B3 Digestion and Absorption Flashcards
How much energy is derived from protein?
40%
What is the first macromolecule metabolised?
Protein
What is the last macromolecule metabolised?
Fat
What are essential amino acids?
Those that cannot be synthesised in the body
How are essential amino acids provided for the body?
Through the diet
What are non-essential amino acids?
Those that can be synthesised in the body
How are non-essential amino acids made in the body?
From common metabolic intermediates via transanimation
What are semi-essential amino acids?
Amino acids that become essential under conditions of metabolic stress or trauma
Why is glutamine important?
Used to make purines and pyrimidines in DNA synthesis
What are essential precursor amino acids?
Amino acids that can be made provided that there are enough of other amino acids
What are the two essential precursor amino acids?
Cysteine and tyrosine
What amino acid is important in surgical trauma and sepsis?
Glutamine
What amino acid is relevant at times of high protein intake
Arginine
What amino acid is important at times of high growth?
Arginine
What amino acid is present with high intakes of some xenobiotics?
Glycine
What amino acid is present in severe trauma?
Proline
Why is proline important in severe trauma?
It’s required for collagen synthesis
How are high concentrations of glycine gotten rid of?
Excreted as glycine conjugates
What macromolecule would you expect to see a decrease in after trauma?
Protein
What is amino acid metabolism closely related to?
Carbohydrate and fat metabolism
What does amino acid breakdown give rise to?
Intermediates of carbohydrate and fat metabolism
What are amino acids without their amino groups known as?
Carbon skeletons
Where do amino acids travel to from the small intestine?
Portal vein
What is an acceptor in amino acid metabolism?
A different keto-acid that takes the amino acid group from the transanimase enzyme
What vitamin is the co-factor for transaminase enzymes?
Vitamin B6
What does keto refer to in keto-acid?
The carbon skeleton
What are the 3 main transaminase enzymes?
Alanine aminotransanimase (ALT) Aspartate aminotransferase (AST) Glutamate aminotransferase
What do raised levels of alanime aminotransferase and aspartate aminotransferase indicate clinically?
Liver damage
What is the consequence of cholestasis?
Bile can’t get out of the liver
What is ALP?
Alkaline phosphatase
What do increased ALP levels indicate?
Increased synthesis by bile cannaliculi
Infiltrative disease of liver
Cirrhosis
What is GGT?
Gamma glutamyl transpeptidase
What do increased GGT levels indicate?
Cholestasis
What does raised GGT but normal ALP indicate?
Alcohol damage
What does raised ALP with normal GGT indicate?
Bone disease (e.g. Paget’s)
What do small increases in aminotransferases with large increases in both ALP and GGT indicate?
Biliary obstruction
What would large increases in amino transferases and a small increase in ALP indicate?
Hepatocellular damage
What is the major protein of the liver and blood?
Albumin?
Why is it important that the amino group gets removed from amino acids?
The keto acid can then be added to glutamate and sent through the krebs cycle
What are glucogenic amino acids?
Amino acids which can be converted back to glucose and continue like that through the krebs cycle
What are ketogenic amino acids?
Give rise to ketones or lose their carbons in breakdown pathways
Where is ammonia concentration highest in the body?
Liver
True or false? Ammonia being converted into urea involves mitochondria?
True
What enzymes can be responsible for forming ammonia?
Glutamate dehydrogenase
Aspartate
What is appreciable recycling?
Urea diffusing into gut lumen then being hydrolysed by gut bacteria
True or false? Ammonia being made into urea is a reversible process?
True
What is responsible for the conversion of urea to ammonia?
Bacteria urease
What is insulin’s effect on gluconeogenesis and lipolysis?
Decreases it
What is glucagon’s effect on gluconeogenesis?
Increases it
Where do short chain fatty acids come from?
Anything derived from milk
Where do we get phospholipids from?
Cell membranes
Where do we get cholesterol esters from?
Animal cell fat stores
Where do we get cholesterol from?
Animal cell membranes
Why does TAG need to be emulsified?
They are oil based which means they would otherwise be immiscible in the aqueous environments of the intestine and blood
What is emulsification?
The breakdown of oils into smaller droplets
How are fats emulsified?
Adding energy in the stomach via churning
Stabilise the droplets with bile salts
Where does digestion of fats begin?
The mouth
Which enzyme starts breaking TAG down?
Lingual Lipase
What is secreted by the duodenum in response to fat?
CCK
What is the purpose of fat?
Inhibits gastric secretion and motility; stimulates pancreatic bicarbonate and enzyme
What are zymogens?
Inactive precursors which get activated after gastric secretion to avoid the stomach and duodenum from being digested away from all the secreted enzymes.
