Endocrine and Nervous SystemSimilarities and Differences

Similarities: Both the Nervous system and the Endocrine system use several of the same chemicals such as Epinephrine. The regulation of several physiological processes involve structural and functional overlap between the two systems. Each system affects the output of the other. They both use positive and negative feedback when regulating.

Differences: The Nervous system and Endocrine system use difference methods of communication among the cells and tissue. How quickly the desired response occurs and how long the response continues is also difference in the two systems. Also the area affected by the signal is different.

Negative and Positive FeedbackNegative Feedback is a primary mechanism

of the homeostasis, where by a change in a physiological variable being monitored triggers a response that counteracts the initial fluctuation.

Positive Feedback is also a physiological control mechanism in which a change in a physiological variable triggers a response that amplifies the change.

Steroid and Protein ModelProtein Model: Chemical signals secreted by

sending cell either (a)bind to receptor proteins on the surface of a target cell or (b) penetrate the target cell’s plasma membrane and bind with a receptor protein in the cytoplasm.

Steroid Model: Lipid-soluble steroid hormone passes through the plasma membrane and binds to a receptor protein present only in target cells. The hormone-receptors complex then enters the nucleus and binds to a specific regulatory site, stimulating the transcription of a specific gene into mRNA, which is then translated into a specific protein.

Signal-Transduction PathwaysSignal-transduction pathways convert the

extracellular chemical signal to a specific intracellular response, thereby changing the behavior of the target cells.

Hormone and receptor interactions are based on Signal-Transduction pathways.

Paracrine SignalingParacrine Signaling: signaling molecules released

by a cell only affect target cells in close proximity. A signal molecule released by one cell travels through the extracellular environment and acts on the receptor molecule of adjacent cells. The influence of the signal molecule is short-lived, as it reacts with the receptor cell and is removed from the environment.

An example of Paracrine Signaling agents include growth factors and clotting factors.

LigandLigand is a small molecule that specifically

binds to a larger one.

G-Protein-receptorsG-Protein: a plasma-membrane receptor that

works with the help of a protein called a G protein.

When a GTP is bound to a G-protein is activated. When the activated G-protein binds to another protein it alters that proteins activity.

Tyrosine-Kinase ReceptorsTyrosine-Kinase Receptors: membrane

receptors that attach phosphate to a protein tyrosine.

Activation occurs in three steps: (1) The ligand binding causes two receptor polypeptides to aggregate, forming a dimer. (2) This aggregation activates the tyrosine-kinase parts of both polypeptides, each of which then (3) phosphorylates the tyrosine on the tail of the other polypeptide.

Ligand-gated channelLigand-gated channels are protein pores in

the plasma membrane the when stimulated by chemical signals, open or close allowing or blocking the flow of specific ions, such as Na+ or Ca².

Models for Ligand/Receptor Interactions

Models for Ligand/Receptor Interactions

Models for Ligand/Receptor Interactions

Steroid Hormones and Cell Signaling

Steroid hormones initiate cell signaling by binding to a signal receptor in the cell. This causes a signal transduction pathway leading to a response from the cell. In some cases the response is to release a cell signal.

Phosphorylation CascadeA phosphorylation cascade is a sequence of

events where one enzyme phosphortlates another, causing a chain reaction leading to the phosphorylation of thousands of proteins.

This can be seen in signal transduction of hormone messages.

An advantage of the phosphorylation cascade is that is can be helpful to regulate the activation of proteins

Second MessengersMolecules that serve as “second messengers”

are cyclic AMP, Ca² ions, diacyglycerol and inositol trisphosphate.

Second Messengers transport the signal throughout the cell quickly as well as amplifying it.

Calcium and inositol trisphosphate in signaling pathway

(1) A signal molecule binds to a receptor, leading to (2) activation of an enzyme called phospholipase C.(3) This enzyme cleaves a plasma0membrane

phospholipid called PiP2 into DAG and IP3. Both can function as second messengers.

(4) IP3 a small molecule, quickly diffuses through the cytosol and binds to a ligand0gated calcium channel in the ER membrane, causing it to open.

(5) Calcium ions flow out of the ER, raising the Ca²+ level in the cytosol.

