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FHB II > GI Exam Lecture 3 > Flashcards

GI Exam Lecture 3 Flashcards

1
Q

The Gastric phase is when food is ______

What are the major functions of the stomach?

(hint there are 7)

A

Gastric Phase is when food is in the stomach

Major functions of the stomach are:

  • Storage: temp storage of a meal
  • Secretion of H+ (kills microorganisms and activates pepsin)
  • Secretion of Intrinsic Factor: essential for absorbption of vitamin B12
  • Secrete mucus and HCO3- : protects gastric mucosa
  • Secretes water
  • Motor activity: mixing secretions with bolus
  • Coordination of motor activity of smooth muscle and emptying of stomach contents into duodenum
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2
Q

Regulation of Stomach Function:

  • Regulation of moth motor and secretory responses via:
  • Neural: _____ and _____
  • Paracrine: histamine is a powerful stimulator of ____ stimulation
  • Endocrine:
    • gastrin (____ and _____): stimulates _____ secretion
      • somatostatin: (___, ___, ___): _____ gastrin secretion
A

Regulation of Stomach Function:

Regulation of both motor and secretory responses via:

  • Neural: intrinsic and extrinsic
  • Paracrine: histamine is a powerful stimulator of H+ secretion
  • Endocrine
    • Gastrin (stomach and duodenum) - stimulates gastric acid secretion
    • Somatostatin (stomach, duodenum, pancreas) - inhibits gastric secretion
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3
Q

Functional Anatomy of the Stomach:

Explain the three regions, what they secrete, and what kind of motolity they do

A
  1. LES and cardia: secrete mucus and HCO3- (important for prevention of reglux, entry of food, belching)
  2. Fundus and body: secrete H+, IF, Pepsinogens, Lipase, mucus HCO3- (important for food reservoir, tonic force during emptying)
  3. Antrum and pylorus: secrete mucus and HCO3- (important for mixing, grinding, sieving, regulation of emptying)
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4
Q

Functional Anatomy of the Stomach:

  • The lining of the stomach contains _____ epithelium folded into “______”
  • Each _____ is the opening where gastric glands empty
A

Functional Anatomy of the Stomach:

  • The lining of the stomach contains columnar epithelium - folded into gastric pits
  • Each gastric pit is the opening where gastric glands empty
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5
Q

The fundus and antrum contains 6 types of secretory cells…. name them

A

The fundus and antrum contains 6 types of secretory cells:

  • Parietal Cells
  • Mucous Neck cells
  • Chief/peptic cells
  • ECL cells
  • D cells
  • G cells
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6
Q

Explain what the following cells secrete in the fundus and antrum:

  1. Parietal cells
  2. Mucous Neck Cells
A

Within the Fundus/Antrum:

  1. Parietal Cells secrete:
  • HCl : kills bacteria. allows activation of pepsin from pepsinogen, low pH for effective pepsin action
  • Intrinsic Factor : essential factor, it is a glycoprotein that binds vitaming B12 making it absorbable

Reminder: Intrinsic Factor is the ESSENTIAL FACTOR

  1. Mucous Neck Cells secrete
    * Mucus : protects gastric mucosa
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7
Q

Explain what the following cells within the fundus/antrum secrete:

Chief/Peptic Cells

ECL cells

D cells

G cells

A

Chief Cells: secrete pepsinogens (which are cleaved into pepsin in acidic enviornment)

ECL Cells: secrete histamine (paracine): most powerful stimulator of HCl secretion

D cells: secrete somatostatin (endocrine) - powerful inhibitor of HCl secretion

G cells (pyloric region): secrete Gastrin (endocrine)

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8
Q

Summary Slide:

Draw a gastric pit

Show the 6 types of cells within the gastric pits of the stomach and show what they secrete

A
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9
Q

The cells of the gastric mucosa secrete a fluid called ____________

The major gastric secretions are:

1.

2.

3.

4.

