Week 12: Renal Physiology Flashcards
1
Q
What are the basic structures of the Urinary System?
A
Two Kidneys
Two Ureters
Bladder
Urethra
2
Q
What is the Function of the Urinary System?
A
- Remove and excrete wastes from the body (urine)
- Establish fluid, electrolyte and acid-base balance
- Assist in managing blood pressure
- Involved in the production of red blood cells (RBCs)
- Regulate calcium and phosphorous balance
3
Q
What is the normal appearance of Urine?
A
Clear yellow
4
Q
What gives urine its colour?
A
Urochrome
5
Q
What impacts the colour of urine?
A
Levels of hydration
Lighter = hydrated
Darker = dehydrated
6
Q
What is the normal pH of urine?
A
4.5 - 8
7
Q
What is normal urine production for 1 day?
A
1-2 L
8
Q
What is Polyuria?
A
> 2.5 L/day
9
Q
What can cause Polyuria?
A
Diabetes mellitus; diabetes insipidus; excess caffeine or alcohol; kidney disease; certain drugs, such as diuretics; sickle cell anemia; excessive water intake
10
Q
What is Oliguria?
A
300-500mL/day
11
Q
What can cause Oliguria?
A
Kidney failure; obstruction, such as kidney stone or tumor; enlarged prostate
12
Q
What is Anuria?
A
Dehydration; blood loss; diarrhea; cardiogenic shock; kidney disease; enlarged prostate
13
Q
What causes Anuria?
A
<50mL/day
14
Q
This organ is encased by fibrous capsule, perirenal (around) fat capsule and renal fasciae (layer of connective tissue)…
A
Kidneys
15
Q
Why is the right kidney slightly lower than the left?
A
To make room for the liver
16
Q
Where are the kidneys located?
A
Located in the posterior abdominal wall (retroperitoneum) on either side of the vertebra, protected by anterior abdominal content
17
Q
How much fluid do the kidneys filter each day?
A
~45 gallons (170L)
18
Q
What are the 3 regions of the Kidney?
A
- Renal Cortex
- Renal Medulla
- Renal Pelvis
19
Q
What is the Renal Cortex?
A
The outermost region of the kidney that lies between renal capsule and renal medulla
contains blood filtering mechanisms, highly vascular area
20
Q
What is the Renal Medulla?
A
The inner region of kidney;
Composed of cone shaped masses (pyramids) containing tubules and capillaries (eg. Loop of Henle spans between the cortex and medulla), 6-18 pyramids per kidney, base of pyramid lies towards the cortex, top lies toward renal pelvis
21
Q
What is the Renal Pelvis?
A
Funnel-shaped tube with branching extensions called calyces (singular=calyx), cuplike containers that collect urine from each pyramid; Minor calyces form 2-3 major calyces
22
Q
How does urine flow?
A
Pyramids –> renal pelvis –> ureter –> bladder
23
Q
How does urine move?
A
Through peristalsis
24
Q
Renal calyces, pelvis and ureters are lined with smooth muscle, controlled by _______.
A
Autonomic nervous system
(involuntary action i.e. you don’t have to think about doing it, it happens automatically)
25
What are Ureters?
Fibromuscular tubes that transport urine from the kidneys to the bladder
26
How do the ureters connect the kidneys to the bladder?
Descend from the kidneys, enters obliquely (slanting direction) through posterior bladder wall (helps prevent backflow of urine)
27
Why is the left ureter longer than the right?
Because the right kidney is lower than the left
28
What are the 3 layers of the Ureters?
1. Mucosa layer
2. Muscularis
3. Adventitia
29
What is the Mucosa layer?
Innermost layer, contains transitional epithelium
30
What is the Muscularis?
Contains longitudinal and circular smooth muscle layers, middle layer
31
What is the Adventitia?
External surface of fibrous connective tissue
32
What is the Bladder?
Hollow, smooth, collapsible, muscular organ that stores urine
33
How much urine does the Bladder store?
