Transcript Physiology - Lake Stevens School District

Ch. 18.4, 47.2-3, 35.5
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Regulation of gene
expression that
orchestrates development
Activities of the cell
depend on the genes it
expresses and the
proteins it produces
All cells have the same
genome, but genes are
regulated in each cell type
◦ Depends on activators
present
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Induction: changes in the target cells (communicated via surface
proteins and cell receptors)
Homeotic (Hox) genes: regulate pattern formation in the embryo
(direct the developmental process)—what genes, and where
located
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Morphogen: determines an embryo’s axes, stimulate
differentiation and development
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Apoptosis: programmed cell death
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Differentiation: process by which cells become specialized in
structure and function
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Determination: process by which a group of cells becomes
committed to a particular fate
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Morphogenesis: process that gives an organism its shape
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Induction: changes in the target cells by environmental stimuli or
other cell contact (induce differentiation)
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In multicellular organisms a fertilized egg
must give rise to cells of many different types,
each with different structure/function
◦ Cell tissue organ organ system organism
◦ Mutations result in abnormal development
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Animal Embryonic Development…in general…
Fertilization (zygote) 
Cleavage (mitosis—produce blastula) 
Gastrulation (folding of cells into 3 layers—gastrula) 
Organogenesis (changes in cell shape/location—
rudimentary organs) 
Developing embryo (grow and develop, specialized
cells)
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First zygote divides into a large number of
cells (ball of cells--blastula)
◦ It then divides and folds to form a gastrula
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Then differentiation occurs, cells become
specialized (organogenesis)
◦ Results from the expression of specific genes for
that tissue/organ type
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Morphogenesis occurs next, specialized cells
become organized into tissues and organs
◦ Occurs throughout embryo’s development
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Begins with egg cytoplasm.
◦ “Cytoplasmic Determinants”—molecules that will trigger
development of different cells (unevenly distributed)
 Results in division of cells with different information
◦ Induction.
 Changes that induce differentiation and timing of
developmental events
 “Hedgehog”—signaling molecule (limb bud development)
◦ Observable differentiation marked by expression of
genes for tissue specific proteins
 Gives characteristic structure and function, regulated by
transcription
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Body plan (cytoplasmic
determinants)
◦ Spatial organization of
tissues and organs
 Determine where/when
segments will be (embryo
has cues to determine
this)
◦ Controlled by “Homeotic
(Hox) Genes” and
“morphogens”
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Growth, morphogenesis,
differentiation
◦ All controlled by gene
expression
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Plant organs: roots,
stems, and leaves
“Root” or “Shoot” systems
◦ Made of tissue layers
 Vascular (xylem and phloem)
 Dermal (epidermis)
 Ground
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Apoptosis: programmed cell death
◦ Cells die and are engulfed by neighboring cells
 Tadpole tail
 Webbing between digits
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microRNAs (miRNA): bind to mRNA and
blocks translation by degrading the mRNA
◦ RNA interference (RNAi): regulate gene expression
at transcription
 Important in development of organisms and control of
cellular functions
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Single-celled
organisms use signals
to influence their
response to the
environment
Multi-cellular
organisms use signals
to coordinate activities
within cells
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Cells most often communicate by chemical
signals
◦ Secretion of messenger molecules that target nearby
cells
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Hormones (fight-or-flight—epinephrine)
Mating pheromones (yeast)
Quorum sensing (bacteria density)
Growth factors (stimulate division)
Neurotransmitters (signaling at synapses)
Cells also communicate via cell-cell contact
◦ Cytoplasmic materials can pass through junctions in cell
wall/membrane between cells
◦ Surface molecules on membrane aid in cell recognition
 Important in embryonic development and immune system!
