Homeostasis Flashcards
Fluid compartments, feedback loops, skin as an example of homeostasis
What fluid compartments are there in the human body?
Plasma (liquid component of blood)
Interstitial fluid (surrounds and bathes body cells)
Intracellular fluid
Describe the fluid distribution in the human body.
2/3 - Intracellular fluid
1/3 - Extracellular fluid
1/4 EF - Plasma
3/4 EF - Interstitial fluid
Define interstitial fluid.
Fluid that bathes and surrounds the body cells
What does the lymphatic system do with regard to interstitial fluid?
Lymphatics remove excess interstitial fluid from interstitial space by draining it into the bloodstream
What are 5 means of fluid output?
Kidney
Faeces
Skin
Sweat
Lungs
What are the factors affecting body water content?
Gender (males 60% > females 55%)
Age (young > old)
Body fat (more body fat - less water)
Reasons for increased output of fluid.
Diarrhoea, vomiting
Reasons for decreased output of fluid
Kidney failure leading to decreased urination, causing accumulation of water in the body
Define osmolarity.
A measure of the concentration in solution expressed as the number of solute molecules per litre of solvent
Unit - mOsm/L
Define osmolality.
A measure of the number of solute molecules per kilogram.
Unit - mOsm/kg
Compare the osmolarity of the three fluid compartments.
Same throughout due to osmotic equilibrium
Compare the ionic composition of the three fluid compartments.
Potassium: Intracellular fluid > Plasma, Interstitial fluid
Sodium and chloride: Plasma, Interstitial fluid > Intracellular fluid
Plasma and interstitial fluid contain phosphate
Compare the protein content of the three fluid compartments.
Intracellular fluid: Intracellular proteins
Plasma: Plasma proteins
Interstitial fluid: Only a small amount of proteins
How is interstitial fluid formed?
Through filtration of fluids across capillaries
Capillaries have highly permeable walls to solutes and water
Arteries and veins are usually impermeable to solutes and water
Define the Starling forces.
Forces that determine the movement of fluid between capillaries and interstitial space, and they determine the rate of filtration across capillary.
What are the Starling forces?
1) Hydrostatic pressure: force generated by the pressure of fluids
2) Colloid osmotic pressure / Oncotic pressure: force generated by proteins in plasma or interstitial fluid attracting water (works like a sponge)
How does hydrostatic pressure act as a Starling force?
Hydrostatic pressure of capillary (Pc) is higher than that of interstitial space (Pi)
Hence, pressure gradient forces fluid out of the capillary into the interstitial space
How does colloid osmotic pressure act as a Starling force?
More proteins in plasma, more pressure generated, hence more water is drawn out of interstitial space into the plasma.
What is oedema?
Accumulation of excessive fluid in the body
How do low plasma protein concentration cause oedema?
Low plasma proteins
Low colloid osmotic pressure
Reduced forces promoting fluid reabsorption into capillary
Increased interstitial fluid volume, oedema
Define homeostasis.
Maintenance of a relatively stable internal environment.
What are some examples of homeostatically-regulated functions?
1) Fluid volume
2) Blood glucose levels
3) Concentration of mineral content (electrolytes)
4) Blood pressure
5) Concentration of O2 and CO2
6) Adequate nutrients
7) Temperature
8) pH
9) Concentration of waste products
What are homeostatic control systems?
Functionally interconnected network of body components that operate to maintain a given factor in the internal environment at a relatively constant level
What must homeostatic control systems be able to do?
1) [SENSOR] Detect a deviation of a particular factor in the internal environment from set point
2) [INTEGRATOR/CONTROLLER] Integrate this information
3) [EFFECTOR] Make changes to the internal environment to restore the deranged variable
Which systems control the homeostatic response in the body?
Nervous and endocrine
How does a feedback loop work?
1) Controlled variable is measured b y sensor
2) Sensor sends input to integrator
3) Integrator sends input to effector
4) Effector changes controlled variable
What kind of feedback drives homeostasis?
Negative feedback
Example of a positive feedback loop
Oxytocin release during birth
1) nerve impulses from cervix transmit signals to brain
2) brain stimulated pituitary gland to release oxytocin
3) oxytocin carried to uterus through blood stream
4) oxytocin stimulates uterine contractions, pushes baby towards cervix
How does genetic markup affect homeostasis?
Genetic markup determines one’s individual characteristics and set pointsn
Name and describe one illness where homeostasis is disrupted.
Diabetes; despite high blood glucose concentration, liver is not stimulated to secrete insulin to take up glucose to convert to glycogen, leads to high blood glucose and damage to blood vessels, kidneys, heart and eyes
What are the roles of skin in the human body?
1) Protective
2) Thermoregulation
3) Water balance
4) Vitamin D synthesis
How does skin fulfil its function as a form of protection?
Forms a mechanical barrier between internal and external environment
Prevents water from leaving the skin
Prevents microorganisms from entering
How to measure body surface temperature? (places)
Forehead
Armpit
Oral
Ear
Rectal
Which one is higher: body core or body surface temperature?
Body core temperature
How does internal heat production occur?
1) Metabolism in al cells
2) Muscle activity
3) Hormone action (thermogenic effect)
4) Sympathetic stimulation
5) Digestion, absorption, storage of food
What are the 4 methods of heat transfer between body and external environment?
1) Evaporation
2) Conduction - direct transfer of thermal energy from molecule to molecule
3) Convection - transfer of heat by air currents
4) Radiation - transfer of heat via electromagnetic waves
What are the two types of thermoreceptors?
Peripheral thermoreceptors and central thermoreceptors (in the hypothalamus, abdominal organs)
What is non-shivering thermogenesis?
Thermogenesis stimulated by cold stress. Cold stress leads to sympathetic nervous system activation, releasing NE and adrenaline that stimulates increase in metabolic activity and heat generation.
Describe three ways that skin is involved in thermoregulation.
1) Skin and subcutaneous fat act together as a heat insulator
2) Vasoconstriction and vasodilation of the blood vessels in the skin
3) Sweating
What causes hyperthermia?
Excessive rise in body temperature
What causes hypothermia?
Excessive drop in body temperature
Name the causes of hypothermia.
Severe hypothyroidism (inability to generate heat)
Severe infections (vasodilation, increased heat loss)
Extremely cold weather
Burns (natural insulator is damaged)
Name the effects of hypothermia.
Confusion (leading to further inability to respond to temperature changes)
Respiratory depression
Abnormal heart rhythms
May be fatal
Name the causes of hyperthermia.
Severe hyperthyroidism (high thyroxin levels; too much heat generation)
Infections
Hypothalamic disorders (damage to temperature control centre)
Heat exhaustion/Heat stroke
Certain drugs
How is the skin involved in water balance?
Acts as a barrier to prevent/minimise water loss.
Stratum corneum acts as a mechanical barrier between skin and external environment.
Lipids in stratum corneum create a hydrophobic barrier that prevents evaporation of water.
How is water lost through skin?
1) Transepidermal water loss (TEWL) - diffusion through skin layers
2) Sweating (mediated by autonomic control)
How is the skin involved in pain?
Presence of nociceptors (pain receptors) in the skin
Describe the pain pathway.
Pain receptors stimulated
First order neuron transmits nerve impulse
Second order neuron in spinal cord transmits nerve impulse
Reaches brain via spinothalamic tract
