Biology 2402 Anatomy and Physiology II Exam 1 Notes - Endocrine System Ch. 11
The endocrine system, along with the nervous system, coordinates and regulates the
activity of the body:
- the nervous system works via an electrochemical message and is quicker and
usually short term.
- the endocrine system works via a chemical messenger and is slower but longer
lasting.
Glands can be divided into two groups, exocrine and endocrine (see pg 101 in text):
- exocrine glands secrete their product into a duct that carries the secretion to a
surface; for example sweat glands, digestive glands, mucus glands.
- endocrine glands, also called ductless glands, and endocrine cells secrete their
product into the intercellular fluid; the hormone secreting cells.
Hormones are chemical messengers that are transported via the circulatory system to
affect cells in other tissues (circulating hormones):
- hormones that work within a tissue are called local hormones (paracrine and
autocrine), like prostaglandins
- hormones can be divided into two groups based on their chemical structure:
- amino acid based - water soluble - amines, peptides, proteins
- lipid based steroid - fat soluble, from cholesterol (some local hormones
from fatty acid)
* List the two chemical groups of hormones and give two specific examples of each
group. (see Table 11.2)
* How are hormones transported from their point of production to the cells they affect?
Target cells are the cells that are affected by a particular hormone:
- some hormones have many target cells throughout the body, other hormones
have very particular target cells.
- target cells have a receptor protein that will bind with the hormone (shape must
fit, only cells with the correct shape receptor will be affected)
- hormones that are not fat soluble bind to receptors of cell membrane, causing
change of enzyme in cytoplasm - second messenger like cyclic AMP.
- fat soluble hormones enter cell and bind to receptors in the cytoplasm or
nucleus.
- hormones alter the metabolic activity or gene expression of the target cell.
- the receptors are continually replaced; more receptors are produced if the
hormone is at low level (up regulation), fewer are produced if the hormone
is at high level (down regulation).
Hormones rarely work alone, usually a hormone’s action is determined by the relative
concentration and combination of several hormones:
- antagonistic - have opposite effects
- synergistic - work together to have greater effect
- permissive - first hormone allows second hormone to have an effect
*Describe three ways that hormones may interact and give an example of each.
The production of hormones by the endocrine glands is controlled by negative feedback.
Several feedback pathways are used:
- direct feedback where the endocrine gland is sensitive to a changing condition;
- through the nervous system by nerve stimulation from the hypothalamus;
- via regulatory hormones from the hypothalamus to the anterior pituitary.
Hormones are removed from the body by excretion by the kidneys, in the liver or by
inactivation by an enzyme.
*Describe the three methods of negative feedback used to regulate hormone production
by endocrine glands and list the endocrine glands that use each method.
*Why are these methods of regulating hormone levels called "negative feedback"?
*List the endocrine glands, the hormones produced by each gland and the primary action
of each hormone. Tables 11-3 through 11-6 will be helpful.
The endocrine glands:
Pituitary is located beneath the brain and is attached to the hypothalamus. It is composed
of a posterior part that develops from the brain and an anterior part that develops from the
embryonic skin.
Posterior pituitary - two hormones are produced by nerve cells in the hypothalamus and
transported to the posterior pituitary by axons. The hormones are stored and released
from the posterior pituitary.
antidiuretic hormone (ADH) oxytocin Anterior pituitary - six hormones are produced by endocrine cells in the anterior
pituitary gland. These endocrine cells are the target cells (regulated by) of releasing and
inhibiting hormones produced in the hypothalamus. The hormones from the
hypothalamus are moved to the pituitary via the hypophyseal portal system.
growth hormone (hGH)prolactin (PRL) thyroid-stimulating hormone (TSH) adrenocorticotropic hormone (ACTH) follicle-stimulating hormone (FSH) luteinizing hormone (LH) -
*Describe the hypophyseal portal system and explain what it does (why it is important).
*What are topic hormones, or tropins?
* Describe how the production of tropic hormones is controlled - What causes an increase
and what causes a decrease in the production?
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Thyroid - located just below the larynx and anterior to the trachea in the neck. The
thyroid is composed of spheres of glandular cells (follicular cells) with a cavity in the
center. This structure is called a follicle. The central space is used to store a colloidal
mixture that contains precursor molecules and the thyroid hormones. Iodine atoms are a
component of the thyroid hormones T3 and T4.
Small patches of cells are located between the follicles - these are extrafollicular cells.
thyroxine (tetraiodothyronine or T4 ) and triiodothyronine (T3) - produced in
follicular cells
calcitonin - produced by extrafollicular cells
*How is the production of thyroid hormones (thyroxine) regulated?
*How is the production of calcitonin regulated?
Parathyroid - four small lumps of endocrine cells on the posterior side of the thyroid.
parathyroid hormone *How do parathyroid hormone and calcitonin interact?
Adrenal - an adrenal gland is located on the superior surface of each kidney. Each
adrenal gland is composed of a central portion called the adrenal medulla and an outer
layers called the adrenal cortex. These glands look “fatty” because they store and use fats
as a precursor to produce the cortical (steroids) hormones.
Adrenal Medulla - stimulated by preganglionic neurons of sympathetic nerves.
epinephrine and norepinephrine Adrenal Cortex - produces a series of hormones called corticosteroids.
mineralocorticoids - aldosterone glucocorticoids - cortisol gonadocorticoids - androgens *How is the adrenal medulla related to the “fight-or-flight” reaction (alarm stage)?
*How is secretion by the adrenal medulla regulated?
*How is secretion by the adrenal cortex regulated?
*Why is the adrenal gland called the “stress gland”?
*Which part of the adrenal gland dominates during the resistance stage of stress?
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Pancreas - an elongated gland just below the stomach. It is mostly (99%) an exocrine
gland that secretes digestive enzymes. Small islands of endocrine cells called pancreatic
islets (or islets of Langerhans) secrete hormones.
insulin (from beta cells) glucagon (from alpha cells) *What is the difference between an exocrine gland and an endocrine gland?
*How do the hormones insulin and glucagon interact?
*How is the production of glucagon regulated?
Pineal - located in superior surface of thalamus of brain. It receives nerves from the
visual pathway and is, therefore, stimulated by light and dark.
melatonin Thymus - located in the thoracic cavity in the mediastinum, just behind sternum. It is
large at birth and increases in size until puberty. After puberty it begin a steady decrease
in size.
thymosin Testes - gonads that produce sperm in males, located in the scrotal cavities. Interstitial
cells are patches of endocrine cells within the testes.
testosterone inhibin Ovaries - gonads that produce eggs in female, located in the pelvic cavity. Follicles are
spheres that contain developing eggs. The follicle cells produce a series of hormones.
estrogen progesterone inhibin -
Stress !! How is this course related to stress and stress hormones?
*Describe three ways that hormones can interact and give an example of each.
*Why do some cells respond to a particular hormone but other cells do not, even though
all cells are surrounded by the hormone?
*What are the cells called that respond to a particular hormone?
*How can one cell respond to a hormone one way, yet another cell respond a different
way to the same hormone?
*Why must the receptors for peptide (protein) type hormones be located on the outside of
the cell membrane, instead of inside the cell like lipid type hormone receptors?
*Why is the pituitary gland called the “master” endocrine gland?
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