1. Human Anatomy & Physiology - P. Wilson
Chapter 11
The Endocrine System
Human Anatomy & Physiology - P. Wilson

2. Human Anatomy & Physiology - P. Wilson
The nervous system & the endocrine system function coordinately to enable body parts to communicate with each other & to constantly adjust to changing incoming signals. (see table on page 277)
Nervous System
Endocrine System
Cells
Neurons
Glandular epithelium
Chemical signal
Neurotransmitter
hormone
Specificity of response
Receptors on postsynaptic cell (neuron)
Receptors on target cell
Speed of onset
Seconds
Seconds to hours
Duration of action
Very brief unless neuronal activity continues
May be brief or may last for days even if secretion ceases
Human Anatomy & Physiology - P. Wilson

3. Human Anatomy & Physiology - P. Wilson

4. II. 11.1 Introduction & Clinical Example
Pheromones are chemical signals (messengers) sent between individuals of the same species
The message communicated is usually sexual in nature ( the pheromones stimulate sexual / reproductive behavior).
It is thought pheromones lead animals to chose mates that are genetically dissimilar to themselves.
Hormones are chemicals that interact with specific target cells & affect the functioning of that cells. (Within the individual!!)
Human Anatomy & Physiology - P. Wilson

5. II. 11.1 Introduction & Clinical Example
Exocrine Glands
Secrete their products to the outside of the body through tubes or ducts.
Ex: sweat & saliva glands
Endocrine Glands
Secrete their products into the internal environment; the hormones diffuse from the interstitial fluid into the bloodstream.
Ex: testes, ovaries, thyroid
Human Anatomy & Physiology - P. Wilson

6. II. 11.1 Introduction & Clinical Example
Paracrine gland secretions affect only cells in their immediate surroundings
Ex: mast cells (a type of white blood cell secrete histimines)
Autocrine gland secretions affect only the cell which secretes them
Ex: neurons secrete neurotransmitters
Human Anatomy & Physiology - P. Wilson

7. III. 11.2 General Characteristics
As a group, endocrine glands regulate metabolic processes.
To accomplish their functions endocrine glands:
control the rate of chemical reactions
aid in the transport of substances across membranes
help regulate water & electrolyte balances
also, play vital roles in reproduction, growth, & development
Human Anatomy & Physiology - P. Wilson

8. Human Anatomy & Physiology - P. Wilson
IV Hormone Action
The specific site of a hormone’s action is called a target cell.
There are 2 types of hormones: steroid & nonsteroid:
steroid hormones are synthesized from cholesterol
all other hormones are amines, peptides, proteins, or glycoproteins and are synthesized from amino acids
Human Anatomy & Physiology - P. Wilson

9. Human Anatomy & Physiology - P. Wilson
IV Hormone Action
Steroid hormones are soluble in lipids and lipids make up the bulk of cell membranes, therefore steroid hormones can diffuse into cells easily & rapidly.
steroid hormone binds to receptor
hormone-receptor complex binds to a particular region on the DNA and activates the transcription of a mRNA molecule
the mRNA molecule leaves the nucleus, links with a ribosome and directs the synthesis of a specific protein
the newly synthesized protein (may be an enzyme, a transport protein, or a hormone receptor) carry out the specific effects associate with the particular steroid hormone
Human Anatomy & Physiology - P. Wilson

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11. Human Anatomy & Physiology - P. Wilson
IV Hormone Action
Nonsteroid hormones are not soluble in lipids and must follow a more complicated path through a process called signal conduction
This path employs a binding site, an activity site, a first messenger, a second messenger
Cyclic adenosine monophosphate (cAMP) is a second messenger associated with one group of hormones
Human Anatomy & Physiology - P. Wilson

12. Human Anatomy & Physiology - P. Wilson
IV Hormone Action
Prostaglandins are biochemical (lipids) synthesized from a fatty acid in cell membranes. Their effect is more localized than hormones, usually affecting only the organ where they are produced. Prostaglandins
are potent & are present in very small quantities
are not stored in cells but are synthesized just prior to release
produce diverse & even opposite effects (some may relax smooth muscles, others may contract smooth muscles
stimulate secretions of other hormones, influence blood pressure & inflammation, and have powerful effects on male & female reproductive physiology
Human Anatomy & Physiology - P. Wilson

