Table of contents

1. Introduction to Biology2h 42m
2. Chemistry3h 37m
3. Water1h 26m
4. Biomolecules2h 23m
5. Cell Components2h 26m
6. The Membrane2h 31m
7. Energy and Metabolism2h 0m
8. Respiration2h 40m
9. Photosynthesis2h 49m
10. Cell Signaling59m
11. Cell Division2h 47m
12. Meiosis2h 0m
13. Mendelian Genetics4h 44m
14. DNA Synthesis2h 27m
15. Gene Expression3h 6m
16. Regulation of Expression3h 31m
17. Viruses37m
- Viruses
  37m
18. Biotechnology2h 58m
19. Genomics17m
- Genomes
  17m
20. Development1h 5m
21. Evolution3h 1m
22. Evolution of Populations3h 53m
23. Speciation1h 37m
24. History of Life on Earth2h 6m
25. Phylogeny2h 31m
26. Prokaryotes4h 59m
27. Protists1h 12m
28. Plants1h 22m
29. Fungi36m
- Fungi
  19m
- Fungi Reproduction
  17m
30. Overview of Animals34m
- Overview of Animals
  34m
31. Invertebrates1h 2m
32. Vertebrates50m
33. Plant Anatomy1h 3m
34. Vascular Plant Transport1h 2m
- Water Potential
  1h 2m
35. Soil37m
- Soil and Nutrients
  20m
- Nitrogen Fixation
  16m
36. Plant Reproduction47m
- Flowers
  33m
- Seeds
  14m
37. Plant Sensation and Response1h 9m
38. Animal Form and Function1h 19m
39. Digestive System1h 10m
- Digestion
  1h 3m
- Blood Sugar Homeostasis
  7m
40. Circulatory System1h 49m
41. Immune System1h 12m
42. Osmoregulation and Excretion50m
- Osmoregulation and Excretion
  50m
43. Endocrine System1h 4m
- Endocrine System
  1h 4m
44. Animal Reproduction1h 2m
- Animal Reproduction
  1h 2m
45. Nervous System1h 55m
- Neurons and Action Potentials
  1h 8m
- Central and Peripheral Nervous System
  46m
46. Sensory Systems46m
- Sensory System
  46m
47. Muscle Systems23m
- Musculoskeletal System
  23m
48. Ecology3h 11m
49. Animal Behavior28m
- Animal Behavior
  28m
50. Population Ecology3h 41m
51. Community Ecology2h 46m
52. Ecosystems2h 36m
53. Conservation Biology24m
- Conservation Biology
  24m

43. Endocrine System

Endocrine System

General Biology

43. Endocrine System

Endocrine System

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1:14 minutes

Problem 3

Textbook Question

The body is able to maintain a relatively constant level of thyroid hormone in the blood because
a. Thyroid hormone stimulates the pituitary to secrete thyroid-stimulating hormone (TSH).
b. Thyroid hormone inhibits the secretion of TSH-releasing hormone (TRH) from the hypothalamus.
c. TRH inhibits the secretion of thyroid hormone by the thyroid gland.
d. Thyroid hormone stimulates the hypothalamus to secrete TRH.

Verified step by step guidance

Understand the concept of negative feedback in endocrine systems: Negative feedback is a regulatory mechanism in which a change in a physiological variable triggers a response that counteracts the initial change, helping to maintain homeostasis.

Identify the key players in the regulation of thyroid hormone levels: The hypothalamus secretes thyroid-releasing hormone (TRH), which stimulates the pituitary gland to release thyroid-stimulating hormone (TSH). TSH then stimulates the thyroid gland to produce thyroid hormones (T3 and T4).

Recognize the role of thyroid hormone in feedback regulation: When thyroid hormone levels in the blood are sufficient, they inhibit the secretion of TRH from the hypothalamus and TSH from the pituitary gland. This prevents overproduction of thyroid hormones, maintaining a stable level.

Analyze the options provided: Option (a) suggests a positive feedback loop, which is incorrect because thyroid hormone does not stimulate TSH secretion. Option (b) aligns with the concept of negative feedback, where thyroid hormone inhibits TRH secretion. Option (c) incorrectly states that TRH inhibits thyroid hormone secretion, which is not true. Option (d) incorrectly suggests that thyroid hormone stimulates TRH secretion, which contradicts the negative feedback mechanism.

Conclude that the correct answer is based on the negative feedback mechanism, where thyroid hormone inhibits the secretion of TRH from the hypothalamus, as described in option (b).

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Thyroid Hormone Regulation

Thyroid hormones, primarily thyroxine (T4) and triiodothyronine (T3), play a crucial role in regulating metabolism and energy levels in the body. Their levels are maintained through a feedback loop involving the hypothalamus and pituitary gland, ensuring that hormone production is adjusted based on the body's needs.

Hypothalamic-Pituitary-Thyroid Axis

The hypothalamic-pituitary-thyroid (HPT) axis is a complex set of interactions between the hypothalamus, pituitary gland, and thyroid gland. The hypothalamus releases thyrotropin-releasing hormone (TRH), which stimulates the pituitary to secrete thyroid-stimulating hormone (TSH), prompting the thyroid to produce thyroid hormones. This axis is essential for maintaining hormonal balance.

Negative Feedback Mechanism

Negative feedback is a regulatory mechanism in biological systems where an increase in a substance leads to a decrease in its production. In the context of thyroid hormones, elevated levels of T3 and T4 inhibit the release of TRH and TSH, thereby reducing further thyroid hormone production, which helps maintain homeostasis.

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Related Practice

Textbook Question

The hypothalamus

a. Synthesizes all of the hormones produced by the pituitary gland.

b. Influences the function of only one lobe of the pituitary gland.

c. Produces only inhibitory hormones.

d. Regulates both reproduction and body temperature.

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Textbook Question

Which correctly matches a hormone to the gland from which it is produced and to its effect on target cells?

a. Thyroid hormone: Anterior pituitary, regulates metabolism

b. Prolactin: Anterior pituitary, raises blood calcium levels

c. Androgens: Thyroid, promotes male characteristics

d. None of the choices are correct.

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Textbook Question

What is a hormone-response element?

a. A receptor for a steroid hormone

b. A receptor for a polypeptide hormone

c. A segment of DNA where a hormone–receptor complex binds

d. An enzyme that is activated in response to hormone binding and produces a second messenger

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Textbook Question

Growth factors are local regulators that

a. Are produced by the anterior pituitary.

b. Are modified fatty acids that stimulate bone and cartilage growth.

c. Are found on the surface of cancer cells and stimulate abnormal cell division.

d. Bind to cell-surface receptors and stimulate growth and development of target cells.

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Textbook Question

Which of the following assertions regarding hormones is correct? Select True or False for each statement.

T/F Growth and metamorphosis are controlled by hormones.

T/F Cortisol stimulates the production of ACTH.

T/F Hormones produced by the hypothalamus are considered neurohormones.

T/F Hormonal changes during puberty and pregnancy are forms of endocrine disruption.

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Textbook Question

Which hormone is incorrectly paired with its action?

a. Oxytocin — stimulates uterine contractions during childbirth

b. Thyroxine — inhibits metabolic processes

c. ACTH — stimulates the release of glucocorticoids by the adrenal cortex

d. Melatonin — affects biological rhythms and seasonal reproduction

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Textbook Question

Explain how the hypothalamus controls body functions through its action on the pituitary gland. How does control of the anterior and posterior pituitary differ?

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Textbook Question

True or False: In hormone systems, negative feedback occurs when the presence of a hormone inhibits release of the hormone.

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