Help with Hormone Origins and Targets

The adrenal medulla produces epinephrine and norepinephrine, which cause the fight or flight response. The thyroid gland produces triiodothryonine and thyroxine, which are used for metabolism, growth, and development. The ovaries and placenta produce estrogen and progesterone, which are used for fetal/maternal development and egg production. Lastly, the stomach and small intestines produce gastrin and secretin, which are used to assist digestion and nutrient absorption.

The liver secretes angiotensinogen and insulin-like growth factors. Only angiotensinogen is responsible for increasing blood pressure by acting on blood vessels. Cortisol is released by the adrenal cortex, oxytocin is released by the posterior pituitary, and vitamin D3 is found being activated in the skin. Angiotensinogen is a zymogen that is converted into angiotensin I by renin (secreted by the kidney). Then angiotensin converting enzyme (ACE) converts angiotensin I into angiotensin II, which is a potent vasoconstrictor. Angiotensin II also promotes the release of aldosterone from the adrenal cortex, which increases sodium reabsorption. Lastly, antidiuretic hormone (ADH) is released from the posterior pituitary to act on the distal convoluted tubule and the collecting duct to increase the permeability of water via upregulation of aquaporins. Together, these hormones act to increase blood pressure.

Parathyroid hormone (PTH) is released when blood calcium levels are low, and functions to raise blood calcium levels via a negative feedback mechanism. It does this by increasing osteoclast activity and degrading bone to release calcium into the blood. It also increases absorption of calcium in the renal tubule, increases production of 25-hydroxyvitamin D3, and increases absorption of calcium in the intestines.

The heart secretes atrial natriuretic peptide, which acts on the kidneys. Oxytocin is secreted by the posterior pituitary. Thymosin is secreted by the thymus gland. Androgens are secreted by the adrenal cortex.

Gastrin is a hormone secreted by the stomach and small intestine that acts on the gastrointestinal tract and pancreas. Many hormones, such as vasopressin (antidiuretic hormone) and aldosterone act on the kidneys. Hormones that target bone are calcitonin and parathyroid hormone. Hormones that target gonads include follicle stimulating hormone and luteinizing hormone.

The hormones secreted by the alpha and beta cells of the pancreas are glucagon and insulin, respectively. These hormones are associated with the metabolism glucose. Glucagon increases blood glucose levels, while insulin does the opposite. Follicle-stimulating hormone is responsible for egg or sperm development. Tropic hormones from the hypothalamus are what release or inhibit pituitary hormones. Lastly, thymosin and thymopoietin are what regulate blood calcium and phosphate levels.

Adipose tissue secretes leptin, adiponectin, and resistin which affect food intake, metabolism, and reproduction. The thymus gland is responsible for secreting thymosin and thymopietin. Ovaries and the placenta secrete estrogen and progesterone. The adrenal medulla secretes epinephrine and norepinephrine.

Peptide hormones are large polar hormones that are able to freely float in the bloodstream. Once they reach their target cells, peptide hormones attach to transmembrane receptors on the target cell. This generally initiates a second messenger signal cascade to amplify the response, eventually driving a change in genetic expression and transcription.

In contrast, steroid hormones are small and nonpolar. These characteristics allow them to freely diffuse across the plasma membrane of the cell and enter the nucleus, where they can directly act as transcription factors to regulate genetic expression.

Hypersecretion, or oversecretion, of the growth hormone in adulthood results in a condition called acromegaly. The adult individual no longer has growth plates at this point, so the excess hormones interact with the receptors on the surface of bones. This results in coarse facial features, thickening of the dermis, and large hands and feet.

Gigantism is also a result from hypersecretion of the growth hormone, but it occurs during childhood when the individual still has his or her growth plates. Dwarfism is a result from hyposecretion, or undersecretion, of the growth hormone.

The adrenal cortex secretes androgens, cortisol, and aldosterone. The adrenal medulla is what secretes epinephrine. The kidney secretes erythropoietin. Lastly, the pancreas is what secretes insulin.