Digestive System
T or F: Goblet cells are the only mucus secreting cells in the GI tract.
FALSE Goblet cells secrete mucus in the small & large intestine, but *mucous cells and mucous neck cells* are found in the stomach
T or F: The duodenum JUST receives *chyme* coming from the stomach. Explain?
FALSE It also receives secretions from the *liver, gall bladder, and pancreas.*
T or F: The liver is the largest organ in the body.
FALSE It is the *second* largest, next to the skin itself.
T or F: The layers of the stomach wall are similar to the rest of the GI tract with *no modifications.*
FALSE The stomach has certain modifications in the layers compared to the rest of the GI tract.
T or F: Only the contractions of the sphincters cause the defecation reflex.
FALSE Voluntary contractions of our *diaphragm and abdominal muscles* and PARASYMPATHETIC stimulation along with the pressure cause the reflex.
Describe what the hormone *Gastrin* does.
It stimulates parietal cells to secrete HCl and chief cells to secrete it's pepsinogen. Also contracts esophageal sphincter while relaxing pyloric sphincter.
The terminal portion of the GI tract is the _____ _______. What are it's functions?
LARGE INTESTINE -complete absorption (water) -produce vitamins -form & expel feces
What accessory organ produces a fluid that *emulsifies* dietary fats?
Liver-- bile salts emulsify.
This FOLD (portion) of the peritoneum is largely responsible for carrying blood and lymph vessels to the intestines...
MESOCOLON
What are the quadrate and caudate lobes of the liver?
They are smaller lobes that belong to the left lobe of the liver.
What do the *haustra* (teniae coli) cause the large intestine to do ?
They cause it to be permanently contracted & give the colon a a puckered appearance
What do the teniae coli form as a whole?
They gather in the colon in pouches called *haustra.*
The most abundant lipid in the diet are __________ which are broken down by enzymes called _______.
Triglycerides; lipases (lingual, pancreatic, gastric)
The _______ keeps food from going into the nasal cavity by closing off the nasopharynx and the _______ keeps food our of the respiratory tract by sealing off the larynx.
Uvula; epiglottis
Why is the chemical digestion of the large intestine considered a *symbiosis?*
We use the bacteria's byproducts to aid in our own digestion. (bacteria live in us but help us)
The major functional cells of the liver are __________. What % do they make up?
hepatocytes make up 80% volume of the liver.
1% Endocrine cells secrete.. 99% Exocrine cells secrete..
hormones pancreatic juices
This digestive *AID*, produced by the stomach, begins digestion by denaturing proteins
hydrochloric acid (this aids pepsin to digest proteins)
We *ingest* ___ liters of solids & liquids a day but we *secrete* __ liters.
ingest: 2.3 liters secrete: 7 liters
This plexus is located between the longitudinal and circular smooth muscle layers of the muscularis
myenteric plexus
What are FECES made up of?
water, inorganic salts, our epithelial cells, bacteria, byproducts of bacteria, unabsorbed materials, indigestible parts of food (cellulose)
What types of cells are located in the small intestine's *intestinal gland?* (secretory cells of mucosa)
*Absorptive cells:* release enzymes, contain microvilli to absorb *Goblet cells:* mucus *Paneth cells:* secrete a lysosome responsible for regulating MICROBES. *Enteroendocrine cells:* (3 types) secrete secretin, cholecystokinin (CKK) and GIP (glucose independent peptide)
What are the THREE special structural features of the small intestines? Describe what each does.
*Circular folds:* (plicae circulates) permanent ridges in mucosa & submucosa; increase SA & cause chyme to move in a spiral movement; CAN EXTEND AROUND THE ENTIRE ORGAN *Villi:* fingerlike projections of mucosa; give small intestine velvety look; contain a *LACTEAL* *Microvilli:* projections of the absorptive cell's membrane; too small to be seen and referred to as a BRUSH BORDER extending to the lumen.
Describe the three regions of the small intestine and how they connect.
*Duodenum* is the first and SHORTEST portion; it starts at the pyloric sphincter and extends until it merges with the *jejunum.* This is then extended to the *ileum* which is the final and LONGEST region that joins the large intestine at the ileocecal sphincter.
