1. Endocrine System
Chapter 16

2. Overview
Overall goal of endocrine system: maintain a stable internal environment (homeostasis)
Endocrine glands are “ductless glands”
Endocrine glands secrete hormones which travel through the blood to a target cell
Receptor must be present on target cell

3. Endocrine vs Nervous System
Both systems function to maintain homeostasis
Main differences:
Feature
Endocrine System
Nervous System
Effector cells
Target cells throughout the body
Postsynaptic cells in muscle and glandular tissue only
Chemical messenger
Hormone-chemical
Neurotransmitter
Distance traveled by messenger
Long – in blood
Short – across synaptic cleft
Regulatory effects
Slow to appear; long-lasting
Appear rapidly; short

4. Endocrine vs Nervous System

5. Major Endocrine Glands

6. Classification of Hormones
Classified by Function
Tropic hormones: target other endocrine glands and stimulate their growth & secretion
Sex hormones: target reproductive tissues
Anabolic hormones: stimulate anabolism in their target cell

7. Chemical Classifications of Hormones

8. How Hormones Work Hormones bind to receptors on target cells
Lock & key
Hormone-receptor interactions produce regulatory changes within the target cell
Ex: initiating protein synthesis; activation/inactivation of enzymes; opening/closing of ion channels

9. How Hormones Work
Synergism: combinations of hormones have a greater effect on the target cell compared to a single hormone acting alone
Permissiveness: a small amount of one hormone allows a second hormone to exhibit its full effect on the target cell
Antagonism: two hormones produce opposite effects

10. Regulation of Hormone Secretion
Hormone secretion is controlled by a negative feedback loop
Ex: parathyroid hormone (PTH) and blood calcium levels (fig 16-10)
Ex: insulin and blood glucose levels

11. Endocrine Feedback Loop

12. Hyper vs Hyposecretion
Tumors or abnormalities of the endocrine glands cause secretion of too much or too little hormone
Hypersecretion: production of too much hormone
Hyposecretion: production of too little hormone
Results in lack of target cell response
Also caused by target cell insensitivity

13. Pituitary Gland Also called hypophysis
Located on ventral surface of brain, inferior to the hypothalamus
“Master gland” because functions are crucial to life
Composed of two parts: Anterior Pituitary and Posterior Pituitary

14. Anterior Pituitary Hormones secreted from Anterior Pituitary:
Growth Hormone
Prolactin
Trophic hormones
Thyroid-stimulating hormone (TSH)
Adrenocorticotropic hormone (ACTH)
Gonadotropic hormones
Follicle-stimulating hormone (FSH)
Luteinizing hormone (LH)

15. Growth Hormone
Growth Hormone (GH) – promotes growth by stimulating protein anabolism
Increased protein anabolism allows increased growth rate
Target cells:
Promotes growth of bone and muscle
GH has a hyperglycemic effect; antagonist of insulin
Hyperglycemic effect because GH stimulates fat metabolism
Interaction vital to maintaining homeostasis of blood glucose levels
GH stimulates fat metabolism
Shift cells away from glucose catabolism towards lipid catabolism for an energy source
Less glucose is used by cells; causes hyperglycemia

16. Growth Hormone Abnormalities
Hypersecretion
Prior to ossification of the epiphyseal plates hypersections of GH results in rapid skeletal growth  Gigantism
After closure of epiphyseal plates hypersecretion causes cartilage to continue to form new bone  Acromegaly
Distorted appearance; enlarged hands, feet, face, jaw; thickened skin

18. Growth Hormone Abnormalities
Hyposecretion
Results in stunted body growth  pituitary dwarfism
Treated with genetically engineered growth hormone

19. Prolactin (PRL) Also called lactogenic hormone
Initiates milk secretion (lactation)
Target cells: Mammary glands
During pregnancy PRL promotes development of breasts
At birth PRL stimulates milk production

20. Prolactin Abnormalities
Hypersecretion:
Lactation in non-nursing women
Disruption of menstrual cycle
Impotence in men
Hyposecretion:
Insignificant unless mother wishes to breastfeed

21. Trophic Hormones
Review: a trophic hormone stimulate effects of other endocrine glands
Trophic hormones released from anterior pituitary gland:
Thyroid-stimulating hormone (TSH)
Adrenocorticotropic hormone (ACTH)
Gonadotrophic hormones
Follicle-stimulating hormone (FSH)
Luteinizing hormone (LH)

22. Thyroid-stimulating hormone (TSH)
Promotes and maintains growth and development of thyroid gland
Required for thyroid gland to secrete its hormones

