2. Endocrine System
• Endocrine system regulates long term ongoing
metabolic activity
• The endocrine system uses chemicals messenger called
hormones to “communicate”.
• Hormones alter metabolic activities of tissues
• A hormone is secreted by a group of specialized cells
called gland
• Hormones are transported by the blood vessels
• Paracrine communication involves chemical
messengers between cells within one tissue
3. 3
Overview of the Endocrine System
• System of ductless glands that secrete hormones
• Hormones are “messenger molecules”
• Circulate in the blood
• Act on distant target cells
• Target cells respond to the hormones for
which they have receptors
• The effects are dependent on the programmed
response of the target cells
• Hormones are just molecular triggers
6. • Based on their chemical structure hormones are
classified into three general classes (groups) of
hormones.
• 1) Amino acid derivatives hormones e.g. epinephrine
• Structurally similar to amino acids
• 2) Peptide hormones e.g. insulin
• Chains of amino acids
• 3) Lipid derivatives hormones e.g. steroid hormones
(prostaglandin is an example of a steroid hormone)
Hormone structure
7. Hormones Transportation
• Hormones can be
• Freely circulating
• Rapidly removed from bloodstream
• Bound to transport proteins e.g. albumin or
globulin
8. • Each hormone’s shape is specific and can be
recognized by the corresponding target cells
• The binding sites on the target cells are called
hormone receptors.
• Receptors for peptide hormones, are located
on the surface of cell membranes because they
can not cross the membrane to enter the cell
• Thyroid and steroid hormones can cross the
membrane and bind to receptors in the
cytoplasm or nucleus
Mechanisms of hormone action
9. • Hypothalamus regulates the activity of the
nervous and endocrine systems
• Hypothalamus secrets regulatory hormones
(releasing hormones and inhibiting hormones)
that control the activity of the pituitary gland
• Releasing/inhibiting hormones secreted by the
hypothalamus either stimulate or inhibit
activity of pituitary gland
Control of endocrine activity
11. • The pituitary gland is called the “master gland”
but it is under the control of the hypothalamus.
• Hypothalamus and pituitary gland control many
other endocrine functions.
• Pituitary Gland releases nine important peptide
hormones
• All nine bind to membrane receptors
• Pituitary gland is divided into posterior and
anterior lobe
The Pituitary Gland
13. • Anterior lobe of pituitary gland produces 7
hormones
• 1) Thyroid stimulating hormone (TSH)
• TSH triggers the release of thyroid hormones by the thyroid
glands
• Thyrotropin releasing hormone promotes the release of TSH
• 2) Adrenocorticotropic hormone (ACTH)
• ACTH stimulates the release of glucocorticoids by the adrenal
gland
• Corticotrophin releasing hormone causes the secretion of ACTH
• 3) Follicle stimulating hormone (FSH)
• FSH stimulates follicle development and estrogen secretion in
females and sperm production in males
Hormones of the adenohypophysis
The anterior lobe (adenohypophysis)
14. • 4) Leutinizing hormone (LH)
• LH causes ovulation and progestin (progesterone) production in
females and androgen (testosterone) production in males
• Gonadotropin releasing hormone (GNRH) promotes the secretion
of FSH and LH
• 5) Prolactin (PH)
• PH stimulates the development of mammary glands and milk
production
• 6) Growth hormone (GH or somatotropin)
• GH stimulates cell growth and replication
• Growth-hormone releasing hormone
(GH-RH)
• Growth-hormone inhibiting hormone
(GH-IH)
• 7) Melanocyte stimulating hormone (MSH)
• Stimulates melanocytes to produce melanin
The anterior lobe (adenohypophysis)
15. • The posterior lobe of the pituitary gland secretes two
hormones: Antiduretic Hormone and Oxytocin.
• 1) Antidiuretic hormone (ADH)
• Decreases the amount of water lost at the
kidneys
• Elevates blood pressure
• 2) Oxytocin
• Stimulates contractile cells in mammary glands
• Stimulates smooth muscle cells in uterus
The posterior lobe of the pituitary gland
(neurohypophysis)
16. 16
Hypothalamus
• Releasing hormones (releasing factors) of hypothalamus
Secreted like neurotransmitters from neuronal axons into capillaries and
veins to anterior pituitary (adenohypophysis)
TRH (thyroid releasing hormone) -----turns on* TSH
CRH (corticotropin releasing hormone) -----turns on ACTH
GnRH (gonadotropin releasing hormone) ---turns on FSH and LH
PRF (prolactin releasing hormone) -----turns on PRL
GHRH (growth hormone releasing hormone) ----turns on GH
*
17. • Inhibiting hormones of hypothalmus
PIF (prolactin inhibiting factor) -----turns off PRL
GH (growth hormone) inhibiting hormone ---turns off GH
The hypothalamus controls secretion of hormones which in
their turn control the secretion of hormones by the thyroid
gland, the adrenal cortex and gonads: in this way the
brain controls these endocrine glands
18. • Thyroid gland is located near the thyroid cartilage
of the larynx
• The two lobes of thyroid gland is connected by an
isthmus
• Microscopically it has 2 distinct population of cells:
Flicular Cell (produce thyroid hormone) and C cell
(produce calcitonin)
The thyroid
19. 19
• Thyroid is composed of spherical follicles
• Follicle cells: produce thyroglobulin, the
precursor of thryoid hormone (thyroxin)
• Colloid lumen is of thyroglobulin
• Parafollicular “C” cells: produce calcitonin
21. • Thyroid gland release several hormones such
as thyroxine (T4) and triiodothyronine (T3)
• Thyroid hormones (T4 and T3) are
transported by to thyroid binding globulins
(TBG), and albumin
22. Functions of Thyroid hormones include:
• Increases the basal metabolic rate
• The rate at which the body uses oxygen to transform
nutrients (carbohydrates, fats and proteins) into energy
• Increasing ATP production, when bound to
mitochondria.
