Week 7 - endocrine system Flashcards
endocrine system
- organs of system work by SYNTHESIZING & SECRETING chemical messengers (HORMONES)
- HORMONES interact w/ specific target cells & influence their functions in order to maintain fluid electrolyte, and acid-base homeostasis, promote growth & regulate metabolic reactions
Endocrine vs nervous - similarities
- use chemicals to communicate w/ other cells
- regulated primarily negative feedback loops
Endocrone vs nervous - differences
- nervous has neurons that DIRECTLY affect the target cells via NEUROTRANSMITTER, effects are almost IMMEDIATE but are short lived unles stimulation is REPETITIVE
- cells in endocrone: not close to target cells → hormones in blood stream
- effect in seconds can take hours or days
effect is longer lasting than neurons
chemical signalling - Paracrine
- chemicals are secreted by cells into extracellular space to affect NEARBY but DIFF TYPES OF CELLS
chemical signalling - autocrine
- chemicals are secreted by cells, interstitial fluid, elicits from SAME cell or cell type
chemical signalling- endocrine
- chemical messengers that are secreted by endocrone cells into the blood stream & travel to other tissues or organs
endocrine glands
Diverse group of organs found throughout body; all regulate other cell types by producing & secreting hormones:
- DUCTLESS CELLS: secrete hormones into extracellular fluid for transport by blood stream. consists of:
PRIMARY ORGANS → only endocrine funct.
SECONDARY ORGANS → both endocrine and non endocrine
endocrine glands - organs
Anterior pituitary gland: in sphenoid bone of skull
Thyroid gland: in anterior neck
Parathyroid gland: on posterior side of thyroid gland
Adrenal cortices: on superior side of each kidney
Endocrone pancreas: in left side of abdominal cavity, mostly posterior to stomach
Thymus: in superior mediastinum
hormones
- CHEMICAL MESSENGERS secreted by endocrine glands that regulate functions of other cells
- once released, hormones can cause widespread eddects
- hormones can travel as FREE, UNBOUND chemicals in blood or BOUND chemicals attached to PLASMA PROTEIN CARRIERS
- hormones continue to circulate in blood stream until are taken up by target cell or BROKEN DOWN
- ammount of particular hormone in blood at given moment depends on how fast/ much hormone an endocrine gland has produced & how fast secreted
Hormones - target cells & receptors
Hormones only affect target cells →contain specific protein receptors which hormones bind to
- 3D shapes of receptor → highly specific
- either embedded in PLASMA MEMBRANE or reside in CYTOSOL or NUCLEUS of target cell
receptor location largely repends on chemical structure
- HYDROPHILIC: cannoy readily cross plasma membrane, interact w/ receptors found embeded in cells PM
- HYDROPHOBIC: able to cross through PM → interact w/ receptors found in CYTOSOL OR NUCLEUS
Hormones - classification
A-A hormones: consist of one or more AA ranging in size from solitary (amine hormones) to multiple (peptide) → even complete proteins; generally hydrophilic, binding to plasma membrane receptors
STEROID HORMONES: derived from CHOLESTEROL; HYDROPHOBIC, bind to receptors in cytosol or nucleus
Hormones - hydrophilic
- BINDS TO RECEPTOR IN PM
- receptor activates PERIPHERAL protein (g-protein)
- G-protein may activate and ENZYME → catalyses formation of a SECOND MESSENGER → initiates series of events in cell that leads to change in its activity
Hormones - hydrophobic
- cross PM & interact w/ receptors in cytosol or nucleus
- forms complex w/ its receptor, generally interacts w/ DNA of target cell
- complex exerts its effects by changing RATE of PROTEIN SYNTHESIS
Hormones - regulation
secretion can be initiated or inhibited by stimuli:
- HORMONAL STIMULI: some endocrine cells inc. or dec. their secretion in response to secretion of other hormones- ADRENOCORTICOTROPHIC HORMONE & CORTISOL
- HUMORAL STIMULI: many endocrine cells respond to conc. of a certain ion or molecule in blood or EXC fluid → INSULIN AND HIGH BLOOD GLUCOSE
- NEURAL STIMULI: some endrocrine cells respond to signals from NS → HYPOTHALAMUS & PITUITARY GLAND
hypothalamus
- ANATOMICAL & FUNCTIONAL RELATIONSHIP betw. hypothalamus and pituitary gland
- provides highest level of endocrine control
