Endocrine System
Introduction
• The nervous system and the endocrine
system coordinate functions of all body
systems
Introduction
• Nervous system controls body actions via
nerve impulses
Introduction
• Endocrine system controls body activities
by releasing hormones
Introduction
Two kinds of glands
1. Exocrine
2. Endocrine
Introduction
• Exocrine – secrete their products into
ducts
Example: salivary and sweat glands
Introduction
• Endocrine – secrete hormones into blood
Introduction
Endocrine glands;
1. Pituitary
2. Thyroid
3. Parathyroid
4. Adrenal
5. Pineal
Introduction
• The pancreas has exocrine and endocrine
functions
Introduction
Stomach, intestines, and kidneys also
produce hormones
Hormone Receptors
• Although travel in blood throughout the
body, they affect only specific cells
Hormone Receptors
• Hormones bind to receptors on target cells
Hormone Receptors
• Down Regulation – When a hormone is
present in excess, a decrease in the
number of receptors may occur
Hormone Receptors
• Up Regulation – When a hormone is
deficient, an increase in the number of
receptors may occur
Hormones
• Two main types;
1. Circulating
2. Local
Circulating Hormones
• Hormones that travel in blood and act on
distant target cells
Local Hormones
• Hormones that act locally without first
entering the blood stream
Local Hormones
Two types;
1. Paracrine
2. Autocrine
Local Hormones
• Paracrine – act on neighboring cells
Local Hormones
• Autocrine – act on the same cell that
secreted them
Hormone Chemistry
• Some are lipid soluble and others are
water soluble
Lipid-soluble hormones
Include;
Steroids, thyroid hormones, and nitric oxide
Water-soluble hormones
Include;
Peptides, proteins, and glycoproteins
Hormone Transport
• Water-soluble hormones travel free in
plasma
Hormone Transport
• Lipid soluble hormones bind to transport
proteins to be carried in blood
Action of Lipid Soluble Hormones
1. Hormone binds to and activates
receptors within cells
Action of Lipid Soluble Hormones
2. The activated receptors alter gene
expression, which results in the formation
of new proteins
Action of Lipid Soluble Hormones
3. The new proteins alter the cells activity
Action of Water Soluble Hormones
1. The hormone binds to the membrane
receptor
Action of Water Soluble Hormones
2. The activated receptor activates a
membrane G-protein which turns on
adenylate cyclase
Action of Water Soluble Hormones
3. Adenylate cyclase converts ATP into
cyclic AMP which activates protein
kinases.
Action of Water Soluble Hormones
4. Protein kinases phophorylate enzymes,
which either become more or less active
than the nonphosphorylated form
Hormonal interactions
•
The responsiveness of a target cell to a
hormone depends on;
1. Hormone’s concentration
2. Number of receptors
3. Influences exerted by other hormones
Hormonal interactions
•
1.
2.
3.
Three types;
Permissive
Synergistic
Antagonist
Hormonal Interactions
1. Permissive – one hormone required to
act before another can be effective
Hormonal Interactions
2. Synergistic – Two hormone produce an
effect that is greater than the sum of
individual effects
Hormonal Interactions
3. Antagonistic – When hormones oppose
each other
Control of Hormone Secretions
•
1.
2.
3.
4.
5.
Controlled by;
Nervous system
Chemical changes in blood
Other hormones
Negative feedback
Positive feed back
Control of Hormone Secretions
• Negative feedback – High levels of one
substance may feed back and lower the
secretion of the other substance
Control of Hormone Secretions
• Positive feedback – high levels of one
substance may feedback and increase the
secretion of the other substance
Pituitary Gland
• Hypophysis
Pituitary Gland
• Located in the sella turcica of the sphenoid
bone
Pituitary Gland
1. Anterior pituitary (adenohypophysis)
2. Posterior pituitary (neurohypohysis)
Anterior Pituitary
• Hormones of the A.P. are controlled by
hormones produced by the hypothalamus
Anterior Pituitary
•
1.
2.
3.
4.
5.
6.
7.
