Intestines, Absorption, Digestion Flashcards
Glucose can only be absorbed with what ion?
What happens to carbs of plant origin that can’t be digested?
Na+
Utilised and partially digested by bacteria in colon, providing nutrients for colonic mucosa
Name 3 common dietary carbohydrates
- Starch
- Lactose
- Sucrose
Describe the structure of starch
- Straight chains of glucose called Amylose, held together by Alpha 1-4 bonds
- Branched chain of glucose called Amylopctin, held together by Alpha 1-6 bonds
Describe digestion of Starch into glucose
- Salivary and pancreatic amylase break Alpha-1,4 bonds in Amylose, releasing Maltose (Maltese converts to glucose)
- Amylase breaks Alpha-1,4 bonds in Amylopectin, releasing Alpha Dextrins
- Isomaltase needed to break Alpha-1,6 bonds of Alpha Dextrins into Amylose. Amylase converts this into glucose
What are the 3 monosaccharides we get from digesting common carbohydrates
- Glucose (from starch, lactose, sucrose)
- Galatose (from lactose)
- Fructose (from sucrose)
Describe monosaccharide absorption into an enterocyte
- Na-K ATPase on BM moves Na into blood
- Na and Glucose/ Galctose diffuse in through SGLT 1 on AM (from gut lumen, requires Na+ binding to monosaccharide)
- Fructose diffuses in through GLUT5 on AM
- All 3 monosaccharides leave cell through GLUT2 on BM-> blood to reach liver
What are the 4 stages of protein digestion?
- Stomach (H+, Pepsin)
- Intestinal lumen (Trypsin)
- Brush border of enterocytes
- Cytosol peptidases
Describe the 1st stage of protein digestion (in stomach)
- Pepsinogen released from Chief cells and gets converted to Pepsin by HCl
- Pepsin acts on proteins-> Oligopeptides and amino acids then move to SI
Describe the 2nd stage of protein digestion (in intestine)
- Pancreases releases Proteases as zymogens
- Trypsinogen converted to Trypsin by Enteropeptidase/ Enterokinase (a brush border enzyme)
- Trypsin activates other Proenzymes/ Zymogens as well as itself
List 5 Proenzymes/ Zymogens converted by Trypsin into Active Enzymes
- Trypsinogen
- Chymotrypsinogen
- Proelastase (Becomes elastase)
- Procarboxypeptidase A (Becomes carboxypeptidase A)
- Procarboxypeptidase B (Becomes carboxypeptidase B)
(All released by Pancreas)
Compare the 2 groups of Proenzymes released from Pancreas, after they have ben activated by trypsin
Endopeptidases;
- Break bonds in middle of polypeptide
- Produce shorter polypeptides
Exopeptidases;
- Break bonds at ends of polypeptide
- Produce dipeptides/ amino acids
Name 3 Endopeptidases and 2 Exopeptidases
Endo;
- Trypsin
- Chymotrypsin
- Elastase
Exo;
- Carboxypeptidase A and B
Describe the 3rd stage of protein digestion (Brush border enzymes)
- Brush border of enterocytes also contain Proteases, but sometimes can’t completely digestion into amino acids
- Short peptides and amino acids can be absorbed into enterocyte via PepT1
- Amino acids are taken in with Na+ via a Symport
Describe the 4th stage of protein digestion (Cytosol)
- Small peptides broken down by cytosolic peptidases into amino acids
- Certain di- and tri-peptides can also be absorbed into blood, as can amino acids
In the SI, water absorption is driven by the Na-K ATPase, Sodium movement into Enterocytes and Osmosis.
(Water follows sodium)
What are 2 pathways it takes?
- Transcellular
- Paracellular
Compare water/ electrolyte uptake in SI and LI
- Both have Na-K ATPase on BM
On AM;
- In SI, Na is transported with Glucose/ Amino acids
- In LI, Na channels exist which are induced by Aldosterone
Na is the ion that drives water absorption in intestines.
Which ion drives water secretin into intestinal lumen?
Cl-
Describe Water Secretion into Intestinal Lumen
- Cl enters enterocyte with Na and K, through Symport on BM
- cAMP levels rise in cell, activating CFTR protein on AM
- Cl leaves cell via CFTR on AM and Na+ follows it across tight junctions
- Water follows the sodium via osmosis
What are 4 causes of Vit B12/ Cobalamin deficiency?
- Lack of IF
- Hypochlorydia (inadequate stomach acid, needed to make Vit B12 available for binding to IF)
- Inadequate intake (strict vegetarians)
- Inflammatory disorders of Ileum (Crohn’s)
Why do Lactose Intolerance patients get the following when they ingest lactose;
- Diarrhoea
- Flatulence/ Bloating
Diarrhoea;
- Lactose remain in gut creating a high osmotic effect, pulling water into lumen
Flatulence/ Bloating-
- Lactose fermented in colon producing ‘gas’
Irritable Bowel Syndrome (IBS) is common, affecting 10-15% of adults
List 5 symptoms
- Ab pain (often cramping, relived by defecation
- Bloating
- Flatulence
- Diarrhoea/ constipation (sometimes alternating)
- Rectal urgency (urgent need to defecate)
The causes of IBS are multi-factorial
Describe the Aetiology of IBS
- More common in females (2:1)
- Most affected in age range of 20s to 40s
- Commonly associated with psychological disorders
Describe the physiological basis of Coeliac disease
Immune response to Gliadin component of Gluten, leading to damage of intestinal mucosa
List 3 foodstuffs that contain gluten (the Gliadin component to be exact)
Wheat
Rye
Barley
What are 3 ways the intestinal mucosa can be damaged in coeliac disease?
What do these lead to overall?
- Flattening, then absence of Intestinal Villi
- Hypertrophy/ Lengthening of Intestinal Crypts
- Lymphocytic infiltration of Epithelia and Aamina Propria
All these combine to lead to impaired digestion/ malabsorption
Coeliac disease is under diagnosed, in fact 1% of the western population is thought to be affected
Describe the Aetiology
What’s the treatment?
- Cause unknown but thought to be due to genetic factors
- Guten free diet (quick clinical improvement, slower histological improvement)
List 3 groups of symptoms of Coeliac Disease
- Most symptoms related to malabsorption (diarrhoea, weight loss, flatulence, ab pain)
- Anaemia (impaired iron absorption)
- Neurological symptoms (Hypocalcaemia)
What are 2 types of investigations that can be done to look for Coeliac disease
- Bloods;
- IgA antibodies
- Smooth Muscle Endomysium
- Tissue Transglutaminase - Upper GI endoscopy + biopsies to look for mucosal pathology (absent/ reduced villi)
