Digestive I Flashcards
What is the primary function of the digestive system?
move nutrients, water and electrolytes from the external environment into the body’s internal environment
The digestive system is central to regulation and integration of _______ processes throughout the body
and proper functioning necessary for whole-body __________
metabolic, homeostasis
The digestive system extends from ______
to the _____ intestine (~15 ft length in live person)
mouth, large
___ _____: a long tube with muscular walls lined by transporting and secretory epithelial cells
GI tract
Stomach to the anus = ___
GUT
________: mechanical and chemical breakdown of food primarily occurs in the gut (breakdown of macromolecules into smaller substances that can be transported across the epithelial cell layer
Digestion
The digestive system is joined by secretions from accessory glandular organs like the ______ ______, _____, ________, and ________
salivary glands, liver, gallbladder, pancreas
Technically GI tract is continuation of ______ environment (bacteria)
external
A lot of those bacteria in the large intestine serve functions that help us:
- breaking down certain _____ compounds
- creating certain _______
- releasing _________ into the body that are important in many processes like modifying the nervous system, angiogenesis, promoting the storage of fat, etc
food, vitamins, substances
____ refers to structures in the abdominal cavity, stomach down, most of digestion occurs here
Gut
Digestion begins in the mouth with ________ (chewing) and the addition of _____. Tongue and lips also helps manipulate food
mastication, saliva
Three pairs of salivary glands: ?
Parotid – at the hinge point of your jaw
Sublingual – under the tongue
Submandibular – along the mandible
Three pairs of salivary glands with multiple functions: ?
- Moisten and lubricate food
- Amylase partially digests polysaccharides
- Dissolve some food molecules (taste)
- Lysozyme kills bacteria
__________ also exist in the saliva
Immunoglobins
_______: passageway from mouth to stomach
-upper and lower esophageal sphincters
Esophagus
Esophagus wall: top 1/3 is ______ muscle, bottom 2/3 ______ muscle
skeletal, smooth
Esophagus moves food via _______ waves
peristaltic
Digestion continues in stomach, mixing food with acid and enzymes to create _____
chyme
What are the 3 main sections of the stomach (starting at the esophagus)?
Fundus, Body, Antrum
What and where is the pylorus?
At the end of the antrum, it is a valve/sphincter
_____ esophageal sphincter relaxes during swallowing
_____ esophageal sphincter permits the movement of food from esophagus into the stomach and prevents backflow
Upper, Lower
Majority of digestion and absorption takes place here ?
Small intestine
What are the 3 main portions of the small intestine (starting from the stomach)?
Duodenum (first 25cm)
Jejunum
Ileum
Liver and pancreas release exocrine secretions into the _______ (there’s another sphincter here that does this)
duodenum
What are the 5 main portions of the Large intestine (starting from the ileum)?
Cecum - initial pouch
Ascending colon
Transverse colon
Descending colon
Sigmoid colon
Feces entering the terminal section of the large intestine (rectum) trigger a __________ reflex
defecation
______ ________: 1.5 L of watery chyme pass into here each day; water and electrolytes removed to create semisolid feces
Large intestine
Basic structure of GI wall is similar in both the stomach and intestines with ______ variations from one section to another
slight
The four main GI layers:
mucosa, submucosa, muscularis externa, serosa
Starting from the lumen, it goes to mucosa, which is made up of three separate layers: ?
epithelial, lamina propria, and muscularis mucosa, not the normal muscle for digestion
Then we have the submucosa (contains the submucosal ______), next is the major muscle layer: muscularis ________.
plexus, externa
Finally, we have a dense connective tissue layer surrounding the entire outside of the GI tract called the _______.
serosa
Within the muscularis externa, we have another plexus (nerve network) known as the _________ plexus
myenteric
Enteric is technically under peripheral but what is different is that the ENS can function ________, it does not need input from the CNS to function. It does receive input but it can function normally without to some degree
autonomously
The _________ plexus – tends to influence the mucosal layer and the epithelial cells
The _________ plexus – tends to influence the muscle as well as communicate with the submucosal plexus
submucosal, myenteric
Mucosa is divided into 3 further layers:
- The _________: the layer that lines the single layer of cells that lines the innermost portion. A variety of different cells exist in the epithelium which facilitates the transport of substances from the lumen into the interstitial fluid and into the blood vessels
- _______ ______: connective tissue layer, largely contains interstitial space as well as vasculature (small blood vessels) and small lymph vessels
- _______ ______: not the normal smooth muscle layer, thin layer of smooth muscle that believes to influence the amount for surface area available for absorption
epithelium, Lamina Propria, Muscularis Mucosa
Gastric folds increase surface area: ______
Rugae
In the stomach, surface area is increased by invagination called _______ _______
gastric glands
Intestinal surface area is enhanced by fingerlike villi and invaginations called _____
crypts
______ further increase surface area
Plicae
_____ increase surface area so that you can absorb large amounts
Villi
There are also gastric glands contain a large number of cells that are responsible for _______ secretion and _________ secretion
exocrine, endocrine
Epithelium changes depending on the _______ of the GI tract
region
Most transport is ________, but there are areas where there is higher amount of _________ transport
transcellular, paracellular
Massive turnover in epithelial cells in the GI tract due to constantly being exposed to _____ _______
harsh substances
Epithelium (most variable):
- Include transporting epithelial cells, endocrine and exocrine secretory cells
- Junctions very _____ in stomach and colon, ______ in small intestine
- _______ lifespan (a few days) GI stem cells constantly producing new cells.
