GI system

4 layers of the oesophagus (GI tract) + histological features

• Mucosa: non-keratinised stratified squamous

• Submucosa: loose connective tissue

• Muscularis propria: smooth + skeletal m. → inner circular, outer longitudinal

• Adventitia/serosa

How do adventitia and serosa differ

Adventitia → secures organ to surrounding tissue (more fibrous)

Serosa → covers external surface of organ

What are the layers of oesophagus mucosa

• Non-keratinised stratified squamous epithelium

• Lamina propria (loose connective tissue)

• Muscularis mucosa (smooth muscle)

Auerbach’s plexus function + location

Allows for peristalsis

Found between circular + longitudinal muscle layers

Oesophagus, stomach + small/large intestine

What is Gastroesophageal reflux disease (GORD) + complication?

Acid reflux caused by weakened oesophageal sphincter

Can lead to barret’s oesophagus

Signs + symptoms of GORD

• heartburn

• Acid regurgitation

• Dysphagia

GORD/ Barret’s oesophagus risk factors

• smoking

• Alcohol

• Obesity

• Caffeine

• Bulimia

What is Barrett’s oesophagus+ complication

Metaplasia of squamous epithelium to columnar (premalignant lesion) due to chronic acid exposure (lower 1/3) + goblet cells

Oesophageal Adenocarcinoma

GORD treatment/management

• weight loss

• Avoiding large meals + trigger foods

• Lying flat after eating

• Antacids

• Proton pump inhibitors (omeprazole)

Barrett’s oesophagus investigations

Endoscopy w/ biopsy in all 4 quadrants

Three anatomical regions of stomach (top to bottom)

• Cardia → contains mucous secreting glands

• Fundus → body containing gastric glands

• Pylorus → secretes mucus + gastrin

Gastric/fundic gland cells + secretions

• Surface mucous: alkaline fluid

• Mucous neck: acidic fluid

• Parietal: intrinsic factor + HCL

• Chief: pepsinogen + gastric lipase

• G: gastrin

Brunner’s Glands

found in duodenum submucosa → secrete alkaline mucus to neutralise acidic chyme

Protects membrane + optimal pH for digestion

Plicae circulares

Villi covered folds in mucosa/submucosa →slow passage + increased absorption SA

Primarily found in jejunum

Peyer’s patches

Organised lymphoid follicles found in lamina propria/submucosa of ileum

Involved in immune defence against microbial + dietary antigens (M cells)

Serosa

Visceral peritoneum → connective tissue+ mesothelium

Mesothelium lubricates peritoneal cavity

Ulcerative colitis

• Autoimmune→ affects colon + rectum

• Superficial ulcers

Clinical features of ulcerative colitis (5 Ps)

• pseudopolyps

• Poo → diarrhea, tenesmus, blood

• Pyrexia

• Proctitis

• Lead Pipe appearance (xray)

• Anaemia

• Weight loss

IBD investigations

• bloods → FBC, ESR/CRP, LFT, U&Es, B12, iron

• Colonoscopy w/ biopsy (diagnostic)

• Faecal calprotein

Complications of ulcerative colitis

• toxic megacolon (bowel dilates risk of perforation)

• Colorectal cancer

Treatment/management of Ulcerative Colitis

• corticosteroids

• Biologics

• Aminosalicylates

• Colectomy (curative)

• Smoking (protective)

Crohn’s Disease

• autoimmune → can affect anywhere in GI (ileum most common) transmural

• Associated with non-caseating granulomas

Clinical features of Crohn’s

• Cobblestone mucosa

• pyrexia

• Skip lesions

• Abdominal pain

• Malabsorption + weight loss

• Fistula formation

Crohn’s management

• Antibiotics

• Corticosteroids

• immunosuppressants

• Biologics

• Aminosalicylates

• Smoking cessation

What type of epithelium is found at recto-anal junction

Simple columnar → stratified squamous non-keratinised

What cells are found in hepatic sinusoid + functions

• endothelial:

• Kupffer: macrophages

• Pit:

• Fat-storing:

Functions of the liver

• Bile production

• Detoxification

• Glycogen storage

• Clotting factors, CRP, etc synthesis

Lacteals

dilated lymph vessels involved in fat absorption in duodenum/jejunum

Paneth cells

located in crypts

Contain red cytoplasmic granules → produce defensin + lysosymes

Enteroendocrine cells

found in duodenum + jejunum

Produce gastric inhibitory peptide → suppresses acid secretion

Crypts of lieberkuhn

Pits between villi (extend down to muscularis mucosa) → contain stem cells

How does small intestine structure help to aid in digestion/absorption

1) secretes enzymes + mucous producing glands

2) highly folded mucosa → villi/microvilli/plicae circulares

Meissner’s plexus location + function

• secretion

• Mucosal movement

• Localised blood flow

Found in submucosa

What cells are found in the pancreatic islets of Langerhans + what do they produce

