Physiology - gastrointestinal tract A Flashcards
What us the role of Gastrin?
Stimulate gastric acid secretion and growth of gastric mucosa
Where is gastrin produce and what triggers the production?
In G cells of stomach in responce to ingestion of food and protein
What is the role of Cholecystokinin CCK
Contract gallbladder and inhibit stomach contractions
Where is CCK produce and when?
Duodenum and jejunum in response to fat, fatty acids and monoglycerides
What is the role of secretin?
Promotes pancreatic secreation of bicarbonate to neutralize acid in small intestine
Where is secretin secreated from and when?
By S cells in mucosa of duodenum in response to acidic gastric juice
What is the role of Gastric inhibitory peptide (GIP)?
Reduce motor activity of stomach (also stimulate insulin secretion)
Where is GIP secreted and in response to what?
By mucosa of the upper small intestine in response to fatty acids, amino acids and to some extent carbohydrates
Where are digestive enzymes secreted?
From most areas of alimentary tract
What is the role of mucus in alimentary tract?
Lubrication and protection
What affect the type of enzyme and the quantity?
The amount of food and the composition
Where are single-cell mucus glands located?
On surface of epithelium in most part of gastrointestinal tract. Called mucous glands
What do single-cell musuc glads do?
Excrude mucus directly onto epithelium surface to act as a lubricant. Responds to local irritation.
What do gastric pits do?
Small pores called gastric pits contain many exocrine cells that secrete digestive enzymes and hydrochloric acid into the lumen, or hollow region, of the stomach.
Invaginations of the epithelium into submucosa
Where are the tubular glands?
In the stomach and upper part duodenum
What are glands?
a collection of cells or an organ responsible for secretions and excretions
What makes the shape of tubular glands?
cells of a consistant shape that form a uniform tubular lumen
What is secreted from tubular glands?
Acid and pepsinogens
What are some roles of salivary glands, pancreas and liver?
Provide secretion for digestion and emulsification of food
What stimulate the production of mucus ?
When food touch the surface
Connection between gastric pits and gastric glands?
The glands themselves are in the lamina propria of the mucous membrane and they open into the bases of the gastric pits formed by the epithelium
How is the enteric nervous system stimulated by local epithelial stimulation?
- Tactile stimulation
- Chemical irritation
- Distention of the gut wall
Where are the glands most affected by parasympathic nervs?
upper portion of the tract (salivary glands, esophageal glands, gastric glands and pancreas)
How does parasympathic nerves stimulate alimentary tract?
Increases rate of alimentary glandular secretion
How does sympathic nerves stimulate alimentary glands?
Cause slight to moderate increase by some of the local glands - short
But at the same time also shrink the blood vessle flow so long term it reduces the production of the glands
What happens if there is a copious secretion by the glands as a response to parasympathic or horminal stimulation?
Superimposed sympathic stimulation usually reduces secretion
Where are hormones liberated and when?
From the gastrointestinal mucusa in response of food in lumen
Where are the hormones absorbed ?
Absorbed into blood and carries to glands where they stimulate secretion
When is it important to increase the output of gastric juice and pancreatic juice
when food enters the stomach or duodenum
What is mucus?
Water, electrolytes, and a mixture of several glycoproteins that are composed of large polysaccharides bound with much smaller quantities of protein
What does mucus inhibit/provide?
the ability to allow easy slippage of food along the gastrointestinal tract and to prevent excoriative or chemical damage to the epithelium
What is beneficial about glycoproteins of mucus?
have amphoteric properties, which means that they are capable of buffering small amounts of either acids or alkalies
How does mucus neutralize acids?
Often contains moderate quantities of bicarbonate ions, which specifically neutralize acids.
What’s beneficial about adherant quality of mucus?
make it adhere tightly to the food or other particles and to spread as a thin film over the surfaces.
Also causes fecal particles to adhere to one another to form the feces
Saliva contains two major types of protein secretion, which?
- ptyalian (an alpha-amylase) which is an enzyme digesting starches
2- mucus secretion that containes mucin for lubrication and for surface protective purposes
Saliva is especially large quantities of two ions, which?
Potassium and bicarbonate ions
Difference in sodium and chloride concentration between saliva and plasma
Concentrations of sodium and chloride ions are several times less in saliva than in plasma
What control salivary glands?
mainly parasympathic nervous signals
Those signals that induce copious salivation also moderately dilate the blood vessels
What other ways can stimulate salivation?
- taste and tactile stimuli from tungue and other area of mouth and pharynx
- in response to reflexes originating in the stomach and upper small intestines
- Can stimulate by CNS
- Ympathis stimulation can also increase a slight amount - but much less than parasympathic
What is parasympathic and sympathic nervous system a part of?
The autonomic nervous system
What is the role of kallikrein?
kallikrein secreted by the activated salivary cells, which in turn acts as an enzyme to split one of the blood proteins, an alpha2globulin, to form bradykinin, a strong vasodilator
vasodilator effect is also caused by what?
Kallikrein
Why is the increased blood flow important?
To increase the salivary production
What does Esophageal secretions consist of and why?
entirely mucous and mainly provide lubrication for swallowing
What are the role of compound glands in esophagus?
The compound glands located near the esophagogastric junction protect the esophageal wall from digestion by acidic gastric juices
Stomach mucosa has two important types of tubular glands, which?
oxyntic glands (also called gastric glands) and pyloric glands
What do the oxyntic glands do?
they are acid-forming
secrete HCl, pepsiogen, intrinsic factor and mucus (proximal 80%)
What do pyloric glands do?
