Renal System Flashcards
Where are ADH and oxytocin produced?
In the cell bodies of the paraventricular and supraoptic nuclei of the hypothalamus
Where are ADH and oxytocin stored after their production?
In the posterior pituitary gland until released
What do osmoreceptors do?
- Sense increased solute concentration/osmolality
- Signal PVN and SON to produce ADH
Where are osmoreceptors located?
Hypothalamus
What does ADH do?
Helps to increase water reabsorption in the kidneys so that water is retained by kidneys and returned to blood, not lost to urine
What is blood/plasma osmolality?
Measure of plasma [solute] including Na+, Cl-, K+, urea, glucose, etc.
What is the normal range of blood/plasma osmolality?
280-303 mOsm/kg
What affects osmolality?
Water content changes
What is special about Brattleboro rats? What is the result?
- Do not produce ADH
- Result of a naturally occurring mutation
- Kidneys cannot retain water
- Excessive thirst
- Dilute urine
- Diabetes insipidus (increases risk of seizures secondary to dehydration)
When does ADH typically increase?
During sleep to increase water reabsorption and decrease nocturnal urine production (Circadian pattern)
How can ADH production be related to kids who wet the bed?
They may underproduce ADH
What does body water content vary with?
- Biological sex
- Age
What is the typical body water content for babies?
75%
What is the typical body water content for women?
50%
What is the typical body water content for men?
60%
What is the typical body water content for elderly men/women?
45%
How is water homeostasis maintained?
Water intake must equal water loss
What contributes to water intake?
- Drinking fluid and water in food (most)
- Water produced by metabolism (little bit)
What contributes to water loss?
- Urine (1500 mL)
- Lungs (700 mL)
- Sweat (200 mL)
- Feces (100 mL)
What proportion of water is found intracellularly?
2/3
cytoplasm
What proportion of water is found extracellularly?
1/3
Interstitial fluid/blood plasma
What is the survival rule of 3s?
You can live…
- 3 mins without air
- 3 hrs in a harsh environment
- 3 days without water
- 3 weeks without food
What is the longest that people have survived without water?
8-10 days
How do Arabian camels regulate water?
- Cannot shut kidney activity down
- Lipid is stored in hump
- Lipid metabolism provides significant amount of metabolic water
- Dry food also provides some water
- Kidney is efficient at water recovery
How do Arabian camels thermoregulate when hydrated vs. dehydrated?
Hydrated: - Panting - 36.5-38.5C Dehydrated: - Supercooling in night - Overheating in day - 34.5-40.5C
Ability to turn off thermoregulation is a water conservation mechanism
How do kangaroo rats regulate water?
- Obtains water from dry food/metabolism
- Lives in colonies underground (moist air reduces respiratory water loss)
- Nocturnal (avoid heat of day)
- Produce very dry feces
What is the typical human urine concentration and urine:blood ratio?
Urine conc. = 1400
Urine:Blood ratio = 4.6
How do marine mammals regulate water?
- Obtain water from food and metabolism
- Produce very concentrated urine
How do hibernating bears regulate water?
- Live off of stored fat reserves
- Reduce body temp., heart rate, metabolic rate
- Water from lipid metabolism balances respiratory water loss
- Urea recycled to produce protein
- Water and urea reabsorbed from kidney
What is the function of the kidneys?
- Regulate extracellular fluid environment by filtering blood, producing urine
- Involved in homeostasis of blood volume, metabolic waste products, water and electrolyte balance, pH balance
What are the parts of the renal system?
- Renal artery and vein
- Ureters
- Urinary bladder
- Urethra
What is the function of the ureters?
Drain urine from the kidneys by peristalsis
What is the function of the urinary bladder?
Urine storage
What is the function of the urethra?
Drains the bladder
Describe the branching of the renal artery and vein?
Renal artery/vein -> Interlobar artery/vein -> Arcuate artery/vein -> Interlobular artery/vein
What are the parts of the kidney (6)?
- Renal cortex
- Renal medulla
- Renal pyramids and papillae
- Renal artery and vein
- Renal pelvis
- Ureter
What is the kidney of marine mammals called? Why is it like this?
