Alimentary system.docx

[Alimentary system ] Mouth -- contains salivary glands which secrete amylase (starch maltose + isomaltose) 3x Salivary Glands -- Parotid, Sublingual, Submandibular Oesophagus -- transports food from pharynx to stomach, Outer longitudinal muscle and inner circular muscles, Lumen is surrounded by m...

[Alimentary system ] Mouth -- contains salivary glands which secrete amylase (starch maltose + isomaltose) 3x Salivary Glands -- Parotid, Sublingual, Submandibular Oesophagus -- transports food from pharynx to stomach, Outer longitudinal muscle and inner circular muscles, Lumen is surrounded by mucosa (stratified squamous epithelium), also has mucous glands present. Stomach: Mechanical -- Churning = increased contact with enzymes Chemical -- Pepsinogen, HCL, Renin / Chymosin 3 muscle layers: 1. Outer = longitudinal 2. Middle = circular 3. Inner -- oblique \*Wrinkly is present when stomach is empty called Rugae Mucosa (Simple columnar epithelium with gastric pits): - Chief Cells a. produce pepsinogen (protein smaller peptides) b. Rennin / Chymosin -- coagulates milk, important in very young - Parietal Cells a. HCL -- kills bacteria, minor digestive affect, maintain acidity b. Intrinsic factor -- glycoprotein, binds to vitamin B12 - Mucous secreting cells [Foregut Fermentation ("grass eaters") RUMINANTS ONLY] Ruminants have 4 chambers in stomach Specialised stomach for cellulose digestion by commensal bacteria Break down cellulose into polysaccharides using 'cellulase enzyme' Structure of Ruminants stomach: - 4 Chambers - Rumen -- received food, holding and fermentation vat, food can be regurgitated, remasticated and reswallowed, distinct papillate mucosa - Reticulum -- Small chamber, 'honeycomb' mucosa, contract to slosh chyme between itself and rumen - Omasum -- epithelium folded into laminae, pumps food into abomasum - Abomasum -- distinctive simple columnar, glandular epithelium, enzymatic digestion, highly acidic [Ruminoreticula Groove:] Ingesting of milk: fermentation is necessary Milk bypasses rumen through this Closes into connecting oesophagus to omasum [Liver and Gall bladder (accessory glands):] - Liver produces and secrete bile - Stored and concentrated in Gall bladder - Bile is not the same as digestive enzymes - Liver has 4 anatomical lobes: right and left lobe, quadrate lobe and caudate lobe - Gall bladder lined by simple columnar epithelium - Call bladder is a pear-shaped sac under right lobe of liver - Gall bladder release bile into duodenum during meals - Gall bladder is not present in horse, rats, dear and llamas [Pancreas] Produces most of the digestive enzymes in small intestines - Proteolytic enzymes e.g. trypsin, carboxypeptidase - Nucleic acid enzymes, digest DNA + RNA - Pancreatic amylase for polysaccharide digestion [Small intestine ] Chemical digestion: Pancreatic juice, Bile and interstitial juice Absorption: Proteins, Fats and Carbohydrates [Duodenum:] - C-shaped, encircles the pancreas - Contains Brunner glands which secrete alkaline mucus [Jejunoileum] - Microvilli are lined with membrane bound enzymes for final breakdown of nutrients for absorbable constituents - E.g. Disaccharide monosaccharides, peptide chains amino acids, DNA nucleic bases - Mucosa of small intestine is highly folded - Mucosa lined with villi - Villi possessed microvilli - All these adaptations increase surface area [Colon / Large Intestine ] (Food moves in this direction) 1. Caecum 2. Ascending colon 3. Transverse colon 4. Descending colon 5. Sigmoid colon 6. Rectum [Midgut Fermentation] - Cellulose digestion by commensal bacteria in the ascending colon - Only in Grass eaters - Animals have simple single chambered stomachs - Smooth mucosa (no villi) - Fermentation of complex carbohydrates - Absorption of salts + water - Excretion of faeces [Rectum + Anus ] - Pelvic part of GI tract - Supports and stores faecal mass before defection - Build up pressure against walls - Internal sphincter relaxes to open and allow faeces into canal - Relaxation of