Digestive System

6 Processes of Digestion Ingestion Mechanical Digestion Chewing, swallowing Peristalsis Segmentation Chemical Digestion Enzymes breaking chemical bonds Secretion Goblet cells secreting mucus Organs secreting enzymes Absorption Nutrients pass into blood stream Defecation Removal of solid waste Ingestion Food Mechanical digestion Pharynx • Chewing (mouth) Esophagus • Churning (stomach) Propulsion • Segmentation (small intestine) • Swallowing (oropharynx) Chemical • Peristalsis (esophagus, stomach, small intestine, large intestine) digestion Stomach Absorption Lymph vessel Small intestine Blood vessel Large intestine Mainly H2O Feces Defecation Anus

Digestive System in Action Salivary glands Digestive System in Action Accessory Organs to S. Intestines stomach Small Intestine Blood stream Large Intestine

Histology of Digestive Tract Stratified squamous Mouth, pharynx & esophagus Simple Columnar Stomach thru L.I. Goblet cells Villi Microvilli

Mouth Main Functions Ingestion Physical digestion Chemical digestion Tongue, teeth Chemical digestion Saliva and salivary glands

Accessory Organs of Mouth Tongue Taste buds Responsible for gripping food Mixes food with saliva Initiates swallowing Bolus

Peristalsis vs. Segmentation From mouth (a) Peristalsis: Adjacent segments of alimentary tract organs alternately contract and relax, which moves food along the tract distally. (b) Segmentation: Nonadjacent segments of alimentary tract organs alternately contract and relax, moving the food forward then backward. Food mixing and slow food propulsion occurs.

Salivary Glands Parotid, submandibular and sublingual Functions Produce saliva 99% water Contains enzyme amylase Mucin – forms mucus Growth Factor Functions of Saliva Cleanses mouth Growth factor and lysosomes Dissolves food for taste Moistens food; creates bolus Enzyme amylase begins the chemical digestion of starch A C B

Amylase Starch (polysaccharide) disaccharides maltose

Pharynx and Esophagus 1 Pharynx Esophagus 2 = epiglottis 4 Pharynx Back of throat Passage way for food Esophagus Food chute Stratified squamous tissue 2 = epiglottis

Stomach Four Primary Functions Temporary storage tank for food Mechanically break down food Food is converted into creamy paste called chyme Chemical breakdown of protein begins Production of intrinsic factor; necessary for absorbing Vitamin B12.

Regions of the Stomach Cardiac region Fundus Body Upper area around cardiac sphincter Fundus Dome-shaped part of stomach Body Pylorus- inferior portion Pyloric sphincter: controls the emptying of the stomach into the S.I.

Stomach Physiology Rugae Peristalsis Controlled by pacemaker cells Becomes more forceful closer to the pyloric region

Gastric Wall Gastric Pit Gastric gland Secretes mucus and enzyme pepsinogen Parietal cells Secrete HCl and instrinsic factor HCl is needed to convert pepsinogen into pepsin Kills bacteria that is ingested with food Rennin Chief cells – produce pepsinogen; inactive form of pepsin Gastric Wall

Converting Pepsinogen to Pepsin HCl Mitochondria Parietal cell Chief cell Enteroendocrine cell (c) Location of the HCl-producing parietal cells and pepsin-secreting chief cells in a gastric gland

Regulation of Gastric Activity Cephalic phase prepares stomach to receive food Sight, smell, taste of food Controlled by vagus nerve and parasympathetic system Only lasts a short time

2. Gastric Phase Stimulation of stretch receptors and chemoreceptors stimulate the release of hormone gastrin Gastrin causes release of HCl and pepsinogen Increase in stomach contraction intensity Small amounts of caffeine and alcohol stimulate chemoreceptors causing an increase in gastric secretions

3. Intestinal phase Begins when food starts to enter S.I. Controls the rate of gastric emptying Slows down gastric activities by releasing three hormones Cholecystokinin (CCK) Secretin Gastric inhibitory peptide (GIP)

