GI Lectures 4+5

Which of the following salivary glands secretes serous secretions?

A. sublingual salivary gland

B. submandibular salivary gland

C. parotid salivary gland

D. intrinsic salivary glands

E. all of the above

E. all of the above

Which of the following secretions is entirely under neuronal control?

A. gastric secretions

B. salivary secretions

C. pancreatic secretion

D. small intestinal secretion

E. large intestinal secretions

B. salivary secretions

In response to the daily intake of 2L in food and drink, how much is secreted into the

GI tract?

A. 1L

B. 3L

C. 7L

D. 9L

E. 10ml

C. 7L

Alpha-Amylases, the enzyme that digests starch and glycogen is secreted by

___________.

A. salivary glands only

B. gastric glands only

C. the pancreas only

D. salivary glands and gastric glands

E. salivary glands and pancreas

E. salivary glands and pancreas

Salivary secretion is stimulated by

A. a simple reflex in response to the presence of a substance in the oral cavity that is

detected by mechanoreceptors

B. a simple reflex in response to the presence of acidic foods in the oral cavity that is

detected by chemoreceptors

C. a conditioned reflex such as the sight or smell of food

D. all of the above

E. during the so called “fight or flight” reflex during acute stress

D. all of the above

Which of the following is NOT a function of hydrochloric acid in the stomach

A. complexes with Vitamin B12

B. breaks chemical bonds in food

C. activates pepsin from pepsinogen

D. kills bacteria

E. denatures proteins

A. complexes with Vitamin B12

Which of the following cells secretes somatostatin?

A. parietal cells

B. G-cells

C. Chief cells

D. D-cells

E. enterochromaffin-like (ECL) cells

D. D-cells

What is the source of hydrochloric acid in the small intestine?

A. Hydrochloric acid is produced by secretory cells in the small intestine.

B. Hydrochloric acid is produced by secretory cells in the pancreas.

C. Hydrochloric acid is produced by secretory cells in the liver.

D. Hydrochloric acid comes into the small intestine as part of chyme.

E. There is no hydrochloric acid in the small intestine

D. Hydrochloric acid comes into the small intestine as part of chyme.

Which of the following components is NOT secreted by cells of the small intestine?

A. digestive enzymes

B. water

C. ions

D. hormones

E. mucus

A. digestive enzymes

Mucus has a functional role in ________.

A. protection only

B. lubrication only

C. enzyme activation only

D. protection and lubrication

E. protection, lubrication, and enzyme activation

D. protection and lubrication

In the pancreas, HCO3- is secreted by

A. parietal cells

B. duct cells

C. acinar cells

D. hepatocytes

E. islet of Langerhans cells

B. duct cells

Which of the following cells of the gastric glands are expected to have a high

concentration of the enzyme carbonic anhydrase (CA)?

A. mucus cells only

B. parietal cells only

C. D cells only

D. mucus and parietal cells

E. Chief cells

D. mucus and parietal cells

Bile is _____________.

A. produced by hepatocytes in the liver

B. produced in the gallbladder

C. produced in the pancreas

D. produced and secreted by enterocytes in the small intestine

E. produced by cells in the gastric glands

A. produced by hepatocytes in the liver

Which of the following digestive enzymes is secreted as an inactive zymogen?

A. Amylase

B. Maltase

C. Sucrase

D. Lactase

E. Pepsin

E. Pepsin

Which of the following is NOT a function of saliva?

A. lubrication of ingested food particles

B. protection against mechanical damage of the epithelial cell layer in the oral cavity by

ingested food particles

C. protection against ingested harmful microorganisms

D. digestion of proteins

E. digestions of carbohydrates

D. digestion of proteins

Bile is important for the digestion and absorption of ingested fats. Which of the

following is NOT a component of bile?

A. Bile salts

B. Bilirubin

C. Water

D. Lipase

E. Phospholipids

D. Lipase

Which of the following is not part of the gastric juice?

A. HCl

B. Pepsinogen

C. Amylase

D. Intrinsic factor

E. Gastric lipase

C. Amylase

Which of the following is a function of the gall bladder?

A. production of bile

B. storage of bile

C. production of digestive enzymes

D. production of bicarbonate

E. all of the above

B. storage of bile

Which of the following statements is true regarding the secretion of HCl?

