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Food Intake and Digestion Will Brown Lecture 3. Questions? Does everyone have a lab manual? Reminder: Lab worksheets due Thursday at 7PM Any questions.

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Presentation on theme: "Food Intake and Digestion Will Brown Lecture 3. Questions? Does everyone have a lab manual? Reminder: Lab worksheets due Thursday at 7PM Any questions."— Presentation transcript:

1 Food Intake and Digestion Will Brown Lecture 3

2 Questions? Does everyone have a lab manual? Reminder: Lab worksheets due Thursday at 7PM Any questions for me? – Subject material – Logistics – Testing/Grading

3 Objectives and Content Objective: Outline the process of digestion and the major organs and tissues involved Content – “Eat this: not that!” – Digestive system Anatomy and physiology of digestive tract Common digestive issues

4 Which should you eat? Nutrition Facts Serving Size: 2 cups popped 70 cal 4 g fat (2 g saturated) 50 mg Sodium Nutrition Facts Serving Size: 2 cups popped 80 cal 3.5 g fat (0.5 g saturated, 1.5 trans) 40 mg Sodium

5 McDonald’s: Which one? McDopnald’s Big N’ Tasty Nutrition Facts Serving Size: One burger 460 cal 24 g fat (8 g saturated; 1.5g trans) 720 mg Sodium Nutrition Facts Serving Size: One sandwich 530 cal 20 g fat (3.5 g saturated) 1150 mg Sodium

6 Starbucks: Which one? Venti Caramel Cappuccino Venti Caramel Latte Nutrition Facts 180 cal 4 g fat (2.5 g saturated) 18 g Sugar Nutrition Facts 1320 cal 8 g fat (5 g saturated) 43 g Sugar

7 Digestive System: Overview In order to be used, food must be extensively altered for the human body to use This process has 2 parts – Digestion – the breakdown of food; both mechanical and chemical – Absorption – The uptake of nutrients from the intestine Takes place in the Gastrointestinal (GI) tract – A long tube that stretches from mouth to anus

8 Digestive system: Overview Mechanical Digestion – Physical breakdown of food – Chewing – Peristalsis – muscle contractions along the GI tract that move and mix food (process called motility) Chemical Digestion – The breakdown of food by chemicals secreted by the GI tract – Stomach acid – Pepsin

9 Digestive Tract: Overview Involved in waste elimination Houses commensal bacteria – Vitamin K – Biotin Most processes under autonomic control – Nervous system – Endocrine system


11 Mouth Responsible for primary mechanical digestion – Teeth – Tongue – to a lesser degree Taste – allows for sensation of flavors – 5 main flavor components: salty, sweet, bitter, sour and umami; taste buds on tongue – Nose is highly involved in taste sensation Volatile compounds reach the nasal passages – Signals rest of GI to prepare for food

12 Mouth Produces Saliva via the salivary glands – Provides lubrication – Acts as a solvent Produces mucus – Lubricates food and surfaces of GI tract Produces Salivary Amylase – Enzyme that begins the breakdown of starch

13 Enzymes: A slight digression Follow “Lock and Key” model – An enzyme only acts on one substrate – Lactase only digests lactose (milk sugar) Enzymes are diffusion rate limited Sensitive to pH – Stomach is acidic, small intestine is alkaline – Enzymes designed to work in acidic pH do not work so well in basic conditions


15 Esophagus Connects the pharynx (the back of the mouth) to the stomach The epiglottis covers the trachea when food is swallowed Peristalsis begins at the top of esophagus

16 Esophagus Esophageal sphincter – muscle at the end of esophagus that prevents stomach contents from entering the esophagus – There are numerous sphincters along the GI; all prevent flow of contents from going backwards The reason for “heartburn” is stomach contents in the esophagus

17 Stomach Large sac at the end of the esophagus Holds ~1 quart of food – This can be different for each person; depends on genetics and diet Once in the stomach, food mixes with gastric juice – Maintains acidic environment of stomach – Destroys biological activity of foreign enzymes – Activates stomach enzymes – Makes minerals soluble Release of chyme into small intestine is about 1 tsp at a time

18 Anatomy of Stomach

19 Physiology of Stomach Mucous producing cells produce mucous that coats the entire stomach and prevents self- digestion Parietal cells produce hydrochloric acid Chief cells produce digestive enzymes Releases gastrin (a hormone) in order to control release of other digestive enzymes and acid Releases intrinsic factor – required for vitamin B- 12 absorption Can absorb alcohol

20 Small Intestine Pyloric sphincter joins stomach and small intestine 3 parts of the SI are the duodenum, jejunum and ileum ~ 10 ft long Called small because of narrow diameter; 1 in More peristalsis to mix food with digestive juices – Enzymes to breakdown carbohydrates, protein, and fat – Prepares vitamins and minerals for absorption  Gastric = stomach; digestive = small intestine

