Chapter24: Lecture Midterm II Flashcards
Digestive system
consists of a group of organs that break down the food we eat into smaller moelcules that can be used by body cells
The digestive canal (gastrointestinal tube)
a continuous tube that extends through the thoracic and abdominal cavities from the esophagus to the anus through the thoracic and abdominopelvic cavities
Organs of the digestive canal include
- esophagus
- stomach
- small intestine
- large intestine
- anal canal
The accessory digestive organs include
- mouth
- teeth
- tongue
- salivary glands
- pharynx
- liver
- gallbladder
- and pancreas
What helps to breakdown food in the stomach
muscular contractions in the wall of the digestive canal physically breakdown the food by churning it and propelling the food along the canal from the esophagus to the anus
6 Basic functions of the digestive system
- ingestion
- secretion
- mixing and propulsion
- digestion
- absorption
- defecation
What does the secretion phase of the digestive system do
releases water, acid, buffers and enzymes into the lumen of the digestive canal
What does the mixing and propulsion stage of the digestive system do
churns, and moves food through the digestive canal
Each day, cells within the wall of the digestive canal and accessory digestive organs secrete a total of
7 litres of water, acid, buffers and enzymes into the lumen of the digestive canal
From the esophagus to the anal canal there are 4 layers of tissues from deep to superficial:
- mucosa
- submucosa
- muscular layer
- serosa/adventitia
The mucosa
- inner lining of the digestive canal
- composed of epithelium, lamina propria and muscularis mucosae
The epithelium layer of the mucosa in the mouth, pharynx, esophagus and anal canal is
non keratinized stratified squamous epithelium that serves a protective function
The stomach and intestines epithelium layer is
simple columnar epithelium; functions in secretion and absorption
the type of exocrine cells that secrete mucus and fluid into the lumen of the digestive canal
enteroendocrine cells
The lamina propria
is areolar connective tissue containing many blood and lymphatic vessels, which are routes by which nutrients absorbed into the digestive canal reach other tissues of the body
The lamina propria supports the
epithelium and binds to the muscularis mucosa
The lamina propria contains what cells
MALT
- prominent lymph nodules contain immune system cells that protect against disease
Muscularis mucosae
thin layer of smooth muscle fibers
- throws the mucous membrane of the stomach and small intestine into many small folds, which increase the surface area for digestion and absorption
Movement of the muscularis mucosae ensures that
all absorptive cells are fully exposed to the contents of the digestive canal
The submucosa
consists of areolar connective tissue that binds the mucosa to the muscularis
- contains many blood and lymphatic vessels that recieve absorbed food molecules
- contains glands and lymphatic tissue
The submucosa also contains an extensive network of
neurons known as the submucosal neural plexus
Muscular layer of the mouth, pharynx, superior and middle parts of the esophagus contains
skeletal muscle that produces voluntary swallowing
- skeletal muscle also forms the external anal sphincter which permits voluntary control of defecation
Throughout the rest of the digestive canal the muscular layer consists of
smooth muscle that is found in two sheets;
- inner sheet: circular fibers
- outer sheet: longitudinal fibers
Involuntary contractions of smooth muscle in the digestive tract…
help break down food, mix it with digestive secretions and propel it along the digestive canal
Those portions of the digestive canal that are suspended in the abdominal cavity have a superficial layer called the
serosa
Serosa
serous membrane composed of areolar connective tissue and simple squamous epithelium
The esophagus lacks…
serosa; instead, only a single layer of areolar connective tissue called the adventitia forms the superficial layer of this organ
The digestive canal is regulated by an intrinsic set of nerves called
enteric nervous system
The enteric nervous system is known as the
brain of the gut
The neurons of the ENS are arranged in two neural plexuses;
- myenteric neural plexus
- submucosal neural plexus
Myenteric neural plexus
located between the longitudinal and circular smooth muscle layers
Submucosal neural plexus
found within the submucosa
The ENS consists of
