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The Endocrine System
chapter 16
Endocrine System: Definitions
• Endocrine – releasing substances into
blood
– Endo = within or internal
– Contrast with Exocrine – releasing
substances outside the body
• Hormone – a chemical that influences
the function of a remote tissue (acts at a
distance)
Endocrine System: Overview
9 glands in total
Endocrine glands
1. pituitary
2. thyroid
3. parathyroid
4. adrenal
5. pineal
6. thymus
Mixed glands
A. produce both hormones
and exocrine products
1. pancreas
2. gonads
B. produce hormones and
has neural functions
1. hypothalamus
Pineal gland
Hypothalamus
Pituitary gland
Thyroid gland
Parathyroid glands
(on dorsal aspect
of thyroid gland)
Thymus gland
Adrenal glands
Pancreas
Ovary
(female)
Testis
(male)
Hormones
• How they work
– Regulate the metabolic function of other
cells
– Have lag times ranging from seconds to
hours
– Tend to have prolonged effects
– Are classified as amino acid-based
hormones, or steroids
2 Main Types of Hormones
• Amino acid based
– Water-soluble
– Do not enter the cell
– e.g., insulin, norepinepherine, epinephrine
• Steroids
– Lipid soluble
– Act intracellularly and activate genes
– e.g., testosterone, estrogen, cortisol
Mechanism of Hormone Action
• Act on receptors in the plasma membrane
• Amino acid–based hormones
– e.g., epinephrine- binds to smooth muscle cells in blood
vessels - causing contraction
• Direct gene activation
• Steroid hormones, thyroid hormones
– e.g., growth hormone - stimulates cells to increase in size
and divide
• The precise response depends on the type of
the target cell
• The ONLY tissue to respond is the Target
Tissue (may be very specific (1) tissue, or
multiple tissues)
Hormone Blood Concentrations
• Concentrations of circulating hormone reflect:
– Rate of release
– Speed of inactivation and removal from the body
• Hormones are removed from the blood by:
• Degrading enzymes
• The kidneys
• Liver enzyme systems
Hypothalamic Control
• Hypothalamus “releasing hormones” and
“inhibiting hormones” tells of central control by
brain
– GHRH (growth hormone RH) and GHIH (growth
hormone IH) control GH from Ant. Pituitary
– PRH (prolactin RH) and PIH control PL from Ant.
Pit.
– TRH  thyrotropin RH – release of TSH from Ant.
Pit.
– CRH  corticotropin releasing hormone – release
of hormones from adrenal cortex  Stress
– GnRH  gonadotropin RH – release of gonadal
hormones from Ant. Pit.  LH and FSH
Pituitary (Hypophysis)
• Pituitary gland
– two-lobes
– secretes 9 major hormones
• Connected to the hypothamus by
– Posterior Lobe
• Neurohypophysis – neural tissue) and the infundibulum
• Receives, stores, and releases hormones from the
hypothalamus
– Anterior Lobe
• Adenohypophysis – made up of glandular tissue
• Synthesizes and secretes a number of hormones
Pituitary (Hypophysis)
Figure 16.6
Anterior Pituitary Hormones
• regulate other endocrine glands
•
•
•
•
•
•
GH – growth hormone
TSH – thyroid stimulating hormone
ACTH – adrenocorticotrophic hormone
FSH – follicle stimulating hormone
LH – luteinizing hormone
PRL - prolactin
(latter 3 are called gonadotropins)
Growth Hormone (GH)
• Underproduction in children  dwarfism
• Overproduction in children  gigantism
• Overproduction in adults  acromegaly
Posterior Pituitary Hormones
• Posterior pituitary
– stores antidiuretic hormone (ADH) and oxytocin
– ADH and oxytocin are synthesized in the
hypothalamus
• Oxytocin stimulates smooth muscle contraction
in breasts and uterus
– “cuddle hormone”
• Both are amino acid based
– Receptor location?
Pancreas
• both exocrine and endocrine cells,
• Acinar cells  enzyme-rich juice used for
digestion (exocrine product)
• Pancreatic islets (islets of Langerhans)
produce hormones (endocrine products)
• The islets contain two major cell types:
– Alpha () cells that produce glucagon
– Beta () cells that produce insulin
Regulation of Blood Glucose
Levels
• hyperglycemic
 glucagon 
glucose uptake
• hypoglycemic
 insulin 
glucose release
Figure 16.18
Diabetes Mellitus (DM)
• Results from hyposecretion or hypoactivity
of insulin
• The three cardinal signs of DM are:
– Polyuria – huge urine output
– Polydipsia – excessive thirst
– Polyphagia – excessive hunger and food
consumption
Thyroid Gland
• thyroid hormone
metabolism, BP,
growth
– T3 (10x)
– T4
• calcitonin
response to rising
blood calcium –
inhibit gut
absorption and
kidney reabsorption
of Ca++
Thyroid Disorders
• Hypothyroidism
– Thyroid gland defect, inadequate TSH, lack
of iodine
• Low metabolic rate, feeling chilled
• Goiter formation ( if cause is lack of
iodine)
• Cretinism = Hypothyroidism in infants
• Stunted growth, low mentality
• can be prevented by hormone
replacement therapy
Grave’s Disease
– Hyperthyroidism
• Autoimmune disease- body attacks and
stimulates the thyroid cells - increased thyroid
hormone
• High BMR, Weight loss, Increased heart rate,
Protrusion of the eyeballs, goiter
– Treated by surgical removal of the thyroid gland
Parathyroid Glands
• PTH (parathormone)
– response to falling
calcium in blood –
promotes gut
absorption and kidney
reabsorption of Ca++
– Question:
• what two hormones
regulate calcium in
blood?
Adrenal (Suprarenal) Glands
• Adrenal glands
– cope with stressful events
• Structurally and functionally,
they are two glands in one
– Adrenal cortex – glandular tissue
– Adrenal medulla – neural tissue
that acts as part of the SNS
Adrenal Cortex Hormones
• Aldosterone - dehydration
– causes kidney to reabsorb Na+  reabsorb
water
– stimulated by angiotensin (remember
Renin)
• Cortisol - stress
– increases blood glucose levels & reduces
edema of tissues
– prolonged high levels  changes in neural
and circulatory function, depressed
bone/cartilage growth, suppressed immune
response
Adrenal Cortex Hormones
• Androgens (masculinizing hormones)
– most important is testosterone
• the onset of puberty
• secondary sex characteristics
• sex drive in females
– testosterone can be converted to estrogen
in females after menopause
Disorder
• Addison’s disease
– Hyposecretion of the adrenal cortex
• Deficiency in cortisol and aldosterone
• Low BP
• Hypoglycemia
• Cushings disease
– Hypersecretion of adrenal cortex (tumor of the
adrenal cortex)
• Hyperglycemia
• “buffalo hump” (fat on upper back)
Adrenal Medulla
• secretes the catecholamines
– epinephrine
– norepinephrine
• “Fight or Flight” secretion causes:
– blood glucose levels to rise
– blood vessels to constrict
– faster heart rate
– blood diversion to brain, heart, and skeletal
muscle
Adrenal Medulla
• Epinephrine is the more potent
stimulator of the heart and metabolic
activities
• Norepinephrine is more influential on
peripheral vasoconstriction and blood
pressure
Stress and the Adrenal Gland
Figure 16.16