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Small Intestine Flashcards

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1
Q

SMALL INTESTINE; brief description

A

The small is the intermediary between the stomach and the large intestine.

It is 5-7m long.

It consists of three parts; the duodenum, ileum and jejunum. They are almost similar histologically, showing little distinct differences in characteristics.

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2
Q

SMALL INTESTINE; function

A

The major function of the small intestine is for the FINAL digestion of food and the absorption of nutrients into the capillary network.

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3
Q

What are the structural modifications of the small intestine for absorption

A

There are three major structural modifications of the small intestine for absorption are;

Plicae circulares
Villi
Microvilli

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4
Q

PLICAE CIRCULARES

A

These are permanent, spiral longitudinal folds of mucosa and submucosa of the small intestine, which is most prominent in the jejunum.
It increases the absorptive surface area by THREE- FOLD.
It is most prominent in the proximal section of the S.I where most absorption takes place and decreases towards the ileum.

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5
Q

VILLI (brief description)

A

They are finger- like projections of the lamina propria that extends into the intestinal lumen.

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6
Q

VILLI; what it its epithelial lining

A

It is lined by SIMPLE COLUMNAR EPITHELIUM

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7
Q

VILLI; what are the cells lining the villi

A

Absorptive cells(enterocytes), plasma cells, enteroendocrine cells and goblet cells

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8
Q

VILLI; describe the core and makeup of a villus

A

It consists of LOOSE CONNECTIVE TISSUE that
contains many LYMPHATIC CAPILLARIES known as LACTEALS, Blood vessels, Lymph vessels, Lymphoid nodules, smooth muscle fibres, fibroblasts.
The villus opens into the intestinal glands

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9
Q

The villus opens into the intestinal glands, True or false

A

True

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10
Q

The epithelium of the villi is continuous with the epithelium of the intestinal glands, True or false

A

True

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11
Q

By how many fold does the villi increase the absorptive surface area of the small intestine

A

By ten fold

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12
Q

How does the distribution of the VILLI change along the length of the S.I

A

They are more prominent in the proximal portion of the S.I and decrease in HEIGHT towards the ileum this is because the rate and need for absorption decreases towards the ileum.

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13
Q

The villi are said to serve as a storehouse for chromaffin cells, True or false

A

False; they serve as a store house for immune cells (e.g, mast cells, macrophages, lymphocytes, tissue esinophils)

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14
Q

MICROVILLI; (brief description)

A

They are apical modification of absorptive cells, enterocytes.
They form a STRAITED BRUSH BORDER that’s in contact with the intestinal lumen.

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15
Q

Briefly describe the brush border

A

It is formed by the microvilli arranged on the apical surface of the absorptive cells. It is in contact with the intestinal lumen. It is covered by glyocalyx and embedded within the glycocalyx are the brush border enzymes.

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16
Q

What are the brush border enzymes

A

They are embedded within the glycocalyx covering the brush border. They are enzymes that are responsible for the digestion and breakdown of DISACCHARIDES, PEPTIDES and LIPIDS. They include; sucrases, lactases, lipases, peptidases.

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17
Q

How many microvilli are present on each enterocyte

A

3000

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18
Q

How much microvilli are present per 1mm2 of absorptive surface

A

Over 200 million

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19
Q

MICROVILLI; by how much fold does it increase the surface absorptive area

A

By 20- fold

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20
Q

PLICAE CIRCULARES; by how much fold does it increase the surface absorptive area

A

Three

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21
Q

Mention the cells that are of functional importance in the histologic make up of the S.I and play major role in the function of the S.i

A

Enterocytes, enteroendocrine cells, goblet cells, M (microfold) cells, paneth cells, regenerative cells

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22
Q

The ENTEROCYTES; brief description

A

They are the most common cells in the intestinal epithelium.
They are tall columnar cells who apices have numerous microvilli for increasing the absorptive surface area.
They have STRAITED brush border coated with glyocalyx with brush border enzymes for the digestion of food.

