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BSC 216: Endocrine System
Terms in this set (96)
-anterior pituitary gland
-posterior pituitary gland
In humans, two systems: the ___________ and the ___________ communicate with neurotransmitters and hormones
the nervous and endocrine
The endocrine system is in ________ to _________.
adaptation to stress
Both serve for internal communication
-Nervous: both electrical and chemical
-Endocrine: only chemical
Speed and persistence of response
-Nervous: reacts quickly (1 to 10 ms), stops quickly
-Endocrine: reacts slowly (hormones release in seconds or days), effect may continue for weeks
Adaptation to long-term stimuli
-Nervous: response declines (adapts quickly)
-Endocrine: response persists (adapts slowly)
-endocrine=slower than nervous system
-as long as hormone is present in endocrine system, the reaction will keep going (no adaptation)
Area of effect
-Nervous: targeted and specific (one organ)
-Endocrine: general, widespread effects (many organs)
Several chemicals function as both hormones and neurotransmitters
norepinephrine, cholecystokinin, thyrotropin-releasing hormone, dopamine, and antidiuretic hormone
Some hormones secreted by neuroendocrine cells (neurons) that release their secretion into bloodstream:
oxytocin and catecholamines
(cells in the hypothalamus and endocrine glands are important)
Both systems with overlapping effects on same target cells
norepinephrine and glucagon cause glycogen hydrolysis in liver
Nervous and Endocrine systems regulate each other
-Neurons trigger hormone secretion
-Hormones stimulate or inhibit neurons
Target organs or cells:
Those organs or cells that have receptors for a hormone and can respond to it
-Have ducts carry secretion to an epithelial surface or the mucosa of the digestive tract: "external secretions"
-Extracellular effects (food digestion)
-Contain dense, fenestrated capillary networks which allow easy uptake of hormones into bloodstream
-Intracellular effects such as altering target cell metabolism
Liver cells defy rigid classification--release hormones, release bile into ducts, release albumin and blood-clotting factors into blood (not hormones)
The Body has 4 principal mechanisms of communication between cells:
1. Gap Junctions
3. Paracrine (local) hormones
Pores in cell membrane allow signaling molecules, nutrients, and electrolytes to move from cell to cell
Released from neurons to travel across synaptic cleft to second cell
Paracrine (local) hormones
Secreted into tissue fluids to affect nearby cells
Chemical messengers that travel in the bloodstream to other tissues and organs
Endocrine pathway (Chemical signaling)
Secreting cell: Endocrine cell
Substance secreted: Hormones
Transport medium: Blood (released into bloodstream)
Target cell location: Distant cell
Target cell type: Different cell type
Paracrine pathway (Chemical Signaling)
Secreting cell: Tissue cell
Substance secreted: paracrine chemical
Transport medium: extracellular fluid
Target cell location: near cell
Target cell type: Different type of cell
Autocrine pathway (Chemical signaling)
Secreting cell: Specialized cell
Substance secreted: autocrine chemical
Transport medium: Extracellular fluid
Target cell location: same cell or near cell
Target cell type: Same cell or cell type
glands, tissues, and cells that secrete hormones
the study of the endocrine system and the diagnosis and treatment of its disorders
organs that are traditional sources of hormones:
-Primary: Only endocrine functions (Anterior pituitary, thyroid, parathyroid, etc.)
-Secondary: Both endocrine and various other functions (Heart, kidneys, small intestine)
-Neuroendocrine Organs: Consist of nervous tissue, yet secrete hormone-like chemicals (neurohormones). Organs include the hypothalamus, pineal gland, adrenal medulla
chemical messengers that are transported by the bloodstream and stimulate physiological responses in cells of another tissue or organ, often a considerable distance away
Classes of Hormones
Two Basic Types:
1. Amino Acid Based
-one-multiple amino acids long
Whether the hormone is hydrophilic or hydrophobic decides it's mechanism of action (how they interact with target cells)
