1. Disruption to homeostasis
Text: Chapter 10
Human Biology Stage 3

2. What happens if homeostasis fails?
If homeostasis cannot be maintained within tolerance limits, our body cannot function properly – consequently, we are likely to get sick and may even die.
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3. Body temperature
Disruption to thermoregulation

4. Body temperature
If body temperature is not maintained in the thermoneutral zone homeostasis is disrupted resulting in heat stress, and possibly death.
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5. Keywords Thermoneutral zone Hypothermia Hyperthermia Heat exhaustion
Lower critical temperature
Upper critical temperature
Hypothermia
Hyperthermia
Heat exhaustion
Heat stroke

6. Temperature ranges
The average oral temperature ranges from ˚C to 37.8 ˚C – the average is 36.8 ˚C, though this can vary by as much as one degree over 24 hours.

7. The thermoneutral zone
The thermoneutral zone (TNZ) is the temperature range bounded by the lower critical temperature (the point at which shivering starts) and the upper critical temperature (the point at which sweating starts).
The average TNZ is around 36 ˚C to 38 ˚C.

8. Hyperthermia
Failure of the body’s homeostatic mechanisms to control body temperature within the thermoneutral zone results in hyperthermia (abnormally high body temperature).
Failure to lower the temperature results in heat stroke and, ultimately, death

9. Heat exhaustion
At temperatures between 38 ˚C and 40 ˚C people sweat, become flushed and feel increasingly uncomfortable. Their heart rate increases and they may experience nausea, headache and may feel dizzy, become confused or faint.
Heat exhaustion is treated by resting in a cool area and drinking water.

10. Heat stroke At temperatures above 41 ˚C people experience heat stroke.
The heart rate becomes very fast, sweating stops and the skin becomes dry and hot.
Beyond this point it is difficult for the body to maintain homeostatic balance and the temperature rises rapidly.
Above 42 ˚C people are likely to lapse into a coma and will die if their temperature rises above 43 ˚C - 44 ˚C.

11. Disease
Diabetes
Renal failure
Disorders of the thyroid gland

12. Keywords Diabetes Hyperglycaemia Diabetes mellitus Pancreas
Type I diabetes (early onset)
Type II diabetes (lifestyle)
Pancreas
Insulin
Isle of Langerhans
Beta cells
Renal failure
Acute renal failure
Chronic renal failure
Haemodialysis
Transplant
Thyroid disorders
Thyroxine
Hyperthyroidism
Graves disease
Hypothyroidism
Hashimoto’s disease
Iodine

13. Diabetes
Diabetes is a disease characterised by abnormally high levels of blood glucose.
This is called hyperglycaemia
Diabetes results from the body being unable to maintain the blood sugar level in homeostatic balance.

14. Diabetes mellitus
There are 2 types of diabetes: Diabetes mellitus – Type 1 Diabetes mellitus – Type 2
Neither form of diabetes can be cured; however, both types can be managed through diet, exercise and the use of insulin.
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15. Type 1 Diabetes Usually begins in childhood
An islet of Langerhans
Usually begins in childhood
It occurs because of a fault in the immune system which causes the destruction of the pancreatic beta cells in the islets of Langerhans
As a result, the person does not produce insulin, which must be injected

16. Type 2 Diabetes
Type 2 diabetes usually develops in people over the age of 45
The beta cells still produce insulin, but the body cells have become less responsive
Type 2 diabetes is a life style disease
Treated by dietary control, exercise and insulin injections.
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17. Symptoms of diabetes Hyperglycaemia Being excessively thirsty
Passing more urine
Feeling tired and lethargic
Always feeling hungry
Having cuts that heal slowly
Itching, skin infections
Blurred vision
Weight change (Type 1 – weight loss, Type 2 – weight gain)
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18. Problems that arise if homeostasis is not restored
High levels of blood sugar can damage blood vessels. This can lead to:
Blindness
Kidney failure
Cardiovascular disease
Loss of sensation
Ulcers and gangrene sometimes requiring amputation of the toes or foot.

