Endocrine SystemEndocrine SystemChapter 16Chapter 16

HormonesHormones

Released from glands “Looking for” receptors on cells, or

target cells

Two types of hormones• Steroid: cholesterol

• Non steroid: proteins,modified amino acids

Peptide and Steroid Hormones Have Different Modes of Signaling

Non-Steroid (Peptide) Hormones are protein based hormones.• Responses are faster but do not last as long.

Steroid Hormones are lipid based• These responses take longer to initiate but

have a longer duration.

Hormones in ActionHormones in ActionSteroid Hormone

Target cell membrane

mRNACytoplasm

Protein synthesis

Altered cellular function

Receptor

Hormone-receptor complex

Nucleus

DNA

Nonsteroid hormone (first messenger)

Receptor Target cell membrane

cAMP (second

messenger)

Enzyme activities

Altered cellular function

Cytoplasm

Nucleus

Endocrine GlandsEndocrine GlandsHypothalamusThe hypothalamus makes hormones that control the pituitary gland. In addition, it makes hormones that are stored in the pituitary gland.

Pituitary glandThe pituitary gland produces hormones that regulate many of the other endocrine glands.

Parathyroid glandsThese four glands release parathyroid hormone, which regulate the level of calcium in the blood.

ThymusDuring childhood, the thymus releases thymosin, which stimulates Tcell development.

Adrenal glandsThe adrenal glands release epinephrine and nonepinephrine, which help the body deal with stress.

Pineal glandThe pineal gland releases melatonin, which is involved in rhythmic activities, such as daily sleep-wake cycles.

ThyroidThe thyroid produces thyroxine, which regulates metabolism.

PancreasThe pancreas produces insulin and glucagon, which regulate the level of glucose in the blood.

OvaryThe ovaries produce estrogen and progesterone. Estrogen is required for the development of secondary sex characteristics and for the development of eggs. Progesterone prepares the uterus for a fertilized egg.

Testis The testes produce testosterone, which is responsible for sperm production and the development of male secondary sex characteristics

Animals Have Two Systems of Internal Communication and Regulation.

Nervous System• Movement of body parts as a quick response to

sudden environmental changes.

• Pulling your hand a way from a hot flame.

Endocrine System• Longer lasting and slower response

• Chemical response

Homeostasis depends on the overlap of the nervous and endocrine systems.

The endocrine system endocrine system is made up of glandsglands that release their productsproducts into the bloodstream. These products deliver messages throughout the bodybody.

Nervous System Endocrine System

Neuron Bloodstream

Fast Slow

Small # of cells effected Large # of cells

effected

Endocrine Glands

Endocrine glands• Ductless glands that secrete substances

directly into the blood stream.• Pancreas secretes insulin into the blood stream

Exocrine Glands• These glands have ducts

• Secrete mucus, sweat from glands through ducts

• Pancreatic duct secretes digestive enzymes.

Nervous System and Endocrine System are Closely Related Many endocrine organs contain nervous tissue composed

of neurosecretory cells (nervous system and endocrine system working in concert)• These cells secrete hormones in response to a stimulus.

• The suckling of an infant stimulates a nervous response which is sent to the brain.

• The result is the hypothalamus tells the pituitary gland to secrete oxytocin (a chemical signal) that causes the secretion of milk.

• Epinephrine is a hormone and a neurotransmitter.• Produced by adrenal glands as the “fight or flight” hormone.

• Also acts as a neurotransmitter that is involved in nerve cell communication.

Positive and Negative Feedback Loops are Important in Maintaining Homeostasis.

A rise in blood calcium causes calcitonin to be released from the thyroid gland which triggers calcium to be put into bone formation. (osteoblasts)

A lack of blood calcium causes the parathyroid gland to release parathyroid hormone to release calcium back into blood from bones. (osteoclasts)

Calcium Balance

GoiterThyroid enlarges due to lack of iodine, necessary for thyroid hormone production (pg. 504)

Chemical Signals Are Important in the Endocrine System

Some chemicals have to travel long distances to their target cells while others act locally.

The receptors on the target cells are specific and the same hormone can elicit different responses depending on the target cell and its receptor.• Acetylcholine

• Skeletal muscle contraction

• Relaxation of heart muscle

Growth Factors• Growth hormone (secreted by anterior pituitary somatotrophs) stimulates rapid

entrance of amino acids from blood into cells by stimuating growth factors production in liver

• Accelerated protein anabolism within cells increases growth rate

• Nitric Oxide• Stimulate cell destruction in the immune system• Stimulate vasodilatation in the circulatory system• Functions as a neurotransmitter in the nervous system.

• Prostaglandins• Modified fatty acids derived from lipids• Stimulate uterine contractions, fever, inflammation and the sensation of pain.• PGE and PGF are antagonistic and stimulate the contraction and dilation of blood

vessels in the lung.

• Pheromones• Chemical signals that serve as communication between animals.• Warning signals, territorial ,markers.

Local Regulators

Anterior Pituitary

Produces its own hormones and releases• Growth Hormone-Stimulate growth factors

produced in the liver called somatomedins which stimulate cartilage and bone growth.• Excessive GH production causes gigantism and

acromegaly.

• GH deficiency causes hypopituitary dwarfism.

Not enough GH

Too much GH

Hypothalamus and Pituitary Glands. Hypothalamus

• Controls the pituitary• Neurosecretory cells release hormones that control the pituitary gland.

• Important connection between the endocrine and nervous system. Pituitary

• “Master Gland”• Anterior and Posterior

• Posterior pituitary stores and releases hormones produced by the hypothalamus.

Examples:• ADH –water absorption in the kidney

• Oxytocin-uterine contractions and milk production in the mammary glands.

Pancreas

By means of the

OverviewOverview

GrowthWater

balance Reproduction Metabolism Calcium

and glucoselevels

Responseto stress

The Endocrine

System

Pituitary

Ovaries

Testes Thyroid Pancreas Adrenals

Parathyroids

regulates

By means of the

By means of the

By means of the

By means of the

By means of the