Digestive system - A & B

activies required of the GI tract:

• movement of food

• secretion of digestive juices and food digestion

• absorption of digestive products, water, and electrolytes

• circulation of blood through GI organs to carry away absorbed substances

• control of such functions via nervous/hormonal systems

oral cavity → esophagus → stomach → small intestine (duodenum, jejunum, ileum) → large intestine (ascending, transverse, descending colons → rectal column → anal canal → anus

the alimentary tract:

___cavity → ___→ ___→ small intestine (___um, ___um, ___um) → large intestine (___ing, ___, ___ing colons) → ___column → ___canal → ____

• includes liver, pancreas and gallbladder

oral cavity

first breakdown of food

• continues w/ the pharynx, then the esophagus

esophagus

passage of food

• enters abdominal cavity via diaphragm muscle

stomach

storage, second breakdown of food

• on the left upper side of the abdominal cavity

liver, pancreas, gall bladder, small/large intestines

organs of alimentary canal that focus on digestion and absorption

• oblique

• longitudinal

• circular

types of smooth m. in the stomach (3)?

• longitudinal

• circular

  • enteric innervated

types of smooth m. in the small intestine (2)?

strutures of the GI tract include:

• mucus membrane

• muscularis mucosa

• muscle layer

• circular muscle

• longitudinal muscle

• serosa (Adventitia)

strutures of the GI tract include:

• mucus ___

• muscularis ___

• muscle ___

  • ___ muscle

  • ___ muscle

• serosa (Adventitia)

mucus membrane

made of specialized epithelial cells for secretion/absorption

muscularis mucosa

wide spread muscle fiber under the lamina propria

• when it contracts it causes change in surface area for secretion/absorption

muscle layer of GI tract

made of inner circular and outer longitudinal muscle layers

circular muscle of GI tract

contraction decreases the diameter lumen of the GI tracts

longitudinal muscle

contraction causes shorterning of a segment of the GI tract

serosa (adventitia)

external peritoneal covering layer

submucosal plexus of meissner and myenteric plexus of auerbach

• INTRINSIC ENTERIS NERVOUS SYSTEM

what 2 parasympathetic plexuses are the digestive system is supplied by?

submucocal plexus of meissner and myenteric plexus of auerbach

intergrate and coordinate motility, secretory, and endocrine functions of GI tract

• have sympathetic fibers interspersed between

• INTRINSIC ENTERIC NERVOUS SYSTEM

accelerates:

• peristalsis

• endocrine/hormone/enzyme function

• HCl secretion

what is the role of the parasympathetic system in the GI tract?

sympathetic and parasympathetic

extrinsic innervation of the GI tract includes what systems?

efferent fibers

carry info from brainstem and spinal cord to the GI tract

afferent fibers

carry sensory info (chemoreceptors/mechanoreceptors) from GI trac to brainstem/spinal cord

vagus … pelvic splanchnic

• excitatory function

• excitatory

• preganglionic …. myenteric … submucosal

parasympathetic system includes the ___ n. and ___n.

• it is ____ on GI function

• has ____ fibers hat synapse on the ___ and ___ plexuses

vagus (CNX)

sends info to the esophagus, stomach, pancreas, intestine, and down to the UPPER parts of the large intestine

pelvic splanchni nerve (S2-4)

carries info to the lower parts of the large intestine and pelvic organs

• origin of the sacral spinal cord

sympathetic system

originates from the spinal cord and comes via abdominal splanchnic nerves (T5-L2)

preganglionic cholinergic fibers (sympa)

synapse in prevertebral ganglia

postganglionic adrenergic fibers (sympa)

leave the prevertebral ganglia and synapse in the myenteric and submucosal plexuses

sympathetic system function in GI tract

inhibit peristalsis and gastric/hormone/enzyme secretion

• cause pyloric contraction and convey pain

post … adrenegic … blood … smooth

direct ___ganglionic ___ innervation of ___ vessels and ___ muscle cells also occur

smooth muscle

contractile tissue of the GI tract is unitary….?

