1. Chapter 34 Endocrine Control

2. 34.2 The Vertebrate Endocrine System
Animal cells communicate with one another by way of a variety of short-range and long-range chemical signals
Animal cells communicate with adjacent cells through gap junctions and by releasing molecules that bind to receptors in or on other cells

3. Mechanisms of Intercellular Signaling
Many cells secrete local signaling molecules – such as prostaglandins released by injured cells – which affect only neighboring cells
Animal hormones are secreted into interstitial fluid, enter the blood, and are distributed throughout the body

4. Hormones and the Endocrine System
Internal secretions carried by the blood that influence the activities of specific body organs are called hormones
Endocrine glands and other structures that secrete hormones make up an animal’s endocrine system
Some of the major endocrine glands also have functions unrelated to hormone secretion

5. Hypothalamus
Pineal gland
Parathyroid glands
Pituitary gland
Thyroid gland
Thymus gland
Adrenal glands
Figure 34.2 Animated Main components of the human endocrine system and the effects of their secretions. Hormone-secreting cells are also present in the glandular epithelia of the stomach, small intestine, liver, heart, kidneys, adipose tissue, skin, placenta, and other organs.
Pineal gland
• Melatonin (affects sleep/wake cycles)
Thyroid gland
• Thyroid hormone (affects development, metabolism)
• Calcitonin (lowers blood calcium level)
Thymus gland
• Thymosins, thymulin
(enhance immune function)
Adrenal glands
Adrenal cortex
• Cortisol (affects metabolism,
immune response)
• Aldosterone (acts in kidneys)
Adrenal medulla
• Epinephrine, norepinephrine (cause
fight–flight response)
Gonads: ovaries or testes (not shown)
• Estrogens, progesterone, testosterone (regulate gamete production
and influence secondary sexual traits)
Pancreas
• Insulin (lowers blood glucose)
• Glucagon (raises blood glucose)
Pituitary gland
Anterior lobe makes and secretes:
• Adrenocortocotropic hormone
(ACTH; stimulates adrenal gland)
• Thyroid-stimulating hormone
(TSH; stimulates thyroid gland)
• Luteinizing hormone (LH;
stimulates ovaries and testes)
• Follicle-stimulating hormone
(FSH; stimulates ovaries,testes)
• Prolactin (stimulates mammary
glands)
• Growth hormone (affects growth)
Posterior lobe secretes:
• Antidiuretic hormone (ADH; acts
on kidney; concentrates urine)
• Oxytocin (makes smooth muscle
of reproductive tract and milk
ducts contract)
Hypothalamus
• Hormones that regulate pituitary’s
anterior lobe
• Antidiuretic hormone (ADH), and
oxytocin (both released by the
posterior Parathyroid glands (not shown, on rear of thyroid) pituitary)
• Parathyroid hormone (raises blood calcium level)
Pancreas
Gonads
Figure 34-2 p587 5

6. ANIMATED FIGURE: Major human endocrine glands

7. 34.3 The Nature of Hormone Action
For a hormone to have an effect, it must bind to protein receptors on or inside a target cell
Hormone action involves three steps:
A hormone activates a target cell receptor
The signal is transduced (changed into a form that affects target cell behavior)
The cell makes a response

8. From Signal Reception to Response
Signal Transduction
Cellular Response

9. Table 34-1 p588

10. Intracellular Receptors
Steroid hormones are made from cholesterol and can diffuse across the plasma membrane
Most steroid hormones form a hormone-receptor complex that binds to a promoter inside the nucleus and alters the expression of specific genes

11. hormone– receptor complex
A steroid hormone molecule is moved from blood into interstitial fluid bathing a target cell. 1
Being lipid soluble, the hormone easily diffuses across the cell’s plasma membrane. 2
The hormone diffuses through the cytoplasm and nuclear envelope. It binds with its receptor in the nucleus. 3
Figure 31.3 Mechanisms of hormone action.
A Example of steroid hormone action inside a target cell.
1. A steroid hormone molecule is moved from blood into interstitial fluid bathing a target cell.
2. Being lipid soluble, the hormone easily diffuses across the cell’s plasma membrane.
3. The hormone diffuses through the cytoplasm and nuclear envelope. It binds with its receptor in the nucleus.
4. The hormone– receptor complex triggers transcrip-tion of a specific gene.
5. The resulting mRNA moves into the cytoplasm and is transcribed into a protein.
The resulting mRNA moves into the cytoplasm and is transcribed into a protein. 5
receptor
The hormone– receptor complex triggers transcrip-tion of a specific gene. 4
hormone– receptor complex
gene product
Figure 34-3a p589

