Campbell Biology Chapter 45 Review: Hormones and the Endocrine System

45.1 Chemical signals, receptors and responses

pp. 975–980

On the AP exam? Yes

Topics 4.1–4.3 test how far a signal travels, where its receptor sits and why one signal can cause different responses, and Topic 6.5 covers hormone-receptor complexes switching genes on. Words like paracrine and autocrine, and the insect molting hormones, are background.

In the course: Topic 4.1 Cell Communication, Topic 4.2 Introduction to Signal Transduction, Topic 4.3 Signal Transduction Pathways, Topic 6.5 Regulation of Gene Expression (notes, videos and more questions)

Key points

Animal cells talk by releasing chemicals, but a chemical only affects cells that make a matching receptor. Every other cell ignores it, even when the chemical washes right past.
Signals are sorted by who releases them and how far they go. Hormones ride the blood (or an insect's hemolymph) to targets anywhere in the body. Local regulators drift only to neighboring cells (paracrine) or act back on the cell that released them (autocrine).
Nerve cells signal two ways: neurotransmitters cross a tiny gap to the next cell, while neurosecretory cells release neurohormones into the blood. Pheromones leave the body entirely and carry messages to other members of the same species.
Hormones come in three chemical families: polypeptides, steroids (built from cholesterol) and amines (built from a single amino acid). Polypeptides and most amines dissolve in water, can't cross the membrane and bind receptors on the cell surface, which start a signal transduction pathway inside.
Steroids and thyroid hormones dissolve in lipids, so they get across the membrane (thyroid hormone with help from transport proteins) and bind receptors in the cytoplasm or nucleus. The hormone-receptor pair then acts as a transcription factor, turning particular genes up or down.
One hormone can cause different responses in different tissues, because the cells may carry different receptor types or different relay and effector proteins behind the same receptor.
Local regulators include growth factors (proteins that tell cells to divide or specialize), nitric oxide (a short-lived gas that relaxes smooth muscle around blood vessels) and prostaglandins (modified fatty acids involved in inflammation, fever and pain, whose production aspirin and ibuprofen block).

Key terms (14)

hormone: A signaling chemical that endocrine cells release into the blood (or hemolymph), which carries it to target cells that may be far away.
target cell: Any cell that has the right receptor for a particular signal. Only target cells respond; all others ignore it.
endocrine system: The body's set of hormone-making cells and glands. With the nervous system, it's one of the two big ways the body coordinates itself.
local regulator: A signal that travels only a short way, by diffusing through the fluid between cells, and acts within seconds or less.
paracrine signaling: Signaling in which a cell's released molecules act on nearby neighbor cells.
autocrine signaling: Signaling in which a cell responds to a molecule it released itself.
neurohormone: A hormone released into the blood by a specialized nerve cell (a neurosecretory cell) rather than by an ordinary gland cell.
pheromone: A chemical one animal releases into its surroundings that changes the behavior or body of another member of its species, for example to mark a trail or attract a mate.
endocrine gland: A ductless organ that releases hormones straight into the fluid around its cells, from which they enter the blood. The thyroid is one.
exocrine gland: A gland that sends its product through a duct to a body surface or cavity, the way sweat and salivary glands do.
steroid hormone: A nonpolar hormone made from cholesterol, such as cortisol or testosterone. It crosses membranes and binds a receptor inside the cell.
intracellular receptor: A receptor protein in the cytoplasm or nucleus. It binds signals that can cross the membrane and often controls which genes are transcribed.
prostaglandin: A local regulator made from a fatty acid. Prostaglandins promote inflammation, fever and pain, among many other jobs.
juvenile hormone: An insect hormone that keeps a larva in its young form. While its level is high, each molt produces another larva instead of a pupa.

Check yourself: 45.1 Chemical signals, receptors and responses

4 questions on 45.1 Chemical signals, receptors and responses. Pick an answer to see if you got it, and why.

