4. Physiology Flashcards by J L

Mucosa of GI is ____

* Muscular layers involved in movements that propel and mix foods with secretions of mucosa

secretory

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Basic Structures in the G.I. System
 • \_\_\_\_ muscle fibers 
– 2-10 mm × 200-500 mm
• 1000 parallel fibers 
• Gap junctions
• Low \_\_\_\_ to ion flow from cell to cell
• Functional syncytium
• Action potential initiates and travels in all \_\_\_\_

• Rich in smooth muscle
	○ BSIII material on smooth muscle
• Located in \_\_\_\_ layer and the \_\_\_\_
• Work as a synctium
	○ When stmulateby AP that stimulates the muscle fiber > it should work as a unit coordinating at the same time
	○ Bc of the orientation > propagation of contrction is faster in \_\_\_\_ direction

smooth
resistance
directions
muscularis
muscular mucosae
longitudinal

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Electrical Activity in the GI System

Slow waves – Not ____
3- stomach, 12 duodenum, 8-9 ileum
Induced by ____ (electrical pacemakers)
Spikes – True ____
Entrance of ____+ through ____ Ca2+/Na+ channels• Two electrical actiivities
○ Slow waves
§ Specific SM celsl that show this change in potentail of their PM > not real AP > just changes in degree of the potential
§ Induced by electrical activity produced by an interstitial cell of cajal
□ Pacemakers embedde din ____ layer
□ In ____ of stimulus, change potential that transmit to muscle fibers
§ Only when the ____ is high > specific stimulus on SM cells is when they can regenerate the real AP and induce the SM cells to contract

action potentials
interstitial cells of cajal

action potential
Ca
slow

muscularis
absence
potential

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Neural Control of the GI System

Two levels:
• Central nervous system (autonomic):
• Parasympathetic – ____, ____.
• Cranial Division: ____–esophagus, stomach, pancreas,
intestines (partial).
• Sacral Division: ____ nerves-distal half of large intestine, external anal sphincter.
• Sympathetic – ____; ____, norepinephrine.

Enteric Nervous System:
____ or Auerbach plexus.
____ or Meissner plexus.

	• CNS
		○ Parasymp stimulates activity
		○ Symp is inhibitory
	• ENS
		○ Completely embedded in GI wall, not part of the CNS
		○ Two plexuses

stimulatory
cholinergic
vagus
pelvic
T5-L2
inhibitory

myenteric
submucosal

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Neural Control of the GI Tract

Intrinsic controls:
Nerve plexuses near the ____ initiate ____ reflexes.
Short reflexes are mediated by local ____ plexuses.
Extrinsic controls:
Long reflexes arising within or outside the ____.
Involve ____ centers and extrinsic autonomic nerves.• Allows presence of two levels of control
○ Intrinsic
§ Short reflexes that take place within the wall of the GI tract in reposns eto local stimuli
§ DO not involve the CNS
§ Local enteric plexuses
□ SI > drop in ____ > receptors that can respond to low pH > trasnmit info through local nerve plexus > plexus induces a repsonse by a specific effector (SM or secretory gland)
® If too acidic - activates a gland that secretes bicarbonate > change in ____ activity
○ Extrinsic
§ ____ is involved
§ ____ may be same (change in pH)
§ Afferent go into the CNS > involved autonomic in response to change in stimulus
§ ____ phase of control > nothing is happening in the GI but our body is repsonding
□ Smell food and hungry > involvement of CNS > GI gets ready for the foodw e’re smelling and we know we’re gonna eat

GI tract
short
enteric

GI tract
CNS
pH
secretory
CNS
stimulation
cephalic

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Function of the Myenteric (Auerbach) Plexus

• Control of muscle activity ____ the GI length.
• Located between ____ and circumferential
musculature.
• Principal effects:
• Increased ____.
• Increased intensity of ____ contractions.
• Slightly increased ____ of rhythmic contractions.
• More rapid movement of ____ waves.

