Ch 15 Notes DIGESTIVE SYSTEM AND NUTRITION DIGESTION

Ch 15 Notes DIGESTIVE SYSTEM AND NUTRITION

DIGESTION � Digestion – breakdown of foods and the absorption of the resulting nutrients. � Two kinds � Mechanical – breaks large pieces into smaller ones without chemically alteration. (chewing) � Chemical – breaks food into simpler chemicals (enzymes)

DIGESTIVE SYSTEM COMPOSITION � Alimentary � From canal mouth to anus � Secretes substances used in digestion � Organs – mouth, pharynx, esophagus, stomach, small intestine, large intestine, rectum, and anus � Accessory organs – salivary glands, liver, gallbladder, pancreas � Surface area – 186 square meters

STRUCTURE OF ALIMENTARY CANAL � Mucosa – Innermost Layer � epithelium, connective tissue, and some smooth muscle � lumen – folds that increase surface area � tubular glands that secrete mucous

STRUCTURE OF ALIMENTARY CANAL � Submucosa � loose connective tissue � glands, blood vessels, lymphatic tissue, nerves � Nourishes surrounding tissues and carries away absorbed materials

STRUCTURE OF ALIMENTARY CANAL � Muscular � Two Layer coats of smooth muscle � Inner coat – circular fibers that decrease diameter � Outer coat – longitudinal fibers that shorten the tube

STRUCTURE OF ALIMENTARY CANAL � Serosa/Serous � Outside Layer – Outermost layer epithelium and connective tissue � Also called visceral peritoneum � Lubricates outer tube to reduce friction between surfaces in the abdominopelvic region

FIG 15. 3

MOTOR FUNCTIONS OF ALIMENTARY CANAL � Mixing Rhythmic contraction of smooth muscles mixes content with gastric juices � Stomach and small intestine � Contents move in many directions at one time �

MOTOR FUNCTIONS OF ALIMENTARY CANAL � Moving (Propelling) Peristalsis – wavelike motion of smooth muscle � As wave moves, contents are pushed ahead of it � Only moves in one direction �

FUNCTIONS OF ORGANS � Fill out the table with the functions of each organ in the digestive system. � We will do the enzyme part later. Organ Functions Table

TEETH � Function: Begin mechanical digestion � Types � Incisors (8) – bite off pieces of food � Canine (4) – grasp and tear food � Bicuspid (8) – grind food particles � Molar (12) – grind food particles � Two main parts � Crown � Root

STRUCTURE OF TEETH - CROWN Crown is covered by enamel � Dentin – harder than bone � Pulp – blood vessels, nerves, connective tissue �

STRUCTURE OF TEETH - ROOT Root is covered by cementum – thin, bonelike layer � Periodontal ligament – blood vessels and nerves, attaches tooth to jaw �

SALIVARY GLANDS � Secrete saliva – dissolves food; begins chemical digestion � Two types of secretory cells: serous and mucous � Serous – salivary amylase � splits starch and glycogen into disaccharides (for carbohydrate digestion) � Mucous – coats food for swallowing � Why is it difficult to swallow something that tastes nasty?

MAJOR SALIVARY GLANDS � Parotid glands – in front of the ear � Largest � Rich in salivary amylase � Submandibular – floor of mouth, near lower jaw � Equally serous and mucous � Sublingual � Primarily – under the tongue mucous

PHARYNX � No digestion – just a passageway � Pharynx – only oropharynx and laryngopharynx are for food

SWALLOWING � Three stages � Voluntary � Tongue rolls food into bolus and pushes it into oropharynx

SWALLOWING � Involuntary � Soft palate raises, epiglottis closes off larynx, tongue presses soft palate � Longitudinal muscles in pharyngeal wall pull the pharynx upward � Esophagus opens � Peristalsis pushes food downward

SWALLOWING � During steps 1 and 2, breathing momentarily ceases � Involuntary – Peristalsis pushes food from esophagus to the stomach.

