5 - Intestines Flashcards
What are some of the structural differences between the jejunum and the ileum?
What is the arterial blood supply to the jejunum and the ileum?
SMA
What is the venous drainage of the jejunum and ileum?
- All drains into portal vein that enters the liver
- Splenic vein and SM vein join to start the formation of the portal vein
How does maximum absorption in the small intestine occur?
- Large surface area: plicae circulares (permanent folds), microvilli, villi
- Slow movement of contents back and forth
What are some of the different epithelial cells in the intestines?
- Columnar enterocytes: absorption
- Goblet cells: mucus
- Enteroendocrine: hormones
In crypts there are stem cells and paneth cells (antimicrobial peptides)
How is starch (polysaccharide) digested so it can be absorbed?
- Consists of amylose and amylopectin
- Salivary and pancreatic amylase break A1-4 bonds to form maltose or alpha dextrins
- Isomaltase breaks A1-6 bonds so dextrins form glucose
- Maltase breaks maltose apart to glucose
- Isomaltase and maltase are brush border enzymes
How are lactose and sucrose (disaccharides) digested into monosaccharides to be absorbed?
Brush border enzymes
How are each of the monosaccharides absorbed from the lumen of the intestine into the blood stream?
- SGLT1
- GLUT5
What molecules do oral rehydration fluids contain?
- Na and monosaccharides as this will drive maximum influx of osmotically active susbstances into cell so water will follow
How are proteins digested in the small intestine?
- Can only be absorbed as amino acids or di/tri peptides
1. Pepsinogen from chief cell converted to pepsin by HCl
2. Trypsinogen converted to trypsin by enteropeptidase (brush border enzyme). Trypsin then activates other proteases
3. PepT1 absorbs small peptides
4. Small peptides broken down in enterocyte
What transporter transports small peptides from the intestine into the enterocyte?
Co transport with H+
What are some major protease released from the pancreas, in an inactive form at first?
Why is there a large amount of water absorption occuring in the small intestine?
- Due to Na and solute absorption
- Water mainly moves paracellularly
- Aldosterone can cause more water to be absorbed
What causes water secretion from the enterocyte into the lumen of the intestine?
- Cl-
- e.g cholera can lead to artifical levels of cAMP
What can be some causes and consequences of Vitamin B12 deficiency?
Causes:
= Lack of IF from parietal cells
= Hypochlorhydria due to atrophy or PPIs
= Vegetarian
= Inflammatory disorders of the ileum e.g Crohn’s
Consequences:
= Megaloblastic anaemia
= Neurological symptoms
What is the pathophysiology of lactose intolerance and its symptoms?
What is the cause of IBS, some symptoms and the main groups of people that it affects?
- No documented abnormalities
- More common in females, 20s to 40s and associated with psychological disorders like anxiety
What is the pathology behind coeliac disease?
- Immunological response to gliadin fraction in gluten (wheat, rye and barley)
- Damages the mucosa of intestines
- Flattens villi
- Hypertrophy of intestinal crypts
- Lymphocytes infiltrate epithelia and lamina properia
- Impaired digestion and malabsorption
What are the symptoms of coeliac disease?
- Mainly due to malabsorption: diarrhoea, weight loss, flatulence, abdominal pain
- Anaemia due to impaired iron absorption
- Neurological symptoms from hypocalcaemia
What investigations should be done if you suspect a patient has coeliacs disease and if they do how would you treat them?
Investigation
- Upper GI endoscopy and biopsy of duodenum to see if villi are absent and mucosal pathology
- IgA to smooth muscle endomysium and tissue transglutaminase
Treatment
- Strict gluten free diet for clinical improvement in days and histological improvement in a few weeks/months
