Physiology 1

Question 1

Describe the major daily inputs and outputs of fluid in the GI tract.

Answer 1

Inputs

• 1200mL ingested
• 1500mL salivary secretions
• 2000mL gastric secretions
• 500mL bile secretions
• 1500mL pancreatic secretions
• 1500mL intestinal secretions

Outputs

• 6700 mL small intestines
• 1400 mL large intestine
• 100mL in feces

Question 2

What serves as the pacemaker/regulator of slow wave activity in GI muscle.

Answer 2

Interstitial cells of cajal, they are located near the enteric plexi, (meissners and auerbachs)

Question 3

Describe slow wave activity.

Answer 3

occurs in four phases
only electrical activity in the stomach
not innervated by neural or hormonal input.

Question 4

Aurbach vs Meissner plexi? Actions, locations.

Answer 4

Auerbach - Myenteric plexus, primarily controls GI motility

Meissner - Submucosal plexus, receives sensory info from chemo and mechanoreceptors in the GI and primarily regulates SECRETIONS and BLOOD FLOW

Question 5

Three types of innervation to the GI tract?

Answer 5

Parasympathetic - excitatory, vagus/pelvic nerves

Sympathetic - inhibitory, adrenergic fibers from prevertebral ganglia, splanchnic nerves

Enteric nervous system (ENS) - primary control of GI motility and secretions, coordinates local reflex information

Question 6

Where are the swallowing centers located?

Answer 6

medulla

Question 7

What nerve carries afferent signals back to the medulla to begin the act of swallowing?

Answer 7

Glossopharyngeal- kicks off the action of

Question 8

What is the mechanism behind slow wave action in the GI tract?

Answer 8

cyclic opening of Ca+ channels (depolarization) followed by opening of K+ channels (repolarization)

Question 9

Describe the action of relaxation of the LES when a food bolus approaches.

Answer 9

Relaxation is vagally mediated via the NT VIP.

Question 10

The term for when teh LES does not relax during swallowing, resulting in food accumulation in the esophagus.

Answer 10

Achalasia

Question 11

Describe 5 major functions of digestion performed in the stomach.

Answer 11

Emulsification of fats (acid lipase)

Breakdown Proteins (pepsin)

Oxidize Iron (HCl)

Release of Intrinsic Factor for use in the duodenum (B12 abs.) (Parietal Cells)

Question 12

What reflex is initiated by distention of the stomach causing stretching of the stomach with increased food intake?

Answer 12

Vagovagal reflex - causes “adaptive relaxation”

“Receptive relaxation” - causes relaxation of stomach tissue in response to swallowing, allowing room for food to enter.

Question 13

What hormone acts on the antrum of the stomach to stimulate gastric emptying into the duodenum?

Answer 13

Gastrin (secreted by G cells) - initiated via vagal stimulation in response to gastric distention.

Question 14

What disease is associated with increased action/secretion of gastrin?

Answer 14

Zollinger-Ellison syndrome

Question 15

Name 4 major pathways of inhibiting gastric emptying

Answer 15

1. Sympathetic stimulation
2. Acid chemoreceptors in duodenum sensing acid relay neg. feedback via direct interneurons.
3. Fat sensed in the duodenum/jejunum causes the release of CCK from I cells
4. Hyper/Hypotonic meals cause slowed emptying via unidentified hormone.

Question 16

What causes hunger pangs?

Answer 16

Migrating myoelectric complexes (MMCs): they are interdigestive electrical oscillations that fire spike potentials, leading to peristaltic waves.

They help prepare for next meal.

Question 17

Describe the simple idea behind the “peristaltic reflex”

Answer 17

local distention causes wave to begin proximal to distention and inhibition distal (an enteric reflex)

Question 18

Functions of saliva?

Answer 18

alpha amylase - carbs
lingual lipase - fats

Lubrication - mucins secreted in saliva, creates bolus

Question 19

compare primary and secondary saliva during a meal and at rest.

