AP Biology Notes Outline
Chapter 45: Hormones and the Endocrine System
CONCEPT 45.1 – The endocrine system and the nervous system act individually and together in regulating an
animal’s physiology.
Animals have two major regulatory systems that release chemicals; the endocrine system and the nervous system. The endocrine
system secretes hormones, while the nervous system secretes neurotransmitters.
• An animal hormone is a chemical signal that is secreted into the circulatory system and communicates regulatory messages
within the body. Hormones may reach all parts of the body, but only certain types of cells, target cells, are equipped to
respond.
• Specialized nerve cells known as neurosecretory cells release neurohormones into the blood. Both endocrine hormones and
neurohormones function as long-distance regulators of many physiological processes
A common feature of control pathways is a feedback loop connecting the response to the initial stimulus. Hormones operate by
negative feedback systems – an excess of the hormone will signal the endocrine gland to temporarily shut down production.
Signaling by any hormonal molecules involves three key events:
• Reception (the target cell’s detection of a signal coming from outside the cell – signal is detected when it binds to a cellular
protein on the cell’s surface).
• Signal transduction (binding changes receptor protein in some way – initiating transduction which converts the signal to a
form that can bring about a cellular response).
• Response (transduced signal triggers a specific cellular response).
FIGURE 45.3 – Mechanisms of Chemical Signaling
FIGURE 45.5
FIGURE 45.6
FIGURE 45.7
Hormonal cell signaling may involve water-soluble hormones (proteins) or lipid-soluble hormones (steroid & thyroid hormones).
Review Figure 45.3 in your textbook. Here are the primary differences between the two:
• Steroid hormones alter gene expression IN the target cell whereas protein hormones activate biochemical pathways or
enzyme systems.
• Steroid hormones are fat-soluble (hydrophobic) and readily cross the cell membrane whereas protein hormones are watersoluble (hydrophilic) and do not readily cross the cell membrane.
• Steroid hormones act as ligand that binds to cytosol receptors INSIDE the cell – this changes the shape of the receptor – the
complex (hormone-receptor) then enters the nucleus and activates the transcription factor. Protein hormones act as ligand
for membrane-bound receptors ON the cell membrane – binding to transmembrane proteins – the hormone is the ligand and
first messanger here.
• The actions of steroid hormones are slow but sustained, whereas the actions of protein hormones are brief but dramatic.
Paracrine Signaling by Local Regulators: http://www.sinauer.com/neuroscience4e/animations7.1.html
In a process called paracrine signaling, various types of chemical signals elicit responses in nearby target cells. Paracrine signaling
involves local regulators – they convey messages between neighboring cells (as opposed to long-distance endocrine signaling by
hormones). These can elicit cell responses more quickly than hormones. Local regulators have various functions and include
– Cytokines and growth factors (immune responses and cell differentiation)
– Nitric oxide (relaxes smooth muscle cells which dilates vessels and improves blood flow)
– Prostaglandins (several regulatory functions – including smooth muscle contraction in female uterine helping sperm
to reach egg). They also act as an alarm that something is threatening the body.
AP Biology Notes Outline
Chapter 45: Hormones and the Endocrine System
NOTE: You absolutely must internalize Table 45.1 – know the glands, hormones produced, action in the body, and regulation
of all major hormones produced by the human endocrine system.
FIGURE 45.10 – Human Endocrine Glands: http://bcs.whfreeman.com/thelifewire/content/chp42/4202002.html
The hypothalamus and the pituitary gland control much of the endocrine system.
The hypothalamus, a region of the lower brain contains different sets of neurosecretory cells, plays an important role in integrating the
endocrine and nervous systems. The hypothalamus receives info from nerves throughout the body and from other parts of the brain,
and it initiates endocrine signals appropriate to environmental conditions.
The pituitary is called the master gland because it releases many hormones that reach other glands and stimulate them to secrete their
own hormones. The pituitary has two parts: the anterior pituitary and the posterior pituitary. Each part secretes its own set of
hormones. The pituitary works in tandem with the hypothalamus.
FIGURE 45.14 – The Posterior Pituitary
The posterior pituitary (neurohypophysis) stores and secretes two hormones that are made by certain neurosecretory cells located in
the hypothalamus.
 Posterior Pituitary Hormones: The two hormones released from the posterior pituitary act directly on nonendocrine tissues
o Oxytocin - induces uterine contractions and milk ejection
