GI Flashcards
- The gastrointestinal (GI) system primarily conveys _________, __________, and _________
into the body
nutrients, electrolytes, and water
___________ digestive system
* Food enters and wastes exit 1 opening
* Examples: protozoans, coelenterates
________ digestive System
* Food enters 1 opening and wastes exit a separate opening
* Length ensure adequate time for breakdown and absorption
* Human digestive system ~ 25 feet long from mouth to anus
Incomplete
Complete
Bringing food into the oral cavity (mouth) is called
Ingestion
_________
* Starts in the oral cavity (mouth)
* Mastication (chewing)
* Muscular movement through digestive tract
_________
* Hydrolysis reactions (enzymes) that break down food particles
into nutrient molecules small enough to be absorbed
* Starts in the mouth and continues through most of the
Mechanical
Chemical
- Chemo- & mechanoreceptors in oral and nasal cavity are stimulated by:
- Tasting
- Chewing
- Swallowing
- Smelling of food
- Thinking of food
- Input via vagus nerve (parasympathetic input)
- Postganglionic fibers innervate gastric glands
- Increases gastric juice production
- Phase generally lasts only a few minutes
Cephalic Phase
This Phase begins when food enters the stomach
This phase can last between _-_hrs
Gastric
3-4
This phase begins when chyme enters small intestine (duodenum)
Intestinal
Passage of nutrients from digestive tract into blood (proteins & carbohydrates) or lymph (lipids) for distribution to tissues is known as
Absorption
Peristalsis happens in what parts of the digestive tract
Esophagus
Stomach
Small intestine
Large Intestine
Segmentation occurs in parts of the digestive tract
stomach
small intestine
large intestine
transit time from ingestion to excretion
24hrs
Hollow tube that leads from the pharynx to the stomach
esophagus
______ __________ ________
* Skeletal muscle, but not under voluntary control
* Opening is triggered by swallowing reflex
Upper esophageal sphincter
- Receives food
- Lower esophageal sphincter prevents retrograde movement of food
Cardia
- Relaxes to accommodate a meal
- Mixes contents with gastric enzymes and acid
Fundus
- Coordinated, circumferential, large amplitude contractions grind the meal into small particles against a closed pylorus
Body
- Sieves 1 – 3 mm particles, permitting passage into the duodenum to mix with bile and pancreatic enzymes
Pylorus
In the stomach thick folds called _____ increase surface are for:
E
S
D
A
Rugae
Expansion
Secretion
Digestion
Absorption
_______ ____ Secrete
* Hydrochloric acid (HCl) (gastric pH ~ 2.0)
* Intrinsic factor (aids intestinal absorption of Ca2+ & vitamin B12)
Parietal
_______ _____
* Secrete mucous and alkaline substances (bicarbonate) to help neutralize HCl in gastric juice
Mucous Cells
__________________-____ ____
* Secrete histamine (stimulates acid production)
Enterochromaffin-like cells
_____ _____ Secrete
* Pepsinogen (inactive enzyme → pepsin)
* Gastric lipase
Chief Cells
_ _____
* Secrete somatostatin (inhibits acid production)
D
_ (______) _____
* Neuroendocrine cells that secrete gastrin into circulation (stimulates parietal cells and overall gastric secretion)
G (Gastrin) Cells
Enzymes embedded in microvilli
are referred to as _____ ______
enzymes
brush border
Smooth Muscle
* Lacks ________ → regulation of cross-bridge
formation is therefore not via tropomyosin like in
skeletal muscle, but rather regulation of myosin
________________
troponin
phosphorylation
All of the contractile tissue of the GI tract is ______-____ _____ ______, except for the pharynx (upper 1/3 of esophagus) & external anal sphincter (both are striated muscle → have a degree of voluntary control)
single-unit smooth muscle
- basal contractions that maintain tone without regular periods of relaxation
- periodic contractions followed by relaxation
Tonic Contractions
Phasic Contractions:
- Progressive wavelike movement that propels contents from the oropharynx to the anus
Peristalsis
The distention created by the bolus stimulates ______ neurons to relax the musculature in front of the bolus and stimulates ________ neurons at the oral end of the bolus → propels the bolus in anal direction (peristaltic reflex)
inhibitory
excitatory
