Download Chapter 18: Digestive System Theory Lecture Outline Objectives

Chapter 18: Digestive System
Theory Lecture Outline
Objectives
1. Describe the general function of the digestive system
2. List the structures and the functions of the digestive system
3. Describe the action of the enzymes on carbohydrates, fats and protein
4. Trace food from the beginning of the digestive process to the end
5. Describe common disorders of the digestive system
6. Define the key words that relate to this chapter
Introduction
The function of the digestive system is to process food into molecules that can be absorbed and used by
the cells of the body. Food is broken down, bit by bit, until the molecules are small enough to be absorbed
and the waste products are eliminated.
Digestive System
• Food must be converted by physical and chemical changes before it can be used by the cells; this
process is called digestion
• Enzymes are chemical substances that promote chemical reactions in living things
The digestive system includes the alimentary canal, also known as the digestive tract or gastrointestinal
(GI) tract, and its accessory organs
• Alimentary canal
a. Organs include:
1. Mouth (oral cavity)
2. Pharynx (throat)
3. Esophagus (gullet)
4. Stomach
5. Small intestine
6. Large intestine (colon)
7. Anus
b. The alimentary canal is a continuous tube some
30 feet in length from the mouth to anus
• Accessory organs
a. Tongue
b. Teeth
c. Salivary glands
d. Pancreas
e. Liver
f. Gallbladder
Layers of the Digestive System
The walls of the alimentary canal are composed of four layers
• Mucosa
a. Innermost lining is made up of epithelial cells
b. Certain cells in the mucosa secrete mucus, digestive enzymes and hormones
o Mucus lubricates aiding in the passage of food
c. Also insulates the digestive tract from the effects of powerful enzymes
• Submucosa
o Consists of connective tissue with fibers, blood vessels and nerve endings
• Circular muscle
• Longitudinal muscle
Ann Senisi Scott & Elizabeth Fong: Body Structures & Functions 11th Edition
Lining of the Digestive System
• Peritoneum
Serous membrane that lines the abdominal cavity
a. Two-layered membrane
1. Parietal
o Lines the abdominal cavity
2. Visceral
o Covers the outside of each organ in the abdominal cavity
b. Specialized layers
1. Mesentery
o Attaches to the posterior wall of the abdominal cavity and the small
intestines
2. Greater omentum
o Contains large amounts of fat and hangs over the abdominal organs like a
protective apron
Functions of the Digestive System
• Break down food physically into smaller pieces
• Change food chemically
• Absorb the nutrients
• Eliminate the waste products of digestion
Organs of Digestion
Many organs contribute to digestion; each serving a specific function in the process
• Mouth (oral or buccal cavity)
a. First part of the digestive tract
b. Functions
1. Receive food by ingestion
2. Break food into small particles by mastication
3. Mix food with saliva
c. Uvula
1. Cone-shaped flap of tissue that hangs from the middle of the soft palate
2. Prevents food from entering the nasal cavity when swallowing
• Tongue/accessory organ of digestion
a. The tongue and its muscles are attached to the floor of the mouth, helping in both
chewing and swallowing
b. Made from skeletal muscles that lie in many different planes allowing movement in
various directions
c. Papillae
1. Projections located on the surface
2. Contain nerve endings , forming the sense organs of taste, or taste buds
o Bitterness, saltiness, sweetness and sourness
o Also sensitive to cold, heat and pressure
The sensation of taste is coupled with the sense of smell
• Salivary glands
a. Three pairs of salivary glands secrete saliva into the oral cavity
1. Parotid (in front and below the ears)
2. Submandibular (lower jaw)
3. Sublingual (under the sides of the tongue)
b. Functions of saliva
1. Cleansing action on the teeth
2. Moistens and lubricates food during mastication and swallowing
3. Dissolves certain molecules so that foods can be tasted
4. Begins the chemical digestion of starches
Ann Senisi Scott & Elizabeth Fong: Body Structures & Functions 11th Edition
Teeth/Accessory Organ of Digestion
• Gingivae or gums
a. Support and protect the teeth
b. Surrounds the narrow portions of the teeth and covers the structures in the upper and
lower jaws
• Teeth
a. Food chewed or masticated
o Breaks food down and enables the digestive enzymes to digest the food more
efficiently and quickly
b. Deciduous and permanent teeth Figure 18-5 pg. 380
1. 20 deciduous teeth (10 in each jaw) that may last up to the age of 12
o incisors (sharp edges for biting)
o canines (pointed for tearing)
o molars (ridges for crushing and grinding)
2. 32 permanent teeth (16 in each jaw)
o 8 incisors
o 4 canines
o 8 premolars (bicuspids for grinding)
o 12 molars
• Structure of the tooth
a. Three major parts
1. Crown (visible portion of the tooth)
2. Neck (where the tooth enters the gumline)
3. Root (portion that is embedded in the jaw)
b. Pulp cavity
1. Inside of tooth
2. Contains nerves and blood supply