What are the types of *mechanical digestion* in the large intestine? (3)
*Haustral churning*: haustra relax and contract, squeezing contents to the next haustra. *Peristalsis*: occurs at much slower rate *Mass* peristalsis: strong wave that quickly moves content from colon to rectum
Describe briefly how *bile* gets from the liver to the duodenum.
*Hepatocytes secrete bile to the bile canaliculi* (grooves between hepatocytes). --> *Bile passes from grooves to bile ducts* --> *right & left hepatic ducts* --> *common hepatic duct* --> *bile enters duodenum*
What is a chylomicron made from? How is it made?
*Large short fatty acids, long fatty acids, and monoglycerides* (not short fatty acids) form *micelles* which help get the molecule into the absorptive cell. All three molecules recombine to form a *chylomicron* but are too big to enter a blood capillary so they enter the lacteal & are transported through lymphatic vessels *bypassing liver processing*
Describe what enzymes are in the pancreatic juice and what each does.
*Pancreatic amylase:* digest starch *Trypsin, chymotrypsin, carboxypeptidase:* proteins into peptides *Pancreatic lipase:* principal fat digestion (triglycerides) *Ribonuclease, deoxyribonuclease:* digests nucleic & ribonucleic acids into nucleotides
Describe mechanical digestion of the small intestine.
*Segmentation* (a form of peristalsis) mixes chyme and brings it in contact with mucosa layer allowing absorption to happen After a most of meal absorbed, segmentation stops and peristalsis begins. (segmentation does NOT actually push food along the tract)
What are the four main regions of the large intestine? (in order)
-*Cecum* (appendix attached) -*Colon* (ascending, transverse, descending, sigmoid) -*Rectum* -*Anal canal* (not anus on test)
Describe the anatomy of the LIVER.
-2nd largest -two principal lobes: right & left (smaller) connected by falciform ligament -*primary metabolic & DETOX organ.*
So what can the stomach absorb?
-Alcohol & drugs -Some water -ions -short fatty acids
Describe the anatomy of the gallbladder in relationship to the liver.
-Inferiorly and slightly posterior to the liver -receives, stores AND releases *excess bile* from the liver.
Describe the pancreas.
-Posterior to stomach (retroperitoneal gland) -Head, body & tail -Connected to duodenum by two ducts: *pancreatic duct & accessory duct* -99% EXOCRINE (acini) and 1% ENDOCRINE (islets)
What are the other functions of the liver (other than secreting bile) ?
-maintaining blood glucose levels (carb metabolism) -lipid metabolism (break down fatty acids for ATP) -protein metabolism (make amino acids available to be used as ATP) -*Detoxify* drugs and hormones (alcohol, penicillin) -excrete bilirubin into bile
What is located in the lamina propria and muscularis portion of the small intestine's *mucosal layer?*
-mucosa associated lymphoid tissue (MALT) -Peyer's patches -*smooth muscle*
What does the *chemical/bacterial* action of the large intestine do? (symbiotic)
-mucus is secreted, but *NO ENZYMES* -*ferment* any remaining carbs -convert remaining proteins to amino acids & simpler substances -produce *B & K vitamins* that are needed for normal metabolism
What amount of water is excreted in the feces each day ?
0.1 liters
How long can food stay in the fundus before being mixed w/ gastric juices?
1 hour
Where does water absorption of the large intestine occur? Why is this important?
10% of all water absorption occurs in the *absorptive cells* in order to MAINTAIN OUR WATER BALANCE (homeostasis)
How many hours does it take the stomach to empty contents into the duodenum? What type of molecule spends the longest time in the stomach?
2-4 hours; foods high in protein remain the longest time
Total amount of fluid that is *absorbed* DAILY = ?
9.2 liters
Total amount of fluid *ingested & secreted* DAILY = ?
9.3 liters
__% of absorption occurs in the small intestine. __% occurs in the stomach & large intestine. Where does the undigested material thats left go?
90% in small intestine 10% in stomach & large intestine The leftover undigested material passes onto large intestine.
Each *villus* (not microvilli contain what two things?
