1. Module 5: Communication, Homeostasis & Energy
5.1.4 Hormonal Communication and Regulation of Blood Glucose
By Ms Cullen

2. Hormones From Greek ‘To Set In Motion’.
Chemical messenger from one cell/group of cells to another.
Mainly secreted from endocrine glands into bloodstream to act on distant organs.
Most hormones are polypeptides or proteins, some such as testosterone are steroids.
Rate of production often linked to a negative feedback system.
Neurones may stimulate production.
Most hormones have a short life and are broken down by enzymes in the blood or cells, often in the liver, or are lost in urine.

3. Endocrine Gland
A gland that excretes hormones directly into the blood stream.
They are ductless glands.
Exocrine Gland
A gland that carries a secretion into a duct.
eg salivary glands secrete saliva into the salivary ducts, which transport saliva to the mouth.

4. Major endocrine glands - what hormones do they produce?
Pineal gland
Pituitary gland
3. Thyroid gland
4. Thymus
5. Adrenal gland
6. Pancreas
7. Ovary
8. Testis
Male Female

5. Hormones
Although hormones are carried in the blood all over the body, they only affect their particular target cells.
This is because these target cells have the correct receptors.
Target cells are usually grouped together to form target tissues.
Protein hormones, eg insulin, will bind with a receptor on the outer surface of the plasma membrane & bring about a response without actually entering the cell.
Steroid hormones are lipid-soluble, so they diffuse through the plasma membrane to receptors in the cytoplasm.

6. The Role of the Pancreas
The pancreas is both an exocrine and endocrine gland. Explain why?

7. Histology of the Pancreas
The pancreas is composed of 2 main types of tissue:
Endocrine tissue – islets of Langerhans, large spherical clusters which produce and secrete hormones.
Exocrine tissue – pancreatic acini (singular acinus), small berry-like clusters which produce and secrete digestive enzymes.

8. Histology of the Pancreas
The pancreas is composed of 2 main types of tissue:
Endocrine tissue – islets of Langerhans, large spherical clusters which produce and secrete hormones.
Exocrine tissue – pancreatic acini (singular acinus), small berry-like clusters which produce and secrete digestive enzymes.
Within the islets of Langerhans there are 2 types of cell:
α cells which produce and secrete glucagon.
β cells which produce and secrete insulin.

9. Histology of the Pancreas

10. Histology of the Pancreas
It is difficult to distinguish between α and β cells in the islets of Langerhans.
There tend to be more α cells and they are slightly larger.
Differential stains are used to stain them.

11. Histology of the Pancreas

12. Task – Microscope Work Observe pancreatic slides under the microscope.
Draw a section of tissue, to include cells, under highest magnification, remembering rules for scientific drawings.
Identify and label ancini and islets of Langerhans.
Annotate your labels.
Include magnification and using eyepiece graticules calculate the size of one of the ancini clusters and label on your diagram.

13. Eyepiece graticules These are used to measure the size of a specimen.
These are microscopic rulers, 1mm long and divided into 100 divisions.
Each division is 0.01mm or 10μm.
Eyepiece lens magnification
Objective lens magnification
Total magnification
Value of 1 eyepiece division (μm)
X 10
X 4
X 40 25
X10
X 100 10
X 400
2.5
X 100 (oil immersion lens)
X 1000
1.0

14. Magnification and micrographs
Actual size = image size magnification I
A x M

15. Scientific Diagrams – Remember!
Clear, continuous lines for your sketch, use a SHARP pencil!
NO SHADING!
Diagram should cover at least 50% of space given.
All label lines should be straight – use a ruler.
Label lines should touch the structure you are identifying.
Label lines should not have arrows on the end.

16. Controlling Blood Glucose Concentration
Normal blood glucose concentration for a human is 90mg per 100cm3 of blood.
Below this level and cells have insufficient glucose for respiration, brain cells are particularly affected as they can only use glucose as a respiratory substrate.
Above this level and the glucose as a solute will affect the water potential of the blood.
Therefore blood glucose concentration must be maintained at an optimum level using a negative feedback mechanism.
The hormones involved in this are insulin and glucagon.

17. Negative Feedback Mechanisms

18. Controlling Blood Glucose Concentration - Insulin
Insulin has several effects all reducing the level of glucose in the blood. Insulin binds to a receptor on the plasma membrane of a cell and triggers a response inside the cell eg.
Insulin causes more protein carriers to be sent into the plasma membrane to allow more glucose to enter the cell by facilitated diffusion.
Insulin activates enzymes in some cells (liver and muscle cells) that speed up the conversion of glucose into insoluble glycogen, which is stored in the cytoplasm. This process is called glyogenesis (glycogen forming) and results in the cells taking up more glucose from the blood, as the diffusion gradient of glucose within the cell increases when it is converted to glycogen.
Insulin activates intracellular enzymes which speed up the synthesis of proteins and lipids, meaning that their components are not available as respiratory substrates, so more glucose will be respired.
It also inhibits release of glucagon from α cells.

19. Controlling Blood Glucose Concentration - glucagon
The effect of glucagon is to raise the level of glucose in the blood, it does this by:
Activating enzymes in the liver which speed up the conversion of insoluble glycogen to glucose. This process is known as glycogenolysis (glycogen splitting). Glucose molecules now diffuse out of cells into the blood as there will be a higher concentration in the liver cells.
Glucagon increases the production of glucose from other nutrients eg amino acids and fatty acids in liver cells. This process is called gluconeogenesis (new glucose formation). The glucose then enters the blood.

20. Controlling Blood Glucose Concentration – negative feedback

21. Questions:
a) Explain why it is true to say that blood glucose is controlled by two separate negative feedback systems (dual control).
(1 mark)
b) Why is this important? (2 marks)
2. Blood flowing from the pancreas passes into the hepatic portal vein which carries blood directly to the liver. Why is this important in the control of glucose? (2 marks)

22. Control of Insulin Secretion
P.26 OCR A2 Bio

23. Control of Insulin Secretion
β cells store insulin in vesicles and will secrete it when they detect high blood glucose. This is the process:
When blood glucose is high, more glucose enters the cell by facilitated diffusion.
More glucose in β cell causes rate of respiration to increase, producing more ATP.
The rise in ATP triggers potassium ion channels in β cell membrane to close.
This means K+ ions can’t get through the membrane and so accumulate inside the cell.
The inside of the β cell becomes less negative and more positively charged because of the K+ ions, the cell is depolarised.
Depolarisation triggers calcium ion channels to open, so calcium diffuses into the β cell.
This causes the vesicles to fuse with the membrane and secrete insulin by exocytosis.

24. Diabetes Mellitus
Explain the difference between Type 1 and Type 2 diabetes and treatments.

25. Blood glucose and insulin levels in a healthy and diabetic person
P.27 OCR A2 book

26. Genetic Engineering of Insulin