1. Chapter 9
The Endocrine System

2. Along with Nervous System, the Endocrine System coordinates and directs the activities of body cells
Nervous System uses impulses to make muscles and glands to respond quickly to changes inside and outside the body
Endocrine System uses chemical messengers released into the blood to respond slowly to changes

3. Hormones Chemical messengers are called hormones
Hormones control several major processes
Reproduction
Growth and development
Mobilization of body defenses
Maintenance of much of homeostasis
Regulation of metabolism

4. Hormones are produced by specialized cells
Cells secrete hormones into extracellular fluids
Blood transfers hormones to target sites
These hormones regulate the metabolic activity of other cells

5. Hormones regulate processes that go on for long periods
Hormones can be classified as
Amino acid-based molecules – proteins, peptides, amines
Steroids – made from cholesterol
Prostaglandins – made from highly active lipids

6. Mechanisms of Hormone Action
Hormones work by binding to target cell membrane
Hormones affect only certain tissues or organs (target cells or organs)
Target cells must have specific protein receptors
Hormone binding influences the working of the cells

7. Effects Caused by Hormones
Changes that follow hormone binding depend on the specific hormone and the target cell type
Typical changes include:
Changes in plasma membrane permeability or electrical state
Synthesis of proteins, such as enzymes
Activation or inactivation of enzymes
Stimulation of mitosis

8. Mechanisms of Hormone Action
Two hormone mechanisms trigger changes in the cell
Figure 9.1
Direct gene activation – the steroid hormone mechanism
A second messenger system – nonsteroid (amino acid-based) mechanism

9. Steroid Hormone Action
Diffuse through the plasma membrane of target cells – lipid-soluble
Enter the nucleus
Bind to a specific protein within the nucleus
Bind to specific sites on the cell’s DNA
Activate genes that result in synthesis of new proteins

10. Steroid Hormone Action
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TO PLAY
STEROID HORMONE ANIMATION
Figure 9.1a

11. Nonsteroid Hormone Action
Hormone binds to a membrane receptor
Hormone does not enter the cell
Sets off a series of reactions that activates an enzyme
Catalyzes a reaction that produces a second messenger molecule – cAMP or various other possiblities
Oversees additional intracellular changes to promote a specific response

12. Nonsteroid Hormone Action
PRESS
TO PLAY
NONSTEROID HORMONE ANIMATION
Figure 9.1b

13. Prostaglandins
Group of biochemicals that also regulate cells like hormones
Produced by many types of cells
Act more locally than hormones
Effect organs where they are produced
Synthesized just before release, not stored in cells

14. Control of Hormone release
Negative Feedback mechanisms
Regulate blood levels of hormones
Secretion is triggered (internal or external stimulus), rising hormone levels inhibit further hormone release
Blood levels of hormones vary within a narrow range

15. 3 major categories of stimuli to activate endocrine organs
Hormonal stimulation – organs stimulated by other hormones
Humoral stimulation – changing blood levels stimulate release of hormones
Neural stimulation – nerve fibers stimulate release of hormones

16. Hormonal Stimuli of Endocrine Glands
Endocrine glands are activated by other hormones
Hypothalamus hormones stimulate pituitary gland secretion
Pituitary hormones stimulate other endocrine organs
Figure 9.2a

17. Hormones secreted by thyroid, adrenal cortex, testis (final target glands) “feed back” to pituitary gland and inhibit more pituitary gland secretion
When target gland secretion is too low, hypothalamus again stimulates the pituitary gland

18. Humoral Stimuli of Endocrine Glands
Changing blood levels of certain ions stimulate hormone release
Low blood Ca levels stimulate release of PTH
When Ca levels rise, PTH release is inhibited
Figure 9.2b

19. Neural Stimuli of Endocrine Glands
Nerve impulses stimulate hormone release
Most are under control of the sympathetic nervous system
Figure 9.2c

20. Sympathetic Nervous System stimulation of the adrenal gland releases norepinephrine and epinephrine during periods of stress.

