Flashcards in Excretion and Kidney Deck (41)
Describe the location of the kidneys in humans and draw and label a diagram to show the human urinary system.
- The kidneys are attached to the top of the abdominal cavity. They are surrounded by a thick, protective layer
- The kidneys are supplied with blood at arterial pressure by the renal arteries that branch off from the abdominal aorta.
- Blood is removed by the renal vein that drains into the inferior vena cava.
- From the kindey, the urine travels down the ureter into the bladder and then out via the urethra.
Name the 3 main areas of the kidney and describe the role of each area.
Dark outerlayer where the blood is filtered. Has a very dense capillary network that carries the blood from the renal artery to the nephrons.
Lighter in colour,. Contains tubules of the nephrons that form the pyraminds of the kidney and the collecting ducts.
Pelvis is latin for basin. The central chamber when urine collects before passing out down the ureter.
Draw and label a diagram to show the internal structure of a kidney.
- Very outer layer is the capulse, then the cortex.
- The inner layer is the medulla. In the medulla are nephrons (which form kidney pyramids).
- The inner section of the medulla is the pelvis.
- The renal artery and vein run on top of the pelvis.
Name the functional unit of the kidney.
Draw and label a diagram of a nephron.
- Glomerulus is a bed of capillaries which is fed blood by the renal artery.
- The glomerulus is inside the Bowman's capsule which leads to the proximal convoluted tubule.
- The descending limb of the loop of henle follows the PCT and then the ascending limb.
- Ascending limb of the loop of henle to the distal convoluted tubule, which then leads to the collection ducts.
The glomerulus, Bowman's capsule, PCT and DCT are in the cortex. The loop of henle and the collecting duct are in the medulla.
Define the term “Bowman’s capsule”.
A cup shaped structure that contains the golmerulus and is the site of ultra filtration in the kidney.
Define the term “glomerulus”.
A bed of capillaries within the Bowman's capusule. Is under very high pressure as this is where ultrafiltration happens.
Define the term “proximal convoluted tubule".
The first twisted section of the nephron after the Bowman's capsule where many substances are reabsorbed into the blood.
Define the term “loop of Henle”.
A long loop of tubule that creates a steep concentration gradient across the medulla.
Define the term “distal convoluted tubule”.
The second twisted section of the nephron where the permeability of the walls varies in response to the ADH level of the blood.
Define the term “collecting duct”.
The final part of the tubule that passes through the renal medulla and the place where hypertonic urine is produced if needed. The permeability of the wallls is affected by ADH levels and it is the main site of water balancing.
Describe the functions of the kidney.
- Removing waste products from the blood.
Define the term “osmoregulation”.
The balancing and control of the water potential of blood.
Label and annotate a photomicrograph of kidney tissue at low and high power to show key histological features.
- The glomeruli are white blobs with lots of RBCs visible.
Describe the role of the glomerulus.
- The glomerulus is supplied with blood by a wide afferent (incoming) arteriole from the renal artery. The blood leaves through a narrower efferent (outward) arteriole and as a result a high pressure is built up in the capillaries of the glomerulus.
- This pressure forces blood out through the capillary walls.
- The fluid then passes through the basement membrane (a network of collagen fibres and other proteins). This acts as a sieve which prevents anything greater than 69,000 relative molecular mass passing through.
- Most of the plasma contents pass through but the blood cells and many proteins are retained because of their large size.
Describe the role of the Bowman's capsule.
- Part of ultrafiltration.
- Bowman's capsule has specialised cells called Podocytes that act as an additional filter. They have small extensions called pedicels which wrap around the capillaries forming slits that make sure any cells, platelets or plasma proteins that have got through the basement membrane do not pass through into the tubule.
- The filtrate which enters the capsule contains glucose, salt, urea and other substances at the same concentrations that they were in blood plasma.
Define the term “ultrafiltration”.
The process by which the blood plasma is filtered through the walls of the Bowman's capsule under pressure.
Define the term “ultrafiltrate”.
The fluid that passes into the tubules of the nephron after having been filtered through the Bowman's capsule under high pressure. It contains nothing greater than 69,000 relative molecular mass.
Define the term “podocyte”.
Podocytes are cells in the Bowman's capsule wrap around capillaries of the glomerulus, preventing any molecules larger than 69,000 relative molecular mass reaching the tubules.
