Download Rhythms and Blues

A. Rhythms and Blues
B. The pineal gland in the brain secretes melatonin.
1. Melatonin secretion increases after dusk to promote sleep.
2. The reverse occurs at sunrise to cause wakefulness.
C. The sleep/wake cycle is part of a biological clock, which can upset by international travel and long winter nights.
D. The Endocrine System
1. Hormones and Other Signaling Molecules
1. Signaling molecules are hormones and secretions that can bind to target cells and elicit in
them a response; this integrates the vertebrate body's functions.
2. There are four main types of signaling molecules:
a. Hormones are secreted from endocrine sources and some neurons and are then
transported by the blood to nonadjacent targets.
b. Neurotransmitters are secreted from neurons and act on immediately adjacent
target cells for a short time.
c. Local signaling molecules are secreted from cells of many different tissues; they
alter chemical conditions in the immediate vicinity and are quickly degraded.
d. Pheromones, secreted by exocrine glands, have targets outside the body; they
integrate social activities between animals.
3. The sources of hormones may be collectively called the "endocrine system," which shows
intimate connections with the nervous system.
a. In an opposing interaction the effect of one hormone opposes the effect of
another; for example: insulin and glucagon.
b. In a synergistic interaction the sum total of the actions of two or more hormones is
necessary to produce the required effect on target cells; for example: prolactin,
oxytocin, and estrogen.
c. In a permissive interaction one hormone exerts its effect only when a target cell
has been "primed" to respond; for example: estrogens are secreted first in
pregnancy, followed by progesterone.
E. Signaling Mechanisms
1. Overview of Hormone Action
1. A target cell’s response to a hormone is dependent on two
factors:
a. Different hormones activate different cellular response
mechanisms.
b. Not all cells have receptors for all hormones; the cells
that respond are selected by means of the type of
receptor they possess.
2. Hormones are either derived from cholesterol, tyrosine, or other
amino acids.
1. Steroid Hormones
i. Steroid hormones, synthesized from cholesterol, are lipid-soluble and therefore cross plasma
membranes readily.
a. Once inside the cell, they penetrate the nuclear
membrane and bind to receptors in the nucleus,
activating transcription.
b. Steroids stimulate or inhibit protein (especially
enzyme) synthesis by switching certain genes on or off.
2. Testosterone is the male hormone with receptors throughout the
body; however, in testicular feminization syndrome, none of the
target cells respond correctly, so the XY individual develops
female characteristics.
F. Amine, Peptide, and Protein Hormones
1. This group includes peptides, amines, polypeptides, and glycoproteins.
2. Protein hormones and other water-soluble signaling molecules cannot cross the plasma
membrane of target cells so they must first bind to a receptor on the plasma membrane.
3. The hormone-receptor complex enters the cell to stimulate the production of cyclic-AMP, a
"second messenger," which amplifies the signal by activating numerous enzymes.
G. The Hypothalamus and Pituitary Gland
1. The hypothalamus and pituitary gland work jointly as the neural-endocrine control center.
i. The hypothalamus is a portion of the brain that monitors internal organs and conditions.
ii. The pituitary is connected to the hypothalamus by a stalk.
a. The posterior lobe consists of nervous tissue and releases two neurohormones
made in the hypothalamus.
b. The anterior lobe consists of glandular tissue and secretes six hormones and
controls the release of hormones from other endocrine glands.
1. Posterior Lobe Hormones
i. Neuron cell bodies in the hypothalamus produce antidiuretic hormone (ADH) and oxytocin, which
are released from axon endings in the capillary bed of the posterior lobe.
ii. ADH acts on the walls of kidney tubules to control the body’s water and solute levels by stimulating
reabsorption.
iii. Oxytocin triggers uterine muscle contractions to expel the fetus and acts on mammary glands to
release milk.
1. Anterior Lobe Hormones
i. The anterior lobe releases six hormones that stimulate ("tropic") other glands and cells:
a. Corticotropin (ACTH) stimulates the adrenal cortex.
b. Thyrotropin (TSH) stimulates the thyroid gland.
c. Follicle-stimulating hormone (FSH) causes ovarian follicles to develop and
produce an egg.
d. Luteinizing hormone (LH) also acts on the ovary to release an egg.
e. Prolactin (PRL) acts on the mammary glands to stimulate and sustain milk
production.
f. Somatotropin (STH), also known as growth hormone (GH), acts on body cells in
general to promote growth.
ii. The hypothalamus produces releasing and inhibiting hormones that target the anterior pituitary.
H. Examples of Abnormal Pituitary Output
1. Gigantism results from an oversecretion of growth hormone in childhood.
1. Pituitary dwarfism results from an undersecretion of GH.
1. Acromegaly is a condition resulting from an oversecretion of GH in adulthood.
I. Sources and Effects of other Hormones
1. Hormones often interact with one another as described in section I.B.3.
1. Many hormones are linked to the neuroendocrine control center by homeostatic feedback loops.
1. The response of target cells depends on the number of their receptors and the concentration of the hormone.
J. Feedback Control of Hormone Activity--Some Examples
1. Negative Feedback from the Adrenal Cortex
i. One adrenal gland is located on top of each kidney.
ii. Among the secretions of the outer portion are the glucocorticoids such as cortisol, which helps
control blood glucose levels and suppresses inflammatory response.
a. Cortisol promotes gluconeogenesis--glucose from
amino acids--and dampens the uptake of glucose from
the blood.
b. Cortisol secretion is an example of negative feedback
loop.
c. When the body is stressed, as in painful injury, the
nervous system provides an override mechanism in
which the levels of cortisol remain high to promote
healing.
