1. Lab Exercise 33
Endocrine System

2. Major Endocrine Organs
Figure 16.1

3. Hormones
Hormones – chemical substances secreted by cells into the extracellular fluids
Regulate the metabolic function of other cells
The precise response depends on the type of the target cell

4. Target Cell Specificity
Hormones circulate to all tissues but only activate cells referred to as target cells
Target cells must have specific receptors to which the hormone binds

5. Gross Anatomy -Hypophysis
Pituitary gland – two-lobed organ that secretes nine major hormones
Neurohypophysis – posterior lobe (neural tissue) and the infundibulum
Receives, stores, and releases hormones from the hypothalamus
Adenohypophysis – anterior lobe, made up of glandular tissue
Synthesizes and secretes a number of hormones

7. Pituitary (Hypophysis)
Figure 16.6

8. Pituitary-Anterior Lobe
There is a vascular connection, the hypophyseal portal system, consisting of:
The primary capillary plexus
The hypophyseal portal veins
The secondary capillary plexus

9. Adenophypophyseal Hormones
The six hormones of the adenohypophysis:
Abbreviated as GH, TSH, ACTH, FSH, LH, and PRL

10. Activity of the Adenophypophysis
The hypothalamus sends a chemical stimulus to the anterior pituitary
Releasing hormones stimulate the synthesis and release of hormones
Inhibiting hormones shut off the synthesis and release of hormones

11. Activity of the Adenophypophysis
The tropic hormones
Stimulates an endocrine gland instead of a target organ. They are:
Thyroid-stimulating hormone (TSH)
Adrenocorticotropic hormone (ACTH)
Follicle-stimulating hormone (FSH)
Luteinizing hormone (LH)

12. Thyroid Stimulating Hormone (Thyrotropin)
Stimulates the normal development and secretory activity of the thyroid
Triggered by hypothalamic thyrotropin-releasing hormone (TRH)

13. Adrenocorticotropic Hormone (Corticotropin)
Stimulates the adrenal cortex to release corticosteroids
Triggered by hypothalamic corticotropin-releasing hormone (CRH) in a daily rhythm

14. Gonadotropins
Gonadotropins – follicle-stimulating hormone (FSH) and luteinizing hormone (LH)
Regulate the function of the ovaries and testes
FSH stimulates gamete (egg or sperm) production
Triggered by the hypothalamic gonadotropin-releasing hormone (GnRH)

15. Functions of Gonadotropins
In females
LH promotes synthesis and release of estrogens and progesterone
In males
LH stimulates synthesis of testosterone by the testes

16. Adenohypophysis- Growth Hormone (GH)
Stimulate most cells, but target bone and skeletal muscle
Promote protein synthesis and encourage the use of fats for fuel
Dwarfism, gigantism, acromegaly

17. Prolactin (PRL) In females, stimulates milk production by the breasts
Regulated by the hypothalamic prolactin-releasing hormone (PRH) and prolactin-inhibitory hormone (PIH)

18. Pituitary - Posterior Lobe
The posterior lobe is a downgrowth of hypothalamic neural tissue
Has a neural connection with the hypothalamus (hypothalamic-hypophyseal tract)
Nuclei of the hypothalamus synthesize oxytocin and antidiuretic hormone (ADH)
These hormones are transported to the posterior pituitary

19. The Posterior Pituitary and Hypothalamic Hormones
ADH stimulates reabsorption of water from the urine
Produced by the supraoptic nuclei of the hypothalamus
Oxytocin stimulates smooth muscle contraction in breasts and uterus
Produced by the paraventricular nuclei of the hypothalamus

20. Thyroid Gland
Consists of two lateral lobes connected by the isthmus

21. Thyroid Gland
Figure 16.8

22. Thyroid Hormone Consists of two related iodine-containing compounds
T4 – thyroxine has four iodine atoms
T3 – triiodothyronine; has three iodine atoms

23. Effects of Thyroid Hormone
TH is concerned with:
Increasing metabolic rate
Heat production
Cellular oxidation
Hyperthyroidism
Hypothyroidism

24. Calcitonin Produced by the parafollicular, or C, cells
Lowers blood calcium levels
Antagonist to parathyroid hormone (PTH)

25. PART 2

26. Parathyroid Glands
Tiny glands embedded in the posterior aspect of the thyroid
PTH (parathormone) increases the level of calcium in the blood

27. Parathyroid Glands
Figure 16.11

28. Effects of Parathyroid Hormone
PTH release increases Ca2+ in the blood as it:
Stimulates osteoclasts to digest bone matrix
Enhances the reabsorption of Ca2+ and the secretion of phosphate by the kidneys
Increases absorption of Ca2+ by intestinal mucosal
Hyperparathyroidism
Hypoparathyroidism

