Endocrine Flashcards
The anterior pituitary gland releases:
- Thyroid Stimulating Hormone (TSH)
- Adrenocorticotropic Hormone (ACTH)
- Follicle Stimulating Hormone (FSH) and Luteinising Hormone (LH)
- Growth Hormone (GH)
- Prolactin
The posterior pituitary releases:
Oxytocin
Antidiuretic Hormone (ADH)
Explain the hormone cycle in the thyroid
The hypothalamus releases thyrotropin-releasing hormone (TRH). This stimulates the anterior pituitary to release thyroid stimulating hormone (TSH). This in turn stimulates the thyroid gland to release triiodothyronine (T3) and thyroxine (T4).
T3 and T4 are sensed by the hypothalamus and anterior pituitary, and they suppress the release of TRH and TSH. This results in lower amounts of T3 and T4. In this way, the level of thyroid hormone is closely regulated to keep it within normal limits. This is called negative feedback.
Explain the hormonal cycle of the adrenal gland
Cortisol is secreted by the two adrenal glands, which sit above each kidney. The release of cortisol is controlled by the hypothalamus. Cortisol is released in pulses and in response to a stressful stimulus (it is a “stress hormone“). It has diurnal variation, which basically means that it is high and low at different times of the day. Typically cortisol peaks in the early morning, triggering us to wake up and get going, and is at it’s lowest late in the evening, prompting us to relax and fall asleep.
The hypothalamus releases corticotrophin release hormone (CRH). This stimulates the anterior pituitary to release adrenocorticotrophic hormone (ACTH). This in turn stimulates the adrenal gland to release cortisol.
The adrenal axis is also controlled by negative feedback. Cortisol is sensed by the hypothalamus and anterior pituitary, and it suppresses the release of CRH and ACTH. This results in lower amounts of cortisol. In this way, cortisol is closely regulated to keep it within normal limits.
Cortisol has several actions within the body
WHat are these actions:
- Inhibits the immune system
- Inhibits bone formation
- Raises blood glucose
- Increases metabolism
- Increases alertness
What is the phsyiology of GH
Growth hormone releasing hormone (GHRH) is released from the hypothalamus. This stimulates growth hormone (GH) release from the anterior pituitary. Growth hormone stimulates the release of insulin-like growth factor 1 (IGF-1) from the liver.
Through this mechanism growth hormone works directly and indirectly on almost all cells of the body and has many functions. Most importantly growth hormone:
Stimulates muscle growth
Increases bone density and strength
Stimulates cell regeneration and reproduction
Stimulates growth of internal organs
Explain the physiology of PTH
Parathyroid Hormone (PTH) is released from the four parathyroid glands (situated in four corners of the thyroid gland) in response to low serum calcium. It is also released in response to low magnesium and high serum phosphate. It’s role is to increase the serum calcium concentration.
PTH increases the activity and number of osteoclasts in bone, causing reabsorption of calcium from the bone into the blood thereby increasing serum calcium concentration.
PTH also stimulates an increase in calcium reabsorption in the kidneys meaning that less calcium is excreted in the urine.
Additionally, it stimulates the kidneys to convert vitamin D3 into calcitriol, which is the active form of vitamin D that promotes calcium absorption from food in the small intestine.
These three effects of PTH (increased calcium absorption from bone, the kidneys and the small intestine) all help to raise the level of serum calcium. When serum calcium is high this suppresses the release of PTH (via negative feedback) helping to reduce the serum calcium level.
Angiotensin II acts on blood vessels to cause ___________ This results in an increase in blood pressure.
Angiotensin II also stimulates the release of ___________ from the adrenal glands.
Angiotensin II acts on blood vessels to cause vasoconstriction. This results in an increase in blood pressure.
Angiotensin II also stimulates the release of aldosterone from the adrenal glands.
Aldosterone is a mineralocorticoid steroid hormone. It acts on the nephrons in the kidneys to:
Increase sodium reabsorption from the distal tubule
Increase potassium secretion from the distal tubule
Increase hydrogen secretion from the collecting ducts
When sodium is reabsorbed in the kidneys water follows it by osmosis. This leads to an increase in _________ ________ and subsequently blood pressure.
When sodium is reabsorbed in the kidneys water follows it by osmosis. This leads to an increase in intravascular volume and subsequently blood pressure.
The body ideally wants to keep blood glucose concentration is between?
4.4. and 6.1 mmol/l.
What type of hormone is glucagon
catabolic
Explain Ketogenesis
Ketogenesis occurs when there is insufficient glucose supply and glycogens stores are exhausted, such as in prolonged fasting.
