Bio Midterm 2 Flashcards
Mechanisms of Intercellular Communication (ie between cells)
- Direct communication
- Gap junctions
- Membrane (tunneling) nanotubes
- Mechanosignals
(GMM) - Indirect Communication
- Chemical messengers
Gap junctions
- Connexons and intercalated disks are gap junctions
Connexons: subunits that form a channel (gap function), pore size is very small: permits passage of sugars, amino acids, ions between cells ie metabolic and electric exchange found in ALL CELLS EXCEPT MATURE SKELETAL MUSCLE
- since bones do not connect
Intercalated (cardiac) disks: type of gap junction in cardiac muscle. Allows for rapid and coordinated propagation of action potentials for rhythmic contractions. Smaller than connexons; can be acutely regulated (activated/deativated) by phosphorylation/dephosphorylation
Membrane Nanotubes
Nanotubes are formed in the plasma membrane. They are longer than gap junctions and have a larger pore diameter
- Transfer of nucleic acids, even small organelles, between cells
- Might be a way to transfer cellular componenents from stressed to healthy cells
Mechanosignal Tranduction
Conversion of mechanical stimuli into a cellular response
- Direct physical stress to cells, eliciting a chemical or metabolic response
eg 1: pulsatile and shearing stresses from blood flow on arterial endothelial cells
- Can induce formation of new blood vessels
- If excessive, mediates vascular inflammation and progression of atherosclerosis
eg 2: mechanical stress to muscle fibers from weightlifting resulting in increased protein synthesis
eg 3: remodelling of bone and cartilage through physical stresses (such as weightlifting)
ex 4: conversion of pressure on skin into a neural (electrical) impulse
eg 5: conversion of a sound wave in an electrical signal (hearing)
What are indirect intercellular communication
- Chemical messengers
Autocrine communication is also possible when a messenger acts back on the cell that produced the chemical messenger, but this would probably be considered more of a direct communication
What are the types of indirect intercellular communication?
(a) Paracrine (para close)(acts on a nearby cell): examples of signalling; clotting factors, growth factors eg estrogen (promotes ovary maturation)
- Remember that lots of secreted hormones can act in a paracrine manner and can also act in an endocrine manner
(b) neurostransmitters: synapse is a short distance, neurostransmitter signal must be tightly controlled, not too many molecules released, need an auto shutoff (reuptake or deviation) axons can be long!
(c) hormones: can be water or lipid-soluble, must corss boundaries (membranes), and have target specificity (receptors)
What are the different types of hormones?
Hydrophilic: Water loving: eg insulin, epinephrine, serotonin
- Typically stored in secretory cell
- Dissolved in plasma; no need for carrier!
- Crossing a lipid membrane presents a barrier-so, generally secreted by fusing secretory vesticles to membrane and releasing (exocytosis)
Hydrophobic messenger: Water hating (or lipid-loving)
- Eg steroid and sex hormones (estrogen, testerone, cortisol)
- Storage is typically more limited (ie made on demand)
- Cannot dissolve in plasma; needs a carrier
- Crossing a lipid membrane shouldn’t present a barrier
What is the goal of chemical signal transduction?
To change overall profile of cellular protein/enzymatic activity
What is the process of hydrophobic lipid-soluble chemical messengers
They bind to cystosolic or nuclear receptors (fatty), turns on genes to make new proteins (eg enzymes)
What is the process of hydrophilic lipid-soluble chemical messengers
Binds to cell surface (plasma membrane) receptor, directly, or via second messengers, alters the activity of exisiting enzymes/proteins
Where does amplifiication and signal transduction occur in lipophilic messengers (hydrophobic)
Where does amplification occur?
- Step 3: one hormone/receptor complex can cause many mRNA to be formed
- Step 5: many proteins are formed from each mRNA
Where does signal and hydrophilic messengers take place in hydrophilic messengers
An example with G-proteins
(guanosine nucleotide-binding proteins)
-cAMP is the second messenger
Note the ensuing cascade… activation of one protein (protein kinase A) activates another
- In cytoplasm: A “kinase” phosphorylates a target, and usually uses ATP as the phosphate donor
ONE MESSENGER MOLECULE LEADS TO PHOSPORYLATION OF MILLIONS OF PROTEINS
Signaling systems include?
Can also include, channel-linked receptors (neurostransmitters), and other second messengers (Ca2+, cGMP)
What is phenomenal amplification?
