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Endocrine Flashcards

1
Q

Autocrine

A

Chemical has it affect on the cell that produced it

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2
Q

Paracrine

A

Chemical that has it affect on a neighbouring cell

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3
Q

Endocrine

A

Chemical that has its affect on a distant cell by travelling in circulation

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4
Q

Endocrine hormone

A

A chemical produced at a low concentration by part of the body (endocrine gland) that is transported in circulation to the target organ

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5
Q

Can hormones initiate new reactions

A

No, they can only modify the rate of a reaction already taking place

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6
Q

Is hormonal or neural control faster in producing a response?

A

Neural control is more rapid but has a shorter duration. Endocrine signals tend to be slower in onset but longer in duration

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7
Q

Do the endocrine and neural systems work in isolation?

A

No, they work in a coordinated manner

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8
Q

What are the 3 categories of hormones?

A

Protein hormones, Steroid hormones, Amine hormones

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9
Q

How are protein hormones synthesised?

A

Synthesised initially on ribosomes as prepohormones that undergo a change in the endoplasmic reticulum to prohormones before being stored in secretory granules

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10
Q

What is a hormone?

A 
A chemical produced by an endocrine organ, transported by the vascular system affecting a distant target organ.
›Helps co-ordinate and control physiological
processes.
- Digestive processes
- Metabolism
- Growth and development
- Fluid and electrolyte balance
- Reproduction
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11
Q 
Which of the following are influenced by hormones
A. Stress
B. Exercise
C. Heart contractility
D. Brain function
E. All of the above
A

E

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12
Q

How are protein hormones secreted?

A

Basal level of secretion, a specific signal stimulates co-ordinated exocytosis of granules

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13
Q

How are protein/peptide hormones transported?

A

Transported in blood in their dissolved form as they are hydrophilic

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14
Q

Steroid hormones

A

Synthesised from cholesterol
E.g. Adrenocortical and sex
hormones

There is no storage of these hormones, rather synthesis is initiated by a stimulus and there is immediate release.

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15
Q

Production of steroid hormones

A

The production of specific hormones is dependent on presence of specific enzymes.
There is no storage of these hormones, rather synthesis is initiated by a stimulus and there is immediate release.

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16
Q

How are steroid hormones transported?

A

The lipophilic hormones are transported in blood bound to specific (globulin) and non-specific (albumin) binding proteins
Restricts diffusion and prolongs action since there is slow degradation and elimination

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17
Q

Amine hormones

A

Hormones derived from tyrosine

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18
Q

Circadian rhythms

A

Hormone secretion may be affected by circadian (over 24hrs) and ultradian (within the hour) rhythms and when analysing blood levels of a hormone you must be aware of the time of sampling.
Circulating hormone levels themselves feedback generally in a negative manner on further hormone release (or mechanisms that would normally lead to its release)

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19
Q

How is the action of hormones specific and localised?

A

Target cells have specific receptors with high affinity for a particular hormone.

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20
Q

Where are the receptors for protein/peptide hormones located?

A

The plasma membrane of the cell

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21
Q

Where are the receptors located for steroid and amine hormones located?

A

In the cytoplasm or nucleus of the cell which they can access because of their lipophilic nature

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22
Q

What determines tissue specificity?

A

Presence of receptors

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23
Q

What determines tissue sensitivity?

A

The concentration of receptors

24
Q

Why are steroid and thyroid hormones slower acting?

