Small Intestine Flashcards
Describe the structural layers of the small intestine
- Mucosa, with crypts of lierberkuhn, areolar connective tissue, MALT, lymphatic nodules and muscularis mucosae
- Submucosa with Brunners Glands
- Inner thicker layer of circular muscle
- Outer thinner layer of longitudinal muscle
What additional advantage does the submucosa and mucosa provide to aid in absoprtion?
Villi
Microvilli
Circular folds upto proximal - spiral food
List the cells and relative function of the crypts of lierberkuhn
- Absorptive cells
- Goblet Cells
- Paneth cells - secrete lysosome
- S cells - secrete secretin
- CCK cells - secrete CCK
- K cells - Secrete Glucose-dependent Insulino-tropic Peptide to encourage insulin release upon glucose in duodenum
Where are the Brunners glands found and what is their function/
In duodenum - secrete alkaline mucous to neutralise acidic chyme
Describe the digestive process in the small intestine
Majority of digestion carried out by pancreatic juice with final step done by brush-border enzymes:
- alpha-dextinase breaks alpha-dextrins into glucose - Maltase breaks maltose into glucose - Sucrase breaks sucrose into glucose and fructose - lactase breaks lactose into glucose and galactose - Aminopeptidases cleave off end amino acid - Dipeptidases break up 2 amino acids joined - Nucleosidases and phosphatases - break down nucleotides into nitrogenous bases, phosphayes and pentoses
How are carbohydrates absorbed?
In the small intestine as monosaccharides. Fructose is absorbed via facilitated diffusion whilst glucose and galactose are absorbed via secondary active transport with Na co-transporter
How are proteins absorbed?
In small intestine as amino acids or di/tripeptides.
Amino acids are absorbed via active transport or secondary with sodium.
Di/Tripeptides are absorbed via active trasnport with hydrogen
How are fats absorbed?
Short chain fatty acids simply diffuse across
Long chain fatty acids and monoglycerides are too large so are encircled by bile salts to produce micelle. Due to properties of bile salts, these can now diffuse into enterocyte where they are recombined into triglycerides. They are then packed together with phospholipids and cholesterol and encircled by proteins to produce a chylomicron. This is released into lacteal by exocytosis where it travels in lymphatic system to thoracic duct. It enters into circulation here at left subclavian vein.
How are electrolytes absorbed?
Sodium - co-transporter pumps via active ransport and with negatively chrged electrolytes such as carbonate, chloride etc
Calcium - actively absorbed after stimulation from calcitriol
How are vitamins absorbed?
Fat soluble vitamins are packed in chylomicrons - A, D, E and K
Water soluble B and C can simply diffuse
Vitamin B12 binds to intrinsic factor and absorbed in ileum
How is water absorbed?
Via osmosis:
- 90% in small intestie
- 9% in large intestine
- 1% left in faeces
What is Coeliac Disease?
Gluten-sensitive Enteropathy with small intestinal villous atrophy which resolves when gluten is withdrawn from diet
How is coeliac disease cause?
Inapproriate T cell-mediated immune response to genetically susceptible individuals - alpha-gliadin is most toxic moeity. HLA-DQ2 (95%) and HLA-DQ8
Adenovirus 12- peptide on alpha-gliadin similar to that on virus so cross-reactivity occurs and leads to disease
What is alpha-gliadin and how does it contribute to coeliac disease?
protein found in gluten, digesting into a stable protein and absorbed into lamina propria where it is exposed to tissue transglutaminase antibody (TTG) from damaged epithelium. This leads to the deamination of glutamine residues, enabling bonding to HLA-DQ2 (or 8) and the activation of a pro-inflammatory T cell response
What are histological signs of coelias disease?
musocal inflammation (and damage) Loss of vilous height - either completely flat or short and broad Elongated crypts Increase in plasma cells and IELs
