Cell Signaling Cells of multicellular organisms are specialized in order to perform specific functions. Many biological processes require that cells work in a coordinated manner. The coordination occurs by means of cellular signaling mechanisms. For their survival cells must communicate with surrounding cells, control the conditions of their environment and respond to various stimuli that come to their surface. Cell signaling may be related to any aspect of the structure and function of the cell.

Alberts et al., L’ESSENZIALE DI BIOLOGIA MOLECOLARE DELLA CELLULA, Zanichelli editore S.p.A. Copyright © 2005  The communication or cell signaling involves signals incoming and outgoing  The signals are agents that affect cell properties  The signals affect the conformation of a receptor causing a response in the cell Cell Signaling

Alberts et al., L’ESSENZIALE DI BIOLOGIA MOLECOLARE DELLA CELLULA, Zanichelli editore S.p.A. Copyright © 2005 Why cells must respond to the signals? 1.Need to respond to environmental changes – The adaptation or cellular response is critical for survival – Activation of specific metabolic pathways (catabolic and / or anabolic) 2. It is required to coordinate cellular activities in a multicellular organism 3. An important reason of cellular communication is the promotion of cell division

1.direct intracellular Cell junctions allow signal molecules to move from one cell to another 2. contact-dependent Some molecules are bound to the surface of cells and act as signals for the cells that come in contact with them Cell communicate with each other through the signaling mechanisms of:

Signaling with direct contact

ENDOCRINE: Hormone produced by the pituitary cells passes into circulation and acts distantly on the target gland (eg. Thyroid); Neuroendocrine: the hormone is secreted by a neuron directly into circulation and reaches a target organ (eg. Kidney); Paracrine: the hormone acts on a cell present in the same gland; Autocrine: the hormone acts on the same cells from which it was secreted. Different ways of hormonal signals

Paracrine signalingSynaptic signaling Communicate using local regulators Local Signaling w/o Direct Contact

Long Distance Signaling Both plants and animal use hormones

THE TWO SYSTEMS OF COMMUNICATION Hormones diffuse long distance, through the blood where they are diluted. They act at low concentration (10-8 M); Neurotransmitters are released at high concentrations in the synapses (5 x M).

The endocrine system is a communication system aimed to adjust, integrate and coordinate various physiological processes such as: 1.Digestion, use and storage of nutrients 2.Growth and development 3.Electrolyte metabolism 4.Reproductive function ENDOCRINE SYSTEM

Hypothalamic-pituitary axis

Regulator and coordinator of multiple biological functions powerful and specialized organic molecule produced by endocrine cells in response to specific stimuli that exerts its action on specific TARGET CELLS; CELL TARGET: cell with receptor that recognizes with specificity and affinity the hormone; RECEPTOR: protein molecule or glycoprotein that placed on the cell surface or inside recognizes and binds to the hormone. HORMONE

HALF-LIFE, ONSET AND DURATION OF HORMONE ACTIVITY 1. The concentration of a hormone reflets its rate of release and the rate of inactivation and removal from the body; 2. The half-life of a hormone is the duration of time a hormone remains in the blood and is shorter for a water- soluble hormones; 3. Target organ response and duration of response vary widely among hormones

PITUITARY THYROID THYME PARATHYROIDS ENDOCRINE PANCREAS ADRENAL GLANDS OVARIES AND PLACENTA FOR WOMEN TESTICLES FOR MEN MAIN ENDOCRINE ORGANS