Eye Problems Caused by Severe Conditions

Hormones and Their Classification

• Hormones are chemical messengers that exert their action on a specific target
• Classified into four main categories based on their structure:
  • Amines and amino acids (e.g., epinephrine, norepinephrine, thyroid, dopamine)
  • Peptides and glycoproteins (e.g., growth hormone, thyrotropin-releasing hormone, insulin)
  • Steroids (e.g., derivatives of cholesterol, sex hormones such as estrogens and testosterones)
  • Fatty acid derivatives (e.g., arachidonic acid, leukotrienes, prostaglandins)

General Characteristics of Hormones

• Have specific rates and rhythms of secretion
• Affect only cells with appropriate receptors
• Liver metabolizes hormones, making them more water-soluble for excretion by the kidneys
• Operate within a feedback system

Negative Feedback Mechanism

• Most hormone control in the body operates by negative feedback
• Similar to a thermostat on a heating system
• When the monitored value decreases below the set point, the feedback mechanism causes the value to increase
• When the monitored value is increased above the set point, the feedback mechanism causes it to decrease
• Example: negative feedback system that controls blood glucose levels

Hormone Release and Circulation

• Hormones are released into the circulation by endocrine glands
• Water-soluble hormones circulate in the bloodstream in free forms (unbound)
• Can cause severe eye problems, including paralysis of extraocular muscles, involvement of optic nerve, and corneal ulcerations

Thyroid Storm

• An extreme and life-threatening form of thyrotoxicosis
• Occurs in individuals with undiagnosed or partially treated severe hyperthyroidism
• Precipitated by stress, infection, diabetic ketoacidosis, or manipulation of the gland during surgical removal
• Manifestations: very high fever, extreme cardiovascular effects, severe central nervous system effects, and high mortality
• Treatment: cooling, beta blockers, glucocorticoids to correct relative adrenal insufficiency

Goiter and Thyroid Function

• Goiter is an enlarged thyroid gland
• Goiter only describes the size of the gland and says nothing about thyroid function
• Diffuse enlargement of the thyroid gland caused by prolonged elevation of TSH, seen in hypothyroidism
• Hormone binding to a receptor is referred to as a first messenger, which sets off the next step in the "cascade" to activate signal transduction

Signal Transduction

• Process in which hormones are communicated into the cell
• Binding of hormone to receptor activates the receptor through enzymes, producing a "second messenger"
• The end result is the activation of intracellular enzymes needed for hormone action
• Second messengers include calcium, cyclic AMP, and cyclic GMP

Hypothalamic-Pituitary Axis

• The hypothalamus is the part of the brain that integrates the activity of the autonomic nervous system and the endocrine glands
• The pituitary gland is the partner to the hypothalamus, responding to input from the brain and the body
• Together, they form the hypothalamic-pituitary axis (or neuroendocrine axis)

Hypothyroidism

• A deficiency of thyroid hormone, which can be either congenital or primary
• Etiologies of primary hypothyroidism:
  • Subacute thyroiditis (nonbacterial inflammation of the thyroid)
  • Hashimoto's thyroiditis (autoimmune disorder)
  • Painless thyroiditis (similar to subacute thyroiditis)
  • Postpartum thyroiditis (occurs within 6 months of delivery)
  • Myxedema coma (medical emergency with client exhibiting diminished level of consciousness, hypothermia, hypoventilation, and hypoglycemia)

Myxedema

• Indicative of severe or long-standing hypothyroidism
• Presence of non-pitting edema caused by increased mucopolysaccharide in connective tissues
• Manifestations: puffy face, enlarged tongue, hoarse and husky voice, mucopolysaccharide deposits in the heart

Congenital Hypothyroidism

• Result of absent thyroid tissue or defects in thyroid synthesis
• Common cause of preventable mental retardation affecting 1 in 4000 infants
• Important to identify, can be identified within the first week of life through state-mandated infant metabolic screenings (IMS)

Endocrine Pancreas

• Produces hormones that help regulate carbohydrate metabolism in the body
• Composed of the islets of Langerhans, which secrete hormones
• Three types of secreting cells:
  • Alpha cells (produce glucagon)
  • Beta cells (produce insulin)
  • Delta cells (produce somatostatin, which can stimulate the release of insulin or glucagon)

Diabetes Mellitus

• A syndrome characterized by chronic hyperglycemia and other disturbances of carbohydrate, fat, and protein metabolism