Segmental, non-propulsive contractions of the ______ muscle layer in the digestive tract
circular
GI Motility by Segment
___-_______
* Swallowing
* Esophagus
______ __________
* Reservoir Function
* Receptive Relaxation
* Mixing and Digestion
* Gastric Emptying
_______ _________ _________
* Segmentation Contractions
* Peristaltic Contractions
_____ _________ _________
* Segmentation Contractions
* Mass Movements (peristaltic contractions)
* Defecation
Pre-Gastric
Gastric Motility
Small Intestine Motility
Large Intestine Motility
3 Phases involved with Swallowing
Oral
Pharyngeal
Esophageal
- Initiated when the tongue (T) pushes bolus of food (F) towards pharynx
- Stimulates somatosensory receptors that trigger involuntary swallowing reflex
Oral Phase of swallowing
Purpose is to propel food bolus from the mouth into the esophagus
* Soft palate moves upward to cover opening to the nasopharynx
* Epiglottis covers the opening to the larynx
* Breathing is inhibited
* Upper esophageal sphincter relaxes → bolus moves into esophagus
* A peristaltic wave is initiated
Pharyngeal Phase
- Esophageal sphincter closes behind bolus
- Food is propelled through the esophagus to the stomach via peristalsis
- Controlled by both the involuntary swallowing reflex and the enteric nervous system
Esophageal phase of swallowing
If the primary peristaltic contraction in the esophagus does not clear the esophagus of food, a secondary peristaltic contraction is initiated that is mediated
by the _______ ________ system
enteric nervous
3 Components of Gastric Motility
- Relaxation of orad region (Orad = Proximal body/fundus)
- Contractions to reduce size and mix bolus by gastric secretions
3.Gastric Emptying propelling chyme into small intestine
Distention of the lower esophagus by food produces relaxation of the lower esophageal sphincter and simultaneously relaxation of the fundus and upper portion of the body (i.e., the orad region) is known as ________ ________
Receptive relaxation
_______ _________ is the process by which the contents of the stomach are moved into the duodenum
Gastric emptying
3 mechanisms for gastric emptying:
- ________ ______ initiated in the fundus
- ___________ ______ of the antrum
- When the antrum contracts, the duodenum relaxes, allowing a small volume of gastric chyme to enter the duodenum
- ________ in size of the stomach
Peristaltic waves
Systolic contractions
Reduction
Small intestine motility:
Two types are….
Segmentation
Peristaltic
Smooth muscle contractions in the small intestine are due to the generation of ______ ______
- These waves are not action potentials, but rather oscillating ________ and _________ of the membrane potential
Slow waves
depolarization and repolarization
Large waves of contractions called _______ _______ ________ occur every 90 minutes to clear the small intestine of residual chyme
Can be modified by _____________ (↑ SM contraction) and __________ (↓ SM contraction) inputs
migrating myoelectric complexes
parasympathetic
sympathetic
The _______ _______ _______ is a distinct pattern of
electromechanical activity observed in GI smooth muscle during the periods between meals (fasting)
migrating motor complex
Intrinsic regulation
* _______ _______ → slow waves
* _______ ________ ________ (ENS)
Extrinsic Regulation
* _______ _______ ______ (ANS)
* ________ __________
Reflexes
* ________ __________
* ________ __________
Inherent Rhythmicity
Enteric Nervous System
Autonomic Nervous System
Endocrine Inputs
Long Reflexes
Short Reflexes
_______ _________ produces contractions in the gastrointestinal smooth muscle is preceded by electrical activity (i.e., action potentials)
_____ ______are not action potentials, but rather oscillating depolarization and repolarization
of the membrane potential
Inherent Rhythmicity (Tonic/Phasic Contractions)
Slow waves (Tonic Contractions)
- Initiated in Pacemaker Cells (interstitial cells of Cajal)
- Abundant in the myenteric plexus - Occur spontaneously (i.e., inherently) and spread rapidly from cell-to-cell via gap junctions
Slow Waves
The _______ (↑) & ______ (↓) of Na+/K+-ATPase activity
Variable opening of membrane voltage-gated _____ channels (appears to be the most likely candidate)
waxing waning
Ca2+
The various neurons of the ENS perform functions in 2 primary areas:
