Digestive system Flashcards
What are the accessory organs to the digestive tract?
Salivary glands
Pancreas
Liver
Gallbladder
What is the innermost layer of the digestive tract and what is its function?
Mucosa layer
- protection, secretion, absorption
The exocrine glands of the mucosa layer of the gi tract secrete into
Lumen
The endocrine glands of the mucosa layer of the gi tract secrete into
Liver
Is there blood supply in the mucosal layer of the gi tract?
No
Submucosa contains blood and lymph vessels to collect blood and lymph from capillaries of mucosa because they carry
Absorbed nutrients
Muscularis layer is composed of smooth muscle and is _____
involuntary
Muscularis layer functions to
Provide mechanical processing and movement of materials along GI tract
The movements of the muscularis layer are coordinated by
ANS
Enteric nervous system
Hormones
Paracrine factors
The enteric nervous system is
network of neurons that covers the GI tract (especially the stomach)
If it is attached to the body wall, the outermost connective layer is
Adventitia
_______ covers muscularis of all parts of digestive tract that are free to move
Serosa
The enteric nervous system is
Dually innervated
What branch of the ANS speeds up digestion?
Parasympathetic
What three factors control and coordinate movement and gland secretion of the GI tract?
Neural, endocrine, paracrine factors
What three factors excite the stomach?
Neural: ACh
Endocrine: Gastrin
Paracrine: Histamine
What factors inhibit the stomach?
Neural: Epinephrine
Endocrine: CCK, GIP, Secretin
What is a long reflex?
Effects in a grand scheme of things, top to bottom of GI tract
What is an example of a long reflex?
When you start to eat, your brain immediately sends ACh from top to bottom of GI tract to tell it to start contracting
What is a short reflex?
Little local responses
What is an example of a short reflext?
Before you eat, you make your stomach more active to accommodate for all of the work the stomach will have to do during digestion
Define segmentation
Churn and fragment a bolus of digestive contents, mixing in intestinal secretions
Define peristalsis
Waves that move a bolus down the length of the tract
What muscle layers work together to create peristalsis?
Longitudinal and circular muscle layers
What is the first thing the buccal cavity does during digestion?
Analyzes the food before swallowing (tasting it)
What is the 2nd thing the buccal cavity does during digestion?
Mastication
What is the 3rd thing the buccal cavity does during digestion?
Lubricates the food via salivary secreations
What enzyme is secreted in the mouth to break down carbs?
Salivary Amylase
What enzyme is secreted in the mouth to break down lipids?
Lingual lipase
What glands are responsible for most of the salivary secretion?
Submandibular glands
What are the functions of saliva?
- Moisten food
- Lubricate food
- buffers pH
- Control bacteria
Why does saliva lubricate the food?
Because glycoproteins are present to prevent blockage inside the esophagus
What type of antibody is present in saliva?
IgA’s
Xerostomia (lack of saliva) can be a side effect of many medications, radiation treatment, or autoimmune diseases. Which of the following would not be a typical symptom?
A. difficulty swallowing
B. progressive erosion of the teeth
C. increased oral infections
D. reduced strength of muscles of mastication
E. reduced ability to taste food
D. reduced strength of muscles of mastication
The pharynx is the ____ passageway for food, liquids, and air
Common
You can start to initiate swallowing, but eventually ______ takes over
Smooth muscle
The esophagus carries solids and liquids from
pharynx to the stomach
What is degluttition?
Swallowing
Is the buccal phase involuntary or voluntary?
Voluntary
Is the pharyngeal phase involuntary or voluntary?
Involuntary
During the buccal phase of deglutition, what happens
Soft palate and uvula rise to close off nasopharynx, and tongue moves bolus into pharynx
During the pharyngeal phase of deglutition, what happens?
Larynx elevates, epiglottis closes, breathing stops, pharyngeal muscles move bolus down
Is the esophageal phase of deglutition involuntary or voluntary?
Involuntary
When the bolus reaches the stomach, what chemical breakdown occurs at first, and when does it stop?