~ 500mls, max= 800-1000mls,
34
Where is the Bladder located?
Lies retroperitoneally in pelvic cavity and is posterior to the symphysis pubis (joint between two pubic bones)
35
The interior of bladder contains openings for _______.
Both ureters and the urethra
36
What is the name of the smooth triangular region of bladder created by the openings for the ureters and urethra?
Trigone (where infection is likely to occur)
37
What are the 3 layers the Bladder is made up of?
1. Mucosa layer
2. Muscular (detrusor muscle) layer
3. Adventitia
38
What is the Mucosa layer?
Innermost layer, contains transitional epithelium
39
What is the Muscular (detrusor muscle) layer?
Combination of circular and longitudinal smooth muscle, middle layer
40
What is the Adventitia layer?
External surface of fibrous connective tissue covers everything EXCEPT superior surface (covered by peritoneum)
41
What is the Urethra?
Thin, muscular tube channeling urine from bladder to outside the body
42
How long is a Female's urethra?
3-4cm long
43
How long is a Male's urethra?
20cm long
44
What are the 3 regions of a Male Urethra?
Prostatic urethra
Membranous urethra
Spongy urethra
45
Where does the detrusor muscle thickens to form the internal urethral sphincter?
At junction of urethra and bladder
46
What is the Internal Urethral Sphincter?
Controlled by autonomic nervous system (involuntary), prevents leakage of urine when not actively urinating
47
What is the External Urethral Sphincter?
Made up of skeletal muscle and in conjunction with the levator ani muscle (located in pelvic floor) serves as a voluntary sphincter
48
The kidneys are influenced by ______.
The adrenal glands
49
How many adrenal glands per kidneys?
Just 1
50
Where are the adrenal glands located by the kidneys?
They lie on top
51
The adrenal glands are affected by the release or what renal hormone?
Renin
52
What happens when the adrenal glands release aldosterone?
It impacts sodium/water reabsorption and blood pressure
53
How much blood do the kidneys receive per minute by the renal artery?
1.2 L
54
Describe the direction blood flows from the kidneys
Blood flows from renal artery to the interlobular artery, to the arcuate artery, to the cortical artery, to the afferent (towards) arteriole (conveys blood to the glomerulus), then through membranes of glomerulus, the efferent (away) arteriole, peritubular capillaries, then the venules, the interlobular vein, the inferior vena cava, then the right side of heart for re-circulation
55
The Peritubular capillary network serves as the reservoir where substances are reabsorbed from the ________.
Renal tubules
56
What supplies the nerve supply to each kidney and ureter?
The renal plexus
57
The renal plexus are supplied by the ________.
Sympathetic nervous system (part of autonomic nervous system, involved with “fight or flight” response).
58
What are Nephrons?
The kidneys basic functional unit and site of urine formation
59
How many nephrons does each kidney have?
Over 1 million
60
What are the 2 ways nephrons function?
1. Mechanical filtration of fluids, wastes, electrolytes, acids, and bases into tubular system
2. Selectively reabsorbs and secretes ions-allows for homeostasis of fluid-electrolyte balance
61
What is each nephron composed of?
A renal corpuscle and renal tubule
62
What are Renal Corpuscles?
This is where arterial blood (via renal arteries) is filtered of larger particles (i.e. protein) and enters renal tubules as filtrate.
63
Where are Renal Corpuscles located?
In the renal cortex
64
What do Renal Corpuscles consist of?
They consist of glomerulus situated inside hollow collecting duct known as the Bowman’s capsule.
65
How much filtrate is reabsorbed?
99%, the remainder makes up urine
66
What are Podocytes?
Extending finger-like arms (pedicels) cover glomerular capillaries-pedicels form filtration slits leaving small gaps between the digits to form a sieve (filter)
67
What are Mesangial cells?