tight, leaky, Short
The epithelium alternates between many kinds of cells including simple columnar epithelium with microvilli and _________ _____
enteroendocrine cells
Lamina propria
Subepithelial tissue containing _____ fibres, small _____ vessels and _____ vessels
nerve, blood, lymph
Muscularis mucosae
Thin layer of ________ muscle that can alter the surface area available for ________
smooth, absorption
____________: middle distensible layer containing larger vessels (lymph and blood) and the submucosal plexus; one of the major nerve networks in the enteric nervous system
Submucosa
Submucosa is another layer of connective tissue that is relatively ________ (loose)
distensible
_______ _____: 2 or 3 layers of smooth muscle: circular decrease diameter, longitudinal shortens the tube. Contains myenteric plexus
Muscularis externa
_______: outer covering of connective tissue that is a continuation of the peritoneal membrane, sheets of mesentery hold intestines in place
Serosa
These are the four basic functions and processes of the GI tract: ?
Digestion, Secretion, Absorption, and Motility
Secretion can mean a few different things in the Gi tract:
1. It can mean the movement of substances from the ____ into the ______ (classic secretion)
2. It can also be the movement of substances that are produced in ________ cells into the lumen
ECF, lumen, epithelial
Motility is necessary for _________ digestion
mechanical
3 main challenges of the digestive system: ?
avoiding autodigestion, defense, and maintaining mass balance
________ _______: breaking food down into small enough molecules to be absorbed without digesting the cells of the GI tract
Avoiding autodigestion
_______: absorbing water and nutrients while preventing bacteria, viruses and other pathogens from entering the body. Mechanisms to help with this defense include mucus, digestive enzymes, acid and the largest collection of lymphoid tissue
Defense
80% of lymphocytes in ______ intestine
small
We _______ a lot more than we actually _______
secrete, ingest
What are 3 fluid secretions?
Water, Digestive enzymes, and Mucus
________: Ions are transported from ECF into the lumen, creates osmotic gradient for water movement
Water
________ ______:
Exocrine glands (salivary and pancreas)
Epithelial cells in stomach and small intestine
Digestive enzymes
Some enzymes are released in an inactive form: ________ (stock pile without cellular damage)
zymogen
_______: Viscous glycoprotein (mucins) secretions that protect GI cells and lubricate the contents; Serves as a protective function; Mucus cells in stomach and salivary glands, goblet cells in intestine
Mucus
Most fluids facilitate _______
digestion
Epithelial cells in one area may release certain enzymes and epithelial cells in certain areas may release different one and the reason for that is basically to suit where the enzymes _______ best
function
What is the total input into the lumen from the digestive system?
9.0L
________: movement of material through the GI tract as a result of muscle contraction
Motility
Motility has two purposes: ?
Moves food from mouth to anus
Mechanically mixing food breaks it into uniformly small particles
GI motility determined by properties of ______ muscle and modified by ______ input from nerves, hormones and paracrine signals
smooth, chemical
When we are looking at motility in the digestive tract, most of the smooth muscle is arranged in single unit, or unitary formation where you have the presence of ______ junctions which allow contraction to occur in a uniform manner
gap
True or False: the entire digestive tract is liked by gap junctions?
False, there are small sections throughout the digestive tract that would be linked together
The cycles of contraction in the GI tract are driven by pacemaker cells that create _____ waves that can lead to contraction, they are depolarizations followed by repolarizations that will occasionally reach threshold and cause an action potential to fire
slow
_____ waves: alternations of depolarization and repolarization that occur due to presence of a variety of ion channels
Slow
Slow waves are almost always occurring, it’s the addition of ________ stimuli will cause threshold to be reached and contraction to occur
additional
A tonic smooth muscle that is usually contracted. This is usually in the shape of a singular V and is found in _______
sphincters
A phasic smooth muscle that cycles between contraction and relaxation. This is usually found in the _______ region of stomach, small, and large intestines
posterior
_____ waves modified by chemical input from neurons, hormones and paracrine signals
Slow
The force and duration of muscle contraction are directly related to the _____ and frequency of action potentials
amplitude
Slow waves likely originate in a network of cells known as the ? (ICC)
interstitial cells of cajal
? :modified smooth muscle cells serving as the pacemaker for slow wave activity
ICC
Slow waves begin ________ in ICC and spread to adjacent smooth muscle through gap junctions, and are electrically coupled. 3-12 waves/min
spontaneously
Three basic patterns of contraction occur in the GI system bringing about different types of movement: ?
