Gastrointestinal physiology Flashcards
what are the 4 major activities of the Gastrointestinal (GI) tract?
- ingestion
- digestion
- absorption
- excretion
what is the transit time in context of the GI tract?
refers to the duration it takes for ingested material to travel through specific portions of the digestive system
transit times of the mouth, oesophagus, stomach, SI and LI
mouth = 5 sec - 2 mins
oesophagus = 8 - 10 seconds
stomach = 15 mins - 4 hours
SI = 1-5 hours
LI = 12-24 hours
what does transit time determine?
the health of the GI tract
what are the main functions of the stomach: (6)
- storage of ingested food
- mechanical digestion
- chemical digestion
- initiation of protein digestion
- killing of microorganisms
- controlled emptying into the SI
what is ‘intrinsic factor’, and why is it essential? (3)
- it is a glycoprotein
- produced by parietal cells in stomach lining
- essential for absorption of vitamin B12 into SI
why is the absorption of vitamin B12 needed?
- crucial for RBC production and neurological function
the 3 topographic areas of the stomach
- fundus
- corpus
- antrum
what do chief and parietal cells do?
chief cells - pepsinogen secretion
parietal cells - secrete HCL
what are gastric pits? (2)
- small invaginations in the lining of the stomach
- lead to gastric glands
where are gastric pits located in the stomach (2)
- lining of the stomach
- primarily upper portion
where are the oxyntic glands primarily found?
upper portion of the stomach
where are the pyloric glands primarily fond?
antrum (lower portion)
how does the proton pump effects hydrogen secretion? (2)
- exchange K+ ions for H+ ions across apical membrane of parietal cells
- H+ ions are secreted into stomach lumen
what is the canaliculus? (2)
- a small canal structure in parietal cells
- where the process of acid secretion takes palce
what is the enterogastric reflex? (2)
- where vagal stimulation of the stomach is inhibited
- inhibits stomach
what are the 3 main functions of the SI?
- secretion
- digestion
- absorption
what are the main functions of the large intestine (4)
- sstore faecal material and regulate its release
- secretion
- absorption
- provide environment for bacteria
what does the secretion function of the LI involve?
- secretion of high concentrations of K+ and HCO3-
- secretion of a thick mucinous substance to lubricate passage of faeces
why is it important that the LI provides an environment for bacteria?
- some of them produce vitamins of B complex and vitamin K
what pattern recognition receptors does the gut epithelium express?
- Toll- like receptors (TLRs)
- Nucleotide binding oligomerization domain 2 (NOD2)
what transcription factor controls epithelial integrity and the interaction between mucosal immune system and gut microflora?
NF-kB
what do M cells do in the epithelium? (3)
antigen sampling:
* they facilitate the uptake and transportation of antigens
* including pathogens
* takes from inestinal lumen to underlying lymphoid tissue
fundamental cell biological pathways in the regulation of GI function: (3)
- autophagy
- intracellular bacterial sensing
- unfolded protein response
what essentially is autophagy?
a cellular process involving the degradation and recycling of cellular components
the physiological responses of autophagy (2)
- to remove damaged organelles and microorganisms (selective)
- cellular starvation (non-selective)
what is the main molecule involved in the autophagy induction?
- ATP proteins
what is the generating step in the autophagy pathway? (3)
- the recruitment of ATG8 (LC3-1)
- to the autophagosomal membrane
- via membrane anchoring
what blocks and initiates the autophagy pathway?
- the mTOR complex
what is the main abcterial intracellular sensory?
- NOD2
where is NOD2 located?
cytosol
how NOD2 is activated?
binding to muramyl dipeptide (MDP)
other bacterial sensors aside from NOD2 within the cell, and the main difference
Toll-like receptor
* membrane bound bacterial sensor
what essentially is unfolded protein response? (3)
- a cellular stress response mechanism
- activated when there is an accumulation of unfolded or misfolded proteins
- in the ER of the cell
what sense the cumulated unfolded/misfolded proteins in the ER?
Grp78 protein
what is inflammatory Bowel disease?
a term used to describe a group of chronic inflammatory conditions that affect the GI tract
what is inflammatory Bowel disease characterised by? (3)
- rectal bleeding
- severe diarrhoea
- weight loss
what is coeliac disease? (3)
- an immune-mediated inflammatory disease
- of the small intestine
- caused by sensitivity to dietary gluten and related proteins in genetically predisposed individuals
symptoms of coeliac disease: (3)
- chronic diarrhoea
- weight loss
- anameia
what is the prevalence of coeliac disease?
