Endocrine System and
Disorders
BIO 110
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Introduction
Endocrine system provides slow, long lasting
coordination of body functions
 It consists of glands and tissues that secrete
hormones
 Hormones are transported by blood to other
tissues and organs

Hormones
only affect target cells
• Cells that possess specific receptors
for the hormone
• Hormone receptors can be located on
the plasma membrane or inside the
cell
Non-target
cells have no receptors
and are unaffected by hormones
 Mechanisms
of Hormone Action
◦ Hormones affect target cells by
altering their metabolic activities
◦ There are two types of hormones
that produce different effects on
target cells
 Steroid hormones
 Non-steroid hormones
◦ Steroid and Steroidlike Hormones
 Lipid soluble hormones that pass through
the plasma membrane
 Bind to receptors in the nucleus
 Act upon the DNA in the nucleus
 Cause production of mRNA that exits the
nucleus
 Lead to the production of specific proteins,
usually enzymes
• Nonsteroid Hormones
• Usually proteins or peptides that are not fat
soluble
• Relies on two messengers to produce an
effect
• First messenger (hormone) binds to the plasma
membrane
• Binding triggers the release of membrane enzymes
that lead to cAMP (second messenger) formation
• cAMP activates other enzymes that can change cell
function
 Prostaglandins
◦ Called local, or tissue, hormones
 They exert control over the cells near where they
are produced
◦ They are produced by cells in nearly every
organ
◦ They can increase or decrease cAMP levels
 Can modify effects of nonsteroid hormones
Actions:
• Promote inflammation, with pain and fever
• Constrict or dilate blood vessels
• Promote blood clotting
• Promote excretion of water of electrolytes
by kidneys
 Control
of Hormone Production
◦ Hormone secretion is tightly regulated
to avoid
 Hyposecretion
 Hypersecretion
◦ Glands are activated by different
stimuli
 Another hormone
 A chemical product of a hormone
 Neural impulses
◦ Stimuli can either stimulate or inhibit
secretion
◦ Hormone secretion is regulated by
negative feedback
 A hormone secreted when the
concentration of a substance is too low
 The hormone causes body cells to bring
the substance level back to normal
 Once normal levels are reached, hormone
secretion and concentration decreases
• Negative feedback keeps hormones levels in the blood
relatively stable
Pituitary Gland
Attached to the hypothalamus by a short stalk
 Resides in and is protected by the sella turcica of the
sphenoid bone
 Consists of two parts with different functions
◦ Anterior lobe
◦ Posterior lobe


Control of the Anterior Lobe
◦ Regulated by releasing hormones from the hypothalamus
 Hypophyseal portal veins carry hormones from hypothalamus into
anterior lobe
◦ There is a releasing hormone for each
hormone made by the anterior lobe
 Some releasing hormones promote and
others inhibit hormone production
◦ Production of releasing hormones is
regulated by negative feedback

Control of the Posterior Lobe
• Controlled by neural impulses that travel down
neurosecretory neuron axons from hypothalamus to the
posterior lobe
• Axons to release hormones into the posterior lobe then into
blood
Anterior Lobe Hormones
 Growth
hormone (GH)
◦ Stimulates the division and growth of body cells
 Promotes synthesis of proteins and other
biological molecules
 Increases available energy for producing these
molecules
◦ Most abundant during growth years
• Secretion is regulated by two
hypothalamic releasing hormones
• GH-releasing hormone (GHRH)
stimulates GH secretion
• GHRH production is triggered by strenuous
exercise, hypoglycemia, excess amino acids
• GH-inhibiting hormone (GHIH) inhibits
GH secretion
• GHIH production is triggered by hyperglycemia

Thyroid-Stimulating Hormone (TSH)
◦ Stimulates the thyroid gland to produce thyroid
hormone
◦ Secretion is regulated thyrotropin-releasing
hormone (TRH) from hypothalamus
 Low blood thyroid hormone levels cause TRH to be
released
 TRH causes production of TSH
 High thyroid hormone levels inhibit TRH, which
decreases TSH release

