Endocrine System
Chapter 13
General Outcome:
Students will explain how the endocrine
system contributes to homeostasis
Main Function:
• To control and regulate all important aspects
of life-growth
– Physical and mental development, maintenance
and reproduction
Characteristics:
• More diffuse, less rapid and more prolonged
effect than the nervous system
• Pituitary gland is referred to as the “master
gland”- controls the endocrine system as brain
controls the nervous system
– Both systems are coordinated by the hypothalamus
• Does not have its own transport system- works by
using the circulatory system’s blood vessels to
transport its chemical messengers – called
hormones
Characteristics:
• Endocrine glands are different from exocrine glands
in that they release hormones and secrete these
substances directly into the blood
• Exocrine glands produce secretions released via
tubular ducts (ex: mammary glands secrete milk
through ducts and therefore they are considered
exocrine)
Hormones:
• Biochemical molecules of two general types- steroid
(Estrogen, testosterone, progesterone) or protein
(ADH, Insulin)
• Produced by endocrine glands and secreted directly
into the blood
• Can stimulate other glands to secrete their hormones
Hormones:
• Exert their control by influencing/modifying enzyme
activity or by changing the permeability of a membrane for
a particular molecule
• Act only with certain target cells- which have receptor
molecules in or on them for particular hormones (An
example of Lock and Key Principle)
Homeostasis:
• Tendency to maintain a constant internal
environment (Balance)
• Maintenance of this internal steady state is
most important – if it fails illness or death
• Talk about body temperature 37.1⁰C
• To keep within healthy parameters, our body
needs to be able to respond appropriately to
change
Control System:
• Internal environment must be kept in constant
equilibrium with respect to temperature,
chemical composition, number of blood cells,
among other things- if life is to continue
• Each organism receives stimuli from its external
and internal environment and it must respond to
such stress in a self-preserving way. To do this,
organisms require a control system
Feedback Loops:
• There are two types of Feedback loops:
Positive and Negative
• Negative: The stimulus is received, change is
effected, system is shut down
• Positive: Stimulus is responded to but system
is never shut down
Homeostasis:
is the steady
state
Some Factors included in homeostasis:
•
•
•
•
•
•
•
Heartbeat
Blood Pressure
Respiration Rate
Amount of CO2 and O2
Calcium Level
Blood Glucose Level
Hormone Level
Negative Feedback
• Response made by
the control system
is returned as a Increase in CO2
Concentration in
new stimulus to
Blood
the system and
negates the
original response.
• Eg: CO2
Concentration
Increase in
Physical
Activity as
Registered by
the Brain
Increase in
Breathing
Movement
(Diaphragm and
Intercostals)
Muscles)
Positive Feedback Loop
• relatively uncommon in the human body
• a change in the homeostatic condition is
detected by receptors and the information is
transmitted to the control center
• the control center activates effectors which
generate a response which increases the
stimulus further reinforcing the initial change
• acts to reinforce or strengthen the stimulus
or change
Human Positive Feedback
• Oxytocin - Dilation of the cervix triggers stretch receptors
which transmit nerve impulses to the hypothalamus
• results in oxytocin (OT) being released from the posterior
pituitary.
• oxytocin is carried by the blood to the uterus where it
causes uterine contractions.
• uterine contractions begin to force the fetus through the
cervix.
• As the fetus is pushed through the cervix this further
stretches the cervix which results in more oxytocin being
released.
• This positive feedback will continue until the baby has
cleared the birth canal and the cervix is no longer
stretched.
Do Section 13.1 Review page 442 # 1-5
Pituitary Gland
• Located in the brain
• Responds to nervous
stimulation and
chemical releases
from the
hypothalamus
• Divided into posterior
and anterior lobes –
each one releasing a
variety of hormones
into the blood
Posterior Lobe:
• Stores and secretes two hormones produced
by the hypothalamus, which have traveled to
the pituitary via specialized nerve cells
Antidiuretic Hormone (ADH)
– Targets the kidneys
– Controls the re-absorption of water by the kidney
tubules during the formation of urine
– Raises the blood pressure by constricting blood
vessels
Posterior Lobe:
Oxytocin
– Targets the mammary glands and uterus
– Stimulates the contraction of smooth muscles of
the uterus during labor
– Stimulates the ejection of breast milk
Anterior Lobe:
• Produces its own hormones but their release is regulated
by the hypothalamus
• Hormones released from hypothalamus → transported
in blood to the pituitary →pituitary releases required
hormones → hormones move to target
tissues/organs/cells
Anterior Lobe:
Growth Hormone (GH)
• Targets most cells
• Promotes growth by increasing cell division
• Disorder related to GH include:
– ↑ production before growth plates fuse :
Gigantism
– ↑ production after growth plates fuse :
Acromegaly (wide fingers, face, ↑ bone width)
– ↓ production before growth plates fuse: Dwarfism
Acromegaly
Anterior Lobe:
Thyroid Stimulating Hormone (TSH)
• Targets thyroid gland, stimulating it to release
thyroxine which regulates body metabolism
and helps develop the nervous system
Anterior Lobe:
Adrenocorticotropic Hormone (ACTH)
•Targets the adrenal glands
– Adrenal Cortex: Produces three different hormones –
aldosterone (water balance): cortisol (Balances glucose by
doing protein and carb. metabolism) and Sex hormones
Water
Anterior Lobe:
Prolactin (PRL)
Targets the mammary glands
Stimulates the Production of milk
Also promotes uterine contractions
Anterior Lobe:
Gonadotropic Hormones- hormones released
which target the testes in males and the ovaries
in females
Follicle Stimulating Hormone (FSH): Stimulates
the maturation of the egg and the production of
sperm
Lutenizing Hormone (LH): Stimulates ovulation in
females and the production of testosterone in
males
Tropic vs. Non-Tropic
–Prolactin, and GH are considered nontropic hormones because they
stimulate tissues other than endocrine
glands
–All other anterior lobe hormones are
considered tropic because they
activate endocrine glands
Do Investigation 13.A page 447
The Thyroid Gland
• Two lobes of tissue that are joined by a narrow portion
(looks like a
• bowtie)
• Lies over the trachea
• Releases thyroid hormone Thyroxine (iodine containing)
• Regulates overall basal metabolic rate
• Important in bodily growth
• Controls the development of the nervous system
Effect of the Thyroid
Thyroxine
• Directly or indirectly affects every tissue of the body
• Increases the body’s metabolic rate (O2 consumption
to produce energy)
– By product of this reaction is heat and therefore the body
feels warmer
– Other factors that contribute to metabolic rate are
exercise, food intake, muscle tone, etc.
Effect of the Thyroid
• Stimulates the secretion of GH and promotes
its effect on synthesis of proteins
• Required for the development of the CNS in
children and for normal CNS activity in adults
Calcitonin: responsible for decreasing blood
calcium levels by increasing storage in bones
and teeth, increasing excretion in kidneys, and
decreasing absorption in intestines.
• 65% of thyroid secretions are thyroxine
Disorders of the Thyroid Gland:
Hypothyroidism: deficient hormone secretion
• Causes:
– Thyroid gland fails
– Not enough iodine in diet
– TSH hormone deficiency
• Results:
– Reduced metabolic rate – intolerant to cold,
weight gain, diminished alertness, easily fatigued
Disorders of the Thyroid Gland:
Hypothyroidism cont’t:
• Disorders:
– Cretinism: Hypothyroidism from birth causes
dwarfism and possible mental retardation
• Treatment:
– Hormone therapy
– More Iodine in diet (Dairy, Canned Veggies,
seafood, cured meat)