1
Q
Glomerular Filtration
A
- the movement of substances from the blood within the glomerulus into the capsular space of the renal corpuscle due to pressure differences across the filtration membrane
2
Q
Filtrate
A
- Seperated fluid
- protein-free plasma
3
Q
Tubular Reabsorption
A
- the movement of substances from the tubular fluid back into the blood
- all vital solutes and most water that was in the filtrate are reabsorbed- the excess solutes, some water, and waste products remain within the tubular fluid
4
Q
Tubular Secretion
A
- the movement of solutes, usually by active transport, out of the blood within the peritubular and vasa recta capillaries into the tubular fluid
- materials are moved selectively into tubules to be eliminated or excreted from the body
5
Q
Describe the filtration membrane
A
-the filtration membrane is porous, thin, and negatively charged structure that is formed by the glomerulus and visceral layer of the glomerular capsule
composed of:
- Endothelium of fenestrated capillary
- Basement membrane of capillary
- Filtration slits of visceral layer
6
Q
Endothelium of fenestrated capillary
Filtration membrane
A
-allows plasma and its dissolved substances to be filtered, while restricting the passage of large structures such as the formed elements
7
Q
Basement membrane of capillary
filtration membrane
A
- porous
- composed of glycoprotein and proteoglycan molecules
- restricts the passage of large plasma protein such as albumin while allowing smaller structures to pass
8
Q
Filtration slits of visceral layer
filtration membrane
A
-composed of specialized cells called podocytes
9
Q
Podocytes
A
- octopus like cells that have long, “foot-like” processes called pedicals that wrap around glomerular capillary to support it
- pedicals are separated by thin spaces called filtration slits that are covered with membrane and prevent the passage of most small proteins
10
Q
What is allowed through the basement membrane?
A
water glucose amino acids ions urea many hormones vitamin B and C ketones very small amounts of protein
11
Q
Glomerular hydrostatic pressure
A
HPg
- blood pressure in the glomerulus that pushes water and some solutes out of the glomerulus and into the capsular space of the renal corpuscle
- has a higher value than blood pressure of other systemic capillaries to allow for filtration to occur and is due to relative size of afferent and efferent arteriole
- larger diameter of afferent arteriole than efferent arteriole
12
Q
Blood Colloid Osmotic Pressure
A
OPg
- Osmotic pressure exerted by the blood IN
- due to the dissolved solutes that it contains (most important is the plasma)
- opposes filtration because it pulls fluids into glomerulus
13
Q
Capsular Hydrostatic pressure
A
HPc
- The pressure in the glomerular capsule due to filtrate that is already present in the capsular space
- opposes filtration
14
Q
Net Filtration pressure
A
NFP
- filtration occurs if the pressure that promotes filtration (HPg) is greater than the pressures that oppose filtration (OPg and HPc)
- the difference in these pressures is the Net Filtration pressure
- NFP = HPg – (HPc+OPg)
15
Q
Glomerular Filtration Rate
A
- important variable influenced by net filtration pressure
- is defined as the rate at which the volume of the filtrate is formed and it is expressed as volume per unit time
- the net filtration pressure directly influences the GFR-if HPg increases so does GFR
16
Q
Describe the JG apparatus function
A
- important structure in regulating filtrate formation and systemic blood pressure
- releases renin into the blood in response to low blood pressure or stimulation by the sympathetic nervous system
17
Q
describe JG apparatus composition
A
composed of:
- Granular Cells
- Macula Densa Cell
18
Q
Granular Cells
A
-modified smooth muscle cells of the afferent arteriole located near its entrance into the renal corpuscle
19
Q
Granular Cells function
A
- They contract when stimulated either by blood pressure or the sympathetic division
- they synthesize, store, and release the enzyme renin to decrease the GFR
20
Q
Renin
A
required for the produciton of angiotensin I
21
Q
Macula Densa Cells
A
- a group of modified epithelial cells in the wall of the distal convoluted tubule where it contacts the granular cells
- located only on the tubule side next to the afferent arteriole and they are narrower and taller than other distal convoluted tubule epithelial cells
22
Q
Macula Densa Cells Fucntion
A
- detect changes in the sodium chloride (NaCl) concentration of tubular filtrate and signal granular cells to release renin though paracrine stimulated
- Decreased BP=Decrease NaCl
23
Q
Renal Autoregulation
A
- the intrinsic ability of the kidney to maintain a constant blood pressure and glomerular filtration rate despite change in systemic arterial pressure
- allows the kidneys to produce urine at a constant rate despite fluctuations in systemic blood pressure
24
Q
What two mechanisms does renal auto-regulation utilize
A
myogenic response
tubuloglomerular feedback mechanism
25
Myogenic Response
-compensates for systemic blood pressure changes by causing constriction/dilation of smooth muscle in afferent arteriole wall in response to changes in stretch
26
Tubuloglomerular feedback mechanism
- based on the detetection of NaCl levels in the tubular fluid
- the back up to the myogenic responding to increased blood pressure
27
For the Tubuloglomerular feedback mechanism if the glomerular blood pressure increases then...
