Endocrine System

hormones

chemical signals that are secreted into the circulatory system and communicate regulatory messages within the body

Where do hormones reach?

all parts of the body, but only target cells have receptors for that hormone

Function of Endocrine System

chemical signaling by hormones

Nervous system

a network of specialized cells - neurons - that transmit signals along dedicated pathways

What system does the endocrine system often overlap with in function?

nervous

2 criteria for classifying the ways that signals are transmitted

\-type of secreting cell

\-route taken by the signal in reaching its target

How do hormones secreted into extracellular fluids reach their targets?

through the bloodstream

What does endocrine signaling do in the body?

maintains homeostasis, mediates responses to stimuli, regulates growth and development

Local regulators

molecules that act over short distances, reaching target cells solely by diffusion

paracrine signaling

target cells lie near the secreting cells

example of paracrine signaling

growth factors

autocrine signaling

target cell is also the secreting cell

example of autocrine signaling

cytokines

synaptic signaling

neurons form specialized junctions with target cells, called synapses, where they secrete neurotransmitters that diffuse short distances and bind to receptors on target cells

neurotransmitters

molecules secreted by neurons that diffuse short distances and bind to receptors on target cells

Neuroendocrine signaling

specialized neurosecretory cells secrete molecules called neurohormones that travel to target cells via the bloodstream

Neurohormones

molecules secreted by neurosecretory cells in neuroendocrine signaling, travel to target cells through bloodstream

3 major classes of hormones

polypeptides, steroids, amines

Which classes of hormones are water-soluble

polypeptides and most amines

which classes of hormones are lipid-soluble?

steroids and other largely nonpolar hormones (some amines)

Path of water-soluble hormones

secreted by exocytosis, travel freely in bloodstream, bind to cell-surface receptors

Path of lipid-soluble hormones

diffuse across cell membranes, travel in bloodstream bound to transport proteins, diffuse through the membrane of target proteins;

Bind to receptors in the cytoplasm or nucleus of target cells

Difference between water-soluble and lipid-soluble hormone binding

water-soluble hormones bind to cell-surface receptors while lipid-soluble bind to receptors in cytoplasm or nucleus

What is the effect of the binding of a water-soluble hormone?

initiates a signal transduction pathway, which can lead to changes in cytoskeleton, enzyme activation, or gene expression

Example of water-soluble hormone that triggers signal transduction pathway

epinephrine

epinephrine

hormone that has multiple effects in mediating the body’s response to short-term stress

Binding pathway of epinephrine

binds to receptors on the plasma membrane of liver cells, which triggers release of messenger molecules that activate enzymes and result in the release of glucose into bloodstream

What is the usual response to a lipid-soluble hormone?

a change in gene expression

Binding pathway of a steroid (like estradiol)

binds to its cytosolic receptor, then a hormone-receptor complex forms that moves into the nucleus. There, the receptor part of the complex acts as a transcriptional regulator of specific target genes.

Steroid Hormones

\-lipid soluble, chemically derived from cholesterol

\-enter target cells

\-bind to intracellular receptor

\-activate specific genes to produce specific proteins

\-slower acting than nonsteroid hormones; minutes to hours

Why do steroid hormones act slowly and have long lasting effects?

because they activate DNA and form new proteins

Nonsteroid hormones

\-water soluble

\-bind to receptors on target cell membranes

\-work through intermediate mechanisms to activate existing enzymes

\-may involve a “second messenger” within the cell, such as cAMP

\-faster action than steroid hormones; seconds to minutes

Why do non-steroid hormones act quickly and have short lasting effects?

because they only change existing proteins

How could the same hormone have different effects on target cells?

\-if there are different receptors for the hormone

\-if there are different signal transduction pathways

Example of multiple effects of one hormone

epinephrine can increase blood flow to major skeletal muscles but decrease blood flow to the digestive tract

Epinephrine with Liver cells

bind to beta receptor, causes glycogen to be broken down, glucose is released from cell and enters blood

Epinephrine with Smooth Muscle cell in wall of blood vessel that supplies skeletal muscle

binds to beta receptor, causes cell to relax -- blood vessel dilates which increases blood flow to skeletal muscle

Epinephrine with smooth muscle cell in wall of blood vessel that supplies intestines

binds to alpha receptor, cell contracts, blood vessel constricts which decreases flow to intestines

Endocrine glands

ductless organs of grouped endocrine cells

\-thyroid and parathyroid glands, testes, ovaries

Exocrine glands

have ducts to carry secreted substances onto body surfaces or into body cavities

\-salivary glands

Pineal gland

produces melatonin, which participates in regulation of biological rhythms

Hypothalamus

\-releases oxytocin and vasopressin (ADH) from posterior pituitary

\-releases and inhibits hormones to regulate anterior pituitary

Anterior Pituitary

\-follicle-stimulating hormone and luteinizing hormone (stimulate ovaries and testes)

