E. Seminario 5.A Adrenal. UA2. FMED. UBA

Name: E. Seminario 5.A Adrenal. UA2. FMED. UBA
Uploaded: 2022-03-12T03:32:55.000Z
Duration: 1 h 40 min 44 s

Overview of Adrenal Glands and Hormones

Introduction to the Seminar

The speaker, Dr. Osvaldo Pons, introduces the topic of adrenal glands and hormones in the fourth seminar on endocrine physiology.

Emphasis is placed on understanding the anatomy and function of adrenal glands located at the superior poles of both kidneys.

Anatomy and Blood Supply

The right adrenal gland drains directly into the inferior vena cava, while the left drains into the renal vein, which is crucial for clinical practice.

A tomographic cut can help locate adrenal glands; an example includes a benign adenoma increasing gland size.

Histological Structure

The adrenal gland consists of two main tissues: mesodermal (cortex) and neuroectodermal (medulla) origins. Histological cuts show distinct differentiation between cortex and medulla regions.

The cortex is divided into three zones: zona glomerulosa, zona fasciculata, and zona reticularis, each with unique histological characteristics.

Blood Flow Dynamics

Blood flow within the adrenal gland forms plexuses that connect different regions with a centripetal arterial flow from capsule to interior areas where steroid concentration occurs. A small centrifugal venous flow allows hormonal interaction among zones.

Functions of Adrenal Cortex Regions

Cortical Zones Overview

Zona glomerulosa primarily produces mineralocorticoids like aldosterone; this zone's role is critical in human physiology compared to other species where different steroids may predominate.

Zona fasciculata synthesizes glucocorticoids such as cortisol but can also produce some androgenic activity under certain conditions.

Hormonal Synthesis Pathways

All steroid hormones are synthesized from cholesterol via specific enzymatic pathways starting with pregnenolone formation in mitochondria; this process involves several key enzymes including 17-hydroxylase and 21-hydroxylase for further transformations into active hormones like cortisol or aldosterone.

Clinical Relevance of Hormonal Production

Importance of Enzymatic Actions

Enzymes play a vital role in converting precursors into active hormones; for instance, progesterone transforms into corticosteroids through various hydroxylation processes leading to cortisol production as a primary glucocorticoid in humans.

Summary of Androgen Production

Androgens and Their Biosynthesis

Overview of Androgen Production

The adrenal gland produces androgens, including dehydroepiandrosterone (DHEA), androstenedione, and a smaller amount of 17-hydroxyprogesterone.

These androgens are precursors for testosterone synthesis, which can further convert to dihydrotestosterone (DHT).

Cholesterol serves as the starting material for steroid hormone biosynthesis, with LDL cholesterol being converted into free cholesterol in the mitochondria.

Hormonal Functions and Types

Key adrenal hormones include cortisol, corticosterone, and synthetic glucocorticoids like cortisone; cortisol has significant mineralocorticoid activity.

Cortisol is produced daily at approximately 8-25 mg, while aldosterone production is around 150 micrograms per day.

Hormonal Concentration and Activity

Only about 10% of circulating cortisol is free; the rest binds to proteins such as transcortin or albumin.

The free fraction of hormones is crucial for biological activity since it interacts directly with receptors.

Metabolism of Cortisol

Cortisol maintains a metabolic equilibrium with cortisone; both can interconvert through enzymatic processes.

Approximately 10% of steroids metabolized relate specifically to cortisol metabolism; most are related to other steroid hormones.

Regulation of Adrenal Gland Function

Stimuli for Cortisol Production

The adrenal cortex's secretion of cortisol is stimulated by adrenocorticotropic hormone (ACTH), produced by the pituitary gland.

Neurohormones from the hypothalamus also influence ACTH release, including corticotropin-releasing hormone (CRH), antidiuretic hormone (ADH), angiotensin II, and others.

Activation and Modulation of the HPA Axis

Circadian Rhythm and Stress Response

The activation of the hypothalamic-pituitary-adrenal (HPA) axis can be modulated by various factors, including stress, and follows a circadian rhythm. This system is regulated through inhibition and feedback mechanisms in both the pituitary gland and hypothalamus.

Loss of this inhibitory regulation can disrupt adrenal axis function, leading to specific pathologies. The modulation of corticotropin-releasing hormone (CRH) involves stimulation from other regions of the pituitary as well as the autonomic nervous system.

CRH has a negative modulatory effect due to cortisol but is also influenced by important inhibitory neurotransmitters like gamma-aminobutyric acid (GABA), which is stimulated by norepinephrine.

Hormonal Dynamics Throughout the Day

Various neurotransmitters from different brain nuclei stimulate CRH production in the hypothalamus, activating both adrenal axis and sympathetic nervous systems.