- the amount of NaCl in the tubular fluid will increase
- Detected by macula densa cells in the juxtaglomerular apparatus which respond by releasing a signaling molecule (Most likely ATP) that binds to, and stimulates contraction of smooth muscle cells in the afferent arteriole wall
- Mesanigial cells stimulated to contract which decreases filtration membrane surface area
- Results in further vasoconstriction of the afferent arteriole and a decreased volume of blood entering the glomerulus
28
What are some limits to auto regulation?
- insufficient urine production
| - excessive urine production
29
Insufficient urine production
Arterioles at maximum dilation due to decrease in glomerular blood pressure
-If GFR is extremely low, it will stop waste elimination in urine
30
Excessive urine production
arterioles at maximum constriction results in an increase in glomerulus blood pressure and GFR, which will increase urine formation
31
Extrinsic controls
physiological processes to change GFR to adjust urine output based on physiologic need
- GFR can be decreased when the kidney is stimulated by the sympathetic division
- GFR can be increased when the kidney is stimulated by atrial natriuretic peptide stimulation
32
Decreasing the GFR through sympathetic stimulation
- sympathetic division sends increased nerve signals to the kidneys during exercise or in an emergency
- Results in a vasoconstriction of the afferent/efferent arterioles which reduces blood flow into glomerulus
- sympathetic stimulation can also causes the granular cells of the JG apparatus to release renin which produces angiotensin 2
- results in contraction of mesangial cells and decreased GFR
33
Increasing GFR through atrial natriuretic peptide
- the peptide hormone is released from atrial cardiac muscle cells into the blood in response to dimension of these chambers
- this occurs when there is either an increase in blood volume return or an increase in blood pressure
- ANP is transported in the blood to the kidney following its release from the heart
- ANP relaxes the afferent arteriole and inhibits the release of renin from the granular cells to ultimately cause relation of the mesangial cells to increase filtration membrane surface area
34
What is the purpose of ANP when increasing GFR
to increase urine output to decrease blood volume and blood pressure to within normal limits
35
Renin-Angiotensin-Aldosterone Mechanism
- Inactive Angiotensinogen is continuously produced by the liver and circulated in the blood stream
- Kidney receptors detect low blood pressure or are stimulated by the sympathetic nervous system to release Renin
- Renin converts angiotensinogen into angiotensin
- Angiotensin-coverting enzyme (ACE) is anchored to the internal walls in capillaries, especially capillaries in the lung
- ACE converts angiotensin I into angiotensin II
- Angiotensin II increases blood volume/pressure
36
How does angiotensin II increase blood volume/pressure?
- Vasoconstriction of systemic blood vessels
- Stimulating the thirst center
- Aldosterone
37
What is the purpose of aldosterone?
to enhane sodium reabsorption and potassium secretion
38
What are the two ways in which a substance can pass between the epithelial cells of the tubular wall
```
Paracellular transport
Transcellulr transport(most common)
```
39
Paracellular transport
movement of small ions
40
Trancellular transport
-a substance must cross two plasma membranes
41
What are the plasma membrane involved in transcellular transport
- Luminal membrane that is in contact with tubular fluid
| - Basolateral membrane that rests on the basement membrane
42
In transcellular transport which way do substances cross the membranes for reabsorption?
Crosses luminal then basolateral on the way to the blood
43
In trancellular transport which way do substances cross the membranes for secretion
crosses basolateral then luminal to get added to the tubular fluid
44
Glucose reabsorption
- occurs int he proximal convoluted tubule (PCT)
| - in healthy individuals, 100% of the glucose is reabsorbed
45
How is Glucose transported
- across the luminal membrane against its concentration gradient.
