1. Chapter 40
The endocrine system

2. Learning Objectives Define Hormones
List and explain the process of the 4 major pathways of endocrine signaling
List and define the 4 common classes of chemicals used for endocrine signaling
Compare and contrast hydrophilic and hydrophobic hormones
Explain the roles of the hypothalamus and the pituitary gland in the body

3. 40.1 Hormones and Their Secretion
Endocrine system includes four major types of cell signaling
Hormones and local regulators are grouped into four classes based on their chemical structure
Hormones are regulated by feedback pathways
Body processes are regulated by coordinated hormone secretion

4. Hormones
Substances secreted by cells that control the activities of cells elsewhere in the body
Target cells respond to a specific hormone
Endocrine system secretes the best-known hormones

5. 4 Major types of signaling
Classical Endocrine
Neuroendocrine
Paracrine
Autocrine

6. 4 Major Types of Cell Signaling
Classical endocrine signaling: Endocrine glands secrete hormones

7. 4 Major Types of Cell Signaling
2. Neuroendocrine signaling: Neurosecretory neurons release neurohormones into the circulatory system

8. 4 Major Types of Cell Signaling
3. Paracrine regulation: Cells release local regulators that diffuse through extracellular fluid to regulate nearby cells

9. 4 Major Types of Cell Signaling
4. Autocrine regulation: Cells release local regulators that regulate the same cells that produced it

10. 4 Types of Molecules 1. Amines 2. Peptides Based on tyrosine
Examples: epinephrine, norepinephrine, thyroxine
2. Peptides
Amino acid chains
Example: growth factors

11. 4 Types of Molecules 3. Steroids 4. Fatty acids Based on cholesterol
Examples: aldosterone, cortisol, sex hormones
4. Fatty acids
Paracrine and autocrine regulation
Example: prostaglandins

12. Thyroid-releasing hormone (TRH)
Hypothalamus
Thyroid-releasing hormone (TRH)
Pituitary
Thyroid hormones inhibit TSH secretion by pituitary.
Thyroid-stimulating hormone (TSH)
Figure 40.2: A negative feedback loop regulating secretion of the thyroid hormones.
As the concentration of thyroid hormones in the blood increases, the hormones inhibit an earlier step in the pathway (indicated by the negative sign).
Thyroid
Thyroid hormones
Fig. 40.2, p. 912

13. 40.2 Mechanisms of Hormone Action
Hydrophilic hormones bind to surface receptors, activating protein kinases inside cells
Hydrophobic hormones bind to receptors inside cells, activating or inhibiting genetic regulatory proteins
Target cells may respond to more than one hormone, and different target cells may respond differently to the same hormone

14. Hydrophilic Hormones
Bind to receptor proteins embedded in the plasma membrane, activating them
Activated receptors transmit a signal through the plasma membrane
Signal transduction pathways cause a cellular response

15. a. Hormone binding to receptor in the plasma membrane
Outside cell
Hydrophilic hormone
Blood vessel
1. Hormone binds to surface receptor and activates it.
Signal
Reception
Cytoplasmic end of receptor
Activation
Pathway molecule A
Activation
2. Activated receptor triggers a signal transduction pathway.
Transduction
Pathway molecule B
Figure 40.3: The reaction pathways activated by hormones that bind to receptor proteins in the plasma membrane (a) or inside cells (b).
In both mechanisms, the signal—the binding of the hormone to its receptor—is transduced to produce the cellular response.
Activation
Molecule that brings about response
Pathway molecule C
Response
3. Transduction of the signal leads to cellular response.
Change in cell
Cytoplasm
Fig. 40.3a, p. 913

16. Hydrophobic Hormones
Bind to receptors in the cytoplasm or nucleus, activating them
Activated receptors control the expression of specific genes
Gene products cause the cellular response

17. Control sequence of gene
b. Hormone binding to receptor inside the cell
Outside cell
Blood vessel
Hydrophobic hormone
1. Hydrophobic hormone passes freely through plasma membrane.
Reception
Steroid hormone receptor
2. Hormone binds to receptor, activating it.
Transduction
3. Activated receptor binds to control sequence of a gene, leading to gene activation or inhibition.
Figure 40.3: The reaction pathways activated by hormones that bind to receptor proteins in the plasma membrane (a) or inside cells (b).
In both mechanisms, the signal—the binding of the hormone to its receptor—is transduced to produce the cellular response.
Gene activation or inhibition
Response
DNA
Cytoplasm
Control sequence of gene
Gene
Nucleus
Fig. 40.3b, p. 913

18. Adrenal glands Control sequence
1. Adrenal glands secrete
aldosterone into the blood when Na+ concentration falls in the body fluids.
Outside cell
Adrenal glands
Aldosterone
2. Aldosterone enters kidney cell and combines with the aldosterone receptor, activating it.
Kidney cell plasma membrane
Active hormone- receptor complex
3. Active hormone- receptor complex enters the nucleus, where it activates transcription
of the gene coding for aldosterone-induced protein.
Aldosterone receptor
DNA
Control sequence
Target gene
Nuclear envelope
Figure 40.4: The action of aldosterone in increasing Na+ reabsorption in the kidneys when concentration of the ion falls in the blood.
mRNA
Protein synthesis
4. Aldosterone-induced protein is synthesized in the cytoplasm and inserted into the plasma membrane, where it increases Na+ reabsorption by the kidney cell.
Aldosterone-induced protein (an Na+ channel)
Cytoplasm
Fig. 40.4, p. 914