In a healthy human, ______ is the only essential component of gastric juice

A

The cells of gastric mucosa secrete a fluid called Gastric Juice

The major gastric secretions are:

  • HCl (H+ activates pepsinogen to pepsin, pepsin initiates protein digestion in stomach 20% but is not essential)
  • Pepsinogen : inactive proenzyme of pepsin
  • Bicarb + Mucus : protects gastric mucosa
  • Intrinsic Factor: glycoprotein, required for normal absorption of vitamin B12 in the ileum

In a healthy human, intrinsic factor is the only essential component of gastric juice, the functions of other components are redundant

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10
Q

Parietal Cells secrete ___ and have distint ultrastructure

Explain a resting parietal cell vs an activated parietal cell

A

Parietal Cells secrete HCl and have distinct ultrastructure

Resting parietal cell cytoplasm contains a tubulovesicular system (whose membranes contain transport proteins needed to secrete H+ and Cl-). In the resting state, that system is all over cytoplasm

Once activated, the tubulovesicular membranes fuse with the plasma membrane of secretory caniculi (increases the amount of things that can be transported) and opens to the lumen of the gland

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11
Q

Draw a gastric parietal cell

Show which transporters are on the lumanal and blood side

What enzyme is within the cell itself?

Whtat reaction is it stimulating?

A

In the intracellular fluid: Carbonic Anhydrase produces H2CO3 from CO2 and H20

H2CO3 then dissociates into H+ and HCO3-

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12
Q

Draw a gastric parietal cell

Show what transporters are on the lumal surface, vs blood surface

In the lumen (or apical membrane): __ is secreted via the ______. This is inhibited by the drug ____

___ follows ____ by diffusing through channels

Icreased intracellular __ and ___ increase luminal conduction

A

Gastric Parietal Cell:

In the lumen (or apical membrane): H+ is secreted via the H-K ATPase - active process that transports both H+ and K+ uphill. This transporter is inhibited by the drug omeprazole that is used to treat ulcers and reduce H+ secretion

Cl- follows H+ by diffusing through Cl- channels

Increased intracellular Ca2+ and cAMP increases luminal conduction of Cl- and K+

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13
Q

Gastric Parietal Cells:

Draw a gastric parietal cell, show which transporters are on the blood membrane vs lumen side

In the basolateral membrane: ___ is absorbed into the blood via the ___- exchanger. This absorbed ___ is the reason for the “______” in the gastric venous blood after a meal.

Combination of all of the events leads to net secretion of ____ and net absorption of _____

A

Gastric Parietal Cell:

In the basolateral membrane: HCO3- is absorbed into the blood via the Cl- HCO3- exchanger. This absorbed HCO3- is the reason for the “alkaline tide” (high pH) in the gastric venous blood after a meal.

This HCO3- is eventually secreted back in the GI tract by the pancreas

Combination of all these events leads to a net secretion of HCl and net absorption of HCO3-

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14
Q

Secretion of HCO3-:

The _________ of the stomach also secrete a watery fluid that contains Na, Cl, K, HCO3

Although Na and Cl concentrations are ___ to plasma, K and HCO3- concentrations are ____

This HCO3- is entrapped by the viscus mucus that coats the stomach lumen - forms a ____

A

Secretion of HCO3-

The surface epithelial cells of the stomach secrete a water fluid that contains Na, Cl, K, and HC03

Although Na and Cl concentrations are similar to plasma, the K and HCO3 concentrations are higher

This HCO3- is entrapped by the viscous mucus that coats the stomach lumen - together forms a mucosal barrier

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15
Q

Secretion of Mucus:

  • Mucus: secretions containing ____ are viscous and sticky - collectively called mucus
  • Secreted by ______ cells
  • They are 80% ______
  • Intact mucins are ____ of 4 similar monomers
  • The _____ of the mucin tetramer is susceptible to digestion by ____
A

Secretion of Mucus:

  • Mucus: secretions containing mucins are vicous and sticky - collectively called mucus
  • Secreted by mucus neck cells
  • They are 80% carbohydrate
  • Intact mucins are tetramers of 4 similar monomers
  • The central portion of the mucin tetramer, is suceptible to proteolytic digestion by pepsins
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16
Q

Gastric Mucosal Protection and Defense:

  • ______ and ____ protects the surface of the stomach from H+ and pepsins
  • The protective mucus layer on the luminal side and the alkaline secretions trapped within this form the _________ (protects gastric mucosa)
  • Mucus: protects cells from ____ and inactivates ____ that cannot hydrolyze membrane proteins
A