• pharynx

• upper 1/3 esophagus

• external anal sphincter

  • HAVE STRIATED muscle

what are the 3 exceptions to the unitary smooth muscle of GI tract contractile tissue that have striated muscles instead?

contraction of circular muscle

leads to decrease in diameter of that segment of the GI tract

contraction of longitudinal muscle

leads to decrease in length of that segment of the GI tract

phasic contraction

found in the esophagus, gastric antrum, and small intestine which contract and relax periodically

• not continous

tonic contraction

found in the LES, orad (upper) stomach, and ileocecal/internal anal sphincters

• not continuous

EMG of GI smooth muscles

has threshold values for spikes

slow waves

oscillating membrane potentials inherent to smooth muscle cells of some parts of the GI tract that occur spontaneously

slow waves:

• originate from cajal interstitial cells

• not action potentials

• determine pattern of action potential and contraction

• very thick contraction → always under threshold

slow waves:

• originate from ___ cells

• ___ action potentials

• determine pattern of action ___and ___

• very ___ contraction → always ___ threshold

cajal interstitial cells

pacemaker of GI tract smooth m. under threshold (slow waves) that normally exist in GI tract wall

mechanism of slow wave production

cycle of activation and deactivation of the membrane with 2 cycles: depol (inward Ca2+) and repol (outward K+)

depolization of slow wave

characterized by INWARD CA2+

depolarization

what brings membrane potential of smooth muscle closer to threshold → increases action potential probability

top … background … contraction

action potentials are produced on ___ of the ___ of slow waves → initiates ___ of smooth muscle cells

repolarization of slow wave

characterized by OUTWARD K+

varies … constant

frequency of slow waves ___ along the tract but is ___ in each part

• not … neuronal/hormonal

  • axn potentials … top

    • stomach … duodenum`

frequency of slow waves:

• not influenced by neuronal/hormonal input

  • frequency of axn potentials that happen at the top are influenced

• lowest in the stomach and highest in the duodenum

• 12x/min

• 9x/min

• 3x/min

frequency of slow waves location:

• duodenum: ___

• ileum: ___

• stomach: ___

spike potentials

action potentials of GI tract

-40 mV

• -50 … -60 mV

• -56 mV

spike potentials are triggered at ___.

• resting membrane potential floats between ___ and ___

• avg. resting membrane is ___

threshold

• i.e bursts of 1-10

the number of spikes triggered is proportional to the rise and time above what?

10-40 … large nerve … 10-20

• calcium-sodium channels (depol)

the axn potential of GI muscle is ___ as long as that in ___ fiber (___ ms)

• its caused by ___

the the GI tract recieved food content

when is slow wave converted into spike wave

depol characteristics

• ___

• ___

• ___stimulation

  • specific ___ homrmones

• stretching

• AcH

• parasympathetic stimulation

  • specific gastrointestinal homrmones

• norephinephrin or epinephrine

• sympathetic stimulation

• relaxation/inhibition

hyperpolarization/repol characterstics

• ___ or ___

• ___ stimulation

• ___ /___

calmodulin

calcium ions and gi tract muscle contraction:

• acts through ___ coordinator instead of troponin C for myosin/acting filament binding:

• Ca2+ and calmodulin combine → Ca binds to TpC → interweve of filaments

tonic contraction of GI smooth muscle

in GI smooth muscle, there is always at least weak contraction even during sub-threshold slow waves

• basal contraction exhibited when smooth muscles isn’t completely relaxed

• nervous

• hormonal

• calcium .. variable

• relative (top … underlying)

tonic contraction is controlled by:

• ___ input (non-slow wave associated spikes)

• ___ input

• ___ entry w. __ resting membrane potential

• peristalsis happens relative to this contraction (happen on ___ of ___ baseline tonic contraction)

cholecystokinin (CCK)

hormone that increases contractility of gallbladder to release bile and concomittantly decreases stomach contractility

• from jejunjum

from jejunum mucosa and holds fats still for digestion

where is CCK from and what does it hold still for digestion ?

secretin

hormone that has mild inhibitroy effect on GI motility to moderate acid load to small intestine

• from duodenum

from duodenum mucosa

where is secretin from?

gastrin inhibitory peptide

hormone secreted in response to fats and carbs (to a lesser extent) to decrease motor function/peristalsis when the upper small intestine is already full

• from the upper small intestine

upper small intestine

where is gastric inhibitory peptide from?

propulsive movement

aka peristalsis of GI tract → forward flow

• strong contraction

mixing movement

movement within the biomass of the digesting contents themselves

• regional

• distension … 2-3cm

• circular … longitudinal

• relax … contraction

propulsive movement/peristalsis:

• stimulated by ___ every ___ of GI tract

• coordinated contraction of ___ muscles

  • muscles ___to receive food → distension → ___

it creates churning

• but little absorption is done around the sphincters → other small movement dynamics are important

if a sphincter is present that what does peristalsis create and what is the result?

