Ch 16 Endocrine System

Hormone Regulation

• ACTH stimulates the release of cortisol by the adrenal cortex.
• Cortisol increases the concentration of blood amino acids, releases fatty acids, and forms glucose from non-carbohydrate sources.
• Secretion of glucagon from the pancreas and growth hormone from the anterior pituitary increases.
• Glucagon and growth hormone aid in mobilizing energy sources and stimulating the uptake of amino acids by cells.

Renin-Angiotensin-Aldosterone System

• Renin increases the blood level of angiotensin II, which acts as a vasoconstrictor and stimulates aldosterone secretion by the adrenal cortex.
• Aldosterone increases Na+ retention by the kidneys.

Thyroid Gland Disorders

Hyperthyroidism

• Grave's disease: Autoantibodies bind TSH receptors on thyroid cell membranes, mimicking the action of TSH, over-stimulating the gland, leading to hyperthyroidism.
• Symptoms: high metabolic rate, sensitivity to heat, restlessness, hyperactivity, weight loss, protruding eyes, and goiter.

Hypothyroidism

• Hashimoto's disease: Autoantibodies attack thyroid cells, producing hypothyroidism.
• Symptoms (infantile): Cretinism - stunted growth, abnormal bone formation, mental retardation, low body temperature, and sluggishness.
• Symptoms (adult): Myxedema - low metabolic rate, sensitivity to cold, sluggishness, poor appetite, swollen tissue, and mental dullness.

Sequence of Steroid Hormone Action

• Endocrine glands secrete steroid hormone.
• Steroid hormone diffuses through the target cell membrane.
• Hormone combines with a receptor molecule.
• Steroid hormone-receptor complex binds to DNA and promotes synthesis of mRNA.
• mRNA enters the cytoplasm and directs protein synthesis.
• Newly synthesized protein produces hormone's specific effects.

Action of Protein Hormones

• A protein hormone is transported in the blood or lymph by itself, without a transporter.
• When it arrives at the target cell, the protein hormone binds with a specific receptor embedded in the cell membrane of the target cell.
• This binding activates a series of chemical reactions in the cytoplasm of the target cell.

Effects of Hormone Action

• Change in cell membrane permeability.
• Change in chemical reaction rate.
• Enzyme activation.
• Activation of cell secretion.

Protein Hormones

• Protein hormones never diffuse to the DNA of target cells, so no new proteins or enzymes are made at the end.
• The sequence of protein hormone action:
  • Endocrine gland secretes non-steroid hormone.
  • Hormone combines with receptor site on membrane of target cell, activating G protein.
  • G protein activates adenylate cyclase within target cell's membrane.
  • Adenylate cyclase converts ATP into cyclic AMP (cAMP).
  • cAMP activates protein kinases.
  • Protein kinases activate protein substrate in the cell, changing metabolic processes.
  • Cellular changes produce the hormone's effects.

Control of Hormone Secretion

• Hormone secretion is regulated by negative feedback mechanisms.
• Negative feedback: once the desired effect is achieved in the target cell, an inhibitory signal is sent from the target cells to the endocrine gland.

Steroid Hormones

• Steroid hormones diffuse through target cell membrane.
• The sequence of steroid hormone action:
  • Endocrine gland secretes steroid hormone.
  • Steroid hormone diffuses through target cell membrane.
  • Hormone combines with a receptor molecule.
  • Steroid hormone-receptor complex binds to DNA and promotes synthesis of mRNA.
  • mRNA enters the cytoplasm and directs protein synthesis.
  • Newly synthesized protein produces hormone's specific effects.

Action of Hormones

• Protein hormones bind to a specific receptor embedded in the cell membrane of target cells.
• Binding activates a series of chemical reactions (cascade reactions) in the cytoplasm of target cells.
• Steroid hormones bind to a specific receptor located on a particular gene of target cell's DNA.

Thyroid Gland

• The thyroid gland is involved in the synthesis of hormone using protein or lipid anabolism.
• Hormone secretion occurs through exocytosis or diffusion.

Effects of Hormones

• Hormones can:
  • Change cell membrane permeability (e.g., insulin causes muscle cells to have a higher permeability for glucose).
  • Change chemical reaction rates (e.g., growth hormone stimulates higher chemical reaction rates in muscle and bone cells).
  • Activate enzymes (e.g., epinephrine increases enzyme action in muscle cells).
  • Activate cell secretion (e.g., melanocyte-stimulating hormone activates more melanin secretion from melanocytes).

Endocrine System

• The endocrine system interacts with the nervous system to coordinate and integrate body activities through hormones.
• Endocrine tissues and organs secrete hormones directly into body fluids (mainly blood and lymph) using diffusion.

Functions of Hormones

• Hormones regulate metabolic processes (e.g., thyroid hormones).
• Hormones control the rate of chemical reactions (e.g., growth hormone).
• Hormones aid in the transport of substances across the cell membrane of target cells (e.g., insulin and glucagon).
• Hormones regulate water and electrolyte balances (e.g., antidiuretic hormone, calcitonin, and aldosterone).
• Hormones play a vital role in reproduction, growth, and development (e.g., estrogens, progesterone, and testosterone).

Major Endocrine Organs

• Pituitary gland
• Thyroid gland
• Adrenal glands
• Pancreas
• Ovaries and testes
• Pineal gland
• Thymus gland
• Heart
• Digestive organs
• Kidneys
• Placenta