- 1-2%
- raising over the current decades and we do not know why
the 4 lobes of the liver
right lobe (largest)
left lobe
quadrate lobe - undersurface of liver
caudate lobe- posterosuperior surface
what is the liver supplied by?
- portal vein
- hepatic artery
what are sinusoids? (3)
- specialised blood vessels
- that recieve blood both from hepatic artery and portal vein
- to supply hepatocytes
what are the metabolising functions of the liver? (8)
- energy metabolism
- carbohydrate metabolism
- fat metabolism
- protein metabolism
- hormone metabolism
- bilirubin metabolism
- metabolism of vitamins, minerals drugs
- toxin metabolism
what are the other functions of the liver aside from metabolism: (5)
- detoxification
- bile production
- filtration of pathogens
- storage of nutrients
- self-regeneration
what is cholesterol required for? (5)
- synthesis of cell membranes
- repair of cell membranes
- hormone synthesis
- bile salt production
- myelin sheath formation
what do VLDL’s do (very low-density lipoproteins)?
- transport cholesterol to various tissues thoughout the body
what does the ouput pathway of ‘bile acid synthesis’ insinuate?
cholesterol can be converted into bile acids
what is the reticuloendothelial system? (3)
- a network of cells and tissues found throughout the body
- play a crucial role in the immune system, and clearance of particles in the blood stream
- consist mainly of phagocytic cells
how does erythrocyte breakdown have anything to do with the liver?
- kupffer cells engulf the erythrocytes and they undergo haemolysis
what happens to the globin (1) and iron (2) in the breakdown of the erythrocyte? (2)
globin
* hydrolysed to amino acids and returned to blood
iron:
* carried to bone marrow
* used to make a new haemoglobin for RBC’s
what does conjugation and un-conjugation mean?
- refers to the chemical modifications involving the attachment or removal of certain molecules to form a compound
where is bile stored
gall bladder
what is bilirubin? (4)
- a natural by-product of RBC breakdown
- yellow/brown pigment
- principle constituent in bile
- insolube
how is bilirubin transported in the blood?
- binding to a protein called albumin
what is conjguated bilirubin also known as?
direct bilirubin
the main roles of bilirubin in bile: (2)
digestion and absorption of fats in SI
what is jaundice? (2)
- a yellowish pigmentation of the skin, the conjunctival membranes over the sclerae, and other mucous membranes
- caused by high blood bilirubin levels (hyperbilirubinemia)
which form of bilirubin is undetectable in urine and why?
- unconjugated bilirubin
- it isnt water soluble due to binding to albumin
what is a similar symptomatic disease that is harmless that may be mistaken for jaundice?
- carotenemia
typical disease that you see elevated bilirubin levels in: (2)
liver diseases:
* hepatitis
* liver cancer
what causes hepatic hyperbilirubinemia?
defects in conjugation of bilirubin within the liver (UDP-glucuronyl transferase)
what is more dangerous, conjugated or unconjugated hepatic hyperbilirubenmia?
conjugated
the main causes of jaundice: (3)
- haemolysis
- hepatocellular
- cholestasis
what is portal hypertension? (2)
- the development of collateral vessels that bypass the liver and connect portal and systemic venous system
- can be caused by liver cirrhosis that causes obstruction
what is a hepatotoxic disorder?
- a condition or substance that has the potential to cause damage to the liver
what is hepatotoxicity?
- a term used to describe the adverse effects of certain drugs, chemicals, infections, or diseases on the liver
what are some therapeutic drugs that have been withdrawn from the market primarily because of their hepatotoxicity? (2)
- troglitazone
- bromfenac
the 2 phases of drug metabolism in the liver:
- chemical modifications or inactivation by cytochrome P450
- conversion of lipid-soluble substances to water soluble derivatives
what is the most common cause of acute liver failure?
- paracetamol - 40 % of cases
what makes paracetamol overdose more likely?
- other substances such as alcohol that reduce GSH levels
what cell of the stomach secretes acidic solution?
- parietal cell
what are the stimulants of acid secretion (3)
- acetylcholine
- Gastrin
- Histamine
what is the main digestive gland in the GI tract, and why
pancreas
* exocrine pancreas provides all the enzymes needed to digest food
what is one of the main disorders of the pancreas?
- acute pancreatitis - the pancreas digests itself and its surroundings
what is the cell of the pancreas that produces the digestive enzymes?
the acinar cell
what are the cell types that play an important role in the development of acute pancreatitis (3)?
- the acinar cell
- stellar cells
- immune cells (macrophages)