Hydrophilic hormone and second-messenger system
1. Hydrophilic hormone (first messenger) binds to its receptor in the plasma membrane.
2. Receptor activates a peripheral protein.
3. Peripheral protein activates an enzyme.
4. Enzyme catalyzes formation of a second messenger.
5. The second messenger initiates a series of events in the cell that leads to changes in its activity.
Hydrophobic hormone and intracellular receptor mechanism
1. Hydrophobic hormone diffuses into the target cell.
2. Hormone binds to an intracellular receptor and enters the nucleus of the cell.
3. Hormone-receptor complex interacts with the DNA to initiate a cellular change.
Mechanisms of hormone action:
-hydrocphilic system: needs a transmembrane receptor
-hydrophilic = faster b/c all of the needed enzymes, proteins, etc. are already present; they just need to be turned on.
-hydrophobic: must be transcribed
Mechanism of Hydrophilic hormones:
-secondary messenger usually initiates the cellular change
-some hormones bind ion channel receptors
Mechanisms of Hydrophobic hormones:
-able to diffuse across the cell membrane
-bind to an intracellular receptor
-hormone/receptor complex binds DNA and promotes transcription (can bind plasma membrane receptors and cause a hydrophilic-like cascade.)
Effects of Hormone Actions:
-Stimulating secretion from an endocrine or exocrine cell
-Activating or inhibiting enzymes
-Stimulating or inhibiting cellular division
-Opening or closing ion channels
-Activating or inhibiting DNA transcription
Hormone Secretion can be activated via hormonal, humoral, or neural stimuli:
Hormonal stimulation: Growth hormone-releasing hormone (GHRH) stimulates secretion of growth hormone (GH) from an anterior pituitary cell.
Hormonal Inhibition: Somatostatin inhibits secretion of growth hormone from an anterior pituitary cell.
Humoral Stimulus: Glucose uptake by a pancreatic cell triggers insulin secretion.
Neural Stimulus: Sympathetic neurons stimulate secretion of epinephrine and norepinephrine from an adrenal medulla cell.
-Some endocrine cells increase or decrease secretion in response to other hormones
-Ex: Hypothalamus secreting releasing or inhibiting hormones that directly affect secretion in the anterior pituitary
-refer back to hormonal stimulation and hormonal inhibition in previous slide
Humoral and Neural Stimuli
-other endocrine cells respond to the concentration of ions in the blood or extracellular fluid
-Ex: Pancreas releasing insulin in response to glucose levels in the blood.
-some cells respond to signals from nervous system, such as the adrenal medulla
-refer back to humoral stimulus and neural stimulus in previous slide
Regulation of Secretion:
Negative Feedback Loop:
Stimulus: A regulated physiological variable deviates from its normal range.
Receptor: Receptors on endocrine cells detect the deviation of the variable.
Control Center: The stimulated control center (often the endocrine cell) increases or decreases its secretion of a particular hormone.
Effector/Response: The hormone triggers a response in its target cells that moves conditions toward the normal range.
Variable returns to homeostatic range.
Anatomy of the Hypothalamus
-regulates primitive functions of the body from water balance and thermoregulation to sex drive and childbirth
-many of its functions carried out by pituitary gland
-Pituitary gland (two structures)
1. Adenohypophysis (anterior pituitary)
2. Neurohypophysis (posterior pituitary)
Anatomy of the Hypothalamus (2)
Hypothalamic-releasing and inhibiting hormones travel in hypophyseal portal system from hypothalamus to anterior pituitary
Relationship between the hypothalamus and posterior pituitary:
