Digestion and Nutrition You are what you eat

Digestion and Nutrition You are what you eat. . From your plate to yourself

Why digestion? l l l We must make molecules small enough to transport and move easily through cell membranes Digestion: mechanical and chemical breakdown of foods so absorption through membranes can happen Digestive system consists of the alimentary canal and accessory organs which secrete their wares into the alimentary canal.

The Alimentary Canal l l l Mouth Pharynx Esophagus Stomach Small intestine Large intestine Anal canal

Accessory Organs l l Salivary glands Liver Gallbladder Pancreas

Alimentary, My Dear Watson: Canal Characteristics l l l 9 meters long Passes through ventral cavity The wall consists of 4 layers: Mucosa l Submucosa l Muscular Layer l Serosa Muscular movements involve mixing movements and propelling movements: peristalsis l

Mucosa l l l Surface epithelium, underlying connective tissue, small amt. of smooth muscle in this layer In some areas, folds, projections stick out into lumen Can contain glands

Submucosa l l l Loose connective tissue Glands Blood vessels Lymphatic vessels Nerves organized in a plexus

Muscular layer l l 2 coats of smooth muscle Nerves in a plexus Circular muscle fibers ring tube and cause it to shrink in diameter when they contract Longitudinal fibers run the length of tube: when these contract, it shortens

Serosa (serous layer) l l Aka: Visceral peritoneum Outer covering of the tube Protection for underlying tube Secrete serous fluid: lubrication for easy organ sliding

Alimentary Canal

Wall of the alimentary canal

Wall of the small intestine

Oral Cavity

Sagittal Section, Mouth

Teeth

Salivary Glands

Pharynx and Esophagus l Pharynx: cavity behind mouth l l Nasopharynx: Continuous w/ nasal cavity, provides passage for breathing Oropharynx: Opens behind soft palate into nasopharynx: passage for food and air. Laryngopharynx: just below oropharynx Esophagus: Muscular tube which leads to the stomach

Pharynx

Swallowing 1. 2. 3. 4. 5. 6. Soft palate raises, blocking nasal cavity Hyoid, larynx elevated, epiglottis closes Tongue presses against soft palate, further sealing nasal cavity Longitudinal muscles of pharynx contract, pulling pharynx upward Muscles in lower pharynx relax, opens esophagus Peristalsis starts here, works downward

Esophagus l l l Straight, collapsible tube, 25 cm long. Located behind trachea in mediastinum Passes through diaphragm through a hole called the esophageal hiatus. The lower esophageal sphincter (cardiac sphincter. . heartburn, get it? ) contracts and closes connection to the stomach. Acid reflux results from this not closing properly Mucus glands throughout esophagus

Stomach l l l J-shaped, pouch-like in upper left corner of abdominal cavity Capacity of 1 liter or more. Lining of thick folds (rugae) made of mucosa, submucosa. These folds disappear when the stomach is full. Protein digestion begins here, some absorption Mixes food with gastric juice, hands it off to small Intestine

Can you stomach it? Stomach parts: l Cardiac Region: small area near esophagus. l Fundic Region: temporary storage area. l Body Region: main part of stomach l Pyloric Region: Lower part, narrows into Pyloric Canal. l Pyloric Sphincter: blocks food from entering small intestine.

The stomach

Gastric Secretions Gastric glands end in gastric pits, which are openings in the mucus membrane Gastric glands have 3 kinds of secretory cells: l l 1. 2. 3. Mucous (goblet) cells near pit openings Chief cells: secrete enzymes Parietal cells: secrete HCl which activates the enzymes such as pepsin

Gastric Juice l l l Pepsin is the most important enzyme It’s called pepsinogen in its inactive form HCl activates it, and its optimal p. H is acidic Gastric gland mucous cells produce thin mucous Mucous membrane secretes alkaline, thick mucous Parietal cells make Intrinsic Factor: necessary for B 12 absorption in Sm. Intestine

