1. Maintaining Balance (Homeostasis)

2. Endocrine system Nervous system Homeostasis
The process by which our body maintains an internal balance of all body systems.
Usually it is regulated by one of two major systems
Endocrine system
Nervous system

3. The Endocrine System works with the Nervous System
Two systems coordinate communication throughout the body: the endocrine system and the nervous system.
The endocrine system secretes hormones that coordinate slower but longer-acting responses including reproduction, development, energy, metabolism, growth, and behavior.
The nervous system conveys high-speed electrical signals along specialized cells called neurons; these signals regulate other cells.
The endocrine system is made of a series of glands that produce chemicals called hormones. A number of glands that signal each other in sequence are usually referred to as an axis, for example, the hypothalamic-pituitary-adrenal axis.

4. Coordination of Endocrine and Nervous Systems in Vertebrates
The hypothalamus receives information from the nervous system and initiates responses through the endocrine system.
Attached to the hypothalamus is the pituitary gland, composed of the anterior pituitary and the posterior pituitary.
The anterior pituitary makes and releases hormones under regulation of the hypothalamus.
The posterior pituitary stores and secretes hormones that are made in the hypothalamus.
Ask students if they know the locations of the hypothalamus, anterior pituitary gland and posterior pituitary gland. They illustrated on the next slide.
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5. Feedback Loops

6. Types of Feedback
NEGATIVE FEEDBACK
POSITIVE FEEDBACK

7. Feedback Regulation
A negative feedback loop inhibits a response by reducing the initial stimulus, thus preventing excessive pathway activity. NEGATIVE= OPPOSITE
Positive feedback reinforces a stimulus to produce an even greater response. POSITIVE= INCREASE OUTPUT
For example, in mammals oxytocin causes the release of milk, causing greater suckling by offspring, which stimulates the release of more oxytocin.

8. The Process of Communication: Signal-Transduction Pathway
Three stages of the Signal-Transduction Pathway
1. reception
2. transduction
3. response
Most cell communication involves three basic steps, reception, transduction and response. Today, we will see this signal transduction pathway being initiated by hormones. We will look at specific examples of how communication is completed using this pathway.

9. Typical Signal Transduction Pathway
The diagram shows a typical signal transduction pathway. In our example today, we will consider a ligand or signal molecule to be a hormone produced by one of the endocrine glands we discussed earlier.
The word transduce means to convert. A signal transduction pathway “converts” the original signal molecule into a cellular response. This conversion requires several intermediate messenger molecules (sometimes called “second messengers”), so the signal is actually “converted” or transduced several times, as shown in the blue box above labeled Transduction. The concept of signal transduction pathways will be seen over and over again in AP Biology and is certain to be on the exam.

10. Ligand = Chemical Messenger
Three major classes of molecules function as hormones in vertebrates (ligands)
Polypeptides (proteins and peptides)
Amines derived from amino acids
Steroid hormones
The hormones we consider today fall into three main categories. Polypeptides, amines and steroid hormones. The chemical make up of each is different so it is not surprising that these ligands impact cells very differently.

11. Cellular Response Pathways
Water- and lipid-soluble hormones differ in their paths through a body
Water-soluble hormones are secreted by exocytosis, travel freely in the bloodstream, and bind to cell-surface receptors
Lipid-soluble hormones diffuse across cell membranes, travel in the bloodstream bound to transport proteins, and diffuse through the membrane of target cells
Protein/peptide hormones are released by exocytosis, steroid hormones are able to leave their secretory cells by way of diffusion. Once in the blood stream, both travel to their target cells.. Upon arrival at the target cell, these two types of hormones have different methods of communicating with the target cells.

