3 (23) The Digestive System Flashcards
What is digestion?
the process of breaking down larger food molecules into smaller food molecules
What is absorption?
the passage of the smaller molecules into blood and lymph
What is the alimentary canal? What structures are accessory organs?
- (GI tract) tube that runs from mouth to anus; digests food and absorbs fragments (mouth, pharynx, esophagus, stomach, small intestine, large intestine)
- accessory organs: teeth, tongue, salivary glands, liver, gallbladder
What is the splanchnic circulation?
all blood flow originating from the celiac, superior mesenteric, and inferior mesenteric arteries, which is widely distributed to all abdominal viscera
- receives about 25% of cardiac output when at rest
What is the “tube within a tube” model?
- one for food to enter the body (mouth), one for wastes to leave the body (anus)
- the tube-within-a-tube plan allows specialization of parts along the tube, such as a stomach, intestine, etc.
What are the four structural layers of the alimentary canal?
mucosa
submucosa
muscularis
serosa
The mucosa can be further divided into what three parts?
1 - EPITHELIUM => strat. squam. epithelium, simp. col. epithelium, and enteroendocrine glands
2 - LAMINA PROPRIA => areolar CT; blood, lymph vessels and nodules
3 - MUSCULARIS MUCOSAE => two layers of smooth muscle
In which of these parts would we find MALT?
lamina propria
How does the epithelium of the mucosa change throughout the alimentary canal?
mouth, esophagus, anal canal => strat. squam. epithelium
stomach and intestines => simp. col. epithelium
What are the three functions of the mucosa?
1 - SECRETION => mucus, digestive enzymes/hormones
2 - ABSORPTION => nutrients from digestion
3 - PROTECTION => from infectious diseases
Where would you find the submucosal plexus? The myenteric plexus?
SUBMUCOSAL PLEXUS => found in submucosa; autonomic nerve supply to muscularis mucosae, blood vessels, and secretory cells
MYENTERIC PLEXUS => found in muscularis mucosae;
How does the type of muscle found in the muscularis layer change along the alimentary canal?
mouth, pharynx, superior esophagus, external anal sphincter => voluntary (skeletal) muscle
the rest of GI tract => smooth muscle
In general, how do parasympathetic fibers and sympathetic fibers affect the alimentary canal?
PARASYMPATHETIC => stimulate digestive activities
SYMPATHETIC => inhibit digestive activities
What is another name for the serosa? What is its function?
serous membrane = visceral peritoneum
- lubricates
Where does adventitia replace the serosa?
esophagus
What is mastication?
chewing
What is the oral cavity?
buccal cavity; mouth
(cheeks, lips, tongue, hard/soft palates)
lies between teeth and gums
What is the vestibule?
the area between the teeth, lips and cheeks
What is the labial frenulum? The lingual frenulum?
LABIAL => the soft tissue that attaches the lip to the anterior surface of the maxillary gingiva
LINGUAL => a fold of mucous membrane connecting the ventral tongue to the floor of the mouth
What is ankyloglossia?
tongue-tie => an unusually short, thick or tight band of tissue (lingual frenulum) tethers the bottom of the tongue’s tip to the floor of the mouth
What type of muscle is found in the tongue? Where does this muscle attach?
- skeletal muscle
- attaches at lingual frenulum at the floor of the mouth
What covers the surface of the tongue?
papillae cover the surface of the tongue: filiform, fungiform, circumvallate, foliate (foliate does not have taste buds)
What kind of epithelium lines the oral cavity? Why is this helpful?
- non-keratinized stratified squamous epithelium
- helpful bc it is stratified squamous, it is protective to the tissue behind it and regenerates quickly
Where would you find the lingual tonsils? The palatine tonsils? The pharyngeal tonsils (adenoids)?
LINGUAL => near back of tongue, underneath it
PALATINE => found near roof of mouth near soft palate
PHARYNGEAL => near opening of auditory tube and near base of nasal cavity
What bones make up the hard palate?
palatine bones, palatine processes of maxillae
What is the function of the soft palate and the uvula?
SOFT PALATE => closes off nasopharynx during swallowing
UVULA => projects downward from its free edge and aids the soft palate
How many sets of teeth do you get? How many teeth does a normal adult have?
- two sets of teeth
- normal adult = 32 teeth (20 baby teeth)
What are the basic parts of a tooth?
- crown
- root
- neck
- dentin
- enamel
- pulp cavity
- root canal
- apical foramen
Where would you find dentin in a tooth? Enamel?
