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Year 2 Physiology > Introduction to the Endocrine System: Hormones and Receptors > Flashcards

Introduction to the Endocrine System: Hormones and Receptors Flashcards

1
Q

What is the endocrine system?

A

Consists of DUCTLESS endocrine glands, occurring at numerous locations in the body, that secrete hormones into the bloodstream

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2
Q

What are exocrine glands?

A

E.g: sweat glands - the duct emerges at another body site

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3
Q

Examples of a relationship between the anterior pituitary and adrenal cortex?

A

Anterior pituitary released adrenocorticotrophic hormones (ACTH), which causes the adrenal cortex to synthesis and release cortisol

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4
Q

3 ways in which specificity of signalling is achieved?

A
  1. Chemically distinct hormones
  2. Specific receptors for each hormone
  3. Distinct distribution of receptors across target cells, providing an address at which the hormone acts
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5
Q

What are the 7 classic endocrine organs?

A 
Pituitary gland
Thyroid gland
Parathyroid glands 
Adrenal glands
Pancreas
Ovary (female)
Testis (male)
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6
Q

Other areas of the body that have an endocrine function?

A

There are other endocrine organs, e.g: pineal gland, hypothalamus, thymus

There are also organs that have an endocrine function, amongst others:
• Heart (ANP)
• GI tract
• Kidneys (erythropoietin)

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7
Q

4 types of hormones?

A

Modified amino acids, e.g: from tyrosine, tyramine - these inc. adrenaline, thyroid hormones (T3, T4)

Steroid hormones (derived from cholesterol) - these inc. cortisol, progesterone, testosterone

Peptides (from large precursor proteins/polypeptides) - these inc. ACTH, ADH, oxytocin

Proteins - these inc. insulin

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8
Q

Which hormone types have the shortest and longest duration of action, in general?

A

Shortest - modified amino acids

Longest - steroid hormones

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9
Q

Main hormones produced by the anterior pituitary and their main targets and function?

A

ACTH - adrenal cortex (metabolism)

GH - liver, bones and muscle (growth)

FSH - gonads (reproduction)

LH - gonads (reproduction)

Prolactin - mammary glands (reproduction)

Thyroid-stimulating hormone (TSH) - thyroid (growth, metabolism)

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10
Q

Main hormones produced by the intermediate pituitary and their main targets and function?

A

Melanotrophin-stimulating hormone (MSH) - melanocytes (homeostasis)

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11
Q

Main hormones produced by the posterior pituitary and their main targets and function?

A

ADH - kidney (homeostasis)

Oxytocin - mammary glands and uterus (reproduction)

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12
Q

Main hormones produced by the pineal and their main targets and function?

A

Melatonin - hypothalamus (homeostasis)

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13
Q

Main hormones produced by the thyroid and their main targets and function?

A

Thyroxine (T4) - most tissues (growth and metabolism)

Triiodothyronine (T3) - most tissues (growth and metabolism)

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14
Q

Main hormones produced by the parathyroid and their main targets and function?

A

Calcitonin - bone, gut (homeostasis)

Parathyroid hormone - bone, gut (homeostasis)

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15
Q

Main hormones produced by the pancreas and their main targets and function?

A

Insulin - liver, muscle, adipose tissue (growth, metabolism, homeostasis)

Glucagon - liver, muscle, adipose tissue (growth, metabolism, homeostasis)

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16
Q

Main hormones produced by the adrenal cortex and their main targets and function?

A

Glucocorticoids (inc. corticsol) - multiple sites (growth, metabolism)

Mineralocorticoids (aldosterone) - kidney (homeostasis)

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17
Q

Main hormones produced by the adrenal medulla and their main targets and function?

A

Adrenaline - multiple sites (growth, metabolism)

Noradrenaline - multiple sites (homeostasis, metabolism)

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18
Q

Main hormones produced by the male gonads and their main targets and function?

A

Testosterone - testes (reproduction)

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19
Q

Main hormones produced by the female gonads and their main targets and function?

A

Oestradiol - ovaries and uterus (reproduction)

Progesterone - ovaries and uterus (reproduction)

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20
Q

Main hormones produced by the placenta (in pregnancy) and their main targets and function?

A

Human chorionic gonadotrophin (hCG) - uterus (reproduction)

Oestradiol - ovaries and uterus (reproduction)

Progesterone - ovaries and uterus (reproduction)

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21
Q

Describe paraneoplasmic syndromes

A

Some neoplasms that are not “endocrine” produce hormone that cause these, e.g: in Zollinger-Ellison syndrome

22
Q

Types of chemical signalling?

