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BBS1002 > CASE 10 > Flashcards

CASE 10 Flashcards

1
Q

long reflex integrated in the CNS

A
  • begins with stimulus transmitted along a sensory neuron to CNS
  • digestive reflexes integrated in the CNS are called long reflexes
  • long reflexes that originate completely outside the digestive system are called cephalic reflexes
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2
Q

short reflexes integrated in the ENS

A
  • ENS can work in isolation, but it also coordinates function with ANS bringing signals from CNS
  • processes controlled by ENS include motility, secretion, growth
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3
Q

reflexes involving GI peptides

A
  • By GI cells released peptides may act as hormones or paracrine signals. GI hormones are secreted into the blood and act on GI tract and brain.
  • paracrine molecules in ECF act locally, on cells close to where they were secreted
  • in GI- peptides, excite or inhibit motility and secretion
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4
Q

The enteric nervous system

A
  • one of the main division of the ANS
  • functions autonomously, independent on efferent signals from CNS, shares many features with CNS:
    1. intrinsic neurons
    2. neurotransmittres and neuromodulators
    3. glial support cells
    4. diffusion barrier
    5. integrating center
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5
Q

intrinsic neurons

A
  • lie completely within the wall of the gut
    1. sensory
    2. inter
    3. motor neurons
  • autonomic neurons that bring signals from the CNS to the digestive system are called extrinsic neurons
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6
Q

neurotransmitters and neuromodulators

A
  • ENS neurons release neurotransmitters and neuromodulators
  • sometimes called nonadrenergic, noncholinergic to distinguish them from traditional autonomic neurotransmitters norepinephrine and acetylcholine
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7
Q

Glial support cells

A
  • similar to astroglia of the brain
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8
Q

diffusion barrier

A
  • capillaries that surround ganglia in ENs are not very permeable and create a diffusion barrier that is similar to the blood brain barrier of cerebral blood vessels
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9
Q

integrating center

A
  • reflexes that originate in GI can be integrated and acted on without neural signals leaving ENS.
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10
Q

Composed of two plexuses embedded in wall of GI

A
  1. submucosal nerve plexus: ascending and descending part connected to mucosa and circular muscle, senses and secretes
  2. myenteric nerve plexus: ascending and descending part connected to circular and longitudinal smooth muscle layers; controls motility of intestines.
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11
Q

submucosal plexus, Meissner

A
  • regulates the configuration of luminal surface
  • controls glandular secretions
  • alters electrolyte and water transport
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12
Q

myenteric plexus, Auerbach

A
  • regulate peristaltic waves

- control local muscular contractions that are responsible for stationary mixing and churning

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13
Q

SNS on digestive activity

A
  • inhibits digestion activity
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14
Q

PNS on digestive activity

A
  • stimulates digestive activity
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15
Q

Parasympathetic stimulation

A
  • increases activity of ENS
  • divided into:
    1. cranial: in the vagus nerves. Provide extensive innervation to esophagus, stomach and pancreas
    2. Sacral divisions: originate in 2nd 3rd 4th sacral segments of spine and pass through pelvic nerves to distal half of large intestine and all the way to the anus.
    3. post-ganglionic neurons: located mainly in myenteric and submucosal plexuses. Stimulation of these nerves causes general increased activity of entire ENS
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16
Q

Sympathetic stimulation

A
  • usually inhibits GI-activity
  • fibers mainly secrete norepinephrine
  • inhibiting causes many effects opposite to parasympathetic system:
    1. to a slight extent by direct effect of secreted norepinephrine to inhibit intestinal tract smooth muscle
    2. to a major extent by an inhibitory effect of norepinephrine on the neurons of the ENS
  • strong stimulation can inhibit motor movements, it can block movement of food through GI tract
17
Q

GI hormones divided into three families

A
  1. the gastrin family
  2. the secretin family
  3. third family
18
Q

The gastrin family

A
  • both gastrin and CCK can bind to and activate the CCKB receptor found on parietal cells
    a. gastrin: secreted in stomach
    i. stimulus: peptides and amino acids ; neural reflexes
    ii. target: ECL cells and parietal cells
    iii. effect: stimulates gastric acid secretion and mucosal growth
    iv. other info: somatostatin inhibits its release

b. Cholecystokinin (CCK); secreted in intestine
i. stimulus: fatty acids and some amino acids
ii. target: gallbladder, pancreas, stomach
iii. effects: stimulates gallbladder contraction and pancreatic enzyme secretion. Inhibits gastric empyting and acid secretion.
iv. other info: promotes satiety

19
Q

the secretin family

A

a. secretin: released in small intestine
i. stimulus: acid in small intestine
ii. target: pancreas and stomach
iii. effect: stimulates HCO3- secretion and inhibits gastric emptying and acid secretion

b. vasoactive intestinal peptide (VIP): secreted in small intestine. It is a neurocrine molecule. It maintains general homeostasis

c. glucose-dependent insulinotropic peptide (GIP): secreted in small intestine
i. stimulus: glucose, fatty acids and amino acids in small intestine
ii. target: beta cells pancreas
iii. effect: stimulates insulin release and inhibits gastric emptying and acid secretion

d. glucagon-like-peptide-1 (GLp-1): secreted in small intestine
i. stimulus: mixed meal that includes carbohydrates or fats in lumen
ii. target: endocrine pancreas
iii. effect: stimulates insulin release and inhibits glucagon release and gastric function

