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AHS 1 > Wk 2 Homeostasis / Water distribution > Flashcards

Wk 2 Homeostasis / Water distribution Flashcards

1
Q

Difference between positive and negative feedback?

A

Positive: divergence from equilibrium
Negative: maintenance of equilibrium

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2
Q

What are the 5 components of a Negative Feedback Mechanism?

A
  1. Controlled variable (body temperature)
  2. Receptors (sensors)
  3. Processor (integrating centre)
  4. Set point (to return to)
  5. Effector mechanisms
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3
Q

What happens when an animal has low blood pressure?

A

Baroreceptors -> brain -> increase cardiac output + vasoconstriction

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4
Q

What 5 variables in the body are kept constant?

What 3 effector mechanisms help to correct disturbances of controlled variables?

A
  1. Core body temp
  2. Blood pressure
  3. Blood glucose
  4. Osmolarity of plasma
  5. Blood oxygen levels

Effector mechanisms which help to correct disturbances of controlled variables:

  1. Heart Rate
  2. Urine concentration
  3. Respiratory rate
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5
Q

What is the relationship between ECF and ICF?

A

All cells are bathed in ECF. Changes in ECF (ion concentration affect function of excitable cells such as nerve and muscle cells) affect changes in ICF.

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6
Q

Solid:water

ECF:ICF

A

Solid 40%
Water 60%

ECF: 20% 1/3
ICF: 40% 2/3

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7
Q

Where is ECF found?

A
  1. Plasma (blood)
  2. Interstitial fluid (inbetween cells)
  3. Cerebrospinal fluid
  4. Fluid in GI tract
  5. Joint fluid (synovial)
  6. Lymph
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8
Q

What can and can’t cross the cell membrane?

A

Can: small, uncharged molecules such as O2, CO2 and NH3 (and H20).

Cannot: Big such as suger and protein, or small but charged such as Na+, K+, Cl-, Ca++.

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9
Q

What is Brownian motion?

A

Diffusion in liquids:

random thermal motion of particles

speed is inversely related to size

Molecules collide, changing direction continuously

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10
Q

What is Fick’s law of diffusion?

A

Transport rate of a substance by diffusion.

It is driven by difference of concentration across membrane, and also the permeability.

Jx = Px([X]o-[X]i)

J = Flux
P = permeability coefficient
[X]o-[X]i = difference in concentration
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11
Q

What are 4 specialised pathways across a membrane?

A
  1. Pores
  2. Channels
  3. Carriers (transporters)
  4. Pumps
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12
Q

Explain pores

A
  • simple diffusion (no active participation of the pore)
  • always open
  • are inserted and removed t control solute concentration

eg.
Porins (mitochondria), perforins (lymphocytes), aquaporins

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13
Q

What are channels, how do they work?

A
  • Gated (voltage, ligand or second messenger)
  • Eg. Na+, K+, Ca2+

Non gated also exist, for example, K+ leak channel.

Open or close, also simple diffusion.

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14
Q

What are carriers / transports, how do they work?

A

Facilitated diffusion
passive transport of small molecules.

Molecule binds and conformational change allows movement into cell.

Hence, facilitated.

May carry different solutes in and out, at the same time. May required two different types to transport into the cell, or two different types (one in and one out).

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15
Q

What are pumps, how do they work>?

A

Active transport (hydrolysis of ATP).

Net transport against electrochemical gradients.

eg. Na+/K+, H+-K+ pump

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16
Q

What is secondary active transport?

A

Relying on a gradient that has been set up by active transport.

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17
Q

What is exocytosis?

A

Vesicles fused to membrane and move outside of the cell.

Constitutive: Unregulated, happens all the time
Regulated: release triggered by something (hormone).

18
Q

What is endocytosis

A

Move into the cell through vesicles.

Pinocytosis: fluid filled

Receptor mediated endocytosis: fluid filled vesicels

Phagocytosis: particulate matter (macrophages)

19
Q

Competition of fluid compartments: how much inside and outside of K+, Protein-, Na+ and Cl-?

A

Inside: great K+, Protein-
Outside: greater Na+, Cl-

20
Q

What is the driving force of passive transport?

A

electro-chemical gradient

21
Q

What is hypo/hyper kalaemia?

A

Extracellular changes in potassium concentration effecting excitable cells:

Hypokalaemia: muscle weakness, cardiac arrhythmias.