internal sphincter permits defecation Gut functions -- Motility, Secretion, Digestion, Absorption, Storage [Gut Control] - Intrinsic - Neuronal - Enteric nervous system - Hormonal - Secretin, Gastrin, CCK, GIP, Motilin - Extrinsic - Neuronal - Vagus and Splanchnic nerves - Hormonal - Aldosterone [The Tract ] Myenteric plexus -- Regulates motility and muscle action (parasympathetic and sympathetic) Submucosal plexus -- Regulates local fluid and hormone release (parasympathetic only) Layers of the tract: (inner to outer) 1. Mucosa 2. Submucosa 3. Tunica muscularis 4. Serosa / Adventitia [Luminal Receptors] Mechanoreceptors -- detect stretch and stimulate contractions Chemoreceptors -- sense chemical composition of the chyme and regulate pH Osmoreceptors -- sense osmolarity and control motility and secretion \*Digestive secretions and motility increase with parasympathetic and decrease with sympathetic nervous systems. [Hormonal Signalling:] "-crine" = Secrete Endocrine = into blood Neurocrine. = Secreted by nerves Paracrine = Secreted by adjacent cells Autocrine = Secreted by self Gut endocrine cells = columnar epithelial: Narrow apex -- sensory, Wide base -- secretory (Apex is exposed to gut lumen) [Phases of Digestion:] [Cephalic Phase:] Salivation, stimulated by parasympathetic innervation (cranial nerves). Increased blood flow to glands. Brainstem regulates visual or olfactory salivation. [Gastric Phase:] Acid and enzyme production and secretion. Sphincter is relaxed as well as stomach and duodenum to accommodate chyme Stimulation of acid: Gastrin produced by duodenum, stomach and pancreas \*Increases acid, pepsinogen secretion Parasympathetic stimulation: - Presence of amino acids - Stomach distension Stimulation of Bile: Secretin - produces which stimulates bile and prevents acid secretion Cholecystokinin - stimulates bile and pancreatic secretion Parasympathetic chain: - Acidity in duodenum - Fat and protein in duodenum [Intestinal Phase:] Stimulation of motility Motilia -- increased motility / peristalsis in the gut, 'clears' tract between meals Cholecystokinin --decreases gastric emptying [Hunger and Satiety:] Hypothalamus - Ventro Medial area = "satiety centre" - Lateral area = "appetite centre" Low blood sugar sensory input appetite stimulated Ghrelin -- "hunger hormone" - Stimulated by empty stomach - Released by stomach and pancreas - Stimulates hunger Leptin -- "satiety hormone" - Oppose action of Ghrelin - Produces by adipocytes - Crosses blood brain barrier to reach hypothalamus [Satiety Hormones ] Cholecystokinin, Peptide YY, Glucagon-like Peptide 1 (GLP-1) GLP-1: \*Secreted by gut cells and neurons Increases - Insulin (Duodenum) Decreases -- Glucagon (Duodenum), GI motility (Stomach), gastric emptying (Stomach), food and water intake (Hypothalamus) [Pancreatic Endocrine cells:] Islet of Langerhans: A cells (Glucagon) -- Secreted when blood glucose falls, triggers breakdown of glycogen into glucose in the liver B cells (Insulin) -- Secreted when blood glucose is high, triggers storage of glucose in liver, skeletal muscle, and fat cells D cells (Somatostatin) -- Secretion induced by low pH and supresses the release of hormone from A and B cells, inhibits gut motility and exocrine secretion [Obesity:] BMI over 25 = overweight BMI over 30 = obese BMI under 18.5 = underweight Ideal BMI = 18.5-24.9 BMI = Weight (kg) / Height ^2^ (m) Alternatives to measure BMI include: Waist circumference, Waist-to-Hip ratio, Skinfold thickness, Bioelectrical impedance, MRI or DEXA [Drugs:] Orlistat -- Inhibits pancreatic and gastric lipases, prevents around 1/3 of fat from food being absorbed Semaglutide (diabetes medication) -- Binds to and activates GLP-1 receptor [Bariatric Surgery:] Restrictive (Reduces stomach size and dietary intake) Malabsorptive (bypassing the stomach and small intestine) - Gastric band -- restrict amount you eat - Gastric bypass (Roux-en-Y) - bypasses stomach and duodenum by attaching jejunum to gastric pouch so food is not absorbed at stomach