\-Thyroid-stimulating hormone

\-ACTH (stimulates adrenal cortex)

\-Prolactin: (stimulates mammary gland)

\-Growth Hormone (stimulates growth and metabolic functions)

\-Oxytocin

\-Vaspopressin

FSH

follicle-stimulating hormone; stimulates testes/ovaries

LH

luteinizing hormone; stimulates testes/ovaries

Melatonin

participates in regulation of biological rhythms

TSH

thyroid-stimulating hormone; stimulates growth of thyroid gland and secretion of thyroid hormone

ACTH

adrenocorticotropic hormone; stimulates growth of the adrenal cortex and secretion of the steroid hormone cortisol -- increases blood glucose in response to stress

Prolactin

stimulates growth of the mammary glands in the breasts and the production of milk. Its function in men is not well understood.

GH

growth hormone; stimulates growth and metabolic functions

Oxytocin

stimulates contraction of smooth muscle cells in uterus and mammary glands

Vasopressin

aka ADH (antidiuretic hormone); promotes retention of water by kidneys; influences social behavior and bonding

Thyroid gland

\-thyroid hormone (T3 and T4); stimulates and maintains metabolic processes

\-calcitonin; lower blood calcium

Thyroid hormone (T3 and T4)

stimulates and maintains metabolic processes

Calcitonin

lowers blood calcium level

Posterior pituitary

releases oxytocin and vasopressin

Parathyroid glands

\-Parathyroid hormone : raises blood calcium level

PTH

parathyroid hormone; raises blood calcium level

Adrenal medulla

\-releases epinephrine and norepinephrine

Epinephrine and norepinephrine

raise blood glucose level; increase metabolic activities; constrict certain blood vessels

Adrenal cortex

releases glucocorticoids and mineralocorticoids

Glucocorticoids

raise blood glucose level

Mineralocorticoids

promote reabsorption of Na+ and excretion of K+ in kidneys

Pancreas

release insulin and glucagon

insulin

lowers blood glucose level

glucagon

raises blood glucose level

Ovaries

release estrogen and progestins

estrogen

stimulate uterine lining growth; promote development and maintenance of female secondary sex characteristics

Progestins

promote uterine lining growth

Testes

release androgens

Androgens

support sperm formation; promote development and maintenance of male secondary sex characteristics

________ _________________ and __________ with the nervous system are common in endocrine signaling

feedback regulation; coordination

Hormones are assembled into _________ ______________

regulatory pathways

Secretin signaling

\-release of acidic contents of stomach into the duodenum stimulates endocrine cells there to secrete secretin

\-this causes target cells in the pancreas, a gland behind the stomach, to raise the pH of the duodenum by releasing bicarbonate

\-negative feedback

General Neuroendocrine pathway

\-stimulus is received by a sensory neuron

\-this stimulates a neurosecretory cell

\-neurosecretory cell secretes a neurohormone

\-neurohormone enters the bloodstream and travels to target cells

Example of Neuroendocrine Pathway

\-suckling of infant stimulates signals in the nervous systems that reach the hypothalamus

\-nerve impulses from hypothalamus trigger release of oxytocin from the posterior pituitary

\-causes mammary glands to secrete milk

\-positive feedback

Oxytocin stimulates…

milk “let-down”

negative feedback loop

inhibits a response by reducing the initial stimulus, thus preventing excessive pathway activity

Positive feedback loop

reinforces a stimulus to produce an even greater response

hypothalamus

receives information from the nervous system and initiates responses through the endocrine system

pituitary gland

attached to hypothalamus, composed of posterior and anterior parts

posterior pituitary

stores and secretes hormones that are made in the hypothalamus

anterior pituitary

makes and releases hormones under regulation of the hypothalamus

Target of ADH

kidney tubules

Target of oxytocin

mammary glands, uterine muscles

What synthesizes the two posterior pituitary hormones?

neurosecretory cells of the hypothalamus

What controls the hormone production in the anterior pituitary?

releasing hormones and inhibiting hormones secreted by the hypothalamus

Prolactin-releasing hormone

from the hypothalamus, stimulates the anterior pituitary to secrete prolactin

Prolactin (PRL)

released from anterior pituitary, role in milk production

Target of FSH and LH

testes or ovaries

Target of TSH

thyroid

Target of ACTH

adrenal cortex

Target of prolactin

mammary glands

target of MSH

melanocytest

target of GH

liver, bones, other tissues

Anterior pituitary hormones with Tropic Effects Only

FSH, LH, TSH, ACTH

Anterior pituitary hormones with Nontropic effects only

Prolactin, MSH

Anterior pituitary hormone with both tropic and nontropic effects

GH

Tropic effects

affects release of other hormones

Nontropic effects

directly affects target cells