Homeostasis Flashcards
Define homeostasis
Homeo=sameness stasis=standing still
Detailed homeostasis definition
Ability of a living organism to keep the internal conditions at dynamic equilibrium, despite intrinsic and extrinsic changes
What fundamental technique does homeostasis use?
Feedback loops
State the four components of a feedback loop
Stimulus/variable, sensor, control centre, effector
When does a negative feedback loop stop
When the effector ceases
When does a positive feedback stop
When the stimulus ceases
What does each feedback loop do to the stimulus? - give an example
Negative - removes it, insulin removing glucose
Positive - exaggerates or enhances it, oxytocin causing the uterus to stretch
What is the normal range of human body temperature?
36-38 degrees
SSCcE for temperature
S - change in temp
S - skin, hypothalamus
Cc - hypothalamus (in the thermostat)
E - fat, hair, blood vessels, sweat glands
What is the range of pH for humans?
And why?
7.35-7.45
Normal cellular metabolism happens in this range
Organs responsible for maintaining acid base balance
Lungs and kidneys
Range of acidosis and alkalosis
7-7.35
7.45-7.8
What is the pH of stomach acid?
What can it cause if it enters the oesophagus
Or through the stomach lining?
1.5-3.5
Oesophagitis and stricture (closes)
Gastric ulceration
What is the limit of human tissue survival for pH?
6.8 - 7.8
What is the normal plasma pH?
7.35-7.45
What is the [H+] for pH of 7.4?
So what is 7.1, 6.8 and 7.7
40nM
80, 160, 20
What colour is arterial blood in comparison to venal and why?
Bright red, more O2 bonded to haemoglobin to make oxyhaemoglobin - more alkali
Venal blood has more CO2 -more acidic
Symptoms of acidosis
Headaches, confusion, tired, tremors, coma
What compounds in the blood are used to control treat acidosis?
Bicarbonate solution - increases pH
Mechanical ventilation - drives CO2 out (dissolved CO2 is acidic)
What percentage water is for a standard adult?
60%
Proportion of water that is extra cellular and intracellular
1/3
2/3
How is extra cellular water divided?
Interstitial - 3/4
Plasma - 1/4 - 0.5L in the transmembrane space
What happens if there is not enough or too much water, in general?
Dehydration
Toxicity, metabolic failure
Comparison of total body water between elderly, man, woman, child?
Elderly and women - lower proportion of muscle and higher proportion of fat
Man - higher muscle
Child - high sa:mass so high total body water
More muscle - higher total body water (muscle is mainly made of water)
Describe a hypotonic SOLUTION
Inc description of osmotic pressure
- higher conc of water - more dilute
- lower conc of solutes
- lower osmotic pressure
What is osmolality?
Conc of a solution, expressed as the total number of solute particles per kg
Osmolality calculation when positive metal ions are involved
E.g. Sodium 140
You must double the amount with each metal, as it dissociates with Cl- (the Cl- are osmotically active)
So Na 140 + Cl 140 = 280
Summarise what happens when there is not enough water (outside of the cell)
Shift in osmotic pressure
Cells and tissue give up their water into the interstitial fluid compartment
They shrink
Summarise what happens when there is too much water consumed
Reduction in Na+ conc in the extracellular fluid
Shift in osmotic pressure
Water osmoses into the cells
Cells and tissue swell (oedema)
What kind of solutions do patients need?
Isotonic
IV = 0.9% NaCl
What controls bulk water flow?
Via integral aqua protein
What is oedema?
Fluid retention - ‘dropsy’
What is an equation that explains how odeomas form?
Hydrostatic pressure>osmotic pressure
(Out>in)
What is hydrostatic pressure?
Force exerted by fluid on the vessel wall
What is osmotic pressure?
Force applied by the solute to prevent osmotic movement across the membrane
What is the control centre?
Something that retains the desired value of the variable/stimulus and can compare it to the current value - which is provided by the sensor
What happens to the body at high or low temperatures?
High - enzymes denature
Low - insufficient energy to maintain metabolic processes
What are the two sensors in humans
Skin
Hypothalamus
What happens to the temperature when infected with bacteria?
Why?
Toxins from bacteria and chemicals produced by the immune system
Increase the set point in the hypothalamus
Initiating shivering and increased metabolic rate
Higher temperature
What is pyrexia?
A fever
Abover 38 degrees
Why is a fever good when you are infected?
Immune system works optimally
Equation of pH in relation to [H+]
pH=-log10[H+]
Two general causes of acidosis
Where are they controlled?
Metabolic - kidneys
Respiratory - lungs
How is stomach protected by gastric juice?
Special issued epithelial cells that secrete substances, like mucus
What is the movement of water across semi permeable membranes dependent on? (2)
Define both
Hydrostatic pressure - pumping of heart
Osmotic pressure - conc of solute particles
Describe the protective mechanism, to prevent over consumption of water
Increase in plasma osmolality detected by the hypothalamus
Before fluids absorbed from the GI tract
Feeling of thirst is quenched
Symptoms of dehydration
Dry mouth, thirst, low urine output, fever, dizziness
What does a loss of blood plasma volume lead to
Increased conc of blood components (viscosity)
^ so an increased workload of the heart
Tachycardia
What is the name of the condition when the body temp is above 38 degrees?
Pyrexia
What is rigor?
What triggers it?
An episode of shaking or exaggerated shivering which can occur with a high fever
Triggered by pyrogens
What are febrile seizures?
Seizure of an infant between 6 months-3 years
Response to high temp
What molecule is the highest contributor to oncotic pressure?
Albumin
