Intro To GI Physiology-1/13/16

Question 1

List the functional layer of the GI tract:

Answer 1

Mucosa (epithelium, lamina propria, muscularis mucosae)
Submucosa (meissner’s plexus)
Muscularis layer (CIrcular muscle-Auerbach’s plexus-Long.Muscle)
Serosa or adventitia

Question 2

The GI tract is innervated by the:

Answer 2

ANS and Enteric NS

Question 3

Where does the extrinsic NS have cell bodies?

Answer 3

Located OUTSIDE the gut wall

Question 4

Where does the intrinsic NS have cell bodies?

Answer 4

located WITHIN the wall of the gut

Question 5

Describe the PARASYMPATHETIC NS for the gut

Answer 5

Via Vagus and Pelvic splanchnic nerves

Preganglionic nerve cell bodies are located in the brainstem or the Sacral SC

Postganglionic neurons lies in the wall of the organ (enteric neuron in the gut wall)

Synapse between pre- and post-ganglionic cells in nAChR’s

Question 6

Describe the SYMPATHETIC NS for the gut

Answer 6

Via nerves that run between the SC and prevertebral ganglia & between these ganglia and the organs of the gut

Preganglionic EFFERENT fibers arises within the SC and end in the prevertebral ganglia

Postganglionic fibers from the prevertebral ganglia innervates the MYENTERIC and SUBMUCOSAL plexuses and other elements of ENS

Mostly, preganglionic EFFERENT fibers release Ach, while postganglionic EFFERENT nerves release NE

Question 7

What type of PARASYMPATHETIC receptor is found in the Prevertebral ganglion?

What type of SYMPATHETIC receptor is found in the Prevertebral ganglion?

Answer 7

nAChr

nAChr

Question 8

Where do you find a prevertebral ganglion in PARASYMPATHETICS?

Where do you find a prevertebral ganglion in SYMPATHETICS?

Answer 8

Wall of the organ within plexuses

Outside the GI tract

Question 9

What type of postganglionic receptor is in PARASYMPATHETICS?

What type of postganglionic receptor is found in SYMPATHETICS?

Answer 9

mAChr

Alpha-adrenergic and/or beta-adrenergic

Question 10

Describe the basic pathway of the ENS integrating center

Answer 10

Stimuli in the wall of the gut –> sensory neuron (ENS) –> Interneuron (ENS) –> Motor neuron (ENS) –> Output response

CNS can exert influence in the pathway

Question 11

This type of cellular communication is local and the signals reach their target cells by diffusion over short distances

Answer 11

Paracrine regulation

Question 12

Paracrine mediators are released by ___ cells or other sensing cells and use peptides (i.e., somatostatin) or other messenger molecules (histamine)

Answer 12

Enteroendocrine

Question 13

This peptide is secreted by D cells (delta) of the GI mucosa and act to DECREASE luminal pH.

Answer 13

Somatostatin

Question 14

Somatostatin acts to inhibit ___ secretion and is secreted ___ the GI tract

Answer 14

Gastric H+ and secretion of other GI hormones

Outside (hypothalamus or delta cells of exocrine pancreas)

Question 15

In the stomach, ____ is stored and secreted by enterochromaffin-like (ECL) cells in gastric glands.

Answer 15

Histamine

Question 16

What is the TARGET of histamine and its ACTION?

Answer 16

Target=Parietal cells

Action=stimulate acid production

Question 17

This type of cell communication involves hormones being secreted in the portal circulation, passing through the liver, reaching systemic circulation, and finally binding to specific receptors on target cells

Answer 17

Endocrine regulation

Question 18

Where is the site of secretion and stimuli of secretion for GASTRIN?

Answer 18

Site of secretion–> G cells of stomach

Stimuli of secretion –> Small peptides and AA’s, distention of stomach, and Vagal stimulation (via GRP)

Question 19

Where is the site of secretion and stimuli of secretion for CCK?

Answer 19

Site of secretion –> I cells of duodenum and jejunum

Stimuli of secretion –> Small peptides and AA’s, fatty acids

Question 20

Where is the site of secretion and stimuli of secretion for SECRETIN?

Answer 20

Site of secretion –> S cells of duodenum

Stimuli of secretion –> H+ in the duodenum, fatty acids in the duodenum

Question 21

Where is the site of secretion and stimuli of secretion for GIP?

Answer 21

Site of secretion –> Duodenum and jejunum

Stimuli of secretion –> fatty acids, AA’s, oral glucose

Question 22

What are the actions of GASTRIN?

Answer 22

Increase gastric H+ secretion

Stimulate growth of gastric mucosa

Question 23

Zollinger-Ellison syndrome is a ____ tumor

Answer 23

Gastrin-secreting

Results in: increased circulating levels of gastrin, increased acid secretion by parietal cells, hypertrophy of gastric mucosa, duodenal ulcers, and steatorrhea

Question 24

What are the actions of CCK?

Answer 24

Increase pancreatic enzyme secretion
Increase pancreatic HCO3- secretion (not a direct effect, potentiates the effects of secretin)
Stimulate contraction of gallbladder and relaxation of sphincter of oddi
Stimulate growth of exocrine pancrease and gallbladder (trophic effect)
Inhibit gastric emptying
Can also act as a paracrine signal

Question 25

What are the actions of secretin?

