Network of ductless glands that secrete hormones directly into the blood
Endocrine system
It is considered to be the regulatory hormone of the body
It is regulated by means of control of hormone synthesis rather than by degradation
Hormones
Chemical signals produced by specialized cells, secreted into the blood stream and carried to a target tissue
Hormones
Play an important role in the growth and development of an individual
Regulated by metabolic activity either positive or negative feedback mechanism
Major function of hormones
To maintain the constancy of chemical composition of extracellular and intracellular fluids, and control metabolism, growth, fertility and responses to stress
Positive feedback mechanism
A system in which an increase in the product results to elevation of the activity of the system and the production rate
Negative feedback mechanism
A system in which an increased in the product results to decreased activity of the system and the production
Types of hormone secretion
Endocrine
Paracrine
Autocrine
Juxtracrine
Intracrine
Exocrine
Neurocrine
Neuroendocrine
Peptide and protein hormones
Synthesized and stored within the cell in the form of secretory granules and are cleaved as needed
Cannot cross the cell membrane due to their large molecular size and thus produce the effects on the outer surface of the cells
They are water soluble and not bound to carrier protein
Steroid hormones
Lipid molecules that have cholesterol as a common precursor
Produced by adrenal glands, ovaries, testes, and placenta
Water insoluble (hydrophobic) and circulate bound to a carrier protein
Examples of steroid hormones
Aldosterone
Cortisol
Estradiol
Progesterone
Testosterone
Activated vitamin D
Amine hormones
Derived from an amino acid and they are intermediary between steroid and protein hormones
Examples of amine hormones
Epinephrine
Norepinephrine
Triiodothyronine
Thyroxine
Hypothalamus
Portion of the brain located in the walls and floor of the third ventricle
Above the pituitary gland, and is connected to the posterior pituitary by the infundibulum (pituitary stalk)
The link between the nervous system and the endocrine system
Anterior pituitary
Largest portion of the gland
The "true endocrine gland"
Regulates the released and production of hormones such as prolactin, growth hormone, gonadotropins (FSH and LH), TSH and ACTH
Hormones secreted by the anterior lobe are either peptides or glycoproteins
Intermediate lobe
Little functional capacity
Posterior pituitary
For storage and release of oxytocin and vasopressin
Five types of cells in anterior pituitary
Somatotrophs
Lactotrophs or Mammotrophs
Thyrotrophs
Gonadotrophs
Corticotrophs
Growth hormone (somatotropin)
Most abundant of all pituitary hormone
Controlled by GH-RH (the amount of release) and somatostatin (governs the frequency and duration of secretory pulse)
Structurally similar to prolactin and human placental lactogen
Secretion is erratic and occurs in short bursts
Overall metabolic effect is to metabolize fat stores while conserving glucose
Major stimuli for growth hormone
Deep sleep (markedly increased GH)
Stress
Fasting
High protein diet
Pharmacologic stimuli for growth hormone
Sex steroids
Apomorphine
Levodopa
GH suppressors
Glucocorticoids
Elevated fatty acids
Conditions with increased GH
Acromegaly
Gigantism
Chronic malnutrition
Renal disease
Cirrhosis and sepsis
Conditions with decreased GH
Hyperglycemia
Obesity and hypothyroidism
GH deficiency (GHD)
Idiopathic Growth Hormone Deficiency is the most common cause in children
In children with pituitary dwarfism, normal proportions are retained and show no intellectual abnormalities
Pituitary Adenoma is the most common etiology in adult-onset GH deficiency
Acromegaly
Due to overproduction of GH (>50 ng/ml or 2210 pmol)