Excretion is the removal from the body of the waste products of metabolic activities
What is label A?
What is label B?
What is label C?
What is label D?
What is label E?
What is label F?
What is label A?
WHat is label B?
WHat is label C?
What is label D?
WHat is label E?
Proximal convoluted tubule
WHat is label F?
Distal convoluted tubule
WHat is label G?
WHat is label H?
What is label I?
Loop of Henle
What is function of the afferent arteriole?
Brings blood to the nephron to be filtered
What is the function of the efferent arteriole?
Removes blood from nephron (minus filtered components)
What is the function of the glomerulus?
Capillary tuft where filtration occurs
What is the function of the Bowman's Capsule?
First part of nephron where filtrate is collected
What is the function of the proximal convoluted tubule?
Where selective reabsorption occurs
What is the function of the loop of henle?
Important for establishing a salt gradient in the medulla
What is the function of the distal convoluted tubule?
Final site of selective reabsorption
What is the function of the collecting duct?
Feeds into ureter and is where osmoregulation occurs
What is the function of the vasa recta?
Blood network that reabsorbs components from the filtrate
When does ultrafiltration occur?
Ultrafiltration occurs when hydrostatic pressure forces blood through a semi-permeable membrane, separating blood cells and large proteins from the remainder of the serum
Where does ultrafiltration occur?
Ultrafiltration occurs between the glomerulus and the Bowman's capsule
How does hydrostatic pressur relate to ultrafiltration?
The glomerulus increases blood pressure by forming narrow branches (which also increases surface area for filtration)
This pressure is maintained by a narrow efferent arteriole (relative to the afferent arteriole), which restricts the outflow of blood, keeping pressure high
The net pressure gradient in the glomerulus forces blood into the capsule space
How does the basement membrane relate to ultrafiltration?
The basement membrane is a fine mesh that restricts the passage of blood cells and proteins - it is the sole filtration barrier
Blood can exit the glomerulus directly through pores as the capillaries are fenestrated
The filtrate can enter the Bowman's capsule directly because the podocytes that surround the glomerulus contain filtration slits between their pedicels
The basement membrane lies between the glomerulus and Bowman's capsule
Osmoregulation is the control of the water balance of the blood, tissue or cytoplasm of a living organism
Explain the reabsorption of glucose, water and salts in the proximal convoluted tubule, including the roles of microvilli, osmosis and active transport (8)
The proximal convoluted tubule extends from the Bowman's capsule and is where most selective reabsorption in the nephron occurs
All glucose, amino acids, vitamins and hormones are reabsorbed here, along with most (~80%) of the mineral ions and water
The proximal convoluted tubule has a microvilli cell lining to increase the surface area for the absorption of materials from the filtrate
There are also a large number of mitochondria in these cells, as reabsorption from the filtrate involves active transport
Once materials have been activly reabsorbed into the tubule cells, they can passively diffuse into the bloodstream (along the concentration gradient)
Mineral ions and vitamins are actively transported via protein pumps or carrier proteins
Glucose is actively transported across the membrane in symport with sodium
Water follows the movement of the ions passively (via osmosis)
Explain the roles of the loop of Henle, medulla, collecting duct and ADH (vasopressin) in maintaining the water balance of the blood (10)
Creating a Salt Gradient in the Medulla
The function of the loop of Henle is to create a salt bath concentration in the fluid surrounding the tubule
The descending limb of the loop of Henle is permeable to water, but impermeable to salts
The ascending limb of the loop of Henle is permeable to salts, but impermeable to water
This means that as the loop descends into the medulla, the interstitial fluid becomes more salty (and less salty as it ascends into the cortex)
As the vasa recta blood network that surrounds the loop flows in the opposite direction (counter-current exchange), this further multiplies the effect
As the collecting duct passes through the medulla as it drains into the ureter, the hypertonic solution of the deep medulla will draw water by osmosis
Antidiuretic hormone (ADH or vasopressin) is a hormone released from the posterior pituitary in response to dehydration (detected by hypothalamus)
ADH increases the permeability of the collecting duct to water, allowing more water to be reabsorbed by osmosis (via the production of aquaporins)
This means less water remains in the filtrate and the urine becomes more concentrated
When the individual is suitably rehydrated, ADH levels will decrease and less water will be reabsorbed from the collecting ducts
Explain the difference in the concentration of proteins, glucose and urea between blood plasma, glomerular filtrate and urine (9)
Proteins will be present in blood plasma, but not present in glomerular filtrate or urine
This is because proteins cannot pass across the basement membrane during ultrafiltration and thus cannot form part of the filtrate
Glucose will be present in blood plasma and glomerular filtrate, but not present in urine (normally)
This is because the glucose is selectively reabsorbed in the proximal convoluted tubule
It is reabsorbed from the filtrate into the blood by active transport (symport with Na+ ions)
Urea will be present in blood plasma, glomerular filtrate and urine
Only about 50% of urea is reabsorbed (some urea is reabsorbed to help regulate the medullary osmolarity gradient)
Because water is reabsorbed from the filtrate (by osmosis, due to the hypertonicity of the medulla), urea becomes more concentrated in urine
The concentration of urea in the urine will depend on the amount of water in the urine
Explain the presence of glucose in the urine of untreated diabetic patients (4)
The urine of non-diabetic patients should contain no glucose as it is selectively reabsorbed from the filtrate in the proximal convoluted tubule
Diabetics have higher levels of blood glucose due to either a lack of insulin secretion (type I) or insensitivity to insulin secretions (type II)
Because of this, not all of the glucose in diabetics is reabsorbed into the blood (protein pumps in tubule wall become saturated)
This results in the presence of glucose in the urine of untreated diabetics, which can be detected using test strips