7. Homeostasis of body temperature and body fluids Flashcards
completed
What is the normal human body temperature?
36.8C
What is thermoregulation?
The precise balance between heat production and heat loss
Why is heat important in homeostasis?
Because the chemical reactions occuring in the cells are heat sensitive, and cells function in a stable manner at around 37C
Is body temperature generally higher or lower than outside temperature?
Under most conditions it is higher than the surrounding environmental temperature, and the heat produced from metabolic activity helps maintain this
Why does excess heat need to be removed when exercising?
Increased body temperature can cause nerve malfunction, change in proteins and death
Why might there be variation in body temperature?
Variation may result from illness, physical activity, changes in external temperature
Body goes through daily cycle, temperature is lowest in the morning and highest at night
women have higher temperatures during the second half of the menstrual cycle due to progesterone
What is released during cellular respiration?
Energy in carbohydrates, lipids and protein that are carried in chemical bonds
What is energy used for from cellular respiration?
Energy is used for muscle contraction, active transport, or building new complex molecules but most is released in heat
What is the metabolic rate?
The rate at which energy is released by the breakdown of food
How can exercise influence the metabolic rate?
It can increase it by up to 40x
How does stress change the metabolic rate?
It increases due to the activities of the autonomic nervous system
What do sympathetic nerves release?
Noradrenaline which increases metabolic rate. Strong sympathetic stimulation may cause dramatic increases in metabolic rate but only for a few minutes
How does the rate of biomechanical reactions change for every 1 degree rise in temperature?
For every 1C rise, the rate of biomechanical reactions increase by 10%
High fevers can double the metabolic rate
Where are peripheral thermoreceptors located?
Located in the skin and in some mucous membranes
Where are central thermoreceptors located?
Located in the hypothalamus
What do peripheral thermoreceptors do?
They provide the hypothalamus with information about the external environment
When are cold peripheral thermoreceptors stimulated?
They are stimulated by environmental temperatures that are lower than normal
What happens after the hypothalamus has received the message from cold thermoreceptors?
It initiates heat conservation and heat production mechanisms
What do heat peripheral thermoreceptors do?
They detect temperatures higher than normal
Where are central thermoreceptors found?
They are located in the hypothalamus and various internal locations (spinal cord, abdominal organs)
What do central thermoreceptors do?
They are all connected to the hypothalamus and control the core body temperature
How is heat lost from the skin?
Through conduction, convection, radiation and evaporation
What nerves control the diameter of blood vessels to the skin?
Autonomic nerves
How can increasing/decreasing the rate of blood flow change the rate of heat loss?
If the body needs to cool down, more blood will be pumped around the body and if the body needs to heat up, less blood will be pumped around the body
What is sweating?
The active secretion of fluid by the sweat glands, and the periodic contraction of cells surrounding the ducts to pump the sweat to the skin surface
When does sweating occur?
Sweating occurs when large amounts of heat must be lost and skin and blood vessels are already at maximum dilation
How is sweat produced and transported?
Sweat is produced and transported to the skins surface by sympathetic nerves
What is sweat made up of?
Water containing dissolved substances, primarily sodium chloride, along with urea, lactic acid and potassium ions
How does sweating have a cooling effect?
The evaporation of sweat has a cooling effect as heat is removed from the skin when liquid sweat changes into vapour
How does water leave a body?
By sweating, water evaporates from the lungs and respiratory passages, which accounts for a large portion of the daily heat loss from the body
What is vasoconstriction?
A physiological response to a decrease in temperature
What occurs in vasoconstriction?
Impulses stimulate sympathetic nerves that cause blood vessels in the skin to contract
How does vasoconstriction reduce heat loss?
By reducing the flow of warm blood to the skin from internal organs, decreasing the transfer of heat from the internal body organs to the skin
What is the Adrenal Medullas role in maintaining body temperature in conditions of rapid heat loss?
It is stimulated by sympathetic nerves, directed by the hypothalamus
Results in the medulla secreting adrenaline and noradrenaline, hormones that increase cellular metabolism, increasing heat production
How does shivering increase the production of heat?
