Absorption And Digestion Flashcards
What form does a carbohydrate have to be in order to be absorbed into the body?
Monosaccharide
What ion needs to be present for glucose to be absorbed?
Na+
What are the 3 main absorbable monosaccharides?
Glucose
Galactose
Fructose
What are the 2 types of bonds found in starch?
Alpha 1-4 and 1-6 bonds
What are the 2 types of chains in starch?
Amylose (joined by a 1-4 bonds)
Amylopectin (joined by a 1-6 bonds)
What enzyme breaks a 1-4 bonds in amylose in starch?
Amylase
What is the product of amylase breaking down the amylose in starch?
Maltose
What is the enzyme that breaks a 1-6 bonds in amylopectin in starch?
Isomaltase
What is left behind when isomaltase breaks down the 1-6 bonds in amylopectin?
Alpha dextrin which = chains of amylose
What enzyme breaks down maltose to glucose and glucose?
Maltase
What type of carb is lactose?
Disaccharide
What enzyme breaks down lactose?
Lactase
What 2 monosaccharides are formed when lactose is broken down to lactase?
Glucose + galactose
Where is the enzyme lactase located?
Brush border of enterocytes
What enzyme breaks down sucrose?
Sucrase
What is sucrose broken down into?
Glucose + fructose
How are glucose and galactose absorbed from intestinal lumen through enterocyte into blood?
SGLT1 with Na+
Then across GLUT2 into veins that drain to portal vein
Na+/K+ ATPase creates gradient
How is Fructose absorbed from intestinal lumen through enterocyte into blood?
Through GLUT 5 into enterocyte then across GLUT2 into veins leading to portal vein
What are zymogen?
Granules containing inactive enzymes
Where does protein digestion begin?
Stomach
What cells are important in starting protein digestion in the stomach?
What do they secrete?
Chief cells
Produce Pepsinogen (inactive pepsin)
How does pepsin become activated to start digesting protein in the stomach?
Hydrochloride acid activates pepsinogen to pepsin
What is the function of pepsin?
Breaks down proteins to oligopeptides and some free amino acids in stomach
Where in the stomach are chief cells located?
Gastric glands
What happens when the broken down proteins and acidic chyme enter into duodenum (what is the pancreas stimulated to do)?
Zymogen/inactive digestive enzymes secreted
What are the 5 major zymogens (proteases) produced by the pancreas?
Trypsinogen
Chymotrypsinogen
Proelastase
Procarboxypeptidase A
Procarboxypeptidase B
What are the active forms of the 5 zymogen proteases produced by the pancreas?
Trypsin
Chymotrypsin
Elastase
Carboxypeptidase A
Carboxypeptidase B
How does Trypsinogen activated and why is this important?
Enteropeptidase in brush border of small lumen activates it
Trypsin then goes on to activate the other inactive Proteases
What are endopeptidases?
What are exopeptidases?
Endopeptidases make shorter peptide chains by breaking in middle
Exopeptdiases break bonds at the ends leading to amino acids and shorter peptides being made
What are the endopeptidases?
Trypsin
Chymotrypsin
Elastase
What are the exopeptidases?
Carboxypeptidase A
Carboxypeptidase B
What is the function of the brush border proteases?
Further break down di and tri peptides to individual amino acids
How are dipeptides and tri-peptides brought into the enterocyte?
PepT1
What happens to the dipeptides and tripeptides in the enterocyte?
Broken down to amino acids
What ion are amino acids absorbed with into the enterocyte?
Na+
Briefly outline where proteins are digested?
Starts in stomach
Pancreas releases inactive proteases into small intestine
Brush border enzymes in intestine break down di-tripeptides
Enzymes in enterocyte break down tri/di peptides
What are the 2 ways water is absorbed from the intestinal lumen into the body?
Paracellularly
Transcellularly
How is an osmotic gradient created so water can be absorbed from the intestinal lumen?
Na+/K+ ATPase on basolateral membrane pumps sodium into blood out of enterocyte
What is drawn into the enterocyte then to the interstitial space due to the Na+ gradient?
How does this help draw water through?
Glucose and amino acids
Makes solution in intercellular space/interstital space very hypertonic
What is the important ion needed for water secretion?
Cl-
What protein moves Cl- out of the cell so water can be secreted?
Cystic Fibrosis Transmembrane Conductance Regulator protein
What leads to increased CFTR expression?
cAMP levels rise
More CFTR
More Cl- removed
Describe trans cellular absorption of water:
Water follows sodium as it enter enterocyte
Describe paracellular absorption of water:
Sodium pumped into intercellular space between cells
Creates hyperosmotic environment so water moved through tight junctions
What are some symptoms of vitamins B12 deficiency?
Neurological problems
Megaloblastic anaemia
What can cause Vitamin B12 deficiency?
Lack of intrinsic factor
Hypochlorhydria
Inadequate B12 intake
Crohn’s disease (inflammatory disorders of ileum where B12 absorbed)
What cells produce intrinsic factor?
Parietal cells
What is hypchlorhydria?
Inadequate stomach acid production
What can cause hypochlorhydria?
Gastric atrophy
Proton Pump inhibitors (omeprazole)
What causes lactose intolerance?
Deficiency in lactase
What age does lactase levels usually drop from?
2
What symptoms do people with lactose intolerance have?
Diarrhoea
Bloating
Flatulence
What leads to diarrhoea in lactose intolerance?
Lactose remains in lume of gut
Leads to oncotic pressure in lumen increasing drawing water into gut lumen
What leads to flatulence and bloating in lactose intolerance?
Lactose fermented in intestine releasing gases
What are the symptoms of irritable bowel syndrome?
Abdominal pain(cramping)
Bloating
Flatuelnce
Diarrhoea
Rectal urgency
Constipation
Who is IBS most common with?
Women
Between 20s and 40s and often associated with psychological disorders
What is Coeliac disease?
An immune response to Gluten (specifically the gliadin fraction)
What happens as a result of the immunological response to gluten in coeliac disease?
Damages the intestinal mucosa
Flattening the villi
Hypertrophy of crypts
Lymphocytic invasion into epithelium and lamina propria
This leads to impaired digestion and malabsorption
What are the symptoms of Coeliac disease?
All symptoms of malabsorption
Diarrhoea (osmotic pressure in lumen)
Weight loss
Flatulence (sugars fermented) leading to distension
Anaemia (reduced Fe absorption)
Neurological symtpoms (reduced calcium)
How is Coeliac disease treated?
Strict gluten free diet
Leads to improvement in symptoms and intestinal healing
How is coeliac disease diagnosed?
History
Blood tests for IgA to smooth muscle endomysium + tissue
Upper gastrointestinal endoscopy with biopsy of duodenum
