Chapter 16 Notes
Homeostasis: the process of maintaining the internal environment of the body in a narrow
The hypothalamus plays a key role in the regulation of body temperature, fluid balance, and
Hypothalamus regulation of homeostasis involves three components:
1. Humoral response: neurons respond to sensory signals by stimulating or inhibiting the
release of pituitary hormones
2. Visceromotor response: neurons respond to sensory signals by adjusting the balance of
sympathetic and parasympathetic outputs of the ANS
3. Somatic motor response: neurons (particularly in the lateral hypothalamus) respond to
sensory signals by inciting an appropriate somatic motor behaviour response
Motivated behaviours to correct a situation (such as shivering when cold) are incited by the
The condition in which blood is filled with nutrients, such as after a meal, is called the prandial
The energy is stored as either glycogen (liver and skeletal muscle) or triglycerides
The fasting phase between meals is called the postabsorptive phase, in which the glycogen and
triglycerides are broken down. Glucose is used by all cells, but triglycerides are not used by
If the intake of energy exceeds the usage, the amount of body fat, or adiposity, increases,
resulting in obesity. If vice versa, starvation occurs.
Neurons found in the periventricular zone (from ch. 15) seem to act as monitors.
Neurons that incite feeding behaviour are found in the lateral hypothalamus (i.e. feeding is a
The idea that the brain monitors the amount of body fat and acts to defend this energy store
against perturbations is called the lipostatic hypothesis.
An example of this is a forcefully fed rat when given opportunity to eat freely will cut
down on caloric intake to reach optimal adiposity. Vice versa occurs for starved rats.
The ob gene found in mice was hypothesized to tell the body that fat reserves are normal. The
ob gene encoded the protein leptin. It regulates body mass by acting directly on neurons of the
hypothalamus that decrease appetite and increase energy expenditure.
Mice with the ob/ob defective gene are fooled into thinking stores are low, hence they
Tested this using parabiosis, the union of two mice physiologically and anatomically
Lesions on both sides of the hypothalamus can have large effects on feeding behaviour and
adiposity Bilateral lesion of the lateral hypothalamus caused anorexia. Anorexia in humans caused
by damage to the same area is called lateral hypothalamus syndrome. Anorexia =
lateral hypothalamus syndrome
Bilateral lesions of the ventromedial hypothalamus caused animals to overeat and
become obese. Overeating and obesity in humans caused by damage to the same area is
called ventromedial hypothalamic syndrome.
In the Case of Elevated Leptin Levels: Leptin molecules are released into circulation by
adipocyte cells. They activate leptin receptors of the arcuate nucleus of the hypothalamus.
Alpha MSH and CART neurotransmitter molecules are found in the arcuate nucleus
(activated by high leptin levels)
Read pg 515-516 (the effects of elevated.... section)
Basically, the high leptin activate the Alpha MSH and CART neurons in the arcuate
nucleus. These then activate the paraventricular nucleus that then causes the release of
ACTH and TSH hormones. Alpha MSH and CART also inhibit the lateral hypothalamic
area, inhibiting feeding.
ACTH and TSH+ Paraventricular nucleus+MSH and CART-Lateral
hypothalamic area (inhibits feeding)
The injection of alpha MSH and CART into the brain mimics the response to high leptin
levels. Thus they are called anorectic peptides – they diminish appetite.
In the Case of Decreased Leptin Levels
Alpha MSH and CART responses are turned off
Decreased levels stimulate release of NPY (Neuropeptide Y) and AgRP, both found in the
Basically, a fall in leptin levels stimulat