Lab 8 Prelab Flashcards
What is methacholine? What does it bind to?
An analog of ACh that will bind to mAChR
What does epinephrine bind to?
Beta 2 AR
What does ADP bind to?
P2Y purinergic receptors
List the main and accessory organs of the GI system.
- Main: mouth, pharynx, esophagus, stomach, small and large intestine, rectum
- Accessory: salivary glands, pancreas, liver, appendix
What are the basic functions of the GI system?
- Taste, digestion of foods
- Production of enzymes, hormones, etc.
- Motility of foods through tract
- Absorption of nutrients
List the 4 basic layers of the GI tract from outermost to innermost.
- Serosa
- Muscularis externa
- Submucosa
- Mucosa
What is the mucosa of the GI tract? Function? Components?
- Epithelial layer where absorptive and secretory functions occur
- Made up of the lamina propria and lamina muscularis mucosae
What is the submucosa of the GI tract? Function? Components?
Loose connective tissue, blood vessels and glands that nourish and support the GI tract
What is the muscularis externa of the GI tract? Function? Components?
2 layers of smooth muscle
- inner layer of circular smooth muscle changes diameter
- outer layer of longitudinal smooth muscle changes length
What is the serosa of the GI tract? Function? Components?
Connective and epithelial tissue that supports and surrounds the GI tract
What are the 2 primary patterns of gastrointestinal motility?
- Segmentation
- Peristalsis
What happens during segmentation (GI motility)?
Mixes the bolus of food
- pushes contents back and forth in small segments
- increases time for enzymes to act and nutrient absorption
What happens during peristalsis (GI motility)?
Propels bolus forward through the contraction of circular muscle and relaxation of longitudinal muscle proximal to the bolus and the opposite distal to the bolus
What characteristics differentiate smooth muscle from skeletal muscle?
- No striations
- Contains tropomyosin but no troponin
- Doesn’t contain sarcomeres or myofibrils
- Doesn’t contain T-tubules or lateral sacs
- Poorly developed SR
What are dense bodies?
Anchor points for actin on smooth muscle
What do gap junctions do?
Electrically join cells on smooth muscle for communication
Describe multi-unit smooth muscle. Where is this type of smooth muscle found?
- Individual cells not electrically coupled –> one-to-one innervation
- Cells can contract independently
- Capable of fine muscle control
- Found in eyes, skin, some blood vessels
Describe unitary smooth muscle. Where is this type of smooth muscle found?
- Smooth muscle cells are electrically coupled in groups
- Contract in a coordinated manner
- Multiple cells innervated by single neuron
- Pacemakers can initiate AP independently
- Found in GI tract, uterus, large blood vessels
What facet of the nervous system innervates the GI tract?
Enteric Nervous System
What type of smooth muscle does the GI tract have?
Unitary
What are pacemaking cells in the gut called?
Interstitial Cells of Cajal
What do the Interstitial Cells of Cajal do?
Create a slow wave (Basal Electrical Rhythm) that varies throughout the tract
What channels in the GI tract create the slow wave?
- Voltage gated Ca2+ channels
- Ca2+ dependent K+ channels
When do spike potentials superimpose on the basal electrical rhythm? Significance?
- When threshold is reached
- More spike potentials = more contraction
What are the 2 sources of Ca2+ for contraction?
- Voltage gated Ca2+ channels –> influx of extracellular Ca2+
- Ca2+ release from the SR –> CICR
When there is an increase in cytosolic Ca2+, what does it bind to?
Calmodulin (CaM)
What can the Ca-CaM complex bind to?
- Caldesmon or calponin
- Myosin Light Chain Kinase (MLCK)
What happens when Ca-CaM binds to caldesmon or calponin? Where does this occur?
On actin/tropomyosin complex
-To unmask myosin binding site
What happens when Ca-CaM binds to Myosin Light Chain Kinase?
Activates MLCK –> MLCK phosphorylates myosin light chain regulatory protein to increase binding activity of myosin to actin
What causes smooth muscle relaxation?
- Decrease in intracellular Ca2+ by pumping out of cytosol via Na/Ca exchanger
- Myosin Light Chain Phosphatase dephosphorylates myosin light chain
What occurs to MLCK activity when intracellular Ca2+ is high? Low?
- High: MLCK activity becomes higher than MLCP
- Low: MLCK activity is lower than MLCP
Through what nerve do sympathetic neurons travel?
Splanchnic nerve
Describe the effects of sympathetic innervation on the GI tract. What neurotransmitter is released? How does this affect tension?
- Release norepinephrine
- Results in a decrease in tension but doesn’t significantly decrease frequency
- Fight or flight response suppresses GI
Describe the effects of parasympathetic innervation on the GI tract. What neurotransmitter is released? How does this affect tension?
- Release acetylcholine
- Results in an increase in baseline tension
- Rest and digest response stimulates GI
What is the Enteric Nervous System?
Primary neural mechanism that controls GI functions
Where are the 2 places ENS neurons are mostly found?
- Submucosal plexus (b/t submucosa and muscularis layers)
- Myenteric plexus (b/t 2 layers of smooth muscle)
List he 4 major processes of the GI system.
- Secretion
- Digestion
- Motility
- Absorption
What are endocrine secretions? Function?
Hormones that regulate GI function
What are exocrine secretions? Functions?
Enzymes, HCl, and HCO3- are important components of digestion
Define motility.
Muscular contractions that mix the luminal contents w/ digestive secretions
How did epinephrine affect gut activity?
DECREASE ACTIVITY
- decreased baseline tension
- decreased amplitude
What part of the autonomic nervous system does epinephrine mimic?
Norepinephrine
How did MCh affect gut activity?
INCREASE ACTIVITY
- increased baseline tension
- decreased amplitude
How did ADP affect gut activity?
DECREASE ACTIVITY
- decreased baseline tension
- decreased amplitude
How did Ca2+ free ringers affect gut activity?
DECREASE ACTIVITY
- decreased baseline tension
- decreased amplitude
- decreased frequencies
Why does frequency of gut activity decrease in Ca2+ free Ringers?
ICCs rely on Ca2+ to generate BER
Where does absorption occur in the GI tract?
Microvilli of the small intestine
Through what nerve do parasympathetic neurons travel?
Vagus nerve
