1. Communication within multicellular organisms
Ah biology
Communication within multicellular organisms

2. Communication within multicellular organisms
This topic will look at 3 areas
Coordination
Hydrophobic signals and control of transcription.
Hydrophilic signals and transduction.

3. Coordination in animals is produced through nervous transmission and hormonal secretion.
Compare and contrast the two modes of communication.
Challenge students to name the glands shown in the diagram:
1. pineal; 2. pituitary; 3. thyroid; 4. thymus; 5. adrenal; 6. pancreas; 7. ovary; 8. testis

4. electrical impulse and extracellular
Comparing the 2 systems
Nature of signal
electrical impulse and extracellular
extracellular signalling signalling
molecules molecules
Transmission of
signals
along neuron axons bloodstream
Target cells
cells with connections almost any cells in
to neurons (effectors) the body
Time for response
faster slower
Duration of response
transient longer lasting
As an analogy: a person on a desert island can send messages to the outside world in bottles (hormonal communication) or use a telephone (nervous communication).
For extent of response: one hormone can act on many spatially separate organs: a nerve impulse results in the contraction of one muscle in one part of the body or the secretion of a chemical from one gland in the body.
Extent of response
localised widespread

5. Coordination is important for homeostasis. What is homeostasis?
What are the main features of homeostatic control?
Controlled system
Monitoring centre
Mechanisms of correction
Set point re-established
Brainstorm all the physiological variables that must be maintained within a narrow range of values.

6. Coordination allows humans to cope with physiological challenges
Exercise
What challenges does it bring?
Cardiovascular
Ventilatory
Metabolic
Thermoregulatory
Osmoregulatory
What responses would be needed to meet these challenges? No need to mention specific hormones just yet.
Cardiovascular challenge: increased blood flow to muscles, decreased blood flow to gut, increased heart rate and force of contraction (to raise arterial blood pressure to compensate for decrease in total peripheral), constriction of veins to increase rate of venous return so heart does not run out of blood to pump.
Respiratory challenge: Increased rate of ventilation (actually an anticipatory response), dilation of bronchi.
Metabolic challenge: More glucose must be supplied to respiring tissue, increased glycogenolysis in muscles and liver, and increased gluconeogenesis in liver, release of free fatty acids from adipose tissue. All responses are promoted by adrenaline.
Thermoregulatory challenge: Heat loss must increase. Increased sweating and vasodilation of skin blood vessels.
Osmoregulatory challenge: Reduced volume of urine produced, increased reabsorption of salt.

7. Extracellular signalling
Signalling cells
Specific signalling molecules released as a result of a change in internal state
Signalling molecules carried to target cells
Target cells
Arrival of signalling molecules at target cells is linked to a change in the internal state of the cells (cell response)
Feedback response may cause original cells to stop producing signalling molecules

8. Different cell types produce specific signalling molecules.
Challenge students to name the hormones produced by the glands shown and describe what their target cells are and what is produced by the nerves (neurotransmitters).
Pineal gland: melatonin (regulates circadian rhythms).
Pituitary gland: ADH and GH.
Thyroid gland: thyroxine.
Thymus gland: thymosins (promote development of lymphocytes).
Adrenal glands: adrenaline and aldosterone (salt retention).
Pancreas: insulin and glucagon.
Ovaries: estrogen and progesterone.
Testes: testosterone.

9. How does a target cell ‘know’ that it should respond to a specific signal?

10. Cells can only detect and respond to signals if they possess a specific receptor.
Insulin
Insulin receptor protein
Adrenaline
Adrenaline receptor protein

11. Different cell types may show a specific tissue response to the same signal.
Beta-receptor
Adrenaline
Cell in mammalian salivary gland
Cell in mammalian liver
Amylase release stimulated
Glycogen breakdown stimulated

12. Hydrophobic signals and the control of transcription
Hydrophilic signals and transduction
One way of classifying extracellular signalling molecules is by hydrophobicity.

13. What are hydrophobic signals and how are they involved in the control of transcription?
One way of classifying extracellular signalling molecules is by hydrophobicity.

14. Hydrophobic signals can pass through membranes so their receptor molecules can be within the nucleus.
They can directly influence the transcription of genes.
They include the thyroid hormone thyroxine and steroid hormones

15. General action of hydrophobic signalling molecules
Hormone
Altered rate of protein synthesis (long-lasting effects)
Intracellular receptor protein
Altered rate of gene transcription

16. Thyroxine is a hydrophobic hormone that regulates the metabolic rate.

17. Thyroxine is released from the thyroid gland.

18. Thyroxine absent Thyroid receptor protein bound to DNA
Transcription of Na+/K+ ATPase gene inhibited

19. Thyroxine present Thyroxine Receptor protein
undergoes conformational change
Synthesis of Na+/K+ ATPase
Transcription of
Na+/K+ATPase gene

20. More Na+/K+ATPases in cell membrane
ATP degraded faster
Increased metabolic rate
Transcription of
Na+/K+ATPase gene
Synthesis of Na+/K+ ATPase
Insertion into membrane

21. Steroid hormones are hydrophobic signalling molecules.
Animation of mechanism of steroid hormone action.

22. The steroid hormone receptor proteins are transcription factors.
Inhibitory protein complex
Inactive transcription factor
Hormone-binding site
Steroid hormone
Active transcription factor
DNA-binding site
exposed

23. Animation of regulation of transcription.
Hydrophobic signalling molecules can bind to nuclear receptors to regulate gene transcription.
Animation of regulation of transcription.

