Chapter 11 The Endocrine System Human Anatomy & Physiology - P. Wilson1

Human Anatomy & Physiology - P. Wilson 1

Chapter 11The Endocrine System


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



II. 11.1 Introduction & Clinical Example

A. 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.

B. Hormones are chemicals that interact with specific target cells & affect the functioning of that cells. (Within the individual!!)



C. Exocrine Glands• Secrete their products to the

outside of the body through tubes or ducts.

• Ex: sweat & saliva glands

C. Endocrine Glands• Secrete their products into

the internal environment; the hormones diffuse from the interstitial fluid into the bloodstream.

• Ex: testes, ovaries, thyroid



D. Paracrine gland secretions affect only cells in their immediate surroundings

Ex: mast cells (a type of white blood cell secrete histimines)

D. Autocrine gland secretions affect only the cell which secretes them

Ex: neurons secrete neurotransmitters


III. 11.2 General Characteristics

A. As a group, endocrine glands regulate metabolic processes.

B. 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


IV. 11.3 Hormone Action

A. The specific site of a hormone’s action is called a target cell.

B. 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



C. 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

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C. 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

D. Cyclic adenosine monophosphate (cAMP) is a second messenger associated with one group of hormones



E. 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


V. 11.4 Control of Hormonal Secretions

A. Hormone secretions are controlled in 3 ways, all of which employ negative feedback:1. The release of trophic hormones from the hypothalamus controls

secretions of the anterior pituitary.2. The nervous system influences certain endocrine glands directly.3. Other glands respond to changes in the composition of internal

fluids.


V. 11.4 Control of Hormonal SecretionsB. 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.


V. 11.4 Control of Hormonal Secretions

C. 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.


VI. 11.5 Pituitary Gland

A. 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



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) The hypothalamus releases a prolactin- stimulating hormone

Sustains milk production. Hormone release is stimulated by the suckling of an infant.

Thyroid stimulating hormone - TSH

The hypothalamus releases a 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)

The hypothalamus releases a gonadotropin-releasing hormone (GnRH)(these are sex hormones)

Stimulates the male & female reproductive organs.


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


VII. 11.6 Thyroid GlandSee figure 11.10 on page 287


VII. 11.6 Thyroid GlandB. Thyroid hormones:

1. Iron is essential for the synthesis of triiodothyronine (T3) and thyroxine (T4).

2. 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).


VIII. 11.7 Parathyroid Gland

A. The parathyroid glands are located on the posterior surface of the thyroid gland

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VIII. 11.7 Parathyroid Gland

B. Parathyroid hormone (PTH) increases blood calcium ion concentration and decreases phosphate ion concentration.

C. 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.


IX. 11.8 Adrenal GlandsA. The adrenal glands sit like a cap on top of the kidneys and

are enclosed in a layer of fat.

B. 1. The adrenal medulla secretes 2 hormones: epinephrine and norepinephrine.

B. 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”


IX. 11.8 Adrenal Glands

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IX. 11.8 D.

Adrenocorticotropic hormone (from anterior pituitary)

Corticotrophin-releasing hormone


IX. 11.8 Adrenal Glands C. Adrenocortical HormonesHormone Stimulus for

secretionEffects 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

noncarbohydratesThe 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


X. 11.9 PancreasThe pancreas is posterior to the

stomach and

anterior to the spine


X. 11.9 PancreasHormone 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.



XI. 11.10 Other Endocrine GlandsA. 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.


XI. 11.10 Other Endocrine GlandsB. 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


XII. 11.11 Stress & HealthA. 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


XII. 11.11 Stress & HealthA. 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


XII. 11.11 Stress & Health

C. The positive effects of stress syndrome are increased alertness & endurance.

D. The negative effects of stress syndrome are increased risk of hypertension, atherosclerosis (hardening & narrowing of the arteries due to plaque buildup), & gastrointestinal ulcers.

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Chapter 11 The Endocrine System Human Anatomy & Physiology - P. Wilson1