WEEK 9: Gastrointestinal Health Flashcards
T or F
Most of the GI tract can function independently of the CNS
T
T or F
The cavities of the GI tract are internal
F
They are external (E.g. rectum and oral cavities)
What is the nervous system of the GI tract called?
The enteric nervous system (ENS)
T or F
The enteric nervous system cannot communicate with the central nervous system
F
It can but it largely acts independently
T or F
The enteric nervous system has as many nerves as are present in the spinal cord.
T
In a fasting state high lvls of … and low lvls of … and … are sensed in areas of the hypothalamus responsible for feeding behavior. This causes a hunger sensation.
Ghrelin
Leptin and Insulin
When a hungry body is presented with food, signals from the … and … are transmitted via the hypothalamus to the gastrointestinal tract to prepare for the meal.
eyes and nose aka. visual and olfactory cues
How does the gastrointestinal tract prepare for an incoming meal
By initiating involuntary salivation and increasing the secretions of the stomach.
As food is chewed it is formed into a lubricated bolus to facilitate what?
passage through the esophagus
Name the three types of salivary glands
Parotid, sublingual and submaxillary
memory tool: a paranoid linguist named max sub
The salivary glands produce what two distinct secretions?
A mucus secretion containing musin (a type of sugar-modified protein) and a serous secretion that contains the enzyme alpha-amylase.
memory tool: serous mucous
What purpose does the mucus secretion of saliva have?
The mucus secretion is important for lubricating the bolus of food that will be swallowed.
What purpose does the serous secretion of saliva have?
The alpha-amylase that makes up serous secretion begins the process of digestion of complex carbohydrates.
On average the salivary glands produce about … litre of secretions per day.
1 litre
How does the esophagus transport food to the stomach?
By peristalsis
T or F
The only role of the esophagus is to transport food from the mouth to the stomach
T
What is peristalsis?
The coordinated contraction and relaxation of muscle layers to propel the food bolus into the stomach.
What three main things does the stomach do?
The stomach has very muscular walls that churn food to process it
The stomach chemically processes food through hydrolysis
The stomach stores the food until it can be delivered as chyme to the duodenum
The rate of release of chyme from the stomach is partly regulated by…
the stomach but mostly regulated by the duodenum.
What does the pyloric sphincter of the stomach do?
The pyloric sphincter regulates the output of chyme into the duodenum.
The lining of the stomach contains many complex folds that contain a variety of cells responsible for … into the stomach as well as secretion of … hormones
secretion into the stomach as well as secretion of endocrine hormones
The entire surface of the stomach is lined by …-producing cells which also line the openings of the glands producing other secretions.
mucus-
Within the folds of the stomach are oxidic/parietal cells which produce … acid.
hydrochloric acid.
Hydrochloric acid secreted by parietal cells requires approx. … kilojules of energy per litre to produce.
6
What is the role of hydrochloric acid?
The role of hydrochloric acid is to hydrolyse a protein and carbohydrate, kill bacteria and activate protease (pepsinogen which is secreted by the peptic or cheif cells).
Parietal cells also secrete … factor (a glycoprotein that is required for absorption of vitamin B12.)
intrinsic factor
What is intrinsic factor?
a glycoprotein that is required for absorption of vitamin B12.
What is a zymogen?
an inactive substance which is converted into an enzyme when activated by another enzyme.
The pepcinogen secreted by the chief cells is a zymogen and is activated to … by …. at low pH.
pepsin
autocatyolic cleavage
T or F
Pepsin is a short spectrum peptidase that cleaves proteins at shorter peptide chains in the acidic environment of the stomach.
F
Broad spectrum
In total about … litres of gastric juice is produced per day depending on diet.
1.5 litres
Past the initial phase of secretion that occurs prior to the meal ingestion, the remaining …% of secretion occurs in response to the presence of food in the stomach.
70%
What is the vagovagal reflex?
Vagovagal reflex refers to gastrointestinal tract reflex circuits where afferent and efferent fibers of the vagus nerve coordinate responses to gut stimuli via the dorsal vagal complex in the brain.
Stimulation of secretion through the presence of food in the stomach is quite complex with a … component via the hypothalamus, local signaling of the …., and local … … signaling.
vagovagal
enteric nervous system
paracrine hormone
Parasympathetic release of … , enteric … signaling, and local release of … from endocrine cells all contribute to gastric secretion.
acetocholine
histamine
gastrin
… cells in the stomach monitor contents and secrete the hormone … which assists with digestion and … in response to the absence of nutrients in the stomach.
endocrine
gastrin
ghrelin
T or F
Most contractions in the stomach are weak and are involved in the mixing of food.
