Chapter 45 Guided Reading Answers

Insulin Hyposecretion

Diabetes mellitus Lowers blood glucose level; insulin resistance, which could lead to diabetes.

15. What endocrine gland secretes epinephrine?

Adrenal glands secrete epinephrine.

neurotransmitters

At synapses, neurons secrete molecules called neurotransmitters that diffuse a very short distance to bind receptors on the target cells. Example- acetylcholine

5. Explain the difference between an endocrine gland and an exocrine gland. Give an example of each.

Endocrine glands, such as the thyroid and parathyroid glands, secrete hormones directly into the surrounding fluid. Exocrine glands, such as salivary glands, have ducts that carry secreted substances onto body surfaces or into body cavities.

3. The body has two long-distance regulating systems. Which involves chemical signals by hormones?

Endocrine system

hormones

Hormones are secreted into the extracellular fluid, circulate in the hemolymph or blood, and communicate regulatory messages throughout the body. Example- insulin

2. Why does a hormone elicit a response only with target cells?

Hormones elicit responses only with a target cell because those target cells have a matching receptor; cells without that receptor are unaffected.

8. Figure 45.2 in your text shows five different types of signals. Label and explain each one.

See page 994 in your text for the labeled figure and explanations.

17. Use the following figure to explain the signal transduction pathway for epinephrine.

See page 997 in your text for the labeled figure and explanation.

1. What is a hormone?

In multicellular organisms, a hormone is one of the many types of secreted chemicals that are formed in specialized cells, travel in body fluids, and act on specific target cells in other parts of the body, changing the target cells' functioning. Hormones are thus important in long-distance signaling.

local regulators

Many types of cells produce and secrete local regulators, molecules that act over short distances and reach their target cells solely by diffusion. Example- cytokines

Lipid-Soluble

MoS- diffuse across the membranes of endocrine cells, MoT- bind to transport proteins that keep them soluble in the aqueous environment of the bloodstream, LoR- intracellular signal receptors, Eg- -thyroxine, testosterone

Water-soluble

MoS-exocytosis, MoT- travel freely in bloodstream, LoR- cell surface signal receptors, Eg- Epinephrine

4. What is the other major communication and control system?

Nervous system

pheromones

Pheromones are chemicals that are released into the external environment to affect members of the same species. Example- the compound secreted by termites that results in others "following"

23. How is oxytocin an example of a hormone that is under positive regulation?

Positive feedback involves reinforcing a stimulus, leading to an even greater response. Oxytocin is an example of this because its release is triggered by sensory neurons triggered by a suckling infant, and its release then triggers the production of milk in the mammary gland.

11. Recall that target cells have receptors for specific hormones. Where are the receptors for lipid-soluble hormones found?

Receptors for lipid-soluble hormones typically reside in the cytoplasm or nucleus.

12. Where are the receptors for the water-soluble hormones found?

Receptors for water-soluble hormones are found on the cell surface. This is different from steroid hormones that are lipid-soluble because water-soluble hormones cannot pass through the membrane of cells.

TRH Hypersecretion

Results in a release of TSH that stimulates the release of thyroid hormone, which increases cellular metabolism; symptoms of hyperthyroidism include: high body temperature, profuse sweating, weigh tloss, irritability, and high blood pressure.

TRH Hyposecretion

Retarded skeletal growth and poor mental development

TSH Hyposecretion

Retarded skeletal growth and poor mental development

Growth hormone Hyposecretion

Retards long bone growth and can lead to pituitary dwarfism

10. What are the three major classes of molecules that function as hormones in vertebrates?

See figure 45.4

22. What two hormones are released by the posterior pituitary and what are their actions?

See figure 45.9 and 45.14

24. The anterior pituitary secretes seven different hormones. Each hormone has a specific target tissue. Select two pituitary hormones and give the target and response for each.

See figure 45.9 and 45.15 (p. 1003)

18. Lipid-soluble hormones, such as estradiol, bind to intracellular receptors. Explain the action of this steroid in the following figure.

See page 997 in your text for the labeled figure. Steroid hormone receptors are located in the cytosol prior to binding to a hormone. When a steroid hormone binds to its cytosolic receptor, a hormone-receptor complex forms, which moves into the nucleus. There, the receptor portion of the complex alters transcription of particular genes by interacting with a specific DNA-binding protein or response element in the DNA.

FSH, LH Hyposecretion

Sexual complications and/or sterility

FSH, LH Hypersecretion

Stimulate production of ova and sperm; stimulate ovaries and testes

Growth hormone Hypersecretion

Stimulates growth (especially bones) and metabolic functions; can lead to gigantism

TSH Hypersecretion

Stimulates the thyroid gland; symptoms of hyperthyroidism include- high body temperature, profuse sweating, weight loss, irritability, and high blood pressure.

21. How does the hypothalamus integrate information?

The hypothalamus directly secretes hormones that travel to the posterior pituitary and regulating hormones that affect secretions of hormones by the anterior pituitary. The anterior pituitary secretes seven different hormones.

19. One hormone can have several different effects. For example, epinephrine can cause the release of glucose from liver cells, dilate blood vessels to skeletal muscles, and constrict intestinal blood vessels. All these effects prepare the body for "fight or flight." Explain how these multiple effects are possible.

Tissues vary in their response to epinephrine because they vary in their receptors, their signal temperatures, or their signal transduction pathways. For example, with epinephrine, target cell recognition involves G protein-coupled receptors. Liver cells have a B-type epinephrine receptor that activates the enzyme protein kinase A, which in turn regulates enzymes in glycogen metabolism. In blood vessels supplying skeletal muscle, the same kinase activated by the same epinephrine receptor inactivates a muscle-specific enzyme. The result is smooth muscle relaxation and hence increased blood flow.

25. What is the importance of tropic hormones? List three tropic hormones and their action.

Tropic hormones stimulate other glands to produce hormones. Three examples are follicle-stimulating hormone (FSH), luteinizing hormone (LH), and adrenocorticotropic hormone (ACTH). FSH and LH stimulate the activities of both the male and female gonads, the testes and ovaries. ACTH stimulates the production and secretion of steroid hormones by the adrenal cortex.

16. What are the two intracellular responses in the liver to epinephrine? How do these help the body deal with short-term stress?

When epinephrine reaches the liver, it binds to a G protein-coupled receptor in the plasma membrane of target cells. The binding of hormone to receptor triggers a cascade of events involving synthesis of cyclic AMP as a short-lived second messenger. Activation of protein kinase A by cAMP leads to activation of an enzyme required for glycogen breakdown and inactivation of an enzyme necessary for glycogen synthesis. The net result is that the liver releases glucose into the bloodstream, providing the fuel you need to deal with short-term stress.

nitric oxide

gas; functions as local regulator and neurotransmitter. Secreted by endothelial cells in blood vessels and results in vasodilation (increased blood flow)

prostaglandins

modified fatty acids; local regulator that is secreted by most tissues and perform a variety of physiological functions

cytokines

polypeptide; local regulator --- communication between immune cells

growth factors

polypeptide; local regulator ---promote growth, division and development

20. Review the basics of negative feedback - explain negative feedback using the following terms

receptor, control center, effector, and efferent signal.:In a negative feedback loop, the response reduces the initial stimulus. For example, regulation of blood glucose concentration by insulin and glucagon are examples of negative feedback. The initial stimulus of high blood glucose after eating a meal triggers the release of insulin, which reduces the amount of blood glucose. Likewise, when the initial stimulus is low blood glucose, the pancreas releases glucagon, which releases stored glucose into the bloodstream.