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 – 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