Chapter 16 (lectures)

1. Nervous system: controls processes that happen quickly

2. Endocrine system: controls relatively slower processes

The two control systems of the body

1. Communication

2. Integration (information from various sources coming in to create a common desired goal)

3. Control

The endocrine and nervous system have three main functions that work together (or alone) to maintain homeostasis. What are the three general functions?

Hormones

Chemical messengers secreted by cells of endocrine glands; how the endocrine system communicates.

Endocrine glands

Ductless glands that secrete hormones directly into the blood

1. Reproduction

2. Growth and development

3. Electrolyte, water, and nutrition balance in the blood

4. Regulation of cellular metabolism and energy balance

5. Mobilization of body defenses (immune system)

What are the main processes that are controlled by hormones? [5]

1. Pineal gland

2. Pituitary gland

3. Thyroid gland

4. Parathyroid gland

5. Adrenal gland

What are the five main glands of the endocrine system?

1. Pancreas

2. Gonads (ovaries and testis)

3. Thymus

What are some organs that, in addition to their organ function, also secrete hormones? [3]

Hypothalamus

A neuroendocrine gland (has both nervous and endocrine function) that releases hormones but is also part of the nervous system.

essentially transported in water (blood and lymph)

How are hormones transmported?

1. How they are transported

2. How long they last

3. What receptors they act on

What does solubility of a hormone determine? [3]

how soluble the chemical is in water

What does the structure of a hormone determine?

1. Amino Acid based

2. Steroid based

What are the two broad classes of hormones?

Amino acid based hormone

Hormones that are lipid soluble and cannot cross the plasma membrane.

All hormones except for the gonadal hormones (gonads) and adrenocortical hormones (adrenal gland)

Which hormones are amino-acid based hormones?

Steroid based hormone

Hormones that are lipid soluble and can cross the plasma membrane

Gonadal and adrenocortical hormones

Which hormones are steroid-based?

1. Alter membrane permeability (what can get through, alters membrane potential)

2. Stimulate creation of enzymes or other proteins in the cell

3. Activate or deactivate enzymes (more of less active)

4. Induce secretory activity

5. Stimulate mitosis

What are the effects of hormones? (hormones will produce one or more of the following five effects)

Hormones are secreted by glands directly into the blood. Wherever there is blood circulating, hormones will be present

Why are hormones present in most tissues?

Target cell. the hormone will only act on cells with receptors they can bind to

Cells/tissues that have receptors for the specific hormone.

By their receptor

How are target cells identified?

Can vary depending on the target cell. Specific effect depends on target cell, makes endocrine system very complicated.

How does the effect of a given hormone vary?

1. Lipid soluble steroid, and thyroid: crosses plasma membrane, using intracellular receptors

2. water soluble: cannot cross plasma membrane, using second messenger system

What are two ways a hormone can effect a cell? How does it do what it needs to do?

Intracellular receptors

Receptors inside lipid-soluble target cells, once the hormone goes into the cytoplasm. Affects from the inside

All amino acid hormones except thyroid hormone

Which hormones use a second messenger system?

1. First messenger (hormone) binds to receptors on plasma membrane

2. Sets in place a series of events in the cytoplasm

3. Ultimately results in the creation of a substance called a second messenger, that has an effect inside the cell

4. Like a chain reaction

How does a second messenger system work? (broad) [4]

Negative feedback: Stimulus triggers hormone secretion, hormone levels rise, observable effect in target organ, feedback occurs to inhibit further hormone release.

What kind of homeostatic mechanism regulates and controls the release of hormones?

1. Humoral

2. Neural

3. Hormonal

Three types of stimuli that trigger hormone release by endocrine glands are:

Humoral stimulus

Refers to hormone release caused by altered levels of certain critical ions/nutrients. Means moisture of bodily fluids, presence of ions in the body.

Neural stimulus

Hormone is released by stimulus from the nervous system. Action potential stimulated a gland and hormone is released.

Hormonal stimulus

Release of a hormone stimulated by the release of another hormone. Most common type of stimulus of endocrine system. Pituitary releases hormones that stimulate thyroid, testis, adrenal cortex, etc.

Example: In times of high stress, increased levels of glucose are needed for energy (fight or flight). The nervous system overrides glucose control system to enable higher blood glucose levels. Temporary, goes back to normal once stress is over

How can nervous system have ability to override normal endocrine function?