• Plexus is embedded in the \_\_\_\_ layer of the gut
	○ All actions are related to muscle functions

along
longitudinal
tonic contraction
rhythmic
rate
peristaltic
muscularis

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Function of the Submucosal (Meissner) Plexus

Control of function ____ the inner wall.
Principal effects:
Control of ____.
Control of ____.
Local contraction of the ____ (infolding).• Located in the ____ layer of the wall
○ Control activities in submucosal and mucosal layers
§ Mostly secretion and absorption (main role!)
§ Only in segemnt wtish muscularis mucosae > activation of the SM plexus may have effect on contraction of SM
□ Control degree of infolding of mucosa

within
local intestinal secretion
local absorption
muscularis mucosae
submucosal

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Hormonal Control of the GI Tract

Gastric and intestinal ____, osmolality, texture, pH, affects the motility, secretion and digestion
Hormones: ____, Ghrelin, Cholecystokinin (CCK); ____; Gastric Inhibitory Peptide (GIP)

content
gastrin
secretin

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Movements in the GI Tract
• Movements require stimulation of the myenteric plexus.

• Movement of segmentation
	○ Movement that allows contents of gut to \_\_\_\_
	○ Important in \_\_\_\_ and in SI
	○ Induced by contracting a certain region of wall of tract that's not coordinated with a \_\_\_\_ downstream or upstream
		§ Net effect: \_\_\_\_, no movement of material along gut
• Peristaltic
	○ Contraction > also a \_\_\_\_ somewhere else (usually \_\_\_\_)
	○ Food movement is \_\_\_\_ and coordinated
		§ Net effect: \_\_\_\_ of food from oral to uboral side; some \_\_\_\_ as well (not as much)

mix
stomach
relaxation
mixing
relaxation
downstream
unilateral
movement
mixing

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Secretory activities in the GI tract

TAKE A LOOK!!

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Basic Mechanisms of Gland Secretion Control

Local stimulation:
Effect of ____.
Activation of the ____ system:
____ stimulation.
Chemical irritation.
____ of the gut wall.
Autonomic stimulation:
Parasympathetic:
Generally increases ____ of secretion, especially in the ____ (salivary, esophageal, gastric, pancreas and Brunner’s glands).
Sympathetic:
Slight to moderate ____ by some glands.
Reduces overall secretion due to ____.
Hormonal:
Increased gastric and pancreatic ____.

food
enteric nervous
tactile
distension

rate
upper tract
increase
vasoconstriction

secretions

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2.1. Digestive Processes in the Mouth and Esophagus.

Food is ingested.
____ digestion begins (chewing).
Propulsion is initiated by ____.
Salivary amylase begins breakdown of ____.
Pharynx and esophagus serve as conduits to pass food from the mouth to the stomach.• No chemical digestion during mechanical digestion (except for thilaine?)

mechanical
swallowing
starch

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Neural Control of the Pharyngeal Phase of Swallowing

Bolus stimulates pharyngeal sensory receptors that induce a ____ controlled by the motor center in the medulla and pons via the ____, vagus (X) and ____ nerves.
Goal is to block all passages except to the ____.
Chewing reflex:
Presence of ____ → inhibition jaw muscles → lower ____ drop → stretch reflex of jaw muscles → jaw muscle ____ → compression of bolus → ____ → repeat cycle• Chew food > chewing reflex
○ Bc food is in the mouth > mechanoreceptors > feel the oral cavity is filling up > creates a reflex that starts movement of lower jaw > drops > stretch reflex (bc of mechanos in lower jaw) > induces contraction of jaw muscle back up > compresses bolus of food > lower jaw inhibited > back to initial stage
• Once cycle advances enough > bolus is mechanically digested and mixed with ____ secretions > cycle completes; and reflex to swallow bolus of food takes place
○ These are all ____ activities (chewing and swallowing)
§ Nerves involved in these mechanisms are ____, and muscles are ____
• Presence of food when ready to swallow > induce reflex that controlled by ____ > block all passages in oral cavity except the passage to the esophagus (prevent food from going larynx/lungs)

reflex
glossopharyngeal
accessory
esophagus

food
jaw
contraction
inhibition

salivary gland
voluntary
somatic
skeletal
medulla/pons

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deglutition

* Food in oral cavity > chewing reflex > \_\_\_\_ is contracted and no food can reach esophagus > \_\_\_\_ is open
* When ready to swallow > move tongue retrograde > bolus is pushed > \_\_\_\_ is open (relaxed) > opening esophagus to bolus
* After passing sphincter > \_\_\_\_ closes > prevents reflux of food to oral cavity
* To ensure reaches stomach > esophagus induces \_\_\_\_ movements > just upstream of food is contracted, and below the esophagus is relaxed > having a wave of contraction going from oral cavity to lower sphincter > wave of contraction/relaxation ensures bolus reaches the stomach
* GES opens > bolus reaches the stomach
* Initial steps are voluntary, but once food in \_\_\_\_ > involuntary controlled by ANS