Esophagus
• Muscular tube to transport swallowed food to stomach
a. Lies behind the trachea and in front of the vertebral column
b. Passes through an opening in the diaphragm and then empties into the stomach
• Muscles in the upper third are voluntary and lower portion is smooth muscle, or involuntary
Stomach
Located in the upper part of the abdominal cavity, just to the left of and below the diaphragm
• Divided into 3 portions
a. Fundus
o Upper part
b. Body or great curvature
o Middle section
c. Pylorus
o Lower portion
• Sphincters
a. Cardiac sphincter
b. Pyloric sphincter
• Four layers of the stomach wall
a. Mucous, submucous, muscular and serous layers
b. The muscular layer in the wall of the stomach provides mixing movements to mix the
food with enzymes and other fluids; when the stomach is empty, the mucosa and
submucosa exhibit longitudinal folds, called rugae (roo-jee); these folds allow the
stomach to expand, and as it fills the rugae becomes less apparent
Ann Senisi Scott & Elizabeth Fong: Body Structures & Functions 11th Edition
Gastric Juices
The gastric mucosa contains millions of gastric glands which secrete gastric juice necessary for digestion
• Enteroendocrine glands
o Secrete gastrin – hormone that stimulates gastric gland secretion
• Parietal cells
o Produces HCL (hydrochloric acid) which kills bacteria and intrinsic factor which
facilitates the absorption of vitamin B12
• Chief type cells
o Produce pepsinogen (active form of pepsin) which begins digestion of proteins into
polypeptides
• Mucus cells
o Secrete alkaline mucus which helps neutralize the effects of HCL acid and the other
digestive juices
Small Intestine
• About 20 feet long
• Same four layers as the stomach
• Divided into 3 sections
a. Duodenum
b. Jejunum
c. Ileum
• Functions
a. Finishes the process of digestion
b. Absorbs the nutrients
c. Passes the residue on to the large intestine
Digestive Juices in the Small Intestine
The combined action of pancreatic juice, bile and intestinal juice completes the process of changing
carbohydrates first into starch then into glucose, protein into amino acids and fats into fatty acids and
glycerol
• Enzymes, secretin, and cholecystokinin
o Stimulate the digestive juices of the pancreas, liver and gallbladder
• Pancreatic juices
a. Protease or trypsin break down proteins to amino acids
b. Amylase or amylopsin break down starches to glucose
c. Lipase or steapsin break down fats to fatty acids and glycerol
• Bile
o Necessary to break down or emulsify fat into smaller fat globules to be digested by lipase
and steapsin
• Intestinal juices
a. Maltase, lactase and sucrase change starch into glucose
b. Peptidase changes protease and peptone into amino acids
c. Steapsin changes fat into fatty acids and glycerol
Absorption in the Small Intestine
• Villi
o Makes absorption possible
• Each villi contains a network of blood and lymph capillaries
• Digested portion passes through the villi into the bloodstream and lacteals
• Undigested portion passes on to the large intestine
Accessory Organs of Digestion
• Pancreas
a. Feather-shaped organ located behind the stomach
Ann Senisi Scott & Elizabeth Fong: Body Structures & Functions 11th Edition
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b. Functions both as an exocrine and as an endocrine
1. Endocrine – islets of Langerhans secretes the hormones insulin and glucagon into
the blood
2. Exocrine – secretes digestive enzymes from the pancreatic duct into the
duodenum
Liver
a. Largest organ in the body
b. Located below the diaphragm, in the upper right quadrant of the abdomen
c. Functions
1. Manufactures bile, a yellow to green fluid, which is necessary for the digestion of
fat
2. Produce and store glucose in the form of glycogen
3. Detoxify harmful substances such as alcohol and drugs
4. Manufacture blood proteins necessary for blood clotting
5. Store vitamins A, D and B complex
6. Converts ammonia into urea, chief waste product of protein metabolism
7. Break down hormones no longer useful
8. Remove worn-out red blood cells from circulation and recycle the iron content
Gallbladder
a. Small green organ in the inferior surface of the liver
b. Function is to store and concentrate bile when it is not needed by the body
Large Intestine
Begins at the ileocecal junction, where the ileum enters the large intestine, and ends at the anus
• Also called the colon
• About 5 feet long
• Ileum empties chyme (semi-liquid food) through ileocecal valve into large intestine
• Regions of the large intestine
a. Cecum and appendix
1. Cecum is a blind pouch that extends from the ileocecal junction
2. Vermiform appendix is attached to the cecum and has no digestive function
(contains lymphatic tissue)
b. Ascending, transverse, and descending colon
o Frames the abdomen
c. Sigmoid colon
o S-shaped curve that becomes the rectum
d. Anal canal
o Guarded by two anal sphincters (internal sphincter is involuntary and the external
sphincter is voluntary)
• Functions
a. Absorption of fluid and electrolytes and the elimination of waste products
