Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
225 Cards in this Set
- Front
- Back
What is the endocrine system?
|
It acts as a means of internal communication, coordinating the activities of the organ systems
|
|
What do the endocrine glands do?
|
They synthesize and secrete chemical substances called hormones directly into the circulatory system
|
|
What do exocrine glands do?
|
They secrete substances that are transported by ducts
|
|
What do hormones do?
|
They regulate the function of target organs or tissues
|
|
What are the glands that synthesize and or secrete hormones?
|
The pituitary, hypothalamus, thyroid, parathyroids, adrenals, pancreas, testes, ovaries, pineal, kidneys, gastrointestinal glands, heart, and thymus
|
|
Do all hormones regulate a single type of cell or organ?
|
No, some do, while others have more widespread actions
|
|
What is the specificity of hormonal action determined by?
|
The presence of specific receptors on or in the target cells
|
|
What is the pituitary gland?
|
It is a small tri-lobed gland lying at the base of the brain
|
|
How many lobes does it have?
|
2, the anterior and posterior
|
|
Do they do the same thing?
|
Do they do the same thing?
|
|
What does the anterior pituitary do?
|
It synthesizes both direct hormones, which directly stimulate their target organs, and tropic hormones, which stimulate other endocrine glands to release hormones
|
|
What re the hormonal secretions of the anterior pituitary regulated by?
|
The hypothalamic secretions called releasing/inhibiting hormones or factors
|
|
What does growth hormone do?
|
Growth hormone promotes bone and muscle growth, inhibits the uptake of glucose by certain cells, and stimulates the breakdown of fatty acid, thus conserving glucose
|
|
What is GH secretion stimulated by?
|
The hypothalamic releasing hormone GHRH
|
|
What is GH secretion inhibited by?
|
Somatostatin
|
|
What other control is secretion under?
|
Neural and metabolic control
|
|
In children, what can GH deficiency lead to?
|
Stunted growth (dwarfism)
|
|
What does overproduction of GH lead to in children?
|
Gigantism
|
|
What does overproduction of GH in adults cause?
|
Acromegaly, a disorder characterized by a disproportionate overgrowth of bone, localized especially in the skull, jaw, feet, and hands
|
|
What is prolactin?
|
A hormone that stimulates milk production and secretion in female mammary glands
|
|
What are endorphins?
|
They inhibit the perception of pain
|
|
What is Adrenocorticotropic hormone (ACTH)?
|
ACTH stimulates the adrenal cortex to synthesize and secrete glucocorticoids
|
|
What is ACTH regulated by?
|
The release of the hormone corticotrophin releasing factor (CRF)
|
|
What does thyroid stimulating hormone (TSH) do?
|
It stimulates the thyroid gland to absorb iodine and then synthesize and release thyroid hormone
|
|
What is TSH regulated by?
|
It is regulated by releasing the hormone thyroid regulating hormone (TRH)
|
|
What is luteinizing hormone (LH)?
|
n females, LH stimulates ovulation and formation of the corpus luteum
|
|
What does it do in males?
|
It stimulates the interstitial cells of the testes to synthesize testosterone
|
|
What is LH regulated by?
|
Estrogen, progesterone, and gonadotropin releasing hormone (GnRH)
|
|
What is follicle-stimulating hormone (FSH)?
|
In females, FSH causes maturation of ovarian follicles
|
|
What does it do in males?
|
It stimulates the maturation of the seminiferous tubules and sperm production
|
|
What is FSH regulated by?
|
Estrogen and by GnRH
|
|
What does the posterior pituitary do?
|
It does not synthesize hormones
|
|
Where are oxytocin and ADH made
|
They are produced by neurosecretory cells of the hypothalamus
|
|
What is hormone secretion stimulated by?
|
Action potential descending from the hypothalamus
|
|
What is oxytocin?
|
It is secreted after childbirth. It is secreted and induced by suckling
|
|
What does it stimulate?
|
It stimulates milk secretion in mammary glands
|
|
What is Antidiuretic Hormone (ADH, vasopressin)?
