Hormones and the
Endocrine System
COURTNEY LLINARES &
BRENDA YIK
THE ENDOCRINE SYSTEM AND HORMONES




What are hormones?
Molecules that are diffused throughout the body to communicate various
regulatory messages to specific target cells
What is the endocrine system?
One of two major bodily communication systems (the other being the
nervous system)
TYPES OF CELLULAR COMMUNICATIONS

Intercellular communications: different ways signals are
sent between animal cells



Types of intercellular communications are endocrine, paracrine, autocrine
synaptic, and neuroendocrine sigaling
Extracellular communications:
Pheromones
Intercellular
communication
by secreted
molecules
Blood
vessel
(a) Endocrine
Response
signaling
Response
(b) Paracrine
signaling
Response
(c) Autocrine
signaling
Synapse
Neuron
Response
(d) Synaptic
signaling
Neurosecretory
cell
Blood
vessel
(e) Neuroendocrine
Response
signaling
EARLY ENDOCRINE/HORMONAL SYSTEMS
CNIDARIANS: HYDRA
Endocrine system was not yet developed, but
evidence has shown neurohormones in effect
 Contains neuropeptides that stimulate processes

EARLY HORMONES/ENDOCRINE SYSTEM
ANNELIDS: NEREIS
Marine worm
 Long ventral nerve cord with a segmented
ganglion
 Produces the peptide hormone neredine, in the
ganglion (early brain)

EARLY HORMONES/ENDOCRINE SYSTEM
ARTHROPODS: BUTTERFLY


Has an endocrine system and hormones for
molting, development, and more
A brain hormone stimulates release of ecdysone from the
prothoracic glands
HORMONES/ENDOCRINE SYSTEM
MAMMALS: HUMANS

Have fully developed endocrine system with a
variety of functional hormones

The endocrine systems is made of eight functional glands:
•
Hypothalamus
•
Pituitary
•
Thyroid
•
Parathyroids
•
Thymus
•
Adrenals
•
Gonads
Major endocrine glands:
Hypothalamus
Pineal gland
Pituitary gland
Thyroid gland
Parathyroid glands
Organs containing
endocrine cells:
Thymus
Heart
Adrenal
glands
Testes
Liver
Stomach
Pancreas
Kidney
Kidney
Small
intestine
Ovaries
CHEMICAL CLASSES OF HORMONES

Three classes of hormones:
1.
Polypeptides
2.
Steroids
3.
Amines

Hormones vary in solubility in aqueous and lipid
environments

Water soluble hormones: polypeptides and most amines

Lipid soluble hormones: steroids
Hormones
differ in
form and
solubility
Water-soluble
Lipid-soluble
0.8 nm
Polypeptide:
Insulin
Steroid:
Cortisol
Amine:
Epinephrine
Amine:
Thyroxine
EFFECTS OF HORMONES

•
•
Many hormones cause more than one type of
cellular response
Example: Epinephrine triggers glycogen breakdown in the liver,
increases blood flow to many skeletal muscles, and more simultaneously
Signaling by local regulators: local regulators are molecules that send
chemical signals in seconds unlike hormones, but have the same pathways
as hormones
Ex: Growth factors, and nitric oxide
FEEDBACK REGULATION


In simple endocrine pathways cells responds
directly to and internal or environmental
stimulus by secreting certain hormones
These responses link back to deduce the initial
stimulus (negative feedback) or enhance the
initial stimulus (positive feedback)
Signal Transduction Pathway
Example
–
Stimulus
Low blood glucose
Endocrine
cell
Pancreas alpha cells
secretes
glucagon
Blood
vessel
Target
cells
Response
Liver
Glycogen breakdown,
glucose release into blood
ANTAGONISTIC HORMONES AND DIABETES
Insulin and glucagon are antagonistic hormones
that help maintain homeostasis in blood glucose
levels
 Diabetes mellitus: disorder caused by insulin
level or response abnormalities
 Treatment involves insulin injections, lifestyle
changes, or medication

COORDINATION OF ENDOCRINE AND
NERVOUS SYSTEMS


Hypothalamus connects the nervous and
endocrine systems
Pituitary gland receives signals from the
hypothalamus for various hormone excretions
Cerebrum
Pineal
gland
Thalamus
Cerebellum
Pituitary
gland
Hypothalamus = brain
Spinal cord
Endocrine glands in the human brain
Hypothalamus
Posterior
pituitary
Anterior
pituitary
THYROID REGULATION


In thyroid regulation a hormone cascade pathway
occurs where a hormone stimulates the release
many other hormones
The last of the secreted hormones activates a
nonendocrine target cell
Pathway
A hormone
casade
pathway
Example
Stimulus
Cold
Sensory
neuron
–
Hypothalamus secretes
thyrotropin-releasing
hormone (TRH )
Neurosecretory
cell
Blood
vessel
–
Negative feedback
Anterior pituitary secretes
thyroid-stimulating
hormone (TSH
or thyrotropin )
Thyroid gland secretes
thyroid hormone
(T3 and T4 )
Target
cells
Response
Body tissues
Increased cellular
metabolism
Disorders of Thyroid Function
Hypothyroidism occurs when there is low secretion of
thyroid hormones
-Treatment:
-Levothyroxine medication commonly used to replace
lacking thyroid hormone

Disorders of Thyroid Function Continued
In humans, hyperthyroidism is condition in
which thyroid gland produces excessive amount
of thyroid hormone
 Treatment:
-Antithyroid medications
-Radioactive iodine

TROPIC AND NONTROPIC HORMONES

Tropic hormones: regulate the function of other
endocrine cells or glands
Examples:
-TSH (thyroid-stimulating hormones) regulate the thyroid gland
-Follicle-stimulation hormone

Growth hormones: stimulates growth through
tropic and nontropic effects
PARATHYROID HORMONE AND VITAMIN D

•
•
•
Parathyroid glands release the parathyroid
hormone (PTH)
Maintains homeostatic control of blood calcium levels directly and
indirectly
PTH synthesizes Vitamin D in the kidneys which acts directly by
activating the release of Ca²⁺
calcitonin is a hormone that inhibits bone absorption and enhances calcium
release by the kidney
COORDINATION OF THE ENDOCRINE AND
REPRODUCTIVE SYSTEM
Gonadal sex hormones: affect growth,
development, reproductive cycles, and sexual
behavior
-The gonads produce and secrete three major
categories of steroid hormones
(androgens, estrogens, and progestins)
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
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