HOMEOSTASIS

A state of balance in the body

• Homeostasis is the maintenance of a steady state in the body despite changes in the external environment

• The steady state is the optimum level for the body functions

In animals there are two communication systems

• The endocrine system based upon hormones • The nervous system based upon nerve

impulses

Hormones

• Organic substances • Produced in small quantities • Produced in one part of an organism (an

endocrine gland)• Transported by the blood system • To a target organ or tissue where it has a

profound effect

© 2008 Paul Billiet ODWS

The endocrine system • The endocrine system produces chemical signals

• Each hormone is different and they travel relatively

quickly through the blood stream all over the body

• Their effects may be very slow (e.g. growth hormone over years)

• Some are very fast (e.g. adrenaline which acts in seconds)

© 2008 Paul Billiet ODWS

Nerve impulses

• All nerve impulses look the same

• So the nervous system sends signals along nerves to specific parts of the body

• The nerve impulses travel very quickly and affect their target tissues in milliseconds

© 2008 Paul Billiet ODWS

The nervous system organisation

• A Central Nervous System (CNS) made of the brain and spinal cord…

• and peripheral nerves connecting it to sensors and

effectors

Stimulus

Effector

eg muscle or gland

Central Nervous System

Receptor or Sensor

eg photoreceptor

Sensory nerve

Response

Motor nerve

© 2008 Paul Billiet ODWS

Negative Feedback

• Is one where there is change from normal level or compensation (norm) is detected and triggers a response which opposes change and restores the norm. the return to the norm is then detected and the corrective response is switched off.

Negative Feedback Loop• Negative feed back loop consists of:• Receptor - structures that monitor a controlled condition and detect changes

• Control center - determines next action

• Effector– receives directions from the control center– produces a response that restores the controlled condition

Negative Feedback Loop

Negative Feedback Loop

Positive Feedback during Childbirth

• Stretch receptors in walls of uterus send signals to the brain

• Brain induces release of hormone (oxytocin) into bloodstream

• Uterine smooth muscle contracts more forcefully• More stretch, more hormone, more contraction etc.• Cycle ends with birth of the baby & decrease in

stretch

BLOOD GLUCOSE REGULATION

Dual control of One factor

• Different mechanisms restore the norm from deviations in different directions from the normal level.

• The operation of different mechanisms gives more precise control and restores the norm quickly, thereby keeping the fluctuation from the norm conditions to a minimum.

BLOOD GLUCOSE REGULATION

• Pancreas------------ Islet of Langerhans• Alpha (α) cells-------Glucagon• Beta (β) cells-------- Insulin.

• Stimulus – Glucose (increase)• Receptor- Pancreas

» Beta cells in the islet of langerhans of the pancrease is triggered to secrete Insulin.

Role of Insulin on the Effector

• Insulin’s target organ is the Liver i.e. The Effector

• Insulin binds to protein molecules on the cell surface membrane (CSM) of muscle and Liver cells. This triggers the cell to send more of these protein molecules from within vesicles of the cytoplasm to the CSM.

• The role of these protein on the CSM is to uptake glucose from the blood into the cell.

• An increase of the protein in the CSM will leaf to an ____________ uptake of ___________ into the cell

Inside the Liver

• Within the liver and muscle and liver cells are enzymes which speed up the conversion of glucose to glycogen.

• Glucose---enzyme--- Glycogen = Glycogenesis• ( Glycogen forming)

• Glycogen is an insoluble molecule stored as granules in the cytoplasm.

• The liver can store 75mg of glycogen• The uptake and conversion of the glucose causes the glucose

level to return to Norm.

If there is too much glucose in the blood, Insulin converts some of it to glycogen

Glycogen

Insulin

Glucose in the blood

Time

Glucose Concentration

Meal eaten

Insulin is produced and glucose levels fall to normal again.

Glucose levels rise after a meal.

Normal

• Stimulus – Glucose (decrease)• Receptor- Pancreas

» Alpha cells in the islet of Langerhans of the pancreas is triggered to secrete Glucagon.

Role of Glucagon

• Effector : Liver.• Glucagon activates enzymes in the liver cells

to speed up the conversion of the insoluble glycogen to glucose.

• Glycogen---enzyme---- Glucose = Glycogenolysis• (glycogen splitting)

• The glucose molecules will then diffuse out of the liver in the blood where it needed.

Gluconeogenisis= new glucose formation

• The glucagon released also increases glucose production from other nutrients such as : amino acids and or fatty acids from liver cells.

• This glucose also enters the blood

Diabetes mellitus

• Abnormally high concentration of blood sugar is called Hyperglycaemia (Hyper=excessive; Glycemia=blood sugar)

• However, an abnormally low blood sugar concentration, is called Hypoglycemia (Hypo=less; Glycemia=blood sugar)

• High blood sugar (hyperglycemic) type of curve obtained after 100 grams of glucose. Note sharp rise to around 250 mg. after 1 hour with rapid fall during the second and third hours..

• Low blood sugar (hypoglycemic) type of curve obtained after 100 grams of glucose. Note the sharp rise to 150 mg. At ½ hour followed by a sharp fall to abnormally low levels after 1½ hours. Note that the blood sugar remained at abnormally low levels for about 2½ hours. Hatched area indicates the extent and duration of the low blood sugar period.

Please Revise and Study!

Questions??http://www.montana.edu/wwwai/imsd/alcohol/Vanessa/vwbloodsugar.htm

The End