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DIET 408 Physiology and Genetics > Endocrine > Flashcards

Endocrine Flashcards

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1
Q

Distant communication is coordinated by endocrine and nervous systems. What is the difference between these?

A

Nervous system is fast. The response is specific and short in duration. Signals travel alond neurons via neurotransmitters.

Endocrine system is slower. Hormones are released into the bloodstream that bind to target cells. The response is of longer duration.

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2
Q

What are the three types of hormones? Give an example of each.

A
  1. Polypeptides e.g. insulin, leptin, growth hormones
  2. Amino Acid Derivatives e.g. adrenaline, dopamine, melatonin
  3. Steroids e.g. cortisol, testosterone, oestrogens
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3
Q

Where, in terms of the cell, are the receptors for each type of hormone located?

A
  1. Polypeptides - water soluble, not lipid soluble so need to bind to receptors on surface of target cells.
  2. Amino acid derivatives - most are not lipid soluble so also bind to receptors on surface of target cells.
  3. Steroids - lipid soluble so can pass through membrane. Often bind to receptors inside target cell.
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4
Q

What is the difference between exocrine and endocrine?

A

Exocrine: relating to glands which secrete their products through ducts opening on an epithelium rather than directly into the blood. DUCTS. e.g. tear glands, sweat glands.

Endocrine: relating to glands which secrete hormones or other products directly into the blood. NO DUCTS. e.g. pituitary glands, thyroid glands (release hormones).

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5
Q

What is the difference between how peptide hormones and steroid hormones are transported in the blood?

A
  • Most peptide hormones are water-soluble, transported dissolved in blood plasma unbound.
  • Steroid hormones are lipid soluble and bind to carrier proteins.
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6
Q

Describe how peptide hormones are synthesised and packaged.

A
  1. A prepropeptide is synthesized and released into rough ER.
  2. Enzymes in RER cleave off some amino acids to yield propeptides.
  3. In smooth ER propeptides are packaged into transport vesicles.
  4. Vesicles transported to Golgi complexes.
  5. Golgi complexes package propeptide into secretory vesicles. More amino acids are cleaved to yield final peptide.
  6. Peptides are released by exocytosis.
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7
Q

What is meant by biphasic release? Give an example.

A

Biphasic release involves a quick release of a specific amount of drug/hormone, followed by sustained release.

Biphasic insulin is a mixture of rapid acting insulin with an intermediate acting insulin. This can be used to cover a mealtime and basal insulin requirements.

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8
Q

Describe the action of steroid hormones on target tissues.

A
  • Steroid hormones are lipid soluble so readily pass through cell membranes (without carrier protein)
  • Receptor is located inside cells in cytosol.
  • Hormone/receptor complex then translocate into nucleus.
  • Hormone receptor complex binds to DNA and initiates synthesis of specific proteins.
  • New proteins are responsible for the cellular response to steroid.
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9
Q

What three things control hormone release?

A
  • Plasma concentration of ions or nutrients e.g. insulin secretion by glucose
  • Neurotransmitters e.g.
  • Another hormone
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10
Q

Describe the insulin secretion by glucose.

A
  1. After food, blood glucose levels rise so there is an up-regulation of GLUT-2 receptors
  2. This causes glucose diffusion into the cell.
  3. Phosphorylation of glucose causes a rise in ATP:ADP ratio.
  4. This inactivates the ATP-sensitive potassium channel, causing a build up of positively charged potassium in the cell.
  5. The membrane depolarises.
  6. Voltage-gated calcium channels open and Ca enters.
  7. Calcium activates vesicles storing insulin so insulin is released by exocytosis.
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11
Q

In what 4 ways can endocrine disorders be categorized?

A
  1. Hyposecretion - do not secrete enough e.g. Type 1 diabetes
  2. Hypersecretion - secrete too much e.g. endocrine tumour, overactive thyroid.
  3. Hyporesponsiveness - do not respond sufficiently e.g. Type 2 diabetes
  4. Hyperresponsiveness - respond too much e.g. increased response to thyroid Hormones.
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12
Q

What is glycogenesis?

A

After a meal, blood glucose levels rise and glucose enters the liver. Glycogenesis is when the liver converts excess glucose into glycogen for storage.

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13
Q

What is glycogenolysis?

A

The breakdown of glycogen to glucose.

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14
Q

What is glyconeogenesis?

A

The synthesis of glucose from non-carbohydrate precursors in the liver.

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15
Q

What is glyconeogenesis?

A

The synthesis of glucose from non-carbohydrate precursors in the liver.

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16
Q

The endocrine cells of the pancreas are call Islets of Langerhans. What two major hormones do these cells produce?

A

Insulin and glucagon.

