Cell structure and transport Flashcards
What proportion of total body water is extracellular?
1/3
What proportion of total body water is intracellular?
2/3
Of the extracellular water, how much of it is interstitial?
3/4
Of the extracellular water, how much of it is intravascular (in the plasma)?
1/4
Describe the features of an isotonic solution
The concentration of solutes on both sides of the membrane are equal. Therefore, the net movement of water is zero
Describe the features of a hypertonic solution
The concentration of solutes is greater outside the cell. Therefore, there is a net movement of water out of the cell, resulting in the cell shrinking
Describe the features of a hypotonic solution
The concentration of solutes is greater inside the cell. Therefore, there is a net movement of water into the cell, resulting in the cell swelling
List five broad functions of the circulatory system
- Exchange of substances with the environment
- Transport oxygen to cells
- Remove metabolites and carbon dioxide from cells
- Thermoregulation
- Transport immune cells and mediators
Where would you find continuous capillaries?
- Muscle
- Skin
- Lungs
- Fat
- Connective tissue
- Neural tissue
Where would you find fenestrated capillaries?
- Kidneys
- Intestines
- Endocrine glands
- Joints
Where would you find discontinuous capillaries?
- Bone marrow
- Liver
- Spleen
What are the three forces driving movement of substances across capillary walls?
- Diffusion
- Pinocytosis
- Bulk flow (starlings forces)
What is the main starlings force driving filtration of substances out of capillaries?
Hydrostatic pressure of the capillary
What is the main starlings force driving filtration of substances into of capillaries?
Oncotic pressure of capillaries
What propels lymph down initial lymphatics?
Extrinsic lymphatic pump, relying on external muscle contraction to propel lymph downstream. Other contributing factors are:
- Respiration
- External tissue compression
- Vasomotion and pulse pressure changes in neighbouring arterioles
What prevents back flow of lymph from the collecting lymphatics back into the initial lymphatics?
Bicuspid valves
What propels lymph down collecting lymphatics?
Contractile smooth muscle
What is the difference between oedema and lymphoedema?
The difference relates to the cause of the excess fluid. Oedema can be caused by decreased plasma protein, increased vascular permeability or increased venous pressure. However, lymphoedema relates specifically to excess fluid caused by a defective lymphatic system. General causes include obstruction, lack of skeletal muscle contraction (defective extrinsic lymphatic pump) or damaged lymphatic vessels.
Define osmolarity
The concentration of particles in one litre of solution, independent of the size and weight of the particles
Define osmolality
The concentration of particles in one kilogram of solution, independent of the size and weight of the particles
Define tonicity
The state of a solution with respect to its osmotic pressure (isotonic, hypertonic, hypotonic)
What are factors which decrease membrane fluidity?
- Longer tails
- Increasing saturation
- Decreasing temperature
- Increasing cholesterol
What are factors which increase membrane fluidity?
- Shorter tails
- Increasing unsaturation
- Increasing temperature
- Decreasing cholesterol
What are the components of Fick’s law?
Flux = concentration difference x surface area x diffusion coefficient / membrane thickness
Are hydrophobic or hydrophilic molecules better at diffusing through membranes?
Hydrophobic, because they are lipid soluble. Therefore, they diffuse through phospholipid membranes faster.
What type of molecules pass through membranes most readily?
Non-polar molecules
Briefly describe simple diffusion
Movement of molecules down their concentration or electrical gradient. Directly though the membrane, through pores or through protein channels.
Briefly describe Facilitated diffusion
Movement of molecules down their concentration or electrical gradient. Facilitated by a carrier molecule, transporter, or binding of another molecule inducing a conformational change.
Briefly describe active transport
Movement of molecules up their concentration or electrical gradient. Movement is carrier mediated and energy dependent.
What is an example of a ligand gated ion channel?
- Acetylcholine binding to nicotinic ACh receptors on the post-synaptic neuron, opening sodium channels and promoting action potential generation
- GABA binding to receptors in the CNS, opening Cl- channels and inhibiting action potential generation
What is an example of a voltage gated ion channel?
Voltage gated calcium channels on the sarcoplasmic reticulum in skeletal muscle fibres, channels open when there is sufficient depolarisation
What is an example of primary active transport?
The sodium potassium pump, using ATP to pump both sodium and potassium against their concentration gradients. 3 sodium molecules leave for every 2 potassium molecules which enter, this sets up a chemical gradient for both ions and also an electrical gradient across the cell membrane (inside more negative than outside)
What is an example of secondary active transport?
- Sodium calcium antiporters, allowing sodium to re-enter the cell based on the electrochemical gradient set up by the sodium potassium pump.
- Sodium glucose symporters, allowing sodium to re-enter the cell based on the electrochemical gradient set up by the sodium potassium pump. In the gut and renal tubules the coupled glucose is moving up its concentration gradient.
What are reticulocytes?
Immature red blood cells. They compose about 1% of RBC and circulate for a day before maturing
What species has nucleated reticulocytes?
Chickens. Mammalian reticulocytes don’t have nuclei
What is the oxygen bearing molecule in RBC?
Haemoglobin
How many ahem subunits does each haemoglobin have?
4, hence each RBC can carry 4 Oxygen molecules (O2)
How is the majority of carbon dioxide carried by RBC
As bicarbonate ions
Briefly describe haemolytic anemia
The body destroys RBC at a faster rate than they are being produced
What are platelets?
Also known as thrombocytes, they are involved in clotting
What is meant by aggregation?
Formation of a platelet plug in response to small endothelial injuries
What is meant by coagulation?
Formation of a fibrin clot (thrombus) in response to larger injuries
What causes fibrinogen to polymerize into fibrin during the coagulation pathway?
Thrombin
Where are the sites of haemopoiesis during foetal development?
- Liver
- Spleen
- Bone marrow
Where are the sites of haemopoiesis during embryogenesis?
- Liver
- Spleen
- Yolk sac
What are haemopoietic stem cells?
Multipotent cells which can form cells of any blood line (Myloid, Lymphoid and Erythroid)
What hormone controls erythropoiesis in mammals? Where is it produced?
Erythropoietin (EPO), produced by fibroblast-like cells in the cortex and outer medulla of the kidney
What is a typical stimulus for EPO production by renal peritubular cells?
Fall in effective circulating volume resulting in tissue hypoxia
What are the thee specific effects of EPO?
- Shortens cell cycle time by increasing mitotic division rate of stem cells and erythroblasts
- Increased rate of maturation of erythroblasts into reticulocytes within the bone marrow
- Increased rate of reticulocyte release from the bone marrow
What would you expect to find in a plasma sample?
- Water
- Proteins (albumin, globulins, fibrinogen)
- Salts
- Hormones
What would you expect to find in a serum sample
Same as plasma sample except without the proteins involved in clotting (fibrinogen)