21. Major Endocrine Organs
Pituitary, thyroid, parathyroid, adrenal, pineal, thymus, pancreas, gonads (ovaries and testis)
Hypothalamus is part of the CNS, but is also considered an endocrine organ since it produces several hormones

23. Some glands are purely endocrine, others are mixed – endocrine and exocrine
Exocrine glands – release substances onto body substances or into body cavities through ducts
Endocrine glands – release substances into blood

24. Pituitary Gland Size of a grape Hangs by a stalk from the hypothalamus
Protected by the sphenoid bone
Has two functional lobes
Anterior pituitary – glandular tissue
Posterior pituitary – nervous tissue

25. Hormones of the Anterior Pituitary
Six anterior pituitary hormones
Two affect non-endocrine targets
Growth hormone
Prolactin
Four stimulate other endocrine glands (tropic hormones)
Thyrotropic hormone
Adrenocorticotropic hormone
2 Gonadotropic hormones

26. Hormones of the Anterior Pituitary
Figure 9.4

27. Characteristics of all anterior pituitary hormones
Proteins (or peptides)
Act through second-messenger systems
Regulated by hormonal stimuli, mostly negative feedback

28. Hormones of the Anterior Pituitary
Growth hormone - GH
Effects growth of skeletal muscle and long bones
Builds up proteins
Cells grow in size and divide
Breaks down fats to produce energy

29. Adrenocorticotropic hormone - ACTH
Prolactin – PRL
Stimulates and maintains milk production in mothers after birth
Function in males is not known
Adrenocorticotropic hormone - ACTH
Regulates endocrine activity of adrenal cortex

30. Thyroid-stimulating hormone– TSH
Also called thyrotropic hormone - TH
Influences growth and activity of thyroid gland

31. Gonadotropic hormones Follicle-stimulating hormone – FSH
Matures follicles of ovaries, produces estrogen
In males, stimulates sperm development
Luteinizing hormone – LH
Triggers ovulation of egg from the ovary
Produces progesterone and estrogen
In males, called interstitial cell-stimulating hormone, stimulates testosterone production

32. Pituitary-Hypothalamus
Anterior pituitary controls the activity of other glands : adrenals, thyroid, ovaries, testes
Anterior pituitary is controlled by hypothalamus
Hypothalamus produces 2 other hormones that are transported along neurosecretory axons to posterior pituitary – figure 9.5

34. Hormones of Posterior Pituitary
Hormones are made by hypothalamus and transported to and stored by posterior pituitary
Nerve impulse from hypothalamus triggers release of posterior hormones
Oxytocin
Released during childbirth and nursing
Stimulates contraction of uterine muscles

35. Antidiuretic hormone – ADH
Diuresis – urine production
ADH causes kidneys to reabsorb water from urine, urine volume decreases, blood volume increases
Alcoholic drinks inhibit ADH secretion resulting in increase in urine output, dehydration
Diuretic drugs inhibit ADH

36. Thyroid gland Located at the base of the throat
Consists of 2 lobes joined by a central isthmus
Composed of hollow structures called follicles which are filled with a colloid which produces thyroid hormones
Produces 2 iodine-containing hormones and calcitonin

39. Thyroid Hormones Thyroxine – T4 Triiodothyronine - T3
Major hormone of the thyroid follicles
4 iodine atoms
Controls metabolism
Triiodothyronine - T3
Formed by conversion of thyroxine at the target cell
3 iodine atoms

40. Calcitonin
Decreases blood calcium levels by helping calcium to be deposited in the bones
Made by C cells, parafollicular cells, in the connective tissue around the follicles
Released into blood in response to high blood levels of calcium

41. Parathyroid Glands
Tiny masses of gland tissue found on posterior surface of thyroid
Secretes parathyroid hormone which acts antagonistically to calcitonin

42. Parathyroid Hormone Parathyroid hormone – PTH
Increases calcium levels in the blood by stimulating osteoclasts to break down bone tissue to increase calcium levels in blood

44. Adrenal Glands Bean-shaped gland on top of kidneys
Contains glandular cortex and neural tissue medulla region
Adrenal cortex produces 3 groups of steroid hormones called corticosteroids: mineralocorticoids, glucocorticoids, and sex hormones
Adrenal medulla produces catecholamines: epinephrine and norepinephrine

