Ch 16 Digestive system

Essentials of Anatomy and Physiology, Seventh Edition
Valerie C. Scanlon and Tina Sanders
Copyright © F.A. Davis Company 2015
Chapter 16
The Digestive System

The digestive system breaks down complex food into
simple chemicals.
The chemical end products of digestion are absorbed into
the blood or lymph and utilized by cells.
Divisions of the digestive system:
Alimentary tube—extends from the mouth to the anus—
Accessory organs—contribute to digestion—

Types of digestion:
Mechanical—breaks food into smaller pieces, increases
surface area:
Chemical—enzymes change complex organics to simple
organics; each enzyme is specific:
End products of digestion:
Carbohydrates—
Proteins—
Fats—
Other end products—

Oral Cavity
Teeth and tongue break up food and mix it with saliva.
Tooth structure:
Enamel covers the crown—
Dentin is within the enamel, forms the roots—
Pulp cavity—contains blood vessels and nerve endings:
Periodontal membrane—lines the tooth socket:
Questions: The set of deciduous teeth typically consists of how many? The set
of permanent teeth?

Answers
The set of deciduous teeth usually consists of 20 teeth.
The set of permanent teeth usually consists of 32 teeth.

Oral Cavity (continued)
The tongue is made of skeletal muscle.
Motor nerves—hypoglossal
Papillae on the upper surface contain taste buds.
Sensory nerves—
Other functions:
Chewing—
Swallowing—

Oral Cavity (continued)
Salivary glands—ducts take saliva to the oral cavity.
Parotid—
Submandibular—
Sublingual—
Saliva—mostly water:
Lysozyme—
Amylase digests starch to maltose.

Pharynx—food passageway from the oral cavity to the
esophagus; no digestion takes place.
Contraction of pharyngeal constrictor muscles—
Esophagus—food passageway from the pharynx to the
stomach; no digestion takes place.
Lower esophageal sphincter: at the junction with the
stomach—

Structure of the Alimentary Tube—four layers are
typically present.
Mucosa—the lining
Epithelium—produces the digestive secretions:
Lymph nodules—contain macrophages:
Submucosa—areolar connective tissue:
Meissner’s (submucosal) plexus—part of the enteric
nervous system:

Structure of the Alimentary Tube (continued)
External muscle layer—an inner circular and an outer
longitudinal layer—
Function:
Auerbach’s (myenteric) plexus—part of the enteric nervous
system:
Questions: What effect do parasympathetic impulses have on peristalsis?
Sympathetic impulses?

Answers
Parasympathetic impulses increase peristalsis (motility).
Sympathetic impulses decrease peristalsis.

Structure of the Alimentary Tube (continued)
Serosa (outer layer)—above the diaphragm; it is fibrous
connective tissue.
Below the diaphragm, it is the visceral peritoneum or
mesentery.
The peritoneum (parietal) lines the abdominal cavity.
Questions: What kind of membranes are the peritoneum and mesentery? What do
they produce, and what is its function?

Answers
The peritoneum and mesentery are serous membranes that
produce serous fluid.
Serous fluid prevents friction between the serous layers.

Stomach—in the upper left abdominal quadrant
(see Tables 16–1 and 16–2)
Functions: A reservoir for food:
Begins the digestion of proteins
Parts: Cardiac orifice:
Body:
Pylorus:
Pyloric sphincter:

Stomach (continued)
Mucosa—rugae:
Gastric pits—the glands
Mucus cells:
Chief cells:
Parietal cells:
G cells:
External muscle layer—three layers:
Question: Which cranial nerve pair innervates the stomach?

Answer
The vagus nerves innervate the stomach (and intestines).

Small Intestine—extends from the stomach to the cecum;
encircled by the large intestine
Parts: Duodenum:
Jejunum:
Ileum:
Mucosa—many cells have microvilli:
Peyer’s patches:
External muscle layer—two layers:
The completion of digestion requires secretions from the liver
and pancreas as well as from the small intestine.