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17
Q

Name the four cell types in the Islets of Langerhans, what they produce and their abundance.

A
  1. The α-cells produce glucagon - 25%
  2. The β-cells produce insulin - 60%
  3. The γ-cells produce somatostatin - 10%
  4. The F cells produce pancreatic polypeptide - 1%
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18
Q

Explain the process by which insulin is secreted by glucose.

A
  1. After food, blood glucose levels rise causing up-regulation of GLUT-2 receptors so glucose diffuses into beta cell.
  2. Phosphorylation of the glucose causes a rise in the ATP:ADP ratio.
  3. ATP binds to ATP-sensitive potassium channels causing them to close and depolarising the cell.
  4. Voltage-gated Calcium channels open causing calcium to enter the cell.
  5. Calcium enters the cell and causes exocytosis of vesicles containing insulin and amylin which then enter the blood.
    - The level of glucose in the blood corresponds to the level of insulin and amylin released.
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19
Q

Increase in blood glucose is the major stimulus for insulin release. Give four other factors that may also stimulate insulin release.

A
  1. Plasma amino acid levels
  2. Increase in plasma fatty acid levels
  3. The gastrointestinal hormones CCK and secretin
  4. Parasympathetic nervous system.
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20
Q

What may inhibit insulin release?

A
  1. Activity in the sympathetic nervous system - because we need the energy for the fight or flight response.
  2. Stress. Probably mediated by an increase in sympathetic nervous system activity.
21
Q

What is GLUT-4?

A

Glucose transporter type 4 is an insulin-regulated glucose transporter responsible for insulin regulated glucose uptake into fat and muscle cells. It is present in muscle and adipose tissue.

In the presence of insulin GLUT4 vesicles fuse with the plasma membrane, allowing glucose to enter the cell. Under the influence of insulin there can be a 10-20x increase in the movement of GLUT4 to the membrane.

22
Q

Insulin acts to decrease blood glucose and maintain homeostasis. Give 3 ways in which it does this.

A
  1. Increases glucose uptake
  2. stimulates glycogen synthesis and inhibits glycogen breakdown
  3. Inhibits gluconeogenesis.
23
Q

What is glucagon?

A

A small peptide hormone of 29 amino acids secreted from alpha cells of the pancreas.

It acts in the opposite direction to insulin l, and is released when plasma glucose levels are low.

24
Q

What are the effects of glucagon ?

A

Major effect is to raise plasma glucose level:
1.stimulated glycogen breakdown and inhibits glycogen synthesis.
2. Stimulates gluconeogenesis in liver.
3. Stimulates fat breakdown (lipolysis): fat is used for a fuel in preference to glucose.
4. Promotes the conversion of fatty acids to ketone bodies in the liver.

25
Q

What are the thyroid hormones?

A

• Thyroxine, T4, major hormone produced by thyroid.

• triiodothyronine, T3

Both contain iodine : T3 has 3 iodine and T4 has 4

26
Q

Where are thyroid hormones synthesised and stored?

A

Follicular cells

27
Q

How are thyroid hormones synthesised?

A
  1. Uptake of iodide [I-] from plasma into follicular cells. This is an active process that pumps I- into cells (‘iodide trapping’). Iodide is cotransported with sodium via a sodium-iodide symporter.
  2. Iodide is oxidised to iodine by enzymes located on the surface of follicular cells.
  3. Iodine is enzymatically transferred to tyrosyl resides on thyroglobulin molecule which is found in colloid. Each tyrosyl residue can have one iodine added to form T1, or two iodines added to form T2. A T1 and T2 molecule join to form T3, or two T2 molecules join to form T4.
  4. The thyroid hormones formed are stored as part of the thyroglobulin molecule in the colloid.
28
Q

What is the effect of T3 on heat production? Explain why hypothyroidism cause you to feel cold?

A
  • T3 stimulates Na/K ATPase pump in cells
  • This causes the cell to use more ATP
  • Low cell ATP triggers glucose to be used to generate more ATP, producing heat as a bi-product.
  • Without T3, heat production would decrease and body temperature would be compromised (feel cold).
29
Q

What are the permissive effects of thyroid hormones?

A
  • Boosts actions of adrenaline and NA in sympathetic nervous system. This can cause a ‘racing heart’.
30
Q

What is the effect of T3 on growth and development?

A

-T3 is needed for the production of normal growth hormones. Absence of T3 in foetal life leads to poor developmeng of the Nervous system which can cause mental retardation. A common cause of this is maternal iodine deficiency.

31
Q

What is the most common cause of hyperthyroidism?

A

Graves disease - autoimmune disease where your body produces antibodies to stimulate the thyroid gland which produces excessive thyroid hormone.