Adrenocorticotropic Hormone (ACTH)
◦ Controls secretion of hormones by the cortical portion of the
adrenal cortex
◦ Secretion controlled by corticotropin releasing hormone
(CRH) that works by negative feedback
◦ Excess stress can cause excess ACTH production

Gonadotropins
◦ There are two types of gonadotropins
 Follicle-stimulating hormone (FSH)
 Luteinizing hormone (LH)
◦ Secretion is caused by gonadotropin releasing
hormone (GnRH) from the hypothalamus
• FSH functions
• Females: promotes development of
ovarian follicles
• Males: promotes sperm production
• LH functions
• Females: stimulates ovulation and
progesterone production
• Males: stimulates testosterone production

Prolactin
◦ Initiates and maintains milk production by
mammary glands after child birth
◦ Secretion regulated by prolactin releasing
hormone and prolactin inhibiting hormone from
the hypothalamus
Posterior Lobe Hormones
Hormones are produced by neurons in the
hypothalamus
 Two types of hormones are released from the
posterior lobe

◦ Antidiuretic hormone (ADH)
◦ Oxytocin
Antidiuretic Hormone (ADH)
• Promotes water reabsorption by the kidneys to reduce
water volume in urine
• Helps regulate blood volume and blood pressure
• Secretion regulated by neurons that monitor water
concentration in blood
• Decrease in water concentration of blood causes ADH secretion
to increase
• Increase in water concentration of blood causes ADH secretion to
decrease
Oxytocin
• Stimulates and strengthens contraction of
smooth muscle of the uterus during labor
• Causes milk ejection due to infant suckling
• Secretion is controlled by positive feedback
Thyroid Gland
Located below the
larynx
 Two lobes connected by
and anterior isthmus


Thyroxine (T4) and T3
◦ Iodine is necessary for production in the thyroid
◦ Functions
 Increase metabolic rate
 Promote protein synthesis
 Enhance neuron function
Effects of insufficient levels of T3 and T4
• Moderately low: chronic fatigue
• Very low: impaired mental and physical growth and
development
 Secretion
is stimulated by TSH
 Calcitonin
◦ Another hormone produced by the
thyroid gland
◦ Lowers blood calcium by stimulating
calcium deposition by osteoblasts in
bones
Parathyroid Glands
Small glands on posterior
surface of the thyroid gland
 Two glands on each lobe

Parathyroid
Hormone (PTH)
• Increases the concentration of blood
calcium levels three ways
• Promotes calcium removal from bones by
osteoclasts and inhibiting calcium
deposition by osteoblasts
• Inhibits excretion of calcium by kidneys
• Promotes calcium absorption into blood
by the intestine
Adrenal Glands
2 adrenal glands, one
atop each kidney
 Glands consist of two
portions

◦ Inner adrenal medulla
◦ Outer adrenal cortex
 Hormones
of Adrenal Medulla
• Secretes epinephrine and norepinephrine
• Regulated by sympathetic division of the
autonomic nervous system
• Secreted during times of stress
• Hormone effects
• Decrease blood flow to viscera and skin
• Increase in blood flow to skeletal muscles, lungs, and
nervous systems
• Increase blood glucose levels
• Increase rate of cellular respiration
Hormones of the Adrenal Cortex
• Aldosterone, a mineralocorticoid
• Functions
• Regulates electrolyte concentration in body fluids
• Maintain blood volume and blood pressure
• Effects
• Causes kidneys to retain Na+ (and negative ions) and excrete K+
• Causes water to be reabsorbed by osmosis
• Secretion is stimulated by
• Decrease in Na+
• Increase in K+
• Decrease in blood pressure
 Cortisol,
a glucocorticoid
◦ Secretion caused by ACTH stimulation
 Glucocorticoids exert negative feedback control
on ACTH
◦ Effects
 Maintain blood glucose levels by changing noncarbohydrates into glucose
 Respond to stress by making more glucose
available to body cells
 Reduce inflammation but reduce immune
reactions

