1. Lecture 18, The Endocrine System
Lecturer: Dr. Barjis
Room: P313
Phone: (718)
The Endocrine System

2. Learning Objectives
Compare the major chemical classes and general mechanisms of hormones.
Describe the location and structure of the pituitary gland, and explain its structural and functional relationships with the hypothalamus.
Describe the location and structure of each of the endocrine glands.

3. Learning Objectives
Identify the hormones produced by each of the endocrine glands and specify the functions of those hormones.
Describe the functions of the hormones produced by the kidneys, heart, thymus, testes, ovaries and adipose tissue.
Explain how hormones interact to produce coordinated physiological responses.

4. Intercellular Communication
Endocrine versus Nervous system
Endocrine System
Endocrine system regulates long term ongoing metabolic activity
The endocrine system uses chemicals messenger called hormones to “communicate”.
Hormones alter metabolic activities of tissues
A hormone is secreted by a group of specialized cells called gland
Hormones are transported by the blood vessels
Paracrine communication involves chemical messengers between cells within one tissue
Nervous System
Nervous system performs short term crisis management
The nervous system sends electrical messages to control and coordinate the body
Nerve impulse is delivered by the axon of a nerve cell called neuron

5. Endocrine system
Includes all cells and endocrine tissues that produce hormones or paracrine factors
Following are important endocrine glands
Hypothalamus
Pituitary gland
Pineal Gland
Thyroid gland
Parathyroid gland
Thymus
Adrenal Gland
Gonads (testes/ovaries)
Pancreatic Islet
Heart
Kidney
Digestive Tract

6. The Endocrine System

7. Hormone structure
Based on their chemical structure hormones are classified into three general classes (groups) of hormones.
1) Amino acid derivatives hormones e.g. epinephrine
Structurally similar to amino acids
2) Peptide hormones e.g. insulin
Chains of amino acids
3) Lipid derivatives hormones e.g. eicosanoids and steroid hormones (prostaglandin is an example of a steroid hormone)

8. A Structural Classification of Hormones

9. Hormones Transportation
Hormones can be
Freely circulating
Rapidly removed from bloodstream
Bound to transport proteins e.g. albumin or globulin

10. Mechanisms of hormone action
Each hormone’s shape is specific and can be recognized by the corresponding target cells
The binding sites on the target cells are called hormone receptors.
Receptors for peptide hormones, are located on the surface of cell membranes because they can not cross the membrane to enter the cell
Thyroid and steroid hormones can cross the membrane and bind to receptors in the cytoplasm or nucleus

11. G Proteins and Hormone Activity
Hormones that can not cross the membrane (e.g. Peptide hormones) bind to the receptor on the surface of the cell
Binding of hormones to the receptor activate secondary messenger (in this figure binding of hormone activates G protein, and activated G protein activates adenylcyclase
or activate PDE or activates PLC

12. Hormone Effects on Gene Activity
Hormones that can cross the membrane (e.g. steroid hormones) bind to the receptor inside the cell, at the cytoplasm, or they will enter the nucleus and bind to the receptor at the nucleus and initiate transcription)

13. Control of endocrine activity
Hypothalamus regulates the activity of the nervous and endocrine systems
Hypothalamus secrets regulatory hormones (releasing hormones and inhibiting hormones) that control the activity of the pituitary gland
Releasing/inhibiting hormones secreted by the hypothalamus either stimulate or inhibit activity of pituitary gland

14. Three Methods of Hypothalamic Control over the Endocrine System

15. The Pituitary Gland
The pituitary gland is called the “master gland” but it is under the control of the hypothalamus.
Hypothalamus and pituitary gland control many other endocrine functions.
Pituitary Gland releases nine important peptide hormones
All nine bind to membrane receptors and use cyclic AMP as a second messenger
Pituitary gland is divided into posterior and anterior lobe

16. The Anatomy and Orientation of the Pituitary Gland

17. Hormones of the adenohypophysis
The anterior lobe (adenohypophysis)
Hormones of the adenohypophysis
Anterior lobe of pituitary gland produces 7 hormones
1) Thyroid stimulating hormone (TSH)
TSH triggers the release of thyroid hormones by the thyroid glands
Thyrotropin releasing hormone promotes the release of TSH
2) Adrenocorticotropic hormone (ACTH)
ACTH stimulates the release of glucocorticoids by the adrenal gland
Corticotrophin releasing hormone causes the secretion of ACTH
3) Follicle stimulating hormone (FSH)
FSH stimulates follicle development and estrogen secretion in females and sperm production in males

18. The anterior lobe (adenohypophysis)
4) Leutinizing hormone (LH)
LH causes ovulation and progestin (progesterone) production in females and androgen (testosterone) production in males
Gonadotropin releasing hormone (GNRH) promotes the secretion of FSH and LH
5) Prolactin (PH)
PH stimulates the development of mammary glands and milk production
6) Growth hormone (GH or somatotropin)
GH stimulates cell growth and replication through release of somatomedins or IGF
Growth-hormone releasing hormone (GH-RH)
Growth-hormone inhibiting hormone (GH-IH)
7) Melanocyte stimulating hormone (MSH)
Stimulates melanocytes to produce melanin