20
Q

third family

A
  • contains peptides that don’t fit in the other two families
    a. motilin: primary member of this family. Increases in motilin secretion are associated with the migrating motor complex. Secreted in small intestine
    i. stimulus: fasting: periodic release every 1.5-2 hours
    ii. target: gastric and intestinal smooth muscle
    iii. effect: stimulates migrating motor complex, which are waves of electrical activity that sweep through intestines in a regular cycle during fasting:
    iv. other info: inhibited by eating a meal

b. histamine: effect in the small intestine: histamine induces intestinal secretion by stimulating the production of prostaglandins, which then activate the secretory process

21
Q

three phases

A
  1. cephalic phase
  2. gastric phase
  3. intestinal phase
22
Q

cephalic phase

A
  • CNS most prominent in this phase
  • smelling or seeing food create a response
  • stimulus of food in oral cavity activate neurons in medulla oblongata –> sends efferent signal through autonomic neurons to salivary glands through vagus nerve to the ENS –> stomach, intestine begin secretion and increase motility to get ready for the food to come
  • salivary amylase contains lysozyme, disable bacteria and viruses
  • chemical digestion begins in mouth
  • mechanical digestion begins in oral cavity with mastication
  • deglutition: stimulus is pressure created when the tongue pushes the bolus against the soft palate and the back of the mouth
23
Q

gastric phase

A
  • stomach has 3 general functions:
    1. storage: stomach stores food and regulates its passage into the small intestine
    2. digestion: stomach chemically and mechanically digests food into chyme
    3. protection: stomach protects the body by destroying many of the bacteria and pathogens swallowed with food or trapped in airway mucus.
  • receptive relaxation: when food arrives in stomach, it relaxes and expands
  • acid secretion
  • enzyme secretion
  • paracrine secretion
  • hormone secretion
24
Q

acid secretion

A
  • parietal cells secrete gastric acid –> activates pepsinogen and denatures proteins –> makes peptide bonds between amino acids accessible to pepsin
  • gastric acid also helps killing bacteria and inactivates salivary amylase, which stops carbohydrate digestion
25
Q

enzyme secretion

A
  • chief cells secrete inactive enzyme pepsinogen, which is cleaved to active pepsin in the lumen of stomach by the action of H+.
  • endopeptidase that carries out initial digestion of proteins, particularly active on collagen, meat digestion
  • chief cells also secrete gastric lipase, although very little fat digestion happens in stomach
26
Q

paracrine secretion

A
  • enterochromaffin-like cells (ECL cells) secrete histamine, which is a paracrine signal that promotes acid secretion by parietal cells
  • D cells secrete somatostatin (SS), shuts down acid secretion directly and indirectly and also inhibits pepsinogen secretion
27
Q

hormone secretion

A
  • G cells secrete the hormone gastrin into the blood

- gastrin release is stimulated by the presence of amino acids and peptides in the stomach

28
Q

mucous cells

A

in the neck of gastric glands secrete both mucus and bicarbonate.

29
Q

intestinal phase

A
  1. chyme in intestine activate the ENS which slows gastric motility and secretion –> three hormones reinforce motility feedback: secretin, CCK and GIP
  2. secretin inhibits acid production and gastric motility and stimulates production of pancreatic HCO3- to neutralize acidic chyme
  3. CCK is secreted in bloodstream if a meal contains fats.
  4. GIP and GLP1 are released if the meal contains carbohydrates –> promote insulin release by the endocrine pancreas
  5. the mixture of acid, enzymes and digested food in chyme usually forms a hyperosmotic solution. When osmoreceptors are stimulated by high osmolarity the receptors inhibit gastric emptying
30
Q

zie pagina 130 voor plaatje

A
31
Q

hepatic portal system

A
  • most absorbed nutrients move into capillaries in villi and from there into hepatic portal system
  • specialized region has two sids of capillary beds: one picks up absorbed nutrients at intestine and another delivers the nutrients directly to the liver
32
Q

ileocecal valve

A
  • large intestine concentrates water
  • chyme enters large intestine through ileocecal valve –> contracted region of muscularis that narrows the opening between ileum and cecum (first part of large intestine)
33
Q

tenia coli

A
  • discontinuous longitudinal muscle layer concentrated into three bands
  • contractions pull wall into bulging pockets called haustra
34
Q

mass movement, colonic contraction

A

chyme in colon is moved primarily via mass movement.

- The defecation reflex removes undigested feces from the body

35
Q

gastral ileal reflex

A

stomach relaxes when food leaves the stomach

36
Q

little bit liver

A

gets blood by hepatic artery and portal hepatic vein, which supplies liver with nutrients and toxins.
- fats are first taken up into the lymphatic vessels, than enter the blood system –> go through heart –> go to liver –> blood leaves liver via hepatic vein

BBS1002 (10 decks)

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