Ch. 46 The Endocrine System
By: Jose Solorzano, Jose Arambulo, Daniel Guevarra, Eric Galicia, and Jarod
Smith
Group C: Endocrine Systems
= Regulation of body processes by chemical messengers
- 4 mechanisms of cell communication: direct contact, synaptic signaling, endocrine signaling,
and paracrine signaling.
- axons of neurons secrete chemical messengers (neurotransmitters) into the synaptic cleft, with
transmissions only affecting the postsynaptic cell that receives the neurotransmitter
- hormone: a regulatory chemical that is secreted into extracellular fluid and carried by the blood
and can therefore act at a distance from its source
- endocrine gland: an organ that is specialized to secrete hormones
- the liver and kidney can both produce hormones and perform other functions
- endocrine system: the collective organs and tissues that produce hormones
- only target cells with the appropriate receptor for a given hormone can respond to it, with the
receptor proteins binding the hormone to it and activate signal pathways that create a response
to the hormone
- paracrine regulators: molecules that are released and cat within an organ on nearby cells as
local regulators
- paracrine regulators do not travel through the blood to reach their target, but endocrine
hormones do
- cells can release signaling molecules that affect their own behavior, or autocrine signaling
- pheromones: chemicals released into the environment to communicate among individuals of a
single species, aiding in communication between animals and may alter the behavior of the
receiver
- A molecule produced by an endocrine gland and used as a hormone may also be produced
and used as a neurotransmitter, like norepinephrine
- neurohormones: a class of hormones secreted by neurons that are carried by blood
- specialized regions of the brain contain neurotransmitting neurons and clusters of neurons
producing neurohormones
- secretory activity is controlled by the nervous system, but some can be independent of neural
control, such as the release of insulin by the pancreas
- endocrine system includes the thyroid gland, pituitary gland, adrenal glands, and others
- the hormones diffuse into surrounding blood capillaries in extracellular fluid
- hormones have two basic characteristics: being sufficiently complex to convey regulatory
information to their targets, and they must be adequately stable to resist destruction prior to
reaching their target cells
Ch. 46 The Endocrine System
By: Jose Solorzano, Jose Arambulo, Daniel Guevarra, Eric Galicia, and Jarod
Smith
- three categories meet these requirements: peptides and proteins, amino acid derivatives, and
steroids
- hormones can be classified as lipophilic (fat-soluble and non-polar), or hydrophilic (polar and
water-soluble); lipophilic hormones include steroids and thyroids, but other hormones are
hydrophilic
- hydrophilic are freely soluble in blood but cannot pass through the membrane target cells,
activating receptors outside the cell membrane, but lipophilic hormones travel in blood attached
to transport proteins, crossing all membranes and binding to intracellular receptors
- growth factors: proteins that promote growth and cell division and are among the most
important paracrine regulators
- paracrine regulation occurs in most organs and among the cells of the immune system
- epidermal growth factor: activates mitosis of skin and development of connective tissue cells
- nerve growth factor: stimulates the growth and survival of neurons
- insulin-like growth factor: stimulates cell division in developing bone as well as protein
synthesis in many other tissues
- cytokines: growth factors specialized to control cell division and differentiation in the immune
system
- neurotropins: growth factors that regulate the nervous system
- damage to the genes coding for growth factors can lead to the unregulated cell division and
development of tumors
- endothelium of blood vessels is a rich source of paracrine regulators
- endothelin: stimulates vasoconstriction
- bradykinin: promotes vasodilation
- prostaglandins: a diverse group of paracrine regulators that are 20-carbon-long fatty acids that
contain the precursor molecule arachidonic acid, released from phospholipids in the cell
membrane under hormonal or other stimulation
- prostaglandins are produced at locations of tissue damage, where they promote inflammation
- aspirin helps inhibit prostaglandin synthesis, relieving the symptoms of inflammation
- nonsteroidal anti-inflammatory drugs: a class of drugs that includes indomethacin and
ibuprofen that act to inhibit cyclooxygenase-1 and 2
46.3 The Pituitary and Hypothalamus: The Body’s Control Centers
● The Pituitary is a compound endocrine gland.
Ch. 46 The Endocrine System
By: Jose Solorzano, Jose Arambulo, Daniel Guevarra, Eric Galicia, and Jarod
Smith
- The anterior pituitary is composed of glandular tissue derived from epithelial tissue; the
posterior pituitary is fibrous and is derived from neural tissue.
● The posterior pituitary stores and releases two neurohormones.
