Bill
• Explain how a nerve impulse passes through a neuron
• Resting potential creates electrical chemical gradient
between external and internal environments of neuron,
creating membrane potential
• Depolarization occurs, where Na and K ions diffuse in and
out of membrane channels, creating nerve impulse
• Self-propagating action, travels down the axon
• Repolarization occurs, where charges return to resting state
• Refractory period- when neuron cannot carry another
nerve impulse until fully returned to resting potential
Topic 6.5
Endocrine System
IB Biology II Van Roekel
6.5.7 – 6.5.12 Statements
•
•
6.5.7 State that the endocrine system consists of glands that release hormones
that are transported in the blood.
•
•
•
6.5.8 State that homeostasis involves maintaining the internal environment
between limits, including blood pH, carbon dioxide concentration, blood
glucose concentration, body temperature and water balance.
•
•
6.5.9 Explain that homeostasis involves monitoring levels of variables and
correcting changes in levels by negative feedback mechanisms.
•
•
•
6.5.10 Explain the control of body temperature, including the transfer of heat in
blood, and the roles of the hypothalamus, sweat glands, skin arterioles and
shivering.
•
•
6.5.11 Explain the control of blood glucose concentration, including the roles of
glucagon, insulin and 􀀀 and 􀀀 cells in the pancreatic islets.
•
6.5.12 Distinguish between type I and type II diabetes.
Endocrine System
• Nervous System (autonomic nervous system) and
endocrine system work closely together in order to
maintain homeostasis
• Endocrine System: consists of all an animal’s hormone
secreting cells and glands
• Endocrine Glands: called ductless glands because they
secrete chemical messengers directly into body fluids
• Hormones: chemical signals formed in specialized cells
that travel through body fluids and coordinate various
parts of the organism by interacting with target cells
Lipid-soluble
Hormones
• Two types of signaling
• Hormones penetrate
cell membrane and
bind to receptor
protein inside cell
• Acts as transcription
factor and changes
gene expression
hormone
(testosterone)
1
Target
cell
Nucleus
DNA
2
3
Receptor
protein
Hormonereceptor
complex
4 Transcription
mRNA
New
protein
Cellular response:
activation of a gene and
synthesis of new protein
Water-soluble
Hormone
• Hormones bind to
external protein
receptor, triggering a
signal-transduction
pathway
• Can result in either
change in gene
expression or
cytoplasmic activity
hormone
(epinephrine)
Target
cell
Relay
molecules
1
2
Receptor
protein
Plasma
membrane
Signal
transduction
pathway
Bill
• What are the two types of signaling pathways we
see used with hormones?
• Internal- hormones diffuse through cell
membrane and bind to intracellular protein
receptor. Change gene expression/protein
production
• External signaling- hormones bind to external
protein receptor and trigger signal transduction
pathway. Can alter cytoplasmic activity or gene
expression
Homeostasis
• Human Body has adapted several mechanisms to deal with
homeostasis (maintaining balance)
• Uses negative feedback mechanisms (physiological changes
that bring a value back closer to a set point) to maintain
homeostasis
– so if levels vary too far, a series of steps occurs to return it to
normal.
• Body must control:
–
–
–
–
–
blood pH
carbon dioxide concentration
blood glucose concentration
body temperature
water balance within tissues
Homeostasis and Negative Feedback
Hypothalamus and Pituitary Gland
• Hypothalamus: region of lower brain that
receives info from nerves throughout body
and initiates endocrine signals appropriate to
environmental conditions (monitors levels of
variables)
• Pituitary Gland: small organ regulated by
hypothalamus that stores and/or regulated
multiple endocrine secretions (initiates
negative feedback mechanisms)
Brain
Posterior pituitary:
Composed of nervous tissue;
stores and secretes hormones
made by hypothalamus
Hypothalamus:
Master control
center of the
endocrine system
Anterior pituitary:
Composed of
endocrine tissue;
controlled by
hypothalamus;
produces and
secretes its
own hormones
Homeostatic Control of Body
Temperature
• Body has
thermoreceptors that
detect heat and send
message to
hypothalamus.
