A & P - Gi System, Stomach

Front 1

What is the etymology of stomach?

Back 1

Greek

stómachos

opening; akin to stoma

Front 2

What and where is the hypochondrium?

Back 2

Anatomically, the hypochondrium is the region behind the lowest ribs of the thorax.

In clinical situations, the part of the abdominal wall just below the right and left costal margins are referred to as the right and left hypochondriac regions respectively.

Front 3

What is the etymology of hypochondriasis?

Back 3

From hypochondrium, the region behind the lowest ribs of the thorax.

Greek, hupochondros, meaning abdomen, or literally under cartilage.

Front 4

What is the most distensible portion of the GI tract?

Back 4

The stomach

Front 5

Name the four main anatomical regions of the stomach.

Back 5

The four main regions of the stomach are:

1) Cardia
2) Fundus
3) Body
4) Pylorus

Front 6

What is the cardia?

Back 6

The cardia is the region surrounding the superior opening of the stomach.

In other words, the cardia is the region just distal to the lower esophageal sphincter, also called the cardiac sphincter.

Front 7

Which region of the stomach is referred to as the fundus?

Back 7

The fundus is the rounded portion superior to and to the left of the cardia.

Front 8

What is the body of the stomach?

Back 8

The body is the large central portion of the stomach.

Front 9

What is the pylorus?

Back 9

The pylorus is the region of the stomach that connects to the duodenum.

The pylorus is divided into two parts: the pyloric antrum and the pyloric canal.

The pyloric antrum connects to the body of the stomach and the pyloric canal leads into the duodenum.

Front 10

What type of muscle forms the lower esophageal sphincter?

Back 10

The lower esophageal sphincter, also referred to as the cardiac sphincter, is composed of smooth muscle.

This is in contrast to the upper esophageal sphincter which is composed of skeletal muscle.

Front 11

What is the etymology of fundus?

Back 11

Latin, literally "bottom"

Think "el fondo."

Front 12

What is the etymology of pylorus?

Back 12

Greek:

Pylōrós

Literally, gatekeeper

Front 13

What is meant by the lesser curvature of the stomach?

Back 13

The lesser curvature of the stomach is the concave medial border of the stomach.

Front 14

What is meant by the greater curvature of the stomach?

Back 14

The greater curvature is the convex lateral border of the stomach.

Front 15

The convex lateral border of the stomach is called the...

Back 15

Greater curvature

Front 16

The concave medial border of the stomach is called the...

Back 16

Lesser curvature

Front 17

What is the name of the smooth muscle sphincter separating the stomach from the duodenum?

Back 17

The pyloric sphincter

Front 18

How much gastric juice is secreted by the gastric mucosa each day?

Back 18

2-3L

Front 19

What is the primary function of the gastric fundus?

Back 19

Storage

Front 20

Describe gastric mixing and emptying.

Back 20

Mixing waves begin at the body of the stomach and intensify as they reach the pylorus.

The pyloric sphincter normally remains almost, but not completely, closed. As food reaches the pylorus, each mixing wave periodically forces about 3 mL of chyme into the duodenum, a phenomenon referred to as gastric emptying.

Most of the chyme is forced back into the body of the stomach, were mixing continues. The next wave pushes the chyme forward again and forces a little more into the duodenum.

These forward and backward movements of the gastric contents are responsible for most mixing in the stomach.

Front 21

The soupy liquid formed in the stomach that is a mixture of gastric juice and macerated food is called...

Back 21

Chyme

Front 22

What is chyme?

Back 22

Chyme is the soupy liquid mixture of gastric juice and macerated food that is formed in the stomach and subsequently enters the duodenum.

Front 23

What enzyme do parietal cells possess that allows them to secrete hydrogen ions into the lumen of the stomach?

Back 23

Carbonic anhydrase.

Carbonic anydrase catalyzes the reaction of CO2 and H2O to carbonic acid, or H2CO3.

Carbonic acid subsequently dissociates to form bicarb and and hydrogen ions.

