Download Endocrinology Features of Endocrine system:

Endocrinology
Chapter 9
Features of Endocrine system
Along with nervous system, endocrine system
coordinates and directs the body activities
• (Homeostasis dynamic equilibrium of internal
environment( blood and tissue fluid that surrounds
the body cells)
• How? By regulating sugar, electrolyte balance in
the body fluids such as blood, extra cellular fluid
Endocrine system
 Comprises of glands, which secrete
chemicals – Hormones
 Hormones: Defined as chemical
substances secreted by endocrine
glands into
– extracellular fluids from where
they enter
– blood stream via capillaries
– And regulate metabolic activity
of the body cells
 The scientific study of hormones and
endocrine organs - Endocrinology
Difference between endocrine and exocrine
gland secretions
• Exocrine Glands:
• Exocrine glands secrete
their contents into a duct
• The duct transports the
secretions to the surface
where its action is seen
• E.g. sebaceous glands
Difference between endocrine and exocrine
gland secretions
• Endocrine glands:
• Endocrine glands secreted
contents (hormones) are picked
up by the blood capillaries
• Transported to the target organ
or tissue through the blood
• And stimulate a specific
response through the receptors
present on the specific organ
Comparison of endocrine system to
nervous system
• Similarity: It helps in regulating the activities of various
organ systems like nervous system
• Differences:
• It conveys its message through blood instead of neurons
• The response of target organ is slow and for longer
duration instead of quick and short duration
Chemistry of Hormones
• Hormone derived from a Greek word meaning
– to arouse ( causing a change in cell’s physiology by
increasing or decreasing cellular activity)
• Hormones are classified as:
– Amino acid–based: which includes
• Proteins
• Peptides
• Amines
– Steroids— made from cholesterol, includes sex
hormones (ovary & testes)
– Prostaglandins— made from highly active lipids from
cell membranes
Mechanisms of Hormone Action
• Hormones affect only certain tissues or organs (target cells
or target organs)
• Each target tissue has a specific receptor for a specific
hormone
• Hormone-binding alters cellular activity
Mechanisms of Hormone Action
• Two mechanisms in which hormones act
– Direct gene activation
– Second-messenger system
Second-Messenger System
•
If the hormone is a proteinous in nature
•
Hormone binds to a membrane receptor
( also known as primary messenger)
•
And activates enzymes which activates
cAMP from ATP
•
cAMP acts as a secondary messenger
•
cAMP stimulates a set of enzymes known
as protein kinases
•
This triggers a series of reactions known as
signal transduction mechanism
Second-Messenger System
• Which will ultimately activate
or inhibit the enzymatic
activity
• Affects metabolic pathway
• Activate or shut down
•
eg. Glycogen breakdown
by hormone glucagon
Direct Gene Activation
(Steroid Hormone Action)
• If the hormone (lipid soluble hormone) is
steroid in nature
• Hormones diffuse directly through the
plasma membrane of target cells
• Enter the nucleus
• Bind to a specific receptor protein within
the nucleus
• Forms hormone-receptor complex
• And then binds to specific sites on the
cell’s DNA
• Activate genes that result in synthesis of
new proteins
• Directly stimulates or inhibits gene
expression
• e.g. sex hormones
Control of Hormone Release
• Hormone secretion is regulated by negative feed back
mechanism
• A stimulus or low hormone levels in the blood triggers the
release of more hormone
• Hormone release stops once an appropriate level in the
blood is reached
• So that concentration of hormone remains relatively
constant in the blood with slight fluctuations
Negative feed back loop e.g. thyroxine hormone
Hypothalamus
in response to internal and external stimuli
release thyrotropin releasing factor
Pituitary
thyrotropin (TSH)
Thyroid gland
Thyroxine
Other types of regulation
• Hormonal Stimuli:
• Endocrine glands are
activated by other
hormones eg. Anterior
pituitary hormones
Other types of regulation
•
•
Humoral Stimuli:
Changing blood levels of
certain ions stimulate
hormone release
– Parathyroid hormone
– Calcitonin
– Insulin
• eg. Insulin is released in
blood from pancreas to
regulate glucose level
Other types of regulation
• Neural Stimuli:
• Stimulation by
nervous system. e.g.
stress stimulates
adrenal gland to
secrete epinephrine
and norepinephrine
Endocrine glands
•
•
•
•
•
•
•
•
•
Hypothalamus
Pituitary gland
Thyroid Gland
Parathyroid gland
Adrenal glands
Pancreas
Pineal gland
thymus gland
Reproductive glands
Hypothalamus
• Part neuronal and part endocrine
in function
• Located in the diencephalon
below the thalamus
• It is the connecting link between
the environment and the endocrine
glands
• By perceiving the changes in the
environment (internal/external)
• And controlling the activities of
pituitary gland
Pituitary Gland
• It is also known as hypophysis
• It is a small gland about the size
of a pea
• It is attached to the hypothalamus
of the brain by a stalk called
infundibulum
• It is called the master gland
because it releases hormones that
affect the working of other glands
such as thyroid, gonads etc.