|
ADH increases the permeability of the nephron’s collecting duct to water
|
|
What does this do?
|
It promotes water reabsorption and increases blood volume
|
|
When is ADH secreted?
|
When plasma osmolarity increases
|
|
How is plasma osmolarity sensed?
|
By osmoreceptors in the hypothalamus
|
|
How else is it sensed?
|
When blood volume decreases, baroreceptors sense it in the circulatory system
|
|
What is the hypothalamus?
|
It is part of the forebrain and is located directly above the pituitary gland
|
|
What does it do?
|
It receives neural transmissions from other parts of the brain and from peripheral nerves
|
|
What do the transmissions trigger?
|
They trigger specific responses from the neurosecretory cells
|
|
What do neurosecretory cells regulate?
|
They regulate pituitary gland secretions via negative feedback mechanisms and through the actions of inhibiting and releasing hormones
|
|
What are hypothalamic releasing hormones?
|
They are hormones that stimulate or inhibit the secretions of the anterior pituitary
|
|
What is an example?
|
GnRH stimulates the anterior pituitary to secrete FSH and LH
|
|
Where are releasing hormones secreted into?
|
The hypothalamic-hypophyseal portal system
|
|
What happens in this circulatory pathway?
|
Blood from the capillary bed in the hypothalamus flows through a portal vein into the anterior pituitary, where it diverges into a second capillary network
|
|
What does this accomplish?
|
It allows the release of hormones to immediately reach the anterior pituitary
|
|
What does oversecretion of hormones do?
|
It is potentially harmful to an organism
|
|
What stops it from occurring?
|
A preventative mechanism called negative feedback has evolved
|
|
How does it work for hormones?
|
A high hormone level inhibits further production of that hormone
|
|
What is an example of this?
|
When plasma levels of adrenal cortical hormones reach a critical level, the hormones themselves exert an inhibitory effect on the pituitary and on the hypothalamus
|
|
What does this do?
|
It inhibits CRF and ACTH release
|
|
What happens in the absence of CRF?
|
The anterior pituitary stops ACTH secretion, and the adrenal cortex stops secreting adrenal cortical hormones
|
|
What happens when adrenal hormone levels are too low?
|
The hypothalamus is stimulated to release CRF
|
|
What does this stimulate?
|
It stimulates the anterior pituitary to secrete ACTH, which in turn, stimulates the adrenal cortex to release adrenal cortical hormones
|
|
How do neurosecretory cells in the hypothalamus work
|
They synthesize both oxytocin and ADH and transport them via their axons into the posterior pituitary for storage and secretion
|
|
What is the thyroid gland?
|
It is a bi-lobed structure located on the ventral surface of the trachea
|
|
What does it do?
|
It produces and secretes thyroxine, triiodothyronine (the thyroid hormones), and calcitonin
|
|
What are thyroxine and triiodothyronine?
|
They are derived from the iodination of the amino acid tyrosine they are necessary for growth an neurological development in children
|
|
What do they do?
|
They stimulate the rate of cellular respiration and the rate of protein and fatty acid synthesis and degradation in many tissues
|
|
What do high plasma levels of thyroid do?
|
They inhibit TRH and TSH secretion, thereby returning plasma levels to normal
|
|
What does inflammation of the thyroid or iodine deficiency cause?
|
Hypothyroidism
|
|
What is that?
|
It is when thyroid hormones are undersecreted or not secreted at all
|
|
What are common symptoms?
|
Slowed heart rate and respiratory rate, fatigue, cold intolerance, and weight gain
|
|
What is hypothyroidism in newborn infants called?
|
Cretinism
|
|
What is it characterized by?
|
Mental retardation and short stature
|
|
What is hyperthyroidism?
|
The thyroid is overstimulated, resulting in the oversecretion of thyroid hormones
|
|
What are symptoms of it?
|
Increased metabolic rate, feelings of excessive warmth, profuse sweating, palpitations, weight loss, and protruding eyes
|
|
What happens to the thyroid in both disorders?