- Reniculate kidney
- Increase surface area
- More efficient at reabsorbing water and getting rid of solute
What is the functional unit of the kidney?
Nephron
How do things travel through the kidney?
1 - Blood in at glomerulus
2 - Filtered through nephron
3 - Urine out collecting duct
How many nephrons are cortical vs. juxtamedullary?
Cortical - 80%
Juxtamedullary - 20%
How many nephrons are in the kidney?
10^6
How are nephrons affected by aging?
- Lost as we age
- Cannot be replaced
What are the 4 regions of a nephron?
1 - Renal corpuscle (Bowman’s capsule, containing the glomerulus)
2 - Proximal convoluted tubule
3 - Loop of Henle (only region that dips into medulla)
4 - Distal convoluted tubule (BC/glomerulus are close to DCT)
What are the nephron associated blood vessels?
Afferent and efferent arterioles
- Interlobular artery extends to afferent arteriole
- Efferent arteriole eventually empties into interlobular vein
Peritubular capillaries (vasa recta)
- Extension of efferent arteriole
Are the collecting ducts part of the nephron?
- No
What 3 steps lead to urine formation in the nephron?
1 - Filtration
2 - Reabsorption
3 - Secretion
What does the filtration step of urine formation consist of?
Movement of fluid from blood to lumen of nephron (‘filtrate’)
- Only takes place in the ‘renal corpuscle’
What is the reabsorption step of urine formation?
After filtrate leaves Bowman’s capsule, it is modified by reabsorption - solutes in the nephron tubule’s filtrate are moved back to blood
Describe secretion in urine formation?
Blood moves select solutes back to nephron tubule’s filtrate (form concentration urine)
How much fluid enters/exits the nephron each day?
180 L fluid enters the nephron, only 1.5 L of urine
What are the 3 layers of filtration fluid must pass through to enter the nephron tubule network?
1 - Capillary fenestrae (holes in glomerular capillaries)
2 - Basement membrane of glomerular capillaries (rich in collagen)
3 - Inner layer of Bowman’s capsule, consisting of podocytes
What is the inner layer of Bowman’s capsule made up of? What is their function?
- Podocytes
- Podocyte processes and pedicels attached to glomerulus aid in filtration; cell body floats
- Intricate interdigitation of pedicels
- Slits between pedicels act as filters
- Diaphragm slits are negatively charged = barrier to proteins
What enters the glomerular filtrate?
Only a very small proportion of plasma proteins are filtered, but smaller plasma solutes easily enter the glomerular filtrate
What forces blood plasma fluid out of glomerulus into Bowman’s capsule?
Blood hydrostatic pressure
What is the typical rate of glomerular filtrate production?
Men - 180 L/day
Women - 150 L/day
Equivalent to entire blood volume being filtered every 40 minutes
What is glomerular filtration rate?
Volume of filtrate produced by both kidneys together per minute
Does GFR change?
BHP can change, but GFR is relatively constant
Relatively stable GFR ensures a constant flow of glomerular filtrate that allows reabsorption and secretion
What is the usual GFR?
115-125 mL/min
How does blood pressure affect GFR?
Increased BP:
- Afferent arteriole constricts and efferent arteriole dilates to reduce glomerular BP
Decreased BP:
- Afferent dilates and efferent constricts to increase glomerular BP
What are juxtoglomerular cells?
Smooth muscle cells of the afferent arteriole
What are macula densa cells?
Sensory cells in a region of the DCT
What are mesangial cells?
Communication cells between JG and MD cells via gap junctions
What are the sympathetic nerve fibres in the juxtaglomerular apparatus associated with?
Afferent arterioles
How do JG, MD, MC cells modulate glomerular BP?
Vasodilation and vasoconstriction of the afferent arteriole
- Change in BP sensed by MD cells -> communicate via MC cells to JG cells -> JG cells vasodilate or vasoconstrict afferent arteriole
What is the function of the sympathetic nerve fibres in the juxtaglomerular apparatus?
