• The nervous system sends electrical signals through nerves; the endocrine system sends chemical signals through the circulatory sytem.
• The endocrine systme has a more general effect, acts more slowly, and has a longer-lasting effect than the nervous sytem

Hormones

• Endocrine glands produce hormones that are released into the circulatory system and travel some distance, where they act on target tissues to produce a response.
• Target tissue for a given hormone has a receptor molecule for that hormone (IE receptor sites!)
• Chemistry--Hormones are either proteins, peptides, or lipids
• Hormone Action--Protein and peptide hormones bind to receptors on the cell membrane and cause a permeability changes or the production of a second messenger inside the cell. Lipid-soluble hormones such as steroids and thryoid hormones enter the cell and bind to the receptors inside the cell.
• The combining of hormones with their receptors results in a response
• Regulation of Hormone Secretion--The secretion of hormones is controlled by negative-feedback mechanisms
• Secretion of hormones from a specific gland is controlled by blood levels of some chemcial, another hormone, or nerve impulses

The Endocrine system

• The endocrine system consists of ductless glands
• Some glands of hte endocrine system perform more than one function

The endocrine system and their hormones

• The pituitary and Hypothalamus--The pituitary is connected to the hypothalamus of the brain by the infundibulum. It is divided into the anterior and posterior pituitary
• Secretions from the anterior pituitary are controlled by hypothalamic-releasing hormones that pass through the hypothalamic-pituitary portal system from teh hypothalamus
• Hormones secreted from the posterior pituitary are controlled by nervous impulses that pass from the hypothatlamus through the indfundibulum
• The hormones released from the anterior pituitary are: growth hormone (GH), thyroid-stimulating hormone (TSH), adrenocorticotropic hormone (ACTH), luteinizing hormone (LH), follicle-stimulating hormone (FSH), prolactin, and melanocyte-stimulating hormone (MSH).
• Hormones released from the posterior pituitary include antidiuretic hormone (ADH) and oxytocin.
  
  
• The Thyroid Gland--The thyroid gland secretes thyroid hormones, which control the metabolic rate of tissues, and calcitonin, which helps regulate blood levels of calcium
  
  
• The parathyroid gland--The parathyroid glands secrete parathyroid hormones, which help regulate blood levels of calcium. Active vitamin D also helps regulate blood levels of calcium
  
  
• The adrenal glands--The adrenal medulla secretes primarily epinephrine and some norepinephrine. These hormones help prepare the body for phsyical activity
• The adrenal cortex secretes three classes of hormones.
  • Glucocorticoids (cortisol) reduce inflammation and break down fat and protein, making them available as energy sources to other tissues.
  • Mineralocorticoids (aldosterone) help regulate sodium and potassium levels and water volume in the body. Renin helps regulate blood pressure by increasing angiotensin II and aldosterone production. These hormones cause blood vessels to constrict and enhance sodium and water retention by the kidney.
  • Adrenal androgens increase female sexual drive; normally adrenal androgens have little effect in males.
  
  
  
• The pancreas, insulin, and diabetes-The pancreas secretes insulin in response to elevated levels of blood glucose and amino acids. Insulin increases the rate at which many tissues, including adipose tissue, liver, and skeletal muscles, take up glucose and amino acids.
• The pancreas secretes glucagon in response to reduced blood glucose and increases the rate at which the liver releases glucose into the blood.
  
  
• the testes and ovaries--The testes secrete testosterone, and the ovaries secrete estrogen and progesterone. These hormones help control reproductivity processes.
• LH and FSH from the pituitary gland control hormone secretion from the ovaries and testes.
  
  
• The Thymus Gland--The thymus gland secretes thymosin, which enhances the ability of the immune system to function
• The pineal body--The peinal body secretes melatonin, which may help regulate the onset of puberty by acting on the hypothalamus.

Other Hormones

• Hormones secreted by cells in the stomach and intestine help regulate stomach, pancreatic, and liver secretions.
• The prostaglandins are hormones that have a local effect, produce numerous effects on the body, and play a role in inflammation.
• Erythropoietin from the kidney stimulates red blood cell production.
• The placenta secretes human chorionic gonadotropin, estrogen, and progesterone, which are essential to maintenance of pregnancy