Endocrine Physiology Flashcards
1
Q
Describe endocrine communication
A
- Hormones travel in the blood to their target organs/tissues
- Tissues detect hormones through the presence of specific receptors for that chemical on/in the cells
2
Q
Describe neural communication
A
- Neurotransmitters released from the presynaptic neurons travels across the synaptic cleft to the postsynaptic cell to influence its activity
- The neurotransmitter is released by the neuron and acts locally on the synaptic cleft (in contrast with endocrine hormones)
3
Q
Describe the neuroendocrine system and give an example
A
- When the endocrine and nervous systems combine
- The nerves release hormones which enter the blood and travel to their target cells
- E.g. hypothalamic - posterior pituitary axis
4
Q
Describe how the autocrine system works
A
Cells secrete chemicals that bind to receptors on the same cell
5
Q
Describe how the paracrine system works
A
Chemicals diffuse in the ECF to affect neighbouring cells
6
Q
List the features of an endocrine hormone
A
- Produced by a cell or a group of cells
- Secreted from those cells into the blood
- Transported via the blood to distant targets
- Exert their effects at very low concentrations
- Act by binding to receptors on target tissues
- Have their action terminated, often via negative feedback loops
7
Q
List the classifications of endocrine hormones
A
- Peptide hormones
- Amine hormones (derived of amino acids)
- Steroid hormones (derived from cholesterol)
8
Q
Describe how peptide hormones are produced and give examples
A
-Synthesised as preprohormone in advance of need then cleaved into prohormone and stored in vesicles until required
9
Q
What is C-peptide?
A
- The inactive fragment cleaved from the insulin prohormone
- Levels of C-peptide in plasma or urine are often measured to indicate endogenous insulin production from the pancreas (levels of C-peptide are typically about 5x higher than endogenous insulin)
10
Q
Describe the mechanism of action of peptide hormones
A
- Water soluble so cannot cross cell membrane so bind to membrane bound receptors on the target cell
- Once bound these receptors create fast responses
- Most peptide hormones work by modulating either the GPCR (rapid response) or tyrosine kinase linked (slower, longer lasting response) signalling pathways
11
Q
Describe how steroid hormones are produced
A
- Steroid hormones are synthesized as needed
- Once synthesized they diffuse across the membrane into the ISF and the blood
- They are bound to carrier proteins such as albumin
12
Q
Name the places where steroid hormones are produced
A
- Gonads: sex steroids
- Placenta: hCG and sex steroids
- Kidney: vitamin D3
- Adrenal Cortex: corticosteroids
13
Q
Describe the mechanism of action of steroid hormones
A
- As they are lipid soluble their receptors are located within the cell and trigger either activation or repression of gene function
- These genes control the synthesis of proteins
- This is a relatively slow process so there is a lag time between hormone release and biological effect
14
Q
Describe the activity of lipophilic hormones
A
- There is a small amount of unbound free steroid/thyroid hormone
- Only free hormone can diffuse across the capillary walls to target cells
15
Q
Describe the features of hormone carrier proteins
A
- Increases solubility and protects from degradation
- As steroid is taken up more is released from carrier
- Allows for a reservoir of hormone
- Can be specific or non-specific
16
Q
Name the two hypothalamic centres which determine food intake and what they do
A
- Feeding Centre: promotes feelings of hunger and drive to eat
- Satiety Centre: promotes feelings of fullness by suppressing the Feeding Centre
17
Q
What is glucostatic theory?
A
Food intake is determined by blood glucose (as BG increases, the drive to eat decreases)
18
Q
What is lipostatic theory?
A
Food intake is determined by fat stores (as fat stores increases the drive to eat decreases_
19
Q
What is the function of leptin?
A
It is a hormone released by fat store which depresses feeding activity
20
Q
Name the 3 categories of energy output
A
- Cellular work
- Mechanical work
- Heat loss
21
Q
Name the 3 elements of metabolism
A
- Extracting energy from nutrients in food
- Storing that energy
- Utilising that energy for work
22
Q
Describe what is meant by the brain being an obligatory glucose utiliser
A
- The brain can only use glucose for energy
- It can’t use fats, carbohydrates or protein
- This means that we must maintain a sufficient blood glucose
- This is done by glucogenolysis or gluconeogenesis
23
Q
What is the normal blood glucose levels?
A
4.2-6.3mM
24
Q
Which two hormones control [BG]?
