Chapter 9 (Maintaining Internal Balance) Flashcards
direct vs. indirect cell signalling
- direct: cells communicate via aqueous pores that connect adjacent cells (through gap junctions)
- indirect: signalling cell releases a chemical messenger into the extracellular environment
differentiate between the types of indirect cell signalling: paracrine, autocrine, endocrine
- paracrine: chemical messengers diffuse to nearby cells
- autocrine: chemical messenger binds to receptors on the same signalling cell
- endocrine: hormones travel via circulatory system
exocrine vs. endocrine glands
- exocrine: secretions via ducts onto body surface (or gut surface)
- endocrine: secrete hormones carried by circulatory system (long distance)
hormones
- circulate through blood
- activate receptors on target tissue cells
- act as first messengers in a series of messengers that lead to a specific response
- released into the blood in small quantities
direct feedback loop
stimulus is detected and integrated by the same endocrine organ to secrete hormone
first-order feedback loop
- one step (one neuron) between integration centre and target organ
- stimulus detected by sense organ that sends signal via sensory neuron to integrating centre, signal sent via neuron to target organ
second-order feedback loop
- two steps from integrating centre to target organ
- integrating centre to endocrine gland via neuron; endocrine gland to target organ via circulatory system (hormone)
third order feedback loop
- three steps from integrating centre to target organ
- integrating centre to endocrine gland 1 via neuron
- endocrine gland 1 to endocrine gland 2 via circulatory system and hormone 1
- endocrine gland 2 to target organ via circulatory system and hormone 2
Describe the synthesis of peptide hormones.
- ribosomes on RER synthesize large preprohormone
- preprohormone enters RER, signal sequence gets cleaved off and resulting prohormone is packaged into vesicle
- vesicle move to Golgi apparatus for processing and sorting
- prohormones from Golgi get packaged into secretory vesicles
- inside these secretory vesicles the prohormone is cleaved into the active hormone
- secretory vesicle fuses with plasma membrane, exocytosis releases hormone into extracellular environment
Amino acids typically act as ___.
neurotransmitters
cytokines
paracrine peptides that are synthesized only on demand
How do peptide messengers act on their target cells?
- dissolve in extracellular fluid and bind to transmembrane receptors
- they are hydrophilic so cannot pass through membrane
Steroid hormones are derived from ___.
cholesterol (lipids)
What are the major classes of steroid hormones?
- mineralocorticoids
- glucocorticoids
- reproductive hormones
mineralocorticoids
- regulate kidney sodium uptake
- fluid and electrolyte balance
- example: aldosterone
glucocorticoids
- aka stress hormones
- metabolism
- glucose production
- breakdown of proteins
- release of fatty acids
- regulate immune system and inflammatory response
- example: cortisol
Are steroids hydrophilic or hydrophobic? How does that affect its synthesis?
- steroids are hydrophobic
- since they can pass through membranes, they cannot be stored
- must be synthesized on demand
Explain the equilibrium formed between messengers (e.g. steroids) and carrier proteins (e.g. albumin)
- high concentration of messenger near signalling cell diffuses into blood
- equilibrium is established between free messenger and messenger bound to carrier protein
- as free messenger diffuses into target cell, concentration decreases and more messengers dissociate from carriers (and vice versa)
What are biogenic amines derived from? What are some examples? Hydrophobic/hydrophilic?
- amino acid derivatives
- examples: catecholamines (epinephrine, norepinephrine, dopamine), serotonin, histamine, acetylcholine, thyroid hormones
- most hydrophilic but thyroid hormone is hydrophobic
agonist vs. antagonist
- agonist: chemical binds to and activates receptor
- antagonist: binds to but does not activate receptor; prevents binding of natural ligand and prevents response
law of mass action
- binding of receptor to ligand will produce complex; active complex produces response
- reversible binding
- balance between concentration of ligand and proportion of receptors bound (as one increases the other increases)
What does affinity refer to? What does high vs. low affinity mean?
- affinity is the ability of a receptor to recognize and bind to ligand and induce response
- high affinity = more binding with lower concentration of ligand (lower Kd)
- low affinity = higher Kd
- Kd is concentration of ligand at which 50% receptors bound
down-regulation vs. up-regulation
- down-regulation: less receptors produced (due to action of agonist) (e.g. when more heroin is consumed, less endorphin receptors are produced)
- up-regulation: more receptors produced (due to action of antagonist) (e.g. when more caffeine is consumed, more adenosine receptors are produced)
Describe signal transduction by intracellular receptors.
- hydrophobic ligand passes through cell membrane and binds to ligand-binding domain on intracellular receptor
- intracellular receptor undergoes conformational change
- receptor-ligand complex translocates to nucleus
- DNA binding domain of receptor binds to DNA and interacts with other transcription factors
- rate of transcription of target genes is altered
Do intracellular receptors produce short term or long term effects and why?
- effect is long term because receptor-ligand complex binds to regulatory elements in DNA
Describe signal transduction by receptor-enzymes using the example of guanylate cyclase.
- ligand binds to guanylate cycle, changing its conformation and activating it
- activated receptor catalyzes conversion of GTP to cGMP
- cGMP acts as second messenger, binding to PKG
- PKG is activated and phosphorylates proteins on serine/threonine residues
What are the 3 domains that make up receptor-enzymes
- extracellular ligand-binding domain
- transmembrane domain
- intracellular catalytic domain
Describe signal transduction via G-protein coupled receptors.
- ligand binds to GPCR, causing conformational change
- activates G protein; alpha subunit releases GDP and binds GTP
- some subunit(s) translocate through membrane to interact with amplifier enzyme, which activates a second messenger
- activated second messenger can activate or inhibit cellular pathways
