Title: Chemical Signals in Animals
1Chemical Signals in Animals
2Chemical Signals in Animals
- Hormone - chemical signal that circulates
through the blood or other bodily fluids and
affects distant target cells. - The endocrine system is responsible for the
production and secretion of hormones. - There are six major categories of chemical
signals in animals - Six chemical messenger classes do not coincide
with six structurally distinct classes of
molecules
3Hormone Structure and Function
4Autocrine Signals
- Autocrine signals act on the same cell that
secretes them. - An example is cytokines most cytokines amplify
the response of a cell to a stimulus - Like in bone marrow cells for defense
- IL-1 is one of the most important immune
responses, enhances the activation of T-cells in
response to antigen
5Paracrine signals
- Paracrine signals diffuse locally and act on
neighboring cells - May be due to degradation
- Growth factors that are important in coordination
of development - Responses to allergens
- Has been linked to tumor growth and cancer
6Endocrine Signals
- Endocrine signals are produced by cells that may
be organized into discrete organs called glands
or may be interspersed among the cells of other
organs - May be carried by blood or interstitial fluid
- Act on target cells throughout the body
- Hormones such as testosterone and estrogen
7Neural Signals
- Neural signals are the chemical messengers called
neurotransmitters - Cause an action potential to be created in a
neuron and create a neural signal - Held in vacuoles within the neuron
- Acetylcholine stimulates muscle neurons
- Norepinephrine stimulates wakefulness
8Neuroendocrine Signals
- Neuroendocrine signals are released from neurons
but act on distant cells instead of acting at the
adjacent synapse - Signals from stomach stimulate pituitary and
brain cells to tell the brain and pituitary gland
that it is full or it is empty
9Chemical Characteristicsof Hormones
- The three types of chemical messengers
polypeptides, amino acid derivatives, and
steroids - All are similar in that they are
- Organic compounds
- Synthesized and secreted from the cells
- Act on target cells remote from their point of
origin
10Chemical Characteristicsof Hormones
- Similarities
- Present in extremely small concentrations yet
have large effects - Key difference in these hormone types is that
steroids are lipid soluble but polypeptides and
amino acid derivatives are not. - Steroids cross cell membranes much more readily
than do other types of hormones.
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12The Human Endocrine Systeman Overview
- Organs that secrete hormones into the
bloodstream are called endocrine glands - The major human endocrine glands are
13Hypothalamus
- The hypothalamus, a region of the lower brain
- Contains different sets of neurosecretory cells
- Receive nerve signals from throughout the body
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15Pituitary Gland
- The pituitary gland, which sits just below the
hypothalamus and has distinct anterior and
posterior regions
16Posterior Pituitary Hormones
- The two hormones released from the posterior
pituitary - Act directly on nonendocrine tissues
- Oxytocin
- Induces uterine contractions and milk ejection
- Antidiuretic hormone (ADH)
- Enhances water reabsorption in the kidneys
17Anterior Pituitary Glands
- The anterior pituitary
- Produces both tropic and nontropic hormones
- The four strictly tropic hormones are
- Follicle-stimulating hormone (FSH)
- Luteinizing hormone (LH)
- Thyroid-stimulating hormone (TSH)
- Adrenocorticotropic hormone (ACTH)
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19Thyroid Gland
- The thyroid gland
- Situated in the Neck
- Consists of two lobes located on the ventral
surface of the trachea - Produces two iodine-containing hormones,
triiodothyronine (T3) and thyroxine (T4)
20Thyroid Hormones
- The thyroid hormones
- Play crucial roles in stimulating metabolism and
influencing development and maturation - Also important in maintaining homeostatic
functions - Hyperthyroidism, excessive secretion of thyroid
hormones - Can cause Graves disease in humans
- Hypothyroidism can cause weight gain
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22Thyroid and Parathyroid Hormones
- The four parathyroid glands are embedded in the
thyroid gland - Act in opposition to thyroid
- Calcitonin, secreted by the thyroid gland
- Stimulates Ca2 deposition in the bones and
secretion by the kidneys, thus lowering blood
Ca2 levels - PTH, secreted by the parathyroid glands
- Has the opposite effects on the bones and
kidneys, and therefore raises Ca2 levels - Also has an indirect effect, stimulating the
kidneys to activate vitamin D, which promotes
intestinal uptake of Ca2 from food
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24Kidneys and Adrenal Glands
- The two kidneys, which lie in the posterior part
of the abdominal cavity - The two adrenal glands, which sit atop the
kidneys and have an outer cortex and a central
medulla - The adrenal medulla secretes epinephrine and
norepinephrine - In response to stress-activated impulses from the
nervous system
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26Pancreas
- Located in the anterior part of the abdominal
cavity - Two types of cells in the pancreas
- Secrete insulin and glucagon, antagonistic
hormones that help maintain glucose homeostasis
and are found in clusters in the islets of
Langerhans
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28Gonadal Sex Hormones
- Suspended below the pelvic cavity, respectively
- Produce most of the bodys sex hormones
androgens, estrogens, and progestins
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30What Do Hormones Do?
