Gin4 - Electrolyte And Fluid Balance Exchange

GIN 5 - Electrolyte and Fluid Balance Exchange Proscribe: Zack Mahdavi Dr. Simon Lewis 9/13/07

Reviewer: Rebekah Garcia Chief Reviewer: Kimberlyn Fitchett

Electrolyte and Fluid Balance Exchange •

Dr. Lewis did not cover Vitamins as well as Calcium/Iron transport. He has placed a handout on Blackboard, so please make sure you study the handout!

•

These scribes are based on the 2009 scribes.

This is the third and final lecture by Dr. Lewis. We now have a mixture of particles that are rich in monosaccharides, amino acids, di- and tripeptides, free fatty acids, monoglycerides, sterols, salts, vitamins, trace elements, nucleic acids, etc. These particles need to be absorbed from the lumen of the intestine into the blood. Absorption I.

Daily Load – How much do we have to deal with in a 24 hour period? A. Water = 5 – 8 L, Na+ = 1 mole, Cl- = 1 mole, K+ = 0.06 moles (K+ mostly ingested)

B. Fat 12-160g, Protein 60-120g, Carbs 280-800g C. Not much of the daily load is lost in feces. Most of it is absorbed. D. Difference in daily load and ingestion gives what is secreted by GI tract via: i. Salivary secretion – 1.5L of saliva ii. Biliary secretion – 0.5L of bile and sodium bicarbonate iii. Pancreatic secretion – 1.5L of sodium bicarbonate and zymogens iv. Gastric secretion – 2L of HCl v. Intestinal secretion – 1.5L of HCl solution secreted by crypts to wash bacteria and food particles off of the villi E. Difference in daily load and what we lose in the feces gives what we absorb i. Two structures aid in absorption: 1. Small intestine – large majority of absorption (8.5 L / day) a. Water, sodium, chloride, and a good chunk of potassium is absorbed b. Amount of potassium absorbed by the small intestine is larger than

the total net amount of potassium absorbed? This is due to the large intestine… 2. Large intestine – acts as “clean up” (absorbs 0.4 L / day) Page 1 of 17

GIN 5 - Electrolyte and Fluid Balance Exchange Proscribe: Zack Mahdavi Dr. Simon Lewis Reviewer: Rebekah Garcia 9/13/07 Chief Reviewer: Kimberlyn Fitchett a. Actively secretes a small amount of potassium

b. Sequesters remaining amounts of water, sodium, and chloride II. Surface area required for absorption A. If the small intestine were viewed as a simple tube that is 4 cm in diameter and 260 cm in length,

it would have a surface area of 3,330 cm2 B. However, the epithelial surface thrusts towards the central axis to increase surface area exponentially. This increases the length of contact that the food has with the surface, which aids in absorption. Ways to increase surface area include: i. Epithelial folds (Kerking’s folds) – amplify the SA by a factor of 3 to reach about 10,000

cm2 ii. Villi on the folds – amplify the SA by a factor of 10 to reach 100,000 cm2 iii. Individual cells have brush border membrane with finger-like projections – amplify the

SA by a factor of 20 to reach 2,000,000 cm2 of absorptive area – (equivalent to SA of an average house!) iv. There is a total of 600 fold of amplification!

v. Could lose about half of this surface area and not face any consequences (depending on which areas sustain the most cutbacks) – any more loss than this can result in malabsorption syndrome III. Components of intestinal tract

A. Villi – absorb B. Crypts – secrete and have proliferative zone i. Cell starts at base  migrates to villi tip and differentiates into absorptive cell 

extruded  exfoliation of cells at villi tip C. Turnover rate of intestinal cells is the fastest in the body – lifetime is 5-7 days IV. Structure of intestinal tract A. Duodenum – huge paddle-like villi, large SA, nicely elaborated crypt system

B. Jejunum – lower density and smaller villi, less SA C. Ileum – even less SA, blunted villi, crypt system is still well developed D. Colon – smooth surface epithelium with no villi, well developed crypt system Page 2 of 17