Question 1 of 4

Once activated, a certain type of T cell releases the protein interleukin-2 (IL-2) and also puts IL-2 receptors on its own surface. In this case, IL-2 binding to those receptors makes the same T cell divide. What kind of signaling is this?

Question 2 of 4

A biologist isolates a new hormone from a shark and finds it is a small, nonpolar molecule made from cholesterol. Where is its receptor most likely found, and what response is most likely?

Question 3 of 4

Researchers attach a peptide hormone to plastic beads that are far too large to enter cells. Target cells exposed to the bead-bound hormone respond just as strongly as cells exposed to the free hormone. Which conclusion is best supported?

Question 4 of 4

Hormone R binds the same receptor protein on kidney cells and on bone cells. Kidney cells respond by reclaiming more calcium from the urine, while bone cells respond by releasing calcium into the blood. Which explanation best accounts for the different responses?

0 of 4 answered

45.2 Feedback and opposing hormone pairs

pp. 981–984

On the AP exam? Yes

Topic 4.4 uses insulin and glucagon as its main negative-feedback example and oxytocin as a positive-feedback one, and it asks what happens when feedback breaks down, as in diabetes. The names of gut hormones such as secretin are background.

In the course: Topic 4.4 Feedback, Topic 4.1 Cell Communication, Topic 4.3 Signal Transduction Pathways, Topic 2.7 Tonicity and Osmoregulation (notes, videos and more questions)

Key points

In a simple endocrine pathway, the hormone-making cells sense a change themselves and release a hormone. A simple neuroendocrine pathway instead starts with sensory neurons, which pick up the change and signal neurosecretory cells, which release a neurohormone into the blood.
Negative feedback means the response removes the stimulus, so the pathway switches itself off and doesn't overshoot. Most hormone loops that keep conditions steady work this way.
Positive feedback means the response strengthens the stimulus, so the pathway keeps building until something outside it ends the process. Oxytocin works this way during birth and while a baby nurses.
Some conditions are held steady by two antagonistic hormones, which push in opposite directions. Each is under negative feedback, so together they keep a variable in a narrow range.
Blood glucose is the classic case. Clusters of pancreatic cells called islets contain beta cells, which release insulin when glucose rises, and alpha cells, which release glucagon when it falls. The rest of the pancreas makes digestive enzymes and bicarbonate that leave through ducts, so this one organ has both endocrine and exocrine jobs.
Insulin lowers blood glucose: most cells in the body pull in more glucose, and the liver stores it as glycogen. Glucagon raises it, mainly by making liver cells break down glycogen and build new glucose from amino acids and glycerol. Neurons don't need insulin to absorb glucose.
Diabetes mellitus is a breakdown of this loop. In type 1, the body's own immune cells wipe out the beta cells, so little or no insulin is made. In type 2, which accounts for most cases, cells respond weakly to insulin. Either way, blood glucose runs high, glucose spills into the urine, and urine volume rises.

Key terms (14)

simple endocrine pathway: A hormone pathway in which the endocrine cells detect the change themselves and respond by releasing their hormone.
simple neuroendocrine pathway: A pathway in which sensory neurons detect a change and signal neurosecretory cells, which release a hormone into the blood.
negative feedback: A loop where the response cancels out the stimulus, bringing a variable back toward its normal value and shutting the pathway down.
positive feedback: A loop where the response adds to the stimulus, so the change keeps growing until an outside event stops it.
antagonistic hormones: Two hormones with opposite effects on the same variable, such as insulin lowering blood glucose and glucagon raising it.
insulin: A protein hormone from pancreatic beta cells that lowers blood glucose by getting cells to take up glucose and the liver to store it.
glucagon: A protein hormone from pancreatic alpha cells that raises blood glucose, mainly by making the liver break down glycogen and release glucose.
pancreatic islets: Small clusters of hormone-making cells scattered through the pancreas. They contain the alpha and beta cells.
beta cell: A cell in a pancreatic islet that releases insulin when blood glucose rises.
alpha cell: A cell in a pancreatic islet that releases glucagon when blood glucose falls.
glycogen: A branched polysaccharide of glucose that liver and muscle cells use as short-term fuel storage.
diabetes mellitus: A disease in which blood glucose stays too high because the body makes too little insulin or its cells respond poorly to it.
type 1 diabetes: Diabetes in which the immune system attacks and kills the beta cells, so the person must take insulin.
type 2 diabetes: Diabetes in which insulin is made but target cells respond weakly to it. It's the most common form and is linked to genes, weight and inactivity.