Draw and label a diagram to show the microstructure of the interface between the glomerulus and the Bowman’s capsule.
- To the left is the capillary endothelial cells with gaps between them.
- Next layer is the basement membrane.
- Next layer is the Bowman's capsule with podocyte cells.
- Podocytes attach pedicels to capillaries.
Compare the composition of the blood and the ultrafiltrate.
The filtrate which enters the Bowman's capsule contains glucose, salt, urea and other substances at the same concentrations that they were in blood plasma.
Cells, platelets and plasma proteins greater than 69,000 RMM are not present in the ultrafiltrate.
Describe the role of the proximal convoluted tubule.
- First stage of selective reabsorption.
- Once the substances have been removed from the nephron they diffuse into the capillary network which surround the tubules down steep concentration gradients.
- These conc grads are maintained by a constant flow of blood through the capillaries.
- The filtrate that reaches the loop of henle at the end of PCT is isotonic ( at same conc) with the tissue fluid surrounding the tubules. Also isotonic with blood in the surrounding capillaries.
- At this stage, over 80% of the glomerular filtrate has been reabsorbed back into the blood.
What substances are reabsorbed in selective reabsorption?
- All glucose
- All amino acids
- All hormones
- All vitamins
- All mineral ions
What substances are reabsorbed in the proximal convoluted tubule?
- All glucose
- All amino acids
- All hormones
- All vitamins
- All mineral ions
--- These are reabsorbed by active transport.
- After these have been reabsorbed some water is reabsorbed by osmosis down the water potential gradient (WPG).
Explain how the cells of the proximal convoluted tubule are adapted for their function.
- Cells lining the proximal convoluted tubule are covered with microvilli (increase SA for reabsorption).
- Also have many mitochondria to provide ATP for active transport.
Describe the role of the loop of Henle. (Detail of counter-current multiplier.)
- Enables the kidney to produce urine more concentrated than their own blood.
- Different areas of the loop have different permeability to water. Central to its role.
- It acts as a counter-current multiplier, using energy to produce concentration gradients that result in the movement of substances such as water from area to another.
- Cells use ATP to transport ions using active transport and this produces a diffusion gradient in the medulla.
- The changes that take place in the loop of henle are dependent on high concs of sodium and chloride ions in the tissue fluid in the medulla. These high concs are the result of events in the ascending limb of the loop of henle.
Describe what happens in the descending limb of the loop of henle.
- Leads on from PCT.
- Region where water moves out the filtrate down a concentration gradient.
- The upper part is impermeable to water but the lower part (which runs down into the medulla) is permeable to water.
- The concentration of sodium and chloride ions in the tissue fluid of the medulla is high (because a lot is diffusing out/ being actively transported out of the ascending limb of the loop of henle).
- The filtrate entering the descending limb of LOH is isotonic (at some conc) with the blood.
- As it travels down the limb, water passes out of the loop into the tissue fluid by osmosis down a WPG. It then moves down a WPG into the blood of the surrounding capillaries.
- Descending limb is not permeable to sodium and chloride ions and no active transport takes place. The fluid that reaches the bottom of the LOH is very concentrated and hypertonic (higher conc) to the blood in capillaries.
Describe what happens in the ascending limb of the loop of henle.
- First section of the ascending limb of the LOH is very permeable to sodium and chloride ions and they diffuse out down a conc grad.
- In the second section, sodium and chloride ions are actively pumped out into the medulla tissue fluid against the conc grad.
- Causes a very high conc of sodium and chloride ions in the medulla tissue fluid (provides WPG for descending limb).
- The ascending limb is not permeable to water so water cannot follow the sodium and chloride ions by osmosis.
- This means the filtrate in the ascending limb becomes increasingly dilute (as sodium and chloride ions are moving out and water is staying in). Filtrate at the top of the ascending limb is hypotonic (lower conc) to the blood.
Describe the roles of the distal convoluted tubule and explain how it can perform these roles.
- Osmoregulation happens here.
- The permeability to water of the DCT walls vary with the levels of ADH.
- Cells lining DCT also have many mitochondria so they can carry out active transport.
- If the body lacks salt, sodium ions will be actively pumped out of the distal convoluted tubule with chloride ions following down an electrochemical gradient.
- Water can also leave the distal tubule concentrating the urine, if the walls of the tubule are permeable in response to ADH.
- DCT also plays a role in balancing blood PH.