The liver takes fatty acids and converts them to ketones. Ketones are water soluble fatty acids that can be used as fuel. They can cross the blood brain barrier and be used by the brain as fuel. Producing ketones is normal and not harmful in healthy patients when under fasting conditions or on very low carbohydrate, high fat diets. Ketones levels can be measured in the urine by “dip-stick” and in the blood using a ketone meter. People in ketosis have a characteristic acetone smell to their breath.
Ketone acids (ketones) are buffered in normal patients so the blood does not become acidotic. When underlying pathology (i.e. type 1 diabetes) causes extreme hyperglycaemic ketosis this results in a metabolic acidosis that is life threatening. This is called diabetic ketoacidosis.
What i sType 1 Diabetes
What is triggered by?
Type 1 diabetes mellitus (T1DM) is a disease where the pancreas stops being able to produce insulin. What causes the pancreas to stop producing insulin is unclear. There may be a genetic component. When there is no insulin being produced, the cells of the body cannot take glucose from the blood and use it for fuel. Therefore the cells think the body is being fasted and has no glucose supply. Meanwhile the level of glucose in the blood keeps rising, causing hyperglycaemia.
It may be triggered by certain viruses, such as the Coxsackie B virus and enterovirus
When does DKA occur
Diabetic ketoacidosis occurs in type 1 diabetes where the person is not producing adequate insulin themselves and is not injecting adequate insulin to compensate for this. It occurs when they body does not have enough insulin to use and process glucose. The main problems are ketoacidosis, dehydration and potassium imbalance.
What is Ketoacidosis
As the cells in the body have no fuel and think they are starving they initiate the process of ketogenesis so that they have a usable fuel. Over time the patient gets higher and higher glucose and ketones levels. Initially the kidneys produce bicarbonate to counteract the ketone acids in the blood and maintain a normal pH. Over time the ketone acids use up the bicarbonate and the blood starts to become acidic. This is called ketoacidosis.
How are people dehydrated in DKA
Hyperglycaemia overwhelms the kidneys and glucose starts being filtered into the urine. The glucose in the urine draws water out with it in a process called osmotic diuresis. This causes the patient to urinate a lot (polyuria). This results in severe dehydration. The dehydration stimulates the thirst centre to tell the patient to drink lots of water. This excessive thirst is called polydipsia.
Explain the potassium imblance in people with DKA
Insulin normally drives potassium into cells. Without insulin potassium is not added to and stored in cells. Serum potassium can be high or normal as the kidneys continue to balance blood potassium with the potassium excreted in the urine, however total body potassium is low because no potassium is stored in the cells. When treatment with insulin starts patients can develop severe hypokalaemia (low serum potassium) very quickly and this can lead to fatal arrhythmias.
Presentation of DKA
This is a life threatening medical emergency. The pathophysiology described above leads to:
- Hyperglycaemia
- Dehydration
- Ketosis
- Metabolic acidosis (with a low bicarbonate)
- Potassium imbalance
The patient will therefore present with symptoms of these abnormalities:
- Polyuria
- Polydipsia
- Nausea and vomiting
- Acetone smell to their breath
- Dehydration and subsequent hypotension
- Altered Consciousness
- They may have symptoms of an underlying trigger (i.e. sepsis)
The most dangerous aspects of DKA are ________ ________ ________ and _______. These are what will kill the patient. Therefore the priority is _____ __________ to correct the dehydration, electrolyte disturbance and acidosis. This is followed by an insulin infusion to get the cells to start taking up and using glucose and stop producing ketones.
The most dangerous aspects of DKA are dehydration, potassium imbalance and acidosis. These are what will kill the patient. Therefore the priority is fluid resuscitation to correct the dehydration, electrolyte disturbance and acidosis. This is followed by an insulin infusion to get the cells to start taking up and using glucose and stop producing ketones.
Diagnosing DKA
Check the local DKA diagnostic criteria for your hospital. To diagnose DKA you require:
- Hyperglycaemia (i.e. blood glucose > 11 mmol/l)
- Ketosis (i.e. blood ketones > 3 mmol/l)
- Acidosis (i.e. pH < 7.3)
Treating DKA (FIG-PICK)
- F – Fluids – IV fluid resuscitation with normal saline (e.g. 1 litre stat, then 4 litres with added potassium over the next 12 hours)
- I – Insulin – Add an insulin infusion (e.g. Actrapid at 0.1 Unit/kg/hour)
- G – Glucose – Closely monitor blood glucose and add a dextrose infusion if below a certain level (e.g. 14 mmol/l)
- P – Potassium – Closely monitor serum potassium (e.g. 4 hourly) and correct as required
- I – Infection – Treat underlying triggers such as infection
- C – Chart fluid balance
- K – Ketones – Monitor blood ketones (or bicarbonate if ketone monitoring is unavailable)
DKA
Remember as a general rule potassium should not be infused at a rate of more than __ mmol per hour.
Remember as a general rule potassium should not be infused at a rate of more than 10 mmol per hour.