Stomach Lining

To squirt or not to squirt: gastric secretion regulation l l l Gastric secretion is pretty much constant, but rates are controlled by the nervous and endocrine systems Smell, look, taste of food causes acetylcholine to be released, which causes a rush of gastric juice, and a rush of Gastrin, which further increases secretions When food enters sm. Intestine, Cholecystokinin reduces gastric juice, along with the nervous system reduces appetitie

Absorption l l With all that mucous, not much, BUT Water, salts, alcohol, lipid soluble drugs are absorbed here

Time for Chyme l l Mixing action of stomach along with enzymes changes food to Chyme: A semi-fluid paste Stomach turns one big meal into smaller balls of chyme called boluses, spreads their entrance into the intestine out. Liquids rush through, solids won’t leave until soaked in gastric juice Fatty foods can stay for 3 -6 hours, proteins move through more quickly, carbs faster yet.

Stomach stapling

Pancreas l l l Endocrine and Exocrine Pancreatic Acinar Cells make pancreatic juice The above are clustered around tubes where they secrete, these form larger tubes which merge into the pancreatic duct Connects to duodenum of small intestine at same spot of bile duct The hepatopancreatic sphincter controls flow

Pancreatic Juice l l l l Digests proteins, lipids, carbs, nucleic acids Pancreatic amylase digests starch and glycogen into disaccharides Pancreatic lipase breaks down fats Nucleases break down nucleic acids Trypsin, chemotrypsin, carboxypeptidase break bonds between specific amino acids The above enzymes are stored in zymogen granules, and stored in inactive form. These are activated in the intestine by other enzymes

Pancreatic Secretion Regulation l l Nervous and endocrine systems regulate pancreatic secretions Nerve impulses tied to gastric secretion When acidic chyme enters intestine, the duodenum secretes secretin which triggers pancreatic juice secretion, which is alakaline. Proteins and fats in intestine cause intestinal wall to secrete cholecystokinin into blood, which travels to pancreas and causes secretion

Pancreas

Pancreas

Liver’s Functions l l l l It’s so important to living, they named it the LIVEr Storage of glycogen, release of glucose Lipid metabolism: oxidizes fatty acids, synthesizes lipoproteins, phospholipids, cholesterol, changes parts of carbs and proteins into fat molecules Protein metabolism: deamination of amino acids, production of urea, clotting factors, plasma proteins, and transforming certain amino acids to other amino acids Storage of Iron, vitamins A, D, B 12 Destroys damaged red blood cells, phagocytosis of foreign particles Detoxification of blood (like alcohol) Bile production

The Liver l l l l In upper right abdomen, below diaphragm Well vascularized A fibrous capsule surounds liver and divides it into 2 lobes Hepatic lobules are the liver’s functional units A hepatic lobule= hepatic cells radiating out from a central vein Hepatic sinusoids separate plate-like groups of these cells from each other Blood from the portal vein from digestive tract feeds the liver

The Liver

More of the Liver’s Structure l l Kupffer Cells are large macrophages fixed to the inner linings of the hepatic sinusoids: Filter bacteria or other foreign substances Blood passing through liver exits through central veins Bile canals run through the liver and collect hepatic cell secretions These merge to form Hepatic Ducts, which then merge to form the Common Hepatic Duct

Cirrhosis

Cirrhosis

Bile l l Yellow/green Liver cells secrete it non-stop Contains water, bile salts, bilirubin and biliverdin (bile pigment), cholesterol and electrolytes The pigments are produced as red blood cells break down and are excreted in bile

Gallbladder l l l l Pear shaped sac on inner surface of liver Connects to the cystic duct, which joins the common hepatic duct, which join to form the common bile duct, which dumps into the duodenum This leads to the hepatopancreatic sphincter Lined with epithelial cells, and has a muscular layer in its wall STORES BILE Reabsorbs water to concentrate bile Releases bile into small intestine.

