Nerves, Hormones & Homeostasis

Assessment Statements Obj.

6.5.1 State that the nervous system consists of the central nervous system (CNS) and peripheral nerves, and is composed of cells called neurons that carry rapid electrical impulses. 1

6.5.2 Draw and label a diagram of the structure of a motor neuron. 1

6.5.3 State that nerve impulses are conducted from receptors to the CNS by sensory neurons, within the CNS by relay neurons, and from the CNS to effectors by motor neurons. 1

6.5.4 Define resting potential and action potential (depolarisation and repolarisation). 1

6.5.5 Explain how a nerve impulse passes along a non-myelinated neuron. 3

6.5.6 Explain the principles of synaptic transmission. 3

6.5.7 State that the endocrine system consists of glands that release hormones that are transported in the blood. 1

6.5.8State that homeostasis involves maintaining the internal environment between limits, including blood pH, carbon dioxide concentration, blood glucose concentration, body temperature and water balance.

1

6.5.9 Explain that homeostasis involves monitoring levels of variables and correcting changes in levels by negative feedback mechanisms. 3

6.5.10 Explain the control of body temperature, including the transfer of heat in the blood, and the roles of the hypothalamus, sweat glands, skin arterioles and shivering. 3

6.5.11 Explain the control of blood glucose concentration, including the roles of insulin, glucagon and α and β cells. 3

6.5.12 Distinguish between type I and type II diabetes. 2

Assessment statements from: Online IB Biology Subject GuideCommand terms: http://i-biology.net/ibdpbio/command-terms/

Diagram from: http://commons.wikimedia.org/wiki/File:Anatomy_and_physiology_unlabeled_neuron.jpg

The Motor Neuron

nerve impulse

http://msjensen.cehd.umn.edu/1135/Links/

http://bcs.whfreeman.com/thelifewire/content/chp44/4402s.swf

From McGraw Hill: http://goo.gl/tI2MD

http://www.blackwellpublishing.com/matthews/actionp.html

http://www.blackwellpublishing.com/matthews/channel.html

http://www.mindhacks.com/blog/2005/09/synapse_wins_science.html

http://outreach.mcb.harvard.edu/animations/synaptic.swf

Insulin and Glucagon: Control of Blood Glucose

• Two types of cells in the pancreas– Secrete insulin and glucagon, antagonistic

hormones that help maintain glucose homeostasis

• Glucagon– Is produced by alpha cells

• Insulin– Is produced by beta cells

• Maintenance of glucose homeostasis

Beta cells ofpancreas are stimulatedto release insulininto the blood.

Insulin

Liver takesup glucoseand stores itas glycogen.

Body cellstake up moreglucose.

Blood glucose leveldeclines to set point;stimulus for insulinrelease diminishes.

STIMULUS:Rising blood glucoselevel (for instance, aftereating a carbohydrate-rich meal)

Homeostasis:Blood glucose level(about 90 mg/100 mL)

Blood glucose levelrises to set point;stimulus for glucagonrelease diminishes.

STIMULUS:Dropping blood glucoselevel (for instance, afterskipping a meal)

Alpha cells of pancreasare stimulated to releaseglucagon into the blood.

Liver breaksdown glycogenand releasesglucose intoblood.

Glucagon

Figure 45.12

High blood glucose levels Low blood glucose levels

1. pancreas (beta) produces

insulin

2. Insulin stimulates muscle

and liver to take glucose

from blood and convert to

glycogen.

3. resulting in lowering the

glucose level in the blood.

1. pancreas (alpha) produces

glucagon

2. Glucagon stimulates liver

to convert glycogen back

into glucose.

3. releasing of glucose into

blood

• Diabetes mellitus, perhaps the best-known endocrine disorder– Caused by a deficiency of insulin or a decreased response to insulin in

target tissues– Is marked by elevated blood glucose levels

• Type I diabetes mellitus (insulin-dependent diabetes)– Is an autoimmune disorder in which the immune system destroys the

beta cells of the pancreas– Juvenile

• Type II diabetes mellitus (non-insulin-dependent diabetes)– Is characterized either by a deficiency of insulin or, more commonly,

by reduced responsiveness of target cells due to some change in insulin receptors

– Adults– Body produces insulin, pancreas either cant produce enough or body

cant use it adequately (glucose cant get into cells so there is a build up of glucose in blood)