1. Chemical Control in Animals: The Endocrine System
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Biology: Life on Earth (Audesirk)
Chemical Control in Animals: The Endocrine System
Chapter 32

2. Definition of hormone
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Hormone: Chemical substance produced in one part of the body and transported usually by the blood stream to specific sites (target tissue) where it regulates an appropriate response.

3. Animal Hormones Classes of animal hormones
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Classes of animal hormones
Peptide hormones
Amino acid derivatives
Steroid hormones
Prostaglandins
Functions of animal hormones
Binding to surface receptors
Binding to intracellular receptors
Negative feedback for hormone synthesis and release

4. Mode of Action 1. Affect membrane to alter transport of substances
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1. Affect membrane to alter transport of substances
2. Affect activity of the gene (transcription)
3. Affect protein synthesis (translation)
4. Change the amount of availability of a cofactor

5. Mode of Action cont’d 5. Act as a coenzyme itself
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5. Act as a coenzyme itself
6. Stimulate or inhibit the formation of cyclic AMP (2nd messenger)
7. Play a role in maintenance of specific receptor molecules

6. The Major Endocrine Glands of Humans
Biology: Life on Earth (Audesirk)
The Major Endocrine Glands of Humans
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Click boxes to go to expanded views
The major mammalian endocrine glands are the hypothalamus-pituitary gland complex, the thyroid and parathyroid glands, the pancreas, the sex organs (ovaries in females, testes in males), and the adrenal glands. Other organs that secrete hormones include the pineal gland, thymus, kidneys, heart, and parts of the digestive tract.
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7. Endocrine Glands, Hormones, and Target Cells
Biology: Life on Earth (Audesirk)
Endocrine Glands, Hormones, and Target Cells
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Hormone enters bloodstream
Hormone distributed throughout body
Endocrine cells release hormone
Endocrine glands consist of hormone-producing cells embedded in a network of capillaries. These cells secrete hormones into the extracellular fluid, from which they diffuse into the capillaries. Each hormone is transported around the body by the bloodstream but binds to (and influences) only those cells that contain specific receptors for the hormone. Muscle cells but not neurons have receptors for the particular hormone shown here.
Receptor on target cell
Capillary
Nerves w/o right receptors: no binding occurs; no hormonal effects
Hormone- receptor Complex
Muscle w/right receptors: binding occurs; hormonal effects appear
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8. Peptide and Amino-Acid Hormones
Biology: Life on Earth (Audesirk)
Peptide and Amino-Acid Hormones
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1) Peptide and amino-acid hormones, which are not soluble in lipids, bind to a receptor on the outside of the target cell’s plasma membrane. 2) Hormone-receptor binding triggers the synthesis of cyclic AMP (cAMP). 3) Cyclic AMP activates enzymes that 4) promote specific cellular reactions, producing new products. This cAMP “cascade” may generate a variety of responses, such as an increase in glucose synthesis (induced by epinephrine) and an increase in estrogen synthesis (induced by luteinizing hormone).
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9. Lipid-Soluble Steroid Hormones
Biology: Life on Earth (Audesirk)
Lipid-Soluble Steroid Hormones
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1) Lipid-soluble steroid hormones diffuse readily through the plasma membrane into the target cell and into the nucleus, where they combine with a protein receptor molecule. 2) The hormone-receptor complex binds to DNA and facilitates the binding of RNA polymerase to promoter sites on specific genes, accelerating 3) the transcription of DNA into messenger RNA (mRNA). 4) The mRNA then directs protein synthesis. In hens, for example, estrogen promotes the transcription of the albumin gene, causing the synthesis of albumin (egg white), which is packaged in the egg as a food supply for the developing chick.
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10. Steroid and lipid hormones
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Hormone Target Major response
Glucocorticoids Liver, gluconeogenesis,
lymphatic anti-inflammatory
tissue, catabolic
muscle
Mineralo- kidney Na+ absorption
corticoids
Progesterone Uterus decrease
mobility,
preparation for
implantation

11. Steroids cont’d Chapter 32 Hormone Target Major response
Androgens Accessory differentiation
sex organs, 2° sex char.,
muscle anabolic
Estrogen Accessory uterotrophic
sex organs transport, secondary sex char.
Prostaglandins Accessory inhibit or sex organs stimulate
uterine contractility