Small Intestine Digesting & Absorbing Organ Anatomy Consists of 3 sections Duodenum Jejunum Ileum ileocecal spincter: controls flow into colon Mesentary

Modifications for Absorption Folds Mixes chyme and slows down movement Villi Fingerlike projections increases surface area Microvilli

Lining of Small Intestine

Regulation with Intestinal Hormones Secretin: released when pH falls in duodenum (Why would this happen?) Result: causes water and buffers to be secreted into S.I. by pancreas Cholecystokinin (CCK): secreted when protein and lipid dense chyme arrives in S.I. Result: increases the secretion of digestive enzymes from the pancreas and bile from the liver Gastric Inhibitory Peptide (GIP): released when food begins to enter S.I. Result: inhibit digestive activity in stomach; causes release of insulin from pancreas

Chyme enter- Bile salts and, to a lesser extent, ing duodenum causes release of cholecystokinin (CCK) and secretin from duodenal cells. 1 Bile salts and, to a lesser extent, secretin transported via bloodstream stimulate liver to produce bile more rapidly. 4 CCK (via bloodstream) causes gallbladder to contract ; bile enters duodenum. 5 CCK (red dots) and secretin (yellow dots) enter the bloodstream. 2 CCK induces secretion of enzyme-rich pancreatic juice. Secretin causes HCO3–-rich 3 During cephalic and gastric phases, vagal nerve stimulation causes weak contractions of gallbladder. 6

Organs affected by digestive hormones

Chemical Digestion Brush Border Enzymes Intestinal juice is water, mucus and enzymes Sucrase Lactase Maltase Peptidases/proteases

Lactose Intolerance

Functions of Small Intestine Segmentation: movement of food through S.I.; moves very slowly so chemical digestion can occur Chemical Digestion: Very few Enzymes come from S.I. Need assistance from accessory organs Absorption: the building blocks of food are passed into blood stream by Active Transport Most absorption is completed b4 it reaches the ileum Ilieum’s main function is to return bile salts to liver Mesentary

Accessory Organs: Pancreas Endocrine Gland Produces hormones Exocrine Gland Produces digestive enzymes Empties into duodenum

Pancreatic duct fuses with Common bile duct and enters the duodenum

Pancreatic Secretions Secretes (Exocrine Gland) Bicarbonate ions (NaHCO3-); turns acidic chyme from stomach into basic solution (ph 7-8) Enzymes Trypsinogen (inactive form) Amylase Lipase Nucleases

Conversion of Trypsinogen into Trypsin Increase in pH from bicarbonate ions and another enzymes converts trypsinogen into its active form trypsin Trypsin is a protease and continues protein digestion

Digestion of Lipids Lipase breaks down lipids into fatty acids and glycerol. Fatty acids and glycerol can then be absorbed into the blood stream Bile assists in this process by physically breaking down fats into smaller droplets.

Pancreas Secretions Endocrine Gland Islets of Langerhans are specialized cells Responsible for secreting 2 hormones Glucagon Insulin

Anatomy of Liver and gall bladder Hepatic duct allows bile to leave the liver Gall Bladder Lies under liver; appears like a slightly inflated green balloon Stores bile Bile leaves the liver via the cystic duct Cystic duct and hepatic duct join to make Common Bile Duct.

Functions Bile Production Only digestive process Physically separates fats into smaller droplets; allows lipase to digest faster (Remember fats don’t dissolve in water) I.e. scatters fat droplets throughout solution

Functions of liver Metabolic Regulation Processes all nutrients absorbed into blood Helps regulate cholesterol levels Forms nonessential amino acids; byproduct is ammonia (toxic) Converts ammonia into urea (less toxic) Stores glucose as glycogen (polysaccharide) Stores fat soluble vitamins (A,D,E,K) Detoxifies alcohol and drugs (both legal and illegal) Blood leaving liver has fewer waste products than the blood that enters it.