32
Q

What is the impact of low dietary iodine?

A
  • Iodine is a constituent of T3 and T4.
  • If iodine is low, excessive levels of TRH and TSH continue to try and stimulate T3 and T4. This build up can lead to a goiter.
33
Q

What is the difference between primary and secondary hypothyroidism?

A
  • In primary hypothyroidism the thyroid gland is unable to produce sufficient amounts of thyroid hormone.
  • In secondary hypothyroidism the thyroid gland is normal but it receives insufficient stimulation because of low secretion of thyroid stimulating hormone [TSH] from the pituitary.
34
Q

Stress is recognised by the hypothalamus. What two areas does it signal to and what do they releases?

A
  1. Adrenal gland (on top of kidney) - produces adrenaline.
  2. Anterior pituitary gland - ACTH - CRH - cortisol.
35
Q

What hormone is released when under short-term stress?

A

Adrenaline and noradrenaline are released to prepare the body for a ‘fight or flight’ response. They act to:
- breakdown glycogen to glucose
- increase HR
- dilate bronchioles

36
Q

What is released when under long-term stress (e.g. injury or illness)?

A

ACTH is released which stimulates the production of corticosteroids, including glucocorticoids and mineralocorticoids.

Glucocorticoids (e.g. cortisol) stimulate synthesis of glucose and inhibit theimmune system. Mineralocorticoids regulateionand water balance of the body by stimulating the kidneys to excrete less water and sodium ions in the urine.

37
Q

What is cortisol and what is its function?

A

A stress hormone which:

-regulates body’s stress response ( stress e.g. immune factors, cold, low blood glucose, anxiety, sleep deprivation, pain.)
- regulates metabolism, the inflammatory response, and immune function.

38
Q

What is the effect of cortisol on metabolism?

A

Cortisol mobilises energy sources to increase plasma concentrations of glucose, amino acids, glycerol, and free fatty acids:

  • Liver increased gluconeogenesis
  • Adipose decreased glucose uptake and increased breakdown of fat.
  • Skeletal muscle breakdown of protein to give amino acids for gluconeogenesis. Also inhibits insulin.
39
Q

What does an absence of cortisol result in?

A
  • Cortisol is needed for normal tone in blood vessels. Absence causes vasodilation and low blood pressure.
40
Q

Explain what can happen when cortisol levels are low e.g. addisons disease.

A
  • Bronze pigmentation of skin
  • Changes in distribution of body hair
  • GI disturbances
  • Weakness
  • Hypoglycemia
  • Postural hypotension
  • Weight loss
41
Q

Explain what can happen when cortisol is in excess e.g. Cushings syndrome.

A
  • personality changes
  • hyperglycemia
  • Increased susceptibility to infection
  • osteoporosis
42
Q

What are the pharmacological actions of cortisol? What conditions may it be used for?

A
  1. Anti-inflammatory effect
  2. Immunosupressive effect

Useful in treating conditions with large inflammatory components e.g. rheumatoid arthritis and asthma.

43
Q

What are some short term responses to stress?

A
  • Increased heart rate
  • Increased blood pressure
  • Increased metabolic activity
  • Increased blood glucose
44
Q

What are the effects of adrenaline on the heart?

A
  • Increased heart rate by acting on SAN.
  • Increased strength of heart contraction.

These both act to increase cardiac output.

45
Q

What are the metabolic effects of adrenaline?

A
  1. Stimulation of glycogen breakdown in liver. Releases glucose for use by the heart and muscles.
  2. Stimulation of lipolysis (fat breakdown) in adipose tissues. This releases fatty acids to use as fuel in cells.

These combined effects allow sufficient glucose for ATP production in brain, heart and muscles, but not for general metabolic activity not immediately involved in the ‘fight or flight’ response.

46
Q

What are the three major effects of thyroid hormones?

A
  1. Metabolic actions
  2. Permissive actions (presence of one hormone is required in order for another hormone to exert its full effects).
  3. Growth and development.
47
Q

What are the effects of thyroid hormones on carbohydrate metabolism?

A
  1. Increased rate of gluconeogenesis. (generation of glucose from non-carbohydrate carbon substrates such as lactate and glycerol and glucogenic amino acids.
48
Q

What are the effects of thyroid hormones on protein metabolism?

A
  • Increases protein breakdown to provide amino acids for gluconeogenesis.
49
Q

Explain why hyperthyroid conditions can cause decreased fat stores.

A
  • Thyroid hormones cause an increase in the rate of lipolysis (breakdown of fats)
  • They can also increase the rate of lipogenesis hence can create futile cycles of synthesis and breakdown and use up futile energy

DIET 408 Physiology and Genetics (8 decks)

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