Gi 8- 3 Tract Lecture

Front 1

where does digestion take place

Back 1

OUTSIDE our body in the lumenog our GI tract

Front 2

Anything that we feel we are aware of, meaning that neurons in the __ are firing

Back 2

cerebral cortex

Front 3

which brain region is associated with emotional content and memory associated with in eating?

Back 3

limbic cortex

Front 4

What causes those limbic cortical neurons to begin firing action potentials?

Back 4

hypothalamus

Front 5

what are the 2 nuclei in the hypothalamus that are assiciated with hunger

Back 5

feeding center and the satiety center

Front 6

when nuerons in the feeding center excite what is the feeing that is produced?

Back 6

the feeling of hunger

Front 7

what type of neurons are in the feeding center?

Back 7

glucosensitve neurons

Front 8

why would glucosensitive neurons fire

Back 8

they fire if blood glucose gets low, amongst other inputs

Front 9

wehn neurons of the satiety center fire what is produced

Back 9

they inhibit the Feeding Center, leading to the lack of hunger (because the Feeding Center stops stimulating the cortex).

Front 10

what type of neurons are in the satiety center?

Back 10

glucoreceptor neurons

Front 11

why causes the glucoreceptor neurons to fire?

Back 11

which fire when blood glucose levels are normal or elevated

Front 12

what does the arcuate nucleus impact?

Back 12

the firing of the fedding center

Front 13

what are the two groups of neurons that are located in the arcuate nucleus?

Back 13

AGRP Neurons
POMC Neurons

Front 14

what does AGRP stand for

Back 14

agouti-related peptide

Front 15

what is the function of AGRP neurons?

Back 15

which is a potent and long-lasting appetite stimulant; it also decreases metabolism

Front 16

HOw does the AGRP Neurons affect the feeding center

whats the affect

Back 16

stimulate

generating hunger

Front 17

what does POMC stand for

what type of neurotransmitter is POMC neurons

Back 17

Proopiomelanocortin; a polypeptide neurotransmitter

Front 18

HOw does the POMC Neurons affect the feeding center

whats the affect

Back 18

inhibit

generating satiety

Front 19

do AGRP neurons and POMC neurons inhibits each other as they fire

Back 19

yes
will cause the feeling and simultaneously inhibt

Front 20

what inputs stimulate the feeding center

Back 20

AGRP Neurons stimulate the Feeding Center
Low blood glucose

Front 21

what inputs inhibit the feeding center?

Back 21

POMC Neurons inhibit the Feeding Center
Satiety Center neurons inhibit the Feeding Center
Blood glucose inhibits the Feeding Center
Insulin inhibits the Feeding Center
Mouth touch receptors inhibit the Feeding Center
Peptide YY (from the colon) inhibits the Feeding Center

Front 22

The most important input to the Satiety Center is from

Back 22

Vagal afferents

Front 23

what is the affect of excited vagus afferent on the satiety center

Back 23

stimulated the satiety center

Front 24

how are vagal afferents stimulated?

Back 24

distension of the stomach

Front 25

Why do we stop eating once we have begun?

Back 25

In large part because stomach distension stimulates the Satiety Center to inhibit the cortical neurons causing us to feel hungry!

Before absorption occurs!!

Front 26

POMC Neurons are stimulated by:

Back 26

1) Insulin (a pancreatic hormone released during the “Good Times”)
2) Cholecystokinin (a duodenal hormone released when food, especially fat, enters the duodenum from the stomach)
3) Cocaine (a local anesthetic better known as a drug of abuse)

Front 27

POMC neurons are inhibited by

Back 27

1) AGRP Neurons

Front 28

AGRP neurons are stimulated

Back 28

Ghrelin

Front 29

what cells secrete ghrelin

Back 29

a polypeptide hormone released by oxyntic cells of the stomach

Front 30

why does ghrelin get secreted by oxyntic cells of the stomach

Back 30

An empty stomach begins secreting Ghrelin and indirectly produces a feeling of hunger!

Front 31

how does lack of sleep affect ghrelin secretion

Back 31

increase

Front 32

what inhibits the Ghrelin effects?

