1. 13
The Endocrine System 1

2. The Endocrine System Produces Hormones
Endocrine system: collection of specialized cells, and tissues that secrete hormones
Endocrine glands: ductless organs that secrete hormones into blood, interstitial fluid, lymph
Hormones
Chemical messengers secreted by endocrine glands
Circulate in the bloodstream
Act on specific cells in the body (target cells) that have the appropriate hormone receptor

3. Hypothalamus Pituitary gland Hypothalamus Pineal gland Pituitary gland
Figure 13.1
Hypothalamus
Pituitary gland
• Anterior lobe
• Posterior lobe
Hypothalamus
• Releasing hormones
• Inhibiting hormones
Pineal gland
Pituitary gland
• Melatonin
Anterior lobe
Thyroid gland
• Adrenocorticotropic hormone (ACTH)
• Thyroid-stimulating hormone (TSH)
• Thyroxine
• Follicle-stimulating hormone (FSH)
• Triiodothyronine
• Luteinizing hormone (LH)
• Calcitonin
• Prolactin
Parathyroid glands
• Growth hormone
• Parathyroid hormone (PTH)
Posterior lobe
• Antidiuretic hormone (ADH)
Thymus gland
• Oxytocin
• Thymosin
• Thymopoietin
Adrenal glands
Heart
Cortex
• Atrial natriuretic hormone
• Cortisol
Stomach
Figure 13.1 Components of the human endocrine system.
• Aldosterone
Medulla
• Gastrin
• Epinephrine
Pancreas
• Norepinephrine
• Glucagon
• Insulin
Kidneys
• Somatostatin
• Erythropoietin
Intestines
• Renin
• Secretin
Ovaries (Female)
• Cholecystokinin
• Estrogen
Testes (Male)
• Progesterone
• Testosterone 3

4. The Endocrine System Produces Hormones
Hormones have access to every cell
Each hormone acts only on specific cells (target cells)
Only specific cells have receptors for specific hormones
Endocrine control is slower than nervous system
Endocrine and nervous systems interact

5. Hormones Are Classified as Steroid and Nonsteroid
Steroid hormones
Structurally related to cholesterol
Lipid soluble
Nonsteroid hormones
Structurally related to proteins
Lipid insoluble

6. Steroid Hormones Enter Target Cells
Lipid soluble, chemically derived from cholesterol
Enter target cells
Bind to intracellular receptor
Activate specific genes to produce specific proteins
Slower acting than nonsteroid hormones; minutes to hours

7. Capillary Interstitial fluid 1 Nucleus 2 3 4 Cell cytoplasm
Figure 13.2
Capillary
Steroid hormone
Interstitial fluid 1
Hormone diffuses
Target cell membrane
Hormone receptor
Hormone- receptor complex
Nucleus 2
DNA
Gene activated
RNA
Figure 13.2 Mechanism of steroid hormone action on a target cell. 3
Protein synthesis
New protein 4
New protein alters cell activity
Cell cytoplasm 7

8. Nonsteroid Hormones Bind to Receptors on Target Cell Membranes
Water soluble
Bind to receptors on target cell membranes
Work through intermediate mechanisms to activate existing enzymes
May involve a “second messenger” within the cell, such as cyclic AMP (cAMP)
Faster action than steroid hormones; seconds to minutes

9. Cyclic AMP (second messenger)
Figure 13.3
Capillary
Nonsteroid hormone (first messenger) 1
Interstitial fluid
Hormone binds to receptor; cyclic AMP generated within the cell
Receptor
Enzyme
Target cell membrane
Cyclic AMP (second messenger)
ATP 2
Enzyme 1 activated
Cell cytoplasm 3
Figure 13.3 Mechanism of nonsteroid hormone action on a target cell.
Enzyme 2 activated 4
Enzyme 3 activated 5
Nucleus
Final product alters cell activity 9

10. Hormones Participate in Negative Feedback Loops
Many hormones participate in internal homeostatic control mechanisms
Negative feedback loop involving hormones includes the following:
Endocrine gland serves as the control center
Hormone is the pathway between the control center and the effectors
Target tissues or organs are the effectors

11. Controlled variable Hormone Higher Set point Lower
Figure 13.4
Controlled variable
Higher
Set point
Lower
(Reversal of initial change)
Endocrine gland (control center)
Figure 13.4 A negative feedback loop involving a hormone.
Hormone
Target cells, tissues, and organs (effectors) 11

12. The Hypothalamus and the Pituitary Gland
Homeostatic control center of the brain
Links nervous system and endocrine system
Produces two hormones of its own
Monitors and controls hormone secretions of the pituitary gland
Pituitary gland
“Master” gland
Secretes eight different hormones that regulate other endocrine organs
Two lobes: posterior and anterior

