Hypothalamus and Pituitary Flashcards
Describe the anatomy of the blood-brain barrier.
Capillary endothelial cells in the brain have extremely tight junctions that do not allow the passing through of catecholamines or
Describe the anatomy of the blood-brain barrier
The capillary endothelial cells in the brain have extremley tight junctions that prevent the circulating neurotransmitters (catecholamines and glutamate) from initiating action potentials in the brain’s neurons (no paracellular travel). Glial cells provide a dense arrangement of supporting podocyte processes.
Lipid-soluble gases (O2 and CO2), lipid-soluble drugs (heroine and nicotine), and lipid-soluble hormones can also cross the blood brain barrier.
The blood brain barrier is unusually leaky in some places: The posterior pituitary gland, the pineal gland, the median eminence and the circumventricular organs. Here there are fenestrations in the blood brain barrier.
The blood brain barrier also has transporters for particular water soluble hormones, amino acids and glucose.
What are the circumventricular organs?
The subfornical organ, the OVLT and the area postrema. These detect hormones and chemicals in the blood.
What is the hypothalamus made up of?
A number of intercommunicating nuclei, which are bodies made up of multiple cells. Homeostatic changes usually involve communication between multiple nuclei.
How does leptin regulate fat levels in the body?
If there is a high amount of white fat in the body, then more leptin will be produced. Leptin is a water-soluble protein hormone, that is transported across the blood brain barrier. It then reaches the arcuate nucleus of the hypothalamus, which uses the leptin level along with other signals to determine the nutitional status of the body. If leptin levels are high, then these functions will occur:
The paraventricular nucleus will initiate the hypothalamic-pituitary-thyroid axis through the release TRH, which will cause the release of T3 (triiodothyronine), which will increase metabolism.
Feeding behaviour will be somewhat supressed.
The hypothalamic-pituitary-gonadal axis is stimulated, which results in reproductive fertility. Leptin levels must be above a threshold in order for the animal to be fertile.
Describe the hypothalamic-pituitary-thyroid axis. What is a well known problem related to it?
The paraventricular nucleus of the hypothalamus releases TRH. TRH reaches the thyrotrophs in the anterior pituitary gland, and they release TSH (thyroid stimulating hormone). TSH then reaches the thyroid gland, and T3 and T4 are released. T4 is inactive and travels in the blood until the liver and kidneys convert it to T3. T3 is active, and results in an increase in metabolic rate. It is also its own regulator: T3 is detected by the paraventricular nucleus in the hypothalamus, and in response it stops the production of TRH. Thus, if the body is low on iodine, and the thyroid gland cannot produce T3, then there will be be a buildup of TSH in the thyroid gland, and it will swell, causing a goitre.