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23
Q

The GOBLET CELLS; brief description

A

They are mucus- producing cells with apical cytoplasm and basal nucleus. They are interpersed between the enterocytes.

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24
Q

Describe how mucus is produced by the goblet cells of the S.I

A

The goblet cells secrete mucinogen into the intestinal lumen. Mucinogen is hydrated to form mucus that lubricates the lining of the intestinal lumen.

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25
The ENTEROENDOCRINE cells; brief description
They are fewer in number and scattered throughout the epithelium and intestinal glands. They are endocrine cells i.e, hormone- secreting cells.
26
Examples of hormones secreted by the EED cells
Gastrin, cholecytokinin (cck), Gastic Inhibitory Peptide (GIP)
27
How is the microvilli of the EED cells modified for their function
The microvilli of EED cells have nutrient- sensing mechanism
28
EED cells; the nutrient- sensing mechanism of their microvilli is similar to _____
To the gustatory cells of the taste buds
29
EED cells; what is the process of how the EED cells carry out their function (hormone Secretion)
They are activated by nutrients which trigger the release of peptide factors from its basolateral surface including satiation peptides. Diffuse through the ECF to enter endo- crinally bind to receptors on nerve terminals, smooth muscle cells or other cells (paracrine).
30
What are the functions of the hormones EED cells secrete
To control guy motility To regulate the secretion of enzymes, HCl, bile and other components of digestion Produce the sense of satiety in the brain
31
PANETH cells; brief description
They are cells of INNATE immunity. They are PYRAMIDAL cells found at the bases of the intestinal glands in duodenum to ileum. They have deep- staining esinophilic granules in their cytoplasm.
32
What are the secretions of the PANETH cells and its function
They secrete anti- bacterial enzymes LYSOZYME that destroy bacteria and pathogens. They also secrete defensins, antibacterial agents, phospholipase A2 and alpha- necrosis factors.
33
What is the contribution of the PANETH cells to the functions of the S.I
Play important role in innate immunity and the regulating the microenvironment of the intestinal crypts.
34
PAYER PATCHES; brief description
They are large continuous aggregations of lymphoid nodules that extend from the lamina propria even to the submucosa
35
Which part of the S.I are peyer patches most prominent
Ileum
36
The peyer patches are covered by _____
M (microfold cells)
37
What is the function of the payer patches
They are phagocytic in nature, they phagocytose/ endocytose bacteria and present their antigens to lymphocytes for immune response.
38
_______ is responsible for the phagocytic nature of the payer patches
The overlying M- cells
39
M (MICROFOLD) cells; brief description
They are specialized epithelial cells to that overly the Lymphoid follicles of peyer patches in the ileum
40
What is the function of the M- cells
M- cells selectively endocytose antigens and transport them to the underlying lymphocytes and dendritic cells, which then migrate to the lymph node for immune response.
41
Microfold cells are derived from ______
Undifferentiated cells of the crypts of Lieberkuhn
42
REGENERATIVE CELLS; brief description
These are undifferentiated epithelial cells to that are found at the base of the intestinal glands.
43
What are the functions of the regenerative cells
They replace worn out cells of the epithelium and differentiate to give rise to the other cells types of the small intestine
44
PLASMA CELLS, B AND T- LYMPHOCYTES; brief description and function of the plasma cells
Plasma cells manufacture IgA which is transported across the glycocalyx, where it remains as immunological defense against bacteria and antigens in the lumen
45
PLASMA CELLS, B AND T- LYMPHOCYTES; brief description and function of the B and T- lymphocytes
B- and T- lymphocytes are found in the lamina propria involved in immune defense. B- lymphocytes differentiate to form plasma cells
46
What are the glands present in the S.I
``` Intestinal glands (crypts of Lieberkuhn) Duodenal (Brunner's) gland ```
47
Intestinal glands (crypts of Lieberkuhn); what is their epithelial lining
