Renal System Flashcards
1
Q
What are the functions of the kidney (3)?
A
- Homeostatic regulation of water and ion content of blood
- Excretion of metabolic waste products e.g. urea, creatinine
- Production of hormones
2
Q
Homeostatic regulation of water and ion content of blood
A
- Regulation of osmolarity - maintenance of ion balance
- Regulation of extracellular fluid volume – blood pressure
- Regulation of pH
3
Q
Excretion of metabolic waste products
A
- e.g. urea, creatinine
4
Q
Production of hormones (3)
A
- Renin - sodium balance
- Activation of vitamin D – Ca2+ balance, bone
- Prostaglandins and kinins - renal blood flow
5
Q
What is the nephron?
A
- nephron is the functional unit of the kidney
6
Q
What is the nephron closely associated with ?
A
- specialized blood vessels
7
Q
What is the first part of the nephron + what does it contain ?
A
- Bowman’s capsule
- which contains a network of capillaries called the glomerulus, where plasma fluid is ultra-filtrated.
8
Q
What does the Bowman’s capsule contain?
A
- contains a network of capillaries known as the glomerulus, where plasma fluid is ultra-filtrated
9
Q
Where does fluid filtered from the glomerulus flow into ?
A
- flows into the proximal tubule
10
Q
Fluid from proximal tubule flows into………..
A
- loop of Henle
- descending limb (dips into medulla)
- ascending limb (returns to cortex)
11
Q
fluid from loop of henle enters………
A
- distal tubule
12
Q
What happens to the fluid from the distal tubule?
A
- distal tubules of up to 8 nephrons drain into a single larger tubule called the collecting duct, which passes from the cortex into the medulla
13
Q
Where do collecting ducts drain into?
A
- collecting ducts drain into the renal pelvis
14
Q
What is the fluid called at this stage, and where does it go next?
A
- fluid is now called urine, and it flows into the ureter on its way to excretion
15
Q
How does blood flow into and out of the glomerulus?
A
- from the afferent arteriole into the glomerulus
- leaves via the efferent arteriole
- which connects to a second set of capillaries known as the peritubular capillaries that surround the tubule
16
Q
What happens to the renal capillaries after the peritubular capillaries?
A
- renal capillaries join to form venules, which conduct blood out of the kidney.
17
Q
What is the function of the renal portal system?
A
- to filter fluid out of the blood and into the lumen of the nephron at the glomerulus.
18
Q
What happens to the fluids after they are filtered?
A
- fluids are reabsorbed from the tubule back into the blood at the peritubular capillaries.
19
Q
What is the process of filtration in the nephron?
A
- filtration is the movement of fluid from the blood into the lumen of the nephron.
- It takes place in the Bowman’s capsule
20
Q
What is reabsorption?
A
- the movement of the filtrate from the lumen of the tubule back into the blood, through the peritubular capillaries.
21
Q
What is secretion in the nephron?
A
- removes selected molecules from the blood and adds them to the filtrate in the tubule lumen.
22
Q
What is excretion in relation to the nephron?
A
- refers to anything filtered from the glomerulus that is destined for excretion, unless it is reabsorbed
23
Q
How is the amount of excretion (urine) calculated?
A
- Amount of excretion (urine) = Amount filtered - Amount reabsorbed + Amount secreted.
24
Q
What is the Glomerular Filtration Rate (GFR)?
A
- approximately 180 liters/day or 125 mL/min
25
How many times is the total plasma filtered per day?
- total plasma is filtered approximately 40 times per day
26
What is the osmolarity of the filtrate?
- filtrate is isosmotic with the plasma
- with an osmolarity of 300 mOsm.
27
What is the filtration fraction?
- the percentage of plasma that filters into the nephron
- which is approximately 20%
28
How much of the filtrate is reabsorbed in the proximal tubule?
- 66% of the filtrate is reabsorbed in the proximal tubule
29
What happens to the filtrate as it passes through the loop of Henle?
- more solute is reabsorbed than water, making the filtrate hyposmotic relative to plasma ((100 mOsm))
30
How is reabsorption and secretion regulated in the distal tubule and collecting duct?
- reabsorption and secretion of salt and water are finely regulated by hormones, making the volume of the final filtrate 1.5 L/day with an osmolarity of 50-1200 mOsm (large range depends on diet)
31
What is clearance?
- the volume of plasma from which a substance has been removed and excreted into urine per unit time.
32
How is clearance calculated?
- Clearance = (Urine concentration x Urine flow rate) / Plasma concentration
33
How is creatinine involved in clearance?
- amount of creatinine that is filtered by the glomerulus is equal to the amount that is excreted in the urine
- which is used to estimate the glomerular filtration rate (GFR).
34
How does the capillary endothelium function in filtration?
