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Week 11 - Nutrition & Digestion

Terms in this set (25)

Gastrointestinal tract
1. Mouth - chewing & swallowing
2. Oesophagus - swallowing
3. Stomach - storage; regulated emptying & secretion
Pancreatic juice & absorption
4. Small intestine: duodenum, jejunum, ileum - digestion & absorption
5. Large intestine - storage of faecal matter
6. Anus - Desfaecation
Carbohydrates
Polysaccharides (starch, glycogen) >> bulk; starch is branched
Disaccharides (sucrose, lactose) >> lactose = milk sugar
Monosaccharides (glucose, fructose) >> fruit sugar
Describe digestion
The break-down of large, insoluble molecules into small, soluble ones, through both mechanical and chemical digestion
Mechanical - Teeth and stomach muscles
Chemical - Enzymes and bile
Saliva = salivary amylase - catalyses the hydrolysis of starch into polysaccharides into disaccharides
Pancreatic amylase = produces disaccharides and monosaccharides
Intestinal enzymes (peptidases, lipases, lactases) = hydrolyse disaccharides into monosaccharides
They are absorbed in the upper part of the small intestine
Intestinal enzymes are found at the brush border
Brush border = inner wall of the small intestine, has microvilli - simple cuboidal & columnar epithelium
Protein
Long chain of amino acids
11 non-essential amino acids (produced by the body)
9 essential amino acids (diet)
Proteins are hydrolysed into amino acids, tripeptides and dipeptides
1. Stomach = pepsin
2. Pancreas = trypsin, chymotrypsin, carboxypeptidase
3. Intestine = brush border enzymes
Fats - triglycerides = storage in plants and animals
Hydrolysed into two free fatty acids and one monoglyceride
Most fatty acids are synthesised by the body
Essential fatty acids from:
Linoleic w-6 and Linolenic 3 = produce signalling molecules and prevents risk of heart attacks
Hydrolysed by:
Gastric lipase 10%
Pancreatic lipase + bile salts 90%
Saliva = 99% water and 1% proteins (mucus, alpha-amylase, anti-bacterial)
Functions:
Lubrication
Solvent
Protects teeth and gums
Sjogren's syndrome
Autoimmune disease - destruction of minor salivary glands and lacrimal glands
Dry mouth = leads to dry eyes
Nutrients needed:
20% protein
35% fat
45% carbohydrate
2300 calories a day
Water, vitamins (fat & water soluble), minerals (iron, calcium, zinc)
Salivary glands
1 - 1.5 L saliva a day
Controlled by food in mouth - conditioned by sight or sound
Parasympathetic nerves (ACh) stimulate the production of saliva
Sympathetic nerves (noradrenaline) stimulate the production of saliva
Swallowing
1. Voluntary stage - food pushed towards pharynx by the tongue
2. Involuntary stage - swallowing reflex
1. Contraction of pharyngeal muscles (inhibition of respiration and closure of glottis)
2. Opening of upper oesophageal sphincter
3. Peristalsis in oesophagus
4. Opening of lower oesophagus sphincter
5. Receptive relaxation of the stomach
The sphincter should be tightly closed when not swallowing due to the pressure in the stomach
This ensures food does not come up into the oesophagus (acid reflux = heart burn)
When peristalsis reaches the stomach, the stomach relaxes momentarily to prevent the food coming back up
1. Fundus 2. Body 3. Antrum 4. Pylorus
After each wave of peristalsis, 1 ml of food moves from the stomach to the small intestine - duodenum
3 ml/min = 3 waves a minute
Mixing: mechanical digestion = waves of peristalsis & churning
Emptying via the pyloric sphincter = regulated to avoid exceeding digestive and absorptive capacity of the small intestine
Gastric juice
HCl - kills microbes & solubilisation
Pepsinogen -> converted to active Pepsin by HCl in the stomach
Gastric lipase
Intrinsic factor - glycoprotein produced by parietal cells of the stomach; absorbs vitamin B12 = keeps nerve and blood cells healthy & helps make DNA
Mucus - protection & lubrication
Gastric gland:
Mucous cell = mucus
Parietal cell = HCl & Intrinsic factor
Gastric pit:
Chief cell = pepsinogen
HCl secretion
1. Water and CO2 combine within the parietal cell cytoplasm to produce carbonic acid
2. Carbonic anhydrase converts carbonic acid into a hydrogen ion and a bicarbonate ion
3. Bicarbonate ion is transported out of the cell into the blood via a transporter protein (anion exchanger) in exchange for Cl-
4. Chloride ion is transported into the stomach lumen via a chloride channel
5. H+ is transported in the stomach lumen via the H+/K+ ATPase which uses ATP
6. H+ and Cl- are now present in the lumen of the stomach = HCl
Regulation of Gastric Activity
1. Cephalic phase - vagus nerve
2. Gastric phase - nerves & hormones
3. Intestinal phase - nerves & hormones
Cephalic phase - vagus nerve
Activated upon sight, smell & taste of food
Leads to the release of acetylcholine via the vagus nerve = stimulates parietal cells to secrete H+
Gastric phase - nerves & hormones
Activated when intrinsic nerves detect distension of the stomach (food in the stomach)
G cells are activated by the vagus nerve = gastrin secreted
Gastrin travels in the blood and binds to CCK receptors on the parietal cells
This elevates calcium levels and stimulates gastric juice production
Intestinal phase - nerves & hormones
Partially digested food arriving in the duodenum slows down the production of gastric juices and motility (contractions of gastric smooth muscle)
Gastrin and acetylcholine stimulate parietal cells to produce protons
1. Endocrine cells in the wall of the stomach (ECL) have gastric and ACh receptors
2. ECL cell releases histamine which binds to the H2 receptors on the parietal cell
Ucler = acid or enzyme damage to the stomach or intestinal wall
Excess acid production
Treatment of ulcers
1. Histamine (H2) receptor antagonists
2. H+/K+ ATPase (proton pump) inhibitors
3. Antibiotics to kill bacterium - H. Pylori
THIS SET IS OFTEN IN FOLDERS WITH...