UES
glottis
UES
UES
peristaltic
esophagus

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Neural Control of the Esophageal Phase of Swallowing

Primary peristalsis: continuation of pharyngeal ____.
Secondary peristalsis (if food doesn’t reach stomach): esophageal wall ____.
Receptive relaxation of the ____.
Receptive relaxation of the ____.• Upper 1/3 of esophagus > muscularis made of ____ voluntary muscles
• Lower 2/3 of esophagus > ____, involuntary autonomic
• In the middle you find both, a transitions
• When swallow food and crosses the UES > involuntary > mediated by ANS
○ Usually one wave of peristalsis > primary peristalsis > continuation of pharyngeal swallowing > ensures bolus reaches stomach in one wave
§ If food gets stuck > new wave of peristalsis induced > secondary peristalsis > reflex to relax the esophageal wall
□ Takes lpace until distention is gone and food reaches the stomach

swallowing
distension reflex
lower esophageal sphincter
stomach

skeletal
SM

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2.2 Digestion in the Stomach

Digestion of proteins:
Secretion of ____.
Secretion of pepsinogen and activation to ____.
Secretion of Intrinsic Factor for ____ absorption
____ absorption.
Gastric secretions + food = formation of ____.• Digestion of proteins begins > secretion of HCl (denaturant of proteins) and pepsinogen (protease; secreted in stomach and converted to pepsin, only takes place in high acidity)
• Secretory cells in stomach > IF > binds to B12 in order for it to be absorbed
○ Absorption of B12 doesn’t take place in the stomach
○ Only absorption in the stomach > ____ absorption
§ Good > blood levels of alcohol go up quickly > noticing effects quickly
□ If alcohol absorbed in SI/LI > would take hours for alcohol to absorbed

HCl
pepsin
vitamin B12
alcohol
chyme
alcohol

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Stomach Secretions

Stomach glands:
Cardiac glands: ____.
Gastric glands:
Parietal (oxyntic) cells: ____, ____.
Chief (peptic) cells: ____.
Mucous neck cells: ____.
Pyloric glands:
Mucous cells: ____.
G-cells: ____.

mucins
HCl
IF
pepsinogen
mucins

mucins
gastrin

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Mechanism of HCl Secretion by Parietal Cells

• Parietal are rich in \_\_\_\_ and contain caniliculi > highly secretory; efficient for \_\_\_\_ pumpung
• All transporters of ion that contain P > active > ATPases > move ions against graient
	○ \_\_\_\_ > drives whole process
1. NaK ATPase > epxorting Na ions thorugh basal domain of cell > simple diffusion is enough to ensure traffick of Na from canaliculis; but cell has an extra ATPase that’s moving Na into the cell > \_\_\_\_ cxn of Na in lumen; at same time cell is exporting Cl- against the gradient into the \_\_\_\_ (into the cavity of the stomach); reason why cell is interested in pumping Na+ in is bc if cell is pumping Cl- out and the cxn the Na+ is high > formatino of NaCl (doesn't want this! Wants HCl!)
	a. Active pumping of Cl- and Na+ ensures that canilcular side of cell is more \_\_\_\_ charged than the cell in the basal domain (-70 mV)
	b. A positive ion has to balance the electrical charge > \_\_\_\_ bc the cell wants to produce HCl
		i. Pump that exhanges H+ for \_\_\_\_ that's located outside
		ii. Another \_\_\_\_ expense
		iii. Where are H+ coming from > coming from activity of \_\_\_\_ in the parietal cell > uses CO2 to combine with H2O to produce HCO3 > dissociates into bicarbonate and H+ > H+ pumped into canaliculus > and bicarb is allowed to exit the cell through a transporter in the ECF
		iv. Source of CO2 to make carb acid is dual > some is from the \_\_\_\_ through simple diffusion, and most of the CO2 is produced \_\_\_\_ by the parietal cell
			1) Mitochondria is where a lot of CO2 is made > parietal cell is RICH in \_\_\_\_ bc of pumping activities that require a lot of ATP
			2) Formation of HCl in the lumen

mitochondria
ion
NaK ATPase
low
canaliculus
neg
K+
energy
CA
BS
intracellularly
mitochondria

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Mechanism of HCl Secretion by Parietal Cells