- Migrating motor complex (motilin)
- Peristaltic Contractions
- Segmental Contractions
? : between meals, when the GI tract is empty; usually begins in the stomach and passes from section to section, terminating at the ileum. Sweeps food remnants and bacteria out of the upper GI tract and into the large intestine
90-120 minutes (first 45-60 minutes quiescent) in between meals. 20-30 min period of infrequent peristaltic contractions. 5-15 minute cycle rapid forceful contractions
Migrating motor complex (motilin)
__________ _________: contractions that cause forward movement, contraction of circular muscle behind a bolus of food and relaxation in front of the bolus to push the bolus forward. You would see this in the stomach and esophagus
Peristaltic Contractions
__________ _________: in the small and large intestine during a meal and after a meal, serve as a mixing function, alternating contraction between circular and longitudinal
Segmental Contractions
Motility is mainly consisted of ________ with a bit of __________ contractions mixed in
segmental, peristaltic
_______ and ________ are the primary regulated functions in the GI system
Motility, secretion
Two categories of regulation of GI function: ?
Neural
GI Peptides
_______: through the ENS, the reason why the ENS can be almost considered independent is due to the short reflexes that can drive motility and secretion without influence from the CNS
Neural
___ ________: cytokines can act as paracrines or autocrines
GI Peptides
The ENS shares similarities with the CNS:
_______ neurons: entirely within the ENS
~30 ____________ many identical to CNS
______ support cells: similar to astrocytes
_______ barrier: like BBB
Integrating center: can function __________
Intrinsic, neurotransmitters, Glial, Diffusion, autonomously
_______ reflexes originate in the enteric nervous system and are carried out entirely within the wall of the gut
______ reflexes are integrated in the CNS. Some long reflexes originate outside the GI tract, but others originate in the enteric nervous system
Short, Long
_________ plexus: motility
___________ plexus: secretion from GI secretory cells
Myenteric, Submucosal
If a long reflex begins in the brain it is a ________ reflex (feedforward and emotional)
cephalic
ENS receives information from the CNS via __________ neurons
autonomic
__________ increases/enhances GI function
__________ parasympathetic output causes increased motility and increased secretion
________ sympathetic output is inhibitory
Parasympathetic, Increased, Increased
___ _________: Can act as hormones or paracrine signals; Excite or inhibit motility and secretion; Can be secreted in to lumen to act on apical membrane receptors or ECF to act on neighboring cells
GI Peptides
True or False: GI peptides only act in the GI tract?
False, some act in the brain
What are the 3 main hormone families?
Gastrin, Secretin, and Other
Hormones are put into families based on similar _____ _____ structure or _______ receptors
amino acid, identical
Integrated function within the digestive system is often described in three phases: ?
Cephalic/oral phase
Gastric phase
Intestinal phase
_______ phase: digestive processes occurring before food enters the stomach and are reinforced once food enters the GI tract. Long reflexes beginning in the brain. Increased ___________ output from medulla to salivary glands and to the enteric nervous system
Cephalic, parasympathetic
_______ phase: digestive processes in the stomach. 3.5 liters of food, drink and saliva enter the stomach each day. Motility and secretion initiated during cephalic phase now reinforced
Gastric
_________ phase: digestive processes in the intestines
Intestinal
Saliva is an _______ secretion
exocrine
1.5 L/day of ______ is produced: 99.5% water, 0.5% solutes (Na+, Cl-, K+, HCO3-, PO4-)
saliva
Secretory cells found in clusters known as _____
acini
Glands are not identical:
_______: watery solution with amylase
__________: similar to parotid plus some mucus
_______: mainly mucus
Parotid, Submandibular, Sublingual
Saliva tends to be __________
hypoosmotic
Saliva is primarily under __________ control
parasympathetic
When looking at salivary glands, there are 2-3* main types of cells:
_______ Cell: produces mucous
_______ Cell: produces a thinner, more liquid component
*_________ Cell: smooth muscle-like cell, contracts to squeeze saliva out of the lumen of the acini into the duct
Mucous, Serous, Myoepithelial
__________ is a reflex that pushes a bolus of food or liquid into the esophagus
Deglutition
Pressure against soft palate and back of mouth (voluntary) activate sensory neurons going to the ________
medulla
________ (swallowing center): somatic motor outputs to pharynx and upper esophagus and autonomic outputs to the lower esophagus
Medulla
Soft palate closes off nasopharynx, contraction moves larynx up and forward, glottis closes trachea, upper esophageal ________ relaxes and opens
sphincter
