Excretory system Flashcards
What are the roles of the excretory system? Describe them.
- Excretion – removal of toxic waste products of metabolism (cells -> intercellular space -> blood -> kidneys)
- Osmoregulation – control of internal solute concentration with the purpose of controlling the movement of H2O
Definition of osmotic concentration
the measure of solute C defined as the number of osmoles of solute per liter of solution (osmol/L)) Osmol/L is the number of moles of fully dissolved solute in one liter (e.g. of water)
NaCl (1 mol) -> Na+ (1 mol) + Cl- (1 mol) => 2 osmol/L
The three nitrogenous byproducts of metabolism – rank by toxicity and expensiveness
Ammonia – the most toxic byproduct, created as a product of the deamination of excess a-a in the liver, the amine group is highly toxic and water-soluble so it either has to be diluted in a large volume of water (like fish do) or it has to be neutralized by CO2 (like humans do)
Urea – byproduct of a-a digestion (when ammonia is combined with CO2), polar because it does H-bonds (water-soluble, hydrophilic) – fish don’t produce it, they use no E but humans do
Uric acid – one step further for desert animals and birds – in crystal form, even more E needed to produce but it’s worth it because those organisms don’t have water to spare to neutralize urea’s toxicity
What is the effect of properly functioning kidneys?
- Volume, pH, composition of body fluids and blood pressure are regulated
- Metabolic wastes are removed from blood
- Rate of RBC formation is controlled (disbalance in erythrocytes attributed to kidney disease)
Kidney structure and functions
Located on the dorsal body side.
1. Renal cortex – tightly packed, outer layer of the kidneys
2. Renal medulla – less tightly packed, the border between the cortex and the medulla contains a capillary network
3. Renal pelvis – urine accumulates in it “drop by drop” and from there goes into the ureter
4. Renal pyramids – kidney section containing structures in the cortex and in the medulla
5. Renal artery – pumps blood into kidney, containing oxygenated, unpurified blood, branch of the aorta
6. Renal vein – leads blood aways form the kidney, containing deoxygenated and purified blood, a branch of inferior vena cava
Renal pyramid structure – draw an annotated diagram
1) Renal artery – between the cortex and the medulla, branches into afferent renal arteriole
2) Afferent renal arteriole enters the Bowman’s capsule and branches into glomerulus (dense capillary network and a place of filtration of blood from waste products)
3) The filtered blood goes away from the capsule by the narrower efferent renal arteriole
4) The waste products filtered out and flow through the proximal convoluted tubule (PCT) then the loop of Henle which is narrower and divided onto the descending limb and the ascending limb
5) Then it flows in the distal convoluted tubule (DCT) which is, again, thicker, and finally, flows into the connecting duct (connects many nephrons and which drains the urine into the renal pelvis, ureter, the bladder and the urethra)
6) All throughout the nephron there are peritubular capillaries, branches of the renal artery, which surround the tubules and ducts and flow back into the renal vein
7) Transport epithelium – cells lining the nephron tubules, transport of water with dissolved particles
Nephron
basic structural and functional subunit of kidneys, tubular, partly convoluted, sometimes wider, sometimes narrower hollow tube strongly associated with blood vessels
Bowman’s capsule – function and structure
where renal arteriole goes into, branches into dense capillary network called glomerulus – there is a filtration process going on, the capillary wall lets through sufficiently small molecules (blood cells cannot pass as well as big plasma proteins) and what is filtered through goes into the proximal tubule
two sides of wall cells, one wall in contact with the capillary has greater space between podocytes and has little extensions towards the capillary – capillary and capsule are divided by the basement membrane (fenestras are slightly larger in kidney capillaries, glycoprotein). Podocytes wrap around the capillaries – the substances from blood do not enter the podocytes, they enter the tubule in between the cells (slits)
Reabsorption of particles in the nephron tubule
In proximal convoluted tubule, all glucose, a-a, and majority of Na’+ Cl- and most of H2O reabsorbed – blood is deoxygenated in the peritubular arterioles because they provide oxygen to cells in the tubules to enable them to do their function (pumping of sodium ions to enable reabsorption)
why is the efferent arteriole much narrower than afferent
to create higher pressure in the glomerulus and increase the speed and effectiveness of filtration – outflow of blood is restricted to enable ultrafiltration in the glomerulus
other than that, ultrafiltration is enabled by:
1) High blood pressure in glomerulus
2) Fenestrated blood capillaries
3) Basement membrane
4) Podocytes with filtration slits
Role of PCT
one layer of cells with microvilli (brush border) on the inner side, extensions of the plasma membrane increase SA and make reabsorption more efficient – 20% of the original filtrate V flows into the loop of Henle – efficient, major reabsorption happens in the PCT – ALL glucose gets reabsorbed by Na-cotransport (Na passive, glucose active)
role of the loop of Henle
reabsorption of water – limbs are opposite in term of permeability: descending limb only permeable to H2O not Na, ascending limb only to Na not to H2O – ascending pumps sodium across the ascending limb of LH, interstitial fluid concentration will increase, ATP is used for pumping (O2 from peritubular capillaries) – not interested in Na, just a method to pull water out – descending limb H2O leaves by osmosis because the ascending limb raised the C of interstitial fluid by pumping Na out
summarized roles:
1. To increase the C of interstitial fluid in the medulla which affects the processes in the rest of the nephron (descending limb and connecting duct)
2. To reduce the V of the filtrate by extracting water
How does the medulla of aquatic and terrestrial organisms differ?
aquatic animals have a thin medulla because not as much water reabsorption is needed so LH is shorter (not in a water-scarce environment)
ADH role
Anti-diuretic hormone or vasopressin – it increases the permeability of DCT and collecting duct to water, it decreases the V of urine by increasing reabsorption (used during dehydration and sleep) – it stimulates the release of aquaporins from the endoplasmic reticulum into the plasma membrane and thus increases the cell’s permeability to water