A. H+ is actively pumped out of the cell against a concentration gradient on the basolateral side of cells

B. As a by-product of HCl secretion, HCO3- is transported out of the cell from the basolateral side of the cell.

C. Cl- is pumped out of the cell on the basolateral side against an electrochemical gradient

D. the enzyme Carbonic Anhydrase converts H20 and CO2 into H+ and Cl-

E. Cl- is pumped out of the cell on the apical side against an electrochemical gradient.

B. As a by-product of HCl secretion, HCO3- is transported out of the cell from the basolateral side of the cell.

What is the function of secretions in the large intestine?

A. Bicarbonate is secreted to neutralize acid that is a byproduct of bacterial metabolism

and can damage the GI tract wall.

B. Mucous is secreted to ease the passage of feces.

C. HCl is secreted to kill the microorganisms in the large intestine.

D. Amylase is secreted to digest dietary fibers.

E. A and B.

E. A and B.

the volume of fluid entering the GI tract by intake or secretions must equal

the volume leaving the lumen

fluid input into digestive system: intake

2L

fluid intake into digestive system: secretions

7L (1.5 saliva, 0.5 bile, 2.0 gastric secretions, 1.5 pancreatic secretions, 1.5 intestinal secretions)

fluid removed from digestive system: absorption

8.9L (7.5 from small intestine, 1.4 large intestine)

fluid removed in digestion: excretion

0.1L in feces

secretions include what 3 things

water, ions, proteins

water secretion method

paracellular

ion secretion methods

membrane channels and paracellular

protein secretions

secreted by cells

osmosis

Paracellular transport of water in the GI tract in response to a solute concentration gradient to reach an equilibrium

serous secretions

watery solutions containing ions and enzymes

mucous secretions

mucus, sticky solutions of glycoproteins and proteoglycans (goblet cells)

secretions are in response to

a stimulus

acinus / acini

rounded terminal end/s of exocrine gland (acinar cells)

2 kinds of salivary glands

extrinsic and intrinsic

extrinsic salivary glands

-sublingual

-submandibular

-parotid

what is unique about the parotid salivary gland

it only has serous secretions

lumen of salivary glands

oral cavity

Composition of saliva

Water

Inorganic Ions (Na+, K+, Cl-, HCO3-, F-)

Organic compounds (enzymes, mucins)

Functions of saliva

lubrication, taste, protection, digestion

saliva as lubrication: molecules involved

Water, Mucus

saliva for taste: molecules involved

Water : Food molecules must be dissolved for recognition by taste receptors

saliva as protection: molecules involved

Mucus

Cl-, HCO3-

Antibacterial enzymes: Lysozyme and IgA F-

saliva in digestion: molecules involved

α-amylase

Lingual lipase

are α-amylase and Lingual lipase essential for digestion

no

salivary secretion: simple reflex

pressure receptors and chemoreceptors in mouth activate salivary center in medulla

salivary secretion: conditioned reflex

other inputs such as smell or sound activate cerebral cortex, which then activates salivary center in medulla

salivary secretions during fight or flight

decreased

Reduction of salivary secretions during fight-or-flight (acute stress) response is controlled by

sympathetic nervous system

Mechanism of Water Secretion in the GI tract

1. Na, K, and Cl enter by cotransport

2. Cl enters lumen through Cl channel

3. Na is reabsorbed

4. Negative Cl in lumen attracts Na by paracellular pathway; water follows

what cells secrete isotonic NaCl solutions

intestinal and colonic crypt cells, pancreatic and salivary gland acini

Esophageal Secretion of Mucus

important for motility and mechanical protection

4 functions of the stomach

Storage, Mixing, Secretes gastric juice, Secretes chemical messengers

exocrine role of stomach

Secretes gastric juice

endocrine function of stomach

Secretes chemical messengers

Components of gastric juice

Hydrochloric acid (HCl)

Pepsinogen

Gastric Lipase

Intrinsic factor

Mucus/Bicarbonate (HCO3- )

Pepsinogen

proenzyme that is converted to pepsin (zymogen)

Intrinsic Factor

vitamin B12-binding protein

functions of gastric juice

digestion, protection, intestinal absorption of vitamin B12

gastric juice in digestion: molecules involved and their roles

HCl: denatures proteins by breaking chemical bonds; activates pepsin from pepsinogen