DENTIN => found under enamel and around pulp cavity
ENAMEL => the outer, protective covering of a tooth
What is in the pulp cavity?
contains blood vessels, nerves, and connective tissue
What are incisors good for? Cuspids? Molars?
INCISORS => chisel shaped for cutting
CUSPIDS => fanglike teeth that tear or pierce
MOLARS => best for grinding
What are the three sets of salivary glands? Where are they located? Where do they enter the mouth?
PAROTID => found close to ear (Stensen’s duct, drains saliva from the parotid gland into the mouth)
SUBMANDIBULAR => under jaw
SUBLINGUAL => found under the tongue
What are mumps?
inflammation of parotid glands
Do all the salivary glands produce the same type of saliva?
NO
there are two types of secretory cells from saliva:
- serous cells = parotid, submandibular
- mucous cells = sublingual
What digestive enzyme is found in saliva and what does it break down?
AMYLASE => digests starches
What else is found in saliva and what else is saliva good for?
- mostly water
- amylase
- lingual lipase
- mucin
- metabolic wastes (urea)
- lysoyzme, IgA, cyanide compound to protect from microorganisms
How is saliva production affected by input from the parasympathetic and the sympathetic nervous system?
PARASYMPATHETIC => increases saliva production
SYMPATHETIC => decreases saliva production
What are the three sections of the pharynx?
- nasopharynx
- oropharynx
- laryngopharynx
What is deglutition? What are the three stages? Which are involuntary?
swallowing
- voluntary stage
- pharyngeal stage (involuntary)
- esophageal stage (involuntary)
What 3 areas close off to be sure food goes in the right direction?
mouth
pharynx
epiglottis
What is the esophagus? Where is it located in relation to the trachea?
- connects pharynx to stomach
- behind the trachea
What opening in the diaphragm does the esophagus pass through? What happens if this area becomes enlarged and the stomach becomes entrapped in the diaphragm?
esophageal hiatus => opening in diaphragm
- hiatal hernia = when the stomach comes up through the esophageal hiatus and is trapped in the diaphragm
The esophagus contains a lower sphincter. What is it called? When is it open and when is it closed?
lower sphincter => gastroesophageal (cardiac) sphincter
OPEN => when moving food into stomach
CLOSED => to prevent stomach acid from entering esophagus
How does food travel through the esophagus?
food is pushed through the esophagus and into the stomach by means of a series of contractions called PERISTALSIS
What are the divisions of the stomach?
cardiac region fudic region body pyloric region pyloric canal
What sphincter is located between the stomach and the small intestines?
pyloric sphincter
What additional muscle layer do we find in the stomach?
inner oblique of muscularis externa
What is the function of the stomach?
chemical digestion
What are rugae?
folds in the empty stomach
What are gastric pits?
pores in the stomach that release gastric juices produced by the gastric glands
How often is the surface epithelium of the stomach replaced?
every 3-6 days
What do goblet cells produce?
mucus
What do the chief cells produce?
- pepsinogen (an inactive enzyme activated to pepsin by HCl and pepsin itself)
- gastric lipase
What do the parietal cells make?
- hydrochloric acid (HCl)
- intrinsic factor (for the absorption of vitamin B12 important for DNA synthesis)
What is intrinsic factor, and what does it do?
- a substance secreted by the stomach which enables the body to absorb vitamin B12
- it is a glycoprotein
Why don’t we digest our own stomach?
we have a fluid (mucosal) layer of bicarbonate rich ions mucus that neutralizes any acid to protect our stomach from digesting itself
What is the primary type of biological molecule broken down in the stomach? What enzyme does this?
- proteins are the primary type of biological molecule broken down in the stomach
- performed by the enzyme PEPSIN
What is rennin?
(in infants) digests milk proteins
What do the enteroendocrine cells or G cells of the stomach make?
gastrin
histamine
serotonin
somatostatin
What do you get when you mix food and gastric juice?
food + gastric juice = CHYME
What happens to gastric motility and secretion during the cephalic phase? What is the stimulus for this phase?
stimulation of TASTE AND SMELL receptors cause an INCREASE in stomach secretory activity
What is the gastric phase and what affects it?
- stomach distension activates stretch receptors
- affected by food chemicals
What is the intestinal phase and what affects it?