____ Na+ import at the canalicular side.
____ Cl- export at the canalicular side (together with [1] creates a negative potential between -40 and -70 mV).
The negative potential induces the diffusion of ____ to the canaliculus.
H+ generated from the dissociation of HCO3- by carbonic anhydrase.
____ export of H+ to the canaliculus in exchange of K+ by a H+, K+-ATPase.
____ follows the osmotic gradient.
HCO3- generated in step [4] is exchanged for ____ at the interstitial side to balance the electrical potential. HCO3- is used in the protection of the gastric wall. Cl- is used in step [1].

ative
active
K+
active
water
Cl-

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Secretion of HCl – Control Mechanisms

• How is secretion controlled:
• Antrum
	○ In pits > have secretory glands > produced of mucus > speicif population of cells that are endocrine > many different pops based on hormone produce
	○ One population > G cell > \_\_\_\_ > respond to presence of \_\_\_\_ in the chyme (in the stomach) > circulates in BS > reaches \_\_\_\_ of stomach > where gastric glands are located > two main pops:
		§ Parietal cells (HCl)
		§ Chief cells (pepsinogen)
	○ In gastric glands > endocrine cells > ECL cells > when stim > produce \_\_\_\_, acts as short distance endo activator > acticates secreiton of \_\_\_\_ by parietal cells
	○ Activation of chief cells to produce pepinsogen is more unclear
		§ \_\_\_\_ may activate also
		§ \_\_\_\_ may directly activate
		§ Direct activation of \_\_\_\_ system through ACh can activate Chief or ECL cells
• Response of parietal/chief is due to \_\_\_\_ which is due to \_\_\_\_ in the chyme
• Mechanism to inhibit is mediated by a diff pop in the antrum > \_\_\_\_ cells
	○ Repond to high cxn of protons (low pH) by secreting \_\_\_\_ (somatostatin) > inhibits the \_\_\_\_ so they do not produce gastrin > inhibiting productino of HCl and pepsinogen

gastrin
AA
fundus
histamin
HCl
ECL
gastrin
parasymp

gastrin
AA
D
SST
G cells

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Secretion of HCl and Pepsinogen – Control Mechanisms

• Regulation of gastric acid and pepsin secretion by soluble mediators and neural input:
• Gastrin is released from G cells in the ____ (in response to the presence of peptides/amino acids in the stomach and to secretion of GRP from vagal fibers).
• Gastrin travels through the circulation to influence the activity of ECL cells and parietal cells.
• The specific agonists of chief cells are not well understood.
• Gastrin release is negatively regulated by luminal ____ via the
release of somatostatin from antral D cells.

antrum

acidity

Protection Mechanisms of the Gastric Wall

* Just outisde basal domain > capillaries that run in close prox to gastric glands > get the \_\_\_\_ that's secreted by parietal cells through basal domain > flow of blood goes from bottom of gastric gland up on the \_\_\_\_ of the stomach
* Caps reach top of glands (pit) > bicarb is \_\_\_\_ resorbed by secretory epithelium > cells absorb bicarb from cap > and export the bicarb through apical domain into the surface of the stomach
* Surface of stomach is not naked > epi is highly sec of mucus > the bicarb is exported into the \_\_\_\_ layer > if any HCl diffuses into the mucus > react with \_\_\_\_ > buffers the effect of the HCl > only way it doesn't eat away the wall of the stomach

bicarb
surface
mucus
bicarb

Phases of Gastric Secretion: Cephalic Phase

Originates in the ____ cortex, and appetite centers of the ____ and ____.
Excitatory events include:
Sight or thought of ____.
Stimulation of taste or ____.
Inhibitory events include:
Loss of appetite or ____.
Decrease in stimulation of the ____ division.

cerebal
amygdala
hypothalamus
food
smell receptors
depression
parasympathetic

Phases of Gastric Secretion: Gastric Phase

Neural control:
____ reflexes.
Local ____ reflexes.

• Excitatory events include:
• Stomach \_\_\_\_ and activation of stretch
receptors.
• Activation of \_\_\_\_ by peptides, caffeine, and rising pH.
• Release of \_\_\_\_ in to the bloodstream.

Inhibitory events include:
pH

vagovagal
enteric
distension
chemoreceptors
gastrin
2
parasympathetic

``` hases of Gastric Secretion: Intestinal Phase • Excitatory events: • Low ____. • Partially ____ foodi int he duodenum: • Reverse enterogastric reflex: ↑ ____ activity. ``` * Inhibitory events: * ____ of duodenum. * Presence of fatty ,acidic, or ____ chyme, and/or irritants in the duodenum. * Inhibition of ____ reflexes and vagal nuclei. * Closure of the ____. * Release of ____ that inhibits gastric secretion.

