ch 20: digestive system Flashcards
what does the digestive system consist of
alimentary canal and accessory glands
what are the main parts of the human alimentary canal
oral cavity, esophagus, stomach, small
intestine, large intestine, rectum and
anus.
what are the accessory digestive glands?
salivary glands, gallbladder and pancreas
All the following are considered organs of
the gastrointestinal tract EXCEPT
a) pharynx
b) small intestine
c) gallbladder
d) stomach
e) esophagus
gallbladder because it’s an accesory organ
what are the different kinds of the peritoneum (thing that covers organs) in the digestive system
◦ Serous membrane of the
abdominal cavity
* Visceral peritoneum covers the
abdominal organs
* Parietal peritoneum lines the
abdominal wall
* Serous fluid between visceral
and parietal peritonea prevents
friction and adhesion
folds of the peritoneum: falciform ligament
: attaches liver
to anterior abdominal wall and diaphragm
GREATER OMENTUM
from the transverse
colon, it covers the folds of the small intestine.
Contains much adipose tissue (beer belly). Contain
many lymph nodes (part of the immune system)
lesser omentum
connects the
stomach and duodenum to the liver.
Pathway for blood vessels entering the liver
the mesocolon
binds the large intestine to the
posterior abdominal wall.
Contains blood and lymphatic vessels.
the mesentery
binds small
intestine to posterior wall.
Contains lots of adipose tissue
and contributes extensively to
the large abdomen in obese
individuals. Contains multiple
blood and lymphatic vessels,
as well as lymph nodes.
what is peritonitis and what is it caused by?
Inflammation of the peritoneum
Most often due to infection by microorganisms
◦ life-threatening
◦ could be due to surgery
◦ could be due to perforation of intestine
Can be due to rubbing of inflamed peritoneal surfaces
◦ not life-threatening, but still painfu
Which of the following peritoneal folds
suspends the liver in place?
a) Greater omentum
b) Falciform ligament
c) Lesser omentum
d) Mesentery
e) Mesocolon
B
The mesentery
a) binds the transverse and sigmoid colon to the posterior
abdominal wall
b) drapes over the transverse colon and coils of the small intestine
c) extends from the posterior wall to wrap around the small
intestine
d) suspends the stomach and duodenum from the liver
c) extends from the posterior wall to wrap around the small
intestine
layers of the GI tract: mucosa
: The inner lining of the
tract; is a mucous membrane
consisting of an epithelium
moistened by glandular secretions
and a lamina propri
layers of the GI tract: submucosa
A layer of areolar
connective tissue that
surrounds the mucosa; has large
blood vessels and lymphatic
vessels; in some regions also
contains exocrine glands that
secrete buffers and enzymes
into the lumen of the digestive
tract. Contains extensive
network of neurons
muscularis
Is dominated by
smooth muscle cells - an inner
circular layer and an outer
longitudinal layer – that play an
essential role in mechanical
processing and in the movement of
materials along the digestive tract
serosa
A layer of visceral
peritoneum that covers organs
along most portions of the
digestive tract; attaches the
digestive tract to adjacent
structures; Connective tissue
contains blood vessels and nerves
where is simple stratified squamous mucosa found and what is its function?
stratified squamous in mouth, pharynx, esophagus and anal canal
◦ offers protection against abrasion
where is simple columnar mucosa found and what is its function
simple columnar in stomach and intestines
◦ secretes enzymes and absorbs nutrients
◦ specialized cells (goblet) secrete mucous onto cell surfaces
describe the lamina propria in mucosa
thin layer of areolar connective tissue
◦ contains blood vessels, nervous tissue, glands and immune cells
describe muscularis mucosae
thin layer of smooth muscle
◦ causes folds to form in mucosal layer to increase surface area
Stretching of the GI tract by chyme will
activate a gastrointestinal reflex pathway.
