Introduction to the functions and control of the alimentary tract 2 Flashcards
What do the splanchnic nerves innervate?
Where do they send signals?
- The splanchnic nerves contribute to the innervation of the internal organs; they are described as paired visceral nerves;
- They carry fibres of sensory fibres from the organs (visceral afferents) as well as fibres of the ANS (visceral efferent);
- All carry sympathetic fibres except for the pelvic splanchnic nerves which carry parasympathetic fibres.
How does the ANS enable food to move through the duodenum?
When does the PS close?
What does repulsion allow?
What is the sieving effect?
- Ripples of contraction move the food towards the antrum (thicker muscle layer)
- Pyloric sphincter is often relaxed but closes upon arrival of peristaltic wave
- Repulsion of chyme causes the opening of pyloric sphincter
- Small partially digested material is squirted through the pyloric sphincter into duodenum
- Repulsion of antral contents backwards towards the body allows mixing/grinding
- Sieving effect: viscous and solid matter are retained in the stomach
What type of hormones are produced by the gut and how are they transported?
hormones produced by the gut are peptides (sequence of amino acids
Hormones are carried in the blood from their site of production to their target site
Describe the structure of the stomach
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Describe the gastrin mediated effects
Gastrin-mediated effects A= acetylcholine GRP: gastrin-releasing peptide G: gastrin H: histamine ECL: enterochromaffin-like cell - a neuroendocrine cell found in the gastric glands of the gastric mucosa
Describe the release of paracrine hormones
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Describe the vago-vagal pathway
Where is the signal sent from?
What two things does it promote?
• It is reflex circuit within the GIT
• Pathway is via the brain stem (medulla)
Describes reflex control of responses to gut stimuli via the NTS and DMVN (dorsal vagal complex in the brain)
Thus the vago-vagal reflex is active during the receptive relaxation of the stomach in response to swallowing – reflex goes from stomach to brain and then back to stomach → active relaxation of smooth muscles of the stomach
• It also promotes motility and acid secretion
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What two nerve fibres are intrinsic in the gut?
What do they do?
Describe the neurotransmitters involved
- Myenteric plexus (Auerbach’s plexus): motor function
- Submucosal plexus (Meissner’s plexus): intestinal secretions
• Reflexly regulate GI functions entirely within the wall of the gut
• Connected to CNS by parasympathetic and sympathetic fibres, but can function autonomously without these connections
• Those effects are mediated entirely by the enteric nervous system (the third component of the ANS)
It has a similar number of neurons (100 million) as the spinal cord
• Neurotransmitters: ACh, NO, NA, 5-HT, GABA, ATP
Where are the Auerbach’s and Meissner’s plexuses located?
• Auerbach’s and Meissner’s plexuses are in wall of colon – receive input from both Parasympathetic and sympathetic nervous system
What does the parasympathetic nervous system cause?
• Parasympathetic activity → ↑ contraction of proximal colon
What does the sympathetic nervous system cause?
• Sympathetic activity → ↓ colonic movement
Auerbach’s plexus (myenteric plexus), what does cholinergic and adrenergic innervation cause?
- Most prominent plexus
- Cholinergic innervation ↑ gastric motility and secretion
- Adrenergic stimulation ↓ gastric motility and secretion
Describe the rate at which foods are absorbed: carbs, fats, proteins and fats
- Rate of emptying is dependent upon the material’s ability to be absorbed
- Carbohydrates emptied quickly into duodenum
- Proteins – slow emptying
- Fatty foods – even slower
- Fatty acids in the duodenum → ↓ in gastric emptying by increasing the contractility of pyloric sphincter
What is Peristalsis and how does it work?
- Slower in large intestine compared to small intestine
- Wave of propulsive contractions moves contents of gut towards the anus
- Distension initiates contraction
- Vagal inhibitory and excitatory fibres control movement
