1. The Endocrine System Pages 522-537
17 PART 1
The Endocrine System
Pages

2. The Endocrine System: An Overview
A system of ductless glands
Secrete messenger molecules called hormones
Interacts closely with the nervous system
Endocrinology
Study of hormones and endocrine glands

3. Scattered throughout the body Pure endocrine organs
Pituitary, pineal, thyroid, parathyroid, and adrenal glands
Organs containing endocrine cells
Pancreas, thymus, gonads, and the hypothalamus
Hypothalamus is a neuroendocrine organ
Produces hormones and has nervous functions
Endocrine cells are of epithelial origin

4. Location of the Major Endocrine Glands
Pineal gland
Hypothalamus
Pituitary gland
Thyroid gland
Parathyroid glands
(on dorsal aspect
of thyroid gland)
Thymus
Adrenal glands
Pancreas
Ovary (female)
Testis (male)
Figure 17.1

5. Hormones Classes of hormones Basic hormone action
Amino acid–based hormones
Steroids—derived from cholesterol
Basic hormone action
Circulate throughout the body in blood vessels
Influences only specific tissues—target cells
A hormone can have different effects on different target cells

6. Control of Hormones Secretion
Secretion triggered by three major types of stimuli
Humoral—simplest of endocrine control mechanisms
Secretion in direct response to changing ion or nutrient levels in the blood
Parathyroid monitors calcium
Responds to decline by secreting hormone to reverse decline

7. Control of Hormones Secretion
Secretion triggered by three major types of stimuli (continued)
Neural
Sympathetic nerve fibers stimulate cells in the adrenal medulla
Induces release of epinephrine and norepinephrine
Hormonal
Stimuli received from other glands
Certain hormones signal secretion of other hormones
Hypothalamus secretes hormones  stimulates pituitary  stimulates other glands

8. Types of Endocrine Gland Stimuli
(a) Humoral stimulus
(b) Neural stimulus
(c) Hormonal stimulus
Capillary (low Ca2+
in blood)
Parathyroid
glands
Thyroid gland
(posterior view)
PTH
CNS (spinal cord)
Medulla of
adrenal gland
Preganglionic
sympathetic
fibers
Capillary
Hypothalamus
Thyroid
gland
Adrenal
cortex
Gonad
(Testis)
Pituitary
Capillary blood contains
low concentration of Ca2+,
which stimulates…
Preganglionic sympathetic fibers
stimulate adrenal medulla cells…
The hypothalamus secretes
hormones that…
…stimulate
the anterior
pituitary gland
to secrete
hormones
that…
…secretion of parathyroid hormone
(PTH) by parathyroid glands. PTH acts to
increase blood Ca2+.
…to secrete catecholamines
(epinephrine and norepinephrine)
…stimulate other endocrine glands
to secrete hormones 1 2 3
Figure 17.2

9. Control of Hormones Secretion
Always controlled by feedback loops
Blood concentration declines below a minimum
More hormone is secreted
Blood concentration exceeds maximum
Hormone production is halted

10. Secretes nine major hormones
The Pituitary Gland
Secretes nine major hormones
Attached to the hypothalamus by the infundibulum
Two basic divisions of the pituitary gland
Adenohypophysis (anterior lobe)
Has three major divisions
Pars distalis, pars intermedia, and pars tuberalis
Neurohypophysis—has two major divisions
Pars nervosa and infundibular

11. Figure 17.3 The pituitary gland (hypophysis).
Corpus callosum
Thalamus
Pineal
Hypothalamus
Mammillary body
Brain stem
Pituitary (hypophysis)
Posterior lobe
Anterior lobe
Optic chiasma
Mammillary body
Median eminence of hypothalamus
Chromophobe cells
Tuber cinereum
Anterior lobe
Posterior lobe
Basophil cells
Pars tuberalis
Infundibulum
Pars intermedia
Pars nervosa
Acidophil cells
Pars distalis
Pituicytes (neuroglia)

13. http://www. vivo. colostate

14. The pars distalis—largest division of the anterior lobe
Contains five different endocrine cells
Makes and secretes seven different hormones
Tropic hormones regulate hormone secretion by other glands
Include: thyroid stimulating hormone (TSH), adrenocorticotropic hormone (ACTH), FSH, LH

15. The Anterior Lobe
GH (growth hormone), PRL (prolactin), and MSH (melanocyte-stimulating hormone)
Act directly on non-endocrine target tissues

16. Growth hormone (somatotropic hormone)
The Anterior Lobe
Growth hormone (somatotropic hormone)
Produced by somatotropic cells
Stimulates body growth by stimulating increased protein production and growth of epiphyseal plates
Stimulates growth directly and indirectly by the liver’s secretion of insulin-like growth factor-1.