- has pores small enough to prevent blood cells from leaving the capillary
- also has negatively charged proteins on the pore surface that repel negatively charged plasma proteins (e.g., albumin)
- so no blood + protein in urine
35
What are the 3 layers of the filtration barrier in the glomerulus?
- capillary endothelium (pores)
- basal lamina (negatively charged)
- podocytes (foot processes)
36
What is the basal lamina, and what is its role in filtration?
- basal lamina is a layer of extracellular matrix that separates the capillary endothelium from the epithelium of Bowman’s capsule
- negatively charged, which helps exclude most plasma proteins from filtration
37
What are podocytes, and what is their role in filtration?
- specialized cells present in the Bowman’s capsule
- have long cytoplasmic extensions called foot processes that interdigitate with the basal membrane, leaving narrow filtration slits
38
what substances are filtered ?
- water
- Na+
- K+
- Ca2+
- Cl-
- glucose
- urate
39
which 2 substances are not filtered ?
- red blood cells
- serum albumin
40
How is glucose and amino acid reabsorption in the proximal tubule carried out?
- Na+/K+ pump is located on the basolateral (blood-facing) membrane and uses ATP to pump 3 Na+ ions out of the cell and 2 K+ ions
- creates inwardly directed electrochemical gradient for Na+
- Na+-coupled transport systems allows for transport of glucose and amino acids
41
How much filtered Na+ and water is recovered from the tubular fluid?
- 65% of filtered Na+ is recovered
- creating an osmotic gradient that allows the recovery of 65% of water
42
percentages of re-absorption in the PCT
- 65% Na+, H2O, K+, Cl-
- 100% Glucose, amino acids
- 50% Urea, urate
- 80% HCO3-
- secretion of organic anions, cations, H+, K+
43
What is the key feature of the epithelium in the descending limb of the Loop of Henle?
- epithelium of the descending limb is water permeable
- allowing water to move out, but it is impermeable to NaCl.
44
What happens to the osmolarity as the filtrate moves through the descending limb?
- osmolarity increases because water is reabsorbed, concentrating the solutes
- the osmolarity reaches a maximum of around 1200 mOsm at the loop.
45
What happens in the ascending limb of the Loop of Henle?
- impermeable of water
- Na+, K+, and Cl- are actively transported out
- in a ratio of 1:1:2
46
What happens to the osmolarity as the filtrate moves up the ascending limb?
- osmolarity decreases because salt is being reabsorbed
- minimum of 100 mOs, at the top of the loop
47
Percentages of Loop of Henle re-absorption
- ~25% Na+, K+, Cl-
~15% H2O, urate, HCO3-
- secretion of H+
48
How is NaCl reabsorbed in the initial segment of the distal tubule?
- through the action of the Na+ - Cl- co-transporter, which is dependent on the Na+/K+ pump
49
What happens to the osmolarity in the initial segment of the distal tubule?
- NaCl is reabsorbed in the initial segment of the distal tubule, osmolarity falls further
- reaching around 70 mOsM.
50
What does "reabsorption" mean in the nephron?
- substances (like water, ions, glucose, etc.) leave the nephron tubule and enter the bloodstream
51
What is the action of thiazide diuretics on the distal tubule?
- inhibit the Na+ - Cl- co-transporter
- reduces the reabsorption of sodium and chloride
- increased excretion of sodium, chloride, and water
- reducing blood pressure
52
How does decreasing Na+ reabsorption affect water reabsorption?
- decreases water reabsorption
- more water stays in the tubule
- excreted in the urine
53
What happens in the last segment of the distal tubule and the collecting duct?
- Epithelial Na+ channel (ENaC) facilitates Na+ reabsorption
- Aquaporins are water channels that allow water reabsorption
54
How does aldosterone control sodium balance in the nephron?
- Aldosterone is secreted by the adrenal cortex when [Na+] is reduced
- increases Na+ recovery by increasing expression of ENaC in the distal tubule and collecting duct
- more Na+ reabsorbed into blood
- makes urine more concentrated
55
How does antidiuretic hormone (ADH) control water balance in the body?
- Vasopressin (ADH) increases water reabsorption
- by promoting the insertion of aquaporin channels
- allows more water to be reabsorbed
- makes urine more concentrated
56
What is the role of the last segment of the distal tubule and collecting duct in regulating pH?
- composed of cells thatreabsorb K + and secrete H+ through a K+/H+ antiporter
- therefore, these cells are important to regulate the pH
57
what % of plasma that passes through the glomerulus is filtered ?
- 20% is filtered
- only 1 % is excreted
58
what % of filtrate is reabsorbed + what % is reabsorbed in the PCT ?
- 99% filtrate reabsorbed
- 66 % of reabsorption occurs in the PCT
59
In a healthy individual what would you expect to see in a urine sample ?
- creatine
- sodium
60
what hormone increases water reabsoprtion in the collecting duct via aquaporin ?
- vasopressin
