1
Q
Name the two different types of glands
A
- exocrine
- endocrine
2
Q
Describe exocrine glands
A
- don’t release hormones
- secrete products into ducts which lead to site where secretion is required
- not released into bloodstream
3
Q
Describe endocrine glands
A
- releases hormones directly into bloodstream
- ductless glands
- consist of groups of cells that manufacture and release the hormone directly into the blood in capillaries running through the gland
- have groups of cells with associated capillaries, but no visible ducts
4
Q
Describe hormones
A
- molecules (proteins or steroids) that are released by endocrine glands directly into the blood
- carry a signal from endocrine gland to a specific target organ/tissue
- bloodstream transports materials all over the body, and therefore any hormone released into the blood will be transported throughout the body
5
Q
Describe target cells
A
- possess a specific receptor on plasma membrane or inside cell
- shape is complementary to shape of hormone molecule
- similar cells may be grouped together in a target tissue e.g. epithelium of the collecting ducts
- or may be more widely dispersed in a number of tissues, such as receptors for adrenaline found in the CNS and the tissues innervated by the peripheral nervous system incl. heart, smooth muscle and skeletal muscles
6
Q
Name the 2 different types of hormones
A
- Steroid
- Protein (and Peptide and derivates of Amino acids)
7
Q
Briefly outline the action of non-steroid hormones
A
- Non-steroid hormones are first messengers- signalling molecules outside the cell that bind to the cell surface membrane and initiate an effect inside the cell
- Usually cause the release of another signalling molecule in the cell- called the second messenger- this stimulates a change in the activity of the cell
8
Q
Describe in detail the action of most non-steroid hormones (excluding insulin)
A
- Many non-steroid hormones act via a G protein in the membrane
- The G protein is activated when the hormone binds to the receptor
- The G protein in turn activates an effector molecule- usually an enzyme that concerts an inactive molecule into the active second messenger
- In many cells the effector molecule is the enzyme adenyl cyclase, which converts ATP to cyclic AMP- cAMP)- cAMP is the second messenger
- This second messenger may act directly on another protein (such as an ion channel), or it may initiate a cascade of enzyme-controlled reactions that alter the activity of the cell
9
Q
Describe steroid hormones
A
- Can pass through plasma membrane (as lipid soluble)
- Can enter cell nucleus and have direct effect on the DNA in the nucleus
- E.g. Oestrogen, Testosterone
10
Q
Describe protein hormones
A
- Proteins are not soluble in phospholipid membrane and do not enter the cell
- Need to bind to plasma membrane and release a second messenger inside the cell
- E.g. Adrenaline, insulin and glucagon
11
Q
Describe the action of steroid hormones
A
- The steroid hormone passes through the plasma membrane of the target cell
- The steroid hormone binds with a specific receptor (with a complementary shape) in the cytoplasm
- The receptor-steroid hormone complex enters the nucleus of the target cell and binds to another specific receptor on the DNA
- Binding stimulates the production of mRNA molecules, which code for the production of proteins
12
Q
Describe the location and structure of the adrenal glands
A
- Found lying anterior (just above) the kidneys
- One on each side of body
- Each gland divided into the outer adrenal cortex and the inner adrenal medulla
- Both regions are well supplied with blood vessels and produce hormones that are secreted directly into the blood vessels
13
Q
What hormones does the adrenal medulla secrete
A
adrenaline, non-adrenaline
14
Q
Describe the action of adrenaline
A
- Polar molecule derived from amino acid tyrosine
- Means that it cannot enter cells through the plasma membrane like a steroid hormone can
- Therefore, must be detected by specialised receptors on the plasma membrane of the target cells (see notes on action of non-steroid hormones)
- Many cells and tissues have adrenaline receptors- therefore the effects of adrenaline are widespread
- Noradrenaline works in same way
15
Q
Describe the effects of adrenaline
A
Role of adrenaline is to prepare the body for activity:
- Relaxing smooth muscle in the bronchioles
- Increasing stroke volume of the heart
- Increasing heart rate
- Causing general vasodilation to raise blood pressure
- Stimulating conversion of glycogen to glucose
- Dilating the pupils
- Increasing mental awareness
- Inhibiting the action of the gut
- Causing body hair to stand erect
Noradrenaline works in same way
16
Q
Describe the structure of the adrenal cortex
A
Has an outer capsule surrounding three distinct layers of cells:
- Zona glomerulosa- outermost layer which secretes mineralocorticoids e.g. aldosterone
- Zona fasciculata- the middle layer which secretes glucocorticoids e.g. cortisol
- Zona reticularis- innermost layer which is thought to secrete precursor molecules that are used to make sex hormones
17
Q
Outline the hormones released by the adrenal cortex
A
- The adrenal cortex uses cholesterol to produce a range of hormones
- These hormones are steroid based and are able to enter cells directly by diffusing through the plasma membrane (see notes on action of steroid hormones)
18
Q
Describe Mineralocorticoids
A
- help to control the concentrations of sodium and potassium in the blood