Mucus and HCO3- protects the surface of the stomach from H+ and pepsins

  • The protective mucus layer on the luminal side and the alkaline secretions trapped within this - form the gastric mucosal barrier protects the gastric mucosa
  • Mucus: protects cells from H+ and inactivates pepsins that cannot hydrolyze extracellular portions of membrane protens

So the mix of bicarb and mucus make up the gastric mucosal barrier

17
Q

Regulation of Gastric Secretion:

Parasympathetic stimulation via the ___ nerve is the strongest stimulant for gastric H+ secretion

Extrinsic efferent fibers terminate on intrinsic neurons that innervate : ____ cells, ____ cells, _____ cells

Vagal stimulation also secretes ____, ____, ____, and ____

A

Regulation of Gastric Secretion:

Parasympathetic Stimulation via the vagal nerve is the strongest stimulant for gastric H+ secretion

Extrinsic efferent fibers terminate on intrinsic neurons that innervate: Parietal cells, ECL cells, and G cells

Vagal stimulation also secretes pepsinogen, mucus, HCO3, and intrinsic factor

18
Q

Stimulation of Gastric Acid Secretion:

Stimulation: Three substances stimulate H+ secretion by parietal cells:

1.

2.

3.

A

Stimulation of Gastric Acid Secretion:

Three substances stimulate H+ secretion by parietal cells:

ACh (neurocine)

Gastrin (endocrine)

Histamine (paracrine)

19
Q

Three substances stimulate H+ secretion by parietal cells: ACh, Histamine, and Gastrin

Acetylcholine:

  • released from _____ nerve innervating gastric mucosa
  • binds to _____ receptor on parietal cells
  • 2nd messengers are ______
    • ______ (inhibits muscarinic receptors) to block ACh effects on parietal cells
A

Acetylcholine:

  • released from vagus nerve innervating the gastric mucosa
  • binds to muscarinic (M3) receptors on the parietal cells
  • 2nd messengers are IP3/Ca stimulates H+ secretion
  • Atropine (inhibits muscarinic receptors) blocks ACh effects on parietal cells
20
Q

Stimulation: Three substances stimulate H+ secretion by parietal cells: ACh, Histamine, Gastrin

Histamine:

  • released from gastric ____ cells : ___ effect
  • binds to ___ receptors
  • 2nd messenger is _____ : stimulates H+ release by parietal cells
    • _______ blocks H2 receptors - blocks histamine’s effect
A

Histamine:

  • released from gastric ECL cells - paracrine effect on parietal cells
  • binds to H2 receptors
  • 2nd messenger cAMP - stimulates H+ secretion by parietal cells
  • Cimitidine blocks H2 receptors - blocks histamine effect
21
Q

Gastrin:

  • secreted into circulation by G cells - endocrine effect
  • binds to _____ receptors on parietal cells
  • second messengers are ____

Histamine potentiates the actions of ___ and ___… therefore cimitidine will

ACh potentiates the actions of histamine and gastrin…atropine will

A

Gastrin:

  • secreted into circulation by G cells - endocrine effect
  • binds to CCKB receptors on parietal cells
  • second messengers are IP3/Ca

Histamine potentiates the actions of ACh and gastrin: cimitidine will block direct histamine effects, block histamine potentiated effects of ACh and gastrin

Ach potentiates actions of histamine and gastrin - atropine will block direct effects of ACh, block potentiated effects of histamine and gastrin

22
Q

Draw a picture showing Vagus Nerve, G cells, ECL cells

what they secrete

what their secretions bind to

the second messenger cascades they have

and their final effects

ALSO, show the effects of atropine, cimitidine, and omeprazole

23
Q

Stimulation of Gastric Secretion by Parietal Cells:

Cephalic and Oral Phase:

  • 30% of total HCl secretion
  • Stimuli are smelling, tasting, chewing, swallowing
  • Several mechanisms that promote HCL secretion during this phase:
  • Direct stimulation of parietal cells by vagus nerve secreting _____ (neural effect)
  • INdirect stimulation of G cells to produce gastrin
  • Indirect stimulation of ECL cells by ACh and gastrin to produce ____
A

Several Mechanisms that promote HCl secretion during this phase:

  • Direct stimulation of parietal cells by vagus via ACh
  • Indirect stimulation of G cells by vagus to produce gastrin
  • Indirect stimulation of ECL cells by vagus and gastrin to produce histamine
24
Q

