1. Animal Structure and Function Organization of cells into systems that are specialized for particular functions. –Tissues- 4 general categories 1.Epithelial tissue 1.outer skin layers and internal protective coverings 2.Connective tissue 1.Bone, cartilage, blood 3.Nervous tissue 4.Muscle tissue

2. Animal Structure and Function Organ –A group of different tissues functioning together to perform a particular activity. –Example Heart –Consists of tissues from all four categories functioning together to pump blood through the body

3. Animal Structure and Function Organ system –Two or more organs working together to accomplish a particular task. –Example Digestive system –Coordinated activities of many organs Mouth, stomach, small intestine, large intestine, pancreas, and liver

4. Animal Structure and Function Homeostasis –Maintaining a stable, internal conditions within narrow limits –Negative feedback Sensing mechanism (receptor) –Detects a change in conditions beyond specific limits Control center (integrator) –Often a brain –Evaluates the change and activates a second mechanisms (effector) to correct the condition When the condition is corrected, the corrective action is discontinued.

5. Animal Structure and Function Positive feedback –An action intensifies a condition so that it is driven further beyond normal limits –Examples Labor contractions lactation

6. Endocrine signals trigger homeostatic mechanisms in target tissues Coordination and Control Functions of the Endocrine and Nervous System –Endocrine and Nervous systems coordinate the body’s activities. Endocrine cells secrete hormones in the bloodstream. Body cells with matching receptors respond to these signaling molecules. Neurons deliver signals via axons directly to target cells, which include other neurons, muscle cells, endocrine cells, and exocrine cells.

7. Simple Endocrine Pathway Endocrine cells secrete a hormone in response to a stimulus. The hormone travels in the bloodstream to target cells, –Which produces a response. Example: endocrine cells of the duodenum secrete the hormone secretin in response to a low pH caused by the entry of acidic stomach contents. –Target cells in the pancreas release bicarbonate, which raises the pH.

8. Neuroendocrine Pathways The hypothalamus often integrates nervous system and endocrine pathways (neuroendocrine pathways) –In response to nerve signals it receives from throughout the body, the hypothalamus sends hormonal to the pituitary gland, located at its base. Hypothalamic hormones are carried through short blood vessels called portal vessels to the anterior pituitary, where they trigger the synthesis and release of specific hormones. –Many of these hormones, called tropic hormones,, regulate other endocrine glands.

9. Neuroendocrine Pathways In a hormone cascade pathway, the hypothalamus secretes a hormone that stimulates or inhibits release of a particular anterior pituitary hormone. –This hormone, called a tropic hormone or tropin, acts on a target endocrine tissue, stimulating the release of the hormone that produces a response.

10. Neuroendocrine Pathways Example –In response to nervous stimulation signaling a drop in thyroid hormones levels, the hypothalamus secretes thyrotropin-releasing hormone (TRH), which stimulates the anterior pituitary to secrete thyrotropin or thyroid- stimulating hormone (TSH). –TSH stimulates the thyroid gland to release thyroid hormone, a hormone that stimulates and maintains metabolic processes.

11. Neuroendocrine Pathways Hormone cascade pathways are typically regulated by negative feedback. –In this case, high levels of thyroid hormone block the secretion of TRH and TSH.

12. Neuroendocrine Pathways The posterior pituitary, which is an extension of the hypothalamus, stores and releases two hormones by neurosecretory cells of the hypothalamus. –Neurosecretory cells are specialized neurons that secrete hormones, often neurohormones. In response to nerve signals from the nipples, the hypothalamus triggers the release of the neurohormone oxytocin, –Which stimulates the mammary glands to secrete milk.

13. Neuroendocrine Pathways Antidiuretic Hormone (ADH) is the other posterior pituitary hormone. Water balance

14. Neuroendocrine Pathways Feedback Regulation in Endocrine Pathways –Most endocrine pathways are regulated by negative feedback. –In positive feedback, the response to a stimulus reinforces the stimulus, leading to a further increase in response.

15. Pathways of water-soluble and lipid soluble hormones Water-soluble hormones bind to cell-surface receptors, –Triggering a series of changes, Called signal transduction, –That leads to a cellular response. Lipid-soluble steroid hormones through the plasma membrane and bind to cytosolic receptors, –which then move into the nucleus, the receptor- hormone complex then acts as a transcription factor and influence gene expression.

16. Pathways of water-soluble and lipid soluble hormones Example –Testosterone enters the cell and binds to its specific receptor, This complex then enters the nuclei of the target cells, binds to the DNA, and stimulates transcription of a specific gene.

17. Multiple Effects of Hormones A given signal can have different effects on different target cells as a result of different types of receptors (such as alpha and beta epinephrine receptors) or the specific signal transduction pathway and/or effector proteins present in the cell. –For example, epinephrine, secreted by the adrenal glands in response to stress, stimulates glucose release from liver cells, vasodilation of blood vessels supplying skeletal muscle cells, but vasoconstriction of blood vessels to the intestines.

18. Evolution of Hormone Function –The hormone prolactin has effects ranging from milk production and secretion in mammals, to delay metamorphosis in amphibians, to osmoregulation in fishes. The diversity of action in different vertebrates species suggest that prolactin is an ancient hormone whose functions diversified during the evolution of vertebrate groups.