Chapter 17: Endocrine Flashcards
What are the 4 principal mechanisms of communication between cells?
1) Gap junctions
2) Neurotransmitters
3) Paracrines
4) Hormones
Define gap junctions
Allow molecules, nutrients, and electrolytes to move from cell to cell
Neurotransmitters are released from ________ neurons to ______ neurons
presynaptic; postsynaptic
Define paracrines
Secreted into tissue fluids to affect nearby cells
Define hormones
Chemical messengers that travel in the bloodstream to other tissues and organs
Define endocrine system and endocrinology
-The endocrine system is the glands, tissues, and cells that secrete hormones
-Endocrinology is the study of this system and the diagnosis and treatment of its disorders
What type of glands have ducts, and which don’t?
Exocrine glands have ducts, endocrine glands don’t
Describe exocrine and endocrine glands
1) Exocrine glands
-Have ducts to epithelial surface or mucosa
-“External secretions” with extracellular effects (food digestion)
2) Endocrine glands
-No ducts
-Contain dense, fenestrated capillary networks for easy uptake of hormones into bloodstream
-“Internal secretions” with intracellular effects such as altering target cell metabolism
What contains dense, fenestrated capillary networks for easy uptake of hormones into bloodstream?
Endocrine glands
What do the nervous and endocrine systems have in common?
Both systems serve for internal communication
Describe the difference in speed and persistence of response between the nervous and endocrine systems
Nervous: reacts quickly (ms timescale), stops quickly
Endocrine: reacts slowly (seconds or days), effect may continue for days or longer
Describe the difference in adaptation to long-term stimuli between the nervous and endocrine systems
Nervous: response declines (adapts quickly)
Endocrine: response persists (adapts slowly)
Describe the differences in areas of affect in the nervous and endocrine systems
Nervous: targeted and specific (one organ)
Endocrine: general, widespread effects (many organs)
Several chemicals function as both hormones and neurotransmitters; give 3 examples
Norepinephrine, dopamine, and antidiuretic hormone
Give an example of the nervous and endocrine systems having a similar effect on target cells
Norepinephrine and glucagon both cause glycogen hydrolysis in liver
Describe how the nervous and endocrine systems can regulate each other
Neurotransmitters can affect glands, and hormones can affect neurons
_________ cells share characteristics with both the nervous and endocrine systems
Neuroendocrine
What do both the nervous and endocrine systems require?
Both systems require receptors
Describe what part of the nervous system requires receptors and what part of the endocrine system requires receptors
1) Nervous system: Postsynaptic neuron requires receptors
2) Endocrine system: Target organs or cells must have receptors for a particular hormone; some target cells possess enzymes that convert a circulating hormone to its more active form
What forms the floor and walls of third ventricle of brain?
The hypothalamus
What does the hypothalamus do?
Regulates primitive functions: water balance, thermoregulation, sex drive, childbirth, etc.
The pituitary gland is suspended from __________ by a stalk called the infundibulum
hypothalamus
Describe the two parts of the pituitary gland
Adenohypophysis (anterior pituitary)
Neurohypophysis (posterior pituitary)
True or false: The anterior and posterior pituitary have independent origins and separate functions
True
Describe the adenohypophysis (anterior lobe) of the pituitary gland (what is it linked to, and what hormones regulate it?)
-Constitutes anterior three-quarters of pituitary
-Linked to hypothalamus by hypophyseal portal system
-Hypothalamic hormones regulate adenohypophysis cells (6 hormones): 4 releasing hormones and 2 inhibiting hormones
Name at least 3 examples of hypothalamic hormones
1) Prolactin-inhibiting hormone
2) Growth hormone-releasing hormone
3) Somatostatin
4) Gonadotropin-releasing hormone
5) Thyrotropin-releasing hormone
6) Corticotropin-releasing hormone
Name at least 3 examples of anterior lobe hormones
1) Prolactin
2) Growth hormone
3) Follicle-stimulating hormone
4) Luteinizing hormone
5) Thyroid-stimulating hormone (thyrotropin)
6) Adrenocorticotropic hormone
Define and describe the neurohypophysis (posterior lobe) of the pituitary gland
Definition: Neurohypophysis (posterior lobe) constitutes the posterior one-quarter of the pituitary
-Nerve tissue, not a true gland
-Nerve cell bodies in hypothalamus pass down the stalk as hypothalamo–hypophyseal tract and end in posterior lobe
-Hormones produced by cell bodies transported and stored in axon terminals in neurohypophysis
Nerve cell bodies in hypothalamus pass down the stalk as _______________ tract and end in _______ lobe of the pituitary gland
hypothalamo–hypophyseal; posterior
What two hormones are stored in the posterior pituitary?