a) True
b) False
a) True
what are the 2 sets of nervous systems that innervate the GI tract
enteric nervous system (ENS-intrinsic) and autonomic nervous system (ANS-extreinsic)
describe the enteric nervous sytem that regulates the neural innervation of the GI tract
◦ “Brain of the gut” – can function
independently
◦ Myenteric plexus
◦ Located between the longitudinal and
circular smooth muscle layers
◦ Controls GI tract motility
◦ Submucosal plexus
◦ Located within the submucosa
controls secretions of organs in GI tract
describe how the autonomic nervous system regulated the innervation of the GI tract
◦ Regulate neurons of the ENS
◦ Parasympathetic (CN X; sacral
nerves) – increase ENS activity
◦ Sympathetic (thoracic and upper
lumbar nerves – decrease ENS
what kins of sensory receptors are involved in the enteric nervous system
mechanoreceptors,
chemoreceptors
describe the oral cavity
oral cavity formed by cheeks, hard and soft palates and tongue
* mouth opens posteriorly into
oropharynx
hard palate separates oral from nasal cavity
soft palate moves up to
block entrance to nasal
cavity during swallowing
sublingual glands vs submandibular glands bs parotid glands
sublingual: deep to the tongue in the floor of the mouth. Secretes mucus that serves as buffer
\
Submandibular: medial in inferior body of mandible, secretesalivary amylase and mucuc
Paratoid: inferior/anterior to the ears b/w skin and masseter, secrete watery liquid with salivary amylase
The parotid glands are found
a) in the tongue
b) between the skin and the masseter muscle
c) in the floor of the mouth
d) beneath the tongue
e) in the palate
B
Sympathetic nerve impulses
a) promote continuous secretion of a moderate amount of saliva
b) stimulate production of saliva in response to the feel and taste of
food
c) decrease salivation in times of stress
d) A and B are both correct.
e) A, B, and C are all correct.
C
describe the composition of saliva
Saliva is 99.5% water and 0.5% solutes
◦ Ions (Na+, K+, Cl-, HCO3-, phosphates)
◦ Dissolved gases
◦ Organic substances such as urea (waste) , uric acid (waste), mucus, IgA,
lysozyme, salivary amylase
what are the functions of saliva?
*Wet food for easier swallowing
*Dissolves food for tasting
*Bicarbonate and phosphate ions buffer acidic foods
*Chemical digestion of starch (salivary amylase)
*Chloride ions activate salivary amylase
*Removal of metabolic wastes (urea and uric acid)
*Enzyme (lysozyme) → helps destroy bacteria
*IgA = antibodies that prevent attachment of microbes to epithelium
what are the different kinds of digestion in the mouth
mechanical digestion and chemical digestion
describe mechanical digestion in the mouth
(mastication or chewing)
◦ breaks into pieces
◦ mixes with saliva so enzymes can access food molecules
◦ forms a bolus
describe chemical digestion in the mouth
Salivary amylase
◦ begins starch digestion (pH 6.5 or 7.0 in mouth)
◦ inactivated by gastric juices (pH 2.5)
◦ Lingual lipase
◦ Although it is secreted in the mouth, it begins the digestion of triglycerides
in the stomach
describe the pharynx
structure
tube of skeletal muscle lined by mucous membrane
deglutition (swallowing) steps
- Bolus is forced into the oropharynx by
tongue movement - Soft palate moves up, blocking the nasal cavity
- Epiglottis blocks the
trachea, preventing
food from entering - Food moves
from the pharynx
to the esophagus
describe deglutition (swallowing)
2 stages
It consists of voluntary and involuntary stages
Voluntary stage begins when the bolus is forced into the oropharynx by tongue
movement
Receptors in oropharynx stimulate deglutition center in brain
Soft palate moves up, blocking the nasal cavity and epiglottis blocks the trachea – prevents food entry (involuntary)
Food moves from the pharynx to the esophagus
what does the esophagus do?
squeezes food along to the stomach
what does peristalsis do?
moves food boluses into the stomach
what does the cardiac sphincter do?
(lower esophageal
sphincter) regulates the passage of food through
the esophagus and into the stomach.
describe the layers of the esophageal wall (upper sheet region)
The mucosa and submucosa form large folds
that allow for expansion during the passage
of a large bolus; tone in the walls keeps the
lumen closed, except when you swallow.
