Endocrine Lecture Flashcards
Endocrine Gland
Ductless gland that secretes its product (hormone) into circulation, influences activity of distant tissues
Hormone
Chemical substance synthesized and secreted by an endocrine gland into blood to all parts of the body
Target
Tissue with specific receptors that respond to hormonal stimulus
Paracrine
Hormone secreted by cell, diffuses into extracellular fluid, affects neighboring cell function
Autocrine
Hormone secreted by cell, affect its own function by binding to its cell surface receptors
Neuroendocrine
Hormone secreted by neuron, reaches the circulation, influences the function of other cells at another location in the body
Neurotransmitter
Chemical substance released by axon terminal into synapse, acts locally to control nerve cell function
NE and Epi
Secreted by adrenal medulla = hormone
Secreted by SNS = neurotransmitter
Anterior pituitary
Growth Hormone Adrenocorticotropin hormone Thyroid stimulating hormone Follicle-stimulating hormone Luteinizing hormone Prolactin
Posterior pituitary
Vasopressin (antidiuretic hormone)
Oxytocin
Adrenal cortex
Cortisol
Aldosterone
Androgens
Adrenal medulla
NE
Epi
Thyroid gland
Thyroxine
Triodothyronine
Calcitonin
Pacreas
Insulin
Glucagon
Ovaries
Estrogen
Progesterone
Testosterone
Testes
Testosterone
Estrogen
Placenta
Chorionic gonadotropin
Estrogens
Progesterone
Somatomammotropin
Chemical Classes of Hormones
Proteins & Polypeptides (3-200 aa) – (pp: >100)
Steroids (cholesterol= precursor)
Amines ( derived from tyrosine)
Protein hormones
Pituitary
Pancreas
Parathyroid Hormones
- Usually hydrophilic (hard to diffuse by themselves)
Protein and Polypeptide Hormone synthesis
Stored in secretory vesicles until needed
- Synthesized in rough ER as PREPROhormone
- Cleaved to PROhormone in ER and transferred to golgi
Packaged into secretory vesicles and cleaved to active form and inactive fragments
Secreted via exocytosis
Peptide hormones?
Water soluble
Easily enter circulatory system
Diffuse to target cells
Steroid Hormone Synthesis
Synthesized from cholesterol Not stored within cells Lipid soluble Diffuse across membrane Enter interstitial fluid and then blood where they bind to plasma proteins (not water soluble)
Thyroid Hormone Synthesis (amine)
Bind to a protein called thyroglobulin stored in follicles
Secretion: spllit from this protein
Combine with plasma protein thyroxine-binding globulin
– Thyroxine and triiodothyronine
Adrenal Medullary Hormones (amine)
Taken up into preformed vesicles and stored until secreted
Released by exocytosis
Exist in bound and free forms in plasma
– Epi and NE
Regulation of hormone secretion
Feedback control
Neural control: pathways controlling release
Chronotropic (time) Control: cycles of the body (period, sleep-wake, etc)
Feedback Control Positive vs Negative?
Negative: Limits the hormone effect
Positive: Acts to amplify the hormonal effect
Water soluble hormones
Peptide hormones & catecholamines
- Dissolved in plasma, transported to target tissues
- Diffuse to target cells
Steroid and Thyroid hormones
Circulate in blood bound to plasma proteins
Protein bound hormones are inactive until dissociated bc its too large to get out of the capillary and cause an effect
– Act as a reservoir when bound
– Are in the blood longer
Clearance from Blood
Metabolic destruction by tissues
Binding with tissues
Excretion into bile or urine
Increase half-life with increase plasma protein binding
Receptor Locations
Target cell membrane: Protein, peptide and catecholamine hormones
Cytoplasm: Steroid hormones
Nucleus: thyroid hormones
Target cell membrane
Protein, peptide, and catecolamine
- Fast response
Alter permeability, activate second messengers or activate intracellular enzymes
Cytoplasm
Steroid hormones
- Longer response times (minutes to hours)
Activate gene transcription and protein synthesis
Nucleus
Thyroid hormones
Longest response times (hours to days)
Activate gene transcriptions and protein synthesis
Cell surface receptors
Ion channel-linked receptors: open or close ion channels
Enzyme-linked hormone receptors: activated receptors function directly as enzymes or activate closely related enzymes
G Protein-linked: heterotrimeric GTP binding proteins, activates second messenger systems
Regulation and sensitivity?
Number of receptors in a tissue changes with time
- Down regulation of receptors occurs due to increase hormone concentration
- Decrease responsiveness to hormone
Decrease responsiveness to hormone
Inactivation of some receptors or intracellular protein signaling molecules
Temporary sequestration of receptors inside the cell
Destruction of receptors by lysosomes
Decreased production of the receptors
Upregulation of receptors and intracellular signaling proteins?
Hormones induces greater than normal formation of receptors or intracellular signaling molecules
Greater availability of the receptor for interaction with the hormone
Target tissue becomes more sensitive to the stimulating effects of the hormone
Adenylyl Cyclase- cAMP Second Messenger system
Catecholamines, peptide and protein hormones
- Rapid effects
Gs proteins and Gi proteins
ANTERIOR pituitary hormones
Membrane Phospholipid Second Messenger system
G protein –> PL-C –> PIP2 –> DAG + IP2 –> Active PKC –> Protein - PO4 or Protein + Ca2+ –> cell response
POSTERIOR pituitary hormones
Calcium-Calmodulin Second Messenger system
Calcium enters via open channels bc of hormone receptor interaction or membrane potential change
- Ca binds calmodulin which activated calmodulin-dependent PK to produce response via phosphorylation of different proteins
Transcriptional Mechanism
Thyroid and gonadal hormones bind with intracellular protein receptors
Primary: alters gene transcription and protein synthesis
Activated hormone receptor binds to a promoter region of DNA
Activates or repress specific gene transcriptions
Measurement in Blood
Very minute quantities
Sensitive methods for hormone estimations: Radioimmunoassay or ELISA
