Blood water potential (16) Flashcards
What is meant by osmoregulation?
control of blood water potential via homeostatic mechanisms
What are the 7 structures of a kidney and where are they on a diagram?
1) fibrous capsule
2) cortex
3) pelvis
4) medulla
5) renal vein
6) renal artery
7) ureter
What is the role of the fibrous capsule?
protects kidney
What is the cortex and what does it consist of?
outer region
consists of Bowman’s capsules, convoluted tubules and blood vessels
What is the role of the pelvis?
collects urine into ureter
What is the medulla and what does it consist of?
inner region
consists of collecting ducts, loops of Henle and blood vessels
What is the role of the renal vein?
returns deoxygenated blood from kidney to heart
What is the role of the renal artery?
supplies kidney with oxygenated blood
What is the ureter and its role?
tube that carries urine to bladder
Were is a nephron found?
section of kindey
What are the 5 structures of a kidney?
1) bowman’s capsule
2) proximal convoluted tubule
3) distal convoluted tubule
4) loop of Henle
5) collecting duct
Describe the bowman’s capsule.
- at start of nephron
- cup-shaped
- surrounds glomerulus
- inner layer of podocytes
Describe the proximal convoluted tubule?
- series of loops surrounded by capillaries
- walls made of epithelial cells with microvilli
How does the distal convoluted tubule structure differ to that of the proximal convoluted tubule?
fewer capillaries
Describe the loop of Henle.
hairpin loop that extends from the cortex into the medulla
Describe the collecting duct.
Distal convoluted tubules from several nephrons empty into collecting duct, which leads into pelvis of kidney
What are the 2 arterioles associated with a nephron?
wide afferent arteriole
narrow efferent arteriole
Describe the wide afferent arteriole.
enters the renal capsule and forms the glomerulus
Describe the narrow efferent arteriole.
branches to form capillary network that surrounds the tubules
Describe the glomerulus.
branches knot of capillaries which combine to form the narrow efferent arteriole
What are the 3 steps on how glomerular filtrate is formed?
1) ultrafiltration in Bowman’s capsule
2) high hydrostatic pressure in glomerulus forces small molecules (urea, water, glucose, mineral ions) out of capillary fenestrations against the osmotic gradient
3) basement membrane acts as filter so blood cells and large molecules (proteins) remain in capillary
What are 2 ways cells in Bowman’s capsule are adapted for ultrafiltration?
- fenestrations between epithelial cells of capillaries
- fluid can pass between and under folded membrane of podocytes
What is selective reabsorption?
when useful molecules from glomerular filtrate (e.g. glucose) are reabsorbed back into the blood
Where does selective reabsorption occur?
proximal convoluted tubule
What are 3 ways in which cells in the proximal convoluted tubules are adapated for selective reabsorption?
- microvilli for large surface area for co-transporter proteins
- many mitochondria to produce ATP for active transport of glucose into intercellular spaces
- folded basal membrane creating large surface area
What is the transport process of selective reabsorption?
glucose from glomerular filtrate > (co-transported with sodium ions) > cells lining proximal convoluted tubule > (active transport) > intercellular spaces > (diffusion) > blood capillary lining tubule
What is the role of the collecting duct?
reabsorption of water from filtrate into interstitial fluid via osmosis through aquaporins
What are the 2 roles of the distal convoluted tubule?
- reabsorption of water via osmosis
- reabsorption of ions via active transport
(permeability of walls is determined by action of hormones)
What is the role of the posterior pituitary gland in osmoregulation?
stores and secretes ADH produced by the hypothalamus
What are the 4 steps that occur in the loop of Henle?
1) active transport of sodium ions and chloride ions out of the ascending limb
2) water potential of interstitial fluid decreases
3) osmosis of water out of descending limb
4) water potential of filtrate decreases as it goes down the descending limb
Where is water potential, in the loop of Henle, at its highest?
top of ascending limb
Where is water potential, in the loop of Henle, at its lowest?
medullary region
What are 2 differences between the ascending and descending limbs in the loop of Henle?
Ascending is wider and impermeable to water.
Descending is narrower and highly permeable to water.
What 4 factors might cause blood water potential to change?
1) level of water intake
2) level of ion intake in diet
3) level of ions used in metabolic processes or excreted
4) sweating
What are 2 reasons why it is important to maintain the sodium ion gradient?
- for counter current multiplier (filtrate in collecting ducts is always beside area of interstitial fluid that has a lower water potential)
- maintains water potential gradient for max reabsorption of water
What is the role of the hypothalamus in osmoregulation and how does this occur?
osmosis of water out of osmoreceptors in hypothalamus causes them to shrink, this triggers the hypothalamus to produce more ADH
What does ADH stand for?
antidiuretic hormone
What is the role of ADH in osmoregulation?
makes cells lining the collecting duct more permeable to water and urea
How does ADH make cells lining the collecting duct more permeable to water?
1) binds to receptor
2) activates phosphorylase
3) vesicles with aquaporins on membrane fuse with cell-surface membrane
How does urine become more concentrated?
when water potential in interstitial fluid decreases causing more water to be reabsorbed