ESOPHAGUS � ~25 cm long � Penetrates the diaphragm through the esophageal hiatus � Mucous glands throughout to lubricate food � Lower espohageal sphincter – closes entrance to stomach so contents don’t come back into the espophagus

STOMACH � Receives food from esophagus � Mixes with gastric juices � Rugae – gastric folds � Starts protein digestion � Limited absorption � Small � Moves amounts of water, salts, alcohol food to small intestine

STOMACH - STRUCTURE � Cardia – area near esophogeal opening � Fundus – balloons inferior to cardia; temporary storage area � Body region – main part of the stomach � Pylorus – Area that tapers to the duodenum � Pyloric canal – approaches the small intestine � Pyloric sphincter – muscle valve that controls gastric emptying

STOMACH - SECRETIONS � Gastric glands – have gastric pits at the end. � Mucous cells – secrete thick mucous to prevent the stomach from digesting itself � Chief cells – secrete enzymes � Parietal cells – secrete hydrochloric acid � Intrinsic factor – helps small intestine absorb Vitamin B 12.

STOMACH – ENZYME � Pepsinogen � Starts + HCl -> pepsin the digestion of protein

GASTRIC SECRETION REGULATION � Secretion is regulated by both the brain and by hormoes � Stomach – gastrin � Small intestine - cholecystokinin � When you see, smell, or taste food, your stomach begins releasing gastric juices. � As food moves into the intestine, gastric juice secretion is inhibited

STOMACH ACTIONS � Mixing creates a semifluid paste called chyme. � When chyme reaches the pylorus, it relaxes the pyloric sphincter, pushing it into the small intestine

STOMACH ACTIONS � Food content determines time � Liquids – fastest � Carbs – very fast � Proteins – a little slower � Lipids – very slow

PANCREAS � Pancreas has both endocrine and exocrine qualities. � Secretes digestive fluids called pancreatic juices.

PANCREAS STRUCTURE � Located behind the stomach, with its head in the c-shaped curve of the duodenum and its tail against the spleen

PANCREAS STRUCTURE � Mostly made up of pancreatic acinar cells that produce pancreatic juices � These lead into a pancreatic duct, which carries juices to the duodenum. � Coincides with the bile duct from the gall bladder. � Hepatopancreatic sphincter controls release.

PANCREATIC JUICE - ENZYMES � Pancreatic amylase – breaks down carbs � Pancreatic lipase – breaks down lipids � Nucleases – breaks down nucleic acids � Trypsin, chymotrypsin, carboxypeptidase – break down proteins � Several are necessary because no one enzyme can break all peptide bonds. � Cannot be activated until they come into contact with other enzymes (i. e. – enterokinase, cholecytokinin)

PANCREATIC SECRETION - REGULATION � Controlled by nervous and endocrine systems � When chyme reaches the duodenum, the hormone secretin is released, which stimulate the release of pancreatic juice into the duodenum. � Pancreatic juice, high in bicarbonate ions, neurtalizes the acid in the chyme to provide a more favorable environment in the intestine

LIVER Location – Upper right quadrant just under the diaphragm � Well supplied with blood vessels � Heaviest organ – weighs about 3 lbs �

LIVER Enclosed by fibrous capsule and split into the left and right lobes by connective tissue. � Lobes are subdivided into hepatic lobules – hepatic cells radiating from a central vein. �

LIVER - STRUCTURE � Blood from digestive tract’s hepatic portal vein bring absorbed nutrients in � In the hepatic sinusoids, there are large phagocytic macrophages called Kupffer cells. � They remove bacteria and other foreign particles that enter through hepatic portal vein � Hepatic cell secretions -> bile canuliculi -> bile ductules -> hepatic ducts ->common hepatic duct

LIVER - FUNCTIONS � Carbohydrate metabolism – controlled by hormones insulin and glucagon which can lower or raise blood glucose levels � Lipid metabolism – breaks down, synthesizes cholesterol, converts sugars to fats for storage � Protein metabolism – forms urea, makes plasma proteins (clotting factors), changes amino acids into other amino acids

LIVER - FUNCTIONS � Storage – Vitamins A, D, B 12, and iron � Protection – destroy defective red blood cells, phagocytize foreign substances and toxins (i. e. – alcohol) � Secretes bile

BILE � Yellowish-green liquid secreted by hepatic cells � Contains – water, bile salts, bile pigments (i. e. biliruben), cholesterol, and electrolytes � Bile salts are the only substances that have digestive function. � They break fat molecules into much smaller droplets (emulsification) so they can more easily be digested � Also help with absorption of vitamins A, D, E, and K.

