Download Internal Environment

AREA OF STUDY 2
Detecting and Responding
Chapter 5
Coordination and
Regulation: Endocrine
Systems
Homeostasis
reading pages 136 - 137
Homeostasis is:
the maintenance of the internal environment in a relatively stable
state despite changes in either the external or internal
environment.
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is the condition of a relatively stable internal, maintained within narrow limits
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when changes occur in the internal environment, homeostatic mechanisms
act to restore it to the ‘normal’ state
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if the body deviates too far from the normal steady state of a variable,
death can occur.
Internal and External Environments
The external environment is the medium
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surrounding an organism
The internal environment, or extracellular fluid, is the
internal fluid that surrounds cells in multicellular
organisms
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Defining the Internal Environment
reading page 134
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the body’s internal environment consists of the tissue fluid (surrounding
cells) and blood plasma
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plasma is the liquid part of the blood.
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both tissue fluid and plasma are located outside of cells. Together they are
called extracellular fluid
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the composition of the extracellular fluid is regulated so that body cells can
operate at their optimum
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fluids located outside cells are extracellular.
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fluids located inside the cells are intracellular.
Task
Quick Check 1-4
Definitions to learn by heart!
Internal environment = extracellular fluid
Extracellular fluid = interstitial (tissue)
fluid, blood plasma and cerebrospinal fluid.
Unicellular Organisms
The environment of unicellular organisms is the external
environment in which they live.
Unicellular organisms can do little to control their
environment.
They are either
– able to tolerate the conditions or
– they die.
Simple Organisms
Homeostasis occurs in all living organisms.
Even unicellular organisms are able to sense and
respond to changing environmental conditions,
generally moving away from light and heat, and
towards food.
In this Petri dish, tiny green
Volvox colonies have moved
towards the light source,
allowing increased levels of
photosynthesis.
Key Variables controlled in the internal environment
reading page 136 -138
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core body temperature
blood glucose concentration
water levels in body tissues
ph (hydrogen ion concentration)
ions, such as sodium, calcium and chloride ions
blood oxygen concentration
carbon dioxide concentration
blood volume
blood pressure
Key Body Systems
reading page 137
• nervous system
• endocrine system
• respiratory system
• circulatory system
• digestive system
• excretory system
• integumentary (skin)system
contributing to homeostasis
Stimulus-Response Model
• a change in the internal or external environment acts as a stimulus
that is detected by receptors
• if the intensity of the stimulus is sufficient (threshold), messages
are transferred to a control centre
• messages are then passed to effectors which produce a response
Stimulus-Response Model copy
Transmission to nerves
Stimulus
Receptor
Control Centre
Response
Effector
Transmission to
nerves or hormones
Negative Feedback in the Stimulus-Response Model
reading page 139
In the stimulus-response model, negative feedback occurs when the effector brings
about a response that counteracts the original stimulus, so that the variable within
the internal environment is returned to its optimal level.
Transmission to nerves
Stimulus
Increase in blood carbon dioxide
Receptor
In arteries and
brain
Control Centre
Respiratory centre in brain
Response
Decreased carbon dioxide
In blood
Effector
Respiratory muscles in
lungs (increased
ventilations)
(Negative feedback is normal, good!)
Transmission to
nerves or hormones
Positive Feedback rare but does exist
Case Study: production of oxytocin page 144
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Far less common than negative feedback
Involve a situation where a hormone produced by a gland acts on the same
gland to stimulate it to produce even more hormone
Example: production of oxytocin
• Produced by the pituitary gland during childbirth
• Once birthing process commences, oxytocin stimulates uterine contractions
that help push baby out of the uterus
• Also acts on the pituitary to produce more oxytocin
• Continues until baby is born
Tasks
Biozone page 55-56
Quick Check 9-12
Stimulus Response
• Stimulus: some change in the internal or external environment.
• Receptors: specialised cells that detect a stimuli.
• A receptor transmits information about the detected change to the
central nervous system.
• The CNS coordinates the action to be taken and transmits this to the
tissue/s or organ/s which will respond (effector).
• Two systems that are involved in this coordination: nervous and
endocrine (hormonal).
BIOZONE
1. Principles of Homeostasis Page 55-56
Role of the Endocrine System
reading page 134
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acts with the nervous system to coordinate and regulate the activity of body cells and
so maintain homeostasis
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endocrine glands are ductless glands that secrete hormones into the bloodstream
Hormones
reading page 134
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hormones are signalling molecules (proteins) that:
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Are produced by cells within an organism
act on target cells by binding to a receptor either on a plasma membrane or within a target cell
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can communicate signals to a cell only if the cell has receptors that recognise hormone
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the receptor- hormone complex brings about a change in the target cell
Examples: Hormones – Chemical Messengers
Gland
Hormone
Action
Hypothalamus
Many
Many body activities
Pituitary
Growth Hormone
The master gland
Thyroid
Thyroxine
Metabolism
Growth
Adrenals
Cortisol
Adrenaline
Metabolism
Responds to stress
Pancreas
Insulin
Glucagon
Blood glucose concentration
Gonads
Testosterone
Oestrogen
Fertility and sex characteristics
Different hormones
• there are three different kinds of hormones based on their chemical
structures:
- amino acid derivatives
- steroid hormones
- protein hormones and peptide hormones.
• hormones may be hydrophilic or lipophilic; this effects the way in
which hormones are transported through the blood and how a signal
is transmitted across the membrane.
Different hormones
reading page 146
• the key difference in different types of hormones can be summarised
in table 5.3, page 146.
• position of the cell receptors are important for cell response.
• figure 5.15 page 147 illustrates the sequence of events in the
signaling pathways.