GIN 5 - Electrolyte and Fluid Balance Exchange Proscribe: Zack Mahdavi Dr. Simon Lewis 9/13/07 V. Tight epithelia vs. Leaky epithelia

Reviewer: Rebekah Garcia Chief Reviewer: Kimberlyn Fitchett

A. Leaky epithelia (duodenum) – bulk transport of iron, water, electrolytes, and non-electrolytes i. Cannot maintain any osmotic or concentration gradients of ions or substances ii. Duodenum will be an active absorber iii. Jejunum is similar to duodenum (cannot maintain osmotic or ion concentration gradient) iv. Ilium is slightly tighter: cannot maintain osmotic gradient but will start to maintain a small ion concentration gradient B. Tight epithelia (colon) – less water permeable (not impermeable) i. Can support ion concentration gradients, but not osmotic gradients ii. Sodium concentration in colon is 30 mmol but blood sodium level is about 140 mmol; colon can absorb a lot of sodium yet still maintain ion concentration gradient iii. The osmotic pressure of feces is always isosmotic VI. Chyme is isosmotic from the duodenum all the way through the colon

A. Chyme is isosmotic in the colon because it contains lots of osmotically active particles that the colon cannot absorb B. Colon can easily absorb water and electrolytes, but it cannot transport non-electrolytes such as sugars, amino acids, and some of the fats VII. Osmolality of small intestine (osmolality = concentration of solutes in a solvent) C. Reference plasma osmolality is ~290 mOsm D. Hypotonic meal (i.e. steak dinner with water) - ~230 mOsm

i. Acid secretion in stomach makes it less hypotonic ii. In duodenum, it becomes isosmotic rather quickly. How? 1. Two hypotheses as to how this is possible: a. Move osmotic particles from blood to lumen b. Move water from lumen to blood – CORRECT theory i. Water content in the lumen decreases as you move along the

length of the intestinal tract Page 3 of 17

GIN 5 - Electrolyte and Fluid Balance Exchange Proscribe: Zack Mahdavi Dr. Simon Lewis 9/13/07

Reviewer: Rebekah Garcia Chief Reviewer: Kimberlyn Fitchett

ii. So a hypotonic meal is made isosmotic due to water movement from the lumen into the blood. E. Hypertonic meal (i.e. milk + donuts  Krispy Kreme will be out of bankruptcy!) - ~660 mOsm

(2x the normal osmotic pressure) i. Water content of lumen increases along length of intestinal tract ii. So a hypertonic meal is made isosmotic by movement of water from blood into the

lumen. iii. So drinking milk on a hot day just makes you more dehydrated iv. There are osmoreceptors in the duodenum that will slow down gastric emptying so that

we don’t end up losing too much of our circulatory volume from water movement out of the blood v. Dumping syndrome – no regulation of movement of water from blood into the lumen

because there is no control on gastric emptying vi. What’s happening: 1. Absorption of some carbohydrates

2500

2. Production of osmotically active particles by break down of starches by “-ases”

) L 2000 m ( n e m u 1500 L n it n et n 1000 o C re t a W 500

3. 1 starch will have 300 osmotic particles after it is broken down

Hypotomic Hypertonic

0 Pylorus Ligament of Treitz

Ileocecal Valve

4. Initially there is a jump in water concentration followed by a gradual decrease in concentration because of absorption of these osmotically active particles that are being produced simultaneously – the water follows the particles F. Ion concentrations along the length of the small intestine: i. Na+

1. Low in the stomach

Page 4 of 17

GIN 5 - Electrolyte and Fluid Balance Exchange Proscribe: Zack Mahdavi Dr. Simon Lewis 9/13/07

Reviewer: Rebekah Garcia Chief Reviewer: Kimberlyn Fitchett

2. Na increases quickly in the duodenum. This is because the pancreas duct cells produce sodium bicarbonate that is transported to the lumen. ii. K+

1. High in meals 2. Slowly goes down because of

diffusion along its gradient – passive process; moves between cells from lumen into the blood. So no active transport. iii. Cl-

