GI Tract Flashcards
Functions: chemical & mechanical digestion, absorb nutrients, and excrete unabsorbed material
GI Tract
not an endocrine gland, but endocrine cells are dispersed throughout
There are more than 20 distinct endocrine cell types, and they secrete more than 30 peptide hormones
GI Tract
General Functions of GI Hormones
- Stimulate secretion of acids and enzymes necessary for digestion
- Modulate hormone release from the pancreas
- Act on smooth muscle to move food through GI tract
- Signal to brain to regulate food intake
pancreatic hormone
that reduces blood glucose
insulin
most are peptide hormones
GI tract
2 families of GI hormones
Gastrin/Cholecystokinin
Secretin
Location: G cells in the stomach
Gastrin
Function: stimulates gastric acid (HCl) secretion
Gastrin
Gastric distention (food in stomach)
triggers secretion of Gastrin
Amino acids (products of protein digestion)
triggers secretion of Gastrin
Smell, taste, or thoughts of food (parasympathetic stimulation)
triggers of secretion Gastrin
low pH (too acidic)
inhibits the secretion of Gastrin
secretin does what to the secretion of Gastrin?
inhibits
Location: S cells in duodenum
secretin
Function: stimulates bicarbonate &
digestive enzymes from pancreas and
bile from gallbladder
Secretin
Secretion is triggered by:
* low pH (high acidity)
Secretin
Secretion is inhibited by:
* pH >4.5 Contact of intestinal mucosa
with acidic food
secretin
Location: I cells in duodenum
Cholecystokinin (CCK)
Function: augments secretin to further
stimulate release of digestive enzymes
and bile from the pancreas and
gallbladder (digests fat and protein)
Cholecystokinin (CCK)
Secretion is triggered by:
* Food (fats and proteins)
Cholecystokinin (CCK)
Secretion is inhibited by:
* Stops when stimuli is removed (digestive products move on)
Cholecystokinin (CCK)
Location: K cells in duodenum
Gastric inhibitory polypeptide (GIP)
Function: stimulates insulin secretion from
pancreas (prepares body for incoming
glucose) and inhibits gastric secretions in
non-human animals
Gastric inhibitory polypeptide (GIP)
glucose and fat triggers the secretion of this hormone
Gastric inhibitory polypeptide (GIP)
secretion is inhibited when the stimuli is removed (digestive products move on)
Gastric inhibitory polypeptide (GIP)
The GI hormones
discussed to this
point (GIP, CCK, Secretin, Gastrin) are all secreted
in response to eating
and are associated
with
digestion
(parasympathetic nervous
system) regulates involuntary processes
like digestion. Here, it conveys muscular distension in the stomach to the brain, triggering a full sensation
vagus nerve
the two primary hormones that convey
more specific information to the brain to control appetite
Leptin and Ghrelin
the only peripheral
orexigenic (appetite stimulating) signal thus far known.
Ghrelin
Location: GI tract (primarily stomach), some
from brain & peripheral neurons
Ghrelin
Function: increases food intake & stimulates
gastric contraction and emptying (accelerates
movement of food)
Ghrelin
Regulation: produced by an empty stomach
(increases just before eating) and is suppressed
by eating (fats and carbohydrates)
Ghrelin
increases food intake
Ghrelin
decreases food intake
Leptin
Location: adipose tissue
leptin
Function: decreases food intake and increases energy expenditure (increases basal metabolic rate)
Leptin
Regulation: body fat (circulating leptin
correlates with the size of body fat stores)
Leptin
produce lots of
leptin but the brain stops
acknowledging the signal
leptin resistance
Increases hunger and slows metabolism even though fat stores are sufficient
One of the main biological
contributors to obesity
Leptin resistance
Causes of Leptin Resistance
- Desensitization due to
chronically high leptin - Obesity causes inflammation:
- Produce cytokines that interfere with leptin signaling
*Increase C-reactive protein (CRP) from liver
-> binds leptin, preventing it from crossing the
blood-brain barrier
Coordinates activity of both the nervous
system and the pituitary, controlling body temperature, thirst, hunger, and other homeostatic systems
Hypothalamus
“Switchboard”
Receives signals from circulation & regulates the feeding center
Arcuate Nucleus of
the Hypothalamus
Feeding Center
(hunger sensation)
Lateral Hypothalamic
Area
inhibits the appetite
anorexigenic neurons
stimulates the appetite
orexigenic neurons
one of the most potent
stimulators of feeding
Neuropeptide Y (NPY)
Co-express NPY and AgRP
Orexigenic Neurons
NPY and AgRP
increase food intake & decrease energy expenditure
stimulated by Ghrelin
Co-express POMC and CART
Anorexigenic Neurons
POMC and CART
suppress food intake & increase energy expenditure
stimulated by leptin
