endocrine 1 Flashcards
What is an endocrine system
The endocrine system consists of ductless endocrine glands that secrete hormones that are essential for homeostasis
special gland: thyroid gland, adrenal gland, etc
Name the endocrine cells in tissues
The hypothalamus, adipose tissue, and the gastrointestinal tract
Name the types of hormones (got 3)
- Peptides:
Small peptides:TRH (GluHisPro), vasopressin (nonapeptide)
Proteins: Insulin, growth hormones
Glycoproteins: Long polypeptides bound to 1 or more carbohydrate groups (FSH & LH) - Amines: epinephrine derived from tyrosine (non-essential a.a)
- Steroids: hydrophobic hormones derived from cholesterol
The effects of hormones are ___ by ___ hormone receptors in the cell (copy paste and fill in the blanks)
The effects of hormones are mediated by specific hormone receptors in the cell
(complimentary 3d configuration at active site)
The location of the hormone receptor depends on the chemical nature of the hormone. State the location of hormone receptors for hydrophobic and hydrophilic hormones.
Hydrophilic hormones: on the cell surface membrane (as hormone cannot pass through the lipid bilayer of the CSM)
(Primarily acts through a 2nd messenger systems to alter the activity of pre-existing proteins)
Hydrophobic hormones: Intracellular hormone receptors (nuclear or cytoplasmic as the hormone can pass through the hydrophobic phospholipid bilayer of the CSM)
The actions of hydrophilic hormones are mediated by membrane receptors (I), name the 3 membrane receptors.
- G-Protein Linked Receptor (GPLR): activate 2nd messenger pathway (cAMP/Ca2+)
- Ion-Channel Linked Receptor: mostly for neuropeptide hormones (actiavtion of ion channel allows the ion to pass through the CSM, allowing neural activation to occur)
- Enzyme-Linked receptor: most are protein kinases (receptor itself has enzymatic activity, like insulin receptor, a tyrosine kinase receptor, but is also able to trigger a cascade of activating kinases)
Action of hydrophobic hormones is mediated mainly by nuclear receptors. Where are the hormone receptors located?
The hormone receptors are embedded in the CSM or can be in the plasma cell
How does hormone secretion regulate endocrine function?
- Respond to changes in the internal and external environment
-Via negative feedback, positive feedback, feed forward - Neuroendocrine reflexes (release of hormone from brain to blood/blood to brain) to produce a sudden increase in hormone secretion in response to specific stimulus (external from body)
- Circadian (around the day) / Diurnal (day-night) rhythms where the secretion rates of hormone rhythmically fluctuate up & down as a function of time (repetitive oscillations in hormone levels, very regular)
- Course of time in a cyclic pattern (provides temporal coordination) where endocrine rhythms are entrained to external cues
-> inherent hormonal rhythmicity & entrainment is a result of the CNS changing the set point of the glands
How does tissue sensitivity regulate the endocrine function
Via tissue receptors and transcription cofactors (co-repressors and co-activators)
Hormone binding to ___ ___, ___ & activation in organs (liver and kidneys) help regulate the endocrine functions. (copy paste and fill in the blanks)
Hormone binding to plasma proteins, metabolism & activation in organs (liver and kidneys) help regulate the endocrine functions.
Causes and treatment of endocrine disorders due to hyposecretion
- Causes can be primary or secondary: hereditary (inborn absence of enzyme), dietary deficiency, immunology factors, chemical/toxic (destroyed glands), iatrogenic (surgical removal), idiopathic (causes unknown)
- Most can be treated by Hormone Replacement Therapy
Causes of endocrine disorder due to hypersecretion
- Causes can be primary or secondary, depending on whether the defect lies in the gland or results from excessive stimulation from the outside
- Due to tumours of endocrine glands, autoimmune diseases/immunological factors, substance abuse
Causes and treatment of endocrine disorder due to hyposecretion
- Causes can be primary or secondary, hereditary (inborn absence of enzyme), dietary deficiency, immunology factors, chemical/toxic, iatrogenic (surgical removal), idiopathic (causes unknown)
- Most can be treated by Hormone Replacement Therapy
Target-cell responsiveness to the hormone is abnormally low leads to?
