A&P Chapter 14 The Digestive System
1. Summarize the functions of the digestive tract.
---digestion is mechanical and chemical breakdown of foods
into nutrients that cell membranes can absorb
---organs of digestive system carry out these processes
---digestive system consists of alimentary canal
(also called gastrointestinal [GI] tract)
-extends from mouth to anus
--includes several accessory organs that release
secretions into canal
---alimentary canal DIGESTS food—breaks it down into smaller
fragments-and ABSORBS the digested fragments through its
lining into the blood
---accessory organs (teeth, tongue, and several large digestive
glands assist digestive breakdown in several ways
---digestive system makes nutrition possible
2. Sequence the organs of the digestive system that a bolus of food passes through from the mouth to the anus.
---mouth-->pharynx-->esophagus-->stomach-->small intestine-->
large intestine-->anal canal
---accessory organs include salivary glands, liver, gallbladder,
and pancreas
3. Name the tissue layers of the digestive tract.
---wall of alimentary canal consists of four distinct layers
that are developed to different degrees from region to region
--INNERMOST MUCOSA (MUCOUS MEMBRANE) layer composed of surface
epithelium, underlying connective tissue, and small amount of
smooth muscle
--mucosa develops folds and tiny projections in some regions that extend into passageway (called LUMEN )
-INCREASE MUCOSA’S ABSORPTIVE SURFACE AREA
--may also contain glands that are tubular invaginations
into which lining cells secrete mucus and digestive enzymes
--mucosa secretes and absorbs; protects tissue beneath it
--SUBMUCOSA contains much loose connective tissue plus glands
blood vessels, lymphatic vessels, and nerves organized into
structure called PLEXUS
--its vessels nourish surrounding tissues and carry away
absorbed materials
--MUSCULAR LAYER moves the tube and consists of 2 coats of
smooth muscle tissue and some nerves (in a plexus)
--fibers of inner coat encircle the tube ( circular )
-when these fibers contract, tube diameter gets smaller
--fibers of outer coat run lengthwise ( longitudinal )
-when these fibers contract, the tube length gets shorter

--SEROUS (SEROUS LAYER) is comprised of visceral peritoneum
--is the outermost layer
--cells of serosa protect underlying tissues and secrete
serous fluid which moistens/lubricates tube’s outer surface
--organs within abdominal cavity slide freely against one another
4. State the function of the stomach.
---stomach is J-shaped organ that hangs under diaphragm in upper
left portion of abdominal cavity
--has capacity of about 1 liter
---thick folds ( RUGAE ) of mucosal and submucosal layers mark
inner lining and disappear when stomach distends
---receives food from esophagus, mixes food with gastric juice,
initiates protein digestion, does limited amount of
absorption, and moves food into small intestine
---stomach divided into CARDIAC, FUNDIC, BODY, AND PYLORIC
REGIONS
--cardiac region is small area near esophageal opening
-fundic region balloons above cardiac portion & is temporary storage area
-dilated body region is main part of stomach
-lies between the fundic and pyloric portions
-pyloric region narrows and becomes pyloric canal as approaches the small intestine
--**at end of pyloric canal, muscular wall thickens forming a powerful circular muscle called pyloric sphincter (or pylorus)
-this muscle is valve that controls gastric emptying
---after meal, mixing movements of stomach wall help produce
semifluid paste of food particles and gastric juice called
CHYME
---peristalic waves push chyme toward pyloric region
--as chyme accumulates near pyloric sphincter, it begins
to relax allowing stomach contractions to push chyme
a little at time into small intestine
---rate stomach empties depends on chyme’s fluidity and type
of food present
--liquids pass through stomach quite rapidly
--solids remain until well mixed with gastric juice
--fatty foods may remain in stomach 3-6 hours
--liquids-->carbohydrates-->proteins-->fatty foods
5. Describe the digestive secretions of the stomach.
---mucous membrane that form stomach’s inner lining is thick
and surface studded with small openings called gastric pits
--gastric pits are ends of tubular gastric glands
---gastric glands typically contain 3 types of secretory cells