Deglutition begins as a ________ reflex then turns into a largely involuntary reflex once it is initiated, means its hard to stop
voluntary
Order these in accordance with “deglutition:”
1. Food moves downward into the esophagus, propelled by peristaltic waves and aided by gravity. Lower esophageal sphincter tension relaxes
2. Breathing is inhibited as the bolus passes the closed airway. The epiglottis covers airways
3. Tongue pushes bolus against soft palate and back of mouth, triggering swallowing reflex
3, 2, 1
? : churning action of stomach contraction can cause backflow; negative intrapleural pressure during inspiration can cause esophagus to expand drawing gastric acid and pepsin from the stomach
Gastroesophageal reflux disease (heartburn)
Lower Esophageal Sphincter technically not a true anatomical ________ as it does not have a circular thickening of muscle
sphincter
Stomach has three general functions:
________: stores food and regulates its passage into the small intestine
________: chemical and mechanical digestion into chyme
________: Destroys bacteria and other pathogens in food and pathogens trapped in airway mucus (mucociliary escalator)
Storage, Digestion, Defense
A lot of the digestive processes that are regulated, motility and secretion, within the stomach are driven by _________
distension
Upon swallowing food, parasympathetic neurons to the ENS cause the fundus of the stomach to relax: ________ _______
receptive relaxation
Distension of stomach enhances _______
motility
Weak peristaltic waves that increase in force proceeding down to the antrum moves chyme toward pylorus (_________) and then larger particles are moved back to the body (_________). Mixes food with acid and digestive enzymes, small amounts of chyme squeeze through pylorus
propulsion, retropulsion
Gastric secretions _______ and ______
protect, digest
G-cells release ________ (hormone) in response to amino acids, peptides and distension (short reflex-GRP)
gastrin
____________ neurons→ ENS: stimulate gastrin production during cephalic phase (long reflex). This stimulates gastric acid secretion directly from _______ cells
Parasympathetic, parietal
_______: gastrin will go to parietal cells and simulate acid secretion from parietal cells
_________: Stimulates histamine release from enterochromaffin-like cells (ECL), which then stimulates parietal cells
Directly, Indirectly
___ cells: stimulates gastric acid secretion
G
________ Cells: activates pepsin; kills bacteria
Parietal
_______ Cells: 1-3L of gastric acid (HCl) produced daily with a pH as low as 1. Stimulated by gastrin from G-cells, histamine from enterochromaffin-like cells (ECL) or ACh from from ENS neurons via long and short reflexes
Parietal
______ acid stimulates release of pepsinogen from chief cells, cleaves pepsinogen to pepsin (digests proteins)
Gastric
Gastric acid denatures proteins making it easier for _____ to function and kills bacteria and other ingested microorganisms
pepsin
Gastric acid inactivates _______ from saliva and stimulates D cells to release somatostatin
amylase
Pepsinogen is the inactive form of ______
pepsin
Order these statements in accordance with “acid secretion:”
1. HCO3- exchanged for Cl- at basolateral membrane
2. Water dissociates to H+ and OH- freeing up more H+ to be actively transported
3. Cl- diffuses across apical membrane through open channels following electrochemical gradient
4. OH- combines with CO2 via CA to generate HC03-
5. Free H+ actively transported across apical membrane
5, 2, 4, 1, 3
In acid secretion:
H/K ATPase is important as a ______ pump
Bicarbonate/Cl transporter on the __________ membrane
proton, basolateral
Here are 3 stimuli for acid secretion:
- ______ H+/K+ ATPase, Cl- and K+ transporters stored in vesicles
- Stimuli cause _______ and insertion of apical transporters
- Excessive _____ treated with H2 receptor antagonists or proton pump inhibitors
Apical, exocytosis, acid
_________ hormones can also inhibit acid secretion
Intestinal
Gastric digestive enzyme secretion is stimulated by acid secretion via ______ reflex
short
_______ Cells: primarily produce pepsinogen, and small amounts of gastric lipase
Chief
Primarily the digestion of proteins that occurs in the stomach is in response to _______
pepsin
Paracrine secretion:
____: Histamine; activates H2 receptors on parietal cells to stimulate HCl secretion
________ cell: intrinsic factor; forms a complex with Vit B12 so it can be absorbed
___ cell: somatostatin; negative feedback for acid secretion (G cells, parietal cells and ECL cells); inhibits pepsinogen release
ECL, Parietal, D
Mucus and HCO3- secreted from ______ cells. Mucus secretion stimulated by _________ input and irritation. HCO3- by parasympathetic input and H+
mucous, parasympathetic
_____ _____: a sore or break in the lining of the stomach or duodenum
Peptic ulcer
_____ ______ are caused by excessive acid production and gastrin secreting tumors
Peptic ulcers
