Endocrine and Nervous Systems: Functions and Hormones
Endocrine and Nervous Systems
Nervous System: Fast action and very short duration. Effect is localized and fleeting.
Endocrine System: Action is slow but long-lasting. Effect is widespread, medium and long term.
Major Glands
Pituitary, Thyroid, Parathyroid, Adrenal, Pancreas, and Ovary/Testicle.
Hormones
A hormone is any chemical secreted in body fluids by a cell or a group of cells that has a control function. It is secreted and acts at a specific location.
Local Hormones
Produced in the system itself or by the cell to be used. Example: Acetylcholine.
General Hormones
Produced by a cell or group of cells and travels throughout the body to be used elsewhere. Example: Insulin.
Liaison with Hormone Receptors
- Activates enzymes.
- Alters cellular permeability.
- Causes muscle contraction or relaxation.
- Causes protein synthesis.
- Causes secretion.
GH with its receptor does not need a second messenger (the hormone is the first). Channels open with hormone binding.
Hypothalamus
It produces hormones called releasing factors and inhibiting factors. These hormones arrive via the blood to a large tangle called the pituitary portal system. Hypothalamus > GHRH > Anterior Pituitary > HGH > Pineal Gland.
Pituitary
It is a gland that is an invagination of the hypothalamus. It consists of the posterior neuro-pituitary and the anterior adeno-pituitary.
Anterior Pituitary Gland
Secretes hormones: GH, ACTH, TSH, LH, FSH, and prolactin.
Posterior Pituitary Gland
Secretes hormones: ADH and oxytocin (2 general and 6 local hormones).
Locations: The releasing and inhibiting factors produced in the hypothalamus are secreted by the pituitary.
Anterior Pituitary: Destinations
- ACTH – Adrenal cortex (zona fasciculata and zona reticularis)
- FSH, LH – Ovaries and Testes
- TSH – Thyroid
- Prolactin – Mammary Glands
- GH – Growth Hormone
Growth Hormone (GH)
Induces growth of muscles and bones, acts in the nuclei of cells. Increases the size and the core of the mitochondria. Increases mitosis. GH stimulates mitochondrial renewal.
Side Effects of GH
Taking GH may lead to diabetes. High doses cause acromegaly. A lack leads to dwarfism.
Effects of GH
- Increases the transport of amino acids across cell membranes.
- Increases protein synthesis by ribosomes.
- Increases the formation of RNA (mechanism is unknown).
Stimuli for GH Secretion
Sleep, physical stress, hypoglycemia, low levels of cellular amino acids, and an increase in plasma amino acids.
Metabolic Effects of GH
- Increases the rate of protein synthesis.
- Reduces the use of carbohydrates.
- Increases the use of fats.
- Increases the rate of growth.
GH maintains glucose levels by stimulating triglycerides – free fatty acids. It conserves glucose because it uses free fatty acids and blocks glucose in the muscle.
Antidiuretic Hormone (ADH)
Produced by neurons of the hypothalamic nucleus above the optic chiasm, which have osmoreceptors (detecting decreased blood volume). Increases reabsorption of water into the interstitium. Alcohol inhibits the production of ADH, increasing diuresis. Acts by preventing water loss through the kidneys, acting on the collecting ducts. It acts with less intensity in the distal tubule and loop of Henle, permeabilizing them.
Oxytocin
Responsible for milk ejection (for the duration of breastfeeding). Causes uterine contractions during sex, and the control of oxytocin helps bring sperm to the egg. The child pressing on the birth canal helps release oxytocin, causing uterine contractions.