17. Thyroid-stimulating hormone
The Anterior Lobe
Thyroid-stimulating hormone
Produced by thyrotropic cells
Signals thyroid gland to secrete thyroid hormone
Adrenocorticotropic hormone
Stimulates the adrenal cortex to secrete hormones that help cope with stress

18. Melanocyte-stimulating hormone
The Anterior Lobe
Melanocyte-stimulating hormone
In humans, MSH functions in appetite suppression
Gonadotropins—are produced by gonadotropic cells
FSH and LH
In females, FSH and LH stimulate maturation of follicles, secretion of androgen, estrogen & progesterone

19. Prolactin—produced by prolactin cells
The Anterior Lobe
Prolactin—produced by prolactin cells
Targets milk-producing glands in the breast—stimulates milk production
Endocrine cells of the pars distalis
Clustered in spheres and branching cords

20. Figure 17.3d The pituitary gland (hypophysis).
Posterior lobe
Anterior lobe
Chromophobe cells
Basophil cells
Acidophil cells
Pituicytes (neuroglia)

21. Hypothalamic Control of Hormone Secretion from the Anterior Lobe
The hypothalamus
Controls secretion of anterior lobe hormones
Exerts control by secreting
Releasing hormones—prompt anterior lobe to release hormones
Inhibiting hormones—turn off secretion of anterior lobe hormones

22. Hypothalamic Control of Hormone Secretion from the Anterior Lobe
Releasing hormones
Are secreted like neurotransmitters
Enter a primary capillary plexus
Travel in hypophyseal portal veins to a secondary capillary plexus
From the secondary capillary plexus, hormones secreted by the anterior lobe enter general circulation and travel to target organs

23. Tuber cinereum
Mammillary
body
Infundibulum
Pars nervosa
Pars tuberalis
Pars intermedia
Pars distalis
Median eminence
of hypothalamus
Optic chiasma
(c)
Anterior lobe
Posterior lobe

24. The Anterior Lobe When appropriately Hypothalamic neuron Hypothalamus
stimulated, hypothalamic
neurons secrete releasing
and inhibiting hormones into
the primary capillary plexus.
Hypothalamic hormones
travel through the portal
veins to the anterior pituitary
where they stimulate or
inhibit release of hormones
from the anterior lobe.
Anterior pituitary
hormones are secreted into
the secondary capillary
plexus.
Hypothalamus
Hypothalamic neuron
cell bodies
Hypophyseal
portal system
Superior hypophyseal
artery
(a) Relationship between the anterior pituitary and the hypothalamus
Anterior lobe
of pituitary
TSH, FSH, LH,
ACTH, GH, PRL
Primary capillary
plexus
portal veins
Secondary
capillary 1 2 3

25. Is structurally part of the brain
The Posterior Lobe
Is structurally part of the brain
Its axons make up the hypothalamic– hypophyseal tract
Arises from neuronal cell bodies in the hypothalamus
Supraoptic nucleus
Paraventricular nucleus

26. Relationship Between the Posterior Pituitary and Hypothalamus
Hypothalamic neurons
synthesize oxytocin and
ADH.
Oxytocin and ADH are
transported along the
hypothalamic-
hypophyseal tract to the
posterior lobe.
stored in axon terminals
in the posterior pituitary.
released into the blood
when hypothalamic
neurons fire.
Paraventricular nucleus
Supraoptic nucleus
Optic chiasma
Hypothalamus
Inferior
hypophyseal
artery
Oxytocin
ADH
Infundibulum (connecting stalk)
Hypothalamic-
tract
Axon
terminals
Posterior
lobe of
pituitary
(b) Relationship between the posterior pituitary and the hypothalamus 1 2 3 4

27. Stores and releases hormones made in the hypothalamus
The Posterior Lobe
Does not make hormones
Stores and releases hormones made in the hypothalamus
Releases two peptide hormones
Antidiuretic hormone (ADH)
Oxytocin

28. The Posterior Lobe ADH (vasopressin) Oxytocin
Made in supraoptic nucleus
Targets kidneys to resorb water
Oxytocin
Produced in the paraventricular nucleus
Induces smooth muscle contraction of reproductive organs, ejects milk during breast feeding, and signals contraction of the uterus during childbirth