19. The posterior lobe of the pituitary gland (neurohypophysis)
The posterior lobe of the pituitary gland secretes two hormones: Antiduretic Hormone and Oxytocin.
1) Antidiuretic hormone (ADH)
Decreases the amount of water lost at the kidneys
Elevates blood pressure
2) Oxytocin
Stimulates contractile cells in mammary glands
Stimulates smooth muscle cells in uterus

20. The thyroid
Thyroid gland is located near the thyroid cartilage of the larynx
The two lobes of thyroid gland is connected by an isthmus
Microscopically it has 2 distinct population of cells: Flicular Cell (produce thyroid hormone) and C cell (produce calcitonin)
Thyroid gland release several hormones such as thyroxine (T4) and triiodothyronine (T3)
Thyroid hormones (T4 and T3) are transported by to thyroid binding globulins (TBG), and albumin
Functions of Thyroid hormones include:
Increasing ATP production, when bound to mitochondria.
Activating genes that control energy utilization, when bound to receptors
Exert a calorigenic effect
C cells of thyroid gland produce calcitonin
Calcitonin helps to regulate calcium concentration in body fluids

21. The Thyroid Gland

22. Parathyroid glands
Four parathyroid glands embedded in the posterior surface of the thyroid gland
Chief cells produce parathyroid hormone (PTH) in response to lower than normal calcium concentrations
Parathyroid hormones plus calcitriol are primary regulators of calcium levels in healthy adults

23. The Homeostatic Regulation of Calcium Ion Concentrations
When calcium levels decrease in the blood, parathyroid glands produce PTH
PTH increase blood calcium level by:
Releasing stored calcium from the bones
Stimulating production of calcitriol at the kidney. Calcitriol increases absorption of calcium by the digestive system
Enhance reabsorption of calcium by the kidneys
When calcium levels increase in the blood, thyroid glands produce calcitonin.
Calcitonin decreases blood calcium level by:
Increasing excretion of calcium by the kidneys
Increase calcium deposition in the bones
Stop osteoclast

24. The Adrenal Glands Adrenal cortex
Manufactures steroid hormones derived from cholesterol (corticosteroids).
Corticosterioid hormones are divided into 3 functional groups
Mineralocorticoids (Aldosterone)
Regulate mineral and salt balance by renin-angiotensis-aldosterone system
Glucocorticoids (cortisol and cortisone)
Regulate glucose levels i.e. they increase gluconeogenesis and decrease protein synthesis
Decrease inflammation response
Androgens also called sex hormones

25. The Adrenal Glands Adrenal medulla
Responsible for flight-or-fight response
Produces epinephrine and norepinephrine

26. Pineal gland Contains pinealocytes Synthesize melatonin
Suggested functions include inhibiting reproductive function, protecting against damage by free radicals, setting circadian rhythms (biological clock)

27. The Pancreas The pancreatic islets
Clusters of endocrine cells within the pancreas called Islets of Langerhans or pancreatic islets
Alpha cells secrete glucagons
Glucagon raises blood glucose by increasing the rates of glycogen breakdown and glucose manufacture by the liver
Beta cells secrete insulin
Insulin lowers blood glucose by increasing the rate of glucose uptake and utilization
Delta cells secrete GH-IH
F cells secrete pancreatic polypeptide

28. Diabetes Type I – Insulin dependent diabetes
Caused by autoimmune destruction of beta cells
Type II – non insulin dependent diabetes
Caused by body resisting the effects of insulin at its receptor.
Symptoms: Polyuria (inreased frequency of urination), polydipsia (increased thirst)

29. The Regulation of Blood Glucose Concentrations

30. The kidneys
Produce calcitriol and erythropoietin (EPO) and the enzyme rennin
Calcitriol = stimulates calcium and phosphate ion absorption along the digestive tract
EPO stimulates red blood cell production by bone marrow
Renin converts angiotensinogen to angiotensin I
Angiotensin I is converted to angiotensin II at the lungs
Agiotensin II:
Stimulates production of aldosterone by the adrenal glands
Stimulates release of ADH by the pituitary gland
Promotes thirst
Elevates blood pressure

31. Endocrine Functions of the Kidneys

32. Endocrine Functions of the Kidneys

33. The heart, The intestines and the Thymus
Specialized muscle cells produce natriuretic peptides in response to high blood pressure
Natriuretic peptide generally has the opposite actions of angiotensin II
The Intestine
Produce hormones important to the coordination of digestive activities
The Thymus
Produces thymosins
Help develop and maintain normal immune defenses

34. The gonads Interstitial cells of the testes produce testosterone
Most important sex hormone in males
In females, oocytes develop in follicles
Follicle cells produce estrogens
After ovulation, the follicle cells form corpus luteum. Corpus luteum releases a mixture of estrogens and progesterone

35. Hormones and growth
Normal growth requires the interaction of several endocrine organs
Six hormones are important GH
Thyroid hormones
Insulin
PTH
Calcitriol
Reproductive hormones

36. Adipose tissues secrete
Leptin, a feedback control for appetite
Resistin, which reduces insulin sensitivity

37. Hormones and behavior Many hormones affect the CNS
Changes in the normal mixture of hormones significantly alters intellectual capabilities, memory, learning and emotional states