Bile Salts l l l Help digestive enzymes Emulsification of fat globules Smaller drops=more surface area=better digestion Lipases then digest fats faster Enhance absorption of fatty acids, cholesterol, vitamins A, D, E, K

Gallstones

Small Intestine l l l Stretches from pyloric sphincter to large intestine Fills most of abdomen Receives secretions from pancreas, liver and gallbladder Completes digestion of chyme in no time, most absorption of nutrients here Transports leftovers to large intestine

Parts of the small intestine l l l Duodenum: 25 cm long, 5 cm. in diameter, lies behind the parietal peritoneum and is the most anchored part of the small intestine. It’s roughly C shaped Jejunum: top 2/5 of the remaining intestine, can move around inside the peritoneal cavity: thicker and wider than the ileum Ileum: Bottom 3/5 of the small intestine Mesentery: a double layered fold of membrane which suspends intestine loosely from back of abdominal wall, keeps intestines in a relative shape. Full of nerves, blood vessels, lymph vessels Greater Omentum: membrane loosely covering intestine; thought to combat the spread of infection

Do You Have the Intestinal Fortitude to Study the Structure of Intestinal Wall? l l l Villi. Yes, and lots of them. Densest in the duodenum and top of the jejunum. Massively increase surface area Each villus is made of a layer of simple columnar epithelium, with a core of connective tissue with nerve fibers, capillaries and a lacteal. Intestinal glands extend into the membrane between villi

Small Intestine Why did mom have to dress me in BROWN today?

Secretions of the Small Intestine l l Goblet cells secrete mucus Mucus-secreting glands secrete a thick, alkaline mucus Intestinal glands secrete liquid which enhances absorption, but lack enzymes Epithelial cells lining intestinal mucosa secrete peptidases, sucrase, maltase, lactase, and intestinal lipase

Regulation of small intestine secretion l l Chyme mechanically and chemically triggers goblet cells Stretching of the intestinal wall triggers more secretion

Absorption l l Villi increase surface area Very little absorbable material makes it to the large intestine Simple sugars and amino acids are absorbed into the capillaries of the villi (active transport or facilitated diffusion) Fatty acids and glycerol are absorbed by epithelial cells, and reconstituted by the ER back into fats. These fats are then coated in proteins to form chylomicrons which are then absorbed into the lacteals and into lymph, eventually finding their way to the blood stream

More Absorption l l Fatty acids with short carbon chains can be absorbed directly into the blood Water and electrolytes are absorbed in the small intestine, too.

Movements of the small intestine l l l Peristalsis and mixing movements which cut chyme into segments (boluses) and move them back and forth Chyme moves through slowly. . . 3 -10 hours If irritated or over-stretched, peristalsis speeds up and diarrhea is a result The ileocecal valve regulates chyme passage into the large intestine After a meal, the gastroileal reflex increases perisatlsis in the ileum and relaxes the sphincter and chyme passes into the colon

Large Intestine l l l Bigger in diameter, not length 1. 5 meters long From lower rt. Abdomen, up, over, down left side and out Reabsorbs water and electrolytes Forms and stores feces

Parts of the Large Intestine l l Cecum: beginning of large intestine, is wide, pouchlike, and hangs below the ileocecal opening. The appendix hangs from it. Colon: Ascending, transverse (most moveable), descending, sigmoid Rectum: Lies near sacrum, ends in anal canal. Waste storage Anal canal: last 2. 5 -4 cm. The mucous membrane folds into 6 -8 anal columns, ends at the anus. Two sphincters regulate the anus: The internal and external anal sphincter muscles. The internal is involuntary (smooth muscle), the external is voluntary (skeletal).

Large Intestine

Structure of the Large Intestine Wall l Same as the small intestine Lacks villi Longitudinal muscle is not uniform; It forms 3 bands (tenia coli) which create pouches (haustra).

Functions of the Colon l l Little or no digestive function Many goblet cells; Mucus is the only secretion of the colon Mucus protects against abrasion, binds feces together, controls p. H The proximal end of the colon absorbs water and electrolytes

Movements. l l l Similar to sm. Intestine Peristalsis only 2 -3 X per day, and includes large portions of the intestinal contents To pass the waste out, peristalsis in descending colon leads to the inner anal sphincter to relax, peristalsis increases, abdominal wall muscles contract, rectum is squeezed by pressure.

Feces l l l Whatever’s not absorbed plus water (75% of feces), electrolytes, mucus, and bacteria Color is due to bile pigments which have been worked on by bacteria. The lovely smell is due to bacterial action