Control of GI

Question 1

Describe sympathetic control of the GI tract

Answer 1

T5-L3
Short preganglionic fibres, post ganglionic fibres long
Form presynaptic sphlanchnic nerves, synapse with prevertebral ganglia - Coeliac, renal, superior and inferior mesenteric.
Release NA
Innervate blood vessels
Inhibits GI function

Question 2

Describe parasympathetic control of the GI tract

Answer 2

Vagus - oesophagus to transverse colon
Pelvic splanchnic (s2-s4)
Release Ach, gastrin releasing peptide, vaso inhibitory peptide (cholinergic and peptidergic)

Question 3

Describe enteric control of the GI tract

Answer 3

Innervates oesophagus to anus
Submucosal division - controls secretions and blood flow
Myenteric division - Between circular and longitudinal muscle, controls motility

Question 4

Describe paracrine control of the GI tract

Answer 4

D cells in antrum of stomach and pancreas
Secrete somatostatin when stimulated by H+ in stomach lumen
Inhibits G cells and histamine release

Question 5

What cells secrete histamine in the GI tract?

Answer 5

Enterochromafin

Question 6

Describe neurocrine control of the GI tract

Answer 6

Gastrin releasing peptide, increases release of gastrin from g cells

Question 7

Describe the gastrin family of hormones

Answer 7

Gastrin: G cells in antrum, increases gastric acid secretion
Cholecystokinin: I cells in duodenum and jejunum, stimulates pancreatic and contracts gallbladder to increase secretions, stimulated by fat and protein,

Question 8

Describe the secretin family of hormones

Answer 8

Secretin: S cells in duodenum, increases HCO3 from pancreas and gallbladder, decreases gastric acid secretion. Stimulate by H+ and fatty acids
Gastric inhibitory peptide: release from duodenum and jejunum, increases insulin and decreases gastric acid secretion. Stimulated by sugar, protien and fatty acids

Question 9

Where in the GI tract does not have smooth muscle?

Answer 9

Pharynx
Upper 1/3 oesophagus
External anal sphincter

Question 10

What is tonic contraction and where does it occur?

Answer 10

Constant level of contraction
Upper stomach
Ileocaecal valve
Internal anal sphincter

Question 11

What is peristalsis?

Answer 11

Adjacent segments of the canal contract proximal to contents, relax distally to propel contents distally

Question 12

What is segmentation?

Answer 12

Non-adjacent segments of canal relax and contract, moving food backwards and forwards, mixing it and mechanically breaking down.

Question 13

What is mass movement?

Answer 13

A gastrocolic reflex that moves contents from distal colon into rectum

Question 14

Describe the autonomic control of GI motility

Answer 14

Sympathetic- releases NA to reduce motility

Parasympathetic - releases Ach to increase motility

Question 15

What is Hirschprung’s disease?

Answer 15

Lack of myenteric and submucosal plexuses, results in functional obstruction - newborns wont have 1st poo

Question 16

What is achalasia?

Answer 16

Failure of lower oesophageal sphincter to relax, causing dysphagia

Question 17

What is paralytic ileus?

Answer 17

Often following GI surgery, obstruction of intestine causing failure of forward movement of bowel contents

Question 18

What are the cites of GI secretion?

Answer 18

Acini of salivary glands
Gastric glands in the stomach
Brunner’s glands in duodenum
Crypts of lieberkuln in the intestines
Acini of exocrine pancreas
Hepatocytes, secretions stored in gallbladder
Goblet cells (increasing numbers from duodenum to colon)

Question 19

What is the function of stomach acid?

Answer 19

Innate barrier to infection
Prepares proteins for digestion
Activates enzymes

Question 20

What is the function of HCO3 and where is it secreted?

Answer 20

Neutralises acid
Saliva
Stomach 
Duodenum 
Pancreas
Liver (as bile)

Question 21

What is the function of liver waste products?

Answer 21

Bile contains waste products
Cholesterol - used in cell membranes
Bilirubin - breakdown of RBCs

Question 22

What is the function of emulsifiers?

Answer 22

Bile salts that increase the surface area of lipids, aiding digestion by lipases and allowing it to be transported as micelles in gut

Question 23

What is the function of mucus?

Answer 23

Protects against acid in stomach
Protects against bacteria in small intestine (antibacterial)
Provides food source for bacteria in large intestine while seperating them from epithelium
Lubricates

Question 24

How is a large surface area created in the gut?

Answer 24

Permanent folds - plica circulares
Villi
Microvilli

Question 25

How is water absorbed in the GI tract?

Answer 25

Passively - after a meal, water uptake driven by sodium co-transporters In between meals, Na and Cl are absorbed, water follows In colon - ENaC channels so water can be reabsorbed before excreted in stool

Question 26

Where does the gatrocolic ligament connect?

Answer 26

Stomach to transverse colon

Question 27

Where does the gastrosplenic ligament connect?

