A&P 2 - Endocrine system

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List and describe the 4 principal methods of intercellular communication

1) Gap junctions - join single-unit smooth muscle, cardiac muscle, and epithelial cells. Allow cell to pass nutrients between each other
2) Neurotransmitters (NTM) - released by neurons and bind to receptor of adjacent cell
3) Paracrines - local hormones that are secreted from one cell, diffused to and act on adjacent cell of same tissue
4) Hormones - Chemical messengers transported through bloodstream that stimulate cells a distance away

Define the term autocrine

Similar to paracrine, local hormone that act on the same cell that secretes them

Compare the structure and function of exocrine glands to that of endocrine glands.

- Exocrine glands - contain ducts that secrete products of the gland onto an epithelial surface. Secretions have extracellular effects, such as digestion
- Endocrine glands - ductless glands that release secretions into bloodstream. Secretions have intracellular effect, alter metabolism of target cell

Compare and contrast the activities of the nervous and endocrine systems in terms of type of chemical messenger released.

Endocrine - hormones
Nervous - neurotransmitters

Compare and contrast the activities of the nervous and endocrine systems in terms of location of target cell

Endocrine - widespread throughout body
Nervous - precisely targeted and specific

Compare and contrast the activities of the nervous and endocrine systems in terms of onset of response to stimuli

Endocrine - responds w/in several seconds to days
Nervous - responds w/in milliseconds

Compare and contrast the activities of the nervous and endocrine systems in terms of duration of action of chemical messenger

Endocrine - reacts more slowly to stimuli
Nervous - reacts quickly to stimuli

Compare and contrast the activities of the nervous and endocrine systems in terms of specificity of response to chemical messenger

Endocrine - Depends on receptors in the receiving cell
Nervous - Depends on receptors in the receiving cell

Compare and contrast the activities of the nervous and endocrine systems in terms of duration of response to stimuli

Endocrine - May continue responding long after stimulus stops
Nervous - adapts quickly to continual stimulation

Compare and contrast the activities of the nervous and endocrine systems in terms of duration of action of chemical messenger

Endocrine - may continue after stimulus stops
Nervous - Stops when stimulus stops

Describe the differences in the origin, structure and function of the two parts of the pituitary gland: the anterior pituitary (adenohypophysis) and the posterior pituitary (neurohypophysis).

Origin:
- Andenohypophysis - arises from hypophyseal pouch growing upward from embryonic pharynx
- Neurohypophysis - arises as downgrowth of neurohypophyseal bud of brain
Structure:
-Andenohypophysis - anterior 3/4 of pituitary; contains 2 lobes; linked to hypothalamus via blood vessels
-Neurohypophysis - posterior 1/4 of pituitary; made of nervous tissue
Function:
-Andenohypophysis - controlled by hormone secretions of the hypothalamus
-Neurohypophysis - receive hormones from hypothalamus via axons, where they're stored until nerve signal triggers their release

Describe the structure of the hypophyseal portal system. Explain how this arrangement of blood vessels is unique compared to other capillary networks in the body and the functional advantages of such an arrangement.

- Has two primary sets of capillaries in hypothal and anterior pit, vs only one set in rest of body connected by very small veins
- Advantages allow for quicker movement of hormone directly to source, greater regulation of hormones, and smaller concentration of hormones needed to have effect on anterior pit

Describe the components of a hypothalamic-pituitary-target organ axis, identify three such axes and explain how secretion of the hormone is regulated by negative feedback inhibition in each axis.

- Axis - a system of glands and hormones involving the hypothalamus, anterior pituitary gland and a "target" gland and the hormones by which they communicate with one another.
1) thyroid gland
2) Adrenal Glands
3) gonads
Negative feedback - Pituitary stimulates another endocrine gland to secrete its hormone to target cell, that hormone released from target cell feeds back to pituitary or hypothalamus and inhibits further secretion of pituitary hormone.

Explain how hormones are released from the posterior pituitary gland and how this differs from the mechanism of release of anterior pituitary hormones.

- Hormones are synthesized in hypothalamus, transported to posterior pituitary and stored until released on command.
- Hormones are synthesized in hypothalamus, transported to anterior pituitary via hypophyseal portal system where they are secreted immediately

Identify each zone of the adrenal cortex and medulla and the class and function of hormones that zone secretes

Zona glomerulosa (top layer) - secretes Mineralocorticoids - electrolyte balance
Zona fasciculata (middle layer) - secretes glucocorticoids - glucose maintenance
Zona reticularis (inner layer) - secretes sex steroids - males and female hormone maintenance
Adrenal medulla (inner most layer of adrenal gland) - secretes catecholamines - increase alertness and prepare body for physical activity

Explain why the pancreas can be considered both an endocrine and exocrine gland

Gland is primarily exocrine because of ducts for digestive purposes;
Gland is also endocrine because of secreting cells of the pancreatic islet that release hormones into the blood stream

List the 2 cell types in the pancreatic islets (islets of Langerhans), the major hormone produced by each cell type and the major function(s) of each hormone.

