Homeostasis Flashcards
What do homeostatic systems do? What do they involve?
They detect a change and respond by negative feedback
They involve receptors, a communication system and effectors
What is homeostasis
The maintenance of a constant internal environment
Why does homeostasis involve more than 1 negative feedback mechanism
Having more than 1 gives more control over changes in the internal environment. Having multiple mechanisms means you can actively increase or decrease a level so it returns to normal
What would happen if you only had one negative feedback mechanism
All you could do is turn it on or turn it off. You would only be able to actively change a level in one direction so it returns to normal. Only one mechanism means a slower response and less control
What does a positive feedback mechanism do
Amplify a change from the normal level. The effectors respond to further increase the level away from the normal level
what are positive feedback mechanisms useful for? Example.
To rapidly activate something. Eg blood clot after injury…
Platelets activated, release chemical which triggers more platelets to be activated, and so on
Platelets very quickly form blood clot at injury site
Process ends with negative feedback when body detects the blood clot has been formed
Why isn’t positive feedback involved in homeostasis
Because it doesn’t keep your internal environment constant
Examples of ectotherms
Reptiles
Fish
Examples of endotherms
Mammals
Birds
How do ectotherms control their body temp
They can’t control their body temp internally, instead control their temp by changing their behaviour (eg reptiles laying in sun)
Their internal temp depends on the external temp
Their activity level depends on the external temp, they’re more active at higher temps
Have a variable metabolic rate and generate little heat themselves
How do endotherms control their body temp
Control temp internally by homeostasis. Can also control their temp by behaviour (eg finding shade)
Their internal temp is less affected by external temp, they can be active at any temp
Their activity level is largely independent of external temp, can be active at any temp
Have a constantly high metabolic rate, generate lots of heat from metabolic reactions
Body temp in mammals is maintained at a constant level by a part of the brain called the…
hypothalamus
What is the hypothalamus and what is its role
A part of the brain which maintains body temp at a constant level in mammals
How does the hypothalamus work
It receives info from both internal and external temp from thermoreceptors
Info about internal temp comes from thermoreceptors in the hypothalamus that detect blood temp
Info about the external temp comes from thermoreceptors in the skin which detect skin temp
Thermoreceptors send impulses along sensory neurones to hypothalamus, which sends impulses along motor neurones to effectors (muscle and glands)
The neurones are part of the autonomic nervous system, so is done unconsciously
The effectors restore body temp back to normal
What does FSH do
Stimulates the development of follicles in the ovaries. Stimulates the follicles to produce oestrogen
What is a follicle
An egg and its surrounding protective cells. Developed in the ovary
What is ovulation
The release of an egg
What does LH do
Causes ovulation and stimulates the ovaries to produce progesterone from corpus luteum
What does oestrogen do
Causes the rebuilding of the uterus lining after menstruation, stimulates the pituitary gland to produce LH and FSH. Can also inhibit both LH and FSH
What does progesterone do
Maintains the lining of the uterus in preparation to receive the fertilised egg. It inhibits the production of FSH and LH from the pituitary gland
Where is FSH secreted from
Pituitary gland
Where is LH secreted from
Pituitary gland
Where is oestrogen secreted from
Ovaries
Where is progesterone secreted from
The corpus luteum in the ovaries
What is the normal concentration of glucose in the blood
90 mg per 100cm3 of blood
What monitors glucose concentration in blood
Cells in pancreas
When does the blood glucose conc increase
After eating food containing carbohydrate
When does the blood glucose conc decrease
After exercise, as more glucose used in respiration to release energy
The hormonal system controls blood glucose conc using which 2 hormones?
Insulin and glucagon
Which system controls the blood glucose conc
Hormonal system
Insulin and glucagon are secreted by…
Clusters of cells in the pancreas called the islets of Langerhans
What are the islets of Langerhans
Cluster of cells in pancreas which secrete insulin and glucagon
What do beta cells do
Secrete insulin into the blood
What do alpha cells do
Secrete glucagon into blood
What is another name for liver cells
Hepatocytes
Role of adrenaline in controlling blood glucose conc
Adrenaline is a hormone secreted from the adrenal glands. Secreted when there is a low conc of glucose in blood. It binds to receptors in cell membrane of liver cells and activates glycogenolysis. It inhibits glycogenesis. It also activates glucagon secretion and inhibits insulin secretion which increases glucose conc. Adrenaline gets the body ready for action by making more glucose available for muscles to respire.
What is glycogenolysis
The breakdown of glycogen to glucose
What is glycogenesis
The synthesis of glycogen from glucose
Diabetes occurs when…
Blood glucose conc is not controlled
What is diabetes mellitus
A condition where blood glucose conc can’t be controlled properly. Two types, type 1 and type 2.
What is type 1 diabetes
The beta cells in the islets of Langerhans don’t produce insulin. After eating, the blood glucose level rises and stays high, called hyperglycaemia, can result in death. The kidneys can’t reabsorb all the glucose so some is excreted in urine. Can be treated by regular injections of insulin, this has to be carefully controlled as too much can produce a dangerous drop in blood glucose levels, called hypoglycaemia. Eating regularly and controlling simple carb intake helps avoid sudden rise in glucose
What is type 2 diabetes
Usually acquired later in life then type 1, often linked to obesity. Occurs when beta cells don’t produce enough insulin or when the body’s cells don’t respond properly to insulin. Cells don’t respond properly because the insulin receptors on their membranes don’t work properly, so the cells don’t take up enough glucose. Means the blood glucose conc is higher than normal. It can be treated by controlling simple carb intake and losing weight. Glucose-lowering tablets can be taken if diet and weight loss can’t control it.
When insulin binds to receptors on liver cells it forms glycogen which lowers the glucose conc in liver cells. how?
When glycogen formed the glucose conc falls below that in blood
Creates diffusion gradient
Glucose enters the cells, leaves the blood via facilitated diffusion
