Lecture 17: Fluid and electrolytes balance Flashcards
The intestine turnovers how many litres of fluids per day
9L
The human microbiota comprises of ____ microbial residents in the human body, vastly outnumbering host cells.
104
There is a degree of heritability of this microbiota, as shown in twin studies, but it is clear that there are many environmental factors that can impact.
Name some of the environmental factors
diet, drugs, physical activity, smoking, stress and natural ageing.
Define diarrhoea
Three or more loose or liquid stools per 24 hours, and/or
Stools that are more frequent than what is normal for the individual
Stool weight greater than 200 g/day
Describe the osmotic diarrhoea
The gut mucosa acts as a semipermeable membrane and fluid enters the bowel if there are large quantities of non-absorbed hypertonic substances in the lumen. This occurs because the patient:
- Has ingested a non-absorbable substance (e.g. a purgative, such as magnesium sulphate or magnesium-containing antacid)
- Has generalized malabsorption, so that high concentrations of solute (e.g. glucose) remain in the lumen
- Has a specific absorptive defect (e.g. disaccharidase deficiency or glucose-galactose malabsorption).
The volume of diarrhoea produced by these mechanisms is reduced by the absorption of fluid by the ileum and colon. The diarrhoea stops when the patient stops eating or the malabsorptive substance is discontinued.
Name some of the causes of osmotic diarrhoea
- Laxatives, antacids,
- Acarbose (alpha-glucosidase inhibitor)
- Orlistat (lipase inhibitor)
- Digestive enzyme deficiencies (lactase)
- Pancreatic insufficiency
- Inflammatory disease
- Short bowel syndrome
The fluid content of the average diet is typically 1.5 to 2.5 L/day. However, the fluid load to the small intestine is considerably greater—8 to 9 L/day. The difference between these two sets of figures is accounted for by what?
by salivary, gastric, pancreatic, and biliary secretions, as well as the secretions of the small intestine itself
SGLT-1 transports what?
Transports glucose and sodium into the enterocyte
Why are electrolytes e.g. sodium put into oral dehydration therapy
Because electrolytes drive the rebasorption of water
Describe secretory diarrhoea
There is both active intestinal secretion of fluid and electrolytes, and decreased absorption.
Name some of the causes of secretory diarrhoea
- Enterotoxins (e.g. cholera, E. coli thermolabile or thermostable toxin, C. difficile toxin)
- Hormones (e.g. vasoactive intestinal peptide in Verner–Morrison syndrome; see p. 512)
- Bile salts (in the colon) following ileal resection
- Fatty acids (in the colon) following ileal resection
- Some laxatives (e.g. docusate sodium).
Describe inflammatory diarrhoea
Diarrhoea occurs because of damage to the intestinal mucosal cell due to inflammation so that there is a loss of fluid and blood.
In addition, there is defective absorption of fluid and electrolytes. Common causes are infective conditions (e.g. dysentery due to Shigella) and inflammatory conditions (e.g. ulcerative colitis and Crohn’s disease).
Name the different types of intravenous fluids
- 9% Normal Saline ( also known as NS, 0.9NaCl, or NSS)
- Lactated Ringers- isotonic crystalloid that contains sodium chloride, potassium chloride, calcium chloride, and sodium lactate in sterile water.
- 5% Dextrose in Water- isotonic carbohydrate (sugar) solution that contains glucose (sugar) as the solute.
- 4.5% Normal Saline- hypotonic crystalloid solution of sodium chloride dissolved in sterile water (unlike 0.9% Normal Saline which is isotonic
Which factors influence the rate of fluid replacement
- Age
- Cardiovascular status
- Renal function
- How much time it took for dehydration to develop
- Severity of dehydration
What are the 3 classifications for diarrhoea in relation it to time duration
Acute < 2 weeks duration
Persistent > 2 weeks duration
Chronic > a month
What is the unique characteristics of inflammatory diarrhoea
- low volume
- mucus and blood in stool
- Tenesmus
- crampy abdominal pain
