ANAPHY Digestive System Reviewer PDF
ANAPHY Digestive System Reviewer PDF
ANAPHY Digestive System Reviewer PDF
1 FUNCTIONS OF THE DIGESTIVE SYSTEM absorb small molecules of nutrients (amino acids,
Digestive system - complex set of organs, glands, and ducts that work monosaccharides, fatty acids, vitamins, minerals, and water)
together to transform food into nutrients for cells 4. Elimination - removal of undigested material
● Food is broken down into smaller and smaller particles
● Enzymes break the particles down, and the small molecules are 16.2 ANATOMY AND HISTOLOGY OF THE DIGESTIVE SYSTEM
absorbed into the blood and transported all over the body Digestive tract (gastrointestinal tract) (OPESSS)
● The molecules are broken down by other enzymes to release 1. Oral cavity (mouth)
energy or are assembled into new molecules 2. Pharynx (throat)
3. Esophagus
4. Stomach
5. Small and large intestines
6. sinus
Organs of the digestive system
1. The salivary glands
2. Liver
3. Pancreas
Liver and pancreas empty into the small intestine
Inner lining of digestive tract serves as a protective barrier to those
indigestible and harmful materials while allow absorption of specific
nutrients across wall of digestive tract -> nutrients enter blood and
distributed to tissues
SALIVA
● Versatile fluid; helps keep the oral cavity moist and contains
enzymes that begin the process of digestion
● Secreted approximately 1L/day
● Serous part of saliva (parotid and submandibular glands)
contains salivary amylase, which breaks down starch.
○ Breaks covalent bonds between glucose molecules in
starch and other polysaccharides
○ Produces disaccharides such as maltose and isomaltose
(sweet taste); digestion of polysaccharides by salivary ● Only about 5% of the total carbohydrates humans absorb are
amylase enhances the sweet taste of food digested in the mouth
● Most starches are contained in plant cells, which have the
TABLE - FUNCTIONS OF DIGESTIVE SECRETIONS polysaccharide cellulose
● Humans lack the necessary enzymes to digest cellulose
● Saliva has protective functions
○ Prevents bacterial infections in the mouth by washing
the oral cavity with a mildly antibacterial enzyme called
lysozyme
○ Saliva neutralizes pH in mouth, which reduces effects of
bacterial acids on tooth enamel
Gastric phase
● Distention of stomach stimulates mechanoreceptors + activates
a parasympathetic reflex. Action potentials are carried by the
vagus nerves -> medulla oblongata
● Medulla oblongata increases action potentials in the vagus MOVEMENT IN THE STOMACH
nerves that stimulate secretions by parietal and chief cells + ● Two types of stomach movement aid digestion and help move
stimulate gastric and histamine secretion by endocrine cells
chyme through the digestive tract: mixing waves and
● Distention of stomach activates local reflexes that increase peristaltic waves
stomach secretions ○ Both result from smooth muscle contractions in the
● Gastrin is carried -> blood -> stomach stomach wall; occur about every 20 seconds and proceed
from body -> pyloric sphincter
Intestinal phase
● Relatively weak contractions -> mixing waves, which mix
● Chyme in duodenum with pH < 2 or containing lipids inhibits ingested food with stomach secretions -> chyme
gastric secretions by 3 mechanisms
● The more fluid part of chyme -> pyloric sphincter, whereas
○ Chemoreceptors in duodenum are stimulated by H+
more solid center -> b ody
(low pH) or lipids. Action potentials generated by the
● Stronger contractions -> peristaltic waves, which force chyme
chemoreceptors are carried by the vagus nerves -> -> pyloric sphincter, which usually remains closed because of
medulla oblongata, inhibiting parasympathetic action
mild tonic contraction
potentials + decreasing gastric secretions
○ Each one is strong to cause partial relaxation of the
○ Local reflexes activated by H+ or lipids also inhibit
pyloric sphincter + pump a few mL of chyme -> pyloric
gastric secretions
opening + duodenum
○ Secretin and cholecystokinin produced by duodenum ● Increased motility -> increased emptying
decrease gastric secretions
Larraine Castillo, 1NUR2