- Hormones coordinate the activities of diverse
groups of target cells - Change according to environment or signals
- The stimuli to which hormones respond can be
simple or complex - Coordinate responses to environmental change
- Direct developmental processes
31Digestive Hormones
- Digestive hormones function in simple
stimulus-and-response circuits - When acidic food passes from the stomach to the
upper part of the small intestine, the food
triggers intestinal cells to release secretin and
cholecystokinin into the bloodstream - Secretin induces the pancreas to secrete a
solution that neutralizes acid - Cholecystokinin causes the pancreas to secrete
digestive enzymes into the small intestine and
the gallbladder to eject bile salts into the
intestine to emulsify fats
32Responses to Stress
- When a person is in danger, hormones regulate
both the short-term and long-term responses - The short-term reactionthe fight-or-flight
responseoccurs through the activation of the
sympathetic nervous system - Long-term stress involves glucocorticoids
produced in the adrenal cortex. - Ensures the continued availability of fuel
molecules to support important body functions
33Stress and the Adrenal Gland
34How Do Hormones Direct Developmental Processes?
- Growth hormones and sex hormones promote cell
division, increase overall body size, and promote
sexual differentiation as an individual matures. - Certain hormones direct the development of
particular cells and tissues at critical
junctures in an individuals life - The major hormonal effects on development are
35Primary Sex Determination
- Events early in development that dictate whether
the sex organs become male (testes) or female
(ovaries) - Once they develop, they begin producing
male-specific hormones (testosterone) or
female-specific hormones (estradiol, a member of
the estrogen family of hormones).
36Puberty
- At puberty, surges of sex hormones lead to the
physical and emotional changes associated with
adolescence - These developmental changes create the adult
phenotype and the ability to produce offspring.
37Full Growth and Development
- In humans and other mammals, the attainment of
full adult stature is mediated by growth factors
that are regulated by growth hormone produced in
the pituitary gland.
38Reproduction
- Most long-lived animals reproduce seasonally
- In many species, environmental cues trigger the
release of sex hormones - Although humans do not breed seasonally, sex
hormones regulate sperm production and the
menstrual cycle
39Hormones and Homeostasis
- Hormones that act as messengers in homeostatic
systems include antidiuretic hormone (ADH),
aldosterone, and erythropoietin (EPO). - Calcitonin and parathyroid hormone work together
to keep Ca2 levels in the blood close to a set
point
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41How are Hormones Regulated?
- In many cases, hormone production is directly or
indirectly controlled by the nervous system. - Adrenocorticotropic hormone (ACTH) is a
regulatory hormone that controls release of
glucocorticoids from the adrenal cortex - These hormones act as regulators and all are
involved in negative feedback, or feedback
inhibition
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4347.4 How Do HormonesAct on Target Cells?
- Differences in lipid solubility influence where a
target cell receives the chemical message. - Steroids often act inside the cell, whereas most
amino acid derivatives and all polypeptides act
at the cell surface. - Steroid hormone-receptor complexes bind to
specific sites in DNA called hormone-response
elements
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45Hormones That Bind to Cell-Surface Receptors
- Epinephrine and the peptide hormones are not
lipid soluble and cannot enter the target cell - They bind to receptors on the cell surface
- Activate the receptor on the cell surface by
signal transduction - Epinephrine produces two distinct patterns of
responses because there are two types of
receptor, alpha and beta
46Identifying theEpinephrine Receptor
- Epinephrine and its agonists (molecules that
bind to the same receptors as the hormone itself)
produce two distinct patterns of responses
because there are two types of receptor, alpha
and beta. In turn, there are two types of alpha
and two types of beta receptor.
47Signal Transduction and the Role of Second
Messengers
- Epinephrine activates phosphorylase, the enzyme
that catalyzes the formation of glucose from
glycogen (Figure 47.15).
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49Epinephrine Signal Transduction
- Epinephrine triggers a signal transduction
cascade that includes cyclic adenosine
monophosphate (cAMP) as a second messenger to
amplify the signal