Chapter 16: Digestive System

finals

is the breakdown of large organic molecules into smaller molecules that can be absorbed.

Digestion

The digestive system consists of the

digestive tract, plus specific associated organs.

The digestive tract is also referred to as the

GI (gastrointestinal tract)

The tract is one long tube from the mouth to the anus.

digestive system/gastrointestinal tract

The digestive tract consists of the:

• oral cavity (mouth)

• pharynx

• esophagus

• stomach

• small intestines

• large intestines

• rectum

• anus

not directly in the digestive tract, but have ducts that lead into the tract.

Associated Organs

associated organs are the:

• salivary glands

• liver

• gallbladder

• pancreas

The layers of the digestive tract wall are also termed

tunics.

Layers of Digestive Tract Wall

• Mucosa

• Submucosa

• Muscularis

• Serosa/adventitia

innermost layer of digestive tract wall, secretes mucus

Mucosa

above mucosa and contains blood vessels, nerves, small glands

Submucosa

above submucosa, consists of longitudinal, circular, and oblique muscles

Muscularis

• outermost layer of digestive tract wall

• peritoneum is present called serosa

• no peritoneum then called adventitia

Serosa/adventitia

outermost layer of digestive tract wall with peritoneum

serosa

outermost layer of digestive tract wall without peritoneum

adventitia

Layer of smooth epithelial tissue

Peritoneum

connective tissue of organs in abdominal cavity

Mesenteries

mesentery connecting lesser curvature of stomach to liver and diaphragm

Lesser omentum

mesentery connecting greater curvature of stomach to transverse colon and posterior body wall

Greater omentum

First part of digestive system

Contains stratified squamous epithelia

Oral Cavity -

• produce saliva which contains enzymes to breakdown carbohydrates into glucose

• cleanse mouth

• dissolve and moisten food

Salivary glands

salivary enzyme that breaks down carbohydrates

Amylase

salivary enzymes that are active against bacteria

Lysozyme

house taste buds and mucus

Tongue

teeth in normal adult

32 -

Teeth:

Incisors, canine, premolars, molars, wisdom -

primary teeth (baby teeth)

20

Center of tooth is

pulp cavity

hard covering protects against abrasions of teeth

Enamel

are breakdown of enamel by acids from bacteria

Cavities

roof of oral cavity

Palate

anterior and posterior part of the roof of mouth

hard and soft palate

• includes submandibular, sublingual, parotid

• produce saliva contains enzymes to breakdown food

• mumps is inflammation of parotid gland

Salivary Glands -

is inflammation of parotid gland

mumps

Throat

Connects the mouth to the esophagus

Pharynx

three parts of pharynx

• nasopharynx

• oropharynx

• laryngopharynx -

Tube that connects the pharynx to the stomach

Transports food to the stomach

Joins stomach at cardiac opening

Esophagus

• occurs when gastric juices regurgitate into esophagus

• caused by caffeine, smoking, or eating or drinking in excess

Heartburn

bolus (mass of food) formed in mouth and pushed into oropharynx

Voluntary phase of swallowing

swallowing reflex initiated when bolus stimulates receptors in oropharynx

Pharyngeal phase

swallowing phase moves food from pharynx to stomach

Esophageal phase

wave-like contractions moves food through digestive tract

Peristalsis

Located in abdomen

Storage tank for food

Can hold up to 2 liters of food

Produces mucus, hydrochloric acid, protein digesting enzymes

Contains a thick mucus layer that lubricates and protects epithelial cells on stomach wall form acidic pH (3)

Stomach

3 muscular layers of stomach to produce churning action

outer longitudinal, middle circular, and inner oblique

large folds that allow stomach to stretch

Rugae

paste-like substance that forms when food begins to be broken down

Chyme

opening between stomach and small intestine

Pyloric opening

thick, ring of smooth muscle around pyloric opening

Pyloric sphincter

stomach is stimulated to contract by low blood glucose levels usually 12-24 hours after a meal

Hunger pangs

• 1st phase of stomach secretion

• stomach secretions are initiated by sight, smell, taste, or food thought

Cephalic phase -

• 2nd phase stomach secretions

• partially digested proteins and distention of stomach promote secretion

Gastric phase -

• 3rd phase of Regulation of Stomach Secretions

• acidic chyme stimulates neuronal reflexes and secretions of hormones that inhibit gastric secretions by negative feedback loops

Intestinal phase -

• weak contraction

• thoroughly mix food to form chyme

Mixing waves

• stronger contraction

• force chyme toward and through pyloric sphincter

Peristaltic waves

Stomach empties every — hours after regular meal, and — hours after high fatty meal