13. V. 11.4 Control of Hormonal Secretions
Hormone secretions are controlled in 3 ways, all of which employ negative feedback:
The release of trophic hormones from the hypothalamus controls secretions of the anterior pituitary.
The nervous system influences certain endocrine glands directly.
Other glands respond to changes in the composition of internal fluids.
Human Anatomy & Physiology - P. Wilson

14. V. 11.4 Control of Hormonal Secretions
When the level of a hormone in the blood rises to a certain level (above the set point), negative feedback inhibits the system & hormone release decreases. As the hormone levels in the blood decrease to the set point, inhibition is lifted & secretion of the hormone increases again.
Human Anatomy & Physiology - P. Wilson

15. V. 11.4 Control of Hormonal Secretions
The brain controls the activity of the pituitary (the master gland) via the hypothalamus.
The location of the hypothalamus allows it to receive a constant flow of information about the body’s internal environment from neural connections and the CSF.
Human Anatomy & Physiology - P. Wilson

16. Human Anatomy & Physiology - P. Wilson
VI Pituitary Gland
The pituitary gland
is about the size of a pea and has a mass of about 0.5 gram
it is located at the base of the brain inferior to the hypothalamus & is surrounded by a bony cavity called the sella turcica
it is attached to the hypothalamus by a stalk called the pituitary stalk or the infundibulum
it consists of an anterior lobe and a posterior lobe
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Hormone
Stimulus for secretion
Actions
Anterior lobe
Growth hormone GH)
The hypothalamus releases a
GH - stimulating hormone
Stimulates cells to increase in size & to divide more frequently. Enhances the movement of amino acids across the cell membrane, & speeds the rate at which cells utilize carbohydrates & fats.
Prolactin (PRL)
prolactin- stimulating hormone
Sustains milk production. Hormone release is stimulated by the suckling of an infant.
Thyroid stimulating
hormone - TSH
thyrotropin - stimulating hormone
Controls secretion of hormones from the thyroid gland
Adenocorticotrophic
hormone - ACTH
Regulated by corticotropic releasing hormone & by stress
Stimulates the release of hormones from the adrenal cortex
Follicle stimulating
hormone (FSH) &
Luteinizing hormone
(LH)
gonadotropin-releasing hormone (GnRH)
(these are sex hormones)
Stimulates the male & female reproductive organs.
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19. Human Anatomy & Physiology - P. Wilson
Hormone
Stimulus for secretion
Actions
Posterior lobe
Antidiuretic hormone
Stimulated by the hypothalamus in response to changes in water concentration
Causes the kidneys to conserve water. In high concentrations, this hormone increases blood pressure
Oxytocin
Stimulated by the hypothalamus in response to stretching of the muscles of the uterine wall and stimulation of the breast
Contracts the muscles in the uterine wall in labor and contract muscles associated with milk secreting glands
This table can be found on page 286 or your text book
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20. Human Anatomy & Physiology - P. Wilson
VII Thyroid Gland
See figure on page 287
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21. Human Anatomy & Physiology - P. Wilson
VII Thyroid Gland
Thyroid hormones:
Iron is essential for the synthesis of triiodothyronine (T3) and thyroxine (T4).
Secretions of T3 & T4 are stimulated by TSH (released by the anterior pituitary).
Both T3 & T4 increase the rate of energy release from carbohydrates, increase the rate of protein synthesis, stimulate the breakdown & mobilization of lipids,
Both T3 & T4 are required for normal growth & development and are essential to nervous system maturation
but triiodothyronine is five times more potent that thyroxine
T3 & T4 are the major factors determining how many calories a body must consume at rest in order to maintain life – the basal metabolic rate (BMR).
Human Anatomy & Physiology - P. Wilson

22. VIII. 11.7 Parathyroid Gland
The parathyroid glands are located on the posterior surface of the thyroid gland
Human Anatomy & Physiology - P. Wilson

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24. VIII. 11.7 Parathyroid Gland
Parathyroid hormone (PTH) increases blood calcium ion concentration and decreases phosphate ion concentration.
Calcitonin increases the rate at which calcium is stored in bones and excreted in the urine.
In short: calcitonin lowers blood calcium ion concentration.
Calcitonin and PTH exert opposite effects in
regulating calcium ion levels in the blood.
Human Anatomy & Physiology - P. Wilson

