Unit 6: Control of Blood water potential Flashcards
What is osmoregulation?
maintaining the water potential of the blood within restricted limits
- involves the hypothalamus pituitary gland and the kidneys
What else are kidneys involved in?
excretion (removal of metabolic waste)
What is the function is the kidneys
- filter blood (ultrafiltration) then selectively reabsorb useful substances (glucose, amino acids, some water)
- metabolic waste (urea) excess ions and water are left behind from urine
What is the functional unit of a kidney?
Nephron
- each kidney has 1 million
What is in the cortex (outer part) of the kidney?
- glomerulus
- renal (bowmans) capsule
- proximal convoluted tubule
- distal convoluted tubule
Which parts of the nephron extend into the medulla?
medulla = inner part of kidney
- loop of Henle
- collecting duct
Where does ultrafiltration occur and what does it form?
between the glomerulus and renal (Bowmans) capsuleof each nephron
- results in formation of the glomerular filtrate
Outline ultrafiltration
- each glomerulus is supplied with blood bu an afferent arteriole which brances from the renal artery
- filtrate is forced out the glomerulus into the renal capsule by the high BP created by the contraction of the left ventricle
- blood pressure is further increased as the afferent arteriole is wider than the efferent arteriole which takes blood away from each glomerulus
- creates bottle neck effect
What are the three filtration layers?
two cells in the barrier between the blood in the capillary and the filtrate job the renal capsule produces 3 layers
- endothelial cells of capillary
- basement membrane
- epithelium cells
What is the function of the endothelial cells of the capillary?
have pores between them which allow all of the plasma to pass through but hold back blood cells
- these are attached to the basement membrane
What is the function of the basement membrane?
acts as the main fine filter and holds back large plasma proteins in the plasma allowing only small molecules such as water,glucose, aa’s and urea to pass through
What is the function of the epithelium cells?
these are cells of the wall of the renal capsual known as podocytes
- have feet like structures which extend to the basement membrane and allow filtrate to pass rapidly between them through filtration slits
What the glomerular filtrate
enters the renal capsule and contains small soluble components of blood:
glucose, aa’s water, ions, urea
- large plasma proteins, blood cells and some water remain in the blood capillary and enter the efferent arteriole
What happens to the filtrate once in the renal capsule?
each efferent arteriole forms a capillary network around the rest of each nephron where substances from the filtrate are selectively reabsorbed
- filtered blood eventually leaves the kidney by the renal vein
Which substances are completely reabsorbed
filtered glucose and amino acids are completely reabsorbed back into the blood as the filtrate passes through the proximal convoluted tubule
How does reabsorption occur
initially by facilitated diffusion then by active transport into cells lining the PCT
- most of the mineral ions and water is also reabsorbed at the PCT
where are substances reabsorbed?
into cells lining the proximal convoluted tubule then into blood
How does the absorption of water occur?
via osmosis
active transport of glucose aa and ions into the blood from the PCT lowers the water potential of blood so water moves down a water potential gradient and is reabsorbed into blood
How does glucose become present in the urine?
presence of glucose in urine is due to carrier protons being unable to reabsorb all the filtered glucose by active transport as the blood glucose concentration is too high
- leads to the diagnosis of diabetes
What ate adaptations of the PCT?
- microvilli provide large surface area
- many mitochondria to provide ATP for aerobic respiration for active transport
- carrier proteins in the cell surface membranes for active transport
What is the function of the loop of Henle?
removes water from the filtrate allowing the production of a concentrated urine
Outline how the loop of Henle produces concentrated urine
1 Ascending limb is in permeable to water
2 Na+ and Cl- actively transported out of the ascending limb
3 Creates high conc of ions in the tissues of the medulla
4 Tissues in my daughter have low WP
5 Descending limb is permeable to water
6 Water moves out of filtrate into medulla by osmosis
7 Filtrate becomes increasingly concentrated
What is the function anti diuretic hormone
makes you piss less
- when dehydrated you release more ADH
How does the filtate travel through the DCT and CD
1 filtrate then passes through distal convoluted tubule and down the collecting duct.
2 Antidiuretic hormone increases the permeability of these structures to water
3 ADH attatches to specific receptors on cells of the DCT and CT stimulating awquaphorins to move into the cell surface membrane
4 aquaphorins enable more water to be reabsorbed by osmosis
5 water that leaves the DCT and CT pass into the medullary tissue fluid then to surrounding blood capillaries which eventually join to form the renal veil
What’s the purpose of having Na+ and Cl- in the medulla
increase in conc down the medulla ensures there’s always a lower WP in the medulla through which the filtrate in the CD travels thus more water can be absorbed
What is the reabsorption of water in the DCR and CD dependent on
the water potential of the blood
wp if blood must be maintained at a constant level
What are osmoreceptors
in the hypothalamus
sensitive to the water potential of blood
what happens if there was a decrease in the water potential of blood?
- osmoreceptors are stimulated
- ADH produced in the hypothalamus travels down neurons to the posterior pituitary gland
- ADH is released into blood by the posterior pituitary gland
- permeability’s ability of the DCT under CD are increased by ADH
- More water reabsorbed from the filtrate by osmosis into the blood leading to less water in urine producing a small volume of a more concentrated urine
- As water is reabsorb the water potential of the blood returns back to normal.
- This is detected by Osmoreceptors and ADH secretion is decreased by negative feedback.
what happens if there’s an increase in the water potential blood?
- Stimulation of Osmoreceptors is reduced
- Less ADH is released into the blood and the permeability of the DCT and the CD is reduced
- Less water is absorbed from the filtrate into the blood leading to more water in the urine producing a larger volume of a more dilute urine
- As less water is reabsorbed water potential decreases back to normal
- This is detected by Osmoreceptors and ADH secretion is regulated by negative feedback
What is positive feedback?
results in greater departures from the normal level of a variable
- often associated with a breakdown of systems
