Download Hormones and the Endocrine System

Hormones and the Endocrine System
CHAPTER 45
You Must Know
•
How hormones bind to target receptors and trigger specific pathways.
•
The secretion, target, and regulation of at least two hormones.
•
An illustration of both positive and negative feedback in the regulation of homeostasis
by hormones.
•
The adult cells of the butterfly start growing in the embryo.
•
They are nourished during the larva stage.
•
Once the caterpillar becomes a stationary pupa, the adult cells take over.
•
What causes this change………HORMONES!
•
ecdysteroid
Intercellular Communication
•
•
Endocrine signaling –Endocrine cells secrete hormones into extracellular fluids and reach target
cells via the bloodstream (hemolymph).
•
Maintains homeostasis, mediates response to environmental stimuli, and regulates growth and
development.
•
Ex. Hormones coordinate the body’s response to stress, dehydration, and low blood glucose levels.
Paracrine Signaling- A hormone diffuses through interstitial fluid and acts on nearby target cells.
•
Many types of cells produce and secrete local regulators, molecules that act over short distances and
reach their target cells solely by diffusion.
•
Target cells lie near the secreting cell.
•
Physiological processes (blood pressure regulation, nervous system function, and reproduction)
•
Autocrine Signaling- A hormone acts on the very cells that produce it.
•
Synaptic Signaling- Neurotransmitters diffuse across synapses and trigger responses in cells of target
tissues (neurons, muscles, or glands).
•
•
Neurons form specialized junctions called synapses with target cells, such as other neurons and muscle cells.
•
At synapses, neurons secrete molecules called neurotransmitters that diffuse a very short distance to bind to
receptors in the target cells.
•
Neurotransmitters are central to sensation, memory, cognition, and movement.
Neuroendocrine Signaling- Neurohormones diffuse into the bloodstream and trigger responses in
target cells anywhere in the body.
•
Specialized neurons called neurosecretory cells secrete molecules that diffuse from nerve cell endings into
the bloodstream.
•
These molecules, which travel through the bloodstream to target cells, are a class of hormones called
Neurohormones.
•
Ex. Antidiuretic hormone, also known as vasopressin, a hormone essential to kidney function and water
balance.
Signaling by Pheromones
•
Not all secrete signaling molecules act within the body.
•
Members of the same animal species sometimes communication via pheromones,
chemicals that are released into the external environment.
•
•
Ex. Ants use pheromones for guidance when they discover a new food source.
Pheromones serve a wide range of functions that include defining territories, warning
of predators, and attracting potential mates.
•
Ex. The giant silk moth releases a sex hormone into the air by a female which enables her to
attract a male up to 4.5 km away.
Endocrine Tissues and Organs
•
Some endocrine system cells are found in organs that are part of other organ systems.
•
The human digestive system, the stomach contains isolated endocrine cells in addition
to the predominant cell and tissue types.
•
Endocrine glands-endocrine cells are grouped into ductless organs, such as the thyroid
and parathyroid glands of the neck.
•
*Note: that endocrine glands secrete hormones directly into the surrounding fluid.
•
Endocrine glands thus contrast with exocrine glands, such as salivary glands, which have
ducts that carry secreted substances onto body surfaces or into body cavities.
Chemical Classes of Hormones
•
Hormone molecules vary substantially in size and chemical properties.
•
Some of these are apparent in: polypeptides (protein and peptides), steroids, and
amines.
•
Polypeptide hormones insulin is made up of two polypeptide chains.
•
Steroid hormones (cortisol and ecdysteroid) are lipids that contain four fused carbon rings.
•
Amine hormones (epinephrine and thyroxine) are each synthesized from a single amino acid,
either tyrosine or tryptophan.
•
Hormones vary in their solubility in aqueous and lipid-rich environments.
•
Polypeptides and most amine hormones are water-soluble.
•
Being insoluble in lipids, these hormones cannot pass through the plasma membrane of
cells.
