Homeostasis of body temperature and fluids Flashcards
What is the constant temperature of the body?
36.8 degrees
What is thermoregulation?
Maintaining the balance between heat production and heat loss
Why is thermoregulation important?
Because the chemical reactions between cells are very heat sensitive
Why does excess heat need to be removed?
In order to prevent the body temperature from rising Other wise it can - cause nerve malfunction - changes in the structure of proteins - death
Thermoregulation feedback…
Negative feedback
- Stimulus: change in body temperature
- Receptors: thermoreceptors
- Modulator: hypothalamus
- Effectors: blood vessels and sweat glands
- Response: vasodilation/vasoconstriction or perspiration rate
- Feedback: change in body temperature
What is metabolic rate?
The rate at which energy is released by the breakdown of food
Factors that effect metabolic rate
Factors such as exercise (greatest effect), stress and body temperature affect the metabolic rate
Exercise (metabolic rate)
- Muscular activity can increase metabolic rate by up to 40 times
- Very large quantities of heat are released
Stress (metabolic rate)
- Sympathetic nerves release nor adrenaline from nerve endings
- Increases metabolic activity of cells
Body temperature (metabolic rate)
- For each 1⁰C rise in body temperature, the rate of biochemical reactions increases by 10%
- When an individual is suffering from a high fever, body temperature may double
Peripheral thermoreceptors
- Located in the skin and some membranes
- Provide information about the external environment
o Cold receptors – stimulated by environmental temperatures lower than usual
o Heat receptors – detect temperatures higher than usual - Both feed information back to the hypothalamus
Central thermoreceptors (location)
Located in the hypothalamus, spinal cord and abdominal organs
Ways heat can be lost from the skin:
- Conduction
- Convection
- Radiation
- Evaporation
Conduction
- Occurs from direct contact with heat source
- EG. Standing on hot sand with bare feet
Convection
- Occurs when hot or cold air passes over a body
- EG. When you get goose bumps when you get cold, there is a layer of air trapped between your hairs and your skin, this air becomes hot and passes over the skin.
Evaporation
- The transformation of water from liquid to gas
- Evaporation of sweat results in heat loss
Radiation
- There is no direct contact with the heat source
Diameter of blood vessels
- Controlled by the autonomic nerves
- Can decrease or increase the flow of blood near the surface of the skin
- Can therefore control the amount of heat lost
- These adjustments are automatic
Sweating
- The active secretion of fluid from the sweat glands
- Periodic contraction of cells surrounding the sweat glands
- Pump sweat to the surface
- Stimulated by the sympathetic nerves
- Is water containing NaCl, small amounts of urea, lactic acid and potassium ions
- When sweat evaporates it has a cooling effect
Where does water also evaporate from?
Water also evaporates from the lungs and respiratory passages
What happens when environmental temperatures fall?
- Cold receptors in the skin are stimulated to send messages to the hypothalamus
- The hypothalamus sends out impulses with the aim of reducing heat loss or increasing heat production
5 responses that prevent body temperature from falling
Vasoconstriction Secretion of hormones Shivering Increased production of thyroxine Behavioral responses
Vasoconstriction (in the skin) to prevent body temperature from falling
- Impulses from the hypothalamus stimulate sympathetic nerves that cause blood vessels in the skin to constrict
- Decreasing the flow of warm blood to the skin
- Decreasing the transfer of hear from the internal organs to the skin
- Skin becomes cooler, as less heat can escape from the body surface
Secretion of hormones to prevent body temperature from falling
- Initiated by the hypothalamus
- Stimulation of adrenal medulla by the sympathetic nerves
- Results in the secretion of adrenaline and noradrenalin
- Increase in cellular metabolism which leads to an increase in heat production
Shivering to prevent body temperature from falling
- The hypothalamus sends nerve impulses to parts of the brain to increase skeletal muscle tone
- Leads to oscillating, rhythmic muscle tremors occurring at a rate of around 10-20 per second
- This increases body heat production
Increased production of thyroxine to prevent body temperature from falling
- Hypothalamus causes the anterior lobe of the pituitary to secrete TSH, causing the thyroid gland to secrete thyroxine
- This increases the metabolic rate, causing an increase in body temperature
- Has a slower, but longer lasting effect. Occurs between warm summer months and cool winter ones
Behavioral responses to prevent body temperature from falling
A person will become consciously aware of cold conditions and may:
- Put on an extra jumper
- Shelter from cold wind
- If they are cold in bed, they may curl up into a ball
Ways to prevent body temperature from rising
- Vasodilation of the blood vessels in the skin
- Sweating
- Decrease in metabolic rate
- Behavioural responses
Vasodilation of blood vessels in the skin (preventing body temperature from rising)
- Increase blood flow to the skin
- Skin becomes a reddish colour
- Surface temperatures rise and therefore there is greater heat loss though radiation and convection
Sweating (preventing body temperature from rising)
- Increases heat loss from the body
- More effective in dry air, sweating cannot evaporate when it is humid
Decreasing metabolic rate (preventing body temperature from rising)
- Less heat is produced in the body
- Brought about by the reduction in the secretion of thyroxine
- Occurs during the summer months
Behavioural responses (preventing body temperature from rising)
- Turning on a fan or air conditioner
- Removing clothing
- Reducing physical activity
Dangerous body temperatures
Over 42 degrees is dangerous
Death usually occurs around 45 degrees
This can result from a high fever
What is heat stroke?