Answer 25

``` Increase pancreatic HCO3- secretion Increase biliary HCO3- secretion Decrease gastric H+ secretion Inhibits trophic effect of gastrin on gastric mucosa Can also act as a paracrine signal ```

Question 26

What are the actions of GIP?

Answer 26

Increase insulin secretion from pancreatic beta cells | Decrease gastric H+ secretion

Question 27

What would be more effective in increasing insulin secretion? A-Oral glucose administration Or B) IV glucose administration

Answer 27

Oral glucose stimulates GIP, which stimulates insulin secretion, and also has direct stimulatory effects on Beta cells

Question 28

List the actions of Ach

Answer 28

Contraction of smooth muscle Relaxation of sphincters Increase: Salivary secretion, Gastric secretion, Pancreatic secretion

Question 29

List actions of NE

Answer 29

Relaxation of smooth muscle Contraction of sphincters Increase salivary secretion

Question 30

List actions of Vasoactive Intestinal Peptide (VIP)

Answer 30

Relaxation of smooth muscle | Increase: intestinal secretion, pancreatic secretion

Question 31

List actions of Gastrin-releasing peptide (GRP)

Answer 31

Increase gastrin secretion

Question 32

List actions of Enkephalins

Answer 32

Contraction of smooth muscle | Decrease intestinal secretion

Question 33

What are actions of Neuropeptide Y?

Answer 33

Relax smooth muscle | Decrease intestinal secretion

Question 34

What are actions of Substance P?

Answer 34

Contract smooth muscle | Increase salivary secretion

Question 35

List the neuronal centers of the hypothalamus that participate in the regulation of food intake:

Answer 35

``` Lateral nucleus Ventromedial nucleus Paraventricular nucleus Dorsomedial nucleus Arcuate nucleus ```

Question 36

This neuronal center is the "feeding center" This neuronal center is the "satiety center"

Answer 36

Lateral nucleus Ventromedial nucleus

Question 37

Most of the integration signaling regulating food intake and energy expenditure happens in the ____

Answer 37

Arcuate nucleus

Question 38

Diagram the alpha-melanocortin pathway

Answer 38

Alpha-MSH released by POMC neurons --> alpha-MSH binds to MCR-4 present in 2nd-order neurons --> INHIBITS FOOD INTAKE AND INCREASES METABOLISM (ANOREXIGENIC) Insulin, leptin, and CCK act as stimulators of POMC neurons by binding to LepR on POMC neurons

Question 39

Diagram the Neuropeptide Y pathway

Answer 39

Hunger stimulates the release of NPY --> NPY binds to Y1r of PVN neuron --> Neurons that release NPY also release Agouti-related peptide (AGRP) --> AGRP is antagonist of MCR-4 --> INCREASE FEEDING BEHAVIOR AND STORAGE OF CALORIES (OREXIGENIC) - Ghrelin is a stimulant of AGRP/NPY neurons - Insulin, leptin, CCK inhibit AGRP/NPY neurons

Question 40

Peptides that stimulate the alpha-MSH pathway ____ the NPY system AGRP released from the NPY pathway is an antagonist of ___

Answer 40

Inhibit MCR-4

Question 41

A patient who has an inhibitory mutation of POMC and MCR-4 genes will likely be predisposed to___

Answer 41

Obesity

Question 42

___ is secreted mainly by endocrine cells in the stomach, binds to GH secretagogue receptors, and stimulates neurons that release NPY in the hypothalamus

Answer 42

Ghrelin

Question 43

What are the actions of ghrelin?

Answer 43

Increase: Appetite, gastric motility, gastric acid secretion, adipogenesis, insulin secretion Appears to initiate the feeding response

Question 44

___ binds to receptors in satiety and hunger centers within the hypothalamus (POMC and NPY systems), inhibits NPY pathway and stimulates POMC pathway

Answer 44

Insulin

Question 45

What are actions of insulin?

Answer 45

Decrease appetite | Increase metabolism

Question 46

What does insulin do to the NPY and POMC pathways?

Answer 46

Inhibits NPY, Stimulates POMC

Question 47

In patients with Type 1 DM, there is an ___ in food intake associated with ___ insulin

Answer 47

Increase | Decreased

Question 48

___ is released by I cells in the duodenum and elicits satiety

Answer 48

CCk

Question 49

How does CCK elicity satiety (pathway)?

Answer 49

Acts on vagal --> NTS --> hypothalamus circuit --> DECREASES ghrelin Decreases gastric emptying --> INCREASES gastric distention

Question 50

___ is released by EECs (L cells) of the ileum and colon following a meal and has the potential as an appetite suppressor

Answer 50

PPY

Question 51

Describe the PPY pathway

Answer 51

PPY released by EECS of ileum and colon after a meal --> Binds to Y2 receptors of the hypothalamus (inhibits NPY neurons, releases inhibition of POMC neurons)

Question 52

___ is secreted by cells in adipose tissue and by endocrine cells in the stomach and is an appetite suppressing hormone

Answer 52

Leptin

Question 53

Describe the leptin pathway

Answer 53

Leptin secreted by cells in adipose tissue and by endocrine cells in stomach --> binds to receptors in satiety & hunger centers in the hypothalamus (POMC & NPY systems --> Inhibits NPY pathway, stimulates POMC pathway Appears to be part of - feedback system for regulation of food intake

Question 54

Describe the effect of Leptin on the following: A) appetite B) metabolism C) ghrelin release

Answer 54

A) decrease B) increase C) decrease

Question 55

What are the main functions of the GI tract?

Answer 55

Digestion and absorption of nutrients Motility Secretions