Homeostasis (Edexcel GCSE Biology)
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What is homeostasis?
Homeostasis is the maintenance of a constant internal environment within set limits.
Why is homeostasis important?
Homeostasis is important because it maintains optimal conditions for enzyme action and cell function.
What conditions are regulated inside the human body as part of homeostasis?
In the human body, homeostasis regulates:
blood glucose concentration
body temperature
water levels
What is the importance of thermoregulation in the body?
Thermoregulation ensures that the temperature inside the body remains optimal for enzyme activity.
What are the structures labelled A-D in the diagram?
Structures A-D are:
A = hair erector muscle
B = sweat gland
C = hair
D = blood vessel
What are the thermoregulation mechanisms that occur in the dermis of the skin?
Thermoregulation mechanisms that occur in the dermis include:
sweat glands produce sweat
blood flow through the blood vessels of the dermis changes in response to temperature
hair erector muscles in the dermis can contract to alter the position of hairs
temperature receptors in the dermis can send information to the hypothalamus
What are the thermoregulation mechanisms that occur in the epidermis of the skin?
Thermoregulation mechanisms that occur in the epidermis include:
sweat evaporates, removing heat energy from the skin
temperature receptors send information to the hypothalamus
What is the role of the hypothalamus in thermoregulation?
The hypothalamus contains the thermoregulatory centre which monitors and controls body temperature.
How does shivering contribute towards temperature regulation?
Shivering aids temperature regulation because the rapid muscle contractions generate heat through respiration; this helps to raise the core body temperature.
Define the term vasodilation. (Higher Tier Only)
Vasodilation is a cooling mechanism in which the diameter of skin arterioles increases. This increases blood flow to capillaries in the skin surface, transferring heat to the environment by radiation.
How do blood vessels respond to an increased body temperature? (Higher Tier Only)
An increase in body temperature causes the arterioles that supply the skin capillaries to dilate; this increases blood flow to the skin surfaces and increases heat loss.
True or False?
Vasodilation occurs during exercise. (Higher Tier Only)
True.
Exercise raises core body temperature due to increased metabolic activity in the contracting muscles. Sweating and vasodilation occur as part of the temperature regulation mechanisms of the skin.
True or False?
When a person enters a colder environment blood flow to the surface of the skin is reduced. (Higher Tier Only)
True.
Vasoconstriction is a heat retention mechanism. The diameter of skin arterioles decreases to reduce blood flow to capillaries in the surface of the skin. This minimises heat loss by radiation.
True or False?
Constriction of the capillaries reduces blood flow to the surface of the skin. (Higher Tier Only)
False.
Capillaries do not have a muscle layer and therefore cannot constrict.
Constriction occurs in the arterioles that supply the skin capillaries, reducing blood flow to the skin surface.
Define the term osmoregulation.
Osmoregulation is the maintenance of the balance of water and salts within the body.
Why is osmoregulation important?
Osmoregulation is important because it ensures that cells do not gain or lose water by osmosis.
What happens to body cells if they lose water by osmosis?
Loss of water by osmosis can impact cells as follows:
cells can shrink and lose their shape
reduction in the volume of cytoplasm can affect the movement of molecules within the cell, reducing the rates of chemical reactions
True or False?
Animal cells can burst if osmoregulation does not occur.
True.
If osmoregulation does not occur and the water concentration of the body fluids increases then cells may take on water by osmosis; in animal cells this can result in cell lysis (bursting).
Which organ system is responsible for the filtration of blood and the production of urine?
The organ system responsible for the filtration of blood and the production of urine is the urinary system.
What are the four main structures of the urinary system?
The four main structures of the urinary system are:
kidneys
ureters
bladder
urethra
Name the tubes that connect the kidneys to the bladder.
The tubes that connect the kidneys to the bladder are the ureters.
What is the role of ADH in the control of water levels? (Higher Tier Only)
ADH affects the permeability of the kidney tubules to water:
More ADH makes the tubules more permeable, leading to more water reabsorption when blood water content is low (urine is concentrated)
Less ADH makes the tubules less permeable when the blood water content is high (urine is dilute)
True or False?
More ADH makes the walls of the collecting duct more permeable to water. (Higher Tier Only)
True.
More ADH makes the walls of the collecting duct more permeable to water. This means that more water is reabsorbed into the blood and urine is more concentrated.
With reference to ADH, how is dilute urine produced? (Higher Tier Only)
The following mechanisms occur to produce dilute urine:
The pituitary gland releases less ADH
The tubules become less permeable to water
Less water is reabsorbed in the collecting duct/tubules of the kidney
The kidneys produce a large volume of dilute urine
What is kidney failure?
Kidney failure is a condition where the kidneys do not function properly, leading to a build-up of toxic waste in the body which can be fatal if not treated.
What is dialysis?
Dialysis is a treatment for kidney failure where a machine acts as an artificial kidney, removing most of the urea and maintaining the water and salt balance in the blood.
What is a kidney transplant?
A kidney transplant is a surgical procedure where a healthy kidney from a donor is implanted into a patient with kidney failure, offering a long-term solution compared to dialysis.
What are the advantages of a kidney transplant over dialysis?
Advantages of a kidney transplant over dialysis are that it provides:
more freedom to the patient
a less restrictive diet
lower cost
a long-term solution
What are the disadvantages of kidney transplants?
Disadvantages of kidney transplants include:
the risk of rejection
the need for lifelong immunosuppressant drugs with side effects
a shortage of donors
True or False?
Urea is produced from the breakdown of excess amino acids in the kidneys.
False.
Urea is produced from the breakdown of excess amino acids in the liver.
Which gland responds to changes in blood glucose by secreting hormones?
The pancreas is the gland that produces hormones in response to changing blood glucose levels.
True or False?
Insulin is a hormone that increases blood glucose levels.
False.
Insulin reduces blood glucose levels by increasing the uptake of glucose from the blood into the body cells, where it is converted into glycogen.
What happens to excess glucose in liver and muscle cells?
In liver and muscle cells excess glucose is converted into glycogen for storage.
What hormone does the pancreas secrete when blood glucose is too low? (Higher Tier Only)
When blood glucose concentration is too low the pancreas produces the hormone glucagon.
What is the role of the hormone glucagon? (Higher Tier Only)
The hormone glucagon is produced when the blood glucose concentration is too low. It causes glycogen to be converted into glucose and released into the blood.
Define Type 1 diabetes.
Type 1 diabetes is a disorder in which the pancreas fails to produce sufficient insulin to control blood glucose levels.
Define Type 2 diabetes.
Type 2 diabetes is a disorder where the body cells no longer respond to insulin produced by the pancreas.
How is Type 2 diabetes controlled?
A carbohydrate-controlled diet and an exercise regime are common treatments for Type 2 diabetes.
What is a major risk factor for Type 2 diabetes?
Obesity is a major risk factor for Type 2 diabetes.
How is Type 1 diabetes controlled?
Type 1 diabetes is controlled by insulin injections.
What is the correlation between body mass and Type 2 diabetes?
Obese individuals have an increased risk of developing Type 2 diabetes compared to non-obese individuals.
An individual with a BMI over 30 has an increased risk of developing Type 2 diabetes.
What is the correlation between waste:hip ratio and developing Type 2 diabetes?
Individuals with a lot of excess fat stored around the abdomen area have an increased risk of developing Type 2 diabetes.
A waste:hip ratio above 1.0 for men and 0.85 for women is associated with an increased risk of developing Type 2 diabetes.