``` pH digested gastric gland distension hypertonic local pyloric sphincter secretin ```

• Three phases of gastric secretion: ○ Cephalic § Involves ____ system § Stimulus: smell/sight/touching of food § Response: through the vagus nerve, increase secretion of ____ and pepsinogen in the stomach even in ____ of food ○ Gastric § Repsonse to food ____ t he somtach § Involves ____ reflexes, and ____ enteric reflexes § Stimuli: distention of wall of stomach, activation of mechanos, activation of chemoreceptors □ Both ____ and ____ are within the stomach > entirely gastric stimulus and responses ○ Intestinal § Response due to stimulation of receptors in ____ , in response to the chyme (food/pep/HCl) reaching the duodenum § Stimuli create an enterogastric reflex > stimulus is in ____ and reflex is in the ____ □ Reflex creates regualtino of gastric gland secretions § Partially digested food > creates more pepsinogen/HCl to ensure the predigesiton in stomach is fine enough so food that reaches duodenumun is smooth and highly digested

upper nervous HCl absence ``` distending vagal local receptors responses duodenum duodenum stomach ```

Motor Functions of the Stomach * ____ of food. * Mixing with gastric secretions to form chyme: * Constrictor ____. * ____ emptying into the small intestine. • Storage of food - temporary in humans

storage waves slow

Gastric Movements A, ____ phase between feeding. B, Entry of food causing dilatation: ____ reflex. C, Propulsion of food into the pyloric canal. D, ____. E, Retropulsion. F, ____ into the duodenum: pyloric pump. • B > food reaching stomach > rtretch of wall > induces presence of local reflexes > contraction of wall > series of ____ movements where food is mixed with gastric juices • F > food has to leave stomach through pyloric sphincter > pyloric pump ○ Highly ____ ○ Duodenumum is capable of sensing how well the food is digested and how acidic the chyme is ○ PS never opens ____ > relaxesa. Little > allows passing of small diameter particles > ensures a very ____ suspension is transferedd

``` interval vagovagal grinding expulsion mixing controlled completely fine ```

Local and Hormonal Regulation of Gastric Movements and Emptying * Gastric factors: * stretch, content: ____ reflexes → ↑ ____pump. * Gastrin: ↑ motor functions, ↑ ____. * Duodenal factors: * Monitoring: * ____, pH, irritants, content, osmolality (hypo-, hypertonicity) * Inhibitory effects of duodenal reflexes: * Directly from the duodenum through the ____ NS. * Through extrinsic nerves to ____ ganglia. * ____ nerves to brain stem. * Hormonal Feedback (CCK, GIP: ↓ stomach ____) • If food is not highly digested, if PS is allowing passage of semi-digested food > duo is irritated > inhibitory reflex from duo into gastric wall > prevents opening of PS

myenteric pyloric pyloric pump ``` distention enteric sympathetic vagus mobility ```

2.3. Digestion in the Small Intestine * As chyme enters the duodenum: * Carbohydrates and proteins are only ____ digested. * No ____ digestion has taken place. * Digestion continues in the small intestine: * Chyme is released ____ into the duodenum. * Because chyme is ____ and with low pH, ____ is required for proper digestion. * Required substances needed are supplied by the ____ (bile acids) and ____ (pancreatic juice: digestive enzymes). * Virtually all nutrient absorption takes place in the ____. • SI > chemical digestion; so far in oral cavity and stomach is ____ digestion (only proteins are being chemically digested) • Chyme from stoamch into duo ○ For proper digestion > chyme must be well mixed (hypertonic and low pH) > duo doesn't like low pH > will neutralize the low pH > secrete bicarb, helped by substances that are secreted by auxillary glands (bile acid from liver, dig enzymes and bicarb from panc) > all nutrients absorbed in the SI