Endocrine dysfunction can also arise from the unresponsiveness of the target cells
- may lead to type II diabetes, testicular feminisation syndrome (inborn lack of receptors)
Responsiveness of target cells can be varied by regulating the no. of hormone-specific receptors.
What are the 3 conditions the target cell’s response to hormone correlates with?
- The no, of target cell’s receptors occupied by that hormone
- The no. of receptors in the target cell for that hormone
- Plasma concentration of the hormone
Down regulation is a gradual ___ in the total no. of target-cell receptors for a hormone as an effect of a sustained ___ of the hormone (copy paste and fill in the blanks)
Down regulation is a gradual reduction in the total no. of target-cell receptors for a hormone as an effect of a sustained elevation of the hormone
e.g. desensitized target cells of insulin, blunts the effect of insulin hypersecretion
↳ Binding of insulin to surface receptor triggers dictated cellular response, then induces receptor-mediated endocytosis of hormone-receptor complex, which is then attacked by intracellular lysosomal enzymes (internalization)
If rate of synthesis is lower than the rate of internalization and degradation, then self-induced loss of target-cell receptors occurs
Inducing receptor-mediated endocytosis of hormone-receptor complex helps with? (got 2)
- Providing pathway for degrading hormone after its effect is exerted
- Helps regulate the no. of receptors available for binding on target cell’s surface
↑ [hormone], ↑ hormonal binding, ↑ rate of receptor internalization & degradation
Influence of activity of other hormones at a given target cell (got 3)
- Permissiveness: 1st hormone enhances target cell responsiveness to the 2nd hormone by ↑ the no. of receptors for the 2nd hormone
e.g. Thyroid hormone ↑ no. of receptors for epinephrine in the target cells, ↑ effectiveness of epinephrine - Synergism: action of several hormones are complimentary & the combined effect is greater than the sum of their separate effect ⇒ result from each hormones’ influence on no./affinity of receptors for other hormone
e.g. FSH & testosterone: both needed to maintain normal rate of sperm production - Antagonism: 1 hormone causes the loss of another hormone’s receptor, ↓ effectiveness of 2nd hormone
e.g. Progesterone inhibits uterine responsiveness to estrogen by causing a loss of estrogen receptors on uterine smooth muscle ⇒ preventing estrogen from exerting its excitatory effect during pregnancy (non0contracting environment)
The hypothalamus
- Forms the ___ lateral walls & floor of the ___ ventricle
- Intimately connected to a no. of structures within the ___ system & ___
- Integrating center for many ___ functions
- Secretes hormones that regulates ___ of the pituitary glands (copy paste & fill in the blanks)
The hypothalamus
- Forms the lower lateral walls & floor of the 3rd ventricle (communicating network of cavities filled with the cerebrospinal fluid which is transported around the brain cavity)
- Intimately connected to a no. of structures within the limbic system (responsible for behavioral & emotional responses) & brainstem (connects brain to spinal cord) [parts of brainstem include the midbrain, pons & medulla]
- Integrating center for many homeostatic functions
- Secretes hormones that regulates secretion of the pituitary glands
The pituitary gland
- Attached to the hypothalamus by the ___
- Structurally & functionally divided into ___ lobe & ___ lobe
(copy paste & fill in the blanks)
The pituitary gland
- Attached to the hypothalamus by the infundibulum (important element in proper functioning of hormone regulation)
- Structurally & functionally divided into anterior lobe & posterior lobe
Anterior lobe/adenohypophysis contains glandular tissues and secretes tropic hormones that:
- Maintains the structure of their endocrine tissues
- Stimulates other endocrine glands to produce their particular hormones
Name the hormones and their functions based on their shortened form:
ACTH
TSH
Gonadotropins: LH, FSH, Prolactin
GH
ACTH: Adrenocorticotropic hormone / corticotropin
- Stimulates adrenal cortex to produce corticosteroids
TSH: Thyroid-Stimulating Hormones / thyrotropin
- Stimulates thyroids to produce thyroxine
Gonadotropins
LH: Luteinizing Hormones
- Stimulate ovulation, formation of corpus luteum, stimulate testes to produce testosterone
FSH: Follicle-Stimulating Hormone
- Required for development of ovarian follicles & sperm development
Prolactin - Induces mammary lobule-alveolar development & milk production
GH: Growth Hormones / Somatotropin
- Promotes growth of tissues & essential for metabolic regulation
How does the hypothalamus regulate the secretion of the anterior pituitary glands?