1. Hypothalamic neurons make either ADH or oxytocin.
2. The hormones travel through the hypothalamic axons in the infundibulum.
3. ADH and oxytocin are stored in the axon terminals in the posterior pituitary.
4. The hormones are secreted into the blood when the hypothalamic neurons fire action potentials.
-Eight hormones produced in hypothalamus
-6 releasing and inhibiting hormones stimulate or inhibit the anterior pituitary
-Two other hypothalamic hormones are oxytocin (OT) and antidiuretic hormone (ADH)
-Both stored and released by posterior pituitary
-Posterior pituitary does not synthesize them
Posterior Pituitary Hormones
Produced in hypothalamus
- transported by hypothalamo-hypophyseal tract to posterior lobe
- releases hormones when hypothalamic neurons are stimulated
ADH (antidiuretic hormone)
-increases water retention, thus reducing urine volume, and prevents dehydration
-also called vasopressin because it can cause vasoconstriction
-hypersecretion causes diabetes insipidus
Relationship between the hypothalamus and anterior pituitary:
1. Hypothalamic neurons secrete releasing and inhibiting hormones into the hypothalamic capillary bed.
2. Hormones travel through portal veins in the infundibulum.
3. Hypothalamic hormones exit the anterior pituitary capillary bed to bind to receptors on anterior pituitary cells.
4. Hypothalamic hormones stimulate or inhibit secretion of hormones from anterior pituitary cells.
Anterior Pituitary Hormones
-Anterior lobe of the pituitary synthesizes and secretes six principal hormones
-2 gonadotropin hormones that target gonads:
1. Follicle-stimulating hormone (FSH) - stimulates secretion of ovarian follicles, and sperm production
2. Luteinizing hormone (LH) - stimulates ovulation, stimulates corpus luteum to secrete progesterone, stimulates testes to secrete testosterone
-both are stimulated from hypothalamic releasing hormone GnRH
3. Thyroid-Stimulating hormone (TSH) - stimulates secretion of thyroid hormone (triggered by hypothalamic releasing hormone thyrotropin releasing hormone (TRH)
Anterior Pituitary Hormones (2)
4. Adrenocorticotropic hormone (ACTH) - stimulates adrenal cortex to secrete glucocorticoids
-Secretion stimulated by corticotropin releasing hormone
5. Prolactin (PRL) - after birth, stimulates mammary glands to synthesize milk; enhances secretion of testosterone by testes
-Secretion stimulated by infant suckling and prolactin releasing hormone
6. Growth hormone (GH) - stimulates mitosis and cellular differentiation
-secretion stimulated by growth hormone releasing hormone (GHRH) and inhibited by somatostatin
-surge of hormone released during sexual arousal and orgasm (stimulate uterine contractions and propulsion of semen)
-promotes feelings of sexual satisfaction and emotional bonding between partners
-stimulates labor contractions during childbirth
-stimulates flow of milk during lactation
-promotes emotional bonding between lactating mother and infant
Hypothalamus releases hormones.
Releasing hormones: TRH, CRH, PRH, GnRH, GHRH
Anterior pituitary releases hormones.
Pituitary hormones: TSH, ACTH, PRL, FSH and LH, GH
Target organs release hormones.
Target organs: thyroid, adrenal cortex, mammary glands, male and female gonads, liver/muscle/bone and fat
-Hormone levels increase.
-Effects on other cells- return to normal range.
Target organ hormones: thyroid hormones, glucocorticoids and adrenal steroids, no new hormones produced, testosterone and estrogen, IGF
A further look at growth hormone:
-GH has widespread effects on the body tissues (especially cartilage, bone, muscle, and fat)
-Induces liver to produce growth stimulants
-Insulin-like growth factors (IGF-I) or somatomedins (IGF-II)
-stimulate target cells in diverse tissues
-IGF-I prolongs the action of GH
-Hormone half-life--the time required for 50% of the hormone to be cleared from the blood
-GH half-life: 6 to 20 mins
-IGF-I half-life: about 20 hours
Mechanisms of GH-IGF action include:
-Protein synthesis increases: boosts transcription of DNA, production of mRNA, amino acid uptake into cells, suppresses protein catabolism
-Lipid metabolism increased: fat catabolized by adipocytes (protein-sparing effect), which provides energy for growing tissues
-Carbohydrate metabolism: glucose-sparing effect, mobilizes fatty acids, reduces the dependence of most cells on glucose. Will not compete with the brain and makes these electrolytes available to the growing tissues.
-Electrolyte balance: promotes Na+, K+, and Cl- retention by kidneys, enhances Ca2+ absorption in intestine
Short term effects of GH
GH released from anterior pituitary then either...