- occurs by secondary active transport via Na+/glucose symporters
- Across the basolateral membrane down its concentration by facilitated diffusion via glucose uriporters
- returned to the blood via peritublar capillaries
46
Sodium Reabsorption
-occurs in the lumen of PCT
47
How is sodium transported
Na+ is transported across the luminal membrane down its concentration gradient by facilitated diffusion via various types of Na+ transport proteins
-across the basolateral membrane against it concentration gradient by Na+/K+ pumps
48
What regulates the amount of Na+ excreted in the urine
regulated in the Distal convoluted tubule, collecting tubules, and collecting ducts by hormones
49
Descending Nephron
- permeable to water
- impermable to the movement of salts out of the tubule
- water is moved from the tubular fluid into the interstitial fluid as a result, whereas salts are retained within the tubular fluid
50
Solute concentration in Descending Nephron
solute concentration in the tubule increase from 300 mOsm to as much as 1200 mOsm by the loss of water and retention of salt
51
Ascending Nephron
- impermeable to water
- actively pumps salt out of the tubular fluid into the interstitial fluid. Resulting in water being retained in the tubular fluid and salt is moved from the tubular fluid into the interstitial fluid
52
Solute concentration in Ascending nephron
-solute concentration becomes diluted from 1200 mOsm to 100 mOsm as it moves through the ascending limp
53
Collecting Duct
- releases urea which diffused back into the tubular fluid in the thin segment of the ascending limb
- since both the thick segment of the ascending limb and DCT are not permeable to urea, urea remains within the tubular fluid until it reaches the collection duct where it is removed from the bulgar fluid
- the urea is part of a cycle
54
Countercurrent exchange
-as blood within the vasa recta travels toward the cortex it becomes less and less concentrated
55
Major functions of PCT
```
o 65% water reabsorption
o 65% Na+ reabsorbed
o 60-80% of K+ reabsorbed
o 80-90% of HCO3- reabsorbed
o 100% of glucose reabsorbed
```
56
Major functions of the descending loop of the nephron
* High water permeability
* Extremely low permeability for ions and urea
* 10% of water reabsorption
57
Major functions of the ascending loop of the nephron
Extremely low water permeability
Permeable to solutes -Reabsorption:25% of Na+, 10-20% of K+, HCO3-
58
Major functions of Distal Convoluted Tubule
Regulated:
- water reabsorption
- Na reabsorption
- K+ rebsorption
- HCO3- and H+ reabsorption and secretion to balance pH
59
Effects of ANP on the nephron
inhibits both the reabsorption of Na+ in the proximal convoluted tubule and collecting tubules and the release of aldosterone
- release of ANP provides a means of increasing urine output to decrease blood volume and blood pressure within it normal limits
- Increases blood flow into the glomerulus and increases filtration at the glomerulus
60
Effects of ADH on the nephron
Binds to receptors of principal cells to increase migration of vesicles containing aquaporins to the luminal membrane.
- provides additional channels for water reabsroption
61
Effects of PTH on the nephron
- inhibits reabsorption of phosphate in the PCT to increase phosphate lost in the urine
- Stimulates reabsorption of calcium in the DCT
- keeps blood calcium levels from dropping
62
Factors that decrease urine volume
- Increase in antidiuretic hormone
- Increase in aldosterone
- decrease in atrial natriretic peptide
- decrease in fluid intake
- decrease in blood pressure
- increase in other fluid output (sweating, vomiting, diarrhea, hemorrhage)
63
Factor that increase urine volume
```
Decrease in ADH
Decrease in Aldosterone
Increase in ANP
Increase in Fluid intake
Increase in blood pressure
Diabetes melltius
Diuretics (medications, alcohol)
```
64
What is the composition of urine
95% water
| 5% solutes K+, Cl-, Na+, Some hormones, drugs with small amounts of ketons
65
Characteristics of Urine
Product of filtered and processed blood plasma stored in bladder
- Sterile unless contaminated with microbes in kidney or urinary tract
- Daily volume 1-2 L
66
Micturition reflex
- When the volume of urine retained within the bladder reaches approximately 200 to 300 mL, the bladder becomes distended, and baroceptors in the bladder wall are activated.
- These baroreceptors send nerve signals through visceral sensory neuron to stimulate the micrurition center within the pons.
- The micturition center alters nerve signal propagated down the spinal cord and through the pelvic splanchic nerves (parasympathetic nerves)
- Parasympathetic stimulation causes the smooth muscle cells composing the detrusor muscle to contract and the internal urethral sphincter to relax. Then voluntary control of external urethral sphincter.
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