13. Posterior Pituitary Stores ADH and Oxytocin
Posterior pituitary is connected to hypothalamus by neuroendocrine cells
Hormones (ADH and oxytocin) made in cell bodies in hypothalamus are transported down axons to axon endings in posterior pituitary for storage and release
Posterior pituitary hormones: nonsteroidal
Antidiuretic hormone (ADH)
Conserves water in kidneys
Regulates water balance in body
Oxytocin
Causes uterine contractions during labor and milk ejection through neuroendocrine reflex

14. Neuroendocrine cells Hypothalamus Anterior pituitary
Figure 13.5
Neuroendocrine cells
Hypothalamus
Anterior pituitary
Posterior pituitary
Oxytocin
ADH
Figure 13.5 Posterior pituitary lobe and hypothalamus. 14

15. Neuroendocrine cells release oxytocin when stimulated.
Figure 13.6
Neuroendocrine cell 3
Neuroendocrine cells release oxytocin when stimulated.
Hypothalamus
Anterior pituitary 4
Spinal cord
Oxytocin is transported by blood to mammary glands. 2
Sensory and spinal nerves carry impulses to the neuroendocrine cells of hypothalamus.
Posterior pituitary
Milk ejected
Figure 13.6 The control of oxytocin secretion by nursing.
Oxytocin 1
Nursing stimulates nerve receptors in nipple. 15

16. The Anterior Pituitary Produces Six Key Hormones
Controlled by hypothalamus
Releasing and inhibiting hormones from hypothalamus travel to pituitary through pituitary portal system
The release of each anterior pituitary hormone is controlled, at least partially, by the hypothalamus

17. The Anterior Pituitary Produces Six Key Hormones
ACTH (adrenocorticotropic hormone)
Stimulates adrenal cortex to release glucocorticoids (cortisol)
TSH (thyroid-stimulating hormone)
Acts on thyroid gland, promoting release of thyroid hormones
FSH and LH (gonadotropins)
Stimulate growth, development, and function of ovaries and testes
Not produced until about age 10–13 (puberty)
Increase in production initiates sexual maturation and development at puberty

18. The Anterior Pituitary Produces Six Key Hormones
Prolactin
Stimulates development of mammary glands and milk production
Growth hormone
Has widespread effects on body
Major effects on bone, muscle
Most of its growth-promoting effects occur during childhood and adolescence

19. Anterior pituitary hormones
Figure 13.7
Neuroendocrine cells
Hypothalamus 1
Neuroendocrine cells in hypothalamus produce and secrete releasing and inhibiting hormones 2
Blood flow
The pituitary portal blood system carries releasing and inhibiting hormones directly to the anterior pituitary
Anterior pituitary endocrine cells 3
The anterior pituitary produces six hormones that enter the general circulation
Posterior pituitary
Anterior pituitary hormones
Figure 13.7 The relationship between the hypothalamus and the anterior pituitary gland.
Adreno- corticotropic hormone (ACTH)
Thyroid- stimulating hormone (TSH)
Follicle- stimulating hormone (FSH)
Luteinizing hormone (LH)
Growth hormone (GH)
Prolactin (PRL)
Adrenal cortex
Thyroid gland
Ovaries or testes
Ovaries or testes
Mammary glands
Skeletal muscle, bone 19

20. Pituitary Disorders: Hypersecretion and Hyposecretion
Diabetes insipidus
Hyposecretion of ADH results in inability to conserve water appropriately
Causes excessive urination, dehydration, thirst
Gigantism
Hypersecretion of growth hormone in childhood
Acromegaly
Excessive growth hormone over a long period in adults
Pituitary dwarfism
Hyposecretion of growth hormone
Treated by administration of GH throughout childhood

21. Figure 13.8
Figure 13.8 Effect of growth hormone on body growth. 21

22. Figure 13.9
Figure 13.9 Effect of excessive growth hormone as an adult. 22

23. The Pancreas Secretes Glucagon, Insulin, and Somatostatin
The pancreas has both exocrine and endocrine functions
Pancreatic hormones are involved in regulating blood glucose levels
Endocrine cells in islets of Langerhans within the pancreas secrete the following three hormones:
Alpha cells: secrete glucagon
Beta cells: secrete insulin
Delta cells: secrete somatostatin

24. The Pancreas Secretes Glucagon, Insulin, and Somatostatin
Raises blood sugar
Causes breakdown of glycogen to glucose in liver
Insulin
Lowers blood sugar
Promotes uptake of sugar by cells in liver, muscle, and adipose tissue
Promotes conversion of glucose into glycogen, proteins, fat,
Somatostatin
Inhibits secretion of glucagon and insulin, regulates other hormones

