1. Detecting and Responding
AREA OF STUDY 2
Detecting and Responding

2. Coordination and Regulation: Endocrine Systems
Chapter 5
Coordination and Regulation: Endocrine Systems

3. 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.
is the condition of a relatively stable internal, maintained within narrow limits
when changes occur in the internal environment, homeostatic mechanisms act to restore it to the ‘normal’ state
if the body deviates too far from the normal steady state of a variable, death can occur.

4. Internal and External Environments
The external environment is the medium
surrounding an organism
The internal environment, or extracellular fluid, is the internal fluid that surrounds cells in multicellular organisms

5. Defining the Internal Environment reading page 134
the body’s internal environment consists of the tissue fluid (surrounding cells) and blood plasma
plasma is the liquid part of the blood.
both tissue fluid and plasma are located outside of cells. Together they are called extracellular fluid
the composition of the extracellular fluid is regulated so that body cells can operate at their optimum
fluids located outside cells are extracellular.
fluids located inside the cells are intracellular.
Task
Quick Check 1-4

6. Definitions to learn by heart!
Internal environment = extracellular fluid
Extracellular fluid = interstitial (tissue)
fluid, blood plasma and cerebrospinal fluid.

7. 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.

8. 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.

10. Key Variables controlled in the internal environment reading page 136 -138
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

11. Key Body Systems contributing to homeostasis reading page 137
nervous system
endocrine system
respiratory system
circulatory system
digestive system
excretory system
integumentary (skin)system

13. 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

14. Stimulus-Response Model copy
Transmission to nerves
Stimulus
Response
Transmission to nerves or hormones
Receptor
Control Centre
Effector

15. 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
Response
Decreased carbon dioxide
In blood
Transmission to nerves or hormones
(Negative feedback is normal, good!)
Receptor
In arteries and brain
Control Centre
Respiratory centre in brain
Effector
Respiratory muscles in lungs (increased ventilations)

16. 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

17. 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).

18. BIOZONE
Principles of Homeostasis Page 55-56

20. Role of the Endocrine System reading page 134
acts with the nervous system to coordinate and regulate the activity of body cells and so maintain homeostasis
endocrine glands are ductless glands that secrete hormones into the bloodstream
hormones are signalling molecules (proteins) that:
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
can communicate signals to a cell only if the cell has receptors that recognise hormone
the receptor- hormone complex brings about a change in the target cell
Hormones reading page 134

21. 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
Responds to stress
Pancreas
Insulin
Glucagon
Blood glucose concentration
Gonads
Testosterone
Oestrogen
Fertility and sex characteristics

22. 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.

23. 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.

24. Hormones &Negative Feedback Case Study: Controlling Blood Glucose page 139-144
the pancreas produces 2 hormones – insulin and glucagon. these hormones are involved in the control of glucose in the blood.
the hormone insulin controls the uptake by cells of glucose from the blood.
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:
some cells called ‘alpha cells’ increase their production of glucagon, which acts on the liver to convert stored glycogen to glucose.
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
See Fig 5.10 pg 141 – Summary of blood glucose regulation.

25. 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

26. 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

27. Communication by Pheromones reading pages 150-151
Pheromones are:
signalling molecules that are released by animals into their environment enabling them to communicate with members of their own species
pheromones can be used for:
attracting mates
inducing mating activity
marking territories
signalling alarm
marking food trails
Tasks
Quick Check17-18 Pages 151
Biozone page 111

28. 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:
growing regions of stems and leaves
young leaves
growing seeds
developing fruits

29. Plant Hormones reading page 152
similar in structure and function to animal hormones
produced in relatively small amounts
able to produce specific effects even in low concentrations
action depends on concentration
(low concentration of a hormone can do opposite effect to high concentration!)
Can result in a signal transduction pathway (see Gibberellins paragraph 3 page 157)
same hormone can produce more than one effect (i.e auxin)
Classifications of plant hormones:
auxins
cytokinins
gibberellins
abscic acid
ethylene
Florigen
Jasmonates
brassinosteroids

30. Tropisms reading page 154
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

31. Auxins reading page
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)
auxins are produced by the growing tips of plants (coleoptile- first leaves)
See figures 5.22b, 5.25

32. Cytokinins reading page 156
Are another group of growth promoting plant hormones
Act on shoots and roots- promote cell replication
high concentration in growing cells: growing fruits

33. Gibberellins reading page 157
promote both cell elongation and replication in stems and leaves
also initiate seed germination and bud development
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
in some plants, gibberelins promote the development of branches with juvenille leaves
See figure 5.28
Example: Gibberellic acid

34. Abscisic acid reading page 158
Found in high concentrations in fruit about to fall (abscission!) and dormant buds
Inhibits growth
stimulates stomatal closure (reduces water loss by causing stomata to close, by interferring with ion concentrations in guard cells
See figure 5.32

35. Ethylene reading page 159-161
is a hormone in gas form!
produced by the metabolism in some plants
interacts with other hormones to influence events such as ripening
increases respiration rate of cells, encouraging ageing (ripening)
Tasks
Biozone 90
Quick-Check 19-22

36. Photoperiodism
refers to the response of plants to particular periods of light and dark
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