Transcript Ch 10 Physiological Adaptations

Homeostasis
Homeostasis is:
the maintenance of the internal environment in a relatively
stable (steady) state despite changes in the external
environment.
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is the condition of a relatively stable internal environment, 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 (beyond its
tolerance limits) of a variable, death can occur.
The Internal Environment
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the body’s internal environment consists of the tissue fluid (surrounding
cells) and blood plasma (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 (extracellular fluid = internal environment).
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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
Internal environment = Extracellular fluid=
Interstitial fluid
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
(**this is a key concept for Year 11/ 12)
• 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
Nerves
&
Nervous System
The Nervous System- Structural Classification
reading pages 301 - 302
When classified according to structure, the nervous system has two
subdivisions.
1. The central nervous system (CNS)
consists of the brain and the spinal cord
acts as the integrating and command center of the
nervous system
interprets incoming information and issues instructions
based on past experience and current conditions
2. The peripheral nervous system (PNS)
the part of the nervous system outside the CNS
consists mainly of nerves that extend from the brain and
spinal cord
The Nervous System
Spinal
Cord
Brain
reading pages 170-172
Nerves
Central Nervous System
Peripheral Nervous System
Neurons
Neurons (Nerve Cells)
reading pages 172-175
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nerve cells or neurons are the basic structure of the nervous
system
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a typical neuron has:
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three types of neurons exist including:
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a nucleus within the cell body
dendrites: highly branched extensions of the cell body that receive
and then carry information towards the cell body
an axon: an extension that carries information away from the cell
body
sensory (affector) neurons
connecting (inter) neurons
motor (effector) neurons
the presence of the myelin sheath (on affector and effector
neurons) increases the rate at which a nerve impulse is conducted
along the axon.
Tasks
Biozone 255 - 256
Cells of the nervous system. (a) A typical sensory neuron (b) A typical
motor neuron (c) Structure of a nerve (d) A typical connector or inter
neuron
Relationship between different kinds of neurons.
Task:
copy and label
Reflex (Arc)
Simplest of neural
responses.
Involves as little as 3
neurons
Shortens link between
stimulus and response.
Receptors: Light
Receptors: Smell - Olfactory Receptors in the Nose
Receptors: Touch
Receptors: Sound
Endocrine System
&
Hormones
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
Produced within ductless glands called endocrine glands
Transported around the body in the bloodstream
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
Homeostasis in action
Detecting & Maintaining Body Temperature
Stimulus: External Temperature Change
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The skin is the barrier between our body and the external environment
and can be two or three degrees below core body temperature.
Core body temperature is maintained at about 37°C but changes in the
external temperature cause changes in the temperature of exposed skin.
Receptor
• Such change is detected by two kinds of temperature receptors in the skin
(see figure 10.10, page 306).
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One kind of receptor detects the (stimulus) cooling of the skin and the
other detects (stimulus) warming.
Transmission of Message
• A change of temperature detected results in an increase in electrical
information along affector (sensory) neurons
Detecting & Maintaining Body Temperature
Control Centre:
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Affector (sensory neurons) transmit impulses from skin receptors to the
hypothalamus in the brain
Detecting & Maintaining Body Temperature
Transmission of Message
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Messages are relayed to effectors (glands and muscles) by effector neurons and/
or hormones (i.e. adrenalin, thyroxin etc)
Effectors
• A number of effectors assist in increasing or decreasing temperature at the skin and
internally including: Smooth muscles;
• Skeletal muscles;
• Sweet glands
• arterioles
Response
• A number of number of responses to high and low temperature are employed by
humans including:
• Vasoconstriction
• Shivering
• Piloerection
• Increased metabolism
• Vasodilation
• Sweeting
Nerve Action
Endocrine system
is faster
Is slower
shorter lived
more sustained
(longer acting)
Why?
Why?
• Nerve action is due to electrical
impulses, which travel very
quickly
(up to 200metres per second)
• Transmitter substance is active
at a
synapse for a fraction of a
second
only and then is inactivated
• endocrine hormones travel
from
their production site via the
bloodstream to their target
cells
• Hormones must be metabolised
before their actions stop and
inactivation time can take
hours or
days.
Research Task
Homeostasis
Due Date: Thursday 31st March
Details of Task:
Choose one of the following variables and produce a handout or PowerPoint
presentation aimed at Year 11 Biology students outlining (addressing all the dot
points) how the organism maintains a stable internal environment despite the
changes in the variable in the external environment:
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Blood glucose levels in humans (Insulin and Glucagon)_
Temperature
Osmotic Control (i.e. H2O concentration in the blood)
Light (plants)
Seasonal changes (plants)
Salt concentrations in freshwater fish
Maintenance of salt concentration in salt water based fish
Calcium levels (Para hormone and Calcitonin)
Level of Thyroxin in the body (Thyroxin and Thyroid Stimulating Hormone)
CounterCurrent Heat Exchange
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Whales and dolphins also maintain their body temperature by using a
countercurrent exchange system (see figure 10.29).