● Peristaltic waves also occur when the stomach is empty ● Duodenum is about 25 cm long; nearly completes a 180-degree
● Hunger pangs - peristaltic waves are increased by low blood arc as it curves within the abdominal cavity
glucose levels and can create these ○ Common bile duct from liver and pancreatic duct from
○ Occur for about 2-3 minutes and can build in strength to the pancreas join and empty into the duodenum
a prolonged contraction ● Jejunum is about 2.5 m long and makes up 2/5 of total length
○ Begin 12 to 24 hours after the previous meals ● Ileum is about 3.5 m long and makes up 3/5 of the small
○ Reach maximum intensity within 3 or 4 days and intestine
progressively weaker
● The major site of digestion and absorption of food; large surface
● If stomach empties too fast -> efficiency of digestion and area
absorption in small intestine is reduced ○ Circular folds, villi, and microvilli
● If rate of emptying is too slow -> highly acidic contents of ● Mucosa + submucosa = circular folds that run perpendicular to
stomach may damage stomach wall long axis of digestive tract
○ Stomach emptying should be regulated ● Villi - formed by mucosa; covered by simple columnar
● Hormonal and neural mechanisms increase stomach motility epithelium; within each loose connective tissue core are a blood
● Major stimulus of gastric motility and emptying = distension capillary network and a lymphatic capillary called a lacteal
of the stomach wall ● Most cells composing surface of villi have numerous cytoplasmic
● Inhibition of gastric motility and empty is accomplished by extensions called microvilli
the
● Cholecystokinin - major inhibitor of motility and emptying; ● Mucosa of the small intestine is simple columnar epithelium
hence, stomach emptying is slower after a fatty meal due to the with 4 major cell types: (AGGE)
release of cholecystokinin ○ Absorptive - microvilli, produce digestive enzymes, and
● Vomiting - protective mechanism against ingestion of toxic or absorb digested food
harmful substances; also irritation anywhere along digestive ○ Goblet cells, which produce a protective mucus
tract ○ Granular cells, which may help protect the intestinal
○ Neural stimuli travel along vagus nerve to vomiting epithelium from bacteria
center in medulla oblongata ○ Endocrine cells, which produce regulatory hormones
● Ileocecal junction - the site where the ileum connects to the ABSORPTION IN THE SMALL INTESTINE
large intestine ● Most absorption occurs in the duodenum and jejunum, but some
● Ileocecal sphincter - ring of smooth muscle occurs in the ileum
● Ileocecal valve - allows intestinal contents to move from ileum
-> large intestine 16.6 LIVER AND PANCREAS
ANATOMY OF THE LIVER
SECRETIONS OF THE SMALL INTESTINE ● Liver processes nutrients and detoxifies harmful substances
● Secretions from mucosa contain: mucus, ions, and water from the blood
○ These secretions protect intestinal wall from acidic ● Produced bile
chyme and action of digestive enzymes ● Largest internal organ of the body and weighs about 1.36 kg (3
○ Keep chyme in small intestine in a liquid form to facilitate pounds)
digestion ● Located in the right upper quadrant of the abdomen, tucked
● Most secretions are produced by the intestinal mucosa against inferior surface of diaphragm
● Posterior surface of liver is in contact with right ribs 5-12
● Peptidases digest proteins ● Two major lobes: right and left lobe
● Disaccharidases digest small sugars, specifically disaccharides ○ Two lobes are separated by a connective tissue septum
called the falciform ligament
● Mucus is produced by duodenal glands and by goblet cells ○ Two smaller liver lobes, caudate lobe and quadrate
● Hormones released from intestinal mucosa stimulate liver and lobe can be seen from an inferior view
pancreatic secretions ○ Porta is seen from an inferior view; gate through which
● Vagus nerve, secretin release, and chemical or tactile irritation of blood vessels, ducts, and nerves enter or exit the liver
the duodenal mucosa all stimulate secretion by duodenal glands ● Liver receives blood from two sources:
○ Hepatic artery delivers oxygenated blood to the liver,
MOVEMENT IN THE SMALL INTESTINE which supplies liver cells with oxygen.
