Endocrine System - Hypothalamus and Pituitary Gland Flashcards
Describe the vascular connections between the hypothalamus & the pituitary
The vascular connection between the hypothalamus and the anterior pituitary is through the hypothalamic-pituitary portal system.
Specialized blood vessels called portal veins directly connect the hypothalamus with the anterior pituitary.
These portal veins carry releasing and inhibiting hormones secreted by the hypothalamus to the anterior pituitary, where they regulate the release of various hormones e.g growth hormone, thyroid-stimulating hormone.
Posterior pituitary - hormones synthesised in the hypothalamus, such as oxytocin and vasopressin are transported down the axons of neurones into the posterior pituitary. These hormones are then released into the bloodstream when needed
Describe the neuronal connections between hypothalamus and pituitary gland.
No direct neuronal connection between the hypothalamus and the anterior pituitary. Instead, the hypothalamus secretes releasing and inhibiting hormones into the hypothalamic-pituitary portal system, which then travel through the portal veins to the anterior pituitary.
Posterior - These neurones extend their axons down into the posterior pituitary, where the hormones are stored and released into the bloodstream when appropriate signals are received.
What hormones are secreted by hypothalamus and posterior pituitary?
The hypothalamus & posterior pituitary form a neuroendocrine system that secretes ADH & oxytocin.
ADH - increases H2O permeability & absorption in renal collecting ducts, vasoconstrictor.
Oxytocin - stimulates uterine contraction & milk ejection
What hormones are secreted by hypothalamus and anterior pituitary?
The anterior pituitary primarily secretes tropic hormones. Regulates hormone secretion by another endocrine gland
Stimulates & maintains endocrine target tissues
E.g thyroid stimulating hormone, growth hormone, Adrenocorticotropic Hormone
How is secretion of anterior pituitary hormones regulated?
Most anterior pituitary hormones are regulated by the hypothalamic-pituitary axis. Achieved by hypothalamus producing releasing or inhibiting hormones and a negative feedback loop from target glands.
How is secretion of posterior pituitary gland regulated?
Neuroendocrine reflexes, primarily controlled by neuronal signals from the hypothalamus.
Sensory inputs or signals from other brain regions can activate or inhibit the release of oxytocin and vasopressin from the posterior pituitary.
Osmoreceptors - specialised cells in the hypothalamus sense changes in blood osmolarity
Changes in blood pressure are detected by baroreceptors.
Explain how the levels of “trop(h)ic” hormones are modulated by feedback from their “target” hormones .
The hypothalamic hypophysiotropic hormones
The hypothalamic regulatory hormones reach the anterior pituitary by means of the hypothalamic-hypophyseal portal system
Negative feedback;
Negative feedback inhibits hormone secretion by inhibiting the hormone’s effects.
When a target hormone’s levels rise, it sends signals to the brain or gland, triggering a decrease in tropic hormone secretion.
This decrease in hormone stimulation reduces the hormone’s secretion, allowing it to be secreted again when needed
Describe the 3 hormone sequence in negative feedback in hypothalamic-anterior pituitary control systems
Hypophysiotropic hormone (neurohormone)
Anterior pituitary tropic hormone
Peripheral target-endocrine gland hormone
What is hypo secretion and its effect?
Hyposecretion refers to the inadequate production or release of pituitary hormones.
Effects may include decreased metabolic rate, low energy levels, weight gain, infertility, and growth disorders
What is hyper secretion and its effect?
Hypersecretion involves excessive production or release of pituitary hormones.
Effects may include accelerated metabolic rate, weight loss, hypertension, hyperglycemia, and emotional disturbances
How does hyper secretion and hypo secretion disrupt normal pituitary function?
The pituitary gland acts as a master gland, secreting hormones that regulate other endocrine glands throughout the body.
It maintains homeostasis by controlling hormone levels in response to feedback from various bodily systems.
Hyposecretion and hypersecretion disrupt this delicate balance, leading to physiological imbalances and related symptoms.
The effects of hypo- and hypersecretion underscore the critical role of the pituitary gland in coordinating various physiological processes and maintaining overall health and well-being