24. What are hydrophilic signals and how are they involved in the transduction of messages?
One way of classifying extracellular signalling molecules is by hydrophobicity.

25. Hydrophilic signals need receptor molecules on the cell surface.
Transmembrane receptors change conformation (shape)when the ligand (messenger) binds to outside of the cell.
The signal molecule does not enter the cell.
The signal is transduced (passed) across the cell membrane.
This often involves cascades of G-proteins or phosphorylation by kinase enzymes.

26. General action of hydrophilic signalling molecules
Hormone (ligand)
Receptor protein
Similarity between mode of action = hormones bind to specific proteins. Hormone – receptor shapes are complementary. Hormones can only act on a target tissue if it possesses its specific receptors.
Signal transduction
Cell responses
(short-lasting effects)

27. Examples include the peptide hormones ADH and insulin
Examples include the peptide hormones ADH and insulin. These are made from short chains of amino acids.
ADH
Insulin

28. Insulin regulates the glucose concentration of the blood
Beta-cells in pancreas release more insulin
Insulin transported in blood
Insulin acts on adipose, liver and muscle cells
Change detected
More glucose is taken up by cells
Blood glucose concentration falls
Blood glucose concentration rises
Blood glucose concentration at set point

29. P P P P P 1. Insulin binds to receptor
2. Kinase enzyme phosphorylates itself
(autophosphorylation) P P P
4. Phosphorylated IRS-1 acts on effectors to trigger cell responses
3. Receptor phosphorylates insulin receptor substrate (IRS-1)
Insulin as example. P

30. Action of insulin on fat and muscle cells
GLUT 4
Note that GLUT4 is an insulin-dependent glucose transporter found in adipose and striated muscle tissue.
Liver has GLUT2 insulin-independent glucose transporter. Liver is still sensitive to insulin. Insulin stimulates liver to convert glucose into glycogen.
Animation of insulin action.
Exercise triggers recruitment of GLUT 4

31. An illness related to blood glucose is Diabetes Mellitus
A disease caused by defects in the insulin
signalling system.
Two types of diabetes mellitus are recognised.
Type 1 and Type 2
What are the general symptoms of diabetes mellitus?
Etymology: Diabetes means excessive urine/flow run through/siphon. Mellitus means sweet.
Diabetes has triad of symptoms: polyuria, polydypsia and polyphagia (excessive urination, thirst and hunger).

32. Type 1 – Insulin dependant diabetes
Type 2 – Non-insulin
Dependant diabetes
Cause
Destruction of beta cells
in pancreas by immune
system
Exact cause unknown
Obesity is a risk factor
Usual age of onset
Childhood
Adulthood
Nature of defect
Pancreas does not
produce any insulin
Target cells develop
Insulin resistance. Loss
of receptor function
Treatment
Daily insulin injections
and management of diet
to control glu. Conc.
Eat less sugar and
saturated fat.
Regular exercise.
Medication to lower
Blood glu. Conc.

33. Global prevalence of diabetes mellitus
The majority of cases are type 2 diabetes mellitus.
Numbers are millions!

34. Terrestrial vertebrates require mechanisms for conserving water
Thank goodness I can make ADH!

35. ADH regulates the body’s water balance
Pituitary gland releases more ADH
ADH transported in blood
ADH acts on kidney collecting ducts
Change detected
More water reabsorbed into blood
Less urine made
Blood water concentration rises
Blood water concentration falls
Blood water concentration
at set point

36. Mechanism of action of ADH
Lumen of collecting duct
Collecting duct cell
Blood
2. ADH receptor
H2O
1. ADH
5. Fusion of vesicles containing AQP2 water channel proteins
Rate-limiting step in water reabsorption is uptake across the luminal membrane. The water permeability of the basolateral membrane is always high.
4. Protein phosphorylation
3. Activation of protein kinase A

37. Aquaporins are protein channels that allow efficient transmembrane movement of water.
Animation of water movement through an aquaporin channel.

38.
Aquaporins

39. An illness related to ADH Diabetes insipidus
Disease in which the water conservation mechanism of the kidneys fails.
How could the system fail to work?
What might the symptoms of diabetes insipidus be?

40. Symptoms of diabetes insipidus
Excessive thirst.
Production of large quantities of dilute urine
(‘insipidus’ = lacks flavour).
Compare these two types of diabetes insipidus to the two types of diabetes mellitus.

41. The two types of diabetes insipidus
Central diabetes insipidus:
insufficient ADH is produced.
Nephrogenic diabetes insipidus:
cells in the lining of the collecting duct are
unable to respond to ADH.
Compare these two types of diabetes insipidus to the two types of diabetes mellitus.
Nephrogenic diabetes insipidus can be caused by mutations to the genes coding for the ADH receptor, signalling proteins or the AQP2 channel protein.

42. Possible causes of diabetes insipidus
Lumen of collecting duct
Collecting duct cell
Blood
ADH receptor insensitive to ADH
AQP2
No ADH
Note that non-functional protein kinase A would have wide-ranging effects.
Phosphorylated target proteins
Protein kinase A

43. Summary of ADH action ADH binds to receptor in collecting ducts.
Recruitment of channel protein aquaporin 2 (AQP 2)
Water moves through aquaporins in membrane
Water is reabsorbed into blood
No ADH or insensitive receptor proteins leads to diabetes insipidus

44. Extended Response Describe and explain with named examples the role of Hydrophobic and Hydrophilic messengers