Week 4 Bioscience Flashcards
1
Q
Water in the body
A
- Water is essential to life
- Body fluids consist largely of water together with dissolved solutes
- Biochemical reactions occur in water
- Sources of water include
◦ Ingested food and fluids
◦ Cellular metabolism (small amount only)
2
Q
Total body water
A
- Influenced by age, body mass, sex and body fat
- In adults, water accounts for
- ~ 60% body weight in males
- ~ 50% body weight in females
- Infants ~ 75% body weight in water
- Less body fat and bone mass
- Amounts reflect differences in
- Adipose Cssue (10% water)
- Muscle Cssue(75% water)
- Total body water declines with age
3
Q
Fluid compartments
A
Two main fluid compartments
1. Intracellular fluid (ICF)
2. Extracellular fluid (ECF)
Three locations in the body
Intracellular– within the cells(cytosol)
Extracellular– outside the cells
◦ Interstitial fluid (IF)
◦ Plasma
4
Q
Composition of body fluids
A
Water – the universal solvent
Body water contains a number of solutes
1. Electrolytes – these dissociate in solution NaCl èNa+ + Cl
2. Non electrolytes - stay together in solution, e.g. glucose, urea.
Electrolytes have greater osmotic power – contribute more than one particle to solution
Each of the fluid compartments has a distinct pattern of solutes
Extracellular fluid
◦ Major cation Na+ ◦ Major anion Cl
Intracellular fluid
◦ major cation K+ ◦ Major anion HPO4 2-
5
Q
Movement of fluid between compartments
A
- There is continuous mixing of fluids between compartments
- Membranes are freely permeable to water but not to solutes
- Fluid moves readily across capillary wall. Facilitated by thin, single layer of endothelial cells.
- Regulated by osmotic and hydrostatic pressures.
- There is a continuous exchange and mixing of body fluids between fluid compartments.
- This is regulated by osmotic and hydrostatic pressures.
- Water can move freely between compartments along osmotic gradients.
- Normally osmolarities of all body fluids are equal. Changes in solute concentrations are followed by osmotic changes.
- Anything that changes solute concentrations in any compartment leads to net water flow.
- In order to reach the intracellular compartment, fluids must pass through both the plasma and the interstitial fluid.
- Exchanges occur between all these compartments almost continuously, leading to compensatory shifts of fluid from one compartment to another.
- So net water movement is equal in all directions.
- Exchange of gases, nutrients, water and wastes occurs.
6
Q
Fluid and electrolyte balance
A
- Adequate cell functioning relies on homeostasis of surrounding fluids.
- Maintenance of fluid homeostasis includes two major tasks:
1. Maintaining water balance within the cells (ICF). This ensures adequate functioning of cells.
2. Maintaining water balance in the plasma. This ensures the tissues of the body are adequately perfused. - Both are achieved by maintaining the correct level of water in the ECF.
- ECF composition and volume maintained within narrow limits.
- Water balance
- Water intake = water output Must maintain solute concentration
- Must replace water losses
7
Q
Water output
A
- Certain amounts of water losses are uncontrollable
- Losses from lungs, skin and digestive tract.
- Kidneys must excrete wastes and some water must accompany them
8
Q
Water input
A
- 60% fluids (approx 1500mls),
- 30% food (approx 750mls),
- plus 10% from cellular metabolism
9
Q
Regulation of water intake
A
- Thirst mechanism the driving force for water intake
- Controlled by the hypothalamus
- Hypothalamic thirst centre stimulated by:
- 1-2% change in osmolarity
- 5-10% change in plasma volume
- Baroreceptor inputs
- Angiotensin II activation
- Feedback mechanisms inhibiting thirst:
- Moistening of mucosa
- Stretch receptors stomach, intestine
- Decrease in osmolarity
10
Q
Influence of hormones on the ECF
A
- Antidiuretic hormone (ADH) inhibits diuresis
- Stimulates water conservation at the kidneys.
- High sodium concentration (increased osmolarity) leads to ADH acts to increase water reabsorption at collecting duct of kidney.
- This conservation of water will dilute Na+ leads to a decrease in osmolarity.
- ADH made by hypothalamus. Stored and released from posterior pituitary.
- ADH works to maintain electrolyte balance of the ECF by conservation of water at the kidneys g decreased urine output.
- Water and electrolyte (in particular Na+ and K+) blood levels are continually adjusted to maintain fluid homeostasis
11
Q
Disorders of water balance
A
- Dehydration- when water output exceed water intake.
- Extracellular fluid loss due to:
◦ haemorrhage
◦ severe burns
◦ severe vomiting and diarrhoea
◦ profuse sweating
◦ low water intake
◦ endocrine disturbances e.g. diabetes insipidus, diabetes mellitus
12
Q
Dehydration
A
- Water is lost from the extracellular fluid.
- Water depletion exceeds Na+ depletion.
- Decreased total body water increases plasma osmolarity (solute concentration).
- Results in hypernatremia (high Na+ in the ECF)
◦ Does not occur in haemorrhage where whole blood is lost (fluids and solutes are lost equally) - Water moves from ICF to ECF via osmosis
- Aim- to equalise osmolarity Cells dehydrate and crenate (shrink)
- Cell functioning is impaired
13
Q
Disorders of water balance
A
- Hypotonic hydration -when water intake exceeds water output.
- Water is added to the ECF, osmolarity decreases.
- Normally ADH would be inhibited → urine output would increase.
- Also called water intoxication or overhydration.
- Occurs with:
◦ renal insufficiency
◦ rapid excess water ingestion
14
Q
Hypotonic hydration
A
- Too much water in the ECF results in relative decrease in solute concentration
- Results in hyponatremia (low Na+ in ECF)
- Water moves from ECF to ICF via osmosis
- Aim - to equalise osmolarity Cells swell, with lysis possible.
- Leads to severe metabolic disturbances
◦ Nausea, vomiting, muscle cramps - Cerebral oedema possible
◦ Disorientation, convulsions, coma, death
15
Q
Oedema
A
- An abnormal accumulation of fluid in the interstitial space.
- A fluid distribution problem where fluid moves from blood to interstitial fluid (IF)
- Caused by:
◦ increases in capillary hydrostatic pressure → Lt or Rt sided heart failure, lymphatic obstruction
◦ increases in capillary permeability → infection
◦ decreases in colloid osmotic pressure →low plasma proteins associated with protein malnutrition, liver disease, kidney disease - Results in swollen tissues, puffy feet, swollen ankles, puffy eyes.
- Can impair tissue functioning because of increased distance oxygen nutrients and wastes must diffuse between cells and blood.
- Fluid shift may severely decrease circulating blood volume.
- Can result in compromised cardiovascular functioning.
- Lymphoedema – accumulation of IF due to surgically removed or blocked lymph glands