Hormones &Negative Feedback
Case Study: Controlling Blood Glucose page 139-144
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the pancreas produces 2 hormones – insulin and glucagon. these hormones are
involved in the control of glucose in the blood.
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the hormone insulin controls the uptake by cells of glucose from the blood.
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the hormone glucagon acts on the liver to release more glucose into the blood.
if the blood glucose level falls below normal – the pancreas responds in 2 ways:
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some cells called ‘alpha cells’ increase their production of glucagon, which acts on
the liver to convert stored glycogen to glucose.
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other cells called ‘beta cells’ decrease their production of insulin. less insulin in the
body results in less glucose being taken from the blood by the cells of the body
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if the blood glucose level falls below normal – the pancreas responds in 2 ways:
See Fig 5.10 pg 141 – Summary of blood glucose regulation.
Positive Feedback rare but does exist
Case Study: production of oxytocin page 144
•
•
Far less common than negative feedback
Involve a situation where a hormone produced by a gland acts on the same
gland to stimulate it to produce even more hormone
Example: production of oxytocin
• Produced by the pituitary gland during childbirth
• Once birthing process commences, oxytocin stimulates uterine contractions
that help push baby out of the uterus
• Also acts on the pituitary to produce more oxytocin
• Continues until baby is born
Tasks
Biozone page 55-56
Quick Check 9-12
Cell Communication
reading page 145-148
As we saw in chapter 2 (pages 52-56), cells have connections with other cells and in
some cases, small molecules can pass from one cell to another through those
connections.this provides only limited communication. In addition, communication
between cells can take place by means of chemical messengers called signalling
molecules of which hormones are one group (also includes pheromones,
neurotransmitters, neurohormones)
• when a hormone is secreted by a cell, only cells with receptors
specific for the hormone respond to the hormone gland.
• some hormones act on one kind of cell only while others act on
different tissue types in the same way.
Tasks
Quick Check 13-16
Communication by Pheromones
reading pages 150-151
Pheromones are:
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signalling molecules that are released by animals into their
environment enabling them to communicate with members of
their own species
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pheromones can be used for:
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attracting mates
inducing mating activity
marking territories
signalling alarm
marking food trails
Tasks
Quick Check17-18 Pages 151
Biozone page 111
Plant Hormones
reading page 152
• hormones are plant growth regulators
• environmental factors control the production and amount of a
particular hormone
• hormones produced in plant cells can diffuse to adjacent target cells
or be transported in the xylem or (particularly) phloem of vascular
plants to target cells
• Some of these hormones stimulate growth, others inhibit it
• parts of a vascular plant most likely to contain hormone producing
cells are:
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growing regions of stems and leaves
young leaves
growing seeds
developing fruits
Plant Hormones
reading page 152
• similar in structure and function to animal hormones
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produced in relatively small amounts
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able to produce specific effects even in low concentrations
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action depends on concentration
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(low concentration of a hormone can do opposite effect to high concentration!)
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Can result in a signal transduction pathway (see Gibberellins paragraph 3 page 157)
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same hormone can produce more than one effect (i.e auxin)
Classifications of plant hormones:
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auxins
cytokinins
gibberellins
abscic acid
ethylene
Florigen
Jasmonates
brassinosteroids
Tropisms
reading page 154
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is a growth response towards (positive) or away from (negative) a given stimulus
Examples:
Positive Phototropism: is growth towards a stimulus (light)
Thigmotropism: change in the direction of growth because of contact another object
Geotropism: is a growth response due to gravity (positive (grows down!- with)
Hydrotropism: growth response due to stimulus of water
See figure 5.22, 5,24 & 5.26
Auxins
reading page 152-156
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are a group of hormones whose major actions is to control (stimulate or
inhibit) the enlargement and elongation of cells
Action of auxins include:
• simulate enlargement and elongation in stems but also, in large
concentrations, inhibit the growth of root cells
• Stimulate growth of lateral and adventitious roots
• Promote growth of flowers and fruits
• Influence the differentiation of unspecialised cells in vascular tissue
• some promotes apical dominance (example IAA)- inhibition of lateral buds!
• promote photropism (auxin moves away from light side!)
• Promote geotropism (auxin builds up on lower side and inhibits root cell
growth in lower cells (upper cells turn over and down – geotropism)
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auxins are produced by the growing tips of plants (coleoptile- first leaves)
See figures 5.22b, 5.25
Cytokinins
reading page 156
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Are another group of growth promoting plant hormones
Act on shoots and roots- promote cell replication
high concentration in growing cells: growing fruits
Gibberellins
reading page 157
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promote both cell elongation and replication in stems and leaves
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also initiate seed germination and bud development
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can result in a signal transduction pathway (gibberelin becomes activated
diffuses with aleurone, and acts on dna to induce synthesis of the enzyme
amylase which converts starch to glucose which is in turn used as a nutrient
for the initial stages of new plant growth
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in some plants, gibberelins promote the development of branches with
juvenille leaves
See figure 5.28
Example: Gibberellic acid
Abscisic acid
reading page 158
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Found in high concentrations in fruit about to fall (abscission!) and dormant
buds
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Inhibits growth
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stimulates stomatal closure (reduces water loss by causing stomata to
close, by interferring with ion concentrations in guard cells
See figure 5.32
Ethylene
reading page 159-161
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is a hormone in gas form!
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produced by the metabolism in some plants
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interacts with other hormones to influence events such as ripening
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increases respiration rate of cells, encouraging ageing (ripening)
Tasks
Biozone 90
Quick-Check 19-22
Photoperiodism
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refers to the response of plants to particular periods of light and dark
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plants may be classified as short day (only flower when the day is short),
day-neutral or long day plants
Tasks
Biozone page 91-92
Biochallenge
Chapter Review