(produces no digestive enzymes and has no villi for the absorption of nutrients)
b. Mucus lubricates the passage of fecal material
General Overview of Digestion
Each part of the alimentary canal contributes to the overall digestive process
•
Mouth
a. Bolus
1. Soft, pliable ball created from saliva and the mechanical breakdown of food in
the mouth
2. Bolus slides down the throat (pharynx) to be swallowed
b. Salivary glands begin chemical digestion of starches
Ann Senisi Scott & Elizabeth Fong: Body Structures & Functions 11th Edition
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Pharynx
a. Swallowing, or deglutition, is a complex process involving the constrictor muscles of the
pharynx
b. Begins as a voluntary process, changes to an involuntary process as the food enters the
esophagus
Esophagus
o Peristalsis
1. Food is pushed along the esophagus, stomach, small and large intestine by
rhythmic, muscular contractions called peristalsis
2. The nervous system stimulates gland activity and peristalsis
Stomach
a. HCL acid prepares the gastric area for enzyme action
b. Pepsin breaks down proteins and lipase acts on emulsified fats
c. The action of the gastric juices is helped by the churning of the stomach walls
o Semiliquid food is called chyme
d. The only known substances to be absorbed in the stomach are alcohol and some
medications
Small intestine
a. Process of digestion is completed and absorption occurs
1. Protein (begins in the stomach) broken down into amino acids
2. Fats (small intestine) changed into fatty acids and glycerol
3. Carbohydrates (completed in the small intestine) converted to simple sugars such
as glucose
b. Absorption of nutrients
Action in the Large Intestine
• The large intestine is concerned with water absorption, bacterial action, fecal formation, gas
formation and defecation
a. Absorption
1. Water is drawn from the undigested food and indigestible material that pass
through the colon
2. Vitamins B complex and K absorption
b. Bacterial action
1. Intestinal bacteria are harmless to their host
2. Act upon undigested food remains, turning them into acids, amines, gases and
other waste products
c. Gas formation
o Produced by swallowed air and the normal breakdown of food
d. Fecal formation
1. Feces consist of bacteria, waste products from the blood, acids, amines, inorganic
salts, gases, mucus and cellulose
2. Cellulose is the fibrous part of plants that humans are unable to digest; it
contributes to the bulk of the feces
e. Defecation
• Purpose of these functions is to regulate the body’s water balance while storing and excreting
waste products of digestion
Effects of Aging
• Decrease sensory ability of taste buds
• Reduction of saliva
• Loss of teeth
• Slowing peristalsis
Ann Senisi Scott & Elizabeth Fong: Body Structures & Functions 11th Edition
Metabolism
After digestion and absorption, nutrients are carried by the blood to the cells of the body
• Within the cells, nutrients are changed into energy
• Aerobic metabolism – nutrients are combined with oxygen within each cell (known as oxidation)
• Anaerobic metabolism – reduces fats without the use of oxygen
• Thyroid hormones
o Metabolism is governed primarily by the hormones secreted by the thyroid gland
Disorders – Digestive System
• Stomatitis
o Inflammation of the soft tissues of the mouth cavity
• Gingivitis or gum disease
• Periodontal disease
o Chronic bacterial infection of the gums and surrounding tissue
• Gastroesophageal reflux disease (GERD)
o Sphincter muscle is weak allowing stomach’s contents to flow up into the esophagus
• Heartburn
o Acid indigestion results from a backflow of highly acidic gastric juice into the lower end
of the esophagus
• Hiatal hernia (rupture)
o Stomach protrudes above the diaphragm through the esophagus opening
• Pyloric stenosis
o Narrowing of the pyloric sphincter at the lower end of the stomach
• Gastritis
o Acute or chronic inflammation on the stomach lining
• Gastroenteritis
o Inflammation of the mucus membrane lining of the stomach and intestinal tract
• Enteritis
o Inflammation of the intestine
• Ulcer
o Sore or lesion that forms in the mucosal lining of the stomach or duodenum where acid
and pepsin are present
• Inflammatory bowel disease (IBD)
o Chronic diarrhea possibly due to an auto immune disease
• Appendicitis
o Inflamed vermiform appendix
• Hepatitis
o Inflammation of the liver
• Cirrhosis
o Chronic, progressive, inflammatory disease of the liver
• Cholecystitis
o Inflammation of the gallbladder
• Gallstones
o Cholelithiasis, collection of crystallized cholesterol in the gallbladder
• Pancreatitis
o Inflammation of the pancreas
• Diverticulosis
o Condition in which little sacs (diverticula) develop in the wall of the colon
• Hemorrhoids
o Condition in which the veins around the anus or lower rectum are swollen and inflamed
• Diarrhea
o Characterized by loose, watery and frequent bowel movements
• Constipation
o Condition in which defecation is delayed due to excessive water absorption
Ann Senisi Scott & Elizabeth Fong: Body Structures & Functions 11th Edition