Liver—two large lobes in the upper right and center of
the abdominal cavity (see Tables 16–1 and 16–2)
Liver lobules—the structural units:
Hepatocytes:
Sinusoids:
Branches of hepatic artery and portal vein:
Central veins of the lobules  hepatic vein 
Digestive function—production of bile to emulsify fats:
Bile canaliculi  hepatic duct 
Secretin—a hormone of the duodenum:

Gallbladder—on the undersurface of the right lobe of
the liver
Functions: Stores bile
Concentrates bile
Cystic duct—
Cholecystokinin—a hormone of the duodenum:

Pancreas—extends from the curve of the duodenum to
the spleen
Acini—secrete enzymes into small ducts  pancreatic duct
Pancreatic amylase:
Lipase:
Trypsin:
Bicarbonate pancreatic juice:
Effect of secretin:
Effect of cholecystokinin:

Completion of Digestion—in the small intestine
(see Tables 16–1 and 16–2)
Bile salts emulsify fats.
Pancreatic enzymes break down all three food types.
Intestinal glands: crypts of Lieberkühn:
Peptidases:
Sucrase, maltase, and lactase:
Enteroendocrine cells:

Absorption of End Products of Digestion
Intestinal surface area is increased by:
Circular folds:
Villi:
Microvilli:
Within each villus:
A capillary network—water-soluble end products:
A lacteal—fat-soluble end products:

Absorption (continued)
Mechanisms of absorption:
Active transport—
Passive transport—
Osmosis—
Special requirements:
For vitamin B12—
For calcium ions—
For fat-soluble nutrients—
Question: To what organ does blood from the small intestine flow first?

Answer
Blood from the small intestine flows through the portal vein to
the liver.

Large Intestine—from the ileum to the anus; encircles
the small intestine
Parts: Cecum
Ileocecal valve
Appendix
Ascending, transverse, and descending colon
Sigmoid colon
Rectum and anal canal
Internal and external anal sphincters

Large Intestine (continued)
Functions:
Absorption of water:
Elimination of undigestible material:
Normal flora (microbiota) of the colon—trillions of bacteria
Benefits:

Large Intestine (continued)
Elimination of feces: defecation reflex
Stimulus—stretching of the rectum, sensory impulses to
spinal cord
Motor impulses from spinal cord to smooth muscle layer of
rectum—
Internal anal sphincter—smooth muscle—
External anal sphincter—striated muscle—
Voluntary control—

Liver—other functions
1. Carbohydrate metabolism—excess glucose—
Fructose and galactose—
2. Amino acid metabolism—transamination—
Deamination—
Excess amino groups 
3. Fat metabolism—synthesis of lipoproteins—
Cholesterol—
Beta-oxidation of fatty acids—

Liver (continued)
4. Synthesis of plasma proteins:
Albumin—
Clotting factors—
Alpha and beta globulins—
5. Formation of bilirubin and its excretion—
Question: From what specific part of RBCs is bilirubin formed, and into what
is it put to be excreted?

Answer
Bilirubin is formed from the heme portion of the hemoglobin
of old RBCs.
Bilirubin is put into bile to be excreted in feces.

Liver (continued)
6. Phagocytosis by Kupffer cells—
7. Storage—of vitamins:
Of minerals:
8. Detoxification—the liver produces enzymes:

Wrap-Up Question
Name the part or aspect of the digestive system described.
1. Produces amylase and lipase
2. Chewing increases surface area of food
3. Increase surface area of intestinal cells
4. Enzyme that begins protein digestion
5. Stores and concentrates bile
6. Prevents backup from the duodenum
7. Brain of the gut
8. Extends from mouth to anus

Answers
1. Produces amylase and lipase—pancreas
2. Chewing increases surface area of food—mechanical
digestion
3. Increase surface area of intestinal cells—microvilli
4. Enzyme that begins protein digestion—pepsin
5. Stores and concentrates bile—gallbladder
6. Prevents backup from the duodenum—pyloric sphincter
7. Brain of the gut—enteric nervous system
8. Extends from mouth to anus—alimentary tube

Ch 16 Digestive system

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Ch 16 Digestive system