The circadian rhythm for CRH shows that stimulation begins between 1 AM and 3 AM when cortisol levels are at their lowest, allowing for increased CRH activity during these hours.

Following this early morning activation, there is a sustained increase in adrenocorticotropic hormone (ACTH) production peaking around 6 or 7 AM, followed closely by a peak in cortisol production.

Daily Fluctuations in Hormone Levels

After reaching its peak in the morning, ACTH leads to an increase in cortisol levels that starts to decline around noon but rises again later in the afternoon at lower levels compared to morning peaks.

This daily fluctuation establishes a pattern where maximum hormone levels occur early in the day while subsequent increases are significantly lower than those observed earlier.

Influences on Circadian Rhythm Establishment

The establishment of this circadian rhythm occurs over years, typically solidifying between ages 7 to 10. Disruptions can arise from light exposure or irregular sleep patterns associated with night shifts or rotating schedules.

Such disruptions lead to altered glucocorticoid functions and physiological changes that may result in various health issues related to hormonal imbalances.

Molecular Mechanisms Behind Corticotropin Activation

At a molecular level, corticotropin activation involves energy systems acting on membrane receptors that activate pathways leading to cyclic AMP production via phospholipase C signaling.

Antidiuretic hormone influences these processes through receptor interactions that mobilize intracellular calcium ions and activate protein kinase C pathways essential for gene expression related to corticotropin synthesis.

Peptide Production from Proopiomelanocortin

Proopiomelanocortin (POMC), upon processing, produces several peptides including ACTH and beta-endorphins. Notably, sequences within ACTH also contribute to melanocyte-stimulating hormones affecting pigmentation processes.

The sequence similarity indicates functional overlaps where ACTH not only stimulates adrenal functions but also has roles beyond traditional endocrine actions such as influencing skin pigmentation through melanocyte activity.

Cholesterol Mobilization for Steroidogenesis

In steroidogenesis within adrenal glands, cholesterol mobilization occurs following phosphorylation events triggered by hormonal signals. This process enhances mitochondrial uptake necessary for synthesizing steroid hormones effectively.

Cortisol and Its Functions

Mechanism of Action

Cortisol, when stimulated by ACTH in the adrenal gland, binds to cytoplasmic receptors, leading to their dimerization and subsequent translocation to DNA sites.

This binding modifies protein synthesis depending on the tissue type, either inhibiting or stimulating it.

Immune System Regulation

One primary function of cortisol is regulating the immune system; increased cortisol levels lead to immunosuppression.

It inhibits thymic release of factors that activate T-cells and decreases interleukin-1 from macrophages, reducing immune cell migration and chemotaxis.

Lower interleukin-1 results in decreased fever response as it affects thermoregulation.

Effects on Lymphocytes

Cortisol reduces T-cell activation by decreasing interleukin-2 production and gamma interferon, leading to a diminished immune response.

It also lowers circulating monocyte levels by inhibiting bone marrow release and promotes apoptosis in circulating lymphocytes.

Anti-inflammatory Properties

Cortisol acts as an anti-inflammatory agent by inhibiting phospholipase A2, which is responsible for synthesizing inflammatory mediators like prostaglandins.

It causes vasoconstriction and reduces vascular permeability, minimizing edema and leukocyte migration.

Metabolic Functions of Cortisol

Glucose Metabolism

Cortisol induces hyperglycemia through increased blood glucose levels while promoting glycogen synthesis for slow release from liver stores.

It stimulates gluconeogenesis using non-carbohydrate precursors such as amino acids and fatty acids from muscle or adipose tissue.

Insulin Resistance

The elevated glucose is not utilized effectively by muscle or adipose tissues due to insulin resistance induced by cortisol, ensuring availability for vital organs during stress responses.

Lipid Metabolism

Cortisol's Impact on Metabolism and Bone Health

Effects of Cortisol on Lipolysis and Protein Metabolism

Cortisol inhibits lipolysis, leading to a catabolic effect on protein metabolism in muscle tissue. This results in decreased protein synthesis and increased breakdown of proteins.

The hormone also affects bone and lymphoid tissues, exhibiting anti-anabolic effects that inhibit muscle degradation while promoting the formation of myopathy.

Anabolic Actions of Cortisol

The only site where cortisol exhibits anabolic activity is the liver, which can be beneficial for metabolic processes. Additionally, it acts positively on bone by stimulating osteoclast activity without causing bone tearing.

Calcium Balance and Bone Catabolism

Cortisol decreases renal reactions to calcium and phosphorus, resulting in negative calcium balance due to inhibited calcitonin action. This accelerates bone catabolism, leading to potential osteoporosis if prolonged exposure occurs.

Inhibition of vitamin D's effects further exacerbates this issue by reducing intestinal calcium absorption and increasing renal calcium expression, contributing to overall bone density loss.

