ENDOCRINE-SYSTEM.docx

**The Endocrine system** - is a complex regulatory system in the human body that controls various physiological processes through the secretion of hormones Endocrine = regulation release of hormones chemical messenger **Characteristics** - composed of endocrine glands and specialized e...

**The Endocrine system** - is a complex regulatory system in the human body that controls various physiological processes through the secretion of hormones Endocrine = regulation release of hormones chemical messenger **Characteristics** - composed of endocrine glands and specialized endocrine cells located throughout the body - hormones then travel through the general blood circulation to target tissues or effectors. - the target tissues are specific sites where hormones produce a particular response. **Chemical communication.** - in the endocrine system relies on specific principles that govern the release and action of hormones. These principles ensure that the endocrine system can effectively regulate various physiological processes 1. Autocrine 2. Paracrine 3. Neurotransmitter 4. Endocrine **Principles of chemical communication** **Hormone secretion** - Hormones are chemical messenger produced by specialized endocrine glands and released into the bloodstream **Target cells** - Hormones travel through the blood stream to reach specific target cells or organs. - Cells have receptors on their surface or within their cytoplasm or nucleus that are capable of recognizing and binding to the hormone. **Specificity** - Hormones are highly specific in their actions. Each hormone typically interacts only with cells that possesses the appropriate receptors for that particular hormone **Feedback loops** - many endocrine processes are regulated by negative feedback loops. When a hormone reaches its desired level, it triggers signals to stop its production or secretion. **Hormone concentration** - The concentration of a hormone in the bloodstream can haven different effects. In some cases, hormones have effects at very low concentration, while in others. **Half-life** - vary in their duration of action. Determined by their half-life, some, hormones have a short half life and exert rapid, transient effects, while others have a longer half life and produce more sustained actions. **Synergy or Antagonism** - Synergistic effects occur when two or more hormones work in together to enhance a response. Antagonistics effect involve hormones that oppose each others actions, leading to a balanced regulation of processes. **Regulation by nervous system** - The nervous system can influence hormone secretion especially in response to immediate and acute stressors. **Hormone clearance** - Are eventually removed prom the bloodstream by mechanisms such as metabolic breakdown in liver, excretion by the kidneys or uptake by target calls **Hormone transport** - Some hormones require binding proteins in the bird h be carried effectively while others can travel freely. The presence of these binding proteins can influence hormone availability and activity. **Hormones** **Lipid-soluble hormones** - Are degraded slowly and are not rapidly eliminated from the circulation - Are small molecules and are insoluble in water-based fluids, such as the plasma of the brain **Water-soluble hormones** - Can dissolve in blood, many circulate as free-hormones - They take slower to diffuse from the blood stream to the tissue space - Tend to diffuse from the blood into the tissue spaces more slowly **Control of Hormone Secretion** **A Stimulation of Hormone Release** 1. **Control by Humoral Stimuli** - other hormones are released when the blood vessels of a certain chemical changes - are sensitive to the blood levels of a particular substance, such as glucose, calcium, or sodium. 2. **Control by Neural Stimuli** - Following action potentials, neurons release a transmitter into the synapse with the cells that produce the hormone 3. **Control by Hormonal Stimuli** - It occurs when a hormone is secreted that, in turn stimulates the secretion of other hormones **B. Inhibition of Hormone Release** 1. **Inhibition of Hormone Release by Humoral stimuli** - when a hormone's release is sensitive to the presence of a humoral stimulus. - exists a companion hormone whose release is inhibited by the same humoral stimulus 2. **Inhibition of Hormone Release by Neural Stimuli** - if the neurotransmitter is inhibitory, the target endocrine gland does not secrete its hormone. 3. **Inhibition of Hormone Release by Hormonal Stimuli** - release of specific hormone, inhibit the release of other hormones - most common mode of hormone regulation. **Regulation of Hormone levels in the Blood** **Negative feedback** - the hormone may inhibit the action of other stimulatory hormones to prevent the secretion of the hormone in question. - it is a self-limiting system **Positive feedback** - Promote the synthesis and secretion of the tropic hormone in addition to stimulating that target cell, in turn, this stimulates - self-propagating system **Hormones Receptors and Mechanism of Action** - hormones exert their actions by binding to proteins called **receptors** - a hormone can stimulate only the cells that have the receptor for that hormone. - Receptor site - Specificity - The portion of each receptor molecule where a hormone binds is called a **reception site.** - Membrane bound and Nuclear Receptors - The tendency for each type of hormone is to bind **Classes of Receptors** 1. **Lipid-soluble hormones bind to nuclear receptors** - Tend to be relatively small and are all nonpolar - Diffuse through cell membrane and bind to nuclear receptors, which are most often found in the cell nucleus 2. **Water-soluble hormones bind to membrane- bound receptor** - are polar molecules and cannot pass through the cell membrane - they interact with membrane - bound receptors, which are proteins that extend the cell membrane, with their hormone binding sites exposed in the cell membranes outer surface. **Action of Nuclear Receptors** - The receptors that bind to DNA have fingerlike projections that recognize and bind to specific nucleotide sequences in the DNA called **hormone response elements.