What is Unit 3 Case 2 about?
There are 2 patients, both suffering from gastrointestinal infections. The first, Lena, who has returned from travelling. The timeline of symptoms indicates the patient has contracted gastroenteritis, due to enterotoxigenic Escherichia coli. She is treated successfully with oral rehydration therapy. The second patient suffers from Crohn’s disease. The patient develops Clostridium difficile enterocolitis due to the long term antibiotics they have taken.
What is dehydration and what are some effects of dehydration?
Dehydration is when your body does not have as much water as it needs.
- effects can be feeling dizzy or lightheaded, feeling tired, increased urea concentration in urine
- With more serious longer-term effects being the formation of kidney stones, and heart problems
What are the properties of Escherichia coli (E.coli)?
E.coli is a rod-shaped, gram-negative bacteria that infects the gastrointestinal tract
What is the physiology behind vomiting (emesis)?
Located near the medulla oblongata are the chemoreceptor trigger zone (CTZ) and the vomiting centre. Activation if the CTZ via chemicals such as dopamine 2 and serotonin receptors activates the vomiting centre. The vomiting centre produces the vomiting reflex, causing the lower oesophagal sphincter to relax and epiglottis to close, diaphragm and abdominal muscles contract to increase intraabdominal pressure and cause the vomit to move up and out.
What are some common types of pathogenic E.coli?
Shiga toxin-producing E.coli (STEC) Enterotoxigenic E.coli (ETEC) Enteropathogenic E.coli (EPEC) Enteroaggregative E.coli (EAEC) Enteroinvasive E.coli (EIEC)
What are the symptoms of gastroenteritis?
Elevated white blood cell count, elevated C-reactive protein (CRP), elevated serum urea, lack of urine, high heart rate, dizziness, dehydration
What is gastroenteritis?
Gastroenteritis is inflammation of the gastrointestinal tract- the stomach and small intestines.
Where are nutrients absorbed into the blood?
Virtually all nutrients from the diet are absorbed into the blood across the mucosa of the small intestine, alongside water and electrolytes.
Describe the absorption of nutrients in the small intestine
- Sodium and glucose are co transported via facilitated diffusion into the cell through apical SGLT1 glucose/sodium transporter.
- Glucose passively moves into the basolateral side. Sodium is transported out of the cell to the basolateral side of the cell while potassium is transported in- this requires ATP
- Potassium passively moves back out of the cell and chloride ions follow the gradient between cells-paracellular
Describe the secretion of nutrients in the small intestine?
- Chloride passes through into the cell and is actively transported out to the lumen. This requires cAMP
- Potassium and sodium follow this movement into the cell and are recycled back to the basolateral side via active transport
- Sodium moves between cells following the electrochemical gradient set by the chloride ion movement
- A small amount of water can then enter the lumen via osmosis
What is the mechanism of action of Picolax?
Contains 2 laxatives; sodium picosulfate which is a stimulant laxative and magnesium citrate which is an osmotic laxative.
- Sodium picosulfate has no effect on the GI tract until it is metabolised by gut bacteria into its active compound, which stimulates increased peristalsis
- Magnesium citrate causes water to be drawn into the lumen which stimulates defecation
What is Picolax used for?
Picolax is used to treat constipation or as in this case to prepare the large bowel before colonoscopy or surgery
What is the mechanism of action of prednisolone?
- It is a glucocorticoid which is used to reduce inflammation. It passes across the cell membrane to bind to glucocorticoid receptors in the cytoplasm
- This then dimerises and moves to the nucleus where it binds to glucocorticoid response elements in the DNA, altering gene expression
- Reducing the production of pro-inflammatory cytokines and IL-2 and increasing levels of anti-inflammatory cytokines e.g IL-10
What is the mechanism of action of adalimumab?
It is a fully human monoclonal antibody that specifically binds to tumour necrosis factor-alpha (TNF-a). The monoclonal antibodies are highly specific to their target and will bind to the cytokine preventing it from binding to its receptor and reducing the downstream inflammatory effects of the cytokine
-disrupts TNF signalling attempting to encourage resolution of the inflammation
What is the mechanism of action of amoxicillin?
It is a broad-spectrum beta-lactam antibiotic. It inhibits bacterial cell wall synthesis through competitive inhibition of penicillin-binding proteins that cross-link peptidoglycan strands. Bacteria are unable to build the cell wall and therefore undergo cell lysis
What is dysentery?
Dysentery is an intestinal inflammation, primarily in the colon.
What is the infection pathogenesis of common bacteria such as C.difficile and E.coli in food poisoning?
Food poisoning- the ingestion of preformed toxins in prepared food, from organisms that have colonised the substance and produced toxins in situ
What is the infection pathogenesis of common bacteria such as C.difficile and E.coli in gastroenteritis?
The colonisation of the small bowel with organisms requires pathogenicity factors to evade the immune system. Once established, the replication of these organisms and subsequent toxin production or immune action will lead to dysregulated water absorption.
-leads to watery-diarrhoea, nausea and vomiting, and dehydration
What is the infection pathogenesis of common bacteria such as C.difficile and E.coli in dysentery?
Invasion of the gastric mucosa following colonisation is more of a serious problem for the body. Destruction of the enterocytes can lead to the spread of the pathogen or toxin into the system circulation. Characterised by bloody diarrhoea and a greater rise in temperature than gastroenteritis
What is rehydration therapy?
Is the process of replacing water and electrolytes into the body which has been lost
-In oral rehydration therapy a mixture of sodium, glucose, potassium and citrate are mixed with clean water and is drunk
What is a gram stain used for?
A gram stain is used to tell whether a bacterium is gram-positive or gram-negative
How is a gram stain carried out?
A sample is taken from a site of suspected infection or from certain body fluids e.g wound sample, blood test, urine test, sputum test
The sample is then placed on a slide and treated with the gram stain
The gram stain stays purple, what does this indicate?
Gram-positive bacteria
The gram stain turns pink or red, what does this indicate?
Gram-negative bacteria
