The main function of the hypothalamus is homeostasis, or maintaining the body’s status quo. Factors such as blood pressure, body temperature, fluid and electrolyte balance, and body weight are held to a precise value called the set-point. Although this set-point can migrate over time, from day to day it is remarkably fixed.
To achieve this task, the hypothalamus must receive inputs about the state of the body, and must be able to initiate compensatory changes if anything drifts out of whack. For example, limbic and olfactory systems.
Once the hypothalamus is aware of a problem, how does it fix it? Essentially, there are two main outputs:
- neural signals to the autonomic system - the (lateral) hypothalamus projects to the (lateral) medulla, where the cells that drive the autonomic systems are located. These include the parasympathetic vagal nuclei and a group of cells that descend to the sympathetic system in the spinal cord. With access to these systems, the hypothalamus can control heart rate, vasoconstriction, digestion, sweating, etc.
- endocrine signals to/through the pituitary - recall that an endocrine signal is a chemical signal sent via the bloodstream. Large hypothalamic cells around the third ventricle send their axons directly to the posterior pituitary, where the axon terminals release oxytocin and vasopressin into the bloodstream. Smaller cells in the same area send their axons only as far as the base of the pituitary, where they empty releasing factors into the capillary system of the anterior pituitary. These releasing factors induce the anterior pituitary to secrete any one of at least six hormones, including ACTH and thyroid-stimulating hormone (TSH).
Ultimately the hypothalamus can control every endocrine gland in the body, and alter blood pressure (through vasopressin and vasoconstriction), body temperature, metabolism (through TSH), and adrenaline levels (through ACTH).
The main function of the hypothalamus is homeostasis, or maintaining the body’s status quo. Factors such as blood pressure, body temperature, fluid and electrolyte balance, and body weight are held to a precise value called the set-point. Although this set-point can migrate over time, from day to day it is remarkably fixed.
To achieve this task, the hypothalamus must receive inputs about the state of the body, and must be able to initiate compensatory changes if anything drifts out of whack. For example, limbic and olfactory systems.
Once the hypothalamus is aware of a problem, how does it fix it? Essentially, there are two main outputs:
- neural signals to the autonomic system - the (lateral) hypothalamus projects to the (lateral) medulla, where the cells that drive the autonomic systems are located. These include the parasympathetic vagal nuclei and a group of cells that descend to the sympathetic system in the spinal cord. With access to these systems, the hypothalamus can control heart rate, vasoconstriction, digestion, sweating, etc.
- endocrine signals to/through the pituitary - recall that an endocrine signal is a chemical signal sent via the bloodstream. Large hypothalamic cells around the third ventricle send their axons directly to the posterior pituitary, where the axon terminals release oxytocin and vasopressin into the bloodstream. Smaller cells in the same area send their axons only as far as the base of the pituitary, where they empty releasing factors into the capillary system of the anterior pituitary. These releasing factors induce the anterior pituitary to secrete any one of at least six hormones, including ACTH and thyroid-stimulating hormone (TSH).
Ultimately the hypothalamus can control every endocrine gland in the body, and alter blood pressure (through vasopressin and vasoconstriction), body temperature, metabolism (through TSH), and adrenaline levels (through ACTH).