T
While most contractions in the stomach are weak and are involved in the mixing of food, a proportion are strong and …
peristaltic
Peristaltic contractions force the stomach contents (chyme) toward the ….
pyloric sphincter
Does the pyloric sphincter have a relatively high or low resting tone?
high
The high resting tone of the pyloric sphincter resists the passage of … through it.
chyme
When there are enough strong peristaltic contractions of the stomach this can force the chyme through the pyloric sphincter into the …
duodenum
T or F
Usually, chyme forced into the duodenum only a few millilitres per contraction
T
T or F
Most of the regulations of the stomach emptying arises from signals from the duodenum.
T
What are the types of signals that regulate stomach emptying?
signals from the duodenum
some regulation also occurs through signals arrising from the stomach.
T or F
The pressure of food in the stomach provides a signal that triggers the emptying the stomach
F
The stretching of the stomach does.
What sensors in what nervous sytem detect the stretching of the stomach which then promotes stomach emptying?
mechanosensors in the enteric nervous system
What 5 signals arise from the duodenum?
- Distension of the duodenum
- Acidity of the duodenal chyme
- Nutrients (the presence of)
- Irritation of the duodenum mucosa
- Osmolarity of the chyme
Some signals from the duodenum to the stomach are sent via the … nervous system
enteric nervous system
T or F
All signals from the duodenum regulate the rate at which stomach emptying occurs.
T
Some signals from the duodenum to the stomach are sent through … nerves via …. and back through … sympathetic nerves
intrinsic nerves via prevertebral sympathetic ganglia and back through inhibitory sympathetic nerves.
Some signals from the duodenum to the stomach are sent through the … nerves that stem to the …. and back.
vagus
brain stem
The small intestine is divided into what three sections?
The duodenum
The jejunum
The ileum
The duodenum is approx. …cm long and shapes like the letter …
30
c
The jejunum and the ileum are collectively about … metres in length
2.5 metres
How are the jejunum and ileum differentiated?
Through their anatomical appearance and blood supplies
T or F
All of the small intestine is involved in the further digestion and absorption of food
T
T or F
From a mechanical standpoint, the three sections of the small intestine operate differently
F
T or F
All of the small intestine is involved in the further digestion and absorption of food.
T
Peristalsis occurs throughout the … segmentation occurs predominantly in the …
gastrointestinal tract
small intestine
T or F
The pyloric sphincter only allows liquids to enter the intestine
T
The regulation of gastric function can be divided into what three phases
Cephalic phase
Gastric phase
Intestinal phase
The cephalic phase results from … stimuli
sensory
(Regarding the cephalic phase of gastric function)
Sensory stimuli stimulate efferent signaling via the … to promote secretion of … and … release from chief cells in the stomach (via GRP).
vagus nerve
histamine
pepsinogen
The vagus nerve is part of the … nervous system
parasympathetic
How does the vagus nerve secrete histamine?
via pituitary adenylate cyclase-activating peptide (PACAP) release onto enterochromaffin-like cells (ECL).
The vagus promotes gastric acid secretion by direct simulation of … cells and by stimulating … to secrete histamine
parietal
enterochromaffin-like cells (ECLs)
What neurotransmitter does the vagus nerve use to directly simulate parietal cells?
acetocholine
Which neurotransmitter promotes the release of HCl from parietal cells in the stomach?
histamine
Cephalic phase vagal signalling stimulates secretion from …. cells, resulting in delivery of as much as 25% of the total pancreatic enzyme secretion into the gastrointestinal tract.
exocrine pancreatic acinar
The gastric phase of the regulation of gastric function begins when …
Food enters the stomach, causing distension
Distension during the gastric phase of the regulation of gastric function, is a stimulus for the … nerve to promote … secretion
vagus
acid
As well as acid secretion distension also results in local ….
enteric reflexes
Once the food is broken down, the …. and … in the stomach also stimulate acid secretion either by stimulating the release of the hormone …, or to a lesser extent, by directly stimulating … cells.
amino acids
peptides
gastrin
parietal
(During the gastric phase of the regulation of gastric function)
Once the pH of the stomach falls below …, a … feedback loop inhibits the release of … to stop the cycle.
