Ethologie (BOOK)
Pagina’s 933----1241
Pagina 933-935
Homeostasis
Setpoint, regulator, conformer, stimulus, sensor, response, positive- and negative
feedback.
A circadian rhythm is intrinsic in the body, but extern stimuli (zeitgebers) can reset the
biological clock. The biological clock has a sleep/wake cycle of 24.2 hours in a constant
environment instead of 24 hours. The circadian rhythm is coordinated by the
suprachiasmatic nucleus (SCN).
Pagina 964-966
Homeostatic control of Ca2+ levels is vital. If the levels fall substantially, skeletal muscle
begin to contract convulsively, if the levels raise substantially, calcium phosphate can form
precipitates in body tissues, leading to widespread organ damage.
In mammals, the parathyroid glands play a major role in blood Ca2+ regulation. When levels
fall below a setpoint of about 10mg/100mL, these glands release parathyroid hormones
(PTH). PTH stimulates Ca2+ release from bones, Ca2+ uptake in kidneys and activation of
vitamin D which increases Ca2+ uptake in intestines. The thyroid gland can release
calcitonin when Ca2+ levels are too high.
Adrenal glands are actually made up of two glands with different cell types, functions and
origins, the adrenal cortex and the adrenal medulla.
Adrenal medulla
Epinephrine and norepinephrine are two hormones of the adrenal medulla, which are
responsible for the fight-or-flight reflex. They increase the rate of glycogen breakdown. Both
are catecholamines and do also function as neurotransmitters.
Effects of epinephrine;
In liver cells it binds to B-type receptors in the plasma membrane, which activates
kinase A which regulates enzymes of glucogen metabolism.
In smooth muscle cells the same kinase is activated which leads to smooth muscle
relaxation which leads to vasodilation and hence blood flow in skeletal muscle.
In the smooth muscle cell lining blood vessels, epinephrine binds to an a-type
receptor which triggers a signalling pathway involving a different G protein and
different enzymes which leads to smooth muscle contraction.
Adrenal cortex
The adrenal cortex becomes active under stressful conditions that include low blood sugar,
decreased blood volume and pressure, and shock. These stimuli can cause the hypothalamus
to secrete releasing hormones that stimulates the anterior pituitary to release
adrenocorticotropic hormone (ACTH) (tropic hormone). When it reaches the adrenal cortex,
it stimulates the endocrine cells to synthesize and secrete corticosteroids, the two main
, types are glucocorticoids (promote glucose synthesis form noncarbohydrate sources) and
mineralocorticoids (maintaining salt and water balance).
Sex hormones
The gonads (testes and ovaries) is the main resource of sex hormones. There are three
major types of steroid sex hormones; androgens (testosterone; male secondary sex
characteristics), estrogens (estradiol; female reproductive system and secondary sex
characteristics) and progesterone (growth and development of embryo).
An endocrine disrupter is a molecule that interrupts the normal function of a hormone
pathway, which can be either harmful or beneficial.
Melatonin is important for regulating functions related to light and seasons and is controlled
by a group of neurons in the hypothalamus, the suprachiasmatic nucleus SCN.
Pagina 1150-1152
An electroencephalogram (ECG) is a registration of the patterns of electrical activity called
brain waves.
The reticular formation is a phylogenetically primitive network of small neurons extending
throughout the brainstem and into the spinal cord.