29. Effects of Parathyroid Hormone
Figure 16.12

30. Adrenal (Suprarenal) Glands
Adrenal glands – paired, pyramid-shaped organs atop the kidneys
Structurally and functionally, they are two glands in one
Adrenal medulla – neural tissue that acts as part of the SNS
Adrenal cortex – glandular tissue

31. Adrenal Cortex
Synthesizes and releases steroid hormones called corticosteroids
Different corticosteroids are produced in each of the three layers
Zona glomerulosa – mineralocorticoids (chiefly aldosterone)
Zona fasciculata – glucocorticoids (chiefly cortisol)
Zona reticularis – gonadocorticoids (chiefly androgens)

32. Aldosterone Electrolyte balance in extracellular fluids
Stimulates reabsorption of Na+ by the kidneys
Stimulates secretion of K+ by the kidney

33. Glucocorticoids (Cortisol)
Help the body resist chronic stress by:
Keeping blood sugar levels relatively constant
Cortisone, hydrocortisone, corticosterone:
Rises in blood glucose, fatty acids, and amino

34. Gonadocorticoids (Sex Hormones)
Most gonadocorticoids secreted are androgens (male sex hormones), and the most important one is testosterone
Androgens contribute to:
The onset of puberty
The appearance of secondary sex characteristics
Sex drive in females

35. Adrenal Medulla Secrete epinephrine and norepinephrine
Secretion of these hormones causes:
Blood glucose levels to rise
Blood vessels to constrict
The heart to beat faster
Blood to be diverted to the brain, heart, and skeletal muscle

36. Pancreas Mixed gland, which has both exocrine and endocrine cells
Acinar cells produce an enzyme-rich juice used for digestion (exocrine product)
Pancreatic islets (islets of Langerhans) produce hormones (endocrine products)
The islets contain two major cell types:
Alpha () cells that produce glucagon
Beta () cells that produce insulin

37. Insulin and Glucagon
Glucagon major target is the liver, where it promotes:
Release of glucose to the blood from liver cells
Insulin:
Lowers blood glucose levels
Enhances transport of glucose into body cells

38. Gonads: Female
Paired ovaries in the abdominopelvic cavity produce estrogens and progesterone and the ova
Estrogen:
Appearance of secondary sexual characteristics
Breast development and cyclic changes in the uterine mucosa

39. Gonads: Female Progesterone: Cycling changes of the uterine lining
Keeps pregnancy
Prepares breast for lactation

40. Gonads: Male
Testes located in an extra-abdominal sac (scrotum) produce testosterone
Testosterone:
Initiates maturation of male reproductive organs
Causes appearance of secondary sexual characteristics and sex drive
Is necessary for sperm production
Maintains sex organs in their functional state

41. Pineal Gland
Small gland hanging from the roof of the third ventricle of the brain
Secretory product is melatonin
Melatonin is involved with:
Day/night cycles
Physiological processes that show rhythmic variations (body temperature, sleep, appetite)

42. Thymus Lobulated gland located deep to the sternum Secrete thymosins
These hormones are essential for the development of the T lymphocytes (T cells) of the immune system

43. Microscopic anatomy of the glands
Thyroid gland
Follicles – simple squamous or cuboidal cells
Colloid – contain thyroglobulin, T3 and T4
Parafollicular cells (C cells)
Between follicles
Secrete calcitonin

44. Microscopic anatomy of the glands
Parathyroid
Fibrous capsule surrounds the organ
Chief cell
Small cells, round nuclei, arranged in clusters, secret PTH
Oxyphil cells
Lager than chief cells
Scattered
Unknown function

45. Microscopic anatomy of the glands
Pancreas
Exocrine acini
Darker cells
Endocrine with Islets of Langehans
Beta cells – located at the center and secrete insulin
Alpha cells – located at the periphery and secrete glucagon

46. Microscopic anatomy of the glands
Anterior Pituitary gland
Chromophils
Acidophils- reddish-brown. GH and PRL
Basophils – deep-blue. Tropic hormones
Chromophobes
Do not take collor (Pale)
Controversial role

47. Microscopic anatomy of the glands
Posterior pituitary gland
Nerve fibers
Pituicytes (glial cells)

48. Microscopic anatomy of the glands
Adrenal gland- cortex
Zona glomerulosa
outermost, spherical clusters of cells, secrete mineralocorticoids
Zona fasciculate
Next layer, cells arranged in parallel cords, secrete glucocorticoids
Zona reticularis
Inneremost, cells arranged in branches, produces mainly sex hormones

49. Microscopic anatomy of the glands
Adrenal gland – medulla
The core of the gland
Modified neurons
Secrete E and NE

50. Microscopic anatomy of the glands
Ovary
Vesicular follicle
Ovum

51. Microscopic anatomy of the glands
Testes
Seminiferous tubules
Produce sperm
Interstitial cells
Between seminiferous tubules.
Secrete testosterone

52. Cat’s Glands to Identify
Thyroid
Thymus
Pancreas
Adrenal
Gonads
Testes
Ovaries