motor neurons, interneurons, and sensory neurons
because the motor neurons of the myenteric neural plexus supply the longitudinal and circular smooth muscle layers of the muscular layer
this neural plexus mostly controls digestive canal motility (movement), particularly the frequency and strength of contraction of the muscular layer
The motor neurons of the submucosal neural plexus supplies the
secretory cells of the mucosal epithelium, controlling the secretions of the organs of the digestive canal
The interneurons of the ENS interconnect
the neurons of myenteric and submucosal neural plexuses
The sensory neurons of the ENS supply the
mucosal epithelium and contain receptors that detect stimuli in the lumen of the digestive canal
The wall of the digestive canal contains two types of sensory receptors
- chemoreceptors
- mechanoreceptors
What nerve supplies parasympathetic fibers to most parts of the digestive canal
the vagus nerve
The large intestine however, is supplied by
parasympathetic fibers from the sacral spinal cord
Parasympathetic preganglionic neurons of the vagus or pelvic splanchic nerves synapse withh
parasympathetic postganglionic neurons located in the myenteric and submucosal neural plexuses
Some of the parasympathetic posganglionic neurons synapse
directly with smooth muscle and glands within the wall of the digestive canal
In general, stimulation of the parasympathetic nerves that innervate the digestive canal causes an
increase in digestive canal secretion and motility by increasing the activity of ENS neurons
Sympathetic nerves that supply the digestive canal arise from
the thoracic and upper lumbar regions of the spinal cord
- make connections with the ENS
Sympathetic postganglionic neurons synapse with
neurons located in myenteric and submucosal neural plexus
In general the sympathetic nerves that supply the digestive canal
cause a decrease in digestive canal secretion and motility by inhibiting the neurons of the ENS
Emotions such as anger, fear and anxiety may
slow digestion because they stimulate sympathetic nerves that supply the digestive system
GI reflex pathways regulate
GI secretion and motility in response to stimuli within the GI tract
Peritoneum
largest serous membrane of the body;
- consists of a layer of simple squamous epithelium with an underlying supporting layer of areolar connective tissue
Parietal peritoneum
lines the wall of the abdominal cavity
Visceral peritoneum
covers some organs in the cavity and is their serosa
Peritoneal cavity
the slim space containing lubricating serous fluid between the parietal and visceral peritoneal cavity
Organs that are retroperitoneal
kidneys, ascending and descending colons of the large intestine, duodenum of the small intestine, and pancreas
Unlike the heart and lungs smooth surface, the peritoneum contains
large folds that weave between the viscera
The folds on the viscera contain
blood vessels, lymphatic vessels, and nerves that supply the abdominal organs
What are the 5 major peritoneal folds
- greater omentum
- falciform ligament
- lesser omentum
- mesentery
- mesocolon
The greater omentum
- drapes over from transverse colon like a fatty apron
- double sheet that folds back on itself (4 layers)
- contains adipose tissue that contributes to beer belly
- contains many lymph nodes that contain macrphages and antibody producing plasmocytes that help combat and contain infections of the digestive canal
The falciform ligament
attaches the liver to the anterior abdominal wall and diaphragm.
- The liver is the only digestive organ that is attached to the anterior abdominal wall
The lesser omentum
arises as an anterior fold in the serosa of the stomach and duodenum
- it connects the stomach and duodenum to the liver
- pathway for blood vessels entering the liver and contains the hepatic portal vein, common hepatic artery and bile duct, along with some lymph nodes
Mesentery
- fan shaped fold of the peritoneum
- binds the jejunum and ileum of the small intestine to the posterior abdominal wall
- forms a double-layered structure
Between the two layered folds of the mesentery, are the
blood and lymphatic vessels and lymph nodes
Mesocolon
- two separate folds of peritoneum
- bind the transverse colon and sigmoid colon of the large intestine to the posterior abdominal wall
What carries blood and lymphatic vessels to the intestines
mesocolon
Together the mesentery and mesocolon