12. Water- soluble hormone Lipid- soluble hormone
SECRETORY CELL
Water- soluble hormone
Lipid- soluble hormone
VIA BLOOD
Transport protein
Signal receptor
Receptor location varies with hormone type. Notice that the water soluble hormones, such as epinephrine or insulin, bind with a membrane bound receptor protein while the lipid soluble hormone can pass directly through the membrane of the target cell to dock with an intracellular receptor..
TARGET CELL
Signal receptor
NUCLEUS
(a)
(b)

13. Water- soluble hormone Lipid- soluble hormone
SECRETORY CELL
Water- soluble hormone
Lipid- soluble hormone
VIA BLOOD
Transport protein
Signal receptor
Receptor location varies with hormone type.
TARGET CELL OR
Signal receptor
Cytoplasmic response
Gene regulation
Cytoplasmic response
Gene regulation
NUCLEUS
(a)
(b)

14. Pathway for Water-Soluble Hormones
Binding of a hormone to its receptor initiates a signal transduction pathway leading to responses in the cytoplasm, enzyme activation, or a change in gene expression

15. Specific Example Notice the presence of the second messenger
Go through the numbered steps in this pathway emphasizing the presence of a second messenger and the amplification of the response inside the cell. Click the blue tip of the arrow to link to a video clip that explains the process of amplification. (The link will only be active in “presentation” mode). Once the video has been viewed ask students to discuss the role of the second messenger and the value of amplification.
Click here to view the animation

16. Pathway for Lipid-Soluble Hormones
The response to a lipid-soluble hormone is usually a change in gene expression
Steroids, thyroid hormones, and the hormonal form of vitamin D enter target cells and bind to protein receptors in the cytoplasm or nucleus
Protein-receptor complexes then act as transcription factors in the nucleus, regulating transcription of specific genes

17. Steroid Hormone Example: Testosterone
Explain the pathway of a steroid hormone using testosterone as an example. Pick a male student with a moustache as your example and explain how testosterone from the testes is secreted and moves into the blood stream The testosterone would move around the male’s body. However, follicular cells have testosterone receptors and respond to the presence of this hormone. Once inside the follicle cell of the lip, the testosterone stimulates the cell to produce keratin by “turning on” the segment of DNA that codes for the protein.”

18. In this case the protein produced could be keratin.

19. Simple Hormone Pathways
Hormones are released from an endocrine cell, travel through the bloodstream, and interact with specific receptors within a target cell to cause a physiological response

20. Simple Hormone Pathways
For example, the release of acidic contents of the stomach into the duodenum stimulates endocrine cells there to secrete secretin.
This causes target cells in the pancreas, a gland behind the stomach, to raise the pH in the duodenum.
The increased pH results in a decrease of secretin secretion.
The pancreas releases sodium bicarbonate to raise the pH which neutralizes acid chyme from the stomach thereby raising the pH (making the environment more alkaline).

21. Simple Hormone Pathways
Example
Pathway
Low pH in duodenum
Stimulus
Endocrine cell
S cells of duodenum secrete the hormone secretin ( ).
Negative feedback
In this simple endocrine pathway a low duodenum pH stimulates endocrine cells in the small intestine (S cells) to secrete the hormone secretin. Secretin travels through the blood stream to its target cells (pancreatic cells) causing them to release bicarbonate solution resulting in an increase in the pH. The increase serves as a negative feedback mechanism resulting in lower levels of secretin released.
Hormone
Blood vessel
Target cells
Pancreas
Response
Bicarbonate release

22. Negative Feedback
Secretin secretion regulation is an example of negative feedback in action.

23. An example of positive feedback
Oxytocin stimulates the uterus to contract. This causes the placenta to make more prostaglandins which signal more vigorous uterine contractions which cause more oxytocin to be produced thereby amplifying the contraction process.

24. Insulin and Glucagon: Control of Blood Glucose
Hormones work in pairs to maintain homeostasis.
Insulin (decreases blood glucose) and glucagon (increases blood glucose) are antagonistic hormones that help maintain glucose homeostasis.
The pancreas has clusters of endocrine cells called pancreatic islets with alpha cells that produce glucagon and beta cells that produce insulin.

