Homeostasis & Waste Flashcards
Homeostasis
“The maintenance of a constant internal environment (for cells) by an organism.” It is the ability to return to the set point of ‘norm’. By environment, this tends to mean tissue fluid
Tissue fluid
formed from blood plasma, supplies nutrients (e.g. glucose) and removes waste (e.g. urea).
Factors that need to be regulated for cells to carry out normally
temp, pH, blood glucose and water potential.
Changes in these factors still take place but they fluctuate around a set point or ‘norm’.
Negative feedback meaning
The process of returning to a set point, as a result of an input (change to system). Movement away from the set point is detected and causes movement back towards it.
Negative feedback flowchart
INPUT -> RECEPTOR -> CO-ORDINATOR -> EFFECTOR -> RESPONSE
What causes the oscillation around the ‘norm’?
Time delays in control systems.
Positive feedback
A system in which the effector increases the change - movement away from (not back to) the ‘norm’. Only a few systems in the body operate under positive feedback.
Give two examples of positive feedback
Blood clotting - platelets secrete signalling molecules which attract more platelets.
Labour ie giving birth.
Target cells
These cells have receptors (like glycoproteins) embedded in the plasma membrane that are complementary shape to the hormones.
What does the process of homeostasis achieve?
Helps maintain optimal conditions for cellular reactions. Gives independence from the external environment. The internal environment can maintain conditions throughout different levels of activity.
What are hormones?
molecules released by endocrine glands directly into the blood that travel to a target organ to produce an effect.
What are endocrine glands?
ductless glands that secrete hormones directly into the blood, e.g. posterior pituitary gland, which secretes anti-diuretic hormone.
Excretion
The removal of metabolic waste made by the body. The mammalian body excretes compounds using four excretory organs: kidneys, lungs, skin and liver.
Egestion
The removal of undigested food material as faeces.
Secretion
The release of useful substances from cells.
Exocrine glands
Glands that secrete substances into a duct.
Duct
A tube lined with epithelial cells that produces a secretion, e.g. the pancreatic duct.
What are the three types of nitrogenous excretory products?
Ammonia, urea and uric acid
Describe ammonia
Molecules are small, very toxic and soluble.
What animals excrete ammonia and how do they excrete it?
Most aquatic animals excrete ammonia.
SOFT-BODIED INVERTEBRATES - Ammonia diffuses across the whole body surface into the water.
FRESHWATER FISH - Most of the ammonia is lost as ammonium ions (NH4+) across the epithelium of the gills.
How do terrestrial animals deal with their ammonia?
Most convert it to urea, to excrete.
How is ammonia created?
Excess amino acids (proteins) are deaminated and this leaving to NH3 molecules (ammonia) that need to be dealt with.
Why do terrestrial animals convert ammonia to urea?
Because they would have to produce lots of urine to get rid of ammonia, because a compound so toxic could only be transported and excreted in a very dilute solution. Urea can be transported in a much more concentrated form because it is about 100,000 times less toxic than ammonia. It is important to conserve water, living on land.
What animals excrete uric acid?
Birds, land snails, insects, some reptiles