2.5
negative
gastrin
Put simply, what does the intestinal phase of the regulation of gastric function do?
facilitates gastric emptying from the stomach and moves the chyme into the intestines.
During the intestinal phase the physical arrival of the bolus into the intestines causes …
distension
What does distension during the intestinal phase cause?
increases the osmotic pressure in the lumen of the intestines which creates a (local) neural reflex that inhibits gastric activity.
During the intestinal phase the presence of nutrients (particularly … and …) stimulates … release
fat
peptides
cholecystokinin
(During the intestinal phase) what does the release of cholecystokinin stimulate?
stimulating gall bladder contraction, exocrine pancreatic secretions (predominantly acinar enzyme secretion) but also a reduction in gastric motility (all through both a vago-vagal mechanism and paracrine signalling).
During the intestinal phase the drop in pH in the Duodenum results in … release
secretin
During the intestinal phase, the release of secretin has what affects?
acts on pancreatic ductal cells to release fluid and bicarbonate (to some extent acinar cells are also stimulated) and this is primarily via a paracrine mechanism.
During the intestinal phase the release of secretin has what affects?
acts on pancreatic ductal cells to release fluid and bicarbonate (to some extent acinar cells are also stimulated) and this is primarily via a paracrine mechanism.
What do K cells secrete?
Gastric Inhibitory Polypeptide (GIP)
What does Gastric Inhibitory Polypeptide (GIP) do?
acts via vago-vagal mechanisms to inhibit gastric motility both paracrine (and probably vago-vagal) mechanisms to potentiate glucose-stimulated insulin secretion from endocrine pancreatic β-cells.
The arrival of nutrients is sensed by … cells
K
What are the three types of bariatric surgery?
Adjustable gastric band (AGB/LAGB)
Verticle Sleeve Gastrenectomy (VSG)
Roux-en Y Gastric Bypass (RYGB)
Vagal pathways send sensory information to the ENS via what neurons?
via intrinsic primary afferent (sensory) neurons (that follow spinal and vagal nerve connections).
Vagal pathways send sensory information to the CNS via what neurons?
via extrinsic primary afferent neurons (that follow spinal and vagal nerve connections).
Vagal pathways send messages to what nervous systems?
ENS and CNS
Pathways from the gastrointestinal tract project towards their destination via what neurons?
intestinofugal neurons
Pathways from the gastrointestinal tract project outwards, via intestinofugal neurons, to what destinations?
CNS, sympathetic ganglia, gallbladder, pancreas and trachea.
T or F
Some neurons in sympathetic prevertebral ganglia (PVG) receive both CNS and ENS inputs.
T
The small & large intestines contain full … reflex circuits.
ENS
What types of neurons are found in the ENS?
Sensory neurons, interneurons, motor neurons, and secretomotor neurons
What role do sensory neurons play in the ENS?
receive signals from the lumen of the GIT from mechanical and sensory stimuli
What part/s of the ENS contain sensory neurons?
the submucosal plexus and the myenteric plexus
What role do interneurons play in the ENS?
allow actions to be coordinated along a length of intestine
What are interneurons?
neurons that connect sensory neurons with motor neurons
What do motor neurons do?
synapse on smooth muscle cells causing them to contract or relax
What role do secretomotor neurons play in the ENS?
control vasodilation of blood vessels as well as fluid secretion across the mucosa
What does the acronym IPANs stand for?
intrinsic primary afferent neurons
The myenteric plexus is primarily responsible for …. while the submucosal plexus is involved in ….
control of motility
secretion, blood flow and immune control
T of F
Only the submucosal plexus has neural wiring that allows for local functioning of the circuit without the need for input from other parts of the nervous system.
F
The myenteric plexus has this also
What type of receptors are Nicotinic receptors?
Ion channel acetyl-choline receptor
What type of receptors are Muscarinic receptors?
GPCR acetyl-choline receptor
What type of receptors are Metabotropic receptors?
GPCR
What type of receptors are ionotropic receptors?
Ion channels
One way to think about the division between ‘upper’ and ‘lower’ gastrointestinal tract is to consider the primary nervous control of these divisions. The ENS is involved in primary control of which division?
The lower
T or F
In very broad terms the parasympathetic nervous system reduces GI tract activity. While the sympathetic nervous system increases activity in the gastrointestinal tract.
