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Lecture

bioa02 chapter 41


Department
Biological Sciences
Course Code
BIOA02H3
Professor
Mary Olaveson

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Chapter 41
41.1 – What are hormones and how do they work?
-the chemical signals are hormones, secreted by cells of the endocrine system into
the extracellular fluid
-the cells that secrete hormones are called endocrine cells, and the cells that
have receptors for those hormones are called target cells
-hormones secreted in the extracellular fluid can diffuse into the blood, so they can
activate target cells far from the site of release
othis is called circulating hormones
-these hormones affect only target cells near their release site, they are called 
paracrine hormones
-when a hormone influences the cell that releases it, it is said to have an 
autocrine function
ocan provide negative feedback to control rates of secretion
-many hormones are secreted by aggregations of endocrine cells forming secretory
organs called endocrine glands
othey do not have ducts
-exocrine glands have ducts that carry their produces to the surface of the skin
osweat gland
-plants do not have nervous systems, but they do have hormones
-the largest group of arthropods are insects and they have rigid exoskeleton
otheir growth is episodic; punctuated with molts
oeach growth stage between two molts is called in instar
-the two hormones working in sequence regulate molting
oprothoracictropic hormone (PTTH) (brain hormone)
oecdysone
-PTTH is transported to and stored in a pair of structures called corpora
cardiaca attached to the brain
oAfter stimulation, the PTTH released from these structures and it diffuses
in the extracellular fluid to an endocrine gland, the prothoracic gland
oPTTH stimulates the prothoracic gland to release the hormone ecdysone
Ecdysone diffuses to target tissues and stimulate molting
-Ecdysone is a lipid-soluble steroid molecule that readily enters its target cells
oIn the target cells, it binds to a receptor that is probably ancestral to the
vertebrate testosterone receptor
oThe hormone-receptor complex acts as a transcription factor and induces
expression of the genes for enzymes involved in digesting the old cuticle
and secreting a new one
oThe control of molting by PTTH and ecdysone is a general arthropod
hormonal control mechanism and is an example of how a hormonal
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system works with the nervous system to integrate diverse information
that help determine the optimal timing for growth and development
oThe nervous system (the brain) then controls the endocrine gland (the
prothoracic gland) producing the hormone (ecdysone) that orchestrates the
physiological processes involved in development and molting
-Because the head of Rhodnius is long, it is possible to remove just the front part
of the head, which contains the brain, while leaving the rear part of the head,
which contains the brain, while leaving the rear part intact
-The substance responsible for preventing maturation is juvenile hormone, which
is released continuously from the same structures that release PTTH in response
to feeding
oAs long as this is present, Rhodnius molts into another juvenile instar
oUsually stop after the fifth instar
-As long as juvenile hormone is present in high concentrations, larvae molt into
larvae
-When the level of juvenile hormone falls, larvae spin cocoons and molt into pupae
oBecause no juvenile hormone is produced in pupae, they molt into adults
-The majority of hormones are peptide or polypeptide
oThese hormones are water-soluble and are thus easily transported in the
blood, but they cannot pass readily through lipid-rich cell membranes
oTherefore, peptide and protein hormones are packaged in vesicles in the
cell that make them and are released by exocytosis
-Steroid hormones such as testosterone and estrogen are derivatives of the steroid
cholesterol
oAre lipid-soluble and easily dissolved in and pass through cell membranes
oThey diffuse out of the cells that make them as they are synthesized
oBecause steroid hormones are not soluble in blood, they much be bound to
carrier proteins in order to be transported to their target cells
-Amine hormones are mostly derivatives of the amino acid tyrosine
oSome amine hormones are water-soluble and others are lipid-soluble
oTheir modes of release differ accordingly
-Lipid-soluble hormones can diffuse through plasma membranes, and therefore
their receptors are inside the cell, in their the cytoplasm or the nucleus
-Water-soluble hormones cannot readily pass through plasma membranes, so their
receptors are on the cell surface
oThese receptors are large glycoprotein complexes with three domains
Binding domain projects outside the plasma membrane
Transmembrane domain that anchors the receptor in the
membrane
Cytoplasmic domain extends into the cytoplasm of the cell
oThe cytoplasmic domain initiates the target cell’s response by activating
protein kinases or protein phosphatases
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They activate or inactivate the cytoplasm, which leads to the cell’s
response, but the signaling cascade initiated by the membrane
receptors can also generate chemical signals that enter the nucleus
and alter gene expression
-Most hormone diffuse through the extracellular fluid and are picked up by the
blood, which distributes them throughout the body
-The same hormone an cause different responses in different types of cells
-Fight-or-flight responses
oSenses detect danger. The brain sends signals to the leg muscles and to the
adrenal glands
oWhich release epinephrine into the circulating blood, triggering a number
of effects
oThe liver breaks down glycogen to supply glucose to the blood
oThe heart beats faster and stronger. Blood pressure rises
oBlood vessels to the but and skin constrict while more blood flows to the
escape muscles
oFat cells release fatty acids to the blood
-Epinephrine (an amine) binds to receptors in the heart and blood vessels,
sustaining the higher heart rate and causing the heart to beat more strongly
oIt causes more of your circulating blood to flow to the muscles by causing
blood vessels in your digestive tract to constrict
oIt decreases blood flow to the skin and to the kidneys and suppresses some
of the functions of the immune system
-Epinephrine also binds to cells in the liver and to receptors on fat cells
oIn the liver, it stimulates the breakdown of glycogen into glucose for a
quick energy supply
oIn fatty tissue, it stimulates the breakdown of fats to yield fatty acids,
another source of energy
41.2 – How do the nervous and endocrine systems interact?
-the pituitary gland sits in a depression at the bottom of the skull just over the
back of the rood of the mouth
oinvolved in the hormonal control of many physiological processes
-hypothalamus is involved in many physiological regulatory systems
-the nervous system is involved in pituitary functions in two ways
otwo hormones produced by nerve cells in the hypothalamus are
transported to the pituitary via long extensions of those nerve cells and
released there
omany of the hormones produced by the pituitary are controlled by other
hypothalamic hormones that reach the pituitary through the blood
-The anterior pituitary originates as an out pocketing of the rood of the embryonic
mouth cavity
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