19. Renal failure
When the kidneys stop working homeostatic disruption is so widespread that the person will die unless they receive urgent medical assistance.
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20. Causes of renal failure
There are many causes for kidney failure – these can be classified as:
acute (sudden) resulting from causes such as toxic drugs, a blockage or injury.
chronic (gradual) resulting from problems such as diabetes, cancer, high blood pressure or polycystic kidney disease.
Polycystic kidney disease
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21. Consequences of renal failure
In both acute and chronic renal failure, urine production is disrupted and water, salts and metabolic wastes are retained in the body.
This causes widespread homeostatic problems which affect almost every system of the body.
The most common cause of death is cardiovascular disease.

22. Treatment In many instances there is no cure for renal failure.
Many people with renal failure have to undergo regular haemodialysis treatment to purify their blood (conventionally three times a week).
Sometimes a kidney transplant is an option.
Surgeons performing a kidney transplant
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23. Haemodialysis
During haemodialysis blood is removed from an artery, toxic substances, metabolic wastes and excess fluid are removed, and the blood is then returned to the body
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24. Kidney transplant
People with renal failure can receive a kidney transplant if a matching donor kidney is available.
The transplanted kidney is lower in the pelvis and attached to the common iliac artery and vein.
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25. Disruption of the thyroid
Another example of hormonal disruption to homeostasis is the over or under secretion of thyroid hormone
Thyroxine effects almost every tissue in the body by stimulating carbohydrate, protein and fat metabolism (thus regulating metabolic rate)
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26. Hyperthyroidism
Hyperthyroidism occurs when the thyroid gland produces too much thyroxine
Symptoms
rapid heart rate
weight loss
increased appetite
fatigue
Sweating
The most common type of hyperthyoidism is called Graves disease, an autoimmune disorder which involves an enlargement of the thyroid
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27. Hyperthyroidism Treatment
Drugs that block the thyroids gland’s use of iodine
Surgery to remove some or all of the gland
Radioactive treatment to shrink the gland by killing off some of the cells
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28. Hypothyroidism
Hypothyroidism occurs when the thyroid produces too little thyroxine
It is either due to problems with the thyroid gland or due to problems with the pituitary or the hypothalamus
Symptoms
slow heart rate
unexplained heart rate
fatigue
intolerance to cold
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29. Hypothyroidism - causes
Lack of iodine
A thyroxine molecule contains 4 iodine atoms (T4)
The thyroid gland may become enlarged in an effort to increase hormone production
Enlargement of the thyroid gland is called a goitre
Treatment
Inclusion of iodine in the diet
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30. Hypothyroidism - causes
Autoimmune disorder
The most common cause of hypothyroidism is Hashimoto’s disease where the immune system attacks the thyroid gland
Treatment
Tablets containing thyroid hormone are prescribed. Dosage must be monitored to avoid hyperthyroidism
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31. Other examples

32. Behavioral causes of disruption to homeostasis
Drugs
Excessive activity
Eating habits
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33. Disease disrupts homeostasis
A disease is any condition in which normal functioning is impaired
Emphysema is a lung disease which the walls of the alveoli break down resulting in abnormally large air spaces
Fever is an elevated body temperature
Hypertension is elevated blood pressure
Injuries
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34. Hormonal treatments for disruption to homeostasis
Hormone replacement therapy
Menopause is when a woman’s ovaries stop releasing eggs and cease secretion of oestrogen and progesterone. This results in mensturation stopping
Hormone replacement therapy involves taking oestrogen and progesterone to try and smooth out irregularities
Associated risks with HRT
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35. Corticosteriods and the treatment of rheumatoid arthritis
Rheumatoid athritis is a condition in which the immune system attacks the synovial membrane of joints which causes painful swelling and deformity.
Corticosteriods act on the immune system by blocking the production of substances that stimulate allergic and inflammatory responses
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36. Risks, ethical concerns and benefits of treatments
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