•
It is divided into two lobes:
– anterior pituitary
– posterior pituitary
Hormones of the Anterior Pituitary
• Six anterior pituitary hormones
– Two affect non-endocrine targets
• Growth hormone
• Prolactin
– Four stimulate other endocrine glands (tropic
hormones)
• Thyroid-stimulating hormone (thyrotropic hormone)
• Adrenocorticotropic hormone
• Two gonadotropic hormones
Hormones of the Anterior Pituitary
• Characteristics of all anterior pituitary
hormones
– Proteins (or peptides)
– Act through second-messenger systems
– Regulated by hormonal stimuli, mostly negative
feedback
Hormones of the Anterior Pituitary
Hormones of the Anterior Pituitary
• Growth hormone
– 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
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
Giganticism
Hypersecretion
causes excessive
growth as shown
in these identical
twins.
Giganticism
12-year old boy with
his mother.
Acromegaly
Hypersecretion after puberty causes acromegaly.
Acromegaly Face
Acromegaly
• Jaws and ridge of frontal bone continues to
grow. Andre the Giant was a WWF
wrestler.
Hormones of the Anterior Pituitary
• Prolactin (PRL)
– Stimulates and maintains milk production following
childbirth
• Adrenocorticotropic hormone (ACTH)
– Regulates endocrine activity of the adrenal cortex
• Thyroid-stimulating hormone (TSH)
– Influences growth and activity of the thyroid gland
Hormones of the Anterior Pituitary
• Gonadotropic hormones
– Regulate hormonal activity of the gonads
• Follicle-stimulating hormone (FSH)
– Stimulates follicle development in ovaries
– Stimulates sperm development in testes
• Luteinizing hormone (LH)
– Triggers ovulation of an egg in females
– Stimulates testosterone production in males
Posterior Pituitary
• Hormones present in posterior
pituitary gland are actually
secreted by hypothalamus
• But stored in posterior pituitary
• Hormone release from posterior
pituitary is regulated by nerve
impulses coming from
hypothalamus
Posterior pituitary
• (i) ADH or antidiuritic hormone:
•
It is an antiurination hormone
• Important for retention of water by
kidneys and prevent dehydration
• By decreasing urine volume increases
Blood volume
• ADH deficiency causes excessive
urine , diabetes insipidus
• It is also called vasopressin because
ADH increases vasoconstriction and
leads to increase blood pressure
Posterior pituitary
• (ii) Oxytocin: works on
uterus
• Important for uterine
contraction during
delivery
• Important for milk
ejection in lactating
women
Thyroid Gland
• Found at the base of the
throat
• Consists of two lobes and
a connecting isthmus
• Produces two hormones
– Thyroid hormone
– Calcitonin
Thyroid Hormone
• Thyroid hormone
– Major metabolic hormone
– Composed of two active iodinecontaining hormones
• Thyroxine (T4)—secreted by
thyroid follicles
• Triiodothyronine (T3)—conversion
of T4 at target tissues
• Iodine is important for thyroxine
formation
• Thyroid hormone is transported
through blood to the target tissue
Thyroid Hormone
• Thyroid hormones increases the rate of body metabolism
(BMR)
• Amount of energy required for an organism to survive in a
resting stage
• Varies from person to person depending on height, weight, age,
stress etc
• It is important for growth and development (protein, lipid and
carbohydrate metabolism of all tissues)
• What happens when the hormone is over-secreted or undersecreted?
Thyroid Hormone
Thyroid hormone disorders
Hyperthyroidism or Graves disease:
•
•
•
•
•
•
Enlargement of thyroid gland
Excess of thyroid secretion production
caused by tumor
Eyes bulge
Patient is hyperactive, irritable, nervous etc
BMR increases
Treatable by surgery and radioactive
Iodine
Grave’s Disease
Simple Goiter: ( Iodine deficiency and hormone deficiency)
• Thyroid over stimulated because of lack of usable thyroid hormone
– due to lack of iodine
• Results in hypothyroidism
• Enlarged thyroid gland
More Goiters
• Hypothyroidism (Lack
of stimulation by TSH):
• Crinitism: in child hood.
Slow growth, mental
retardation low body
metabolism
• In adult: called as
myxedema
• Results in physical and
mental sluggishness
• puffiness of face, fatigue,
obesity, dry skin
Hypothyroidism in Adults
Myxedema
Thyroid Gland
• Calcitonin:
•
Thyroid gland also
secretes calcitonin
•
Important for bone
formation by inhibiting
osteoclast activity and
•
Leading to increase in
osteoblast activity thus
incorporating Calcium
into bone.
Parathyroid gland
• located posterior to thyroid
gland
• 4 in number
• Produces the hormone PTH
( parathyroid hormone)
• regulate calcium levels in the
blood.