o Antidiuretic hormone (ADH) - enhances water reabsorption in the kidneys
These hormones are actually made in the hypothalamus but are STORED in the posterior pituitary.
FIGURE 45.14 – The Anterior Pituitary
The anterior pituitary (adrenohypophysis) consists of endocrine cells that synthesize and secrete different hormones.
 Anterior Pituitary Hormones: The anterior pituitary is a true-endocrine gland. It produces both tropic and nontropic
hormones. The tropic hormones of the hypothalamus control release of hormones from the anterior pituitary. These
hormones regulate the function of the endocrine organs. Each tropic hormone acts on its target endocrine tissue to stimulate
release of hormone(s) with direct metabolic or developmental effects. The four strictly tropic hormones are
o Follicle-stimulating hormone (FSH)
o Luteinizing hormone (LH)
o Thyroid-stimulating hormone (TSH)
o Adrenocorticotropic hormone (ACTH)
 The nontropic hormones produced by the anterior pituitary include
– Prolactin
– Melanocyte-stimulating hormone (MSH)
– -endorphin
The hypothalamus regulates the anterior pituitary by secreting neurohormones that can stimulate or inhibit the actions of the anterior
pituitary.
Growth Hormone
Growth hormone (GH) promotes growth directly and has diverse metabolic effects and stimulates the production of growth factors by
other tissues
Nonpituitary Hormones
Nonpituitary hormones help regulate metabolism, homeostasis, development, and behavior. Many nonpituitary hormones regulate
various functions in the body and include:
Thyroid Hormones
Adrenal Hormones
Sex Hormones
Parathyroid Hormone & Calcitonin
Glucoroticoids (Cortisol)
Insulin and Glucagon
Mineralocorticoids (Aldosterone)
AP Biology Notes Outline
Chapter 45: Hormones and the Endocrine System
http://www.biologyinmotion.com/thyroid/index.html
The thyroid gland consists of two lobes located on the ventral surface of the trachea. It produces two iodine-containing hormones,
triiodothyronine (T3) and thyroxine (T4). The hypothalamus and anterior pituitary control the secretion of thyroid hormones through
two negative feedback loops.
• The hypothalamus secretes TSH-releasing hormone (TRH), which stimulates the anterior pituitary to secrete thyroidstimulating hormone (TSH).
• TSH then stimulates the thyroid gland to synthesize and release the thyroid hormones T3 and T4.
• These hormones exert negative feedback on the hypothalamus and anterior pituitary by inhibiting the release of TRH and
TSH.
• The thyroid hormones play crucial roles in stimulating metabolism and influencing development and maturation
– Hyperthyroidism, excessive secretion of thyroid hormones can cause Graves’ disease in humans.
http://bcs.whfreeman.com/thelifewire/content/chp42/4202003.html
Two antagonistic hormones, parathyroid hormone (PTH) and calcitonin play the major role in calcium (Ca2+) homeostasis in
mammals
• Calcitonin, secreted by the thyroid gland, stimulates Ca2+ deposition in the bones and secretion by the kidneys, thus
lowering blood Ca2+ levels.
• Parathyroid Hormone (PTH), secreted by the parathyroid glands, has the opposite effects on the bones and kidneys, and
therefore raises Ca2+ levels. It also has an indirect effect, stimulating the kidneys to activate vitamin D, which promotes
intestinal uptake of Ca2+ from food.
http://bcs.whfreeman.com/thelifewire/content/chp50/5002002.html
Two types of cells in the pancreas secrete insulin and glucagon, antagonistic hormones that help maintain glucose homeostasis.
• Glucagon is produced by alpha cells and insulin is produced by beta cells
Insulin reduces blood glucose levels by
• Promoting the cellular uptake of glucose
• Slowing glycogen breakdown in the liver
• Promoting fat storage
Glucagon increases blood glucose levels by
• Stimulating the conversion of glycogen to glucose in the liver
• Stimulating the breakdown of fat and protein into glucose
Diabetes mellitus, perhaps the best-known endocrine disorder, is caused by a deficiency of insulin or a decreased response to insulin in
target tissues and is marked by elevated blood glucose levels:
• Type I diabetes mellitus (insulin-dependent diabetes)
– Is an autoimmune disorder in which the immune system destroys the beta cells of the pancreas
• Type II diabetes mellitus (non-insulin-dependent diabetes)
– Is characterized either by a deficiency of insulin or, more commonly, by reduced responsiveness of target cells due
to some change in insulin receptors
AP Biology Notes Outline
Chapter 45: Hormones and the Endocrine System
http://bcs.whfreeman.com/thelifewire/content/chp42/4202002.html
The adrenal glands are adjacent to the kidneys and are actually made up of two glands: the adrenal medulla and the adrenal cortex.
The adrenal medulla secretes epinephrine and norepinephrine, hormones which are members of a class of compounds called
catecholamines. These hormones are secreted in response to stress-activated impulses from the nervous system and mediate various
