Homeostasis Flashcards
What is homeostasis?
The maintenance of a stable internal
environment in the body despite
fluctuations in internal and external
conditions.
Why is homeostasis important?
To ensure optimum conditions for enzymes
and cellular processes in the body
State three conditions within the body that must be
controlled by homeostasis
● Temperature
● Blood glucose concentration
● Water levels
What is thermoregulation?
The maintenance of core body
temperature
Why must body temperature be controlled?
Enzymes work best at their optimum
temperature. Deviations from this optimum
temperature decrease the rate of
enzyme-controlled reactions.
What is the optimum temperature for enzymes in the
human body?
37°C
What does the maintenance of an ideal body
temperature depend on?
A negative feedback system involving:
● Receptors
● Hypothalamus
● Effectors e.g. sweat glands, hair erector muscles
Where are temperature-sensitive receptors located?
● Skin - epidermis (outer layer) and dermis
(below epidermis)
● Hypothalamus
What is the function of receptors in the skin and in
the hypothalamus?
They detect changes in blood
temperature and send information to the
hypothalamus.
What is the function of the hypothalamus?
It coordinates information from the
receptors and sends instructions to the
effectors.
What is the function of the effectors in thermoregulation?
They produce a response to counteract
the change in blood temperature and
return it to the set point.
Outline the responses of the body to an increase in
temperature above 37°C (3)
● Vasodilation
● Sweating
● Erector muscles relax, hairs lie flat
What structure produces sweat?
Sweat glands found in the dermis
How is sweat released from the skin?
Pores in the epidermis release sweat onto
the skin’s surface which then evaporates.
How does sweating help to reduce body
temperature?
Heat energy is used to evaporate sweat.
Increased heat transfer from the skin to the
environment decreases body temperature.
What is vasodilation?
● Dilation of blood vessels near the skin surface
● Blood flows closer to the skin surface
● Greater heat loss to the surroundings
Outline the responses of the body to a decrease in
temperature below 37°C
● Vasoconstriction
● Shivering
● Hair erector muscles contract
● Little sweat is produced
How does shivering help to increase body
temperature?
Involuntary contraction of muscles
generates heat energy from respiration
How does the contraction of hair erector muscles
help to increase body temperature?
Hairs stand on end creating pockets of
air between hairs and a layer of
insulation, which traps the warm air.
What is vasoconstriction?
● Constriction of blood vessels near skin surface
● Less blood flows close to the skin surface
● Less heat loss to the surroundings
Which organ is responsible for the maintenance of
blood glucose concentrations?
Pancreas
How are blood glucose concentrations controlled?
Controlled by the hormones insulin and
glucagon which are secreted by the
pancreas
Insulin and glucagon are antagonistic hormones.
What does this mean?
They have opposite effects which
counteract one another
Describe the role of insulin in the regulation of blood
sugar levels
● Causes liver and muscle cells to increase their
uptake of glucose from the blood
● Glucose is converted into glycogen, a storage
molecule
Describe the role of glucagon in the regulation of
blood sugar levels
● Causes the breakdown of glycogen to
glucose in the liver
● Glucose is released into the blood
What is the control of blood glucose concentration
an example of?
Negative Feedback
Describe what happens when blood glucose
concentrations become too high
● Blood glucose concentration increases above a set point
● Pancreas secretes insulin and stops producing glucagon
● Liver and muscle cells increase uptake of glucose
● Glucose is converted to glycogen and stored
● Some glucose may be stored as lipid in tissues
● Blood glucose concentration decreases, returning to normal levels
Describe what happens when blood glucose
concentrations become too low
● Blood glucose concentration decreases below a set point
● Pancreas secretes glucagon and stops producing insulin
● Liver cells convert glycogen into glucose which is released into blood
● Blood glucose concentration increases, returning to normal level
What is diabetes?
A condition where the homeostatic
control of blood glucose levels stops
working.
What is the cause of type 1 diabetes?
Pancreas does not produce any
insulin
How is type 1 diabetes treated? (3)
● Daily insulin injections at meal times
● Limiting intake of refined sugars
● Regular exercise
What is the cause of type 2 diabetes?
Person develops insulin resistance or
doesn’t produce enough insulin (often
due to obesity)
How is type 2 diabetes treated?
● Balanced diet
(eating fewer simple sugars and replacing them with more
complex carbohydrates)
● Exercise
● Medication or insulin injections (however, these are
less effective)
How does exercise help to control diabetes?
Exercise increases respiration in muscle
cells. Excess glucose is removed from
the blood to produce energy in the form
of ATP.
Why are type 2 diabetics advised to replace simple
carbohydrates with more complex carbohydrates?
● Simple carbohydrates are broken down quickly so
can raise blood glucose levels rapidly.
● Complex carbohydrates take longer to break
down so have a reduced effect on blood glucose
levels.
What is the Body Mass Index (BMI)?
A value based on height and mass used to
categorise an individual as underweight, normal
weight, overweight or obese.
How is BMI calculated?
BMI = kg/m^2
What BMI values indicate obesity and an increased
risk of type 2 diabetes?