Where does carbohydrate digestion begin?
The mouth via salivary amylase
What do salivary and pancreatic amylase do?
Splits starch (and glycogen) into smaller fragments
What happens to ingested disaccharide molecules?
They’re not acted on until they reach the small intestine
What breaks down the disaccharides?
Their respective enzymes in the small intestine
What happens to monosaccharides?
Absorbed by the small intestine
How do monosaccharides get absorbed by the small intestine?
Facilitated diffusion through apical membrane from lumen
How are glucose and galactose transported into absorptive cells of villi?
Secondary active transport via Na+/ glucose symporters
What happens to monosaccharides after entering the absorptive cells of the villi?
Travelling via facilitated diffusion into the capillaries of the villi.
What surfaces do the monosaccharides diffuse through to get to the capillaries
Basolateral
Where are the majority of carbohydrates absorbed?
Ileum/ Jejunum
What happens when there is excess carbohydrate intake?
It’s converted in the liver to fat - made by combining acetyl CoA from the link reaction
What is the function of the mucous cells of the salivary gland?
Secrete a mcus which causes the food to stick together and acts as a lubricant to aid in swallowing
True or false? No significant chemical digestion of protein occurs in the mouth?
True
What protein is secreted in response to protein?
Gastrin
What is the role of gastrin?
Stimulates acid, pepsinogen and gastric motility
What is the name of the enzyme that breaks down phopholipids?
Phospholipase
What is the brush border made from?
Microvilli
Where are proteins first digested?
Stomach
What is the enzyme that first breaks down proteins?
pepsin
What are the main enzymes that digest carbohydrates?
Salivary amylase
Pancreatic amylase
What are the different forms of gut motility?
Peristalsis
Segmentation
What is peristalsis?
Moving the whole bolus from side to side
What is segmentation?
The bolus is broken into little segments (like pushing the ends of toothpaste)
What turns a bolus into chyme?
Segmentation
Stomach churning
What is necessary to stop the stomach and duodenum from being digested by gastric acid?
Zymogens
What is the name of the process that produces short chain fatty acids?
Fermentation
Where are carbohydrates absorbed?
Ileum/ jejunum
Where does triacylglycerol digestion begin?
Mouth
What are zymogens?
Inactive precursors to protein
Where are short chain fatty acids usually absorbed?
Stomach
Why is pancreatic TAG lipase necessary in lipid metabolism?
To aid in emulsification
Where do chylomicrons enter lymphatics?
Thoracic duct
How do chylomicrons get into the fenestrations in capillaries?
Lipoprotein lipase in extrahepatic tissues
What happens to chylomicron remnants after being exposed to lipoprotein lipase?
Taken up by liver for metabolism and recirculation
What stabilises chylomicrons in the blood?
Ampipathic apoproteins, phospholipids and cholesterol
Where is brown adipose tissue especially important?
Neonates
What pairs with fatty acids in the fatty acid cycle in white adipose tissue?
Glycerol-3-P
Is ATP produced by brown adipose tissue?
No
What is the exogenous pathway of cholesterol metabolism?
When eating dietary cholesterol
What is the endogenous pathway of cholesterol metabolism?
Happens everyday- LDL transported to extrahepatic tissues and macrophages
How much of HDLs gets recycled when it returns to the liver?
95%
What cell receptors recognise LDLs in extrahepatic tissues?
B-100
What do HDLs interact with on the cell surface of extrahepatic tissues?
ABC transporters
What is the role of LCAT in cholesterol metabolism?
Converts cholesterol into cholesterol ester
What is the difference between cholesterol and cholesterol ester?
Cholesterol- ampipathic
Cholesterol ester - non-polar
When HDL 3 gets bigger what does it become?
HDL 2
What is the initial shape of HDL molecules?
Discoid
What receptor in the liver recognises returning HDLs?
SR-B1
What enzyme breaks up HDLs in the liver?
Hepatic lipase
What things are necessary for cholesterol synthesis?
Acetyl CoA
HMG CoA reductase
How do macrophages take up LDLs?
Scavenger system?
Is the scavenger system controlled?
No
What increases cholesterol uptake by macrophages?
Opsonization
What enzyme converts haem to biliverdin?
Haem oxygenase
Is bilirubin soluble?
No
What enzyme makes bilirubin?
Biliverdin reductase
What is bilirubin’s precursor?
Biliverdin
What process makes bilirubin more soluble?
Conjugation
Where does bilirubin migrate in its metabolism pathway?
Sinusoids to hepatocytes
What is bilirubin converted to in the colon?
Stercobilogens and urobiligens