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“Signal Transduction Pathway”—Three stages
◦ Reception: detection of a signaling molecule by the
cell (binds to receptor protein in membrane)
◦ Transduction: receptor protein changes with
binding of signaling molecule; converts signal to
specific cellular response (sequence of changes)
◦ Response: specific cellular response is triggered
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Ligand (signaling molecule) binds to receptor
protein, causing a change in shape
◦ This activates the receptor allowing it to interact
with other molecules (initiates transduction)
◦ Each signaling molecule has specific target cells
◦ Some signaling molecules are small enough to pass
through cell membrane and interact with proteins in
the cytoplasm or nucleus
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Example: Ion-Gated Channel
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Signal is converted into a cellular response
◦ “signal transduction pathway”
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The binding of the signaling molecule triggers
transduction pathway
◦ A chain reaction is started that produces a “cascade”,
leading to cellular response
 Often controlled by phosphorylation (taking P from
ATP)…this drives the reaction forward
 this helps amplify the signal and response
 Second messengers: small molecule that help to transmit
signals (Ca++ and cAMP); spread via diffusion
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Response at the end of the pathway that
occurs in the nucleus or cytoplasm
◦ Regulate protein synthesis (on/off)
◦ Affect activity of enzymes
◦ May be altered by blocked or defective transduction
pathways
 Results in diseases such as diabetes, heart disease,
neurological issues, autoimmune diseases, cancer,
cholera
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Long distance
◦ Electrical to chemical signals—nervous system
 Electrical signal travels down nerve, converted to
chemical signal to stimulate other end of nerve
◦ Endocrine system and hormones
 Specialized cells release molecules and travel through
blood stream to target cells
 Plant hormone ethylene—stimulates ripening
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Hormone: molecule secreted into bloodstream
(or hemolymph) to communicate regulatory
messages
◦ Each has specific receptors, only some cells have them
 May either be water (amino acid based—bind to outside) or
lipid-soluble (steroids—pass thru membrane to nucleus)
◦ Elicits a response from target cells
◦ Maintains homeostasis, respond to environment,
regulate growth and development, trigger physical
changes
 Negative or positive feedback
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Pituitary gland:
growth hormone,
thyroid stimulating
hormone, luteinizing
hormone, folliclestimulating hormone,
oxytocin, antidiuretic
hormone
Pineal gland:
melatonin
Thyroid gland:
thyroxine (T4),
Triiodothyronine (T3)
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Adrenal gland:
cortisol,
epinephrine
Pancreas: glucagon
and insulin
Ovaries/testes:
testosterone,
estrogen and
progesterone
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Controlled by the hormones insulin and
glucagon, produced by Islets of Langerhans in
pancreas
◦ negative feedback
◦ Two hormones are antagonistic
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When BG is high—insulin triggers body cells to
take up glucose from blood stream; also inhibits
glucose production/release from liver
◦ Target cells: muscles, adipose tissue, liver
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When BG is low—glucagon triggers the release of
glucose from storage (liver and fatty tissue)
◦ Target cell: liver, adipose tissue
Normal blood sugar is 70-120 mg/ml
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Hyperglycemia: High blood sugar
◦ Symptoms include increase thirst/urination, glucose
present in urine
◦ Extreme cases result in ketoacidosis (body breaking
down fat for energy—releasing ketones leading to
acidic blood), if untreated results in diabetic coma!
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Hypoglycemia: Low blood sugar
◦ Shakiness, irritability (extreme mood changes),
lightheaded, headache, seizures, unconsciousness
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Increased blood glucose, fat is broken down for
energy because cells don’t take up glucose effectively
or at all
◦ Ketoacidosis results (decreased blood pH, Na+, K+)
◦ Kidneys filter some glucose and release in urine
 Lots of water consumed, glucose in urine
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Type 1 “juvenile diabetes”
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Type 2
◦ Insulin-dependent, autoimmune disorder that destroys
pancreatic cells that produce insulin
◦ Target cells don’t respond normally to insulin, don’t take
up glucose
◦ Most common type. Seen in adults mostly…resulting from
excess weight.
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Thyroxine (T4) and Triiodothyronine (T3)
◦ Target nearly all cells in the body
 Affect metabolism, growth and development
◦ Hormone production is stimulated by TSH from pituitary
◦ Iodine helps to regulate production
 Absence results in overproduction of TSH and enlarged thyroid
gland (goiter)
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Hyperthyroidism (excess of hormone)
◦ “overactivce thyroid”; symptoms: mood changes, increased
heart rate, weight loss, muscular weakness
 High T4 and low TSH
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Hypothyroidism (lack of hormone)
◦ Symptoms: weight gain, fatigue; more common in women
 Low T4 and high TSH