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ESA1 - Metabolism > Homeostasis And The Endocrine System > Flashcards

Homeostasis And The Endocrine System Flashcards

1
Q

Give 3 examples of receptors that can detect stimuli and help maintain homeostasis

A
  • Chemoreceptors - hormones and neurotransmitters
  • Thermoreceptors - heat
  • Nocireceptors - pain
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2
Q

Define NEGATIVE FEEDBACK and give 2 examples

A
  • Response that opposes the effect of the stimulus to maintain homeostasis
  • e.g. Control of blood glucose, control of body temperature
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3
Q

Define POSITIVE FEEDBACK and give 2 examples

A
  • Response that acts to increase the effect of the stimulus and causes further change
  • e.g. Blood clotting cascade, ovulation (FSH)
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4
Q

Explain why someone may experience jet lag after a long haul flight

A
  • Cues from environment (ZEITGEBERS) keep body on a 24 hour cycle e.g. light, temperature, eating/drinking, social interaction and exercise
  • Mismatch between environmental cues and body clock during a long haul flight
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5
Q

How is the osmotic pressure of the blood plasma measured?

A

OSMORECEPTORS in the hypothalamus

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6
Q

Why is the total body water (as % lean body mass) less for women than men?

A

Women have a higher fat content than men

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7
Q

Describe the compartmentalism of the total body water in a 70kg man (~42 L)

A
  • INTERCELLULAR FLUID -> ~67% at 28 L
  • EXTRACELLULAR FLUID -> ~22% at 9.4 L
  • BLOOD PLASMA -> ~11% at 4.6 L
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8
Q

Briefly explain how a stimulus can bring about a response in the body

A
  • Receptor detects stimuli and sends signal down AFFERENT pathway leading to the control centre
  • Control centre interprets change to environment and determines a response
  • Response sent down EFFERENT pathway to effectors which cause change and initiate response
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9
Q

What is the difference between OSMOLARITY and OSMOLALITY?

A
  • OSMOLARITY is the number of osmoles per Litre of solution - VOLUME
  • OSMOLALITY is the number of osmoles per Kg of solution - MASS
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10
Q

Explain how the body responds to an INCREASE in blood osmolality

A
  • Hypotonic -> BODY NEEDS TO CONSERVE WATER
  • Osmoreceptors in hypothalamus detect TONICITY of blood plasma
  • Stimulate thirst receptors so you drink more to reduce osmolality
  • Stimulates release of ADH from posterior pituitary so more water absorbed in kidneys and less urine produced
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11
Q

Explain how the body responds to a DECREASE in blood osmolality

A
  • Hypertonic - BODY NEEDS TO GET RID OF WATER
  • Osmoreceptors in hypothalamus detect change in TONICITY of blood plasma
  • Decreased ADH secretion from posterior pituitary so less water absorbed in kidneys and larger volume of urine produced
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12
Q

Name 5 glands that are associated with the endocrine system

A
  • Pituitary gland
  • Thyroid/Parathyroid glands
  • Adrenal glands
  • Hypothalamus
  • Testes/Ovaries
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13
Q

What is a ‘hormone’?

A

CHEMICAL SIGNALS produced and secreted by endocrine glands that travel in bloodstream to target tissues and stimulate an effect

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14
Q

List 3 organs/tissues in the body (apart from endocrine glands) that also secrete important hormones

A
  • STOMACH (gastrin, ghrelin)
  • ADIPOSE TISSUE (leptin)
  • LIVER (IGF1)
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15
Q

Name 4 mechanisms by which hormones can communicate with target cells

A
  • AUTOCRINE (signal acts back on original cell)
  • PARACRINE (signal acts on adjacent cells a short distance away)
  • ENDOCRINE (signal enters bloodstream and is transported to target tissue)
  • NEUROCRINE (signal originates in neurone and is passed down axon and released into bloodstream)
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16
Q

How are neurones and endocrine cells similar?

A
  • Both capable of SECRETION (hormones, neurotransmitters)
  • Both can be DEPOLARISED
  • Mechanism of action requires interaction with specific RECEPTORS on target cells
  • Both work in parallel to maintain HOMEOSTASIS
17
Q

Explain the classification of hormones

A
  • PEPTIDE -> water soluble, chains of AA, e.g. Insulin
  • AA DERIVATIVES -> water soluble (Thyroid Hs are lipid soluble), synthesised from AA, e.g. Neurotransmitters, thyroid hormones
  • STEROID -> lipid soluble, synthesised from cholesterol, e.g. Cortisol
  • GLYCOPROTEINS -> water soluble, protein molecules with carb side chain, e.g. FSH, LH
18
Q

Name 4 steroid hormones that are synthesised by cholesterol

A

PACT:

  • Progesterone
  • Aldosterone
  • Cortisol
  • Testosterone
19
Q

What are the roles of carrier proteins in transportation of some hormones?

A
  • Increase solubility of hormone in plasma
  • Increase half life of hormone
  • Readily accessible reserve
20
Q

Explain why some hormones must be bound to carriers for transportation

A
  • Hormones transported in bloodstream
  • Some hormones are water soluble (peptide, glycoprotein, adrenal medulla hormones)
  • Most hormones are lipid soluble so must bind to proteins (some have specific proteins e.g. Thyroxine-binding globulin TBG)
21
Q

What factors determine the level of hormones in blood plasma?

