Alimentary controls Flashcards
2 categories which control the alimentary system
Nervous (somatic and autonomic) and hormonal
2 categories of autonomic nervous control
Sympathetic and parasympathetic
2 categories of somatic (voluntary) nervous control
Sensory (sensation) and motor (innervate muscles)
Function of sympathetic nervous system
Fight or flight response, increase heart rate and breathing, reduce gut motility
Function of parasympathetic nervous system
Rest and digest, reduce heart rate and breathing, increase gut motility
Example of GIT hormones
Cholecystokinin (CCK), gastrin, Gastrin Inhibitory Polypeptide (GIP), Secretin
Function of cholecystokinin (CCK)
Stimulates contraction of gall bladder to release bile, stimulates synthesis and secretion of enzyme-rich pancreatic juice, relaxes Sphincter of Oddi, and has a weak stimulatory effect on bicarbonate secretion.
Where is cholecystokinin (CCK) released from?
Secreted from endocrine cells in the duodenum in response to high fat and protein in diet.
Function of gastrin
Stimulates HCl production by parietal cells in the stomach gastric glands.
Where is gastrin released from?
Secreted by G cells in the gastric pits of the stomach.
Function of Gastric Inhibitory Peptide (GIP)
Main role is to increase insulin secretion and stop death of pancreatic beta cells (stimulates glucagon and fat accumulation, and is a weak inhibitor of acid secretion.
Function of secretin
Reduces gastric acid secretion from the stomach and increases bicarbonate (HCO3) from the pancreas.
Where in the alimentary system is there mostly somatic nervous control?
Nearer to mouth and anus (choose when to chew and defaecate). Autonomic control in between (e.g. secretions, peristalsis)
In which area of the alimentary system are hormones primarily dominant?
In stomach and duodenum (upper SI)
What secretions occur in the mouth?
Saliva
What motility occurs in the mouth and pharynx?
Chewing and swallowing (mastication and deglutination)
How are saliva secretions controlled?
Entirely neural by cranial nerves
Which cranial nerve innervates anterior 2/3 of the tongue for gustation?
Facial nerve - CN VII
Which cranial nerve innervates the posterior 1/3 of the tongue for gustation and sensation?
Glossopharyngeal nerve CN IX
Which cranial nerve is responsible for olfaction?
Olfactory nerve CN I
Which cranial nerve controls chewing?
Trigeminal nerve CN V in the loading periodontal ligaments
Example of psychic stimuli for saliva secretion
Visual
What is classical conditioning?
Associated unconditioned stimulus (sight of food) with a new conditioned stimulus (bell) to bring about the same response (salivation) - Pavlov’s dog
Order of strengths of salivatory stimuli from weakest to strongest
Visual, olfactory, mechanical (chewing), chemical (taste)
Which taste is the strongest salivary stimuli?
Acid
Which structures are involved in chewing?
Jaw, facial and tongue muscles (muscles of mastication)
Which cranial nerves control chewing?
Trigeminal nerve (CN V) innervates muscles of mastication. Facial nerve (CN VII) innervates facial muscles. Hypoglossal nerve (CN XII) innervates tongue motor function (muscles).
Which structures are involved in swallowing/ deglutination?
Jaw, tongue, pharyngeal muscles (superior, middle, inferior constrictors)
Which part of the nervous system controls swallowing / deglutination?
Skeletal muscle therefore controlled by somatic nerves; however, there is an automatic and reflex component.
Which cranial nerves control swallowing?
Trigeminal nerve (CN V), hypoglossal nerve (CN XII). Pharyngeal plexus is innervated by the glossopharyngeal (CN IX) and vagus nerve (CN X).
What is the swallowing centre?
An area in the medulla oblongata that inhibits respiration while swallowing.
Which types of muscles are found in the oesophagus?
Superior 1/3 is skeletal, middle 1/3 is mixed, lower 1/3 is smooth muscle
Which cranial nerve innervates the muscles in the oesophagus?
Vagus nerve (CN X)
What is secreted into the stomach?
Gastric juice (HCl)
What motility occurs in the stomach?
Filling/relaxation, mixing, propulsive movements (peristalsis), emptying.
In which 3 phases can stimuli affect gastric activity?
Cephalic (head), gastric and intestinal phase
Stimuli in cephalic phase that can trigger gastric activity
Mechanical (muscles of mastication), Chemical (taste, smell), Psychic (visual, emotions, thoughts)
Intra-gastric stimuli in the gastric phase that can trigger gastric activity
Mechanical (distention when bolus enters), chemical (food triggers HCl release from parietal cells)
Intestinal stimuli that increase gastric activity
Mechanical (distention), chemical (acid and protein in duodenum)
How can the cephalic phase can control gastric activity?
