KEY CONCEPTS → In animals, hormones are secreted into the
▪ Glands extracellular fluid, circulate in the
▪ Describe the two types of glands found in vertebrate bloodstream, and communicate regulatory
systems messages throughout the body.
▪ Hormones and their feedback systems → Each hormone binds to specific receptors in
▪ Identify the four main chemical groups to which the body.
hormones are assigned → Although a given hormone can reach all
▪ Describe the regulation of endocrine glands by cells of the body, only some cells have
negative feedback mechanisms receptors for that hormone.
▪ Mechanism of hormonal action → A hormone elicits a response—such as a
▪ Compare the mechanisms of action of steroid and change in metabolism—in specific target
protein-type hormones; include the role of second cells, those that have the matching receptor.
messengers, eg. Cyclic AMP. → Cells lacking a receptor for that hormone
▪ Organisation of the endocrine system are unaffected.
▪ Describe the mechanisms by which the → Chemical signaling by hormones is the
hypothalamus and pituitary gland integrate many function of the endocrine system, one of
regulatory functions; describe the actions of the the two basic systems for communication
hypothalamic and pituitary hormones. and regulation in the animal body.
▪ Reproductive hormones → The other major communication and control
▪ Hormonal control of male reproductive system system is the nervous system, a network of
▪ Describe the endocrine regulation of reproduction in specialized cells—neurons—that transmit
the human male; the role of the principal male signals along dedicated pathways.
reproductive hormones. → These signals in turn regulate neurons,
▪ Hormonal control of female reproductive system muscle cells, and endocrine cells.
▪ Describe the endocrine regulation of reproduction in → Because signaling by neurons can regulate
the human female, and identify the important events the release of hormones, the nervous and
of the menstrual cycle, such as ovulation and endocrine systems often overlap in function.
menstruation
TJW NOTES
, Hormones and other signaling molecules bind to target receptors, triggering specific response
pathways
Glands Intercellular Communication
→ Exocrine glands - secrete their products outside → Communication between animal cells via
the body, have ducts secreted signals is often classified by two
criteria: the type of secreting cell and the route
taken by the signal in reaching its target.
→ Endocrine Signaling
⤷ Hormones secreted into extracellular fluid by
endocrine cells reach target cells via the
bloodstream.
⤷ Maintain homeostasis.
→ Endocrine glands - secrete their products into the ⤷ Hormones regulate properties that include
blood, do not have ducts blood pressure and volume, energy metabolism
and allocation, and solute concentrations in
body fluids.
⤷ Mediates responses to environmental stimuli,
regulates growth and development, and
triggers physical and behavioral changes
underlying sexual maturity and reproduction
→ Paracrine and Autocrine Signaling
→ Synaptic and Neuroendocrine Signaling ⤷ Many types of cells produce and secrete local
⤷ Secreted molecules are essential for the function regulators ~ molecules that act over short
of the nervous system. distances, reach their target cells solely by
⤷ Neurons communicate with target cells, such as diffusion, and act on their target cells
other neurons and muscle cells, via specialized ⤷ Local regulators play roles in many
junctions called synapses physiological processes, including blood
⤷ Neurons secrete neurotransmitters that diffuse a pressure regulation, nervous system function,
very short distance and bind to receptors on the and reproduction.
target cells ⤷ Depending on the target cell, signaling by local
⤷ Such synaptic signaling is central to sensation, regulators can be either paracrine or autocrine.
memory, cognition, and movement ⤷ In paracrine signaling target cells lie near the
⤷ In neuroendocrine signaling, neurons called secreting cell
neurosecretory cells secrete neurohormones, ⤷ In autocrine signaling the secreting cells
which diffuse from nerve cell endings into the themselves are the target cells
bloodstream ⤷ One group of local regulators with diverse and
⤷ Many neurohormones regulate endocrine widespread functions are the prostaglandins
signaling
TJW NOTES
, → Signaling by Pheromones • Prostaglandins
⤷ Not all secreted signaling molecules act within → In the immune system, for example,
the body. prostaglandins promote inflammation and the
⤷ Members of a particular animal species sensation of pain in response to injury.
sometimes communicate with each other via → Drugs that block prostaglandin synthesis, such
pheromones ~ chemicals that are released into as aspirin and ibuprofen, prevent these
the external environment. activities, producing both anti-inflammatory and
⤷ Pheromones serve a wide range of functions pain-relieving effects.
that include defining territories, warning of → Prostaglandins also help regulate the
predators, and attracting potential mates. aggregation of blood components called
platelets, one step in the formation of blood
Hormone properties clots.
1. Hormones are produced and secreted by
endocrine cells Chemical Classes of Hormones
2. They circulate in the blood and reach all tissues – Amines (derived from amino acids, water soluble)
3. They react with specific receptor molecules – Polypeptides (proteins and peptides)
present in certain target cells – Steroid hormones (cholesterol derived, lipid
4. A single hormone may have multiple effects soluble)
– Prostaglandins (lipid derived, local messengers)
Classes of Local Regulators
→ Prostaglandins are modified fatty acids.
→ Many other local regulators are polypeptides, including
cytokines, which enable immune cell communication
→ Growth factors, which promote cell growth, division,
and development.
→ Some local regulators are gases.
⤷ Nitric oxide (NO), a gas, functions in the body as both
a local regulator and a neurotransmitter.
⤷ When the level of oxygen in the blood falls, epithelial
cells in blood vessel walls synthesize and release NO.
⤷ After diffusing into the surrounding smooth muscle
cells, NO activates an enzyme that relaxes the cells.
The result is vasodilation which increases blood flow
to tissues.
⤷ NO’s ability to promote vasodilation enables sexual
function by increasing blood flow into the penis,
producing an erection.
Classes of Hormones
→ Hormones fall into three major chemical classes:
• Polypeptides
• Steroids
• amines
→ The hormone insulin is a polypeptide that contains two chains in its active form.
→ Steroid hormones, such as cortisol, are lipids that contain four fused carbon rings; all are derived from the
steroid cholesterol.
→ Epinephrine & thyroxine are amine hormones, each synthesized from a single amino acid, tyrosine or
tryptophan.
→ Hormones vary in their solubility in aqueous and lipid-rich environments.
→ Polypeptides and most amine hormones are water-soluble. Steroid hormones and other largely nonpolar
(hydrophobic) hormones, such as thyroxine, are lipid-soluble. TJW NOTES