25. Blood glucose concentration (mg/100 mL)
Figure 13.10
Glucagon secretion is inhibited
Pancreas secretes insulin
200
The liver uses glucose to produce glycogen
Muscle cells use glucose to make glycogen and proteins
Adipose tissues use glucose to produce fats for storage
High blood glucose
160
120
Blood glucose concentration (mg/100 mL) 80
Meal
The liver converts stored glycogen to glucose
Figure How the pancreas responds to a meal.
Low blood glucose 40
Insulin secretion is inhibited
Pancreas secretes glucagon 1 1 2 3 4 5 6
Time (hours) 25

26. The Adrenal Glands Comprise the Cortex and Medulla
Adrenal cortex: outer layer of adrenal gland
Glucocorticoids, such as cortisol
Mineralocorticoids, such as aldosterone
Adrenal medulla: inner layer of adrenal gland
Epinephrine (adrenaline)
Norepinephrine (noradrenaline)

27. The Adrenal Cortex: Glucocorticoids and Mineralocorticoids
Glucocorticoids (Cortisol is an example)
Secretion mediated through hypothalamus-pituitary secretions
Maintain blood glucose levels during prolonged fasting
Suppress inflammatory responses
Mineralocorticoids (Aldosterone is an example)
Regulate sodium, potassium, water balance
Act on kidneys, promoting sodium reabsorption and potassium excretion

28. The Adrenal Medulla: Epinephrine and Norepinephrine
Neuroendocrine organ
Secretion stimulated by
Sympathetic nervous system
Hormones: nonsteroidal
Epinephrine and norepinephrine
Enhance function of sympathetic nervous system (fight-or-flight response)

29. Norepinephrine and epinephrine
Figure 13.11
Perceived or real threat
Brain
Activation of sympathetic nerves
Adrenal medulla
Figure Secretion of norepinephrine and epinephrine by the adrenal medulla.
Adrenal cortex
Norepinephrine and epinephrine
Target cells 29

30. Thyroid and Parathyroid Glands
Thyroid located just below larynx in neck
Parathyroid glands embedded in back of thyroid
Both thyroid and parathyroid are involved in calcium balance
Thyroid is also involved in regulating metabolism

31. Anterior (front) Posterior (back)
Figure 13.12
Opening to trachea
Larynx
Thyroid gland
Parathyroids
Trachea
Figure The thyroid and parathyroid glands.
Anterior (front)
Posterior (back) 31

32. The Thyroid Gland: Thyroxine Speeds Cellular Metabolism
Secretion: mediated through hypothalamus-pituitary secretions
Steroidal hormones
Thyroxine (T4) and Triiodothyronine (T3)
Both regulate production of ATP from glucose and modify the metabolic rate
Calcitonin
Lowers blood calcium levels
Decreases rate of bone resorption by inhibiting osteoclasts
Stimulates uptake of calcium by bones

33. Plasma thyroxine concentration
Figure 13.13
Plasma thyroxine concentration
Increase
Set point
Decrease
Thyroxine
Thyroid gland
Hypothalamus
Cold temperatures
Figure Negative feedback control of thyroxine secretion.
TSH
Releasing hormone
Anterior pituitary 33

34. Iodine Deficiency Can Cause Goiter
Iodine is required for the production of active thyroid hormones
Inadequate dietary iodine leads to underproduction of thyroid hormones
The feedback response to inadequate thyroid hormone is for the hypothalamus and pituitary to further stimulate the thyroid gland in a vicious cycle that causes hypertrophy of the thyroid (goiter)

35. Figure 13.14
Figure A goiter caused by dietary iodine deficiency. 35

36. Calcitonin Promotes Bone Growth
Calcitonin inhibits osteoclasts
This decreases bone resorption
Calcitonin also stimulates the uptake of calcium by bones
Particularly important for bone growth and development in children
Combined effects: lower blood calcium levels

37. Parathyroid Hormone (PTH) Controls Blood Calcium Levels
Secretion
Response to lowered blood calcium levels
Action
Removes calcium and phosphate from bone
Increases absorption of calcium by the digestive tract
Causes kidneys to retain calcium and excrete phosphate
Combined effects increase blood calcium levels
Major regulator of blood calcium concentration in adults