A lacteal and a CVS supply (blood capillary)
*Passage of digested nutrients from the GI tract into the blood or lymph.....*
ABSORPTION
How are the cells in the mucosa layer different in the *large intestine?*
Absorptive and goblet cells increase in number compared to the small intestine; they extend the ENTIRE thickness of the mucosa
Describe the four subregions of the large intestine's *colon.*
Ascending: ascends on RIGHT side Transverse: colon continues *across* abdomen to the left side and curves inferiorly past the spleen Descending: continues downward on the LEFT side Sigmoid: begins at iliac crest and terminates at the rectum
*Portal triad = ?* Where are these located?
Bile duct + branch of hepatic *artery* + branch of hepatic *vein* ... Located in between lobules.
What is the principle bile pigment?
Bilirubin
Deciduous molars are replaced with....
Biscuspids (first & second premolars)
What molecules are absorbed into the *blood capillaries* and which molecules are absorbed into *lacteals?*
Blood capillaries: monosaccharides, amino acids, *short* fatty acids Lacteal: reformed triglycerides called *chylomicrons*
IN SMALL INTESTINE: Carbs are broken down into _________. Proteins are broken down into _____ _____. Lipids are broken down into ______ ______ chains and __________.
Carbs--> *monosaccharides* (glucose, fructose galactose) Proteins--> *single amino acids, dipeptides, tripeptides* Lipids--> fatty acid chains (long or short) glycerol, and monoglycerides
Describe the histology of the mucosal layer with the gastric glands and pits of the stomach.
Cells extend into the lamina propria, forming columns of *gastric glands* which open into channels called *gastric pits.* "YOU HAVE TO GO DOWN THE PIT TO GET TO THE GLAND."
The final stage of DIGESTION occurs in the _____ through ________ action.
Colon; bacterial action
Defecation = ?
Elimination of feces from the rectum through the anus
*How do the enzymes that are secreted in the pancreas and stomach not digest THEMSELVES?*
Enzymes are secreted in *inactive forms*
T or F: The anal canal is the anus.
FALSE
T or F: Absorption takes place just as much as digestion in the stomach. Explain?
FALSE Absorption is at a minimal point in the stomach. Only small amount of nutrients get absorbed because the stomach's cells are impermeable to most material.
T or F: Small intestine MECHANICAL digestion moves the bolus along the tract all the way to large intestine.
FALSE First we have *segmentation* which simply sloshes the chyme back and forth, and then we have peristalsis right at the end which is what actually pushes the food onto the large intestine.
The gastric gland of the stomach contains _____ types of *exocrine* cells that secrete products into the lumen. What are they and what does each secrete?
FOUR TYPES Mucous surface/neck cells: secrete mucous Chief cells: pepsinogen & gastric lipase Parietal: intrinsic acid (vitamin B12) & hydrochloric acid G cells (enteroendocrine): the hormone gastrin
Chyme transforms into a solid or semisolid called _____ because of water ________ while in the large intestine.
Feces; absorption
Describe *chemical* digestion in the stomach.
Food molecules are being broken down into absorbable units *Pepsin* (from chief cells) breaks down peptide bonds in amino acids-- not the whole protein. *Gastric lipase* (from chief cells) performs some lipid digestion-- triglycerides into fatty acids & monoglycerides (limited role in the stomach)
_______ glands are in the stomach but ________ glands are in the small intestine.
Gastric; intestinal
*Where do the common bile duct & two pancreatic ducts enter the duodenum?*
HEPATOPANCREATIC AMPULLA (ampulla of Vater)
What is different about the *muscularis layer* of the stomach compared to the rest of the GI tract?
Has *3 layers* of smooth muscle (esophagus = 2)
The liver receives *oxygenated* rich blood from the hepatic _______, and *deoxygenated, nutrient rich* blood from the hepatic _______ ____.
Hepatic artery- oxygenated blood (from systemic circulation) Hepatic portal vein- deoxygenated, nutrient rich
The pancreatic duct enters the small intestine via the ____________ ampulla but the accessory duct enters from the _______.
Hepatopancreatic; pancreas
The large intestine extends from the _______ sphincter to the ____.
