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Questions and Answers
What is the name of the continuous coiled hollow tube that makes up the alimentary canal?
What is the name of the continuous coiled hollow tube that makes up the alimentary canal?
What are the four layers of tissue found in the alimentary canal organs, from deep to superficial?
What are the four layers of tissue found in the alimentary canal organs, from deep to superficial?
What are the three structural modifications that increase the surface area of the small intestine?
What are the three structural modifications that increase the surface area of the small intestine?
Microvilli, Villi, and Circular Folds
Which of the following is NOT a function of the liver?
Which of the following is NOT a function of the liver?
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What is the name of the process that breaks down substances into simpler substances, releasing energy?
What is the name of the process that breaks down substances into simpler substances, releasing energy?
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What is the preferred source for cellular energy production by the body?
What is the preferred source for cellular energy production by the body?
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What are the three phases of deglutition, or swallowing?
What are the three phases of deglutition, or swallowing?
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What are the four main categories of food that are broken down during chemical digestion? (Select all that apply)
What are the four main categories of food that are broken down during chemical digestion? (Select all that apply)
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The large intestine plays a major role in the absorption of nutrients into the bloodstream.
The large intestine plays a major role in the absorption of nutrients into the bloodstream.
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What is the main digestive function of pancreatic enzymes?
What is the main digestive function of pancreatic enzymes?
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Cholesterol is used to make ATP, which is the body's primary energy molecule.
Cholesterol is used to make ATP, which is the body's primary energy molecule.
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Which of the following factors does NOT influence the body's basic metabolic rate (BMR)?
Which of the following factors does NOT influence the body's basic metabolic rate (BMR)?
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What are the two main mechanisms that the body uses to regulate body temperature?
What are the two main mechanisms that the body uses to regulate body temperature?
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A ______ is a controlled hyperthermia that can result from infection, cancer, or allergic reactions.
A ______ is a controlled hyperthermia that can result from infection, cancer, or allergic reactions.
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What are the two types of proteins involved in the transport of cholesterol and fatty acids in the bloodstream?
What are the two types of proteins involved in the transport of cholesterol and fatty acids in the bloodstream?
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What is the name of the metabolic process that builds larger molecules from smaller ones?
What is the name of the metabolic process that builds larger molecules from smaller ones?
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The body's thermostat is located in the ______.
The body's thermostat is located in the ______.
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What are the three metabolic pathways involved in cellular respiration?
What are the three metabolic pathways involved in cellular respiration?
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What is the unit of measure for the energy value of foods and the amount of energy used by the body?
What is the unit of measure for the energy value of foods and the amount of energy used by the body?
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Match the following metabolic functions of the liver with their descriptions:
Match the following metabolic functions of the liver with their descriptions:
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The function of the rooting reflex is to help the infant find the nipple.
The function of the rooting reflex is to help the infant find the nipple.
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Appendicitis is a condition that affects the gastrointestinal tract, but does not specifically involve the appendix.
Appendicitis is a condition that affects the gastrointestinal tract, but does not specifically involve the appendix.
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What is the primary function of the muscularis externa layer in the large intestine?
What is the primary function of the muscularis externa layer in the large intestine?
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Which of the following is NOT a common digestive problem associated with middle age?
Which of the following is NOT a common digestive problem associated with middle age?
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Study Notes
Digestive System Functions
- Ingestion—taking in food
- Digestion—breaking food down physically and chemically
- Absorption—movement of nutrients into the bloodstream
- Defecation—rids the body of indigestible waste
Organs of the Digestive System
- Two main groups of organs:
- Alimentary canal (gastrointestinal or GI tract)—continuous, coiled hollow tube. These organs ingest, digest, absorb, and defecate.
- Accessory digestive organs—include teeth, tongue, and other digestive organs.
Organs of the Alimentary Canal
- Mouth
- Pharynx
- Esophagus
- Stomach
- Small intestine
- Large intestine
- Anus
Mouth (Oral Cavity) Anatomy
- Lips (labia)—protect the anterior opening
- Cheeks—form the lateral walls
- Hard palate—forms the anterior roof
- Soft palate—forms the posterior roof
- Uvula—fleshy projection of the soft palate
- Vestibule—space between lips externally and teeth and gums internally
- Oral cavity proper—area contained by the teeth
- Tongue—attached at hyoid bone and styloid processes of skull; attached to floor of the mouth by lingual frenulum.
- Tonsils (palatine and lingual)—located at posterior end and base of tongue respectively.