Back 32

while gastric bypass and the Ghrelin receptor antagonist developed as an antiobesity serum inhibit

Front 33

AGRP neurons are inhibited by

Back 33

insulin and
leptin

Front 34

what is leptin released by?

Back 34

adipocytes

Front 35

what does leptin also act to do?

Back 35

stimulate sympathetic discharge to increase basal metabolic rate

Front 36

what is gastrin

Back 36

is actually several related short-chain polypeptide hormones

Front 37

what secretes gastrin?

Back 37

secreted by G cells of the stomach and duodenum.

Front 38

gastrin secretion is stimulated by?

Back 38

the presence of food in the stomach and/or duodenum

Front 39

Gastrin stimulates gastric release of

Back 39

hydrochloric acid and, to a lesser extent, also pepsinogen (an inactive precursor of the proteolytic enzyme pepsin).

Front 40

what is somatostatin

Back 40

a mixture of several related polypeptides

Front 41

what cells release somatostatin

Back 41

by cells in gastric glands and also by cells of the pancreas (as well as hypothalamic cells).

Front 42

what is the primary function of somatostatin?

Back 42

to inhibit secretions of the stomach (Gastrin and hydrochloric acid), duodenum (Secretin and Cholecystokinin) and pancreas (Glucagon).

Front 43

what does somatostatin do to the rate of nutrient absorption from the digestive tract

Back 43

reduce the rate
it slows down digestion

Front 44

what is secretin?

Back 44

another polypeptide

Front 45

what is secretin released by?

Back 45

cells of the duodenum in response to the presence of low pH
chyme has reached the duodenum

Front 46

what is the primary effect of secretin?

Back 46

to stimulate the pancreas to release bicarbonate (to neutralize the chyme and thereby allow activation of digestive enzymes).

Front 47

what does secretin do to acid secretion and peristalsis

Back 47

inhibit
slows
allowing the duodenum time to digest the food entering from the stomach

Front 48

what is cholecystokinin

Back 48

agroup of similar small polypeptides

Front 49

what secreted cholecystokinin?

Back 49

are secreted by cells of the duodenum and jejunum

Front 50

what triggers the secretion of cholecystokinin?

Back 50

primarily in response to the presence of lipids and their catabolites

Front 51

what four things does cholecystokinin (CCK) cause in the digestive system?

Back 51

stimulates gall bladder contraction (thereby releasing bile into the duodenum for emulsification of lipids, allowing fats to be digested efficiently), stimulates the pancreas to secrete digestive enzymes, slows the rate of gastric emptying (because it takes quite a while to digest fat compared to protein or carbohydrate), and also stimulates the satiety center (as mentioned previously).

Front 52

what is vasactive intestinal polypeptide (VIP)

Back 52

is a polypeptide hormone that is more of a neurotransmitterbut is released at loose synapses and can also be called a hormone

Front 53

VIP causes what affect in vessels of the gastrointestinal tract during digestion

Back 53

vasodilation

Front 54

VIP produces vasodilation in response to what neural system?

Back 54

increased parasympathetic input to the enteric nervous system

Front 55

what are 3 of the significance of the vasodilation caused by VIP?

Back 55

assuring that the active cells receive sufficient oxygen for working and also sufficient plasma as the precursor for enterocytes (small intestine cells) to produce mucous secretions. Finally, the increased blood flow also assures that nutrients can be efficiently absorbed from the gut.

Front 56

what nervous system plays an important role in regulating gastrointestinal function

Back 56

CNS

Front 57

outflow of CNS system that regulated gastroint fun't is carried by what nervous system

Back 57

autonomic nervous system

Front 58

which part of the autonomic nervous system is more active in gastro fun't

Back 58

parasympathetic > symp

Front 59

what does much of the autonomic outfllow moderate?

Back 59

does not directly innervate gastrointestinal cells, but instead moderates the activity of the Enteric Nervous System (ENS).

Front 60

where does the ENS run from

Back 60

runs much of the length of the digestive tract (from part way down the esophagus until the external anal sphincter) and consists of about as many neurons as are present in the spinal cord.

Front 61

what are the two layers (plexuses) that the ENS are divided into?

Back 61

myenteric (Auerbach's) Plexus
SUbmucosal (Meissner's) plexus

Front 62

what does the myenteric plexus regulate and what is the result of this?

