the kidneys Flashcards
What is Osmoregulation?
Osmoregulation is the control of the water potential of the blood
What substances need to be controlled in order to do this? [3]
- Water
- Salts (sodium ions)
- Urea
Symptoms of Dehydration
Mild dehydration can cause dizziness, a dry mouth and
concentrated urine.
Severe dehydration can cause death.
What causes dehydration? [6]
- heavy sweating
- low water intake
- eating salty food
- breathing dry air
- caffeine and alcohol
- diarrhoea
What does the Urinary System do? [2]
- To filter the blood, remove urea and excess water and
salts, creating urine - Any nutrients that are needed by the body are reabsorbed
List the parts of the Kidney structure [8]
- Renal Artery
- Renal Vein
- Capsule
- Cortex
- Medulla (organised in pyramids)
- Nephrons
- Pelvis
- Ureter
List the parts of the Nephron structure [9]
- Branch of Renal Artery
- Branch of Renal Vein
- Capillary
- Glomerulus
- Renal/Bowman’s Capsule
- Proximal Convoluted Tubule
- Loop of Henlé
- Distil Convoluted Tubule
- Collecting Duct
Stages in the Kidney
Ultrafiltration - between the glomerulus and renal capsule
Selective reabsorption - at the proximal convoluted tubule
Reabsorption of water and the counter-current multiplier - at the loop of Henle, distal convoluted tubule and collecting duct
Renal (Bowman’s) capsule
Surrounds a network of capillaries (the glomerulus). Inner layer is composed of podocytes
Afferent and Efferent Arteriole
Blood vessels entering and leaving the renal capsule. Afferent is wider than efferent, leading to an increase in blood pressure
Ultrafiltration in the Glomerulus [8]
- Diameter of efferent arteriole is smaller than afferent arteriole
- build-up of hydrostatic pressure
- water/glucose / ions squeezed out capillary into Bowman’s capsule through pores in capillary endothelium, basement membrane and podocytes
- large proteins too large to pass
Selective Re-absorption
Any useful substances are reabsorbed in the proximal convoluted tubule (PCT)
Adaptations of the proximal convoluted tubule [3]
Microvilli - increases surface area
Infoldings along the tubule - increases surface area
Protein channels and pumps in the membrane Mitochondria - provide ATP for active transport
The proximal convoluted tubule reabsorbs:
- All of the glucose
- All of the amino acids
- Most of the water
- Blood pH is regulated
- Blood salt levels are regulated
Reabsorbed molecules pass into the surrounding capillaries.
Urea, some water and some salts are left in the nephron filtrate.
Reabsorption - Co-transport [5]
- Sodium ions move into the capillaries from the PCT epithelial cells by active transport
- PCT lining cells have a lower concentration of sodium ions compared to the filtrate
- Sodium ions move down their concentration gradient, using facilitated diffusion from the PCT lumen into the PCT epithelial cells.
- Glucose (or amino acids) move with the sodium ions = co-transport
- The molecules then move into the capillary by facilitated diffusion
Explain why glucose is found in the urine of a person with untreated diabetes
In healthy people
- glucose is removed by ultrafiltration
- glucose is ALL reabsorbed by selective reabsorption via co-transport
In people with untreated diabetes…
- More glucose is removed in ultrafiltration due to high glucose concentration
- Channel/carrier proteins required for selective reabsorption
- Channel/carrier proteins can’t work fast enough to reabsorb it all
The Counter-Current Multiplier [3]
- Exchange of substances is greater if liquids flow in opposite directions rather than the same (e.g. fish gills)
- The loop of Henle acts to maintain a lower water potential in the interstitial fluid (surrounding the cells of the medulla) and the collecting duct
- This allows reabsorption of water into the blood, and concentration of urine through the collecting duct
The Counter-Current Multiplier in the Loop of Henle [3]
- Describes how to maintain a gradient of Na+ in medulla by the loop of Henle.
- Na+ actively transported out ascending limb to medulla to lower water potential
- water moves out descending limb + DCT + collecting duct by osmosis due to this water potential gradient
The Counter-Current Multiplier - Summary
The ascending limb - pumps ions into the interstitial fluid and then to the blood, lowering the water potential
The descending limb - the lower water potential of the interstitial fluid and blood cause the water to move from the limb into the blood by osmosis
The Loop of Henle
Descending limb = narrow, highly permeable to water
Ascending limb = wider, impermeable to water, lots of protein pumps for ions
Difference between osmolarity and water potential
Osmolarity is the tendency of a substance to attract water
Water potential is the tendency of a substance to supply water
The Distal Convoluted Tubule [4]
- The purpose of the DCT is to control the pH of the blood by selectively reabsorbing ions
- It also will reabsorb water
- The levels of reabsorption are controlled by hormones
- The cells of the DCT are adapted with microvilli and mitochondria
The Collecting Duct [3]
- The collecting duct is permeable so water is reabsorbed into the interstitial fluid and then moves into the capillaries
- As the water is reabsorbed, the water potential of the filtrate lowers
- Due to the counter-current multiplier, the water potential of the interstitial fluid is always lower than that of the filtrate
Osmoregulation [4]
- The blood concentration is monitored by osmoreceptors in the hypothalamus
- If the water potential of the blood falls, the osmoreceptor cells shrink (due to osmosis)
- This causes the hypothalamus to produce antidiuretic hormone (ADH)
- ADH is secreted by the posterior pituitary gland
Difference bewtween Diuretic and Antidiuretic
Diuretic - makes you wee more
Antidiuretic - reduces the amount of urine produced
The Action of ADH [6]
The Action of ADH [6]
- ADH travels in the blood to the kidney
- It binds to receptors on the cell-surface membrane (capillary side)
- This activates an enzyme called phosphorylase
- Phosphorylase causes special vesicles to fuse with the membrane (collecting duct lumen side)
- These vesicles contain proteins called aquaporins, which form channels in the membrane
- This increases the permeability of the collecting duct
Osmoregulation and ADH
Stimulus: Reduced water concentration in the blood
Receptor: Osmoreceptors in the hypothalamus
Effector: Hypothalamus produces ADH, secreted by the
posterior pituitary gland
Response: DCT and collecting duct become more permeable
The nephron osmoregulation [3]
- The urine released into the pelvis is more or less concentrated depending upon the blood concentration
- Excessive sweating and eating salty food will produce concentrated urine
- Drinking and cold weather will produce dilute urine
