Hormones and the Endocrine System

Chapter 45

p. 943-963

Hormones: an introduction

Hormone: chemical signal secreted to communicate regulationCarried in blood or hemolymphTarget Cells: specific cells that respond to

hormones Endocrine System: consists of cells &

ductless glands that secrete hormones directly into body fluids

Endocrine-Nervous System Relationship Both systems have structural, functional, &

chemical similarities Regulate each other through + & - feedback systems Nervous System: rapid messages w/ immediate

response Endocrine System: slower, longer-lasting responses

Neurosecretory Cells: nerve cells of endocrine system that secrete hormones i.e.: Epinephrine: acts as both hormone & nervous

system signal

Control Pathways

Endocrine control systems include a receptor, a control center, and an effector

4 Types (see Fig 45.2): 1) Simple Endocrine: involves endocrine cells only 2) Simple Neurohormone: involves neurosecretary

cells only 3) Simple Neuroendocrine: involves endocrine &

neurosecretary cells 4) Complex: involves one hormone controlling

another Most are (-) feedback systems

Classes of Hormones

1) Proteins & Peptides: small polypeptides H2O soluble

2) Amines: derived from amino acids H2O soluble

3) Steroids: lipid w/ 4 C-rings & a functional group attached NOT H2O soluble

All involve reception, signal, and response

The Signal-Transduction Pathway

1) Reception: signal molecule binds to specific receptor protein A) Plasma Membrane Receptors

i.e. for epinephrine, frog’s camouflage

B) Intracellular Receptors (in nucleus)

2) Signal Transduction: results in response i.e. enzyme activation,

uptake/secretion molecules, etc. Target cells determine the

response

Intracellular Receptors

Nucleus is target for small, non-polar molecules that pass easily through cell membrane i.e. steroid & thyroid hormones, vit D, NO

Signal is transducted within cell; stimulates/represses transcription of genes i.e. Estrogen: stimulates female bird cells to produce

ovalbumin (egg white protein)

Chemical Signaling Modes of Action

A) Local Regulators: act on neighboring cells Elicit response much more quickly than hormones 1) target cells take up signal 2) enzymes break down signal (non-target cells) 3) signal is fixed in extracellular matrix (storage) Types: Paracrine & Synaptic

B) Long-Distance: signal travels through blood stream to reach target cell Type: Hormonal

C) Pheromones: act between individuals i.e.: to attract mates

Types of Local Regulators

1) Growth Factors: peptides/proteins; stimulate cell division, growth, & development i.e.: Nerve Growth Factor: speeds dvlpmt of

embryonic nerve cells, WBC, others 2) Nitric Oxide (NO): gas; many functions,

highly reactive, may be toxic i.e.: neurotransmitter, kills bacteria & cancer cells,

relaxes smooth muscle 3) Prostaglandins (PG): modified FA’s;

important in reproductive functions i.e.: uterine contractions, induces fever, antagonistic

muscle action

The Vertebrate Endocrine System Hormones may target few

tissues or many Tropic Hormones: target

other endocrine glands & aid in chemical coordination

Some organs outside endocrine have cells that secrete hormones i.e.: stomach, heart, kidney,

placenta Thymus Gland: important

in the immune system

Endocrine Glands

Chapter 45

p. 948-961

Hypothalamus/Pituitary Relationship Hypothalamus: contains 2

sets of neurosecretory cells in lower brain that regulate the pituitary Integrates endocrine & nervous

system

Posterior Pituitary “neurohypophysis”: extension of the hypothalamus Stores & secretes hypoth.

hormones

Hypothalamus/Pituitary Relationship (con’t)

Anterior Pituitary “adenohypophysis”: endocrine cells that make & secrete hormones into blood Develops from embryonic mouth

tissue Controlled by tropic hormones of

the hypothalamus: Releasing Hormones: cause ant.

pit to release hormones Inhibiting Hormones: stop

secretion from ant. pit Portal vessels connect

hypothalamus to anterior pituitary

Posterior Pituitary Hormones

BOTH are peptides, use simple neurohormone pathway, and are (+) feedback systems1) ADH: acts on kidneys to retain H2O & ↓

urine volume Helps regulate blood osmolarity

2) Oxytocin: induces muscle contractions on birth & milk release during nursing

Anterior Pituitary Hormones

A) Tropic Hormones: all use complex pathways1) FSH & LH “gonadotropins”: stimulate

activity of ovaries &testes2) TSH: promotes development of thyroid

gland & hormones3) ACTH: stimulates production & secretion of

steroid hormones by adrenal cortex

Anterior Pituitary Hormones (con’t) B) Nontropic Hormones: all use simple

neuroendocrine pathways 1) Prolactin: variety of effects in different vertebrates

Indicates evolutionary significance 2) MSH: regulates activity of pigment cells & plays

role in fat metabolism 3) Endorphins: produced by neurosecretary cells;

dull pain perception C) Growth Hormone: tropic & nontropic effects

Variety of actions Helps stimulate bone & cartilage growth, may ↑ blood

glucose (oppose insulin) Abnormal production may lead to gigantism or

dwarfism

Pineal Gland

Near center of brain Contains light-sensitive cells & is

connected to the eye Involved in biorhythms of reproduction

Link between biological clock & activity

Thyroid Gland

On ventral side of trachea Mostly releases T4 which converts to T3 at target

cell – contain iodine Involved in skeletal & mental development Maintains normal BP, HR, muscle tone,

digestion & reproduction Hyperthyroidism: ↑ thyroid hormones cause ↑ body

temp, sweating, weight loss, ↑ BP Hypothyroidism: ↓ hormones cause infant cretinism,

weight gain, lethargy Goiter: ↓ hormones caused by lack of iron (can not

synthesize T4 & T3)

Parathyroid

4 glands embedded in thyroid When blood Ca2+ is low, PTH causes:

1) Osteoclasts to decompose bone matrix to release Ca2+

2) Kidneys to reabsorb Ca2+ into blood & activate vit D

Pancreas

Upper abdominal cavity Both exocrine & endocrine functions Produces bicarbonate & digests enzymes Islets of Langerhans: clusters of endocrine

cells; regulate glucose conc. in blood Alpha: secrete glucagon (↑ [glucose] in blood) Beta: secrete insulin (↓ [glucose] in blood)

Diabetes

Type I Diabetes Mellitus: “insulin-dependent” or “juvenile onset”Autoimmune disorderDestroys ability to produce insulin

Type II Diabetes Mellitus: “non-insulin dependent” or “adult onset”Caused by heredity or obesityCauses insulin deficiency or ↓ target cell

responsiveness

Adrenal Glands

Adjacent to the kidneys Adrenal Medulla: central gland

Hypothalamus controls thru nervous system Secretes epinephrine & norepinephrine (↑ blood

glucose) “Fight-or-Flight”

Adrenal Cortex: outer gland Hypothalamus controls thru hormones Secretes glucocorticoids (glucose synthesis) &

mineralocorticoids (NaCl & H2O balance)

Gonads

Testes (males) & Ovaries (females) Affect growth & development and regulate

reproduction cycles & sexual behavior Controlled by FSH & LH