Gut Motility & Gut Secretions Flashcards
What are the digestive processes in the small intestine?
- Chyme mixed w digestive juices and moves along SI
- chem digestion is completed
- nearly all nutrient absorption occurs
- moves undigested remains to LI
What are the 2 types of contractions in the intestines?
- Mixing/Segmenting Contractions
- Peristaltic Contractions
What do Segmenting Contractions do?
- goes back and forth to break digestive contents down
- the shape allows plenty of time for chyme to mix w digestive enzymes to be chemically broken down
What is the Migrating Myoelectric Complex and what does it do? and what is it initiated by?
= Peristaltic contraction in SI
- Replaces segmenting contractions when most of the meal is absorbed
- Moves undigested remains to LI
- MMC is initiated by increased chyme pH or Motilin
What are the Digestive Processes in the Large Intestine?
- Absorption of H2O and electrolytes
- Chem digestion by enteric bacteria
- Propulsive actions
- Excretion
Describe Mass Movements. What is it facilitated by?
- simultaneous contraction of large segments from caecum to sigmoidal colon
- facilitated by gastrocolic and duodeno-colic reflexes
LI Anatomy
What is Constipation?
= pass stools <2/week
Causes:
- IBS
- Pregnancy
- GI diseases
What is Diarrhoea?
= rapid movement of faecal matter through LI
Causes:
- Enteritis
- Ulcerative colitis
- Potentially Diabetes
Steps of Defecation Reflex
- Activation of stretch receptors -> Activation of Parasymp nerves -> Rectal contractions + relaxes Internal Anal Sphincter
- Activation of Enteric Neurons -> rectal contractions via Myenteric neurons + relaxation of Internal Anal Sphincter by Inhib. Myenteric Neurons
- Both Parasymp & Enteric Neurons -> mucous secretion
- Voluntary movement of external anal sphincter by inhibiting somatic motor neurons casuing external anal sphincter to relax.
What are the 7 functions of Saliva?
- Lubrication
- Digestion
- Protection
- Control of H2O intake
- Speech
- Absorption
- Taste Sensation
Is Salivary Secretion regulated by PNS or SNS?
PNS
Salivary Secretion steps
- Approach of food
- Higher centres (olfactory, visual, aud. cortex)
- Salivatory nucleus of Medulla
- Salivary glands
- Salivation
What happens in salivary glands to release saliva?
Activation of Muscarinic receptors by Ach -> increase in secretion of saliva
What drug could you give someone with excessive salivation and what type of drug is it?
- Atropine
- Muscarinic antagonist
What is Xerostomia and what type of drug could treat it?
- Xerostomia = dry mouth
- Muscarinic agonist can treat it
What are the 3 phases of Swallowing?
- Voluntary/Buccal Phase
- Pharyngeal Phase
- Oesophageal Phase
What does the Voluntary/Buccal Phase involve?
- place food into mouth and chew
- moves from back of mouth to top of pharynx
- after food touches Mechanoreceptors, process becomes involuntary
What does the Pharyngeal Phase involve?
= all of food moves down Pharynx and through Upper Oesophageal Sphincter
- Urula rises and closes of nasal passage
- Epiglottis lowers and closes off trachea
- Involuntary
What does the Oesophageal Phase involve?
= bolus passes through Oesophagus (via Peristalsis) -> through Lower Oesophageal Sphincter -> into Stomach
- Constriction behind bolus (due to activation of circular smooth muscle)
- Shortening ahead of bolus (longitudinal smooth muscles contract)
Describe the Neuronal Control of Swallowing?
- Buccal phase controlled by Cerebral Cortex
- Involuntary phases controlled by swallowing centre in Medulla of brainstem
- Efferent Impulses (Vagus Nerve):
- Skeletal Muscle -> Pharynx, Upper Oeso sphincter, Early Oeso
- Smooth muscle -> Lower Oeso, Gastroesophageal sphincter - Oesophageal Peristalsis controlled by:
- Somatic nerves -> skeletal muscles
- Autonomic nerves & Myenteric plexus -> controls smooth muscles
What is Dysphagia?
encompasses conditions associated w swallowing difficulty
What is Achalasia?
- type of Dysphagia
- Lower Oesophageal sphincter doesn’t fully relax
- due to degeneration of nerves in Myenteric plexus
What are the digestive processes in the Stomach?
- Storage area
- Mechanical digestions & propulsion:
- Peristaltic waves mix food w gastric secretions to from Chyme
- Chyme empties into duodenum
- Protein digestion
- Intrinsic factor secretion
- Absorption of some fat-soluble substances
What are the 4 types of Gastric glands?
- Mucous cells
- Parietal Cell
- Chief Cell
- Enteroendocrine cell
What do Mucous cells do?
- secrete mucus
What do Parietal cells do?
- secretes HCl
What do Chief cells do?
- secrete pepsinogen
What do Enteroendocrine cells do?
- secretes gastrin
Describe the process of Activation of Pepsinogen to Pepsin
- Chief cells secrete Pepsinogen
- Parietal cells secrete HCl
- Optimal pH is 2 -> HCl secretion helps lower pH
Why do we need gastric acid secretions?