Check yourself: 45.2 Feedback and opposing hormone pairs

4 questions on 45.2 Feedback and opposing hormone pairs. Pick an answer to see if you got it, and why.

Question 1 of 4

When the K⁺ concentration of the blood rises, cells of the adrenal cortex detect it directly and release the hormone aldosterone. Aldosterone makes the kidneys excrete more K⁺, and as blood K⁺ falls, aldosterone release slows. How is this pathway best described?

Question 2 of 4

In a hypothetical gland, hormone Z makes target cells release substance S, and S stimulates the gland to release even more Z. Which event would most likely end this loop?

Question 3 of 4

A healthy adult who has not eaten for several hours cycles at a steady pace for 90 minutes. Blood samples are taken during the ride (invented data). Time cycling (min) | Glucose (mg/dL) | Insulin (µU/mL) | Glucagon (pg/mL) 0 | 92 | 10 | 70 30 | 88 | 7 | 95 60 | 86 | 5 | 120 90 | 85 | 4 | 140 Which interpretation is best supported?

Question 4 of 4

0 of 4 answered

45.3 The hypothalamus, pituitary and hormone cascades

pp. 984–989

On the AP exam? Background

You won't need hypothalamus or pituitary hormones by name. What carries over: thyroid and growth hormones are the course's examples of long-distance signals (Topic 4.1), cascades are held in check by negative feedback (Topic 4.4), growth hormone made by bacteria is biotechnology (Topic 6.8), and related hormones across animals reflect common ancestry (Topic 7.6).

In the course: Topic 4.1 Cell Communication, Topic 4.4 Feedback, Topic 6.8 Biotechnology, Topic 7.6 Evidence of Evolution (notes, videos and more questions)

Key points

The hypothalamus, at the base of the brain, is where the nervous and endocrine systems meet. It takes in information from all over the nervous system and responds by controlling the pituitary gland just below it.
The posterior pituitary is really part of the brain. Hypothalamic neurons make oxytocin and antidiuretic hormone (ADH), send them down their axons into the posterior pituitary, and release them into the blood when nerve signals arrive.
Oxytocin makes the uterus contract during birth and makes milk flow during nursing, and it affects bonding behavior. ADH makes the kidneys hold on to water, so urine gets more concentrated.
The anterior pituitary is a true gland that makes its own hormones. The hypothalamus controls it with releasing and inhibiting hormones that travel a short way through a set of portal blood vessels connecting the two.
Many anterior pituitary hormones are tropic, meaning their targets are other endocrine glands: TSH (thyroid), ACTH (adrenal cortex), and FSH and LH (testes and ovaries). Prolactin isn't tropic, and growth hormone acts both directly and by getting the liver to release growth factors called IGFs.
In a hormone cascade, the hypothalamus signals the anterior pituitary, which signals a gland, whose hormone acts on the body. The final hormone usually feeds back to turn down the earlier steps. For example, thyroid hormone (T₃ and T₄) slows the release of TRH and TSH.
Thyroid hormone contains iodine, raises metabolic rate and is needed for normal brain and bone development. Without enough iodine, T₃ and T₄ fall, TSH stays high, and the thyroid swells into a goiter. Too much growth hormone in childhood causes gigantism, and in adults causes acromegaly; too little in childhood causes very short stature, treatable with growth hormone made by bacteria.

