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Prepared by Patty Bostwick-Taylor,
Florence-Darlington Technical College
CHAPTER
9
The
Endocrine
System
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Endocrine System
•https://www.youtube.com/watch?v=gjmS4_7kv
DM
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Major Endocrine Organs
• 1. Pituitary gland
• 2. Hypothalamus
• 3. Thyroid gland
• 4. Parathyroid glands
• 5. Adrenal glands
• 6. Pineal gland
• 7. Thymus gland
• 8. Pancreas
• 9. Gonads (Ovaries and Testes)
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Pineal gland
Hypothalamus
Pituitary gland
Thyroid gland
Parathyroid glands
Thymus
Adrenal glands
Pancreas
Ovary (female)
Testis (male)
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Figure 9.3
1. Pituitary Gland
• Size of a pea
• Hangs by a stalk from the hypothalamus in the brain
• Protected by the sphenoid bone
• Has two functional lobes
• Anterior pituitary — glandular tissue
• Posterior pituitary — nervous tissue
• Often called the “master endocrine gland”
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Releasing hormones
secreted into portal
circulation
Hypothalamus
Anterior pituitary
Posterior pituitary
Hypophyseal
portal system
Adrenocorticotropic
hormone (ACTH)
Growth hormone (GH)
Bones and muscles Prolactin (PRL) Follicle-stimulating Thyrotropic
hormone (TH)
hormone (FSH)
and luteinizing
Mammary
hormone (LH)
glands
Thyroid
Adrenal cortex
Testes or ovaries
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Figure 9.4
Hormones of the Anterior Pituitary
•(1)Growth hormone (GH)
• General metabolic hormone
• Major effects are directed to growth of skeletal muscles
and long bones
• Plays a role in determining final body size
• Causes amino acids to be built into proteins
• Causes fats to be broken down for a source of energy
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Hormones of the Anterior Pituitary
•Growth hormone (GH) disorders
• Pituitary dwarfism results from hyposecretion of GH
during childhood
• Gigantism results from hypersecretion of GH during
childhood
• Acromegaly results from hypersecretion of GH during
adulthood
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Pituitary dwarf (left), Giant (center), Normal height woman (right)
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Figure 9.5
Hormones of the Anterior Pituitary
•(2) Prolactin (PRL)
• Stimulates and maintains milk production following
childbirth
• Function in males is unknown
•(3) Adrenocorticotropic hormone (ACTH)
• Regulates endocrine activity of the adrenal cortex
•(4) Thyroid-stimulating hormone (TSH)
• Influences growth and activity of the thyroid gland
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Hormones of the Anterior Pituitary
•Gonadotropic hormones
• Regulate hormonal activity of the gonads
• (5) Follicle-stimulating hormone (FSH)
• Stimulates follicle development in ovaries
• Stimulates sperm development in testes
• (6) Luteinizing hormone (LH)
• Triggers ovulation of an egg in females
• Stimulates testosterone production in males
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2. Pituitary–Hypothalamus Relationship
•Hormonal release is regulated by releasing
and inhibiting hormones produced by the
hypothalamus
•Hypothalamus produces two hormones
•These hormones are transported to
neurosecretory cells of the posterior pituitary
•Oxytocin
•Antidiuretic hormone (ADH)
• The posterior pituitary is not strictly an endocrine gland, but does
release hormones
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Hormones of the Posterior Pituitary
•(1) Oxytocin
• Stimulates contractions of the uterus during labor,
sexual relations, and breastfeeding
• Causes milk ejection in a nursing woman
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Hormones of the Posterior Pituitary
• (2) Antidiuretic hormone (ADH)
• Inhibits urine production by promoting water
reabsorption by the kidneys
• Urine becomes more concentrated and has a deeper
coloration
• In large amounts, causes vasoconstriction leading to
increased blood pressure
• Also known as vasopressin
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Optic
chiasma
Axon
terminals
Hypothalamic
neurosecretory
cells
Hypothalamus
Arterial blood supply
Posterior lobe
Capillary bed
Venous drainage
Anterior lobe
of the pituitary
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ADH
Oxytocin
Kidney tubules
Mammary glands
Uterine muscles
Figure 9.6
3. Thyroid Gland
•Found at the base of the throat
•Consists of two lobes and a connecting
isthmus
•Produces two hormones:
•Thyroid hormone
•Calcitonin
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Thyroid cartilage
Epiglottis
Common carotid
artery
Isthmus of
thyroid gland
Trachea
Brachiocephalic
artery
Left subclavian
artery
Left lobe of
thyroid gland
Aorta
(a) Gross anatomy of the thyroid gland, anterior view
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Figure 9.7a
Thyroid Gland
• (1) Thyroid hormone (TH)
•Major metabolic hormone
•Composed of two active iodine - containing
hormones
•Thyroxine (T4) — secreted by thyroid
follicles
•Triiodothyronine (T3) — conversion of T4
at target tissues
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Colloid-filled
Follicle cells
follicles
Parafollicular cell
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(b) Photomicrograph of thyroid gland
follicles (125×)
Figure 9.7b
Thyroid Gland
•Thyroid hormone disorders
•Goiters
• Thyroid gland enlarges due to lack of iodine
• Salt is iodized to prevent goiters
•Cretinism
• Caused by hyposecretion of thyroxine
• Results in dwarfism during childhood
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Figure 9.8
Thyroid Gland
•Thyroid hormone disorders (continued)
•Myxedema
• Caused by hypothyroidism in adults
• Results in physical and mental slugishness
•Graves’ disease
• Caused by hyperthyroidism
• Results in increased metabolism, heat intolerance,
rapid heartbeat, weight loss, and exophthalmos
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Figure 9.9
Thyroid Gland
•(2) Calcitonin
• Decreases blood calcium levels by causing its
deposition on bone
• Antagonistic to parathyroid hormone
• Produced by parafollicular cells
• Parafollicular cells are found between the follicles
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Colloid-filled
Follicle cells
follicles
Parafollicular cell
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(b) Photomicrograph of thyroid gland
follicles (125×)
Figure 9.7b
4. Parathyroid Glands
•Tiny masses on the posterior of the thyroid
•Secrete (1) parathyroid hormone (PTH)
• Stimulate osteoclasts to remove calcium from bone
• Stimulate the kidneys and intestine to absorb more
calcium
• Raise calcium levels in the blood
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Calcitonin
Calcitonin
stimulates
calcium salt
deposit in bone.
