Introduction to Endocrine System Flashcards
Describe the different ways in which cells communicate, e.g. autocrine, paracrine, synaptic, contact dependent and endocrine
- CONTACT DEPENDENT = one to one.
eg gap junctions, desmosomes, between 2 smmu cells.
cells must be touching each other
eg between macrophage and T cells activation etc. antigens, membrane bound ligand etc, antibodies. - PARACRINE
short disatance travel eg at synpase. eg mast cells in nose, release histamine, eg hormones ligands chemicals etc secreted. - AUTOCRINE
ligand released which binds back to itself because it expresses that receptor eg cancer cells release a growth factor eg microglia in CNS - secretes ligand to remove the damaged neuron before it causes excitotoxicity
4.ENDOCRINE
one to many. mediators are hormones, like ligands. longest distance travelled in body via the bloodstream. purpose: to regulate parameters in the human body
- SYNAPTIC
Define hormones and the endocrine system
The mediator for the endocrine system is hormone.
Hormone is a signaling molecule that regulates the physiology of specific organ.
endocrine system includes:
- thyroid, parathyroid glands
- pineal glands
- hypothalamus and pituitary gland
- pancreas
- ovary
- testis
- adrenal glands
Describe the different classes of hormones and how they work
- STEROID HORMONES.
enters cell, binds to intracellular receptor - PEPTIDE HORMONES
binds to a membrane bound receptor. activates second messenger. - THYROID HORMONES - aa hormone but CAN enter the cell and binds to intracellular receptor
- AMINO ACID HORMONES - e, ne, all same features as peptide hormones (dissolution, transport)
Describe the synthesis and release of steroid hormones
ALL steroid hormones are derived from cholesterol, requires specific enzymes; involves modification cholesterol’s side chain.
Steroid hormones are only synthesized when needed. storage of building blocks - the cholesterol.
The rate of steroid hormone secretion is correlated to the rate of its synthesis.
Describe the synthesis, storage and release of peptides and amino acid hormones
Peptide hormones are proteins, therefore it is made up of amino acids.
The peptide hormones are first synthesized as preprohormones at the ribosome, which are then processed into active hormone as it moves through the ER and GA.
Process:
- mRNA translated into preprohormone on ribosome
- Processing the preprohormone into active hormone in GA
- Active hormone packed into secretory vesicle
- Release the hormone from the vesicle by exocytosis when stimulated
The rate of peptide hormone secretion is independent of its rate of synthesis since it is presynthesized and is readily released upon stimulation.
Describe how the actions of steroid hormones are mediated via receptors
The intracellular receptor can be found in any compartment of the cells such as cytoplasm, nucleus etc.
(1) Steroid hormone enters into the target cells by simple diffusion.
(2) It binds to the receptor found in the intracellular compartment (which can be in the cytoplasm or the nucleus).
(3) The hormone-receptor complex serves as a transcription factor and
(4) bind to the hormone-responsive element (HRE) in the DNA to activate gene transcription.
(5) The resulting mRNA is then
(6) translated into new protein that could induce a certain
(7) cellular response.
Describe the hormone receptor system, second messengers and activation of target cell transducer systems
Membrane-bound receptors are along the cell surface
Describe the mechanisms regulating hormone release, activation and feedback control
Negative feedback loop – glucose homeostasis:
- Negative feedback mechanism occurs in order to slow down a particular process that is happening.
- The response resulted from the process will feedback (negatively) on the stimulus to slow down the process.
- The operation of negative feedback brings the process back to the setpoint
- eg hypothalamus detects body temperature rise, works to lower it back to normal using effectors for sweating, vasodilation, hairs flat etc.
- eg blood glucos homeostasis. bgl’s increase, beta cells of pancreas release insulin into blood, body cells and liver take up glucose, bgl’s decrease, homeostatic control, bgl fall, alpha cells of pancrease release glucagon, liver breaks down glycogen and releases glucose, blood glucose levels rise back to normal.
Positive feedback loop - oxytocin
Positive feedback mechanism occurs in order to amplify a particular process that is happening.
The response resulted from the process will feedback (positively) as the stimulus to further enhance the process.
The operation of positive feedback deviates the setpoint further.
To break the positive feedback loop, an external factor is required.
-eg in breast feeding suckling gives positive feedback. sends impulses to hypothalamus, which signals ppituitary to release oxytocin, released into bloodstream, causing increased milk ejection, baby continues feeding.
-eg in childbirth - baby moves deeper into birth canal, cervix stretched, hypothalamus signalled, impulses to ppituitary, oxytocin released, oxytocin travels in the blood to the uterine muscles, more vigourous contraction. at birth, stretching of cervix lessens and positive feedback cycle is broken as the child has been born.
4 types of receptors
fast to slow
- Ionotropic - ligand gated: hyperpolarization or depolarization
- Metabotropic - g protein coupled: change in excitability + second messenger systems which can lead to ca release, protein phosphorylation, others, etc.
- kinase-linked receptors : affects protein phosphorylation
- Nuclear receptors: affects gene transcription
G-protein coupled receptor
surface receptor. has Two second messenger systems:
1. cAMP activates PKA, DAG activates PKC,
- Ca2+ activates the CamPK.
These kinases phosphorylate (adding phosphate group) other cellular proteins to either activate or inhibit these proteins.
The activation or inhibition of these proteins will then bring about cellular response.
BASICALLY ligand binds to RECEPTOR –> affects cAMP / Ca2+ production –> affect kinase activation eg PKC, PKA, CamPK –> affect phosphorylation of linked proteins –> cellular response.