Ileocecal sphincter (ileum); anus
What is different about the stomach's *mucosa layer?* (compared to rest of GI tract)
It has a layer of *SIMPLE COLUMNAR cells that secrete mucus* (not stratified squamous). The epithelial cells extend down into the lamina propria where they form secretory columns called *gastric glands.*
What is different about the large intestine's *muscularis layer?*
It has portions of the LONGITUDINAL smooth muscle that are thickened and form bands called *TENIAE COLI*
What does pancreatic juice do?
It is slightly *alkaline* and so it buffers acidic juice in the chyme and creates a proper pH for small intestine.
What is the job of the *small intestine?*
It is the PRIMARY site of chemical digestion and nutrient absorption. (biggest player of all organs in this system)
What stimulates the *defecation reflex?*
Mass periastalsis moves fecal material into rectum which stimulates *stretch receptors* to send impulses to the spinal cord. The rectum contracts & shortens, building up pressure which in turn opens up the internal anal sphincter.
The capability of the GI tract to move material along its length.....
Motility and propulsion
Does the small intestine digest ALL carbs?
NO-- cellulose and fiber are forms of carbs that cannot be digested
How does blood flow through the liver and into the heart? (brief summary)
Oxygenated and deoxygenated blood drains into the *hepatic sinusoids* (capillaires) and into the CENTRAL VEIN and then to the hepatic vein and then into the heart.
Describe the mechanical digestion of the *stomach.*
Peristalsis begins after eating & mascarates food & mixes it with gastric juice *forming chyme* Few mixing in *fundus*, vigorous mixing in *body and intensifies towards pylorus* 3mL of chyme forces into duodenum through *pyloric sphincter* with each wave, most of the chyme is forced back into body for more mixing (retropulsion) 2-4 hours to completely empty content into duodenum
Describe how peristalsis happens in small intestines..
Peristalsis is called *migrating motility complex (MMC)* in the small intestines MMC begins in lower portion of stomach & pushes chyme through small intestines into ileum (90-120min)
The small intestine extends from the ________ sphincter of the stomach to the ________ sphincter of the large intestine.
Pyloric; ileocecal
Passage of chyme from the ileum into the cecum is regulated by what? How fast does this occur and why? (mechanical digestion)
Regulated by ileocecal sphincter; passage of chyme occurs slowly because the sphincter is partially closed (except after we have a meal)
When the external anal sphincter is ________, defecation occurs and feces are expelled. When the sphincter is ________, then defecation is postponed.
Relaxed-- feces are expelled Contracted (constricted-- defecation is postponed
What accessory organ produces a fluid to SOFTEN FOOD?
Salivary glands
*Duodenal glands (Brunner's Gland)* in *submucosal layer* of the small intestines do what?
Secrete *alkaline mucus* to neutralize the gastric acid in chyme
The small intestine absorbs ___ liters of fluid while the large intestine only absorbs ___ liters.
Small intestine: 8.3 liters Large intesine: 0.9 liters
Where does the completion of macromolecules (carbs, proteins, lipids) take place? Explain.
THE SMALL INTESTINE. The collective effort of intestinal juice, pancreatic juice & bile all completely digest it.
Blood flows _______ the central vein while bile flows ____ from the central vein.
TOWARD; away (they flow in opposite directions)
T or F: Both the lamina propria of the mucosa layer and the submucosa layer have vessels ready for absorption
TRUE
T or F: We do NOT get caloric energy when using ribonuclease & deoxyribonuclease.
TRUE they are just breaking down nucleic acids here.
T or F: Hepatocytes CONTINUALLY release bile, but production of it *increases* as digestion & absorption continue in small intestine.
TRUE!!
T or F: The small intestine WALL has the same four basic layers that make up the rest of the GI tract. (but has special structural features for absorbing)
TRUE!!
The anal canal is the _______ end of the large intestine and is arranged into _______ that open to the exterior called the ____.
Terminal; columns; ANUS
What is the net result of mechanical movement in the stomach?
The bolus of food turns into a soupy liquid, *CHYME.*
What is the differences & similarities of the small & large intestine in reference to villi, microvilli, and plicae circulares?
The large intestine has much fewer special structures. There are *no circular folds or villi* here but there ARE MICROVILLI on the absorptive cells.
Brunner's glands (Duodenal) secrete....
alkaline MUCUS
The ______ is attached to the cecum
appendix