|
It often enlarges, forming a bulge in the neck called a goiter
|
|
What does calcitonin do?
|
It decreases plasma Ca2+ concentration by inhibiting the release of Ca2+ from the bone
|
|
What is its secretion regulated by?
|
Plasma Ca2+ levels
|
|
What are the parathyroid glands?
|
They are four small pea-shaped structures embedded in the posterior surface of the thyroid
|
|
What do they do?
|
They synthesize and secrete parathyroid hormone (PTH), which together with calcitonin and vitamin D, regulates plasma Ca2+ concentration
|
|
What does plasma Ca2+ concentration regulate?
|
It regulates PTH secretion by means of negative feedback
|
|
What does PTH do to Ca2+?
|
It raises the Ca2+ concentration in the blood by stimulating Ca2+ release from the bone and decreasing Ca2+ excretion in the kidneys
|
|
What does PTH convert Vitamin D into?
|
It converts it into its active form, which stimulates intestinal calcium absorption
|
|
What are the adrenal glands?
|
They are situated on top of the kidneys and consist of the adrenal cortex and the adrenal medulla
|
|
What does ACTH stimulate the adrenal cortex to do in response to stress?
|
It stimulates it to synthesize and secrete steroid hormones, which are collectively known as corticosteroids
|
|
What are corticosteroids?
|
They are derived from cholesterol, and they include glucocorticoids, mineralcorticoids, and cortical sex hormones
|
|
What are glucocorticoids?
|
They are involved in glucose regulation and protein metabolism.
|
|
What are some examples?
|
Cortisol and cortisone
|
|
What do they do to glucose?
|
They raise blood glucose levels by promoting gluconeogenesis and decrease protein synthesis
|
|
What do they do to the body’s immune system?
|
What do they do to the body’s immune system?
|
|
What is Cortisol secretion governed by?
|
Negative feedback
|
|
What are mineralcorticoids?
|
They regulate plasma levels of sodium and potassium, and ultimately the total extracellular water volume
|
|
What is an example of a mineralcorticoid?
|
Aldosterone
|
|
What does aldosterone do?
|
It causes the active reabsorption of sodium and the passive reabsorption of water in the nephron
|
|
What does this result in?
|
A rise in blood volume and blood pressure
|
|
What does aldosterone stimulate?
|
It stimulates the secretion of potassium ion and hydrogen ion into the nephron and their subsequent excretion in urine
|
|
What is aldosterone secretion regulated by?
|
The rennin-angiotensin system
|
|
How does it work?
|
When blood volume falls, the juxtaglomerular cells of the kidney produce rennin, an enzyme that converts the plasma protein angiotensinogen to angiotensin I
|
|
What happens to angiotensin I?
|
It is converted to angiotensin II, which stimulates the adrenal cortex to secrete aldosterone
|
|
What does aldosterone help to do?
|
It helps to restore blood volume by increasing sodium reabsorption at the kidney
|
|
This leads to what?
|
An increase in water reabsorption
|
|
What does this remove?
|
The initial stimulus for rennin production
|
|
What are cortical sex hormones?
|
The adrenal cortex secretes small quantities of androgens (male sex hormones) in both males and females
|
|
In males, where are most androgens produced?
|
In the testes
|
|
What does this mean?
|
The physiological effect of adrenal androgens is quite small
|
|
In females however, what does this do?
|
Overproduction of the adrenal androgens may have masculinizing effects, such as excessive facial hair
|
|
What can the secretory cells of the adrenal medulla be viewed as?
|
Specialized sympathetic nerve cells that secrete hormones into the circulatory system
|
|
What does the adrenal medulla produce?
|
Epinephrine and norepinephrine
|
|
What do they belong to?
|
A class of amino acid-derived compounds called catecholamines
|
|
What does epinephrine cause?
|
An increased conversion of glycogen to glucose in the liver and muscle tissue
|
|
What does this to do glucose levels in the blood?
|
It causes them to rise
|
|
What does this result in?
|
An increased basal metabolic rate
|
|
What do epinephrine and norepinephrine do to the heart?