• a → glucagon

• b → insulin

• Gamma → Pancreatic polypeptide

• Delta → somatostatin

How does somatostatin affect pancreas + GI tract

pancreas → inhibits release of insulin, glucagon, gastrin + digestive enzymes

GIT → reduces gastric secretion + GI hormones

Gall bladder function

• stores bile

• Contracts + expels bile into duodenum via CCK (Sphincter of oddi relaxes)

Gall bladder → common bile duct → duodenum

Gall bladder histology (+ what is NOT present)

• mucosa → simple columnar epithelium + microvilli

• NO muscularis mucosa + submucosa

• Muscularis externa

• Adventitia where it connects with liver

• Serosa elsewhere (mesothelium + loose CT)

What type of cell is found in gall bladder ducts

cuboidal cholangiocytes

Small intestine divisions

• Duodenum

• Jejunum

• Ileum

large intestine divisions

• Cecum

• Colon → ascending, transverse, descending, sigmoid

• Rectum

• Anal canal

3 main functions of gastrointestinal system

• Digestion

• Absorption

• Excretion

Receptive relaxation of stomach

Fundus relaxes as food moves down oesophagus so no significant pressure difference

How is the stomach involved in digestion

• secretes acid + proteolytic enzymes → forms chyme

• Muscle contractions mix together

Large intestine functions

• Where final water + electrolyte absorption occur

• Microbial flora synthesise vitamin K + B12

• Mix + propel luminal contents

• Haustrations ensure faecal material is exposed to absorptive surface

Where does faeces accumulate

Descending + sigmoid colon → rectum

Parenteral nutrition

Intravenous feeding via peripheral or central vein (bypasses GI)

Used in: short bowel syndrome, IBD, obstruction

Enteral nutrition

Liquid supplemental nutrition orally or via tube

Used when GI system is still functional

Mouth + oral cavity functions

• mastication

• Salivation

• Bolus formation

• Swallowing

Mastication muscles

• masseter

• Temporalis

• Medial + lateral pterygoid

  Innervated by trigeminal + facial n.

3 phases of swallowing

• oral: voluntary: bolus formed

• Pharyngeal: involuntary (PANS): swallow reflex

• Oesophageal: involuntary (Cranial n. X): bolus moves down to stomach

Peristalsis

Wave of muscular contractions that push food down

Neurological causes of dysphagia

• stroke

• Motor neurone disease

• Parkinson’s

• Myasthenia Gravis

• Achalasia

Intramural causes of dysphagia (obstructive)

• stricture caused by GORD,radiotherapy

• Oesophageal cancer

• Oesophagitis

Achalasia pathophysiology

• progressive degeneration of myenteric neurones

• aperistalsis + impaired relaxation of lower oesophageal sphincter

Clinical features of achalasia

• intermittent dysphagia (solid+liquid)

• regurgitation

• Heart burn

achalasia investigations

• CXR - dilated oesophagus

• barium swallow - Bird’s beak

• Endoscopy

achalasia management

• botulinum toxin injection

• endoscopic dilation (pneumatic balloon)

Causes of upper GI bleeds

• gastritis

• Peptic ulcer disease

• Malignancy

• Mallory-weiss tear

• Oesophageal varices (enlarged veins)

Causes of lower GI bleeds

• IBD

• Diverticulitis

• Haemmaroids

• Polyps

• Malignancy

gastritis

inflammation of stomach mucosa - acute or chronic

causes of acute gastritis

• NSAIDs

• stress

• alcohol

• burns (Curling’s ulcer)

• Head trauma (cushing’s ulcer)

Causes of chronic gastritis

• H. pylori

• Autoimmune - type IV hypersensitivity occurs in fundus + body of stomach

autoimmune gastritis pathophysiology

• autoantibodies against intrinsic factor/parietal cells → loss of parital cells

• presents with pernicious anaemia

• less gastric acid + intrinsic factor secretion = B12 malabsorption

Gastritis/H.pylori investigations

• bloods → anaemia, H.pylori IgG

• carbon-isotope urea breath test

• stool antigen test

• endoscopy w/ biopsy

gastritis treatment

• proton pump inhibitor

• antacids/H2 receptor antagonists

H. pylori treatment (Triple therapy regime)

PPI + amoxicillin + clarithromycin (TD) for 7 days

Amoxicillin allergy = clarithromycin + metronidazole

H. pylori pathogenesis

• Gram -ve bacteria colonises gastric antrum

• uses urease: urea → co2 + ammonia (neutralises acid)

H. pylori complications

• gastric/duodenal ulcers

• strictures

• MALT lymphoma

• gastric adenocarcinoma

How do NSAIDs lead to mucosal damage

• inhibit COX1 pathway = less prostaglandin production (E2 + I2)