12. Receptors at the Plasma Membrane
Large amine, peptide and protein hormones bind to a receptor at the plasma membrane
Binding triggers formation of a second messenger (molecule that relays signal into cell)
Enzyme converts ATP to cAMP
cAMP activates a cascading series of reactions

13. unoccupied glucagon receptor at target cell’s plasma membrane
A peptide hormone molecule, glucagon, diffuses from blood into interstitial fluid bathing the plasma membrane
of a liver cell. 1
unoccupied glucagon receptor at target cell’s plasma membrane
cyclic AMP
+ Pi
ATP
Glucagon binds with a receptor. Binding activates an enzyme that catalyzes the formation of cyclic AMP from ATP inside the cell. 2
Cyclic AMP activates another enzyme in the cell. 3
Figure 31.3 Mechanisms of hormone action.
B Example of peptide hormone action inside a target cell.
1. A peptide hormone molecule, glucagon, diffuses from blood into interstitial fluid bathing the plasma membrane
of a liver cell.
2. Glucagon binds with a receptor. Binding activates an enzyme that catalyzes the formation of cyclic AMP from ATP inside the cell.
3. Cyclic AMP activates another enzyme in the cell.
4. The enzyme activated by cyclic AMP activates another enzyme, which in turn activates another kind that catalyzes the breakdown of glycogen to its glucose monomers.
5. The enzyme activated by cyclic AMP also inhibits glycogen synthesis 5
The enzyme activated by cyclic AMP activates another enzyme, which in turn activates another kind that catalyzes the breakdown of glycogen to its glucose monomers. 4
The enzyme activated by cyclic AMP
also inhibits glycogen synthesis.
Figure 34-3b p589

14. Receptor Function and Diversity
Only cells with appropriate and functional receptor proteins can respond to a hormone
Gene mutations that alter receptor structure can prevent or change cell response to a hormone
Examples:
Androgen insensitivity syndrome
Variations in ADH receptors

15. Take-Home Message: How do hormones exert their effects on target cells?
Hormones exert their effects by binding to protein receptors, either inside a cell or at the plasma membrane.
Steroid hormones often enter a cell and act by altering the expression of specific genes.
Peptide and protein hormones usually bind to a receptor at the plasma membrane. They trigger formation of a second messenger, a molecule that relays a signal into the cell.
Variations in receptor structure affect how a cell responds to a hormone.

16. ANIMATION: Hormones and target cell receptors

17. 34.4 The Hypothalamus and Pituitary Gland
The hypothalamus is the main center for control of the internal environment – it connects structurally and functionally with the pituitary gland
The pituitary gland has two parts:
The posterior lobe secretes hormones made in the hypothalamus
The anterior lobe makes its own hormones
The hypothalamus signals the pituitary by way of secretory neurons that make hormones

18. Control of Anterior Pituitary
Hormones from the hypothalamus control the release of anterior pituitary hormones
Releasing hormones encourage secretion of hormones by target cells
Inhibiting hormones reduce secretion of hormones by target cells
Releasing and inhibiting hormones are secreted into the stalk that connects the hypothalamus to the pituitary

19. Feedback Controls of Hormone Secretion
Positive feedback mechanisms
Response increases the intensity of the stimulus
Example: Oxytocin and childbirth contractions
Negative feedback mechanisms
Response decreases the stimulus

20. Take-Home Message: How do the hypothalamus and pituitary gland interact?
Some secretory neurons of the hypothalamus make hormones (ADH, OT) that move through axons into the posterior pituitary, which releases them.
Other hypothalamic neurons produce releasers and inhibitors that are carried by the blood into the anterior pituitary. These hormones regulate the secretion of anterior pituitary hormones (ACTH, TSH, LH, FSH, PRL, and GH).

21. 34.6 Sources and Effects of Other Vertebrate Hormones
In addition to the hypothalamus and pituitary gland, endocrine glands and endocrine cells secrete hormones
The gut, kidneys, and heart are among the organs that are not glands, but include hormone-secreting cells

22. Table 34-3 p593

23. Multiple Hormone Receptors
Most cells have receptors for multiple hormones, and the effect of one hormone can be enhanced or opposed by another one
Example: Skeletal muscle hormone receptors
Glucagon, insulin, cortisol, epinephrine, estrogen testosterone, growth hormone, somatostatin, thyroid hormone and others

24. Take-Home Message: What are the sources and effects of vertebrate hormones?
In addition to the pituitary gland and hypothalamus, endocrine glands and endocrine cells secrete hormones.
The gut, kidneys, and heart are among the organs that are not considered glands, but do include cells that secrete hormones.
Most cells have receptors for multiple hormones, and the effect of one hormone can be enhanced or opposed by that of another.