Muscularis externa contains
skeletal muscle fibers in the
superior portion of the esophagus;
the lower portion of the esophagus
contains smooth muscle tissue
describe the mucosa, submucosa and muscularis in the esophagus
Mucosa = stratified squamous epithelia
Submucosa = large mucous glands
Muscularis = upper 1/3 is skeletal,
middle is mixed, lower 1/3 is smooth
muscle
◦ esophageal sphincters are prominent
circular muscles that control the entry
and exit of food
what tissue does the esophagus have instead of serosa?
Adventitia instead of serosa =
connective tissue without epithelium.
Attaches esophagus to surrounding
structures
what is Gastroesophageal reflux disease (GERD)
When the lower esophageal sphincter fails to close adequately after food has
entered the stomach
stomach content (acidic) can reflux (go back up) into the inferior portion of the
esophagus
causes burning sensation (heartburn)
Which of the following statements is FALSE?
a) The upper esophageal sphincter contains smooth muscle.
b) The upper esophageal sphincter controls movement of food
from the pharynx into the esophagus.
c) The lower esophageal sphincter contains smooth muscle.
d) The lower esophageal sphincter controls movement of food from
the esophagus into the stomach.
e) Gastroesophageal reflex disease may be due to a defect in the
lower esophageal sphincter.
A
describe the stomach
he stomach churns the food (Gentle
mixing waves every 15 to 25 seconds)
with gastric juice to form a mixture called
acid chime (a thin liquid).
The stomach is closed at either ends by
cardiac sphincter and pyloric sphincter.
◦ The pyloric sphincter opens to allow
the passage of chyme into the small
intestine.
Emptying of the stomach into the small intestine occurs ~3ml at a time
describe the layers of the muscularis externa in the stomach
strengthens the stomach wall and assists in the mixing and churning activities essential to the formation of chyme
how does the pyloric sphincter relate to the stomach
Empties as small squirts of
chyme leaves the stomach
through the pyloric sphincter
how is extensive stretching possible in the stomach
die to rugae
describe the mucosa of the stomach wall
simple columnar epthelium
Produces an alkaline carpet of mucus
that covers the interior surfaces of
the stomach and protects epithelial
cells against the acid and enzymes in the gastric lumen.
The myenteric plexus
a) controls the contractile strength and frequency of the muscularis
b) supplies the secretory cells of the mucosal epithelium
c) contains sensory neurons which function as chemoreceptors
d) regulates secretion by gastrointestinal organs.
e) supplies the mucosal epithelium
A
what are gastric pits and gastric glands?
epithelial cells that extend down into the lamina propria
gastrin
hormone
released by G cells in
the stomach when food
arrives to stimulate
additional secretion of
gastric juice
Hydrochloric acid is secreted in the stomach
by
a) parietal cells
b) chief cells
c) G cells
d) mucous neck cells
e) surface mucous cells
a) parietal cells
Pepsinogen is an active protease in the stomach. (protein breakdown)
a) True
b) False
b)
how does protein digestion occur in the stomach
Protein digestion begins in the stomach
◦ HCl denatures (unfolds) protein molecules
◦ HCl turns pepsinogen (inactive) into pepsin (active) which breaks peptide
bonds between certain amino acids
how does fat digestion occur in the stomach?
gastric and lingual lipases split triglycerides
how are the stomach walls protected from being digested
Mucous cells protect stomach walls from being digested with layer of
mucous 1-3mm thick
what is peptic ulcer disease and what are the 3 causes? treatment?
Ulcer (craterlike lesion in a membrane) exposed to
gastric juices can cause bleeding (sometimes severe)
* 3 causes:
* infection with Helicobacter pylori
* bacteria secrete compounds that protect
them from acidity of stomach, but also
destroys mucus
* antibiotics are effective treatment
* use of non-steroidal anti-inflammatory
drugs (NSAIDs)
* hypersecretion of HCl (in certain tumors)
where does nearly all chemical digestion take place?
