Theme 3 Powell Flashcards
Significance of Homeostasis
- Biochemical reactions sensitive to: Temperature, pH, [solute], [water], pressure
- Organisms must regulate many internal variables: nutrients, gasses, pH, waste products, water/solutes, volume, pressure, temperature
Homeostasis – Negative Feedback Loops
Homeostasis is maintained by regulating physiological variables with reference to a setpoint
Homeostasis – Cell Location
- Cell location– implications for how homeostasis is approached
- External cells must face the environment: sometimes dead (i.e. superficial layers of skin)
- But internalized ‘external’ cells must be alive – control access
Internal ‘external’ cells must:
- have a rapid turnover
- produce a lethal environment to microbes
- be covered by secretions to isolate them from the environment
Internal cells: homeostasis regulates the internal environment
- Reduces the amount of work cells have to do to maintain homeostasis if internal cells are not isoosmotic with the environment
- Enables them to specialize
- Regulate circulating fluids
Osmoregulation
regulation of the internal osmotic (water/salt/waste) environment
Circulation
bulk flow of fluid within the body (water, solutes, nutrients, gasses)
Gas Exchange
exchanging gasses with the environment
pH Regulation
controlling the [proton H+] of body fluids
Water potential
- the tendency of water to move, due to osmotic, hydrostatic, gravity, humidity, etc
- sum of osmotic potential, pressure potential, gravity etc.
Fick’s Law - Diffusion Rate
= D A dC/dX
D = diffusion coefficient – depends upon characteristics of solute and solvent, temperature etc.
A = surface area of the membrane, directly a function
dC/dX:
dC – concentration difference;
dX – thickness of the membrane
dC/dX is the force driving the diffusion
Osmolality
- osmoles – total number of dissolved particles of solute per kg of solvent
- osmolality – osmotic concentration of a solution, measured in osmoles
hypoosmotic
- of a solution, having a lower osmolality than the reference solution
- pure water is hypoosmotic to the red blood cell placed in it, which bloats
hyperosmotic
- of a solution, having a higher osmolaity than the reference solution
- a strong saline solution is hyperosmotic to the red blood cell placed within it, which shrivels
isoosmotic
- of a solution, having the same osmolality as the reference solution
- a bath of physiological saline is isoosmotic to the red blood cell placed within it, which stays the same
Osmosis
The tendency of water to cross a selectively permeable membrane towards the side of greater solute concentration when the membrane is impermeable to the solute
Osmotic potential (solute potential in plants) – force exerted on water generated by differences in solute concentration across a semi-permeable membrane
- Pure water has an osmotic potential of zero – the highest osmotic potential possible
- Lower osmotic potential is a negative number (the more solute, the more negative the osmotic potential)
- Water moves from less negative to more negative volumes
Pressure potential
– hydrostatic (=mechanical) pressure affects how water crosses a membrane from a volume of high osmotic potential to a volume of low osmotic potential
- Low osmotic potential requires high pressure to stop water from moving in
Osmosis and the living cell
- Significance to animals: cells will shrink or swell if not in an isoosmotic environment (without work on the cell’s part)
- Significance to plants: Cells will develop turgor pressure (hydrostatic) as water enters, which limits further influx of water
Bulk Flow
- Bulk flow of transport fluids requires application of hydrostatic pressure
- Affects exchange of water between the bulk transport system and the extracellular fluid in closed circulatory systems
Bulk Flow - Animal Example
- Pressure potential in the upstream side of the capillary bed exceeds the osmotic potential of extracellular fluid – water leaves capillaries
- Osmotic potential in the downstream side of the capillary bed exceeds hydrostatic pressure of extracellular fluid – water re-enters capillaries
Osmoregulation in ANIMALS
- Fresh water vs salt water vs plasma
- Osmoconformers vs Osmoregulators
Osmoconformer Strategies
- Adjust osmotic strength of cells [Y] and extracellular fluid [X] to match environment [Z]
- Examples: marine inverts, hagfish, elasmobranchs
Osmoregulators Strategies:
- Adjust osmotic strength of extracellular fluid [X] to match cells [Y] and protect the internal environment from the external [Z]
- Examples: freshwater inverts and most vertebrates
The challenge of water/salt loss and gain
- Terrestrial animals: (water loss)
- Aquatic animals: Marine (water loss), Freshwater (water gain)
Tonicity And The Environment – Water Dwellers
- Body fluid osmolality varies among aquatic organisms
- Some marine groups are isoosmotic with seawater – osmotically stable environment
Marine bony fish
- Hypoosmotic to the environment, lose water and gain ions, especially through the gills
- Drink seawater to offset water loss
- Chloride cells in gills eliminate Na+, K+ and Cl- from blood
- Produce small amounts of urine, which conserves water and eliminates excess solute in feces
Freshwater bony fish
- Hyperosmotic to the environment, lose ions and gain water, especially through the gills
- Do not drink
- Produce large amounts of dilute urine
- Must replace ions from food or from transport across gill membrane