The hypothalamus is surrounded by CSF in the 3rd ventricle ⇒ can sense the changes in the CSF to be regulated
- The hypothalamus neurons secrete releasing & inhibiting hormones that regulates the secretion of the anterior pituitary
- The hypothalamic hormones are transported to AP through the hypothalamic-hypophyseal portal system
What is a portal vessel/portal system?
The blood vessels that joins/connect 2 capillaries together
A “private” route where releasing & inhibiting hormones can be picked up by the hypothalamus & delivered immediately to the anterior pituitary gland at relatively high concentration ⇒ very fast, less dilution as compared to if the hormone is circulated about the body
e.g. hypothalamic-hypophyseal portal system connects the capillaries in the hypothalamus & anterior pituitary together
The hypothalamus regulates the secretion of anterior pituitary gland through hormones. Name the hormones based on their shortened form
TRH
CRH
GnRH
GHRH
GHIH
PRH
PIH
TRH: Thyroid-Releasing Hormone - stimulates TSH release
CRH: Corticotropin-Releasing Hormone - stimulates ACTH release
GnRH: Gonadotropin-Releasing Hormone - stimulates FSH & LH release
GHRH: Growth Hormone-Releasing Hormone: Stimulates GH release
GHIH: Growth Hormone-Inhibiting Hormone/somatostatin - inhibits GH release
PRH: Prolactin-Releasing Hormone
PIH: Prolactin-Inhibiting Hormone = dopamine
The hypothalamus-pituitary-adrenal/gonad/thyroid axis regulates via negative feedback. Explain how this works and name the 3 target endocrine glands involved in this axis.
The hormones from the target gland can act on the anterior pituitary and/or the hypothalamus to inhibit the secretion of stimulating & inhibiting hormones.
The target endocrine glands are: thyroid, adrenal, ovaries/testes
What other factors aside from negative feedback can the hypothalamus-pituitary-adrenal/gonad/thyroid axis be regulated by?
- Stress: Stress leads to ↑ CRH, which leads to ↑ in corticosteroids (cortisol)
- This can also affect the timing of menstruation - ‘Dormitory effect’ / menstrual synchrony may be due to pheromones but is controversial
- Regulated by the circadian / diurnal rhythms
Describe the posterior lobe / neurohypophysis
- Consists of neural tissues
- Posterior pituitary is an anatomical & functional extension of the hypothalamus ⇒ stores & releases vasopressin & oxytocin by the hypothalamus
Describe the location & function of the pineal gland
Tiny pine cone-shaped structure in the center of the brain
- Secretes melatonin which increases with darkness & peaks after middle night (~2am)
- Secretion is controlled by the suprachiasmatic nucleus (SCN) of the hypothalamus ⇒ the master pacemaker of circadian rhythms
How does the suprachiasmatic nucleus (SCN) of the hypothalamus regulate with circadian rhythms?