Thyroid gland
releases calcitonin.
Stimulus
Rising blood
Ca2+ levels
Calcium homeostasis of blood: 9–11 mg/100 ml
BALANCE
BALANCE
Stimulus
Falling blood
Ca2+ levels
Thyroid
gland
Osteoclasts
degrade bone
matrix and
release Ca2+
into blood.
Parathyroid
glands
PTH
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Parathyroid
glands release
parathyroid
hormone (PTH).
Figure 9.10
5. Adrenal Glands
• Sit on top of the kidneys
• Two regions
• Adrenal cortex — outer glandular region has three
layers
• Outermost: Mineralocorticoids
• Middle:
Glucocorticoids
• Innermost: Sex hormones
• Adrenal medulla — inner neural tissue region
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Adrenal
gland
Capsule
Mineralocorticoidsecreting area
Kidney
Adrenal gland
• Medulla
• Cortex
Cortex
Glucocorticoidsecreting area
Sex hormone
secreting area
Medulla
Kidney
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Adrenal
cortex
Adrenal
medulla
Figure 9.11
Hormones of the Adrenal Cortex
• (1) Mineralocorticoids (mainly aldosterone)
• Produced in outer adrenal cortex
• Regulate mineral content in blood
• Regulate water and electrolyte balance
• Target organ is the kidney
• Production stimulated by renin and aldosterone
• Production inhibited by atrial natriuretic peptide (ANP)
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Decreased Na+ or
increased K+ in
blood
Stress
Hypothalamus
Decreased
blood volume
and/or blood
pressure
Corticotropinreleasing hormone
Anterior pituitary
Increased
ACTH blood pressure
or blood volume
Kidney
Renin
Indirect
stimulating
effect via
angiotensin
Angiotensin II
Direct
stimulating
effect
Heart
Atrial natriuretic
peptide (ANP)
Inhibitory
effect
Mineralocorticoidproducing part of
adrenal cortex
Enhanced secretion
of aldosterone targets
kidney tubules
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Increased absorption
of Na+ and water;
increased K+ excretion
Increased blood
volume and
blood pressure
Figure 9.12
Hormones of the Adrenal Cortex
•(2) Glucocorticoids (including cortisone and
cortisol)
• Produced in the middle layer of the adrenal cortex
• Promote normal cell metabolism
• Help resist long-term stressors
• Released in response to increased blood levels of
ACTH
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Short term
Stress
More prolonged
Hypothalamus
Releasing hormones
Nerve impulses
Spinal cord
Corticotropic cells of
anterior pituitary
Preganglionic
Adrenal sympathetic
medulla fibers
ACTH
Adrenal
cortex
Mineralocorticoids Glucocorticoids
Short-term stress response
Catecholamines 1. Increased heart rate
2. Increased blood pressure
(epinephrine and
3. Liver converts glycogen
norepinephrine)
to glucose and releases
glucose to blood
4. Dilation of bronchioles
5. Changes in blood flow
patterns, leading to
increased alertness and
decreased digestive and
kidney activity
6. Increased metabolic rate
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Long-term stress response
1. Retention of sodium 1. Proteins and fats
converted to
and water by kidneys
glucose or broken
2. Increased blood
down for energy
volume and blood
2. Increased blood
pressure
sugar
3. Suppression of
immune system
Figure 9.13
Hormones of the Adrenal Cortex
•(3) Sex hormones
• Produced in the inner layer of the adrenal cortex
• Small amounts are made throughout life
• Mostly androgens (male sex hormones) are made but
some estrogens (female sex hormones) are also
formed
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Adrenal Glands
• Adrenal cortex disorders
• Addison’s disease
• Results from hyposecretion of all adrenal cortex
hormones
• Bronze skin tone, muscles are weak, burnout,
susceptibility to infection
• Hyperaldosteronism
• May result from an ACTH-releasing tumor
• Excess water and sodium are retained leading to
high blood pressure and edema
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Adrenal Glands
• Adrenal cortex disorders
• Cushing’s syndrome
• Results from a tumor in the middle cortical area of
the adrenal cortex
• “Moon face,” “buffalo hump” on the upper back, high
blood pressure, hyperglycemia, weakening of bones,
depression
• Masculinization
• Results from hypersecretion of sex hormones
• Beard and male distribution of hair growth
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Hormones of the Adrenal Medulla
•Produces two similar hormones (catecholamines)
•Epinephrine (adrenaline)
•Norepinephrine (noradrenaline)
•These hormones prepare the body to deal with
short-term stress (“fight or flight”) by
• Increasing heart rate, blood pressure, blood glucose
levels
• Dilating small passageways of lungs