hold the intestines loosely in place, allowing movement as muscular contractions mix and move the luminal contents along the digestive canal
The mouth is formed by
lips, cheeks, hard and soft palates, oral cavity, teeth, salivary glands and tongue
What attaches the lip to its corresponding gum
labial frenulum
What helps keep food between the upper and lower teeth when chewing
contraction of buccinator muscles
Fauces
opening of the mouth to the pharynx
hard palate
anterior portion of roof of the mouth- formed by maxillae and palatine bones
soft palate
posterior portion of roof of mouth - arch shaped muscular partition between oropharynx and nasopharynx
Uvula
during swallowing, the soft palate and uvula are drawn superiorly, closing off the nasopharynx and preventing swallowed foods and liquids from entering the nasal cavity
Salivary glands
releases a secretion called saliva into the oral cavity; to keep the mouth and pharynx moist and clean
When food enters the mouth,
secretion of saliva increases, and it lubricates, dissolves, and begins chemical breakdown of food
The mucosa and submucosa of the mouth contain
about 800-1000 small salivary glands that open directly and indirectly via short ducts into the oral cavity
- these include: ; labial, buccal, and palatal glands and lingual
All small glands located in the mucosa and submucosa are called
minor slaivary glands
Three main pairs of salivary glands
- parotid
- submandibular
- sublingual
Parotid glands
located inferior and anterior to the ears, between the skin and the masseter muscle
Submandibular glands
are found on the floor of the oral cavity proper; they are medial and partly inferior to the mandible
The submandibular glands are lateral to the
lingual frenulum
Sublingual glands
beneath the tongue, and superior to the submandibular glands
What is saliva composed of
99% water and 0.5% other solutes
- solutes include ions: sodium, potassium, chloride, bicarbonate and phosphate
Some dissolved gasses and various organic substances are also present such as
urea, uric acid, mucus, immunoglobulin A, the bacteriolytic enzyme, lysozyme, and salivary amylase (digestive enzyme that acts on starch)
All salivary glands supply the same ingredients; T or F
False
The parotid glands secrete;
watery (serous) liquid containing salivary amylase
Submandibular glands secrete
salivary amylase mixed with mucus
The sublingual glands secrete
mostly mucus and small amount of salivary amylase
The water in saliva provides a medium for
dissolving foods so that they can be tasted by gustatory receptors so that digestive reactions can begin
what activates salivary amylase
chloride ions
salivation is controlled by
the autonomic nervous system
average salivary secreted daily
1000 -1500 mL
Parasympathetic promotes salivation whereas
sympathetic does not
Tongue
accessory digestive organ composed of skeletal muscle covered with mucus membrane
The tongue participates in
chewing, swallowing, and speeth
The upper and lateral surfaces of the tongue are covered with
papillae, some of which contain taste buds
The extrinsic muscles of the tongue
move it from side to side and in and out to maneuver food for chewing
- form the floor of the mouth and hold the tongue in position
intrinsic muscles of the tongue
originate and insert into the connective tissue within the tongue
- alter the size and shape of the tongue for speech and swallowing
Lingual papillae
projections of the lamina propria covered with stratified squamous epithelium
- contain gustatory epithelial cells
some lingual papillae lack taste buds but contain
receptors for touch and increase friction between tongue and food, making it easier for the tongue to move
Lingual glands
in the lamina propria of the tongue
- secreye mucus and watery fluid that contains lingual lipase, which acts on as much as 30% of dietary glycerides
Teeth
accessory digestive organs located in dental alveoli in mandible and maxillae
enamel
consists of calcium phosphate and calcium carbonate
- harder than bone
incisors:
closest to midline
- chisel shaped and adapted for cutting into food
canines:
have a pointed surface called a cusp
- used to tear or shred food
molars;
have four cusps
- used to crush and grind food and prepare food for swallowing
When food is first swallowed, it passes from the mouth to the
pharynx
The pharynx is composed of
skeletal muscle and lined by mucus membrane
the pharynx is divided into 3 portions
- nasopharynx
- oropharynx
- laryngopharynx
Nasopharynx
functions only in respiration
