Lecture 2 - anatomy

Question 1

4 layers of the GI tract

Answer 1

Mucosa (innermost)
Submucosa
External muscles
Serosa (outermost)

Question 2

What does the mucosa consist of?

Answer 2

Epithelial cells
Lamina propria
Muscularis mucosa

Question 3

What does the submucosa contain?

Answer 3

Connective tissue with:

• glands
• arteries
• veins
• nerves

Meissner’s plexus

Question 4

External muscle of the GI tract

Answer 4

Outer longitudinal - divided into 3 bands (taeniae coli). Acts as a shuttle and shortens gut
Inner circular - for peristalsis and contains the Auerbach’s plexus

Question 5

What does the serosa contain?

Answer 5

Blood vessels
Adipose tissue
Lymph vessels

Continuous with the mesenteries

Question 6

Role of the mucosa epithelial layer

Answer 6

Selectively permeable barrier - facilitates the transport and digestion of food

• Promotes absorption via microvilli
• Produces hormones
• Produces mucus via goblet cells

Question 7

Why does the GI tract contain mucus?

Answer 7

Decreases friction
Prevents chemical damage
Reduces bacterial invasion

Question 8

Role of the lamina propria of the GI mucosa

Answer 8

Contains lymphoid nodules and macrophages - immune defense

Produces antibodies (IgA) - resistant to proteases which protects against bacterial and immune invasion

Question 9

Role of the muscularis mucosae of GI mucosa

Answer 9

Layers of the smooth muscle orientated in different directions
Motility - prevents stasis which can cause infection
Keeps the epithelium in contact with the gut contents
Dynamic crypt contents

(peptic ulcers breach the muscularis mucosa)

Question 10

What type of epithelium lines the oesophagus and distal anus

Answer 10

Stratified squamous

Question 11

What type of epithelium lines the stomach and intestines

Answer 11

Simple columnar

Question 12

Adaptations of the enterocyte

Answer 12

Enterocytes line the villi
Microvilli - brush border (increases SA)
Crypts
One cell thick

Question 13

Goblet cells

Answer 13

Scattered between the enterocytes
Increasing number form the duodenum to the colon
Secretes mucus

Nucleus at base due to compression by mucus

Question 14

Foveolar cells

Answer 14

Line the gastric mucosa and gastric pits (in stomach)
Secretes:
- mucus
- HCO3-

Secretions form a barrier to stomach acid

Question 15

Folds of the GI tract

Answer 15

Stomach - rugae (temporary)
Small intestines - plicae circulares
Large intestines - haustra

Villi and microvilli

Question 16

Villi

Answer 16

Found in absorptive areas - small intestines

Question 17

Crypts

Answer 17

In small and large intestines
Crypts of Lieberkuhn
Contain specialised cells:

• Stem cells
• Paneth cells
• Enteroendocrine cells

Question 18

Stem cells

Answer 18

Divide and replicate for epithelium regeneration every 2- 4 days

Question 19

Paneth cells

Answer 19

Guard against infection
Protects stem cells (package and export antimicrobial proteins)

[at base of crypt and bright red]

Question 20

Enteroendocrine cells

Answer 20

Secrete gut hormones:

• G cells - gastrin - stimulates gastric acid secretion from parietal cells

I cells - cholecystokinin - Stimates the gall bladder to contract and release bile

• S cells - secretin - Stimulates the release of HCO3- and water to dilute acid

[deeper in crypts and gastric glands]

Question 21

Describe the glandular tissue of the gut

Answer 21

Acini - produce digestive enzymes
Intercalated ducts - transports secretions Interlobular ducts- secrete sodium bicarbonate into the main duct
Tubules

Question 22

Examples of exocrine glandular structures

Answer 22

Salivary glands
Pancreas
Brunners glands

Question 23

Secretion volumes per day

Answer 23

Saliva - 1.5 L
Bile - 0.5 L
Gastric secretions - 2L
Pancreatic secretions - 1.5 L
Small intestines - 1.5 L

Question 24

Layers of the abdominal wall from superficial to deep

Answer 24

Skin
Fascia
Fat

External oblique
Internal oblique
Transverse abdominis
Rectus abdominis

Transversalis fascia
Peritoneum

Question 25

Rectus sheath

Answer 25

The aponeurosis of the external oblique, internal oblique and transversus abdominis that surrounds the rectus abdominis The superior 3/4 of the rectus abdominis is completely enclosed by the rectus sheath The inferior 1/4 is only covered anteriorly. Posteriorly it is covered by the transversalis fascia and parietal pertitoneum

Question 26

Peritoneal cavity

Answer 26

Seperate from the abdominal cavity Serous membrane containing peritoneal fluid forming a potential space Simple squamous Envelops intraperitoneal viscera (Visceral peritoneum) Lines the cavity wall - (parietal)

Question 27

Retroperitoneal structures

Answer 27

``` Suprarenal glands Aorta and IVC Duodenum Pancreas Ureters and bladder Colon (ascending and descending) Kidneys Esophagus Rectum ```

Question 28

Visceral peritoneum

Answer 28

Sympathetic and parasympathetic afferents - Pain is poorly localised - referred - dependent on nerve

Question 29

Parietal peritoneum

Answer 29

Somatic afferents | - localised pain

Question 30

What does a mesentery contain?

Answer 30

Double fold of peritoneum that contains: - blood vessels - lymph vessels - fat - nerves

Question 31

Arcuate line

Answer 31

Site of transition of the rectal sheath Lower limit of the posterior layer of the rectal sheath Half way between the umbilicus and pubic crest

Question 32

What are the two major divisions of the peritoneal cavity?

Answer 32

Greater and lesser sacs

Question 33

What is the connection between the greater and lesser sac?

Answer 33

The epiploic foramen (Foramen of Winslow)

Question 34

Boundaries of the lesser sac

Answer 34

Anterior: - quadrate lobe of the liver - gastrocolic ligament and stomach - lesser omentum Posterior: - pancreas - left kidney

Question 35

Cavities within the peritoneum that can collect fluid

Answer 35

Rectovisical - between the rectum and bladder Rectouterine (pouch of Douglas) - between the rectum and uterus Visicouterine - between the bladder and uterus

Question 36

Symptoms of peritonitis

Answer 36

- feeling of fullness and bloating - fever - nausea and vomiting - loss of appetite - diarrhoea - thirst - low urine output - inability to pass stool or gas - fatigue

Question 37

How do the splanchnic nerves enter the abdomen

Answer 37

Through the diaphragm at the 4th and 5th intercostal space