1. Inhibits glucose uptake by skeletal muscle
2. Stimulates gluconeogenesis in the liver
**both lead to increased blood glucose concentration
3. Stimulates lipolysis in fat
**leads to increased blood fatty acid concentration
Long-term effects of GH
-GH released from anterior pituitary; then...
-Insulin-like growth factor (IGF) release by the liver, muscle, bone, and other tissues; then either...
1. Stimulates glucose uptake by cells
**leads to decreased blood glucose concentration
2. Stimulates cell division
**leads to increased growth of bone and other tissues
3. Stimulates protein synthesis
**leads to increased mass of muscle and other tissues
hypersecretion of GH prior to puberty
not enough GH prior to puberty
hypersecretion of GH post puberty
Control of Pituitary Secretion
Rates of secretion are not constant
-regulated by hypothalamus, other brain centers, and feedback from target organs
Hypothalamic and cerebral control:
-Anterior lobe control: releasing hormones and inhibiting hormones from hypothalamus
-in cold weather, pituitary stimulated by hypothalamus to release TSH, leads to generation of body heat (shivering)
(control of pituitary secretion cont...)
hormone release in response to nervous system signals
Suckling infant-->stimulates nerve endings--> hypothalamus-->posterior lobe-->oxytocin-->milk ejection
-Hormone release in response to higher brain centers
-Milk ejection reflex can be triggered by a baby's cry
-Emotional stress can affect secretion of gonadotropins, disrupting ovulation, menstruation, and fertility
1. Nursing stimulates nerve receptors in nipple.
2. Sensory and spinal nerves carry impulses to the neuroendocrine cells of hypothalamus.
3. Neuroendocrine cells release oxytocin when stimulated.
4. Oxytocin is transported by blood to mammary glands.
Stimulus: increased solute concentration of the blood
Inhibitor: decreased solute concentration of the blood
Target tissues: kidneys and brain
Effects: water reabsorption from kidney tubules & increases blood volume
Stimulus: stretching of the uterus & infant suckling at the nipple
Inhibitor: lack of appropriate stimuli
Target tissues: uterus and mammary gland
Effects: uterine contractions & milk let-down reflex
Anterior pituitary hormones:
TSH, ACTH, Prolactin, LH, FSH, GH
Thyroid-stimulating hormone (TSH)
Stimulus: thyrotropin-releasing hormone (TRH) from the hypothalamus; exposure to cold; stress
Inhibitor: increased levels of thyroid hormones; somatostatin from the hypothalamus
Target tissues: thyroid gland
Effects: growth and development of the thyroid gland; synthesis of thyroid hormones
Adrenocortitropic hormone (ACTH)
Stimulus: corticotropin-releasing hormone (CRH) from the hypothalamus; stress
Inhibitor: increased level of cortisol; increased level of aldosterone
Target tissue: adrenal cortex
Effects: growth and development of adrenal cortices; release of adrenal steroids and catecholamines
Stimulus: prolactin-releasing hormone (PRH) from the hypothalamus; infant suckling at the nipple
Inhibitor: Prolactin-inhibiting factor (dopamine) from the hypothalamus
Target tissue: mammary gland
Effects: Development of mammary glands; milk production
Luteinizing Hormone (LH)
Stimulus: gonadotropin-releasing hormone (GnRH) form the hypothalamus
Inhibitor: increased levels of testosterone (males) and estrogen and progesterone (females)
Target tissue: male gonads and female gonads
Male gonads: Development of gonads; testosterone production
Female gonads: development of gonads; production of estrogens and progesterone; ovulation
Follicle-Stimulating Hormone (FSH)
Stimulus: GnRG from the hypothalamus
Inhibitor: increased levels of testosterone and estrogens
Target tissues: male and female gonads
Effects: production of factors that bind and concentrate testosterone; production of estrogens; maturation of ovarian follicles
Growth Hormone (GH)
Stimulus: Growth hormone-releasing hormone (GHRH) from the hypothalamus; stress/exercise; ingestion of protein; fasting
Inhibitor: Somatostatin from the hypothalamus
Target tissues: liver, adipose tissue, muscle tissue, bone and cartilage
Effects: Gluconeogenesis; fat breakdown (lipolysis); protein breakdown; production of insulin-like growth factor (IGF), which stimulates cell division and protein synthesis
Anatomy of Thyroid Gland
-Located in the anterior neck, just superficial to the larynx.