25. While it is not necessary to memorize every cell type or gland found within the system, it will be helpful to recognize the endocrine glands and the function of the hormones produced by select glands to use as examples of how both short and long distance chemical communication occurs.
In addition to the specialized endocrine organs mentioned above, many other organs that are part of other body systems, such as the kidney, liver, heart and gonads, have secondary endocrine functions. For example the kidney secretes endocrine hormones such as erythropoietin and renin.

26. Body cells take up more glucose.
Figure 45.13
Insulin
Body cells take up more glucose.
Beta cells of pancreas release insulin into the blood.
Liver takes up glucose and stores it as glycogen.
STIMULUS: Blood glucose level rises (for instance, after eating a carbohydrate-rich meal).
Blood glucose level declines.
Homeostasis: Blood glucose level (70–110 mg/100mL)
Describe the actions that occur when blood glucose levels decline and when they rise. Glucagon and insulin are paired hormones that work together to maintain blood glucose levels between 70 and 110 mg/100mL
STIMULUS: Blood glucose level falls (for instance, after skipping a meal).
Blood glucose level rises.
Liver breaks down glycogen and releases glucose into the blood.
Alpha cells of pancreas release glucagon into the blood.
Glucagon

27. Out of Balance: Diabetes Mellitus
Diabetes mellitus is perhaps the best-known endocrine disorder.
It is caused by a deficiency of insulin or a decreased response to insulin in target tissues.
It is marked by elevated blood glucose levels.
Ask students to explain how a lack of insulin leads to elevated levels of glucose in the blood. Then ask them to suggest reasons this increased level of glucose is harmful to the person with diabetes.

28. Out of Balance: Diabetes Mellitus
Type 1 diabetes mellitus (insulin-dependent) is an autoimmune disorder in which the immune system destroys pancreatic beta cells.
Type 2 diabetes mellitus (non-insulin-dependent) involves insulin deficiency or reduced response of target cells due to change in insulin receptors.
Type 1 has in the past been referred to as Juvenile Diabetes. Just as a point of interest, the incidence varies from 8 to 17 per 100,000 in Northern Europe and the U.S. with a high of about 35 per 100,000 in Scandinavia to a low of 1 per 100,000 in Japan and China.

29. Action of Insulin
When insulin receptors respond properly to the presence of insulin, the result is the transport of glucose from outside the cell to inside the cell via transport protein. People with Type I diabetes do not produce sufficient insulin to maintain a proper level of glucose transport. The disorder is typically treated by providing the patient with insulin.

30. Increases Ca2 uptake in intestines Active vitamin D
Stimulates Ca2 uptake in kidneys
PTH
Parathyroid gland (behind thyroid)
Blood calcium levels need to be approximately 10 mg/100 mL. Two hormones, PTH and calcitonin work in tandem to regulate the blood glucose in mammals.
Stimulates Ca2 release from bones
STIMULUS: Falling blood Ca2 level
Blood Ca2 level rises.
Homeostasis: Blood Ca2 level (about 10 mg/100 mL)

31. Homeostasis in blood calcium levels
PTH increases the level of blood Ca2+
It releases Ca2+ from bone and stimulates reabsorption of Ca2+ in the kidneys.
It also has an indirect effect, stimulating the kidneys to activate vitamin D, which promotes intestinal uptake of Ca2+ from food.
Calcitonin decreases the level of blood Ca2+
It stimulates Ca2+ deposition in bones and secretion by kidneys.
Describe how calcitonin and PTH work together to maintain blood calcium levels. High calcium levels can cause mental confusion, nausea, fatigue. Low blood calcium causes muscle cramps, spasms, twitching and tingling in the fingers and around the mouth.

32. Practice Blood calcium levels rise Blood calcium level falls
Parathyroid releases PTH
Thyroid releases calcitonin
If calcium rises above set point
If calcium falls below set point
Ask students to match the events on the right with the numbers in the picture. The next slide shows the answers.