2. Mineralcorticoids regulate the concentrations of minerals such as K and Na.
a. Aldosterone acts on the distal tubules of the nephrons to stimulate Na reabsorption
and in turn water uptake
b. In Addison's disease the cortex fails to secrete sufficient gluco-and
mineralcorticoids resulting in glucose and mineral imbalances.
c. The adrenal cortex also secretes sex hormones, especially in the fetus and puberty.
1. Local Feedback in the Adrenal Medulla
i. The inner part of the adrenal gland secretes epinephrine and norepinephrine under direction from
sympathetic nerves from the hypothalamus.
ii. Its secretions mobilize the body's blood circulation and glucose metabolism during times of
excitement or stress ("fight-or-flight" response).
1. Cases of Skewed Feedback from the Thyroid
i. The thyroid gland is located at the base of the neck in front of the trachea.
a.
2.
Two of its hormones, thyroxine and triiodothyronine,
influence metabolic rates, growth, and development;
another, calcitonin, lowers the level of calcium in the
blood.
b. If the blood levels of iodine are too low, the pituitary
responds with too much TSH causing the thyroid gland
to enlarge abnormally in what we call a goiter.
Thyroid disorders include the following:
a. Hypothyroidism in adults results in lethargy and weight
gain; in infants, retardation and dwarfism can result
(cretinism).
b. Hyperthyroidism increases heart rate and blood
pressure and causes weight loss; Graves' disease, an
autoimmune disorder, is an example.
K. Hormone Responses to Local Chemical Changes
1. Secretions from Parathyroid Glands
i. The four parathyroid glands are embedded in the thyroid gland and respond to the changing levels
of calcium in the blood.
1. A drop in calcium level causes parathyroid hormone (PTH) levels to rise, resulting in
removal of calcium from bone and an activation of vitamin D (to help in calcium
absorption from the gut).
2. When calcium levels rise, the PTH levels are reduced.
ii. In vitamin D deficiency not enough calcium and phosphorus are absorbed; bones develop
improperly (rickets).
1. Secretions from Pancreatic Islets
i. Three types of cell secrete hormones:
1. Alpha cells secrete glucagon, which causes glycogen stored in the liver to be converted to
glucose, which then enters the bloodstream.
2. Beta cells secrete insulin, which stimulates the uptake of glucose by liver, muscle, and
adipose to reduce levels in the blood, especially after a meal.
3. Delta cells secrete somatostatin, which can inhibit the secretion of glucagon and insulin.
ii. Diabetes mellitus is a disease resulting from imbalances of insulin; its effects include weight loss,
ketone production, water-solute problems, metabolic acidosis and possible death.
1. In type 1 diabetes, the insulin is no longer produced because the beta cells have been
destroyed by an autoimmune response; treatment is by insulin injection.
2. In type 2 diabetes, the insulin levels are near normal but the target cells cannot respond to
the hormone; controlling diet is an effective treatment.
L. Some Final Examples of Integration and Control
1. Melatonin from the Pineal Gland
i. Located in the brain, this gland is a modification of a primitive "third eye" and is sensitive to light
and seasonal influences.
ii. In the absence of light, melatonin is secreted; thus in winter, high levels of the hormone are
instrumental in suppressing reproductive activity in hibernating animals.
iii. Decreased melatonin secretion in humans might help trigger the onset of puberty.
1. Hormones From the Heart, GI Tract, and Elsewhere
i. Atrial natriuretic peptide (ANP) from the heart atria regulates blood pressure.
ii. Gastrin and secretin from the GI tract stimulate release of stomach and intestinal secretions.
iii. The thymus, located behind the breastbone, serves as a place for certain lymphocytes to multiply
and mature; it also secretes groups of hormones called thymosins, which affect the functioning of
lymphocytes that defend the body against disease.
1. Prostaglandins
i. More than sixteen prostaglandins have been identified in tissues throughout the body.
1. When stimulated by epinephrine and norepinephrine, prostaglandins cause smooth muscles
in blood vessels to constrict or dilate.
2. Allergic responses to dust and pollen may be aggravated by prostaglandin effects on
airways in the lungs.
ii. Prostaglandins have major effects on menstruation and corpus luteum function.
1. Growth Factors
i. Epidermal growth factor (EGF) influences the growth of many cell types.
ii. Nerve growth factor (NGF) promotes growth and survival of neurons in the developing embryo.
1.
Pheromones Revisited
i. Pheromones are released to the outside of the body by several animals to serve as sex attractants,
territory markers, and communication signals.
ii. Recent studies suggest that humans also produce pheromones during sexual encounters