Androgens, male sex hormones
◦ Male effects: development of male sex organs,
minor effect in adults
◦ Female effects: female sex drive
◦ Overproduction in both sexes cause exaggerated
male characterizations
Pancreas
Elongated organ
posterior to the
stomach
 Exocrine functions

◦ Secrete digestive
enzymes
◦ Carried by pancreatic
duct into small
intestine

Endocrine function
◦ Islets of
Langerhans
secrete three
hormones
 Glucagon
 Insulin
 Somatostatin
 Glucagon
◦ Increases blood glucose concentration
when it drops too low, even when
carbohydrates are depleted
 Causes liver to convert glycogen to glucose
 Helps convert non-carbohydrates to glucose
◦ Blood glucose controls secretion by
negative feedback
 Low blood glucose stimulates secretion
 High blood glucose inhibits secretion
 Insulin
◦ Decreases blood glucose concentration
when it gets too high
 Aids glucose uptake by body cells, where it can
be used for energy
 Causes the liver to form glycogen for glucose
storage
◦ Insulin may also promote amino acid
uptake
◦ Blood glucose concentration controls
secretion by negative feedback
 Low blood glucose inhibits secretion
 High blood glucose stimulates secretion
 Disorders
◦ Diabetes mellitus is caused by
hyposecretion of insulin
 Symptoms include high blood glucose
levels and acidosis, due to use of fats for
energy
 Two common types of diabetes
 Type 1 diabetes
 Type 2 diabetes
• Type 1, or insulin-dependent, diabetes
• Appears in persons below 20 years and lasts a
lifetime
• Insulin injections are required at regular
intervals
• Type 2, or noninsulin-dependent,
diabetes
• Appears later in life (over 40) and in obese
individuals
• Controlled by diet and medication
◦ Hypoglycemia is due to excessive
insulin production causing excessively
low blood glucose levels
 Symptoms include
 Acute fatigue
 Weakness
 Increased irritability
 Restlessness
 Insulin-triggered coma
Gonads
 Gonads
are sex glands
◦ Females: ovaries
 Produce ova and sex hormones
◦ Males: testes
 Produce sperm and sex hormones
 Female
Hormones
◦ Ovaries
 Located in pelvic cavity
 Small, almond shaped
 Activate at puberty in response to FSH
and LH
 FSH and LH interact in a 28-day ovarian
cycle
◦ Estrogens, primary female sex
hormone
 Secreted by developing ovarian follicles
 Functions
 Development and maturation of female sex
organs
 Secondary sex characteristics
 Maintain uterine lining during pregnancy
◦ Progesterone
 Secreted by an empty follicle after
ovulation
 Functions
 Prepare uterus for receiving an embryo
 Maintains pregnancy
 Prepares mammary glands for milk production
 Male
Hormone
◦ Testes
 Paired, ovoid organs located in scrotum
 Interstitial cells secrete testosterone
◦ Testosterone, male sex hormone
 Functions
 Development and maturation of male sex
organs
 Secondary sex characteristics
 Male sex drive
Other Endocrine Glands and
Tissues
Other glands and tissues in the body can also
secrete hormones

◦
◦
◦
◦
Pineal gland
Thymus gland
Small glands of stomach and small intestine
Placenta
Pineal
Gland
• Small, cone-shaped gland within the brain
• Secretes melatonin
• Melatonin functions
• Controls onset of puberty by controlling
gonadotropic hormones
• Regulates wake-sleep cycles (circadian
rhythms): makes the body sleepy
• When exposed to light, melatonin production is
reduced
• At night, melatonin production is increased
 Thymus
◦ Located in the mediastinum
◦ Large in infants but gets smaller with
age
◦ Functions
 Crucial role in development of immunity
 Produces thymosin, which aid
T-lymphocyte maturation