Oxytocin and antidiuretic hormone (ADH)
How many hormones are produced by the hypothalamus, and what do they do (two groups)?
1) Eight hormones produced in hypothalamus
2) Six regulate the anterior pituitary, two are released into capillaries in the posterior pituitary
Describe the hypothalamic hormones that regulate the anterior pituitary
-Six releasing and inhibiting hormones stimulate or inhibit the anterior pituitary
-TRH, CRH, GnRH, and GHRH are releasing hormones that promote anterior pituitary secretion of TSH, PRL, ACTH, FSH, LH, and GH
-PIH inhibits secretion of prolactin, and somatostatin inhibits secretion growth hormone and thyroid-stimulating hormone by the anterior pituitary
Name 4 hypothalamic releasing hormones that promote anterior pituitary secretion of TSH, PRL, ACTH, FSH, LH, and GH
TRH, CRH, GnRH, and GHRH
List the 6 hypothalamic hormones that regulate the anterior pituitary
1) TRH
2) CRH
3) GnRH
4) GHRH
5) PIH inhibits secretion of prolactin
6) Somatostatin
What gland produces PIH, what organ does it target, and what does it do?
-Produced by hypothalamus
-Targets anterior pituitary
-It inhibits secretion of prolactin
What does somatostatin do?
Inhibits the secretion of growth hormone and thyroid-stimulating hormone by the anterior pituitary
List the 6 hormones made by the anterior pituitary
1) Follicle-stimulating hormone (FSH)
2) Luteinizing hormone (LH)
3) Thyroid-stimulating hormone (TSH)
4) Adrenocorticotropic hormone (ACTH)
5) Prolactin (PRL)
6) Growth hormone (GH)
What are the two gonadotropin hormones that target gonads produced by the anterior pituitary?
1) Follicle-stimulating hormone (FSH)
2) Luteinizing hormone (LH)
What 3 things does follicle-stimulating hormone (FSH) do?
1) Stimulates secretion of ovarian sex hormones
2) Development of ovarian follicles
3) Sperm production
What 3 things does luteinizing hormone (LH) do?
1) Stimulates ovulation
2) Stimulates corpus luteum to secrete progesterone
3) Stimulates testes to secrete testosterone
What does thyroid-stimulating hormone (TSH) do?
Stimulates secretion of thyroid hormone
What does adrenocorticotropic hormone (ACTH) do?
Stimulates adrenal cortex to secrete glucocorticoids
What does prolactin (PRL) do?
After birth, stimulates mammary glands to synthesize milk
What does growth hormone (GH) do?
Stimulates mitosis and cellular differentiation
Name and describe the two main hypersecretion of growth hormone (GH) disorders
1) Acromegaly: Thickening of bones and soft tissues in adults, especially hands, feet, and face
2) Gigantism: In childhood or adolescence before growth plates close
Name and describe the disorder that is characterized by the hyposecretion of growth hormone
Pituitary dwarfism: rarely a problem since GH now made by genetically engineered bacteria
What two hormones are produced in hypothalamus and transported to the posterior lobe of pituitary?
1) ADH (antidiuretic hormone)
2) Oxytocin (OT)
Describe what two things ADH (antidiuretic hormone) does, and name the disorder associated with its hyposecretion
1) It increases water retention, thus reducing urine volume, and preventing dehydration
2) It is also called vasopressin because it can cause vasoconstriction
-Hyposecretion: Diabetes insipidus (chronic polyuria)
What 5 things does oxytocin (OT) do?