CO2 + H2O --> H2CO3 --> H+ + HCO3-

The H+ ions are pumped via an H+/K+ ATPase pump into the lumen, while the HCO3- exits across the basal membrane in exchange for Cl- ions. The HCO3- enters the bloodstream causing the so-called "alkaline tide."

Front 24

Where does all the H+ secreted from parietal cells come from?

Back 24

Parietal cells possess the enzyme carbonic anhydrase. The following reaction therefore ensues within parietal cells:

CO2 + H20 --> H2CO3 --> H+ + HCO3-

The hydrogen ions are pumped into the gastric glands while the bicarb. exits across the basal membrane in exchange for Cl- ions.

The HCO3- ions then enter the bloodstream, causing an "alkaline tide."

Front 25

Which cells pump hydrogen and chloride into the gastric glands?

Back 25

Parietal cells

Front 26

What do parietal cells secrete into the gastric glands?

Back 26

Hydrochloric acid (indirectly via the independent secretion of H+ and Cl-)

Intrinsic factor (required for the absorption of B12)

Front 27

Why might blood pH elevate slightly after a meal?

What is the name of this phenomenon?

Back 27

After a meal the parietal cells are stimulated to secrete more H+ into the gastric glands.

Bicarb. is a byproduct of the reaction by which H+ is formed in the parietal cells.

CO2 + H2O --> H2CO3 --> H+ + HCO3-

While the H+ ions are pumped into the gastric glands and flow onward into the lumen of the stomach, the HCO3- produced in this reaction exits across the basolateral membrane of the parietal cells in exchange for Cl- ions. The HCO3- ions then enter the bloodstream, potentially causing an increase in pH.

This phenomenon of increasing pH following a meal is called the "alkaline tide."

Front 28

How do H+ ions cross the apical membrane of parietal cells to reach the gastric glands and the gastric lumen?

Back 28

H+ ions are pumped across the apical membrane via an H+/K+ ATPase.

The K+ ions pumped into the cells later diffuse into the lumen through open ion channels.

Front 29

How do the parietal cells get all the Cl- ions they subsequently secrete into the gastric glands?

Back 29

Due to the presence of carbonic anhydrase, the following reaction occurs within parietal cells:

CO2 + H2O --> H2CO3 --> H+ + HCO3-

The H+ ions are pumped into the gastric glands.

The HCO3- ions are exchanged for Cl- ions at the basolateral membrane.

In other words, HCO3- exits the cell in exchange for Cl- ions which enter the cell.

These are the Cl- ions that cross the apical membrane into the gastric glands via open Cl- channels.

Front 30

Name 3 chemicals that can stimulate the secretion of HCl by parietal cells.

Back 30

Acetylcholine

Gastrin

Histamine

Front 31

What is the physiologic source of H+ ions in the body?

Back 31

CO2

In the presence of carbonic anhydrase, CO2 is converted to H+ in the following reaction:

CO2 + H2O --> H2CO3 --> H+ + HCO3-

Front 32

What effect does the binding of histamine to its receptor on parietal cells have on gastric secretions?

Back 32

Histamine acts synergistically, enhancing the effects of acetylcholine and gastrin to increase parietal secretion of HCl.

Front 33

What effect does the binding of acetylcholine to its receptor on parietal cells have on gastric secretions?

Back 33

Acetylcholine stimulates parietal cells to secrete more HCl.

The effect of acetylcholine is amplified by the presence of co-stimulation by histamine.

Front 34

What effect does the binding of gastrin to its receptor on parietal cells have on gastric secretions?

Back 34

Gastrin stimulates parietal cells to secrete more HCl.

The effect of gastrin is amplified in the presence of co-stimulation by histamine.

Front 35

What is the cellular source of the histamine that can stimulate parietal cells to secrete more hydrochloric acid?

Back 35

Histamine is release by mast cells in the nearby lamina propria.

Front 36

Why does the hydrochloric acid secreted by parietal cells not normally damage the gastric mucosa?