- The posterior pituitary contains axons from the hypothalamus that release neurohormones.
One of these is ADH, involved in water reabsorption; the other is oxytocin.
● The anterior pituitary produces seven hormones.
- The hormones produced by anterior pituitary include peptide, protein and glycoprotein
hormones. These hormones tend to stimulate growth, and many are tropic hormones that
stimulate other endocrine glands.
● Hypothalamic neurohormones regulate the anterior pituitary
- Releasing and inhibiting hormones produced in the hypothalamus pass to the anterior pituitary
through a portal system and regulate the anterior pituitary hormone production.
● Feedback from the peripheral endocrine glands regulates anterior pituitary hormones.
- The activity of the anterior pituitar is also regulated by the negative feedback; for example,
thyroxine, produced by the thyroid in response to TSH, inhibits further secretion of TSH.
● Hormones of the anterior pituitary work directly and indirectly.
- Three of the seven hormones, GH, prolactin, and MSH, work directly on the nonendocrine
tissues; the other four, ACTH, TSH, LH, and FSH, are tropic hormones that have endocrine
glands as their targets. Defects in GH production can lead to either pituitary dwarfism (low), or
gigatnism (high).
46.4 The Major Peripheral Endocrine glands
The thyroid gland varies in shape in different vertebrate species, but is always found in the neck
area, anterior to the heart.
Calcium is a vital component of the vertebrate body both because of its being a structural
component of bones and because of its role in ion-mediated processes such as muscle
contraction.
Calcitonin- a peptide hormone that plays a role in maintaining proper levels of calcium (Ca2+)
in the blood.
Parathyroid hormone (PTH)- Hormone produced by the parathyroid glands/ synthesized and
released in response to falling levels of Ca2+ in the blood. Normal Ca2+ levels are important for
the functioning of muscles, including the heart, and for proper functioning of the nervous and
endocrine systems.
Thyroid hormones regulate enzymes controlling
carbohydrate and lipid metabolism in most cells, promoting
the appropriate use of these fuels for maintaining the body’s
basal metabolic rate.
Adrenal glands- located just above each kidney/ composed
of an inner portion, the adrenal medulla, and an outer layer,
the adrenal cortex.
Major Endocrine Glands:
Ch. 46 The Endocrine System
By: Jose Solorzano, Jose Arambulo, Daniel Guevarra, Eric Galicia, and Jarod
Smith
Hypothalamus- Underneath the hypothalamus. Center of autonomic nervous system.
Responsible for integration and correlation of many neural and endocrine functions
Pituitary Gland- Consists of an anterior and posterior (glandular and appearing fibrous). In
charge of growth, stimulates cell division.
Parathyroid Glands: produce PTH is response to low calcium. Stimulates kidneys to reabsorb
calcium from urine
Thyroid: secretes thyroid hormone. Responsible for metabolism
Thymus- located beneath sternum. protects body from foreign invaders
Adrenal Glands: above kidneys. 2 parts. Cortex+outer, Medulla=inner, They produce
pinephrine and nor
Pancreas- in charge of blood glucose levels with insulin and glucagon
Testes: produce testosterone
Ovaries- make estrogen
Insulin- Hormone secreted by the beta cells of the islets.
Glucagon- the islets of Langerhans produce another hormone; the alpha cells secrete this,
which acts antagonistically to insulin
Prothoracicotropic hormone (PTTH)- a small peptide secreted by neurosecretory cells on the
brain prior to molting that stimulates a gland in the thorax call the prothoracic gland
Molting Hormone/Ecdysone- secretion that causes, in high levels, the biochemical and
behavioral changes that lead to molting
Juvenile hormone- secreted by the corpora allata, high levels of this prevent the
transformation to the adult and result in a larval-to-larval molt.
True and False Questions
1. A defect in the hypothalamus can lead to dwarfism. False: Not the hypothalamus, but the
pituitary.
2. The pituitary is a compound endocrine gland. True.
3. Hydrophilic hormones can activate their receptors inside the cell membrane as they are freely
soluble in blood. False: hydrophilic hormones cannot pass through the cell membrane, so
they activate their receptors outside the cell
4. Prostaglandins promote inflammation, with the aspects being swelling, pain, and fever. True.
Multiple choice
Dwarfism is caused by hyposecretion of what gland?
a. Hypothalamus
b. Pituitary Gland
Ch. 46 The Endocrine System
By: Jose Solorzano, Jose Arambulo, Daniel Guevarra, Eric Galicia, and Jarod
Smith
c.Thyroid gland
d.Testicles