Homeostasis

Question 1

Define homeostasis

Answer 1

Maintenance of a constant internal environment

Question 2

Describe a simple feedback loop

Answer 2

Set point

Control centre

Effector

Regulated variable

Sensor

Back to the control centre

Question 3

What are the two communication types in homeostasis

Answer 3

Endocrine - hormones

Nervous - electrical

Question 4

Define autocrine signalling

Answer 4

Cells talking to themselves

Question 5

Define paracrine signalling

Answer 5

Cells talking to neighbouring cells a short distance away

• signal diffuses across gaps between cells
• inactivated locally, so does not enter the blood stream

Question 6

Does paracrine signalling enter the blood stream

Answer 6

No

Question 7

Give two examples of paracrine signalling

Answer 7

Interleukins

Platelet derived growth factor

Question 8

Describe interleukins

Answer 8

Signalling in the immune system

Mainly between white blood cells

Question 9

Describe platelet derived growth factor

Answer 9

Released from platelets

Regulates cell growth

Question 10

Describe endocrine signalling

Answer 10

Cells talking to other cells elsewhere in the body

Question 11

Name the endocrine organs

Answer 11

Hypothalamus
Pituitary
Thyroid
Adrenals
Pancreas
Ovaries
Testes

Question 12

Define a hormone

Answer 12

Molecule that acts as a chemical messenger

Question 13

What are the classifications of hormones

Answer 13

By structure

• amino-acid derivatives
• peptide
• steroid

Question 14

Describe peptide hormones

Answer 14

Made of amino acids

Vary in size from few amino acids to small proteins

Some have carbohydrate side chains (glycoproteins)

Hydrophilic (like water)

Question 15

Do peptide and amino acid hormones produce a quick or slow response in the body

Answer 15

Quick

Question 16

Describe the route of a peptide hormone

Answer 16

Hormone pre-made and stored in a cell ready to be released when needed

Hormone dissolved in blood

Receptor on cell membrane

Chemical reactions produces quick response from cell - signal transduction cascade

Question 17

Describe steroid hormones

Answer 17

All made from cholesterol

Different enzymes modify molecule to produce a variety of hormones

Cannot dissolve in water

Can dissolve in lipids

Question 18

Do steroid hormones produce a quick or slow response

Answer 18

Slow

Question 19

Describe the route of a steroid hormone e.g. testosterone

Answer 19

Testosterone made by cell and diffuses out once made

Transported in blood bound to transport protein as cannot dissolve in water

Receptor is in target cell

Slow response as directly affects DNA

Question 20

Of a 70kg male what is the total body water % and L

Answer 20

60%

42L

Question 21

Of a 70kg male what is the intracellular fluid % and L

Answer 21

40%

28L

Question 22

Of a 70kg male what is the extracellular fluid % and L

Answer 22

20%

14L

Question 23

Of 14L of extracellular fluid what is intravascular

Answer 23

3L

Question 24

Of 14L of intracellular fluid what is interstitial

Answer 24

11L

Question 25

Describe ECF

Answer 25

Na main Anions Chloride and bicarbonate Glucose and urea Protein

Question 26

Describe ICF

Answer 26

Main K

Question 27

Describe interstitial fluid

Answer 27

Surrounds the cells but does not circulate

Question 28

What is the calculation for estimated plasma osmolality

Answer 28

2Na + 2K + urea + glucose mmol/L

Question 29

What osmolality are equal

Answer 29

Intra and extracellular

Question 30

What is normal plasma osmolality

Answer 30

275-295 mmol/Kg

Question 31

What are the consequences of dehydration

Answer 31

Thirst Dry mouth Inelastic skin Sunken eyes Raised haematocrit Weight loss Confusion - brain cells Hypotension

Question 32

What are the consequences of water excess

Answer 32

Hyponatraemia Cerebral overhydration - headache - confusion - convulsions

Question 33

Define hydrostatic pressure

Answer 33

Pressure difference between plasma and interstitial fluid Water moves from plasma into interstitial fluid

Question 34

Define oncotic pressure

Answer 34

Pressure caused by the difference in protein concentration between the plasma and interstitial fluid Water moves from interstitial fluid into plasma

Question 35

Describe oedema

Answer 35

Excess accumulation of fluid in interstitial space Disruption of the filtration and osmotic forces in circulating fluids - obstruction of venous blood or lymphatic return - inflammation = increased capillary permeability - loss of plasma protein

Question 36

Define serous effusion

Answer 36

Excess water in body cavity

Question 37

What are the reasons for oedema and serous effusion

Answer 37

Increased fluid leakage into interstitial spaces OR impaired reabsorption of fluids

Question 38

Describe transudate serous effusion

Answer 38

Fluid is pushed through the capillary due to high pressure within the capillary Low protein content

Question 39

Describe exudate serous effusion

Answer 39

Fluid leaks around the cells of the capillaries caused by inflammation and increased permeability of pleural capillaries to protein High protein content

Question 40

Normal reference range for sodium

Answer 40

135-145 mmol/L

Question 41

What is the range for serum calcium

Answer 41

2.1-2.6 mM 50% serum calcium ionised (free) 50% bound to albumin (so cannot diffuse into cells)

Question 42

What are the three routes to get to serum calcium

Answer 42

GI - Vit.D Kidney - PTH/Vit.D/FGF23 Bone - PTH/Vit.D