Week 3 Flashcards
Outline the regional variations in water and electrolyte uptake in the large intestine.
The anatomy behind this?
Structural difference:
– Tight junctional resistance increases towards the colon
– Tight junctions in the small intestine are ‘leaky’
(permeable via the paracellular route)
– Tight junctions in the colon are ‘tight’ (impermeable via the paracellular route
Regional variations in uptake mechanisms:
- H2O (majority in the small intestine 6.5 litres)
- Na+ in the jejunum, ileum and colon
Electrolyte uptake: Na+, Cl-, HCO3- and K+ are absorbed isosmotically with water by the villi (as in the renal proximal tubule)
Describe the mechanism of intestinal secretion from the crypts of Lieberkuhn
Zone of cell proliferation in the base of the crypts replaces the villous cells every 48 – 96 hours
Mechanism:
– Cl- enters the cell via the Na++K++2Cl- basal transporter
– Cl- diffuses across the apical membrane through apical Cl- channels (regulated by secretagogues)
– Na+ follows Cl- secretion passively via the paracellular pathway
– H2O follows NaCl secretion
e) List common secretagogues and briefly explain their mode of action
2 groups:
- Hormones/NTs: VIP, ACh, Bradykinin. Lead to release of second messenger e.g. cAMP, Ca2+
- Bacterial enterotoxins: Cholera, E coli leads to release of second messengers e.g. cAMP, Ca2+
Second messages increase anion secretion and inhibit NaCl absorption.
I.e. Secretagogues –> Bowel movement
Digestion and absorption of lipids
- Dietary lipids are hydrophobic (insoluble in water)
- They must be solubilised before digestion and absorption can occur
- Digestion begins the stomach with the action of lingual and gastric lipases
- Digestion is completed in the small intestine with the action of the pancreatic enzymes
Describe the digestion of lipids in the stomach
Stomach churns and mixes lipids to initiate enzymatic digestion
Lingual and gastric lipases hydrolyse 10% of ingested triglycerides to glycerol and free fatty acids
Key role of gastric lipase in lipid digestion in the stomach?
Slows the rate of gastric emptying so that pancreatic enzymes are able to digest lipid
What is secreted in the duodenal and jejunal mucosa in response to the presence of monoglycerides and fatty acids and small peptides and amino acids?
Cholecystokinin secreted from the I cells of the duodenal and jejunal mucosa
How are lipids digested in the SI?
- Bile salts, lysolecithin and products of lipid digestion emulsify dietary lipids.
- Emulsification produces small droplets of lipids dispersed in an aqueous solution creating a large surface area for pancreatic enzyme digestion
- Pancreatic enzymes (pancreatic lipase, cholesterol ester hydrolase and phospholipase A2) and the protein, colipase are secreted to complete digestion
Stages of digestion and absorption of lipids
- Bile salts from liver coat fat droplets
- Pancreatic lipase and colipase break down fats into monoglycerides and fatty acids stored in micelles
- Monoglycerides and fatty acids move out of micelles and enter cells via diffusion
- Cholesterol is transported into cells by a membrane transporter
- Absorbed fats combine with cholesterol and proteins in the intestinal cells to form chylomicrons
- Chylomicrons are released into the lymphatic system
Chylomicrons:
Structure?
Location?
Transport?
Structure: Chylomicrons (100 nm diameter) have a core of triglycerides and cholesterol ester - phospholipids and apoproteins on the outside (80%/20%)
Location: Chylomicrons are packaged into secretory vesicles on the Golgi membrane and are exocytosed across the basolateral membrane
Transport: The lymphatic circulation carries the chylomicrons to the thoracic duct which empties into the blood stream
What structures in the Si and LI are responsible for absorption and secretion?
Small intestine:
Villi – absorption
Crypts of Lieberkuhn – secretion
Large intestine:
Surface epithelial cells - absorption
Colonic glands – secretion
Effect of cholera toxin on intestinal secretion
Activates GCP in epithelial cells of the crypts. Leads to Cl- released into the lumen –> Diarrhoea
In the clinical examination of abdomen/ GU:
What is looked at during close inspection of the hands/arms?
Finger clubbing: Due to Malabsorption, Inflammatory Bowen disease,lymphoma, cirrhosis Asterixis (coarse flapping tremor): Due to hepatic encaphalopathy Leuconychia: White deposits on nails Koilongchia: Spoon shaped nails Palmar erythema Dupuytrens contracture Spinal naevus Purpura
GU/abdomen examination
Intro General inspection Close inspection of the hands Radial pulse BP/temp (on charts)
Chest/axillae/ abdomen: Close inspection of face Close inspection chest/axillae Palpation of chest/axillae Palpate bladder Palpate of kidneys Feel abdominal aorta Percussion liver, spleen and bladder Percussion for ascites Auscultation of the diaphragm
Back:
Inspect
Palpate for renal tenderness and cervical lymph nodes
Other areas:
• Offers to examine groin
• Offers to examine genitalia
• Requests to do digital rectal examination (DRE)
Conditions to look for during close inspection of the face in GU/abdomen of the face
Jaundice Mouth: - Glossitis - Oral candidiasis - Angular stomatisis - Peutz-jegers syndrome - Telangiectasia
How to examine chest/ axillae during GU/abdomen exam?
Inspect chest for spider naevi, gynaecomastia in men, and both axillae for loss of axillary body hair.
Movement, distension, scars, hernia, masses etx.
Palpation: -Superficial to deep - Ask patient to point to painful area -Palpate all 9 regions - Watch patients face Liver: -Begin in right iliac fossa -Ask patients to breath in and o§ut deeply -Palpate upwards to right costal margin - Feel for liver edge descending on inspiration. Shouldn't feel anything
What is Murphy’s Sign?
• Feel for gall bladder tenderness (e.g. acute cholecystitis)
• Patient breathes in whilst you gently palpate RUQ in mid-
clavicular line
• On liver descent contact with inflamed gallbladder causestenderness and sudden arrest of inspiration
What is Courvoisier’s Sign?
- Painless jaundice and a palpable gallbladder
* Likely due to extrahepatic obstructionmE.g. Pancreatic cancer, UNLIKELY to be gallstones
What is the process to check for splenomegaly?
- Ask the patient to breathe in and out deeply
- Palpate upwards to left hypochondrium
- Feel for edge of an
enlarged spleen as it descends on inspiration
Characteristic notch may be palpable
Move hand between each breath
Percussion of liver, spleen and bladder method
Percuss up to right costal margin for lower border of liver
Percuss downwards from just above right nipple for upper border of liver
Percuss towards left hypochondrium for lower border of spleen
Percuss from umbilicus down in midline for bladder
What is ascites?
Causes?
Method?
Abnormal collection of fluid in peritoneal cavity
Causes: – Hepatic cirrhosis – Intra-abdominal malignancy – Nephrotic syndrome – Cardiac failure – Pancreatitis – Constrictive pericarditis etc.
Method:
Start in mid-line
Percuss towards flanks
Shifting dullness and Fluid thrill
How is the diaphragm auscultated?
Listen for normal bowel sounds (up to 2 min)
Auscultate for abdominal aortic bruits
Auscultate renal arteries
Why are the cervical lymph nodes examined?
May indicate local disease
May indicate more distant disease:
– Tumours of the upper gastrointestinal tract may metastasise to the lower part of the left posterior cervical triangle
– Virchow’s node / Troisier’s sign
Rectal examination:
Indications?
Key points?
Indications: – Rectal bleeding – Prostatic symptoms – Change in bowel habit – Possible spinal cord injury
Key points:
- Explain procedure
- Gain informed consent
- Offer a chaperone