Gastrointestinal: regulation Flashcards
What is the role of the lateral hypothalamus?
Feeding centre (promotes eating)
What is the role of the ventromedial hypothalamus?
Satiety centre (inhibits eating)
What are the 4 satiety signals?
Nervous - reflexes initiated by distension
Hormonal - feedback by cholecystokinin
Chemical - glucostatic and lipostatic
Thermal
What is the cycle of leptin? (4)
- Increased food intake, decreased energy expenditure
- Adipose tissue, increased fat deposits, increased leptin synthesis
- Increased plasma leptin conc.
- Hypothalamus, increased activation of leptin receptors
What are the 5 peptides in the hypothalamus that increase food intake?
Neuropeptide Y Orexins Galanin Melanin Ghrelin (stomach)
What are the 6 peptides in the hypothalamus and intestines that decrease food intake?
CCK - small intestine
Corticotropin-releasing hormone - hypothalamus
a-melanocyte-stimulating hormone - hypothalamus
CART - hypothalamus
Glucagon-like peptide-1 - intestines
PYY 3-36 - intestines
What are the 2 paths for GI regulation?
Neural and endocrine
How is food intake regulated? (3)
Not based on homeostasis concept
Maximise absorption - regardless of need
Lumen of GI tract conditions regulated to max. absorption
What neural pathways are the enteric nervous system comprised of? (2)
Submucosal plexus
Myenteric plexus
What is the short reflex pathway? (4)
Stimulus in lumen
GI receptors
Intrinsic nerve plexus
Effector organ in GI tract
What is the long reflex pathway? (5)
Stimulus in lumen GI receptors Central nervous system Intrinsic nerve plexus Effector organ in GI tract
What are the 4 GI hormones?
Gastrin - stomach
Cholecystokinin - duodenum, jejunum
Secretin - duodenum and jejunum
Glucose-dependent insulinotropic peptide - duodenum and jejunum
What is the role of gastrin? (3)
Stimulates gastric secretion and motility
Stimulates ill motility and relaxes ileocecal sphincter
Stimulates mass movement of colon
What is the role of cholecystokinin? (2)
Inhibits gastric secretion and motility
Stimulates gallbladder
What is the role of secretin? (2)
Inhibits gastric secretion and motility
Potentiates actions of CCK on pancreatic enzyme secretion
What is the role of glucose-dependent insulinotropic peptide? (2)
Inhibits gastric secretion and motility
Stimulates insulin secretion by pancreas
What are the 3 phases of gastrointestinal control?
Cephalic phase - thoughts, taste and smell
Gastric phase - stimuli originate in stomach
Intestinal phase - stimuli originate in small intestine
What is involved in short-term regulation: hunger verses satiety? (3)
Insulin
CCK
Neural input from mechano/chemo receptors
What is involved in long-term regulation? (6)
- Leptin = hormone released from adipose cells when calories exceeds demands
- Leptin suppresses hunger and increases metabolism
- Saliva secretion
- Acid and pepsinogen secretion in the stomach
- Secretion of pancreatic juice and bile
- Rates of fluid movement in the digestive tract
What are the steps in saliva secretion? (5)
Taste and texture of food Mechanoreceptors and taste receptors in mouth Salivary centre of medulla Autonomic nervous system Stimulate salivation
What are the 2 types of autonomic input to salivary glands and what do they produce? (3)
Parasympathetic: watery saliva
Sympathetic: more mucus, thick saliva
How is gastric acid secreted and what does it do? (7)
- Parietal cells produce HCl
- Carbonic anhydrase catalyses bicarbonate and H+
- H+ actively secreted into the lumen of the stomach
- Bicarbonate is transported into interstitial fluid for Cl-
- Cl- diffuses into lumen of stomach
- H+ & Cl- secreted into stomach lumen
- bicarbonate enters the interstitial fluid then blood
How are these secretions regulated? (3)
Parasympathetic nervous system
Gastrin
Histamine
What causes an increase in acid and pepsinogen secretion? (5)
Sight of food Taste Smell Chewing Swallowing
What is the action when there is a stimuli to increase secretions? (5)
- Stimuli
- Increase in parasympathetic activity
- G cells increase gastrin secretion
- Increase in plasma gastrin
- Parietal cells and chief cells increase acid and pepsinogen secretion
What is the gastric phase regulation of secretion? (4)
Stimuli of gastric secretion
- proteins, peptides and A.A.
- distension of stomach
Short and long reflex pathways trigger gastrin, acid and pepsinogen release
Describe the steps in the gastric phase: (6)
- Distension of the stomach
- chemo/mechano detect and respond
- short and long reflexes
- G cells increase gastrin secretion
- increase in plasma gastrin
- parietal cells and chief cells increase acid and pepsinogen secretion
How is secretion inhibited in the gastric phase? (2)
Exit of food removes stimuli for secretion
Increased acidity inhibits gastrin release
How is secretion inhibited in the intestinal phase? (5)
Entry of food into duodenum causes: - increased osmolality - Increased fat and acid - Increased distension Long and short reflex pathways inhibit acid and pepsinogen secretion
How is pancreatic juice secreted? (2, 4)
Acinar cells - small volume of primary section - water, electrolytes, digestive enzymes Duct cells - large volume - bicarbonate rich secretion
What does CCK stimulate?
Acinar cells to secrete enzymes
- small stimulant for bicarbonate release
- CCK potentiates effects of secretin on bicarb. release
What does secretin stimulate? (3)
Duct cells to secrete bicarbonate
- small stimulant for enzyme release
- secretin potentiates effects of CCK on enzyme release
What is the stimuli for CCK release?
Fat and amino acids in duodenum
What is the stimuli for secretin release?
Acidity in duodenum
What does secretin stimulate into the duodenum?
Bile secretion from liver
What does CCK stimulate?
Gallbladder contraction
Relaxation of sphincter of Oddi