25. Human Anatomy & Physiology - P. Wilson
IX Adrenal Glands
The adrenal glands sit like a cap on top of the kidneys and are enclosed in a layer of fat.
1. The adrenal medulla secretes 2 hormones: epinephrine and norepinephrine.
2. The effects of these hormones resemble those of the sympathetic division neurotransmitters of the same name, except that they last up to 10 times longer when they are secreted as hormones.
They are used in times of stress for “fight or flight”
Human Anatomy & Physiology - P. Wilson

26. Human Anatomy & Physiology - P. Wilson
IX Adrenal Glands
Human Anatomy & Physiology - P. Wilson

27. IX. 11.8 D. Corticotrophin-releasing hormone
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IX D.
Corticotrophin-releasing hormone
Adrenocorticotropic hormone (from anterior pituitary)

28. IX. 11.8 Adrenal Glands C. Adrenocortical Hormones
Stimulus for secretion
Effects of the Hormone
Mineralocorticoids
(aldosterone)
Decrease in Na concentration or an increase in K concentration
Conservation of Na &excretion of K, and conservation of water
Glucocorticoids
(cortisol)
Released by the hypothalamus
Increases amino acids by decreasing protein synthesis
Increases the use of fatty acid as an energy source
Stimulates the liver to synthesis glucose from noncarbohydrates
The overall effect is to maintain blood glucose concentration and in times of stress to maintain a constant supply of blood glucose (required when a body is under stress)
Sex hormones
(adrenal androgens)
Not known
May supplement the supply of sex hormones from the gonads and stimulate early development of sexual organs.
The hormones produced are androgens (male type hormones) but some are converted to estrogens (female type hormones) in females
Human Anatomy & Physiology - P. Wilson

29. X. 11.9 Pancreas The pancreas is posterior to the stomach and
anterior to the spine
Human Anatomy & Physiology - P. Wilson

30. Human Anatomy & Physiology - P. Wilson
X Pancreas
Hormone
Source of control
Effects of hormone
Glucagon
Low blood sugar concentrations stimulate the alpha cells of the pancreas to release glucagon
Glucagon stimulates the liver to break down glycogen & noncarbohydrates (such as amino acids) into glucose.
Glucagon raises blood sugar very rapidly
Insulin
High blood sugar concentrations stimulate the beta cells of the pancreas to release insulin
Insulin stimulates the liver to make glycogen from glucose and inhibits the use of amino acids to form glucose.
Insulin also promotes facilitated diffusion of glucose across cell membranes that have insulin receptors
Insulin promotes the transport of amino acids into cells, promotes protein synthesis, & stimulates adipose tissue to store fat
These actions of insulin decreases blood glucose (sugar) concentration.
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32. XI. 11.10 Other Endocrine Glands
Pineal Gland
is located deep between the cerebral hemispheres & is attached to the upper portion of the thalamus.
Secretes melatonin in response to light conditions outside the body. Melatonin acts on certain brain regions that function as a “biological clock” & therefore may help regulate circadian rhythms.
Human Anatomy & Physiology - P. Wilson

33. XI. 11.10 Other Endocrine Glands
Thymus Gland
is located in the mediastinum posterior to the sternum & between the lungs
it is relatively large in children but shrinks with age
secretes a group of hormones called thymosins that affect the production & differentiation of certain WBCs (lymphocytes) so it plays an important role in immunity
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34. Human Anatomy & Physiology - P. Wilson
XII Stress & Health
A factor that can trigger the body’s physiological responses to stress is called a stressor. A stressor can be physical or psychological.
Physical stressors can include exposure to extreme heat or cold, decreased oxygen concentration, infection, injury, prolonged exercise, or loud noises.
Psychological stressors can include thoughts about real or imagined dangers, personal loses, unpleasant social interactions, or feelings of grief, anger, anxiety, depression, & guilt
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XII Stress & Health
Physiological responses to stress (which are under control of the hypothalamus) are referred to as general adaptation syndrome. There are 2 stages to this response: 1) fight or flight; 2)resistance
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36. Human Anatomy & Physiology - P. Wilson
XII Stress & Health
The positive effects of stress syndrome are increased alertness & endurance.
The negative effects of stress syndrome are increased risk of hypertension, atherosclerosis (hardening & narrowing of the arteries due to plaque buildup), & gastrointestinal ulcers.
Human Anatomy & Physiology - P. Wilson