Download The Endocrine System

The Endocrine System
System Overview
• Includes cells, tissues,
and organs that secrete
hormones directly into
the body fluids
• Endocrine vs. exocrine
Functions of Hormones
• Help regulate metabolic processes
• Control the rates of some chemical
reactions
• Aid in the transport of substances across
membranes
• Help regulate water and electrolyte balances
• Play vital roles in reproduction, growth, and
development
What is a Hormone?
• A biochemical
secreted by a cell to
affect the functions of
another cell
• Action of a hormone is
restricted to a specific
target cell that has
protein receptors for
the hormone
Steroid Hormones
• Fat soluble
• Diffuse into cells
easily
• May bind to DNA and
activate genes
• Fast acting
Nonsteroid Hormones
• Usually combine with
cell membrane
receptors
• Binding stimulates
activity site of receptor
(hormone is first
messenger) second
messengers inside cell
trigger cell action
Prostaglandins
• Not really hormones,
but behave similarly
• Affect only the organ
where they are
produced
• Present in very small
quantities, not stored,
and rapidly inactivated
Control of Hormone Secretions
• Hypothalamus
– Controls the anterior
pituitary gland’s
release of hormones
that stimulate other
endocrine glands
• Nervous system
– Stimulates some glands
directly
• Some glands respond
directly to changes in
the internal
environment
Hormone Regulation
Major Endocrine Glands and
Their Hormones
Pituitary Gland
• Located at the base of
the brain
• Attaches to the
hypothalamus by
means of the
infundibulum
• Anterior and posterior
lobes
Anterior Pituitary Gland
• Dense CT capsule
• Blocks of glandular
epithelium around
blood vessels
Anterior Pituitary Hormones
• Growth Hormone
(GH)
– Stimulates most body
cells to increase in size
and divide
– Promotes protein
synthesis
Anterior Pituitary Hormones
• Thyroid-Stimulating
Hormone (TSH)
– Promotes normal
activity and
development of the
thyroid gland
• Adrenocorticotropic
Hormone (ACTH)
– Triggers the release of
hormones from the
adrenal cortex
Anterior Pituitary Hormones
• Follicle-Stimulating
Hormone (FSH)
– Stimulates gamete
production in males
and females
– Stimulates maturation
of ovarian follicles and
eggs in females
• Luteinizing Hormone
(LH)
– Promotes production of
gonadal hormones
– In females, triggers
ovulation and
stimulates maturation
of ovarian follicles and
eggs
Anterior Pituitary Hormones
• Prolactin (PRL)
– Stimulates milk
production in the
breasts
– Enhances testosterone
production ?
Posterior Pituitary Gland
• Consists mostly of
nerve fibers and
neuroglia
• Closely associated
with the hypothalamus
Posterior Pituitary Hormones
• Oxytocin (OT)
– Stimulates contraction
of uterine muscles
– Triggers “letdown” of
breast milk
– “Cuddle hormone” ?
Posterior Pituitary Hormones
• Antidiuretic Hormone
(ADH)
– Inhibits urine formation in
the kidneys
– Stimulates constriction of
blood vessels
– Released in response to
increased blood solute
concentration, low blood
pressure, some drugs
(nicotine, morphine)
– Inhibited by alcohol and
excessive water
consumption
Thyroid Gland
• Highly vascular
• Two lobes connected
by isthmus
• Located below larynx
• Secretory parts are
follicles filled with
colloid
• CT capsule
Thyroid Hormones
• Thryoxine (T4) and
Triiodothyronine (T3)
– Collectively known as
thyroid hormone
– Increases metabolic
rate and body heat
production
– Regulates tissue
growth
Thyroid Disorders
Thyroid Hormones
• Calcitonin
– Lowers blood calcium
– Inhibits osteoclasts
– Stimulates osteoblasts
Parathyroid Glands
• 4 small glands on
posterior of thyroid
gland
Parathyroid Hormone
• Parathyroid Hormone
(PTH)
– Raises blood calcium
– Stimulates osteoclasts
– Triggers reabsorption
of calcium in urine in
kidneys
– Increases intestinal
absorption of calcium
from food
Adrenal Glands
• Located on top of kidneys
• Embedded in adipose
• Adrenal cortex
– Outer portion of epithelial
cells organized into layers
• Adrenal medulla
– Consists of modified
neurons around blood
vessels and nerves of the
sympathetic nervous system
Adrenal Cortex Hormones
• Aldosterone
– Zona glomerulosa
– Reduces excretion of
sodium from kidneys
– Increases reabsorption of
sodium from urine,
perspiration, saliva, and
gastric juice
– Increases excretion of
potassium
– Increases water retention
Adrenal Cortex Hormones
• Cortisol
– Zona fasciculata
– Helps maintain blood
glucose concentration
between meals
Adrenal Cortex Hormones
• Androgens
– Zona reticularis
– Supplements sex
hormones produced by
gonads ?
