Understanding the Hormonal and Endocrine Systems
Hormonal or Endocrine System. Formed by hormones that act as chemical messengers on target cells, they control and coordinate various functions.
Nature of Hormones: Hormones can be classified into several categories:
- Protein hormones (e.g., growth hormone)
- Amino acid derivatives (e.g., epinephrine and thyroxine)
- Peptides (e.g., glucagon, insulin)
- Steroids (e.g., cortisone)
Hormones are produced by cells whose main function is secretion (endocrine and neurosecretory cells), where hormone secretion is a cellular function more prevalent in epithelial cells of the digestive system.
Endocrine Cells: Endocrine glands are grouped, and their products are transported by blood to target cells.
Neurosecretory Cells: Specialized cells that secrete hormones into the blood or lymph, linking the nervous and hormonal systems.
Epithelial Cells: They regulate digestion and produce red blood cells.
Receptors: Specific protein molecules that bind to hormones found in target cells, which are continuously created and destroyed.
Nervous Coordination
Nerve impulses are electrochemical signals.
The action, propagation, and response are instantaneous.
Impulses are transmitted through nerve fibers.
Hormonal Coordination
Hormones act as chemical messengers produced in specialized cells.
Their action is slower but lasts for long periods.
Transportation occurs through the blood (in animals) or from cell to cell.
Their action is exerted on cells distributed throughout the body, which are prepared to respond to hormonal stimulation.
Pheromones: Chemical substances produced and secreted by exocrine glands that affect other members of the same species, causing changes in their social behavior.
Pheromones in marine animals are transmitted through water, while those in air and land are detected by olfactory receptors.
Hypothalamus: Neurosecretory cells produce inhibitory hypothalamic hormones that reach the pituitary and act on target cells, stimulating hormone production.
The hypothalamus secretes two hormones: oxytocin and vasopressin, which are stored in the posterior pituitary and released from there.
The hypothalamus controls the autonomic nervous system and regulates hunger, thirst, and sexual behavior.
Pituitary Gland: A small gland at the base of the skull, attached to the hypothalamus via blood vessels. It has two regions: the anterior pituitary and the neurohypophysis.
The pituitary secretes trophic hormones (tropins) that control other endocrine glands:
- TSH (thyrotropin) regulates the secretion of thyroxine by the thyroid.
- ACTH (adrenocorticotropic hormone) stimulates the adrenal cortex to secrete cortisol (corticosteroids).
- FSH (follitropin) acts on the ovaries in women, maturing their follicles and stimulating sperm production in testes.
- LH (luteotropin) stimulates ovulation and progesterone secretion, as well as testosterone secretion.
Non-trophic hormones:
- LTH (prolactin) stimulates milk production and secretion in breasts.
- GH (somatotropin) is the growth hormone that acts on bones and muscles, stimulating growth and tissue repair in adults.
Pituitary Neurohypophysis: Neurons from the hypothalamus release hormones that accumulate and are stored.
Oxytocin causes uterine contractions during childbirth and stimulates maternal bonding during breastfeeding.
ADH (vasopressin) stimulates water reabsorption by the kidneys, producing concentrated urine.
Pituitary Dwarfism and Gigantism: Result from a defect or excess of growth hormone (GH) during growth. It does not cause mental deficits. Excess GH secretion in adults leads to acromegaly, characterized by disproportionate growth of external body areas and the heart.
Diabetes Insipidus: Results from a deficiency of vasopressin, leading to excessive urine excretion and polydipsia (increased thirst).
The Thyroid Gland: An endocrine gland located in the anterior neck, surrounding the trachea. It is stimulated by TSH from the pituitary and produces two hormones:
- Thyroxine: Active in cell metabolism, protein synthesis, and glucose utilization, increasing heart rate and breathing, promoting normal development of bone and nervous tissue.
- Calcitonin: Inhibits calcium release, decreasing blood calcium levels, and maintaining calcium concentration necessary for blood clotting and nerve impulse transmission.
Exophthalmic Goiter: Caused by thyroid hyperfunction, leading to an increase in volume (goiter) and protrusion of the eyes (exophthalmia). Symptoms include increased metabolism, excessive sweating, tachycardia, and weight loss.
Cretinism: Caused by thyroid hypofunction during childhood, leading to short stature, genital infantilism, obesity, and mental deficiency.
Tetany: Caused by the removal of parathyroid glands, leading to decreased blood calcium levels and triggering violent muscle contractions, which can cause death by asphyxiation.
Diabetes Mellitus: Results from a shortage of pancreatic insulin, leading to elevated blood glucose levels. Normal levels can be restored with periodic insulin injections. Symptoms include polyuria (excessive urination), polyphagia (increased appetite), polydipsia (thirst), and increased protein and lipid metabolism.