HUMAN BIOLOGY

202 Chapter 11

accessory organs: the pancreas,

Liver, and gallbladder

n    The pancreas, liver, and gallbladder assist digestion but are

outside the digestive tube.

n    Links to pH and buffers 2.7, Exocrine glands 4.1

the pancreas produces key

digestive enzymes

The pancreas nestles behind and below the stomach (Fig-

ure 11.9). It contains exocrine cells that release digestive

enzymes into the duodenum, the first section of the small

intestine. The pancreas also contains endocrine cells that

release hormones into the blood. The hormones help regu-

late blood sugar, a topic of Chapter 15.

There are four types of pancreatic enzymes, which

can chemically dismantle the four major categories of

food—complex carbohydrates, proteins, lipids, and nucleic

acids. These enzymes work best when the pH is neutral

or slightly alkaline, so the “pancreatic juice” also contains

bicarbonate (HCO 32 ), which neutralizes the acid in chyme

moving into the duodenum from the stomach. Depending

on how often and what type of food you eat, your pancreas

may make 2 quarts of this fluid each day.

the liver makes bile and the gallbladder

stores it

When the digestive system is processing food, a yellowish

fluid called bile is released into the upper small intestine.

Making bile is a digestive role of the liver. This large organ

secretes as much as 1,500 mL, or almost 1.6 quarts, of bile

every day. Bile is a blend of substances including water and

bile salts synthesized from cholesterol. Bile salts aid in the

digestion and absorption of fats, as you will read in Section

11.6. Bile is stored in the gallbladder, a small sac tucked

behind the liver. As needed, the gallbladder contracts and

Gallbladder

Duodenum

Bile duct

from liver

Liver

Duct

from

pancreas

Exocrine cells

secreting enzymes

into the duodenum

Endocrine

cells secreting

hormones

Stomach

Chyme Pancreas

Figure 11.9 Animated! accessory organs
assist digestion. Ducts deliver the pancreatic
juice and bile into the upper part of the small
intestine. The parts of the pancreas are shown
here larger than actual size. (© Cengage Learning)

Liver Functions

Forms bile used in fat digestion,

rids body of excess cholesterol

and bilirubin from dead red blood

cells

Synthesizes important proteins in

blood plasma. Converts potentially

toxic ammonia to urea

Stores some excess blood glucose

as glycogen

Removes hormones that served

their functions from blood

Removes ingested toxins, such as

alcohol, from blood

Stores some vitamins and minerals

(iron)

11.5

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