Digestive System

5.2 Investigate A&P of digestive system

Objectives

• Label the major organs on a diagram of the digestive system• Identify at least three organs that are located in the mouth and

aid in the initial breakdown of food• Cite two functions of the salivary glands• Describe how the gastric juices act on food in the stomach• Explain how food is absorbed into the body by the villi in the

small intestine• List at least three functions of the large intestine• List a t least four functions of the liver• Explain how the pancreas helps digest foods• Describe at least five diseases of the digestive system

Digestive or GI system

• Physical and chemical breakdown of food so that it can be taken into the bloodstream and used by body cells and tissues.

• Alimentary canal plus accessory organs

Alimentary canal

• Long, muscular tube that begins at the mouth and includes the mouth (oral cavity), pharynx, esophagus, stomach, small intestine, large intestine, and anus.

Accessory organs

• Salivary glands• Tongue• Teeth• Liver• Gallbladder• pancreas

Mouth

• Buccal cavity• Receives food- then food is tasted, broken

down physically by the teeth, lubricated and partially digested by saliva, and swallowed

Teeth

• Special structures in the mouth that physically break down food by chewing and grinding.

• mastication

Tongue

• Muscular organ that contains special receptors called taste buds

• Sweet, salty, sour, and bitter sensations• Aids in chewing and swallowing

Hard palate

• Bony structure that forms the roof of the mouth and separates the mouth from the nasal cavity

Soft palate

• Behind the hard palate, separates the mouth from the nasopharynx

• Uvula- cone-shaped muscular structure, hangs from the middle of the soft palate

• Prevents food from entering the nasopharynx during swallowing

Salivary glands

• Three pairs- parotid, sublingual, and submandibular, produce saliva which lubricates the mouth during speech and chewing and moistens food so it can be swallowed easily. Contains an enzyme called salivary amylase which begins the chemical breakdown of carbohydrates or starches into sugars.

Pharynx

• Food chewed and mixed with saliva is called a bolus.

• When swallowed the bolus enters the pharynx (throat). Carries both food and air.

• Food-esophagus• Air-trachea• During swallowing epiglottis closes over larynx

to prevent bolus from entering respiratory tract.

Esophagus

• Muscular tube dorsal to trachea. Carries bolus to stomach.

• Peristalsis- rhythmic , wavelike, involuntary movement of muscles

Stomach

• Enlarged part of alimentary canal. • Receives food• Mucous membrane lining contains folds called

rugae• Rugae disappear as stomach fills and expands• Cardiac sphincter- circular muscle between

esophagus and stomach, closes after food enters to prevent food from going back up.

Stomach cont.

• Pyloric sphincter- circular muscle between stomach and small intestine, keeps food in stomach until food ready to enter small intestine.

• 2-4 hours• Food converted into a semi fluid material ,

called chyme, by gastric juices produced by glands in stomach

Stomach cont.

• Gastric juices- HCL and enzymes• HCL kills bacteria, facilitates iron absorption,

and activates the enzyme pepsin.• Enzymes- lipases- starts the chemical

breakdown of fats, and pepsin- starts protein digestion

• Infants- enzyme rennin aids in digestion of milk

Small Intestine

• Chyme enters from stomach• Coiled section of alimentary canal• 20 ft length and 1 inch diameter• Duodenum (first 9-10 inches)- bile from the

gallbladder and liver and pancreatic juice from the pancreas enter this section through ducts or tubes.

Small Intestine

• Jejunum- 8 ft length- middle section• Ileum-final 12 ft connects with large intestine at

the cecum.• Circular muscle called ileocecal valve separates

the ileum and cecum- prevents food from returning to ileum.

• Process of digestion completed in small intestine• Products of digestion absorbed into bloodstream

for use by cells

Small intestine- intestinal juices

• Enzymes maltase, sucrase and lactase- breakdown sugars

• Enzymes- peptidases- complete digestion of proteins

• Enzyme Steapsin (lipase) aids in digestion of fat

• Bile from liver and gall bladder emulsifies (physically breaks down) fats.

Small intestine- intestinal juices

• Pancreatic enzymes- amylase (acts on sugars), trypsin and cymotrypsin (acts on proteins), lipase or steapsin (acts on fats).

Small intestine

• After food digested, absorbed into bloodstream• Walls of intestine lined with fingerlike

projections called villi.• Villi contain blood capillaries and lacteals. • Blood capillaries absorb digested nutrients and

carry them to liver where they are stored or released into general circulation for use by body cells.

Small intestine

• Lacteals absorb most of digested fats and carry them to the thoracic duct in lymphatic system which releases them into circulatory system.

• When food completed passage through SI, only wastes, indigestible materials, and excess water remain

Large Intestine

• Final section of alimentary canal• 5 ft long and 2 inch diameter

Functions

• Absorption of water and remaining nutrients• Storage of indigestible materials until

eliminated• Synthesis and absorption of some b-complex

vitamins and vitamin K by bacteria present in intestine

• Transportation of the waste products out of the alimentary canal

Sections

• Cecum• 1st

• Connects with ileum of small intestine• Contains a small projection called the

vermiform appendix

Colon

• Ascending colon continues up on right side of body from cecum to lower part of liver

• Transverse colon extends across the abdomen, below liver and stomach but above small intestine

• Descending colon extends down the left side of the body

• Sigmoid colon• Connects with descending colon• S-shaped section that joins with the rectum

Rectum

• Final 6-8 inches• Storage area for indigestibles or wastes• Narrow canal called the anal canal which

opens at a hole called anus• Fecal material or stool, the final waste product

of digestive process, expelled through this opening

liver

• Largest gland in the body• Accessory organ • Under diaphragm in upper right quadrant of

abdomen

Functions

Secretes bile– Used to emulsify or physically break up fats– Makes fats water soluble, which is necessary for

absorptionStores sugar in the form of glycogen

glycogen is converted to glucoseReleased into the bloodstream when additional blood sugar is needed

Functions cont.

• Stores iron and certain vitamins• Produces heparin (prevents blood clotting)• Produces blood proteins such as fibrinogen and

prothrombin, which aid in clotting of the blood• Produces cholesterol• Detoxifies substances such as alcohol and

pesticides, destroys bacteria that have been taken into the blood from the intestine

Gallbaldder

• Small muscular sac• Under liver attached to it by connective tissue• Stores and concentrates bile (which it receives

from liver)• When bile needed in digestive tract to

emulsify fats, it contracts and pushes the bile through the common bile duct into duodenum

Pancreas

• Fish-shaped organ located behind stomach• Produces pancreatic juices– Juices enter duodenum through pancreatic duct– Contain enzymes to digest food• Pancreatic amylase to break down sugars• Trypsin and chymotrypsin to break down prteins• Lipase to act on fats

Pancreas cont.

• Produces insulin– Secreted into the bloodstream– Regulates the metabolism or burning of

carbohydrates to convert glucose to energy