Adrenal Medulla Hormones
• Epinephrine and
Norepinephrine
– Produce short term
stress response
– Increase heart rate,
blood pressure, and
metabolic rate
– Dilation of bronchioles
– Trigger liver to release
glucose into
bloodstream
Pancreas
• Mixed gland
• Located behind
stomach
• Islets of Langerhans
– masses of endocrine
cells amongst acinar
(exocrine) cells
Pancreas Hormones
• Insulin
– Produced by beta cells
(stain purple)
– Decreases blood
glucose concentration
– Enhances absorption of
glucose into cells for
energy use and storage
• Glucagon
– Produced by alpha
cells (stain pink)
– Stimulates liver to
release glucose from
glycogen
– 1 molecule triggers the
release of 100 million
glucose molecules into
the blood
Ovaries
• Female gonads
• Produce estrogen and
progesterone:
– Stimulate maturation
of the female
reproductive organs
and appearance of
secondary sexual
characteristics
• More info later…
Testes
• Male gonads
• Produce testosterone:
– Stimulates maturation of the
male reproductive organs
and the appearance of male
secondary sexual
characterisics
– Increases sex drive
– Promotes normal sperm
production
• More info later…
Pineal Gland
• Located between
cerebral hemispheres
• Attached to thalamus
• Releases melatonin:
– Released in response to
light
– Helps regulate
circadian rhythms ?
Thymus Gland
• Located between the lungs
posterior to the sternum
• Butterfly-shaped
• Diminishes during
adulthood
• Produces thymosin:
– Essential for the normal
development of T cells and
the immune response
– More info later…
Minor Endocrine Glands
Gland
Hormone
Hormone Actions
Heart
Atrial Natriuretic
Peptide (ANP)
Reduces blood
volume, blood
pressure, and blood
Na concentration;
Increase urine
production in
kidneys
Stomach
Gastrin
Triggers release of
HCl in stomach
Serotonin
Stimulates
contraction of
stomach muscles
Minor Endocrine Glands
Small Intestine
Secretin
Triggers release of
digestive enzymes
from the liver and
pancreas; Inhibits
stomach secretions
Cholecystokinin
Stimulates release of
pancreatic juice from
pancreas; Stimulates
release of bile stored in
gallbladder
Kidney
Erythropoietin
Increases RBC
production in bone
marrow
Uterus and Placenta
Human Chorionic
Gonadotropin (hCG)
Influences the course
of pregnancy
Minor Endocrine Glands
Epidermis
Cholecalciferol
Inactive form of
vitamin D, Activated
by UV, Triggers
absorption of Ca in
intestines
Adipose Tissue
Leptin
Suppresses appetite
STRESS!!!
• Stressor  hypothalamus  stress response
• Physical stressors – extreme temperature,
decreased oxygen, infection, injury, prolonged
heavy exercise, loud sounds
• Psychological stressors – thoughts of real or
imagined dangers, personal losses, unpleasant
social interactions, feelings of fear, anger, grief,
anxiety, depression, guilt
• Stress may even be caused by a pleasant stimulus
Responses to Stress
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Blood glucose increases
Heart rate increases
Blood pressure rises
Breathing rate increases
Air passages dilate
Blood flow redistributed
(away from digestive
organs to muscles)