Functions Continued... Assists in Regulating Blood Produces plasma proteins Conserves iron from old RBC’s

Problems with the Liver Cirrhosis Chronic inflammation of liver Results from severe alcoholism or chronic sever hepatitis Liver cells die are replaced scar tissue and fat deposits. Hepatitis Inflammation of liver Caused by a virus, sewage contaminated water or feces-mouth

Gall Stones Cholesterol in Bile salts crystallize; Gets stuck in duct; causes extreme pain

Chemical Digestion and Absorption of Proteins Protein digestion Enzyme(s) and source Site of action Foodstuff Path of absorption • Amino acids are absorbed by cotransport with sodium ions. Protein Pepsin (stomach glands) in presence of HCl Stomach • Some dipeptides and tripeptides are absorbed via cotransport with H+ and hydrolyzed to amino acids within the cells. Large polypeptides Pancreatic enzymes (trypsin, chymotrypsin, carboxypeptidase) Small intestine + Small polypeptides, small peptides • Amino acids leave the epithelial cells by facilitated diffusion, enter the capillary blood in the villi, and are transported to the liver via the hepatic portal vein. Brush border enzymes (peptidases, proteases) Small intestine Amino acids (some dipeptides and tripeptides)

Chemical Digestion and Absorption of Carbohydrates Carbohydrate digestion Enzyme(s) and source Site of action Foodstuff Path of absorption • Glucose and galactose are absorbed via cotransport with sodium ions. Starch and disaccharides Salivary amylase Mouth • Fructose passes via facilitated diffusion. Pancreatic amylase Small intestine Oligosaccharides and disaccharides • All monosaccharides leave the epithelial cells via facilitated diffusion, enter the capillary blood in the villi, and are transported to the liver via the hepatic portal vein. Brush border enzymes in small intestine (lactase,maltase and sucrase) Small intestine Lactose Maltose Sucrose Galactose Glucose Fructose

Chemical Digestion and Absorption of Fats Fat digestion Enzyme(s) and source Site of action Foodstuff Path of absorption Unemulsified fats • Fatty acids and monoglycerides enter the intestinal cells via diffusion. Emulsification by the detergent action of bile salts ducted in from the liver Small intestine • Fatty acids and monoglycerides are recombined to form triglycerides and then combined with other lipids and proteins within the cells. Pancreatic lipases Small intestine Monoglycerides and fatty acids Glycerol and fatty acids • Some short-chain fatty acids are absorbed, move into the capillary blood in the villi by diffusion, and are transported to the liver via the hepatic portal vein.

Chemical Digestion and Absorption of Nucleic Acids Nucleic acid digestion Enzyme(s) and source Site of action Foodstuff Path of absorption Nucleic acids • Units enter intestinal cells by active transport via membrane carriers. Pancreatic ribo- nuclease and deoxyribonuclease Small intestine • Units are absorbed into capillary blood in the villi and transported to the liver via the hepatic portal vein. Brush border enzymes (nucleosidases and phosphatases) Small intestine Pentose sugars, N-containing bases, phosphate ions

What remains in Small Intestine? Indigestible food materials (cellulose) Lots of bacteria Water Passes through ileocecal valve into Large Intestine

Large Intestine/Colon Anatomy Cecum Appendix Colon Ascending Transverse Descending Sigmoid Rectum Anal Canal

Microscopic Anatomy No villi or microvilli No cells which secrete enzymes Many goblet cells lining the simple columnar tissue for lubrication Rectum tissue becomes stratified squamous

Main functions Absorbs water and electrolytes (Na, Cl, K) Absorbs water soluble vitamins Eliminates undigested food; defecation Haustra = wall pockets (seen in picture)

Other Inhabitants Bacteria Responsible for fermenting undigested food Product of these reactions is gas (H2, N2, CO2, H2S, CH4) Assist in synthesizing vitamin B and vitamin K.