A

Since they produce their effect by stimulating mRNA and protein synthesis

25
Why are protein or peptide hormones faster acting than steroid or thyroid hormones?
Since they act via second messengers to alter enzyme activity. Steroid and thyroid hormones produce their effect by stimulating mRNA and protein synthesis
26
How does the hypothalamus regulate endocrine control? (in general terms)
Through its control of the output of the pituitary gland
27
What are the 4 lobes of the Hypophyseal axis?
1. Hypothalamus 2. Anterioir pituitary gland 3. Posterior pituitary gland 4. Intermediate lobe (Vestigial in mammals)
28
What are the 2 groups of hormones that nuclei in the hypothalamus produce?
1. Group consisting of Antidiuretic hormone (ADH) and oxytocin, produced in the paraventricular and suraoptic nuclei and travels along the nerve tract of the pituatray stalk to the nuerohypophysis bound to specific proteins, the neurophysins. They are stored and released from the neuropophysis. 2. The releasing or inhibitory hormones are released from the neurons in the hypothalamus and travel in the specific blood portal system running from the hypothalamus to the adenohypophysis or the intermediate lobe and regulate the secretion of the anterior pituitary and intermediate lobe hormones
29
How do ADH and oxytocin differ?
Both are made up of 9 amino acids that differ slightly in amino acid sequence but the difference is sufficient for each to essentially only bind to its own receptor
30
ADH
Acts to return water to the animal through increasing the permeability of the distal tubules of collecting ducts of the kidney to water. The medulla of the kidney has a high osmotic pressure and thus increasing the permeability of the duct walls to water allows water to be drawn from the tubules back into circulation. Failure of ADH secretion leads to large volumes of hypotonic urine and an inability of the animal to control its extracellular fluids (diabetes insipidus). ADH is a membrane active hormone with cAMP as the second messenger
31
Control of ADH secretion
Major control: Osmoreceptor cells in the hypothalamus causing increased ADH secretion in the posterior pituitary gland as extracellular osmotic pressure rises. Minor control: Changes in effective blood volume (e.g. haemorrhage) but there needs to be a 10% fall in blood volume before ADH secretion changes. The volume receptors are in the atria and great veins. Control also through CNS - trauma, pain, change in ambient temperature and by drugs - alcohol (decreases), nicotine, morphine (increases). ADH has a rapid onset of action but a very short t1/2 (3-5min) in the circulation. ADH also has a pressor action (increases blood pressure- vasopressin) but this action is only seen with high blood ADH concentration.
32
Oxytocin
Roles in reproduction Its actions are through stimulation of smooth muscle e.g. in sperm transport, milk ejection, myometrial contraction and hormone production.
33
Regulation of Oxytocin secretion
Regulated by neuroendocrine reflexes, involving tactile receptors in mammary teats and cervix stimulated by suckling and coitus/parturition respectively
34
Central diabetes insipidus
No secretion of ADH from hypothalamus
35
Nephrogenic diabetes insipidus
ADH secreted from hypothalamus, but kidney fails to | respond ( usually due to lack of receptors)
36
ADH secretion increased by
- barbiturates - Ether - Chloroform - Morphine - Acetylcholine - Nicotine - Pain
37
Action of growth hormone (GH)
GH stimulates epiphyseal plates of bones. GH is one of a number of hormones essential for growth (e.g. insulin, glucocorticoids, thyroxine, sex steroids) GH also has a number of actions concerned with protein, carbohydrate and lipid metabolism
38
Action of GH in lipid, protein and carbohydrate metabolism
In adipose tissue GH decreases glucose uptake, increases lipolysis. The free fatty acids can be used by muscle cells as alternate energy source. In liver GH increases RNA protein and glucose synthesis as well as synthesis of IGF and IGF binding protein In muscle GH increases amino acid uptake, protein synthesis and lean body mass and decreases glucose uptake Thus GH mobilises fat whilst keeping glucose for those glucose dependent tissues e.g. brain
39
Control of GH secretion
GH release a balance of GHIH and GHRH. GHRH release stimulated by low blood glucose, GH levels increased by stress, fasting, exercise, high protein food intake, sleep. GH also involved in lactogenesis in ruminants
40
Regulation of GH secretion
Two mechanisms involved: Direct negative feedback by insulin-like-growth-factors (IGF) on hypothalamus and glucostat cells in hypothalamus sensitive to blood glucose concentration. The latter allows an animal during starvation to draw on lipid reserves, conserve protein and reduce glucose uptake by muscle preserving it for nerve and erythrocytes. These regulators change the rate of release of GHIH and GHRH
41
IGF's
Increase protein, DNA and RNA synthesis in bone, heart, lung, kidney, pancreas, intestine, parathyroids. In muscle IGFs also increase amino acid uptake and protein synthesis in muscle further increasing lean body mass
42
Does GH or IGF have a longer half life
IGF
43
MSH (Melanocyte stimulating hormone)
Intermediate lobe hormone that is vestigial in mammals but in reptiles controls both the mobilisation (acute response) and synthesis (chronic response) of pigment such as melanin. Involved in defence mechanisms e.g. chameleon
44
T4
Thyroxine
45
T3
Triiodothyronine
46
Thyroxine (T4)
Essential for life, required for normal organ and tissue growth and to maintain optimal level of metabolic activity. Vital during both fetal and postnatally, if its secretion is low or absent the mature form of an animal never develops
47
Functional unit of the thyroid
Follicle, single layer of follicle cells surrounding the colloid. The site of T4 synthesis and storage.
48
Goitre
Result of hyperstimulation of the thyroid causing hypertrophy
49
Synthesis of thyroid hormones
Active transport of iodide from circulation Hydrogen peroxide quickly oxidises iodide to iodine Follicular cells produce a large glycoprotein (many tyrosine molecules) Iodine binds to glycoprotein catalysed by thyroperoxidase to form monoidotryosine (MIT) and diiodotryosine (DIT) Coupling of 2 DITs forms T4 Coupling of a DIT and a MIT forms T3 which remain bound to thyroglobulin T3 is usually formed in the liver
50
How is T4 released
Released by transfer of thyroglobulin from colloid into follicle cell by pinocytosis and T4 split from thyroglobulin by lysosomal enzymes.
51
Transport of thyroid hormones
Transport in circulation bound to 1 of 3 plasma proteins but only free form of the hormone enters the cell. 3 plasma proteins are: 1. Albumin (high capacity, low affinity) 2. T4 binding prealbumin (Intermediate capacity & affinity 3. T4 binding globulin (TBG) (Low capacity and high affinity) T4 binding globulin transports most T4 and as a result of its low capacity and high affinity gives plasma T4 a long half life. This and the high thyroid store of T4 means the body has a large T4 reserve, sufficient for 1-2 months
52
Regulation of thyroid hormone secretion
Regulator of hormone release is thyroid stimulating hormone (TSH) from the anterior pituitary. Stimulates all phases of T4 synthesis and secretion and is the general stimulator of thyroid metabolism. Prolonged TSH secretion leads to an increase in thyroid size (goitre) TSH is regulated by T4 feedback on the hypothalamus and pituitary and by higher centre control e.g. ambient temperature, stress, breeding season though TRH of hypothalamus
53
Action of thyroid hormones
Overall, set metabolic activity. Where secretion is abnormal quality of life or value as a production unit is low. No discrete target organ (effects all body tissues)
54
Calorogenic action of thyroid hormones
Thyroid hormones set the basal metabolic rate, leading to heat production and increased O2 consumption and CO2 production in all tissues EXCEPT lungs, CNS, spleen, gut and reproductive system. Hypothyroid animals tend to be heat seekers as unable to maintain body temperatures.
55
How is there independence between GH and T4?
T4 plays a role in GH secretion

VETS1032 (11 decks)

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