- as a result they also contribute to maintaining blood pressure
- Aldosterone acts on the cells of the distal tubes and collecting ducts in the kidney
- It increases absorption of sodium ions, decreases absorption of potassium ions, and increases water retention so increasing blood pressure
19
Q
Describe Glucocorticoids
A
- Help to control the metabolism of carbohydrates, fats and proteins in the liver
- Cortisol is released in response to stress or as a result of a low blood glucose concentration
- It stimulates the production of glucose from stored compounds (especially glycogen, fats and proteins) in the liver
20
Q
Where else may cortisol be released, describe what happens if this doesn’t
A
- Cortisol may also be released by the zona reticularis, however, if the correct enzymes are not present for the release of cortisol, then the zona reticularis releases precursor androgens into the blood
21
Q
Describe precursor androgens
A
- Taken up by the ovaries or testes and converted into sex hormones (e.g. testosterone in males or oestrogen in females)
- The sex hormones help the development of the secondary sexual characteristic and regulate the production of gametes
22
Q
Endocrine glands in body diagram
A
23
Q
Describe the pancreas
A
- Small organ lying below stomach
- Has both endocrine and exocrine function
24
Q
Describe the exocrine function of the pancreas
A
- Exocrine glands secrete substances into a duct
- Exocrine function is to synthesise and release digestive enzymes
- Exocrine cells are in small groups surrounding tiny tubules
- Each group of cells is called an acinus (plural acini)
- Acini are grouped together into small lobules separated by connective tissue
- The cells of the acini secrete the enzymes they synthesize into the tubule at the centre of the group
- The tubules from the acini to for intralobular ducts that eventually combine to make up the pancreatic duct
- The pancreatic duct carries the fluid containing the enzymes into the first part of the small intestine (duodenum)
25
Describe the contents of the fluid released from the pancreatic duct
- pancreatic amylase- Carbohydrase which digests amylose to maltose
- trypsinogen- inactive protease which will be converted to the active form of trypsin when it enters the duodenum
- lipase- digests lipid molecules
- sodium hydrogencarbonate- makes solution alkaline, helps to neutralise the contents of the digestive system that have just left the acid environment of the stomach
26
Describe the endocrine function of the pancreas
- Islets of Langerhans- endocrine tissue
- Two types of cells- alpha and beta
- Alpha ells- secrete glucagon
- Beta cells- secrete insulin
27
Describe the action of beta cells in the pancreas
1) The cell membranes of the beta cells contain both calcium ion channels and potassium ion channels
2) The potassium ion channels are normally open and the calcium ion channels are normally closed
3) Potassium ions diffuse out of the cell making the inside of the cell more negative- at rest the potential difference across the cell membrane is about -70mV
4) When glucose concentrations outside of the cell are high, glucose molecules move into the cell
5) The glucose quickly used in metabolism to produce ATP- involves the enzyme glucokinase
6) The extra ATP causes the potassium ion channels to close
7) The potassium can no longer diffuse out and this alters the potential difference across the cell membrane- it becomes less negative inside
8) This change in potential difference opens the calcium ion channels
9) Calcium ions enter the cell and cause the secretion of insulin by making the vesicles containing insulin move to the cell surface membrane and fuse with it, releasing insulin by exocytosis
28
Cells in pancreas diagram
29
Tissue plan of islets of Langerhan diagram
30
Describe what happens if blood glucose rises too high
- Detected by the beta cell (in the islets of Langerhans)
- Beta cells respond by secreting insulin into the blood
- Insulin travels throughout body and in the circulatory system
- Target cells are liver cells, muscle cells, and some other body cells including those in the brain
- Target cells posses specific membrane-bound receptors for insulin
- alpha cells stop secreting glucagon
31
Describe insulin
Small protein- 51 amino acids- can’t pass through plasma membrane
32
Describe how insulin works at target cells
- Insulin binds to insulin receptor
- This activates the enzyme tyrosine kinase (which is associated with the receptor on the inside of the membrane)
- Tyrosine kinase causes phosphorylation of inactive enzymes in the cell- activates the enzymes leading to a cascade of enzyme-controlled reactions inside of the cell
- Vesicles containing transporter proteins specific to glucose fuse with the plasma membrane
- More glucose enters the cell
33
Describe ethe effects of insulin
- More glucose enters the cell
- Glucose in the cell is converted to glycogen for storage (glycogenesis)
- More glucose is converted to fats
- More glucose is used in respiration
- These things reduce the blood glucose concentration
34
Describe what happens if blood glucose is too low
- Detected by the alpha cells (in the islets of Langerhans)
- The alpha cells then secrete glucagon into the blood
- Target cells are the hepatocytes (liver cells)- possess the specific receptor for glucagon
- Beta cells stop secreting insulin
35
Describe glucagon
small protein- contains 29 amino acids
36
Describe the action of glucagon
- When the blood passes these cells the glucagon bind to receptors