in the small intestine
describe the pancreas and the liver functions
in terms of digestion what are they and what do they do
The pancreas and the liver are two
accessory glands that are necessary for
chemical digestion to take place in the small
intestine
describe pancreatic juice
Pancreatic juice contains enzymes that digest
◦ starch (pancreatic amylase)
◦ fats (pancreatic lipase)
◦ nucleic acids (ribonuclease and deoxyribonuclease)
◦ proteins (trypsinogen** [trypsin], chymotrypsinogen, [chymotrypsin],
procarboxypeptidase [carboxypeptidase], proelastase** [elastase])
◦ **These enzymes are all inactive in the pancreas and get activated when they
reach the duodenum
sodium bicarbonate from pancreas converts acid chyme to an alkaline pH (7.1-8.2)
◦ promotes activity of pancreatic enzymes
Pancreatic juice does all the following EXCEPT
a) buffer gastric juice
b) provide protein-digesting enzymes in inactive form
c) provide starch-digesting enzymes
d) provide glucagon
e) stop the action of pepsin
d) provide glucagon
describe the liver
structure
Second largest organ after skin
◦ Completely covered by
visceral peritoneum
◦ Two lobes separated by
falciform ligament
describe the gallbladder
Pear-shaped sac that stores
bile until needed for digestion
Bile breaks down fats into monoglycerides
and fatty acids.
a) True
b) False
b) false
Secretions from the liver and gallbladder are united in
the common bile duct and enter the duodenum
through the sphincter of the hepatopancreatic
ampulla.
a) True
b) False
a) true
what are the different functions of the liver
*Role in lipid homeostasis (cholesterol synth.,
lipoprotein synth., break down fatty acids to
generate ATP)
*Synthesis of bile salts from cholesterol; Fats
emulsification
*Role in glucose homeostasis
*Detoxify toxic substances and excrete drugs into bile
*Storage of vitamins (A, B12, D, E, K) and minerals
(iron, copper)
*Phagocytosis of worn out red and white blood cells
and bacteria
describe blood supply to the liver
The liver receives a double supply of blood – Oxygenated blood from the hepatic artery – Deoxygenated blood from hepatic portal
vein; blood in hepatic portal vein comes
from the esophagus, stomach, small
intestine and most of large intestine. It
contains newly absorbed nutrients, drugs,
microbes and toxins from the GI tract.
* All blood eventually leaves the liver via
the hepatic vein
what does the portal triad include
Bile Duct
Branch of Hepatic Portal Vein
Branch of Hepatic Artery
where are liver lobules and what do they do?
arteries and veins of each portal triad deliver
blood to the sinusoids of adjacent liver lobules
steps in blood supply to liver
- Blood enters the liver sinusoids (highly
permeable capillaries) from small branches of
the hepatic portal vein and hepatic artery - As blood flows through liver sinusoids, hepatocytes regulate solute and nutrient levels and
absorb or secrete molecules such as plasma proteins - Phagocytic cells, stellate reticuloendothelial
cells (Kupffer cells), engulf pathogens, cell debris,
and damaged blood cells. They are also store iron,
lipids, and heavy metals (tin or mercury) that are
absorbed by the GI. - The central vein collects blood from the sinusoids of
the lobule. All central veins merge to form the hepatic
veins, which then empty into the inferior vena cava. - Hepatocytes secrete bile into narrow
spaces called bile canaliculi. They extend
outward, away from the central vein. - Bile canaliculi carry bile to bile ducts in the
nearest portal triad. Bile plays an important role
in the digestion of fats in the small intestine
through which structures does blood flow in liver?
Which of the following correctly details the
flow of blood through the liver?
a) hepatic artery > liver sinusoids > central vein > hepatic vein > hepatic portal vein
b) hepatic artery > hepatic portal vein > liver sinusoids > central vein > hepatic vein
c) hepatic artery > central vein > hepatic portal vein > liver sinusoids > hepatic vein
d) hepatic artery and hepatic portal vein > liver sinusoids > central vein >
hepatic vein
e) hepatic artery and hepatic portal vein > liver sinusoids > hepatic vein > central vein
d)
what is hepatitis
inflammation of the liver that can be caused by:
◦ viruses
◦ drugs
◦ chemicals (including alcohol)
can lead to cirrhosis
◦ liver loses its functions because liver cells die and the tissue gets replaced by
scar tissue
◦ remember, scar tissue cannot perform same function
how do gallbladder and bile work?