12. The Hypothalamus Controls the Pituitary
Biology: Life on Earth (Audesirk)
The Hypothalamus Controls the Pituitary
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Pituitary
Hypothalamus
Neurosecretory Cells
Neurosecretory cells of the hypothalamus control hormone release in the anterior lobe of the pituitary by producing releasing hormones (left). These cells secrete their hormones into a capillary network that carries them to the anterior pituitary. There, each releasing hormone stimulates endocrine cells with appropriate receptors to secrete that hormone while leaving other types unaffected. The posterior lobe of the pituitary (right) is an extension of the hypothalamus. Neurosecretory cells in the hypothalamus have cell endings on a capillary bed in the posterior lobe, where the cells release oxytocin or antidiuretic hormone (ADH).
Releasing Hormone
Anterior Lobe
Posterior Lobe
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13. Hormones & Breastfeeding
Biology: Life on Earth (Audesirk)
Chapter 32
Hormones & Breastfeeding
(2) Secretes oxytocin
The control of milk letdown by oxytocin during breastfeeding is regulated by feedback between a baby and its mother. The mammary gland is an exocrine gland. There, clusters of milk-producing cells surround hollow bulbs, where milk collects in lactating women. The bulbs are surrounded by muscle that can expel the milk through the nipple. Milk is expelled when suckling stimulates nerve endings that send a signal to the mother’s hypothalamus, causing the posterior pituitary to secrete oxytocin into the bloodstream. When oxytocin reaches the muscles that surround the milk ducts, it causes them to contract and expel milk through the nipple. This cycle continues until the infant is full and stops suckling. With the nipple no longer being stimulated, oxytocin release stops, the muscles relax, and milk flow ceases.
(3) Causes muscles to contract
(1) Sucking stimulates nerve endings that stimulate hypothalamus
(4) Delivers milk
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14. The Thyroid and Parathyroid Glands
Biology: Life on Earth (Audesirk)
The Thyroid and Parathyroid Glands
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Dietary iodine insufficiency can lead to goiter
(a) The thyroid and parathyroid glands wrap around the front of the larynx in the neck. (b) Goiter, a condition in which the thyroid gland becomes greatly enlarged, is caused by an iodine-deficient diet.
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15. Negative Feedback in Thyroid Gland Function
Biology: Life on Earth (Audesirk)
Negative Feedback in Thyroid Gland Function
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1. Cold stimulates hypothalamus to secrete releasing hormone 6 1
2. Triggers release of thyroid stimulating hormone (TSH)
Anterior Pituitary
1) Low body temperature or stress stimulates neurosecretory cells of the hypothalamus to secrete a releasing hormone. 2) That hormone triggers the release of thyroid-stimulating hormone (TSH) from the anterior pituitary. 3) TSH stimulates the thyroid gland to release thyroxine. 4) Thyroxine causes an increase in the metabolic activity of most body cells, generating heat. 5) Higher thyroxine levels in the blood inhibit the TSH-producing cells. 6) Higher body temperature inhibits the hypothalamic cells.
3. Stimulates thyroid to release thyroxine 2
Thyroid
4. Increases metabolic rate, generating heat 5
5. Thyroxine inhibits production of TSH
6. Higher temperature inhibits hypothalamus 3 4
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16. The Pancreas Controls Blood Glucose Levels
Biology: Life on Earth (Audesirk)
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eating
hunger
insulin-producing cells
high blood glucose
low blood glucose
pancreas
The Pancreas Controls Blood Glucose Levels
glucagon-producing cells in pancreas
glucagon
The pancreatic islet cells contain two populations of hormone-producing cells: one producing insulin; the other, producing glucagon. These two hormones cooperate in a two-part negative feedback loop to control blood glucose concentrations. High blood glucose stimulates the insulin-producing cells and inhibits the glucagon-producing cells; low blood glucose stimulates the glucagon-producing cells and inhibits the insulin-producing cells. This dual control quickly corrects high or low blood glucose levels.
insulin
body cells
body cells
cells burn fat
cells burn glucose
liver
Converts glucose to glycogen
Causes liver to convert glycogen to glucose
Lowers blood glucose
raises blood glucose
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17. Determining endocrine function
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Step 1 Removal of gland suspected of endocrine function
Step 2 Make extract of tissue and administer it to animals with hormone deficiency

18. Function example F. G. Banting and C. H. Best (1922)
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F. G. Banting and C. H. Best (1922)
1. Pancreas removed from dog
effects:
a) glucose content of blood rises rapidly
b) urine gives positive glucose test
c) nitrogen excretion elevated
d) death within 2 or 3 weeks
2. Extract made of pancreas.
3. Extract injected into diabetic dog, abnormalities reversed.

19. Biology: Life on Earth (Audesirk)
The Adrenal Glands
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Adrenal Cortex
Adrenal Medulla
Produces:
glucocorticoids,
testosterone,
aldosterone.
Produces:
epinephrine,
norepinephrine.
Atop each kidney sits an adrenal gland, which is a two-part gland composed of very dissimilar cells. The outer cortex consists of ordinary endocrine cells that secrete steroid homones. The inner medulla, derived from nervous tissue during development, secretes epinephrine and norepinephrine.
(kidney)
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20. Chapter 32
The End