• Hypothalamus (in
conjunction with pituitary
gland) senses an increase
or decrease in body temp
• Employs mechanisms to
return to maintain body
temperature
Homeostatic control of body temp
Cooling Mechanisms
• Increase activity of sweat
glands
– Causes heat loss by
evaporation of water
• Vasodilation of blood
vessels
– Fills capillaries with
blood, heat leaves by
convection/radiation
Heating Mechanisms
• Constricting skin arterioles
so blood is diverted to
deeper organs and tissues,
less heat loss by convection
• Stimulates skeletal muscle
contractions, aka shivering
BILL
• Outline how the body cools itself/warms itself if
temperatures vary too far from 37oC
• If body is too warm:
– Increase activity of sweat glands, causes heat loss by
evaporation of water
– Vasodilation of blood vessels, fills capillaries with blood, heat
leaves by convection/radiation
• If Body is too cold:
– Constricting skin arterioles so blood is diverted to deeper
organs and tissues, less heat loss by convection
– Stimulates skeletal muscle contractions, aka shivering
Control of Blood Glucose
• Blood glucose level is the
concentration of glucose in the
blood plasma
• Cells never cease respiration,
therefore you must have a
constant (steady) supply of blood
glucose available.
• Negative feedback mechanisms
by the body ensure the proper
uptake/release of glucose in the
blood.
• Most blood is acted on by
Hepatocytes, liver cells directed
by insulin and glucagon to
regulated blood glucose
concentration
Control of Blood Glucose
High Blood Glucose Levels
• Beta Cells in Pancreas produce
and secrete insulin into blood
• Insulin signals to cells to open
protein channels to allow
diffusion of glucose into the
cells for cell respiration
• Stimulates Hepatocytes to
convert glucose into glycogen
and store it as granules in
cytoplasm (same in muscle
cells)
• Lowers Glucose level in blood
Low Blood Glucose Levels
• Alpha Cells in Pancreas
produce and secrete
glucagon
• Stimulates hydrolysis of
glycogen, in hepatocytes
and muscle cells, into
glucose
• Glucose enters bloodstream
• Increases Glucose
concentration in blood
Insulin
Body
cells
take up more
glucose
3
2
Beta cells
of pancreas stimulated
to release insulin into
the blood
4
Blood glucose level
declines to a set point;
stimulus for insulin
release diminishes
Liver takes
up glucose
and stores it as
glycogen
1 High blood
glucose level
Stimulus:
Rising blood glucose
level (e.g., after eating
a carbohydrate-rich
meal)
Glucose
level
Homeostasis: Normal blood glucose level
(about 90 mg/100 mL)
Glucose
level
Stimulus:
Declining blood
glucose level
(e.g., after
skipping a meal)
5 Low blood
glucose level
Blood glucose level
rises to set point;
stimulus for glucagon
release diminishes
6
Alpha
cells of
pancreas stimulated
to release glucagon
into the blood
8
Liver
breaks down
glycogen and
releases glucose
to the blood
7
Glucagon
Diabetes
• Disease characterized by hyperglycemia (high
blood sugar)
• People have plenty of glucose in their blood,
but not in their body cells
– Type I caused when Beta cells do not produce
enough insulin, treated with injection of insulin
– Type II caused by body cell receptors that do not
respond properly to insulin, controlled by diet
Diabetes Mellitus
• Type I
– Autoimmune disorder
– Body attacks and destroys
beta cells, therefore no
insulin is produced.
– Blood sugar remains
abnormally high as a
result.
– Less than 10% of diabetics
have Type I.
– Most often develops in
children and young adults
• Type II
– Body cells no longer
respond to insulin (insulin
resistance)
– Body stops creating insulin
because it has developed
resistance typically caused
by constant elevated blood
glucose levels.
– Most common (90%)
– Associated with obesity,
lack of exercise, advanced
age, and genetics
Uncontrolled Diabetes
• If left untreated
– Damage to retina, leading to blindness
– Kidney Failure
– Nerve damage
– Increased risk of Cardiovascular disease
– Poor wound healing (possibly gangrene 
amputation)
Nervous Quiz
• 12 questions (7 multiple choice, 5 short answer)
• 30 minutes in class to take it
• May use notes only
– Parasympathetic vs sympathetic
– Synaptic Transmission
– Action Potential, Resting Potential, and how a nerve impulse
travels down neuron
– Structure of Neuron
– Pupil Reflex
– Parts of Brain and functions
– Temperature control
– Blood Glucose Control
– Production and regulation of Hormones