The hypothalamus stimulates part of the brain to increase skeletal muscle tone
Leads to oscillating, rhythmic tremors occurring at a rate of around 10-20 per second
Can increase body temperature in minutes and all energy released goes to internal heat
How can someone suppress shivering?
Conscious input from the cerebral cortex can suppress the urge to shiver
How does thyroxine increase body temperature?
Thyroxine increases metabolic rate which results in increased body temperature
It is slower to have an effect but is longer lasting
How is thyroxine released?
The hypothalamus stimulates the anterior pituitary gland to secrete thyroid stimulating hormone, which causes the thyroid to release thyroxine into the blood
What are behavioural responses to prevent heat loss?
Getting the urger to put a jumper on
Sheltering from a cold wind
Reduce the surface area from which heat can be lost
What is vasodilation?
The process that occurs when skin blood vessels dilate to increase blood flow through the skin
What occurs in order to know vasodilation has taken place?
Skin becomes a reddish-pink colour
Surface temperature rises
Greater heat loss through radiation and convection
What temperature does the external environment need to reach to provoke sweating?
The external environment needs to be above 28C inorder for sweating to occur to increase heat loss from the body
Why isn’t sweating an effective method of heat loss if the environment is humid?
Because the sweat is only effective when it evaporates from the skin. If the air is too humid, the sweat wont be able to be evaporated off the skin
What happens when external temperatures are greater than 37C?
The evaporation of sweat becomes the only avenue for heat loss
How does a decrease in metabolic rate reduce heat production?
It is a long term shift (seen in summer when there is less heat loss than winter)
Less heat is produced in the body due to a reduction in thyroxine secretion
What are behavioural responses to reduce heat production/increase heat loss?
Turning on a fan/ air con
Removing external clothing
Reducing physical activity
What controls thermoregulation?
The hypothalamus monitors the temperature of the blood and receives impulses from the peripheral thermoreceptors
How is thermoregulation maintained?
Through negative feedback systems (involving the ANS), it controls the diameter of skin blood vessels, sweating, shivering etc.
What are dangerous and deadly core body temperatures?
42C is a dangerous body temperature
45C core body temperature usually results in death
What are the treatments for heatstroke?
It can cause death if brain cells are affected
Treatments consists of cooling the body as quickly as possible by immersing patient in cold water
Why does heat exhaustion occur?
Occurs more frequently than heatstroke
Occurs due to extreme sweating and vasodilation to lose heat, which reduces the volume of blood plasma and resistance to blood flow
Blood pressure decrease and output of blood from the heart decreases
What is hypothermia?
A condition where the body is so cold, the metabolic rate falls so much that heat production is unable to replace heat lost
What is intracellular fluid?
Fluid inside the cell, cytosol
Making up 2/3 of total body water
What is extracellular fluid?
Fluid that is outside the cells and makes up 1/3 of total body water
What is plasma?
The fluid part of the blood
Makes up 1/4 of extracellular fluid
What is intercellular fluid?
Lymph, cerebrospinal fluid, synovial in joints, fluids or eyes and ears, fluid in the chest and abdominal cavities and around the heart, fluids of the alimentary canal, kidney filtrate
Makes up 3/4 of extracellular fluid
How is plasma separated from intracellular fluid?
By thin capillary walls
How is most body fluid taken in?
From the water taken in as liquid of contained in the food that is eaten
What is metabolic water?
A small amount of water taken in as the by-product of chemical processes
How are fluids lost?
Through the kidneys, skin, the surface of the lungs, and from the alimentary canal
How much fluid is lost per day?
2.5 L
What is excretion?
The removal of waste products of metabolism from the body
What organs take part in excretion?
Lungs, sweat glands, alimentary canal and kidneys
What do lungs excrete?
They excrete carbon dioxide which is produced by all body cells during cellular respiration
What do sweat glands secrete?
Secrete water containing by-products of metabolism such as salts, urea and lactic acid
What does the alimentary canal excrete?
Passes out bile pigments (breakdown of haemoglobin)
Which leaves the body with the faeces
What do the kidneys excrete?
Principal excretory organ responsible for maintaining a constant concentration of materials in the body fluids
Excretes urea, produced in the liver in the breakdown of proteins
How much water that is lost each day, is secreted by the kidneys?