1) Stimulates labor contractions during childbirth
2) Stimulates flow of milk during lactation
3) May promote emotional bonding between lactating mother and infant
4) Surge of this hormone released during sexual arousal and orgasm
5) Promotes feelings of sexual satisfaction and emotional bonding between partners
True or false: The rates of pituitary secretion are consistent
False; rates of secretion are not constant
Describe how stress affects ACTH
It triggers the release of ACTH
Describe how pregnancy affects prolactin
It triggers prolactin secretion
Describe how osmoreceptors affect ADH
If they detect an increase in osmolarity they trigger release of ADH
Describe how infant suckling affects oxytocin
It triggers the release of oxytocin
Give 4 examples of hypothalamic and cerebral control
1) Stress: Triggers release of ACTH
2) Pregnancy: Triggers prolactin secretion
3) Osmoreceptors: If they detect an increase in osmolarity they trigger release of ADH
4) Infant suckling: Triggers release of oxytocin
Define negative feedback in the context of pituitary secretion
Increased target organ hormone levels inhibit the release of hypothalamic and/or pituitary hormones
Give an example of negative feedback in pituitary secretion
Thyroid hormone inhibits the release of TRH by the hypothalamus and the release of TSH by the anterior pituitary
Give an example of positive feedback in pituitary secretion
Stretching of the uterus increases OT (oxytocin) release, causes contractions, causing more stretching of uterus, etc. until delivery
After age __ the pineal gland undergoes involution (shrinkage); it loses __% of its size by the end of puberty
Age 7; 75%
What two glands undergo involution, and at what ages?
1) The pineal gland starting at age 7
2) The thymus starting after puberty
What does the pineal gland do?
-May play a role in circadian rhythms since it synthesizes melatonin during the night and fluctuates seasonally with changes in day length
-May influence timing of puberty
What synthesizes melationin at night?
Pineal gland
The thymus plays a role in what 3 organ systems?
Endocrine, lymphatic, and immune
Describe the location of the thymus and what it does
1) It’s a bilobed gland in the mediastinum superior to the heart
2) It’s the site of the maturation of T cells; important in immune defense
What 3 hormones are secreted by the thymus?
Thymopoietin, thymosin, and thymulin
What is the largest gland that is purely endocrine?
Thymus
What color is the thymus and what gives it its color?
It’s dark red due to its rich blood supply
Describe the anatomy of the thymus
-Bi-lobed: It’s composed of two lobes and an isthmus below the larynx.
-Thyroid follicles: sacs that make up most of thyroid that contain protein-rich colloid
Describe the thyroid follicles
-They’re sacs lined with simple cuboidal epithelial cells (follicular cells)
-They make up most of thyroid and contain protein-rich colloid.
The thyroid secretes ___________ and ____________ in response to TSH
thyroxine (T4) and triiodothyronine (T3)
When thyroxine (T4) and triiodothyronine (T3) in are secreted in response to TSH, what increases?
Increases:
1) Metabolic rate
2) O2 consumption
3) Heat production
4) Appetite
5) Growth hormone secretion
6) Alertness
7) Reflex speed
Parafollicular (C or clear) cells secrete ______________ with rising blood calcium
calcitonin
What secretes calcitonin, and what does it do?
-Secreted by the parafollicular (C or clear) cells of the thyroid
-It stimulates osteoblast activity and bone formation in children
Name 3 thyroid disorders
1) Grave’s disease (toxic goiter)
2) Congenital hypothyroidism (Cretinism)
3) Myxedema
Describe Grave’s disease (toxic goiter)
-The most common form of hyperthyroidism
-Occurs when autoantibodies mimic the effect of TSH on the thyroid (bind and activate TSH receptor), causing thyroid hypersecretion
Describe congenital hypothyroidism (Cretinism)
-Thyroid hyposecretion present at birth
-Treat with oral thyroid hormone
Describe myxedema (what is it and how is it treated?)
-Adult hypothyroidism
-Treat with oral thyroid hormone
How many parathyroid glands are there, and where are they?
-Usually four glands partially embedded in the posterior surface of thyroid gland
What do the parathyroid glands secrete?
Parathyroid hormone (PTH)
What does parathyroid hormone (PTH) do, and what 4 things does it trigger to accomplish this?