Redirect blood from kidney to other organ systems
What system regulates whole body BP?
Renin-Angiotensin-Aldosterone System
How does the RAAS regulate whole body BP (5 steps)?
1 - BP falls
2 - JG cells secrete RENIN into the blood
3 - Renin acts on ANGIOTENSINOGEN to produce angiotensin 1 (ANGI)
4 - ANGI is converted to ANGII by Angiotensin Converting Enzyme
5 - ANGII is a vasoconstrictor -> increases BP
How does RAAS affect blood volume?
- ANGII stimulates aldosterone secretion from the adrenal cortex
- ANGII and aldosterone work together to increase salt and water reabsorption from the kidneys -> increases blood volume
What drugs are commonly prescribed for hypertension/heart disease?
ACE inhibitors
Which structures are necessary for reabsorption/secretion?
- Peritubular capillaries
- Vasa recta
What happens at the peritubular capillaries?
- Blood leaves glomerulus and flows to peritubular capillaries (wind around nephron)
- They draw water/solutes out of nephron as needed (reabsorption) and send unnecessary water/solutes to nephron (secretion)
What proportion of the salt and water in original glomerular filtrate is reabsorbed across PCT and returned to vascular system?
65%
Where is 20% of salt/water in glomerular filtrate returned to vascular system?
Descending limb of LH
What are the 2 methods of reabsorption?
- Paracellular
- Transcellular
What is paracellular transport?
The tight junctions of the PCT cells are quite leaky
What is transcellular transport?
Solutes can be transported through the cell
What drives water reabsorption?
Accumulation of salts in interstitial fluid
What is the concentration of normal human blood?
300 mOsm/L
Describe the countercurrent multiplier system?
1 - Active transport of NaCl from ASCENDING limb of LH increases the osmolality of the surrounding interstitial fluid (multiplication occurs)
2 - The descending limb of LH is passively permeable to water, which increases the osmolality of the glomerular filtrate
3 - The deepest region in the renal medulla reaches a concentration of 1200-1400 mOsm/L
What is the function of the loop of henle?
The loop of Henle of juxtamedullary nephrons creates a hyperosmotic environment in renal medulla so urine concentration can occur
Which limb of Henle has thicker walls?
Thicker walled = ascending limb
Describe the ascending limb of the loop of henle?
- Rich in mitochondria
- Salt is actively extruded to the interstitial fluid, so osmolality increases and osmolality of glomerular filtrate decreases to 300 mOsm/L
- Permeable to salt
- Impermeable to water
Describe the descending limb of the loop of henle?
- The glomerular filtrate increases in osmolality as it descends (reaches 1200 mOsm/L as it reaches loop turn)
- Occurs b/c concentrated interstitial fluid draws water out of glomerular filtrate by osmosis
- Impermeable to salt
- Permeable to water
What happens at the collecting ducts?
- Several nephrons drain into each collecting duct
- Under the influence of ADH, water is drawn out of filtrate of medullary collecting ducts via aquaporin channels and reabsorbed into the blood
- ADH must be present to make urine hyperosmotic compared to blood
How do aquaporin channels work?
1 - ADH binds receptor
2 - Signals via cAMP
3 - Insert AQP apical side
4 - H2O reabsorbed by osmosis into blood
What maintains the standing osmotic gradient of the renal medulla?
Vasa recta
What does the vasa recta do?
- Carry blood into and out of renal medulla
- Work via countercurrent exchange
What is the countercurrent exchange system?
Diffusion of salt and water into and salt out of peritubular capillaries changes the hypertonicity of the interstitial fluid in the renal medulla
What do the ureters do?
- Urine moves from renal pelvis to ureter
- Smooth muscle cells in walls carry urine to bladder via peristalsis
What prevents the backflow of urine from bladder?
Flap valve
Describe urine?
- Hyperosmotic
- Sterile
- Pale to dark yellow (urochrome/Hb)
- Rapidly populated by bacteria (ammonia odour)
- pH 4.5-8.2
What are 5 substances not normally found in urine?
- Protein
- Glucose
- Blood cells
- Hemoglobin
- Bile
