Consequences of fluid Loss from the GI Tract Flashcards
what is meant by “Insensible water loss”
water loss by transepidermal diffusion, so it is water that evaporates through the skin and respiratory tract
what do water intake and output do?
balance each other out
excretion (loss) of water and salts is usually small, but when is it large?
diarrhoea
sweating
vomiting
haemorrhage
losing a lot of electrolytes which can cause problems
kidneys can do what?
alter excretion to match gain with loss
why would you decrease salt intake?
to prevent hypotension
intake of salt should be?
similar to the output
list ways in which water, electrolytes and sodium chloride are lost
Defecation, diarrhoea Vomiting Urination Ventilation Sweating Menstruation
list ways in which water, electrolytes and sodium chloride are gained
Drinking
Metabolic (what we eat)
define diarrhoea
characterized by both an increase in frequency and weight of the stool
↑ frequency, with ↑ volume and fluidity of faeces
Greater than 3 unformed stools per 24hrs
give 2 reasons why diarrhoea occurs
- Failure of water absorption (Enterocytes lose ability to reabsorb as Toxins can bind)
- ↑ secretion (HCO3-, enzymes, Na+, due to crypt cell hyperplasia)
OR both
Causes of decreased absorption
↑ number of osmotic particles (osmotic diarrhoea)
↑ rate of flow of intestinal contents (deranged motility diarrhoea)
Abnormal increase in secretions of GIT (secretory diarrhoea)
Osmotic diarrhoea
occurs when too much water is drawn into the bowels
if a person drinks a solution with excessive sugar or excessive salt (an osmotically rich solution), this can draw water from the body into the bowel and cause osmotic diarrhoea
what can the build up of bacteria cause
de-conjugation of bile salts, which can cause osmotic or secretory diarrhoea
Deranged motility diarrhoea
the motility of the small intestine increases, meaning there is reduced time for reabsorption
this means that the volume of the fecal content will increase
some agents may promote secretion as well as motility
Secretory diarrhoea
increased secretion of ions from the crypt cells
very common in cholera
what can cause osmotic diarrhoea?
Disaccharidase deficiency (can be due to carbohydrate intolerance)
e. g. lactose intolerance
- due to lack of the brush border enzyme lactase, lactose cannot be broken down into Glucose and Galactose
what can cause secretory diarrhoea?
ACh, substance P, 5-HT and neurotensin act via ↑[Ca2+] (intracellular calcium levels) to increase rate of intestinal secretion
Excessive laxative use, defects in digestion and absorption, infections (cholera)
cholera survives acidic conditions of gut
enterotoxin stimulates adenylate cyclase, which increases cAMP levels leading to Na+ loss, Cl- loss (from crypt cells) and therefore uncontrolled water loss
what are crypts?
grooves between the villi (small fingerlike projections that line the small intestine and promote nutrient absorption)
how do you combat losing water, electrolytes and glucose
oral rehydration therapy so you can replace it all
what can inflammatory bowels disease cause?
chronic exudative diarrhoea, where you are producing a lot of fluid
why might GI stasis promote diarrhoea?
stimulating bacterial overgrowth, which could deconjugate the conjugated bile acids
what is dysentery?
painful, bloody, low volume diarrhoea
extreme urge to go but very little comes out
what is giardia, and what does it cause
a parasitic cause of diarrhoea
causes steatorrhoea and abdominal pain, maldigestion & malabsorption of lipids, CHOs, vit A, vit B12, folic acid.
causes of bloody diarrhoea?
- Chronic disease
- Ulcerative colitis
- Neoplasm
neoplasm
a new and abnormal growth of tissue in a part of the body, especially as a characteristic of cancer
major consequences of severe diarrhoea
excessive loss of water, nutrients, Na+, K+ and HCO3- causes:
↓ blood volume (hypovolaemia)
metabolic acidosis – due to loss of HCO3-
what can volume depletion lead to?
acidosis/alkalosis
consequences of excessive vomiting
↑ salt and water loss
Severe dehydration
Circulatory problems – as volume of water has dropped
Metabolic alkalosis – due to loss of gastric acid (HCl)
Death
What is lost in vomit?
Food
Mucus with Na+, K+, Cl-, HCO3-
Gastric acid
Upper intestinal contents (incl. bile)
Blood
consequence of vomiting up lots of gastric acid?
can affect the lining of the oesophagus
consequences of fluid loss from GI Tract
Hypovolaemia (decreased blood volume)
Haemoconcentration/polycythaemia leads to an increase in [RBC]
Dehydration
Ionic imbalances (due to loss of electrolytes), poor perfusion of tissues
Malnutrition and ↑ mortality
what does polycythaemia/erythrocytosis mean?
having a high concentration of red blood cells in your blood
-makes the blood thicker and less able to travel through blood vesselsand organs. many of the symptoms of polycythaemia are caused by this sluggish flow of blood
Signs and symptoms of polycythaemia
- headache
- blurred vision
- red skin, particularly in the face, hands and feet
- tiredness
- high BP
- dizziness
- abdomen discomfort
- bleeding problems
- Gout-which can cause joint pain, stiffness and swelling
- Itchy skin- the result of white blood cells releasing histamine
Consequences of hypovolaemia:
↓ venous return
Arterial hypotension
Myocardial dysfunction due to ↑ myocardial oxygen demand, but reduced tissue perfusion
tissues are not able to respire properly in terms of aerobic respiration, so ↑ anaerobic metabolism → acidosis
Acidosis and myocardial dysfunction → multi-organ failure
Haemoconcentration
Decrease in the volume of plasma in relation to the number of red blood cells; increase in the concentration of red blood cells in the circulating blood
how does hypovolaemia come about?