Draw a picture showing the stimulation of gastric acid secretion by parietal cells

Show how neurons directly stimulate parietal cells

and indirectly stimulate parietal cells through ECL and G cells

25
Gastric Phase: - 60% of total HCl secretion - Stimuli are distention of the stomach, presence of AA and peptides in stomach - All the mechanisms that are present in cephalic, oral phase also operate here. Two additional mechanisms exist: * distension of the stomach activates \_\_\_\_\_\_ * A direct effect of amino acids and small peptides on ____ cells \_\_\_\_\_ and _____ also stimulate HCl secretion
Gastric Phase: - 60% of total HCl secretion - Stimuli are distension of the stomach, presence of AA and peptides - All the mechanisms that are present in cephalic and oral phase also operate here Two additional mechanisms exist: * distention of the stomach activates **vasovagal reflexes** to stimulate gastrin release * a direct effect of **amino acids** and **small peptides** on G cells stimulate gastrin release **Alcohol and caffeine** also stimulate HCl secretion
26
Inhibition of Gastric Acid Secretion by Parietal Cells: Acidic chyme in the distal stomach (antrum) initiates a _______ feedback loop to inhibit acid secretion When the pH of the lumen is below 3 (high proton enviornment), _______ is released by D cells - inhibits proton secretion via direct and indirect pathways Direct pathway: Indirect pathway:
Acidic chyme in the distal stomach (antrum) initiates a negative feedback loop to inhibit acid secretion When the pH of the lumen is below 3, somatostatin is released - inhibits via direct and indirect pathways Direct pathway: SS binds to receptors in parietal cells to inhibit H secretion Indirect pathway: SS inhibits histamine relese (ECL cells) and gastrin release (G cells)
27
What is the mechanism of prostaglandins? What do they do?
Prostaglandinds inhibit the stimulatory effect of histamine
28
This card indicates that you should review the video for the parietal cells and chief cells (review from the videos she sent us)
There should be a point where you can explain this without watching the video
29
Review: Parietal cells and chief cells are in the ____ part of the stomach D cells and G cells are in the \_\_\_\_\_\_ If the pH is too high, ____ will secrete ____ (explain the effects of this) If pH gets too low, ____ cells release ___ (explain the effects of this as well)
Parietal cells and chief cells are in the body of the stomach D cells and G cells are in the antrum of the stomach If the pH is too high, G cells will secrete Gastrin (the gastrin will bind to CCK receptors on parietal cells, increase intracellular calcium and increase H secretion) (gastrin will also activate chief cells and ECL cells to secrete pepsinogen and histamine) If pH is too low: D cells will release somatostatin (which directly inhibits parietal cells, and it also binds to and inhibits G cells and ECL cells) It is also important to remember that ACh can itself inhibit D cells (inhibiting somatostatin release)
30
Mucosal barrier review: Explain what it is, what cells are involved and what it does
In the gastric pits of the stomach, there are mucous cells (which secrete the glycoprotein mucin) and neck cells (which secrete bicarb) Together, the mucous and the bicarb (and water) make the mucosal barrier This barrier is important in protecting gastric cells from the very acidic enviornment (HCl and pepsin are corrosive)
31
Gastric Motility: Based on the differences in motility, the stomach can be divided into two regions 1. 2. explain what they contain and how thick their walls are Contractions in the caudad region (generated by strong muscles) mix the food and propel it into the small intestine
Gastric Motility: Based on differences in motility, the stomach can be divided into two regions: 1. **orad** region (proximal): contains fundus, proximal body and is **thin walled** 2. **caudad** region (distal) - contains distal body and antrum (**thick walled**) Contractions in the caudad region (generated by strong muscles) mix the food and propel it into the small intestine
32
Gastric Motility: Explain the concept of receptive relaxation what is it? How is it done? What NT had to be released for it to work?
**Receptive Relaxation**: Distension of the lower esophagus by food causes relaxation of the LES- also relaxation of the orad stomach: called receptive relaxation This is via the **vasovagal reflex** - mechanoreceptors detect stomach distension, relay this info to the CNS via sensory neurons, and then CNS sends efferent info for smooth muscle of orad stomach to relax NT released from postganglionic peptinergic fibers is **VIP**
33
