By

Sila TopcuUoB Foundation

What is homeostasis ?

• Same and steady

Why is it important ?• Rates of biochemical reactions • Movement of water all depend on

it …

How is homeostasis brought about ?

• Negative feedback• http://health.howstuffworks.com/adam-2000

92.htm

What must be kept constant ?

The control of blood glucose concentration

• In 1859 Claude Bernard was the first to recognise the importance of homeostasis.

There are three sources of blood glucose :

• Digestion of carbohydrates in the diet• Breakdown of glycogen [ glycogenesis].• Conversion of non- carbohydrate compounds.

Mechanism of blood glucose control

• Pancreas has a vital role • The islets of Langerhans

High blood glucose concentration

• Detected by - cells • Insulin is released

Low blood glucose concentration

• Detected by - cells • Glucagon is secreted

Summary

What happens when homeostasis goes wrong ?

•DIABETES ! !! • There are two types• Type IAndType II And of course it is treatable !

Past Exam Question• The graph shows the blood glucose and glucagon concentrations in a healthy

person during and after eating a meal.

1 2 0

1 0 0

8 0

1 2 0

11 0

1 0 0

9 0

M e al

G lu co se

G lu ca g o n

O neh ou r

b efo rem eal

M e alb eg in s

Tw o h o u rsafte r m ea l

B lo o d g lu co sec o nc en tra tio n /

m g 1 0 0 cm

B lo o d g lu ca g o nco n ce ntra tio n /a rb itra ty u n its

– 3

• (i) From where is glucagon secreted?• (ii) Explain the changes that occur in the

glucagon concentration over the period on the graph.

• (b) Explain how the information shown in the graph provides an example of negative feedback.

Answers• (a) (i) Cells of islets of Langerhans / pancreas / a cells;

• (ii) High glucagon because –eg stimulated by low glucose/glycogen must be converted to glucose;Low glucagon because –

e.g. body has absorbed glucose;• (b) Clear understanding that a change from the set level

initiates mechanismreturning it;low glucose secretion of glucagon glucose level increases/glucagon increase glucose increase ® glucagon decrease;

END OF THE PRESENTATION

• Referencing• "Homeostasis." 25 February 2005.

HowStuffWorks.com. <http://health.howstuffworks.com/adam-200092.htm> 02 May 2010.

• “Homeostasis” www.biologymad.com http://www.biologymad.com/resources/A2%20Homeostasis.pdf accessed on 28th of April

• Baker M. Indge B. Rowland M. (2001) Further Studies in Biology , Unit 9 Pages 174 - 193