- ________ _______ receive inputs regarding physiologic status of the intestine, translate these into appropriate changes in function of smooth muscle, mucosa, glandular structures, & vasculature
- _______ _______ relay such information to the CNS and in turn integrate information from the CNS with that supplied by the intrinsic circuits to modify functional outcomes
Program circuits
Integration circuits
_____________ Plexus
* Only found in the small & large intestine
* Receive input from mechano- & chemoreceptors in
mucosa
* Communicates directly with:
* _________ plexus
* Endocrine cells in mucosa
* Circular (& longitudinal) muscle layers
__________ Plexus
* Between the circular and longitudinal muscles layers
throughout the GI tract
* Communicates directly with:
* __________ plexus
* Secretory cells in mucosa
* Circular & longitudinal muscle layers
* Neurons from the autonomic nervous system
Sub-mucosal
-Myenteric
Myenteric
-Sub-mucosal
_______Reflexes
* Higher level of control involving interneurons and motor neurons of the CNS
* Involve a sensory neuron that sends digestive information to the brain → parasympathetic motor fibers that synapse
in the myenteric plexus
* Generally, control large-scale peristalsis to move material from 1 region to another
Long
_____ Reflexes (myenteric reflexes)
* Triggered by chemoreceptors or stretch receptors in wall of digestive tract
* Controlling neurons located in the myenteric plexus
* Allows the enteric nervous system to act quickly and effectively
* Motility (peristalsis & segmentation)
* Hormonal & secretory functions
Short
Saliva Production:
* Functional unit is called a _______
Basic secretory unit of a ______ (same as first asnwer) are clusters of cells called an _______
Salivon
acinus
- Secreted by dorsal surface of the tongue from von
Ebner glands - Initiates digestion of dietary lipids into diglycerides
Lingual Lipase
_______ glands are found primarily in the body and fundus regions (proximal
80% of stomach)
* Consist of:
* ________ Cell (HCl & intrinsic factor)
* ______ Cells (pepsinogen)
Oxyntic
Parietal
Chief
_______ glands are found primarily in the antrum (pyloric) region
* Structurally similar to oxyntic glands, but with deeper pits
* Consist of:
* _ cells (gastrin)
* _______ ______ cells (mucus, HCO3-, & pepsinogen
Pyloric
G
Mucous neck
(CEPHALIC PHASE)
Vagal Post-ganglionic release of Ach stimulates:
- ______ cell Secretion
- Histamine release from ___________-_____ cells
- ________ ______ _______ PANS vagal neurons release ______-_______ _______→ ↑ gastrin
release from G cells → ↑ H+ release from parietal cells (direct action) and ↑ histamine release from ECL
(indirect ↑ in H+) - Vagal inhibition of _ cells → ↓ somatostatin release (somatostatin inhibits gastrin)
- Parietal
- Enterochromaffin-like
- -Peptidergic post-ganglionic
-gastrin-releasing peptide (GRP) - D
Enzyme _________ converts trypsinogen → trypsin
enterokinase
___________ component (from acinar cells)
* Low-volume secretion containing enzymes for the digestion of all normal constituents of a meal
* Pancreatic enzymes are essential to normal digestion and absorption (unlike those secreted by the stomach and salivary
glands)
_____________ component (from ductal cells)
* Function is to neutralize the contents in the duodenum in order to protect the intestinal mucosa from gastric acid and
pepsin
* Brings the duodenal pH into the optimal range for pancreatic enzymes to work
Enzymatic (or protein)
Aqueous (or bicarbonate)
Secreted from duodenal epithelial I cells in response to the presence of lipid and protein digestion products
Cholecystokinin (CCK)
________ also produce bile, which is transported
by vessels called canaliculi to bile ducts, which surround the lobule
Hepatocytes
blood entering the liver passes through ________ before exiting the liver
sinusoids
Bile Is continuously produced by _______ and then modified by _________ lining the bile ducts
hepatocytes
cholangiocytes
Once lipase has broken down fats into smaller subunits, other components of bile (i.e., phospholipids) surround lipids and form _____
micelles
glucose and galactose involve a __ dependent cotransport. __ from the Na+/K+-ATPase basolateral membrane
