Renal system Flashcards
1
Q
What are the functions of the kidney? (7)
A
- Regulating blood volume & blood pressure - Renin-Angiotensin System.
- Regulating plasma concentration of ions - quantities lost in the urine
- Maintaining pH - loss of H+ and HCO3- ions in the urine
- Conserving valuable nutrients - prevents the excretion of glucose and amino acids.
- Eliminating toxic/unwanted substances - urea and uric acid.
- Regulation of red blood cell synthesis (production of erythropoietin)
- Vitamin D Synthesis/Activation
2
Q
What are the components of the renal/urinary system? (4)
A
- Kidney - Produces urine.
- Ureter - Transports urine toward the urinary bladder.
- Urinary bladder - Temporarily stores urine before elimination.
- Urethra - Conducts urine to exterior; in males, transports semen as well.
3
Q
What is the basic anatomy of the renal system/kidney? (5)
A
- The kidneys are paired, ~ 150 g each.
- Located high in the abdomen
- Urine drains via 2 URETERS into a single BLADDER.
- The bladder has a wall which contains smooth muscle (the detrusor),
- The detrusor contracts to pass urine via a single URETHRA to the outside.
4
Q
What is the anatomy of the kidneys? (5)
A
- Pale outer region - the cortex
- Darker inner region - the medulla.
- The medulla is divided into conical regions called the renal pyramids.
- The cortex and the medulla are made up of Nephrons
- Each kidney contains over 1 million nephrons.
5
Q
What is the nephron, and what is it comprised of (7)
A
- The functional unit of the kidney responsible for filtration of the blood and reabsorption/secretion of products in the subsequent filtrate.
Each nephron is made up of:
- Glomerulus / Bowman’s Capsule
- Proximal Convoluted Tubule
- Loop of Henle
- Distal Convoluted Tubule
- Collecting duct
6
Q
What are the basic processes involved in urine formation? (3)
A
- Filtration - Plasma = blood → glomerulus→ glomerular-capsular membrane → Bowman’s capsule.
- Reabsorption - In the PCT, the loop of Henle, DCT and collecting tubules
- Secretion - Substances = Blood in capillaries around tubules → DCT & collecting tubules
7
Q
What is urine comprised of (8)
A
- Na+
- K+
- Ca2+
- Phosphate
- Cl-
- Creatinine
- Urea
- Glucose
8
Q
What are the functions of the Glomerulus? (2)
A
- Filtration of water and dissolved substances from the plasma
- Receives the glomerular filtrate
9
Q
What are the functions of the Proximal convoluted tubule? (5)
A
- Reabsorption of glucose; amino acids, creatine, lactic, citric, uric and ascorbic acids; phosphate, sulfate, calcium, potassium, and sodium ions by active transport.
- Reabsorption of proteins by pinocytosis
- Reabsorption of water by osmosis
- Reabsorption of chloride ions and other negatively charged ions by electrochemical attraction
- Active secretion of substances such as penicillin, histamine, creatinine, and hydrogen ions
10
Q
What are the functions of the Descending limb of the nephron loop? (1)
A
Reabsorption of water by osmosis
11
Q
What are the functions of the Ascending limb of the nephron loop (1)
A
Reabsorption of sodium, potassium and chloride ions by active transport
12
Q
What are the functions of the Distal convoluted tubule? (4)
A
- Reabsorption of sodium ions by active transport
- Reabsorption of water by osmosis
- Active secretion of hydrogen ions
- Secretion of potassium ions both actively and by electrochemical attraction
13
Q
What are the functions of the Collecting duct (1)
A
Reabsorption of water by osmosis
14
Q
What are the types of nephrons? (2)
A
- Cortical
- Juxtamedullary
15
Q
What are cortical nephrons (2)
A
- Nephrons lie in the cortex (pale outer region)
- 80% of nephrons
16
Q
What are juxtamedullary nephrons (3)
A
- Nephrons close to the medulla (dark inner region), with a long Loop of Henle
- Approx. 20% of all nephrons
- Involved in making concentrated urine
17
Q
How is blood supplied to the kidneys? (4)
A
- Kidneys receive 25% of the Cardiac Output.
- The blood flow rate/kg of tissue is almost 8 times higher in the kidneys than through muscles doing heavy exercise!
