SNS Biology - Excretion Flashcards
1
Q
Excretion vs Elimination
A
- Excretion - removal of metabolic wastes
- Elimination - removal of indigestible material
2
Q
Invertebrates
Protozoans and Cnidarians
A
- Passive Excretion
- All cells in contact with external, aqueous environment
- Water soluble wastes such as CO2 and ammonia can exit the cells via simple diffusion through cell membrane
- Excess water which continuously diffuses into the cell from the hypotonic environment is periodically pumped from the cell
3
Q
Invertebrates
Annelids
A
- CO2 excretion occurs directly via the moist skin
- Two pairs of nephridia in each body segment excrete water, mineral salts and nitrogenous wastes as urea
4
Q
Invertebrates
Arthropods
A
- In insects, CO2 released from tissues into adjacent tube-like tracheae which are continuous with the external environment via spiracles
- Nitrogenous wastes excreted as solic uric acid crystals - converves water
- Mineral salts and uric acid accumulate in Malphigian tubules and are transported to the intestine to be expelled with solid wastes of digestion
5
Q
Humans
A
- Lungs - CO2
- Skin - water and dissolved salts (and a small amount of urea)
- Liver - processes nitrogenous wastes, blood pigment wastes and other chemicals for excretion - excreted as bile and pass out with faeces. Produces urea by deamination of AAs which diffuses into the blood for excretion by the kidney
- Kidney
6
Q
Humans
Kidney
Nephrons per Kidney
A
~ 1 million
7
Q
Humans
Kidney
Structure
A
- Cortex - proximal and distal convoluted tubules, collecting duct
- Medulla - loop of Henle
- Pelvis - collecting tubules, ureter
8
Q
Humans
Kidney
Filtration
A
- BP forces 20% blood plasma entering glomerulus through capillary walls into surrounding Bowman’s capsule - filtrate.
- Isotonic with blood plasma.
- Passive process driven by hydrostatic pressure of blood
9
Q
Humans
Kidney
Secretion
A
- Nephron secretes substances such as acids, bases and ions (K+, phosphate etc) from interstitial fluid into the filtrate by both passive and active transport
- Materials are secreted from the peritubular capillaried into the nephron tubule
10
Q
Humans
Kidney
Reabsorption
A
- Essential substances such as glucose, salts and AAs are reabsorbed from the filtrate and returned to the blood
- Occurs primarily in the proximal convoluted tubule
- Active process
- Movement of these substances accompanied by the passive movement of water resulting an a concentrated urine, hypertonic to the blood
11
Q
Humans
Kidney
Osmolarity Gradient
A
- Selective permeability of the tubules establishes an osmolarity gradient in the surrounding interstitial fluid
- By exiting and reentering at different segments of the nephron, solutes create osmolarity gradient with tissue osmolarity increasing from cortex to medulla
- Solutes contributing are urea and salt (Na+, Cl-)
12
Q
Humans
Kidney
Osmolarity Gradient
Countercurrent Multiplier
A
- Anatomic arrangement of the Loop of Henle permits establishment of a conc gradient that permits reabsorption of 99% filtrate in the collecting tubulesAllows production of concentrated urine and conservation of water and salts
13
Q
Humans
Kidney
Concentration of Urine
A
- Countercurrent system causes medulla to be hyperosmolar with respect to the dilute filtrate in the collecting tubule
- As filtrate passes through this region, water leaves filtrate by osmosis and is reabsorbed by capillaries
14
Q
Humans
Kidney
ADH
A
- Vasopressin
- Regulates, increases, permeability of the collecting tubule to water
- Increases the concentration of urine produced in response to increased blood osmolarity
15
Q
Plants
A
- No specific excretory system in plants
- Plants can use many of metabolic waste products as simple precursors of complex molecules
- For example CO2 is utilised in photosynthesis and nitrogenous wastes can be used in the synthesis of proteins
- Excess CO2, O2 and water vapour leave the plant via diffusion through stomata in leaves and lenticels in stems
- Transpiration is exit of water vapour through leaves
