101 - Gastrointestinal Tract

Question 1

Functions of the GIT
1
2
3
4

Answer 1

1) Digestion
2) Absorption
3) Movement
4) Protection

Question 2

Layers of GIT wall
1
2
3
4

Answer 2

– Mucosa
– Submucosa
– Muscularis externa
– Serosa

Question 3

Length of GIT

Answer 3

~9M

Question 4

Layers of muscularis externa

Answer 4

Inner circular layer

Outer longitudinal layer

Question 5

Mucosa
1
2
3
4

Answer 5

1) Innermost layer, closest to the lumen
2) Columnar or stratified squamous epithelium, depending on location
3) Supported by a connective tissue layer (lamina propria) that contains nerves, vessels
4) Thin layer of smooth muscle (muscularis mucosae) forms boundary of mucosa

Question 6

Structure of mucosa

Answer 6

Can be thick due to folding of the surface or presence of glands

Question 7

Blood vessels in lamina propria

Answer 7

Blood vessels in lamina propria are small (capillaries and lymphatics)

Question 8

Composition of submucosa

Answer 8

Dense, fibrous connective tissue (rich in collagen, elastin)
Sometimes glands present.
Blood vessels, nerves present.

Question 9

Role of submucosa

Answer 9

Provides strength and elasticity

Question 10

Thickness of muscularis externa

Answer 10

Usually two layers of smooth muscle (circumferential and longitudinal layers)

Question 11

What is responsible for peristalsis?

Answer 11

Muscularis externa

Question 12

What co-ordiantes movement of muscularis externa?

Answer 12

Autonomic nervous system

Question 13

ROle of serosa

Answer 13

Provides non-stick surface of gut

Question 14

What is the serosa?

Answer 14

Layer of connective tissue binding GIT to surrounding structures or an epithelial structure in the free gut (peritoneal cavity)

Question 15

Cell type of serosa

Answer 15

Simple squamous

Question 16

Components of autonomic NS

Answer 16

Sympathetic, parasympathetic, enteric

Question 17

Locations of enteric NS plexuses
1
1

Answer 17

1) Myenteric plexus lies between longitudinal and circular muscle layers
2) Submucous lies in the submucosa

Question 18

Epithelium in oesophagus

Answer 18

Stratified squamous (non-keratinising)
Has submucosal glands for lubrication

Question 19

Unusual aspect of composition of oesophagus muscularis externa

Answer 19

Half smooth muscle and half skeletal muscle

Question 20

Muscle distribution in the oesophagus (of muscularis externa)

Answer 20

Top third is skeletal muscle.
Middle third is mixed.
Lower third is smooth muscle.

Question 21

Macronutrients that stomach is best at breaking down

Answer 21

Proteins (not as good at digesting carbohydrates or fats)

Question 22

Name for material partially digested by stomach

Answer 22

Chyme

Question 23

Epithelium of etomach

Answer 23

Simple columnar

Question 24

Structure of stomach wall
1
2
3
4

Answer 24

1) Simple columnar epithelium
2) Prominent muscularis mucosae
3) Thick submucosa
4) Thick muscularis externa (with a third, oblique layer in parts)

Question 25

Role of rugae

Answer 25

To allow expansion of stomach

Question 26

Surface of stomach wall

Answer 26

Contains many holes (gastric pits) which lead to gastric glands.

Question 27

Structure of gastric pits

Answer 27

Each gastric pit splits into 3-5 gastric glands. These are simple tubular glands that penetrate into lamina propria. Organisation varies across stomach

Question 28

``` Structure of gastric glands (top to bottom) 1 2 3 4 5 ```

Answer 28

Made up of many cell type, arranged in particular areas from top to bottom. 1) Top cells are gastric surface cells and neck cells (produce mucus) 2) Regenerative (stem) cells in neck of gland. 3) Mucous neck cells 4) Parietal cell produce hydrochloric acid 5) Chief cells release pepsinogen at the base of the gland

Question 29

Pepsinogen

Answer 29

Inert form of pepsin, which breaks down proteins

Question 30

Pepsin activation 1 2

Answer 30

1) Pepsinogen is released from chief cells. | 2) Acidic environment activates some pepsinogen to pepsin, which then cleaves and activates more pepsinogen

Question 31

Protection of the stomach from pepsin and low pH

Answer 31

1-2mm layer of mucus released constantly from gastric glands

Question 32

Structure of epithelium of small intestine

Answer 32

Simple columnar epithelium (with microvili) Vili form prominent extensions of epithelium Vili are present on transverse folds (plica circulares) Base of vili give rise to tubular glands (Crypts of Lieberkuhn)

Question 33

Microvili distribution

Answer 33

All columnar epithelial cells in small intestine have microvili except goblet cells. Form brush border

Question 34

Arrangement of vili to maximise surface area

Answer 34

Plica circulares increase surface area by 2-3. | Vili increase surface area by a factor of 10.

Question 35

``` Crypts of Liberkuhn 1 2 3 4 ```

Answer 35

Penetrate into lamina propria from base of vili. Secrete fluid and mucus Mucus secreted from goblet cells on vili (in both vili and crypts) Contain stem cells for renewal of epithelium

Question 36

Where do many of the cancers of the GIT form?

Answer 36

From stem cells in the crypts (intestinal cancers), gastric pits (gastric cancers)

Question 37

Arrangement of lamina propria in a vilus

Answer 37

Extends into the core of each vilus

Question 38

Contents of lamina propria in the small intestine

Answer 38

Contain smooth muscle (muscularis mucosa), blood vessels, lymphatics and immune cells

Question 39

Role of muscularis mucosa in the vili of the small intestine

Answer 39

Move vili to prevent any areas where vili can't absorb nutrients from fluid

Question 40

``` Features of surface of duodenum 1 2 3 4 ```

Answer 40

1) Short (25cm) 2) Has only low plica circulares 3) Fewer goblet cells 4) Receeves secretions from gall bladder and pancreas (bile for digestion of fat

Question 41

Duodenal functions 1 2 3

Answer 41

1) Receives acidic chyme with active pepsin from stomach 2) Has glands in submucosa (Brunner's glands) that release alkaline mucus 3) The pH is raised to ~7.3, which inactivates pepsin

Question 42

Features of surface of jejunum and ileum 1 2 3

Answer 42

1) More plica, shorter vili 2) Lots of goblet cells (increase in number in ileum) 3) Ileum has a lot of Peyer's patches

Question 43

Amount of fluid absorbed by small intestine each day

Answer 43

~8.5L

Question 44

Role of large intestine

Answer 44

Compacts faeces, recovers water and electrolytes

Question 45

Structure of the colon

Answer 45

``` Smooth surface (no vili) Many tubular glands (Crypts of Liberkuhn, mainly producing mucus) ```

Question 46

Composition of faeces

Answer 46

Water, roughage, bacteria, fat, inorganic material, bile pigment. Stuck together with mucus

Question 47

Problem with bacteria living in small and large intestine

Answer 47

Produce acid. HCO3 released from crypts to neutralise this acid

Question 48

Amount of water lost each day in faeces

Answer 48

~50-100mL