Found in the glomerulus, they can contract or relax to regulate filtration rates
68
What is the Juxtaglomerular Apparatus (JGA)?
69
Where is the Juxtaglomerular Apparatus (JGA) located?
Juxtaglomerular apparatus (JGA) lies just outside the Bowman’s capsule and glomerulus.
70
What is the juncture of the Juxtaglomerular Apparatus (JGA)?
Where afferent and efferent arterioles enter and leave Bowman’s capsule.
71
What is the contact point of the Juxtaglomerular Apparatus (JGA)?
Initial part of the distal convoluted tubule (DCT) contacts these arterioles.
72
What is the Macula Densa?
Part of the DCT wall at this point, forming part of the JGA.
73
What is the function of the Macula Densa?
It monitors fluid flow and filtrate composition in the DCT and regulates renin release from juxtaglomerular cells.
74
What occurs during Renin Release?
It leads to production of angiotensin II, a vasoconstrictor that increases blood pressure.
75
What causes the release of paracrine signals like ATP and adenosine?
Response to changes in flow rate and sodium levels,
76
What do Juxtaglomerular Cells do?
Regulates blood flow to the glomerulus based on osmolarity of filtrate in the DCT.
77
What happens to Juxtaglomerular Cells
at HIGH filtrate osmolarity (hyperosmotic)?
1. Juxtaglomerular cells contract.
2. Reduces glomerular filtration rate (less plasma filtered).
3. Leads to less urine formation and greater solute and water retention.
4. Decreases filtrate osmolality.
78
What happens to Juxtaglomerular Cells
at LOW filtrate osmolarity (hypoosmotic)?
1. Juxtaglomerular cells relax.
2. Increases glomerular filtration rate (more plasma filtered).
3. Leads to more water loss in urine.
4. Increases blood osmolality.
79
T or F: Juxtaglomerular Cells use opposite actions to keep glomerular filtration rate constant.
True
Low osmolarity = high glomerular filtration rate
High osmolarity = low glomerular filtration rate
80
What are Renal Tubules?
It begins in the renal cortex, pass into the medulla, and return to the cortex, approx. 3cm long.
Made up of 3 sections with varying capacity to reabsorb water and solutes.
81
What are the 3 sections of the Renal Tubules?
1. Proximal convoluted tubule
2. Nephron loop (loop of Henle)
3. Distal convoluted tubule (DCT)
82
What does section 1: Proximal convoluted tubule do?
Exits from Bowman’s capsule, permeable membrane allows reabsorption of almost all filtrate components (glucose, amino acids, metabolites, electrolytes) and water into surrounding capillary network
83
What does section 2: Nephron loop (loop of Henle) do?
Further divided into descending and ascending regions, together with their accompanying capillary network and collecting tubules, form the renal pyramids in the medulla
84
What does section 3: Distal convoluted tubule (DCT) do?
Winds until it empties into a collecting duct, 80% of water has been recovered by time filtrate reaches DCT, will recover another 10-15% here, cells also recover Ca+, receptors for PTH are found here and when bound induces insertion of Ca+ channels to enhance Ca+ recovery
85
What are the Juxtamedullary Nephrons/their role?
Where urine concentrates; Important in producing concentrated urine
86
Where are Juxtamedullary Nephrons located?
Located near the junction of the renal cortex and medulla
87
What is the Countercurrent Multiplier System?
- 70% of filtrate water reabsorbed by the descending limb of the loop of Henle.
- High concentration of salts (Na+).
- Osmosis draws more water into extracellular spaces, further concentrating filtrate.
88
What is the Distal tubule responsible for?
Filtrate concentration readjusted by secretion of ions (K+, H+, HCO3) into tubules or reabsorption of sodium/water into capillaries.
89
How long is concentration regulated in the distal tubule?
Until the filtrate leaves collection duct as urine
90
What are Collecting Ducts?
Primary function is regulation of urine volume and osmolarity by varying amount of H2O recovered
91
What are the 2 types of cells that line Collecting Ducts?
