Endocrine System I Endocrine system A Endocrine tissues

Endocrine System

I. Endocrine system • A. Endocrine tissues & organs are found throughout the body some along organs part of other systems others found along glands • B. Hormones are the molecules that are secreted by this system into extracellular fluid, circulate in the blood and communicate regulatory messages throughout the body. – 1. Each hormone has specific receptors in the body that can regulate reproduction, development, metabolism, growth & behavior

II. Intercellular Communication • A. There are 2 main criteria that classify how signals are transmitted between cells: the type of secreting cell & the route taken by the signal in reaching its target.

• 1. Endocrine Signaling – hormones secreted into extracellular fluid by endocrine cells & reach target by flowing through blood stream

• 2. Local regulators – secrete molecules that act over short distances & reach target cells solely by diffusion. • Ex. Paracrine – signaling target cells that lie near secreting cell Autocrine – signaling cells are the secreted cell itself

• 3. Synaptic & Neuroendocrine Signaling – allow for signaling through nervous system by neurons – a. Neurotransmitters – signaling at synapses – b. Neurohormones – molecules that are secreted by special neurons into the bloodstream (Ex. ADH)

• 4. Pheromones – chemicals released into the external environment – a. commination within own species

III. Classes of Hormones • A. Hormones vary by size & chemical properties since there are 3 chemical classes of hormones including: – 1. Polypeptides – 2 polypeptides chains (insulin) – 2. Steroids – composed of lipids, 4 fused carbon rings (cortisol) – 3. Amines – one single amino acid (tyrosine/trptophan) • B. The chemical make-up of the hormone explains how the hormone targets the cell; polypeptides & amines are water soluble so they can not pass through the cell membrane unlike steroids that are lipid soluble

IV. Cellular Response Pathways • A. How a hormone causes a response are different between water-soluble & lipid-soluble hormones. – 1. Water-soluble hormones – are secreted by exocytosis & travel through the blood stream & bind to cell-surface protein receptors. • a. can cause changes in transcription by signal transduction (extracellular chemical causing intercellular response) Ex. epinephrine

• 2. Lipid-soluble hormones – diffuse out across a membrane of endocrine cells, they bind to transport proteins that keep them soluble in the blood stream and then diffuse into target cells – a. change in gene expression

V. Effects of Hormones • A. Hormones can cause more than one type of response in your body since target cells can vary in their response to a particular molecule with different receptors. – 1. Epinepherine – mediating body’s response to stress • Triggers glycogen breakdown in liver • Increased blood flow to major skeletal muscles • Decreased blood flow to digestive tract

VI. Signaling by Local Regulators • A. There are several chemical compounds function as local regulators (Paracrine &Autocrine) – 1. Growth factor – stimulate cell proliferation – 2. Nitric oxide – helps regulate the oxygen levels by activating enzymes that relax muscles – 3. Prostaglandins – stimulate muscle contraction in the uterus, promote fever & inflammation, blood clotting

VII. Regulatory Pathways • A. Two basic types of organization – 1. Simple endocrine pathway – endocrine cells respond directly to internal or environment stimulus by secreting a hormone into blood stream • Ex. Stomach contents enter duodenum - pancrease – 2. Simple neuroendocrine pathway – stimulates is received by sensory neuron, stimulates neurosecretory cell then secretes a neurohormone which diffuses into the bloodstreamand travels to target cells • Ex. Suckling stimulates hypothalamus then trigger oxytocin from pituitary gland

Negative vs. Positive

IIX. Control of Blood Glucose • A. Controlled by 2 antagonistic hormones that operate in a simple endocrine pathway & regulated by negative feedback – 1. Insulin – triggers uptake of glucose from the blood, slows down glycogen breakdown – 2. Glucagon – promotes the release of glucose into the blood from energy stores, such as liver glycogen, • B. Both are released by the pancreas into the circulatory system – Alpha cells – make glucagon – Beta cells – make insulin Diabetes mellitus: deficiency of insulin or a decreased response to insulin in target cells. Fat becomes main energy source – acidic metabolites form lowering blood p. H