Phys 1 Peripheral Endocrine Glands

Thyroid Location

Gland is located in the neck, below the larynx/front of the trachea. Consists of two lobes connected by an isthmus.

Thyroid Hormone Control

hypothalamus releases TRH → stimulates anterior pituitary to release TSH → stimulates thyroid to make T3 and T4. High T3/T4 levels stop TRH and TSH release

Thyroid Hormone Effect (T3, T4)

Effects basal metabolic rate, heat production, growth and development, and sympathetic nervous system activity.

T3 (triiodothyronine)

Active and more potent thyroid hormone

T4 (thyroxine)

Hypothyroidism

Symptoms include weight gain, fatigue, cold intolerance, slow heart rate, constipation, dry skin, and mental sluggishness.

Hyperthyroidism

Symptoms include weight loss, heat intolerance, rapid heart rate, anxiety, increased appetite, sweating, and sometimes bulging eyes (exophthalmos).

The adrenal cortex (outer layer)

secretes steroid hormones cortisol, aldosterone, androgens

The adrenal medulla (inner region)

secretes epinephrine and norepinephrine

Aldosterone

Main mineralocorticoid; Increases sodium (NA+) reabsorption and potassium (K+) excretion in the kidneys
Regulates blood pressure and fluid balance.

Cortisol

Main glucocorticoid, often called the “stress hormone”
Increases blood glucose, suppresses the immune system, mood alterations (increased alertness)

Stress Response

Increased heart rate and blood pressure, mobilization of glucose and fatty acids for energy, suppression of nonessential functions (digestion and reproduction), enhanced alertness.

Cortisol Secretion Control

hypothalamus releases CRH → stimulates anterior pituitary to release ACTH → stimulates adrenal cortex. Negative feedback from cortisol regulates CRH and ACTH.

Five parts of Integrated Stress Response

1. Activation of the sympathetic nervous system

2. Secretion of four main hormones (epinephrine, norepinephrine, cortisol, glucagon)

3. Suppression of nonessential processes

4. Mobilization of fuel

5. Increased cardiovascular activity

Anabolism

Metabolic process that builds larger molecules from smaller ones (e.g., proteins from amino acids). Requires energy input.

Catabolism

Metabolic process that breaks down larger molecules into smaller ones (e.g., glycogen into glucose). Releases energy.

Fuel Storage

Provide energy between meals, fasting, or increased energy demand.

Absorptive state

During and right after eating. Anabolic, stores nutrients (glycogen, fat, protein synthesis).

Postabsorptive state

Between meals, fasting. Catabolic, mobilizes stored fuels (glycogenolysis, gluconeogenesis, lipolysis).

Insulin

Triggered by high blood glucose. Causes cells (especially muscle and fat) to take up glucose and store it as glycogen or fat. Lowers blood glucose.

Glucagon

Triggered by low blood glucose. Causes liver to break down glycogen (glycogenolysis) and make new glucose (gluconeogenesis). Raises blood glucose.

Glucose vs Glycogen

Glucose is a single sugar molecule used directly for energy. Glycogen is a polysaccharide storage form of glucose in the liver and muscles.

Insulin & GLUT4

Insulin binds to cell receptors and signals GLUT4 transporters to move to the cell membrane, allowing glucose to enter cells.

Parathyroid Hormone (PTH)

Secreted by the parathyroid glands. Increases blood calcium levels.

PTH on Bone

Stimulates bone breakdown (resorption) by osteoclasts, releasing calcium into the bloodstream. It also increases calcium reabsorption in the kidneys and stimulates calcitriol production to enhance calcium absorption in the gut.

Alpha and Beta cells Pancreas

effects blood glucose

Androgens