Hormones
Human growth hormone (hGH)
Thyroid-stimulating hormone (TSH)
Follicle-stimulating hormone (FSH)
Luteinizing hormone (LH)
Prolactin (PRL)
Adrenocorticotropic hormone (ACTH)
Melanocyte-stimulating hormone (MSH)
Anterior Pituitary
• Hormones travel from the hypothalamus to
the A.P. via a vascular network called the
hypophyseal-portal system
Anterior Pituitary
hGH –
 essential for normal body growth
 responsible for growth spurt during
puberty
 inhibits cell glucose uptake
Anterior Pituitary
• Controlled by Growth hormone-releasing
hormone (GHRH)
Dwarfism
• Deficiency in hGH
Gigantism
• Excess hGH in kids
Acromegaly
• Excess hGH in adults
Anterior Pituitary
TSH
 causes thyroid to secrete thyroid
hormone
Anterior Pituitary
TSH
 Controlled by TRH (thyrotropin releasing
hormone)
Anterior Pituitary
TSH
 High levels of thryoid hormone feed back
and inhibit TSH secretion
Anterior Pituitary
TSH
 Low levels of thyroid hormone cause
TSH levels to go up
Anterior Pituitary
FSH
 In females, FSH initiates follicle
development and secretion of estrogens in
the ovaries
Anterior Pituitary
FSH
 In males, FSH stimulates sperm
production in the testes
Anterior Pituitary
• FSH – Controlled by Gonadotropicreleasing hormone (GnRH)
Anterior Pituitary
LH
 In females, LH stimulates secretion of
estrogen by ovarian cells to result in
ovulation
Anterior Pituitary
LH
 In males, LH stimulates the interstitial
cells of the testes to secrete testosterone
Anterior Pituitary
• LH – controlled by GnRH
Anterior Pituitary
PRL
 High levels of progesterone, estrogen
and prolactin during pregnancy promotes
breast growth
Anterior Pituitary
PRL
 Estrogen blocks the milk-secreting action
of PRL
Anterior Pituitary
PRL
 During labor, the estrogen-secreting
placenta is delivered. After that, PRL
causes the breasts to secrete milk.
Anterior Pituitary
PRL
 Suckling promotes PRL secretion
Anterior Pituitary
• Controlled by Prolactin–releasing hormone
(PRH)
Anterior Pituitary
ACTH
 controls the production and secretion of
glucocorticoids (cortisol) by the cortex of
the adrenal medulla
Anterior Pituitary
ACTH
 Stress stimulates ACTH release, which in
turn stimulates cortisol release.
Anterior Pituitary
• Controlled by Corticotropin-releasing
hormone (CRH)
Anterior Pituitary
MSH
 increases skin pigmentation
Anterior Pituitary
• Controlled by CRH
Posterior Pituitary
 Does not synthesize hormones
Posterior Pituitary
 It does store and release oxytocin (OT)
and antidiuretic hormone (ADH)
Posterior Pituitary
 These hormones are made by the
hypothalamus and stored in the P.P.
Posterior Pituitary
 The neural connection between the
hypothalamus and the P.P. is via the
hypothalmohypophyseal tract
Posterior Pituitary
OT
 stimulates contraction of the uterus
during labor
Posterior Pituitary
OT
 Stimulates ejection of milk from the
breasts
Posterior Pituitary
OT
 As uterine contractions and cervical
dilation increase during labor, they have
positive feedback on the P.P. and
increases OT secretion.