-Butterfly shaped (two lobes connected by an isthmus)
-Two types of hormones:
1. Thyroid hormones (growth and metabolism) (helps generate body heat)
2. Calcitonin (Calcium ion homeostasis)
Anatomy of Parathyroid Glands:
-Glands embedded in the posterior surface of the thyroid gland (anywhere from 3-5 glands)
-Secretes parathyroid hormone (maintenance of calcium ion in the ECF) (Secreted by chief cells)
Structure of Thyroid and Parathyroid Glands
Composed of thyroid follicles
-multiple sphere-shaped sacs
-simple cuboidal epithelial cells
-produce thyroid hormones
-protein-rich gel that fills the inside of the follicle
-stores precursor of thyroid hormone
-lie between follicles
Amino Acid core bound to iodine atoms
-triiodothyronine (T3): three iodine atoms
-Thyroxine (T4): four iodine atoms
-Both forms active, although T3 has higher physiological activity
Although thyroid hormones are amino acid hormones, they are non-polar (hydrophobic- able to cross membrane). What mechanism do you think it employs to activate a cell?
Effects of thyroid hormone:
-regulation of the metabolic rate and thermoregulation
-promotion of growth and development
-synergism with the sympathetic nervous system
Thyroid Hormone Production
1. Iodide ions (I-) and thyroglobulin are secreted into the colloid.
2. Iodide ions are converted to iodine atoms (I^0) that attach to thyroglobulin.
3. Iodinated thyroglobulin enters the follicle cell by endocytosis and is converted to T3 and T4 by lysosomal enzymes.
4. T3 and T4 are released into the blood.
-one cause of hyperthyroidism
-abnormal production of proteins that mimic TSH
-excessive secretion of thyroid hormones
Signs and symptoms:
-weight loss due to elevated metabolism
-exophtalmos (bulging eyes)
-goiter (bulging of neck due to T3 and T4)
-drugs or removal of gland
-relatively uncommon in the developed world (salt & iodine in diet)
Destruction of thyroid by the immune system (Hashimoto's Thyroiditis)
Signs and symptoms:
-weight gain due to decreased metabolism
Hypothyroidism - not enough T3 and T4 so body tries to make too much
Hyperthyroidism - too much T3 and T4
-Produced by chief cells in the parathyroid glands
-Maintains blood calcium ion concentration and is secreted in response to low levels of calcium in the blood (hypocalcemia)
-Raises calcium levels 3 different ways:
1. stimulation of osteoclasts
2. activation of vitamin D to vitamin D3
3. increases the reabsorption of calcium ions form fluid in the kidneys.
-produced by the thyroid's parafollicular cells
-combats hypercelcemia by blocking osteoclast activity
Regulation of Calcium Ion Homeostasis:
Stimulus: Blood Ca2+ level decreases below the normal range.
Receptor: Chief cells in the parathyroid gland detect a low blood Ca2+ level.
Control Center: Chief cells increase parathyroid hormone (PTH) secretion.
Effector/Response: Osteoclasts are stimulated to degrade bone, increasing Ca2+ resorption; More Ca2+ are reabsorbed from the fluid in the kidneys; Kidneys activate calcitriol, increasing Ca2+ absorption in the small intestine.