They are lined by simple columnar epithelium
48
Intestinal glands (crypts of Lieberkuhn); description
Their epithelium is continuous with the epithelium of the villi. These glands open up into the villus.
49
What cells are present in the epithelial lining of the Intestinal glands (crypts of Lieberkuhn)
Goblet cells, enterocytes, enteroendocrine cells, plasma cells, paneth cells, stem cells, e.t.c
50
Duodenal (Brunner's) glands; where are they found
As their name implies they are found primarily in the submucosa of the duodenal mucosa
51
Duodenal (Brunner's) glands; what do they secrete
The cells of the glands secrete ALKALINE FLUID | They secrete UROGASTRONE (human epidermal growth factor)
52
What is the function of the secretions of the Duodenal (Brunner's) glands
The alkaline fluid neutralizes pH of the acidic chyme coming into the duodenum. This helps maintain an optimum pH for the action of the PANCREATIC ENZYMES. Protects the mucous membrane from corrosion or erosion by acidic contents from the pylorus. Urogastrone enhances epithelial cell division and inhibits gastric HCL secretion.
53
Duodenal (Brunner's) glands; brief description
They are branches TUBULO- ACINAR glands with light- staining mucous cells. The ducts of duodenal glands penetrate the muscularis mucosae to discharge their secretory products at the base of the Intestinal glands.
54
MUCOSA; Epithelium of S.I
Simple columnar epithelium that consists of goblet cells, enterocytes and enteroendocrine cells.
55
MUCOSA; Lamina propria
Occupies the core of the villus and interstices between the numerous intestinal glands. Consists of loose connective tissue with blood vessels, lymph vessels, lacteals, nerves, smooth muscle fibres, fibroblasts, mast cells, macrophages, Lymphoid nodules
56
MUCOSA; muscularis mucosae
Inner circular and outer longitudinal layer of smooth muscle
57
Specialised function of the muscularis mucosae
Increases motility of villi Also involved in the movement of plicae circulares that help propel lymph from the lacteals into submucosal and mesenteric lymphatics.
58
SUBMUCOSA; components
Consists of larger blood vessels, lymphoid nodules (Peyer patches in ileum), duodenal glands in the duodenum, submucosal (meissner's) plexus, fibroblasts, lymphatic vessels and nerve fibers.
59
MUSCULARIS EXTERNA
It consists of inner circular and outer longitudinal layer of smooth muscles. AUERBACH (MYENTERIC) PLEXUS between the layers of smooth muscles to produce peristalsis.
60
Where is the ileocecal valve formed
At the ileocecal junction
61
How is the ileocecal Valve formed
At the ileocecal junction, the internal layer of the smooth muscle participated in the formation of the ileocecal valve.
62
The neurons of both the submucosal and myenteric plexuses are largely somatic. True/ false
False; they are largely autonomic and collectively make up the large ENS (ENTERIC NERVOUS SYSTEM)
63
EXTERNAL LAYER;
SEROSA covers all of jejunum, ileum and part of duodenum. ADVENTITIA covers the remainder part of the duodenum.
64
CLINICALS; mention the ones you know
Malabsorption disorder, Crohn disease, Lelomyomas and Celiac disease
65
Malabsorption disorder
This is inability of the enterocytes to absorb major nutrients needed by the body. For example in the malabsorption of Vitamin B12, there's inadequate production of intrinsic factor by the gastric mucosa
66
Crohn disease
Chronic inflammatory bowel disease mostly common in the colon and ileum. Excessive lymphocytic activity and inflammation occur in any or all layers of the tract wall, producing pain, localised bleeding, malabsorption and diarrhoea.
67
Lelomyomas
Benign tumors of smooth muscle cells, most common type of tumor in the stomach, small intestine may become large
68
What is the most common type of tumor in the stomach
Lelomyomas
69
Celiac disease; brief introduction
A disorder of the S. I mucosa that causes malabsorption and can lead to destruction of the villi
70
What is the cause of celiac disease
It is caused by an IMMUNE REACTION against GLUTEN, or any protein in wheat or any grain.
71
What are the clinical implications of celiac disease
There's localised inflammation due to immune reaction and this may affect the enterocytes leading to reduced nutrient absorption

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