Hypothalamus (Chapter 23) Flashcards
What is the main role of the hypothalamus?
The hypothalamus maintains homeostasis via regulation of pituitary hormones.
- Body temp, breathing rate, heart rate, weight, metabolism, ANS function, osmolarity, etc.
Describe the basic mechanism through which the hypothalamus maintains homeostasis.
The hypothalamus receives input from both the brain and blood (can sense blood pressure, glucose, chemicals in blood).
It processes these inputs and releases hormones (including big proteins, neuropeptide, and smaller molecules like DA) that regulate functions like heart rate, metabolism, lactation, hydration, etc.
Describe the role of the hypothalamus in maintaining body temperature.
Human set point = 98.6 degrees.
Hypothalamic temperature-sensitive neurons compute the difference between what is/what should be, based on information from skin and internal organs.
Temperature-sensitive neurons excite pattern generators that generate physiological responses to altered body temp, as well as increasing discomfort leading to behavioral responses.
- Too cold: shivering, vasoconstriction
- Too hot: Sweating, vasodilation, increased breathing rate
Describe the role of the hypothalamus in feeding regulation.
Inputs from the solitary nucleus provide information on stomach distention, contents of stomach, glucose, adipose levels. Ghrelin and leptin are involved in signaling hunger and satiety, respectively.
Signals from the ventromedial nucleus (satiety center) and lateral tuberal regions (feeding center) are combined in the arcuate nucleus to modulate feeding behavior.
Describe the role of the hypothalamus in regulating hydration.
Decreased water volume is detected from decreased blood pressure and increased blood osmolality, as well as decreased blood flow to the kidneys. Sensors for all three project to the hypothalamus (medial preoptic nucleus –> supraoptic/paraventricular nuclei) which produces ADH.
ADH leads to increased reabsorption in the kidneys and signals the cortex with feelings of thirst.
Describe the role of the hypothalamus in regulating circadian rhythms.
The superchiasmatic nucleus is the master clock for circadian rhythms. It receives direct projections from the retina. The SCN is also a major site of melatonin receptors. Melatonin is secreted by the pineal gland, starts production around 9pm and stops early am. This provides a signal to set the circadian clock even without light.
Describe the role of the hypothalamus in regulating sleep/wakefulness via histamine production.
The tuberomamillary nucleus is the major source of histamine. It is released as a neurotransmitter, regulating sleep/wake cycles through outputs to widespread cortical areas and thalamus (via medial forebrain bundle).
What are the two different ways that the hypothalamus controls the pituitary?
Adenohypophyseal (vascular) and neurohypophyseal (neural)
How does the parvocellular hypophyseal system control pituitary output?
Adenohypophysis: Hypothalamic neurons (arcuate nucleus, walls of 3rd ventricle) secrete small peptides that are absorbed by vasculature.
How does the magnocellular hypophyseal system control pituitary output?
Neurohypophysis:
Supraoptic and paraventricular nuclei project to neurohypophysis, which triggers release into bloodstream. ADH/vasopressin and oxytocin travel down axons bound by a carrier protein, which is cleaved into ADH and OT by enzymes when it arrives in the capillaries of the posterior pituitary.
