DIGESTIVE SYSTEM

DIGESTIVE TRACT Tube in which digestion occurs Also called alimentary canal, gastrointestinal tract (GI) Entire canal is about 9 meters along (30 feet) in a cadaver. Shorter in a live person

FUNCTIONS Ingest food Break down nutrients to a form that can cross plasma membranes Absorb nutrients Eliminate undigested parts

PARTS

ORAL CAVITY Mouth - receives food Lips (labia) protects opening Tongue – taste buds, pushes food to back of throat fermium – a fold of mucous membrane that secures the tongue to the floor of the mouth Roof of mouth – contains made up of: 1. hard palate -anterior portion is bone 2. Soft palate posterior portion is muscle

Parts continued Uvula – finger-like projection that closes off nasopharynx keeps food from entering the nasal cavity Tonsils – protects against injection

SALIVARY GLANDS 3 pairs secrete saliva contains enzyme salivary amylase starts digestion of starch feel flaps under tongue and cheeks – where ducts are located Contains substances that inhibit bacteria growth Dissolves food chemicals so they can be tastes

Teeth – mechanical digestion

PHARYNX – region that receives food and air Trachea – also called windpipe lies in front of esophagus Swallowing is a reflex Glottis – opening to the larynx Epiglottis – spoon shaped tissue covering a piece of cartilage covers glottis so food/liquids do not enter trachea

ESOPHAGUS Muscular tube Connects to stomach Remains collapsed until bolus enters Peristalsis – rhythmic contractions that push food along digestive tract No chemical digestion occurs

LAYERS OF GI TRACT Mucosa – inner most – moist membrane that lines the lumen Submucosa- beneath mucosa- made up of connective tissue, and lymph vessels Muscularis external - smooth muscles Serosa – outermost layer

Esophagus continued Sphincters – muscles that encircle a tube act as valves located at point where stomach and esophagus meet when open – food passes into stomach closed – keeps acid from entering esophagus

STOMACH Thick muscular wall Wall has deep folds called rugae Holds 4 liters when full Stores food Empties in 2/6 hours Mechanical digestion – churns and mixes food with gastric juices pyloric sphincter connects to small intestine Cardioesophageal sphincter – connects to esophagus

REGIONS OF STOMACH Fundus – expanded part of the stomach Body – the midportion Pylorus – terminal part of stomach

GASTRIC JUICES Pepsin – digests protein HCL – hydrochloric acid pH 2 kills bacteria breaks down connective tissue of meat activates pepsin Mucus Intrinsic factor – substance needed for the absorption of vitamin B12 in the small intestine

MUCUS Thick layer of mucus Protects stomach from HCL Produced by goblet cells Ulcer – open sore in wall of stomach exposed to gastric juices bacterial infection interferes with mucus production

STOMACH CONTINUED Chyme – contents of stomach thick soupy liquid enters small intestines in small squirts No absorption of food occurs in stomach Alcohol absorption only

SMALL INTESTINE Major site of digestion Has small diameter About 3 meters (9 feet) long

THREE PARTS OF SMALL INTESTINE Duodenum – 1st part of small intestine sphincter muscles control chyme entering receives enzymes from liver and pancreas Jejunum Ileum – terminal part of intestine Ends with the ileocecal valve

WALL OF SMALL INTESTINE Fingerlike projections called villi Microscopic microvilli absorb sugars and amino acids directly into blood stream Components of fats enter smooth ER where they are rejoined and enter the lacteal (small lymphatic vessels)

LARGE INTESTINE 1.5 Meters Absorbs water, salts, and vitamins Parts: cecum colon rectum

CECUM Lind end of large intestine Appendix – small projection may help fight infection subject to inflammation

COLON Ascending Transverse Descending Sigmoid colon – enters rectum

RECTUM 20 cemeters Anus – opening to outside expels feces Stretching of rectal wall sends nerve impulses to spinal cord causing relaxation of anal sphincters Bacteria found in some feces produce vitamins that are reabsorbed by our body

PANCREASE Endocrine functions involves insulin and glucagon Exocrine function involves the secretion of pancreatic juices

PANCREATIC JUICES Sodium bicarbonate Pancreatic amylase Trypsin Lipase NaHCO3 Neutralizes chyme Pancreatic amylase Digest starch Trypsin Digest proteins Lipase Digest fats

LIVER Responsible for maintaining homeostasis of blood Removes poisonous substances Removes Fe and stores it Removes Vitamins A,D,E and K and stores them Makes plasma proteins to maintain osmotic pressure

LIVER CONTINUED Makes cholesterol and regulates amount in blood Maintains blood glucose levels Produces bile which emulsifies fat Produces fact

GALL BLADDER Sac attached to undersurface of liver Stores bile until needed in the duodenum Gall stones - cholesterol comes out of bile solution forming crystals

Feces – more or less solid product delivered to the rectum Resident bacteria of large intestine metabolize the remaining material Gases are released Methane and hydrogen sulfide produce the odor – more gas is produced when food is high in carbohydrates Bacteria make vitamin K and some B vitamins

DISEASES OF THE GI TRACT Acid reflux Appendicitis Cirrhosis Colorectal cancer Colostomy Constipation Diarrhea Gallstones Hemorrhoids Hepatitis Hernia IBS Jaundice Lactose intolerance Mumps Peritonitis Ulcer Vomiting