Alpha cells - secrete glucagon which raises blood glucose levels and releases fatty acids
Beta cells - secrete insulin which stimulates cells to absorb nutrients and store them; promotes of glycogen, fat, and protein

Identify the three chemical classes of hormones and list examples of each class.

Steroids - derived from cholesterol; estrogen, progesterone, testosterone, cortisol
Peptides - oxytocin, ADH, CRH, PRH, GHRH, GnRH, TRH, PIH, GHIH, ACTH, LH, GH, PRL, TSH, FSH
Monoamines - dopamine, epinephrine, norepinephrine, melatonin, thyroid hormone

Identify the dietary mineral that is essential for the synthesis of thyroid hormone.

Iodine

Compare the transport of steroid hormones and thyroid hormones in the blood to that of the peptide, glycoprotein and other monoamine hormones.

-Steroid hormones and thyroid hormones are hydrophobic so they must use a transport protein that is hydrophilic to travel in the blood (bound)
- peptide glycoproteins and monoamines are hydrophilic, so they can travel in the blood unbound.

Explain how the chemical class of a hormone affects its mechanism of action at the target cell.

- Each chemical class of hormone has different effects on the target cell. Different hormones turn on different switches within the cell, enacting different metabolic pathways
- Steroids and thyroid hormone- enter target cell nucleus and act directly on the genes, because they are hydrophobic
- Peptides and Catecholamines - Can't enter cells, so use 2nd-messenger system to activate pathways w/in cell because they are hydrophilic

Explain how the mechanism of "enzyme amplification" allows for a very large response to a small amount of hormone.

One hormone can trigger the synthesis of a large number of other hormones through the use of intercellular enzymes.

Describe the concepts of up-regulation and down-regulation of target cell hormone receptors.

- Up-regulation - cell increases number of hormone receptors and becomes more sensitive to that hormone -- more receptors you have, the more hormones can bind
- Down-regulation - cell reduces its receptor population and becomes less sensitive to that hormone -- less receptors you have, less hormones can bind to it

Explain the three ways in which two or more hormones may affect the same target cell: synergistic effects, permissive effects and antagonistic effects.

- Synergistic effects - 2+ hormones work together to produce effect greater than their individual effects
Ex. FSH and Testosterone on sperm production
- Permissive effects - 1 hormone enhances target organ's response to 2nd hormone that is secreted later (sequential)
Ex. Estrogen and Progesterone (estrogen primes cell for progesterone by up-regulating progesterone receptors)
- Antagonistic effects - 1 hormone opposes action of another hormone
Ex. Glucagon and Insulin on blood sugar

Describe the physiologic roles of the eicosanoids: leukotrienes, thromboxanes, prostacyclin and the prostaglandins.

Leukotrienes - mediate allergic and inflammatory reactions
Prostacyclin - inhibits blood clotting and vasoconstriction
Thromboxanes - in event of injury, override prostacyclin and stimulate vasoconstriction and clotting
Prostaglandins (PGs) - Depending on the family can have different functions. Inflammation, endocrine mimicking, function as neuromodulators, promote ovulation, inhibit gastric secretion, act as vasodilators and vasoconstrictors, constrict or dilate bronchioles, promote blood circulation thru kidneys

Describe Acromegaly including the hormones involved

Acromegaly is the result of oversecretion of growth hormone from a tumor in the anterior pituitary gland that occurs after closure of the epiphyseal plates in the long bones. If such oversecretion occurs before adulthood, it results in gigantism.

Describe a goiter, including the hormones involved

A goiter can occur in either hypothyroidism or hyperthyroidism. It occurs when there is overstimulation of the thyroid gland by TSH.

Describe Hypothyroidism including the hormones involved and potential problems that cause hypothyroidism

- deficiency of thyroid hormone
1) problem is with the thyroid gland production of TH
- T3/T4 low, TSH high
2) problem is with anterior pituitary production of TSH
- T3/T4 low, TSH low

Describe Hyperthyroidism including the hormones involved and potential problems that cause hyperthyroidism

- excess of thyroid hormone
1) problem is with the thyroid gland over-secretion of TH
- T3/T4 high, TSH low
2) problem is with the anterior pituitary over-production of TSH
- T3/T4 high, TSH high

Describe cushing syndrome including the hormones involved

Abnormal storage of fat in face and back due to an oversecretion of glucocorticoids from the adrenal gland.

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