Hormones & the Endocrine System

Campbell and ReeceChapter 45

body‘s long-distance regulators molecules secreted into ECF circulate

thru body communicate regulatory messages thru out body

in animals that undergo metamorphosis hormones stimulate growth of adult cells & apoptosis of larval cells

Hormones

with nervous system in charge of communication & regulation thru out body

Endocrine System

Nervous System Endocrine System

rapid response neurotransimitters short distances regulate neurons,

muscle, glands, endocrine cells (area of overlap)

slower response hormones short or long distances regulate functions of

most organ systems

signaling processes in animals: classified by 2 criteria:1. type of secreting cell2. route signal takes to reach target

Intercellular Communication

hormones ECF bloodstream target cells

functions:1. maintain homeostasis2. mediate responses to environmental

stimuli3. regulates growth & development

Endocrine Signaling

molecules that act over short distances reach target solely by diffusion

◦ ex: cytokines released by T helper cells 2 types:1. paracrine2. autocrine

Local Regulators

http://sites.sinauer.com/cooper5e/animation1501.html

animation

not all secreted molecules act w/in body

method of communication between members of some animal species ◦ ex: 1. foraging ant locates new food source

marks its path back to nest with pheromones

2. define boundaries of territory3. attract mates: female giant silk moth

releases pheromone that can attracgt a male up to 4.5 km away

Pheromones, an Exception

ductless organs secrete hormones directly into

surrounding fluid

Endocrine Glands

1. Polypeptide2. Steroid3. Amines

3 Chemical Classes of Hormones

Cellular Response Pathways

Water-Soluble Lipid-Soluble

secreted by exocytosis

travel thru blood bind to cell-surface

signal receptors induces changes in cytoplasmic molecules might alter gene transcription (signal transduction)

diffuse out of endocrine cell bind to transport molecules in blood diffuse into target cells bind to intracellular receptors trigger gene transcription

Cell-surface hormone receptors trigger signal transduction

Steroid hormone receptors directly regulate gene expression

effects hormone has can vary if target cells differ in molecules that receive or produce the response to the hormone

Multiple Effects of Hormones

pathways by which local regulators trigger responses same as those activated by hormones

growth factors◦ stimulate cell proliferation & differentiation

NO (nitric oxide)◦ synthesized & released by endothelial cell when

O2 levels low activates enzyme in smooth muscle vasodilation increased blood flow

prostaglendins:◦ aggregation of platelets blood clotting◦ promote fever & inflammation in immune

system◦ smooth muscle contraction

Signaling by Local Regulators

occurs in all but simplest invertebrates

Coordination of Neural & Endocrine Signaling

Simple Hormone Pathways

Simple Neuroendocrine Pathway

Feedback Loop Regulations

Negative Feedback Positive Feedback

stimulus initiates a response that will reduce the effect of the stimulus

stimulus initiates a response that reinforces the stimulus

Insulin lowers blood glucose levels by:◦ stimulating nearly all cells *outside the

brain to take up glucose◦ slowing glycogen breakdown in liver◦ inhibiting glycerol (from fats) & a.a.

glucose aka gluconeogenesis *brain cells do not require insulin to

take up glucose

Target Tissues of Insulin

Glucagon influences blood glucose levels mainly thru it effects on target cells in liver

when serum glucose levels < normal (70 – 110 mg/100 mL) glucagon signals liver cells to release glucose blood by: 1. increase glycogen hydrolysis2. convert a.a. & glycerol glucose

Target Tissues of Glucagon

deficiency of insulin in target tissues hi blood glucose levels but cannot get

into cells so cells use fat as main substrate for cellular respiration

acidic metabolites form during fat breakdown ketoacidosis◦ low pH can be life threatening◦ Na+ & K+ ions depleted

Diabetes Mellitus

characterized by failure of target cells to take up insulin from blood elevated blood glucose

7th most common cause of death in USA contributing factors:

◦ genetics (defect in insulin receptor or insulin response pathway)

◦ obesity◦ age (though more children being diagnosed)◦ sedentary lifestyle

Type II Diabetes: Insulin Resistance

Hypothalamus ◦ plays central role in integrating endocrine &

nervous systems◦ receives info initiates endocrine signaling

appropriate to environmental conditions◦ sends releasing hormones to anterior

pituitary gland sends tropic hormones to target glands

◦ sends hormones it makes to posterior pituitary

Coordination of Endocrine & Nervous Systems in Vertebrates

1. ADH: antidiuretic hormone (vasopressin)

◦ 1 of several hormones that act on kidneys◦ increases water retention in kidneys

(decreases urine vol/ increases blood plasma vol : maintains blood osmolarity wnl

2. Oxytocin◦ increases strength on uterine contractions

in labor◦ regulates milk secretion by mammary

glands

Posterior Pituitary Hormones

Anterior Pituitary Hormones

over time functions of a hormone have diverged from species to species

ex: thyroxine (thyroid hormone) regulates metabolism in most animal but in frogs it function to resorb tadpole tail

Prolactin: in mammals develops mammary glands & milk production but in birds: regulates fat metabolism & reproduction; in amphibians: delays metamorphosis; in fish

Evolution of Thyroid Function

Animal Function Mammals develops mammary ` glands & milk synthesis Birds regulates fat

metabolism Amphibians delays metamorphosis Fish regulates salt & water ` balance

Prolactin Functions

Tropic Hormones (not GH orMSH)

Nontropic Hormones of Anterior Pituitary: GH