- Occurs when the temperature and relative humidity are high
- It is difficult for the body to lose heat
- Body temperatures rise and regulatory mechanisms cease
- Can be fatal
What is heat exhaustion?
- Occurs as a result of extreme vasodilation and sweating to lose heat
- The loss of water in sweating reduces the volume of blood plasma
- The vasodilation reduces resistance to blood flow
- Therefore, blood pressure falls and the output from the heart decreases
- The person may collapse
What is hypothermia?
- Occurs if a person’s core body temperature falls below 33⁰C
- The metabolic rate becomes so low that heat production is unable to replace heat loss
- Body temperatures can continue to fall
- Death can occur below 32⁰C (although people have survived lower)
Composition of body fluids in males and females
Males: 65% water
Females: 55% water
What is intracellular fluid?
Fluid found inside the cells
EG. cytosol
What is extracellular fluid and what does it consists of?
Fluid found outside the cells
- Intercellular fluid: between cells
- Blood plasma
Why do some molecules tend to remain in the blood vessels?
Due to their size.
Some molecules are too large to move through capillary walls
How are body fluids obtained?
- Fluid intake
- In food eaten
- Small amounts are as by-products of chemical processes
- Referred to as metabolic water
What is excretion?
The removal from the body of the waste products of metabolism
Why is it important not to let waste products build up in the body?
Because every cell produces wastes and many of them are toxic to the body
What are the organs that take part in excretion?
- The lungs
- Sweat glands
- The alimentary canal
The role of the lungs in excretion
- Excretion of CO2 produced during respiration
- Some water is also lost in the form of water vapour when we exhale
The role of the sweat glands in excretion
- Secrete water containing by-products of metabolism such as salts, urea and lactic acid
Role of the alimentary canal in excretion
- Passes out bile pigments that enter the small intestine with bile
- Broken down haemoglobin from red blood cells
- Leave the body with faeces
After being filtered through the glomeruli, how much water is reabsorbed?
99% of water is reabsorbed (along the entire length of the tubule)
At what places along the tubule is water reabsorption by osmosis?
At the proximal convoluted tubule and the loop of Henle
At what places along the tubule is water reabsorption by active reabsorption?
At the distal convoluted tubule and the collecting duct
Anti-diuretic hormone (ADH)
- Produced in the hypothalamus and released from the posterior lobe of the pituitary. Controls the permeability of the tubule walls
- Increase in ADH causes the tubules to become more permeable to water, water then leaves the tubule and enters the surrounding capillaries
- Increases the concentration of urine
Aldosterone
- Secreted by the adrenal cortex
- Increases the amount of sodium reabsorbed into the blood stream
- Increases the amount of potassium secreted into the urine
- Water is also reabsorbed along with sodium
- Increasing water reabsorption increase blood volume, in which in turn increases blood pressure
What happens to osmotic pressure when water is lost from the blood?
Plasma becomes more concentrated and hence has higher osmotic pressure
What are the events that take place to bring about intake of water?
- As water is lost from the various body fluids, there is a reduction in plasma volume and an increase in osmotic pressure
- Osmoreceptors in the thirst centre of the hypothalamus detect the rising osmotic pressure
- Stimulation of the thirst centres make the person feel thirsty
- The conscious feeling of thirst stimulates a person to drink
- The fluid consumed is absorbed into the plasma from the alimentary canal
- As the blood circulates through the body, it enables the intercellular fluid and intracellular fluid to return to the proper osmotic concentrations
What is dehydration?
- When water loss exceeds water intake
- Symptoms are noticeable when a person has lost about 2% of their normal body water
- Loss could have been from sweating, vomiting or diarrhoea
- Thirst reflexes become less effective as we get older
- Symptoms include server thirst, low blood pressure, dizziness and headaches
What is water intoxication?
- Too much water in the body
- Body fluids become diluted and cells take in extra water via osmosis
- May occur if a person loses a lot of water