Chondrichthyes
- Isoosmotic to seawater, but concentrations of Na+, K+, Cl- all less than seawater – the difference is made up by urea
- Still must deal with inward diffusion of Na+, K+, Cl- through gills
- The rectal gland secretes a highly concentrated salt solution
Tonicity And The Environment – Land Dwellers
- A dry environment = constant water loss through evaporation: across the wet respiratory membrane and across the surface of the skin
- Water loss in urine and feces
- Requires: waterproofing of outer layer of the body, minimal exposure of gas-exchange and digestive surfaces to the air, minimizing electrolyte intake
Terrestrial environments are dry:
- Lose water to the environment
- Consume/produce/conserve water
- Limit salt intake
Marine environments are hyperosmotic (dry):
- Lose water to and gain salt from the environment
- Eliminate salt and consume/produce/conserve water
- Limit salt intake
Migratory salmon (Fresh to Marine to Fresh migrations)
Salmon in freshwater: chloride cells located on lamellae of gill filaments import electrolytes
Salmon in seawater: chloride cells located at base of gill filaments secrete electrolytes
- Basically: pump ions in in freshwater, then once in the ocean turn off those chloride cells for the other chloride cells which then pump out ions
Controlling water loss and gain
- Excretion: elimination of waste/toxins, aids in controlling the content of extracellular fluid (salt/water/pH)
- Diffusion into water
- Excretory organ (liquid waste): Filtration (non-selective), Secretion (selective), Reabsorption (selective)
Ammonia (NH3) excretion
- Ammonia is toxic = must get rid of it
- Aquatic: diffusion into the environment (across body/gills), excretion in filtrate/urine, ammonium (NH+4)/sodium exchangers
- Terrestrial (and some aquatic): cannot use diffusion or ion exchange with the air, only excretion in the filtrate
- Produce Urea (mammals, amphibians, sharks)
- Produce Uric Acid (land snails, insects, reptiles/birds): key for animals that develop in terrestrial eggs
Malpighian Tubules
- large absorptive surface area in contact with haemolymph
- active secretion of uric acid, ions into the lumen of the tubule
- water follows through osmosis
filtrate released into the gut - Na+ and K+ actively transported out, water follows
- Solid uric acid released with feces
Why circulate fluids?
- Processing: regulate pH, osmolarity, waste, add nutrients, gas exchange
- Transportation/communication: hormones, heat, gasses, nutrients, immune components, solutes
- Diffusion is adequate in small (>1 mm thick) or simple organisms, large require a circulatory system
Plants vs Animals: Circulation
Both use a series of tubes, but differ in:
- Nutrient, energy and water sources
- Metabolic rates
- Cell structure
- Muscle (or not)
CIRCULATION in Animals
- Heterotrophs with a digestive system
- High metabolic rates demand rapid circulation
- Tissues require oxygen and nutrients
- Respiratory wastes must be carried away
- Muscular pump and flexible tubes for circulation: a cardiovascular system = Pump (cardio) and vessels (vasculature)
Open circulatory system:
- Low-pressure, slow – suitable for taxa with slow metabolic rates
- May be supplemented with faster-specialized transport systems, ie. Tracheae in insects
Hemolymph
transport fluid in open circulatory systems and comes into direct contact with the tissues
Open Circulatory System in Action
- The heart(s) sit in haemolymph-filled haemocoel
- On contraction, haemolymph expelled from the heart via major arteries to other haemolymph-filled spaces
- On relaxation, haemolymph enters the heart from haemocoel
- Valves in the heart wall maintain unidirectional flow
- Further distributed by body movements – directed flow to active tissues not possible
- Accessory hearts may supply limbs
Closed circulatory system
- Blood under pressure
- Blood vessels and heart form a continuous closed circuit
- Found in forms able to sustain prolonged high activity rates – annelids, cephalopods, some crustaceans, all vertebrates
Blood contained within heart and vessels of the circulatory system, not coming in
direct contact with any of the tissues of the body
Capillary beds connect
veins and arteries, permeating tissues
Confinement makes what possible?
pressure regulation, the direction of flow and high flow rates possible
The Heart – Muscular pump
Creates pressure in vasculature in closed circulatory systems, creates directional flow in open circulatory systems
The Heart and Blood Vessels
- The heart maintains the bulk flow of fluids in the face of resistance
- Ohm’s law: flow = pressure / resistance
In a closed circulatory system:
- Blood pressure drops with distance from heart, due to greater volume occupied
- Blood slows with distance from the heart, due to the smaller diameter of vessels occupied
- Blood pressure drops due to greater friction and turbulence, lengths and diameters of vessels (resistance)
Blood Vessels (in a closed system):
Arteries, veins, and capillaries
Arteries
- Carry fluid away from the heart
- Control blood distribution to the body by controlling vessel diameter (resistance!)
- Depulsate pressure waves from the beating heart (elastic – expand/contract)
Veins
- Carry fluid back to the heart
- Store blood (easily expand)
Capillaries
- Exchange of substances between blood and tissues (gas, fluids, solutes, nutrients, waste)
- Designed to promote diffusion (and leaking in some tissues)