- Extremely important function: to regulate the composition and volume of body fluids
- Blood flows in and out of the kidney, leaving behind the 1%, which becomes urine.
18
Q
How does filtration take place in the kidneys? (9)
A
- Filtration takes place in the Renal Corpuscles (Glomerulus plus Bowman’s Capsule encasing them)
- Water and small molecules (e.g., glucose amino acids) are filtered.
- Blood cells and large molecules (most proteins) do not pass through the filter.
- Glomerular blood pressure causes filtration through the glomerular-capsular membrane.
- Blood Hydrostatic Pressure = 55mmHg
- Osmotic Pressure of plasma proteins = -30mmHg
- The pressure of fluid in the tubule = -15mmHg
- Net Filtration Pressure = 10mmHg
- If glomerular blood pressure drops below a certain level, filtration of the blood and urine formation drops to a minimal obligatory level, which, if continued for some time, could develop into a life-threatening condition.
19
Q
How does the filtration membrane aid in kidney filtration (4)
A
- Selectively allows small molecules and water into the nephron, but not cells or proteins, which remain in the blood.
- Consists of the capillary wall (1 cell thick) that contains pores or fenestrations
- Basement membrane (connective tissue with collagen and glycoproteins which carry a negative charge)
- Podocytes (“footed cells”) are epithelial cells which support the filtration membrane without obstructing the flow of filtrate.
20
Q
What is the Glomerular filtration rate (GFR) (2)
A
- The rate at which the kidney filters blood plasma is called the Glomerular Filtration Rate (GFR)
- It is relatively easy to measure the GFR, and it is a good way of assessing kidney function.
21
Q
How is the glomerular filtration rate calculated (6)
A
- P x GFR = U x V
- GFR = (U X V) / P
- P = plasma concentration of A, in mg/ml
- GFR = glomerular filtration rate of plasma, in ml/min
- U = urine concentration of A, in mg/ml
- V = rate of urine production, in ml/min
22
Q
How does reabsorption take place in the kidneys? (4)
A
- is the movement of substances out of the renal tubules into the blood capillaries located around the tubules (called the peritubular capillaries)
- Substances reabsorbed are water, glucose
and other nutrients, Na+ and other ions - Reabsorption begins in the Proximal Convoluted Tubules and continues in the Loop of Henle, Distal Convoluted Tubules, and Collecting Duct
- Involves a combination of diffusion, osmosis and carrier-mediated transport.
23
Q
How does reabsorption take place in the proximal convoluted tubules (PCT) (3)
A
- PCT reclaims about 60-70% of the volume of filtrate produced at the glomerulus
- The lumen wall of the epithelial cells of the proximal tubule is like the lumen wall of the small intestine - both are bordered with millions of microvilli to increase surface area.
- The role of these epithelial cells is to reabsorb ions, nutrients, and water and transport them to the blood vessels nearby.
24
Q
How is Na+ reabsorbed? (5)
A
- A Na+/K+ ATPase located on the basolateral membrane of the epithelial cell (the side of the cell opposite the lumen) actively pumps Na+ out of the cell into the blood. This sets up a strong concentration gradient in the cell.
- The gradient created by the Na+/K+ ATPase provides a potential to allow Na+co-transporters in the apical membrane to reabsorb nutrients and electrolytes. Water also flows in via osmosis.
- Solutes exit the epithelial cells and enter the blood through channels.
- Water flows from the epithelial cells into the blood via osmosis.
- Note: Because osmosis occurs, the osmolarity of the filtrate remains isotonic. The volume decreases
25
How is Glucose reabsorbed? (9)
1. Glucose is freely filtered at the glomerulus & passes into the proximal tubule.
2. Blood glucose is maintained fairly constant, at approx. 100 mg/100 ml blood (i.e., 100 ml blood delivers 100 mg glucose into the proximal tubule)
3. Since GFR is 125 ml/min → 125 mg, glucose is filtered / min. This is called the FILTERED LOAD.
4. If GFR remains constant, the amount of glucose entering tubules is proportional to glucose concentration in the blood.
5. If blood glucose rises to 200 mg/100 ml, then 250 mg glucose/min enters the tubule.
6. ALL glucose entering the proximal tubule is usually reabsorbed & normally, NO glucose will appear in the urine
7. Reabsorption of glucose is active; the process involves a carrier molecule and ATP. Glucose is co-transported with Na+.