The SCN receives input from the melanopsin (melatonin inhibitor/suppressor)
Special type of retinol ganglion cells (sRGC) detects light
As melanopsin in RGC is a circadian photopigment, it activates in response to light, triggering action potential that is transmitted as nerve impulse to SCN, which in turn suppresses melatonin secretion
Function of vasopressin/anti-diuretic hormone (got 2)
- Promotes H2O reabsorption by the kidneys by stimulating insertion of water channels (aquaporins) into the membranes of the kidney tubules
- High concentration of vasopressin causes the contraction of the arteriolar smooth muscle (vasoconstriction)
Control of vasopressin/ADH
Major stimulus of ADH release is the increase in plasma osmolarity detected by the osmoreceptors in the hypothalamus
Less important input is the decrease in blood volume & blood pressure, detected by the left atrial volume receptor
Osmolarity = no. of particles of solution per liter of solution
High = more solute particles per liter of solution
Low = less solute particles per liter of solution
How does vasopressin have more than 1 effect in the body even though it is a singular hormone
When vasopressin binds to V1 receptors on arteriolar smooth muscles, vasoconstriction of arterioles occur throughout the body
When vasopressin binds to V2 receptors on the distal & collecting tubular cells, it promotes H2O reabsorption by the kidney tubules
Functions of oxytocin (got 4)
- Stimulates contraction of the uterus during labor
- Labor is initiated when oxytocin receptor concentration reaches a critical threshold - Stimulates contraction of mammary alveoli to facilitate milk ejection
- Stimulates contraction of the vas deferens to facilitate sperm and semen ejection
- May also play a role in love & trust between mother-infant bonding, is related to monogamous-pairing in Prairie Voles
- Oxytocin antagonist prevents pair bonding, oxytocin infusion facilitates bonding
Oxytocin receptor is a GPLR
What does prolonged stress-induced secretion of cortisol result in?
Stunted growth
- Antigrowth effect → inhibit growth in long bones & blocking secretion of GH
Functions & mechanism of growth hormones (GH) (got 2 each)
Function:
1. Stimulates the growth of muscle, cartilage & bones
- Hyperplasia: enlargement of tissues/organs due to cell proliferation, increase in no. of cells
- Hypertrophy: increase in muscular site achieved through exercise, increase in size of cells
- Regulates metabolism
- Increases protein synthesis
- Maintains blood glucose levels by decreasing glucose uptake (in peripheral tissues) & enhances glucose synthesis (in liver)
- Mobilizes fat store as energy by stimulating triglyceride breakdown & oxidation in adipocytes (↑ GH, ↓ fats)
mechanism:
1. Direct effect via GH receptors
2. Indirect effect via Insulin-like Growth factor (IGF-1) from the liver & other tissues
Components of the bone cells & bone matrix
Bone cells:
- Osteoblast: bone formation
- Osteoclast: bone remodeling (by dissolving bones to be remodeled)
- Osteocytes: bone maintenance (derived from entrapped osteoblasts)
- Chondrocytes: cartilage cells
Matric (deposited by osteoblasts to the bone):
- Collagen fibers
- Calcium Phosphate crystals → to help build/form the bone
Nerve & blood vessels
What stimulates the bone lengthening process
GH (via IGF-1 which is stimulated by sex hormones) stimulates the proliferation of chondrocytes (cartilage cells) & osteoblast (bone formation) activity on expansion of epiphyseal plate
How does the bone grow in width?
- Osteoblast produces a matrix of osteoid & deposits calcium phosphate
- Osteoclasts carry out bone reabsorption (dissolve bones) on the inner surface of the bone (dissolve then remodel)
- IGF-1 stimulates the activity of osteoblasts & osteoclasts
- chondrocytes (cartilage cells) on the outer plate next to the epiphyseal divide & multiplies
Control of hormone secretion (got 3)
- Secretion of GH is highest during sleep & decreases during wakefulness
- Exercise, high amino acids, low fatty acids & low glucose
⇒ ↑ GH secretion
- GH deficiency: dwarfism
- GH excess: gigantism & acromegaly - Health supplements / ingestion of artificially produced hormones → does it really affect? or is it a placebo effect? Does the hormones ingested digest in the stomach?
Other hormones important for growth (got 4)
- Thyroid hormone (permissive role):
- The effect of GH manifest fully only when sufficient thyroid hormone is present - Androgen:
- important role in pre-pubertal growth spurt & stimulates protein synthesis, depending on the presence of GH
- Responsible for male musculature development
- Promotes ossification of epiphyseal plates (process of bone formation → laying down new bone materials) - Estrogen:
- Pre-pubertal growth spurt
- Adult level stimulates the ossification of the epiphyseal plate
- Ends bone lengthening - Insulin:
- Deficiency blocks growth & hyperinsulinism spurs excessive growth
- Promotes protein synthesis → growth promoting effect
- Structurally resembles IGF-1 → can interact with IGF-1 receptors
