Question

Compare the neural and hormonal control of the GI system (3 basic differences)

Compare the long and short reflexes of the GI tract. (3 basic differences)

Explain the differences between cephalic, gastric and intestinal phases of GI control. (2 differences each)

Answer in dot points!!

Answer 1

Neural control:

• Digestive system is regulated by both intrinsic and extrinsic neural control and the gastrointestinal reflexes modify activities of gastrointestinal tract.
• The intrinsic neural regulation is by enteric nervous system formed by meisiner's plexus and auerbach's plexus. The control local secretion & movement of GI tract and also mediate local or short reflexes.
• The extrinsic neural regulation by sympathetic system is inhibitory and parasympathetic system is stimulatory. It also alters the activity of intrinsic nervous system and mediates long reflexes.

Endocrine control:

• The functions of digestive system are controlled by both intrinsic and extrinsic hormones.
• Intrinsic hormones are secreted from endocrine cells of gastrointestinal tract which makes gastrointestinal tract an endocrine organ. They act in paracrine fashion influencing gastric acid secretion.
• Extrinsic hormones secreted by other endocrine glands like thyroxine and cortisol stimulate intestinal motility and acid secretion respectively.

Long reflexes of GI tract:

• It is mediated by extrinsic nerves.
• The stimulus is processed by the central nervous system thtough afferent nerves.
• The efferent nerves from CNS apps on the smooth muscles are gland in gastrointestinal wall and causes a change in gastrointestinal motility or secretion.

Short reflexes of GI tract:

• It is mediated by intrinsic nerves.
• Change in osmolality, chemical composition stimulates local receptors in GI mucosa and they are processed in the nerve plexus in the gut wall.
• The nerve impulses from the nerve plexus acts on the local effectors like smooth muscle and glands to cause appropriate response.

Cephalic phase:

• It is elicited by smell, sight, thought, taste and chewing of food.
• In this phase, impulses increase acid secretion in stomach and enzymatic secretion in pancreas by vagal stimulation.

Gastric phase:

• ​​​​​​ It starts when food enters the stomach causing it to distend.
• This phase is mediated by vagovagal reflex and increase acid secretion from stomach and enzymatic secretion from pancreas.

Intestinal Phase:

• It starts when chyme enters the intestine.
• Initially increases gastric secretion by vagovagal reflex and later inhibits the secretion by entero gastric reflex while in pancreas, it stimulates both enzymatic and bicarbonate sectretion.