endocrine system and chemical messengers

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2. The Endocrine System and Chemical Messengers
Communication III

3. Chemical Messengers
A chemical messenger is any compound that serves to transmit a
message.
Chemical messenger may be categorized as :
 Local chemical messengers
 Neurotransmitters
 Neuropeptides
 Pheromones
 Hormones

5. Local chemical messenger
 Alter physiological conditions in the immediate vicinity.
 Examples :
1. Lumones _ help to regulate digestion.
2. Histamine _ participate in inflammatory response.

6. Neurotransmitters
 Neurotransmitters are often referred to as the body’s chemical messengers.
 They are the molecules used by the nervous system to transmit messages
between neurons, or from neurons to muscles.
 Communication between two
neurons happens in the synaptic
cleft .

7. Neuropeptides
 Secreted from neurons called neurohormones.
 They are the members of a class of protein-like molecules made in the brain.
 They consist of short chains of amino acids.

8. Hormones
 Hormones are chemical substances that act like messenger molecules in
the body.
 After being made in one part of the body, they travel to other parts of the
body where they help control how cells and organs do their work.

9. Pheromones
 Small molecules that, when released by one organism, act as chemical
signals to induce a certain behavior in another organism.
 Example:
Scents that attract animals to
each other in a mating process.

10. Endocrine System

11. Endocrine System
The endocrine system is the collection of glands that produce hormones
that regulate
 Metabolism
 Growth and development,
 Tissue function,
 Sexual function,
 Reproduction,
 Sleep, and mood

12. How the nervous and endocrine systems are alike?
 Like the nervous system, the endocrine system is a regulatory system.
 However, instead of using electrical impulses for signaling, it produces
and uses chemical signals called hormones, which travel through the
bloodstream and control the actions of cells and organs.

13. Hormones and their Chemistry

14. Hormones
 A hormone is a chemical messenger that enables communication between
cells.
 Hormones are secreted by the glands of the endocrine system.
 They affect the activity of another part of the body (target site).
Hormone serves as
 To maintain homeostasis
 To regulate numerous other systems and processes, including reproduction
and development.

15. Chemistry of Hormones
There are three classes of hormones:
1. Peptide hormones
2. Lipid-derived hormones
3. Monoamine hormones

16. Peptide Hormones
 Comprised of short and long chains of amino acids.
 Secreted by the pituitary gland.
 Regulate osmotic balance.
 They are water-soluble but
cannot pass through the
plasma membrane alone.

17. Lipid-derived hormones
 These are hormones derived from fats or lipids such as linoleic acid
and the phospholipids.
 They are lipid-soluble and can pass through the plasma membrane.
 Main class :
Steroids are derived from cholesterol
Steroid hormones include testosterone, estrogen and cortisol.

18. Monoamine hormones
 Derived from single aromatic amino acids like phenylalanine, tyrosine,
and tryptophan.
For example,
Tryptophan-derived melatonin that is secreted by the
pineal gland regulates sleep patterns.

19. Feedback control system

20. Feedback control system
 A process that uses one component to regulate another.
 They are the Biological mechanisms whereby homeostasis is
maintained.
 Most hormones are regulated by feedback mechanisms.
 Monitors changes in the animal or in the external environment and
sends information to a central control unit such as CNS, which makes
adjustments.

21. Types Of Feedback Systems
1. Positive Feedback System
2. Negative Feedback System

22. Negative Feedback System
 Negative feedback occurs when a product feeds back to decrease its
own production.
 Monitor the amount of hormone secreted ,altering the amount of
cellular activity as needed to maintain homeostasis .
Example:
Suppose that the rate of chemical activity in the body cells of dog slows .

24. Positive Feedback System
 Positive feedback occurs when a product feeds back to increase its
own production.
 Relatively rare in animals because they usually lead to instability or
pathological states.

25. Mechanism Of Hormone Action

26. Mechanisms of Hormone Action
 The mechanism of hormone action is grouped into two classes:
1. Fixed membrane receptor mechanism
2. Mobile receptor mechanism

27. Fixed Membrane Receptor Mechanism
 This type of mechanism is shown by the water-soluble hormones that are
amines or proteins in composition such as the growth hormone, oxytocin,
ADH, etc.
 These hormones can’t pass through the lipid membrane.

29. Mobile Receptor Mechanism
 This type of mechanism is shown by lipid soluble hormones such as fatty
acids and steroids that can easily pass through the plasma membrane.
 They possess intracellular receptors.

31. Hormones of Invertebrates

32. Hormones of Porifera
 Animals in phylum Porifera are the some of the most simple animals
on earth.
They do not have classical endocrine glands because:
 There is no main "pathway" for the hormones
 The sponge regulates growth and
reproductive actions by its specialized
cells.

33. Hormones of Cnidarians
 Cnidarians do not have a certain endocrine system, yet they do
have hormones that are present in the tissues.
 Hydra secrete a hormone called Thyroxin, which regulates asexual
reproduction through budding.
 Growth promoting hormone(in hydra) stimulate
 Budding
 Regeneration and
 Growth.

