Physiology: Control of GI Tract Flashcards
How long is the GI tube?
8 metres long
What are the functions of the GI tract?
Mechanically processes and moves food through the tract
Chemically processes and digests food
Absorbs nutrients and water
What are the accessory glands of the GI system?
Teeth Tongue Salivary glands Liver Gallbladder Pancreas
What is the function of the accessory organs ?
Control secretions and breakdown of food
What part of the nervous system is responsible of sending signals to the GI tract?
Enteric nervous system & Autonomic nervous system
What does the Enteric nervous system control?
Peristalsis & motility
Secretion & absorption
What are the Gut peptides (GI peptides)?
Paracrines
Hormones
How does the ENS (Enteric nervous ) operate?
Intrisi che control: short reflexes - internal stimuli
Communicates with parasympathetic and sympathetic nervous systems but is autonomous
What are the two organised neural plexus in the ENS of the GI tract?
My enteric plexus
Submucosal plexus
Where is the myenteric plexus located? What is its function?
Between longitudinal and circular layers of muscle
Involved in control of digestive tract motility
Where is the submucosal plexus located?
Between the circular muscle and luminal mucosa
What is the function of the submucosal plexus?
Senses the environment of the lumen
Regulates GI blood flow and epithelial cell function
What secretes (22) hormones and paracrines in GI system?
Enteroendocrine cells (EEC)
What are Enteroendocrine cells (EEC)
Single cells scattered through the GI a tract
Density packed secretory vesicles
What are the functions of Enteroendocrine cells (EEC)?
Sense luminal contents: chemical, osmotic and ph
Release hormones and paracrines
What are the main hormones of GI?
Gastric Secretin Cholecystokinin Goucagonlike Somatostatin-like
Which event are part of GI motility?
Physical contractions
Tonic contractions
What are Phasic contractions?
Short lasting contractions : Peristalsis + segmented contractions
What is the function of Phasic contractions?
Movement of material in the small intestine
What are Tonic contractions?
Long lasting contractions
What are the functions of atomic contractions?
Closing of a sphincter
Control movement of material through the GI tract
Maintain ordered sequence of events
Compartmentalisation ensures processes are complete before passing to next area
What is the definition of Peristalsis?
Propulsion of material
Which neurones regulate Peristalsis?
Neurones in myenteric plexus : Interstitial Cells of Cajal (ICC)
What are Interstitial Cells of Cajal (ICC)?
Pacemakers of the gut
Differ in different regions of the GI tract
Where are the Interstitial Cells of Cajal (ICC) found?
In myenteric plexus
What do the Interstitial Cells of Cajal (ICC) do?
Electrical activity spreads via gap junctions from ICCs to muscle
ICCs produce slow waves
What are Slow waves?
Slow undulating changes in rating membrane potential NOT ACTION POTENTIAK
At what threshold do Slow waves cause contraction?
-40 mv
What activates Slow waves?
Distension: bolus of food (chyme) stimulates stretch receptors (local reflex)
Oral contraction
Aboral relaxation
What are the nerves of slow waves?
Parasympathetic nerves (ACh)
What is the neurotransmitter in slow waves ?
Acetylcholine (ACh)
Where do segmented contractions & mass movements take place?
Colon: 99% of the time
What is the function of the Colon?
Retain material - water reabsorption and fermentation
Mixing contents
Mass movement of material into aboral end via Gastro-colic response
How many times does Mass movement of material into aboral end of colon occurs?
2-3 Times per day
What is Hirschprungs disease aka TOXIC MEGA COLON?
Congenital disorder which presents shortly after birth
What are the characteristics of TOXIC MEGA COLON?
All or part of colon has no innervation
The colon is dilated
Treatment:
Surgical removal of the colon
What is mastication?
Breakdown of food
What is the role of Taste in the mouth ?
Inform brain about edibility/ duration
What is the role so Salivary production in the mouth?
Lubrication, protection and digestion
What is the role of Swallowing in the mouth?
Movement of digested macromolecules to stomach
What organs are responsible of Taste in the mouth ?
Papillae: taste organs
What are Papillae?