- haemorrhage
- insufficient fluid intake
- excessive fluid losses from diarrhea or vomiting
- can often be induced by excessive use of diuretics
indicators of hypovolaemia
- absence of perspiration
- light headedness
- dark coloured urine
consequences of dehydration on the organs
brain has priority
-takes water from rest of the body when you’re thirsty
kidneys get overloaded
-toxins accumulate and cannot be flushed. kidneys can be damaged
heart has to work harder
-higher blood viscosity. higher blood pressure. blood clotting
consequences of dehydration
heat shock, headache,
fainting
digestive problems
- constipation
- acid reflux
- indigestion
- toxins accumulate
- reduced nutrients
reduced skin turgor
confusion and lack of mental awareness
Dryness of the lips
There may be reflux
why does dehydration cause confusion and lack of mental awareness?
because the brain cells have shrunk
why might dehydration cause reflux?
the secretions that come from the pancreas to neutralise the duodenal chyme need large amounts of water
reduced water means there is reduces neutralisation, meaning chyme builds up, pressure builds up and it can then be refluxed out
physiological response to water loss (look at powerpoint)
Increased sodium and water loss
volume of plasma goes down, venous return goes down
So, corrective mechanisms will be put in place to correct this
increased activity of renal sympathetic nerves, causing constriction of renal arterioles
decreased net glomerular filtration pressure allowing more time for reabsorption
GFR goes down meaning there is decreased sodium and water secretion
sodium and water blood volume increases
Water loss by sweating and physiological adaptations to it
severe sweating means there is a loss of hypo-osmotic salt solution which causes a:
- decrease in plasma volume, so sodium excretion is reduced by increasing plasma aldosterone and vasopressin, and decreasing GFR
- increase in plasma osmolarity, so H2O excretion is reduced by increasing plasma vasopressin (ADH)
Response of the body to the consequences hypovolaemia: RAAS cascade
look at notes
The RAAS cascade can happen as a result of low sodium, or high potassium
Macula densa senses
[NaCl]fluid passing it; ↓[NaCl] causes
↑renin release
↓ resistance to blood flow in the afferent arterioles via vasodilation →normal GFR
increased renin means increased angiotensin II means increased aldosterone
Physiologic response to the consequences of hypovolaemia with increased potassium concentration
increased plasma potassium causes increase aldosterone secretion into the plasma, leading to increased potassium secretion and excretion
Physiologic response to the consequences of hypovolaemia
- osmolarity goes up in plasma
- osmoreceptors in hypothalamus are stimulated
- secretion of vasopressin from posterior pituitary
- vasopressin will stimulate receptors on the collecting tubules and insert channels on the collecting tubules called aquaporin 2
- increased water reabsorption
Physiologic response to the consequences of hypovolaemia - THIRST
look at notes
The osmoreceptor input is very important
Feeling thirst drives us to seek water and ingest it is stimulated by lower extracellular volume and higher plasma osmolarity
increase in plasma osmolarity is detected by osmoreceptors
also, dryness of the mouth and throat causes thirst which can be relieved by moistening them. decrease in plasma volume detected by baroreceptors which increase angiotensin II
how is over-rehydration stopped?
Metering of water intake by GI tract
what can dehydration do to calcium levels?
increase them
what is hypercalcaemia, and what are the risks associated with it?
↑ [Ca2+]
↑ risk of kidney stones, kidney failure, dementia and arrhythmia
Symptoms of hypercalcaemia
If mild= asymptomatic Nausea Vomiting Loss of appetite Constipation Abdominal pain Excessive thirst
Fatigue, lethargy, muscle weakness
Joint pain, confusion
What regulates water loss?
Vasopressin (antidiuretic hormone, ADH)
ADH stimulates thirst mechanism
Increased osmolarity of body fluids causes what?
ADH release
How does ADH work?
Inserts water channels (aquaporin-2) in collecting duct of kidney
This increases the permeability of the collecting ducts to H2O and results in concentrated urine production
intake of plain H2O leads to what?
a ↓ in osmolarity of blood and interstitial fluid
this decreases ADH secretion and the removal of the water channels
what is osmolarity?
how concentrated a solution is, i.e. the total number of solute particles per litre of solution
Factors that regulate ADH release
Large decrease in blood volume (detected by baroreceptors)
Severe dehydration: under this condition, GFR decreases causing less H2O in urine
Hyperventilation: results in increased fluid loss (exhalation)
Vomiting/diarrhoea: causes increased fluid loss from GIT
Fever, heavy sweating, and burns cause large H2O loss
***ADH secretion in all these cases leads to conservation of body H2O
what happens when there is an intake of copious amounts of water
results in high BP, which causes increased GFR and increased H2O in urine
how in ANP/ANF involved in H2O balance?
Stimulates natriuresis - increased excretion of Na+, Cl- and H2O
Increased loss of water in urine
factors involved in H2O balance?
look at notes
thirst centre in hypothalamus
ANP/ANF
ATII
Aldoesterone
ADH
