Definition
Excretion - the removal of metabolic waste products from the body of an organism
Kidney diagram
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Glomerulus and nephron diagram
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Afferent arteriole - brings blood to nephron
Efferent arteriole - brings blood away from the nephron (excluding filtrate)
Glomerulus - capillary tuft where filtration occurs
Bowman's capsule - first site where filtrate is collected
Proximal Convoluted Tubule - site of selective reabsorption
Loop of Henle - establishing a salt concentration in the medulla
Vasa recta - to absorb components from fitrate
Collecting Duct - osmoregulation
Process of filtration
Blood is brought into the Afferent arteriole. Since the Afferent arteriole is larger wider than Efferent arteriole, there is high enough pressure for ultrafiltration. Ultrafiltration drives substances into a fine sieve-like structure. In the Glomerulus, useful ions, minerals, and sugars (glucose) are forced out of the capillaries into the lumen of the capsule. These substances are driven through a fine sieve-like structure. This structure is the endothelium of the Glomerulus and the epithelium of the capsule.
Definition
Osmoregulation - the maintenance of proper water balance and other dissolved substances in an organism.
Reabsorption of glucose, water and salts in proximal convoluted tubule
Walls are one cell thick and packed with mitochondria (ATP for active transport).
Cell membrane in contact with filtrate, has a brush border of microvilli which enormously increases the surface area for reabsorption - large part of filtrate reabsorbed into capillary network here.
Water - osmosis
Glucose and amino acids - active transport
Mineral ions - active transport, facilitated diffusion, and exchange of ions
Urea - diffusion
Pinocytosis - movement of proteins
Vasa recta - absorb water that has been absorbed into medulla into collecting ducts; remove CO2 and deliver oxygen to metabolically active cells of loop of Henle without removing accumulated salts from medulla.
Roles of the loop of Henle, medulla, collecting duct and ADH in osmoregulation
Loop of Henle uses a countercurrent mechanism. On the ascending limb, the loop is permeable only to Na and Cl ions, but not water. These ions contribute to the solute concentration of the medulla. On the descending limb, because there is a higher solute concentration in the medulla, then more water will be absorbed out of the descending limb and back into the body.
Distal convoluted tubule - adjust composition of blood, particularly pH - if bloods begins to deviate from 7.4 pH, concentration of hydrogen and hydroxl ions in blood is adjusted, along with concentration of hydrogencarbonate ions.
Collecting duct - water content of blood is regulated. When water content low, ADH hormone is secreted so that the walls of the collecting duct are permeable, allowing for water to be reabsorbed. This leads to more concentrated urine. If there is an excessive uptake of water, ADH is not secreted and the walls of the collecting duct are impermeable as there is already enough water in the body. This leads to more dilute urine.
Difference in concentration of proteins, glucose and urea between blood plasma, glomerular filtrate and urine
Proteins are in blood plasma, but not in filtrate or urine.
Proteins cannot pass the basement membrane during ultrafiltration and cannot be part of filtrate.
Glucose in blood and filtrate, but not in urine.
Glucose is selectively reabsorbed in proximal convoluted tubule.
Reabsorbed by active transport.
Urea in blood plasma, filtrate and urine.
Only bout 50% of urea is absorbed.
Due to water being reabsorbed, urea is more concentrated in urine.
Concentration of urea depends on amount of water in urine.
Presence of glucose in untreated diabetic patients
Glucose should not be in non-diabetic patients as it is selectively reabsorbed.
Diabetics have higher levels of blood glucose because of lack of insulin secretion (type 1) or insulin sensitivity (type 2).
Not all glucose is selectively reabsorbed (protein pumps in tubule walls become saturated).
Results in presence of glucose in urine of diabetic patients.
Reabsorption of glucose, water and salts in proximal convoluted tubule
Walls are one cell thick and packed with mitochondria (ATP for active transport).
Cell membrane in contact with filtrate, has a brush border of microvilli which enormously increases the surface area for reabsorption - large part of filtrate reabsorbed into capillary network here.
Water - osmosis
Glucose and amino acids - active transport
Mineral ions - active transport, facilitated diffusion, and exchange of ions
Urea - diffusion
Pinocytosis - movement of proteins
Vasa recta - absorb water that has been absorbed into medulla into collecting ducts; remove CO2 and deliver oxygen to metabolically active cells of loop of Henle without removing accumulated salts from medulla.
Roles of the loop of Henle, medulla, collecting duct and ADH in osmoregulation
Loop of Henle uses a countercurrent mechanism. On the ascending limb, the loop is permeable only to Na and Cl ions, but not water. These ions contribute to the solute concentration of the medulla. On the descending limb, because there is a higher solute concentration in the medulla, then more water will be absorbed out of the descending limb and back into the body.
Distal convoluted tubule - adjust composition of blood, particularly pH - if bloods begins to deviate from 7.4 pH, concentration of hydrogen and hydroxl ions in blood is adjusted, along with concentration of hydrogencarbonate ions.
Collecting duct - water content of blood is regulated. When water content low, ADH hormone is secreted so that the walls of the collecting duct are permeable, allowing for water to be reabsorbed. This leads to more concentrated urine. If there is an excessive uptake of water, ADH is not secreted and the walls of the collecting duct are impermeable as there is already enough water in the body. This leads to more dilute urine.
Difference in concentration of proteins, glucose and urea between blood plasma, glomerular filtrate and urine
Proteins are in blood plasma, but not in filtrate or urine.
Proteins cannot pass the basement membrane during ultrafiltration and cannot be part of filtrate.
Glucose in blood and filtrate, but not in urine.
Glucose is selectively reabsorbed in proximal convoluted tubule.
Reabsorbed by active transport.
Urea in blood plasma, filtrate and urine.
Only bout 50% of urea is absorbed.
Due to water being reabsorbed, urea is more concentrated in urine.
Concentration of urea depends on amount of water in urine.
Presence of glucose in untreated diabetic patients
Glucose should not be in non-diabetic patients as it is selectively reabsorbed.
Diabetics have higher levels of blood glucose because of lack of insulin secretion (type 1) or insulin sensitivity (type 2).
Not all glucose is selectively reabsorbed (protein pumps in tubule walls become saturated).
Results in presence of glucose in urine of diabetic patients.
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