Key terms (14)

hypothalamus: A brain region that links the nervous and endocrine systems. It makes some hormones itself and controls the pituitary.
pituitary gland: A pea-sized gland hanging below the hypothalamus. It has two parts, anterior and posterior, that release different hormones.
posterior pituitary: The back part of the pituitary. It's an outgrowth of the brain that stores and releases hormones made by hypothalamic neurons.
anterior pituitary: The front part of the pituitary. It's a true gland that makes its own hormones when the hypothalamus signals it.
oxytocin: A hormone made in the hypothalamus and released from the posterior pituitary. It triggers uterine contractions and milk flow and affects social bonding.
antidiuretic hormone (ADH): A posterior pituitary hormone, also called vasopressin, that makes the kidneys keep more water so less urine is produced.
releasing hormone: A hypothalamic hormone that tells the anterior pituitary to release one of its hormones. Some pituitary hormones also have an inhibiting hormone.
tropic hormone: A hormone whose target is another endocrine gland, such as TSH, which tells the thyroid to release its hormone.
hormone cascade pathway: A chain of hormones running from the hypothalamus through the anterior pituitary to another gland, usually kept in check by negative feedback from the last hormone.
thyroid hormone: T₃ and T₄, the two hormones of the thyroid gland, both built with iodine. They raise metabolic rate and support growth and brain development.
goiter: A swollen thyroid gland, often caused by too little iodine, which keeps TSH levels high.
growth hormone (GH): An anterior pituitary hormone that drives growth, partly by making the liver release growth factors (IGFs). It also tends to raise blood glucose.
prolactin: An anterior pituitary hormone that stimulates milk production in mammals. In other vertebrates it has quite different jobs.
gonadotropins: FSH and LH, the two anterior pituitary hormones that act on the testes and ovaries.

Check yourself: 45.3 The hypothalamus, pituitary and hormone cascades

4 questions on 45.3 The hypothalamus, pituitary and hormone cascades. Pick an answer to see if you got it, and why.

Question 1 of 4

A radioactive amino acid is injected into a small region of a rat's hypothalamus. Over the next few hours, radioactive ADH shows up first in that region, then along the pituitary stalk, and finally in nerve endings inside the pituitary. Which conclusion is best supported?

Question 2 of 4

A head injury damages the posterior pituitary but leaves the hypothalamus and anterior pituitary working normally. Which symptom would most likely appear?

Question 3 of 4

In a newly studied salamander, two hormones come from the anterior pituitary. Hormone K acts directly on muscle cells, speeding up how fast they build protein. Hormone J travels to the thyroid and makes it release thyroid hormone. How are K and J best classified?

Question 4 of 4

In a region where the soil and water hold little iodine and table salt isn't iodized, many people develop an enlarged thyroid gland. Which sequence best explains this?

0 of 4 answered

45.4 Calcium, stress, sex hormones and daily rhythms

pp. 989–993

On the AP exam? Background

The exam won't ask about PTH, cortisol or aldosterone by name, but they're good practice with tested ideas: antagonistic hormones and negative feedback (Topic 4.4), testosterone and estrogen as long-distance signals (Topic 4.1), chemicals that block a pathway (Topic 4.3) and responding to day length (Topic 8.1).

In the course: Topic 4.4 Feedback, Topic 4.1 Cell Communication, Topic 4.3 Signal Transduction Pathways, Topic 8.1 Responses to the Environment, Topic 2.7 Tonicity and Osmoregulation (notes, videos and more questions)