21 Small intestine Lining folded numerous times – creates villi Villi are fingerlike projects – Trap food as it moves to enhance absorption – Covered with absorptive cells that have a highly folded cap called microvilli – Creates a surface area 600 times greater than if it were a normal tube


23 Absorptive cells Responsible for transporting nutrients and digestive food across the intestinal barrier and into the body Short lived – rapidly turned over and renewed Dead cells are sloughed off, digested and reabsorped Have a highly folded cap, called microvilli, further increases surface area of SI

24 Absorption Passive diffusion – Higher concentration in lumen than in body so nutrients move with a gradient – Fats, water, some minerals – No energy required Facilitated diffusion – Compounds require carrier to assist in diffusion – Fructose – No energy required

25 Absorption Active absorption – Nutrients in low concentration in lumen are taken up into the body, usually with carrier – Glucose, and amino acids – Requires energy input Phagocytosis/pinocytosis – Cell membrane creates a fold that closes off to create a vessicle which can move things from lumen to dorsal side of cell – Phago=eat or devour; pino=sip or drink – In infants, Immune substances from mothers milk – Requires energy; highest energy requirements

26 Absorption Water soluble compounds enter blood stream via capillaries – Glucose – Amino acid – Most vitamins – Some minerals Fat and fat soluble compounds enter the lymph system and then enter the blood stream later Once absorbed into the blood, goes directly to the liver – Hepatic portal – Detoxifies blood – If pregnant, then heads directly to uterus

27 Large Intestine Transition from SI to LI is called the ileocecal sphincter – prevents LI contents from re-entering the SI Very little nutrient absorption occurs in LI Anatomically different from SI – No villi – No digestive enzymes – High number of mucous producing cells Mucous protects LI from bacteria and helps hold feces together

28 Large Intestine Nutrients absorption does occur – Water - ~10-30% of total – Some fatty acids – Sodium and potassium – Some vitamins Houses numerous commensal bacteria – Most are beneficial – probiotic – Recent studies have demonstrated that there are over 2000 types of bacteria that can live in the LI Most people have between 200-500 different species – After birth the colon is rapidly colonized; usually from the mother – Another term to know – prebiotic; substances that help probiotics grow


30 Rectum and Anus Last portion of LI Feces held in rectum until pushed into the anus for elimination The anus contains 2 sphincters – Internal anal sphincter – autonomic control – External anal sphincter – voluntarily controlled

31 Accessory organs Not part of GI tract but play important role in aiding digestion Gall Bladder – Houses bile (which is made in the liver) – Bile release under hormone control Released due to presence of fat in stomach – Bile acts as “soap” to emulsify fat for absorption – Components of bile can be recirculated and reused – process known as enterohepatic circulation – Bile can also house substances for excretion that are to large to exit via the kidneys


33 Accessory organs Pancreas – Makes hormones and pancreatic juices – Hormones: insulin and glucagon; both act on blood sugar levels – Pancreatic juices: bicarbonate, water, and digestive enzymes Bicarbonate is a basic substance that neutralizes acidity of chyme as it moves from stomach to SI Important because not as much mucous in SI compared to stomach; low pH would cause ulceration of SI Liver: makes bile and cleans blood after absorption

34 Digestion Review Mouth Esophagus - ~10 in Stomach – Holds ~1 quart – Food held 2-4 hours Small Intestine – 3-10 hours – Duodenum – 10” long – Jejunum – 4’ long – Ileum – 5’ long Large intestine – up to 72 hours – 3.5 ft long – Cecum, ascending, transverse, descending, and sigmoid colon

35 OrganFunction Mouth & Salivary Gland Chew food; Perceive taste; Moisten food with Saliva; Lubricate food w/ Mucous; Release starch via salivary amylase; Initiate swallowing reflex EsophagusLubricate w/ mucous; Move food to stomach via peristalsis StomachStore, mix, digest; kill microorganisms w/ acid; Release protein digesting enzymes(pepsin); Lubricate & protect stomach w/ mucous; Regulate emptying into SI; Produce intrinsic factor for B-12 absorption Liver`Produce bile to aid in fat digestion and absorption GallbladderStore, concentrate and release bile into SI PancreasSecrete Na bicarbonate and enzymes for digesting carbs, fat & protein Small IntestineMix and propel contents; Lubricate w/ mucous; Digest and absorb Large IntestineMix and propel contents; Absorb Na, K, and water; House commensal bacteria; lubricate w/ mucous; Synthesize some vitamins and short-chain fatty acids; Form feces RectumHold feces and expel via anus From Figure 3-10 pg 97