● Peristaltic contractions - proceed along length of intestine for ○ Hepatic portal vein carries nutrient-rich blood from
variable distances and cause chyme to move along small digestive tract to liver
intestine
Larraine Castillo, 1NUR2
○ Blood exits the liver through hepatic veins, which empty ○ Sphincter regulates the opening into the duodenum
into the inferior vena cava 1. The hepatic ducts from the liver lobes combine to form the
common hepatic duct
● Many delicate connective tissue septa divide the liver into 2. The common hepatic duct combines with the cystic duct from the
lobules with portal triads at their corners gallbladder to form the common bile duct
● Portal triads contain three structures: hepatic artery, hepatic 3. The common bile duct joins the pancreatic duct
portal vein, hepatic duct 4. The combined duct empties into the duodenum at the duodenal
● Hepatic cords - formed by platelike groups of liver cells called papilla
hepatocytes, located between center and margins of each lobule. 5. Pancreatic secretions may also enter the duodenum through an
○ Separated from one another by blood channels called accessory pancreatic duct, which also empties into the
hepatic sinusoids duodenum
● Sinusoid epithelium contains phagocytic cells that help remove
foreign particles from the blood Functions of the liver
● Blood from the hepatic portal vein and the hepatic artery flows
into sinusoids and mixes together
● Mixed blood flows toward the center of each lobule into a
central vein, which unite to form hepatic veins, which carry
blood out of the liver to inferior vena cava
● Parasympathetic stimulation through vagus nerve stimulates bile ANATOMY OF THE PANCREAS
secretion by the liver ● Pancreas is located retroperitoneal, posterior to the stomach in
● Secretin from the duodenum also stimulates bile secretion and the inferior part of the left upper quadrant
release. ● Head near the midline of the body and tail that extends to the
● Cholecystokinin stimulates gallbladder to contract and release left, where it touches the spleen
bile into the duodenum. ● Complex organ composed of both endocrine and exocrine tissues
● Most bile salts are reabsorbed in the ileum. ● Endocrine part consists of pancreatic islets or islets of
● Blood carries the bile salts -> liver, where they stimulate Langerhans, which produce hormones insulin and glucagon that
additional bile salt secretion and are once again secreted -> bile enter the blood, important in controlling blood levels of nutrients
● Loss of bile salts in the feces is reduced by this recycling process (glucose and amino acids)
● Exocrine - compound acinar gland
Control of Bile Secretion and Release ○ Acini - produces digestive enzymes
1. Vagus nerve stimulation -> gallbladder contraction -> releasing ○ Clusters of acini are connected by small ducts, which join
bile into duodenum to form larger ducts, and the larger ducts join to form the
2. Secretin produced by duodenum and carried through the blood pancreatic duct, which joins the common bile duct and
to the liver stimulates bile secretion by liver empties into the duodenum
3. Cholecystokinin produced by duodenum and carried through the
blood -> gallbladder, stimulates gallbladder contraction and FUNCTIONS OF THE PANCREAS
sphincter relaxation -> releasing bile into duodenum ● Exocrine secretions include HCO3- and pancreatic enzymes
4. Bile salts stimulate bile secretion. Over 90% of bile salts are ○ Bicarbonate ions neutralize the acidic chyme that enters
reabsorbed in the ileum and returned -> liver, where they the small intestine from the stomach
stimulate additional secretion of bile salts ○ Increased pH resulting from secretion of HCO3- stops
pepsin digestion but provides the proper environment
for the function of pancreatic enzymes, which are
important in digesting all major classes of food
Larraine Castillo, 1NUR2
● Major protein-digesting enzymes are: trypsin, chymotrypsin, ● About 1.5-1.8 m long and consists of 4 parts: ascending colon,
and carboxypeptidase. These continue the protein digestion transverse colon, descending colon, sigmoid colon
that started in the stomach ● Ascending colon - extends superiorly from the cecum to the
● Pancreatic amylase continues the polysaccharide digestion that right colic flexure, near the liver, where it turns to the left.