-mucous cells (goblet cells) occur in necks of glands near openings of gastric pits
-chief cells and parietal cells are in deeper parts of
glands
-chief cells secrete digestive enzymes
-parietal cells release hydrochloric acid
--products of mucous cells, chief cells, and parietal cells
form gastric juice
---PEPSIN most important enzyme in gastric juice
--made in inactive form called pepsinogen which is converted to pepsin (active form) by contact with HCl
--most active in acidic environment and begins digestion of nearly all proteins
---cells of mucous membrane (associated with inner lining)
release more viscous and alkaline secretion to coat inside
wall of stomach ( MUCUS )
--prevents pepsin from digesting proteins in stomach lining itself
--INTRINSIC FACTOR important component of gastric juice
--secreted by parietal cells
--needed for vitamin B
12
absorption in small intestine
6. Name the digestive secretions received by the duodenum.
---as chyme enters duodenum (first portion of small intestine)
accessory organs add their secretions
--these organs include the pancreas, liver, and gallbladder
--pancreas secretes a digestive juice called pancreatic juice
--liver secretes bile (important to digestion) which is stored
in gall bladder
--bile salts in bile important to digestion
---chyme moving into duodenum contains amylase (from salivary
glands); pepsin (from gastric glands); amylase, lipase, proteolytic enzymes [trypsin, chymotrypsin, carboxypeptidase ]
and nucleases from the pancreas; peptidase, sucrase, maltase,
lactase, lipase, and enterokinase from the duodenum
7. Explain how the absorptive surface area of the small intestine is increased.
---small intestine has 3 structures that increase its absorptive
surface tremendously
-microvilli are tiny projections of plasma membrane of mucosa cells (sometimes called brush border )
-inside each villus is rich capillary bed and modified
lymphatic capillary called a lacteal
-circular folds (plicae circulares) are deep folds of both mucosa and submucosa layer
-Peyer’s patches (local collections of lymphatic tissue) found in patches near end of small intestine
-help prevent bacteria from entering bloodstream

8. Explain the location of the appendix.
---the appendix is a subdivision of the large intestine
---appendix hangs from saclike first part of large intestine
called the cecum
---appendix is wormlike and potential trouble spot
---usually twisted and is ideal location for bacteria to
accumulate and multiply
---inflammation of appendix ( appendicitis ) is result
9. List the accessory digestive organs.
--pancreas, liver, gallbladder, salivary glands, and teeth
10. Describe the fluids produced by the pancreas.
---produces wide spectrum of enzymes that break down all
categories of digestible foods
---pancreatic enzymes secreted into duodenum in fluid rich in
bicarbonate (alkaline at about pH 8) which helps neutralize
acidic chyme
---secretes pancreatic amylase (starch); trypsin, chymotrypsin,
carboxypeptidase, & others (protein); lipases (totally
responsible for fat digestion); and nucleases (nucleic acids)
---pancreas also has endocrine function; it produces the
hormones insulin and glucagon
11. Relate the liver, bile, gall bladder, hepatic duct, and cystic duct.
---liver is largest gland in body; has four lobes and suspended
from diaphragm and abdominal wall by delicate mesentery cord
called falciform ligament
---liver’s digestive function is to produce bile
---bile leaves liver through common hepatic duct and enters
duodenum through bile duct
---bile is yellow-green watery fluid containing bile salts,
bile pigments (bilirubin from hemoglobin), cholesterol,
phospholipids, and variety of electrolytes
--only bile salts and phospholipids aid digestive process
--bile salts EMULSIFY fats by breaking large fat globules
into smaller ones thus providing more surface area for fat-
digesting enzymes to work on
--GALLBLADDER is small, thin-walled green sac residing in
shallow fossa in inferior surface of liver
--when food digesting not occurring, bile backs up cystic
duct and enters gallbladder where it is stored
--while being stored, bile concentrated by removal of water
---later when fatty food enters duodenum, hormonal stimulus
prompts gallbladder to contract and spurt out stored bile
into the duodenum
---bile stored too long or too much water removed = gallstones
--jaundice occurs if there is blockage of common hepatic
bile ducts which prevents bile from entering small intestine

