Bio Exam 3

Front 1

Endocrine secretion

Back 1

the secretion/release of chemicals from cells into body
tissue spaces or fluids. Endocrine glands do not have ducts to direct the
secretion out of the body

Front 2

Exocrine secretion

Back 2

the secretion/release of chemicals to a location outside of
the body. All multicellular exocrine glands are drained by a duct leading to a
body surface.

Front 3

hormone

Back 3

an organic molecule which is produced by
living cells (localized in a specific area of the body) and secreted into the blood
stream, where it travels some distance to target cells having specific receptors, to
cause a response in the target cells leading to physiological regulation.

Front 4

EXAMPLE OF A HORMONE THAT VIOLATES THE CLASSICAL DEFINITION

Back 4

Vitamin D (1,25-Dihydroxyvitamin D3) is produced in an assembly line manner
involving skin, liver and kidneys. The active form of vitamin D stimulates (1) the
gut to absorb more dietary calcium, (2) the kidneys to retain more calcium, and (3)
the bones to deposit more calcium into new bone. Overall, Vitamin D3 causes an
increase in body calcium and helps prevent diseases like rickets and osteoporosis.
The kidneys are legitimate “endocrine glands” because they secrete the active
chemical hormone, but they couldn’t do it without the help of the skin and liver.

Front 5

Peptides / proteins / glycoproteins

Back 5

hormones composed of strings of amino acids.
Peptides are simply small proteins, but there is no specific amino acid length that
demarcates peptides from proteins. Examples: insulin, growth hormone.
Glycoproteins are proteins with carbohydrate side-chains. Examples: FSH, LH,
TSH and chorionic gonadotropin (hCG, which is used for urine pregnancy tests)

Front 6

Amines

Back 6

Produced from modified amino acids; examples include epinephrine,
norepinephrine, dopamine, histamine, serotonin and melatonin.

Front 7

Steroids

Back 7

derived from cholesterol. E.g., progestins, corticoids (mineralocorticoids
and glucocorticoids), androgens, estrogens, and vitamin D.

Front 8

Iodinated amino acids

Back 8

modified amino acids linked to iodine atoms. Made only
by the thyroid. Examples: Triiodothyronine (T3, the more potent form of thyroid
hormone) and Thyroxine (T4, the less potent form of thyroid hormone).

Front 9

Prostaglandins

Back 9

are made from phospholipids obtained from cell
membranes.

Front 10

MECHANISM OF ACTION OF PROTEIN & AMINE HORMONES

Back 10

A. In general, these hormones are very hydrophilic (water loving, water soluble).
Therefore, they do not cross the target cell’s plasma membrane easily.
B. These hormones bind to membrane receptors on the surface of the target cell’s
cell membrane and alter the amount or activity of second messenger chemicals
within the target cells (just like many neurotransmitters do).
C. The second messengers alter the activity of pre-existing enzymes and other
molecules within the target cells, leading to a relatively rapid but brief response to
the hormone.

Front 11

Thyroid hormones may bind to

Back 11

nuclear receptors or to mitochondrial receptors in
the mitochondria (the latter attached to mitochondrial DNA).

Front 12

Steroid hormones bind to either

Back 12

cytoplasmic receptors or they may directly enter
the nucleus and bind to nuclear receptors which are attached to DNA.
i. Note: The effects of steroid hormones are the same regardless of where their
receptors are located initially because hormones bound to cytoplasmic
receptors eventually move with their receptors into the nucleus and bind to
DNA.

Front 13

MECHANISM OF ACTION OF STEROID & IODINATED HORMONES

Back 13

A. These hormones are very hydrophobic (water-fearing, water insoluble). Therefore,
they can’t travel in watery blood easily, but they can diffuse across the target cell’s
plasma membrane easily.

Front 14

Both steroid- and thyroid hormones then alter

Back 14

DNA transcription, which affects
mRNA levels and mRNA translation, which alters protein levels in the target cell.
These changes in cellular proteins then cause the physiological responses of the
target.
E. These effects are slower but longer lasting than the effects of protein/amine
hormones.

Front 15

Endogenous rhythms

Back 15

(pacemakers) within endocrine cells can create selfregulated
patterns of hormone secretion.

Front 16

Neural regulation

Back 16

some endocrine glands are directly influenced to alter hormone
secretion by neural inputs.

Front 17

Endocrine regulation

Back 17

some endocrine glands are controlled by hormones from
other endocrine glands.

Front 18

Substrate regulation

Back 18

when the actual substrate (a plasma ion or organic nutrient)
of a hormone alters the secretion of the hormone.
i. E.g., Pancreatic insulin & glucagon secretion are affected by plasma [glucose].
ii. E.g., Calcitonin & parathyroid hormone secretion are affected by plasma [Ca++].

Front 19

Negative feedback and sometimes positive feedback is also used to

Back 19

alter hormone
secretion.

Front 20

Many protein and amine hormones circulate freely

Back 20

in blood, dissolved in plasma

Front 21

Steroid and thyroid hormones do not dissolve well in

Back 21

plasma and thus their natural
concentration of in the plasma is relatively low.

Front 22

Small peptide hormones dissolve easily in the

Back 22

plasma, but they are subject to
rapid clearance by protein-digesting enzymes in the blood and by excretion at the
kidneys. Thus, these small hormones have a short half life (= the amount of time
needed for a hormone’s blood concentration to decrease to half of its initial level).

Front 23

Many steroid, thyroid, and small peptide hormones circulate in the blood stream
bound to

Back 23

carrier proteins or hormone binding proteins. These carrier proteins are
made in the liver and secreted into the plasma.