Answer 19

Primary: isotonic, similar composition of Na/K/Cl/HCO3 as plasma (gets modified before secretion via duct cells on its way out)

Secondary: after modified by the duct cells the secondary secretion is hypotonic (Na/Cl resorbed, K/HCO3 added, water stays the same)

Question 20

Describe ductal cells and how they modify acinar secretions.

Answer 20

At higher flow rates, the ductal cells act on the saliva less, leaving the saliva closer to isotonicity

Question 21

Describe the autonomic control of salivary secretions

Answer 21

Both para and sympathetic innervations cause saliva production to increase. The only thing that causes decreased saliva is inhibition of the pathways

Question 22

What causes dry mouth

Answer 22

Parasympathetics are much stronger saliva inducers than sympathetic, therefore sympathetic deactivation of parasympathetics can cause fry mouth, via vasoconstriction.

Atropine, fear, dehydration, sjogren syndrome (autoimmune damage to exocrine glands)

Question 23

Describe the secretions of parietal cells.

Answer 23

HCl - activates pepsin to pepsinogen, kills bacteria, emulsifies fats, oxidizes iron

Intrinsic factor - absorption of Vit. B12 in duodenum

Question 24

Discuss the regulation of gastric secretions

Answer 24

Activators: Histamine, Gastrin, Ach

Inhibitors: Somatostatin, Prostaglandins

Question 25

Discuss the stomach mucosal barrier and factors which alter it.

Answer 25

Mucosal barrier forms a gel-like substance that coats the lining of the stomach

Question 26

Discuss the causes of peptic ulcers

Answer 26

Caused by an imbalance between mucous production and acid secretion. (H. Pylori,

Question 27

Discuss the phys causes of zollinger ellison syndrome

Answer 27

A gastrinoma (gastrin secreting tumor) is present. Gastrin causes large amounts of acid secretion due to increased H2 stim.

Leads to peptic ulcers and diarrhea

Dx/ fasting gastrin level, secretin stimulation test (stimulates gastrinoma to secrete gastrin).

Treat with

Question 28

What is the important enzyme needed for parietal cell secretion to happen?

Answer 28

Carbonic anhydrase converts CO2 from plasma into H2CO3, allowing the parietal cells to use H for HCl production

Cl/HCO3 exchanger - creates alkaline tide in the blood that will eventually be used in pancreatic secretion for neutralizing the stomach acid in the bolus

Question 29

What stimulates the release of zymogens (digestive enzymes) from the pancreas/

Answer 29

CCK released from I cells in the duodenum acts on acinar cells

Question 30

What causes the pancreas to increase release of HCO3?

Answer 30

Secretin - released from S cells in the duodenum in response to H+ in the lumen.

Question 31

What cells in the pancreas are responsible for the HCO3 content in pancreatic secretions?

Answer 31

Ductal cells, innervated by secretin from the duodenum?

Question 32

What is deficient in cystic fibrosis patients that causes a deficiency of pancreatic enzymes/malnutrition?

Answer 32

CFTR gene is mutated and does not allow Cl- to leak out of the cells. Thus inactivates Cl-/HCO3- transporter/alkaline tide. Causes a mucin buildup and malabsorption.

Question 33

What causes contraction of the gallbladder and relaxation of the sphincter of oddi?

Answer 33

CCK - both

Ach - contraction olny

Question 34

What stimulates Bile acid production in the liver?

Answer 34

Gastrin

Question 35

What stimulates NaHCO3 secretion from ductal cells in teh Gallbladder?

Answer 35

Secretin

Question 36

Major causes of gall stones?

Answer 36

Too much water absorption from bile

Too much absorption of bile acids from bile

Too much cholesterol in bile

Inflammation of the epithelium

Question 37

Where are brunner’s glands located, and what do they secret?

Answer 37

Located in the submucosa of the proximal duodenum

Secrete HCO3 mucous that neutralizes stomach acid

Question 38

What are the intestinal pits called that secrete things for digestion/protecfion?

Answer 38

Crypts of Lieberkuhn (base of intestinal vili.

Enterocytes in these crypts secrete juices for lubrication of the intestinal tract. (Depend onf Cl getting to the lumen via CFTR… THerfore it is lacking in CF patients)