A
  • Rate of production
  • Rate of delivery
  • Rate of degradation
22
Q

Explain how endocrine hormones travelling in blood have specificity to target tissues

A

Target tissues express SPECIFIC COMPLEMENTARY RECEPTORS on their plasma membranes which are recognised by the hormones and can initiate a response (those cells without specific receptors are unaffected by hormone)

23
Q

Explain why only some hormones must bind to receptors in order to initiate a response within the cell

A
  • Some hormones e.g. Steroid are LIPID SOLUBLE so can diffuse straight across phospholipid bilayer and initiate a response within the cell
  • WATER SOLUBLE hormones e.g. Insulin cannot diffuse through the the lipid bilayer so rely on receptors to initiate response via a cascade mechanism
24
Q

Explain how a G PROTEIN COUPLED RECEPTOR allows a hormone to initiate a response within the cell

A
  • Hormone (e.g. Adrenaline) binds to receptor causing a dissociation of the G protein α subunit
  • Activation of effector protein ADENYL CYCLASE stimulates formation of secondary messenger cAMP from AMP
  • Protein KINASE enzymes activated and PHOSPHORYLATION of target proteins occurs, causing a cellular response
25
Q

Explain how hormones produced in the hypothalamus act in 2 distinct NEUROCRINE pathways

A
  • Hormones produced in hypothalamus are transported to posterior pituitary and secreted to have direct effects on distant target tissues
  • Hormones secreted into HYPOPHYSEAL PORTAL SYSTEM affect endocrine anterior pituitary to initiate release of other hormones which affect distant target tissues
26
Q

Name 2 hormones that are produced by the hypothalamus and secreted by the posterior pituitary and state their effects

A
  • OXYTOCIN affects milk let down and uterine contractions during birth
  • ANTI-DIURETIC HORMONE acts on walls of collecting duct in kidneys for regulation of body water volume
27
Q

What is meant by a TROPIC HORMONE?

A
  • Hormone that stimulates the secretion of another hormone

- Hypothalamus contains 7 tropic hormones that stimulate the secretion of other hormones from the anterior pituitary

28
Q

Name 3 tropic releasing hormones produced by the hypothalamus and state their affect on the anterior pituitary

A
  • Thyrotropin releasing hormone TRH -> stimulates anterior pituitary to release TSH
  • Corticotropin releasing hormone CRH -> stimulates anterior pituitary to release ACTH
  • Gonadotropin releasing hormone GnRH -> stimulates anterior pituitary to release FSH and LH
29
Q

What is the difference between TROPHIC and TROPIC hormones?

A
  • TROPHIC hormones affect growth

- TROPIC hormones affect the release of another hormone

30
Q

Describe the position of the pituitary gland in relation to the hypothalamus and explain why this is advantageous

A
  • Pituitary gland located beneath hypothalamus on a socket of bone called the SELLA TURCICA
  • Allows the neurocrine transition of hormones produced in the hypothalamus to the pituitary for secretion and activation of other hormones
31
Q

Explain how the hypothalamus is physically linked to the posterior pituitary gland

A

Linked via the INFUNDIBULUM (pituitary stalk)

32
Q

Describe the neurocrine function of the posterior pituitary gland

A
  • Hormones e.g. OXYTOCIN and ADH produced in hypothalamus are transported down NERVE AXONS to posterior pituitary
  • Hormones are then STORED
    or SECRETED from posterior pituitary to distant target tissues
33
Q

Explain how the hypothalamus controls the secretion of hormones homeostatically

A
  • TROPIC hormones produced by hypothalamus are stored at axon endings (MEDIAN EMINENCE) and are not released into HYPOPHYSEAL PORTAL SYSTEM unless stimulated by changes in the body’s internal environment
  • Once released they enter the anterior pituitary and can stimulate or inhibit the production of other hormones
34
Q

What is the role of the HYPOPHYSEAL PORTAL SYSTEM?

A
  • System of blood capillaries that connects hypothalamus to anterior pituitary gland
  • Allows rapid transportation of tropic hormones produced in hypothalamus to anterior pituitary which stimulate the production and secretion of other hormones (which can affect distant target tissues)
35
Q

Name 6 hormones produced by the anterior pituitary gland

A
  • TSH (thyroid stimulating hormone)
  • LH (luteinising hormone)
  • FSH (follicle-stimulating hormone)
  • ACTH (adrenocorticotropic hormone)
  • GH (growth hormone)
  • PRL (prolactin)
36
Q

Explain how the hypothalamus-pituitary adrenal axis is an example of negative feedback

A
  • Stress stimulus causes hypothalamus to release CRH into hypophyseal portal system which travels to anterior pituitary
  • CRH stimulates production and secretion of ACTH which stimulates adrenal gland to secrete CORTISOL
  • Cortisol can then inhibit hypothalamus from producing further CRH to inhibit further release of cortisol, maintaining cortisol concentrations in blood
37
Q

Which 2 nuclei in the hypothalamus are involved in the production of oxytocin and ADH?

A
  • PARAVENTRICULAR NUCLEUS controls ADH production
  • SUPRAOPTIC NUCLEUS controls oxytocin production
  • Both hormones are stored and secreted in the posterior pituitary gland (pass down from hypothalamus via infundibulum)

ESA1 - Metabolism (20 decks)

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