A

Autocrine - act on the the same cell that produced it

Paracrine - acting on the cells in the vicinity around the one from which it was produced

Endrocrine - signalling molecule enters circulation

These are not absolute distinctions; a hormone can signal in one way in one tissue but signal in another way in another tissue, e.g: somatostatin acts in a paracrine manner in the pancreas and in an endocrine manner in the brain

23
Q

How does amplification of the cell signal from the hormone occur?

A

Activated receptor engages a signal transduction that differs between individual receptors but causes amplification of the original signal, i.e: the receptor can activate several G-proteins, with each one of these activating several effector molecules

24
Q

How is action of a hormone terminated?

A

Enzyme-mediated metabolic inactivation in the liver, or at sites of action

25
Q

Describe the complementary action of hormones and give examples

A

Of several hormones, can regulate many complex physiological function on short and long-term scales, e.g:
• Adrenaline, cortisol and glucagon all contribute to bodily response to short-term intense exercise, enhancing physical performance and preventing potential hypoglycaemia and hypokalaemia
• GH, insulin, IGF-1 and sex steroids are essential, long-term, for growth

26
Q

Describe antagonistic actions of hormones and give examples

A

Can occur via the balance of opposing influences, e.g:
• Insulin - lower plasma glucose levels by INHIBITING hepatic gycogenolysis and gluconeogenesis and by STIMULATING glucose uptake into muscle and adipose tissue
• Glucagon - increases plasma glucose levels by STIMULATING hepatic glycogenolysis and gluconeogenesis but does NOT antagonise glucose uptake into muscle and adipose tissue

27
Q

Which hormone does antagonise glucose uptake into muscle and adipose tissue?

A

Adrenaline

28
Q

How are amine hormones synthesised, stored, released and transporter?

A

Pre-synthesised from amino acids, e.g: tyrosine is converted into adrenaline

They are stored in vesicles and released in response to receptor stimulation, by a ligand, and then Ca2+-dependent exocytosis

Amines are HYDROPHILIC and are transported mainly “free” in plasma

29
Q

How are peptide and protein hormones synthesised, stored, released and transporter?

A

Pre-synthesised, usually from a longer precursor:
• Precursor protein is synthesised at RER
• Converted into the mature hormone with CONVERTASES

They are stored in vesicles and released in response to stimuli by Ca2+-dependent exocytosis

Peptides are HYDROPHILIC and are transported mainly “free” in plasma

30
Q

How are steroid hormones synthesised, stored, released and transporter?

A

Synthesised and secreted UPON DEMAND; the stimuli increase:

  1. Cellular uptake and availability of cholesterol
  2. Rate of conversion of cholesterol to PREGNENOLONE (rate-limiting step)

Cholesterol is uptaken and, e.g: converted to cortisol, via multiple biosynthetic pathway (all via pregnenolone); this is not stored but is immediately secreted

Steroids are HYDROPHOBIC (and lipophilic) and are transported in plasma bound to plasma protein, mostly

31
Q

Which form of steroid hormone is biologically active?

A

Only the “free” form, that is unbound to carrier protein, is biologically active

32
Q

Which hormones are relatively insoluble in plasma?

A

Steroids, thyroxine (T4), triiodothyronine (T3)

33
Q

Functions of carrier proteins?

A
  1. Increase amount transported in blood
  2. Provide a reservoir of hormone
  3. Extend half-life of the hormone in the circulation (contributing to the long duration of action of, e.g: steroid hormones)
34
Q

3 important specific carrier proteins?

A

Cortisol-binding protein (CBG) - binds cortisol in a selective manner and also some aldosterone

Thyroxine-binding globulin (TBG) - binds thyroxine (T4) selectively and also some triiodothyronine (T3)

Sex steroid-binding globulin (SSBG) - binds mainly testosterone and oestradiol

35
Q

2 important general carrier proteins?

A

Albumin - binds many steroids and thyroxine

Transthyretin - binds thyroxine and some steroids

36
Q

Transport of peptides and proteins?

A

Soluble in plasma and do not require proteins for transport; they typically have a relatively short duration of action because of this

37
Q

Describe the equilibrium in which carrier proteins are involved

A

Act as a buffer and reservoir that helps maintain constant conc. of free lipophilic hormone in the blood; FREE and BOUND hormone are in equilibrium:
• Only free hormone can cross the capillary wall to active receptors in target tissues
• Surges in hormone secretion are buffered by binding to carriers – free concentration does not rise abruptly
• This is replaced by bound hormone dissociating from carrier proteins

38
Q

Factors that influence plasma conc. of hormones?