1. Increases dramatically in stomach during a meal due to increase in HCl (stomach acid) iv. pH 1. Very acidic in stomach 2. Neutral in duodenum due to Na-HCO3 secretion by pancreas •

Sites of mechanisms – What does it absorb? How does it absorb it at the cellular level? a. Duodenum i. Brings chyme into osmotic equilibrium ii. Pancreatic bicarbonate increases pH of chime 1. pH has to be close to neutral (around 6 – 7) because this is the most effective

operating condition for proteases, amylases, and transporters iii. Hydrolysis of carbohydrate and proteins iv. Has capacity to absorb 100% of carbohydrates in normal diet 1. In sugar overload, jejunum will also participate in carbohydrate absorption v. 50-60% amino acids absorbed vi. Na, Cl and K passively; water absorption (follows osmotic gradient) vii. Absorbs calcium and iron Page 5 of 17

GIN 5 - Electrolyte and Fluid Balance Exchange Proscribe: Zack Mahdavi Dr. Simon Lewis Reviewer: Rebekah Garcia 9/13/07 Chief Reviewer: Kimberlyn Fitchett viii. Glucose/galactose absorption is sodium dependent (via SGLT-1 transporters)

1. Glucose/galactose can be absorbed against their concentration gradient using the Na+ concentration gradient ix. Fructose is sodium independent x. Sugar Transport 1. SGLT1 (Sodium Glucose

Transporter 1)

Sugar Transport Lumen

Blood

Cell

Glut2

SGLT1

a. Transports either glucose or

galactose (both compete for the same binding site) along with 2 Na+ molecules from lumen into the cell (across apical membrane)

2 Na +

Glucose Glucose

Galactose/Glucose .

Na +/K + pump K+

Na +

K+

Fructose Fructose Glut5

Fructose

Cl-

Glut2

b. Large sodium gradient favors movement of Na+ into cell, thus favoring the movement of glucose and galactose 2. The imported Na+ is then moved across the basolateral membrane via the Na+/K+ pump 3. Movement of Na+ from lumen into blood will cause blood to be slightly positive

 subsequently, Cl moves through leaky epithelia 4. The glucose that comes in across the apical membrane goes out across basolateral

membrane via GLUT2 (passive transport) 5. The K+ that moves in with the pump then moves out across the basolateral membrane again through a K+ channel a. The movement of K+ outside of the cell creates a negative cell interior 

provides energy for movement of glucose (in addition to the Na+ pump) b. Can accumulate glucose concentration inside cell to 100-1000 fold greater than outside the cell xi. Fructose Transport 1. Across apical membrane Page 6 of 17

GIN 5 - Electrolyte and Fluid Balance Exchange Proscribe: Zack Mahdavi Dr. Simon Lewis Reviewer: Rebekah Garcia 9/13/07 Chief Reviewer: Kimberlyn Fitchett a. GLUT5: fructose into cell; GLUT5 is specific for fructose. b. Fructose movement is a facilitated process (only moves by chemical

gradient) – the fructose concentration with the cell cannot exceed the concentration of the lumen or blood c. In the rare condition where a mutation exists in the SGLT-1 protein, glucose and galactose ingestion cause osmotic diarrhea. However, fructose does not cause these symptoms due to its absorption process. 2. Across basolateral membrane a. GLUT2: fructose out of cell

xii. Most transport occurs in the top 1/2 to top 1/3 of the villi because the bottom 2/3 is still undergoing differentiation xiii. Peptides are absorbed by co-transport with protons

1. 30% of amino acid load is absorbed as free amino acids and 70% is absorbed as di- and tripeptides 2. There is only one transporter that can absorb di – and tripeptides 3. However, there are 6 free amino acid transport systems a. Dr. Lewis told us to NOT memorize these 6 transport systems. KNOW that there are several transport systems for amino acids, but there is only 1 transport system for di- and tripeptides. b. 2 facilitated transport – take hydrophilic amino acid into cell c. 2 Na+ dependent – sodium and amino acid bind to same transport and go into cell d. 1 Na+ and Cl- dependent e. 1 Na+ and K+ dependent 4. Biotin (Na+ dependent) 5. Once inside the cell, peptides can be transported across basolateral membrane or further broken down. xiv. Protein Transport