began in the oral cavity ● Transverse colon - extends from the right colic flexure to the
● Pancreatic enzymes also include lipase and nucleases, which left colic flexure near the spleen, where the colon turns inferiorly
are enzymes that degrade DNA and RNA to their component ● Descending colon extends from left colic flexure to the pelvis,
nucleotides where it becomes the sigmoid colon, which is an S-shaped tube
that extends medially and inferiorly into the pelvic cavity and
● Both hormonal and neural mechanisms control the exocrine ends at the rectum
secretory activity of the pancreas ● Crypts - straight, tubular glands contained by mucosal lining of
colon, which contain goblet cells
Control of Pancreatic Secretion ● Longitudinal smooth muscle layer of colon forms 3 bands called
- Parasympathetic stimulation from vagus nerve -> pancreas teniae coli
releases a secretion rich in digestive enzymes
- Secretin, released from duodenum, stimulates pancreas to Rectum
release a watery secretion rich in HCO3 ions ● Straight, muscular tube that begins at the termination of sigmoid
- Cholecystokinin, released from duodenum, causes pancreas to colon and ends at the anal canal
release a secretion rich in digestive enzymes ● Muscular tunic is composed of smooth muscle and is thicker in
rectum > rest of digestive tract
16.7 LARGE INTESTINE
ANATOMY OF THE LARGE INTESTINE Anal Canal
● Large intestine: cecum, colon, rectum, anal canal ● The last 2-3 cm of the digestive tract
● Begins at the inferior end of the rectum and ends at the anus
Cecum ● Smooth muscle layer is thicker here > rectum and forms the
● Proximal end of large intestine where it joins with the small internal anal sphincter at its superior end. The external anal
intestine at the ileocecal junction sphincter at the inferior end of the anal canal is formed by
● Located in the right lower quadrant of abdomen near iliac fossa skeletal muscle
● Sac that extends inferiorly about 6 cm past ileocecal junction. ● Hemorrhoids are enlarged or inflamed rectal, or hemorrhoidal,
● Attached to it is the appendix veins that supply the anal canal
● Symptoms of appendicitis is abdominal pain in the mcBurney ○ May cause pain, itching, and/or bleeding around the anus
point, which is midway between umbilicus and the right
superior iliac spine of the coxal bone FUNCTIONS OF THE LARGE INTESTINE
● 18-24 hours are required for material to pass through the large
Colon intestine
Larraine Castillo, 1NUR2
● Chyme -> feces in colon, which is eliminated by defecation ~
absorption of water and salts, secretion of mucus, and action of
microorganisms
● Microorganisms reproduce rapidly and constitute about 30% of
dry weight
● Every 8-12 hours, large parts of colon undergo mass
movements that propel colon contents a considerable distance
toward the anus
○ Extends over 20 or more cm of large intestine
● Defecation reflex - occurs when feces distend the rectal wall
○ Local (weak) and parasympathetic reflexes (strong)
○ Action potentials travel along sensory nerve fibers to
defecation reflex center in sacral region of the spinal cord
○ Motor action potentials reinforce peristaltic contractions
in lower colon and rectum + cause internal anal sphincter
Absorption - begins in the stomach, where some small,
to relax
lipid-soluble molecules, such as alcohol and aspirin, can diffuse
○ External anal sphincter prevents feces from moving out
through the stomach epithelium into the blood
of rectum and through the anal opening; if this sphincter
● Occurs mostly in the duodenum and jejunum, some in the ileum
is relaxed voluntarily, feces are expelled
Transport - requires carrier molecules and includes facilitated diffusion,