The gallbladder functions in storing
and concentrating bile
* Bile can flow through the cystic duct in
both directions
* Bile salts emulsify fats and help in
absorption of lipids in duodenum of
small intestine
* Bile contains water, bile salts,
pigments (bilirubin from broken down
RBC), and several ions
describe gallstones
if bile contains insufficient bile salts or excessive cholesterol, cholesterol may
crystallize to form gallstones
partially or completely block ducts
describe the small intestine.
What are the 3 anatomical and physiological regions
The small intestine is the major organ of chemical digestion and nutrient absorption
It is divided in 3 anatomical and physiological regions
duodenum, jejunum and ileum
what is the function of the duodenum in the small intestine
Shortest segment of small intestine (~ 25 cm).
Begins at the pyloric sphincter and merges with jejunum.
Receives and neutralizes the acid chime,
Mixes contents and secretions from pancreas and liver
what is the function of the jejunum in the small intestine?
Digestion of most nutrients
what is the function of the ileum of the small intestine
absorption of bile salts and some vitamins (B12)
Joins to the large intestine at the ileocecal sphincter.
why does the small intestine have a large surface area for absorption?
Folds of the intestinal lining, villi, and microvilli all contribute to the large
surface area
The absorptive surface
area of the small
intestine is about 250 m2 – the size of a tennis
court!
describe the intestinal villus of the small intestine
- Intestinal villus (plicae circulares)– folds of the mucosa and submucosa– cannot stretch out like rugae in the stomach
describe the villi in the small intestine
- villi– Finger-like projections of mucosa– lamina propria contains blood and
lymph capillaries– lined with simple columnar epithelium
describe the microvilli in the small intestine
- microvilli– Finger-like projections of the plasma membrane on
individual cells
describe the histology of each of the 3 segments of the small intestine
deudenum, jejunum and illium
describe the muscularis of the small intestine
structure
formed by two layers of smooth muscle: outgoing longitudinal and inner circular
serosa of the small intestine
CT and epthelial layer - forms portion of visceral peritoneum
where are the lymphati nodules (peyer’s patches) found in the small intestine
found in the lamina propria of the ileum
describe intestinal juices
◦ water and mucus, slightly alkaline
◦ provides a liquid medium to aid for absorption
◦ intestinal enzymes (brush border enzymes) break down foods at the cell
membrane
* Carbohydrate-digesting enzymes
* Protein-digesting enzymes
* Nucleic acid-digesting enzymes
what are the different movements in the small intestine
Segmentation
◦ major movement of the small intestine
◦ localized contraction in areas containing food
◦ Serves for mixing, not moving food along
Peristalsis
◦ propels the chyme onward through the
intestinal tract
describe chemical digestion in the small intestine
Chyme entering the small intestine contains only partially digested
carbohydrates, proteins and lipids.
These compounds need to be broken down into their respective monomers in
order to be absorbed by the small intestine
The completion of the digestion of these compounds is a collective effort of
pancreatic juice, bile and intestinal juice from the small intestine
how are carbohydrates digested?
(oral cavity) salivary amylase breaks down
polysaccharides (glycogen, starch) to
oligosaccharides and disaccharides
(small intestine) pancreatic amylase continues
breaking down glycogen and
starch to smaller oligosaccharides
( small intestine) brush border enzymes → -dextrinase,
maltase, sucrase and lactase act on
oligosaccharides and produce monosaccharides
(fructose, glucose and galactose)
how are proteins digested
(stomach)- HCl denatures proteins- pepsin turns proteins into peptides
(small intestine) proteolitic enzymes (trypsin, carboxypeptidase,
chymotrypsin, elastase) split peptide bonds
between specific amino acids (creates peptides)
(small intestines) brush border enzymes break down
peptides to single amino acids/dipeptides
digestion of lipids
Lingual lipase (secreted in mouth, active
in stomach) and gastric lipase (stomach)
digest triglycerides to diglycerides,
monoglycerides and fatty acids- happens in stomach
– all the rest occur in the small intestine)
emulsification of fat globules
by bile (mechanical digestion)
pancreatic lipase splits triglycerides
into fatty acids & monoglycerides
no brush border enzymes
break down triglycerides
digestion of nucleic acids.