A) It increases blood Ca(2+) levels
B) It does this by:
1) Promoting synthesis of calcitriol
2) Increasing absorption of Ca^(2+) from digestive system
3) Decreasing urinary excretion
4) Increasing bone resorption
Name 2 parathyroid disorders
Hypoparathyroidism and hyperparathyroidism
How does hypoparathyroidism happen? What does it result in?
Happens due to surgical excision during thyroid surgery
Results in fatal tetany (spasms in larynx) in just a few days due to rapid decline in blood calcium level
Define and describe hyperparathyroidism (what is it due to, what 3 things does it result in?)
-Defined as excess PTH secretion
-Often due to a parathyroid tumor
-Result:
a) Bones become soft, fragile, and deformed
b) Ca^(2+) and phosphate blood levels increase
c) Promotes renal calculi formation
Define the adrenal medulla and what organ systems it’s a part of
-The inner core, 10% to 20% of adrenal gland
-It’s both an endocrine gland and a ganglion of the sympathetic nervous system
What is the adrenal medulla innervated by, what is it made out of, and what does it do when stimulated?
1) Innervated by sympathetic preganglionic fibers
2) Consists of modified sympathetic postganglionic neurons called chromaffin cells
3) When stimulated, it releases catecholamines (epinephrine and norepinephrine) directly into the bloodstream
What hormones are released by the adrenal medulla
Catecholamines (epinephrine and norepinephrine) are released directly into the bloodstream
When is the adrenal medulla activated, and what does it mobilize when activated?
-It increases alertness and prepares the body for physical activity
-It does this by mobilizing high-energy fuels, lactate, fatty acids, and glucose (glycogenolysis and gluconeogenesis by liver)
Describe how the adrenal medulla relates to glucose
It mobilizes glucose through glycogenolysis and gluconeogenesis by liver
What does epinephrine do before physical activity? Why?
-Epinephrine inhibits insulin secretion (glucose-sparing effect)
-This is because muscles use fatty acids, saving glucose for brain
What 5 things does the adrenal medulla increase, and what 2 things does it decrease?
Increases:
1) Blood pressure
2) Heart rate
3) Blood flow to muscles
4) Pulmonary airflow
5) Metabolic rate
Decreases:
1) Digestion
2) Urine production
Describe the mineralocorticoids of the adrenal cortex (what is the main mineralocorticoid, what do they do, and what are they a part of)
1) Primarily aldosterone
2) They stimulate Na^+ retention and K^+ excretion
-Water is retained with sodium by osmosis
-Blood volume and blood pressure are maintained
3) Part of the renin-angiotensin-aldosterone (RAA) system
Describe the glucocorticoids of the adrenal cortex (what is the main glucocorticoid, when are they released, and what do they do?)
1) Primarily cortisol
2) Release stimulated by ACTH
3) Effects:
-Stimulate fat and protein catabolism
-Gluconeogenesis
-Help body adapt to stress and repair tissues
-Anti-inflammatory effect becomes immune suppression with long-term use
Name the 2 sex steroids of the adrenal cortex and describe what they do
1) Androgens: set libido throughout life; large role in prenatal male development
2) Estradiol: important after menopause
What 3 things are released by the adrenal cortex?
1) Mineralocorticoids (primarily aldosterone)
2) Glucocorticoids (primarily cortisol)
3) Sex steroids (androgens and estradiol)
Name 3 adrenal disorders
1) Adrenogenital syndrome (AGS)
2) Cushing’s syndrome
3) Addison’s disease
What disorder is characterized by excess cortisol secretion, and what organ controls the release of cortisol?
Cushing syndrome; adrenal cortex
Define and describe the symptoms of cushing syndrome
-Defined as excess cortisol secretion
-Results in:
a) Hyperglycemia, hypertension, weakness, edema
b) Rapid muscle and bone loss due to protein catabolism
c) Abnormal fat deposition; moon face and buffalo hump
Define and describe the symptoms of adrenogenital syndrome (AGS)
1) Defined as adrenal androgen hypersecretion (accompanies Cushing)
2) Characterized by:
-Enlargement of external sexual organs in children and early onset of puberty
-Newborn girls exhibit masculinized genitalia
-Masculinizing effects on women
-Increased body hair, deeper voice, beard growth
Define and describe the symptoms of Addison’s disease
1) Defined as deficient cortisol and/or aldosterone
2) Characterized by:
Hypoglycemia
Hypotension
Weakness
Weight loss
Hyperpigmentation
What two things are secreted from the pancreatic islets, and what types of cells are they secreted from?
