Malabsorption and malnutrition Flashcards
What is malnutrition?
Insufficient dietary intake to meet metabolic requirements
What is malabsorption?
Disorder of the digestive tract resulting in the inability to utilise an appropriate dietary intake
Explain the process of carbohydrate digestion
- Begins in mouth with salivary amylase
- Acidic pH of stomach destroys salivary amylase
- Starches not already broken down are cleaved by pancreatic amylase in pancreatic juice
Where are sucrose, lactose and maltose digested?
In the small intestine
Maltose is digested by which enzyme?
Maltase
Sucrose is digested by which enzyme?
Sucrase
Lactose is digested by which enzyme?
Lactase
How do monosaccharides pass from the lumen of the SI through the apical membrane?
Via facilitated diffusion (fructose) or active transport coupled with Na+ (glucose and galactose)
Explain the process of protein digestion
- Begins in stomach with pepsin
- Enzymes in pancreatic juice (trypsin, chymotrypsin, carboxypeptidase and elastase) continue to break down proteins into peptides
- Protein digestion is completed by two peptidases in the brush border into amino acids
- Amino acids are absorbed by active transport in the duodenum and jejunum
Explain the process of fat digestion
- Lipids combine with bile salts to form emulsification droplets
- These are digested by lipase to form FFAs (monoglycerides) and bile salts
- These combine to form micelles
- Micelles transport poorly soluble monoglycerides to the surface of enterocytes to be absorbed
- Monoglycerides are absorbed once freely dissolved (micelles are not absorbed)
What are the three types of exocrine cells in the stomach glands?
- Mucous neck cells: secrete mucous
- Parietal cells: produce intrinsic factor and HCl
- Chief cells: secrete pepsinogen and gastric lipase
G cells secrete what?
Gastrin which stimulates gastric acid secretion
What is the role of cholecystokinin?
IT is released from the duodenum and stimulates secretion of pancreatic juice, contraction of the gall bladder, relaxed sphincter of Oddi and contraction of pyloric sphincter
What is the role of secretin?
Secreted from S cells in the glands of the small intestine, it stimulates the flow of pancreatic juice rich in HCO3- to buffer acidic chyme
- It inhibits secretion of gastric juice
Which enzymes are released from the pancreas (exocrine function)?
- Amylase
- Lipase
- Proteolytic enzymes
Role of bile?
Emulsifies fats
Micelle formation
What is absorbed in the jejunum?
Macronutrients
- Absorb sugars, amino acids, and fatty acids
What is absorbed in the ileum
Bile acids and vitamin B12
Give an example of a luminal disease of the SI
- Infections
- Bacterial overgrowth
Give examples of mucosal diseases of the SI
Loss of absorptive surface area
- Crohn’s
- Surgery
- Lymphoma
Degradation of absorptive surface area
- Coeliac
Major causes of malabsorption: luminal - infections?
- Giardiasis - Bloat, steatorrhoea
- TB
- Ancylostoma - Fe deficient
- Tripheryma whippelii - Subtotal villous atrophy
- Cryptosporidium, microsporidium, isospera (AIDS)
Major causes of malabsorption: luminal - bacterial overgrowth?
- High folate, low B12
- Jejunal diverticulosis
- Blind loop syndrome - Surgical, fistulation
- Obstruction
- Motility disorders - Autonomic neuropathy (diabetes), scleroderma
- Hypochlorhydria in the elderly
- Miscellaenous
Major causes of malabsorption: mucosal - coeliac?
- Gluten enteropathy
- Immune mediated
- Subtotal villous atrophy
- Crypt hyperplasia
- Intraepithelial lymphocytes
- Loss of surface area and villus maturation
- Autoantibodies
Substrate deficiency in coeliac disease?
- Fe deficiency
- Folate deficiency
- Osteomalacia
