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Flashcards in Histology Deck (36):
1

Difference in alimentary canal and digestive system

Alimentary canal- digestive tract (from oral cavity to anus) while the digestive system is the alimentary canal + the digestive glands (salivary, liver, pancreas, gallbladder)

2

What are the four layers throughout the GI tract



1.Mucosa- which consists of epithelium, lamina propria and muscularis mucosa
2.Submucosa– dense irregular CT
3.Muscularis Externa– which has an inner circular and an outer longitudinal layer
4.Serosa (or Adventitia)– mesenteric covering
 

3

Features of the mucosa

Has three main components- epithelium and lamina propria and muscularis mucosa

Epithelia function


1. barrier between lumen (environment) and body tissues –keeps out pathogens, antigens, toxins, encloses undigested food. Maintains barrier via tight junctions
2.protection from abrasion via stratified type of epithelia
3.absorption – of nutrients and water
4.secretion – via glandular tissue
. Provides lubrication, enzymes, HCl, buffer,
hormones

 

 

 

4

What does the lamina propria house?


1.Microvasculature – for nutrient absorption
2.Lacteals-- lipid uptake
3.Glands (are embedded in and surrounded by LP)
4.Diffuse lymphatic tissue (lymphocytes, plasma cells)
5.Lymphatic Nodules with germinal centers
-Both diffuse and nodular lymphatic tissue in the GI tract is called Gut-Associated Lymphatic Tissue (
GALT)
6. Other leucocytes that function in CT compartments
 

5

Two locations where there is an abrupt change in epithelium

Esophageal-cardiac and the rectal-anal junction

6

Features of the muscularis mucosa

Part of the mucosa (with epithelium and lamina propria)

 

1. Inner circular and outter longitudinal smooth muscle

2. Functions- contraction of the muscularis mucosa produces movement that make transient ridges and facilitates absoption/secretion (NOT FOR PERISTALIC MOVEMENT)

7

Features of the submucosa and  what does it contain

Dense irrefular CT layer (fibroblast and collagen)

1. larger blood vessels (which send/receive branches to/from other three layers)
2.Lymphatics
3.Submucosal nerve plexus comprised of parasympathetic ganglia (nerve cell bodies) and nerve fibers (both motor and sensory)- controls mucosal/submucosal motility and secretory activity of glands
4.Submucosal glands (present only in selected regions of GI tract)
 

8

Features of the muscularis externa

3 main components

1. Inner circular layer spirals around the gut tube- contracts to constrict the lumen--- Also forms sphincters 

2 Outter longitudinal layer that contracts to shorten the tube (peristalsis)

3. Myenteric nerve plexus- located between the two layers of muscle. Comprised of parasym ganglia and nerve fibers (sensroy and motor) and also has sympathetic input that controls mucosa and submucosa

9

Function of the outermost layer of the gut tube. What does it suspend?

Serosa- has a thin layer of squamous epithelium that prodcues serous fluid lubricate that reduces friction

 

Serous covers protions of the GI tract suspended in the peritoneal cavity (intraperitoneal)

10

What is adventitia? What organs have it? Difference between serosa

Dense irregular CT that is found in organs fixed to abdominal wall-- retroperitoneal.

If found between two organs it acts to adhere them where it may have adipose as a shockabsorber rather than the dense CT

11

When would an organ have both serosal and adventitia coverings?

 

Organs/parts of organs that have both coverings? (4)

When one surface is bound to another organ and the other is suspended.

The gallbladder is adventitia where it is bound to th eliver but serosa the rest of the surface.

 

Ascending, descengin and esophagus have both coverings

12

What is the gut mainly controlled by? How is this control center organized?

by the enteric nervous system which is self contained system comprised of repeating ganglia organized into two plexuses 1. Submucosal and 2. Myenteric

13

Features of the submucosal

It's one of the plexuses that make the enteric system

AKA Mesissner

 

1. has neuronal cell bodies located in the submucosa
2. Motor component: controls mucosal and submucosalgland secretion and blood flow
3. Sensory component: consists of mucosal mechanosensitive neurons (convey info
regarding luminal contents, secretory status)
 

14

Features of the myenteric

AKA the Auerbachs

1. Has nueronal cells between the circular and longitudinal layers of the muscularis externa

2. Motor component that controsl the GI motility (contraction and relaxatin)

3. Sensory component that controsl the tension-senstivie neurons and the chemosenstive neurons

15

What other innervation does enteric system have except self?

Self contrain through the submucosal and myenteric plexus but also parasym and sym

 

Para syme- 1. via vagus 2. Stimulates peristalsos and inhibits sphincters 3. Triggers secretory

Sym- 1. via splanchnic nerves, inhibits peristalisis, and activates sphincters

16

Vascular and lymphatics of the gut

Aterial is from the celiac trunk and segmetnal branches of the superior and inferior mesenteric arteries

 

Lymphatics- lacteals in the villus of the SI. Provide route for lipds from intestinal absorptive cells where they join proteins to make CHYLMICRO and drain externally to the musculars and into the mesenteric lympaics to the para-aortic lymphatics to the thoracic duct into genreal circulation

17

Function of esophagus

Type of epothelium? And why?

What's special about the proximal side?


Esophagusa fixed tube that conveys food/liquid from the pharynx to the stomach

Has stratified (non keritinzied epithelium) that provides from abrasion as the bolus passes down

 

The proximal  has thick muscularis mucosa to aid in swallowing

Upper 1/3 muscularis externa is skeletal muscle
 

18

What happens at the esophageal cardiac junction?