F
The parasympathetic nervous system increases activity in the gastrointestinal tract while the sympathetic nervous system reduces GI tract activity.
What is the primary neurotransmitter (postganglionic) from the sympathetic nervous system?
Norepinephrine
What is the primary neurotransmitter from the parasympathetic nervous system?
Acetylcholine
Vagal efferents typically release …, the key neurotransmitter involved in co-ordination of peristalsis by the myenteric plexus in the gastrointestinal tract.
acetylcholine
Vagal efferent also participate in non-adrenergic non-cholinergic (NANC) signalling. Typically, the neurotransmitters involved in NANC are considered to be?
Nitric oxide and purines
Typically, hormonal control of the GI tract is divided into what three sections?
endocrine, paracrine and neurocrine.
T or F
The pancreas is a dual function organ.
T
Pancreatic exocrine secretions are made by … cells that release pancreatic enzymes into the … system of the pancreas.
acinar
ductal
Exocrine pancreatic secretion is regulated by … pathways and … control.
vagal
hormonal
How do pancreatic secretions enter the duodenum?
via collecting accesory pancreatic ducts which merge with the common bile duct.
About …% of pancreatic exocrine secretions into the duodenum occur during the cephalic phase of digestion (under vagal control).
25%
About …% of pancreatic exocrine secretions into the duodenum occur during the gastric phase (gastrin and vagal control) of digestion.
10%
About …% of pancreatic exocrine secretions into the duodenum occur during the intestinal phase (CCK, secretin and vagal control) of digestion.
65%
The Islets of Langerhans contain what three major cell types?
alpha-cells that produce glucagon, beta-cells that produce insulin and amylin and delta-cells that produce somatostatin.
Other than the three main ones. What other two cell types are found in the Islets of Langerhans?
γ (gama)-cells that produce pancreatic polypeptide
ε (epsilon) -cells that produce ghrelin
Islets are responsive to both … signals (and glucose) carried in the blood as well as … signalling (particularly important for the incretin effect).
endocrine
vagal
Inflow of blood to the liver occurs from both the … artery and the …. vein,
hepatic
hepatic portal
The hepatic artery is a branch of the … aorta
Thoracic
The hepatic portal vein collects all the nutrients absorbed in the …. as well as the outflow from the … and …
gastrointestina tract
spleen and pancreas
T or F
The liver is located above the majority of the gastrointestinal tract.
T
Outflow from the liver occurs through the … vein, which joins the inferior ….
hepatic
vena cava
Outflow from the …, … & … all pass through the liver before this venous supply reaches the heart.
gastro-intestinal tract, pancreas and spleen
… in the liver are the major site for expression of enzymes responsible for xenobiotic metabolism.
hepatocytes
T or F
Any drugs that are absorbed via the GIT into the bloodstream will be subject to metabolism in the liver before they pass into general circulation.
T
aka first-pass metabolism
… and …. vitamins are repackaged into chylomicrons in enterocytes and these are secreted into the lymphatic system, which ultimately reaches the circulation via the subclavian veins, bypassing the liver.
fats and fat-soluble vitamins
What is chylomicron?
aka ultra low-density lipoproteins (ULDL), consist of triglycerides (85–92%), phospholipids (6–12%), cholesterol (1–3%), and proteins (1–2%). They transport dietary lipids from the intestines to other locations in the body. Enable fats and cholesterol to move within the water-based solution of the bloodstream.
What is billrubin?
Bilirubin (bil-ih-ROO-bin) is a yellowish pigment that is made during the breakdown of red blood cells.
What is bile mainly composed of?
Bile is comprised mainly of water but with a small amount of bile salts, bilirubin (see red blood cell breakdown tab) and fats.
All bile acids are … metabolites
cholesterol
Without …, fats, and fat soluble vitamins, are very poorly absorbed from the diet.
bile
Why does bile help absorb fats and fat soluble vitamins?
act as surfactants to emulsify fat droplets to provide access to pancreatic lipases for digestion, which is required for absorption.
What is the main glucoregulatory organ of the body?
The liver
Our brain requires glucose for …% of its energy needs
80%
T or F
Erythrocytes contain mitochondria
F
Erythrocytes contain no mitochondria
Erythrocytes are reliant on what two pathways/systems for energy?
glycolysis and pentose phosphate pathways for energy.
