Micro-anatomy

Question 1

What are the different layers of epithelium?

Answer 1

Simple squamous, simple cuboidal, simple columnar, stratified squamous, stratified cuboidal and stratified columnar

Question 2

What are the thickness of the subtypes of epithelium?

Answer 2

Simple = 1
Stratified = more than 1
Pseudo stratified = 1 layer than pretends to be 2
Squamous = flat cell
Columnar = column like cells

Question 3

What is the entire digestive tract?

Answer 3

It is a Continuous tube with some wide and some narrower bits

Question 4

What are the 4 layers that the tube consists of?

Answer 4

Mucosa, sub mucosa, muscularis externa and serosa

Question 5

What are the 3 component layers of the mucosa?

Answer 5

Epithelium, laminate propria and muscularis mucosa

Question 6

Describe the epithelium in the mucosa?

Answer 6

A thin layer that lines the lumen of the tube, can be simple or stratified, squamous or columnar.
It forms a selective barrier that digested molecules must cross
It may contain mucous secreting goblet cells and endocrine cells secreting digestive hormones

Question 7

Describe the laminate propria

Answer 7

Loose connective tissue
It has a good blood supply and it often contains lymphatics and numerous white blood cells, it is the first immunological barrier to pathogens in the GI system

Question 8

Describe the muscularis mucosa

Answer 8

It is a thin layer of smooth muscle cells causing localised contractions in the mucosa

Question 9

What is the sub mucosa?

Answer 9

It is a layer of dense connective tissue that contains the submucosal plexus
Secretion and blood flow are controlled by the submucosal plexus. It relays information from the gut epithelium and stretch receptors in the wall
It is part of the enteric nervous system

Question 10

What is the enteric nervous system?

Answer 10

It is a branch of the autonomic nervous system, it is NOT part of the sympathetic or parasympathetic.
It can operate independently of the CNS

Question 11

What does the enteric nervous system consists of?

Answer 11

It consists of mostly two major plexi within the GI wall - the myenteric and submucosal plexi

Question 12

Describe the muscularis externa

Answer 12

It consists of two layers of smooth muscle - inner circulation and outer longitudinal.
The myenteric plexus, the second plexus of the enteric nervous system lies between the layers of smooth muscle and it is mainly involved with the control of GI motility

Question 13

What happens when the inner circular and outer longitudinal layers go through a wave of contraction and relaxation?

Answer 13

Food is forced along these layers along the digestive tract - called peristalsis

Question 14

What is the serosa?

Answer 14

It is a layer of epithelium that forms part of the peritoneum

Question 15

Describe the microanatomy of the oesophagus

Answer 15

The muscularis externa of the upper third of the oesophagus consists of a skeletal muscle.
Mucus secreting glands are present in the laminate propria and the sub mucosa

Question 16

Describe the microanatomy of the stomach

Answer 16

Gastric puts contains the secretory cells of the gastric epithelium

Question 17

Describe the microanatomy of the small intestine

Answer 17

Villi are finer-like projections that are present, the recessions between the villi are known as crypts.
The epithelial surface of the villi is simple columnar

Question 18

Describe the villi network in the small intestine

Answer 18

There are numerous microvilli on the surface of the cells that form a ‘brush border’
Each villus contains a capillary network that transports adsorbed amino acids and monosaccharides plus a blind-ended lymph vessel that transports absorbed fat. The capillary network drains into the portal vein

Question 19

what is the villus considered to be?

Answer 19

The functional unit of absorption

Question 20

What are the four specialised cells that are present within the epithelium of the villi?

Answer 20

Absorptive cells, goblet cells, granular cells and APUD cells

Question 21

Where do the four specialised cells arise from?

Answer 21

The undifferentiated cells at the base of the crypts

Question 22

What are absorptive cells?

Answer 22

They secrete digestive enzyme and absorb nutrients

Question 23

What are goblet cells?

Answer 23

They produce mucus that lubricates and protects the epithelium from mechanical damage

Question 24

What are granular cells?

Answer 24

They secrete enzymes and protect epithelium from bacteria

Question 25

What are APUD cells?

Answer 25

They produce endocrine secretions that regulate secretions and motility of the GI tract

Question 26

What do absorptive and goblet cells do?

Answer 26

They ascend the villi from the base of crypts

Question 27

When is the epithelium renewed?

Answer 27

Every 3-6 days, the mature cells are usually located at the tip of the villus until they shed

Question 28

Where do granular and APUD cells remain?

Answer 28

At the base of the crypts

Question 29

Describe the microanatomy of the large intestine

Answer 29

The epithelium of the large intestine is not villus, it is simple columnar and contains crypts.

Question 30

What cells are present in the large intestine?

Answer 30

Goblet cells and absorptive cells, APUD cells are present but they are sparse

Question 31

What cells is found in larger number in the large intestine than the small?

Answer 31

Goblet cells which means there is more mucus

Question 32

What is found to be similar in the large and small intestines?

Answer 32

The laminate propria, muscularis and submucosa

Question 33

What surrounds the large intestine?

Answer 33

The outer longitudinal layer of smooth muscle, except it doesn’t cover the rectum

Question 34

What is the is the longitudinal layer of smooth muscle called?

Answer 34

Taeniae coli, it is split into 3 separate bands than run the length of the colon

Question 35

What does the Taeniae coli aid?

Answer 35

It aids peristalsis

Question 36

What is the Taeniae coli not present on?

Answer 36

It is not present on the rectum, anal canal or the vermiform appendix