Need to turn a signal off! phospdiesterase breaks down cAMP very rapidly
Process:
- epinephrine (chemical messenger)
- Increase cAMP formation
- Activates Protein kinase A
- Activates hormone sensitive lipase
- Activates liplysis and release of fatty acids to provide fuel during excercise
Chemical classes for lipophobic (water-soluble) and fat-soluble
Water soluble: amino acids, peptides
Lipophilic (fat-soluble): steroids, eicosanoids, thyroid hormones)
Storage in secretory cell
Water soluble: secretory vesicles
Fat-soluble: none
Mechanism of secretion
Water soluble: exocytosis
Fat-soluble: diffusion
Transport in blood
Water soluble: dissolved water soluble
Fat-soluble: bound to carrier protein
Location of receptor
Water soluble: plasma membrane
Fat-soluble: cystosol or nucleus
Signal transduction mechanism
Water soluble: open/close ion channels, activate membrane-bound enzymes G proteins
Fat-soluble: after transcription of mRNA (alter protein synthesis_
Relative time to onset of response
Water soluble: fast
Fat-soluble: slow
Relative duration of response
Water soluble: short
Fat-soluble: long
Relative half-life
Water soluble: short
Fat-soluble: long
Combining neural and endocrine singaling: the neurendocrine (neurocrine) signaling system
Examples:
- Norepinephrine
- Antidiuretic hormone
Secretory cell
Neuron
Messenger
Neurotransmitter (neurohormones)
Pathway
Bloodstream
Target cell
endocrine cells
Specificity
receptors on target endocrine cells
Time to onset
Delayed; duration of effect: longer
Where is norepinephrine released from?
Released from noradrenergic nerves
Where is antidiuretic hormones released from?
From neurons in anterior pituitary
Secretory cell
Nervous sytem: neuron
Endocrine system: endocrine cell
Target cell
Nervous sytem: neuron, muscle, or gland
Endocrine system: most cell types in body
Messenger
Nervous sytem: neurotransmitter
Endocrine system: hormone
Pathway for communication
Nervous system: across synapse
Endocrine system: via bloodstream
Basis of specificity
Nervous system: recpetors on postsynaptic target cell
Endocrine cell: receptors on target cells throughout body
Time to onset of effect
Nervous system: immediate
Endocrine cell: delayed
Duration of effect
Nervous system: brief
Endocrine cell: long
What are the classic endocrine tissues of the body
- Hypothalamus
- Aneterior pituitary
- Adrenal glands
- Pancreas
- Thyroid
- Sex organs (ovaries, testes)
- Kidneys
Most tissues have an endocrine function
What does adipose tissue secrete?
Hunreds of peptides
What regulates fluid secretion into the intestinal lumen
- Matter of chloride and sodium secretion
- Cl- and Na+ pumps are regualted by a protein kinase (and cAMP)
Cholera Toxin and Life Threatening Diarrrhea
- Cholera grows under the mucus layer in the small intestine
- Secreted choler toxin activates G protein for a prolonged period (ie singal doesnt shut off)
- Causes efflux of Cl-, Na+, and water
- Life threatening diarrhea
CFTR Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) a CI- tranpsorter, how is it characterized
CF characterized by a homozygous mutation in the CFTR gene
- Impairs regulation of sweat, digestive juices and mucus (ie thicker secretions, less water loss)
- Could protect the severe loss of fluid that occurs due to the cholera toxin
What is a regulated healthcare professional?
- Physician, registered nurse, nurse practitioner, registered dietation, pharmacist, genetic counsellor, midwife, physical therapist etc
What is public health?
- Public health dietitian, epidemiologist, infectious disease specialist, health communications specialist, environmental health specialist, health policy analyst, biostatistician
What are the components of the control and communication network (CCN)
The central nervous system, endocrine system, peripheral, local support and defense system
Central nervous sytem
Brain and spinal cord
Peripheral nervous system
somatic (directs voluntary movements) and
autonomic (involuntary bodily activities such as heart and breathing rate)
- Parapsympathetic: governs bodily activities during restful conditions
- Sympathetic: prepares body for stressful or emergency situations
Local support and defense system
- Maintenance and support system
- Adaption and repair system
- Resident defense system
- Migrant defense system
5 Major Cell Types of the Adult Human CNS
- Neurons
- Oligodendrocytes (CNS) and Schwann cells (PNS)
- Astrocytes
- Microglia
- Ependymal Cells
What are neurons built for?
Info flow and speed
What is multiple sclerosis?
Destruction of myelin sheath, due to an autoimmune disorder (decreased communication, less myelin, slows nerve signals)
What does myelination help with?
Speed of neurons
What are the nodes of ranvier?
Gaps between myelination
Neurons release how many neurotransmitters?
One type of neurotransmitter at a given pre-synaptic neuron (eg either dopamine, serotonin, norepinephrine, etc)
Can neurons be either inhibitory or excitatory?
Yes, net response is based on an overall (summation) effect of all inputs
- If thereshold is met enough excitatory
Is norephernephrine excitatory or inhibitory?
Excitatory
When do neurons begin?
At around 10 years of age, lots of remodelling of brains neural network
- Developing new synapses
- Pruning away unused ones
In the teenage/emerging adult brain…
- Growth is 90% complete, but there is a massive reorg and development of synapses ie networking
Are teenagers most likely to have dopamine sensitivity?
Yes, more likely to do things that increase risk more dopamine need it
When you are a teen, there is a large increase in…
Myelination, increase in the transmission speed of neurons
What does oligodendrocytes and Schwann cells produce
Myelin
- Oligo span multiple axons and are found in CNS
- Oligo in CNS and Scwann in PNS, Schwann do not span multiple axons
What does astrocytes do?
Stellate (starlike) morphology, very important for communication, more abudant than neurons
What does micoglia do?
Mobile macrophage-like immune cells
What do ependymal cells do? (epidural)
line ventricles to form a barrier; produces cerebrospinal fluid