Swallowed foods passes from the mouth to
the oropharynx and laryngopharynx; muscular contractions of these areas help propel food to the esophagus and then into the stomach
The mucosa of the esophagus consists of
non-keratinized stratified squamous epithelium, lamina propria, and musuclaris mucosae
Near the stomach, the mucosa of the esophagus contains
mucus glands
At the ends of the esophagus, the muscular layer
becomes slightly more prominent and forms the upper esophageal sphincter and the lower esophageal sphincter
The superficial layer of the esophagus is known as the
adventitia
The adventitia attaches the esophagus to
surrounding structures
The movement of food from the mouth into the stomach is achieved by the act of
deglutition
Deglutition
facilitated by the secretion of saliva and mucus and involves the mouth, pharynx and esophagus
Swallowing occurs in three stages
- voluntary stage
- pharyngeal stage
- esophageal stage
Voluntary stage of swallowing;
bolus is forced to the back of the oral cavity and into the oropharynx by the movement of the tongue upward and backward against the palate
Pharyngeal stage of swallowing;
- The bolus stimulates receptors in the oropharynx, which send impulses to the deglutition center in the medulla
- the returning impulses cause the soft palate and uvula to move upward and close off the nasopharynx
- the bolus moves through the oropharynx and the laryngopharynx
Esophageal stage of swallowing;
- begins once the bolus enters the esophagus
- peristalsis of the circular and longitudinal layers pushes the bolus onward
Stomach
J shaped enlargement of the digestive canal directly inferior to the diaphragm of the abdomen
The stomach connects the
esophagus to the duodenum
Because we can eat faster than the intestines digest…
the stomach serves as a mixing chamber and a holding reservoir
After food is ingested, the stomach
forces a small quantity of material into the duodenum
In the stomach digestion of
starch and triglycerides continues, digestion of proteins begins
- certain substances are absorbed
The semisolid bolus is converted to —- in the stomach
chyme
When the stomach is empty, the mucosa lies in
large gastric folds (rugae)
- can be seen with unaided eye
The pylorus of the stomach communicates with
the duodenum via a smooth muscle sphincter called pyloric sphincter
convex portion of the stomach
greater curvature
concave portion of the stomach
lesser curvature
The surface of the mucosa of the stomach is a layer of
simple columnar epithelial cells called surface mucus cells
In the stomach, the epithelial cells extend down into the lamina propria where they form columns of
secretory cells called gasric glands
Several gastric glands open to the bottom of narrow channels called
gastric pits
The gastric glands secrete three types of exocrine cells
- mucous neck cells
- chief cells
- parietal cells
Both surface mucous cells and —- —– —- secrete mucus
mucous neck cells
Parietal cells produce
intrinsic factor (needed for absorption of vit b12) and hydrochloric acid
The chief cells secrete
pepsinogen and gastric lipase
The secretions of mucous neck, parietal and chief cells produce
gastric juice
G cells of the stomach
secrete gastrin which stimulates parietal cells to secrete HCL and chief cells to secrete pepsinogen;
contracts with lower esophageal sphincter, increases motility of stomach. relaxes pyloric sphincter
Pancreas
retroperitoneal gland that is thick and lies posterior to the greater curvature of the stomach
The pancreas is connected to the
duodenum of the small intestine from the head portion
Pancreatic juices are secreted by
exocrine cells into small ducts that ultimately unite to form two larger ducts
- pancreatic and accessory duct
The pancreatic duct
larger of the two ducts in the pancreas
- joins bile duct from liver and gallbladder
The accessory duct
leads from the pancreas and empties into the duodenum superior to the hepatopancreatic ampulla
Pancreatic acini
make up the exocrine portion
Pancretic acini secrete
digestive enzymes called pancreatic juice
Pancreatic islets
endocrine portion of pancreas
- secrete hormones
Pancreatic juice
- clear, colorless liquid consisting of mostly water, some salts, sodium bicarbonate and several enzymes
What makes pancreatic juice alkaline
sodium bicarbonate and it buffers acidic gastric juice
Sodium bicarb stops the action of
pepsin from the stomach and creates a proper pH for the action of digestive enzymes in the small intestine
