Endocrine System
Chapter 39
Gland
 Group of cells or organ that releases
(secretes) a substance that will be
used somewhere else in body
 Exocrine glands – release secretions
via ducts (ex: sweat glands)
 Endocrine glands – release
secretions directly into bloodstream
Endocrine System
 Made of glands
 Communication system
 Endocrine glands
produce hormones
 Hormones are
distributed to body cells
Hormones
 Chemicals that act on target cells &
tissues
 Travel through bloodstream to target
cells & attach to target cells
 Produce a response on those target cells
 Target cells – have receptors (locations
for hormone to bind) for a hormone
Endocrine System Glands
 Hypothalamus
 Pituitary gland
 Thyroid
 Parathyroids
 Adrenal glands
 Pineal body
 Thymus
 Pancreas
 Reproductive glands (incl. ovaries & testes)
Hypothalamus
 Specialized cells
located in lower central
part of brain
 Influenced by levels of
hormones in blood & by
sensory information
coming from CNS
Hypothalamus
 Main link between
endocrine & nervous
systems
 Controls the pituitary
gland (has nerve cells that
release chemicals that regulate
pituitary gland)
Pituitary Gland
 Located at base of the brain
beneath the hypothalamus
 Makes/secretes hormones
that control body functions &
several other endocrine
glands (most important part of the
endocrine system)
Pituitary & Hypothalamus
 Hypothalamus provides
sensory information from
CNS to pituitary.
 Pituitary production &
release of hormones acts
in response to factors such
as emotions,
environmental changes.
Pituitary & Hypothalamus
Pituitary Gland –
Hormones Secreted
 ADH (antidiuretic hormone)
 Oxytocin
 FSH (follicle-stimulating hormone)
 LH (luteinizing hormone)
 TSH (thyroid-stimulating hormone)
 ACTH (adreno-corticotropic hormone)
 GH (growth hormone)
 Prolactin
 MSH (melanin-stimulating hormone)
Thyroid
 Located at base of neck &
wraps around trachea
 Regulates body’s metabolism
(breaking down, putting together materials such as
food)
Thyroid - Hormones
 Thyroxine – affects metabolic rates of all
body cells
- increased levels of thyroxine = increased rate
of cellular respiration (more energy released by
cells)
 Calcitonin – decreases level of calcium
in blood
Parathyroid Glands
 4 glands on back surface of
thyroid
 Work with thyroid to
maintain homeostasis in
amount of calcium in blood
 PTH (parathyroid hormone)
increases reabsorption of Ca in kidneys & uptake
in digestive system
Adrenal Glands
 2 glands; 1 on top of
each kidney
 Help body respond to
stress
 2 parts: adrenal cortex
& adrenal medulla
Adrenal Glands - Hormones
 Corticosteroids - about 24 different
hormones
produced by adrenal cortex
Aldosterone – regulates reabsorption
of Na+ & excretion of K+ by kidneys
 Cortisol – regulates metabolism of
carbs, fats, proteins

 Epinephrine
 Norepinephrine
Adrenal Glands –
“Fight or Flight”
 Result of adrenal medulla responding to
stress stimulus
 Nerve impulses from sympathetic
nervous system stimulate adrenal
medulla
 Release of epinephrine & norepinephrine
 General increase in body activity
prepares body for intense physical
activity
Pineal Gland
 Located deep within brain
 Involved in biological
rhythms such as sleep
 Secretes melatonin
Thymus
 In top portion of chest
 Stimulates production of cells
involved in immune system
Pancreas
 Also part of digestive system
 As endocrine gland,
regulates amount of glucose
in blood.
 Certain cells in it release
hormones

Islet of Langerhans- cells that
release insulin & glucagon
Pancreas – Insulin & Glucagon
 Insulin – causes cells in liver to take
sugar (glucose) from blood & store it
 Glucagon – stimulates cells in liver to
release glucose
Pancreas – Insulin & Glucagon
 Diabetes mellitus – disease caused
when pancreas does not produce
enough insulin
 What happens if the pancreas does not
produce enough insulin?
 Diabetes type 1- pancreas does not secrete insulin
 Diabetes type 2- typically produce low to normal amount of
insulin but cells do not respond to it
Reproductive Glands
(Gonads)
 Produce gametes
 Secrete sex hormones
 Females


ovaries (produce eggs)
Estrogen, progesterone
 Males
 testes (produce sperm)
 testosterone
Feedback Loops
 How nervous system uses endocrine
system to regulate body conditions
 Feedback inhibition – an increase in a
substance sends signal to inhibit (stop)
process that produces that substance
 Analogy- turning on heater causes it to heat room until
the air in the room reaches set temperature…then that
warmer air causes heater to shut off
Feedback Mechanisms
 Negative – high levels of substance
(hormone) slow production of it
 Positive – low levels of substance
increase production of it
Negative Feedback - Insulin
Regulation of Blood Glucose
 Blood sugar rises after eating
-pancreas secretes insulin
-Glucose stored as glycogen
in liver
 Decrease in blood sugar
- glucagon secreted
- liver breaks down glycogen
glucose released
Feedback Mechanism:
Hypothalamus, Pituitary, Thyroid
 Hypothalamus senses low level




of thyroxine in blood & sends
signal (thyroid-releasing
hormone) to pituitary gland
Pituitary releases TSH
Thyroid secretes thyroxine
Hypothalamus releases less
TSH as thyroxine level rises,
less thyroxine produced
Cycle continues
Feedback Loops - Leptin
 Leptin – hormone that helps
regulate body weight,
metabolism; produced by fat
cells
 Decrease in body fat reserves
= less leptin
 Less leptin in blood stimulates
appetite center of brain
 Increase in leptin inhibits
(prevents) hunger (negative
feedback)