Page 7 of 17

GIN 5 - Electrolyte and Fluid Balance Exchange Proscribe: Zack Mahdavi Dr. Simon Lewis 9/13/07

Reviewer: Rebekah Garcia Chief Reviewer: Kimberlyn Fitchett

1. This is a small component of absorption. Mostly only peptide transport is used. 2. Can be done by transcytosis OR can enter the degradative pathway

xv. Peptide Transport 1. Driving forces are ATP, potassium gradient, sodium gradient, and a voltage and membrane potential

Peptide Transport

2. Peptide and proton enter across brush border membrane driven by pH gradient 3. Proton then recycles across apical membrane through Na+/H+ exchanger 4. Total reabsorption into the cell ends up being Na+ and the peptide xvi. Amino Acid Transport – remember you don’t need to memorize the details!

1. Very selective 2. Multiple amino acid transporters 3. Use different gradients as driving forces xvii. Water Transport Na-glucose

1. Lumen osmolality is almost identical to that of blood – how do we move water? 2. Membranes in the intestine are

highly permeable to water due to the presence of aquaporins; need only 2 mOsm gradient across the apical membrane and 1 or 2 mOsm across basolateral membrane (only a SMALL osmotic gradient is needed) 3. Given this, we still must generate an osmotic gradient – gradient is Page 8 of 17

... ….. …. ... ... ….. …. ... H2O

H2 O

Water Transport

GIN 5 - Electrolyte and Fluid Balance Exchange Proscribe: Zack Mahdavi Dr. Simon Lewis 9/13/07

Reviewer: Rebekah Garcia Chief Reviewer: Kimberlyn Fitchett

generated inside the cell (restricted diffusion). We use the lateral intercellular space. 4. Picture the cells as a six pack of beer (or Coke Zero if you prefer) a. Top is the brush border b. The plastic ring is the tight junction that binds the cell together c. The space between the cans is the lateral intercellular space. 5. Near isosmotic transport a. Movement of glucose, galactose, fructose, Na+ into cell (via Na+/glucose cotransporter, GLUT5, etc) b. Cell becomes hyperosmotic causing a slight increase in osmotic pressure compared to lumen c. Water flows into the cell from the slight osmotic gradient and the spaces swell d. Results in an increased hydrostatic pressure in lateral intercellular spaces e. Bulk flow of water, ions, and non-electrolytes along the length of the lateral space, through the basement membrane, and into the capillaries xviii. Duodenal Bicarbonate Secretion

1. This is basically the same mechanism as the pancreatic bicarbonate secretion model. 2. The whole bile duct intersects the duodenum a little downstream from the pyloric sphincter. How do the villi cells near the pyloric sphincter protect themselves from the acidic nature of the chyme?

Duodenal Bicarbonate Secretion Blood

Lumen K+

ClClHCO3-

Na+

H2O + CO2

↓ c.a.

H+ + HCO3-

H+ Na+ ATP ADP

Na+ K+

K+

3. Answer: They have Brunner’s

glands (large crypt-like cells) that secrete sodium bicarbonate. This gives the surface a coating of alkaline solution to neutralize the acidic properties of the chyme Page 9 of 17

GIN 5 - Electrolyte and Fluid Balance Exchange Proscribe: Zack Mahdavi Dr. Simon Lewis Reviewer: Rebekah Garcia 9/13/07 Chief Reviewer: Kimberlyn Fitchett 4. Generate bicarbonate within the cell: H2O + CO2  H+ + HCO3- (catalyzed by