19. Major Endocrine Cells and Glands of Vertebrates
Hypothalamus
Pituitary gland
Thyroid gland
Parathyroid gland
Adrenal medulla
Adrenal cortex
Testes and ovaries
Islets of Langerhans (pancreas)
Pineal gland

20. Produces hormones that regulate pituitary secretions
Hypothalamus
Produces hormones that regulate pituitary secretions
Pineal gland
Secretes melatonin
Anterior pituitary
Secretes ACTH, TSH, FSH, and LH, prolactin, GH, MSH, and endorphins
Thyroid gland
thyroxine and triiodothyronine, calcitonin
Posterior pituitary
ADH and oxytocin
Adrenal cortex
cortisol and aldosterone
Parathyroid glands Secrete parathyroid hormone
Adrenal medulla
Secretes epinephrine and norepinephrine
Figure 40.6
The major endocrine cells and glands of the human body.
Islets of Langerhans (in pancreas)
Secrete insulin and glucagon
Ovaries (female gonads)
Secrete estrogens and progestins
Testes (male gonads) Secrete androgens
Fig. 40.6, p. 917

21. 40.3 The Hypothalamus and Pituitary
Under regulatory control by hypothalamus, the anterior pituitary secretes eight major hormones
Posterior pituitary secretes two hormones into the circulatory system

22. The Hypothalamus and Pituitary
Hypothalamus and pituitary together regulate many endocrine cells and glands in the body
Pituitary gland has 2 major lobes
Posterior pituitary (contains neurosecretory nerve endings from hypothalamus)
Anterior pituitary (nonneuronal endocrine cells)

23. Neurosecretory neuron that secretes releasing and inhibiting hormones
Hypothalamus
Capillaries in hypothalamus
Releasing and inhibiting hormones
Blood in
Portal vein
Figure 40.7: The hypothalamus and pituitary.
Hormones secreted by the anterior and posterior pituitary are controlled by neurohormones released in the hypothalamus.
Endocrine cells secreting hormones
Posterior pituitary
Capillaries of anterior pituitary
Anterior pituitary
Blood out
Fig. 40.7b, p. 920

24. Fig. 40.7c, p. 920 Figure 40.7: The hypothalamus and pituitary.
Hormones secreted by the anterior and posterior pituitary are controlled by neurohormones released in the hypothalamus.
Fig. 40.7c, p. 920

25. Gonadotropins (FSH and LH) Thyroid- stimulating hormone (TSH)
Prolactin (PRL)
Gonadotropins (FSH and LH)
Thyroid- stimulating hormone (TSH)
Adrenocorticotropic hormone (ACTH)
Growth hormone (GH)
Mammary glands
Testes in males
Ovaries
in females
Thyroid gland
Adrenal cortex
Muscle,
bone and other tissues
Figure 40.7: The hypothalamus and pituitary.
Hormones secreted by the anterior and posterior pituitary are controlled by neurohormones released in the hypothalamus.
Produces milk
Produce gametes and hormones
Increases rate of metabolism
Helps regulate
fluid balance; helps body cope with stress
Promotes growth
Fig. 40.7d, p. 920

26. Melanocyte- stimulating hormone (MSH) Endorphins
Antidiuretic hormone (ADH)
Oxytocin
Melanocytes in skin of some vertebrates
Pain pathways of PNS
Nephrons
in kidneys
Uterus
Mammary glands
Figure 40.7: The hypothalamus and pituitary.
Hormones secreted by the anterior and posterior pituitary are controlled by neurohormones released in the hypothalamus.
Promotes skin darkening
Inhibit pain perception
Increases permeability
Stimulates contraction
Stimulates milk release
Fig. 40.7e, p. 920

27. Hormones of the Hypothalamus
Hypothalamus produces tropic hormones (releasing hormones and inhibiting hormones) that control secretion of anterior pituitary hormones

28. 8 Major Hormones of the Anterior Pituitary
1. Prolactin (PRL)
Breast development, milk secretion
2. Growth hormone (GH)
Bone and tissue growth, glucose metabolism
Stimulates IGF release in liver
3. Thyroid-stimulating hormone (TSH)
Thyroid hormones, thyroid growth

29. 8 Major Hormones of the Anterior Pituitary
4. Adrenocorticotropic hormone (ACTH)
Glucocorticoid secretion in adrenal cortex
5. Follicle-stimulating hormone (FSH)
Egg development, female sex hormones
Sperm production
6. Luteinizing hormone (LH)
Ovulation
Male sex hormones

30. 8 Major Hormones of the Anterior Pituitary
7. Melanocyte-stimulating hormone (MSH)
Produces a darkening of the skin
8. Endorphins
Neurotransmitters that affect pain pathways in the PNS, inhibiting perception of pain

31. Hormones of the Posterior Pituitary
Antidiuretic hormone (ADH)
Regulates body water balance
Oxytocin
Childbirth: Stimulates contraction of smooth muscle in the uterus
Triggers milk release from mammary glands