Secrete mainly mucus for protection of the pyloric mucosa from the stomach acid (distal 20%) + gastrin
Another name for oxyntic cells?
parietal
Where are oxyntic glands located?
in 80% upper part of stomach (proximal = upper)
Where are pyloric glands located?
20% of the lower part of the stomach
What does peptic cells produce?
Pepsinogen
What is secreted from oxyntric glands?
- mucus - from mucus neck cells
- pepsinogen from peptic cells
- HCl and instrinsic factor from parietal (or oxyntic) cells
When is pepsinogen activated?
When it is exposed to acid –> pepsin
What is an isotonic solution ?
An isotonic solution refers to two solutions having the same osmotic pressure across a semipermeable membrane. This state allows for the free movement of water across the membrane without changing the concentration of solutes on either side.
What is the concentration of HCl?
160mol/L
What is the pH of HCl?
0.8
What is needed to concentrate the hydrogen ions?
Alot of calories!
1500 cal of energy per liter of gastric juice
Describe the mechanism of HCl
- each step of ions…
Cl- actively out
Na+ actively in
Outside negatively charged –> diffusion of K+ and Na+
Water dissociated into H+ and OH-
H+ actively exchanged for K+ (which come in again)
Water is dissociated into hydrogen and hydroxyl ions and hydrogen is actively exchanged for potassium
What is canaliculi and what happens there?
They contain an extensive secretory network (called canaliculi) from which the HCl is secreted by active transport into the stomach.
What happens to pepsinogen above pH 5?
Has lamost no proteolytic activity and becomes compleately inactivated in a short time
What activates pepsinogen?
contact with HCl
What is intrinsic factor and why is it important?
Intrinsic factor (IF), also known as gastric intrinsic factor (GIF), is a glycoprotein produced by the parietal cells of the stomach. It is necessary for the absorption of vitamin B12 later on in the ileum of the small intestine. In humans, the gastric intrinsic factor protein is encoded by the GIF gene
What can happen to individuals when their acid-producing parietal cells of stomach are destroyed ?
They develop pernicious anemia
What controls the gastric acid secretion?
endocrine and nervous signals
What is the primary function of enterochromaffin-like cells (ECL cells)?
To secrete histamine (in oxyntic glands)
The parietal cells operate in close association which cells?
enterochromaffinlike cells (ECL cells)
What is the amount of histamine secreted by the ECL cells directly related to?
Secretion of hydrochloric acid by the parietal cells
What is ECL cells stimulated by to secrete histamine?
Hormone gastrin and acetylcholine
What is secreted from G cells and where are they located?
Gastrin
located in pyloric glands in the distal end of the stomach
What is the role of histamine (one of many ofc!)
the stimulation of gastric acid secretion in the stomach
- signal to the oxyntic cells to produce acid
What regulates the secretion of pepsinogen?
- acetylcholine - released from the nerves
2. acid in the stomach
What can happen for people that have lost the ability to secrete normal amounts of acid?
Secretion of pepsinogen is also decreased
The rate of secretion of pepsinogenis strongly influenced by the amount of acid in the stomach
What is the role of the pancreatic acinar?
The pancreatic acinar cell is the functional unit of the exocrine pancreas. It synthesizes, stores, and secretes digestive enzymes. Under normal physiological conditions, digestive enzymes are activated only once they have reached the duodenum.
Whete is bicarbonate produced?
Epithelial cells in pancreatic ducts are the source of the bicarbonate and water secreted by the pancreas. Bicarbonate is a base and critical to neutralizing the acid coming into the small intestine from the stomach.
What happens with the pancreatic duct?
It joins the hepatic duct immediately before it empties into the duodenum
What is the hepatic duct?
Hepatic duct: A duct that carries bile from the liver into the common bile duct which conveys it to the duodenum (the upper part of the small intestine).
How does chyme in upper portions of small intestine affect pancreas?
Pancreatic juice is secreated as a response
The characteristics determined by types of food
What are the most important of the pancreatic enzymes for digesting proteins?
trypsin
chymotrypsin
carboxypeptidase
What do trypsin and chymotrypsin do?
Split protein into peptides of various sizes
What does carboxypeptidase do?
split peptides into individual amino acids
What does pancreatic amylase do?
hydrolyzes starches, glycogen, and most other carbohydrates to disaccharides and trisaccharides
What can pancreatic lipase do?
- it is capable of hydrolyzing neutral fat into fatty acids and monoglycerides
- split fatty acids from lipids
What do phospholipases from pancreas do?
split fatty acids from phospholipids
What does cholesterol esterase do?
Cholesterol esterase catalyzes the hydrolysis of sterol esters into their component sterols and fatty acids. The enzyme is found primarily in the pancreas, but has been detected in other tissues as well.
Why is it important that trypsinogen, chymotrypsinogen and procarboxypolypeptidase are enzymatically inactive?
Because they are proteolytic digestive enzymes that otherwise could digest the pancreas.
So should not become active until after they reach the intestine
How is trypsinogen activated?
By an enzyme called enterokinase - secreated by intestinal mucosa when chyme comes in contact with the mucosa
What is trypsin inhibitor?
A substance produced that is produced by the same cells that secrete the proteolytic enzymes
What is the chemical formula of bicarbonate?
HCO3-
