M E D I C A L T E R M I N O L O G Y

M S . PA S T O R

The Digestive System

Objectives

- Identify and describe the structures of the digestive

using proper medical terminology

- Explore careers relating to this system

Nutrition and Digestion

There are six types of nutrients:

• Water

• Carbohydrates

• Proteins

• Fats

• Minerals

• Vitamins

Carbohydrates

• Carbohydrates are the main source of energy for the body.

• simple and complex carbohydrates supply glucose

• fiber from plant foods helps elimination

• Proteins are necessary for growth and repair of the body’s

cells.

– body makes 12 out of 20 amino acids

– other eight essential amino acids come from food

• Fats provide energy and key building components.

– fats are saturated and unsaturated

– butter, lard and oils

– essential fatty acids come from food

• Minerals are inorganic materials needed in small amounts

– help to build or repair tissues

– replenished by eating variety of foods

• Vitamins are organic molecules that work with enzymes.

– vitamins are fat-soluble and water-soluble

– Fat soluble: A, D, E, K

– Water-soluble: B, C (ascorbic acid) , folic acid

– regulate cell functions, growth, development

• Unbalanced diets can lead to malnutrition or undernutrition

– Malnutrition occurs in when you don’t get the right

nutrients for your body, or you over consume some

nutrients.

– Undernutrition is when you lack the essential nutrients

your body needs in order to function properly.

Key Concept #2 The main stages of food processing are ingestion, digestion, absorption, and elimination

• Ingestion is the act of eating

• Digestion is the process of breaking food down into

molecules small enough to absorb

• Absorption is uptake of nutrients by body cells

• Elimination is the passage of undigested material out of the

digestive compartment

LE 41-12

Pieces of food

Chemical digestion (enzymatic hydrolysis)

Food

Nutrient molecules enter body cells

Small molecules

Undigested material

ELIMINATION ABSORPTION DIGESTION INGESTION

Mechanical digestion

• More complex animals have a digestive tube with two

openings, a mouth and an anus

– This digestive tube is called a complete digestive

tract or an alimentary canal

– It can have specialized regions that carry out digestion and

absorption in a stepwise fashion

Key Concept #3 Each organ of the mammalian digestive system has specialized food-processing functions

• The human digestive system consists of an alimentary

canal and accessory glands that secrete digestive juices through

ducts

• Accessory glands are the

– salivary glands

– pancreas

– liver

– gallbladder

• Food is pushed along by peristalsis, rhythmic contractions of

muscles in the wall of the canal

LE 41-15a

Esophagus

Pharynx

Oral cavity

Stomach

Pyloric sphincter

Cardiac orifice

Liver

Tongue

Parotid gland

Sublingual gland

Submandibular gland

Salivary glands

Ascending

portion of

large intestine

Gall- bladder

Pancreas

Ileum

of small

intestine

Rectum

Anus

Appendix

Cecum

Large

intestine

Small

intestine

Duodenum of

small intestine

The Oral Cavity, Pharynx, and Esophagus

• In the oral cavity, food is

lubricated and digestion

begins

• Teeth chew food into

smaller particles that are

exposed to salivary

amylase, initiating

breakdown of carbohydrates

• The region we call our throat is the pharynx, a junction that

opens to both the esophagus and the windpipe (trachea)

• The esophagus pushes food from the pharynx down to the

stomach by peristalsis

Epiglottis up

Bolus of food

Esophageal sphincter contracted

Esophagus

To stomach To lungs

Trachea

Tongue

Pharynx

Glottis

Larynx

Esophageal sphincter relaxed

Epiglottis down

Glottis up and closed

Epiglottis up

Esophageal sphincter contracted

Relaxed muscles

Glottis down and open

Relaxed muscles

Contracted muscles

Stomach

The Stomach

• The stomach stores food and secretes gastric juice, which

converts a meal to acid chyme

• Gastric juice is made up of hydrochloric acid and the

enzyme pepsin

• Pepsin is secreted as inactive pepsinogen by chief cells;

pepsin is activated when mixed with hydrochloric acid in the

stomach

– It’s purpose is to break down protein

• Mucus protects the stomach lining from gastric juice

Esophagus

Cardiac orifice

Pyloric sphincter

Small

intestine Folds of

epithelial

tissue

Stomach

Epithelium

Pepsin

(active enzyme)

Pepsinogen

HCl

Pepsinogen and HCl

are secreted into the

lumsden of the stomach.

HCl converts

pepsinogen to pepsin.

Pepsin then activates

more pepsinogen,

starting a chain

reaction. Pepsin

begins the chemical

digestion of proteins.

Parietal cell Chief cell

Chief cells

Mucus cells

Parietal cells

Interior surface of

stomach

Gastric gland

5 µ

m

• Gastric ulcers, lesions in the lining, are caused mainly by

the bacterium Helicobacter pylori

Bacteria

Mucus

layer of

stomach

1 µ

m

The Small Intestine

• The small intestine is the longest section of the alimentary

canal

• It is the major organ of digestion and absorption

• The first portion of the small intestine is the duodenum

– Where acid chyme from the stomach mixes with digestive

juices from the pancreas, liver, gallbladder, and the small

intestine itself

Accessory Glands

Stomach

Pancreas

Liver

Gall-

bladder

Duodenum of

small intestine

Intestinal

juice

Bile

Acid chyme

The Pancreas

• The pancreas has both digestive and endocrine

(hormone) functions.

• Digestive Function

– Releases bicarbonate to neutralize the acid

chyme that enters the small intestine

– Releases proteases to help with further digestion

of proteins

• Endocrine Function

– Releases insulin & glucagon to control blood-

sugar levels

The Liver

• The liver produces bile, which aids in digestion and

absorption of fats

The Small Intestine: Absorption of Nutrients

• The small intestine has a large surface area, due to villi and

microvilli that are exposed to the intestinal lumen

• The enormous microvillar surface greatly increases the rate of

nutrient absorption Key

Nutrient absorption

Microvilli (brush border)

Epithelial cells

Lacteal

Lymph vessel

Villi

Large circular folds

Epithelial cells

Blood capillaries

Vein carrying blood to hepatic portal vessel

Muscle layers

Villi

Intestinal wall

The Large Intestine

• The large intestine, or colon, is connected to the small

intestine

• Its major function is to recover water that has entered the

alimentary canal

• Wastes of the digestive tract, the feces, become more solid as

they move through the colon

• Feces is stored in the rectum until it exits via the anus

Glucose Regulation as an Example of Homeostasis

• Animals store excess calories as glycogen in the liver and fats

in the muscles.

• Hormones like insulin & glucagon regulate glucose

metabolism

• When fewer calories are taken in than are expended, fuel is

taken from storage and broken down to be used by cells.

LE 41-3

STIMULUS: Blood glucose

level rises after eating.

STIMULUS: Blood glucose

level drops below set point.

Homeostasis: 90 mg glucose/ 100 mL blood