• submucosal plexus

• few cm

• chopping … churning … biomass

  • meissner’s plexus

local constrictive contractions:

• are under ____ control

• happen every few ___

• create ___ and ___ to increase contact between ___ and gut wall

  • defects in ___ → malabsorption

chewing

peristalsis that lubricates food by mixing it w/ saliva and decreases the size of food particles to faciliate swallowing process and start digestion

swallowing

peristalsis reflex coordinated in the medulla via CNIX - glosspharyngeal and CNX - vagus

• involves the closure of nasopharynx and epiglottis sphincters

• nasopharynx … breathing

• laryngeal … glottis … larynx

• pharynx … UES

events involved in swallowing:

1. ___ closes → ___ prohibited

2. ___ muscles contract → ___ closes and ___ is elevated

3. peristalsis starts in the ___ → ___ relaxes (to propel food towards and into the esophagus)

stomach

• 25-30

• 40

esophagus - propels food into the ___

• ___cm long

• ___cm from the incisor teeth

• upper … air

• aortic … aortic arch

• diaphragmatic … E hiatus

3 narrowings of the esophagus:

• ___ sphincter - prevents ___ entering esophagus

• ___ narrowing - crossed by ___

• ___ narrowing - in the ___

• C6 … cricoid

• vertebral

• R … L … vagus

• T10

• distal … sphincter … gastric acid

• cardia

esophagus:

• starts at ___ vertebra aka ___cartilage

• lies on the ___ column

• accompanied by ___ & ___ vagus nerves

• passes through diaphragm at lvl ___ and ends below it

• ___ part can act as a ___ to prevent ___ entering the esophagus

• enters the stomach via the ___

• T8

• T10

• T12

  • I 8 10 EGGS AT 12

hiatuses of the diaphragm:

• IVC -

• Esophagus -

• Aorta -

• pharynx … oral cavity

• arch of aorta

• close to the stomach

surroundings of the esophagus:

• UES - close to the ___ and ___

• MES - encircled by the ___

• LES - close to the ___

• sympathetic

• parasympathetic (vagus)

innveration of the esophagus includes?

• during swallowing, food content goes into esophagus → UES relaxes → food content recieved → UES closes → food content goes to LES → mediation of vasoactive inhibitory receptor peptide (hormone that controls relaxation of LES) → LES relaxes → good goes to stomach → LES closes

swallowing and the esophagus:

• during swallowing, food content goes into esophagus → ___ relaxes → food content ___ → ___ closes → food content goes to ___→ mediation of ___ ___ ___ peptide (hormone that controls ___ of LES) → ___ relaxes → food goes to stomach → ___ closes

intraesophageal pressure = thoracic pressure

• thoracis pressure is < atmospheric pressure

because the esophagus is in the thorax, intraesophageal pressure is equal to what?

esophageal balloon catheter

can measure intrathoracic pressure

1. UES relaxes → food enters eso

2. UES contracts → prevents food reflux into pharynx

3. primary persitaltic contraction makes causes high pressure behind the food → contraction moves down and is accelerated by gravity

4. secondary peristaltic contraction clears the esophagus of remaining food

5. relaxation of LES by VIP via vagus n.

6. receptive relaxation of orad stomach region → food bolus enters stomach

esophageal motility:

1. ___ relaxes → food enters eso

2. ___ contracts → prevents food ___ into ___

3. primary peristaltic contraction causes ___ behind the food → contraction moves ___ and is accelerated by ___

4. secondary peristaltic contraction ___ the esophagus of ___ food

5. relaxation of LES by ___ via ___ n.

6. receptive ___ of ___ stomach region → food ___enters stomach

gastric reflux

occurs if tone of LES is decreased → LES cant close completely and gastric contents reflux into the esophagus

• can cause heart burn

gastric reflux

retrosternal pain less than <10-20 minutes is a sign of?

achalasia (cardiospasm)

neuromotor disorder of LES resulting from decreased amount of cells in myentric plexus