21.5
Eje hipotalámico-pituitario
La respuesta al estrés,ya sea físico o psicológico, agudo o crónico,implica la activación del eje hipotalámico-pituitario-suprarrenal (HPA). El eje HP…
- [Narrador] Nuestra respuesta al estrés,
física o psicológica,
comienza en el cerebro
con la activación del sistema neuroendocrino,
El eje hipotálamo-hipófisis-suprarrenal o HPA.
El hipotálamo, el H,
libera una hormona liberadora de corticotropina, o CRH,
Lo que activa la glándula pituitaria, la P en el eje.
Si bien esta glándula neuroendocrina tiene muchas funciones,
En tiempos de estrés se libera
la hormona corticotrópica suprarrenal, o ACTH, en la sangre.
La ACTH estimula las cortezas suprarrenales, la A,
Pequeñas estructuras en la superficie de los riñones.
Las suprarrenales liberan dos tipos de hormonas.
Primero están la norepinefrina y la epinefrina,
dos compuestos simpaticomimeticos
Responsable de despertar el cuerpo a la acción
iniciando el sistema nervioso simpático y causando
aumento de la frecuencia cardíaca y el flujo sanguíneo.
En segundo lugar están los glucocorticoides,
específicamente el cortisol.
Activan sistemas en el cuerpo
diseñado para soportar reacciones de estrés
Movilizando las reservas de energía
a través de la glucogénesis incrementada y la supresión
de procesos no vitales como el sistema inmunológico.
Cuando los niveles de cortisol se elevan,
un bucle de retroalimentación negativa
tanto en la hipófisis como en el hipotálamo se inicia.
Esta reacción detiene la liberación de ACTH y CRH,
Poner fin a la respuesta al estrés.
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Q1: What is the hypothalamic-pituitary-adrenal axis and why does it activate during stress?
The hypothalamic-pituitary-adrenal (HPA) axis is a neuroendocrine system that regulates the body's response to stress by coordinating neuronal and hormonal communication. During stress, the hypothalamus releases corticotropin-releasing hormone (CRH), which stimulates the pituitary gland to release adrenocorticotropic hormone (ACTH). ACTH then signals the adrenal glands to release stress hormones that prepare the body for action and mobilize energy reserves.
Q2: What hormones does the adrenal gland release during the stress response?
The adrenal gland releases two types of stress hormones. The adrenal medulla releases epinephrine and norepinephrine, which activate the sympathetic nervous system, increasing heart rate and blood flow. The adrenal cortex releases glucocorticoids, primarily cortisol, which mobilizes glucose reserves and temporarily suppresses non-vital processes like immune function to sustain the stress response.
Q3: How do epinephrine and norepinephrine affect the body during stress?
Epinephrine and norepinephrine are sympathomimetic compounds that activate the sympathetic nervous system, causing increased heart rate, blood flow, and respiration. These hormones prepare the body for immediate action by promoting states of alertness and arousal, enabling rapid physical responses to stressors.
Q4: What role does cortisol play in the stress response?
Cortisol, the primary glucocorticoid in humans, mobilizes energy by promoting glucose production through the breakdown of fatty acids and proteins. It also temporarily inhibits immune and inflammatory responses to prioritize resources for stress management. When cortisol levels rise sufficiently, it triggers a negative feedback loop that deactivates the HPA axis and terminates the stress response.
Q5: How does negative feedback terminate the stress response?
When blood cortisol levels reach a certain threshold, they trigger a negative feedback loop that inhibits both the hypothalamus and pituitary gland. This stops the release of CRH and ACTH, effectively deactivating the HPA axis and ending the stress response, allowing the body to return to homeostasis.
Q6: What are the long-term effects of chronic HPA axis activation?
Chronic stress or repeated acute stress can lead to continuous HPA axis activation, eventually depleting cortisol reserves. This depletion disrupts cortisol's multiple functions during both stress and non-stress periods, potentially causing chronic pain, depression, infertility, and may contribute to substance abuse and addiction.
Q7: How does the HPA axis maintain homeostasis during stress?
The HPA axis regulates metabolic, cardiovascular, and immune systems to maintain homeostasis during stress. Epinephrine and norepinephrine increase cardiovascular activity for immediate response, while cortisol mobilizes energy reserves and temporarily suppresses immune function. This coordinated hormonal response enables the body to sustain stress reactions while preserving critical functions.