38. Figure 13.15
Blood Ca2+ concentration
Increase
Return of blood Ca2+ toward normal
Set point
Decrease
Vitamin D
Bones release Ca2+
Digestive tract absorbs Ca2+
Kidneys save Ca2+
Parathyroid gland
Thyroid gland
PTH
Calcitonin
Responses to a fall in blood calcium.
Blood Ca2+ concentration
Increase
Return of blood Ca2+ toward normal
Set point
Decrease
Figure The homeostatic regulation of blood calcium concentration.
Vitamin D
Bones take up Ca2+
Digestive tract absorbs less Ca2+
Kidneys secrete more Ca2+
Parathyroid gland
Thyroid gland
PTH
Calcitonin
Responses to a rise in blood calcium. The importance of calcitonin is greatest in children, declining once adulthood is reached. 38

39. Testes Produce Testosterone
Functions of testosterone and other androgens (other testosterone-like steroid hormones)
Before birth, responsible for development of external male genitalia
At onset of puberty
Regulates development and normal functioning of sperm, male reproductive organs, and male sex drive
Regulates development of male secondary sex characteristics
Small amounts of androgens produced by adrenal glands in both sexes

40. Ovaries Produce Estrogen and Progesterone
Hormones: steroidal
Estrogen
Initiates development of secondary sex characteristics
Regulates menstrual cycle
Progesterone

41. Table 13.2
Table 13.2 Hormones of endocrine glands other than the hypothalamus and pituitary. 41

42. Other Glands and Organs Also Secrete Hormones
Thymus
Located in the upper chest, over the heart
Secretes thymosin and thymopoietin
Assist maturation of T lymphocytes
Most active during early development and childhood
Pineal gland
Located deep within the brain but receives input from optic nerve
Secretes melatonin
May be important in synchronizing the body’s circadian cycle

43. Endocrine Functions of the Heart, the Digestive System, and the Kidneys
Atrial natriuretic hormone (ANH)
Helps regulate blood pressure by increasing rate of sodium and water excretion in the urine
Digestive system
Gastrin, secretin, cholecystokinin
Effects on stomach, pancreas, gall bladder
Kidney
Erythropoietin
Stimulates production of erythrocytes
Renin
Stimulates aldosterone secretion and constricts blood vessels

44. Table 13.3
Table 13.3 Hormones of the digestive tract, kidneys, and heart. 44

45. Other Chemical Messengers
Histamine
Secreted by mast cells in response to injury or allergy
Initiates and enhances inflammation
Prostaglandins
Local control of blood flow
Contribute to inflammatory response
Nitric oxide
Regulates local blood flow in many tissues
Controls penile erection
Regulates smooth muscle contraction in digestive tract
Antibacterial chemical made by macrophages
Neurotransmitter in the brain
Growth factors
Local acting, modulate development of specific tissues

46. Disorders of the Endocrine System
Diabetes mellitus
Disorder of blood sugar regulation
Inability to get glucose into cells where it can be used, results in high blood sugar levels
Glucose and excess water appear in the urine
Abnormal metabolism of carbohydrates, proteins, and lipids causes most of the complications
Symptoms: dehydration, thirst, fatigue, frequent infections, blurred vision, tingling of hands/feet
Two types: type 1 and type 2

47. Disorders of the Endocrine System
Type 1 diabetes
Pancreas does not produce enough insulin
Also known as insulin dependent diabetes
Treated with insulin injections
Results from autoimmune destruction of beta cells of pancreatic islets
May be a genetic component and/or environmental trigger
Typical onset is during childhood or adolescence
5–10% of all cases of diabetes

48. Disorders of the Endocrine System
Type 2 diabetes
Non-insulin dependent
Characterized by insulin resistance: cells fail to respond appropriately to insulin
Most often seen in adults over 40
Lifestyle factors (diet, exercise) play a role in onset
Treatment: lifestyle changes, variety of medications
90–95% of all cases of diabetes

49. Disorders of the Endocrine System
Hypothyroidism: underactive thyroid gland
Children: cretinism
slowed body growth, altered brain development, delayed puberty
Adults: myxedema
edema, lethargy, weight gain, low BMR
Hyperthyroidism: overactive thyroid gland
Increased BMR, hyperactivity, nervousness, agitation, weight loss
Graves’ disease: autoimmune form of hyperthyroidism

50. Disorders of the Endocrine System
Adrenal gland disorders
Addison’s disease
Failure of adrenal cortex
Hyposecretion of cortisol and aldosterone
Lowers blood glucose and sodium
Slow to develop, chronic fatigue, weakness, abdominal pain, weight loss, bronzing of the skin
Cushing’s syndrome
Excessive cortisol secretion
Excessive production of glucose from glycogen
Retention of too much salt and water
Loss of muscle mass, change in fat distribution
Similar symptoms seen with use of cortisol and cortisol-like drugs

51. Figure 13.16
Figure Cushing’s syndrome.
Before the disease.
During the disease a characteristic hump of fat develops at the back of the neck. 51