36 Important Secretions and Products of GI SecretionSite of ProductionPurpose SalivaMouthPartial starch digestion,lubrication MucousMouth, stomach, SI, LIProtects GI tract; lubricates food EnzymesMouth, stomach, SI and Pancreas Promotes digestion so nutrients are small enough for digestion AcidStomachPromotes digestion; other functions BileLiver (stored in gall bladder)Aids in fat digestion in SI by solubilizing fat in water using bile acids, cholesterol, and lecithin BicarbonatePancreas and SINeutralizes stomach acid in SI HormonesStomach, SI, and pancreasStimulate production/release of acid, enzymes, bile, and bicarbonate. Helps regulate peristalsis and overall GI tract flow Table 3-3 pg.99

37 Common Digestive Issues Lactose intolerance – inability to digest lactose (milk sugar); More on this in carbohydrate lecture Diverticulosis – Inflammation of intestinal tract; more on this in carbohydrate lecture

38 Common Digestive Issues: Ulcers Erosion of stomach lining, esophagus, or duodenum Loss of protective mucous layer In younger people, primarily in SI; older is stomach Millions will develop ulcers sometime in their life resulting in lots of health care $ spent Symptoms include pain ~2 hours after eating Causes; originally thought to be caused by high stomach acid – H. pylori infection found in 80% of ulcers – Stress – Smoking is a complicating factor Treatments – Antibiotics for H. pylori – Proton pump inhibitors (Prilosec, Nexium, and Prevacid) block acid formation – H 2 blockers (Tagamet, Zantac, and Axid) block histamine related acid secretion – Reduce smoking – Limit use of NSAIDs

39 Common Digestive Issues: Heartburn ~50% of Americans experience heart burn occasionally AKA: acid reflux Recurrent form called gastroesophageal reflux disease (GERD) Esophagus has limited mucous protection so easily eroded causing pain Symptoms-For GERD must occur >2 times/week – Pain – Coughing – Nausea Long term untreated GERD can lead to Barrett’s Esophagus Treatments – OTC antacids – short term quick releif – Proton pump inhibitors (Prilosec, Nexium, and Prevacid) block acid formation – H 2 blockers (Tagamet, Zantac, and Axid) block histamine related acid secretion

40 Common Digestive Issues: Constipation Difficult or infrequent evacuation of bowels Common causes – Ignoring “urges” for prolonged periods – LI muscle spasms – Ca and Fe supplements – Medications and antacids Treatments – High fiber foods and plenty of water; good for mild constipation – Develop more regular bowel habits – Laxatives

41 Common Digestive Issues: Irritable Bowel Syndrome Not to be confused with IBD (Inflammatory Bowel Disease) ~25 million adults report IBS symptoms – Cramps and pain – Gassiness and abdominal distention – Bloating – Irregular bowel function – diarrhea, constipation or both, mucous in feces Worth noting that 50% of IBS patients report some type of abuse – verbal or sexual are the most common Treatments – very individualized – High fiber foods – Elimination diets which focus on dairy, caffeine and gas-forming foods – Herbal supplements – Probiotics – Low fat diet and more frequent small meals Aside from discomfort and upset there are no other health concerns

42 Common Digestive Issues: Diarrhea Usually lasts a few days Symptoms – Very loose or liquid stool – Increased frequency of bowel movements Causes – Usually infection in intestine – mostly due to bacteria or virus – Less common is consumption of foods not readily absorbed – sorbitol or very high fiber foods such as bran Treatment – Lots of fluids during affected stage – first 24 to 48 hours Important for those at high risk of dehydration – infants & elderly – If lasting longer than 7 days – seek medical help

43 Common Digestive Issues: Gallstones Affects 10-20% of adults in US Results from formation of solid crystal particles of bile that form in gallbladder Causes – Excess weight – especially in women – Genetic background – Native Americans have increased risk – Advanced age - >60 years – Reduced gallbladder activity – reduced contraction – Altered bile composition – Diabetes – Diet – low fiber food – Rapid weight loss or prolonged fasting

44 Common Digestive Issues: Gallstones Symptoms – Pain in upper right abdomen – Gas – Bloating – Nausea and/or vomitting Treatment – surgical removal of gallbladder is most common Prevention – Avoid becoming overweight – especially for women – Avoid rapid weight loss - >3lbs/week – ↓ animal protein and ↑ plant protein; ie: nuts – High fiber diet

45 Less Common Digestive Disorders Cystic Fibrosis – Inherited disease caused by overproduction of mucous – Usually affects upper respiratory tract – Pancreas produces thick mucous that blocks ducts which causes cell death – result is ↓digestive enzymes Celiac disease – Allergic reaction to gluten Gluten is common in certain cereals like wheat and rye – Damages Absorptive cells reducing surface area in SI – Removing gluten from diet usually results in amelioration of disease

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