fight-or-flight responses. Hormones from the adrenal cortex also function in the body’s response to stress and fall into three classes of
steroid hormones:
• Glucocorticoids, such as cortisol
– Influence glucose metabolism and the immune system
• Mineralocorticoids, such as aldosterone
– Affect salt and water balance
• Sex hormones
– Are produced in small amounts
Stressful stimuli cause the hypothalamus to activate the adrenal medulla via nerve impulses and the adrenal cortex via hormonal
signals. The adrenal medulla mediates short-term responses to stress by secreting the catecholamine hormones epinephrine and
norepinephrine. The adrenal cortex controls more prolonged responses by secreting steroid hormones.
The gonads (testes and ovaries) produce most of the body’s sex hormones: androgens, estrogens, and progestins
• The testes primarily synthesize androgens, the main one being testosterone, which stimulate the development and
maintenance of the male reproductive system. Testosterone causes an increase in muscle and bone mass and is often taken as
a supplement to cause muscle growth, which carries many health risks.
• Estrogens, the most important of which is estradiol, are responsible for the maintenance of the female reproductive system
and the development of female secondary sex characteristics. In mammals, progestins, which include progesterone, are
primarily involved in preparing and maintaining the uterus.
The pineal gland, located within the brain secretes melatonin. Release of melatonin is controlled by light/dark cycles. The primary
functions of melatonin appear to be related to biological rhythms associated with reproduction.
http://bcs.whfreeman.com/thelifewire/content/chp42/4202001.html
In insects, molting and development are controlled by three main hormones:
1. Brain hormone is produced by neurosecretory cells and stimulates the release of ecdysone from the prothoracic glands
2. Ecdysone promotes molting and the development of adult characteristics
3. Juvenile hormone promotes the retention of larval characteristics
AP Biology Notes Outline
Chapter 45: Hormones and the Endocrine System
EXAMPLE #1
Discuss the sources and actions of each of the following pairs of hormones in humans and describe the feedback mechanisms that control their
release.
a. Insulin...glucagon
b. Parthyroid hormone...calcitonin
c. Thyrotropin (TSH)...thyroxine (T4)
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------EXAMPLE #2
Describe the anatomical and functional similarities and differences within each of the following pairs of structures.
a. Artery..vein
b. Small intestine..colon
c. Skeletal muscle..cardiac muscle
d. Anterior pituitary..posterior pituitary
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------EXAMPLE #3
Communication occurs among the cells in a multicellular organism. Choose THREE of the following examples of cell-to-cell communication,
and for each example, describe the communication that occurs and the types of responses that result from this communication.
a. Communication between two plant cells
b. Communication between two immune-system cells
c. Communication either between a neuron and another neuron, or between a neuron and a muscle cell
d. Communication between a specific endocrine-gland cell and its target cell
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------EXAMPLE #4
Feedback mechanisms are used by organisms to maintain the steady-state physiological condition known as homeostasis. Choose three of the
following and for each, explain how feedback mechanisms maintain homeostasis.
a. Blood glucose concentration.
b. Calcium ion concentration in blood.
c. Body temperatures in mammals.
d. Osmolarity of the blood.
e. Pulse rate in mammals.
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------EXAMPLE #5
Hormones play important roles in regulating the lives of many living organisms.
a.
b.
c.
For TWO of the following physiological responses, explain how hormones cause the response in plants.

increase in height

adjustment to change in light

adjustment to lack of water
For TWO of the following physiological responses, explain how hormones cause the response in animals.

increase in height

adjustment to change in light

adjustment to lack of water
Describe TWO different mechanisms by which hormones cause their effects at the cellular level.
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------EXAMPLE #6
Homeostatic maintenance of optimal blood glucose levels has been intensively studied in vertebrate organisms.
a. Pancreatic hormones regulate blood glucose levels. Identify TWO pancreatic hormones and describe the effect of each hormone on blood
glucose levels.
b. For ONE of the hormones you identified in (a), identify ONE target cell and discuss the mechanism by which the hormone can alter
activity in that target cell. Include in your discussion a description of reception, cellular transduction, and response.
c. Compare the cell-signaling mechanisms of steroid hormones and protein hormones.