Topic 8 Excretion and Osmoregulation Flashcards
What is excretion?
Removal of waste products from metabolism, along with excess water, salts and hormones
What is egestion?
Passage of undigested food out of the system
Why does excess salt need to be removed?
- Too much salt in cells -> water travels from blood and tissue fluid surrounding cells (down concentration gradient by osmosis) to enter these cells
- This lowers the volume of the blood and thus lowers the blood pressure
- Extra water entering cells may make them burst
What are amino acids converted to in the liver?
Amino acids that are not needed are converted to urea in the liver
What waste product is produced and then exhaled by the lungs
Carbon dioxide (produced in respiration)
What waste product is produced and then exhaled by the lungs, sweated from skin, removed from blood by kidneys
Water (produced in respiration and ingestion)
How are salts excreted?
Removed from blood by kidneys, urinated out of body
Some sweated
How is urea excreted?
After being converted from amino acids in the liver -> removed from blood by kidneys and excreted as urine
Some sweated out
What is the function of the capsule
Fibrous skin covering the kidney
What is the function of the cortex
Outer region of the kidney (blood filtered here)
What is the function of the medulla
Inner region of the kidney
What is the renal artery’s function?
Carries unfiltered blood to kidney
What is the renal vein’s function?
Carries filtered blood from the kidney
What is the pelvis’ function?
Area where ureter joins kidney (urine collects here)
What is the ureter’s function?
Carries urine to the bladder
What is the function of the nephron?
- Remove all urea from blood
- Remove excess water + salts
This is via ultrafiltration
What is ultrafiltration?
- Movement of small molecules from blood in glomerulus into bowman’s capsule under high pressure (across a partially permeable membrane)
- Capillary leaving glomerlus (efferent) narrower, high pressure, resistance to blood flow, high pressure in glomerulus
- Pressure forces smaller molecules into Bowman’s capsule to form glormerular filtrate
What are the substances forced out of the capillaries (and filtered by the the Bowman’s capsule, which will not let large molecules like protein through)
- Water
- Glucose
- Salt
- Urea
What is the composition of the glomerular filtrate?
- Proteins : 740 mg per 100ml in renal artery, none in glomerular filtrate or urine, 740 mg per 100ml in renal vein
- Glucose : 90 mg per 100ml in renal artery, 90 in filtrate, 0 in urine, 90 in renal vein
- Urea: 30 mg per 100ml in renal artery, 30 in filtrate, 2000 in urine, 24 in renal vein
Explain the composition of the glomerular filtrate
- Protein : stays in blood, doesn’t enter filtrate as too large to be ultrafiltrated into bowman’s capsule
- Glucose: removed from blood into filtrate, all goes into Bowman’s capsule then all selectively re absorbed into proximal tubule
- Urea : all removed from blood into filtrate, some selectively re absorbed to support water potential of blood
Urea in urine is more concentrated due to water re absorption in loop of Henle and collecting duct
What is selective re absorption?
- kidneys re absorb molecules essential to the body via active transport with ATP
Eg. All glucose reabsorbed, as much water as needed (by osmosis) and as many ions as needed
Where and why is glucose selectively reabsorbed?
- Proximal convuluted tubule (lots of mitochondria present in nephron for active transport + microvilli for large sa)
- Reabsorbed into capillary network around nephron
Where and why is water selectively reabsorbed?
- Needed in cytoplasm + tissue fluid
- Absorbed via osmosis in loop of Henle and collecting duct
What happens to the leftover urine?
Goes into collecting duct -> renal pelvis -> ureter -> bladder -> urethra
What is osmoregulation?
Control of body’s water content
How is water content controlled?
Lungs when we exhale
Skin by sweating
Body, in urine produced by kidneys
What part of the brain detects and controls water content of tissue fluid (must be kept constant as too much water in tissue fluid will make cells swell up due to osmosis, and too little, cells will lose water via osmosis)
Hypothalamus
What happens when there is too much water in the blood?
- Detected by hypothalamus
- Hypothalamus signals to pituitary gland to stop releasing ADH
- Collecting duct becomes impermeable to water so no water is reabsorbed by osmosis
- Greater volume of more dilute urine produced
What happens when there is not enough water in the blood?
- Detected by hypothalamus
- Signals to pituitary gland to produce more ADH
- Collecting duct becomes more permeable to water so more is reabsorbed by osmosis
- Smaller volume of more concentrated urine is produced