1. Blood levels of the hormone (higher=greater effect)

2. Affinity of binding between hormone and receptor (stronger binding = greater effect)

3. Relative number of receptors for that hormone (more receptors=greater effect). NOT static; dynamic

The response of a targe cell depends on these three things:

If there is a consistent low level of hormone, cell will increase its number of receptors (up-regulation). If there is a consistent high level of a hormone, cell decreases its number of receptors and cell is less sensitive to that hormone (down-regulation)

Why are the number of receptors on a cell dynamic/changing?

Up-regulation

Cell increases number of receptors due to consistent low levels of a hormone (more sensitive)

Down regulation

Cell decreases number of receptors due to consistent high levels of a hormone. (less sensitive)

Removed by the kidneys (water-soluble) or metablized by the liver (lipid soluble)

How are most hormones removed from the body after having their effect?

1. Permissiveness

2. Synergism

3. Antagonism

Three possibilities when a cell has multiple hormones acting on the same target cell at the same time

Permissiveness

When multiple hormones act on the same taret cell at the same time and one hormone cannot exert its full effect without the presence of another hormone (ex: reproductive do not have full effect without thyroid)

Synergism

When multiple hormones have the same effect on a target cell when occurring together, Their effects are amplified. (ex: glucagon and epinephrine)

antagonism

Multiple hormones acting on the same target cell, one hormone opposes the action of another hormone (ex: insulin and glucagon). Opposite effects, will not work together.

Hypothalamus

Important role in the nervous system, also an endocrine gland. Referred to as the controller of endocrine glands. Releases hormones that are stored in the posterior pituitary, and releases hormones that inhibit activity of other endocrine glands. (ability to affect many other glands in the body

Pituitary gland

Endocrine gland that is closely related to hypothalamus, and hangs by a stalk right below it. Size of a pea, protected by sphenoid bone. 2 lobes.

1. Anterior pituitary: Glandular tissue, produces hormones

2. Posterior pituitary: Neural tissue, stores hormones that are produced in hypothalamus. Can release hormones, but they are not produced there.

Two lobes of the pituitary gland

1. Oxytocin (childbirth and lactation, higher in childbirth)

2. Antidiuretic hormone (Reduces urine production, prevents dehydration)

Two hormones released by the posterior pituitary

Tropic hormones

Hormones that regulate the action of other endocrine glands (responsible for hormone regulation and release)

Trophic hormones

What are most hormones produced by the anterior pituitary?

1. TSH

2. ACTH

3. FSH

4. LH

Four trophic hormones produced by anterior pituitary

1. Growth hormone (GH)

2. Prolactin (PRL)

Two other (non tropic) hormones produced by anterior pituitary

Thyroid gland

Largest pure endocrine gland in the body. Two lateral lobes and an isthmus on anterior neck of trachea, just inferior to larynx.

Thyroid hormone (is actually two hormones, T3 and T4)

The body’s major metabolic hormone produced by the thyroid. Controls rate at which glucose is burned and converted to body heat and chemical energy. Stimulates metabolism, tissue growth and development, maintaining blood pressure.

Calcitonin

Hormone released by the thyroid in response to a rise in blood calcium levels (no known physiological effect, does not need to be replaced in people with thyroid gland removed). When administered as a drug, decreases calcium by inhibiting osteoclast activity and stimulating calcium uptake and incorporation in to bone matrix)

1. Thyroid hormone

2. Calcitonin

Two hormones produces by the thyroid covered in this course:

4

How many parathyroid glands do most people have?

Parathyroid glands

Glands that lie on posterior surface of thyroid gland, produces PTH

Parathyroid hormone (PTH)

Hormone that is the single most important hormone in regulating blood calcium levels. Net effect is an increase in calcium levels in the blood

Adrenal glands

Glands that sit right on top of the kidney like a little had, comprised on two glands.

1. Adrenal medulla (inner)

2. Adrenal cortex (outer)

The adrenal gland is comprised of these two glands:

They produce hormones involved in stress response and electrolyte balance

What do adrenal medulla glands do?