1. Principle cells: maintain water and sodium
2. Intercalated cells: maintain acid-base balance
92
What happens in the collecting ducts when blood is hyperosmotic?
Collecting ducts reabsorb more H2O, LESS urine made
93
What happens in the collecting ducts when blood is hypoosmotic?
Collecting ducts reabsorb less H20, MORE urine made
94
Collecting ducts fuse together in the renal pelvis and open into minor calyces to...
Deliver urine
95
What are the different ways substances move across membranes of renal tubules for reabsorption or secretion?
Active transport
Diffusion
Facilitated diffusion
Secondary Active Transport
Osmosis
96
What is Active Transport?
Uses energy (ATP) to move substances from low to high concentration; Requires specific receptors for the substance (e.g., Na+/K+ pump).
97
What is Diffusion?
Moves substances from higher to lower concentration; No energy required.
Substance must be soluble.
98
What is Facilitated Diffusion?
Moves substances from higher to lower concentration; Requires specific membrane receptors or channel proteins.
Can involve symport (same direction) or antiport (opposite directions) mechanisms; Maintains concentration gradients.
99
What is Secondary Active Transport?
Uses the electrochemical gradient of a driving ion to move another ion or molecule against its gradient.
100
What is Osmosis?
Solutes pass through a semipermeable membrane from less concentrated to more concentrated solution; Equalizes concentrations on both sides of the membrane.
101
What is Glomerular Filtration Rate (GFR)?
Rate at which glomeruli filter blood.
102
What is a normal Glomerular Filtration Rate (GFR)?
~120 mL/min
103
What does a Glomerular Filtration Rate (GFR) of below 60 mL/min mean?
Indicates Chronic Kidney Disease (CKD)
104
Why is Glomerular Filtration Rate (GFR) important?
Important for assessing overall renal function.
105
What is Glomerular Filtration Rate (GFR) influenced by?
Influenced by hydrostatic and colloid osmotic pressures across the glomerulus.
106
What is Hydrostatic Pressure?
Pressure exerted by a fluid against a surface; Net fluid movement is towards the area of lower pressure.
107
What is Colloid Osmotic Pressure?
Induced by plasma proteins pulling fluid back into the capillary.
108
What is Net Filtration Pressure (NFP)?
Sum of hydrostatic and colloid osmotic pressures.
NFP = Glomerular Blood Hydrostatic Pressure – (Capsular Hydrostatic Pressure + Blood Colloid Osmotic Pressure).
109
What is Creatinine Clearance (CrCl)?
Measures how well the kidneys filter creatinine (waste product of creatine in muscles), out of the bloodstream for excretion in urine.
110
How is Creatinine Clearance (CrCl) calculated?
CrCl = (140-age) x weight X sex / 72 x serum creatinine
111
What does a LOW CrCl indicate?
Reduced filtering capacity of kidneys (i.e. from Chronic Kidney Disease (CKD)/renal damage)
112
Kidneys control the amounts of substances reabsorbed and secreted in nephrons; this control is influenced by....
The hormones
- Antidiuretic Hormone (ADH)
-Angiotensin I and II
- Aldosterone
113
What does Antidiuretic Hormone (ADH) do?
Produced by the hypothalamus, stored in the posterior pituitary gland; Regulates fluid balance and urine output.
114
What do HIGH ADH levels indicate?
Increased water absorption and urine concentration.
115
What do LOW ADH levels indicate?
Decreased water absorption and dilute urine.
116
Describe the Regulation of Fluid Balance
1. Low blood volume and increased serum osmolality detected by hypothalamic osmoreceptors, stimulate the pituitary gland.
2. Pituitary gland secretes ADH into the bloodstream.
3. ADH travels to kidneys, making renal tubules and collecting ducts more permeable to water (via aquaporins).
4. Facilitates water reabsorption, increasing plasma volume and blood pressure, and decreasing serum osmolality.
117
ADH is part of a _______ feedback loop.