•
So they bind to cell-surface receptors that relay information to the nucleus through
intracellular pathways.
•
Steroid hormones, such as thyroxine, are lipid-soluble and can pass through cell
membranes readily.
•
Recpetors for lipid-soluble hormones typically reside in the cytoplasm or nucleus.
Cellular Response Pathways
•
Water-soluble hormones are secreted by exocytosis, travel freely in
the bloodstream, and bind to cell-surface signal receptors.
•
Binding of such hormones to receptors induces change in cytoplasmic
molecules and sometimes alter gene transcription.
•
Lipid-soluble hormones diffuse out across the membranes of
endocrine cells.
•
Outside the cell, they bind to transport proteins that keep them
soluble in the aqueous environment of the bloodstream.
•
Upon leaving the bloodstream, they diffuse into target cells, bind to
intracellular signal receptors, and trigger changes in gene
transcription.
Epinephrine
•
Your adrenal gland secretes epinephrine (a hormone also
called adrenaline).
•
When epinephrine reaches the liver, it binds to a G proteincoupled receptor in the plasma membrane of target cells.
•
The binding of hormone to receptor triggers a cascade of
events involving synthesis of cyclic AMP (cAMP) as a shortlived second messenger.
•
Activation of protein kinase A by cAMP leads to activation of
an enzyme necessary for glycogen synthesis.
•
The net result is that the liver releases glucose into the
bloodstream, providing the fuel you need.
Thyroxine (T4)
•
Hormones that are not steroid hormones have receptors that are typically located in the nucleus.
•
These receptors bind hormone molecules that diffuse from the bloodstream across both the plasma
membrane and nuclear envelope.
•
Once bound by a hormone, the receptor binds to specific sites in the cell’s DNA and stimulates the
transcription of specific genes.
Simple Hormone Pathway
47.3 Cytoplasmic determinants and inductive signals
contribute to cell fate specification
•
You Must Know:
•
Programmed cell death (apoptosis) plays a role in normal development and differentiation
(for example, morphogenesis)
•
Cell differentiation results from the expression of genes for tissue-specific proteins and the
induction of transcription factors.
•
All multicellular organisms arise from a single cell, the fertilized egg, or zygote.
•
Somehow, this single cell gives rise to the ordered arrangement of tissues
made up of as many as 200 different cell types, all integrated to function as a
single organism.
•
Understanding embryonic development has long been a passionate interest, to
accomplish this we study embryonic development of other species.
•
We can closely observe cell differentiation, each specialized to perform a
specific function in the whole organism.
The Sea Urchin
•
Fertilization  Zygote  Series of developmental stages.
•
This process involves cell division, cell migration, and
morphogenesis.
•
The overall shape of the skeleton is made up of elements
called spicules, formed by a group of cells called the primary
mesenchyme cells.
•
The primary mesenchyme cells (PMCs) arise from a group of
four precursor cells called micromeres, formed during the
4th cleavage.
•
The process by which the four micromeres turn into the
spicule-forming PMCs is an example of cell differentiation.
•
The patterns of development are due to a combination of different cytoplasmic
determinants and inductive cell signals.
•
Cytoplasmic determinants are chemical signals such as mRNAs and transcription factios
that may be parceled out unevenly in early cleavages.
•
Induction is an interaction among cells that influences their fate, usually by causing
changes in gene expression.
Fate mapping of a frog
•
The dorsal lip of the blastopore is an “organizer” that induces a series of events that
result in formation of the notochord and neural tube.
•
Totipotent cells are capable of developing into all the different cell types of that
species.
•
The cells of mammalian embryos may remain totipotent until the 16-cell stage but have
a limited developmental potential from that point onward.
•
Cells at this early stage that are totipotent are referred to as stem cells.
•
Development is a sequence of events marked by cycles of
signaling and differentiation.
•
Cells in a developing embryo receive and respond to different
signaling molecules that vary with their location within the
embryo, and their developmental potential becomes more
limited as embryonic development proceeds.