1. The Endocrine System

2. System Overview
Includes cells, tissues, and organs that secrete hormones directly into the body fluids
Endocrine vs. exocrine

3. Functions of Hormones Help regulate metabolic processes
Control the rates of some chemical reactions
Aid in the transport of substances across membranes
Help regulate water and electrolyte balances
Play vital roles in reproduction, growth, and development

4. What is a Hormone?
A biochemical secreted by a cell to affect the functions of another cell
Action of a hormone is restricted to a specific target cell that has protein receptors for the hormone

5. Steroid Hormones Fat soluble Diffuse into cells easily
May bind to DNA and activate genes
Fast acting

6. Nonsteroid Hormones Usually combine with cell membrane receptors
Binding stimulates activity site of receptor (hormone is first messenger)
second messengers inside cell trigger cell action

7. Prostaglandins Not really hormones, but behave similarly
Affect only the organ where they are produced
Present in very small quantities, not stored, and rapidly inactivated

8. Control of Hormone Secretions
Hypothalamus
Controls the anterior pituitary gland’s release of hormones that stimulate other endocrine gland
Nervous system
Stimulates some glands directly
Some glands respond directly to changes in the internal environment

9. Hormone Regulation
Negative feedback mechanisms

10. Major Endocrine Glands and Their Hormones

11. Pituitary Gland “Master Gland” Located at the base of the brain
Attaches to the hypothalamus by means of the infundibulum
Anterior and posterior lobes

12. Anterior Pituitary Gland
Dense CT capsule
Blocks of glandular epithelium around blood vessels

13. Anterior Pituitary Hormones
Growth Hormone (GH)
Stimulates most body cells to increase in size and divide
Promotes protein synthesis

14. Anterior Pituitary Hormones
Thyroid-Stimulating Hormone (TSH)
Promotes normal activity and development of the thyroid gland
Adrenocorticotropic Hormone (ACTH)
Triggers the release of hormones from the adrenal cortex

15. Anterior Pituitary Hormones
Follicle-Stimulating Hormone (FSH)
Stimulates gamete production in males and females
Stimulates maturation of ovarian follicles and eggs in females
Luteinizing Hormone (LH)
Promotes production of gonadal hormones
In females, triggers ovulation and stimulates maturation of ovarian follicles and eggs

16. Anterior Pituitary Hormones
Prolactin (PRL)
Stimulates milk production in the breasts

17. Posterior Pituitary Gland
Consists mostly of nerve fibers and neuroglia
Closely associated with the hypothalamus

18. Posterior Pituitary Hormones
Oxytocin (OT)
Stimulates contraction of uterine muscles
Triggers “letdown” of breast milk

19. Posterior Pituitary Hormones
Antidiuretic Hormone (ADH)
Inhibits urine formation in the kidneys
Stimulates constriction of blood vessels
Released in response to increased blood solute concentration, low blood pressure, some drugs (nicotine, morphine)
Inhibited by alcohol and excessive water consumption

20. Thyroid Gland Highly vascular Two lobes connected by isthmus
Located below larynx
Secretory parts are follicles filled with colloid

21. Thyroid Hormones Thyroxine (T4) and Triiodothyronine (T3)
Collectively known as thyroid hormone
Increases metabolic rate and body heat production
Regulates tissue growth

22. Thyroid Disorders

23. Thyroid Hormones Calcitonin Lowers blood calcium Inhibits osteoclasts
Stimulates osteoblasts

24. Parathyroid Glands
4 small glands on posterior of thyroid gland

25. Parathyroid Hormone Parathyroid Hormone (PTH) Raises blood calcium
Stimulates osteoclasts
Triggers reabsorption of calcium in urine in kidneys
Increases intestinal absorption of calcium from food

26. Adrenal Glands Located on top of kidneys Embedded in adipose
Adrenal cortex
Outer portion of epithelial cells organized into layers
Adrenal medulla
Consists of modified neurons around blood vessels and nerves of the sympathetic nervous system

27. Adrenal Cortex Hormones
Aldosterone
Zona glomerulosa
Reduces excretion of sodium from kidneys
Increases reabsorption of sodium from urine, perspiration, saliva, and gastric juice
Increases excretion of potassium
Increases water retention

28. Adrenal Cortex Hormones
Cortisol
Helps maintain blood glucose concentration between meals
Zona fasciculata

29. Adrenal Cortex Hormones
Androgens
Supplements male sex hormones produced by gonads
Zona reticularis

30. Adrenal Medulla Hormones
Epinephrine and Norepinephrine
Produce short term stress response
Increase heart rate, blood pressure, and metabolic rate
Dilation of bronchioles
Trigger liver to release glucose into bloodstream

31. Pancreas Mixed gland Located behind stomach
Islets of Langerhans – masses of endocrine cells amongst acinar (exocrine) cells

32. Pancreas Hormones Insulin Glucagon
Produced by beta cells (stain purple)
Decreases blood glucose concentration
Enhances absorption of glucose into cells for energy use and storage
Glucagon
Produced by alpha cells (stain pink)
Stimulates liver to release glucose from glycogen
1 molecule triggers the release of 100 million glucose molecules into the blood

34. Ovaries Female gonads Produce estrogen and progesterone:
Stimulate maturation of the female reproductive organs and appearance of secondary sexual characteristics

35. Testes Male gonads Produce testosterone:
Stimulates maturation of the male reproductive organs and the appearance of male secondary sexual characteristics
Increases sex drive
Promotes normal sperm production

36. Pineal Gland Located between cerebral hemispheres Attached to thalamus
Releases melatonin:
Released in response to light
Helps regulate circadian rhythms

37. Thymus Gland Located between the lungs posterior to the sternum
Butterfly-shaped
Diminishes during adulthood
Produces thymosin:
Essential for the normal development of T cells and the immune response

38. Disorders of all endocrine glands
Hyposecretion- too little hormone is released
Example: Hypothyroidism= very slow metabolism
Hypersecretion- too much hormone is released
Example: Acromegaly= too much HGH
Video 19mins