1. All Multicellular Organisms Must Coordinate Their Functions
The many cells, tissues, and organs in the animal body need to communicate so that the whole organism can develop and function effectively
The endocrine system consists of different types of secretory cells that release a variety of signaling molecules called hormones

2. The Endocrine System
Animal hormones are produced by specialized cells that are often organized into discrete organs called endocrine glands
Endocrine glands release hormones into body fluids, which then carry these chemical messengers throughout the body
Some endocrine cells are embedded as single cells or clusters of cells within other specialized tissues and organs

3. The Endocrine System
The hypothalamus is responsible for coordinating the endocrine system and integrating it with the nervous system
The hypothalamus contains both neurons that interact with the brain and also endocrine cells that produce hormones

4. The Endocrine System
The hypothalamus makes releasing and inhibiting hormones that direct the pituitary to release another set of hormones
These hormones from the pituitary will travel through the circulatory system to regulate the various endocrine glands.

5. The Endocrine System
Hormones are often distributed through the body by the circulatory system and therefore move only as fast as blood is circulated
Hormones are effective in small amounts because they bind to target cells with great specificity and tenacity

6. Hormones and their Target Cell
A hormone released by one cell causes one or more specific responses in the target cells, which may lie in more than one type of tissue
Hormones can act on target cells by binding to plasma membrane receptors or intracellular receptors

7. Hormones and their Target Cell
A single hormone can produce a diversity of effects in a variety of potential target cells

8. Hormonal Signals to the Cell
Hormonal signals are amplified inside the target cell and alter key cellular processes
There are four main categories of cellular responses produces by a hormonal signal:
Changes in protein production
Changes in metabolism
Changes in the activity of the cytoskeleton
Changes in plasma membrane transport

9. Hormonal Signals to the Cell
Animals usually produce hormones in tiny amounts measured in micrograms
When hormone molecules bind to receptors in the target cell, they set in motion a chain of events that may activate thousands of protein molecules in that cell
Through signal amplification, just a few hormone molecules can have a substantial impact on the whole body

10. Hormonal Signals to the Cell
Signal transduction is the process in which a signal received by a membrane receptor is relayed within the cytoplasm to produce responses from the target cell
Notice the amplification of the singnal

11. Hormonal Signals to the Cell
Some hormones bind to receptors on the plasma membrane
Others, like steroids, are able to cross the plasma membrane and deliver the hormonal message within the cell

12. Specific Hormonal Processes we will Cover
Glucose homeostasis The fight-or-flight response Growth Menstruation

13. Glucose Homeostasis
Hormones that regulate homeostasis must act quickly to maintain a constant internal environment
Glucose homeostasis is controlled by the pancreas
The pancreas, function as endocrine glands and also as exocrine (ducted) glands
The pancreas contains clusters of endocrine cells called islet cells that produce and release insulin and glucagon

14. Glucose Homeostasis
Insulin and glucagon are hormones that act in opposite ways to maintain homeostasis in blood glucose levels
Insulin acts on target cells throughout the body, but especially in the liver, fat tissue, and skeletal muscles, signaling these cells to increase their uptake of glucose from the blood
Insulin= into cell out of blood
Causes decrease blood sugar
Glucagon= gone from cell into blood
Causes increased blood sugar

15. Figure 29.4 Balancing Levels of Glucose in the Blood
Two hormones—insulin and glucagon—work in opposite ways to regulate blood levels of glucose. The width of the red circuit indicates the relative amounts of glucose in the bloodstream at different times.

16. Disruption in Glucose Homeostasis: Diabetes
Too much glucose in the blood results in diabetes
Most cases of type 1 diabetes result from:
autoimmune damage to the islet cells preventing insulin production or
production of a defective form of insulin by the pancreas
Type 2 diabetes occurs when:
too little insulin is produced or
the receptors on target cells respond poorly to insulin

17. Short Term Control: Fight-or-Flight Response
The adrenals regulate the fight-or-flight response
The adrenal glands are a pair of endocrine glands that sit on top of the kidneys and release epinephrine and norepinephrine, which coordinate our response to sudden stress

18. Short Term Control: Fight-or-Flight Response
Epinephrine stimulates glycogen breakdown in liver and skeletal muscle cells, which raises blood glucose levels and in turn increases the speed and force with which the heart contracts

19. Regulating Long-Term Processes: Growth
The pituitary gland produces growth hormone (GH), which promotes the growth of bones and stimulates increases in muscle mass
Too much or too little GH can have lifelong consequences on an individual, resulting in a variety of conditions

20. Regulating Long-Term Processes: Reproduction
Animals rely on hormones to regulate nearly all aspects of reproduction
In humans, hormones influence nearly all aspects of sexual development and reproduction, including sperm production in males and the menstrual cycle of women

21. Sex Hormones Play a Role in Sexual Development before Birth
It is through the action of the hormones that a fetus develops into a male or a female
By the seventh week of the fetus’s development, the sex glands, or gonads, are producing the sex hormones
These sex hormones signal genes in their target cells to begin the process of sexual development
The gonads of both sexes produce estrogens, progestogens, and androgens in varying amounts

22. Sex Hormones Play a Role in Sexual Development before Birth
Estrogen produces female characteristics, while progestogens, including progesterone, create a suitable environment for a developing fetus
Androgens, such as testosterone, stimulate cells to develop the characteristics of maleness

23. Sex Hormones Coordinate Sexual Maturation at Puberty
GnRH
During puberty, the hypothalamus makes Gonadotropin Releasing Hormone (GnRH) that activates the production of gonadatropins made in the pituitary gland
These gonadatropins, Luteinizing hormone (LH) and follicle-stimulating hormone (FSH) coordinate the development of sperm in males and play a role in regulating the menstrual cycle in females

24. Sex Hormones Coordinate the Menstrual Cycle
In humans females, individual eggs mature and are released in a hormone-driven sequence of events known as the menstrual cycle
The menstrual cycle is marked by a succession of hormones that stimulate the release of an egg and prepare the uterine lining to grow and thicken in preparation for a potential pregnancy
Between 40 and 50 years of age, a drop in the levels of estrogen and progesterone results in menopause, in which the menstrual cycle ceases permanently

25. Sex Hormones Coordinate the Menstrual Cycle
The menstrual cycle is marked by a succession of hormones that stimulate the release of an egg and prepare the uterine lining to grow and thicken in preparation for a potential pregnancy

26. Sex Hormones Coordinate the Menstrual Cycle
Figure 29.9 The Human Menstrual Cycle Depends on the Sequential Release of Several Hormones
Follicle-stimulating hormone (FSH) launches a new menstrual cycle by stimulating the growth of ovarian follicles. Developing follicles produce estrogen. When estrogen levels reach a certain threshold, they trigger release of luteinizing hormone (LH) from the pituitary, which triggers ovulation. An estrogen, especially the large amounts of progesterone secreted by the corpus luteum, stimulates a buildup of the uterine lining in preparation for a possible pregnancy. If fertilization fails to occur, the corpus luteum dies after about 14 days, hormone concentrations crash, and the uterine lining is sloughed off.