GALLBLADDER � Pear-shaped sac connected to the cystic duct and to the hapatic duct. � Epithelium lined with strong muscles � Stores bile, absorbs water, releases bile into small intestine

GALLBLADDER AND LIVER CONVERGE Common hepatic duct and cystic duct join to form the bile duct. � Bile duct empties into small intestine. � Controlled by hepatopancreatic sphincter. �

RELEASE OF BILE � Bile is released when the hormone cholocytokinin relaxes the hepatopancreatic sphincter. � It is released along with the pancreatic juices.

SMALL INTESTINE � Tubular organ that goes from pyloric sphincter (stomach) to the large intestine. � Receives secretions from the pancreas and liver, completes digestion of chyme, absorbs products of digestion, transports residues to large intestine.

SMALL INTESTINE – PARTS Doudenum � Jejunum (2/5) – bigger in � diameter, more active Ileum (3/5) � Connected to posterior abdominal wall by the mesentery � � � Blood vessels, nerve and lymphatic tissue, Ileocecal Sphincter

INSIDE THE SMALL INTESTINE LINING � Intestinal villi line the inside of the mucosa. � Increase surface area � Aid in absorption � Lymph vessel (lacteal) and blood vessels inside, which carry away absorbed nutrients. � Nervous Tissue

SMALL INTESTINE ENZYMES � Peptidase – Breaks down peptides (proteins) into amino acids � Sucrase, maltase, lactase – Breaks down disaccharides into monosaccharides � Instestinal Lipase – Breaks down fats into fatty acids and glycerols

REGULATION OF SECRETION � Chyme offers both mechanical and chemical stimulation in the duodenum and along the intestinal wall.

ABSORPTION – SMALL INTESTINE � Small intestine is the most important absorption organ on the alimentary canal. � Very little absorbable material reaches the large intestine. � Carbs – Easily absorbed into blood capillaries by facilitated diffusion or active transport.

ABSORPTION – SMALL INTESTINE � Amino acids (from proteins) – absorbed into the blood. � Fats – Broken down, reassembled, covered in protein coat (chylomicrons), absorbed by lymph vessels, which then take it to blood vessels � Also absorbs – electrolytes and water

MOVEMENTS OF THE SMALL INTESTINE � Mixing – segmentation mixes the contents and “swishes” them back and forth. � Moving – peristalsis over 3 to 10 hours � If contents move too quickly, water and electrolytes that would normally be absorbed are not. This causes diarrhea.

LARGE INTESTINE � Has a larger diameter than small intestine. � Four main parts: cecum, colon, rectum, anal canal � Absorbs water and electrolytes from chyme. � Forms and stores feces.

PARTS Cecum – Connection to ileum � Appendix – lymphatic; no known digestive function �

PARTS � Colon Ascending � Transverse � Descending � Sigmoid � � Rectum

PARTS Anal canal � Anus � Two sphincter muscles: internal anal sphincter muscle and external anal sphincter muscle � Skeletal muscle – voluntary control �

LARGE INTESTINAL WALL � Lacks villi � Longitudinal muscle fibers form 3 distinct bands

FUNCTIONS � Little to no actual digestive properties. � Mucous is the large intestine’s only major secretion. � Will absorb water and electrolytes in the first half. � Substances that remain become feces and are stored in the second half.

FUNCTIONS – INTESTINAL BACTERIA � Bacteria that live in colon (intestinal flora) can break down some materials that are still useful to it at this point. (i. e. cellulose) � They make Vitamins K, B 12, thiamine, and riboflavin � They may also make intestinal gas

MOVEMENTS OF LARGE INTESTINE � Mixing and moving like small intestine, but slower. � Waves happen only 2 -3 times a day. � Typically mass movements follow a meal – gastrocolic reflex � Voluntary – defecation reflex � Internal and external anal sphincters relax

FECES � Material not absorbed during digestion, water, electrolytes, mucus, shed intestinal cells, bacteria � Pigmentation and odor are due to bacterial action