The
Endocrine
System
Chemical Control
The Endocrine System
• The endocrine system has similar
functions to the nervous system
– Controls and integrates functions in the body
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Growth of body and reproductive organs
Mobilization of defences to stress
Balance of chemicals in blood
control of O2 use by cells
Hormones
• The endocrine system uses chemical
messengers to “communicate” with targets
– A hormone is a specific messenger molecule
synthesized and secreted by a group of specialized
cells called an endocrine gland.
– endocrine glands are ductless, their secretions
(hormones) are released directly into the bloodstream
and travel to target organs.
– Note that this is in contrast to digestive glands
(exocrine), which have ducts for releasing the
digestive enzymes.
Endocrine/Parathyroid hormone animation MHHE
Hormones and Receptors
• Each hormone’s shape is specific and can be
recognized by only specific binding sites on
target cells called hormone receptors.
Hormones
• There are two general groups of
hormones. They are classified by
chemical structure, not function
– Steroid hormones
– Peptide hormones (protein related)
Steroid Hormones
• steroid hormones
• Lipid molecules made from cholesterol
• Not water soluble
– Male and Female sex hormones
• testosterone, estrogen, progesterone
– Cortisol
• Enables stress recovery
Peptide Hormones
• peptide hormones
– Chains of amino acids
– Water soluble
– most numerous/diverse group of hormones.
• Insulin, glucagon, growth hormone
Hormones and Receptors
• The regulation of hormones depends on
negative feedback loops to maintain
balance and homeostasis
Endocrine Glands
• Hypothalamus and pituitary gland
– The pituitary gland is called the “master
gland” as many of the hormones released by
the pituitary control the other endocrine
glands of the body
– the pituitary is under the control of the
hypothalamus which uses both neural and
hormonal communication
Hypothalamus and pituitary
Hypothalamus and pituitary
• Neural control by hypothalamus
– Neurons from the hypothalamus run axons
down into the posterior lobe of the pituitary
gland
– ADH and oxytocin are secreted from axon
terminals which then move into capillaries for
circulation
Hypothalamus & post. pit.
Posterior Pituitary Hormones
• ADH
– Promotes water reabsorption from collecting
duct of nephrons in the kidneys
• Oxytocin
– Promotes uterine contraction (+ feedback)
– Promotes lactation (breast milk production)
– Causes smooth muscle contraction in male
and female reprod. organs
Hypothalamus & anterior pit.
• Hormonal control by hypothalamus
– Neurons in hypothalamus secrete
releasing hormones (releasing factors) into
capillaries in the hypothalamus which travel to
the anterior pituitary
Hypothalamus & anterior pit.
Anterior Pituitary Gland
• Hormones released from the anterior pituitary
include:
– Thyroid stimulating hormone (TSH)
– Corticotropin adrenal steroid (ACTH)
– Somatotropin or Growth Hormone
(STH)
or (GH)
– Follicle stimulating Hormone (FSH)
– Luteinizing Hormone (LH)
– Prolactin (PRL)
Two animations Life Wire
Endocrine/TSH animation MHHE
Feedback Control
Other Endocrine Glands
Thyroid Gland
• Thyroid hormones regulate metabolism,
therefore body temperature and weight
Thyroid Gland
• The thyroid hormones contain iodine
which is needed to manufacture the
thyroid’s hormones.
– If a person lacks iodine in their diet, the
thyroid cannot make the hormones, causing a
hormonedeficiency
– In response to the body’s feedback loops
calling for more thyroid hormones,
the thyroid gland enlarges to
attempt to compensate (goiter)
Thyroid Gland
• Thyroid Hormores (TH)
– Thyroxin Hormone
• Regulates metabolic rate
• Increase thyroxine = increase metabolism
• Slower metabolism
– Slower use of glucose = gylcogen storage and any
excess stored as fat
Parathyroid Glands
• Located on the posterior surface of the
thyroid gland
Parathyroid Glands
• Secrete parathyroid hormone (PTH) which
raises blood Ca2+
– Blood Ca2+ increased by
• Being released from bone
• Increase reabsorption from distal tubule of kidney
• Activation of vitamin D (stimulates uptake of Ca2+
from intestine)
– Ca2+ regulation animation
The Adrenal Glands
• Located above each kidney, the adrenal
glands have two main divisions
– Adrenal Medulla
– Adrenal Cortex
Adrenal Medulla
• The adrenal medulla is involved in
responses to stressful stimuli
– Regulated by sympathetic neural pathways
– During stress, epinephrine and
norepinephrine are released into the blood
which promotes increases in:
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blood glucose levels
HR, BP, & vasodilation,
pupil dilation
metabolism
Adrenal Cortex
• Produces steroid hormones that help the body
cope with stress
– Regulated by hormones from the ant. pituitary
– Make sure that brain gets glucose
– Forces other cells to use fat and amino acid
metabolism for energy
– Three types of hormones
• Glucocorticoids
• Mineralocorticoids
• Sex hormones
Adrenal Cortex Hormones
• Glucocorticoids
– Cortisol
• Increases amino acid levels in the blood so that
they can be
– converted to glucose in the liver
– used to repair damaged cells
– Excess amounts have an antiinflammatory action
• Controlled by adrenocorticotropin hormone (ACTH)
– Trace the hormonal control pathway
Adrenal Cortex Hormones
• Mineralocorticoids
– Aldosterone
• Helps maintain body’s water balance
• Secreted when blood pressure/volume drop below
normal
• Increases Na+/water reabsorption in kidneys
• Controlled by ACTH
Adrenal Cortex Hormones
• Sex Hormones from Adrenal Cortex
– Dehydroepiandrosterone (DHEA)
• Stimulates sex drive
• induces labor
• We’ll talk about this when you’re older!
Pancreas
• Produces 2 hormones responsible for
maintaining constant blood glucose levels
– Insulin
– Glucagon
Insulin
• Produced by beta cells in the islets of
Langerhans
– Released into circulatory system when glucose levels
are higher than normal
– where is blood glucose level “sensed”?
– binds with receptors on cell membranes to open
glucose channels
• Liver cells take in glucose and store excess as glycogen
• Note: know Diabetes Mellitus inside and out
Insulin
Glucagon
• Produced by alpha cells in islets of
Langerhans
• Glucagon is released when blood sugar
levels are low
– Promotes release of glucose from glycogen
stores in liver
Honorable Mentions
• Pineal Glands
– Melatonin secreted when dark
– Promotes sleep
• Prostaglandins
– Have affect on
localized cell area
– Aid in response to stress
• Ovary and Testis will be
covered in next section