• decreased gastric defence mechanisms

Symptoms of upper GI bleed

• haematemesis

• Melaena

• Haematochezia

• Epigastric pain

• Haemodynamic instability

Gastric outlet obstruction

blockage that impairs normal stomach emptying

Causes: benign, malignant, functional

Gastric outlet obstruction management

• acid suppression therapy

• Avoid NSAIDs

• Test/treat H. Pylori

• Endoscopic balloon dilation

• Surgical intervention

Clinical presentations of ulcers/PUD

• epigastric pain

• Bloating

• Vomiting

• Belching

• Melaena

• Haematemesis

Peptic ulcer disease

gastric ulcers → lesser curvature of stomach, increased pain while eating due to HCL production, weight loss

Duodenal ulcers → duodenal bulb, decreased pain while eating, weight gain

Main causes: NSAIDs, H.Pylori

Complications of PUD

• malignancy

• Perforation

• Bleeding

Clinical presentation of ulcer perforation

• severe epigastric pain

• Tachycardia

• Hypotension

• Guarding

• Abdominal distension

Perforation diagnosis

• bloods

• Imaging → xray or CT (gold standard)

Perforation management

• Resuscitation

• IV PPI

• NG tube for gastric decompression

• Surgical intervention

• Broad spectrum antibiotics

What is the most common congenital GI defect

Meckel’s diverticulum → pouch on distal ileum (true)

Dual blood supply + venous drainage of liver

• hepatic artery proper (25%) + hepatic portal vein (75%)

• Hepatic veins → IVC

LFTs: blood markers + significance

• bilirubin: quantifies jaundice

• Albumin: liver synthesis function

• AST+ALT: hepatocellular injury

• Alkaline phosphate: raised in biliary obstruction

• Gamma-GT: chronic hepatocellular injury

Bilirubin + its metabolism

• Haemolysis: haem from RBCs broken down into uncojugated bilirubin

• albumin binds + moves to hepatocytes

• conjugated with glucuronic acid → bilirubin (water sol)

• Bilirubin → urobilinogen → sterobilin (faeces colour)

Urobilinogen recycling

• reabsorbed into blood + oxidised → Urobilin

• Sent to liver - recycled into bile

• kidneys - excreted giving urine yellow colour

Jaundice

yellowing of skin + sclera due to accumulation of bilirubin

Clinically detectable >34 µmol/L

Divided into: prehepatic, hepatic + post hepatic

Why does sclera show earliest sign of jaundice

tissue is high in elastin → bilirubin binds with high affinity

Pre-hepatic jaundice causes (excessive haemolysis)

• G6PD deficiency

• Sickle cell anaemia, Thalassaemia

• Hereditary spherocytosis

• Malaria

• Rifampicin

Unconjugated hyperbilirubinaemia

Intrahepatic causes of jaundice

• hepatitis

• Alcoholic liver disease

• cirrhosis

• Haemochromatosis

• Crigler Najjar syndrome

• Gilbert’s syndrome

Crigler Najjar syndrome

• rare autosomal recessive metabolic disorder

• Bilirubin conjugating enzyme (UGT1A1) decreases/absent

• Unconjugated hyperbilirubinaemia

• Can cause neurological impairment

Gilbert’s syndrome

• autosomal recessive

• Decreased activity of UGT enzyme → less conjugation

• Bilirubin increases during physiological stress (episodic)

Causes of hepatitis

• viral → A-E

• Alcohol

• Drug induced

• Autoimmune

Clinical features of liver cirrhosis

• anaemia

• Jaundice

• Bruising

• Palmar erythema

• Dupuytren’s contracture

Post-hepatic causes of jaundice

• head of pancreas carcinoma

• Pancreatitis

• Gall stones

• Cholangiocarcinoma

Bile function + components

Concentrated detergent that aids in lipid absorption + digestion. Composed of:

• Bile acids + salts

• Cholesterol + lecithin

• Pigments

• Bicarbonate

Bile acids

• primary: Synthesised from cholesterol in liver (cholic + chenodeoxycholic acid)

• Secondary: synthesised by intestinal bacteria (deoxycholic + lithocholic acid)

• 95% recycled

Bile salt synthesis

Formed when primary acids are conjugated w/ glycine or taurine

Regulates rate of bile production + can be recycled up to 20 time

What structural feature of bile salts enables emulsification

Amphipathic → hydrophilic + hydrophobic regions

Allows emulsification (smaller particles = larger SA) + transport of lipids → micelles

Consequence of inadequate bile/pancreatic lipase secretion

Poor fat digestion = steatorrhea

Fat soluble vitamins A,D,E +K not absorbed

Exocrine pancreas function

Produces + secretes pancreatic juice → enzymes (produced from acinar cells) + alkaline fluid (ductal epithelial)

Juice flows through pancreatic duct to duodenum

Constitutes for 98% of pancreatic tissue

Functional anatomy of exocrine pancreas

• Serous acinus: secrete enzymes into intercalated ducts

• Intercalated ducts: lined w/ cuboidal epithelium that secrete HCO3-

(Dark pink= exocrine pancreas, light pink= endocrine)

Examples pancreatic digestive enzymes + location of synthesis

• trypsin

• Amylase

• Lipase

• Elastase

• Carboxypeptidase

• Chymotrypsin

Synthesised on RER + transported via Golgi