- Activation of pepsinogen
- Kills ingested bacteria (sterilises the meal)
- Breakdown of cellulose
How do Parietal Cells secrete HCl?
- Cl- absorbed into parietal cell from the stomach veins
- The process CO2 + H2O <-> H2CO3 occurs -> H+ gained from H2CO3
- Cl- goes through channels into stomach lumen
- H+ gets excreted into stomach lumen via H+/K+ ATPase pump
How do we enhance HCl secretion in Parietal cells?
Activation of Gastrin, Histamine, or ACh -> prod of secondary messengers w/in cytoplasm of parietal cell -> insertion of H+/K+ ATPase pumps into luminal membrane -> increased acid secretion
What is Gastrin?
Gastrin is a peptide hormone that stimulates secretion of gastric acid by the parietal cells of the stomach and aids in gastric motility
How do we prevent the H+/K+ ATPase pump from inserting into the stomach lumen?
- Proton pump inhibitors (PPIs) -> Less HCl secretion
What are the 3 phases of HCl secretion after a meal?
- Cephalic phase
- Gastric phase
- Intestinal phase
What happens in the Cephalic phase of HCl secretion?
- Stim: approach of food
- Pathway: from the brainstem (medulla oblongata) -> Activation of parasymp. nerves (via vagus nerve) -> innervates Parietal & G cells
- Stim. to Parietal cell: ACh & Gastrin
What happens in the Gastric phase of HCl secretion?
- Stim: swallowed food enters stomach | Semi-digested protein | rising pH
- Pathway: Local (enteric) and long autonomic (parasympathetic reflexes: Parietal & G cells
- Stim to Parietal cell: ACh & Gastrin
What happens in the Intestinal phase of HCl secretion? (stim? pathway? stim to parietal cell?)
- Stim: Chyme empties into duodenum | Acidity | Protein digestion products
- Pathway: Intestinal endocrine secretions (secretin, gastric, inhib peptide) | Inhib. of Vagal Nuclei in medulla + local neuronal reflexes
- Stim to Parietal cell: Decreased Ach & Gastrin secretion
What is Chyme and what does it do?
= Chyme is Pulpy acidic fluid which passes from the stomach to the small intestine, consisting of gastric juices and partly digested food
- It increases the surface area of food by breaking it down into smaller components
What is Secretin?
= Secretin is a hormone that regulates water homeostasis throughout the body and influences the environment of the duodenum by regulating secretions in the stomach, pancreas, and liver.
What is Bile and what does it do?
= Bile, or gall, is a yellow-green fluid produced by the liver of most vertebrates that aids the digestion of lipids in the small intestine
What is the Optimal pH of different sections of the GIT?
What is the pathway of bile secretion into the gut lumen?
What do bile salts do?
Help to emulsify fats in the small intestine
What is the precursor of bile salts?
Cholesterol
What does Lecithin (a phospholipid) do?
Combines w bile salts to emulsify fats
What are bile pigments produced from?
Produced by the breakdown of haem
What does Pancreatic Lipase do?
Break down triglycerides into fatty acids and monoglycerides
Describe the 6 steps in the Regulation of Bile Secretion
What does acidity in the GIT lead to the secretion of?
Leads to more Secretin to be produced which leads to more bile secretion
What does the presence of fats in the GIT lead to the secretion of?
Leads to more Cholecystokinin (CCK) to be secreted which causes sphincter to relax which allows bile to be secreted into the duodenum lumen
What are the 5 main roles of Cholecystokinin in Fat Emulsification?
- Gallbladder contraction
- Hepatopancreatic sphincter relaxes
- Pancreas secretes Lipase
- Stomach inhibits churning
- Pyloric sphincter constricts -> slows emptying of fatty chyme into duodenum
What does Colipase do and what is it secreted by?
Colipase pushes aside bile salts on emulsion droplet allowing pancreatic lipase to get in contact with the emulsion droplet
What are 2 Endocrine secretions of the Pancreas?
- Insulin
- Glucagon
What do Ductal cells do?
secrete Alkaline pancreatic fluid (HCO3-)
Why do Ductal cells secrete Alkaline Pancreatic Fluid?
- Activation of Pancreatic enzymes
- Protects intestinal mucosa from excess acid
- Micelle formation (fat emulsification/digestion)
What do Acinar cells do?
secrete Pancreatic enzymes
What are the enzymes released by the pancreas?
Describe the activation of Pancreatic Proteases
What is Pancreatitis?
Inflammation of Pancreas
What are 4 causes of Pancreatitis?
- defective ductal secretion of HCO3- and H2O
- significantly decreased release of pancreatic enzymes
- inappropriate activation of pancreatic enzymes
- excessive alcohol intake
What are symptoms of Pancreatitis?
- continuous abdominal pain
- weight loss
- fat malabsorption
What is some treatment for Pancreatitis?
- improve nutrition w pancreatic supplements
- remove alcohol
- pain relief -> aspirin, opiates