Back 62

primarily regulates contractions of smooth muscle that result in peristalsis and sphincter control.

Front 63

what does the submucosal plexus regulate

Back 63

neurons are associated with regulation of secretions and blood flow along the length of the digestive tract.

Front 64

what type of neurons do the plexuses of the ENS have?

Back 64

contain not only motor neurons (for producing secretions and muscle contraction), but also interneurons for coordinating functions (local control) and sensory neurons (to provide information from the gut back to the CNS).

Front 65

what type of stimuli do the different receptors of the ENS respond to

Back 65

mechanical (stretch and tension), thermal (heat and cold), osmotic and chemical (glucose and amino acids) stimuli.

Front 66

how is sensory information primarily conveyed to the CNS

Back 66

afferent fibers of the vagus

Front 67

Parasympathetic outflow to the gut includes?

Back 67

Glossopharyngeal (IX) and Facial (VII) nerves innervating salivary glands, the vagus innervating much of the length of the digestive tract, and sacral nerves innervating the colon.

Front 68

what innervates the salivary glands

Back 68

IX and VII

Front 69

what innervates much of the length of the digestive tract

Back 69

vagus

Front 70

what innervates the colon

Back 70

sacral nerves

Front 71

Sympathetic innervation of the salivary glands travels through what ganglion

Back 71

superior cervical ganglion

Front 72

what nerves conduct impulses to much of the rest of the GI tract

Back 72

splanchnic nerves

Front 73

how are digestive reflexes named?

Back 73

for the site of initiation followed by the site affected

ie Therefore, the gastrocolic reflex refers to how food entering the stomach (“gastro”) results in increased motility of the colon (“colic”)

Front 74

what components are in mouth secretions?

Back 74

saliva

Front 75

what components are in esophagus secretions?

Back 75

The esophagus secretes mucous throughout the length of the esophagus.

Front 76

what is the function of mucous in the esophagus

Back 76

function of the mucous is lubrication (to facilitate the movement of food from the mouth to the stomach) and also protection against excoriation (scraping) and acidic erosion of the lower portion of the esophagus.

Front 77

how is mucous in the esophagus differ from the top vs the bottom of esophagus

Back 77

mucous is thicker and contains a higher level of bicarbonate (for acid neutralization) at the gastric end of the esophagus

Front 78

what does the stomache secrete into the lumen of the digestive tract?

Back 78

gastinr, Hydrochloric acid, pepsinogen, mucous, gastroferrin (for facilitating iron absorption) and Intrinsic Factor (essential for vitamin B12 absorption).

Front 79

what is the function of gastroferrin

Back 79

for facilitating iron absorption

Front 80

what are the fun't of intrinsisc factor

Back 80

essential for vitaminB12 absorption

Front 81

what are the hormones released in the blood by the small intestines?

Back 81

secretin and cholecystokinin

Front 82

what are secreted into the lumen of the small intestine

Back 82

serous mucous and bicarbonate-enriched mucous, lysozyme, and defensins (the later two serving antibacterial functions

Front 83

what is secreted by the colon

Back 83

Mucin-rich mucous is pretty much the whole story for secretions by the colon

Front 84

what hormones does the pancreas secrete into the blood

Back 84

insulin, glucagon and somatostatin

Front 85

what digestive enzymes does the pancreas secrete into the lumen of the gastro tract

Back 85

Trypsinogen, Chymotrypsinogen, Procarboxypeptidase A and B, Pro-elastase (all of the preceding are inactive precursors of proteolytic enzymes), Pancreatic Lipase, Pancreatic Amylase, and Ribonucleases

Front 86

what does the pancreas secrete about 2 liters/day

Back 86

bicarbonate-rich fluid (used to neutralize the acidic chime coming from the stomach).

Front 87

what does the liver synthesizes and releases into the blood?

Back 87

plasma proteins, VLDLs (very low density lipoproteins) and HDLs (high density lipoproteins

Front 88

what is bile consist of

Back 88

bile salts and bile acids for lipid emulsificationand

Front 89

what compound does bile serve as an avenue for excretion

Back 89

bilirubin from heme breakdown