Back 36

The stomach epithelial cells are protected from gastric juices by a 1-3 mm thick layer of alkaline mucus secreted by surface mucous cells and mucous neck cells.

Front 37

What do chief cells secrete into the gastric glands?

Back 37

Chief cells secrete pepsinogen and gastric lipase into the gastric glands.

Pepsinogen is later converted in the gastric lumen to pepsin in the presence of hydrochloric acid.

Pepsin is a proteolytic enzyme involved in the digestion of proteins. It severs certain peptide bonds between amino acids, breaking down a protein chain of many amino acids into smaller peptide fragments.

Gastric lipase splits the the short-chan triglycerides in fat molecules into fatty acids and monoglycerides.

Front 38

Which cell type of the gastric mucosa secretes pepsin?

Back 38

Chief cells

And technically, the chief cells secrete the pepsin precursor pepsinogen which is converted to pepsin in the acidic environment of the stomach

Front 39

What is the role of pepsin?

Back 39

Pepsin is a proteolytic enzyme.

It severs certain peptide bonds between amino acids, breaking down a protein chain of many amino acids into smaller peptide fragments.

Pepsin is most effective in the very acidic environment of the stomach (pH 2).

It becomes inactive at a higher pH.

Front 40

In what conditions is pepsin active?

Under what conditions is it inactivated?

Back 40

For inactive pepsinogen to become pepsin, acidic conditions created by HCl must be present.

Pepsin becomes inactive at a higher pH.

Front 41

What is the role of gastric acid?

Back 41

1) Immunologic
-gastric acid kills many microbes in food

2) Digestion
-HCl partially denatures proteins in food and stimulates the secretion of hormaones that promote the flow of bile and pancreatic juice

Front 42

Which gastric mucosal cell type secretes gastric lipase?

Back 42

Chief cells

Front 43

What is the function of gastric lipase?

Back 43

Gastric lipase, secreted by chief cells, splits the short-chain triglycerides in fat molecules into fatty acids and monoglycerides.

This enzyme has a limited role in the adult stomach. Pancreatic lipase is much more important.

Front 44

There are five principle cells types present in the gastric mucosal epithelium. List them along with their respective secretions.

Back 44

1) Surface mucous cell
-mucous

2) Mucous neck cell
-mucous

3) Parietal cell
-hydrochloric acid
-intrinsic factor

4) Chief cell
-pepsinogen
-gastric lipase

5) G cell
-gastrin

Front 45

Describe the gastric mucosa.

Back 45

The gastric mucosa consists of gastric pits fed by multiple deep gastric glands.

The mucosal epithelium consists of simple columnar epithelial cells of 5 types: surface mucous cells, mucous neck cells, parietal cells, chief cells, and G cells.

Below the epithelium lies the lamina propria and the muscularis mucosae.

Front 46

What is typically meant by the non-specific term "antrum" when discussing the stomach?

Back 46

In the context of the stomach, the antrum refers to the pyloric antrum.

Front 47

What's the difference between mucous and mucus?

Back 47

Mucus is the noun form and mucous the adjectival form.

E.g. mucous membrane/mucous cell vs. mucus-secreting cell

Front 48

What is an oxyntic cell?

Back 48

Oxyntic cell is just another name for the parietal cell.

Front 49

Give an alternate name for parietal cells.

Back 49

Parietal cells are also known as oxyntic cells.

Front 50

What is mucus composed of?

Back 50

Mucus (not "mucous"!) is composed mostly of water (95%) as well as a mixture of phospholipids and mucin.

Front 51

What is mucin?

Back 51

Mucins are a class of heavily-glycosylated proteins that are physiologically useful because of their ability to form gels.

Front 52

What is the pH range between the gastric luminal surface and the gastric epithelial surface?

Back 52

Because of bicarbonate secreted by surface epithelial cells into the gastric mucus, the pH ranges from 1-2 at the luminal surface to 6-7 at the epithelial surface.