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Part of the Organ Systems unit IB Biology Sl
Homeostasis
Mechanisms that help organsims maintain a relatively constant internal environment despite changes that occur in the external environment
Aim of homeostasis
To keep the variables of the body within preset limits despite changes in environment
Types of variables in the body
Blood glucose concentration
Blood osmotic concentration
Body Temperature
Blood pH
What type of feedback is homeostasis
Negative feedback because it opposes a change in the environment (counteracts change).
Positive feedback strengthens change
Which organ maintains blood sugar levels and where is it
Pancreas (behind stomach)
What cells produce the necessary hormones to maintain blood sugar
The islets of Langerhans (in the endocrine tissue in the pancreas)
What hormones are used to maintain blood sugar levels
Insulin (too high) and glucagon (too low)
Insulin:
Where produced
When is it produced
What is its target
What does it stimulate
Effect
Beta cells
Blood glucose levels increase
Targets body cells (mainly muscle and liver)
Stimulates transport of glucose from bloodstream into the cells
Decreases blood glucose level
Glucagon:
Where produced
When is it produced
What is its target
What does it stimulate
Effect
Produced and secreted in alpha cells
Blood sugar too low
Targets liver cells
Stimulates break down of glycogen and fat into glucose and uptake into the blood
Increases blood sugar levels
What causes diabetes
Insufficient insulin production or when the individual is insensitive to insulin. This leads to blood glucose levels to be extremely high
Explain two early signs of diabetes
Kidneys filter excess glucose into urine and dilute the urine by drawing excessive water from the body. This leads to dehydration and excessive urination.
Type 1 diabetes
Origin
When does it occur
Cure
Treatment
When the immune system mistakely attacks beta cells so they cannot produce insulin leading to very high blood sugar levels
Occurs in adolescence
No cure
Insulin injection/patch and dietary modifications
Type 2 diabetes cause and how to reverse it
Insulin insensitivity
Reverse by moderate weight loss, heathly diet and regular excercise.
5 risk factors for diabetes
lifestyle - lack of excersise, more excersise increases insulin sensitivity
diet - high in processed foods, sugar and unhealthy fats
family history
body weight - high weight increases insulin resistance
Age - risk increases as you age
Where does temperature control occur
Hypothalamus and pituatary gland
(hypo is control centre, pituatary gland secretes hormones to regulate temperature)
What do we use to detect changes in temperature
Thermoreceptors (peripheral and central)
Peripheral is in skin and central is in body
What is the role of thyroxin
Increases metaboic rate in cells which results in more heat produced
how is thyroxin released
hypothalamus —> pituitary gland releases thyroid stimulating hormone —> thyroid gland releases thyroxin when it is cold
When hot thyroid stimulating hormone is stopped being secreted so thyroxin prodcution decreases.
what do muscles do when it is cold
involutary contractions (shivering)
hair follicle muscles contract causing them to stand up and trap a layer of air to act as a thermal insulator.
what does the skin do when it is hot
Secretes sweat and water evaporates cooling skin (latent heat of water)
what does the circulatory system do when it is hot
Vasodilation - widens arteriols - increases flow to skin surface so heat can be emitted via conduction and convection
what does the circulatory system do when it is cold
vasoconstriction - narrows arterioles - decreases blood flow rate to prevent heat loss and keep heat around vital organs
What is uncoupled respiration
Brown adipose tissue are fat storing tissues filled with mitochondria.
The mitochondria release energy without using ATP to increase body heat when cold, known as uncoupled respiration
Note 
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