Endocrinologia 2 - Eixo hipotálamo-hipófise

Summary

This lesson focuses on endocrinology, specifically the relationship between the hypothalamus and the pituitary gland. It explains the division of the pituitary gland into anterior (adenohypophysis) and posterior (neurohypophysis) regions, their structure, and their hormonal functions. The hypothalamus regulates hormone release through both neuronal and blood pathways, impacting the release of various hormones from the pituitary. Key hormones include cortisol, growth hormone, prolactin, and thyroid-stimulating hormone, each with specific targets in the body. The lesson also highlights feedback mechanisms that control hormone levels and the roles of oxytocin and vasopressin in physiological processes.

Takeaways

• 😀 The hypothalamus and pituitary gland play a key role in regulating various hormonal functions in the body.
• 😀 The pituitary gland, located below the hypothalamus, is protected by the sphenoid bone and is divided into anterior and posterior sections.
• 😀 The anterior pituitary (adenohypophysis) and posterior pituitary (neurohypophysis) release different hormones, each with distinct functions.
• 😀 The anterior pituitary consists of specialized cells, including thyrotrophs, gonadotrophs, somatotrophs, and lactotrophs, each responsible for releasing specific hormones.
• 😀 Somatotrophs release growth hormone (GH), which acts on the musculoskeletal system and regulates growth and development.
• 😀 The release of prolactin by lactotrophs is important for milk production and is regulated by a combination of stimulating and inhibiting factors.
• 😀 Corticotrophs in the anterior pituitary release ACTH, which stimulates cortisol production in the adrenal cortex.
• 😀 Cortisol, a steroid hormone, regulates metabolism and has both genomic and non-genomic effects on the body.
• 😀 The hypothalamic-pituitary-adrenal (HPA) axis is involved in the regulation of cortisol levels, with negative feedback mechanisms maintaining balance.
• 😀 The posterior pituitary releases two important neurohormones: oxytocin, which facilitates labor and milk ejection, and vasopressin, which regulates water reabsorption in the kidneys.
• 😀 The synthesis of hormones in the neurohypophysis occurs in large neurons (magnocellular neurons) located in the supraoptic and paraventricular nuclei of the hypothalamus.
• 😀 Feedback mechanisms, both long-loop and short-loop, help regulate the release of hormones, ensuring homeostasis in the body.

Q & A

What is the role of the hypothalamus in the regulation of the pituitary gland?

The hypothalamus regulates the pituitary gland by releasing hormones into the portal system that directly affect the pituitary's secretion of various hormones. These include CRH, TRH, and GnRH, which regulate the release of ACTH, TSH, and gonadotropins from the anterior pituitary.

What are the two parts of the pituitary gland, and how do they differ in function?

The pituitary gland is divided into the anterior (adenohypophysis) and posterior (neurohypophysis) regions. The anterior pituitary produces hormones like ACTH, TSH, and LH, while the posterior pituitary releases oxytocin and vasopressin, which are involved in processes like water reabsorption and uterine contraction.

What is the function of the neurohypophysis?

The neurohypophysis (posterior pituitary) is responsible for releasing the neurohormones oxytocin and vasopressin. Oxytocin is involved in labor and milk ejection, while vasopressin regulates water reabsorption in the kidneys.

How does the hypothalamus-pituitary-adrenal (HPA) axis regulate cortisol release?

The hypothalamus releases CRH, which stimulates the anterior pituitary to release ACTH. ACTH then stimulates the adrenal glands to produce cortisol. Increased cortisol levels feed back to inhibit both CRH release from the hypothalamus and ACTH release from the pituitary, maintaining homeostasis through a negative feedback loop.

What are gonadotropins, and how are they regulated?

Gonadotropins are hormones such as LH and FSH that regulate the function of the ovaries and testes. They are regulated by GnRH released from the hypothalamus, which stimulates the anterior pituitary to release these hormones.

What are the effects of cortisol on the body?

Cortisol regulates metabolism, increases blood glucose levels, and helps the body respond to stress. It also has a feedback mechanism that inhibits the release of CRH and ACTH to prevent excess cortisol production.

What is the significance of the negative feedback loops in hormone regulation?

Negative feedback loops are crucial for maintaining hormone levels within optimal ranges. For instance, when cortisol levels rise, they inhibit the release of CRH and ACTH, preventing the overproduction of cortisol and ensuring homeostasis.

How do the anterior pituitary hormones like ACTH and TSH affect target organs?

ACTH stimulates the adrenal glands to release cortisol, while TSH stimulates the thyroid gland to produce thyroid hormones. These hormones regulate various physiological processes such as stress response and metabolism.

What is the difference between magnocellular and parvocellular neurons in the hypothalamus?

Magnocellular neurons have larger cell bodies and their axons project to the posterior pituitary, where they release hormones like oxytocin and vasopressin. Parvocellular neurons have smaller cell bodies and their axons project to the median eminence, where they release hormones that regulate the anterior pituitary.

What role does the feedback inhibition play in the regulation of prolactin?

Prolactin release is regulated by both stimulatory and inhibitory factors. The release of prolactin is primarily inhibited by dopamine, while its stimulation occurs via hypothalamic hormones like TRH. Feedback inhibition ensures prolactin levels do not become excessive.