8. All carrier systems can be saturated.
9. If more glucose is filtered and all the available sites on the carrier molecule are saturated, NO MORE GLUCOSE can be transported. Glucose then appears in the urine.
26
What is the maximum reabsorptive capacity/tubular maximum (Tm) (7)
1. Is the maximum amount of glucose which can be transported in a unit of time
2. The amount of glucose filtered is proportional to the amount in the blood.
3. Up to Tm, ALL glucose filtered is reabsorbed in the proximal tubule.
4. Above this value (Tm for glucose ~ 375 mg/min), some glucose remains in the tubular fluid and is excreted in the urine.
5. The Renal Threshold for glucose is the plasma concentration at which Tm is reached (approx. 300 mg / 100 ml)
6. Extra water will also be excreted due to the osmotic effect of the glucose in the urine.
7. Patients whose kidneys are not reabsorbing all the filtered glucose will, therefore, produce a larger volume of urine than normal.
27
What causes glucosuria (6)
1. Filtration at the glomerulus
2. ≥ 300 mg / 100 ml blood (renal threshold)
3. a Tm ≥ 375 mg/min
4. ALL glucose filtered cannot be reabsorbed in the proximal tubule
5. Glucose in the urine
6. Glycosuria
28
How is glucose reabsorbed (5)
1. Filtration at the glomerulus
2. ≥ 300 mg / 100 ml blood (renal threshold)
3. a Tm ≥ 375 mg/min
4. ALL glucose filtered is reabsorbed in the proximal tubule
5. No glucose in the urine
29
How are amino acids reabsorbed (3)
1. The mechanism is similar to glucose’s, BUT there are several different transporter molecules in the kidney according to the type of amino acid, i.e., basic, neutral, etc. (similar to intestinal transport)
2. Amino acids DO NOT normally appear in urine except in genetic defects.
3. Phenylketonuria, where a missing enzyme results in excess phenylalanine in plasma, which is excreted in the urine
30
How are phosphate reabsorbed (2)
1. Actively reabsorbed, BUT the Tm for phosphate is approx. Equal to the plasma concentration
2. So, phosphate is always present in urine.
31
How are potassium reabsorbed (3)
1. All the K+ filtered at the glomerulus is reabsorbed in the proximal tubule.
2. But K+ is secreted in the DISTAL tubule in exchange for reabsorbing Na+.
3. K+ always appears in urine.
32
How are urea reabsorbed (4)
1. Urea is formed in the liver and then filtered.
2. The concentration in the filtrate increases as NaCl & water are removed.
3. Urea moves passively out of tubules down its concentration gradient.
4. ~50% of the urea is reabsorbed, and 50% is excreted each time blood passes through the kidney
33
What is secretion (4)
1. It is an active process whereby toxic/unwanted substances are secreted FROM the blood into the renal tubules.
2. A few substances (e.g., H+) can be actively secreted into the tubular fluid in the PCT.
3. This plays an important role in the regulation of blood pH.
4. However, active secretion is the primary function of the Distal Convoluted Tubule. The most important ions secreted are H+ and K+.
34
How are potassium ions (K+) secreted (2)
1. In the distal tubule, K+ is secreted into the tubules in exchange for the reabsorption of Na+.
2. This is controlled by a hormone produced in the adrenal glands called Aldosterone.
35
Aldosterone is activated by (3)
1. a fall in plasma [Na+]
2. a decrease in volume
3. an increase in plasma [K+ ]
36
How does acid-base balance affect K+ secretion (2)
1. In the distal tubule, Na+ can be reabsorbed in exchange for the secretion of either H+ or K+.
2. If the pH is low, H+ can be secreted (instead of K+)
37
How are Hydrogen ions (H+) secreted (4)
1. H+ secretion is vital for pH control.
2. On a mixed diet, more acids are produced by metabolism than bases. This excess H+ must be secreted.
3. Once in the renal tubule, H+ can be buffered by combining with phosphates and ammonia (produced in renal tubules), the latter forming ammonium ions.