- intergrates activities of the nervous and endocrine sus
→ endocrine funct. synthesize ADH and oxytocin+
→ transport to posterior lobe of pituitary
→ autonomic centres which exert direct neuronal control via sympathetic activation over endocrine cells in the adrenal medulla
Structure - Pituitary gland:
small organ composed of following two structurally & functionally distinct components
ANTERIOR PITUITARY (adenohypophysis): true gland composed of hormone-secreting GLANDULAR EPITHELIUM; releases 7 peptide hormones that turn on endocrone glands r support functions of other organs
POSTERIOR PITUITARY (neurohypophysis): made of nervous tissue; contains axons of hypothalamus neurons & releases hormones
Hypothalamic- hypophyseal portal system
Specialised blood supply - allows hypothalamus & pituitary to deliver hormones directly
- tiny capillaries merge in hypothalamus to form larger PORTAL VEINS that travel through infundibulum
- portal veins lead to a second group of capillaries in ANTERIOR pituitary gland
PORTAL SYSTEM: capillaries drained by veins that lead to another set of capillaries
Hypothalamus & pituitary - hormones
- Thyroid- stimulating hormone (TSH) (thyrotropin)
- Adrenocorticotrophic hormone (ACTH) ( corticotrophin)
- growth hormone (GH) (somatotrophin)
POSTERIOR
- oxytocin (OT) produced by paraventricular nuclei
- antidiuretic hormone (ADH) → supraoptic nuclei
anterior pituitary - select actions
TSH - stimulates growth of thyroid gland and secretion of TH which has wide spread effects on metabolism
- released in response to thyrotropin: releasing hormone under negative eedback loop control
ACTH - stimulates the adrenal cortex to secrete its hormones = corticosteroids
cortisol - regulates glucose metabolism
- response to stress
thyroid gland
Largest endocrine gland
- butterfly shaped
- anterior and lateral sides of trachea
- two large lobes connected by isthmus
Cell types:
Parafollicular cells: produce calcitonin → regulate calcium ion conc.
Follicle cells: produce thyroglobin; contains tyrosine
Thyroid hormone - functions
- Regulation of metabolic rate & thermoregulation → set basal regulation rate → heat generation
- promotino of growth & development: bone and muscle growth → nervous sys, development
- Synergism w/ sympathetic nerv sys. : increase metabolism, SNS heart rate and BP
Thyroid hormone- regulation
Stimulus: decrease levels of free T3 & T4 in blood/ exposure to cold
Receptor: hypothalamus
1st cont: hypothalamus secretes TRH
2nd cont: anterior pituitary secretes TSH
3rd cont: produce, secrete T3+ T4; grow and develop
effect: inc. level of T3 & T4 in blood → negative FB . inc metabolic rate
parathyroid glands
- In posterior surface of thyroid gland
- 3-5 PT glands that secrete PTH from chief cell
- Produced in response to hypocalcemia
INC IN:
- calcium reabsorption
- calcium release from bone
- calcitriol produced from kidneys → calcium absorption from digestive system
Adrenal gland
Superior pole of kidneys
Cortex:
- typical endocrine gland
- produce steroid hormone → adrenocortical steroids
Medulla:
- Neuroendocrine organe that secrete neurohormone
- produce epinephrine & norepinephrine, response to SYMP activation
Adrenal gland - hormones
feedback loop: hypothalamic-pituitary-adrenocortical (HPA)
- Aldosterone: regulate mineral conc. (Na+ & K+) acid-base homeostasis
- Glucorticoids: body’s response to stress & cortisol
- Adrenogenic steroids: sex hormones → affect reproductive organs
Chromaffin cells: secrete epinephrine
Pancreas
- inferior & dorsal to stomach
- most is exocrine digestive gland
- PANCREATIC ISLETS: produce hormones → paracrine products
Pancreas - example hormones
Alpha → glucagon:
- raises blood glucose levels
- inc. glycogen breakdown & glucose release by liver
Beta →insulin:
- lower blood glucose levels
- inc. rate of glucose uptake & inc. glycogen synthesis in skeletal muscle & liver
hormone dysregulation - diabetes mellitus
HYPERGLYCEMIA: blood glucose levels too high
TYPE I: 5-10%
- autoimmune destruction of beta cells
- damaged blood vessels → decreased circulation to tissue, inc heart rate
- damage to peripheral nerves → PERIPHERAL NEUROPATHY
- eyes & kidneys affected
TYPE II: 90%
- insulin resistance → failure of target cells response to insulin
- oral medication improve insulin secretion or sensitivity