34. Hormones of Platyhelminthes
 Neurosecretory cells are identified in some flatworms.
 The neuropeptide secreted from these cells functions in:
 Regeneration
 Asexual reproduction ,and
 Gonad maturation
 Example
Neurosecretory cells in the scolex of some tapeworms controls
shedding of the proglittids or the initiation of the strobilization.

35. Hormones of Nemerteans
 Have more cephalization than Platyhelminthes.
 They have a large brain , composed of a dorsal and ventral pair of
ganglia connected by a nerve ring.
 The neuropeptide produce from ganglia appears to control :
1. Gonadal development and
2. To regulate water balance.

36. Hormones of Nematodes
 No endocrine glands identified.
 They do have neurosecretory cells associated with CNS.
 The neuropeptide controls ecdysis of the old cuticle.
 Released after the new cuticle is produced and stimulates the
excretory gland to secrete an enzyme leucine aminopeptidase into
the space between the old and new cuticle. The accumulation of fluid
in the space cause the old cuticle to split and be shed.

37. Hormones of Mollusks
 The ring of ganglia that constitutes the CNS is richly endowed with
neurosecretory cells.
 The neuropeptides help to regulate
 Heart rate
 Kidney function and energy metabolism
 Hormones in snails and slugs stimulates:
 Spermatogenesis
 Egg development

38. Hormones Of Annelids
 Have well developed and cephalized NS , a well developed CS ,and a large
coelom.
 The endocrine systems are generally involved in
1. Morphogenesis
2. Development
3. Growth
4. Regeneration
 In polychaetes
 Juvenile hormone inhibit the gonads and stimulates the growth and
regeneration.
 Gonadotropin stimulate development of eggs.

39. Hormones Of Arthropods
 Their endocrine systems are the excellent examples of how
hormones regulate growth , maturation and reproduction.
 The endocrine system of a crustaceans such as crayfish controls
function such a such as:
1. Ecdysis (molting)
2. Sex determination and
3. Color change

41. Hormones Of Echinoderms
 Echinoderms are deuterostomes , they are more closely allied to
chordates than are the protosomes invertebrates.
 Neuropeptide in sea stars called gonad stimulating hormone
involves in:
i. Shedding of gametes
ii. Spawning behavior
iii. Meiosis in oocytes
 Neuropeptide also cause the release of hormone _ maturation
inducing substance which has effects on reproductive system.

42. Overview of Vertebrate Endocrine System

43. Endocrine system
 Studied more than invertebrates _ best understood system of
hormone control.
 The endocrine system is a network of chemical communication among
cells in vertebrate animals.
 Possess two types of glands:
1. Exocrine
2. Endocrine

44. Exocrine Glands
 Secrete chemicals into the ducts.
 Ducts in turn , empties into the body cavities or onto the body
surfaces.
 Examples:
Mammary glands
Salivary glands and
Sweat glands .

45. Endocrine glands
 They have no ducts.
 Secrete chemical messengers called hormones, directly into the tissue
space next to each endocrine cell.
 The hormones than diffuse into the blood stream, which carries them
throughout the body to their target cells.

46. Other Vertebrates Endocrine System

47. Aspects of Endocrinology
 Recent research has revealed the three aspects of endocrinology that
relate to species differences in the vertebrates :
1. Hormone with the same functions in different species may not be
chemically identical.
2. Certain hormones are species specific with respect to their function;
conversely, some hormones produced in one species may be
completely functional in another species .
3. A hormone from one species may elicit a different response in the
same target cell or tissue of a different species.

48. Fishes
 In jawed fishes, three major regions secrete neuropeptides:
1. Pineal gland
2. Preoptic nuclei
3. Urophysis

49. Melatonin
 Hormone from the pineal gland.
 Control variations in the skin color.
 Produced by fishes, amphibians and reptiles.

50. Prolactin
 Produced by pituitary gland.
 Stimulates reproductive migration in many animals.
 E.g., the movement of salamanders to water .
 Causes brooding behavior in some fishes.
 Control water and salt balances.
 Essential for certain saltwater fishes to enter freshwater during
spawning runs.

51. Metamorphosis
 Change of physical form, structure, or substance especially by
supernatural means.
 The metamorphosis in frogs is controlled by the changes in the
concentrations of the hormones
1. Prolactin
2. Thyroxin
3. Triiodothyronine

52. Ultimobranchial glands
 Present in jawed fishes and primitive tetrapods.
 Produce the hormone calcitonin that help to regulate the
concentration of blood calcium.

53. Chromaffin Tissue
 Special endocrine cells
 Present near the kidneys
 Produce two hormones
 Epinephrine
 Norepinephrine
 Cause vasoconstriction, increased blood pressure, changes in the
heart rate, and increased blood glucose levels.