1) Glucagon: secreted by A or alpha (α) cells
2) Insulin: secreted by B or beta (β) cells
________: secreted by A or alpha (α) cells
________: secreted by B or beta (β) cells
Glucagon: secreted by A or alpha (α) cells
Insulin: secreted by B or beta (β) cells
Describe glucagon and what it stimulates
-Secreted by A or alpha (α) cells; released between meals when blood glucose falls
-In liver, stimulates gluconeogenesis & glycogenolysis and stimulates the lipolysis of adipose tissue
Describe insulin and what it stimulates
-Secreted by B or beta (β) cells during and after meal
-Promotes synthesis of glycogen, fat, and protein
>Brain, liver, kidneys, and RBCs absorb glucose without insulin, but other tissues require insulin
>Insufficiency or inaction is cause of diabetes insipidus (*)
What 4 things in the body don’t require insulin to absorb glucose?
Brain, liver, kidneys, and RBCs absorb glucose without insulin
What is the most prevalent metabolic disease in the world?
Diabetes mellitus
Define diabetes mellitus and its symptoms. What tests are done to indicate these symptoms?
1) Defined as the disruption of metabolism due to hyposecretion or inaction of insulin (insulin resistance)
2) Symptoms: Polyuria, polydipsia, and polyphagia
-Revealed by elevated blood glucose, glucose in urine, and ketones in the urine
Why does polyuria occur in diabetes mellitus?
-Polyuria (with thirst and dehydration) occurs because kidneys exhibit a transport maximum-limit to how fast the glucose transporters can work to reabsorb
-Excess glucose enters urine and water follows it
What are the two types of diabetes, and how common are they?
1) Type 1 diabetes mellitus (IDDM): 5% to 10% of cases in United States
2) Type 2 (NIDDM): 90% to 95% of diabetics
Describe what is used to treat type 1 diabetes mellitus and its causes
-Insulin is always used to treat type 1
-Hereditary susceptibility: if a susceptible individual is infected with certain viruses (rubella, cytomegalovirus), autoantibodies attack and destroy pancreatic beta cells
Describe the main problem, risk factors, and treatments of type 2 diabetes (diabetes insipidus)
1) The main problem is insulin insufficiency (**); the failure of target cells to respond to insulin
2) Risk factors are heredity, age (40+), obesity, and ethnicity (Native American, Hispanic, and Asian)
3) Treated with weight-loss program and exercise since:
-Loss of muscle mass causes difficulty with regulation of glycemia
-Adipose signals interfere with glucose uptake into most cells
3) If necessary, also use glycemia-lowering oral medications and, if still not enough, use insulin
Define hyperglycemic hormones and give examples (includes hormones from any gland)
-Defined as hormones that raise blood glucose concentration
-Glucagon, growth hormone, epinephrine, norepinephrine, and cortisol
Define hypoglycemic hormones and name the one hormone in this category
Hypoglycemic hormones lower blood glucose; insulin
Are ovaries and testes endocrine, exocrine, or both?
Ovaries and testes are both endocrine and exocrine
Name the endocrine and exocrine products of the ovaries and testes
Exocrine product (cytogenic glands): eggs and sperm
Endocrine product: gonadal hormones
Name the 3 ovarian hormones and the 4 testicular hormones
Ovarian hormones: Estrogen (Estradiol), progesterone, and inhibin
Testicular hormones: Testosterone, weaker androgens, estrogen, and inhibin
List the 3 general functions of estrogens and progesterone for females
1) Development of female reproductive system and physique including adolescent bone growth
2) Regulate menstrual cycle, sustain pregnancy
3) Prepare mammary glands for lactation
List the 2 general functions of testosterone for males
1) Stimulates development of male reproductive system in fetus and adolescence, and sex drive
2) Sustains sperm production
What suppresses FSH secretion from anterior pituitary in both sexes?
