Small Intestine Structure and Function Flashcards
What functions does the pancreas have?
Endocrine and exocrine
The exocrine pancreas is responsible for
the digestive function of the pancreas
The exocrine pancreas secretes from
Acini -> ducts -> pancreatic sucts
glands via ducts, rather than directly into the blood
Pancreatic duct cells secrete bicarbonate which
What does this allow?
neutralises gastric acid and gastric contents
allows pancreatic enzymes to work
The acinar cells secrete
digestive enzymes
Acing cells contain digestive enzymes stored as
inactive zymogen granules
What does the storing of enzymes as their zymogen granules prevent?
Autodigestion of the pancreas
Enterokinase is bound to
the brush border of the duodenal enterocytes
What is the function of enterokinase?
Converts trypsinogen to trypsin
What does trypsin do?
Converts all other zymogens to their active forms
What are the different categories of pancreatic enzymes?
Proteases Nucleases Elastases Phospholipases Lipases Alpha-amylase
What is the function of proteases?
Cleave peptide bonds
What is the function of phospholipases?
Convert phospholipids to fatty acids
What is the function of lipases?
Convert triglycerides to fatty acids and glycerol
What group of pancreatic enzymes are responsible for hydrolysing DNA and RNA?
Nucleases
What group of pancreatic enzymes are responsible for converting starch to maltose and glucose?
Alpha-amylases
What group of pancreatic enzymes is responsible for collagen digestion?
Elastases
The endocrine functions of the pancreas involve the
secretion of various substances into the blood
Bicarbonate secretion is stimulated by
secretin
Zymogen secretion is stimulated by
cholecystokinin
Bicarbonate secretion is stimulated in response to
acid in the duodenum
Zymogen secretion is stimulated in response to
fat/amino acids in the duodenum
The pancreas is under neural control from vagal and local reflexes which are triggered by
arrival of organic nutrients in the duodenum
What are the three parts of the small intestine?
Duodenum
Jejunum
Ileum
What is the longest part of the small intestine?
Ileum
What are the functions of the duodenum?
Gastric acid neutralisation, digestion and iron absorption
What is the function of the jejunum?
Nutrient absorption
What is the function of the ileum?
NaCl and H2O absorption, chyme dehydration
What features of the small intestine act to enhance its absorptive surface area?
Circular folds
Villi
Microvilli
The fourth layer of the small intestine is
serosa
The small intestinal epithelia contains
crypts
What are the functions of goblet cells in the small intestine?
Create a diffusion barrier
Secrete mucous
What are lacteals?
Lymphatic capillaries found beneath the epithelial surface of the villi which absorb dietary fats
What area of the small intestine has the most extensive vasculature?
Jejunum
The villi are responsible for absorption which the crypts are responsible for
secretion
Give 6 things absorbed by the villi
NaCl Monosaccharides Amino acids Peptides Fats Vitamins Minerals Water
What is secreted by the crypt cells?
Cl ions and water
Active pancreatic enzymes aid the digestion of
fat, proteins and carbohydrates
The small intestine can exhibit both peristalsis and
segmentation
Do segmentation and peristalsis happen simultaneously or at different times?
At different times
Is peristalsis or segmentation more common during a meal?
Segmentation
Segmentation involves the
contraction and relaxation of short intestinal segments
Contraction moves the chyme into
adjacent relaxed areas on either side
What is the function of segmentation?
Thoroughly mixes intestinal contents with digestive enzymes and continuously brings chyme into contact with absorbing surface so maximises absorption
Segmentation contraction is generated by
pacemaker cells in the longitudinal muscle layer
The intestinal basic electrical rhythm produces
oscillations in the membrane potential which release an action potential and cause contraction
The action potential frequency in the intestinal basic electrical rhythm determines
the strength of contraction
The frequency of segmentation is determined by
the basic electrical rhythm
Which nervous system can increase the strength of segmentation contraction?
Parasympathetic system
What kind of mechanism is the frequency of segmentation?
Intrinsic mechanism
Peristalsis starts after
segmentation
In peristalsis, the receiving segment relaxes with
the contraction behind the bolus
Peristaltic waves are generated by
the migrating motility complex
What is the migrating motility complex?
The pattern of peristaltic activity travelling down the small intestine, which starts in the gastric antrum
Where does the migrating motility complex end?
At the terminal ileum
Does the arrival of food in the stomach cause the cessation of the migrating motility complex or segmentation?
Migrating motility complex
The migrating motility complex acts to move undigested food into the large intestine and limit
the bacterial colonisation of the small intestine
What is the hormone involved in the initiation of the migrating motility complex?
Motilin
What nerve is the main innervation from the parasympathetic system to the GI tract?
Vagus nerve
What effect does the parasympathetic system have on the GI tract?
Stimulatory
What nerve is the main innervation from the sympathetic system to the GI tract?
Splanchnic neve
What effect does the sympathetic system have on the GI tract?
Inhibitory