Raised protrusions on the tongue, soft & pallet, pharynx, epiglottis & larynx
Visible to naked eye
Where are te Taste buds found?
In the Papillae
How many types of cell does each taste bud contain?
Epithelial cells
Support cells
Gustatory receptor cells (taste cells)
Which nerves innervate taste buds?
Gustatory afferent nerves
Is the moth a taste bud?
Yes or no
Yes
What do Apical microvilli in the mouth do?
Increase surface area
How are receptor proteins in mouth exposed?
Through taste pore
Where are ion channels and receptors located in the mouth?
On villi
All flavours are encoded by how many taste modalities?
5
What are the taste modalities?
Sweet Salt Sour Bitter Umami
One taste cell responds to one modality
True or false
True
What are the Ionotropic receptors in the mouth?
Salt : Na+
Sour: H+ gated ion channels (K+/H+)
What are the metabotropic receptors in mouth ?
Sweet
Bitter
Umami
What is the Saliva?
Hypotonic solution containing more than 99% water and 1% dry matter such as proteins
What are the components of the Saliva?
Water Bicarbonate ions Enzymes Alpha-amylase Lipase Proteins (100s)
What is the role of Bicarbonate ions in saliva?
Buffering capacity
Protect from acid
What is the role of alpha - amylase in saliva?
Released from parotid gland to initiate carbohydrate digestion
What is the role of lipase in saliva?
Secretes within glands of the mucosa of the tongue (linguinal)
What is the role of Saliva in the mouth?
Anti-bacterial Anti-viral Anti-fungal Tissue coating Lubrification Viscoelasticity Mineralisation Buffering Digestion
Where does swallowing take place?
Mouth and oesophagus
What is the Oral phase?
First phase of swallowing
What are the phases of swallowing?
1- Oral phase
2- Pharyngeal phase
3- Oesophageal phase
What are the events of the oral phase?
Preparatory phase: chewing and biting
Transfer phase: Respiration inhibited and tongue forces bolus into pharynx
What is the Pharyngeal phase?
Movement of bolus from pharynx into oesophagus
What is the oesophageal phase?
Delivers bolus to the stomach
What does the Esophageal manometry measures?
Oesophageal motility & problems swallowing
What is dysphagia?
Problems swallowing
What are the Gastric functions of the stomach?
Motility
Digestion
Protection
Absorption
What are the phases of motility?
Gastric accommodation
Trituration- gastric juices
Gastric emptying
What are 2 Functional/motor regions?
1- Reservoir - tonic contractions
2- Antral pump - Phasic contractions
What are the 4 anatomical regions of the stomach ?
Cardia Fundus Body (Corpus) Antrum Pyloric sphincter
Where is the gastric juice found?
The stomach
What are the components of the gastric juice?
Water and ions HCl Pepsinogens Intrinsic factor Mucus Gastrin
What is the role of HCl in the gastric juice?
Provide low ph (1 or 2)
Prevent bacterial growth
Catalyse cleavage of pepsinogens to pepsin
What is the role is Pepsinogens in the gastric juice?
Proenzyme of pepsin
Pepsin breaks down proteins into peptides
What is the role of Intrinsic factor in the gastric juice?
Glycoproteins
Binds to vitamin B12 to allow digestion in the ileum
What is the role of the Mucus in the gastric juice?
Protects gastric mucosa
What is the role is Gastrin in gastric juice?
(From G cells)
Regulates acid secretion
Which cells are involved in gastric secretion?
Mucus neck cells
Parietal cells
Chief cells
Endocrine cells
What do Mucus neck cells secrete?
Mucus
What do Parietal cells secrete?
HCl
Intrinsic factor
What do Chief cells secrete?
Pepsinogen
What do Endocrine cells secrete?
G cells-gastrin to stimulate acid secretion
D cells-somatostatin to inhibit acid secretion
How is Bicarbonate formed?
CO2 in parietal cells reacts with H2O
How is HCL secreted?
H+ is catalysed by the enzyme carbonic anhydrase
H+ transported actively by proton pumps into gastric lumen in exchange for K+ ions
Both K+ and Cl- diffuse passively down a concentration gradient out of the cell
The bicarbonate produces is transported into the capillaries in exchange for Cl- ions by anti porters
What controls ACID secretion?