Inhibin
What does inhibin do?
Suppresses FSH secretion from anterior pituitary in both sexes
Describe an endocrine function of the skin
Keratinocytes produce cholecalciferol using UV from sun (first step in making vitamin D)
Describe two endocrine functions of the kidneys; name what two endocrine things they secrete and what their targets and actions are
1) Kidneys secrete erythropoietin
-Target: red bone marrow
-Action: stimulates production of RBC’s
2) Kidneys secrete renin
-Target: cortex of adrenal gland
-Action: stimulates production of aldosterone
Describe the endocrine function of the heart; name what endocrine thing it secretes and what its target and action is
Secretes Atrial natriuretic peptides
-Target: kidneys
-Action: reduces blood volume and BP by increasing Na^+ and H_2 O excretion
Describe the endocrine function of the stomach and small intestine; name what endocrine-like cell it has and what it does
-Has enteroendocrine cells
-Action: Coordinate digestive motility and glandular secretion of cholecystokinin, gastrin, and secretin
Enteroendocrine cells coordinate digestive motility and glandular secretion of what 3 hormones?
Cholecystokinin, gastrin, and secretin
Describe the endocrine function of the adipose tissue; name what hormone it secretes and what its action
Secretes leptin
-Action: Slows appetite
Describe the endocrine function of the placenta; name 2 examples of hormones it secretes and what their action is
-Secretes estrogen, progesterone, and others
Action: Regulate pregnancy, stimulate development of fetus and mammary glands
What are the 3 chemical classes of hormones?
1) Steroids
2) Peptides (and glycoproteins)
3) Monoamines (biogenic amines)
What are steroids derived from? Give 2 examples of steroids
-Derived from cholesterol
-Exs: Sex steroids and corticosteroids
What are peptides (and glycoproteins) made of? Give 3 examples of hormones from this class
-Made of chains of amino acids
-Ex: hormones from pituitary, hypothalamus, insulin
What are monoamines (biogenic amines) made from? Give 3 examples of hormones from this class
-Made from amino acids
-Exs: Catecholamines, melatonin, thyroid hormone
Thyroid hormone is composed of what two things?
1) Thyroxine (T4)
2) Triiodothyronine (T3)
Describe how thyroid hormone is synthesized and secreted (3 steps)
1) Thyroid follicles absorb iodine from blood.
2) The follicular cells produce T3 (contains three iodines) and T4 (contains four iodines) when stimulated (by TSH)
3) Thyroid Hormone (mostly T4) is released to the blood.
True or false: Hormones are not secreted at steady rates and levels in bloodstream fluctuate throughout the day
True
True or false: Some hormones are on a daily or monthly rhythm
True
Describe 2 common ways hormones can fluctuate
1) Daily or monthly rhythms
2) Influence of stimuli
What are the 3 hormone secretion stimuli categories?
1) Neural stimuli
2) Hormonal stimuli
3) Humoral stimuli
Give 2 examples of neural stimuli
1) Sympathetic N.S. stimulates adrenal medulla during stress
2) In childbirth, stretch receptors stimulate release of oxytocin
Give an example of hormonal stimuli (Tropic hormones)
Releasing & inhibiting hormones from the hypothalamus (TSH, ACTH, FSH, LH)
Define humoral stimuli and give 2 examples
-Refers to blood-borne stimuli
Examples:
1) High blood glucose stimulates release of insulin
2) Low blood calcium stimulates secretion of parathyroid hormone
Most monoamines and peptides are hydro______. Describe the importance of this.
-Most monoamines and peptides are hydrophilic
-This is important because it allows them to mix easily with blood plasma
Steroids and thyroid hormone are hydro_____. How are they transported through plasma?
-Steroids and thyroid hormone are hydrophobic
-They bind to transport proteins (albumins and globulins)
What type of hormones have a longer half-life? Why?
-Bound (Hydrophobic) hormones have longer half-life
-Because they’re protected from liver enzymes and kidney filtration
Only _______ hormones leaves capillaries to reach target cell
unbound
What is the exception to the rule about bound (hydrophobic) hormones having a longer half-life?