60% is secreted as urine
Describe the kidneys:
A reddish-brown organ in the abdomen either side of the vertebral column about 11cm long the right is lower than the left Held in position by a mass of fatty tissue
How does urea leave the kidneys?
Through the ureter and then drains in the urinary bladder which empties through the urethra
What is a nephron and how many are in each kidney?
A nephron is a functional unit of the kidney that carries out the role in excretion and water regulation
About 1.2 million in each kidney
Explain how urine is filtered through the kidneys:
Blood enters the glomerulus under high pressure
FILTRATION: high bp forces water and small dissolved molecules out of the blood and into the capsule. Large molecules and blood cells are retained in the blood
Filtrate is collected by the glomerular capsule
REABSORPTION: the filtrate passes through the proximal convoluted tubule, the loop of Henle, the distal convoluted tubule and the collecting duct. Water and other substances are reabsorbed into the particular capillaries
SECRETION: Some materials that need to be removed from the body are secreted into the kidney tubule from the peritubular capillaries
URINE: Water and dissolves substances that remain make up the urine. Urine is carried by collecting ducts to the ureter and then to the bladder
How much water is reabsorbed in the kidneys?
About 99% of the water filtered through the glomeruli of the kidneys is reabsorbed, which occurs along the walls of the kidney tubules
Osmosis is used where in the reabsorption of water in the nephron?
At the proximal convoluted tubule and loop of Henle
How is water reabsorbed at the distal convoluted tubule and collecting tubule?
Through active reaborption
How is the level of active reabsorption in the kidneys controlled?
By the antidiuretic hormone
Where is antidiuretic hormone produced?
Produced by the hypothalamus and released from the posterior lobe of the pituitary gland
What does antidiuretic hormone control?
The permeability of the walls of the distal convoluted tubule and collecting duct
How permeable to water are the tubules in the kidney when ADH concentration in blood plasma is high?
They are very permeable and water is able to leave the tubule and enter the capillary network
If outward flow reduces tubule volume, what does it do to the concentration of materials remaining?
It increases the concentration of the remaining materials
What happens when plasma ADH concentration is low?
The tubules aren’t permeable to water, and little water is reabsorbed into the blood
Explain the negative feedback loop for ADH:
Water concentration of blood plasma decreases, osmotic pressure is raised
Osmoreceptors in the hypothalamus detect the increased osmotic pressure of the blood
Hypothalamus stimulates the PPG to release ADH into the bloodstream
ADH is carried all over the body via the bloodstream but it only affects the target organs which are the nephron tubules in the kidneys
Permeability to water of the distal convoluted tubes is increased
More water is reabsorbed into the blood plasma from the tubules and ducts
The reabsorption of water increases water concentration in the plasma, and the osmotic pressure of the blood is decreased
The response is decreased and osmotic pressure of the blood-eliminating/reducing the original stimulus
If you increase water reabsorption, what else do you increase?
Increase blood volume
Increase blood pressure
Restoration of water balance feedback loop:
Water is lost, reduction in plasma volume occurs, increase in osmotic concentration of extracellular fluid
Osmoreceptors in the thirst centre of the hypothalamus detect the rising concentration of the blood, as well as stimuli like a dry mouth
Person feels thirsty
Conscious feeling of thirst stimulates a person to drink
The fluid consumed is absorbed into the plasma from the alimentary canal
Blood circulated through the body, enables the intercellular fluid and intracellular fluid to return to proper osmotic concentration
Thirst centre is no longer stimulated, the desire to take in water ceases
What is dehydration?
When water loss exceeds water intake
What are symptoms of dehydration and when do they become noticeable?
Symptoms include sweating, vomiting, diarrhoea, severe thirst, low blood pressure, dizziness, headache
Become noticeable after a person loses 2% normal body water
What happens to the thirst reflex as we grow older?
It becomes less effective
What is water intoxication?
The presence of too much water in the body
Fluids become too diluted and cells take in extra water by osmosis
When can water intoxication occur?
When a person loses a lot of water and salts through sweating and fails to replace the salts
Symptoms of water intoxication:
Light headedness, headache, vomiting, collapsing