Negative feedback loop
118
What is the mechanism of a Negative Feedback loop?
When a change is detected, the system responds to reverse that change.
119
What is the Renin-Angiotensin-Aldosterone System (RAAS)?
Negative feedbkack loop regulating blood pressure and fluid balance homeostasis
120
What are the 4 parts of the enin-Angiotensin-Aldosterone System (RAAS)?
Renin Release
Renin's Function
Angiotensin I to II Conversion
Angiotensin II Effects
121
What causes Renin Release?
Triggered by low blood pressure, low sodium levels, and sympathetic nervous system stimulation; Secreted by juxtaglomerular cells of the kidney.
122
What is Renin's function?
Circulates in blood and converts angiotensinogen (from liver) into angiotensin I in the blood
123
What is the Angiotensin I to II Conversion?
Angiotensin I is converted to angiotensin II in the lungs by angiotensin-converting enzyme (ACE).
124
What is Angiotensin II Effects?
Constricts arteries, raising blood pressure; Stimulates aldosterone secretion from adrenal glands
Increases sodium and water absorption in the DCT, which is sensed by juxtaglomerular cells/macula densa thereby increasing/decreasing further renin secretion
125
What is Aldosterone?
Aldosterone increases the excretion of potassium and the reabsorption of sodium in the distal tubule.
126
When is Aldosterone released by the kidney?
Kidney (macula densa) senses changes to electrolyte concentration
127
What type of situations call for the release of Aldosterone?
1. Blood levels of potassium increase
2. Blood levels of sodium decrease
3. Blood pressure decreases.
128
The release of Aldosterone is a is a negative feedback loop, increased osmolality of the ECF which inhibits...
The release of further aldosterone.
129
What are medications that impact the Renin-Angiotensin-Aldosterone System (RAAS)?
ACE inhibitors (ACEi)
Angiotensin Receptor Blockers (ARBs)
130
How do ACE inhibitors (ACEi) impact the Renin-Angiotensin-Aldosterone System (RAAS)?
They block conversion of angiotensin I to II (why they may cause cough).
131
How do Angiotensin Receptor Blockers (ARBs) impact the Renin-Angiotensin-Aldosterone System (RAAS)?
They block angiotensin II receptor sites, preventing arterial constriction.
132
How are the kidneys involved in Blood Pressure Regulation/
Afferent and efferent arterioles of the glomerulus constrict or dilate to control volume of blood that is filtered through kidneys. Helps maintain GFR, done via sympathetic nervous impulses
133
What happens to Blood Pressure Regulation during rest?
Reduced sympathetic stimulation leads to vasodilation of arterioles and increased renal blood flow
134
What happens to Blood Pressure Regulation during stress (ie. low BP)?
Increased sympathetic stimulation leads to vasoconstriction of arterioles and decreased renal blood flow.
135
What are Endothelins?
They are powerful vasoconstrictors, made up of 21 amino-acids
136
How many forms of Endothelins are there?
Endothelin 1, 2 and 3
137
How are Endothelins produced?
They are produced by endothelial cells of renal blood vessels, mesangial cells and cells of the DCT
138
What stimulates the release of Endothelins?
Release stimulated by several factors, including hormones: angiontensin II, epinephrine
139
What type of Feedback Loop are Endothelins part of?
A positive feedback loop
Increased endothelin-1 can lead to the production of other vasoconstrictors like angiotensin II, creating a cycle that further elevates endothelin levels
140
What are Natriuretic Hormones?
- Peptides that stimulate kidneys to excrete Na+
- Inhibit aldosterone and ADH release
- Inhibit Na+ and H2O recovery in collecting ducts
- Mechanism to decrease BP, vasodilate
141
EX. What is Atrial natriuretic hormone (ANH)?
Released by atrium of heart; triggered by overstretching of atrial wall (heart failure, HTN)
142
How is the renal system involved in Acid-Base Regulation?
