Chapter 24 Learning Objectives

Functions of the digestive system

Breaks down food, absorbs nutrients/water/vitamins, eliminates waste

Subunits of carbohydrates

Monosaccharides

Subunits of proteins

Amino acids

Subunits of lipids

Fatty acids + glycerol

Subunits of nucleic acids

Nucleotides

Organs of alimentary canal (in order)

Mouth → pharynx → esophagus → stomach → small intestine → large intestine → anus

Accessory organs of digestion

Teeth, tongue, salivary glands, liver, gallbladder, pancreas

Function of accessory organs

Mechanical breakdown, saliva production, bile production/storage, enzyme secretion

Digestion in the mouth

Mechanical (chewing) + chemical (salivary amylase breaks starch)

Mechanical digestion

Physical breakdown of food (mouth, stomach)

Chemical digestion

Enzymes break down molecules (mouth, stomach, small intestine)

Three major salivary glands

Parotid, submandibular, sublingual

Contents of saliva

Water, salivary amylase, lysozyme

Function of saliva

Starts carbohydrate digestion and kills bacteria

Bolus

Soft ball of chewed food

Deglutition

Swallowing

Peristalsis

Wave-like contractions that move food

Location of deglutition center

Medulla

Four layers of GI tract

Mucosa, submucosa, muscularis, serosa

Mucosa function

Secretion and absorption

Submucosa function

Contains blood vessels and nerves

Muscularis function

Movement (mixing and propulsion)

Serosa function

Outer protective layer

MALT function

Immune protection against pathogens

Mechanical digestion in stomach

Mixing food into chyme

Chemical digestion in stomach

Protein digestion by pepsin

Absorption in stomach

Water, alcohol, some lipids

Regions of stomach

Cardia, fundus, body, pylorus

Components of gastric juice

HCl, pepsin, intrinsic factor, gastric lipase

Function of HCl

Kills bacteria and activates pepsin

Function of pepsin

Digests proteins

Function of intrinsic factor

Aids vitamin B12 absorption

Function of gastric lipase

Begins fat digestion

Structures increasing surface area

Circular folds, villi, microvilli

Regions of small intestine

Duodenum, jejunum, ileum

Villi structure

Contain capillaries and lacteals for absorption

Microvilli

Brush border that increases surface area and contains enzymes

Segmentation

Mixing contractions in small intestine

Pancreas role in digestion

Secretes digestive enzymes into small intestine

Pancreatic juice contents

Amylase, lipase, proteases, nucleases

How pancreatic juice enters duodenum

Through pancreatic duct

How bile enters duodenum

Through bile duct

Liver role in digestion

Produces bile

Cells that produce bile

Hepatocytes

Contents of bile

Water, bile salts, cholesterol, pigments

Function of bile

Emulsifies fats for digestion

Other functions of liver

Metabolism, detoxification, nutrient storage, protein synthesis

Hepatic portal vein function

Transports nutrient-rich blood from GI tract to liver

Absorption of glucose

Facilitated diffusion and active transport

Absorption of amino acids

Active transport

Absorption of lipids

Diffusion into lacteals (lymph)

Functions of large intestine

Absorbs water, forms feces, produces vitamins

Regions of large intestine

Cecum → appendix → ascending → transverse → descending → sigmoid → rectum → anal canal

Defecation reflex

Parasympathetic reflex opens internal sphincter; external sphincter is voluntary

Salivary amylase

Breaks down starch (mouth)

Lingual lipase

Begins fat digestion (activated in stomach)

HCl

Activates enzymes and kills bacteria (stomach)

Pepsin

Digests proteins (stomach)

Gastric lipase

Digests fats (stomach)

Pancreatic amylase

Digests carbohydrates (small intestine)

Trypsin

Digests proteins (small intestine)

Chymotrypsin

Digests proteins (small intestine)

Carboxypeptidase

Digests peptides (small intestine)

Pancreatic lipase

Digests fats (small intestine)

Ribonuclease

Digests RNA (small intestine)

Deoxyribonuclease

Digests DNA (small intestine)

Gastrin

Stimulates gastric juice secretion (stomach)

Secretin

Stimulates pancreatic juice and bile secretion

CCK (cholecystokinin)

Stimulates pancreatic enzymes, bile release, and fullness

Enteric nervous system (ENS)

Local control of GI function

Myenteric plexus

Controls motility

Submucosal plexus

Controls secretion