The enzymes in pancreatic juice include
- pancreatic amylase, trypsin, chymotrypsin, carboxypeptidase, elastase, deozyribonuclease, pancreatic lipase
Function of pancreatic amylase
digests starch
Protein digesting peptides
trypsin, chymotripsin, carboxypeptidase, and elastase
Function of pancreatic lipase
digests triglycerides
Function of ribonuclease
digests ribonucleic acid
Protein digesting enzymes of the pancreas are produced in an
inactive form because the enzymes do not digest the cells of the pancreas itself
Liver
heaviest gland of the body,
- located inferior to the diaphragm to the right
Gallbladder
pear shaped sac located in the depression of the posterior surface of the liver
The liver is almost completely covered by
visceral peritoneum and completely covered by a dense irregular connective tissue layer
The liver is comprised of
a large right lobe and a smaller left lobe
The parts of the gallbladder include the broad
fundus which projects inferiorly beyond the inferior border of the liver; central portion and the neck
The liver is composed of these components
- hepatocytes
- bile canaliculi
- hepatic sinusoids
Hepatocytes
- major functional cells of the liver and performa a wide array of metabolic, secretory and endocrine functions
Grooves in cell membranes between neighbouring hepatocytes provide
spaces for bile canaliculi into which hepatocytes secrete bile
Bile
yellow, brownish, or olive green liquid secreted by hepatocytes, serves as both an excretory product and a digestive secretion
Bile canaliculi
small ducts between hepatocytes that collect bile produced by the hepatocytes
From bile canliculi, bile passes into
bile ductules, and then bile ducts
The bile ducts in the liver merge and eventually form
the right and left hepatic ducts
The right and left hepatic ducts unit and exit the liver as
common hepatic duct
The common hepatic duct joins the cystic duct
from the gallbladder and forms the common bile duct
From the common bile duct, bile enters the
duodenum of the small intestine to participate in digestion
Hepatic sinusoids
- highly permeable blood capillaries between rows of hepatocytes that receive oxygenated blood from branches of the hepatic artery, and nutrient rich deoxygenated blood from branches of the hepatic portal vein
The hepatic portal vein brings venous blood from
digestive canal organs to the spleen and liver
Hepatic sinusoids converge and deliver blood into a
central vein
From central veins blood flows into
hepatic veins which flows towards the inferior vena cava
In contrast to blood, which flows towards the central vein, bile
flows the opposite direction
Stellate reticuloendothelial cells or hepatic macrophages
destroy worn out white and red blood cells, bacteria and other foreign matter in the venous blood draining from the digestive canal
Portal triad
a bile duct, branch of the hepatic artery and a branch of the hepatic vein are referred to as portal triad
The hepatocytes, bile duct system, and hepatic sinusoids can be organized into an anatomical and functional unit called
the hepatic acinus
Hepatocytes in hepatic acinus are
arranged in three zones around the short axis with no sharp boundaries between them
Cells in zone one of the hepatic acinus
closest to the branches of the portal triad and the first to receive incoming oxygen and nutrients and toxins from incoming blood
Which cells are the first ones to take up glucose and store it as glycogen after a meal and break down glycogen during fasting
cells in zone one of a hepatic acinus
Cells in zone three are
farthest from portal triad and are the last to show effects of bile obstruction or exposure to toxins
The mucosa of the gallbladder consists of
simple columnar epithelium arranged in mucosal folds (rugae) resembling those of the stomach
The wall of the gallbladder lacks a
submucosa
The middle (muscular) layer of the gallbladder consists of
smooth muscle fibers which ejects the contents of the gallbladder into the cystic duct
Function of the gallbladder
store and concentrate the bile produced by the liver until it is needed by the duodenum
In the concentration process of the gallbladder
water and ions are absorbed by the gallbladder mucosa
The liver receives blood from
- the hepatic artery - obtains oxygenated blood
- hepatic portal vein - receives deoxygenated blood containing newly absorbed nutrients, drugs, and possibly microbes and toxins from the digestive canal.