|
They both increase the rate and strength of the heartbeat
|
|
What do they do to blood vessels?
|
They dilate and constrict blood vessels in such a way as to increase the blood supply to skeletal muscle, the heart, and the brain, while decreasing the blood supply to the kidneys, skin, and digestive tract
|
|
What are these effects known as?
|
The fight or flight response
|
|
What are they elicited by?
|
The sympathetic nervous stimulation in response to stress
|
|
Are these hormones neurotransmitters?
|
Yes
|
|
What is the pancreas?
|
It is both an exocrine and endocrine organ
|
|
What is the exocrine function?
|
The exocrine function is performed by cells that secrete digestive enzymes into the small intestine via a series of ducts
|
|
What is the endocrine function performed by?
|
Small glandular structures called the islets of Langerhans
|
|
What are they composed of?
|
Alpha, beta, and delta cells
|
|
What do alpha cells produce?
|
They secrete glucagons
|
|
What do beta cells produce?
|
They produce and secrete insulin
|
|
What do delta cells produce and secrete?
|
Somatostatin
|
|
What does glucagons do?
|
It stimulates protein and fat degradation, the conversion of glycogen to glucose, and gluconeogenesis
|
|
What do they serve to do?
|
They serve to increase blood glucose levels
|
|
What is glucagons secretion stimulated by?
|
It is stimulated by a decrease in blood glucose and by gastrointestinal hormones, CCK and gastrin
|
|
What is it inhibited by?
|
It is inhibited by high plasma glucose levels
|
|
What are glucagon’s actions in relations to those of insulin?
|
They are largely antagonistic
|
|
What is insulin?
|
It is a protein hormone secreted in response to a high blood glucose concentration
|
|
What does it do?
|
It stimulates the uptake of glucose by muscle and adipose cells and the storage of glucose as glycogen in muscle and liver cells, thus lowering blood glucose levels
|
|
What else does it stimulate?
|
It stimulates the synthesis of fats from glucose and the uptake of amino acids
|
|
What is insulin secretion regulated by?
|
Blood glucose levels
|
|
What does overproduction of insulin cause?
|
Hypoglycemia (low blood glucose levels)
|
|
What does underproduction of insulin or insensitivity to insulin lead to?
|
Diabetes mellitus
|
|
What is that?
|
It is characterized by hyperglycemia (high blood glucose levels)
|
|
What do high blood glucose levels lead to?
|
Excretion of glucose and water loss
|
|
What else is diabetes associated with?
|
Weakness and fatigue
|
|
What may it lead to?
|
Ketoacidosis, which is a dangerous lowering of the blood pH due to excess keto acids and fatty acids in the plasma
|
|
What is somatostatin?
|
Pancreatic somatostatin secretion is increased by high blood glucose or high amino acid levels, leading to both decreased insulin and glucagons secretion
|
|
What is somastatin regulated by?
|
CCK and GH levels
|
|
What do the interstitial cells produce?
|
They produce and secrete androgens
|
|
What does testosterone induce?
|
It induces embryonic sexual differentiation and male sexual development at puberty
|
|
What does it maintain?
|
Secondary sex characteristic
|
|
What is testosterone secretion controlled by?
|
A negative feedback mechanism involving FSH and LH
|
|
What is insensitivity to testosterone result in?
|
A syndrome called testicular feminization, in which a genetic male has female secondary sexual characteristics
|
|
What do the ovaries do?
|
They synthesize and secrete estrogens and progesterone
|
|
What is the secretion of both estrogens and progesterone regulated by?
|
LH and FSH, which in turn are regulated by GnRH
|
|
What are estrogens?
|
They are steroid hormones necessary for normal female maturation
|
|
What do they stimulate?
|
They stimulate the development of female reproductive tract and contribute to the development of secondary sexual characteristics and sex drive
|
|
What are estrogens responsible for thickening?
|
The endometrium
|
|
What are estrogens secreted by?
|
Ovarian follicles and the corpus luteum
|
|
What is progesterone?