Mouth Physiology
- Mastication (chewing) of food
- Mixing masticated food with saliva
- Initiation of swallowing by the tongue
- Allows for the sense of taste
Pharynx Anatomy
- Nasopharynx—not part of the digestive system
- Oropharynx—posterior to oral cavity
- Laryngopharynx—below the oropharynx and connected to the esophagus
Pharynx Physiology
- Serves as a passageway for air and food
- Food is propelled to the esophagus by two muscle layers:
- Longitudinal inner layer
- Circular outer layer
- Food movement is by alternating contractions of the muscle layers (peristalsis)
Esophagus Anatomy and Physiology
- Anatomy:
- About 10 inches long
- Runs from pharynx to stomach through the diaphragm
- Physiology:
- Conducts food by peristalsis (slow rhythmic squeezing)
- Passageway for food only (respiratory system branches off after the pharynx)
Layers of Tissue in the Alimentary Canal Organs
- Four layers from deep to superficial:
- Mucosa
- Submucosa
- Muscularis externa
- Serosa
Mucosa Layer
- Innermost, moist membrane consisting of:
- Surface epithelium
- Small amount of connective tissue (lamina propria)
- Small smooth muscle layer
- Lines the cavity (known as the lumen)
Submucosa Layer
- Just beneath the mucosa
- Soft connective tissue with blood vessels, nerve endings, mucosa-associated lymphoid tissue, and lymphatics
Muscularis Externa Layer
- Smooth muscle
- Inner circular layer
- Outer longitudinal layer
- Serosa—outermost layer of the wall contains fluid-producing cells
- Visceral peritoneum—outermost layer that is continuous with the innermost layer
- Parietal peritoneum—innermost layer that lines the abdominopelvic cavity
Alimentary Canal Nerve Plexuses
- Two important nerve plexuses that serve the alimentary canal.
- Submucosal nerve plexus
- Myenteric nerve plexus
- Function is to regulate mobility and secretory activity of GI tract organs.
Stomach Anatomy
- Location: Left side of abdominal cavity
- Food enters at the cardioesophageal sphincter
- Food empties into the small intestine at the pyloric sphincter (valve)
- Regions of the stomach:
- Cardiac region—near the heart
- Fundus—expanded portion lateral to the cardiac region
- Body—midportion
- Pylorus—funnel-shaped terminal end
- Rugae—internal folds of the mucosa
- Stomach can stretch and hold 4 L (1 gallon) of food when full
- External regions:
- Lesser curvature—concave medial surface
- Greater curvature—convex lateral surface
Stomach Layers
- Muscularis externa has a third layer (oblique)
- Layers of peritoneum attached to the stomach:
- Lesser omentum—attaches the liver to the lesser curvature
- Greater omentum—attaches the greater curvature to the posterior body wall; embedded fat insulates, cushions, and protects abdominal organs
Stomach Physiology
- Temporary storage tank for food
- Site of food breakdown
- Chemical breakdown of protein begins
- Delivers chyme (processed food) to the small intestine
Structure of Stomach Mucosa
- Mucosa is simple columnar epithelium
- Mucous neck cells—produce a sticky alkaline mucus
- Gastric glands—situated in gastric pits and secrete gastric juice
- Chief cells—produce protein-digesting enzymes (pepsinogens)
- Parietal cells—produce hydrochloric acid
- Enteroendocrine cells—produce gastrin
Small Intestine
- The body's major digestive organ
- Site of nutrient absorption into the blood
- Muscular tube extending from the pyloric sphincter to the ileocecal valve
- Suspended from the posterior abdominal wall by the mesentery
Subdivisions of the Small Intestine
- Duodenum —attached to the stomach; curves around the head of the pancreas
- Jejunum—attaches anteriorly to the duodenum
- Ileum—extends from jejunum to large intestine.
Chemical Digestion in the Small Intestine
- Chemical digestion begins in the small intestine
- Enzymes are produced by:
- Intestinal cells
- Pancreas
- Pancreatic ducts carry enzymes to the small intestine
- Bile, formed by the liver, enters via the bile duct.
Small Intestine Anatomy
- Three structural modifications that increase surface area:
- Microvilli—tiny projections of the plasma membrane
- Villi—fingerlike structures formed by the mucosa
- Circular folds (plicae circulares)—deep folds of mucosa and submucosa
Large Intestine
- Larger in diameter, but shorter in length, than the small intestine
- Extends from the ileocecal valve to the anus
- Subdivisions:
- Cecum
- Appendix
- Colon
- Ascending
- Transverse
- Descending
- Sigmoid
- Rectum
- Anal canal
Large Intestine Anatomy
- Cecum—saclike first part of the large intestine; appendix hangs from the cecum
- Appendix—accumulation of lymphatic tissue that sometimes becomes inflamed (appendicitis)
- Colon (ascending, transverse, descending, sigmoid)—travels up right side of abdomen, across abdominal cavity, down left side, and into the pelvis.
