ENDOCRINE SYSTEM
Module 11
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Endocrine System at a Glance
• Endocrine glands secrete hormones
• Hormones regulate body activities
– Metabolic rate
– Water and mineral balance
– Immune system reactions
– Sexual functioning
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Endocrine System at a Glance
• Organs of the Endocrine System
– Adrenal glands
– Ovaries
– Pancreas (islets of Langerhans)
– Parathyroid glands
– Pineal gland
– Pituitary gland
– Testes
– Thymus gland
– Thyroid gland
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Anatomy and Physiology
• Collection of glands
• Secrete hormones directly into
bloodstream
– Chemicals that act on target organs
– Increase or decrease target’s activity level
• Instrumental in maintaining homeostasis
– Maintain stable internal environment
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Types of Glands
• Two types of glands in body
– Exocrine glands and endocrine glands
• Exocrine glands
– Release secretions into duct that carries them to
outside of body
– Example: sweat glands
• Endocrine glands
– Release hormones directly into bloodstream
– Have no ducts, referred to as ductless glands
– Example: thyroid gland
Glands of the Endocrine System
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Adrenal glands – two
Parathyroid glands – four
Pancreas
Pineal gland
Pituitary gland
Ovaries – two in females
Testes – two in males
Thymus gland
Thyroid gland
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Adrenal Glands
• Two glands, one located above each kidney
• Each gland is composed of two sections:
– Adrenal cortex
– Adrenal medulla
The adrenal glands.
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Adrenal Cortex
• Hormones are referred to as
corticosteroids
– Secreted by adrenal cortex
– Steroid hormones
• Three different families of corticosteroids
– Mineralocorticoids
– Glucocorticoids
– Steroid sex hormones
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Adrenal Cortex
• Mineralocorticoid
– Example: aldosterone
– Regulates sodium (Na+) and potassium (K+)
levels
• Glucocorticoid
– Example: cortisol
– Regulates carbohydrates
• Steroid sex hormones
– Androgens, estrogen, and progesterone
– Regulate secondary sexual characteristics
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Adrenal Medulla
• Inner portion
• Secretes epinephrine and
norepinephrine
– Epinephrine is also called adrenaline
• Critical during emergency situations
– Increases blood pressure
– Increases heart rate
– Increases respiration rate
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Ovaries
• Two ovaries located in pelvic cavity of
females
• Secrete female sex hormones, estrogen and
progesterone
• Estrogen is responsible for:
– Female sexual characteristics
– Regulation of menstrual cycle
• Progesterone
– Maintains suitable uterine environment for
pregnancy
The ovaries.
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Pancreas
• Located along lower
curvature of stomach
• Only organ that has
both endocrine and
exocrine functions
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Pancreas
• Exocrine portion
– Releases digestive
enzymes through duct
into duodenum
• Endocrine sections of
the pancreas
– Islets of Langerhans
– Produce insulin and
glucagon
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Pancreas
• Insulin
– Produced by beta cells
– Stimulates cells of body to take in glucose
from bloodstream
– Lowers blood sugar level
– Occurs after eating a meal and absorbing
carbohydrates
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Pancreas
• Glucagon
– Produced by alpha cells
– Stimulates liver to release stored glucose into
bloodstream
– Raises blood sugar levels
– Occurs when body needs more glucose
The pancreas.
Parathyroid Glands
• Four tiny glands
• Located on dorsal
surface of thyroid
gland
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Parathyroid Glands
• Secretes parathyroid hormone (PTH)
– Regulates level of calcium in bloodstream
• If calcium levels in blood fall too low:
– Parathyroid hormone levels in the blood
increase
– Stimulate bone breakdown
– Releasing more calcium into bloodstream
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Pineal Gland
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Small pine cone-shaped gland
Part of thalamus region of brain
Secretes melatonin
Not well understood, but plays a role in
regulating body’s circadian rhythm
– 24-hour clock that governs periods of
wakefulness and sleepiness
The pineal gland is a part of the thalamus
region of the brain.
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Pituitary Gland
• Small marbleshaped gland
• Located
underneath brain
• Divided into
anterior and
posterior lobes
• Regulated by
hypothalamus
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Anterior Pituitary
• Referred to as “master gland”
– Secretes hormones that regulate other
endocrine glands
• Thyroid-stimulating hormone (TSH)
– Regulates function of thyroid gland
• Adrenocorticotropin hormone (ACTH)
– Regulates function of adrenal cortex
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Anterior Pituitary
• Gonadotropins
– Follicle-stimulating hormone (FSH)
– Luteinizing hormone (LH)
• FSH
– Responsible for development of ova and sperm
– Also stimulates ovary to secrete estrogen
• LH
– Stimulates secretion of sex hormones
– Plays a role in releasing ova in females
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Anterior Pituitary
• Growth hormone (GH)
– Also called somatotropin
– Stimulates cells to grow and divide
• Prolactin (PRL)
– Stimulates milk production in breast
• Melanocyte-stimulating hormone (MSH)
– Stimulates melanocytes to produce more
melanin
The different hormones and target tissues for the
anterior pituitary.
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Posterior Pituitary
• Antidiuretic hormone (ADH)
– Also called vasopressin
– Promotes water reabsorption by the kidney
tubules
• Oxytocin
– Stimulates uterine contractions during labor
and delivery
– After birth stimulates release of milk from
breast
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Testes
• Two oval glands located in scrotum
• Secrete male sex hormone, testosterone
• Testosterone
– Produces male secondary sexual
characteristics
– Regulates sperm production
The testes.
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Thymus Gland
• Located in
mediastinum
• Part of immune
system
• Also endocrine gland
– Secretes thymosin
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Thymus Gland
• Thymosin
– Essential for growth and development of
thymic lymphocytes or T cells
– Critical part of body’s immune system
• Present at birth and grows to largest size
during puberty
• At puberty begins to shrink and eventually
is replaced with connective and adipose
tissue
The thymus gland.
Thyroid Gland
• Located on either side
of trachea
• Resembles a butterfly
in shape
• Divided into right and
left lobes
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Thyroid Gland
• Thyroid hormones
– Thyroxine (T4)
– Triiodothyronine (T3)
• Needs iodine to make hormones
• These hormones:
– Regulate energy production
– Adjust metabolic rate
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Thyroid Gland
• Also secretes calcitonin
– Regulates level of calcium in bloodstream
• If calcium levels in blood rise too high:
– Calcitonin levels in blood increase
– Increases deposition of calcium into bone
– Lowers levels of calcium in bloodstream
• Its action is opposite of parathyroid
hormone
The thyroid gland is divided into a
left and right lobe.
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PERSPECTIVE
• Diabetes is one on the most
commonly known diseases
related to the endocrine
system- do you know any
one diagnosed with diabetes
mellitus? They watch their
insulin levels very closely.
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SYSTEM
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