Regulated by system of chemical and physiologic buffering provided by the lungs and kidneys
143
H+ ions do what to pH?
acid, decrease pH.
144
HCO3 ions do what to pH?
base, increase pH
145
T or F: Kidneys rid the body of BOTH acid and base.
True
146
How does the Renal system secrete Acids?
- PCT cells actively secrete H+ ions into forming urine as Na+ is reabsorbed.
- Collecting ducts use active transport to secrete H+ ions into renal tubules.
- Removes excess H+, increases blood pH.
147
How does the Renal system reabsorb Bases?
- In PCT lumen, when there is an excess of H+ ions, HCO3 combines with H+ to form H2CO3.
Carbonic anhydrase enzyme converts H2CO3 into CO2 and H2O, which diffuse across the cell membrane to be exhaled and excreted
Inside the cell, CO2 and H2O are converted back into HCO3 by carbonic anhydrase.
HCO3 is co-transported with Na+ into the interstitial space around the PCT and is reabsorbed
Na+/H+ antiporter excretes H+ into the PCT lumen
H+ ion is recycled to recover bicarbonate.
- Reabsorption of HCO3 increases blood pH
148
How is the Renal System involved in Red Blood Cell production?
By releasing Erythropoietin (EPO)
149
What is Erythropoietin (EPO)?
Hormone secreted by the kidneys in response to low arterial oxygen levels; travels to bone marrow where it stimulates production of RBCs thus improve oxygen carrying capacity of the blood
150
How does the Renal System respond to Decreased Ca+ (HYPOcalcemia) in Blood?
- Parathyroid glands sense low Ca+ and secrete Parathyroid hormone (PTH)
- PTH stimulates kidney enzymes to convert Vitamin D to active form (calcitriol).
- PTH blocks phosphate reabsorption (lost in urine).
151
What does Calcitriol do?
Calcitriol increases Ca+ and Phos absorption in the intestine.
152
Calcitriol and PTH reduce calcium loss in urine (DCT) and...
Release calcium and phosphorus from bone.
153
PTH blocks phosphate reabsorption (lost in urine) which prevents what?
Prevents formation of calcium phosphate, maintaining free Ca+ levels.
154
How does the Renal System respond to Increased Ca+ (HYPERcalcemia) in Blood?
- Calcitonin is secreted by the thyroid gland
- Lowers blood calcium levels by inhibiting osteoclast activity (reducing bone resorption) and increasing calcium excretion in the kidneys
- Although PTH increases blood calcium levels, its secretion is reduced when calcium levels are high
155
What can lead to a disruption in Ca+ balance?
Hypo/hyperparathyroidism, vitamin deficiency/surplus,
renal failure, cancer, medications, genetic disorders, pancreatitis etc.
156
What are potential consequences of deficient and/or surplus levels of Ca+?
Osteoporosis, osteomalacia (rickets), problems with cell proliferation, neuromuscular function, blood clotting, and inflammatory response.
157
How does the Renal System regulate Nitrogenous Wastes?
Proteins are broken down into amino acids, then the amino groups are converted into ammonia, urea, or uric acid, which is then excreted in urine
158
How does the Renal System Eliminate Drugs and Hormones?
Water-soluble drugs are excreted in the urine
159
How does the Renal System contribute to Vitamin D Synthesis?
- Hydroxylation in kidney (calcidiol to calcitriol).
- Activated Vitamin D is responsible for:
Absorption of Ca+ in digestive tract, reabsorption of Ca+ in the kidneys, maintenance of normal serum concentrations of Ca+ and phosphate.
160
Why is calcium important in the body?
Bone health, muscle contraction, hormone secretion, neurotransmitter release.
161
What are deficiencies of Vitamin D?
Osteoporosis, osteomalacia (adults), rickets (children); Issues with cell proliferation, neuromuscular function, blood clotting, inflammation
