Chapter 26: Hormones and the Endocrine System

Hormones

• A chemical signal that is carried by the circulatory system and that communicates regulatory messages throughout the body

• Made and secreted by organs called endocrine glands

• Endocrine system

Target cells

• Hormones may travel to all parts of the body but only certain types of cells are equipped to respond

Neurosecretory cells

• Specialized nerve cells• Conduct nerve signals• Make and secrete

hormones into the blood

• Epinephrine: function in flight or fight hormone

Water soluble hormones• Embedded in the plasma

membrane of target cells and project outward from the cell surface

1. Hormone molecule binds to the receptor protein and activates it

2. A signal transduction pathway begins

3. The final relay molecule activates a protein that carries out the cell’s response

Lipid soluble hormones

• Steroid hormones• Bind to receptors inside

the cell

Endocrine system

• Pineal gland: a pea sized mass of tissue near the center of the brain– Synthesizes and secretes

melatonin (a hormone that links environmental light condition with biological rhythms

Thymus gland: lies under the breastbone, secretes hormones that stimulate the production of T cells

Hypothalamus

• Receives information from nerves about the internal condition of the body and about the external environment, then responds this information by sending out appropriate nervous or endocrine signals

• Its hormonal signals directly controls the pituitary gland

Pituitary Gland• 2 distinct parts: a posterior

lobe and an anterior lobe• Posterior pituitary: actually an

extension of the hypothalamus and stores and secretes two hormones that are made by the hypothalamus

• Anterior pituitary: synthesizes and secretes numerous hormones directly into the blood, they control the activity of other endocrine glands

Hormones secreted by the pituitary gland

• Oxytocin: stimulates the contraction of uterus and mammary gland cells

• ADH• Growth hormone: stimulates growth

and metabolic functions• Prolactin: stimulates milk production• Follicle Stimulating Hormone:

stimulates the production of ova and sperm

• Lutenizing hormone: stimulates ovaries and testes

• Thyroid stimulating: stimulates the thyroid gland

• Adrenocorticotropic: stimulates the adrenal cortex to secrete glucocorticoids

Thyroid

• Located just under the larynx

• Produces thyroxine (T4) and triiodothyronine (T3) hormones which play crucial roles in development and maturation and maintain normal blood pressure, heart rate, muscle toner, digestion and reproductive function

Parathyroid

• Four glands embedded in the surface of the thyroid

• Calcitonin (from thyroid) and parathyroid hormone (PTH) regulate blood calcium levels

• Calcitonin lowers calcium levels and PTH raises it

Calcium homeostasis

Pancreas

• Produces 2 hormones that play a large role in managing the body’s energy supplies

• Islets of Langerhans: clusters of cells in the pancreas that release insulin and glucagon

• Insulin and glucagon regulate the concentration of glucose in the blood

Glucose homeostasis

Diabetes

• Hormonal disease in which the body cells are unable to absorb glucose from the blood

• Type I diabetes- an autoimmune disease-white blood cells of the body’s own immune system attack and destroy the pancreas beta cells-generally develops in childhood

• Type II diabetes-either a deficiency of insulin or by reduced responsiveness of target cells to insulin in the blood-generally appears after the age of 40

• Gestational diabetes

Adrenal Glands

• Sit on top of the kidneys• Made up of adrenal

medulla and adrenal cortex• Produce the fight or flight

hormones which ensure a rapid, short term response to stress

• Triggered by epinephrine (adrenaline) and norepinephrine (noradrenaline)

Adrenal Gland hormones

• Mineralocorticoids-act mainly on salt and water balance– Aldosterone-reabsorbs

Na ions and water so increases the volume of the blood and raises blood pressure in response to stress

• Glucocorticoids-mainly mobilizes cellular fuel, reinforcing glucagon– Promote the synthesis of

glucose from noncarbohydrates such as fats and proteins

– Very high levels can suppress the body’s defense system

Sex hormones

• Gonads-sex cells• 3 major categories– Estrogen– Progestins– androgens

Sex hormones

• Estrogens-maintain the female reproductive system and promote the development of such female features as smaller body size, higher-pitched voice, breasts and wider hips

• Progestins-primarily involved in preparing and maintaining the uterus to support an embryo

Sex hormones

• Androgens- stimulate the development and maintenance of the male reproductive system– Testosterone-trigger

development of male characteristics like lower pitched voice, facial hair, and large skeletal muscles