• 4

• 6 to 8

Measures 6 meters in length

Major absorptive organ

Chyme takes 3 to 5 hours to pass through

Contains enzymes to further breakdown food

Contains secretions for protection against the acidity of chyme

Small Intestine

• first part of small intestine

• 25 cm long

• contains absorptive cells, goblet cells, granular cells, endocrine cells

• contains microvilli and many folds

• contains bile and pancreatic ducts

Duodenum

• second part of small intestine

• 2.5 meters long and absorbs nutrients

Jejunum

• third part small intestine

• 3.5 meters long

Ileum

The mucosa of the small intestine is simple columnar epithelium with four major cell types:

• Absorptive cells

• Goblet cells

• Granular cells

• Endocrine cells

cells which have microvilli, produce digestive enzymes, and absorb digested food

Absorptive cells

cells which produce a protective mucus

Goblet cells

cells which may help protect the intestinal epithelium from bacteria

Granular cells

cells which produce regulatory hormones.

Endocrine cells

The epithelial cells are located within tubular glands of the mucosa, called intestinal glands or —, at the base of the villi.

crypts of Lieberkühn

The submucosa of the duodenum contains mucous glands, called —, which open into the base of the intestinal glands.

duodenal glands

contractions that proceed along the length of the intestine for variable distances and cause the chyme to move along the small intestine.

Peristaltic contractions

contractions that are propagated for only short distances and mix intestinal contents.

Segmental contractions

prevents movement from the large intestine back into the ileum.

ileocecal valve

Weighs about 3 lbs.

Located in the right upper quadrant of the abdomen under the diaphragm

Consists of right, left, caudate, and quadrate lobes

Liver Anatomy

• gate where blood vessels, ducts, nerves enter and exit

Receives arterial blood from the hepatic artery

Porta

divisions of liver with portal triads at corners

Lobules

contain hepatic artery, hepatic portal vein, hepatic duct

Portal triad

• between center margins of each lobule

• separated by hepatic sinusoids

Hepatic cords

contain phagocytic cells that remove foreign particles from blood

Hepatic sinusoids

• center of each lobule

• where mixed blood flows towards

• forms hepatic veins

Central vein

Liver Ducts

• Hepatic duct

• Common hepatic duct

• Cystic duct

• Common bile duct

transport bile out of liver

Hepatic duct

formed from left and right hepatic duct

Common hepatic duct

• joins common hepatic duct

• from gallbladder

Cystic duct

formed from common hepatic duct and cystic duct

Common bile duct

Functions of the Liver

Digestive and excretory functions

Stores and processes nutrients

Detoxifies harmful chemicals

Synthesizes new molecules

Secretes 700 milliliters of bile each day

dilutes and neutralizes stomach acid and breaks down fats

Bile

Located posterior to stomach in inferior part of left upper quadrant

Head near midline of body

Tail extends to left and touches spleen

Endocrine tissues have pancreatic islets that produce insulin and glucagon

Exocrine tissues produce digestive enzymes that travel through ducts

Pancreas

continues the polysaccharide digestion that began in the oral cavity

Pancreatic amylase

Function is to absorb water from indigestible food

Contains cecum, colon, rectum, anal canal

Large Intestine -

• joins small intestine at ileocecal junction

• has appendix attached

Cecum

9 cm structure that is often removed

Appendix

• 1.5 meters long

• contains ascending, transverse, descending, sigmoid regions

Colon

straight tube that begins at sigmoid and ends at anal canal

Rectum

• last 2 to 3 cm of digestive. tract

Anal canal

is product of water, indigestible food, and microbes

feces

Digestive Process:

• Digestion

• Propulsion

• Absorption

• Defecation

breakdown of food occurs in stomach and mouth

Digestion

moves food through digestive tract includes swallowing and peristalsis

Propulsion

digestive process primarily in duodenum and jejunum of small intestine

Absorption

elimination of waste in the form of feces

Defecation

Polysaccharides split into disaccharides by salivary and pancreatic amylases

Disaccharides are broken down into monosaccharides by disaccharidases on the surface of intestinal epithelium

Glucose is absorbed by cotransport with Na+ into the intestinal epithelium

Glucose is carried by the hepatic portal vein to the liver and enters most cells by facilitated diffusion

Carbohydrate Digestion

Lipase breaks down triglycerides into fatty acids and monoglycerides.

Bile salts surround fatty acids and monoglycerides to form micelles.

Micelles attach to the plasma membranes of intestinal epithelial cells, and the fatty acids and monoglycerides pass by simple diffusion into the intestinal epithelial cells.

Within the intestinal epithelial cell, the fatty acids and monoglycerides are converted to triglycerides.

Proteins coat the triglycerides to form chylomicrons, which move out of the intestinal epithelial cells by exocytosis.

The chylomicrons enter the lacteals of the intestinal villi and are carried through the lymphatic system to the blood.

Lipid Digestion

breaks down triglycerides into fatty acids and monoglycerides.

Lipase