Via nerves (long reflex to the brain)
How can gastric activity be controlled in the gastric phase?
Nerves (short and long reflexes), hormones (gastrin from G cells)
How do controls from the intestinal phase tend to affect gastric activity?
Tends to slow gastric emptying
How can gastric activity be controlled from the intestinal phase?
Nerves (long and short reflexes), Hormones (GIP - weak inhibitor of HCl secretion - and secretin - reduces HCl secretion from parietal cells and increases HCO3 production from pancreas)
Sequence of long nervous reflex in the control of GIT function
stimulus -> receptors -> CNS -> nerve plexus -> smooth muscle/glands -> response
Sequence of short nervous reflex in the control of GIT function
Stimulus -> receptors -> nerve plexus -> smooth muscle/glands -> response
Sequence of hormonal action in the control of GIT function
Stimulus -> receptor -> endocrine cells -> release hormones that enter circulation -> smooth muscle/glands -> response.
Secretions of the small intestines
intestinal juice
Motility of the small intestine
mixing, villus movements, segmentation contractions, peristalsis
How is the activity of the small intestine controlled?
Mainly by local nerves (short reflexes) in response to intra-luminal stimuli.
Which 3 phases control the release of bicarbonate within pancreatic juice?
Cephalic phase and Gastric phase have a small effect via the vagus nerve. The intestinal phase has the biggest influence.
How does the intestinal phase control the release of bicarbonate within pancreatic juice?
Hormones - secretin, CCK and VIP. Secretin stimulates secretion of bicarbonate-rich pancreatic juice. CCK and VIP have weak stimulatory effect on bicarbonate secretion.
Where is secretin released from?
The duodenum in response to acid (HCl)
What is VIP?
Vasoactive Intestinal Polypeptide
Function of VIP
In the gut, Vasoactive Intestinal Polypeptide breaks down glycogen and relaxes smooth muscle of the gall bladder and stomach
Which phases stimulate the release of enzymes in pancreatic juice?
Cephalic and Gastric phase have a small effect involving the vagus nerve. The intestinal phase has the greatest influence via hormones.
Which hormones in the intestinal phase stimulate the release of enzyme-rich pancreatic juice?
CCK, Gastrin and GIP (weak stimulatory effect on enzyme secretions)
Where is cholecystokinin released from?
Duodenum in response to fat and protein
Where is gastrin released from?
G cells in stomach, duodenum and pancreas.
Which phases control bile secretion?
Cephalic, gastric and intestinal phases.
How is bile secretion stimulated by the cephalic phase?
The vagus nerve relaxes the sphincter of Oddi
How is bile secretion stimulated in the gastric phase?
The vagus nerve has a small stimulatory effect
How is bile secretion stimulated in the intestinal phase?
CCK and secretin (weaker effect than CCK)
What secretions occur in the large intestine and rectum?
Mucus, some water and electrolytes
What motility occurs in the large intestine and rectum?
Mixing, mass movements, defaecation
How are mixing/segmentation movements controlled in the large intestine?
Food entering the stomach triggers local reflexes that control the motility - neural
Name of the neural reflexes in the large intestine that are triggered by gastric activity
Gastro-ileal reflex and gastro-colic reflex
Which reflex increases motility in the ileum?
gastro-ileal reflex
Which reflex increases motility in the colon?
gastro-colic reflex
Which division of the nervous system controls the large intestine and rectum?
Autonomic nervous system
Which nerve innervates the large intestine up to the splenic flexure?
Vagus nerve
Which nerves innervate the descending colon and rectum?
The pelvic nerves (sacral nerves 2-4)
What is the internal anal sphincter controlled by?
Autonomic nervous system
What is the external anal sphincter controlled by?
Somatic nerves (sacral 2-4) - voluntary control.
What muscle is the external anal sphincter made up of?
Skeletal muscle (voluntary control)
Name of the reflex that relaxes the internal anal sphincter
Retrosphincteric reflex (reflex therefore passes through spinal cord)
How is the retrosphincteric reflex triggered?
By distention of the rectum
How can defaecation be voluntarily delayed?
Contraction of external anal sphincter by brain intervention
Which reflexes occur when defaecation is appropriate?
External anal sphincter relaxes, abdominal wall muscles contract, pelvic wall muscles relax. Peristaltic waves facilitate movement of faeces through anal canal.