How is it protected>

There is an abrupt change in epithlium from stratified squamous to simple columnar

 

The esophageal glands in the submucosa secrete neutral pH mucus protecting the junctional region from the stoamch acids

 

The muscularis externa becomes thickened to form the inferior esophageal sphincter

19

Location and function of the stomach

What are the parts



Stomach-- The stomach is an expanded part of the gut tube and lies beneath the diaphragm.

Function: mixes and partially digests food to produce a mixture called chyme
.
It has three histologically distinct regions:
1.Cardiac region

2.Fundic/Body region
3.Pyloric region
 

20

4 distinguishing features of the stomach

1. Epothelium comprised of surface mucus cells and gastric gland which are embedded in the lamina propria

2. Longitudinal submucosal folds that are called rugae are present that allow the stoamch to expand when food is present

3. Muscularis externa has three poorly distinguished layers. Inner oblique, middle circular, and outer longitudinal

4. Outter most is serosa

21

Special features of the cardiac region

Cardiac gastric glands are shallow simple mucus glands form gastric pits

Esophageal glands in the submucosa under transition zone

22

Features of the fundic region of the stomach

1. Gastric pits 2-3 gastric glands

2. Mucus gastric cells line the lumen

3. Relatively thick mucosa due to the bits and fundic glands

 

Cells present

1 Mucus neck cells

2. Parietal- upper half of glands

3. Cheif- bottom half of glands produce pepsinogen and lipase

4. Enteroendorcine cells- usually in bottom half secrete across basal lamina

G-cells- make gastrin that produces HCl

D Cells- produces somatostain that inhibits gastrin

Enterochromaffin- produce histamine which stimulates HCl

23

Pyloric features

Shallow glands

Simple tubular glands that appear s-curves

Secrete highly basic mucus to neutralize the acidity of chyme before it enters the duodenum

 

 

No epithelial transition here

24

Histo of Stomach Wall Identify

25

Cells of the stomach... Note their positioning

26

What increases the SA of the SI on a gross level?

What about cellular level?

What glands are present?

Gross level SA inrcease bu the submucosal folds call plicae circularis which are mucosal villa that protrude from the itnestinal surface

 

Cellular level by microvilli of columnar intestinal absorptive cells that populate the epithelium

SI has intestinal glands call crypts that orginate at the base of villi and protrude the underlying lamina propria

27

Cell types in the crpyts of the SI


1.absorptive cells (enterocytes): located both on villi and in crypts; have microvillus
border, produce glycoproteins which reside in apical plasma membrane
a.crypt enterocytes secrete water, electrolytes
b.villus enterocytes absorb nutrients and water
2.Goblet cells: located on villi; produce mucus to protect and lubricate gut tube
3.Enteroendocrine cells: more than 10 types
4.M-cells: overlie lymphoid nodules of GALT and function to transport antigensfrom lumen to macrophages (Ag presenting cells) to eventually activate
lymphocytes
5.Paneth cells eosinophilic cells located at base of crypts; produce lysozyme
6.Stem cells (undifferentiated cells)
originate in base of gland

28

Differnece in the abroptive cells in SI

Crypt enterocytes secrete water and electrolyes

Villus enterocytes absorb nutrients and water

29

Features of the duodenum



Duodenum:Initial segment of small intestine; is approx. 25 cm long
Receives chyme from stomach and secretions from pancreas, liver and gallbladder

Has prominent submucosal folds (valves of Kiekring) that house:
Submucosal
Brunner’s Glands
 

30

characteristics of the brunners glands

They are in the duodenum of the SI

THey are simple alveolar glands located in the submucosa underlying crypts

brunner cells make alkaline mucusal cells that protect the mucosal surface and neutralize the acidic chyme from the stomach

Have ducts that perforate the muscularis mucosa and empty into the base of the crypts

31

Features of the jejunum..length, fcuntion, desceibe villa

 

 approx. 2.5 meters long
Principal site of absorption
Villi are long and finger-like
 

32

Features of the ileum... length, main function, compare villa to jejunum... contains what??





Ileum:
Is approx. 3.5 meters long
Site of water and electrolyte
reabsorption in small intestine
Villi are broader compared to
jejunum

 

Contains collections of lymphoid
nodules called
Peyer’s patches
that are located in the lamina
propria and usually extend into
the submucosa
 

33

LI main function and general features

 

Name parts

Villa?

How is the muscularis externa organized?

main function is to reabsorb water and electrolytes and eliminate
undigested food and wastes (bile salts, bacteria, desquamated cells)


General features:
Is comprised of:
-cecum
-appendix
-colon
-rectum
-anal canal

 

NO VILLA NO PLICAE CIRCULARIS

Outer longitufinal layer of muscularis externa is organized in 3 bands called teniae coli

has both serosa and adventitia coverings

 

34

How does the appendix varying from normal LI features

Has sprase crypts compared to the colon

Relatively thin muscularis externa with 2 uniform layer (no teniae coli- the outer muscularis externa organized in 3 parts)

35

Rectal anal junciton function

 

Differences from colon

Function to eliminate feces

 

Rectum has colonic glands, but also has mucosal surface infolding (not smooth like the colon)

Has abrupt epithelial transition from simple columnar to stratified squamous

 

Sphincters are in the muscularis externa

 

36

What is present in the perianal (skin) part of the rectal anal junction

Hair follicles and apocrine sweat glands