Lecture 22: The Small Intestine Flashcards
What are the three regions of the small intestine?
- duodenum
- jejunum
- ileum
What is the longest region of the small intestine?
ileum
In which region of the small intestine does most of the absorption take place?
in the jejunum
Is the duodenum retroperitoneum of intraperitoneum?
retroperitoneum
Why is the duodenum retroperitoneum?
Because it does not move, it is just a receiving chamber
The duodenum is fixed and bound to the _______ _______ _______ but it has the _______ _________ which is covering the anterior surface
posterior abdominal wall
visceral peritoneum
Which parts of the small intestine are retroperitoneum and which parts are intraperitoneum?
The duodenum is retroperitoneum and the ileum and jejunum are intraperitoneum
What are the two movements of the small intestine?
- peristalsis (propulsion of food along the small intestine)
- segmentation (mixing pattern)
The small intestine is held in place by
mesentary
What four things are in the messentery?
- arteries
- veins
- nerves
- lymphatics
What are the purposes of the mesenteric arteries and veins?
To deliver oxygenated blood to the mesentery and to remove deoxygenated, nutrient rich blood
We need to protect the mucosa in the small intestine from the chyme. What features are present in the small intestine that allow us to do this?
There are goblet cells secreting mucus and glands in the submucosa that transports mucus to the surface
Mucus secreting glands are only present in which part of the intestine?
the duodenum
What is present that can help neutralise the pH of the chyme?
bicarbonate from the pancreas
By the time the food reaches the small intestine, all the mechanical digestion has taken place but chemical digestion is still required. What do we need to do that?
enzymes
How is the small intestine modified for secretion and absorption?
increase surface area by
- being long
- fold the mucosa to make plicae circulares
- fold the mucosa is the villi
- microvilli
What are the plicae circulares?
permanent large folds of the small intestine
The plicae circulares have a core of ______ with overlying _________
submucosa
mucosa
What is the purpose of the plicae circulares?
to increase surface area and to spiral food as it is travelling through the lumen and slowing down its passage so we have more time for digestion and absorption
Are the plicae circulares permanent or not?
yes they are
What is the fold in the mucosa that increases surface area for excretion and absorption?
villi
What are villi including what they are fold of?
they are folds of mucosa with a core of lamina propria with epithelium covering the surface
What is the consequence to the villi when the muscularis mucosa contract?
the villi move back and forward to be exposed to all the luminal contents
The core of each villi is made of the lamina propria. What is this made of?
fibrous connective tissue
What does each vessel contain?
lymph lacteal
capillary network
What does the lymph vessel contain?
The products of fat digestion
What are the products of fat digestion?
fatty acids and monoglycerides
What does the capillary network carry?
the products of protein and carbohydrate digestion
What are the products of protein and carbohydrate digestion?
amino acids and monosaccharides
Where does nutrient rich, deoxygenated blood absorbed in the small intestine enter?
The mesenteric veins
Where do the mesenteric veins carrying nutrient rich, deoxygenated blood drain into?
The hepatic portal vein
What happens when the nutrient rich, oxygenated blood is carried to the hepatic portal vein in the liver?
It is detoxified
Describe the lymph drainage
The products drain into the central lymphatic lacteal which drains into the lymphatic vessels and then into the cysterna chyli at the base of the thoracic duct. Then they travel into the left subclavian vein and enter the blood vascular system
What is the role of mesentery?
connect an organ to a body wall
About how long is the small intestine?
6m
the folds in the submucosa are called
plicae circulares
the folds in the mucosa (not the muscularis mucosa) are called
villi
How can you give each cell a bigger surface area without increasing the volume of the cell?
by having microvilli on the apical surface of the simple columnar epithelium of the small intestine to further increase the surface area
What is glycocalyx and where is it located?
it is associated with the microvilli
- it is glycoproteins with branched filaments
- its role is to tether enzymes, to break down anything that touched them in contact digestion
The nutrients from the lumen has to pass over the plasma membrane of the epithelium. Describe the PM including its permeability and its features
it is selectively permeable and it has proteins (channels and transporters)
There are ______ junctions holing the epithelium togethr
tight
What can diffuse over the plasma membrane and what can’t?
Lipid soluble can (the products of digestion from fat) but water soluble can not (the products of digestion from carbohydrates and proteins)
What is the paracellular pathway?
The pathway in between cells
What are 5 epithelium of the small intestine?
enterocytes goblet cells stem cells paneth cells endocrine cells
What are enterocytes?
they are the simple columnar epithelium with microvilli that are for absorbtion
What is the purpose of the goblet cells?
they secrete mucous for protection
What is the purpose of the stem cells?
to divide to replace all cell types
What is the purpose of the paneth cells?
they secrete granules and antibacterial enzymes for an immune role
What is the purpose of the endocrine cells?
they secrete hormones into the blood vessels in the lamina propria for regulation of the function of the small intestine or the stomach
What are the folds in the apical plasma membrane of the epithelium called?
microvilli
What is at the base of the villi?
crypts
What are the cell types in the crypts?
- stem cells
- paneth cells