- Rectum—and anus also located in the pelvis
- Anus—opening of the large intestine; has external and internal sphincters (normally closed except during defecation)
Large Intestine Anatomy
- No villi present
- Goblet cells produce alkaline mucus which lubricates the passage of feces
- Muscularis externa layer is reduced to three bands of muscle called teniae coli
- These bands cause the wall to pucker into haustra (pocketlike sacs)
Accessory Digestive Organs
- Teeth
- Salivary glands
- Pancreas
- Liver
- Gallbladder
Teeth
- Function is to masticate (chew) food
- Humans have two sets of teeth:
- Deciduous ("milk") teeth—20 teeth by age two
- Permanent teeth—32 teeth (some people don't have wisdom teeth); replace deciduous teeth between ages 6 and 12
- Classification of Teeth:
- Incisors-cutting
- Canines (eyeteeth)—tearing or piercing
- Premolars (bicuspids)—grinding
- Molars—grinding
Regions of a Tooth
- Crown—exposed part
- Enamel—hardest substance in the body
- Dentin—found deep to the enamel and forms the bulk of the tooth
- Pulp cavity—contains connective tissue, blood vessels, and nerve fibers.
- Root canal—where the pulp cavity extends into the root.
- Neck—region in contact with the gum
- Cementum—covers outer surface of root; attaches tooth to periodontal membrane
Salivary Glands
- Three pairs of salivary glands empty secretions into the mouth:
- Parotid glands—found anterior to the ears
- Submandibular glands
- Sublingual glands —both empty saliva into the floor of the mouth through small ducts
- Parotid glands—found anterior to the ears
Saliva
- Mixture of mucus and serous fluids
- Helps to form a food bolus
- Contains salivary amylase to begin starch digestion
- Dissolves chemicals so they can be tasted.
Pancreas
- Found posterior to the parietal peritoneum (retroperitoneal)
- Extends across the abdomen from spleen to duodenum
- Produces digestive enzymes that break down all categories of food.
- Enzymes enter the duodenum
- Alkaline fluid introduced with enzymes neutralizes acidic chyme coming from the stomach; hormones produced by the pancreas (insulin, glucagon).
Liver
- Largest gland in the body; located on the right side of the body under the diaphragm.
- Consists of four lobes
- Suspended from the diaphragm and abdominal wall by the falciform ligament
- Connected to the gallbladder via the common hepatic duct
Bile
- Produced by cells in the liver
- Leaves the liver through the common hepatic duct
- Composition:
- Bile salts
- Bile pigments (mostly bilirubin from the breakdown of hemoglobin)
- Cholesterol
- Phospholipids
- Electrolytes
- Function: Emulsify fats; physically break large fat globules into smaller ones.
Gallbladder
- Sac found in a hollow fossa of the liver
- When no digestion is occurring, bile backs up the cystic duct for storage in the gallbladder
- When digestion of fatty food is occurring, bile is introduced into the duodenum from the gallbladder.
- Gallstones are crystallized cholesterol which can cause blockages.
Functions of the Digestive System
- Ingestion—placing food into the mouth
- Propulsion—moving foods from one region of the digestive system to another
- Peristalsis—alternating waves of contraction and relaxation that squeezes food along the GI tract
- Segmentation—moving materials back and forth to aid with mixing in the small intestine.
Digestion in the Small Intestine
- Enzymes from the brush border function to:
- Break double sugars into simple sugars
- Complete some protein digestion
- Pancreatic enzymes play the major digestive function:
- Help complete digestion of starch (pancreatic amylase)
- Carry out about half of all digestion of protein
- Digest fats using lipases from the pancreas
- Digest nucleic acids using nucleases
- Alkaline content neutralizes acidic chyme.
Regulation of Pancreatic Juice Secretion
- Release of pancreatic juice into the duodenum is stimulated by:
- Vagus nerve
- Local hormones
- Secretin
- Cholecystokinin (CCK)
- Hormones travel the blood to stimulate the pancreas to release enzyme- and bicarbonate-rich product.
- Secretin causes the liver to increase bile output.
- CCK causes the gallbladder to release stored bile.
