We first see what is the Small Intestine – It connects the stomach and the large intestine. It is called as Small because it is smaller than Large Intestine. It is divided into three sections (duodenum, jejunum & ileum). Three parts are as follows: The three sections of the small intestine look similar to each other at a microscopic level, but there are some important differences in terms of structures. The jejunum and ileum do not have Brunner\'s glands in the submucosa, while the ileum has Peyer\'s patches in the mucosa, but the duodenum and jejunum do not. Now we will see the structure in detail: The small intestine has four tissue layers as follows Brunner\'s Glands Brunner\'s glands (or duodenal glands) are compound tubular sub-mucosal glands found in the duodenum. The main function of these glands is to produce a mucus-rich, alkaline secretion (containing bicarbonate) in order to neutralize the acidic content of chyme that is introduced into the duodenum from the stomach, and to provide an alkaline condition for optimal intestinal enzyme activity, thus enabling absorption to take place and lubricate the intestinal walls. Peyer\'s Patches Peyer\'s patches are organized lymph nodules. They are aggregations of lymphoid tissue that are found in the lowest portion of the small intestine, which differentiate the ileum from the duodenum and jejunum. Because the lumen of the gastrointestinal tract is exposed to the external environment, much of it is populated with potentially pathogenic microorganisms. Peyer\'s patches function as the immune surveillance system of the intestinal lumen and facilitate the generation of the immune response within the mucosa. Intestinal Villi Intestinal villi (singular: villus) are tiny, finger-like projections that protrude from the epithelial lining of the mucosa. Each villus is approximately 0.5–1.6 mm in length and has many microvilli (singular: microvillus), each of which are much smaller than a single villus. Explain how structure of the intestinal lining enhances surface area. Now we will see how this Villi are important for enhancing the surface area in details. Villi increase the internal surface area of the intestinal walls. This increased surface area allows for more intestinal wall area to be available for absorption. An increased absorptive area is useful because digested nutrients (including sugars and amino acids) pass into the villi, which is semi- permeable, through diffusion, which is effective only at short distances. Microvilli are microscopic extensions of the outer surface of the absorptive cells that line each villus. Because of their brush like appearance (microscopically), the microvilli facing the lumen form the brush border of the small intestine. Like the villi; the microvilli increase the surface area over which digestion and absorption take place. In other words, the increased surface area (in contact with the fluid in the lumen) decreases the average distance traveled by the nutrient.

1. We first see what is the Small Intestine – It connects the stomach and the large intestine. It is
called as Small because it is smaller than Large Intestine. It is divided into three sections
(duodenum, jejunum & ileum).
Three parts are as follows:
The three sections of the small intestine look similar to each other at a microscopic level, but
there are some important differences in terms of structures. The jejunum and ileum do not have
Brunner's glands in the submucosa, while the ileum has Peyer's patches in the mucosa, but the
duodenum and jejunum do not.
Now we will see the structure in detail: The small intestine has four tissue layers as follows
Brunner's Glands
Brunner's glands (or duodenal glands) are compound tubular sub-mucosal glands found in the
duodenum. The main function of these glands is to produce a mucus-rich, alkaline secretion
(containing bicarbonate) in order to neutralize the acidic content of chyme that is introduced into
the duodenum from the stomach, and to provide an alkaline condition for optimal intestinal
enzyme activity, thus enabling absorption to take place and lubricate the intestinal walls.
Peyer's Patches
Peyer's patches are organized lymph nodules. They are aggregations of lymphoid tissue that are
found in the lowest portion of the small intestine, which differentiate the ileum from the
duodenum and jejunum.
Because the lumen of the gastrointestinal tract is exposed to the external environment, much of it
is populated with potentially pathogenic microorganisms. Peyer's patches function as the
immune surveillance system of the intestinal lumen and facilitate the generation of the immune
response within the mucosa.
Intestinal Villi
Intestinal villi (singular: villus) are tiny, finger-like projections that protrude from the epithelial
lining of the mucosa. Each villus is approximately 0.5–1.6 mm in length and has many microvilli
(singular: microvillus), each of which are much smaller than a single villus.
Explain how structure of the intestinal lining enhances surface area.
Now we will see how this Villi are important for enhancing the surface area in details. Villi
increase the internal surface area of the intestinal walls. This increased surface area allows for
more intestinal wall area to be available for absorption. An increased absorptive area is useful
because digested nutrients (including sugars and amino acids) pass into the villi, which is semi-
permeable, through diffusion, which is effective only at short distances.
Microvilli are microscopic extensions of the outer surface of the absorptive cells that line each
villus. Because of their brush like appearance (microscopically), the microvilli facing the lumen