29. Located in the anterior neck Largest pure endocrine gland
The Thyroid Gland
Located in the anterior neck
Largest pure endocrine gland
Composed of follicles and areolar connective tissue
Produces two hormones
Thyroid hormone (TH)
Calcitonin

30. The Thyroid Gland Hyoid bone Epiglottis Thyroid cartilage
Common carotid
artery
Epiglottis
Superior thyroid
External carotid
Isthmus of
thyroid gland
Left subclavian
Left lateral
lobe of thyroid
gland
Inferior thyroid
Trachea
Right
subclavian
Aorta
(a) Gross anatomy of the thyroid gland, anterior view

31. Figure 17.5b The thyroid gland.
Parafollicular cells (secrete calcitonin)
Follicular cells (secrete thyroid hormone)
Colloid-filled follicles
Photomicrograph of thyroid gland follicles (315)

32. The Parathyroid Glands
Lie on the posterior surface of the thyroid gland
Contain two types of endocrine cells
Chief cells/parathyroid cells
Produce parathyroid hormone (PTH)
Increases blood concentration of Ca2+
Oxyphil cells
Function unknown

33. Figure 17.6 The parathyroid glands.
Pharynx (posterior aspect)
Capillary
Parathyroid cells (secrete parathyroid hormone)
Thyroid gland
Esophagus
Oxyphil cells
Parathyroid glands
Trachea
Photomicrograph of parathyroid gland embedded within the thyroid gland (2)
Illustration of parathyroid glands embedded within the thyroid gland, posterior view
Photomicrograph of parathyroid gland (205)

34. The Adrenal (Suprarenal) Glands
Pyramid-shaped glands located on the superior surface of each kidney
Two endocrine glands in one
Adrenal medulla—a cluster of neurons
Part of the sympathetic nervous system
Adrenal cortex—forms the bulk of the gland
All adrenal hormones help one cope with danger, terror, or stress

35. Location of the Major Endocrine Glands
Pineal gland
Hypothalamus
Pituitary gland
Thyroid gland
Parathyroid glands
(on dorsal aspect
of thyroid gland)
Thymus
Adrenal glands
Pancreas
Ovary (female)
Testis (male)
Figure 17.1

36. The Adrenal Medulla Chromaffin cells
Are modified ganglionic sympathetic neurons
Secrete amine hormones epinephrine and norepinephrine
Enhance “fight-or-flight” response
Hormones are stored in secretory vesicles
Are arranged in spherical clusters and some branching cords

37. Figure 17.7 The adrenal gland, gross and microscopic structure.
Hormones secreted
Capsule
Zona glomerulosa
Aldosterone
Zona fasciculata
Adrenal gland
Cortex
Medulla
Cortex
Cortisol and androgens
Kidney
Zona reticularis
Medulla
Adrenal medulla
Epinephrine and norepinephrine
Drawing of the histology of the adrenal cortex and a portion of the adrenal medulla
Photomicrograph (120)

38. Stress and the Adrenal Gland
Short-term stress
More prolonged stress
Stress
Hypothalamus
CRH (corticotropin-
releasing hormone)
Corticotroph cells
of anterior pituitary
To target in blood
Adrenal cortex
(secretes steroid
hormones)
Glucocorticoids
Mineralocorticoids
ACTH
Catecholamines
(epinephrine and
norepinephrine)
Short-term stress response
1.Increased heart rate
2.Increased blood pressure
3.Liver converts glycogen to glucose and releases
glucose to blood
4.Dilation of bronchioles
5.Changes in blood flow patterns leading to decreased
digestive system activity and reduced urine output
6.Increased metabolic rate
Long-term stress response
1.Retention of sodium
and water by kidneys
2.Increased blood volume
and blood pressure
1.Proteins and fats converted
to glucose or broken down
for energy
2.Increased blood glucose
3.Suppression of immune
system
Adrenal medulla
(secretes amino acid–
based hormones)
Preganglionic
sympathetic
fibers
Spinal cord
Nerve impulses
Figure 17.8

39. Secretes lipid-based steroid hormones
The Adrenal Cortex
Secretes lipid-based steroid hormones
Cortex is composed of three layers (zones)
Zona glomerulosa—cells arranged in spherical clusters
Zona fasciculata—cells arranged in parallel cords; contains lipid droplets
Zona reticularis—cells arranged in a branching network

40. Figure 17.7 The adrenal gland, gross and microscopic structure.
Hormones secreted
Capsule
Zona glomerulosa
Aldosterone
Zona fasciculata
Adrenal gland
Cortex
Medulla
Cortex
Cortisol and androgens
Kidney
Zona reticularis
Medulla
Adrenal medulla
Epinephrine and norepinephrine
Drawing of the histology of the adrenal cortex and a portion of the adrenal medulla
Photomicrograph (120)

