2. 29.1 Hormones
A hormone is a chemical signal that is produced in one part of the body and that acts at a distant site
Three advantages to using chemical signals
1. Can spread to all tissues via the blood
2. Can persist much longer than electric signals
3. Many can act as hormones
Different hormones can target different tissues

3. Hormones are produced by endocrine glands
These glands do not have ducts
Hormones are secreted directly into the blood
Hormones are under the control of the neuroendocrine system
The hypothalamus is the main switchboard
Issues commands to the nearby pituitary gland
Pituitary sends chemical signals to the various hormone-producing glands in body

4. Fig. 29.1 Major glands of the human endocrine system

5. The path of communication of a hormone signal 1. Issuing the command
Hormones are effective because they are recognized by specific receptors
These are on or in target cells
The path of communication of a hormone signal
1. Issuing the command
By the hypothalamus
2. Transporting the signal
By the blood
3. Hitting the target
Binding to the receptor
4. Having an effect
A change in cell activity

6. Fig. 29.2 How hormonal communication works

7. 29.2 How Hormones Target Cells
Steroid hormones
Manufactured from cholesterol
Lipid-soluble and thus can across the lipid bilayer of the cell membrane
Bind to receptors within the nucleus usually
The hormone-receptor complex binds to DNA causing changes in gene activity
Anabolic steroids
Synthetic compounds resembling testosterone
Cause muscle cells to produce more protein

8. Fig. 29.3 How steroid hormones work

9. Short peptides or full-sized proteins
Fig. 29.4
Peptide hormones
Short peptides or full-sized proteins
Bind to receptors embedded in the cell membrane
Induce a change in cytoplasmic end of the receptor protein
Triggers events within the cytoplasm

10. Trigger a cascade of enzymic activation within cell
The change in cellular activity is facilitated by second messengers such as cAMP
Trigger a cascade of enzymic activation within cell
Fig. 29.5

11. 29.3 The Hypothalamus and the Pituitary
The pituitary gland is located in a bony recess in the brain below the hypothalamus
It produces nine major hormones
It is actually two glands
Posterior lobe
Anterior lobe

12. The Posterior Pituitary
Stores and releases two short peptide hormones
Vasopressin (antidiuretic hormone, ADH)
Regulates water conservation by the kidney
Oxytocin
Initiates uterine contractions during childbirth
Causes milk letdown
Both synthesized within hypothalamus neurons
Transported down nerve axons to the posterior lobe

13. Fig. 29.6 Posterior pituitary

14. The Anterior Pituitary
A complete gland that produces seven major hormones
1. Thyroid-stimulating hormone (TSH)
2. Luteinizing hormone (LH)
3. Follicle-stimulating hormone (FSH)
4. Adrenocorticotropic hormone (ACTH)
5. Growth hormone (GH)
6. Prolactin
7. Melanocyte-stimulating hormone (MSH)

15. Fig. 29.7 The role of the pituitary

16. The hypothalamus controls the anterior pituitary
Secretes releasing and inhibiting hormones into capillaries
Hypothalamo-hypophyseal portal system carries the hormones to the pituitary
Fig. 29.8

17. Hypothalamus and anterior pituitary are themselves controlled by negative feedback inhibition
Regulated by the hormones whose secretion they stimulate!
Fig. 29.9
Thyrotropin-releasing hormone
Gonadotropin-releasing hormone
Corticotropin-releasing hormone

18. 29.4 The Pancreas The pancreas gland is located behind the stomach
Secretes a number of digestive enzymes into the small intestine through a narrow tube
Islets of Langerhans govern blood glucose levels
Insulin
Secreted by beta cells
Storage hormone that promotes accumulation of glycogen in liver and triglycerides in fat cells
Glucagon
Secreted by alpha cells
Cause release of stored glucose and fat breakdown

19. Fig

20. Diabetes mellitus
Affected individuals cannot take up glucose from the blood
Type I
~ 5-10% of diabetics
Autoimmune disorder in which immune systems attacks the Islets of Langerhans
Develops before age 20 (juvenile-onset diabetes)
Treated by daily injections of insulin
Type II
~ 90-95% of diabetics
Caused by abnormally low number of insulin receptors
Develops after age 40 (adult-onset diabetes)
Typically in obese individuals
Treated by diet and exercise

21. 29.5 The Thyroid, Parathyroid and Adrenal Glands
The thyroid gland lies just below the Adam’s apple in front of the neck
Its two most important hormones are
Thyroxine
Increases metabolic rate and promotes growth
Contains iodine
Lack of iodine in diet causes goiters
Calcitonin
Stimulates calcium deposition in the bone

22. Fig. 29.11 The thyroid gland secretes thyroxine
Goiter

23. The parathyroid glands are four small glands attached to the thyroid
Produce parathyroid hormone (PTH)
One of only two hormones essential for survival
Acts as a fail-safe mechanism ensuring that calcium levels never fall too low
Calcium ions are key to muscle contractions
When levels are low, PTH stimulates osteoclast cells to break down bone matrix
This raises calcium levels in the blood
PTH also acts on kidneys to reabsorb calcium ions from the urine

24. Fig. 29.12 Maintenance of proper calcium levels in the blood

25. The adrenal glands are two glands, one located just above each kidney
Each composed of two parts
Medulla – Inner core
Adrenaline and norepinephrine
Released in times of stress to stimulate rapid deployment of body fuel
Cortex – Outer shell
Cortisol – Stimulates carbohydrate metabolism and reduces inflammation
Aldosterone – Stimulates the kidney to uptake sodium and other ions from the urine
This is the other hormone that is absolutely essential for survival

26. 29.6 A Host of Other Hormones
Steroid sex hormones
Estrogen, progesterone and testosterone
Produced by gonads to regulate sexual development
Atrial natriuretic hormone
Secreted by the right atrium of the heart
Stimulate kidneys to excrete salts and water in the urine
Erythropoietin
Secreted by the kidney
Stimulates the bone marrow to produce RBC

27. Molting and Metamorphosis in Insects
Molting is triggered by the molting hormone, also called ecdysone
The production of ecdysone is itself controlled by the brain hormone
These two hormones are balanced by a third hormone, the juvenile hormone
If present in high levels, it inhibits the formation of the pupa and adult forms

28. Fig. 29.13 The hormonal control of metamorphosis in the silkworm moth, Bombyx mori