Pepsin: protease for protein digestion

Gastric Lipase: fat digestion

gastric juice as protection: molecules involved and their roles

HCl: kills bacteria

Mucus/ HCO3: protects stomach wall from HCl, pepsin, and mechanical trauma

gastric juices in intestinal absorption of B12: molecules involved and their role

Intrinsic factor: complex with Vitamin B12

Activation of Pepsin by HCl

-Pepsinogen has an inhibited catalytic domain

-Treatment with acid (HCl) creates an uninhibited catalytic domain

-Autolytic activation activates pepsin

mucous surface cell: secretion and its function

-secretes mucous

-acts as a physical barrier between lumen and epithelium

mucous surface cell: stimulus for release

tonic secretion: irritation of mucosa

mucous neck cell: secretion and its function

-secretes bicarbonate

-acts as a buffer with gastric acid to prevent damage to epithelium

mucous neck cell: stimulus for release

secreted with mucus

parietal cells: secretion and its function

-secretes both gastric acid and intrinsic factor

-gastric acid acts to activate pepsin and kill bacteria

-intrinsic factors acts to complex with vitamin B12 to permit absorption

parietal cells: stimulus to release

acetylcholine, gastrin, histamine

enterochromaffin-like cells: secretion and their function

-secretes histamine

-histamine acts to stimulate gastric acid secretion

enterochromaffin-like cells: stimulus to release

acetylcholine, gastrin

chief cells: secretion and their function

-secrete pepsin (ogen) and gastric lipase

-pepsin acts to digest proteins

-gastric lipase acts to digest fats

chief cells: stimulus to release

acetylcholine, acid secretion

D cells: secretion and its function

-secretes somatostatin

-acts to inhibit gastric acid secretion

D cells: stimulus to release

acid in the stomach

G cells: secretion and its function

-secretes gastrin

-acts to stimulate gastric acid secretion

G cells: stimulus to release

acetylcholine, peptides, amino acids

Hydrochloric Acid Secretion by Parietal Cells

H+ is actively pumped into lumen against electrochemical gradient

Cl Secretion by Parietal Cells

Cl- follows H+ into lumen through open chloride channels along the electrochemical gradient

Bicarbonate in Parietal Cells

Bicarbonate is absorbed into blood -> “alkaline tide” after meal

Endocrine function of Pancreas

Secretion of insulin and glucagon ➔ facilitates glucose storage and release

Exocrine Function of Acinar Pancreas Cells

secretion of digestive enzymes

Exocrine Function of Pancreas Duct Cells

Secretion of HCO3- ( as NaHCO3)

Reason for HCO3 secretion of pancreatic duct cells

-Acid can damage the duodenum

-Acid inactivates digestive enzymes

Pancreatic Exocrine Digestive Enzymes: 2 ways to be secreted

as zymogens (inactive precursors) or active form

Trypsinogen, Chymotrypsinogen, Procarboxypeptidase A and B, Proelastase: How are they secreted and for what

-secreted as zymogens

-proteases (break down proteins)

Procolipase: what is it secreted as and for what

-zymogens (inactive precursors)

-break down fats

alpha-Amylase: how is it secreted and for what

-in active form

-to break down carbs

Lipase, Carboxyl ester lipase: how are they secreted and for what

-in active form

-to break down fats

Bicarbonate Secretion in Pancreas and Duodenum

-cells that produce bicarbonate have high concentrations of carbonic anhydrase

-chloride enters cells by indirect active transport and leaves apical side through CFTR channel; Cl- then reenters cell in exchange for bicarb

-leaky junctions allow paracellular movement of ions and water. negative ions in the lumen attract Na by the paracellular pathway, water follows

The Hepatic Portal System

connects digestive tract arteries to liver

hepatocytes

liver cells that face the sinusoids to maximize the exchange between the blood and the cells

lobule of liver cell

centered around central veins that drains blood into hepatic vein

lobule around its periphery

associated with branches of the hepatic portal vein and hepatic artery

sinusoids

formed by vessel branching among the hepatocytes, blood flows through them

bile canaliculi

small channels into which bile is secreted; canaliculi come together into bile ducts that run through liver alongside portal veins

components of bile

bile salts, bile acids, bilirubin, water, ions, phospholipids, cholesterol

common hepatic duct

takes bile made in the liver to the gallbladder for storage

common bile duct

takes bile from the gallbladder to the lumen of the small intestine

hepatic artery

brings oxygenated blood containing metabolites from peripheral tissues to the liver