45. Adrenal cortex Hormones
Mineralcorticoids, mainly aldosterone, produced by outermost cortex cell layer
Regulates concentration of sodium and potassium ions by causing kidney to absorb sodium ions and water, and excrete potassium ions
Increases blood volume and blood pressure

47. Glucocorticoids including cortisone and cortisol are produced by the middle cortical layer
Promote normal cell metabolism, especially breakdown of fats and proteins, to help the body resist long-term stresses (Figure 9.12)
Increase blood glucose levels
Control inflammation
Regulated by blood levels of ACTH

48. Sex hormones including androgens and estrogens produced by innermost cortex layer
Both are produced regardless of gender

49. Adrenal Medulla Hormones
Stimulated by sympathetic nervous system, releases catecholamines epinephrine and norepinephrine
Epinephrine - also called adrenaline
Coping with short-term stressful situations
Increase heart rate, blood pressure, blood glucose level, dilate air passageways in lungs
Increase oxygen to the brain

50. Controlling stress Glucocorticoids ( ) vs. Catecholamines ( )
Figure 9.12
Cortisone & cortisol – adrenal cortex
Cope with prolonged or continuing stressors, resistance stage
Epinephrine – adrenal medulla
Prepare body for alarm stage of stress

52. Pancreas Located close to the stomach in abdominal cavity
A mixed gland – Figure 9.13
Exocrine cells – acinar tissue – work with the digestive system, produce enzymes
Endocrine gland cells – pancreatic islets – scattered throughout acinar tissue, produce 2 hormones: insulin & glucagon
Insulin produced in beta cells, glucagon produced in alpha cells

55. Pancreatic Hormones Insulin – beta cells
Increases cells ability to transport glucose from the blood into cell through the cell membrane
Speeds up cell’s ability to convert glucose into energy or glycogen to be stored in the liver
Insulin secretion is stimulated by high glucose levels in blood. As glucose levels decrease, insulin release ends. Negative feedback
Without insulin, no glucose gets into cells

56. Figure 9.14 – antagonistic effects of insulin and glucagon
Glucagon – alpha cells
Antagonist to insulin
Stimulates liver to break down glycogen to glucose and release glucose into blood
Stimulated by low blood glucose levels
Figure 9.14 – antagonistic effects of insulin and glucagon

58. Pineal Gland Small, cone-shaped Roof of third ventricle of brain
Only one hormone secreted, melatonin
“sleep trigger”
Establishes the body’s day-night cycle
Peak levels at night cause drowsiness, low levels at daylight

59. Thymus Gland Upper thorax, posterior to sternum
Large in infants and children
Size decreases in adulthood
Produces thymosin
Incubator to help white blood cells mature
Important role in immune response

60. Gonads
Male and female gonads produce same sex hormones as those produced in adrenal cortex
Female gonads – ovaries
Male gonads - testes

61. Ovaries Almond-shaped, located in pelvic cavity
Produce sex cells, eggs
Produce 2 steroid hormones: estrogen and progesterone
Do not function until gonadotropic hormones of anterior pituitary gland stimulate them at puberty

62. Ovarian Hormones Estrogen Progesterone
stimulates maturation of reproductive organs
Prepares uterus to receive fertilized egg by causing cyclic changes in uterine lining – menstrual cycle
Progesterone
Acts with estrogen to bring about menstrual cycle
Assures that uterine muscle will not abort implanted embryo
Produced by corpus luteum, glandular structure of ovary

63. Testes Suspended in a sac outside pelvic cavity
Produce sex cells, sperm
Produce testosterone
Stimulates maturation of reproductive organs
Necessary for production of sperm
Stimulated by gonadotropic hormone of anterior pituitary hormone at puberty

64. Development of Endocrine System
Embryonic development varies
Pituitary – epithelium of oral cavity, neural tissue of hypothalamus
Pineal – neural tissue
Thyroid, thymus, pancreas – mucosa of digestive tract
Late middle age – estrogen production declines
menopause
Most endocrine organs function well until old age