(6) The calcium ions activate the next protein in one or more signaling pathways, often acting via calmodulin, a ubiquitous Ca²+ binding protein. DAG functions as a second messenger in still other pathways.

Typical Cellular Response to a Cell Signaling Pathway

The typical cellular response to a cell-signaling pathway has to do with relaying information from one place to another. This can include direct contact between the neurons and or gap functions. The neurotransmitter receptor GABA produces action potentials by activating a cell surface receptor that is part of an ion channel. By binding to a GABA A receptor, a neuron opens a chloride-selective ion channel that is part of the receptor. This allows the negatively charged chloride ions to move in the neuron. However for some cell surface receptors, ligand-receptor interactions are not related to the cell response. The activated receptor must first interact with other proteins inside the cell before the effect of the action potential is produced.

Duct and Ductless GlandsDuct and ductless glands differ because

ductless glands secrete their product directly on a surface, unlike duct glands which empty into a duct. Many endocrine glands are ductless glands. This only makes sense because they secrete the hormones they produce directly into the blood or lymph system so it will be circulated to the entire body. The pineal gland, the thymus gland, the pituitary gland, the thyroid gland, the spleen, and the two adrenal glands are all ductless glands.

Anterior PituitaryThe anterior pituitary is the back part of the

pituary gland, and is a main playmaker in the endocrine system. Under the instruction of the hypothalamus, the anterior pituitary produces and secretes several peptide hormones that regulate physiological processes including stress, growth, and reproduction. Six different hormones released by endocrine cells from the hypothalamus stimulates the anterior pituitary.

The HypothalamusThe hypothalamus’s main job is to regulate

certain metabolic processes. This region on the underside of the brain, has a major role in the integration of the vertebrate endocrine and nervous systems. Besides conducting hormone production in the anterior pituitary gland, it also receives information from nerves throughout the body and other parts of the brain, initiating these endocrine signals appropriate to the environmental conditions.

Thyroid and Parathyroid GlandsThe thyroid stimulate and maintain metabolic

processes. The thyroid also lowers blood calcium.

The parathyroid raises blood calcium level.

Iodine DeficiencyIodine deficiency can cause many major problems because

of the basic and obvious reason that Iodine is an essential micronutrient. (also known as trace element) The thyroid hormones thyroxin and triodotyronine contain iodine. In places where there is little iodine in the diet, typically in remote inland areas where there are no marina foods, or perhaps where people eat little in general, iodine deficiency is developed. When this happens, one can develop goiter and cretinism, resulting in developmental delays and other health problems. This includes a low amount of hormones in the blood, due to lack of iodine to make them, giving rise to high levels of the pituitary hormone TSH, which in turn stimulates abnormal growth of the thyroid gland. Iodine deficiency also causes mental retardation and an IQ lowered by ten to fifteen points.

Cretinism is a condition associated with iodine deficiency and goiter, commonly characterized by mental deficiency, deafness, squint, disorders of stance, and delayed growth.

Thymus GlandThe Thymus Gland located in the thoracic

cavity of the vertebrate where maturation of the T cells is completed

Pancreas and Blood RegulationThe Pancreas uses both insulin and glucagon

to lower and raise glucose concentration in the blood

Insulin: When the blood glucose exceeds a certain level insulin is released and its effects lower blood glucose concentration

Glucagon: When blood glucose drop drops below the set point, glucagon is released, and its effects increase blood glucose concentration

Adrenal GlandThe Adrenal Gland are adjacent to the

kidneys and in mammals each adrenal gland is made up of two glands with different cell types and functions; The adrenal cortex, or outer portion, and the adrenal medulla, or central part.

The Adrenal Gland is stimulated by epinephrine and norepinephrine.

EpinephrineWhen epinephrine is released by the Adrenal

Gland it gives rapid bioenergetics boost, Increase rate and stroke volume of heart beat, increased blood supply to the heart, brain and skeletal muscle.

Role of Gonadotropic Hormones in Male and Females

The Gonadotropic Hormones are FSH and LH. The Synthesis of both estrogens and androgens is controlled by gonadotropins, FSH and LH, from the anterior pituitary gland.

Secondary Sex Trait HormonesThe hormones that are responsible for the

secondary sex traits in male and females are androgen, estrogen and progestin.