• Activating genes that control energy utilization,
when bound to receptors
• Exert a calorigenic effect
23. 23
Some Effects of Thyroid Hormone
(Thyroxine)
• Affects many target cells throughout the body; some
effects are
• Protein synthesis
• Bone growth
• Neuronal maturation
• Cell differentiation
24. • C cells of thyroid gland produce calcitonin
• Calcitonin helps to regulate calcium
concentration in body fluids
26. 26
Parathyroids
(two types of cells)
• chief cells
• oxyphil cells (unknown
function)
• Chief cells produce PTH
• Parathyroid hormone, or
parathormone
• A small protein hormone
27. • Chief cells produce parathyroid hormone (PTH)
in response to lower than normal calcium
concentrations
• Parathyroid hormones plus calcitriol are primary
regulators of calcium levels in healthy adults
Parathyroid glands
28. The Homeostatic Regulation of Calcium Ion
Concentrations
• When calcium levels decrease in the blood, parathyroid glands produce
PTH
• PTH increase blood calcium level by:
1. Releasing stored calcium from the bones
2. Stimulating production of calcitriol at the kidney. Calcitriol
increases absorption of calcium by the digestive system
3. Enhance reabsorption of calcium by the kidneys
• When calcium levels increase in the blood, thyroid glands produce
calcitonin.
• Calcitonin decreases blood calcium level by:
1. Increasing excretion of calcium by the kidneys
2. Increase calcium deposition in the bones
3. Stop osteoclast
32. • Manufactures steroid hormones derived from
cholesterol (corticosteroids).
• Secretes lipid-based steroid hormones, called
“corticosteroids” – “cortico” as in “cortex
The Adrenal Glands
Adrenal cortex
33. • Corticosterioid hormones are divided into 3 functional
groups
• Mineralocorticoids (Aldosterone)
• Regulate mineral and salt balance by renin-
angiotensis-aldosterone system
• Aldosterone is the main one
• Glucocorticoids (cortisol and cortisone)
• Regulate glucose levels i.e. they increase
gluconeogenesis and decrease protein synthesis
• Cortisol (hydrocortisone) is the main one
• Decrease inflammation response
• Androgens also called sex hormones
34. The Adrenal Glands
Adrenal medulla
• Responsible for flight-or-fight response
• Produces epinephrine and norepinephrine
35. 35
The Pineal Gland
• At the end of a short stalk on the roof of the
diencephalon
• Contains pinealocytes
• Synthesize melatonin
• Pinealocytes with dense calcium particles
• Can be seen on x-ray (because of Ca++)
37. 37
The Pancreas
Exocrine and endocrine cells
• Acinar cells (forming most of the pancreas)
• Exocrine function
• Secrete digestive enzymes
• Islet cells (of Langerhans)
• Endocrine function
38. • Clusters of endocrine cells within the pancreas
called Islets of Langerhans or pancreatic islets
• Alpha cells secrete glucagons
• Glucagon raises blood glucose by increasing the rates
of glycogen breakdown and glucose manufacture by
the liver
• Beta cells secrete insulin
• Insulin lowers blood glucose by increasing the rate of
glucose uptake and utilization
• Delta cells secrete GH-IH secrete somatostatin
• inhibits glucagon
• F cells secrete pancreatic polypeptide
The pancreatic islets
40. Diabetes
• Type I – Insulin dependent diabetes
• Caused by autoimmune destruction of beta
cells
• Type II – non insulin dependent diabetes
• Caused by body resisting the effects of insulin
at its receptor.
• Symptoms: Polyuria (inreased frequency of
urination), polydipsia (increased thirst)
42. • Produce calcitriol and erythropoietin (EPO) and the
enzyme rennin
• Calcitriol = stimulates calcium and phosphate ion
absorption along the digestive tract
• EPO stimulates red blood cell production by bone
marrow
• Renin converts angiotensinogen to angiotensin I
• Angiotensin I is converted to angiotensin II at the lungs
• Agiotensin II:
1. Stimulates production of aldosterone by the
adrenal glands
2. Stimulates release of ADH by the pituitary gland
3. Promotes thirst
4. Elevates blood pressure
The kidneys
44. 44
The Gonads (testes and ovaries)
main source of the steroid sex hormones
• Testes
• Interstitial cells secrete androgens
• Primary androgen is testosterone
• Maintains secondary sex characteristics
• Helps promote sperm formation
• Ovaries
• Androgens secreted by thecal folliculi
• Directly converted to estrogens by follicular granulosa cells
• Granulosa cells also produce progesterone
• Corpus luteum also secretes estrogen and progesterone
45. • The Heart
• Specialized muscle cells produce natriuretic peptides in
response to high blood pressure
• Natriuretic peptide generally has the opposite actions
of angiotensin II
• The Intestine
• Produce hormones important to the coordination of
digestive activities
• The Thymus
• Produces thymosins
• Help develop and maintain normal immune defenses
The heart, The intestines and the Thymus
46. • Normal growth requires the interaction of several
endocrine organs
• Six hormones are important
• GH
• Thyroid hormones
• Insulin
• PTH
• Calcitriol
• Reproductive hormones
Hormones and growth
47. • Leptin, a feedback control for appetite
• Resistin, which reduces insulin sensitivity
Adipose tissues secrete
48. • Many hormones affect the CNS
• Changes in the normal mixture of hormones
significantly alters intellectual capabilities,
memory, learning and emotional states
Hormones and behavior