A
- Insulin
- Glucagon
25
Name the four types of cells found in the pancreas and what they produce
- A: glucagon
- B: insulin
- Delta: somatostatin
- F: pancreatic polypeptide
26
Describe the normal physiological process when we are in a fed state
- Insulin dominates
- BG decreases
- Glucose oxidation increases
- Glycogen synthesis increases
- Fat synthesis increases
- Protein synthesis increases
27
Describe the normal physiological process when we are in a fasted state
- Glucagon dominates
- BG increases
- Glycogenolysis increases
- Gluconeogenesis increases
- Ketogenesis increases
28
Name some of the features of insulin
- Peptide hormone produce by pancreatic B cells
- Stimulates glucose uptake by cells
- Synthesised as preproinsulin which is converted to proinsulin in the ER
- Proinsulin is then packaged as granules in secretory vesicles.
- It is then cleaved again to give insulin and C-peptide
29
Name the stimuli of insulin secretion
- [BG]
- Glucose
- Amino acids
30
Where is excess glucose stored?
- Liver and muscle as glycogen
| - Liver and adipose tissue as triacylglycerols
31
How are excess amino acids stored?
They are converted to fat
32
Describe how [BG] controls insulin secretion
- B cells have a specific type of potassium ion channel that is sensitive to the [ATP] in the cell
- When glucose is abundant it enters the cells through glucose transport proteins (GLUT) and metabolism increases
- This increases [ATP] within the cell, causing the Katp channel to close
- Intracellular [K] rises, depolarising the cell
- Voltage dependent Ca2+ channels open and trigger insulin vesicle exocytosis into the circulation
- When [BG] is low the Katp channels are open so the cell is hyperpolarized and insulin is not secreted
33
What is the primary action of insulin and how does it work?
- It binds to tyrosine kinase receptors on the cell membrane of insulin-sensitive tissues to increase glucose uptake
- In muscles and adipose tissue, insulin stimulates the mobilization of GLUT-4 which migrates to the cell membrane and transports the glucose into the cell
34
Name the GLUT transporters that are not insulin dependent
- GLUT-1: basal glucose uptake (brain, kidneys, RBCs etc.)
- GLUT-2: B cells of pancreas and liver
- GLUT-3: similar to GLUT-1
35
Is the liver insulin-dependent?
No but glucose transport into hepatocytes is affected by insulin status
36
Name the additional actions of insulin
- Increases glycogen synthesis in muscle an liver
- Increases amino acid uptake into muscle
- Increases protein synthesis and inhibits proteolysis
- Increases triacylglycerol synthesis in adipocytes and liver
- Inhibits the enzymes of gluconeogenesis in the liver
- Promotes K+ ion entry into the cells
37
Name the stimuli which increase insulin release
-Increased [BG]
-Increased plasma
[amino acids]
-Glucagon
-Hormones controlling GI secretion and motility (gastrin, secretin, CCK, GLP-1 and GIP etc.)
-Vagal nerve activity
38
Name the stimuli which inhibit insulin release
- Low [BG]
- Somatostatin (GHIH)
- Sympathetic a2 effects
- Stress e.g. hypoxia
39
Describe the effect that vagal activity has on insulin
- Vagal activity stimulates the release of major GI hormones and also stimulates insulin release
- Insulin therefore responds less to IV glucose than it does oral
40
What is glucagon and what is its function
- It is a peptide hormone produced by alpha cells in the pancreas
- Its primary function is to raise blood glucose
- It does this by mobilising glucose stores
41
Name the actions of glucagon
- Opposing insulin
- Increasing glycogenolysis
- Increasing gluconeogenesis
- Formation of ketones from fatty acids
42
Name the stimuli that promote glucagon release
- Low [BG]
- High [amino acids]
- Sympathetic innervation, epinephrine and B2 effect
- Cortisol
- Stress e.g. exercise, infection
43
Name the stimuli that inhibit glucagon release
- Glucose
- Free fatty acids and ketones
- Insulin
- Somatostatin
44
Describe how ANS activity effects islet cells
- Parasympathetic activity: increases insulin and to a lesser extent glucagon in preparation for digestion
- Sympathetic activity: promotes glucose moblilisation (via glucagon), increased epinephrine and inhibition of insulin
45
Name the features of somatostatin
- Peptide hormone secrete by D cells of the pancreas and the hypothalamus (GHIH)
- It inhibits activity in the GI tract
- It strongly suppresses the release of insulin and glucagon
- It also inhibits the secretion of GH from the anterior pituitary
46
What is the effect of exercise on [BG]?
- The entry of glucose into skeletal muscle is increased during exercise
- Exercise increases the insulin sensitivity of muscle and increases the number of GLUT-4 transporters in the muscle membrane
- This effect can last for several hours after exercise
47
What does the body do for energy when it is starved?
- Adipose tissue is broken down and fatty acids are released.
- FFAs can be readily used by most tissues to produce energy and the liver will convert excess to ketone bodies
- After a period of starvation, the brain adapts to be able to use ketones
- This helps to spare protein
