1. Human Anatomy & Physiology University of Washington PMT
Endocrine System
Human Anatomy & Physiology
University of Washington PMT

2. The Endocrine System

3. Endocrine System The Endocrine System Regulates long-term processes
Growth
Development
Reproduction
Uses chemical messengers to relay information and instructions between cells
Direct communication
Paracrine communication
Endocrine communication
Direct Communication
Exchange of ions and molecules between adjacent cells across gap junctions
Occurs between two cells of same type
Highly specialized and relatively rare
Paracrine Communication
Uses chemical signals to transfer information from cell to cell within single tissue
Most common form of intercellular communication
Endocrine Communication
Endocrine cells release chemicals (hormones) into bloodstream
Alters metabolic activities of many tissues and organs simultaneously

4. Hormonal Action Target Cells Hormones
Are specific cells that possess receptors needed to bind and “read” hormonal messages
Hormones
Stimulate synthesis of enzymes or structural proteins
Increase or decrease rate of synthesis
Turn existing enzyme or membrane channel “on” or “off”

5. Hormone Actions
“Lock and Key” approach: describes the interaction between the hormone and its specific receptor.
Receptors for nonsteroid hormones are located on the cell membrane
Receptors for steroid hormones are found in the cell’s cytoplasm or in its nucleus
Free Hormones
Remain functional for less than 1 hour
Diffuse out of bloodstream:
bind to receptors on target cells
Are broken down and absorbed:
by cells of liver or kidney
Are broken down by enzymes:
in plasma or interstitial fluids

6. Non Lipid Soluble Hormonal Action
Hormones and Plasma Membrane Receptors
Bind to receptors in plasma membrane
Cannot have direct effect on activities inside target cell
Use intracellular intermediary to exert effects
First messenger:
leads to second messenger
may act as enzyme activator, inhibitor, or cofactor
results in change in rates of metabolic reactions
Hormones and Plasma Membrane Receptors
Catecholamines (E, NE & D) and peptide hormones (ADH, ACTH, oxytocin)
Are not lipid soluble
Unable to penetrate plasma membrane
Bind to receptor proteins at outer surface of plasma membrane (extracellular receptors)

7. Hormones and Plasma Membrane Receptors
Important Second Messengers
Cyclic-AMP (cAMP)
Derivative of ATP
Cyclic-GMP (cGMP)
Derivative of GTP
Calcium ionsThe Process of Amplification
Is the binding of a small number of hormone molecules to membrane receptors
Leads to thousands of second messengers in cell
Magnifies effect of hormone on target cellDown-regulation
Presence of a hormone triggers decrease in number of hormone receptors
When levels of particular hormone are high, cells become less sensitive
Up-regulation
Absence of a hormone triggers increase in number of hormone receptors
When levels of particular hormone are low, cells become more sensitive
Hormones and Plasma Membrane Receptors
G Protein
Enzyme complex coupled to membrane receptor
Involved in link between first messenger and second messenger
Binds GTP
Activated when hormone binds to receptor at membrane surface and changes concentration of second messenger cyclic-AMP (cAMP) within cell:
increased cAMP level accelerates metabolic activity within cell

8. Lipid Soluble Hormonal Action
Steroid Hormones:
Lipid soluble
Diffuse through cell membranes
Endocrine organs
Adrenal cortex
Ovaries
Testes
Thyroid
Examples are testosterone, thyroxine (T3), triiodothyronine (T4), Calciitonin

9. Hormones and Intracellular Receptors
Alter rate of DNA transcription in nucleus
Change patterns of protein synthesis
Directly affect metabolic activity and structure of target cell
Includes steroids and thyroid hormones

10. Pituitary Gland A marble-sized gland at the base of the brain
Controlled by the hypothalamus or other neural mechanisms and therefore the middle man.

11. Pituitary Gland

12. The Pituitary Gland and its Hormones
Posterior Lobe
Antidiuretic hormone (ADH)
Oxytocin
Anterior Lobe
Adrenocorticotropic (ACTH)
Growth hormone (GH)
Thyroid-stimulating hormone (TSH)
Follicle-stimulating hormone (FSH)
Luteinizing hormone (LH)
Prolactin (PRL)
GH Deficiency: Pituitary Growth Failure / Dwarfism – Retarded growth, abnormal fat distribution, low blood glucose hours after meals
GH Overproduction: Gigantism / Acromegaly – Excessive growth
ADH Deficiency: Diabetes Insipidus – Polyuria, dehydration, thirst (Central DI vs. Nephrogenic DI)
ADH Overproduction: SIADH (Syndrome of Inappropriate Antidiuretic Hormone Secretion) – Increased water content / body mass