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There is a fine network of vascular tissue within the fins, tail flukes and
other appendages.
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An outgoing artery is paired with an incoming vein.
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Blood coming from the body core to the skin is warm.
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Blood flowing from the skin back to the body core has been cooled.
Torpor
Torpor: a state of lowered body temperature and metabolic activity
assumed by many animals in response to adverse environmental
conditions, especially cold and heat. The torpid state may last overnight,
as in temperate-zone hummingbirds and some insects and reptiles; or it
may last for months, in the case of true hibernation and the winter torpor
of many cold-blooded vertebrates
Antifreeze Substances
"Groundsels also grow here [on Mount Kenya]. They are relatives of the dandelions
and ragworts that flourish as small yelllow-flowered weeds in European gardens. On
Mount Kenya, they have evolved into giants. One grows into a tree up to thirty feet
tall. Each of its branches ends in a dense rosette of large robust leaves. As the
branches grow, so each year the lower ring of leaves in the rosette turn yellow and
die. But they are not shed. Instead, they remain attached and form a thick lagging
around the trunk. This is of crucial importance to the groundsel. The living leaves in
the rosette contain special substances that prevent frost damage to the tissues and
even though they may become covered by hoar frost during the night, they thaw out
rapidly in the powerful warmth of the morning sun.
Plant responses to temperature in a hot
environment
• Text 322 – 325
• Quick Check 19 – 2
Green plants depend on radiant energy from the sun to
carry out photosynthesis.
However, only a small fraction of energy absorbed is used.
To prevent overheating, a plant must lose much of the
radiant energy it absorbs.
A plant does this in the following ways (see figure 10.30)
(summarise)
Plants in a cold environment
Many plants survive in sub-zero temperatures without
being damaged by these extremely low temperatures.
Unlike animals, plants do not produce an ‘antifreeze’.
They gradually become resistant to the potential danger of
ice forming in their tissues as the temperature falls below
0°C.
How does this occur?
Water Balance in mammals
• Read pages 330 – 335
• Quick check 25 – 30
Tonicity, page 28
Key Terms:
• Tonicity
• Isontonic
• Hypertonic
• Hypotonic
Homework
• PRAC Preparation
• . Reading 362 - 364
Water Balance in fish
Water in living organisms must be maintained at a
relatively stable level.
Water loss from and water gain by an organism occur in
many ways.
Kidneys are essential organs for water balance.
Kidneys eliminate nitrogenous wastes from the body at the
same time as maintaining water balance.
Vasopressin, renin and aldosterone are important
compounds in the control of water balance and blood
pressure in humans.
Water Balance in Plants
Water makes up about 90–95 per cent of the living tissues of
plants.
Plants often grow in situations where they are continually losing
water.
Plants cannot move around and search for water.
They have features that help them obtain and retain sufficient
water for their cells to operate effectively.
Under conditions of water shortage, plants maximise their
opportunity to obtain and conserve water and at the same time
minimise loss.
They do these things in a number of special ways.
Transpiration
The movement of water from the roots, through the stem,
and to the leaves where it may pass through the stomata
as water vapour is called the transpiration stream.
The loss of water vapour from a plant is called transpiration
and occurs mainly through the stomata with some loss
through the cuticle.
Up to 98 per cent of water absorbed by a plant can be lost
through transpiration.
Only 2–5 per cent is retained within the plant.
Leaf Structure and water loss
The waterproof outer layer of a leaf, the cuticle, reduces water
loss.
The thickness of the cuticle is just one of the ways in which the
structure of a leaf can vary depending on its particular
environmental conditions (see figure 10.45).
The thinner the cuticle, the more transpiration occurs.
Plants that live in dry areas are known as xerophytes and
show a variety of specialised features.
The shape of a leaf is important in relation to the amount of
water it loses through transpiration.
The edges of some flat leaves curl over and form a protective
layer above the stomata in order to reduce transpiration rate.
Factors affecting Transpiration
The transpiration rate is much greater on a hot windy day than
on a hot still day.
On a still day, a boundary of still air surrounds the leaf. Water
vapour leaving stomatal pores tends to stay close to the leaf,
keeping the humidity of the boundary layer similar to the
humidity inside the leaf.
On a windy day, water vapour that diffuses out of stomatal
pores is immediately blown away from the leaf; there will still
be a significant difference in humidity inside and outside the
leaf, and more water vapour will diffuse from the leaf.
The windier a day is, then the higher is the transpiration rate.
Air temperature is another factor that influences the
transpiration rate of a plant.
The higher the temperature, the greater will be the amount
of water lost from the plant.
As water evaporates from the surfaces of a
plant,particularly the leaves, heat is required so the
evaporating process cools the surface of the leaf.
Stomatal pores close if excessive water loss occurs.
As long as there is sufficient water in the soil to replace the
water that is being lost by a plant, stomata stay open.