|
It is a steroid hormone secreted by the corpus luteum during the luteal phase of the menstrual cycle
|
|
What does progesterone stimulate?
|
The development and maintenance of the endometrial walls in preparation for implantation
|
|
What is the menstrual cycle?
|
It is a monthly cyclical pattern resulting from interactions between hormones
|
|
What can the menstrual cycle be divided into?
|
The follicular phase, ovulation, the luteal phase, and menstruation
|
|
What is the follicular phase?
|
It begins with the cessation of the menstrual flow from the previous cycle
|
|
During this phase, what hormones act together?
|
FSH and LH act together to promote the development of several ovarian follicles, which grow and begin secreting estrogen
|
|
What do rising levels of estrogen in the latter half of this phase stimulate?
|
GnRH secretion, which in turn further stimulates LH secretion
|
|
What is ovulation?
|
Midway through the cycle, it occurs- a mature ovarian follicle bursts and releases an ovum
|
|
What is ovulation caused by?
|
It is caused by the surge in LH which is preceded, and in part caused, by a peak in estrogen levels
|
|
What is the luteal phase?
|
LH induces the ruptured follicle to develop into the corpus luteum, which secretes estrogen and progesterone
|
|
What does the progesterone do?
|
It causes the glands of the endometrium to mature and produce secretions that prepare it for the implantation of an embryo
|
|
What are progesterone and estrogen essential for?
|
The maintenance of the endometrium
|
|
What do they together inhibit?
|
They inhibit secretion of GnRH
|
|
What does that ultimately stop?
|
It inhibits LH and FSH secretion
|
|
What does this prevent?
|
It prevents the maturation of additional follicles during the remainder of the cycle
|
|
What is menstruation?
|
It is what occurs if the ovum is not fertilized
|
|
What occurs?
|
The corpus luteum atrophies
|
|
What happens next?
|
The resulting drop in progesterone and estrogen levels causes the endometrium to slough off
|
|
What does this give rise to?
|
The flow
|
|
What happens to hormone levels from here?
|
Progesterone and estrogen levels decline and GnRH is no longer inhibited
|
|
What does GnRH do?
|
It restimulates LH and FSH secretion, and so the cycle begins anew
|
|
What happens during the first trimester of pregnancy?
|
The corpus luteum is preserved by human chorionic gonadotropin, HCG
|
|
What is HCG?
|
A hormone produced by the blastocyst and the developing placenta
|
|
What does this mean for Progesterone and Estrogen?
|
It means their levels of secretion by the corpus luteum are maintained during the first trimester
|
|
What happens during the second trimester?
|
HCG levels decline, but progesterone and estrogen levels rise
|
|
How come?
|
Because they are now secreted by the placenta itself
|
|
What do high levels of progesterone and estrogen do?
|
They inhibit GnRH secretion
|
|
What does this prevent?
|
FSH and LH secretion and the onset of a new menstrual cycle
|
|
What is menopause?
|
t is the period in a woman’s life, between 45-55, when menstruation first becomes irregular, and eventually stops
|
|
What is it the result of?
|
It results from the progressive decline in the functioning of the ovaries with advancing age
|
|
What happens?
|
Some follicles fail to rupture, ovulation does not occur, and less estrogen is produced by the ovaries, thereby disrupting the hormonal regulation of other glands
|
|
What symptoms do woman have during menopause?
|
Bloating, hot flashes, and headaches
|
|
What is HCG?
|
A hormone produced by the blastocyst and the developing placenta
|
|
What does this mean for Progesterone and Estrogen?
|
It means their levels of secretion by the corpus luteum are maintained during the first trimester
|
|
What happens during the second trimester?
|
HCG levels decline, but progesterone and estrogen levels rise
|
|
How come?
|
Because they are now secreted by the placenta itself
|
|
What do high levels of progesterone and estrogen do?
|
They inhibit GnRH secretion
|
|
What does this prevent?
|
FSH and LH secretion and the onset of a new menstrual cycle
|
|
What is menopause?
|
t is the period in a woman’s life, between 45-55, when menstruation first becomes irregular, and eventually stops
|
|
What is it the result of?