carbonic anhydrase) 5. Cell gets rid of the proton with the Na+/proton exchanger 6. Na+/K+ ATPase: Na+ out, K+ in 7. K+ recycles through the K+ channel, which makes the cell interior electrically negative 8. Bicarbonate exits across the apical membrane via the bicarbonate/Cl- exchanger in which bicarbonate goes out and Cl- comes in 9. Cl- then recycles by crossing apical membrane via Cl- channel 10. The whole process produces a net negative charge within the lumen. This causes the movement of Na+ into the lumen from the blood, so we have sodium bicarbonate secretion into the lumen. 11. This increases the osmotic pressure causing water to flow in. Because the lumen is a tube, hydrostatic pressure occurs, which results in bulk flow of a sodium bicarbonate solution. b. Jejunum absorbs:

i. NaHCO3 absorption 1. Across the apical membrane: a. Na+/H+ exchanger: Na+ in, H+ out b. Reaction in lumen: H+ + Na+HCO3-  H2CO3 + Na+  H2O + CO2 c. CO2 easily and readily diffuses across the membrane d. Reaction in cell: H2O + CO2  H2CO3  dissociates to H+ + HCO3-

(catalyzed by carbonic anhydrase) e. The proton is recycled (see the diagram) 2. Across the basolateral membrane:

Jejunal Sodium Bicarbonate Absorption Lumen H+ NaHCO3

H2CO3

Page 10 of 17

Na+

H2O + CO2

Blood H+ Na+

H+ + HCO3-

ATP ADP

Na+

K+ CO2 H2O c.a.

H2CO3 HCO3-

K+

GIN 5 - Electrolyte and Fluid Balance Exchange Proscribe: Zack Mahdavi Dr. Simon Lewis 9/13/07

Reviewer: Rebekah Garcia Chief Reviewer: Kimberlyn Fitchett

a. HCO3- exits via HCO3- selective channel b. Na+/K+ ATPase: Na+ out, K+ in c. K+ exits cell via K+ channel d. Na+ comes in, proton goes out 3. Electro-neutral process: NO voltage is generated across the cell (does not

influence sodium or potassium movement) ii. 20-30% of amino acids (same transporters as duodenum)

iii. Na, Cl, K, and water absorption iv. Calcium and Iron

v. Biotin, Thiamin, and Riboflavin (Na dependent) vi. Nicotinic acid, Folic acid (facilitated diffusion) c. Ileum absorbs:

i. NaCl absorption

Ileal Sodium Chloride Absorption

1. This process is exactly Lumen the same as the jejunum absorption of bicarbonate, Na Na EXCEPT the ileum has H CO H H an additional HCO HCO HO bicarbonate/chloride Cl Cl + CO CO exchanger as well as a H O c.a. chloride channel instead of a bicarbonate channel. Thus the process is the same, but bicarbonate is exchanged for chloride, and chloride has an exit on the basolateral side. +

2

3

+

+

+

3

2

Blood

-

-

3

-

H+ + HCO 3 -

ATP ADP

K+

-

2

2

H 2 CO 3

Na +

Cl-

K+

2

2. Across the apical membrane: a. Na+/H+ exchanger: Na+ in, H+ out b. Reaction in lumen: H+ + Na+HCO3-  H2CO3 + Na+  H2O + CO2 c. CO2 easily and readily diffuses across the membrane Page 11 of 17

GIN 5 - Electrolyte and Fluid Balance Exchange Proscribe: Zack Mahdavi Dr. Simon Lewis Reviewer: Rebekah Garcia 9/13/07 Chief Reviewer: Kimberlyn Fitchett d. Reaction in cell: H2O + CO2  H2CO3  dissociates to H+ + HCO3-

(catalyzed by carbonic anhydrase) e. H+ and HCO3- are recycled (gets back in through diffusion of CO2 into

the cell) f. Cl-/HCO3- exchanger: Cl- in, HCO3- out 3. Across the basolateral membrane: a. Cl- exits cell via Cl- channel b. Na+/K+ ATPase: Na+ out, K+ in c. K+ exits cell via K+ channel and recycles ii. 10-20% of amino acids iii. Na, Cl, K, and water absorption iv. Cobalamin (Vitamin B12) – in terminal ileum

v. Ascorbic acid (Na dependent) vi. Bile salts (Na dependent in terminal ileum)