Gastric Motility: Mixing and Digestion: Caudad region - waves of strong contraction start in mid part of stomach- move distally towards pylorus increasing in strength towards pylorus They mix gastric contents and periodically propel a portion of these into duodemun for sensing Much of the chyme is propelled back into stomach for further mixing and breakdown - this is known as \_\_\_\_\_\_
Mixing and Digestion: Caudad region: waves of strong contraction start in the mid portion of the stomach, move distally towards pylorus, increasing in strength towards the pylorus They mix gastric contents and periodically propel a portion of these in the duodenum through pylorus followed by closure of pylorus Much of the chyme (not emptied into duodenum) is propelled back into the stomach for further mixing and break-down - this is known as **retropulsion**
34
Control of Gastric Motility: Parasympathetic innervation via the vagus nerves is _____ ( ) in the lower stomach causing ___ motility In the gastric phase, the pylorus is usually \_\_\_\_\_, the antral contractions mix the gastric contents and reduce size (grinding function)
Control of Gastric Motility: **Parasympathetic innervation** via vagus nerves is **excitatory** (ACh and Substance P) in the lower stomach causing **increased motility**, magnitude of contractions is regulated by neural input In the gastric phase, the pylorus is usually closed, the antral contractions mix the gastric contents and reduce size (grinding functions)
35
Gastric Emptying: After a meal, the stomach contains 1.5 L of material Emptying of gastric contents into the duodenum is \_\_\_\_ Liquids empty ___ than solids Solids must be reduced to particles size of ____ via retropulsion
Gastric Emptying: After a meal, stomach contains 1.5 L of material Emptying of gastric contents into duodenum is slow (3 hours) Liquids do empty more quickly than solids Solids must be reduced to particles of \< 1 mm3
36
Gastroduodenal Junction: Pylorus contains two ring like circular smooth muscle cells Coordination of contraction/relaxation follows general rules Functions of the pyloric sphincter are: 1. 2. 3.
Pylorus consists of two ring-like thickenings of circular smooth muscle cells Coordination of contraction/relaxation follows general rules Functions of pyloric sphincter are: 1. **filtering large particles of food** **2. emptying gastric content at a rate consistent with duodenum's ability to digest chyme** **3. prevention of reflux of bolus into stomach**
37
Control of Pyloric Muscle Tone SNS ______ sphincter PSNS ____ sphincter PSNS can also _____ sphincter via \_\_\_\_\_
Control of Pyloric Muscle Tone: SNS activates pyloric cphincter via NE (pyloric constriction, slowing gastric emptying) PSNS can activate pyloric sphincter via ACh (pyloric constriction, slowing gastric emptying) PSNS can also use vagal inhibitory fibers and realx pyloric sphincter via VIP and NO (pyloric relaxation, speeds gastric emptying)
38
Peptic Ulcer Disease: Ulcerative lesion of gastric or duodenal mucosa due to loss of protective mucousal barrier and excessive H+ and pepsin secretion Explain Gastric Ulcers vs Duodenal Ulcers
Gastric Ulcers: * forms **primarily** because of defects in mucosal barrier * major cause is **H. pylori bacteria** that releases cytotoxins that destroy protective layer * net **H+** secretory rates are **lower** and gastrins secretion is increased Duodenal Ulcer: * more common than gastric ulcers because H+ secretions are high, excess protons in duodenum overpowers protective bicarb * excess H+ and pepsin damage duodenal mucosa
39
Zollinger-Ellison Syndrome: - In these patients a tumor (gastrinoma) located in the pancreas secretes high quantities of \_\_\_\_ - That high level of ___ produces two direct effects: * * Excess H+ produces duodenal ulcer Also leads to _____ (fatty stool) Treatment includes what?
Zollinger -Ellison Syndrome: - In these patients a tumor (**gastrinoma**) located in the pancreas secretes a high quantity of gastrin That high level of gastrin causes: * increased H+ secretion by parietal cells * increased parietal cell mass causes a **duodenal ulcer** This leads to **steatorrhea** (fatty stool) because low duodenal pH inactivates pancreatic lipase Treatment includes **cimitidine, omeprazole** and surgical removal of the tumor

FHB II (14 decks)

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