Salivary enzymes continue to break down carbs and lipids. It stops when pH drops low enough in the presence of HCl and deactivates these enzymes.
What sphincter controls the movement of bolus from stomach to intestine?
Pyloric
Where do you find the bulk storage of undigested food?
Stomach
The stomach churns to break down bolus further into
Chyme
How long can food stay in the stomach?
Up to four hours
The stomach contains gastric pits that
- produce mucous to protect epithelial cells from acidity
- contain stem cells to produce new epithelial cells
Pyloric glands contain G cells that secrete
The gastrin hormone
Gastric glands contain parietal and chief cells. Chief cells secrete _______ and parietal cells secrete_______
Pepsinogen
HCl and intrinsic factor
Pepsinogen is needed because
It is converted by HCl to its active form, pepsin, to digest proteins
Intrinsic factor is needed for
Vitamin B12 absorption
What cells have receptors to determine if the stomach is excited?
Parietal cells
What happens when a parietal cell binds with ACh, Histamine, and Gastrin?
Cell actively pumps H and Cl ions into the cell. Bicarbonate and chloride ion exchange occurs, bicarbonate is sent into blood stream, chloride is let into the stomach.
What does HCl do in the stomach?
Drops the pH to inactivate salivary enzymes
kills bacteria
breaks cell walls and connective tissue
What is absorbed in the stomach?
Lipid soluble drugs (alcohol and aspirin)
Most of the absorption of nutrients occurs in the ____ during digestion
Jejunum
The cephalic phase occurs
Before anything gets to your mouth
The cephalic phase is made up of entirely ______
autonomic, long reflexes
What is the product of the gastric phase?
Chyme
During the gastric phase, you mix the bolus with
Digestive enzymes and acid
What tells the body to start the gastric phase?
Distension of stomach wall
The ____ phase overlaps with the intestinal phase
Gastric
During the intestinal phase chyme is released in really small quantities and
Stomach is inhibited to create a pause to neutralize chyme released by the stomach
The intestinal phase inhibits gastric movement due to
- stretched intestinal wall
- pH decrease in intestine
- Undigested lipids and carbs
The secretion of _____ will overpower inhibitory hormones such as CCK, GIP, and Secretin
ACh
As chyme is processed and moves forward
- inhibition decreases
- increased motility in the stomach occurs
Gastric ulcers are caused by the bacteria
Helicobacter pylori
What happens with a gastric ulcer?
H pylori bacteria eat through mucous lining of the stomach, so HCl damages the gastric epithelial cells
Why does stress effect ulcers?
Stress inhibits digestion and can ultimately inhibit mucous production allowing the acid to do more damage to the cells
Gastric bypass
Removes part of the stomach and bypasses intestine
Stomach banding
Places a band on the stomach to limit quantities of ingested food
Chemical digestion is completed in the
Small intestine
What is secreted in the small intestine to aid in chemical digestion
- Pancreatic exocrine secretions
- Bile
- Alkaline buffers
Pancreatic amylase breaks down starch to
Disaccharides
Pancreatic lipases break down lipids to
Fatty acids
Pancreatic nucleases break down nucleic acids to
Nucleotides
Pancreatic proteolytic enzymes break down proteins to
polypeptides to aminoacids
What are the two proteolytic enzymes used to break down proteins?
Trypsin and chymotrypsin
Bile salts are necessary for
emulsification of lipids
Bile salts are synthesized
In the liver from cholesterol
Bilirubin is a waste pigment formed from
Heme of red blood cells
What controls the release of both pancreatic secretions and bile?
Hepatopancreatic sphincter
What controls the hepatopancreatic sphincter and how?
CCK, GPI, and Secretin cause it to relax
CCK is released
In response to undigested food
What does CCK do?
- Inhibit stomach
- Stimulate secretion of pancreatic enzymes
- Contracts gallbladder
- relaxes hepatopancreatic sphincter
Secretin is released
In response to acid chyme
What does secretin do?
- Inhibits stomach
- Tells pancreas to release buffers
- Tells liver to increase bile secretion
What does VIP do?