1. Removal of terminal ileum results in “bile salt diarrhea” d. Colon

Colonic Sodium Absorption

i. Proximal colon NaCl

absorption is similar to ileum

Lumen

ii. Distal colon Na absorption is

Blood K+

Na +

Na +

different! A Na+ channel is modulated by aldosterone

ATP ADP

Na + K+

K+

1. Across apical membrane:

Cl-

a. Na+ enters cell Na+ channel b. Hormonally regulated by aldosterone 2. Across basolateral membrane: a. Na+/K+ ATPase: Na+ out, K+ in Page 12 of 17

via

GIN 5 - Electrolyte and Fluid Balance Exchange Proscribe: Zack Mahdavi Dr. Simon Lewis Reviewer: Rebekah Garcia 9/13/07 Chief Reviewer: Kimberlyn Fitchett b. K+ exits via K+ channel  negative electrical gradient in cell 

additional electrical driving force draws Na+ into cell c. Tight junctions are high in resistance, which causes a positive voltage to be formed d. Cl- movement through trans-cellular pathway through tight junctions along the lateral space e. A little K+ is secreted going from lumen into the blood, but this is not the

major route of K+ secretion. iii. Cl/HCO3 exchange – important because bicarbonate is necessary to buffer the protons

produced by the bacteria that resides in the colon iv. K secretion

1. Major route occurs through a K+ channel in the apical membrane 2. This channel lies parallel to the sodium channel through which Na+ absorption occurs (this has been left out of the diagram for the sake of clarity)

Colonic Potassium Secretion Blood

Lumen K+

ATP ADP

K+

3. Potassium can leave through the apical membrane or the basolateral membrane (how much leaves through each channel depends on respective permeability of K+ through each membrane a. Usually, you see a net K+ SECRETION

4. Also regulated by aldosterone 5. Across apical membrane: a. K+ exits via K+ channel b. Na+ enters via Na+ channel 6. Across basolateral membrane: a. Na+/K+ ATPase: Na+ out, K+ in b. K+ exits via K+ channel Page 13 of 17

Na + K+

GIN 5 - Electrolyte and Fluid Balance Exchange Proscribe: Zack Mahdavi Dr. Simon Lewis 9/13/07

Reviewer: Rebekah Garcia Chief Reviewer: Kimberlyn Fitchett

c. Net movement v. Na, Cl, and water absorption e. Large and small intestines i. Cl- secretion occurs in the crypts 24

hours a day, 7 days a week

Intestinal Chloride Secretion Lumen

1. Across apical membrane:

Blood

K+

Cl-

a. Cl- exits cell via CFTR

Cl-

ATP ADP

channel (stimulated by cAMP)

2 ClNa+ K+ Na+ K+

K+

Na+

b. Lumen becomes electrically negative 2. Across basolateral membrane: a. Na+/K+/2Cl- cotransporter – movement into cell b. Na+/K+ ATPase: Na+ out, K+ in c. K+ exits cell via K+ channel 3. Crypt movement: a. Net favorable gradient for Cl- to move from interior of cell to the lumen – makes lumen electrically negative b. Na+ and K+ move from blood to lumen c. Water flow will follow into lumen d. Hydrostatic pressure increases causing secretion and washing of villi to reduce bacterial colonization 4. Most important during inter-digestive phases.

Cholera (an “aside”… he talked about this disease, but there is no slide for it) •

Toxin consists of an alpha subunit and four beta subunits

•

The beta subunit binds a ganglioside on the small intestine surface Page 14 of 17

GIN 5 - Electrolyte and Fluid Balance Exchange Proscribe: Zack Mahdavi Dr. Simon Lewis Reviewer: Rebekah Garcia 9/13/07 Chief Reviewer: Kimberlyn Fitchett • The alpha subunit then enters the cell and ribosylates adenylate cyclase (adenylate cyclase is now

irreversibly turned on)  continuous production of cAMP  continuous activation of pKa  pKa phosphorylates a chloride channel  continuous secretion of NaCl  lots of water loss and diarrhea •

Also, the increased cAMP inhibits NaCl reabsorption mechanisms (so we increase secretion and block absorption… ouch!)

