Chemical Signals in Animals

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 Control of metamorphosis of a butterfly. Homeostasis depends on the overlap of the nervous and endocrine systems.

Endocrine glands Exocrine 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 neurosecretory cells. 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.

Insects Possess Hormones that affect Metamorphosis

Positive and Negative Feedback Loops are Important in Maintaining Homeostasis. An drop in blood calcium causes calcitonin to be released from the thyroid gland which removes calcium from bones. A rise in blood calcium causes the parathyroid gland to release parathyroid hormone to put calcium back into bones.

Calcium Balance

Water Balance Neurosecretory cells within the hypothalamus respond to s drop in osmolarity in the blood by slightly shrinking. This sends a message to the brain to make you feel thirsty. In addition the hypothalamus releases a chemical signal to the posterior pituitary gland to release ADH into the blood stream which causes water to be reabsorbed in the kidneys. A decrease in the osmolarity of the blood decreases thirst and the hypothalamus releases less ADH.

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

Local Regulators Nitric Oxide Prostaglandins Pheromones Growth Factors Proteins that stimulate cell proliferation Nerve Growth Factor 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.

Peptide and Steroid Hormones Have Different Modes of Signaling Peptide Hormones are protein based hormones. Signal Transduction Pathways. Response is faster but do not last as long. Steroid Hormones are lipid based Pass through the membrane and to a receptor in the cytoplasm that bind to a promoter and activate a gene. These responses take longer to initiate but have a longer duration.

Peptide and Steroid Hormones

Peptide Hormones and Second Messengers Cyclic AMP is a cytoplasmic messenger that is activated when a single hormone molecule binds to the receptor on the surface of the cell that initiates a cascade of biochemical reactions. Amplification of the response results in one hormone molecule activating the release of thousands of products. Epinephrine catalyzes glycogen hydrolysis.

Hypothalamus and Pituitary Glands. 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. Releases ADH –water absorption in the kidney Oxytocin-uterine contractions and milk production in the mammary glands.

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.

Too much GH Not enough GH

Goiter

Thyroid Gland

Anterior Pituitary Prolactin(PRL) Tropic hormones controls mammary gland growth and d the synthesis of milk in mammals. delays metamorphosis in amphibians regulates salt and water balance in fish. Tropic hormones Thyroid Stimulating Hormone (TSH) Stimulates the release of Thyroxin Follicle Stimulating Hormone (FSH) Lutineizing Hormone (LH) Involved in reproduction Adrenocorticotropin (ACTH) Causes the adrenal cortex to secrete steroid hormones involved in “fight or flight” responses. Melanocyte Stimulating Hormone (MSH) Involved in color changes in amphibians. Endorphins and Enkephalins Produced by certain neurons in the brain and inhibit pain reception.

Stimulation of the Anterior Pituitary Releasing factors are produced at the base of the hypothalamus and are released by capillaries in an area called the median eminence

Pancreas

Adrenal Glands

Fight or Flight