55. Endocrine Systems of Birds

57. Some Unique Hormones in Birds
Prolactin:
 Secreted by pituitary gland.
 Stimulate the production of “pigeon’s milk” by desquamation
(sloughing of cells) in the pigeon’s crop .
 Also stimulate and regulate the following functions:
1. Broodiness
2. Certain kinds of parental behavior
3. Along with estrogen stimulate full development of brood patch.

58. What is Brood Patch?
 A robin’s single brood patch appears (due to the effect of the hormone
prolactin) a few days before eggs are laid.
 The brood patch helps keep the
eggs at a temperature between 33
and 37° C.

59. Thyroxin
 In addition to the major vertebrate functions thyroxin regulates:
 The normal development of feathers and the molt cycle.
 Plays a role in the onset of migratory behavior.

60. Testosterone
 Produces from testes in male birds
 Controls the secondary sexual characteristics of the male such as
 Bright plumage color
 Comb
 Spurs

61. Calcitonin
 Secreted from the Ultimobranchial glands
 Are the small paired structures in the neck just below the
parathyroid glands
 Involved in regulating blood calcium concentrations.

62. Bursa of Fabricius
 This is a sac that lies just dorsal to the cloaca and empties into it.
 Well developed during the bird’s embryological development but it
begins to shrink soon after hatching.
 Its tissues produce secretions that are responsible for the maturation
of white blood cells

63. Brief overview of Mammalian Endocrine System
Endocrine system of Mammals

65. Pituitary Gland
 Present directly below the hpothalamus.
 Two distinct lobes:
 Anterior lobe (adenohypophysis)
 Posterior lobe (neurohypophysis)
 The pituitary of many vertebrates also has a functional intermediate
lobe of mostly glandular tissue.

66. Hormones of Neurohypophysis
 Secrete two hormones,
Antidiuretic hormone
 Diuretics stimulate urine excretion and anti diuretics decrease it .
Oxytocin
 Plays a role in mammalian reproduction by its effect on smooth
muscle.

67. Hormones of Adenohypophysis
 Synthesize 6 different hormones
1. Growth hormone or STH
2. Prolactin
3. Thyrotropin or TSH
4. Adrenocorticotropic hormone
5. Follicle stimulating hormone
6. Gonadotropins

68. Thyroid Gland
 Present at the neck ,anterior to trachea
 Produce two secretions:
 Thyroxin
 Triiodothyronine
 Both influences :
1. Growth
2. Development
3. Metabolic rates
 Calcitonin is also secreted to control levels of calcium ions

69. Parathyroid Gland
 Tiny pea sized glands embedded in the thyroid lobes .
 Secrete Parathormone
 Regulates calcium concentration and
 Phosphate ions in blood

71. Adrenal Glands
 In mammals, two adrenal glands rest on top of the kidneys.
 Each gland consists of two separate glandular tissues.
 Medulla _ inner portion
 Cortex _the outer portion, which surrounds the
medulla

72. Adrenal Cortex
 Secretes three classes of steroid hormones:
1. Glucocorticoids
2. Mineral
3. Sex hormones

74. Adrenal Medulla
 It contains neurosecretory cells.
 Secretes:
1. Epinephrine
2. Norepinephrine
 Both of which help control heart rate and carbohydrate metabolism.

75. Pancreas
 Elongated, fleshy organ posterior to the stomach.
 It functions both as:
1. Exocrine gland
2. Endocrine gland
 The endocrine portion of the pancreas makes up only about 1% of
the gland.

77. Pancreatic islets
 Pancreatic portion synthesizes, stores , and secretes hormones from
clusters of cells called pancreatic islets.
 The pancreas contains 200,000 to 2,000,000 pancreatic islets
scattered throughout the gland.
 Each islet contains four special groups of cells:
1. Alpha
2. Beta
3. Delta
4. F cells

78. Gonads
 The gonads secrete hormones that helps to regulate
reproductive functions.
 In the male, the testes secrete testosterone,
which acts with LH and FSH that the adenohypophysis produces to stimulate
spermatogenesis.
Functions of Testosterone:
1. Necessary for the growth and
2. Maintenance of the male sex organs,
3. Promotes the development and maintenance of sexual behavior,
4. In humans, stimulates the growth of facial and pubic hair.
5. The testes also produce inhibin, which inhibits the secretion of FSH.

79. Ovarian hormones
 Four major classes help to regulate female reproductive functions.
1. Estrogens_ regulate the menstrual and estrus cycles.
2. Progestins _aid in placenta formation during pregnancy.
3. Relaxin_ softens the opening of the uterus at the time of delivery.
4. Inhibin_ inhibits the secretion of FSH.

80. Thymus
 The thymus gland is near the heart.
 It is large and conspicuous in young birds and mammals, but
diminishes in size throughout adulthood.
 Hormonal product:
1. Thymopoietin
2. Alpha1 and
3. Beta4 thymosin
 Essential for the normal development of the immune system.

81. Presented By
Saba Shahzadi
Thank You