Control Flashcards
What brain region controls what we eat?
Hypothalamus
Which 2 nuclei of the hypothalamus are fundamental in central control of appetite?
Arcuate nucleus and paraventricular nucleus
Describe the arcuate nucleus
- It is located at the base of the brain and has incomplete blood brain barrier, allowing peripheral signals to directly activate it.
- It has 2 cell populations; NGY/AGRP (stimulatory) and POMC (inhibitory).
- These neuropeptides are released to receptors in paraventricular nuclei.
- a-MSH from POMC binds to MC4R receptor. Receptor agonised and food intake reduced.
- Agrp from NPY/AGRP bind to MC4R receptor. Receptor antagonised and food intake behaviours maintained.
Which 2 deficiencies can cause morbid obesity in humans?
POMC and MC4R deficiency.
Describe leptin - long term appetite regulation
- Secreted from white adipose tissue cells
2. Binds to hypothalamic receptors and stimulates anorexigenic behaviours (suppresses appetite)
What is leptin resistance associated with?
Obesity
Describe ghrelin
- “Hunger hormone”
- Secreted from stomach cells (in increasing quantities in build)
- Peptide hormone that regulates short term appetite control - promotes eating behaviours
Describe peptide YY3-36
- “Satiety hormone”
- Secreted from cells in ileum and colon
- Binds to hypothalamic receptors - reduces perception of hunger and urge to eat
- Regulates short term appetite -suppresses eating behaviours
Where are osmoreceptors found?
In the brain, adjacent to structures with incomplete blood brain barrier. Bathed in ECF.
Mainly hypothalamus
What thresholds must be met for responsive action?
- 2-3% increase in osmolality
2. 10-15% decrease in volume/pressure
What does vasopressin do?
Fundamentally decreases osmolality
- Released from PPG
- Inserts aquaporin-2 channels into collecting duct
- Stimulates vasoconstriction
- Stimulates thirst
What is the threshold for osmolality?
290mOsm/kg
2 ways in which thirst can be quenched
- Water in GI tract can quench thirst temporarily (Short term feedback)
- Once osmolality/BP corrected, thirst perception no longer felt. (Long term feedback)
5 primary effects of Ang 2
- Vasoconstriction of VSMC
- Upregulates sympathetic NS
- Stimulates aldosterone secretion - increases Na reabsorption and so water reabsorption
- Directly influences Na reabsorption (so water reabsorption)
- Stimulates ADH release and stimulates thirst
GI Tract wall - how may nerve cells
10-100 million
What does the enteric NS consist of?
Rich plexus of ganglia with unmyelinated fibres
“2nd brain” - independent
4 things that can cause dysfunction of the enteric NS?
- Inflammation
- After invasive abdominal surgery
- IBS
- Ageing
Where is myenteric plexus?
Between longitudinal and circular muscle. Efferently controls both - gives coordinated control of motor function and motility
Where is submucosal plexus?
Between mucosa and submucosa
What are the afferent and efferent functions of submucosal plexus?
Afferent: senses lumen environment using mechanoreceptors, chemoreceptors and osmoreceptors
Efferent: fine tune local blood flow, epithelial transport and secretory/paracrine/endocrine cell function
SNS vs PNS
SNS: Lower thoracic and upper lumbar region. Postanglionic cell bodies in pre/paravertebral ganglia
PNS: preganglionic cell bodies in brainstem and sacral spinal cord. Postganglionic cell bodies very close to target organs
Compare/contrast the length of SNS and PNS
SNS : short preganglionic nerves, long post ganglionic nerves
PNS: long preganglionic, short postganglionic
Describe SNS innervation
Preganglionic neurone = splanchnic nerves arising from thoracic and lumbar regions
Thoracic branches = innervate foregut
Lumbar = hindgut
Describe PNS innervation
Mostly arises from vagus nerve.
Descending colon onwards is innervated by pelvic splanchnic nerves
What are the main neurotransmitters of SNS and PNS?
SNS = NE
PNS = ACh
Describe enteroendocrine cells
Small apical membrane, with lots of sensory apparatus.
Broad basolateral surface, many vesicles near basolateral membrane.
Where are most of the gut hormones secreted from?
Stomach, SI and pancreas
Describe paracrine regulation of function
D cells secrete somatostatin - inhibits acid secretion
ECL cells secrete histamine - binds to H2 receptors on parietal cells and stimulates acid secretion
Name 3 types of hormonal regulation of function
Glucose - insulin
Appetite - ghrelin, NPYY
Gut function - somatostatin, cholecystokinin, gastrin, glucose dependent insulinotropic peptide
Describe gastrin
- G cells secrete
- Located in gastric Antrum, upper duodenum
- Stimulated by AA, stomach distension, PNS
- Increases acid secretion, increases gastric emptying, increases pepsinogen secretion
- release inhibited if pH < 3
Describe secretin
- S-cells secrete
- Located in duodenum and jejunum
- Stimulated by pH drop in duodenal lumen
- Increase pancreatic HCO3.
- Excess secretin can inhibit acid secretion and inhibit gastric emptying
Describe somatostatin
- D-cells synthesise
- Located in stomach, gut mucosa, pancreas
- Stimulated by reduced pH.
- Reduces acid secretion (by inhibiting G-cells and ECL cells).
- Reduces motility, exocrine secretion, endocrine secretion, absorption
- UNIVERSAL INHIBITOR
Describe cholecystokinin
- Secreted by I cells
- Located in SI
- Stimulated by fats and peptides
- Increases secretion of pancreatic enzymes. Reduces gastric emptying, reduces gall bladder contraction, reduces appetite.
- Acts independently of vagus nerve
Describe gastric inhibitory peptide (glucose-dependent insuliotropic peptide)
- Secreted from K cells
- located in duodenum and jejunum
- Stimulated from mixed meal nutruents
- Increases insulin secretion.
- Inhibitory effects on stomach function at high concentrations
Which plexus controls gut motor function?
Myenteric plexus (controls muscular externa)
Majority of sympathetic nerve fibres do not directly innervate GIT structures - terminate on neurone in intramural plexuses
Vasoconstrictor sympathetic fibres DO directly innervate blood vessels of GIT
Where else are osmoreceptors found?
Organum vasculosum, subfornical organ
