Hormones & Receptors Flashcards
Paracrin effectors act on?
Neighboring cells, released in ECF.
Autocrine effectors act on?
the cell releasing the effecto
What is a hormone?
A chemical produced by certain cells, released into blood stream in minute amounts and acts on distant targets.
General methods of classifying hormones
Chemical
Functional
Types of hormones
- Tyrosine derivatives
- Cholesterol derivative
- Proteins/peptides
Describe protein/peptide synthesis
- Pre-prohormone is synthesized on ribosome
- Taken into RER and presequence is cleaved.
- Prohormone taken to golig for processing and put in vesicles
- Exocytosis in a Ca++ dependent manner in reponse o stimuli
Transport of peptide/protein hormones in blood
Most are free form excet for GH, IGF, and PRL. Short half life
Properties of steroid hormones
- lipophilic, cross membrane easily
- Immedate release following synthsis
- Require a protein carrier
- longer half life due to carriers.
What is the active hormone: free hormone or atached to carrier
Free hormone, only 1–5% is free in blood and the rest acts like a resevoir. Free hormones are responsble for regulating secretion via feedback mechanisms.
Ways to measure [Hormone] in blood:
- Bioassay: tests for function on exogenous systems.
2. Immunoassay: tests for protein levels using radio immunoassays or ELIZA.
Types of peptide/protein hormone receptors
- G-protein coupled (EPI & NE)
- Cytokine receptors, aka JAK/STAT (GH & PRL)
- Ectodermal Growth Factor (EGF) receptors (insulin & IGF)
Explain G-proteins
Hormone receptors are associtaed with a G protein that couples it to enzymes such as adenylate cyclase (cAMP) or phospholipase C (DAG & IP3).
-Has 3 subunits (alpha, beta, gamma)
-Alpha has inherent GTPase activity.
Alpha can be inhibitory or stimulatory
JAK/STAT receptors: hormones
GH and PRL
JAK/STAT mechanism
Activation of these receptors results in coupling and activation of a tyrosine kinase (Janus kinase or JAK), which then causes the phosphorylation of a group of proteins called signal transducers and activators of transcription (STATs).
Insulin & IGF receptors
EGF receptors are a large family of protein tyrosine kinase receptors. In this case the receptors themselves are tyrosine kinases that can be activated upon hormone binding
Steroid hormone signaling
Receptors are cytoplasmic or nuclear, forming a complex and migrating to nucleus to bind to Hormone Responsive Elements (HREs) and acting as transcription factors.
How is hormone secretion regulated?
Feedback loops
Classes of feedback loops
- Hormone level is the regulated variable (usually -ve feedback)
- Plasma concentration of a metabolite or a mineral acts as the regulated variable
Feedback loops can be direct or indirect.
T or F: +ve feedback loops are common
False, very rare (ex: oxytocin secretion during birth)
Termination of +ve feedback loop
The only way a positive feedback loop can be terminated is by the exhaustion of the hormone or by an explosive event such as ovulation
Patterns of hormone secetion
- Hormone secretion often occurs in a pulsatile fashion.
- levels of many hormones are regulated by diurnal variation showing characteristics of circadian rhythms.