``` partially fat slowly hypertonic mixing liver pancreas SI mechanical ```

2.3.1. Pancreatic secretion * Exocrine function: * Secretes pancreatic juice which breaks down all categories of foodstuff and provides ____ * Acini (clusters of secretory cells) contain ____ with digestive enzymes. * Pancreatic juice enters the GI tract at the ____. * Panc juice contain enzymes and bicarb * Reach duo through the major duodenal papilla

alkalinity zymogen granules duodenum

Composition of Pancreatic Juice • Water solution of enzymes and electrolytes (primarily HCO3–): • ____ acidic chyme: HCl + NaHCO3 → NaCl + H2CO3 H2CO3 → H2O + CO2 (lung) • Provides ____ for pancreatic enzymes. • Composition depends on the type of ____ in the chyme. • ~ 1 L/day. • Chyme is ____ • Duo doesn't like low pH ○ Digestive enzymes don't work at low pH ○ Important secretion by duo and panc > secretion of ____ § Allows buffer of HCl coming from the stomach > HCl neutralized > producig NaCl and H2CO3 □ Carb acid > ventilated in lung to ____ catalyzed by CA ○ Neutralization of acidity > optimal enzymes produce dby panc and SI

neutralizes optimal environment food acidic bicarb CO2

Mechanisms of Pancreatic Secretion * Acinar fluid is ____ and resembles ____ in its concentrations of Na+, K+, Cl-, and HCO3-. * Secretion of acinar fluid and the proteins that it contains is stimulated primarily by ____. * ____ stimulates secretion of water and electrolytes from the cells that line the extralobular ducts. * The secretin-stimulated secretion is richer in ____ than the acinar secretion because of Cl-/ HCO3- exchange. • Make protein > digestive enzymes produce dby acinar cells • Bicarb is produce din the ____ • In response to stimulus > panc juice is enriched in enzymes, or it can be more enriched in bicarb ○ Stimuli from SI

``` isotonic plasma cholecystokinin secretin HCO3- ducts ```

Pancreatic Ion Secretion 1. Secretin activates cAMP signaling cascade to open CFTR Cl- channels causing outflow of ____- into the duct lumen. 2. Higher [Cl-] drives the activity of the ____. 3. HCO3- derives from: a. Import from the ____ via the Na+/ HCO3- and symporter NBC-1. b. Intracellular generation by ____. 4. ____ follows via the paracellular route to maintain osmotic equilibrium. ____ export balances electrical charge. • How is bicarb produced? ○ In response to low ____ in duo § ____-cells produce hormone secretin > activate duct cells > CL- channels are open > into the lumen of the duct in panc > reabsorbed in exhcnage for bicarb > bicarb comes from the BS (from basal domain by a Na-bicarb symporter) or from the metabolic activity of the cell (converting CO2 into carb acid and bicarb via CA) § Mechanism is similar to secretion of HCl, but the result is that the secretion is alkaline □ Water/sodium follow osmotic gradient > ____ rich secretion containing sodium bicarb (buffering agent)

``` Cl Cl-/HCO3- antiporter bloodstream carbonic anhydrase water Na+ pH S water ```

``` Digestive Enzymes in the Pancreatic Juice • Secreted as active enzymes: • ____ • Trypsin inhibitor • Phospholipase A2 • RNAse; DNAse • Lipases ``` * Secreted as inactive zymogens: * ____. * Chymotrypsinogen. * Procarboxypeptidase. * Proelastase • Big difference bt the two: ○ ____ aren't on the active enzymes ○ All inactive are proteases > ensure that they do not attack the ducts or acinar cells when secreted • None of the targets of active enzymes are on the surface of the cells > no damage

alpha-amylase trypsinogen proteases

Activation of Pancreatic Zymogens • Won't be activated until lumen of ____ ○ When environement is at ____ pH, but cascade through proteolysis has taken place ○ On surface of enterocytes > ____ > protease that is specific for activation of trypsiogen into trypsin active form § Cascade begins with activation that only takes place in lumen of SI (enterokinease is) § Once activated > starts cutting other molecules of trypsinogen in trypsin > amplified > and starts cutting other ____ (chymo > chymo) • Highly regulated bc only takes place in ____ of SI

``` duodenum neutral enterokinase zymogens lumen ```

Regulation of Pancreatic Secretions * Cephalic phase: * Parasympathetic, vagus: * ____ – stimulatory. * Gastric phase: * ____, vagal. * ____secretion. * Intestinal phase: * Intestinal acidity - ____ (duodenal S cells): * Induces secretion of ____–-rich juice. * Lipids, protein products – ____ (duodenal____ cells): * Induce secretion of ____-rich juice. • Cephalic phase ○ In repsonse to food and sight of food also ○ Starts secretion of panc befor eeating phase • Gastric phase ○ Mediated by HCl in the stomach > induce a reposnse by panc to produce substances that ____ the acidity • Intestinal phase** (most important!) ○ When chyme reaches duo: § If pH is low > duo ____ cells produce secretin > in the panc bicarb is made (panc juice is more rich in bicarb than zynogens) § Chyme rich in lipids > duo ____ cells produce CCK > panc produces juice rich in zymogens/enzymes

acetylcholine neuroendocrine HCl ``` secretin HCO3 CCK I enzyme ``` neutralize S I

