1. Body Fluids Flashcards
Define homeostasis
the tendency towards a relatively stable equilibrium between interdependent elements maintained by physiological processes
Simple homeostasis definition
the process by which cells, tissues and organisms maintain the status quo
What needs to be kept constant within the internal environment?
oxygen, carbon dioxide and salt concentration.
waste, nutrients, temperature, pH, volume, pressure
What are the components of a feedback loop?
Stimulus
Sensor
Control
Effector
Describe the temperature negative feedback loop
Body temperature exceeds 37 +- 0.5
Nerve cells in skin and brain sense this
Temperature regulatory centre in brain responds
Sweat glands respond to act on stimulus
Describe some responses to rise in body temperature
Sweating, vasodilation, pilorelaxation, stretching
Describe some responses to a decrease in body temperature
Curling up, shivering, vasoconstriction, piloerection
Describe the feedback loop for glucose levels
Blood glucose levels rise
Detected by the insulin-secreting cells in the pancreas
Pancreas secretes insulin
Insulin causes liver cells to store glucose as glycogen
Glucose also taken up by fat adipose tissue
Glucose levels decline
Insulin secretion turned off
Examples of positive feedback
Blood clotting by platelets and release of chemokines
Release of oxytocin during childbirth
What stops positive feedback?
When the initiator ceases
What stops negative feedback?
When the effector ceases
Describe the positive feedback system present during childbirth.
Baby pushes on cervix Nerve impulses sent to hypothalamus Release of oxytocin from posterior pituitary Oxytoxin causes uterus to contract Continues until the baby has been born
What is the core body temperature?
37 +- 0.5 C
What is defined as the core body temperature?
The head and thorax, head and neck by extension
Define heterostasis, within core body temperature
New set point is reached, new core body temperature established
Outline the process for temperature regulation
Hypothalamus is main set point, thorax is another control point. Thermal error signals are released and integration of these within the body causes effectors to act.
Symptoms of elevated body temperature
Heat exhaustion: unconscious, dizzy, fits
Heat stroke: dry skin, hot, bounding pulse
Fever: sweaty skin, cramping and pale
Symptoms of hypothermia
shivering, fatigue, slurred speech, drowsiness.
Severe: rigid, weak pulse, unresponsive
At what temperature is heat stroke and exhaustion?
Above 40
At what temperature is hypothermia?
Below 35
What is our normal body pH?
Between 7.35-7.45
What two major organs are responsible for maintaining the acid-base balance?
Short term: the lungs - respiratory balance
Long term: the kidneys - metabolic balance
What pH is considered alkalosis?
Between 7.45 and 7.8
Above 7.8 - death
What pH is considered acidosis?
Between 7 and 7.35?
Below 7 - death
What is the blood buffer equation?
H+ + HCO3- H2CO3 H20 + CO2
What happens in the blood as a result of hyperventilation?
Blood is too alkaline due to increase in carbon dioxide and little oxygen
Describe the kidneys’ regulation of pH
If blood is too acidotic: kidneys excrete H and retain HCO3
If the blood is alkylotic, kidneys retain H and excrete HCO3
What is gastric pH?
It is between 1.5-3.5
Describe some symptoms if acid in the stomach affects the body.
Oesophagitis (inflammation)
Stricture (closing)
Gastric ulceration and perforation.
What is the limits of human tissue survival?
6.8 to 7.8
What is the concentration of H at:
- pH 7.4
- pH 7
7.4 = 40 nanomoles/litre 7 = 100 nanomoles/litre
What buffer systems are present within the ECF?
Carbonic acid bicarbonate and protein buffer system
What buffer systems are present within the ICF?
Phosphate buffer system and protein buffer system for plasma proteins, amino acids and RBCs
What is the buffer system for the blood?
Carbonic acid bicarbonate buffer system
How many litres of fluid is needed to maintain a healthy adult?
2.5 litres
What are the body fluid compartments?
60% of the body is water: 2/3 is ICF 1/3 is ECF, of which: - 80% interstitial fluid - 20% plasma
How much water is present within a 70kg man?
60% = 42 litres/kg
What is the volume of blood within a standard male?
5 litres
What is the relationship between total body water (TBW) and body fat?
Greater amount of fat = lower TBW.
Infants have the highest, and males more than females.
Define isotonic
The same amount of water on both sides of the plasma membrane
Define hypertonic
Less water inside the cell, soluble concentration inside the cell is lower. Cell shrinkage occurs.
Define hypotonic
Less water outside the cell, solute concentration inside the cell is higher and so water moves into the cell.
Cell inflates and eventually bursts.
What is the process if there is not enough water within the body?
Cells and tissues initially absorb water from the intersitial space. Then from other cells.
Then from the brain, liver, kidneys, heart.
What are some causes of dehydration?
Extreme warm weather, excessive sweating, vomiting, diarrhoea, burns.
Define osmosis
A process by which a solvent, usually water, passes through a semi permeable membrane, from a less concentrated solution to a more concentrated one.
What allows bulk flow of water through a cell membrane?
Aquaporins allow for discrete water flow.
What regulates bulk water flow through aquaporins?
The amount of glycerol within the cell.
Define osmolality
The concentration of a solution expressed as the total number of solute particles per kilogram.
It is a function of the concentration of particles in solution expressed in milliOsmoles (mOsm/kg)
How do you calculate osmolality?
For a solute that ionises, e.g. NaCl dissociates into Na and Cl as each is independently osmotically active - so each millimole in solution would provide 2 mOsm.
For example, 140 mmol/L of sodium would mean 140 of Cl too.
What is oedema?
Oedema is fluid retention within the interstitial space. Peripheral oedema is swollen ankles.
It is when hydrostatic pressure is greater than osmotic pressure.
What causes oedema?
- Raised hydrostatic pressure in the capillary - vasodilation, congestion heart failure.
- Decreased oncotic pressure in the capillary - low albumin.
- Increased oncotic pressure in the interstitium, leakage of plasma proteins.
- Impaired lymphatic drainage.