4. NH3 + H+ → NH4+, which is excreted in the urine
38
What is the renal concentration/diluting mechanism (5)
1. Concentrated urines are more concentrated than hypertonic plasma.
2. The ability to produce hypertonic urine correlates with the presence of a large medulla & long loops of Henle
3. The LONGER the loop of Henle, the MORE concentrated the urine produced (Kidney Countercurrent Multiplier)
4. In the human kidney, some nephrons do not have long loops - filtration can be switched between nephrons with short and long loops to control the urine concentration.
5. When an animal is well hydrated, mainly short loop nephrons are used, and more dilute urine is produced
39
What is the antidiuritic hormone (ADH) (6)
1. Allows production of either concentrated or dilute urine by controlling the permeability of the last part of the distal tubule & collecting duct
2. ONLY these two tubules are affected by ADH
3. When ADH is present, the walls of the distal tubule & collecting duct are water-permeable. Water passes out of the tubules, and concentrated urine is produced.
4. If the body is well hydrated, ADH secretion is switched off.
5. ADH is absent, so the collecting tubules are NOT water permeable, and a large volume of dilute urine is produced (DIURESIS)
6. If you drink 2-3 pints of water – a delay occurs before the urine becomes dilute. This is about 20-30 minutes and is due to the metabolism of the circulating ADH in the liver.
40
How is osmotic pressure regulated (6)
1. Na+ ions are the most abundant cations in the ECF (>90%)
2. Na+ ions determine the osmotic pressure of the ECF.
3. Osmoreceptors (located in the supraoptic nucleus of the HYPOTHALAMUS) detect changes in osmotic pressure.
4. As water is lost, the osmotic pressure of body fluids increases and stimulates the hypothalamic thirst centre (drinking)
5. These stimuli also cause the release of ANTI-DIURETIC HORMONE (ADH)
6. ADH is released from the posterior pituitary and causes the kidney to retain water & produce less urine
41
What is the role of ADH in regulating urine concentration and volume (9)
1. The concentration of water in the blood decreases.
2. An increase in the osmotic pressure of body fluids stimulates osmoreceptors in the hypothalamus.
3. The hypothalamus signals the posterior pituitary gland to release ADH.
4. Blood carries ADH to the kidneys.
5. ADH causes the distal convoluted tubules and collecting ducts to increase water reabsorption by osmosis
6. Urine becomes more concentrated, and urine volume decreases.
7. The ADH and thirst mechanism control osmotic pressure in the ECF by adjusting body water content
8. ADH stimulates water reabsorption by stimulating the insertion of "water channels" or aquaporins into the membranes of kidney tubules.
9. The channels transport solute-free water through tubular cells back into the blood, causing a decrease in plasma osmolarity and an increase in urine osmolarity.
42
How is the total volume of the extracellular fluid regulated via the renin-angiotensin-aldosterone system (6)
1. When blood volume falls, the kidneys release the enzyme renin into the bloodstream.
2. Renin leads to the activation of Angiotensin II.
3. Angiotensin II causes the muscular walls of small arteries (arterioles) to constrict, increasing blood pressure.
4. Angiotensin II also triggers the release of the hormone Aldosterone from the adrenal glands.
5. Aldosterone causes the kidneys to help retain Na+ in the blood. The sodium causes water to be retained, thus increasing blood volume and blood pressure.
6. Renin is produced by the granular cells of the afferent arteriole at the juxtaglomerular apparatus, a structure formed by the distal convoluted tubule and the afferent glomerular arteriole, which helps in the regulation of blood pressure and glomerular filtration rate.
43
How is the total volume of the extracellular fluid regulated via the atrial natriuretic peptide (ANP) (5)
1. When blood volume rises, ANP is released (in response to stretch in the atria)
2. ANP causes the muscular walls of small arteries (arterioles) to dilate, decreasing blood pressure
3. Reduces renin release, inhibiting the renin-angiotensin system
4. Reduces aldosterone secretion by the adrenal cortex
5. Increased Na+ and water excretion in the kidney
44
How do carbonic acid/Hb buffers work (8)
1. When an excess of acid or base occurs in the body, buffers can absorb
2. excessive H+ or OH- to prevent a significant change in pH
3. The most important buffer systems in the blood are the bicarbonate buffer and haemoglobin.
4. The body contains a large bicarbonate reserve, allowing this system to cope with large amounts of acids.
5. CO2 + H2O → H2CO3 H+ + HCO3- (catalysed by carbonic anhydrase)
6. The bicarbonate system operates in both the lungs and the kidneys. While the lung can eliminate the CO2 produced from H2CO3, the kidney can both reabsorb and regenerate HCO3- and can secrete H+.