Branches of both the hepatic artery and hepatic portal vein carry blood into
hepatic sinusoids, where oxygen, most of the nutrients, and certain toxic substances are taken up by hepatocytes
Products manufactured by hepatocytes and nutrients needed by other cells are
secreted back into the blood, which then drains into the central vein and eventually passes into the hepatic vein
Because blood passes from the digestive canal to the liver
the liver is often a site for metastasis of cancer that originates in the digestive canal
pH of bille
7.6 - 8.6
the principle pigment in bile is
billirubin
Bile plays a role in
emuslification, the breakdown of large lipid globules into a suspension of small lipid globules
As digestion and absorption continue in the small intestine
bile release increases
The liver performs other functions in addition to bile production
- carbohydrate metabolism
- lipid metabolism
- protein metabolism
- processing of drugs and hormones
- excretion of billirubin
- synthesis of bile salts
- storage: of glycogen
- phagocytosis
- activation of vitamin D
Most digestion and absorption of nutrients occurs in the
small intestine
The area for digestion and absorption is further increased by
- circular folds
- intestinal villi
- microvilli
Three regions of the small intestine
duodenum
jejunum
ileum
Longest and shortest region of small intestine
short: duodenum
- long: lieum
The small intestine joins the large intestine through a smooth muscle sphincter called
ileal orifice
The epithelium of the mucosa for the small intestine consists of
- absorptive cells
- goblet cells
Absorptive cells of the small intestine
contain enzymes that digest food and posess intestinal microvilli that absorb nutrients in small intestinal chuyme
Goblet cells of the small intestine
secrete mucus
Cells lining the crevices of the small intestine form
intestinal glands
The intestinal glands of the small intestine also contain
- paneth cells
- enteroendocrine cells
Paneth cells of the small intestine
secrete lysozyme, bactericidal enzyme and are capable of phagocytosis
What cells have a role in regulating microbial population in the small intestine
paneth cells
There are 3 types of enteroendocrine cells
S cells, CCK cells, and K cells, which secrete the hormones secretin, cholecystokinin, and glucose dependant insulinotropic peptide
The lamina propria of the small intestine contains an abundance of
MALT
The submucosa of the duodenum contains
duodenal glands
Duodenal glands secrete
an alkaline mucus that helps neutralize gastric acid in the chyme
Circular folds of the small intestine enhance
absorption by increasing the surface area and causing the chyme to spiral, rather than moving in a straight line
Intestinal villi
finger like projections of the mucosa
- increase the surface area
Nutrients absorbed by the epithelial cells covering the intestinal villus pass through
the wall of blood capillary or a lymphatic capillary to enter the blood plasma or lymph plasma
Microvilli in the small intestine
projections of the apical membrane of the absorptive cells
the microvillus border contains several enxymes that
have digestive functions
The enzymatic digestion occurs at the
surface of absorptive cells that line the intestinal villi (microvillus border)
Two types of movements by the small intestine
segmentations and a type of persistalsis called migrating motility complexes
Segmentations
localized, mixing contractions that occur in portions of the intestine distended by a large volume of chyme
Segmentations mix
chyme and digestive juices and bring particles of food into contact with the mucosa for absorption; they do not push the intestinal contents along the digestive canal
Segmentation starts with contractions of
circular smooth muscle
After most of a meal has been absorbed which lessens the distention of the wall of the small intestine,
segmentation stops and peristalsis begins
Migrating motility complex begins
in the lower portion of the stomach and pushes chyme forward along a short stretch of small intestine before dying out
Acidic pH in the stomach destroys
salivary amylase
The small intestine digests
carbohydrates
proteins
lipids
nucleic acids
Salivary amylase digests —- into
starches (polysaccharides) into:
- maltose
- maltoriose
- a- dextrins
Pancreatic amylase digests — into —– in the small intestine
starches (polysaccharides) into:
- maltose
- maltriose
- a - dextrins
Trypsin digests —- into ——
proteins into peptides in the small intestine
Chymotrypsin digests —- into —–
proteins into peptides
Elastase digests —- into —-
proteins into peptides
Carboxypeptidase digests —- into —–
amino acid at carboxyl end of peptides into amino acids and peptides
Pancreatic lipase digests —- into —–
triglycerides that have been emulsified by bile salts into fatty acids and monoglycerides
Ribinuclease digests —- into
ribonucleic acid into nucleotides
Deoxyribonuclease digests — into
deoxyribonucleic acid into nucleotides
a-dextrinase at the small intestine digests a-dextrins to produce
glucose
Maltase at the small intestine digests maltose to produce
glucose
Sucrase in the small intestine digests sucrose to produce
glucose and fructose
Lactase in the small intestine digests lactose to produce
glucose and galactose
Enterokinase in the small intestine digests trypsinogen into
trypsin
Gastric banding
procedure which places an inflatable band around cardia o stomach to make the person feel full after eating only a small amount of food
Sleeve gasterectomy
stomach is removed to leave only a banana shaped section
- decrease in size causes person to feel full faster
Gastric bypass
stomach is made smaller
Large intestine
portion of the digestive canal extending from the ileum of the small intestine tot he anus and divided structurally into cecum, colon, rectum and anal canal
The mucus membrane of the anal canal is arranged in longitdinal folds called
anal columns
external anal sphincter is
skeletal muscle, therefore voluntary
The epithelium of the large intestine contains mostly of
absorptive and goblet cells
The absorption cells of the large intestine function primarily in
water absorption
the goblet cells of the large intestine
secrete mucus and lubricates the passage of colonic contents
The longitudinal muscles of the large intestine are
thickened and form three bands called teniae coli
Tonic contractions of the teniae coli gather the colon into
pouches called haustra
Immediately after a meal the gastoileal reflex intensifies
peristalsis in the ileum and forces chyme into the cecum
Haustral churning
haustra remain relaxed and become distended while they fill up.
