alimentary control Flashcards
what are the nerve divisions involved in alimentary control?
somatic (voluntary)
- sensory
- motor
autonomic (involuntary)
- sympathetic
- parasympathetic
what are the hormones in the GIT?
- cholecystokinin (CCK)
- gastrin
- gastric inhibitory peptide (GIP)
- secretin
where is CCK secreted from and what is its function?
the duodenum endocrine cells
- functions to help digest fats and proteins
where is gastrin secreted from and what is its function?
G cells in the stomach
- functions to stimulate HCL by parietal cells
what is the function of GIP?
increases insulin secretion
what is the function of secretin?
increase HC03 (bicarbonate) from the pancreas
where are hormones most active?
at the level of the stomach
what is secretory control done by?
entirely neural via some cranial nerves
what are the cranial nerves involved with chemical taste and smell secretion control?
taste- 7 and 9
smell- 1
what cranial nerve is involved with mechanical chewing secretion control?
loading periodontal ligaments CN 5
what are the stimuli involved with salivatory secretion?
- vision
- olfactory (smell)
- mechanical (chewing)
- chemical (taste)
what muscles are involved in chewing?
jaw, facial and tongue muscles
which cranial nerves are involved in chewing?
5, 7, 12
what muscles are involved in swallowing?
jaw, tongue and pharyngeal muscles
what cranial nerves are involved with swallowing?
5, 9, 10 and 12
what muscles are involved in the oesophagus?
mix of skeletal and smooth muscle
what cranial nerve is involved with the oesophagus?
10- vagus
what are the functions of the stomach?
- secretion (gastric juice)
- motility (filling, relaxation, mixing, peristalsis, emptying)
what are the stimuli of gastric activity?
cephalic phase
- mechanical chewing (muscles of mastication)
- chemical (taste, smell)
- psychic (visual, emotional)
gastric phase- stimulates secretion
- mechanical (distension)
- chemical (food in stomach)
intestinal phase
- mechanical (distension)
- chemical (acid, protein in duodenum)
what is distension?
knowing you’re full
what are the controls of gastric activity?
cephalic phase
- nerves (long reflex)
gastric phase
- nerves (long & short reflexes)
- hormones (gastrin)
intestinal phase
- nerves (long & short reflexes)
- hormones (GIP and secretin)
- tends to slow gastric emptying
short vs long nerve reflexes
long- to brain
short- locally at that site
what are the functions of the small intestine?
- absorption
- secretions (intestinal juice)
- motility (mixing, villus movements, segmentation contractions, peristalsis)
what are the controls of the small intestine?
mainly by local nerves/short reflexes in response to intra-luminal stimuli
describe the role of bicarbonate in pancreatic juice
Intestinal phase
- secretin (released from the duodenum in response to acid to neutralise, stimulates secretion of bicarbonate rich pancreatic juice)
- CCK and VIP- weaker stimulation of bicarbonate
what is CCK?
Cholecystokinin (bile sac mover) and mainly works by promoting the digestion of fat and protein. It also is an appetite suppressant.- stimulates secretion of bicarbonate, enzyme rich pancreatic juice
what is VIP?
Vasoactive intestinal polypeptide – many functions and production sites but for the gut it breaks down glycogen and relaxes the smooth muscle of the gall bladder and the stomach.
where is gastrin released from?
g cells in the stomach, duodenum and pancreas
what is the function of gastrin?
increases the secretion of HCl by the parietal cells in the stomach
what is GIP?
Gastric Inhibitory Peptide (Polypeptide) – weak inhibition of stomach acid secretion, but actually stimulates insulin secretion, stops death of pancreatic beta cells (insulin producing cells), stimulates glucagon and also accumulation of fat.
what are patients with their gallbladder removed advised?
to reduce their fat intake
secretion of bile CCK
- Stimulates contraction of gall bladder (gall bladder needed to store bile)
- relaxation of the sphincter of oddi
what are the functions of the large intestine and rectum?
- secretions (mucus to protect, water and electrolytes)
- motility (mixing, mass movements- peristalsis and defaecation)
describe neural control in the large intestine
- mixing and segmentation is controlled by local reflexes
- long reflexes are triggered by food entering the stomach- increases motility in the intestine
- gastro-ileal reflex- gastric activity increases motility in the ileum
- gastro-colic reflex- gastric activity increases motility on the colon
describe neural control in the large bowel
- mixing and segmentation is controlled by local reflexes
- long reflexes are triggered by food entering the stomach- increases motility in the intestine
- gastro-ileal reflex- gastric activity increases motility in the ileum
- gastro-colic reflex- gastric activity increases motility on the colon
describe control in the large intestine and rectum
- mainly nueral
- ANS, Vagus, pelvic nerves
describe control in the rectum
- ANS control of internal and sphincter
- voluntary control of external sphincter
- somatic nerves
what are the two main anal sphincters?
internal and external
what is the internal anal sphincter controlled by
parasympathetic fibres which relax involuntarily
what type of muscle is the external anal sphincter?
skeletal muscle
what controls the external anal sphincter?
somatic nerves from the inferior anal branch of the pudendal nerve- allows conscious control of defecation
what are the reflexes which take place is defecation is appropriate?
Relaxation of the external sphincter
Contraction of abdominal wall muscles
Relaxation of pelvic wall muscles
Peristaltic waves then facilitate the movement of faeces through the anal canal.