Why is our brain so reliant on glucose for energy?
Free fatty acids are poorly transported across the BBB
Plasma concentrations of other energy sources are low
What organ (apart from the brain) is responsible for sensing hypoglycemia?
The pancreas
How does the pancreas respond to hypoglycemia?
Alpha cells in the pancreas secrete more glucagon which suppresses insulin thus raising blood sugar lvls.
What affect does glucagon have on the liver?
Inhibits glycogenesis
Stimulates glycogenolysis and gluconeogenesis
What does the brain do in response to hypoglycemia?
Sympathetic stimulation (direct and via catecholamine release from adrenals)
What effect does catecholamine release from adrenals and sympathetic stimulation have on the liver?
Stimulates glycogenolysis and gluconeogenesis
What effect does catecholamine release from adrenals and sympathetic stimulation have on the kidneys?
stimulates gluconeogenesis
What effect does catecholamine release from adrenals and sympathetic stimulation have on muscle?
inhibits glucose uptake
stimulates glycogenolysis
What effect does catecholamine release from adrenals and sympathetic stimulation have on adipose tissue?
lipolysis
What four main anatomical targets are affected when the brain stimulates the sympathetic nervous system and releases catecholamine from adrenals in response to hypoglycemia?
Adipose tissue, muscles, liver and kidneys
What does the pancreas do in response to hyperglycemia?
Increases secretion of insulin which suppresses glucagon
What does the liver do in response to an increase in insulin?
stimulates glycogenesis
inhibits glycogenolysis and gluconeogenesis
What do the kidneys do in response to an increase in insulin?
Inhibit gluconeogenesis
What do the muscles do in response to an increase in insulin?
stimulate glucose uptake (glycogenesis)
What does adipose tissue do in response to an increase in insulin?
Stimulates glucose uptake (lipogenesis)
Inhibits lipolysis
What do the CNS do in response to an increase in insulin?
hepatic glucose production
peripheral glucose reuptake
What does the GIT do in response to hyperglycaemia?
Secretes incretin hormones (GIP and GLP-1)
What effects do the secretion of incretin hormones (GIP and GLP-1) have on the pancreas?
Protentiate GSIS
Inhibits glucagon secretion
What effects do the secretion of incretin hormones (GIP and GLP-1) have on the CNS?
Appetite, satiety
Gastric emptying
HGP
T or F
Proteins can be stored in the body
F
T or F
Fats can be stored in the body
T
Easily stored
T or F
Carbohydrates can be stored in the body
T
Albeit limitedly
T or F
Proteins are dispensable in the body
F
T or F
Fats are dispensable in the body
F
T or F
Carbohydrates are dispensable in the body
T
Completely dispensable
What is the final digestion product of proteins?
Amino acids
What is the final digestion product of carbohydrates?
Sugars (e.g. glucose)
What is the final digestion product of fats?
Fatty acids and glycerol
ATP is primarily produced by…
oxidative phosphorylation
T or F
Macronutrients are oxidised via a series of controlled reactions in the cell
T
What is the respiratory exchange ratio (RER)?
CO2 per O2
Immediately after a mixed meal RER is close to … whereas during a fasting state it is …
1
0.7
Does fat or glycogen store more energy?
Fat stores 6x more energy than glycogen
T or F
Fat can be stored anhydrous in the body?
T
Glucose is stored as … in the … and …
glycogen
liver and mucscle
T or F
The chemoreceptor trigger zone is also commonly known as the area postrema.
T
Omeprazole is a … proton pump inhibitor
H+/K+-ATPase
The main effect of proton pump inhibition is to…
Decrease acid secretion into the stomach, increasing pH
Increasing the stomach pH slows gastric emptying because?
Pepsinogen is less efficiently cleaved to pepsin at higher pH and slower digestion is sensed in the duodenum, causing a vago-vagal reflex to slow gastric emptying.
T or F
Although Metoclopramide has pro-cholinergic activity, it does not typically increase gastric acid secretion.
T
What is the clinical definition of dyspepsia?
recurring indigestion with no obvious cause.
Is dyspepsia more common in women or men?
women
Which is more common, dyspepsia or gastritis?
dyspepsia
T or F
Gastritis is more common in younger people.
F
Older people
T or F
It is quite common for people to experience acid reflux from time to time.
T
Although persistent or chronic acid reflux, that would meet the clinical definition of GORD, is not that common.