- Bile is necessary for fat absorption and absorption of fat-soluble vitamins (K, D, A).
Absorption in the Small Intestine
- Water is absorbed along the length of the small intestine
- End products of digestion:
- Most substances are absorbed by active transport through cell membranes
- Lipids are absorbed by diffusion
- Substances are transported to the liver by the hepatic portal vein or lymph
Propulsion in the Small Intestine
- Peristalsis is the major means of moving food
- Segmental movements
- Mix chyme with digestive juices
- Aid in propelling food
Food Breakdown and Absorption in the Large Intestine
- No digestive enzymes are produced
- Resident bacteria digest remaining nutrients
- Produce some vitamin K and B
- Release gases
- Water and vitamins K and B are absorbed
- Remaining materials are eliminated via feces
- Feces contains:
- Undigested food residues
- Mucus
- Bacteria
- Water
Propulsion in the Large Intestine
- Sluggish peristalsis
- Mass movements
- Slow, powerful movements
- Occur three to four times per day
- Presence of feces in the rectum causes a defecation reflex
- Internal anal sphincter is relaxed
- Defecation occurs with relaxation of the voluntary (external) anal sphincter
Nutrition
- Nutrient-substance used by the body for growth, maintenance, and repair
- Major nutrients:
- Carbohydrates
- Lipids
- Proteins
- Water
- Minor nutrients:
- Vitamins
- Minerals
Dietary Sources of Major Nutrients
- Carbohydrates (mostly from plants; exceptions: lactose from milk and small amounts of glycogen from meats)
- Lipids (saturated fats from animal products; unsaturated fats from nuts, seeds, and vegetable oils; cholesterol from egg yolk, meats, and milk)
- Proteins (complete proteins from animal products, essential amino acids that our bodies cannot make must be consumed via our diet. Legumes and beans are incomplete proteins)
- Vitamins (used as coenzymes, found in all major food groups)
- Minerals (play many roles in the body, found in vegetables, legumes, milk, and some meats).
Metabolism
- Chemical reactions necessary to maintain life
- Catabolism—substances are broken down; energy released
- Anabolism—larger molecules are built from smaller ones.
Carbohydrate Metabolism
- Carbohydrates are the body's preferred source to produce cellular energy (ATP)
- Glucose (blood sugar)
- Major breakdown product of carbohydrate digestion
- Fuel used to make ATP
Cellular Respiration
- Oxygen-using events within the cells to create ATP from ADP.
- Carbon leaves cells as carbon dioxide (CO2)
- Hydrogen atoms combine with oxygen to form water
- Energy produced adds a phosphorus to ADP to produce ATP
- ATP can be broken down to release energy for cellular use
Metabolic Pathways Involved in Cellular Respiration
- Glycolysis—energizes a glucose molecule so it can be split into two pyruvic acid molecules and yield ATP.
- Krebs cycle—produces virtually all the carbon dioxide and water resulting from cell respiration, yields small amounts of ATP
- Electron transport chain—hydrogen atoms removed during glycolysis and the Krebs cycle are delivered to protein carriers; hydrogen is split into hydrogen ions and electrons in the mitochondria; electrons give off energy in steps to enable the production of ATP
Metabolism of Carbohydrates
- Hyperglycemia—excessively high levels of glucose in the blood; Excess glucose stored in body cells as glycogen; if blood glucose levels are too high, excesses are converted to fat.
- Hypoglycemia—low levels of glucose in the blood; Liver breaks down stored glycogen and releases glucose into the blood
Fat Metabolism
- Handled mostly by the liver
- Use some fats to make ATP
- Synthesizes lipoproteins, thromboplastin, and cholesterol
- Releases breakdown products into the blood
- Body cells remove fat (and cholesterol) to build membranes and steroid hormones.
- Fats must first be broken down to acetic acid, in mitochondria, acetic acid is completely oxidized, producing water, carbon dioxide, and ATP
- Acidosis (ketoacidosis) results from incomplete fat oxidation in which acetoacetic acid and acetone accumulate in the blood; breath has a fruity odor. common with "no carbohydrate" diets, uncontrolled diabetes mellitus, starvation.
Protein Metabolism
- Proteins are conserved by body cells (they are used for most cellular structures)
- Ingested proteins are broken down to amino acids
- Cells remove amino acids to build proteins
- Synthesized proteins are actively transported across cell membranes
- Amino acids are used to make ATP only when proteins are overabundant or there is a shortage of other sources.
