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Endocrine > Endocrine Physiology > Flashcards

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
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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)
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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
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4
Q

Describe how the autocrine system works

A

Cells secrete chemicals that bind to receptors on the same cell

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5
Q

Describe how the paracrine system works

A

Chemicals diffuse in the ECF to affect neighbouring cells

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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
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7
Q

List the classifications of endocrine hormones

A
  • Peptide hormones
  • Amine hormones (derived of amino acids)
  • Steroid hormones (derived from cholesterol)
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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

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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)
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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
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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
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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
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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
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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
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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
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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
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17
Q

What is glucostatic theory?

A

Food intake is determined by blood glucose (as BG increases, the drive to eat decreases)

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18
Q

What is lipostatic theory?

A

Food intake is determined by fat stores (as fat stores increases the drive to eat decreases_

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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
Q

Name the four types of cells found in the pancreas and what they produce

A
  • A: glucagon
  • B: insulin
  • Delta: somatostatin
  • F: pancreatic polypeptide
26
Q

Describe the normal physiological process when we are in a fed state

A
  • Insulin dominates
  • BG decreases
  • Glucose oxidation increases
  • Glycogen synthesis increases
  • Fat synthesis increases
  • Protein synthesis increases
27
Q

Describe the normal physiological process when we are in a fasted state

A
  • Glucagon dominates
  • BG increases
  • Glycogenolysis increases
  • Gluconeogenesis increases
  • Ketogenesis increases
28
Q

Name some of the features of insulin

A
  • 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
Q

Name the stimuli of insulin secretion

A
  • [BG]
  • Glucose
  • Amino acids
30
Q

Where is excess glucose stored?

A
  • Liver and muscle as glycogen

- Liver and adipose tissue as triacylglycerols

31
Q

How are excess amino acids stored?

A

They are converted to fat

32
Q

Describe how [BG] controls insulin secretion

A
  • 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
Q

What is the primary action of insulin and how does it work?

A
  • 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
Q

Name the GLUT transporters that are not insulin dependent

A
  • GLUT-1: basal glucose uptake (brain, kidneys, RBCs etc.)
  • GLUT-2: B cells of pancreas and liver
  • GLUT-3: similar to GLUT-1
35
Q

Is the liver insulin-dependent?

A

No but glucose transport into hepatocytes is affected by insulin status

36
Q

Name the additional actions of insulin

A
  • 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
Q

Name the stimuli which increase insulin release

A

-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
Q

Name the stimuli which inhibit insulin release

A
  • Low [BG]
  • Somatostatin (GHIH)
  • Sympathetic a2 effects
  • Stress e.g. hypoxia
39
Q

Describe the effect that vagal activity has on insulin

A
  • 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
Q

What is glucagon and what is its function

A
  • 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
Q

Name the actions of glucagon

A
  • Opposing insulin
  • Increasing glycogenolysis
  • Increasing gluconeogenesis
  • Formation of ketones from fatty acids
42
Q

Name the stimuli that promote glucagon release

A
  • Low [BG]
  • High [amino acids]
  • Sympathetic innervation, epinephrine and B2 effect
  • Cortisol
  • Stress e.g. exercise, infection
43
Q

Name the stimuli that inhibit glucagon release

A
  • Glucose
  • Free fatty acids and ketones
  • Insulin
  • Somatostatin
44
Q

Describe how ANS activity effects islet cells

A
  • 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
Q

Name the features of somatostatin

A
  • 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
Q

What is the effect of exercise on [BG]?

A
  • 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
Q

What does the body do for energy when it is starved?

A
  • 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

Endocrine (5 decks)

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