2. form the brush border of the small intestine. Like the villi; the microvilli increase the surface
area over which digestion and absorption take place.
In other words, the increased surface area (in contact with the fluid in the lumen) decreases the
average distance traveled by the nutrient molecules, so the effectiveness of diffusion increases.
The villi are connected to blood vessels that carry the nutrients away in the circulating blood.
The villi of the mucosa have the following characteristics and because of these characteristics
Villi are responsible to carrying out various functions related to absorption, digestion and
secretion of certain enzymes:
We will briefly see what are the cells types of an outer epithelial layer (facing the lumen) of
Villi:
1) Absorptive cells, the primary cell type of the epithelial layer, synthesize digestive enzymes
called brush border enzymes that become embedded in the plasma membranes around the
microvilli. Various nutrients in the chyme that move over the microvilli are broken down by
these brush border enzymes and subsequently absorbed.
2) Goblet cells, located throughout the epithelial layer, secrete mucus that helps protect the
epithelial layer from digestion.
3) Enteroendocrine cells secrete hormones into blood vessels that penetrate the villus.
4) Paneth cells, located in the epithelial layer facing the intestinal crypts, secrete lysozyme, an
enzyme that destroys bacteria.
5) An inner core of lamina propria (connective tissues) contains blood capillaries and a small
lymphatic capillary called a lacteal.
This is how villi in the small intestine greatly increase the surface area of the small intestine,
which in turn greatly increases the absorption capacity of the tissues.
Solution
We first see what is the Small Intestine – It connects the stomach and the large intestine. It is
called as Small because it is smaller than Large Intestine. It is divided into three sections
(duodenum, jejunum & ileum).
Three parts are as follows:

3. The three sections of the small intestine look similar to each other at a microscopic level, but
there are some important differences in terms of structures. The jejunum and ileum do not have
Brunner's glands in the submucosa, while the ileum has Peyer's patches in the mucosa, but the
duodenum and jejunum do not.
Now we will see the structure in detail: The small intestine has four tissue layers as follows
Brunner's Glands
Brunner's glands (or duodenal glands) are compound tubular sub-mucosal glands found in the
duodenum. The main function of these glands is to produce a mucus-rich, alkaline secretion
(containing bicarbonate) in order to neutralize the acidic content of chyme that is introduced into
the duodenum from the stomach, and to provide an alkaline condition for optimal intestinal
enzyme activity, thus enabling absorption to take place and lubricate the intestinal walls.
Peyer's Patches
Peyer's patches are organized lymph nodules. They are aggregations of lymphoid tissue that are
found in the lowest portion of the small intestine, which differentiate the ileum from the
duodenum and jejunum.
Because the lumen of the gastrointestinal tract is exposed to the external environment, much of it
is populated with potentially pathogenic microorganisms. Peyer's patches function as the
immune surveillance system of the intestinal lumen and facilitate the generation of the immune
response within the mucosa.
Intestinal Villi
Intestinal villi (singular: villus) are tiny, finger-like projections that protrude from the epithelial
lining of the mucosa. Each villus is approximately 0.5–1.6 mm in length and has many microvilli
(singular: microvillus), each of which are much smaller than a single villus.
Explain how structure of the intestinal lining enhances surface area.
Now we will see how this Villi are important for enhancing the surface area in details. Villi
increase the internal surface area of the intestinal walls. This increased surface area allows for
more intestinal wall area to be available for absorption. An increased absorptive area is useful
because digested nutrients (including sugars and amino acids) pass into the villi, which is semi-
permeable, through diffusion, which is effective only at short distances.
Microvilli are microscopic extensions of the outer surface of the absorptive cells that line each
villus. Because of their brush like appearance (microscopically), the microvilli facing the lumen
form the brush border of the small intestine. Like the villi; the microvilli increase the surface
area over which digestion and absorption take place.
In other words, the increased surface area (in contact with the fluid in the lumen) decreases the
average distance traveled by the nutrient molecules, so the effectiveness of diffusion increases.
The villi are connected to blood vessels that carry the nutrients away in the circulating blood.

4. The villi of the mucosa have the following characteristics and because of these characteristics
Villi are responsible to carrying out various functions related to absorption, digestion and
secretion of certain enzymes:
We will briefly see what are the cells types of an outer epithelial layer (facing the lumen) of
Villi:
1) Absorptive cells, the primary cell type of the epithelial layer, synthesize digestive enzymes
called brush border enzymes that become embedded in the plasma membranes around the
microvilli. Various nutrients in the chyme that move over the microvilli are broken down by
these brush border enzymes and subsequently absorbed.
2) Goblet cells, located throughout the epithelial layer, secrete mucus that helps protect the
epithelial layer from digestion.
3) Enteroendocrine cells secrete hormones into blood vessels that penetrate the villus.
4) Paneth cells, located in the epithelial layer facing the intestinal crypts, secrete lysozyme, an
enzyme that destroys bacteria.
5) An inner core of lamina propria (connective tissues) contains blood capillaries and a small
lymphatic capillary called a lacteal.
This is how villi in the small intestine greatly increase the surface area of the small intestine,
which in turn greatly increases the absorption capacity of the tissues.