--jaundice also results from hepatitis or cirrhosis
12. Name the locations of the salivary glands.
---there are three pairs of salivary glands
--parotid glands are large and lie anterior to the ears
--mumps is an inflammation of the parotid glands
--submandibular glands and small sublingual glands empty their
secretions into floor of mouth through tiny ducts
---salivary glands produce saliva which is mixture of mucus and
serous fluids
--mucus moistens and helps bind food together into bolus
--clear, serous portion contains enzyme called salivary amylase which begins process of starch digestion in the
mouth
---saliva also contains lysozyme and IgA antibodies that inhibit
bacteria
---also dissolves food chemicals so they can be tasted
13. Name the enzyme produced by the salivary glands.
--SALIVARY AMYLASE
14. Name the teeth on one side of human dentition.
---are 32 permanent teeth in a full set
---same number and arrangement of teeth exist in both upper and
lower jaw
---2 incisors; 1 canine, 2 premolars (precuspids), 3 molars (3 rd
molar = wisdom tooth)
---chisel-shaped incisors adapted for cutting, fanglike canines
for tearing or piercing, premolars and molars have broad
crowns best suited for grinding
15. Distinguish crown, neck, and root of a tooth.
---tooth consists of two major regions: crown and root
---enamel-covered crown is exposed part of tooth above the gingiva (gum)
---portion of tooth embedded in jawbone is the root
---root and crown connected by tooth region called the neck
---outer surface of root covered by cementum which attaches
tooth to periodontal membrane (ligament)
--this ligament holds tooth in place in bony jaw
--dentin (bonelike material) underlies enamel and forms bulk
of tooth
--dentin surrounds central pulp cavity which contains connective tissue, blood vessels, and nerve fibers
collectively called PULP
---pulp supplies nutrients to tooth tissues and provides for
tooth sensations
---where pulp cavity extends into root, it becomes the root
canal which provides route for blood vessels, nerves, & other
pulp structures to enter pulp cavity of tooth

16. Distinguish between mechanical and chemical digestion.
--mechanical digestion prepares food for further degradation
by enzymes
---biting and chewing, mixing of food in mouth by tongue,
churning of food in stomach, and segmentation in small
intestine are examples of physical processes contributing to
mechanical digestion
--chemical digestion is the sequence of steps in which large
food molecules are broken down to their building blocks by
enzymes
-hydrolysis reactions because water is required
---INGESTION-->PROPULSION-->MECHANICAL DIGESTION-->CHEMICAL
DIGESTION-->ABSORPTION-->DEFECATION
17. Explain why digestion is necessary for absorption.
---food consumed generally a polymer composed of monomers
---polymers must be torn apart into monomers that are small
enough to be moved across plasma membranes of cells lining
small intestine
---ingested materials not broken apart by enzymes into monomers
cannot be absorbed by body (cellulose)
18. Describe the composition of carbohydrates.
---building blocks of carbos are monosaccharides
---most common in human diet are glucose, fructose, and
galactose
---only carbos are to digest (break down) to simple sugars are
sucrose, lactose, maltose, and starch
---care for some fiber, anyone?
19. Describe the composition of proteins.
---protein is polymer composed of monomers of amino acids
--20 of them, 8 are essential and 12 are nonessential
---intermediate digestive produces of proteins are polypeptides
and peptides
20. Describe the composition of fats.
---when lipids are digested, the yield is fatty acids and
glycerol
21. Discuss digestion in the mouth.
---once food placed in mouth, both mechanical and chemical
digestion begin
---food physically broken down into smaller particles by chewing
---food mixed with saliva and salivary amylase begins starch
digestion by breaking it down into maltose
---essentially no food absorption occurs in mouth
--some drugs such as nitroglycerin and alcohol are easily
absorbed through oral mucosa
---pharynx and esophagus have NO digestive functions
--simply provide passageways to carry food to next processing site-the stomach

22. Discuss digestion in the stomach.
---to get to stomach, food must be swallowed (DEGLUTITION)
---complicated process involving coordinated activity of tongue,
soft palate, pharynx, and esophagus
--BUCCAL PHASE occurs in mouth when food has been chewed and
well mixed with saliva
-bolus is forced in pharynx by the tongue
--as food enters pharynx, it passes out of our control and
into realm of reflex activity
--PHARYNGEAL-ESOPHAGEAL PHASE transports food through pharynx
and esophagus
--parasympathetic division of ANS controls events (VAGUS)
-promotes motility of digestive organs from this point on
---once food reaches end of esophagus, it presses against cardioesophageal sphincter causing it to open and food
enters stomach
---secretion of gastric juice regulated by both neural and
hormonal factors
---presence of food in stomach and falling pH stimulate stomach
cells to release GASTRIN
--gastrin stimulates stomach glands to release more protein- digesting enzymes (pepsinogens), mucus, and HCl
---occasionally, cardioesophageal sphincter fails to close
tightly and gastric juice backs up into esophagus = heartburn
--hiatal hernia
---acid environment activates pepsinogen to pepsin
--rennin also produced stomach of young
---food enters stomach, its wall begins to stretch which
activates the three muscle layers of stomach
--compress and pummel the food, breaking it apart, mixing
it with enzymes, and forming semifluid CHYME
---other than beginning process of protein digestion, little
chemical digestion occurs in stomach
---with exception of alcohol and aspirin, NO absorption occurs
through stomach walls
---pylorus-->pyloric valve-->duodenum
23. Discuss digestion and absorption in the small intestine.
---food reaching small intestine is only partially digested
---carbohydrate and protein digestion have begun but virtually
NO fats have be digested
---chemical digestion speeded up as food now takes wild 3 to 6
hour ride through looping coils of small intestine
---by journey’s end, digestion complete and nearly all food
absorption has occurred
---microvilli of small intestine cells bears a few important
enzymes called brush border enzymes

