Hormone Synthesis and Receptor Binding

Steroid Hormone Synthesis and Receptor Binding

• Steroid hormones are synthesized in the adrenal cortex, gonads (testes and ovaries), and placenta.
• When a steroid hormone binds to its receptor, the hormone-receptor complex translocates to the cell nucleus, acting as a transcription factor to regulate gene expression.

Prohormone Definition

• A prohormone is a precursor to a hormone, usually an inactive molecule that requires conversion into its active form.
• Peptide hormones are often synthesized as prohormones.

Pituitary Gland and Hypothalamus

Anterior Pituitary

• Produces hormones like ACTH, TSH, GH, PRL, FSH, and LH.

Posterior Pituitary

• Releases oxytocin and vasopressin (ADH).

Hypothalamus

• Produces releasing and inhibiting hormones (e.g., TRH, CRH, GnRH) that control the anterior pituitary.
• Produces oxytocin and vasopressin, which are stored in the posterior pituitary.

Half-Life of a Hormone

• The half-life of a hormone is the time it takes for the concentration of the hormone in the blood to be reduced by half.

Upregulation and Downregulation of Receptors

• Upregulation: Increase in the number of receptors on the surface of target cells, making them more sensitive to the hormone.
• Downregulation: Decrease in the number of receptors, making the target cells less sensitive to the hormone.

Trophic, Permissive, Antagonist, and Synergist Hormones

• Trophic: Hormones that stimulate the growth of tissues and the release of other hormones (e.g., TSH).
• Permissive: One hormone enhances the effect of another (e.g., thyroid hormones enhance the effects of catecholamines).
• Antagonists: Hormones that have opposite effects (e.g., insulin and glucagon).
• Synergists: Hormones that work together to produce a greater effect (e.g., glucagon and epinephrine on blood glucose levels).

Primary and Secondary Pathologies in Endocrine Glands

• Primary Pathology: Dysfunction originates in the endocrine gland itself.
• Secondary Pathology: Dysfunction originates in the pituitary gland.

Action of Enzyme Aromatase

• Aromatase converts androgens (e.g., testosterone) into estrogens (e.g., estradiol).

Grave's Disease

• Caused by an autoimmune disorder that results in the overproduction of thyroid hormones (hyperthyroidism).

Acromegaly, Dwarfism, and Gigantism

• Acromegaly: Caused by excessive growth hormone in adults.
• Dwarfism: Often caused by insufficient growth hormone.
• Gigantism: Caused by excessive growth hormone in children.

Cushing Syndrome and Addison's Disease

• Cushing Syndrome: Caused by excessive cortisol.
• Addison's Disease: Caused by insufficient production of cortisol and aldosterone.

Primary and Secondary Hypothyroidism

• Primary Hypothyroidism: Thyroid gland dysfunction.
• Secondary Hypothyroidism: Pituitary gland dysfunction.

Genomic Effects of Hormones

• Hormones can alter gene expression, typically a slow process.

Pain

• Referred Pain: Pain perceived at a location other than the site of the painful stimulus, often due to shared nerve pathways.
• Gate Control Model: Theory that suggests the spinal cord contains a neurological "gate" that can block or allow pain signals to pass to the brain.

Taste Pathways

• Taste receptors → Cranial nerves (VII, IX, X) → Medulla → Thalamus → Gustatory cortex.

Pitch, Frequency, and Loudness of Sound

• Pitch: Perception of frequency.
• Frequency: Number of sound wave cycles per second (Hz).
• Loudness: Perception of sound intensity, measured in decibels (dB).

Distinguishing Sound Waves

• We distinguish sound waves by their frequency and amplitude.

General Anatomy of the Ear and Eye

Ear

• Outer ear (pinna, auditory canal)
• Middle ear (ossicles: malleus, incus, stapes)
• Inner ear (cochlea, semicircular canals)

Eye

• Cornea
• Lens
• Retina
• Optic nerve
• Macula
• Fovea

Frequency Determination in Ear

• The cochlea has hair cells tuned to specific frequencies, translating sound waves into electrical signals.