23. Adrenocorticotropic hormone (ACTH)
Promotes and maintains normal growth and development of the cortex (outer portion) of the adrenal gland
Required for adrenal cortex to secrete its hormone

24. Gonadotrophic hormones
Target cells: gonads (testes & ovaries)
Follicle-stimulating hormone (FSH)
Females:
Stimulates growth & development of an ovum that is released each month during ovulation
Stimulate estrogen release from the ovaries
Males
Stimulates development of seminiferous tubules and maintains sperm production in the testes

25. Gonadotrophic hormones
Luteinizing hormone (LH)
Females:
Triggers ovulation
Promotes development of corpus luteum which secretes progesterone and estrogen; these hormones help maintain pregnancy
Males:
Stimulates cells of the testes to synthesize and secrete testosterone

26. Control of Anterior Pituitary Secretion
The hypothalamus releases chemical called releasing hormones which influence hormone secretion from the anterior pituitary gland
This regulatory mechanism is a negative feedback loop

27. Posterior Pituitary Hormones secreted from Posterior Pituitary:
Antidiuretic Hormone (ADH)
Oxytocin (OH)

28. Antidiuretic Hormone (ADH)
Target cells: kidney
Prevents formation of large volumes of dilute urine
Antidiuresis
Helps conserve water balance
Example:
Blood is hypertonic  change detected by osmoreceptors  ADH is released  water reabsorbed in kidneys and returned to blood

29. ADH Abnormalities Hyposecretion Hypersecretion Diabetes insipidus
Increased urine output of dilute urine
“high and dry”
Na+ levels are increased; ICF dehydrated
Hypersecretion
Syndrome of inappropriate antidiuretic hormone (SIADH)
Decreased urine output
Fluid overload; low Na+ levels

30. Oxytocin (OT) Target cells: mammary glands & uterine smooth muscle
Operates on a positive feedback loop
Stimulates uterine smooth muscle contractions
During childbirth stretching of receptors causes continued release of oxytocin until after delivery of the placenta
Ejection of milk into ducts of the breast of lactating women
When breastfeeding the suckling action of the baby causes secretion of additional oxytocin increasing milk production
Breastfeeding also helps the uterus continue to contract back to normal size during the postpartum period

31. Pineal Body Regulates the body’s biological clock Secretes melatonin
Patterns of eating
Sleeping
Female reproductive cycle
Behavior
Secretes melatonin
Induces sleep
Secretion is inhibited by sunlight
Target cell in humans is unknown

32. Melatonin & Seasonal Affective Disorder
Also know as “winter depression”
During shorter days, melatonin secretion increases causes a depressed feeling in affected patients
Treatment
Exposure to high-intensity lights to inhibit melatonin secretion

33. Thyroid Gland
The thyroid gland is composed of two lateral lobes connected by an isthmus
Located on the anterior and lateral surfaces of the trachea, below the larynx

34. Thyroid Hormones Tetraiodothyronine or thyroxine (T4)
Most abundant thyroid hormone
Contains 4 iodine atoms
May have effect on target cells, but mostly serve as precursor to T3
Triodothyronine (T3)
“principal thyroid hormone”
Contains 3 iodine atoms

35. Thyroid Hormones
Both hormone bind to plasma proteins once secreted into the bloodstream
Function:
Regulate metabolic rate of all cells
Regulate cell growth
Regulate tissue differentiation
Target cells: “general” because thyroid hormones can potentially interact with all cells of the body

36. Hypersection Graves Disease
Autoimmune condition (thyroid stimulating antibodies causes abnormal secretion)
Weight loss
Increases basal metabolic rate
Increased heart and respiratory rate
exophthalmos

38. Exophthalmos

39. Hyposecretion of Thyroid Hormone
Cretinism – develops during the growth years due to hypothyroidism
Low metabolic rate
Retarded growth and sexual development
Mental retardation (possibly)
Hypothyroidism later in life
Decreased metabolic rate
Loss of mental & physical vigor
Weight gain
Loss of hair
Yellow discoloration of the skin
myxedema

41. Goiter Caused by lack of iodine in the diet
Iodine is needed to synthesize thyroid hormone
Lack of iodine causes drop in thyroid hormone production/secretion
Negative feedback loop informs hypothalamus and anterior pituitary to release releasing hormones and TSH
Lack of iodine causes enlargement of thyroid gland

43. Calcitonin The 3rd hormone secreted from the thyroid gland
Target cells – bone
Function – regulates calcium levels in the blood by decreasing blood calcium levels
Increases action of osteoblasts (build bone) and inhibits action of osteoclasts (breakdown bone)
Antagonist to parathyroid hormone