--break down double sugars into simple sugars and complete
protein digestion
-dextrinase, glucoamylase, lactase, maltase, sucrase
--aminopeptidase, carboxypeptidase, dipeptidase
---foods entering small intestine deluged with enzyme-rich
pancreatic juice
**see IO 10
---when chyme enters small intestine, stimulates mucosa cells
to produce SECRETIN AND CHOLECYSTOKININ (CCK) which influence
release of pancreatic juice and bile
---absorption of water and end products of digestion occurs
all along the length of small intestine
--most substances absorbed through intestinal cell plasma membranes by active transport
---enter capillary bed in villus to be transported in blood
to liver via hepatic portal vein
---**exception seems to be lipids which are absorbed by
diffusion
--lipid products enter capillary bed and lacteal in villus
for transport to liver by blood and lymphatic fluids
---at end of ileum, all that remains is some water, indigestible
food materials, and large amounts of bacteria
--debris enters large intestine through the ILEOCECAL VALVE
24. Discuss the role of the large intestine.
---colon itself produces NO digestive enzymes
---debris spends about 12 to 24 hours in large intestine
---some normal flora bacteria metabolize some remaining
nutrients-->release some methane and hydrogen sulfide gas
---bacteria important in vitamin K and some B vitamin synthesis
---absorption by large intestine limited to these vitamins, some
ions, and most of remaining water
---feces contains undigested food residues, mucus, millions of
bacteria, and just enough water to allow smooth passage
---delivered to the rectum for elimination
25. Define metabolism, anabolism, and catabolism.
--metabolism is broad term referring to ALL the chemical
reactions that are necessary to maintain life
---metabolism divided into two parts: anabolism & catabolism
--anabolism involves building larger molecules from smaller
ones (building polymers from monomers)
--catabolism involves breaking down larger substances into
smaller ones (tearing polymers apart into their monomers)
26. Define glycogenesis, glycogenolysis, and gluconeogenesis.
--glycogenesis is process of combining glucose molecules to
form large polysaccharide molecules called glycogen
--process occurs in liver
--glycogen stored in liver and muscle cells

--glycogenolysis means “glycogen splitting”
--opposite of glycogenesis
--blood glucose levels drop, liver begins to break down
glycogen and release glucose bit by bit
--gluconeogenesis means “formation of new sugar”
--if necessary, liver can make glucose from noncarbohydrate
sources such as fats and proteins
27. Summarize carbohydrate metabolism using figure 14.19a on page 461.
28. Summarize fat metabolism using figure 14.19b on page 461.
29. Summarize protein metabolism using figure 14.19c on page
461.
30. Summarize ATP formation using figure 14.19d on page 461.
31. Distinguish hypoglycemia and hyperglycemia.
--hypoglycemia : blood glucose levels TOO LOW; liver breaks
down stored glycogen and releases glucose into blood for
cellular use
--hyperglycemia: excessively high levels of glucose in the
blood results in liver converting glucose to glycogen
and storing in liver cells or muscle cells
--still too much, some stored as FAT
32. Define basal metabolic rate.
--basal metabolic rate (BMR) is amount of heat produced
by body per unit of time when it is under basal conditions
(at rest)
---reflects energy supply person’s body needs just to perform
essential life activities such as breathing, maintaining the
heartbeat, and kidney function
---average 70-kg adult has BMR of about 60 to 72 kcal/hour
---amount of THYROXINE produced by thyroid gland most important
factor in determining person’s BMR
--thyroxine been dubbed “metabolic hormone”
--more thyroxine produced the > the use of oxygen and the more ATP produced
33. Summarize the maintenance of body temperature.
---less than 40% of energy from food utilized and rest escapes
as heat
---heat released warms the tissues and the blood which
circulates to all body tissues, keeping them at homeostatic
temperatures and allowing metabolism to occur efficiently
---body temperature is balance between heat production and heat
loss
---body’s thermostat is in the hypothalamus
---heat-promoting mechanisms include short-term utilization of
vasoconstriction and shivering
--frostbite and hypothermia
---heat loss mechanisms include radiation and/or evaporation

--heat exhaustion, heat stroke, and fever
--fever is controlled hyperthermia
-pyrogens produced by macrophages, WBCs and injured tissue
reset thermostat in hypothalamus