|
It results from the progressive decline in the functioning of the ovaries with advancing age
|
|
What happens?
|
Some follicles fail to rupture, ovulation does not occur, and less estrogen is produced by the ovaries, thereby disrupting the hormonal regulation of other glands
|
|
What symptoms do woman have during menopause?
|
Bloating, hot flashes, and headaches
|
|
What is the pineal gland?
|
It is a tiny structure at the base of the brain that secretes the hormone melatonin
|
|
What is melatonin’s purpose?
|
It role in humans in unclear, but it is believed to play a role in the regulation of circadian rhythms
|
|
What are those?
|
They are the physiological cycles lasting 24 hours
|
|
What is melatonin secretion regulated by?
|
Light and dark cycles in the environment
|
|
What does glandular tissue found in the mucosa of the stomach and intestines do?
|
The primary stimulus for gastrointestinal hormone release is the presence of food in the gut, though neural input and exposure to other hormones also affect their release
|
|
How many gastrointestinal peptides have been isolated?
|
Over 20
|
|
What are some important examples?
|
Gastrin, secretin, and CCK
|
|
What does Renin, an enzyme secreted by the kidney do
|
It is involved in the regulation of aldosterone secretion
|
|
What is erythropoietin?
|
It is secreted by the kidney in response to decreased renal oxygen levels and stimulates bone marrow to produce red blood cells
|
|
How is the heart an endocrine gland?
|
It releases atrial natriuretic hormone
|
|
What does that do?
|
It is involved in the regulation of salt and water balance
|
|
What is the thymus gland?
|
It is located in the front of the neck region and secretes hormones such as thymosin during childhood
|
|
What does thymosin do?
|
It stimulates T lymphocyte development and differentiation
|
|
What happens to the thymus by adulthood?
|
It atrophies, after the immune system has fully developed
|
|
How are hormones classified?
|
By the basis of their chemical structure
|
|
How many groups are there?
|
3
|
|
What are they?
|
Peptide hormones, steroid hormones, and amino acid-derived hormones
|
|
What are the two ways in which hormones affect the activities of their target cells?
|
Via extracellular receptors or intracellular receptors
|
|
What are peptides?
|
They range from simple short peptides (amino acid chains) such as ADH, to complex polypeptides such as insulin
|
|
How does synthesis of peptide hormones begin?
|
With the synthesis of a large polypeptide
|
|
What happens to the polypeptide?
|
It is cleaved into smaller protein units and transported to the Golgi apparatus, where it is further modified into the active hormone
|
|
How is the hormone packaged?
|
It is packaged into secretory vesicles and stored until it is released by the cell via exocytosis
|
|
How do peptide hormones act as messengers?
|
They are first messengers
|
|
What does that mean?
|
It means they bind to specific receptors on the surface of their target cells, triggering a series of enzymatic reactions within the each cell
|
|
What is usually the first reaction?
|
The conversion of ATP to cAMP
|
|
What is this reaction catalyzed by?
|
The membrane-bound enzyme adenylate cyclase
|
|
How does Cyclic AMP act?
|
It acts as a second messenger
|
|
What does this mean?
|
It relays messages from the extracellular peptide hormone to cytoplasmic enzymes, initiating a series of successive reactions within the cell
|
|
What happens to the hormone’s effects with each step?
|
They are amplified
|
|
How is cyclic AMP activity inactivated?
|
By the cytoplasmic enzyme phosphodiesterase
|
|
What are amino acid derivatives?
|
They are hormones composed of one or two modified amino acids
|
|
Where are they synthesized?
|
In the cytoplasm of glandular cells
|
|
Are any modified further?
|
Some are further modified and stored in granules until the cell is stimulated to release them, while others are initially synthesized as component parts of larger molecules and stored
|
|
How do some work?
|
Some, like epinephrine, activate their target cells as peptide hormones do, via second messengers
|
|
What about the others?
|
Others, like thyroxine, act in the same manner as steroid hormones, entering the nucleus of their target cells and regulating gene expression
|