A

Rate of secretion is the primary determinant

Rate of excretion also contributes

39
Q

Controls on secretion of hormones?

A
  1. Negative feedback - maintains plasma conc. at a set level
  2. Neuroendocrine - elicits a sudden burst in secretion to meet a specific stimulus
  3. Diurnal (Circadian) rhythm - secretion rate fluctuates (up and down) as a function of time, i.e: it is entrained to certain cues, like night and day (e.g: plasma cortisol conc. peaks just before midday and troughs just before midnight)
40
Q

An example of a negative feedback system?

A

Hypothalamus is influenced by stress and secretes corticotrophin-releasing hormone, which acts on the anterior pituitary and causes release of adrenocoticotrophic hormone

This acts on the adrenal cortex (has multiple physiological effects), which secretes cortisol; this then -vely feedbacks to regulate its own secretion

41
Q

What does trophic mean?

A

A hormone that acts upon another endocrine gland to regulate its secretion of hormone

42
Q

Route by which hormone elimination occurs?

A

There are several but, generally, metabolism by the liver and excretion by the kidney are most important

[Hormone]p = secretion - elimination

43
Q

Half-lives of different types of hormones?

A

Amines e.g. adrenaline - t½ ~ seconds

Proteins and peptides - t½ ~ minutes

Steroids and thyroid hormones - t½ ~ hours-days, due to extensive protein binding

44
Q

3 types of hormone receptors?

A
  1. GPCRs - activated by amines and some proteins/peptides; major signalling pathways inv. coupling to Gs, Gi, or Gq
  2. Receptor kinases - activated by some proteins/peptides
  3. Nuclear receptors - can be subdivided into class 1 and 2 and a hybrid class
45
Q

Different classes of nuclear receptors?

A

Class 1 - activated by many steroid hormones and move to the nucleus when activated (in the absence of activating ligand, mainly located in the cytoplasm bound to inhibitory heat shock proteins)

Class 2 - activated mostly by lipids and are constitutively present in the nucleus

Hybrid class - activated by thyroid hormone (T3) and other substances; they are similar in function to class 1

46
Q

Which of the hormone receptors are cell-surface receptors and which are the intracellular receptors:

A

Cell-surface receptors:
• GPCRs
• Receptor kinases

Intracellular receptors (ligand is lipophilic, allowing diffusion across the plasma membrane):
• Nuclear receptors
47
Q

Mechanism of signalling via GPCRs (cAMP pathway?

A

cAMP can act as a secondary messenger

Hormones, e.g: adrenaline, corticotrophin-releasing hormone and glucagon, bind to the GPCR; this modulates Gs to +vely modulate adenylyl cyclase, which allows conversion of ATP to cAMP. In turn, cAMP activates protein kinase A that phosphorylates target proteins and has cellular effects

Hormones, e.g: melatonin, bind to the GPCR; this modulates Gi, which -vely modulates adenylyl cyclase, preventing the conversion of ATP to cAMP

48
Q

Mechanism of signalling via GPCRs (IP3, PKC pathway)?

A

Hormones, e.g: angiotensin II, gonadotrophin-releasing hormone and thyrotropin-releasing hormone, modulate Gq to +vely modulate phospholipase C, converting PIP2 to IP3

IP3 binds to its receptor on the ER, allowing Ca2+ efflux which has cellular effects

Another pathway is the release of DAG from phospholipase C, which +vely modulates protein kinase C (PKC) to phosphorylate target proteins that have cellular effects

49
Q

Examples of a hormone that signals via receptor kinases?

A

Insulin receptor:
• Binding of insulin causes auto-phosphorylation of intracellular tyrosine residues
• Recruitment of multiple adapter proteins, notably IRS1 (these are also tyrosine-phosphorylated)

The insulin receptor substrate proteins have cellular effects

50
Q

What are nuclear receptors?

A

Ligand-gated transcription factors

51
Q

Mechanism of signalling via nuclear receptors (class 1)?

A
  1. Steroid hormones are lipophilic molecules that enter cells via diffusion across the plasma membrane
  2. Within the cell, they combine with an intracellular receptor producing dissociation of inhibitory HSP proteins; in the case of the steroid (but not thyroid hormone) receptors, the inactive receptor is located in the cytoplasm
  3. Receptor-steroid complex moves to the nucleus, forms a dimer and binds to hormone response elements in DNA
  4. Transcription of specific genes is either ‘switched-on’ (transactivated) or ‘switched off’ (transrepressed) to alter mRNA levels and the rate of synthesis of mediator proteins

Year 2 Physiology (21 decks)

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