Hormones and the Pituitary Gland

Overview of Hormones

• The endocrine system uses ductless glands which produce hormones.
• Hormones are chemical messengers secreted from one location to travel via the blood to target organs elsewhere.
• Understanding where a hormone comes from, its target organs, its function, and how it's regulated is vital.
• Hormones are protein or fat-based.
• Hormone secretion is often controlled by negative feedback, where rising levels inhibit further production, like a thermostat.
• Positive feedback is less common but occurs, such as during childbirth when contractions intensify until delivery.

Pituitary Gland

• The pituitary gland hangs from the brain's bottom and consists of two parts.
• The anterior pituitary is epithelial tissue linked to the hypothalamus via a portal system of blood vessels.
• The posterior pituitary consists of nervous tissue and is essentially an extension of the hypothalamus.

Anterior Pituitary Hormones

• These hormones are secreted by the Anterior Pituitary

Growth Hormone (GH)

• GH targets cells throughout the body.
• Promotes growth in children and regulates metabolism in adults.
• Regulation is controlled by hypothalamic hormones and negative feedback.

Prolactin

• Prolactin targets mammary glands.
• It promotes milk production.
• Regulation is triggered by a baby's suckling and influenced by other hormones.

Thyroid Stimulating Hormone (TSH)

• TSH targets the thyroid gland.
• It stimulates release of thyroid hormones T3 and T4.
• Regulation is controlled by TRH from the hypothalamus and negative feedback.

Adrenocorticotropic Hormone (ACTH)

• ACTH targets the adrenal glands.
• It stimulates the release of cortisol.
• Regulation is controlled by CRH from the hypothalamus and negative feedback.

Follicle Stimulating Hormone (FSH) and Luteinizing Hormone (LH)

• FSH and LH target the gonads (testes/ovaries).
• They stimulate the production of sex hormones.
• Regulation is controlled by GnRH from the hypothalamus and negative feedback from sex hormones.

Posterior Pituitary Hormones

• These hormones are secreted by the Posterior Pituitary.

Antidiuretic Hormone (ADH)

• ADH targets the kidneys.
• It tells the kidneys to hold onto water, preventing excessive urination.
• Secretion is increased during dehydration; alcohol interferes with ADH.

Oxytocin

• Oxytocin targets the uterus and mammary glands.
• It causes uterine contractions during labor and milk let-down during breastfeeding.
• Regulation is triggered by suckling and by positive feedback during labor.

Other Endocrine Glands

Thyroid Gland

• The thyroid gland is located in the neck in front of the trachea and larynx.

Thyroid Hormones (T3 and T4)

• Secreted from follicular cells of the thyroid
• Target most cells in the body
• Regulate metabolism
• Regulated by TSH and negative feedback

Calcitonin

• Secreted from parafollicular cells of the thyroid
• Targets bones, kidneys, and the GI tract
• Decreases blood calcium
• Responds to high calcium levels

Parathyroid Glands

• Four small glands found on the posterior surface of the thyroid.

Parathyroid Hormone (PTH)

• PTH targets bones, kidneys, and the GI tract
• Increases blood calcium
• Responds to low calcium levels

Adrenal Glands

• Located on top of the kidneys.

Adrenal Medulla (inner region)

• Produces epinephrine and norepinephrine.
• Associated with the fight-or-flight response.
• Increases blood sugar.

Adrenal Cortex (outer region)

• Produces cortisol, aldosterone, testosterone, and estrogen.
• Often remembered as "sugar, salt, sex".
• Cortisol is the stress hormone that increases blood sugar.

Pancreas

• Produces hormones that regulate blood glucose.

Insulin

• Insulin decreases blood sugar.

Glucagon

• Glucagon increases blood sugar.