• stimulate osteoclasts when ever
calcium levels falls in blood
• PTH and calcitonin work
against one another and
regulate Ca+2 levels in the
blood
Hormonal Regulation of Calcium in Blood
Calcitonin
stimulates
calcium salt
deposit
in bone
Calcitonin
Thyroid gland
releases
calcitonin
Thyroid
gland
Rising
blood
Ca2+
levels
Calcium homeostasis of blood
9–11 mg/100 ml
Falling
blood
Ca2+
levels
Thyroid
gland
Osteoclasts
degrade bone
matrix and release
Ca2+ into blood
Parathyroid
glands
PTH
Parathyroid
glands release
parathyroid
hormone (PTH)
Adrenal glands
• Two adrenal glands are located
superior to kidney
• It has two parts.
• A. Adrenal cortex
• B. Adrenal medulla
• Adrenal glands activities are
controlled by hypothalamus
• By producing Adrenocorticotropic
(ACTH ) hormone
Adrenal glands
Adrenal cortex:
•
•
outer region of adrenal gland.
It secretes several hormones.
•
These hormones are essential for
human survival
•
•
Minerocorticoids
(e.g. aldosterone) help kidneys to
retain Na+ and excrete K+ levels in
blood
•
This helps in conservation of water
by kidney and maintains blood
volume and blood pressure
•
Glucocorticoid (including cortisone and
cortisol)
•
It regulates glucose metabolism
•
When glucose levels in blood are low and
glycogen levels are down
•
Releases Cortisol
•
Stimulate liver to build glucose from amino
acids, fatty acids and glycerol
•
In the process, it maintains blood sugar level
•
In addition, cortisol relieves inflammation
and stress
•
Thus cortisol is released under SANS
stimulation
•
Adrenal cortex also produces
Sex hormones
– Produced in the inner
layer of the adrenal
cortex
– Small amounts are made
throughout life
– Mostly androgens (male
sex hormones) are made
– Some estrogens (female
sex hormones) are also
formed
Adrenal medulla:
Functions as a part of
sympathetic nervous system. It
secretes
Epinephrine (adrenaline) and
norepinephrine (noradrenaline)
which are important for physical
activity such as increase blood
sugar levels, heart rate
The release of these hormones
is stimulated by emotions,
injury, stress etc.
Pancreas
• Is located along small
intestine and stomach
• It is made of pancreatic
islets
(islets of Langerhans)
 Each islet is made of
a cells, which secrete
hormone called Glucagon.
•
It works on liver and
releases sugar into blood
to be used for energy.
•
b cells secrete insulin
•
Its target organ is liver, muscle
and adipose tissue.
•
It helps in uptake of excess
sugar in blood
• Low levels of insulin results in
diabetes mellitus
•
•
•
•
Cannot store sugar in the body
excretes sugar in urine
( hyperglycemia)
Starts breaking fat and protein
stores leading to production of
ketones ( acidosis)
• Treatable by taking insulin
shots
Pancreas
Pancreas
• In general, parasympathetic nervous stimulation increases
insulin secretion and helps in storage of sugar into glycogen
• Sympathetic stimulation inhibits secretion of insulin and
helps so that sugar is released into blood and used for
physical activity
Insulin-secreting
cells of the pancreas
activated; release
insulin into the
blood
Elevated
blood sugar
levels
Stimulus:
rising blood
glucose levels
(e.g., after
eating four
jelly doughnuts)
Uptake of glucose
from blood is enhanced in most
body cells
Liver takes up
glucose and stores
it as glycogen
Homeostasis: Normal blood glucose
levels (90 mg/100ml)
Blood glucose
levels decline
to set point;
stimulus for
insulin release
diminishes
Stimulus:
declining blood
glucose levels
(e.g., after
skipping a meal)
Low blood
sugar levels
Rising blood
glucose levels
return blood sugar
to homeostatic set
point; stimulus for
glucagon release
diminishes
Liver breaks down
glycogen stores and
releases glucose to
the blood
Glucagon-releasing
cells of pancreas
activated;
release glucagon
into blood; target
is the liver
Gonads
• Ovaries
– Produce eggs
– Produce two groups of steroid hormone
• Estrogens
• Progesterone
• Testes
– Produce sperm
– Produce androgens, such as testosterone
Hormones of the Ovaries
• Estrogens
– Stimulate the development of secondary female
characteristics
– Mature female reproductive organs
• With progesterone, estrogens also
– Promote breast development
– Regulate menstrual cycle
Hormones of the Ovaries
• 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
Other hormone producing tissues
• Thymus gland:
 Present above the
heart in the thoracic area.
 Produces thymosin
hormone important for
maturation of T
lymphocytes (WBC)
Pineal Body
 Cone shaped
structure present behind
midbrain attached to roof
of the third ventricle.
 Important for the
production of melatonin
which regulates the sleep
and wake cycles
• with the help of the rods
and cones of retina
Prostaglandins

Made by most of the cells of the body
 Important for promotion of inflammation,
• constriction of blood vessels and bronchial tubes ,
• cramps caused by the contraction of uterine wall
during menstrual cycle.
 Antiprostaglandins( aspirin, ibuprofen) block
production of prostaglandins thus reducing
inflammation etc.