- as more food enter the small intestine, it inhibits the stomach
- cholesystokinin (CCK) and intestinal somatostatin
What hormones are involved in the cephalic, gastric, and intestinal phases?
CEPHALIC => cephalic phase induces ECL cells in the gastric glands to secrete histamine and increase HCl in the stomach
GASTRIC => gastrin? who knows…
INTESTINAL => cholesystokinin (CCK) and intestinal somatostatin
How do Tagamet and Zantac block the production of stomach acid?
H2-blockers inhibit the action of histamine on the cells, thus reducing the production of acid by the stomach
What substances are absorbed from the stomach?
water
ions
lipid soluble drugs
alcohol
Which types of food cause the stomach to empty the fastest? The slowest?
FASTEST => carbohydrates
SLOWEST => fats
What is the enterogastric reflex?
THREE reflexes:
1 - inhibit vagal nuclei in medulla oblongata
2 - inhibit local reflexes
3 - increases sympathetic fibers (decreases PS fibers)
[protects the small intestine from receiving too much acid from the stomach]
How and why does vomiting occur?
HOW => deep breath, salivation, raise soft palate, close epiglottis, relax lower esophageal sphincter, contract diaphragm and abdominal wall
WHY => unpleasant smells, sounds, sights, stress, irritation, distension, unpleasant stimuli in small intestine
Where is your pancreas?
pancreas is retroperitoneal - behind parietal peritoneum
What other duct does the pancreatic duct join? Where does it empty?
- pancreatic duct joins common bile duct to form hepatopancreatic ampulla
- pancreatic duct empties into duodenal pilla (duodenum)
What does pancreatic juice contain?
watery, alkaline solution containing water, salts, electrolytes, enzymes (proteases, amylase, lipases, nucleases) [digests proteins, carbs, nucleic acids, lipids]
Why is trypsin important?
active form of trypsinogen and also activates other enzymes
What neutralizes the stomach acid?
a watery alkaline solution at pH of 8 neutralizes stomach acid (found in pancreatic juice)
Locate your liver. Name the four lobes.
right lobe, left lobe, caudate lobe, quadrate lobe
How are the cells of the liver organized?
hexagonally
What is the portal triad?
1 - a branch of hepatic portal vein
2 - a branch of hepatic artery
3 - bile duct
What are Kupffer’s cells and what do they do?
fixed macrophages
- stellate reticuloendothelial cells
- remove debris such as bacteria and worn out cells
The liver receives two kinds of blood from two sources. What are they?
hepatic artery
hepatic portal vein
What happens to the remaining liver when a piece of it is surgically removed?
1 - liver hepatocytes secrete vascular endothelial growth factor (VEGF)
2 - endothelial cells proliferate and release hepatocyte growth factor (HGF) and interleukin 6, which cause hepatocytes to proliferate
3 - this process can replace the entire liver if up to 80% is remove
The hepatic portal system is different from the hepatic vein. Know the difference and why the hepatic portal system is there!!
this is in blue, probably not on the test
How does the liver function in carbohydrate metabolism?
gluconeogenesis
How does the liver function in lipid metabolism?
it just does it
How does the liver function in protein metabolism?
makes plasma proteins and clotting factors, removes amino groups
How does the liver function in storage of vitamins and minerals?
stores glycogen, fat soluble vitamins, iron
How does the liver function in phagocytosis?
removal of drugs
How does the liver function in the removal of drugs?
some drugs are eliminated by the liver in the bile and excreted in feces
What is the liver’s only role in digestion?
synthesis of bile, excretion of bilirubin
What structures move bile from the liver to the gallbladder?
Bile canaliculi => bile ducts => right and left hepatic duct => common hepatic duct => joins cystic duct => forms common bile duct
Where is the gallbladder located?
underneath the liver
What does bile contain? What do bile salts do in digestion?
water, bile salts, cholesterol, lecithin, bile pigments, electrolytes
bile salts functions: aid digestive enzymes, enhance absorption of fatty acids, reduce surface tension (emulsification), increase the surface area, forms complexes with fatty acids and cholesterol called micelles
What is enterohepatic circulation?
bile salts are reabsorbed by ileum and brought back to liver through hepatic portal system and can be re-secreted into the bile
What affects bile secretion?
stimulated by secretin => it simulates biliary duct cells to secrete bicarbonate and water, which expands the volume of bile and increases its flow out into the intestine
What does the gallbladder actually do? How does CCK affect it? What happens when it is removed?