- Stimulates a G protein- series of actions (see notes on action of protein hormones)
37
Describe the effects of glucagon
- Glycogen is converted to glucose (glycogenolysis) by phosphorylase A (one of the enzymes activated in the cascade)
- More fatty acids are used in respiration
- Amino acids and fats are converted into additional glucose, by gluconeogenesis
- These changes increase the blood glucose concentration
38
Describe negative feedback (blood glucose levels)
- Involves insulin and glucagon- antagonistic as have opposite effects on blood glucose concentration
- Hormones inhibit the effects of the opposing hormones
- Blood glucose concentration fluctuates around the required concentration
39
Describe blood glucose concentration
- Normal range is between 4-6 mmol dm-3
- Too low- hypoglycaemia
- Too high- hyperglycaemia
40
Describe Hypoglycaemia
- If allowed to drop below 4 mmol dm-3 and remains too low for long periods, person is a hypoglycaemic
- Hypoglycaemia- causes an inadequate delivery of glucose to the body tissues- in particular to brain
- Mild hypoglycaemia- tiredness and irritability
- Severe hypoglycaemia- impairment of brain function and concussion- may lead to seizures, unconsciousness and even death
41
Describe Hyperglycaemia
- Happens if blood glucose is allowed to rise too high for long periods
- Permanently high glucose concentration can lead to significant organ damage
- A blood glucose that is consistently higher than 7 mmol dm-3 is used as the diagnosis for diabetes mellitus
42
Briefly outline diabetes
- Diabetes mellitus
- Condition in which the body is no longer able to produce sufficient insulin to control its blood glucose concentration
- Can lead to hyperglycaemia (high) or hypoglycaemia (low)
43
Type 1 Diabetes- outline
- AKA insulin-dependent diabetes or juvenile-onset
- Usually starts in childhood
44
Type 1 Diabetes- Causes
- May be effect of an autoimmune response- body’s immune system attacks and destroys the beta cells- receptors on T/B/antibody cells complimentary to antigens on beta cells
- May also result from a viral attack
45
Type 1 Diabetes- Effects
- Person no longer able to synthesise sufficient insulin
- Can’t store excess glucose as glycogen (in liver and muscles)
- Extra glucose in the blood is not removed quickly- leaves prolonged period of high concentration
- When blood glucose falls, there is no store of glycogen that can be used to release glucose- blood glucose falls too low- diabetic may suffer a ‘hypo’ (period of hypoglycaemia)
46
Type 1 diabetes- treatment
- Effects are severe and worsen with time- important to diagnose early to treat ASAP
- Usually treated using insulin injections
- Blood glucose concentration must be monitored and the correct dose of insulin administered to keep the glucose concentre fairly stable
[extreme cases- glucagon injection]
47
Describe alternatives to insulin injections (type 1)
* Insulin pump therapy small device constantly pumps insulin (at controlled rate) into the bloodstream through a needle that is permanently inserted under the skin
* Islet cell transplantation- healthy beta cells from the pancreas of a deceased donor are implanted into the pancreas of some with type 1 diabetes
* Complete pancreas transplant
48
Describe sources of stem cells for diabetes treatment
Stem cells- most common sources are bone marrow and placenta, but scientists found precursor cells in pancreas of adult mice- capable of developing into variety of cell types and may be true stem cells- if similar cells can be found in the human pancreas then they could be used to produce new beta cells in patients with type 1 diabetes- freedom from daily insulin injections
49
Type 2 diabetes- outline
- AKA non-insulin dependent diabetes
- Can produce insulin, but not enough
50
Type 2 diabetes- causes
- As people age, responsiveness to insulin declines- specific receptors on the surface of liver and muscle cells become less responsive and the cells lose their ability to respond to insulin in the blood
- Risk factors for earlier onset- obesity, lack of regular exercise, diet high in sugars (particularly refined), being of Asian or Afro-Caribbean origin, Family history
51
Type 2 diabetes- effects
- Blood glucose concentration is almost permanently raised
- This can damage the major organs and circulation
52
Type 2 diabetes- treatment
- Usually treated by change in lifestyle
- Advised to lose weight, exercise regularly, and carefully monitor diet- taking care to match carbohydrate intake and use
- May be supplemented by medication that reduces the amount of glucose in the liver releases to the bloodstream or that boosts the amount of insulin released from the pancreas
- In severe cases, further treatment may include insulin injections or the use of other drugs that slow down the absorption of glucose from the digestive system
53
Describe insulin sources (diabetes treatment)
- Traditionally extracted from the pancreas of animals- usually pigs (matched human insulin most closely)
- More recently, insulin has been produced by Escherichia coli bacteria that have undergone genetic modification to manufacture human insulin
54
Advantages of using insulin from genetically modified bacteria
- Less chance of rejection due to an immune response
- Lower risk of infection
- Cheaper to manufacture insulin that extract from animals
- Manufacturing process more adaptable to demand
- Some people less likely to have moral objections to using insulin produced from bacteria than to using that extracted from animals
