Hypothalamus Flashcards
What are the two primary parts of the pituitary gland that are regulated by the hypothalamus, and how do they differ in function?
The anterior pituitary (adenohypophysis) and posterior pituitary (neurohypophysis). The anterior pituitary produces hormones like ACTH, TSH, LH, FSH, GH, and prolactin in response to hypothalamic releasing hormones. The posterior pituitary stores and releases hormones (oxytocin and vasopressin) that are synthesized in the hypothalamus and transported via axons.
What is the hypophyseal portal system, and why is it essential for anterior pituitary regulation?
It is a network of blood vessels connecting the hypothalamus and anterior pituitary. It allows hypothalamic hormones (e.g., CRH, TRH, GnRH) to travel directly to the anterior pituitary to regulate hormone secretion efficiently without dilution in systemic circulation.
How are hormones released from the posterior pituitary, and what is the hypothalamus’s role in this process?
Hormones like oxytocin and vasopressin are synthesized by hypothalamic neurons (in the paraventricular and supraoptic nuclei) and transported down axons to the posterior pituitary, where they are released into the bloodstream.
How does the hypothalamus initiate the body’s stress response, and which endocrine structures are involved?
It activates the hypothalamic-pituitary-adrenal (HPA) axis. In response to stress, the hypothalamus secretes corticotropin-releasing hormone (CRH), stimulating the anterior pituitary to release adrenocorticotropic hormone (ACTH), which then prompts the adrenal cortex to produce cortisol.
Describe how the hypothalamus integrates with the autonomic nervous system (ANS) during stress.
The hypothalamus acts as the master regulator of the ANS by coordinating sympathetic and parasympathetic responses. It sends descending signals to brainstem centers (medulla and pons) to control functions like heart rate, digestion, pupil dilation, and blood pressure.
Besides the hypothalamus, which other brain regions influence autonomic function and how?
The medulla and pons handle immediate autonomic reflexes. The cerebellum and basal ganglia coordinate motor-autonomic activity. The limbic system integrates emotion-driven responses, and the frontal cortex manages higher-order control (e.g., stress perception, anticipation).
List at least five key physiological functions regulated by the hypothalamus to maintain homeostasis.
The hypothalamus controls thirst and water balance, hunger and energy balance, reproduction and sexual behavior, thermoregulation (body temperature), and endocrine control via the pituitary.
How does the hypothalamus maintain body temperature within a narrow range?
It detects blood temperature and peripheral thermoreceptor input, then triggers responses like vasodilation/sweating (to cool down) or vasoconstriction/shivering (to warm up). The preoptic area plays a major role in thermoregulation.
What triggers a fever, and how does the hypothalamus respond?
Pyrogens (like interleukin-1 and prostaglandins from immune cells) signal the hypothalamus to raise the set point for body temperature, leading to heat-generating behaviors (shivering, seeking warmth) to produce fever.
What is the biological purpose of developing a fever during infection?
Fever enhances immune function (e.g., T-cell activity), slows microbial replication, and improves the efficiency of antibody production—acting as a defense mechanism against infection.
Which hypothalamic nuclei are responsible for producing oxytocin and vasopressin, and where are these hormones released?
The paraventricular and supraoptic nuclei synthesize these hormones. They are transported down the hypothalamo-hypophyseal tract and released into circulation from the posterior pituitary.
What are the main physiological effects of vasopressin (antidiuretic hormone, AVP)?
AVP increases water reabsorption in the kidneys by acting on V2 receptors in the collecting ducts, helping conserve body water and maintain blood pressure. It also causes vasoconstriction via V1 receptors.
What are the functions of oxytocin in the body, particularly in reproduction?
Oxytocin induces uterine contractions during labor and stimulates the milk ejection reflex during breastfeeding. It also plays roles in bonding and social behavior.
Which hypothalamic areas regulate hunger and satiety, and how do they interact?
The lateral hypothalamic area (LHA) promotes hunger, while the ventromedial nucleus (VMN) signals satiety. The arcuate nucleus integrates hormonal signals (ghrelin, leptin, insulin) to modulate these centers.
How do ghrelin, leptin, and insulin affect hypothalamic appetite regulation?
Ghrelin (from the stomach) stimulates hunger via the arcuate nucleus. Leptin (from fat cells) and insulin (from the pancreas) signal energy sufficiency and suppress appetite by acting on POMC/CART neurons in the arcuate nucleus.
Which hypothalamic nuclei are primarily responsible for producing oxytocin and AVP?
The supraoptic nucleus and paraventricular nucleus synthesize and send oxytocin and AVP (also called ADH) to the posterior pituitary for release into the bloodstream.
What is a key structural feature of most hypothalamic afferent and efferent pathways?
They are predominantly unmyelinated fibers, allowing for flexible and local communication within the hypothalamus and to the pituitary.
How is hormone release from the posterior pituitary (neurohypophysis) different from that of the anterior pituitary?
The posterior pituitary releases hormones directly via axons from hypothalamic neurons, while the anterior pituitary relies on a vascular portal system and endocrine signaling.
What is another name for AVP, and what are its primary functions?
Arginine vasopressin is also known as antidiuretic hormone (ADH). It conserves body water by acting on the kidneys and causes vasoconstriction to increase blood pressure.
How is dopamine involved in anterior pituitary hormone regulation?
Dopamine, released by the arcuate nucleus, inhibits prolactin secretion from the anterior pituitary.
Why is it significant that the hypothalamic-pituitary vascular system lies outside the blood-brain barrier (BBB)?
It allows hormones in systemic circulation to exert negative feedback on hypothalamic and pituitary hormone secretion, enabling endocrine regulation.
How does the hypothalamus act as a link between the endocrine and nervous systems?
By secreting releasing hormones that respond to environmental cues and modulate pituitary output, integrating both neural signals and endocrine responses.
What type of tissue comprises the anterior pituitary, and how does it differ from the posterior pituitary in structure?
The anterior pituitary is made of glandular epithelial tissue; the posterior pituitary is composed of axonal projections from hypothalamic neurons.
What are the major hypothalamic releasing hormones and their anterior pituitary targets?
• GHRH → stimulates GH
• GnRH → stimulates LH & FSH
• CRH → stimulates ACTH
• TRH → stimulates TSH
• Dopamine (inhibitory) → inhibits prolactin