** - The combination of the hormone and its receptor forms a complex binds to the hormone-response element, it regulates the transcription of specific messenger ribonucleic **Membrane-Bound Receptors and Signal Amplification** - are examples of **membrane proteins** - These receptions activate responses in two way: **(1) some receptors alter the activity of a proteins at the inner surface of the cell membrane, (2) other receptors directly alter the activity of intracellular enzymes.** - Activation of G proteins, or intracellular enzymes, elicits specific responses in cells, including the production of molecules called **second messenger.** - Second messenger system. Coordinated set of events when the second manager then activates specific cellular processes in response to the hormone - are chemical messengers produced by specialized endocrine glands and tissues. - released into the bloodstream and travel to target cells or organs, where they exert their effects **Endocrine glands** - The major endocrine glands in the body include the **pituitary gland, thyroid glands, parathyroid glands, adrenal glands, pancreas, ovaries (in females), and testes (in male)**. - Each gland produces specific hormones that regulate various bodily functions. **Regulation** - The endocrine system plays a crucial role in **maintaining homeostasis**, which is the body's ability to balance and regulate internal conditions, such as blood pressure blond sugar levels, and metabolism. **Hypothalamus and Pituitary Gland** - The hypothalamus in the brain controls the pituitary gland, often referred to as the **\"masters gland\"**. - The pituitary glands releases hormones that stimulate other endocrine glands to release their hormones, thus coordinating various physiological various **Infundibulum** - what connects the pituitary and hypothalamus. **Pituitary Gland** - location: base of the brain, housed in a bony stricture called the **sella turcia** - Structure: Divided into two lobes - the **anterior pituitary (adenohypophisis)** and the **posterior pituitary (neurohypophysis)** **Hypothalamus** - **Location**: just above the brainstem - **Structure**: Though not a gland, the hypothalamus is crucial in endocrine regulation. it produces releasing and inhibiting hormones that the pituitary glands secretion. **Thyroid gland** - The thyroid Gland produces hormones that regulate metabolism and play a role in energy production, body temperature, and growth, and development. - **Location**: Front of the neck, below the larynx (rice box) - **Structure**: compared of two lobes connected by a narrow isthmus consists of follicles, that produce and store thyroid hormones **Parathyroid Gland** - These glands produce parathyroid hormone (PTH), which regulates calcium and phosphate levels in the blood, crucial for bone health and nerve and muscle function. - **Located**: Four small glands located on the posterior surface of the thyroid gland. - **Structure**: usually there are four parathyroid glands, each about the size of a grain of rice. **Adrenal glands** - Secrete hormones like adrenaline and cortisol, which help the body responds to stress, regulate blood pressure, and control inflammation. - **Location:** situated on top of each kidney. - **Structure:** each adrenal gland has an outer cortex and an inner medulla **Pancreas** - Produces insulin and glucagon, which regulate blood sugar levels. Insulin lowers blood sugar levels while glucagon raises them. - **Location:** Behind the stomach - **Structure:** Has both endocrine and exocrine functions - Endocrine portion consists of clusters of cells called the **islets of langerhans**, which produces insulin and glucagon. **Ovaries** progesterone, estrogen - menstrual cycle, pregnancy, and secondary sexual characteristics - LH & FSH received by ovary - location: lower right & left abdomen above the uterus - Paired organs that produce estrogen & progesterone, influencing the menstrual cycle & reproductive functions **Testes** produce testosterone - location: in the scrotum - Paired organs influencing male sexual characteristics and reproductive functions. **TESTES** 1. Testosterone - found in most cells 2. Inhibin - anterior pituitary glands - Inhibits FSH **OVARIES** 1. Estrogen 2. Progesterone 3. Inhibin - Inhibits FSH 4. Relaxin - increases flexibility of connective tissue in pelvic area (symphysis pubis) **PINEAL GLAND** - secretes hormones that act on the hypothalamus & gonads to inhibit reproductive function, such as inhibiting secretion of reproductive hormones - deep within the brain attached to the roof the 3^rd^ ventricle - to secretes melatonin, involved in the regulation of the circadian rhythms & steep-wake cycle **THYMUS** - secretes thymosin - development of IT cells (WBC) - important for immune function - plays a role in the development & maturation of immune system. **EFFECTS OF AGING** - Aging can have a significant impact on the endocrine system, which is responsible for producing & regulating hormones - Varies from person to person **1. HORMONE PRODUCTION** - as Individuals age, the production of certain hormones can decrease - growth, sex hormones, thyroid hormones. 0 **2. THYROID FUNCTION** - Hypothyroidism -- underactive thyroid - Symptoms: fatigue, weight gain, cold intolerance - common in older adults **3.ANDROPAUSE (MEN)** - Gradual decline in sperm production and testosterone levels **4. MENOPAUSE (WOMEN)** - late 40s -- early 50s - Significant decline in estrogen & progesterone production - low chance of pregnancy **5. INSULIN SENSITIVITY** - Aging is often associated with a decrease in insulin sensitivity - contribute to the development of type 2 diabetes - can result from various factors, including changes in body composition & lifestyle **6. CORTISOL REGULATION** - Dysregulation of cortisol can have various effects on the body, including susceptibility to stress-related condition & changes in metabolism **7.) BONE DENSITY** - Decrease in bone density & an increased risk of osteoporosis - parathyroid hormones and calcitonin regulates Ca2+ levels **8.) CARDIOVASCULAR CHANGES** - Hormonal changes, such as decrease in estrogen during menopause, can impact cardiovascular health. - Reduced estrogen levels can lead to an increased risk of heart disease **9.) COGNITIVE FUNCTION** - Some hormones, like cortisol & certain sex hormones can influence cognitive function & mood - cognitive decline & mood disorders **10.) BODY COMPOSITION** - decrease in muscle mass - increase in body fat **11.) PITUITARY FUNCTION** - Regulates many hormonal functions - may experience changes with age - potentially affecting the overall balance of hormone production & regulation