Anatomy of the Adrenal Gland
Pyramid shaped glands located on the superior end of the kidney
Two distinct regions:
-inner medulla (neuroendocrine organ)
Production of two types of hormones:
The Adrenal Cortex
Zona glomerulosa (outermost, touches capsule)
-densely packed cells
Zona fasciculata (middle)
-cells stacked on top of each other
-glucocorticoids & androgenic steroids
Zona reticularis (innermost layer, touches adrenal medulla)
-cells arranged in loose clusters
-glucocorticoids & androgenic steroids
Regulate the concentration of minerals in the body
-maintaining the concentrations of extracellular sodium and potassium ions within their normal ranges
-regulating extracellular fluid volume
-maintaining blood pressure
-maintaining acid-base homeostasis
Produced in the zona fasciculata and zona reticularis
Help mediate the body's response to stress and regulate blood glucose levels
-gluconeogenesis in the liver
-release of amino acids from muscle tissue
-release of fatty acids form adipose tissue
Also known as the stress hormone
-running away form an alligator
Androgenic Steroids: produced largely as a bi-product of cortisol synthesis
Over-secretion of cortisol
-release fatty acids from limbs and re-deposits them in the torso and face
Hormones of the Adrenal Medulla
Adrenal Medulla consists of neuroendocrine cells called chromaffin cells
-stimulated by acetylcholine released by the sympathetic nervous system
-products released are catecholamines
Hormonal epinephrine and norepinephrine have similar effects on target cells
-increased heart rate, bronchiole dilation, pupil dilation, decreased digestive function
The Pancreatic Islets
Glucagon- secreted by A or alpha (a) cells
-released between meals when blood glucose concentration is falling
-in liver, stimulates gluconeogenesis, glycogenolysis, and the release of glucose into the circulation raising blood glucose level
-in adipose tissue, stimulates fat catabolism and release of free fatty acids
-glucagon also released to rising amino acid levels in blood, promotes amino acid absorption, and provides cells with raw material for gluconeogenesis
The Pancreatic Islets (2)
Insulin- secreted by B or beta (B) cells
-secreted during and after meal when glucose and amino acid blood levels are rising
-stimulates cells to absorb these nutrients and store or metabolize them lowering blood glucose levels: promotes synthesis glycogen, fat, and protein; suppresses use of already-stored fuels; brain, liver, kidneys, and RBCs absorb glucose without insulin, but other tissues require insulin
-insufficiency or inaction is cause of diabetes mellitus
Most prevalent metabolic disease in the world
-Disruption of metabolism due to hyposecretion or inaction of insulin
-Symptoms: Polyuria (excess urine output), polydipsia (intense thirst), and polyphagia (hunger); revealed by elevated blood glucose, glucose in urine, and ketones in urine
Transport maximum- limit to how fast the glucose transporters can work to reabsorb
-excess glucose enters urine and water follows it (causes polyuria, dehydration, and thirst)
Type 1 DM
5-10% of cases in US
-caused by destruction of insulin producing beta-cells by the immune system
-unable to uptake glucose, constantly hungry
-insulin is always used to treat type 1: insulin injections, insulin pump, or dry insulin inhaler; monitoring blood glucose levels and controlled diet
-hereditary, susceptibility if infected with certain viruses (rubella, cytomegalovirus)
cells cannot absorb glucose, must rely on fat and proteins for energy needs, thus weight loss and weakness
-fat catabolism increases free fatty acids and ketones in blood :
-Ketonuria: promotes osmotic diuresis, loss of Na+ and K+, irregular heartbeat, and neurological issues
-Ketoacidosis: occurs as ketones decrease blood pH
-deep, gasping breathing and diabetic coma are terminal result
Type 2 DM
90-95% of diabetics
-problem: insulin resistance (failure of target cells to respond to insulin)
-Risk factors are heredity, age (40+), obesity, and ethnicity (Native American, Hispanic, and Asian)
-Treated with weight-loss program and exercise since:
1. Loss of muscle mass causes difficulty with regulation og glycemia
2. Adipose signals interfere with glucose uptake into most cells
-Oral medications improve insulin secretion or target cell sensitivity
-Usually doesn't lead to ketoacidosis
Chronic pathway (chronic hyperglycemia)
-Leads to neuropathy and cardiovascular damage from atherosclerosis and microvascular disease
-arterial damage in retina and kidneys (common in type 1), atherosclerosis leads to heart failure (common in type 2)
-Diabetic neuropathy: nerve damage from impoverished blood flow can lead to erectile dysfunction, incontinence, poor wound healing, and loss of sensation from area
ALSO KNOW LAST 3 CHARTS IN SLIDESHOW
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