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Adrenal
gland
Capsule
Mineralocorticoidsecreting area
Kidney
Adrenal gland
• Medulla
• Cortex
Cortex
Glucocorticoidsecreting area
Sex hormone
secreting area
Medulla
Kidney
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Adrenal
cortex
Adrenal
medulla
Figure 9.11
6. Pineal Gland
•Found on the third ventricle of the brain
•Secretes melatonin
• Helps establish the body’s wake and sleep
cycles
• Believed to coordinate the hormones of fertility
in humans
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7. Thymus Gland
•Located posterior to the sternum
•Largest in infants and children
•Produces thymosin
• Matures some types of white blood cells
• Important in developing the immune system
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8. Pancreatic Islets
• The pancreas is a mixed gland and has both endocrine
and exocrine functions
• The pancreatic islets produce hormones
• Insulin — allows glucose to cross plasma membranes
into cells from beta cells
• Glucagon — allows glucose to enter the blood from
alpha cells
• These hormones are antagonists that maintain blood
sugar homeostasis
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Stomach
Pancreas
(a)
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Figure 9.14a
Exocrine
cells of
pancreas
(b)
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Pancreatic
islets
Figure 9.14b
Exocrine
cells of
pancreas
Alpha (α)
cells
Capillaries
Cord of beta (β) cells secreting
insulin into capillaries
(c)
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Figure 9.14c
Uptake of glucose
from blood is
enhanced in most
body cells
Insulin-secreting cells
of the pancreas
activated; release
insulin into the blood
Insulin
Pancreas
Elevated blood
sugar level
Tissue cells
Glucose Glycogen
Liver takes up
glucose and stores
as glycogen
Stimulus
Blood
glucose level
(e.g., after
eating four
jelly doughnuts)
Stimulus
Blood glucose
level (e.g., after
skipping a meal)
Blood glucose rises
to homeostatic
set point; stimulus
for glucagon
release diminishes
Glucose Glycogen
Liver breaks
down glycogen
stores and
Liver
releases
glucose to the
blood
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Blood glucose
falls to homeostatic
set point; stimulus
for insulin release
diminishes
Low blood sugar level
Glucagon-releasing
cells of pancreas
activated; release
glucagon into blood
Glucagon
Figure 9.15
9. Gonads
•Ovaries
•Produce eggs
•Produce two groups of steroid hormone
•Estrogens
•Progesterone
•Testes
•Produce sperm
•Produce androgens, such as testosterone
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Pineal gland
Hypothalamus
Pituitary gland
Thyroid gland
Parathyroid glands
Thymus
Adrenal glands
Pancreas
Ovary (female)
Testis (male)
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Figure 9.3
Hormones of the Ovaries
•(1) Estrogens
•Stimulate the development of female
secondary sex characteristics
• Maturation of female reproductive organs
•With progesterone, estrogens also
• Promote breast development
• Regulate menstrual cycle
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Hormones of the Ovaries
•(2) Progesterone
•Acts with estrogen to bring about the
menstrual cycle
•Helps in the implantation of an embryo in the
uterus
•Helps prepare breasts for lactation
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Hormones of the Testes
•Produce several androgens
•(1) Testosterone is the most important
androgen
•Responsible for adult male secondary sex
characteristics
• Promotes growth and maturation of male
reproductive system
• Required for sperm cell production
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Other Hormone-Producing Tissues and
Organs
• Parts of the small intestine
• Parts of the stomach
• Kidneys
• Heart
• Many other areas have scattered endocrine cells
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Endocrine Function of the Placenta
•Produces hormones that maintain the
pregnancy
•Some hormones play a part in the delivery of
the baby
•Produces human chorionic gonadotropin
(hCG) in addition to estrogen, progesterone,
and other hormones
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Developmental Aspects of the Endocrine
System
•Most endocrine organs operate smoothly until
old age ~ late 30’s – 40’s in
• Menopause is brought about by lack of efficiency of
the ovaries
• Problems associated with reduced estrogen are
common
• Growth hormone production declines with age
• Many endocrine glands decrease output with age
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