BMI value larger than 30
How is an individual’s waist-to-hip ratio calculated?
waist-to-hip ratio = waist circumeference (cm)/ hip circumference (cm)
What does a waist-to-hip ratio higher than 1.0 in
males or 0.85 in females indicate?
● Abdominal obesity
● Increased risk of developing type 2 diabetes
What is osmoregulation?
The maintenance of constant water
levels in the body fluids of an organism
Why is osmoregulation important?
Prevents cells bursting or shrinking when
water enters or leaves by osmosis
Describe what happens to an animal cell if it is
placed into a solution with a higher water
concentration
● Higher concentration of water in surrounding solution
● Water molecules move down their water concentration
gradient into the cell by osmosis
● Pressure inside the cell increases, cell bursts (lysis)
Describe what happens to an animal cell if it is
placed into a solution with a lower water
concentration
● Lower concentration of water in surrounding solution
● Water molecules move down their water concentration
gradient out of the cell by osmosis
● Pressure inside the cell decreases, cell shrinks (crenation)
Describe what happens to an animal cell if it is
placed into a solution with an equal water
concentration
No net movement of water molecules
into or out of the cell
Describe the function of the kidneys
● Removes toxic waste substances from the body
● Alters blood water levels
● Alters blood ion levels
What is urine?
Waste product of the kidney that
contains urea, excess water and excess
ions
How is urea produced?
In the liver, urea is produced from the
breakdown of excess amino acids.
Identify the structures of
the urinary system
labelled in the diagram
A= kidney B = renal vein C = renal artery D = ureter E = urethra F = bladder
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What is the function of the renal artery?
Supplies blood to the kidneys
What is the function of the renal vein?
Drains blood from the kidneys
What is the function of the ureter?
Takes urine to the bladder from the
kidneys
What is the function of the urethra?
Releases urine from the bladder, out of
the body
What is a nephron?
Functional unit of the kidney where
filtration and selective reabsorption takes
place
Describe filtration in the kidneys
● Blood flows through the glomerulus under high
pressure
● Small molecules (e.g. urea, glucose), water and
ions are filtered out of the blood and into the
Bowman’s capsule of the nephron
Why do large molecules (e.g. red blood cells,
proteins) remain in the blood?
They are too large to fit through the
pores in the capillary walls
Which substances are selectively reabsorbed from
the nephron tubule?
● All sugars
● Some water
● Some ions
What happens to the molecules not selectively
reabsorbed?
They travel down the kidney tubule as
urine and are transported to the bladder
via the ureter. Here they are stored and
eventually excreted.
How is the concentration and volume of urine
controlled?
Controlled by the secretion of
anti-diuretic hormone (ADH)
What producesADH?
Pituitary gland
Describe how ADH affects the reabsorption of water
from the kidney tubules
ADH increases the permeability of the
collecting ducts, enabling more water to
be reabsorbed into the blood.
What is required to maintain the ideal water content
of blood?
A negative feedback system involving:
● Receptors in the hypothalamus
● Hypothalamus
● Effector i.e. pituitary gland
Describe the negative feedback loop which occurs
when low blood water concentration is detected
● Pituitary gland detects low blood water content.
● Pituitary gland increases ADH secretion.
● ADH increases collecting duct
permeability so more water is reabsorbed.
● Blood water content increases. More concentrated urine is produced.
●Blood water levels returns to normal
Describe the negative feedback loop which occurs
when high blood water concentration is detected
● Pituitary gland detects high blood water levels
● Pituitary gland secretes less ADH.
● Collecting duct becomes less permeable so less water is reabsorbed.
● A large volume of dilute urine is produced.
● Blood water levels return to normal.
How can kidney failure be treated?
● Kidney dialysis
● Kidney transplant
What is kidney dialysis?
A machine artificially filters a patient’s
blood
How does kidney dialysis work?
● Selectively permeable barrier or membrane separates patient’s blood from
dialysis fluid
● Materials are exchanged across the barrier e.g. urea, excess
ions and water move out of the blood and into the dialysis fluid through osmosis
● Large cells and proteins remain in the blood
Describe the composition of dialysis fluid
● Same concentration of glucose and ions as in normal blood plasma
● No urea
What does a kidney transplant involve?
Taking a kidney from a living donor or
someone recently deceased and
implanting it into the patient.
What is the risk associated with kidney transplants?
Risk of the body rejecting the
transplanted kidney
What precautions are taken to minimise the risk of
rejection?
● Tissue typing ensures that the transplanted
organ is ‘compatible’ with the recipient
● Immunosuppressant drugs help prevent the
immune system from rejecting the organ
Ultrafiltration?
Water, glucose and Urea move into the Nephron at the Bowman’s capsule, out of the glomerulus under high pressures.
Selective Reabsorption
Selective Reabsorption of glucose and some mineral ions by active transport in the first convoluted tubule.
Reabsorption of water?
Reabsorption of water by osmosis, depending on how much the body needs. This happens in the loop of Henle and collecting duct.
Urine formed
At the end of Nephron, the remaining fluid flows into the ureter. It contains excess water, urea and other substances.