7. The two systems are very effective together, and their responses to changes in acid/alkali production in the body are very rapid.
8. The buffering power of Hb - is great, but there is no physiological process to regulate or remove the product, HHb.
45
How does compensation work (6)
1. Buffers soak up small amounts of acid or alkali without changing pH. Larger amounts of acid/alkali cause pH changes as buffering capacity is used up.
2. It is then necessary to adjust the functions of the Respiratory and Renal system to return pH to normal.
3. Respiratory and renal adjustments to changes in pH are known as COMPENSATION.
4. The lung compensates for pH changes by increasing or decreasing the loss of CO2 in expired air.
5. The kidney compensates for pH changes by producing more acidic or more alkaline urine.
6. Kidneys can neutralise more acid or base than either the respiratory system or the buffers.
46
What is the role of the kidney in buffering and pH control (5)
1. The kidney has a major role in maintaining normal blood pH because it not only reabsorbs filtered HCO3 but also secretes H+.
2. The cell membrane of the luminal surface of the tubular cells is IMPERMEABLE to HCO3-
3. The kidney also increases total body HCO3-
4. Mechanisms generate extra bicarbonate to replace the bicarbonate used up in buffering strong acids.
5. This mechanism is part of the Renal Compensation, which occurs when excess acids are produced in the body.
47
What is the role of the respiratory system in pH control (3)
1. A rise in blood pH causes a decrease in respiration rate and depth.
2. This allows CO2 to build up and lowers the pH.
3. Conversely, if pH falls, respiratory rate and depth are increased to eliminate more CO2, and pH rises.
48
What are the symptoms of renal disease which are directly related to the urinary tract (2)
1. Flank pain
2. Red urine
49
What are the symptoms of renal disease which is induced by the renal disease (2)
1. Oedema
2. Hypertension
50
How is asymptomatic renal disease discovered (1)
Incidentally discovered when routine lab tests revealed an elevated plasma creatinine.
51
What are the classifications of renal disease (3)
1. Pre-renal disease - Reduced renal perfusion is the primary abnormality.
2. Post-renal disease - Obstruction at some site in the urinary tract
3. Intrinsic renal disease - Caused by glomerular, vascular or tubule-interstitial disorders
52
What are other useful indicators of kidney disease (8)
1. Volume, frequency, colour, odour
2. Specific gravity, osmolality
3. pH
4. Protein
5. Glucose, ketones
6. Blood
7. Bilirubin, urobilinogen
8. Cellular material
53
What is urinalysis (4)
1. Performed on a fresh specimen within 30 – 60 min of voiding
2. The first part of the analysis is direct visual observation.
3. Normal = clear, pale to dark yellow or amber
4. Turbidity or cloudiness may be caused by cellular material or precipitation of salts at room temperature.
54
Urine dipstick chemical analysis (5)
1. pH: Range = 5 – 6.5
7.5 – 8.0 suggests urinary tract infection with urea splitting organism (consumption of hydrogen ions)
2. Glucose: Diabetes mellitus or proximal tubular defect
3. Ketones: Presence indicates ketoacidosis in uncontrolled diabetes mellitus
4. Nitrite: Bacteria can convert nitrate into nitrite. A positive test indicates a urinary tract infection.
5. Haem: Red cells in the urine. Must be co
55
What is glomerular proteinuria (3)
1. Increased permeability of the glomerular capillary wall
2. Abnormal filtration
3. Excretion of larger, normally non-filtered proteins
56
What is tubular proteinuria (3)
1. Low molecular weight proteins are normally reabsorbed.
2. Tubulointerstitial diseases interfere with reabsorption.
3. Excretion of smaller proteins
57
What are the causes of haematuria (8)
1. Glomerular damage
2. Tumours
3. Kidney trauma
4. Stones
5. Renal infarcts
6. Tubular necrosis
7. Infection
8. Nephrotoxins
58
What factors favour cast formation (3)
1. Low flow rate
2. High salt concentration
3. Low pH