- Amine groups are removed from proteins as ammonia, the rest of the protein molecule enters the Krebs cycle in mitochondria; the liver converts harmful ammonia to urea.
Role of the Liver in Metabolism
- Several roles in digestion, manufactures bile, detoxifies drugs and alcohol, degrades hormones, produces cholesterol, blood proteins (albumin and clotting proteins), plays a central role in metabolism, can regenerate.
Metabolic Functions of the Liver
- Glycogenesis—"glycogen formation"; glucose molecules are converted to glycogen, stored in the liver.
- Glycogenolysis—"glucose splitting"; glucose is released from the liver after conversion from glycogen.
- Gluconeogenesis—"formation of new sugar"; glucose is produced from fats and proteins.
- Fats and fatty acids absorbed by the liver; some are oxidized for liver energy production. Rest are broken down into simpler compounds and released into bloodstream.
Cholesterol Metabolism and Transport
- Cholesterol is not used to make ATP; Functions of cholesterol:
- Serves as a structural basis of steroid hormones and vitamin D
- Is a major building block of plasma membranes
- Most cholesterol is produced in the liver (85 percent)
- Cholesterol and fatty acids cannot freely circulate in the bloodstream; transported by lipoproteins (lipid-protein complexes).
-Low-density lipoproteins (LDLs) transport to body cells; rated "bad lipoproteins" since they can lead to artherosclerosis
- High-density lipoproteins (HDLs) transport from body cells to the liver
Body Energy Balance
- Energy intake = total energy output (heat + work + energy storage)
- Energy intake is the energy liberated during food oxidation
- Energy produced during glycolysis, Krebs cycle, and the electron transport chain
- Energy output: energy lost as heat (60 percent) and energy stored as fat or glycogen.
Regulation of Food Intake
- Body weight is usually relatively stable
- Energy intake and output remain about equal
- Mechanisms that may regulate food intake: levels of nutrients in the blood, hormones, body temperature, psychological factors.
Metabolic Rate and Body Heat Production
- Basic metabolic rate (BMR)—amount of heat produced by the body per unit of time at rest.
- Average BMR is about 60 to 72 kcal/hour
- Kilocalorie (kcal) is the unit of measure for the energy value of foods and the amount of energy used by the body
- Factors that influence BMR: surface area, gender, age, amount of thyroxine produced. More thyroxine means a higher metabolic rate.
- Total metabolic rate (TMR) = Total amount of kilocalories the body must consume to fuel ongoing activities; TMR increases with an increase in body activity; TMR must equal consumed calories to maintain weight homeostasis and a constant weight.
Body Temperature Regulation
- Most energy is released as foods are oxidized, most energy escapes as heat.
- The body has a narrow range of homeostatic temperature, must remain between 35.6°C and 37.8°C (96°F to 100°F)
- The body's thermostat is in the hypothalamus
- Initiates heat-loss or heat-promoting mechanisms
- Heat-promoting mechanisms:
- Vasoconstriction of blood vessels
- Blood rerouted to deeper, more vital body organs
- Shivering (contraction of muscles produces heat)
- Heat-loss mechanisms:
- Heat loss from the skin via radiation and evaporation
- Skin blood vessels and capillaries are flushed with warm blood
- Evaporation of perspiration cools the skin
- Fever—controlled hyperthermia (results from infection, cancer, allergic reactions, CNS injuries); if the body thermostat is set too high, body proteins may be denatured and permanent brain damage may occur.
Developmental Aspects of the Digestive System
- The alimentary canal is a continuous tube by the fifth week of development
- Digestive glands bud from the mucosa of the alimentary tube
- The developing fetus receives all nutrients through the placenta
- In newborns, feeding must be frequent, peristalsis is inefficient, and vomiting is common
- Newborn reflexes:
- Rooting reflex (helps infant find the nipple)
- Sucking reflex (helps infant hold on to the nipple and swallow)
- Teething begins around age six months
- Problems of the digestive system:
- Gastroenteritis (inflammation of the gastrointestinal tract)
- Appendicitis (inflammation of the appendix)
- Metabolism decreases with old age
- Middle-age digestive problems
- Ulcers
- Gallbladder problems
- Activity of digestive tract in old age: fewer digestive juices, peristalsis slows, diverticulosis and cancer are more common.
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Description
This quiz covers the essential functions of the digestive system, including ingestion, digestion, absorption, and defecation. It also explores the various organs involved, particularly focusing on the anatomy of the alimentary canal and accessory digestive organs. Test your knowledge about how our digestive system processes food and nutrients.