13. Endocrine Reflexes Neuroendocrine Reflexes Complex Commands
Functional counterparts of neural reflexes
In most cases, controlled by negative feedback mechanisms
Stimulus triggers production of hormone whose effects reduce intensity of the stimulus
Endocrine reflexes can be triggered by
Humoral stimuli
Changes in composition of extracellular fluid
Hormonal stimuli
Arrival or removal of specific hormone
Neural stimuli
Arrival of neurotransmitters at neuroglandular junctions
Simple Endocrine Reflex
Involves only one hormone
Controls hormone secretion by the heart, pancreas, parathyroid gland, and digestive tract
Complex Endocrine Reflex
Involves
One or more intermediary steps
Two or more hormones
The hypothalamus
Neuroendocrine Reflexes
Pathways include both neural and endocrine components
Complex Commands
Issued by changing
Amount of hormone secreted
Pattern of hormone release:
hypothalamic and pituitary hormones released in sudden bursts
frequency changes response of target cellsTwo Classes of Hypothalamic Regulatory Hormones
Releasing hormones (RH)
Stimulate synthesis and secretion of one or more hormones at anterior lobe
Inhibiting hormones (IH)
Prevent synthesis and secretion of hormones from the anterior lobe
Rate of secretion is controlled by negative feedback
Negative feedback is the primary mechanism through which your endocrine system maintains homeostasis
Secretion of a specific hormone s turned on or off by specific physiological changes (similar to a thermostat)
EXAMPLE: plasma glucose levels and insulin response

14. Hypothalamus Two Classes of Hypothalamic Regulatory Hormones
Releasing hormones (RH)
Stimulate synthesis and secretion of one or more hormones at anterior lobe
Inhibiting hormones (IH)
Prevent synthesis and secretion of hormones from the anterior lobe
Rate of secretion is controlled by negative feedback

15. Pituitary Gland

16. Thyroid Gland Thyroid Gland Located along the midline of the neck
Secretes two nonsteroid hormones
Triiodothyronine (T3)
Thyroxine (T4)
Calcitonin: calcium metabolism (osteoblast)
Regulates metabolism
increases protein synthesis
promotes glycolysis, gluconeogenesis, glucose uptake

17. Thyroid Gland

18. Thyroid Gland Thyroid Hormones Enter target cells by transport system
Thyroid-Stimulating Hormone (TSH)
Absence causes thyroid follicles to become inactive
Neither synthesis nor secretion occurs
Binds to membrane receptors
Activates key enzymes in thyroid hormone production
Thyroid Hormones
Enter target cells by transport system
Affect most cells in body
Bind to receptors in
Cytoplasm
Surfaces of mitochondria
Nucleus
In children, essential to normal development of
Skeletal, muscular, and nervous systems
Calorigenic Effect
Cell consumes more energy resulting in increased heat generation
Is responsible for strong, immediate, and short-lived increase in rate of cellular metabolism
T3/T4 Deficiency: Myxedema / Cretinism – Low metabolic rate / low body temperature / impaired physical & mental development
T3/T4 Overproduction: Hyperthyroidism / Graves Disease – High metabolic rate / temperature

19. Parathyroid Glands Embedded in posterior surface of the thyroid gland
Parathyroid hormone (PTH)
Produced by chief cells
In response to low concentrations of Ca2+

20. Parathyroid Gland Four Effects of PTH It stimulates osteoclasts
Accelerates mineral turnover and releases Ca2+ from bone
It inhibits osteoblasts
Reduces rate of calcium deposition in bone
It enhances reabsorption of Ca2+ at kidneys, reducing urinary loss
It stimulates formation and secretion of calcitriol at kidneys
Effects complement or enhance PTH
Enhances Ca2+, PO43- absorption by digestive tract
PTH Deficiency: Hypoparathyroidism – Muscular weakness, neurological problems, formation of dense bones, tetany due to low blood Ca
PTH Overproduction: Hyperparathyroidism – Neurological, mental, muscular problems due to high blood Ca, weak brittle / bones

21. Suprarenal (Adrenal) Gland
Lie along superior border of each kidney
Subdivided into:
Superficial suprarenal cortex
Stores lipids, especially cholesterol and fatty acids
Inner suprarenal medulla
Secretory activities controlled by sympathetic division of ANS

