8: Endocrine System
- Page ID
- 100062
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)- 8.1: Overview of the Endocrine System
- The endocrine system regulates long-term body processes by releasing hormones into the bloodstream, allowing signals to act on distant target organs over extended periods. Working closely with the nervous system, endocrine signaling maintains homeostasis by controlling growth, metabolism, reproduction, stress responses, and other vital functions through slower but longer-lasting chemical communication.
- 8.2: Hormones
- Hormones are chemical messengers that travel through the bloodstream but act only on target cells that possess the correct receptors. Their chemical structure determines how they are transported, where their receptors are located, and whether they trigger rapid signaling cascades at the cell membrane or directly alter gene expression inside the cell.
- 8.3: Review of the Negative Feedback Loop
- Negative feedback loops are the primary mechanism the body uses to maintain homeostasis by reversing changes that move conditions away from normal. Sensors detect a disturbance, the control center compares it to a set point, and effectors are activated to restore balance. This process is clearly seen in temperature regulation, where thermoreceptors and the hypothalamus work together to keep core body temperature within a narrow, healthy range.
- 8.4: The Major Endocrine Organs
- The major endocrine organs are specialized glands that release hormones into the bloodstream to regulate growth, metabolism, stress responses, reproduction, and fluid balance. Each gland has distinct hormonal functions, but they work together as an integrated system to maintain homeostasis throughout the body. Disruptions in hormone production or signaling can lead to endocrine disorders, highlighting the importance of precise hormonal control.
- 8.5: Pituitary Gland and Hypothalamus
- The hypothalamus–pituitary complex serves as the primary control center of the endocrine system, linking neural input to hormonal output. The hypothalamus monitors the body’s internal conditions and regulates the pituitary gland, which releases hormones that control other endocrine glands and key physiological processes. The anterior pituitary synthesizes and secretes its own hormones under hypothalamic control, while the posterior pituitary stores and releases hormones made in the hypothalamus.
- 8.6: Thyroid Gland
- The butterfly-shaped thyroid gland regulates metabolism, body temperature, growth, and development by producing the hormones T₃ and T₄ under the control of the hypothalamic–pituitary–thyroid feedback loop. Thyroid hormones increase the rate at which cells use energy and are essential for normal brain development, especially before and shortly after birth. The thyroid also releases calcitonin, which helps maintain calcium balance by lowering blood calcium levels.
- 8.7: Disorders of Thyroid Function- Hypo- and Hypersecretion
- Disorders of thyroid function occur when the gland produces too little or too much thyroid hormone, disrupting metabolism and homeostasis. Inadequate iodine intake or autoimmune conditions can lead to hypothyroidism, characterized by slowed body processes and elevated TSH, while autoimmune overstimulation, most commonly Graves disease, causes hyperthyroidism with accelerated metabolism.
- 8.8: Meet the Pancreas — Dual Roles in Digestion and Hormone Control
- The pancreas has dual roles as an exocrine gland that aids digestion and as an endocrine gland that regulates blood glucose levels. Specialized cells in the pancreatic islets release insulin and glucagon, two opposing hormones that work together to keep blood sugar within a narrow, healthy range. Disruption of this hormonal balance leads to diabetes mellitus, a common metabolic disorder with serious long-term consequences if untreated.
- 8.9: Adrenal Glands
- The adrenal glands are dual-function endocrine organs, regulating stress responses, metabolism, fluid balance, and blood pressure through hormone secretion. The adrenal cortex produces steroid hormones that support long-term homeostasis, while the adrenal medulla releases epinephrine and norepinephrine for rapid fight-or-flight responses. Imbalances in adrenal hormones can lead to serious endocrine disorders.