Endocrine System I: Superior Glands Homeostatic Mechanisms Endocrine System vs Nervous System Endocrine vs Exocrine Glands Types and Actions of Hormones Interaction of Hormones with Target Cells Effects of Hormones on Target Control Mechanisms of Endocrine Glands Endocrine Signaling as Simple/Complex Reflexes Major Superior Endocrine Organs Pituitary Anterior: GH, Pl, FSH, LH, TSH, ACTH Posterior: Oxytocin, ADH Thyroid: TH synthesis and release; Calcitonin Parathyroids: PTH

Homeostasis Maintenance of a stable internal environment = a dynamic state of equilibrium

Feedback Mechanisms Example of Negative feedback Receptor and Low blood glucose

Feedback Mechanisms Examples of Positive feedback

Endocrine System I: Superior Glands Homeostatic Mechanisms Endocrine System vs Nervous System Endocrine vs Exocrine Glands Types and Actions of Hormones Interaction of Hormones with Target Cells Effects of Hormones on Target Control Mechanisms of Endocrine Glands Endocrine Signaling as Simple/Complex Reflexes Major Superior Endocrine Organs Pituitary Anterior: GH, Pl, FSH, LH, TSH, ACTH Posterior: Oxytocin, ADH Thyroid: TH synthesis and release; Calcitonin Parathyroids: PTH

The Endocrine System A more broad-based and long-lasting communication system than the nervous system Uses chemical messages (hormones) that are released into the blood Hormones control several major processes Reproduction Growth and development Mobilization of body defenses Maintenance of much of homeostasis Regulation of metabolism

Comparing Two Control Systems Mode of Messaging Speed of Signaling Length of Response Time Range of Focus Nervous System Endocrine System Short duration; response stops in seconds or minutes Neuron “wiring” leading directly to and from target Narrow & specific, a few cells to part of one organ Rapid, in milliseconds Hormones travel through blood stream systemically Broad & general; many target tissues and organs stimulated collectively Long-lasting; minutes to days Slow; minutes, hours, or days

Endocrine System I: Superior Glands Homeostatic Mechanisms Endocrine System vs Nervous System Endocrine vs Exocrine Glands Types and Actions of Hormones Interaction of Hormones with Target Cells Effects of Hormones on Target Control Mechanisms of Endocrine Glands Endocrine Signaling as Simple/Complex Reflexes Major Superior Endocrine Organs Pituitary Anterior: GH, Pl, FSH, LH, TSH, ACTH Posterior: Oxytocin, ADH Thyroid: TH synthesis and release; Calcitonin Parathyroids: PTH

Glandular Epithelium Gland – one or more cells that secretes a particular product Two major gland types Endocrine gland Ductless Secretions are hormones Exocrine gland Empty through ducts to the epithelial surface Include sweat and oil glands

Types of Hormones Peptide-based hormones Steroid hormones Prostaglandins and catecholamines Insulin Growth hormone

Hormones as Chemical Messengers Endocrine gland (source) Target organs or glands Hormones move through the bloodstream to target organs

Endocrine System I: Superior Glands Homeostatic Mechanisms Endocrine System vs Nervous System Endocrine vs Exocrine Glands Types and Actions of Hormones Interaction of Hormones with Target Cells Effects of Hormones on Target Control Mechanisms of Endocrine Glands Endocrine Signaling as Simple/Complex Reflexes Major Superior Endocrine Organs Pituitary Anterior: GH, Pl, FSH, LH, TSH, ACTH Posterior: Oxytocin, ADH Thyroid: TH synthesis and release; Calcitonin Parathyroids: PTH

Hormone Interaction with Target Cells Hormones bind to receptors sticking out from the plasma membrane of target cells or within target cells growth factor insulin epinephrine Hormones Receptors Examples of receptors found in the plasma membrane of cells

Two Mechanisms of Hormone Action Non-steroid hormone action 1. Hormone binds to a membrane receptor; does not enter cell 2. Sets off a reaction where a G protein with bound GTP activates adenylate cyclase enzyme. 3. Adenylate cyclase produces cyclic AMP (second messenger) by converting ATP --> cAMP 5. cAMP, in turn, activates phosphorylating activation proteins (protein kinases) that trigger additional intracellular changes (enzyme activation, secretion, ion channel changes) to promote a specific response (A few peptide hormones activate Ca+2 release via second messengers in the PIP2 calcium signaling system). Adenylate Cyclase G protein cAMP Steroid hormone action Diffuses through the plasma membrane of target cells Enters the nucleus or binds to cytoplasmic receptor Binds to a specific protein within the nucleus if not already bound Binds to specific sites on the cell’s DNA Activates genes that result in synthesis of new proteins

Endocrine System I: Superior Glands Homeostatic Mechanisms Endocrine System vs Nervous System Endocrine vs Exocrine Glands Types and Actions of Hormones Interaction of Hormones with Target Cells Effects of Hormones on Target Control Mechanisms of Endocrine Glands Endocrine Signaling as Simple/Complex Reflexes Major Superior Endocrine Organs Pituitary Anterior: GH, Pl, FSH, LH, TSH, ACTH Posterior: Oxytocin, ADH Thyroid: TH synthesis and release; Calcitonin Parathyroids: PTH

Effects Caused by Hormones Changes in target cells by hormonal activation Changes in plasma membrane permeability or electrical state Synthesis of proteins, such as enzymes Activation or inactivation of enzymes Stimulation of mitosis Activation of transcription of certain genes Target cell activation depends on three factors Blood levels of the hormone Relative number of receptors on or in the target cell Affinity of binding between receptor and hormone

Target Cell Activation Hormones influence the number of their receptors Up-regulation—target cells form more receptors in response to the hormone Down-regulation—target cells lose receptors in response to the hormone Hormones are removed from the blood by Degrading enzymes Kidneys Liver Half-life—the time required for a hormone’s blood level to decrease by half

Control of Hormone Release Hormone levels in the blood are maintained by negative feedback A stimulus or low hormone levels in the blood triggers the release of more hormone Hormone release stops once an appropriate level in the blood is reached

Endocrine System I: Superior Glands Homeostatic Mechanisms Endocrine System vs Nervous System Endocrine vs Exocrine Glands Types and Actions of Hormones Interaction of Hormones with Target Cells Effects of Hormones on Target Control Mechanisms of Endocrine Glands Endocrine Signaling as Simple/Complex Reflexes Major Superior Endocrine Organs Pituitary Anterior: GH, Pl, FSH, LH, TSH, ACTH Posterior: Oxytocin, ADH Thyroid: TH synthesis and release; Calcitonin Parathyroids: PTH

Control Mechanisms of Endocrine Glands Hormonal: Chemical stimulus (i.e. endocrine glands are activated by other hormones Humoral: Changing blood levels of certain ions stimulate hormone release Neural: Nerve impulses stimulate hormone release; most are under control of the sympathetic nervous system

Endocrine Signaling (Reflexes) Simple Endocrine Reflex Involves only one hormone Controls hormone secretion by the heart, pancreas, parathyroid gland, and digestive tract Complex Endocrine Reflex Involves: One or more intermediary steps Two or more hormones (tropic hormones cause secretion of a second hormone in target glands) The hypothalamus Figure 9.3

Location of Major Endrocrine Organs Figure 9.3