Digestive System

Digestive System

–Breaks food down into molecules small enough to be absorbed into the internal environment

–Stores and eliminates unabsorbed materials

–Promotes homeostasis by its interactions with other organ systems

Food

•provides a source of energy and essential molecules that the animal body is not able to manufacture for itself

–an optimal diet contains more carbohydrates than fats and also a significant amount of protein

Nutrient

•a component of food that is needed for a specific physiological function

Deficiency disorders

occur when the body lacks a nutrient required for a function

Carbohydrates

•obtained primarily from cereals, grains, and breads

–Monosaccharides, dissaccharides

–Starch -

–carbohydrates contain 4.1 calories per gram

–the body uses carbohydrates for energy

Fats

•obtained from oils, margarine, and butter and are abundant in fried foods, meats, and processed snack foods

–contain 9.3 calories per gram

–the body uses it to construct cell membranes, to insulate nervous tissue, and to provide energy

Proteins

•obtained from poultry, fish, meat, and grains

–Have 4.1 calories per gram

–Are used for energy and as building materials for cell structures, enzymes, hemoglobin, hormones, and muscle and bone tissue

Fiber

Part of plant food that cannot be digested by humans

–slows the rate of simple sugar absorption, allowing utilization of the energy from the food we eat at a steadier rate

Insoluble Fiber

stimulates movement of feces in the bowel

Soluble Fiber

Binds to compounds in the intestine to deter their absorption and enhance their excretion

Minerals

Calcium, phosphorous, iron, iodine zinc

Trace Minerals

Larger amounts, macro

calcium, phosphorous, sodium, etc

Vitamins

Organic substances that are required cofactors for enzymes

Heterotrophs

Divided into three groups on the basis of their food sources

Herbivores

Eat plants exclusively

Carnivores

Meat eaters

Omnivores

Eat both plants and animals

intracellular

Type of digestion done by single-celled organisms as well as sponges

Extracellular

Type of digestion done by all non-single celled animals within a digestive cavity

Gastrovascular cavity

Found in cnidarians and flatworms

Alimentary Canal

A digestive tract with a separate mouth and anus

–Ingests food

–Breaks down food into smaller molecules

–Absorbs nutrients in molecules

–Eliminates indigestible waste

Four essential functions

mastication

teeth mechanically tear, grind food and chew

salivary glands

Release the enzyme amylase, in saliva, into the mouth to degrade starch to maltose

Bolus

partially digested food material that is swallowed

Epiglottis

The part that food is being prevented from going into the respiratory tract

Pharynx

In many animals, the digestive and respiratory systems share a common passage behind the mouth

Esophagus

The flow of food through the pharynx and into

…

epiglottis

Covers the respiratory passage

–A coughing reflex helps expel materials that accidentally enter the trachea

Peristalsis

The rhythmic contractions of the esophagus that move food to the stomach

Sphincter

The movement of food from the esophagus into the stomach is controlled by a ring of circular smooth muscle

heartburn

The relaxing of the sphincter may lead to acid reflux, which is when stomach acid moves into the esophagus

Pepsin

The low pH of the stomach and the presence of this enzyme that accomplishes the digestion of proteins

Stomach

The organ in which proteins in food begin being digested

A saclike portion of the digestive tract

Churning food

the stomach contains an extra layer of smooth muscle

Gastric juice

Released by gastric glands in the lining of the stomach

•secretes hydrochloric acid (HCl) & pepsinogen

•Pepsinogen (inactive enzyme) is activated by HCl to form pepsin (active enzyme

Gastric ulcer

Overproduction of gastric acid can occasionally eat a hole through the wall of the stomach

Alkaline mucus

Protection of the stomach epithelial cells

replaced every 3 days

Small intestine

–Additional digestion of food material

–Absorption of nutrients

chyme

The digested food material that exits the stomach and enters the small intestine

Three additional organs that assist the small intestine

– Liver

– Gallbladder

– Pancreas

Liver

•produces bile to emulsify fats for digestion and absorption

•Excess bile is stored in the gallbladder

pancreas

•produces a juice that contains substances that enhance digestion.

Pancreatic enzymes

•Amylase

•Chemotrypsin

•Nucleases

•Lipase

Duodenum

Where pancreatic juice is dumped

jejunum

where digestion continues and absorption starts

ileum

–where water and digested products are absorbed

Large Intestine

–no digestion takes place here

–only about 6% to 7% of fluid absorption occurs here

•some water, sodium, and vitamin K

Feces

compacting and storing of undigested material by the main function of the large intestine

Appendix

A pouch of the large intestine – immunity contribution

Rectum

Where feces are stored

endocrine function of the pancreas

•involves secretion of insulin and glucagon into the bloodstream

Exocrine function of the pancreas

involves the secretion of pancreatic juice into the small intestine

Liver

–Glucose in blood is converted to glycogen and stored in the liver

–Synthesizes many proteins including blood clotting proteins and lipoproteins that transport fats and cholesterol

–Changes toxins to less toxic forms

–Produces bile

–Produces urea, a nitrogenous waste

Hepatitis

A viral infection of the liver

cirrhosis

liver tissue changes to become fatty and then non-functional scar tissue.