Human Digestion and Absorption Chapter 4.
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Transcript of Human Digestion and Absorption Chapter 4.
Mouth (Oral Cavity)
• Chewing increases surface area• Mixed with saliva food becomes a bolus• Saliva
– Lysozyme• Breaks down bacteria
– Mucus• Lubricates and hold bolus together
– Amylase• Breaks down starch
– Enhances perception of flavor
Taste and Smell
• Taste buds – contain receptors– Salty– Sour– Sweet – Bitter– Umami
• Olfactory cells in nose (smell)– Stimulated with chewing
Stomach Secretions• Parietal Cells
– Hydrochloric Acid• Inactivates proteins• Destroys bacteria and viruses• Dissolves minerals to aid in absorption• Converts pepsinogen into pepsin
– Pepsinogen• Protein digesting enzyme
• Gastrin– Hormone that controls release of HCl and pepsinogen
Other Stomach Secretions
• Chief cells– Gastric lipase
• Mucus– Protects the stomach from being digested– Production relies on prostaglandins
Small Intestine• Most digestion and absorption occurs here• Pyloric sphincter allows chyme into the
small intestine– Gastric inhibitory peptide (hormone) slows
release of chyme• Sections
– Duodenum, jejunum and ileum
Small Intestine (2)
• Circular folds• Villi – lined with:
– Goblet cells - make mucus– Endocrine cells - produce hormones– Enterocytes - produce digestive enzymes and
absorb nutrients• Contain a brush border of microvilli covered with
glycocalyx
Liver, Gallbladder and Pancreas
• Liver– Provides bile– Enterohepatic circulation (recycling of bile)
• Gallbladder– Bile storage
• Pancreas– Produces sodium bicarbonate, lipases, proteases
and pancreatic amylase
Gallstones are the most common cause of pancreatitis in the US and accounts
for 35–50% of all cases. Despite aggressive and intensive early
management, the mortality rate is approximately 10%. Obstruction of the major papilla by the stone causes reflux
of bile into the pancreatic duct.
Hormones of the GI Tract
• Gastrin– Stomach release of HCl and pepsinogen
• Cholescystokinin (CCK)– Release of bile
• Secretin– Release of pancreatic bicarbonate
• Gastric Inhibitory Peptide– Limits release of gastric juices
Absorption
• Primarily occurs in small intestine• Passive diffusion
– Concentration gradient• Facilitated diffusion
– Concentration gradient + carrier protein• Active
– Carrier protein + energy (regardless of concentration)• Endocytosis
– Engulfment of compounds or liquids
Moving Nutrients around the Body
• Blood– Water-soluble
nutrients transported via capillaries in villi to portal vein to liver
• Lymphatic System– Fat-soluble nutrients transported via lacteals
into the lymph vessels to thoracic duct
Large Intestine
• Ileocecal valve• Colon
– Cecum, ascending colon, transverse colon, descending colon and sigmoid colon
• Rectum• Anus
Functions of Large Intestine
• Absorption of water and electrolytes• Formation and expulsion of feces• Housing of bacteria (microbiota)
Microbiota (bacterial flora)• Beneficial bacteria
– Control pathogenic bacteria– Synthesize Vitamin K and Biotin– Aid dig and fermentation of fibers
• Probiotics– Live bacteria in food & supplements– Health benefits
• Prebiotics– Non digestible carbohydrates in food that promote the
growth of bacteria-– E.g. inulin, resistant starch
When Digestive Processes Go Awry
• Heartburn and Gastroesphogeal reflux disease (GERD)– Foods that increase reflux:
• Citrus, caffeine, chocolate, fatty foods, spicy foods, onion, garlic and tomato based foods
• (Peptic) Ulcers– Causes: H. pylori and NSAID medications– Treatment:
• Medications • Avoid foods that increase symptoms
When Digestive Processes Go Awry (2)
• Food Intolerances• Intestinal Gas
(Flatulence)• Constipation
– Fiber, fluid and exercise
– Laxative use
• Diarrhea– Replace fluid and
electrolytes
• Irritable Bowel Syndrome (IBS)– Cause unknown
• Inflammatory Bowel Disease (IBD)– Ulcerative colitis and Crohn’s disease
• Hemorrhoids• Gallstones
Celiac Disease
• Intolerance to gluten• 1 in 133 people affected
– Many undiagnosed
• Can affect many body systems– GI and others
• Gluten-free diet for life– Corn, rice, quinoa, and buckwheat OK