Aldosterone (hydrophobic): short half-life; 85% unbound, 15% binds weakly to albumin and others
Hydro_____ hormones are bound, and hydro______ hormones are unbound
Hydrophobic are bound, hydrophilic are unbound
True or false: Hormones stimulate all cells they touch
False; hormones stimulate only those cells that have receptors for them
Define receptors and name the 3 places they can be found
-Defined as protein (or glycoprotein) molecules
-Located on plasma membrane, in the cytoplasm, or in the nucleus
What do receptors do?
Act like switches turning on metabolic pathways when hormone binds to them
A target cell has about how many receptors for a given hormone?
A few thousand receptors for a given hormone
Receptor–hormone interactions exhibit what two properties? How so?
They exhibit specificity and saturation
-Specific receptor for each hormone
-Saturated when all receptor molecules are occupied by hormone molecules
Describe the mode of action of peptide hormones
Cannot penetrate target cell, so they bind to surface receptors and activate intracellular processes through second messengers
What type of hormones use second messengers?
Peptide hormones
Describe the mode of action of steroid hormones and how long it takes
-Penetrate plasma membrane and bind to internal receptors (usually in nucleus) to influence expression of genes of target cell
-Take several hours to days to show effect due to lag for protein synthesis
Describe the mode of action of thyroid hormone (3 steps)
1) It enters the target cell by means of an ATP-dependent transport protein
2) Within target cell, T4 is converted to more potent T3
3) Then T3 binds to nuclear receptors and activates genes; one gene is for the sodium-potassium pump
Describe the potency of hormones
-Hormones are extraordinarily potent chemicals; one hormone molecule can activate many enzyme molecules
-Very small stimulus can produce very large effect
-Therefore, hormone concentrations in blood are low
Are hormone concentrations in the blood low or high?
Low
How is target-cell sensitivity adjusted?
By changing the number of receptors
What are the two ways in which target-cell sensitivity can be regulated?
Up-regulation and down-regulation
Define and describe what happens after up-regulation and down-regulation
1) Up-regulation: number of receptors is increased
-Which means sensitivity is increased
2) Down-regulation reduces number of receptors
-Which means sensitivity is decreased
When does down-regulation happen?
Happens with long-term exposure to high hormone concentrations
Are most cells sensitive to one hormone or more?
Most cells sensitive to more than one hormone and exhibit interactive effects
What are the 3 kinds of effects of hormone interaction? Give a brief definition for each
1) Synergistic effects: multiple hormones enhance each other
2) Permissive effects: one hormone enhances an organ’s response to another hormone
3) Antagonistic effects: one hormone opposes the action of another
Define and give an example of synegistic effects
-When multiple hormones act together for greater effect
-Ex: Synergism between FSH and testosterone on sperm production
Define and give an example of permissive effects
-When one hormone enhances the target organ’s response to a second later hormone
-Ex: Estrogen prepares uterus for action of progesterone
Define and give an example of antagonistic effects
-When one hormone opposes the action of another
-Ex: Insulin lowers blood glucose and glycogen raises it
True or false: Hormone signals must be turned off when they have served their purpose
True
Most hormones are taken up and degraded by _________ and ______________. Where are they then excreted?
-Most hormones are taken up and degraded by the liver and kidneys
-Excreted in bile or urine
List the 6 hypothalamic hormones that inhibit or stimulate the release of another hormone, and state what hormone they stimulate or inhibit
1) TRH promotes secretion of TSH and PRL
2) CRH promotes secretion of ACTH
3) GnRH promotes secretion of FSH
4) GHRH promotes secretion of GH
5) PIH inhibits secretion of prolactin
6) Somatostatin inhibits secretion of GH and TSH
What are the 5 steroid hormones that can cross the phospholipid bilayer (i.e. are not water soluble)?
What is the one water soluble hormone that acts like it’s not?
1) Testosterone
2) Estrogen
3) Progesterone
4) Aldosterone
5) Cortisol
1) Thyroid hormone (TH) acts lipid-soluble
The receptors of _______ hormones and ________ hormone are inside the cell, since they can cross the phospholipid bilayer to enter the cell.
steroid; thyroid
