid and hind gut?
Endoderm forms the mucosa of the bowl some layers are from mesoderm
What types of folding happens in the embryo?
Lateral the mesoderm and endoderm come round to make boweltube and is surrunded by the mesoderm to form the mesentry and peritoneal membrane
What deos the endoderm give rise to in the GI tract?
The endothelium of the bowel the hepatocytes of the liver and exo and endocrine pancreas
What does the visceral mesoderm give rise to?
The muscular wall connective tissue and cisceral peritonium
What is interesting about innervation of perietial peritonium?
It is the same as the overlying skin
What is interesting about innervation of visceral peritoneum?
It is supplied by separate nerves the greater for foregut lesser for mid and least for hind and causes refered pain
Where do the lungs develop from?
The foregut
Where is the boundary of the foregut and midgut?
Where the pancreatic duct joins the bowel.
What is the first stage of the GI developmen?
There is a forward looping supplied by the superior mesenteric artery
Where is refered pain for the heart and lungs?
T1-T5 inside of forarm and upper arm and on chest
Where is referred pain for the Foregut?
T5-T9 below nipples and umbilicus
Where is referred pain for the midgut?
T10-T11 the umbilicus
Where is referred pain for the Hindgut?
T12 just above hair bearing area
Describe the stages of the tube?
Elongation, physiological herniation, rotation, retraction and fixation
What happens in elongation and herniation?
it elongates and then most of midgut loop passes through the umbilicus. elongates in the cephalic limb close to the head. it has rapid growth while the liver and pancreas grows in week 6
Describe the rotation of the tube?
the caecum rotates infront of the bowl clockwise from above to put it in the right lower part.
Describe retraction?
the abdominal area is big enough the mesentry facilitates this as it doesnt extend/ the transverse colon and the duodenum comes in first.
Where is the appendix?
In a variable position which leads to variable presentation of diseases.
What is the fixation stage?
on organs that are retroperitoneal the two layers fuse together and fix it to the wall
Which parts of the GI tract are fixed?
The duodenum apart from very first part. Ascending colon and descending and rectum
Where is the mesentry for the transverse colon passing?
Above the duodenum and across.
Where is the small intestine mesentry running from?
The duodena jejunal flecture to the illio cecal valve.
How can you look at the bowel?
Barium ennema and pump air in to xray it.
What embryological faults can happen?
retraction- part of bowl in the umbilical cord or can rupture the cord.
rotation- caecum not in right place
What is the function of saliva?
Lubricant for mastication, swallowing and speech
Oral hygiene to wash the mouth buffer the acidity, and offer immune defence
Adds digestive enzyme and aids taste and without it can lead to infection and pain
What is the flow rate of saliva?
0.3-7ml per minute arount 1-1.5L over a day
What is the pH of saliva?
6.2-7.4
What is in the saliva?
Water serous secretion of amylase alpha and mucus secretion other enzymes such as water etc
Which salivary gland only produces serous secretions?
Parotid gland
What factors affect the composition of the saliva?
Flow rate, circadian rhythm, type and size of gland, duration and type of stimulus, diet, drugs, age ,gender
What defenses are there in the mouth?
The mucous provides a physical barrier. the palatie tonsils that have lymohocutes and dendritic cells, salivary glands wash away food and bacteria
Which glands continuously produce saliva?
Submandibular, sublingual and minor glands are continuously producing
Which gland only produces secretions when stimulated?
The parotid
What is the balance between mucous and serous secretions?
Unstimulates is mixed
stimulated is mainly serous
What is whole saliva?
Saivary gland secretions, blood, oral tissue, microorganisms and food reminants
What are Exosomes?
Cell specific lipid microvesicles, can migrate through the vasculature. reside in a number of biofluids eg urin blood breast milk and saliva and we don’t yet know their function but could be to do with immune response and contain DNA
What could the saliva be used for?
Diagnostic or prognostic tests
What are the structure of the salivary glands?
They have two distinct epithelial layers. Acinar cells which surround ducts which form a large duct enterig the mouth. There are many channels and transporters in the apical and basolateral mebranes enabling transport of fluid and electrolytes.
What are the two types of acinus?
Serous and mucous.
Describe the two types of acinar cells histologically
serous are dark staining nucleus in basal third and small central ducts secrete water and alpha amylase. mucous are pale staining nucleus at the base large central duct and secrete water and glycoproteins.
What are the types of ducts in the glands?
Intralobular ducts and main excretory
What are the two divisions of intralobular ducts?
Intercalated short and narrow segments with cuboidal cells that connect acini to striated ducts. And striated ducts are major site for sodium chloride reabsorption
What is the appearace of striated ducts histologically?
Look striated basal membrane has many microbilli for transport many mitochondria for transport
Other than conduction what are the fuctnios of the ducts?
Primary saliver has lots of NaCL and is isotonic but it becomes hypotonic and NaCl also have secretions of potassium and HCO3
Which glands are the major salivary glands?
Parotid submandibular and sublingual.