Long-term Consequences: Osteopenia and Osteoporosis

Prolonged elevated cortisol levels can lead to osteopenia or osteoporosis, significantly increasing fracture risk due to reduced bone density over time. Understanding these risks is crucial when evaluating patients with suspected high cortisol levels or those receiving glucocorticoids long-term.

Effects of Glucocorticoids on Skin and Muscle

Impact on Collagen Synthesis in Skin

Glucocorticoids inhibit collagen synthesis primarily in fibroblasts located in subcutaneous tissue, leading to skin thinning and striae formation as collagen fibers weaken under stress from elevated cortisol levels.

Patients may exhibit transparent skin with visible blood vessels due to reduced subcutaneous collagen content; this condition is particularly notable among those with chronic glucocorticoid use.

Implications for Wound Healing

Reduced collagen synthesis delays wound healing processes; however, glucocorticoids are sometimes used locally to manage excessive scarring conditions like keloids by inhibiting collagen production effectively.

Systemic Effects of Cortisol

Muscle Catabolism

Chronic exposure to glucocorticoids leads not only to inhibition but also degradation of skeletal muscle mass, resulting in decreased contractility and strength—particularly affecting limb muscles where most skeletal mass resides. This contributes significantly to muscular weakness observed in affected patients.

Cardiovascular Effects

Cortisol exerts pressor effects through catecholamine potentiation via beta-adrenoceptors while simultaneously inhibiting vasodilatory prostaglandins (e.g., prostacyclin), which can lead to hypertension as vascular tone diminishes under excess glucocorticoid influence.

Mechanisms Behind Hypertension

Elevated blood pressure may arise from both direct receptor activation (mineral corticoid receptors) at high concentrations due to structural similarities between corticosteroids and mineral corticoids despite lower affinity binding capabilities compared with aldosterone-like hormones.

Effects of Cortisol on the Body

Gastrointestinal Effects

Cortisol increases gastric blood flow and hydrochloric acid secretion while inhibiting gastric epithelial proliferation, leading to a weakened mucosal barrier.

The reduction in gastric epithelium and mucosal barrier can result in gastrointestinal lesions or ulcers due to excessive acid secretion.

Renal and Hematological Impacts

In the kidneys, cortisol enhances glomerular filtration and counteracts antidiuretic hormone (ADH), resulting in increased water elimination.

Cortisol plays a crucial role during prenatal development by stimulating pulmonary surfactant production, essential for gas exchange post-birth.

Neurological and Behavioral Consequences

Elevated cortisol levels can initially induce euphoria but may lead to irritability or emotional instability over time.

Chronic high cortisol levels are linked to cognitive decline, including memory loss due to neuronal damage in the hippocampus.

Appetite and Sleep Regulation

High cortisol can cause decreased libido, insomnia, and altered appetite; low levels may lead to apathy and heightened sensitivity of taste and smell.

Chronic stress elevates cortisol levels, which affects hypothalamic function, leading to persistent hormonal imbalances that exacerbate stress responses.

Clinical Implications of Elevated Cortisol

Chronic stress results in sustained high levels of ACTH (adrenocorticotropic hormone), leading to continuous cortisol production with various health implications.

Patients with depression often exhibit elevated plasma cortisol levels; this relationship underscores the connection between stress, hormonal regulation, and mental health disorders.

Pathological Conditions Related to Cortisol

Understanding physiological effects of cortisol helps identify clinical manifestations in conditions like Cushing's syndrome characterized by excess cortisol production.

Persistent high cortisol disrupts glucose regulation mechanisms, potentially causing carbohydrate intolerance or diabetes among affected individuals.

Immune System Effects

Cushing's Syndrome: Understanding Cortisol Effects

Overview of Cushing's Syndrome

Cushing's syndrome is characterized by elevated cortisol levels, leading to protein catabolism and potential osteoporosis. The condition was named after Dr. Harvey Cushing, who first described it.

Patients often experience muscle wasting in limbs due to lipolysis while simultaneously developing central obesity, resulting in a prominent trunk and features like facial fullness or "moon facies."

Physical Manifestations

Common physical signs include thin extremities with a bulky torso, delayed wound healing, and the presence of striae (stretch marks) on the skin.

Hypertension is prevalent among individuals with excess cortisol due to its vasoconstrictive effects and reduced vasodilatory prostaglandins.

Mechanisms Behind Symptoms

Understanding cortisol functions and mechanisms is crucial for recognizing symptoms associated with both endogenous (adrenal production) and exogenous (medication-induced) sources of excess cortisol.

Addressing the underlying cause of hypercortisolism can lead to significant improvements in symptoms; for instance, removing a tumor that produces cortisol can reverse many effects.

Case Study Insights

A case study illustrates dramatic changes in a patient's appearance post-treatment for Cushing's syndrome, highlighting how effective management can restore normalcy over time.

Conclusion & Next Steps