2.3.2. Small Intestine Secretions * Brunner’s glands (duodenal): * ____ mucus (Mucin + HCO3-): * Neutralization of HCl: Protects duodenal wall from digestion. * Regulation: * Stimulation: * ____ or irritating stimuli on the duodenal mucosa. * ____ stimulation. * Gastrointestinal hormones esp. ____. * Inhibition: * ____ stimulation. * Crypts of Lieberkühn: * ____ cells: mucins. * Enterocytes: * Water, electrolytes: 1800 ml/day, pH 7/5-8/0. * Digestive Enzymes: * Several ____. * Four disaccharidases: ____, maltase, ____, lactase. * Intestinal ____. • SI also secretes bicarb (not as much as panc) ○ Regulation is similar to panc

``` alkaline tactile vagal secretin sympathetic goblet peptidases sucrase isomaltase lipase ```

2.3.3. Movements of the Small Intestine * Mixing Contractions (Segmentation contractions) * Induced by ____. * Maximal frequency depends on electrical ____ waves. * Requires ____ plexus. • Movements of SI are highly regulated • Two movmeents: ○ Segmentation contraction § Stretching of SI wall by presence of ____ § Require an active myenteric plexus □ ____ spaced contractions of the SI wall faciliates the mixing of the dig products with panc and enterocyte secretion ○ Peristaltic movements § ____ § Push movement of food 3-5 cm every time contract § Regulation □ ____ reflex ® Stimulus at stomach; response at SI ® By filling up the stomach > can induce GE reflex > ____ in wall of stomach > initiate reflex that results that transmission of myenteric plexus through GI tract > acting ont ____ in SI by stimlauting contractino of the wall • ____ is produced in repsonse to intestinal acidity ○ Why secretin inhibitory in persistalsis > SI doesn't want the chyme that is acidic to keep going down the SI and creating damage until it is well mixed in the duodenum and neutralized § ____ contractions but not peristaltic movmeentms > ensures chyl well mixed

``` stretching slow myenteric chyme regularly weak gastroendocrine mechanos myenteric plexus secretin mixing ```

Movements in the Small Intestine * Propulsive Movements: Peristalsis: * 0.5-2.0 cm/sec, weak, travel ____ cm. * Control of Peristalsis in the Small Intestine: * Gastroenteric reflex: * Initiated by stomach ____. * Transmitted through the ____. * Hormones: * Stimulatory: ____, CCK, ____, motilin, ____ * Inhibitory: ____, glucagon.

``` 3-5 distention myenteric plexus gastrin insulin serotonin secretin ```

Absorptive Function of the Small Intestinal Mucosa ``` folds of kirkring - 3x 10-40 villi/mm - 10x 600 microvilli/mm2 - 20x Absorptiv area - 600-1000x total - ____ m2 ``` • Critical funciton of SI: absorption of substances ○ Several degrees of folding ○ Plicali circ = FoK • 250m2 is area of the lecture hall

250

Water Absorption • 95% of water is absorbed in the small intestine by ____. 1. Water moves in ____ directions across intestinal mucosa. 2. Net absorption occurs when a concentration gradient is established by ____ of solutes into the mucosal cells. 3. Water uptake is coupled with s____ uptake, and as water moves into mucosal cells, substances follow along their concentration gradients. • How effective the absorption of water is • Lose very little water in stool ○ Most is reabsorbed at level of ____

``` osmosis both active transport solute SI ```

Carbohydrate Digestion and Absorption • Digestion of macromolecules in SI ○ Talked about in FSI • GI tract is disassembly line > absorbed in SI is ____ molecule possible

