DIGESTIVE PHYSIOLOGY Mastication – the act of chewing Deglutition- the act of swallowing Bolus- a mass of chewed food Peristalsis- involuntary contractions of smooth muscle to propel food through GI tract Chyme: yellow fluid which leaves stomach for duodenum – consists of partially digested food and secretions

Chemical vs mechanical digestion a) mechanical – chewing, mixing, churning b) chemical – adding water via enzymes = H Y D R O L Y S I S (see handout)

Organic molecules (food) A)Carbohydrates (C H 2 O) -sugars, fibers, sweeteners 1) polysaccharides – cellulose(fiber), starch 2) disaccharides sucrose, lactose, maltose 3) monosaccharides glucose, fructose, galactose *you can only absorb monosaccharides

B)Proteins (C H O N) all proteins are polypeptides composed of combinations of 20 types of amino acids *you only absorb amino acids

C)Lipids (CHO) fats, oils, cholesterol, waxes, some steroids 1) triglycerides – common food lipid composed of 3 fatty acids + glycerol 2) phospholipids – cell membranes composed of 2 FA, glycerol, phosphate *You can only absorb fatty acids, glycerol, etc

FOOD LABEL BASICS 1)Calories = kilocalories # grams X 4(carbs,proteins) or 9 (lipids) 2) Vitamins a)water soluble - B, C, b) fat soluble – A D E K 3) Minerals – think periodic table – needed in trace amounts – Ca, K, Fe, etc

Enzymes of Digestion A)Mouth (saliva) 1)salivary amylase- targets starches- results in smaller saccharides and disaccharides 2) Lipase – minimal effect? –targets lipids

B) Stomach- enzymes produced by “chief cells “ in gastric pits- 1) Pepsin –targets proteins- results in smaller peptide chains 2) Lipase – minimal effect?- targets lipids * HCl is produced by “parietal cells” in gastric pits

C) Pancreas - enzymes are produced by acini (acinar cells) 1) protease – targets proteins – results in smaller peptides 2) lipase – targets lipids – most effective *enters small intestine with bile

Pancreas (continued) 3) Amylase – targets carbohydrates – results in disaccharides

D) Small intestine brush border (duodenum) 1) Peptidase – targets peptides(protein) – finalizes their breakdown to amino acids 2) Amylases (specific) a)sucrase – targets sucrose – results in one glucose and one fructose b)lactase-targets lactose-results in one glucose and one galactose

Sm. Int. (continued) c)maltase – targets maltose – results in two glucose

B I L E Bile emulsifies lipids (forces them into water soluble droplets) so that they can be more readily hydrolyzed Bile is not an enzyme or hormone. Bile is made by the liver, stored in the gall bladder Bile consists of cholesterol, pigments *, bile salts, water

Absorption of nutrients A)Proteins 1) absorbed as amino acids 2) enter into capillaries of villi then to the liver via the hepatic portal vein 3) amino acids can be converted to monosaccharides or fatty acids upon removal of the amine (NH2) group (see handout)

B)Carbohydrates 1) absorbed as monosaccharides 2) enter into capillaries of villi, then to liver via hepatic portal vein 3) can be converted to fatty acids or even some amino acids

C)Lipids 1) absorbed as fatty acids/glycerol 2) absorbed into lymph in lacteals (usually in ileum)and enter blood stream near heart 3) Must be transported in blood as lipoproteins – why? 4) can be converted to some amino acids or even monosaccharides in the liver

LDL vs HDL LDL (low density lipoprotein) -Mainly travel from liver to body cells- especially adipose cells -contain a lot of lipid and little protein - can leave deposits in blood vessels * known as bad cholesterol*

HDL (high density lipoprotein) -Mainly travel from cells back to liver -contain a lot of protein and little lipid - can pick up deposits in vessels - the liver often excretes these lipids as part of the bile ***known as good cholesterol***

Assorted terms a)Diarrhea - too much water lost in feces b)Constipation – too little water in feces

Diabetes 1.Insulin – decreases blood glucose levels “tells” cells to take glucose from blood Glucagon – increases blood glucose levels “tells” liver to break down glycogen stores

2.Pancreatic Islets of Langerhans Beta cells- insulin Alpha cells – glucagon

Early signs of Diabetes 3.a) frequent urination b)dehydration c) acidosis (low blood pH) from metabolizing fatty acids—fruity breath type I d)thirst

4. Type I - IDDM- 20% insulin dependent diabetes mellitus a) destruction/loss of beta cells

5.Type II – DM (NIDDM) – 80% non-insulin dependent diabetes mellitus a) cells don’t respond effectively to insulin b) can lead to type I

Prolonged diabetes 6.a) necrosis –tissue death b) cardiovascular disease c)retinal degeneration d)loss of nerve function e)kidney damage f) serious infections

7.Pancreas a) endocrine gland – produces hormones – Islets (Islets of Langerhans) are cells to produce pancreatic hormones- 1% of pancreatic cells insulin, glucagon

b) exocrine gland- releases products to ducts- acini are cell clusters to produce digestive enzymes – 99% of pancreatic cells protease, lipase, amylase