Neulroendocrine - ACh
Endocrine - gastrin
Paracrine - histamine
What are the phases of motility ?
Cephalic phase: 30%
Gastric Phase : 60%
Intestine phase:10%
Where is the duodenum?
First loop of small Intestine?
What is the role of the duodenum?
Digestion of bolus
Reflex inhibition motility- enterogastric gastric reflex
What are Brunner’s glands in the duodenum?
Secrete alkaline fluid of mucin- anti-acid function coating the duodenal epithelium protecting it from the acidic chyme of the stomach
The duodenum receives secretions from where?
Gall bladder (liver) Pancreas
Which metal ions are absorbed in the duodenum?
Fe2+
Mn2+
Ni2+
Cu2+
What is the name of the exocrine part (85%)of the pancreas secrete?
Acinus
What does the Acinus secrete?
Water and ions- neutralise duodenal contents to prevent damage and ph for enzyme
Bicarbonate
Enzymes- essential for normal digestion
What is the name of the endocrine part do the pancreas?
Islets of Langherans
What do the Islets of Langherans secrete?
Alpha-cells : glucagon
Beta-cells: insulin
What does Pancreas secrete?
Pancreatic juice via hormonal control
Where is the Pancreatic juice secreted?
CCK acts in acidario cells to produce pancreatic juice which in enzymes
What does Secretin do?
Acts on pancreatic ducts to cause large secretion of very alkaline pancreatic juice rich in HCO3 and poor in enzyme
What do CCK and Secretin do together?
Add enzymes to pancreatic juice and ensure that they are washed into the intestine
What are the Pancreatic enzymes? What do they digest?
Trypsinogen - trypsin
Chymotrypsinogen - chymotrypsin
Proelastase - elastase
Procarboxypeptidase - carboxypeptidase
Lipase and phospholipase- Fats
Nucleases- Nucleic acids
α-amylase- Carbohydrates
What is blood supply to the liver?
Hepatic artery - oxygenated blood
Portal vein - nutrient rich blood from gut
Hepatic vein - deoxygenated blood from the liver
What is Bile?
produced by the liver and concentrated in gall bladder (x15) - biliary system
What is the structure of the Liver?
●Divided into lobules
●Portal triad- bile duct, portal vein and hepatic artery
●Central canal- hepatic vein
Bile is alkaline, what is its ph?
7.8-8.6
What are the components of Bile?
Water
Bile pigments- bilirubin
Salts, cholesterol and lecithin - micelles
What do Bile salts do?
Bile salts emulsify fats (micelles) - large surface area (facilitates action of lipase enzymes)
What happens to 95% of bile salts?
95% bile salts reabsorbed in terminal ileum by active transport and returned via hepatic portal vein to liver to be recycled
What is the secretion of abile controlled by?
Secretin stimulates bile secretion
CCK stimulates release of bile by
Relaxing Sphincter of Oddi
Contracting gall bladder
What are the roles of the jejenum & ileum?
Absorption – pancreatic enzymes water Digestion - Carbohydrate – monosaccharides protein – peptides & amino acids lipid - free fatty acids
Secretion of Fluid – Crypt cells- NaCl Goblet cells- mucus EECs-hormones Panneth cells- defensins
What is Malabsorption?
Absent or defective digestive enzymes
Defects in transporter proteins
Diseases or infections of small intestine
What are examples of malabsorption?
Lactase deficiency - lactose intolerance
Coeliac disease – abnormal immune response to gluten – loss of mucosal epithelium
How is the motility of the large intestine?
Slow movement of contents
What are the stages of motion in the large intestine?
Segmented contractions
Mass movements
What are Segmented contractions?
Retain material in the proximal colon (water reabsorption and fermentation)
Mixing contents
What are Mass movements?
2-3 times a day
movement of material into aboral end of colon- ready for defecation
What are the functions of the large intestine?
High mucus secretion- goblet cells
No carrier mediated transport of nutrients (absorption by diffusion)
Efficient water reabsorption - follows Cl- and Na+ movement
HCO3- buffers acid produced by bacterial fermentation