Answer 27

Stomach to spleen

Question 28

Where does the falciform ligament connect?

Answer 28

Liver to anterior abdominal wall

Question 29

Where does the triangular ligament connect?

Answer 29

Liver to diaphragm

Question 30

Define a portal system

Answer 30

Where blood from capillaries of one organ is transported to capillaries of another organ by a connecting vein

Question 31

What are the sphincters of the GI tract?

Answer 31

``` Upper oesophageal Lower oesophageal Pyloric sphincter Sphincter of Oddi Ileo-caecal valve Internal anal External anal - voluntary ```

Question 32

Describe the venous drainage of the GI tract

Answer 32

Foregut - portal vein Midgut - Superior mesenteric vein Hindgut - Inferior mesenteric vein All eventually drain into portal vein

Question 33

Describe the development of the pancreas

Answer 33

Develops from the foregut Dorsal portion forms the gland Ventral portion forms the duct system

Question 34

What happens when the liver grows into the ventral mesentery?

Answer 34

Divides it into 2 parts: Faliciform ligaments Lesser omentum

Question 35

Describe the development of the midgut

Answer 35

Grows faster than the abdominal cavity so by week 6, with liver also growing rapidly there isn't enough space in abdominal cavity so protrudes through abdominal wall into umbilical cord - physiological herniation Herniated midgut forms a loop with superior mesenteric artery within umbilical cord, distal loop develops caecal bulge, proximal part becomes twisted Midgut rotates while in the umbilical cord, undergoes 3X90 degree rotations then returns to the abdomen in week 10

Question 36

What causes umbilical hernias?

Answer 36

Abnormally large opening between abdominal cavity and umbilical cord that persists

Question 37

What is Meckel's diverticulum?

Answer 37

Persistent yolk sac remaining in midgut, can contain ectopic gastric or pancreatic tissue

Question 38

Describe the dual origin of the anal canal

Answer 38

Hindgut forms superior portion of anal canal Hindgut ends blindly at cloacal membrane, which separates it from the proctodaeum. When membrane ruptures, hindgut is connected to exterior

Question 39

What effect does the dual origin of the anal canal have?

Answer 39

Above the pectinate line only stretch detected | Below the pectinate line detects pain and temperature

Question 40

When does the development of the lumen occur and where does it occur?

Answer 40

Recanalisation occurs weeks 6-8 Oesophagus Bile duct Small intestine

Question 41

What are the consequences of failed recanalisation?

Answer 41

Most often in duodenum Atresia (obliteration of lumen) Stenosis (narrowing of lumen)

Question 42

What is pyloric stenosis and what are the consequences?

Answer 42

Not a recanalisation failure, hypertrophy of the circular muscle in the pyloric sphincter Narrows the exit from stomach, causing projectile vomiting

Question 43

What is gastroschisis?

Answer 43

A failure of the abdominal wall to close following the folding of the embryo, causes gut tube and its derivatives to be outside the body

Question 44

What is an omphalocoele and how is it different to an umbilical hernia?

Answer 44

Persistence of a pathological herniation of midgut Different to hernia as hernia has a covering of skin and sub cutaneous tissue, omphalocoele is an incomplete physiological herniation

Question 45

Describe the anal canal above the pectinate line

Answer 45

Supplied by the inferior mesenteric artery S2-S4 pelvic parasympathetics Columnar epithelium Lymph drainage by internal iliac nodes

Question 46

Describe the anal canal below the pectinate line

Answer 46

Supplied by the pudendal artery S2-S4 pudendal nerve Stratified epithelium Lymph drainage by superficial inguinal nodes

Question 47

Describe hindgut abnormalities

Answer 47

Imperforate anus, failure of anal membrane to rupture Anal agenesis Hindgut fistulae

Question 48

Which structures in midgut and hindgut retain mesenteries?

Answer 48

``` Jejunum Ileum Appendix Transverse colon Sigmoid colon ```

Question 49

Which structures in the midgut and hindgut have fused mesenteries?

Answer 49

Duodenum Ascending colon Descending colon Rectum

Question 50

What are the derivitives of the midgut?

Answer 50

``` Small intestine, most of duodenum Caecum Appendix Ascending colon Proximal 2/3 transverse colon ```

Question 51

What types of malrotation can occur?

Answer 51

Incomplete rotation - midgut loop makes only 1X90 degree rotation, results in left sided colon Reversed rotation - midgut loop makes a 90 degree rotation clockwise, transverse colon passes posterior to duodenum

Question 52

What are the risks of midgut defects?

Answer 52

Volvulus - loop of intestine twists around itself and its mesentery, creating a bowel obstruction that results in strangulation and ischaemia

Question 53

What can a persistent vitelline duct cause?

Answer 53

``` Vitelline cyst (forms fibrous strands) Vitelline fistula (direct link between umbilicus and intestinal tract) Meckel's diverticulum (persistent yolk sac remains in midgut) ```