○ Persists only for a few minutes and quickly subsides
cotransport, and active transport (latter two require energy to move
molecules across intestinal wall)
● Can be initiated by voluntary actions that stimulate a defecation
reflex
CARBOHYDRATES
○ Large inspiration of air -> closure of larynx -> contraction
● Consist primarily of starches, cellulose, sucrose, and small
of abdominal muscles -> pressure in abdominal cavity
amounts of fructose and lactose; all derived from plants, while
increases and forces feces into rectum -> stretching of
lactose is derived from animals
rectum -> defecation reflex
● Polysaccharides - large carbohydrates, such as starches,
cellulose, and glycogen, that consist of many chemically bonded
16.8 DIGESTION, ABSORPTION, AND TRANSPORT
sugars
Digestion - breakdown of food to molecules that are small enough
● Starch - energy-storage molecule in plants; cellulose f orms the
to be absorbed into the blood
walls of plant cells; glycogen is an energy-storage molecule in
Mechanical digestion - breaks large food particles into smaller
animals and is contained in muscle and liver
ones
Chemical digestion - uses enzymes to break covalent chemical
● Salivary amylase begins the digestion of carbohydrates in the
bonds in organic molecules to be smaller molecules
mouth
Larraine Castillo, 1NUR2
● Insoluble or slightly soluble in water
● Triglycerides (most common; three fatty acids bound to
DIGESTION OF CARBOHYDRATES, LIPIDS, AND PROTEINS glycerol)), phospholipids, steroids, and fat-soluble vitamins
● Saturated fats are solid at room temperature, whereas
polyunsaturated fats are liquid at room temperature; found in
meat, dairy products, eggs, nuts, and certain oils
● Unsaturated fats are found in fish and most plant-based oils
Lipid transport
1. Bile salts surround fatty acids and monoglycerides to form
micelles
Monosaccharides glucose, galactose, and fructose are absorbed by 2. Micelles attach to the plasma membranes of intestinal epithelial
intestinal epithelial cells. cells, and the fatty acids and monoglycerides pass by simple
diffusion into the intestinal epithelial cells
Transport of glucose across the intestinal epithelium 3. Within the intestinal epithelial cell, the fatty acids and
1. Glucose is absorbed by cotransport with Na+ into intestinal monoglycerides are converted to triglycerides; proteins coat the
epithelial cells triglycerides to form chylomicrons, which move out of the
2. Cotransport is driven by a sodium gradient established by a Na+ intestinal epithelial cells by exocytosis
K+ pump 4. The chylomicrons enter the lacteals of the intestinal villi and are
3. Glucose moves out of intestinal epithelial cells by facilitated carried through the lymphatic system to the blood
diffusion
4. Glucose enters the capillaries of the intestinal villi and is carried PROTEINS
through the hepatic portal vein to the liver ● Chains of amino acids; found in most of the plant and animal
products we eat
LIPIDS
Larraine Castillo, 1NUR2
● Pepsin is a protein-digesting enzyme secreted by the stomach,
breaks down large proteins into smaller polypeptides
● Pepsin digests only about 10-20% of the total ingested protein
● In the small intestine, trypsin, chymotrypsin, and
carboxypeptidase continue protein digestion; these are
synthesized by the pancreas in an inactive state
● Other enzymes called peptidases further break down small
peptides intro tripeptides, dipeptides, or single amino acids.
Amino acids are actively transported into the various cells of the body;
stimulated by growth hormone and insulin
● Partially broken down and used to synthesize glycogen or lipids,
which can be stored
● Most of the excess amino acids are converted to lipids