22. Suprarenal (Adrenal) Gland
Adrenal Medulla
Contains two types of secretory cells
Epinephrine (70-75% of mass)
Increase H.R. and B.P.
Increase respiration
Increase metabolic rate
Increase glycogenolysis
Bronchodilation
Norepinephrine (20-25% of mass)
Vasoconstriction
Interesting that both hormones when released by Adrenal gland, but neurotransmitters when released at synapses
Catacholeamine Deficiency: None known
Catacholeamine Overproduction: Pheochromocytoma – High metabolic rate, elevated temperature, high HR and blood glucose levels

23. Suprarenal (Adrenal) Gland
Adrenal Cortex
Mineralocorticoids (Zona Glomerulosa)
Aldosterone: maintains electrolyte balance
 Na+ reabsorption by kidneys &  K+ urinary loss
Glucocorticoids (Zona Fasciculate)
Cortisol (Hydrocortisone):
Stimulates gluconeogenisis
Mobilization of free fatty acids
Anti-inflammatory agent
Androgens (Zona Recticularis)
Bone growth, muscle growth & blood formation
Aldosterone Deficiency: Hypoaldosteronism – Polyuria, low blood volume, high serum K, low serum Na
Aldosterone Overproduction: Aldosteronism – Increased body weight due to Na & water retention, low serum K
Glucocorticoids Deficiency: Addison’s Disease – Inability to tolerate stress, mobilize energy reserves or maintain normal blood glucose levels
Glucocorticoids Overproduction: Cushing Disease – Excessive break down of tissue proteins and lipid reserves, impaired glucose metabolism

24. Pineal Gland Lies in posterior portion of roof of third ventricle
Contains pinealocytes
Synthesize hormone melatonin
Inhibits reproductive functions
Protects against damage from free radicals
Setting circadian rhythms

25. Pancreas Exocrine / Endocrine Gland
Endocrine Pancreas consists of “clusters” of cells called Islets of Langerhans
4 types of cells of endocrine pancreas
Comprise only 1% of entire pancreas

26. Pancreas Insulin Affects target cells by:
A peptide hormone released by beta cells
Affects target cells by:
Accelerate glucose uptake
Accelerate glucose utilization and enhances ATP formation
Stimulate glycogen formation
Stimulate amino acid absorption and protein synthesis
Stimulate triglyceride formation in adipose tissue
Insulin Deficiency: Diabetes Mellitus – High blood sugars, impaired glucose utilization, dependance on lipids of energy, glycosuria
Insulin Overproduction: (Iatrogenic / Tumor) – Low blood sugars

27. Pancreas Glucagon Affects target cells: Released by alpha cells
Mobilizes energy reserves
Affects target cells:
Stimulates breakdown of glycogen in skeletal muscle and liver tissue
Stimulates breakdown of triglycerides in adipose tissue
Stimulates production of glucose in liver

29. Sex Organs (Testes & Ovaries)
Testes (Gonads)
Produce androgens in interstitial cells
Testosterone is the most important male hormone
Secrete inhibin in nurse (sustentacular) cells
Support differentiation and physical maturation of sperm
Ovaries (Gonads)
Produce estrogens
Principle estrogen is estradiol
After ovulation, follicle cells
Reorganize into corpus luteum
Release estrogens and progestins, especially progesterone
Female:
Estrogens Deficiency: Hypogonadism– Sterility, lack of secondary sex characteristics
Estrogen Overproduction: Adrenogenital Syndrome – Masculinization
Precocious puberty – Premature sexual maturation, related behavioral changes
Male:
Androgen Deficiency: Hypogonadism– Sterility, lack of secondary sex characteristics
Androgen Overproduction: Adrenogenital Syndrome – Breast enlargement

30. Thymus Produces thymosins (blend of thymic hormones)
That help develop and maintain normal immune defenses

31. Endocrine Tissues of Other Organs
Kidneys:
Produce calcitriol and erythropoietin
Produces enzyme renin
Heart:
Produces natriuretic peptides (ANP & BNP)
When blood volume becomes excessive
Action opposes angiotensin II
Resulting in reduction of blood pressure & volume
Kidneys sense lower GFR and lower blood oxygen saturations, release EPO

33. Hormone Interactions General Adaptation Syndrome (GAS)
Also called stress response
How body responds to stress-causing factors
Is divided into three phases:
Alarm phase
Resistance phase
Exhaustion phase

34. Fight or Flight
Epinephrine is dominant hormone

35. Stresses that persist for hours / days / weeks – starvation, acute illness, etc
Mobilization of remaining Lipid & Protein Reserves
Conservation of Glucose for Neural Tissues
Elevation & Stabilization of Blood Glucose concentration
Conservation of Salts & Water and the Loss of K+ and H+