33. Solution 3. Blood calcium level falls 5. Parathyroid releases PTH
1. Blood calcium levels rise
3. Blood calcium level falls
5. Parathyroid releases PTH
2. Thyroid releases calcitonin
6. If calcium rises above set point
4. If calcium falls below set point
The two hormones, calcitonin and parathyroid hormone work together to keep blood calcium levels within a homeostatic range.(10 mg/100 mL)

34. Anterior and Posterior Pituitary
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35. Posterior Pituitary Hormones
The two hormones released from the posterior pituitary act directly on nonendocrine tissues.
Oxytocin regulates milk secretion by the mammary glands and stimulates contraction of the uterus.
Antidiuretic hormone (ADH) promotes retention of water by the kidneys.
Discuss with students the implications of alcohol and diabetes on ADH. Alcohol consumption reduces ADH production resulting in an increase in production of urine. In diabetes insipidus, the pituitary gland produces insufficient ADH which again increases the production of urine.

36. Production and Release of Posterior Pituitary Hormones
Neurosecretory cells of the hypothalamus
Hypothalamus
Neurohormone
Axons
Posterior pituitary
Production and release of posterior pituitary hormones.
Anterior pituitary
HORMONE
ADH
Oxytocin
Kidney tubules
TARGET
Mammary glands, uterine muscles

37. Anterior Pituitary Hormones
Hormone production in the anterior pituitary is controlled by releasing and inhibiting hormones from the hypothalamus.
For example, prolactin-releasing hormone from the hypothalamus stimulates the anterior pituitary to secrete prolactin (PRL), which has a role in milk production and secretion.
Another example is Thyroid Stimulating Hormone (TSH), which stimulates the thyroid gland to produce thyroxine which stimulates and maintains metabolic processes.
Ask students if they know what “lactose intolerant” means. Don’t miss the opportunity to make the connection between lactose (milk sugar) and prolactin.

38. Liver, bones, other tissues
Figure 45.16
Tropic effects only: FSH LH TSH ACTH
Neurosecretory cells of the hypothalamus
Nontropic effects only: Prolactin MSH
Nontropic and tropic effects: GH
Hypothalamic releasing and inhibiting hormones
Portal vessels
Endocrine cells of the anterior pituitary
Production and release of anterior pituitary hormones. “Tropic” hormones are those that target other endocrine glands; so “tropic effects” above refers to hormones produced by the anterior pituitary that in turn stimulate/control other endocrine glands.
Posterior pituitary
Pituitary hormones
HORMONE
FSH and LH
TSH
ACTH
Prolactin
MSH GH
TARGET
Testes or ovaries
Thyroid
Adrenal cortex
Mammary glands
Melanocytes
Liver, bones, other tissues

39. Table 45.1a
Major Human Endocrine Glands and Some of Their Hormones. Have students “pick a favorite” from either this slide or the next so they can use it as an example in their free-response writing.

40. Table 45.1b
Major Human Endocrine Glands and Some of Their Hormones

41. Thyroid Regulation: A Hormone Cascade Pathway
A hormone can stimulate the release of a series of other hormones, the last of which activates a nonendocrine target cell; this is called a hormone cascade pathway.
The release of thyroid hormone results from a hormone cascade pathway involving the hypothalamus, anterior pituitary, and thyroid gland.
Hormone cascade pathways typically involve negative feedback.

42. Figure 45.17
Example
Pathway
Stimulus
Cold
Hypothalamus  
Work with a partner to explain how our body responds to a stimulus indicating that the body is cold. Label and describe the pathway and explain how it is regulated via negative feedback.
Negative feedback
Target cells
Increased cellular metabolism
Response

43. Figure 45.17
Example
Pathway
Stimulus
Cold
Sensory neuron
Hypothalamus 
Hypothalamus secretes thyrotropin-releasing hormone (TRH).
Neurosecretory cell
Releasing hormone
Blood vessel 
Anterior pituitary secretes thyroid-stimulating hormone (TSH, also known as thyrotropin).
Anterior pituitary
How accurate were you?
Tropic hormone
Negative feedback
Thyroid gland secretes thyroid hormone (T3 and T4).
Endocrine cell
Hormone
Target cells
Body tissues
Increased cellular metabolism
Response