GI Physiology Flashcards
Describe the length of the preganglionic and postganglionic fibres of the parasympathetic and sympathetic system
Parasympathetic - longer preganglionic and shorter postganglionic fibre and vice versa for sympathetic
Describe the sympathetic system of the GI tract
- Reduce blood flow to gut and increase blood flow to brain and skeletal muscle
- Nerves that control GI output from T5 to L3 of spinal cord
- Sympathetic fibres to gut do not synapse in sympathetic trunk but synapse in ganglia
- Form abdominopelvic presynaptic splanchnic nerves
- Greater - T5-9
- Lesser - T10-11
- Least - T12
- These splanchnic nerves synapse with prevertebral ganglia
- Eg coeliac ganglia, superior mesenteric, inferior mesenteric
- Form abdominopelvic presynaptic splanchnic nerves
- Mainly innervate blood vessels
- Post ganglionic fibres go to the gut
Describe the parasympathetic system of the GI tract
- Cranialsacral outflow - fibres from head and sacral spine
- Composed mainly of vagus nerve (from cranium) and exits medulla
- Innervates foregut, midgut and half of hindgut
- Pelvic splanchnic nerves have small function to gut from transverse colon
- Innervates half of hindgut
- Composed mainly of vagus nerve (from cranium) and exits medulla
- Parasympathetic stimulates gut digestion
- Preganglionic fibres synapse in walls of viscera
- Innervate smooth muscle/endocrine and secretory
- Left vagal nerve becomes anterior and right vagal nerve becomes posterior due to rotation of foregut
Describe the plexuses that form the enteric nervous system
- Myenteric / Auerbach’s plexus lies between circular and longitudinal muscle of gut and controls motility through these muscles
- Submucosal / Meissner’s plexus controls blood flow and secretions at epithelial and submucosal level
Differentiate between endocrine, paracrine and neurocrine signaling in GI hormones
- Hormones
- Peptides released from endocrine cells
- Released into portal circulation where it passes through liver before entering systemic circulation
- Paracrine
- Peptides released by endocrine cells
- Act locally over shorter distances
- Neurocrine
- Peptides released by neurones in GI tract
- Released after action potential
Explain the actions of gastrin and CCK
- Gastrin and CCK are structurally similar
- Gastrin can bind to CCK receptor
- Gastrin released by G cells in stomach
- Increase gastric acid secretion
- CCK released by I cells in duodenum and jejunum
- Compresses gallbladder and causes secretions
- Encourages pancreas to produce enzymes
- Relaxes oddi sphincter to allow biliary tree secretions to enter gut
Explain the actions of secretin and GIP
- Secretin released from S cells in duodenum
- Stimulated by H+ and fatty acids
- Controls amount of chyme released into duodenum
- Helps neutralise acidic chyme by increasing bicarbonate secretion from pancreas/ gallbladder
- Decreases gastric acid secretion
- GIP released by cells in duodenum and jejunum
- Stimulated by sugars, amino acids and fatty acids
- Increases insulin
- Decreases gastric acid secretion
Describe visceral and somatic pain using appendicitis as an examples
- When viscera peritoneum becomes inflamed, they have a sensory but that comes from spinal sensory ganglia
- Appendix located at T10-11 spinal sensory ganglia source, so body assumes pain comes from T10-11 dermatome
- If distension of viscera peritoneum is in stomach, then pain felt in T5-9 dermatome
- Stomach - T5-9
- Small intestine to transverse colon - T10-11
- Transverse colon to sigmoid colon - T12
- Pain is vague and midline
- If appendix becomes enlarged, it may contact parietal peritoneum
- Parietal peritoneum is somatic innervated and exact location of source of pain is located
State the name of the midline regions where visceral pain is felt
- Foregut structures - epigastric
- Midgut structures - periumbilical
- Hindgut - suprapubic/hypogastric
Two common types of movements are present in the gut
Peristalsis and segmentation
Describe peristalsis movement in the GI tract
- Circular and longitudinal muscle throughout to move food through peristalsis
- Contraction of muscle behind bolus and relaxation after
- Periodic contractions - propulsion and mixing
- Tonic contractions - constant level of contraction
- Upper stomach, ileocaeval valve, internal anal sphincter
- In long intestine, complete circular muscle but 3 large bands of longitudinal muscle
Describe movement of food through segmentation
- Contraction splits contents, then relaxes (non-adjacent segments contract and relax)
- To and fro movements that mix contents
Describe what mass movement is
- Occurs in distal colon
- Rapid movement of contents into rectum
Describe how surface area can be increased to aid absorption
- Permanent folds (plica circulares)
- Villi
- Microvilli (brush border)
- Rugae
Relate the consequences of pathological water movement in the gut to physical symptoms
- Increased movement of water into the bowels causes diarrhoea
- Can be due to increases osmolality caused solutes such as lactose in lactose intolerance patients