Increases blood flow to intestines and dilates blood vessels in hepatic portal system
What are the brush border enzymes for disaccharides?
Maltase, sucrase, lactase
What are the brush border enzymes for small peptides?
Peptidases
What are the brush border enzymes for nucleic acids?
Nucleases
Enzymes secreted in the ______ are responsible for the breakdown of macromolecules into monomers
Brush border
What is the only sphincter we have complete conscious control over?
External anal sphincter
What are the functions of the large intestine?
- Bacterial digestion
- Absorption
- Formation and expulsion of feces
True or false: there are no digestive enzymes produced by the large intestine
True
Bacteria within the large intestine
- convert bilirubin to breakdown products
- break down peptides to ammonium ions
- digest complex carbs
- give off methane gas
Bacteria in the large intestine manufacture
Vitamin K, Biotin, and B5
What does the large intestine absorb?
- Water
- Vitamins
- Bile Salts
- Organic wastes and toxins
How is feces created?
Absorption of water and segmentation movements compact materials into fesces
The defacation reflex is triggered by the
Distention of rectal walls
Absorption of nutrients and water into epithelial cells of intestinal mucosa layer occurs via
- simple diffusion
- facilitted diffusion
- cotransport
Water moves through the GI tract via
Osmosis
Monomers are absorbed
On lumen side of epithelial cells
Describe movement of absorbed materials in the brush border
Monomers are absorbed into epithelial cells
They are released into interstitial fluid
Diffusion from fluid to capillaries or lacteals occurs
Salivary and pancreatic amylase enzymes break polysaccharides to
Disaccharides
Brush border enzymes break disaccharides to
Monosaccharides
Proteins are broken down in the stomach by low pH destroying
Tertiary and Quaternary structure
Amino acids are absorbed into intestinal epithelia with the use of
AA-specific transport proteins
Amino acids and monosccharides are transported to the
Liver
What precautions does the body take to break lipids down to become small enough for transport?
- emulsification by bile salts
- lipase breaks it down
- micells diffuse into epithelia
- chylomicrons formed by combining glycerol with 3 fatty acids
- chylomicrons released via exocytosis and transported via lymphatic system
Lipids move through the blood using a protein and are transported through the
Lymphatic system
What are lipoproteins?
Soluble complexes of lipids and proteins
What do lipoproteins carry?
Insoluble glycerides and cholesterol
What are the types of lipoproteins?
- chylomicrons
- VLDLs
- HDLs
- LDLs
What lipoproteins are produced by the liver?
VLDLs
HDLs
LDLs
____ is the only lipoprotein produced in the intestinal epithelial cells
Chylomicron
VLDL’s carry
Triglyceride from liver to tissues
LDLs carry
Cholesterol to tissues
HDLs carry
Unused cholesterol from tissues to liver
How much of our cholesterol is created from diet?
20%
What are normal HDL and LDL levels
LDL below 130
HDL above 35
If we do not make enough cholesterol, we cannot absorb ____
Calcium
During the absorptive period, _____ is secreted
Insulin
During the post absorptive period, ______ is secreted
Glucagon, glucocorticoids, epinephrine
Describe what happens during the absorptive period
Blood sugar goes up, insulin is released, insulin travels to target cells to let glucose in
Describe what happens during the post absorptive period
Glucose levels drop, Insulin secretion stops, glucagon and epinephrine are released, cells start using fatty acids for ATP synthesis
When do nutrients enter the blood?
As intestinal absorption proceeds and insulin is created
What does the liver do with excess glucose?
- uses it for energy
- stores it as glycogen
- converts it to triglycerides
Muscle cells store glucose as
Glycogen
During the absorptive period, triglycerides are broken into
Fatty acids
During absorptive period, fatty acids are
- absorbed by adipose
- Absorbed by skeletal muscles
The absorptive period is stimulated by
Insulin
The longer its been since you’ve eaten, the more ___ present
glucocorticoids present
If you do not have enough glucose during postabsorptive period, liver breaks down glycogen and synthesize glucose via
gluconeogenesis