simplest

Carbohydrate Digestion and Absorption • Final stages of metabolism of complex carbs take place in ____ at surface of ____ • At surface of enterocyte > hyrodlases that are specific for carbohydrates ○ ____ > enzyme for catalyzing for splitting glucose and fructose in sugar ○ ____ > membrane of entero that cleave lactose into glucose and galactose • Mechanism of absorption via: ○ ____ § Transport through membrane in association with ____ ○ ____

``` SI enterocytes sucrase lactase symports Na+ facilitated diffusion ```

Protein Digestion and Absorption • Similar in proteins • Cascade of enzymes > degrade into small peptides or free AA ○ ____ also absorb the AA/small peptides (di or tri) using ____ (symport in association with ____ ion)

enterocytes facilitate diffusion Na+

Lipid Digestion and Absorption • Role of ____ produced by liver that allows absorption of fats ○ Required for ____ and absorption of fats

bile acid | emulsification

NaCl Absorption • Symport of Na+ with other ____. • ____ of Cl- in exchange for ____. • Driven by ____ active transport at the ____ domain of the enterocyte. • Na+ is absorbed in cmobo with othe rnutrients ○ Symport mech for AA and carbohydrates ○ Net import of Na+ when absorbing other nutrients • Import of Na+ is the ____ force for absorption of glucose and carbs/proteins • Equilibrium of Na+ cxn is produced by NaK ATPase ○ Net import of Na > Cl- follows the electrical imbalance produced by absorption of Na+ ○ So cellr eabsorbs NaCl

``` nutrients antiport HCO3- Na+/K+ ATPase basal driving ```

Absorption of Vitamin B12 • B12 is present in high levels in animal meat, fish ○ Cannot make B12, only ____ can do it ○ Essential nutrient • B12 is liberated from food > binds ____ (secreted in ____) > ____ cells of stomach produce IF ○ Three compeonets exit stomach and rich duo > salivary R protein is degraded by ____ > B12 released > when in ____ pH > binds gastric IF > IF-B12 > travels to ileum > enterocytes have surface receptor that can recognize the complex > only in ____ does absorption of B12 take place § ____ with formation of small vesicles ○ Some ____ in colon aslo prduce B12 > downstream of ileum, efficiency of recycling from colon in BS is LOW § Why we need it exogenously!

``` bacteria R protein saliva parietal panc proteases neutral ileum receptor-mediated endocytosis bacteria ```

2.4. Digestive Functions of the Large Intestine * ____, ion and vitamin absorption. * Bacterial flora: * catabolize / ferment i____ carbohydrates. * synthesis of some vitamins - ____ and K. * Feces formation: * ____ material, bacteria, sloughed epithelium, ____, electrolytes, mucus. ``` • Vitamins ○ Produced by bacterial flora § B complex § Vitamin K □ Blood clotting • Bacterial flora also digest carbs that are indigestible by our enzymes ```

``` water indigestible B complex indigestible H2O ```

Movements of the Large Intestine ``` • Movements: • ____. • Mixing: • Contractions → Baglike protrusions (____). • Propulsive: • “____”: • Modified type of ____. • Formation of a ____ ring. • Contraction of ~20 cm. • Transport feces to the ____. • ____ and duodenocolic reflexes, autonomic. ``` • Haustrations ○ Back like protrusions that ensure complete mixing of substances in LI • Chyl from the SI when reaches ascending LI is very ____ > through efficient reabsorption of water > when reach rectum > feces are mostly ____ • Mass movement > modified type of peristalsis > formation of ring of contraction > ____cm of LI contracts at same time > efficient movement of feces into the rectum

``` sluggish haustrations mass movements peristalsis constrictive rectum gastrocolic ``` fluid solid 20

Secretion in the Large Intestine * ____ to neutralize bacterial acidity. * Mucus: intestinal wall ____, ____. • Secretion of bicarb from the tubular glands of leiberkuhm ○ Not to neutralized HCl from stoamch, but the ____ (via fermanatation process produce a lot of organic acids)

HCO3- protection bacteriostatic bacterial acidity

Defecation reflex • Defecation reflexes: • Intrinsic (local enteric nervous system): • Rectal distension → ____. • Rectal distension → ____ → Relaxation ____. * Extrinsic: * Parasympathetic → ____, ____ internal anal sphincter. * ____ control of external sphincter. • Two reflexes ○ Intrinsic § Local enteric NS (myenteric plexus in wall of rectum) § Stimulus: distention of rectum when filled with feces > peristaltic movement § Muscles at level of IAS > ____ (involuntarily) ○ Extrinsic § Involves parasymp § Result is the same • When feces fill rectum > second part of defecation process is relaxation of external sphincter > ____ control ○ At this level > ____ muscles innervated by ____ nerve fibers ○ Correlates with the histological structure of the rectum, anal canal and anus

peristalsis myenteric plexus internal anal sphincter peristalsis relaxation voluntary smooth muscles voluntary striated/skeletal somatic