1. Epinephrine

2. Norepinephrine

Two primary hormones produced by adrenal medulla

Hypothalamus→ medulla (reinforced fight or flight response)

Pathway for short term stress response:

1. triggered by the sympathetic nervous system; stressor activates

2. Sends signal to spinal cord, ultimately signal travels to emdulla

3. Fight or flight signals nerve impulse to adrenal medulla to secrete epinephrine and norepinephrine. neural stimulus

Briefly explain short term stress response[3]

1. cardiovascular: Increased blood pressure and heart rate, giving more blood supply to muscles. Shunts blood away from nonessential organs (norepinephrine)

2. Bronchodilation: bronchioles become larger, more air in lungs, more energy for muscles (epinephrine)

3. Metabolic: Increased glucose in the blood (epinephrine)

Effects of short term stress (epinephrine and norepinephrine) (3)

Corticosteroids (steroid hormones)

Hormones secreted by the adrenal cortex

1. Mineral corticoids

2. Glucocorticoids

3. Gonadocorticoids: weak sex hormones

Three main groups of corticosteroids

Mineral corticoids

Corticosteroid that regulates electrolytes (mainly sodium and potassium) in extracellular fluid

Aldosterone. Makes up 95% of mineralcorticoids secreted by adrenal cortex.

Primary mineralcorticoid that regulates sodium and potassium. Works mainly by reducing secretion of sodium in urine

Amount of sodium in extracellular fluid determines volume of extracellular fluid. Can impact blood pressure and blood volume

Why is control of sodium levels important?

Determines resting membrane potential which is essential for action potential generation.

Why is control of potassium levels important?

Glucocorticoids

Corticosteroid released by adrenal cortex that influences the energy metabolism of most cells and helps to resist stressors.

Cortisol

Main glucocorticoid in humans

When stress occurs, cortisol secretion also happens.

Prepares for stress because it increases blood glucose levels.

Causes fats and proteins to break down, and can be sued for energy, make more glucose, cell repair, etc.

Effects of cortisol on the body [3]

anti-inflammatory and auto-immune effects. These can result in:

1. Depressed cartilage and bone formation

2. Depress immune system/ inhibit inflammation

3. Disrupt normal cardiovascular, neural, and digestive function

Too much cortisol can lead to… [3]

Hypothalamus→ Pituitary → Adrenal cortex (HPA)

Long term stress pathway

Mineral corticoids cause kidneys to retain water, Increase blood volume blood pressure. If this is prolonged, can have serious effects:

1. High blood pressure

2. Breakdown of proteins: muscle wasting and loss

3. Elevated blood glucose for too long: Diabetes

4. Fatty acids: increased fatty acid levels in blood can lead to clogged arteries and arteriosclerosis

Renal effects of long term stress [4]

Pineal gland

Gland that secretes melatonin that regulates circadian rhythms.

Pancreas

Mixed gland located partially behind the stomach that has both exocrine and endocrine glands.

Majority of pancreas secretes digestive enzymes

Exocrine function of the pancreas

Pancreatic islet cells secrete glucagon and insulin

Endocrine function of the pancreas

Glucagon

Hyperglycemic hormone secreted by pancreas that increases blood glucose levels

Insulin

Hypoglycemic hormone secreted by pancreas that decreased blood glucose

1. Cells need it to survive (pathways start with glucose)

2. If pathways are inadequate, they cannot produce energy and cannot survive

Why is glucose important?

1. High glucose is sensed by pancreas

2. Pancreas secretes insulin

3. Insulin causes cells to take more glucose in, removing it from bloodstream.

4. Also stimulates glucose to be moved/ stored as glycogen in liver

5. Insulin works as second messenger

6. Glucose falls, blood levels back to normal

What happens if blood glucose levels get above desired range? [6]

1. Low glucose is sensed by pancreas

2. Pancreas secretes glucagon

3. Acts on liver, stimulating release of glucose back into the blood stream

4. Net effect: blood glucose rises and returns to normal

What happens if blood glucose levels fall below desired range?

Type 1 diabetes. Blood glucose keeps rising.

What happens if no insulin is secreted by the pancreas?

Gonads (ovaries and testis)

Important organs of the reproductive system that also produce hormones

1. Estrogen and progesterone (ovaries)

2. Testosterone (testis)

Hormones produced by gonads

Thymus

Endocrine gland key to immune response

Placenta

Temporary hormone organ, secretes hormones that influence the course of pregnancy

Neurotransmitters: relatively short distance

Hormones: relatively long distances

Relative distances that neurotransmitters and hormones travel