•

The only way for the chloride channel to be turned on off is for it to migrate to the surface to get exfoliated. Combat the disease by drinking lots of water. On the field, powdered rice mixed with salt and water is used to rehydrate the system.

Remember to read the handout on Blackboard regarding Vitamins and Iron/Calcium Transport! Wrap Up (Summary of Dr. Lewis’s 3 lectures) I.

Smell, taste, chewing, and swallowing food elicits 3 responses: a. Stimulate salivary action b. Stimulate gastric acid and pepsin secretion c. Stimulate pancreatic enzyme and NaHCO3, secretion

II.

Salivary secretion a. Parasympathetic and sympathetic stimulation of salivary secretion b. Moisten and lubricate food (mucus and serous secretions) c. Control of dental caries, alkalinizing, buffering and cleansing d. Carbohydrate digestion by alpha amylase e. Lipid digestion by lipases

III.

Swallow the Food a. Food entering the stomach results in distension

i. Release of Ach on parietal cells ii. Ach stimulates the release of histamine, gastrin, GRP iii. GRP stimulates gastrin release

iv. Ach inhibits somatostatin release Page 15 of 17

GIN 5 - Electrolyte and Fluid Balance Exchange Proscribe: Zack Mahdavi Dr. Simon Lewis 9/13/07

Reviewer: Rebekah Garcia Chief Reviewer: Kimberlyn Fitchett

v. Inhibition of somatostatin release increases gastrin release vi. Gastrin release stimulates histamine release vii. So end result is acid secretion

b. Acid secretion (Ach, histamine, and gastrin) c. Pepsin secretion (Ach and gastrin) d. Intrinsic factor secretion IV.

Presence of Peptides in the stomach a. Directly stimulates gastrin release b. Gastrin stimulates histamine release c. End result is acid secretion

V.

Increase in gastric pH a. Stimulates gastrin and GRP release

b. GRP release stimulates gastrin release c. Inhibits somatostatin release, increases gastrin release d. Gastrin release stimulates histamine release e. End result is acid secretion

VI.

Food enters the intestine a. Distension, response is similar to distension of the stomach

b. Peptides stimulate gastrin release c. Gastrin stimulates histamine release d. End result is acid secretion

VII.

After stomach is emptied, all pathways return to control levels.

VIII.

Neutralization of stomach acid a. Proton Barrier i. A mucous layer is secreted by the surface cells Page 16 of 17

GIN 5 - Electrolyte and Fluid Balance Exchange Proscribe: Zack Mahdavi Dr. Simon Lewis Reviewer: Rebekah Garcia 9/13/07 Chief Reviewer: Kimberlyn Fitchett ii. The surface epithelium continuously secretes HCO3 into the mucus

iii. This maintains a cell surface pH close to neutral b. Acid chyme enters the duodenum i. Brunners glands secrete NaHCO3

ii. Low pH releases secretin iii. Secretin and Ach (from vagovagal) stimulates NaHCO3 secretion by the pancreas iv. The pH in the duodenum increases IX.

CCK a. Peptides and fat stimulate the release of CCK into the blood and Ach release in the pancreas i. Stimulates the release of pancreatic enzymes ii. Enzymes aid in the digestion of proteins, fats, and carbohydrates. b. CCK also has the following functions i. Causes contraction of the gallbladder ii. Relaxation of the sphincter of Oddi iii. Release bile to aid in fat digestion iv. Slow gastric emptying v. Potentiates the secretin stimulation of bicarbonate secretion vi. Satiety signal

X.

The small and large intestines a. Absorb 4.9-7.9 liters of water, 1 mole of Na and Cl and 0.06 Moles of K b. All nutrients absorbed by the small intestine c. Most of the water and electrolytes absorbed by the small intestine d. Fecal water and electrolyte loss is small

XI.

The remaining slides were direct copies from this lecture, so I am not going to include them in this wrap up.

Page 17 of 17