Hypokalaemia - cardiac arrhythmias.

22
Q

What is the sodium concentration inside cells?

A

Low.

All cells use the Na+ gradient to drive secondary active transport via co-transport /exchangers.

eg: Na/glucose transport into cells.

Basal Na/K pump moves 3Na+ out and 2K+ in.

23
Q

What is osmosis?

A

Movement of water from an area of higher solvent activity to lower solvent activity across a semi-permeable cell membrane.

24
Q

What is osmolarity?

A

A measure of activity of the solvent.

Number of osmoles per unit volume solution (ionic compounds dissociate in solution)

An increase in osmolarity results in a decrease in solvent activity.

25
Q

What is a mole?

A

A unit of quantity. Avogardo’s constant. Same number of particles as there are atoms in 12g of Carton-12 isotope.

6.02 x 10~(23)

26
Q

What is molarity?

A

A unit of concentration.

Number of moles of solute per unit volume of solution eg. mol/l

27
Q

What is one molar solution?

A

Molecular mass of the substance in grams dissolved in enough distilled water to make a volume of 1 litre.

eg. Molecular mass of glucose is 180. 1M solution = 180g/litre.

28
Q

Osmole

A

Unit of quantity.

Avogardo’s number of osmolyte particles.

Each particle will alter the activity of the solvent.

Independent of molecular weight and/or charge of solute particles.

29
Q

How is osmolarity calculated?

A

Osmolarity = g (osmotic coefficient) x molar concentrations of osmolyte particles.

Include all osmolyte particles as ionic molecules may dissociate in solution, though ionic compounds may not completely dissociate (degree of dissociation is given by the osmotic coefficient).

For 1 mole of glucose solute = 1 osmole in solution.

For 1 more of NaCl in solute = 1.86 osmoles in solution (incomplete dissociation).

30
Q

Hypo-osmotic

A

High solvent activity, low osmostic pressure

31
Q

Hyper-osmotic

A

Low solvent activity, high osmotic pressure

32
Q

Iso-osmotic

A

No net flow of water. Same osmolarity on both sides of the semipermeable membrane.

33
Q

The Osmotic Pressure

A

The pressure required to exactly stop osmosis.

Activity of solvent can be increased by applying hydrostatic pressure.

Hydrostatic pressure great than osmotic pressure can reverse osmosis.

34
Q

Effective osmotic pressure

A

How permeable the membrane is to the solute.

(aka reflection coefficient δ)

1 = cannot cross

0 = freely permeable

between 0 and 1 = partially permeable to solute

35
Q

What is tonicity?

A

Tonicity describes the effect of a bathing solution on cell volume.

Call volume changes when water leaves or enters by osmosis.

This is determined by osmolarity of the solution as well as the permeability of the cell membrane to the solutes.

36
Q

What is pressure of IVF?

A

There is a high oncotic (colloid) pressure. This is due to large molecules such as protein in the capillary.

Constant hydrostatic pressure in the capillaries.

37
Q

Starling’s Forces

A

Oncotic and hydrostatic pressure of the IVF.

These forces determine how much water moves in and out of the capillaries.

High hydrostatic pressure inside capillaries forces water out of the capillaries. This is the driving force, there is usually more water out of capillaries than into them.

High oncotic pressure will draw water into the capillaries (osmotic suction).

38
Q

What is the determining factor of water movement IVF?

A

Oncotic pressure, as other smaller molecules can move in and out.

Filtration rate out of capillaries is proportionate to the hydraulic drive (hydrostatic pressure) minus osmotic suction (the oncotic pressure draw water into the capillary).

39
Q

What is the Gibbs-Donnan effect?

A

Intracellular proteins are negatively charges, and will draw in positively charged ions (electrochemical gradient), along with some of their corresponding negatively charged ions. Negative intracellular potential results in an excess of osmotically active particles; the cell becomes hypertonic and will draw in water. However, pumps such as the NA/K ATPase pump removes 3 Na+ for every 2 K+ ion (functioning to remove the excess of osmotically active particles in the cell to avoid swelling).

40
Q

What does Ouabain? (Whah-bain)

A

Demonstrates the Gibbs-Donnan effect. Demonstrates function of Na/K ATPase. This drug stops the pump working. The cells then swell as water move into the cell as the excess of osmotically active particles are not being removed from the cell. The cell swells (oedema) and dies.

AHS 1 (15 decks)

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