42. Hormones are corticosteroids
The Adrenal Cortex
Hormones are corticosteroids
Adrenal corticosteroids are of two main classes
Mineralocorticoids
Glucocorticoids

43. Aldosterone—secreted by the zona glomerulosa
Mineralocorticoids
Aldosterone—secreted by the zona glomerulosa
Secreted in response to decline in blood volume or blood pressure
Is the terminal hormone of the renin-angiotensin mechanism

44. Cortisol is the main type
Glucocorticoids
Cortisol is the main type
Secreted by zona fasciculata and zona reticularis
Helps the body deal with stressful situations

45. Stress and the Adrenal Gland
Short-term stress
More prolonged stress
Stress
Hypothalamus
CRH (corticotropin-
releasing hormone)
Corticotroph cells
of anterior pituitary
To target in blood
Adrenal cortex
(secretes steroid
hormones)
Glucocorticoids
Mineralocorticoids
ACTH
Catecholamines
(epinephrine and
norepinephrine)
Short-term stress response
1.Increased heart rate
2.Increased blood pressure
3.Liver converts glycogen to glucose and releases
glucose to blood
4.Dilation of bronchioles
5.Changes in blood flow patterns leading to decreased
digestive system activity and reduced urine output
6.Increased metabolic rate
Long-term stress response
1.Retention of sodium
and water by kidneys
2.Increased blood volume
and blood pressure
1.Proteins and fats converted
to glucose or broken down
for energy
2.Increased blood glucose
3.Suppression of immune
system
Adrenal medulla
(secretes amino acid–
based hormones)
Preganglionic
sympathetic
fibers
Spinal cord
Nerve impulses
Figure 17.8

46. Pinealocytes secrete melatonin
The Pineal Gland
Located on the roof
of the diencephalon
Shaped like a pine cone
Pinealocytes secrete melatonin
A hormone that regulates circadian rhythms
“Pineal sand” is radiopaque
Used as a landmark to identify other brain structures in X rays

47. (b)
Corpus
callosum
Pituitary (hypophysis)
Brain stem
Mammillary
body
Hypothalamus
Pineal
Thalamus

48. Located in the posterior abdominal wall
The Pancreas
Located in the posterior abdominal wall
Contains endocrine and exocrine cells
Exocrine cells
Acinar cells—secrete digestive enzymes
Endocrine cells
Pancreatic islets—islets of Langerhans
About one million islets—scattered throughout the pancreas

49. Main endocrine cell types
The Pancreas
Main endocrine cell types
Alpha cells ( cells)—secrete glucagon
Signals liver to release glucose from glycogen
Raises blood sugar
Beta cells ( cells)—secrete insulin
Signals most body cells to take up glucose from the blood
Promotes storage of glucose as glycogen in liver
Lowers blood sugar

51. Figure 17.9 Photomicrograph of a pancreatic islet.
Pancreas
Pancreatic islet
 (Glucagon- producing) cells
 (Insulin- producing) cells
Pancreatic acinar cells (exocrine)

52. Pancreatic islets contain two rare cell types
The Pancreas
Pancreatic islets contain two rare cell types
Delta (∂) cells
Secrete somatostatin
Inhibits secretion of insulin and glucagon
F (PP) cells
Secrete pancreatic polypeptide
May inhibit exocrine activity of the pancreas

53. The Thymus
Located in the lower neck and anterior thorax
Important immune organ
Release thymic hormones (thymosin & thymopoietin) from epithelial reticular cells
Site at which T-lymphocytes arise from precursor cells

54. Location of the Major Endocrine Glands
Pineal gland
Hypothalamus
Pituitary gland
Thyroid gland
Parathyroid glands
(on dorsal aspect
of thyroid gland)
Thymus
Adrenal glands
Pancreas
Ovary (female)
Testis (male)
Figure 17.1

55. Main sources of sex hormones
The Gonads
Main sources of sex hormones
Testes and ovaries
Male
Interstitial cells secrete androgens
Primarily testosterone
Promotes the formation of sperm
Maintains secondary sex characteristics

56. Androgens secreted by the theca folliculi
The Gonads
Female
Ovaries
Androgens secreted by the theca folliculi
Converted to estrogen by follicular granulosa cells
Estrogen
Maintains secondary sex characteristics
Progesterone
Prepares the uterus for pregnancy