Physiology Flashcards
Which systems control the gut?
Autonomic
Enteric
Hormones and paracrine substances
How does the ANS control the gut?
Cell bodies in CNS
Pre (ACh)/postganglionic (ACh)
Preganglionic fibres synapse with ganglia outside the CNS – postganglionic fibres synapse on peripheral organs
What is the sympathetic NS role in the gut?
Reduces blood flow to gut inhibiting GI function
Form:
greater (T5-9),
lesser (T10-11)
least (T12) splanchnic nerves
Outline the parasympathetic supply to the GI tract
Craniosacral output
Vagus N (cranial N)
Pelvic splanchnic Ns (S2-4)
Fibres release ACh, gastrin releasing peptide, vaso inhib peptide
What are the 2 major plexuses in the enteric NS?
Submucosal = submucosa, secretions, blood flow
Myenteric = between circular and longitudinal muscle, motility
What is the enteric NS?
Governs the function of the GI tract
Controls motor functions, local blood flow, mucosal transport and secretions, and modulates immune and endocrine functions
Can operate independently
Describe the role of hormones/peptides which affect the motility/secretions in the gut
Somatostatin = inhib gastrin and secretin
Gastrin releasing peptide (GRP) = increase release of gastrin from G cells
What are the 2 broad categories of GI hormones?
Gastrin family = gastrin, cholecystokinin
Secretin family = secretin, gastric inhib polypeptide (GIP)
What is the role of gastrin?
Increases gastric acid secretion
What is the role of cholecystokinin?
Increase pancreatic/gallbladder secretions
Outline the role of secretin
Increases HCO3, decreases gastric acid secretion
Discuss the role of gastric inhib polypeptide
Increases insulin, decreases gastric acid secretion
What is an appendicitis?
Normally follows illness
Lymphoid ring enlarges = blocks
Initial pain = visceral peritoneum = vague and midline
Later pain = grows, coming in contact with parietal peritoneum = somatic, radiates to R iliac fossa
Relate visceral referred pain to the embryological development of the gut
Viscera gets distended
Visceral peritoneum doesn’t have its own nerve supply
Viscera have afferent Ns that trace greater (T5-9), lesser (T10-11), least (T12) Ns = signal goes back to that level = makes assumption pain is coming from that dermatome
Where do certain zones of the gut present their visceral pain?
Foregut = epigastric
Midgut = periumbilical
Hindgut = suprapubic/hypogastric
What are the common types of movements are present in the GI tract?
Peristalsis = propels gut contents, one direction
Segmentation = mixes gut contents
Mass movement = rapid movement of contents into the rectum
What is a paralytic ileus?
Movement temporally impaired
Typically after GI surgery
List the general secretions of the GI
Water = for reactions
Acid = stomach
Alkali = to combat acid
Enzymes = to break things down
Mucus = lubricant for materials that must pass over membranes
Waste products = bilirubin, cholesterol
Emulsifiers = bile salt dealing with fat
Intrinsic factor = to absorb vitamins
Where do GI secretions come from?
Salvia, gastric, intestinal (liver, pancreas)
Classify the major types of gastrointestinal secretions and discuss their function
Stomach acid = barrier to infect, prepare proteins for digestion, activate enzymes
HCO3 = neutralise acid
Waste products = mainly from liver
Emulsifiers = bile salts increase area of lipids to aid digestion by lipases
Mucus = hold bicarb, lubricates, catches bacteria, antibacterial
Enzymes = break down protein, fat, carb
What are the principles of absorption in the gut?
Movement across enterocytes, cytosol, basolateral mem, then into the capillary
Paracellular (tight junctions) movement in the SI
Have to be small enough
What gets absorbed in the gut?
Carb, proteins, lipids, fat sol vits, water sol vits, vit B12, bile salts, Ca, Fe, electrolytes, water
Explain why it is necessary for water to move in both directions across the gut lumen
Water passively follows the movement of electrolytes/nutrients
Stool needs to be desiccated
Too little water and stool wont pass