- when the distention reaches a certain point, the walls contracy and squeeze the cotents into the next hausrum
Mass peristalsis in the large intestine
a strong persistaltic wave that begins at about the middle of the transverse colon and quickly drives the contents of the colon into rectum
Because food in the stomach initiates the gastrocolic reflex in the colon
mass peristalsis usually takes place about 3-4 times a day
The gases contribute to
flatus in the cp;pm
Feces contain
water, inorganic salts, sloughed off epithelial cells, bacteria, products of bacterial decomposition, unabsorbed digested materials, and indigestible parts of food
The large intestine absorbs
ions, sodium, chloride, and some vitamins
Defecation reflex
mass peristaltic movements push fecal matter into the sigmoid colon of the rectum; the distention stimulates the stretch receptors
In response to stretching of the rectal wall
the receptors send sensory nerve impulses to the sacral spinal cord.
- motor impulses from the cord travel along parasympathetic nerves
Three phases of digestion
- cephalic phase
- gastric phase
- intestinal phase
When longitudinal rectal muscles contract
the internal anal sphincter opens
cephalic phase
Prepares the mouth and stomach for the food that is about to be eaten
- salivary glands secrete saliva
- vagus nerve stimulates gastric glands to secrete gastric juice
Gastric phase
In the gastric phase; neural and hormonal mechanisms begin to promote gastric secretion and motility
Neural regulation of Gastric phase
When the stomach alls are distended, the pH increases because proteins have entered the stomach
Hormonal regulation of Gastric phase
Gastrin released from the G cells of the gastric glands in response to several stimuli; stretching of stomach by chyme, high pH of chyme
Gastrin stimulates gastric glands to
secrete large amounts of gastric juice
Intestinal phase; NEURAL REGULATION
distention of the duodenum by the presence of chyme causes the enterogastric reflex;
- inhibit parasympathetic and stimulate sympathetic nerves
Intestinal phase: hormonal regulation
CCK stimulates the secretion of pancreatic juice that is rich in digestive enxymes; also causes contraction of gallbladder which squeezes out bile
Stimulus for gastrin
distension of stomach, partially digested proteins, caffeine in stomach and high pH of stomach chyme
- G cells located in mucosa of stomach
Major effects of gastrin
promotes secretion of gastric juice, increases gastric motility and promotes growth of gastric mucosa
Stimulus for Secretin
- acidic chyme that enters small intestine
- S cells in the mucosa of the duodenum
Major effects of secretin
stimulates secretion of pancreatic juice and bile that are rich in bicarbonate ions (HCO3-)
Stimulus for cholecystokinin
- partially digested proteins, triglycerides, and fatty acids that enter the small intestine and stimulate secretion of CCK by entroendocrine cells
Major effects of CCK (cholecystokinin)
stimulates secretion of pancreatic juice rich in digestive enzymes, causes ejection of bile from the gallbladder and opening of the hepatopancreatic ampulla which induces satiety
Aging results in
- decreased secretory mechanisms and motility
- loss of strength and tone of digestive muscular tissue
- changes in neurosecretory feedback
- diminished response to pain and internal sensations
Dental caries/tooth decay
gradual demineralizaton of the enamel and dentin
Periodontal disease
inflammation of gums, alvolar bone, periodontium and cement
- inflammation of bleeding of gums
Peptic ulcers
ulcers in digestive canal which can cause bleeding and eventually anemia
Divertciular disease
saclike outpouchings of the wall of the colon
- characterized by pain, constipation, frequency of defecation, nausea, vomiting, and low grade fever
Colorectal cancer
polyps dorm
- intake of alcohol, and diets high in animal fat and protein are associated with the risk of colorectal cancer
Hepatitis
inflammation of the liver that can be caused by viruses, drugs, chemicals and alcohol