Key points

Blood calcium has to stay in a narrow range. Too little makes muscles twitch and spasm (tetany), and too much lets calcium phosphate deposit in tissues.
When calcium drops, the parathyroid glands secrete PTH (parathyroid hormone), which makes bone release calcium, makes the kidneys reclaim more of it and gets the kidneys to finish activating vitamin D, which raises calcium uptake from food. Rising calcium then cuts PTH release. Calcitonin from the thyroid pushes the other way, though it matters little in adult humans.
Each adrenal gland is two glands in one. The inner adrenal medulla develops from nervous tissue and releases epinephrine and norepinephrine within seconds when nerves signal it, causing the fight-or-flight response.
Epinephrine and norepinephrine free up fuel (glucose and fatty acids), speed the heart, open the airways and send blood toward skeletal muscles, the heart and the brain and away from the gut, skin and kidneys.
The outer adrenal cortex responds to ACTH from the anterior pituitary, so it's slower, and it makes steroids. Glucocorticoids such as cortisol raise blood glucose, partly by breaking down muscle protein, and at high doses they suppress inflammation and immunity. Mineralocorticoids such as aldosterone make the kidneys keep Na⁺ and water, raising blood volume and pressure.
The testes and ovaries make most sex hormones: androgens such as testosterone, estrogens such as estradiol, and progestins such as progesterone. Both sexes make all three, in different amounts, under control of a GnRH → FSH and LH cascade. In mammal embryos, testosterone from the developing testes steers the body toward male structures; without it, female structures form.
Endocrine disruptors are outside chemicals, such as some pesticides and plastic additives, that mimic or block a hormone. The pineal gland releases melatonin at night, controlled by a brain clock (the suprachiasmatic nucleus) that gets light information from the eyes, so melatonin helps set sleep timing and seasonal breeding.

Key terms (14)

parathyroid hormone (PTH): A hormone from the parathyroid glands that raises blood calcium by acting on bone, the kidneys and, through vitamin D, the gut.
calcitonin: A thyroid hormone that lowers blood calcium. It's important in some animals but plays only a minor role in adult humans.
vitamin D: A steroid-like molecule from food or sunlit skin. Once the liver and kidneys activate it, it acts as a hormone that boosts calcium uptake in the intestines.
adrenal medulla: The inner part of each adrenal gland. It comes from nervous tissue and releases epinephrine and norepinephrine when nerves signal it.
adrenal cortex: The outer part of each adrenal gland. It makes steroid hormones (corticosteroids) when ACTH arrives in the blood.
epinephrine: An amine hormone, also called adrenaline, that triggers the fast fight-or-flight response. It also works as a neurotransmitter.
glucocorticoid: A steroid from the adrenal cortex, such as cortisol, that raises blood glucose during long-term stress and calms inflammation.
mineralocorticoid: A steroid from the adrenal cortex, such as aldosterone, that controls salt and water balance.
aldosterone: The main mineralocorticoid. It makes the kidneys reclaim Na⁺ (with water following), which raises blood volume and pressure.
androgen: A steroid sex hormone, such as testosterone, found at higher levels in males. It drives male development and traits like muscle growth and a deeper voice.
estrogen: A steroid sex hormone, such as estradiol, found at higher levels in females. It maintains the female reproductive system and female traits.
progestin: A steroid sex hormone, such as progesterone, that prepares and maintains the uterus for a pregnancy.
endocrine disruptor: A chemical from outside the body that interferes with a hormone pathway, often by copying or blocking a hormone at its receptor.
melatonin: A hormone the pineal gland releases at night. The length of its nightly release tracks night length, helping set sleep and seasonal cycles.

Check yourself: 45.4 Calcium, stress, sex hormones and daily rhythms

4 questions on 45.4 Calcium, stress, sex hormones and daily rhythms. Pick an answer to see if you got it, and why.

Question 1 of 4

During neck surgery, a patient's parathyroid glands are accidentally removed. Which change in the following days is most likely?

Question 2 of 4

In an experimental animal, the nerves leading to both adrenal glands are cut, but the glands keep their blood supply. When the animal is then startled, which change is expected?

Question 3 of 4

Patients who take high doses of prednisone, a synthetic glucocorticoid, for several months are told to reduce the dose slowly rather than stopping all at once. Which best explains this advice?

Question 4 of 4

After a person loses a lot of blood, the level of angiotensin II in the blood rises. Which hormonal response helps restore blood volume over the next several hours?

0 of 4 answered