44. Parathyroid Glands
Parathyroid glands are embedded in the posterior aspect of the thyroid glands
Usually 4 or 5 parathyroid glands

45. Parathyroid Hormone Secreted from Parathyroid glands
Target cells: bone and kidney
Action: maintains calcium homeostasis
Increases osteoclast activity; decrease osteoblast activity
Calcium absorbed in kidneys and returned to the bloodstream
Activates vitamin D in the kidneys which increases intestinal absorption of calcium
Parathyroid hormone is an antagonist to calcitonin

47. Adrenal Glands Located on top of both of the kidneys
Composed of two parts:
Outer portion  adrenal cortex
Inner portion  adrenal medulla
Both parts of the adrenal glands are structurally and functionally different; often treated as two different glands

48. Adrenal Cortex Composed of three distinct layers or zones
Outer zone  secrete mineralocorticoids
Middle zone  secrete glucocorticoids
Inner zone  secrete glucocorticoids and gonadocorticoids

50. Pancreas Located in the LUQ
Contains both endocrine and exocrine tissue
Endocrine portion is made up of tiny islands of cells called pancreatic islets (also islets of Langerhans)
Alpha cells secrete glucagon
Beta cells secrete insulin

52. Pancreatic Hormones Glucagon Insulin
Increases blood glucose levels
Converts glycogen to glucose in liver cells
Stimulates gluconeogenesis
Target cells  liver
Insulin
Decreases blood glucose levels
Promotes movement of glucose, amino acids, fatty acids into cells
Promotes metabolism of these molecules once by cells
Target cells  general (all cells)
Glucagon and Insulin produce antagonistic effects (fig 16-27, page 512)

54. Diabetes Results from either
1) inadequate or absence of insulin production
2) Insulin resistance – decreased insulin receptors results in decreased effectiveness of glucose uptake

55. Diabetes – Signs & Symptoms
Hyperglycemia – elevated amounts of glucose in the blood
Results glucose not entering the cells properly
Glycosuria – glucose present in the urine
Elevated glucose levels in the blood exceeds kidney’s abilities to reabsorb glucose; glucose “spills over” into the urine
Polyuria – increased urine production
Water follows glucose lost in urine

56. Diabetes – Signs & Symptoms
Polydipsia – excessive thirst
Polyuria causes dehydration
Polyphagia – excessive and continuous hunger
Although blood sugar is high cells are “starving” because cells cannot uptake glucose
**3 P’s = polyuria, polydipsia, polyphagia**

57. Type 1 Diabetes Absolute deficiency of insulin production
Cause of beta cell destruction is unknown
Requires insulin injections or an insulin pump

58. Type 2 Diabetes
Previously called non-insulin-dependent diabetes (NIDDM) or adult onset diabetes
Beta cell produce reduced amounts of insulin
Loss of insulin receptors on target cells leads to insulin resistance
Treated with insulin injections, oral diabetic medication and lifestyle modifications

59. Complications of Diabetes
Untreated or poorly controlled diabetes can lead to many complications that affect almost every system in the body:
Atherosclerosis – build up of fatty materials in the blood vessls
Lead to heart attack, stroke, reduced circulation
Diabetic retinopathy – can lead to blindless

60. Complications of Diabetes
Neuropathy – nerve damage
Amputations
Kidney disease
May require dialysis

61. Gonads – Testes & Ovaries
Composed mainly of coils of seminiferous tubules & interstitial cells
Interstitial cells secrete testosterone
Target cells – general
Function:
Growth & maintenance of male sexual characteristics
Sperm production
Testosterone secretion is regulated by the gonadotropin  leutinizing hormone (LH)

62. Gonads – Testes & Ovaries
Estrogen
Secreted by cells of the ovarian follicles
Target cells: general
Functions:
Promote development & maintenance of female sexual characteristics
Breast development
Regulation of menstrual cycle

63. Gonads – Testes & Ovaries
Progesterone (“pregnancy-promoting hormone”)
Secreted by corpus luteum
Target cells: general
Functions (with estrogen):
Maintains the lining of the uterus to maintain a pregnancy
Remember Estrogen & Progresterone secretion is regulated by FSH and LH (gonadotropic hormones)

64. Placenta Tissue that forms along the lining of the uterus
Serves as the connection between the circulatory systems of the mother and developing fetus
Secretes human chorionic gonadotropin (hCG)
Target cells: ovaries

65. Placenta Function: hCG is high during the 1st trimester
Stimulates hormone (estrogen & progesterone) secretion from the ovaries
High levels of estrogen & progesterone help maintain uterine lining for pregnancy
hCG is high during the 1st trimester
A high hCG level is used to confirm a pregnancy