Posterior Pituitary
OT
 stimulated by suckling
Posterior Pituitary
ADH
 Stimulates water reabsorption by the
kidneys
Posterior Pituitary
ADH
 effect of ADH is to decrease urine volume
and conserve body water
Posterior Pituitary
ADH
 controlled by osmotic pressure of the
blood, which is monitored by the
hypothalamus
Posterior Pituitary
ADH
 Dehydration stimulates ADH secretion
Posterior Pituitary
ADH
 Alchohol inhibits ADH secretion,
increasing the urine output
Diabetes Insipidus
 Due to lack of ADH secretion or when the
kidneys are resistant to ADH
Thyroid
 Located below the larynx and has r. and
l. lateral lobes
Thyroid
 consists of thryoid follicles
Thyroid
 Follicular cells secrete thyroxine (T4) and
triiodothyronine (T3)
Thyroid
 Parafollicular cells secrete calcitonin (CT)
Thyroid Hormones
 Increases metabolism
Thyroid Hormones
 Crucial for brain development
Thyroid Hormones
• Up regulates beta receptors in the heart
Thyroid Hormones
 Important for growth and skeletal
maturation
Thyroid Hormones
 Crucial for G.I. motility
Thyroid
 If you produce excess thyroid hormone, it
feeds back and inhibits TSH secretion
Thyroid
 If the thyroid hormone levels decline,
there is less negative feedback on the
pituitary
Calcitonin
• Reduces blood calcium levels
Parathyroid
 Parathyroid Glands are embedded on the
posterior surfaces of the lateral lobes of
the thyroid
Parathyroid
 Produces parathyroid hormone (PTH)
Parathyroid
 PTH increases blood calcium levels and
decreases blood phosphate levels
Parathyroid
 PTH secretion controlled by blood
calcium and phosphate levels directly via
negative feedback loops
Adrenal Glands
 Located superior to the kidneys
Adrenal Glands
 Consists of an outer cortex and an inner
medulla
Adrenal Cortex
 Divided into three zones
Adrenal Cortex
1. Zona glomerulosa (outer zone) –
secretes mineralcorticoids (aldosterone)
Adrenal Cortex
 Aldosterone decreases potassium levels
and increases sodium levels
Adrenal Cortex
 Aldosterone is stimulated by Angiotensin
II
Adrenal Cortex
2. Zona fasciculata (middle zone) –
secretes glucocorticoids (cortisol)
Adrenal Cortex
 Cortisol increases blood glucose levels
by suppressing insulin and via
gluconeogenesis
Adrenal Cortex
 Cortisol is an immunosuppressant
Adrenal Cortex
 Cortisol raises blood pressure
Adrenal Cortex
 Cortisol controlled by CRH and ACTH
Adrenal Cortex
3. Zona reticularis (inner zone) – secretes
androgens (testosterone)
Adrenal Medulla
 Secretes epinephrine and norepinephrine
Pancreas
• Endocrine and exocrine gland
Pancreas
• Located posterior and slightly inferior to
the stomach
Pancreas
• Its exocrine secretions are drained by the
pancreatic duct into the duodenum
Pancreas
• Contains over a million islets of
langerhans
Pancreas
• It mainly consists of clusters of cells (acini)
• These are enzyme-producing exocrine
cells
Pancreas
• Four types of cells in the Pancreatic Islets
Pancreas
1. Alpha cells secrete glucagon which
increases blood glucose levels
Pancreas
• Beta cells secrete insulin which
decreases blood glucose levels
Pancreas
• Delta cells secrete somatostatin, which
acts as a paracrine and inhibits the
secretion of insulin and glucagon
Pancreas
• F-cells secretes pancreatic polypeptide,
which regulates release of pancreatic
digestive enzymes
Pancreas
• Glucagon and insulin are controlled by
negative feedback
Pancreas/Negative Feedback
• Glucagon is released during fasting or
hypoglycemia
Pancreas/Negative Feedback
• Glucagon promotes glycogenolysis and
gluconeogenesis
Pancreas
• Insulin is secreted after meals
Pancreas
• Insulin increases glucose uptake by
muscle and fat cells
Pancreas
• Insulin stimulates glycogenesis
Pancreas
• Insulin stimulates lipogenesis
Pancreas
• Insulin increases amino acid uptake into
cells and increases protein synthesis
Pancreas
• Insulin inhibits lipolysis
Diabetes Mellitus
• Type I – It is caused by an autoimmune
destruction of beta cells
Diabetes Mellitus
• Type II – Due to obesity. As obesity
progresses, they develop insulin
resistance
Ovaries
• Lie in pelvic cavity and produce sex
hormones (estrogens and progesterone)
Ovaries
These hormones responsible for;
1. Development and maintenance of female
sexual characterisics
Ovaries
2. Reproductive cycle
Ovaries
3. Pregnancy
Ovaries
4. Lactation
Testes
 Lie inside the scrotum and produce
testosterone
Testes
• Testosterone related to the development
and maintenance of male sexual
characteristics
Pineal Gland
• Attached to the roof of the third ventricle
Pineal Gland
• Secretes melatonin
Seasonal Affective Disorder
• SAD
• Due to over-production of melatonin
Thymus
• Secretes several hormones related to
immunity
Thymus
• Thymosin (hormone) – promote
maturation of T cells (white blood cell
involved in immunity)