ENDOCRINE SYSTEM
AND DISORDERS
BIO 238
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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
• Disorders
• Giantism is caused by excess GH during
growing years
• Extremely tall
• Acromegaly is caused by excess GH after
growth years
• Only bones of hands, face, and feet continue to grow
• Hypopituitary dwarfism is caused by too little
GH during growth years
• Well proportioned body parts but small in stature
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)
• Regulates the presence of aquaporins in the distal tubule and
collecting ducts of the nephron
• 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
Disorders
• Diabetes insipidus is caused by severe
hyposecretion of ADH
• Produces large volume of dilute urine
• Afflicted person must drink water constantly
and is always thirsty
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
Disorders
• Exophthalmic goiter (Grave’s
disease) is due to hypersecretion of
T4 and T3
• Autoimmune disorder resulting in
excessive TSH production
• Symptoms
• Restlessness
• Increased metabolic rate with weight loss
• Bulging eyes due to tissue swelling
• Simple goiter
• Enlargement of thyroid gland due to
iodine deficiency
• Thyroid hormones cannot be produced
• Thyroid enlarges in an attempt to make
more hormones
• Prevented by adding iodine to diet
• Cretinism
• Severe deficiency of T4 and T3 in infancy
• Causes severe mental and physical
retardation
•
•
•
•
Stunted growth
Abnormal bone formation
Mental retardation
Sluggishness
• Myxedema
• Severe T4 and T3 deficiency in adults
• Symptoms
•
•
•
•
•
Sluggishness
Weight gain
Weakness
Dry skin
Facial puffiness
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
Disorders
• Hypoparathyroidism is causes a
severe drop in blood calcium levels
• Impairs neural and muscular activity
• Causes cardiac arrest and sudden death
• Tetanic contraction of skeletal muscles
may cause breathing to cease
• Hyperparathyroidism is causes too
much calcium to be removed from
bones and abnormally high blood
calcium levels
• Soft, weak bones prone to fracture
• Excess calcium can lead to kidney
stones or deposits elsewhere in body
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
Disorders
• Cushing’s syndrome is due to hypersecretion by
adrenal cortex
• Due to tumors in cortex or excess ACTH
• Symptoms
• High blood pressure
• High blood glucose level
• Protein loss
• Osteoporosis
• Fat accumulation on trunk
• Fatigue
• Edema
• Decreased immunity
• Full, round face
• Addison’s disease is due to severe
hypersecretion by the adrenal cortex
• Symptoms
• Low blood pressure
• Low blood glucose and sodium
• Increase in blood potassium
• Dehydration
• Muscle weakness
• Increased skin pigmentation
• Without treatment, death occurs in days
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
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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