Lecture 4 - Regulation Flashcards
What kind of receptors does the gut sense with
Chemoreceptors
Mechanoreceptors (stretch)
Chemoreceptors sense a change in…
nutrient concentration
nutrient degradation products
osmotic pressure
pH
What does gastrin induce? When?
Acid secretion
pH too neutral
Wall stretch activates
acetylcholine
What does low pH in the bloodstream activate
Release of secretin, goes into bloodstream then to pancreas, activates bicarbonate release (increase pH)
What cells release bicarbonate
Duct cells
What cells lower the pH of the stomach
Parietal
What are endocrine hormones? Where do they bind?
Hormones released into general circulation
Specificity to property of target tissue, binds specific receptors
Examples of endocrine hormones
gastrin, secretin, cholecystokinin, motilin
What are paracrine hormones
Released from endocrine cells, diffuse through extracellular space to neighbouring target cell
What are autocrine and neurocrine hormones
Autocrine = released substance regulates cell’s own function
Neurocrine = sensory cells secrete neurotransmitter
What activates
1. gastrin
2. GLP
3. CCK
4. secretin
- peptides, AA
- glucose, AA, FA
- FA, AA
- acid
Roles of CCK (4)
Gallbladder = contraction (secrete bile)
Pancreas = acinar secretion (pancreatic enzymes)
Stomach = reduced emptying
Sphincter of oddi = relaxation (opening)
Gastrin stimulates… Secretin stimulates…
Gastric secretion and mucosal growth
Pancreatic HCO3 secretion (increases pH)
Three steps of endocrine system and their roles
- signaling cells (organ): physiological stimulus, hormone synthesis, secretion
- transport by the circulatory system
- target cells (organ): receptor, biological effects
If the endocrine hormone is hydrophilic, it will also require…
Storage for hormone in signaling cell, second messengers in target cell
Can hydrophobic hormones cross the membrane?
Yes, hydrophilic hormones cannot (require secondary messenger)
Memorize slides 11, 13**
Hydrophobic/hydrophilic hormone pathways
Difference btw hydrophobic and hydrophilic hormones in signaling and target cells
Signaling cells = hydrophobic are synthesized on demand (no storage) and diffused, hydrophilic cells are exocytosed (cannot cross membrane)
Target cells = hydrophilic require transmembrane receptors (cannot enter) and second messengers and are rapid. Hydrophobic diffuse, bind inside cell, alter mRNA transcription, slower
How are hydrophobic hormones transported through the blood
Carrier proteins (most have specific)
What acts as a non-specific carrier for hydrophobic hormones
Serum albumin
What does glucagon-like peptide 1 respond to? Enhance? Inhibit? What degrades it? Where is it produced?
Responds to nutrients and short chain f.a.
Enhances insulin secretion
Inhibits gastric emptying
Degraded by DPP IV
Produced in L-cells in intestine and colon
Where is ghrelin produced? When is it secreted? Detects…
Produced by cells lining the fundus of the stomach
Secreted when the stomach is empty
Detects hunger
Ghrelin acts on the hypothalamus to…
increase hunger, gastric secretions, GIT motility
What are the GIT factors that regulate satiety
- Stretch (via vagal afferent nerves)
- CCK (via vagal afferent nerves)
- Nutrient receptors in liver (via vagal afferent nerves)
- Peptide YY (acts on vagal afferents and hypothalamus)
Non-GIT factors regulating satiety
Adipose (leptin acts on hypothalamus)
Pancreas (insulin)
Where is leptin produced?
Adipocytes
Leptin acts on the hypothalamus to…
Reduce hunger (binds leptin receptor)
How does leptin affect fat reserves
Inhibits feeding
Inhibits fat synthesis
Slides 32/33 **
Regulation of leptin/ghrelin
Deletion of what gene is related to obesity in labs
POMC gene
Slide 36**
Review leptin, ghrelin, PYY, insulin
Do fat animals have leptin?
Yes, lots, but their cells have become resistant to it
Slide 38
Leptin responsiveness vs resistance
What is the epigenetic effect
Exposure to excessive nutrients in utero or in early postnatal period = hyperphagia
Utero environment affects POMC expression
What is an additional food intake factor to consider
Hedonic regulation of food intake (reward/pleasure seeking areas of the brain control hypothalamic area)
Is acetylcholine a peptide
No
Which of gastrin, somatostatin, cholecystokinin, GLP and secretin are peptides?
All
What is an anorexic vs orexic hormone
Anorexic = stop eating (leptin)
Orexic = hungry (ghrelin)
What neurons drive anorexic signals? Orexic?
Anorexic = POMC/CART
Orexic = ArRP/NPY
