Chapter 47 Endocrine Regulation

The endocrine system Endocrine glands, cells, and tissues that secrete hormones Hormones are an important type of chemical signal by which cells communicate Secreted into the interstitial fluid and typically transported by the blood Bind with receptors or in specific target cells

Some types of endocrine signaling

Four main chemical groups Fatty acid derivatives Prostaglandins and the juvenile hormone of insects Steroids Secreted by the adrenal cortex, ovary, and testis, as well as the molting hormone of insects

Four main chemical groups, cont. Amino acid derivatives Thyroid hormones and epinephrine Peptides or proteins ADH and glucagon are peptide hormones Insulin is a small protein

Major chemical groups of hormones

Hormone secretion Typically regulated by negative feedback mechanisms Hormone is released in response to some change in a steady state Triggers a response that counteracts the changed condition This process restores homeostasis

Regulation by negative feedback

Steroid and thyroid hormones Hydrophic molecules Pass through the plasma membrane Combine with receptors within the target cell The hormone-receptor complex may activate or repress transcription of messenger RNA coding for specific proteins

Mechanism of action of steroid hormones

Peptide hormones are hydrophillic and do not enter target cells Combine with receptors on the plasma membrane of target cells Many hormones bind to G protein-linked receptors Act via signal transduction

Overview of peptide hormone action

Mechanism of action of hormones that use G protein-linked receptors and second messengers

Most peptide hormones are first messengers Carry out their actions by way of second messengers Cyclic AMP (cAMP) Calcium ions

Phospholipid products as second messengers

Inositol trisphosphat (IP3) and diacylglycerol (DAG) Second messengers that Increase calcium concentration Activate enzymes

Receptor tyrosine kinases Enzyme-lined receptors Bind growth factors, including insulin and nerve growth factors

Signal amplification Occurs as each hormone-receptor complex stimulates the production of second messenger molecules Second messengers activate protein kinase molecules that activate protein molecules

Four functions of hormones in invertebrates Neurohormones secreted by neurons rather than endocrine glands

Four functions of hormones in invertebrates, cont. Help regulate Metabolism Growth and development Regeneration Molting Metamorphosis Reproduction and behavior

Regulation of growth and molting in insects

Human endocrine glands

Some endocrine glands and their hormones

Consequences of endocrine malfunction

Nervous and endocrine regulation Integrated in the hypothalamus, which regulates the pituitary gland

Oxytocin and ADH Produced by the hypothalamus Released by the posterior lobe of the pituitary

Hypothalamus Secretes Releasing hormones Inhibiting hormones These regulate the hormone output of the anterior lobe of the pituitary

Anterior lobe of the pituitary Secretes the growth hormone, prolactin Several tropic hormones that stimulate other endocrine glands

The hypothalamus regulates the anterior lobe of the pituitary gland

Growth hormone (GH) Anabolic hormone that stimulates body growth Stimulates the liver to produce insulin-like growth factors (IGFs), which promote skeletal and tissue growth

Thyroid gland Secretes Stimulate the rate of metabolism Thyroxine Triiodothyronine Stimulate the rate of metabolism

Regulation of thyroid secretion Depends mainly on a negative feedback system Anterior pituitary gland Thyroid gland

Thyroid hyposecretion Childhood cretinism Adult myxedema Thyroid hypersecretion Most common cause is Grave’s disease Goiter associated with both hyposecretion and hypersecretion

Regulation of thyroid secretion by negative feedback

Calcitonin, secreted by the thyroid, acts antagonistically to PTH Parathyroid glands Secrete PTH Regulates calcium level in the blood Stimulates calcium release from bones Calcitonin, secreted by the thyroid, acts antagonistically to PTH

Regulation of calcium homeostasis by PTH and calcitonin

Islets of Langerhans Secrete insulin Secrete glucagon Stimulates cells to take up glucose and so lowers blood glucose Secrete glucagon Raises blood glucose concentration Diabetes mellitus Results in decreased use of glucose

Islets of Langerhans

Adrenal glands Secrete hormones that help the body cope with stress Adrenal medulla secretes Epinephrine Norepinephrine Adrenal cortex secretes Sex hormones

Adrenal gland

Response to stress