- gallbladder stores and concentrates bile
- CCK causes it to contract
- removal of gallbladder causes bile duct to enlarge and act as a storage organ
What sphincters are found at the beginning and end of the small intestine? (Note: this should help you remember the order of the three sections.)
pyloric sphincter
ileocecal sphincter
What are the three sections of the small intestine (in order)?
duodenum
jejunum
ileum
What three structures are used by the small intestine to increase its surface area?
plicae circulares (circular folds)
villi
microvilli
What are the crypts of Lieberkuhn? What types of cells are found here, and what do they make?
- intestinal glands
- enteroendocrine cells (CCK, secretin, GI peptide)
- paneth cells (defensins, lysozyme; phagocytosis)
Where are the digestive enzymes of the small intestine?
- there are no enzymes secreted in intestinal juice
- enzymes are embedded in the brush border and can digest all food groups
Why are intraepithelial lymphocytes (IELs) important and what is unusual about them?
they release cytokines that kill infected cells
What are the two movements of the small intestine, and what do they do? What triggers these movements?
SEGMENTATION => mixes and moves contents toward ileocecal valve; triggered by intrinsic pacemaker cells; rubs food substance against brush borders of small intestine to use some enzymes to break down even further
PERISTALSIS => moves meal remnants, bacteria, and debris to large intestine; triggered by rise in hormone motilin in late intestinal phase
What are carbohydrates, proteins, lipids and nucleic acids broken down to (what are the monomers)?
carbs => monosaccharides
proteins => amino acids
lipids => fatty acids, monoglycerides
nucleic acids => pentoses, phosphates, nitrogenous bases
How are the monomers absorbed?
monosaccharides => facilitated diffusion
amino acids => active transport
fatty acids, monoglycerides => simple diffusion
Where do fats go when they are absorbed?
into the blood
What is the peritoneum?
largest serous membrane of the body that holds the organs of the abdominal cavity together
Which organs are retroperitoneal?
pancreas
duodenum
kidneys
What are the mesentery and the mesocolon?
MESENTERY => surrounds and suspends small intestines
MESOCOLON => double fold of peritoneum that surrounds and suspends the colon (large intestine)
What does the greater omentum look like, and what does it do?
"lace apron" fold of peritoneum that hangs from the greater curvature - fat deposition - immune contribution - infection and wound isolation
What is peritonitis?
inflammation of the peritoneum where the peritoneal covering stick together, localizing infection (causes piercing abdominal wound, perforated ulcer, ruptured appendix)
What is ascites?
accumulation of fluid in the peritoneal cavity
Where is the falciform ligament?
anchors the liver to the anterior part of the abdominal cavity
Where is the lesser omentum?
suspends stomach from liver
Which is longer, the small intestine or the large intestine?
smaller
What three features are unique to the large intestine?
taenia coli => 3 bands of longitudinal muscle
haustra => pouches
epiploic appendages => small bags of lipid
What does the mucosa of the colon look like?
thick simple columnar epithelium tissue except in the anal canal, which is stratified squamous epithelium
- no circular folds, villi, digestive secretions
- abundant deep crypts of goblet cells
What are the sections of the large intestine?
cecum > colon > rectum > anal canal
What is the appendix, and where is it located?
- masses of lymphoid tissue
- part of MALT immune system
- bottom of cecum
What happens in the large intestine? What does the digestion here? What benefit do we get from this?
- no food breakdown except by enteric bacteria (only digestion done here)
- manufacturing of certain vitamins (bacteria)
- completion of absorption (especially water, vitamins, electrolytes)
- formation and expulsion of feces
What movements occur in the colon?
- rhythmic ascending (antiperistaltic) waves of contraction originating at the anal end of the large bowel
- rhythmic longitudinal contractions in the rectum and colon
- irregular contractions
What is the gastroileal reflex?
- stimulated by the presence of food in the stomach and gastric peristalsis
- causes peristalsis in the ileum and the opening of the ileocecal valve (which allows the emptying of the ileal contents into the large intestine, or colon)
What is the gastrocolic reflex?
a physiological reflex that controls the motility of the lower gastrointestinal tract following a meal
How does defecation take place?
- mass movements force feces toward rectum
- distention initiates spinal defecation reflex
- parasympathetic signals stimulate contraction of the sigmoid colon and rectum, relaxes internal anal sphincter
- conscious control allows relaxation of external anal sphincter
- muscles of rectum contract to expel feces, assisted by Valsalva’s maneuver