nucleic acid digestion only
happens in the small intestine
Pancreatic juice contains 2 nucleases: -ribonuclease which digests RNA
into nucleotide-deoxyribonuclease which digests
DNA into nucleotide
Nucleotides are further digested
by brush border enzymes: -nucleosidase and phosphatase
digest nucleotides into pentose,
phosphate & nitrogenous
bases
how are nutrients absorbed?
Nutrients pass into epithelial cells of villi in the jejunum of the small intestine
Fatty acids and glycerol are recombined into fats and transported into lymph
Other absorbed nutrients such
as amino acids and sugars pass
into the blood, which then flows
directly to the liver
how are small fatty acids absorbed?
Small fatty acids enter and exit cells by simple diffusion
how are larger lipids absorbed?
Larger lipids exit the lumen only within micelles (bile salts coatin)
◦ Lipid-soluble vitamins get packaged along in micelles
◦ lipids enter cells by simple diffusion leaving bile salts behind
◦ Bile salts reabsorbed into blood & recycled into bile by liver
what are the final steps in the absorption of lipids
Inside epithelial cells, fats are rebuilt and coated with protein to form chylomicrons
Chylomicrons leave intestinal cells by exocytosis into a lacteal (lymphatic capillary)
◦ travel in lymphatic system to reach subclavian veins
◦ removed from the blood by the liver and adipose tissue
Most proteins are absorbed as amino acids
through _________, while dietary lipids are
absorbed through __________.
a) facilitated diffusion; active transport
b) active transport; facilitated diffusion
c) facilitated diffusion; simple diffusion
d) simple diffusion; active transport
e) active transport; simple diffusion
e) active transport; simple diffusion
describe the absorption of water
> 9 liters of fluid enters GI tract each day
Small intestine reabsorbs > 8 liters
Large intestine reabsorbs 90% of that last liter
Reabsorption is by osmosis through cells into
capillaries in villi
describe digestion in the large intestine
*Undigested material passes to the large intestine or colon.
*No enzymes are secreted - only mucus
*Absorption of some ions (Na+ and Cl-) and vitamins
*Absorption of water (90% in small intestine, ~10% in large intestine)
describe how bacteria contribute to digestion in the large intestine
ferment undigested carbohydrates; produces carbon dioxide and methane gas
* ferment undigested proteins into simpler substances → odor
* turn bilirubin into simpler substances → color
* produce vitamin K and B in colon
describe the rectum of the large intestine and its function
The rectum is a muscular organ at the end of the large intestine
The rectum stores feces until they can be eliminated
what is feces
dead epitheleal cells, undigested food such as cellulose, bacteria (both live and dead)
describe the two sphincters in the large intestine
- Involuntary
Opens from the large intestine to the rectum. - Voluntary
Opens into the anus.
describe the eptithelium of the large intestine
smooth tube,
no villi or folds
simple columnar
epithelia (absorptive
cells) cells absorb
water (have microvilli)
Goblet cells
secrete mucus
what is haustral churning in the large intestine
When the distension of a haustrum reaches a certain point, the walls
contract and squeeze the contents into the next haustrum
peristalsis vs mass peristalsis
◦ Strong peristaltic wave begins at the middle of the transverse colon, quickly
driving the content into the rectum
defecation is a reflex. explain
mass peristalsis causes filling of the rectum
* stretching of the rectal wall initiates the
defecation reflex
* The internal anal sphincter (involuntary)
relaxes
* the external anal sphincter can be
voluntarily controlled (except in infants) to
allow or postpone defecation
* voluntary contractions of the diaphragm
and abdominal muscles aid in defecation
The descending colon empties into:
a) Transverse colon
b) Sigmoid colon
c) Cecum
d) Rectum
e) Anal canal
b) Sigmoid colon
