Week 3 - The Urinary System Flashcards
define elimination
- the excretion of waste products primarily through the urinary system (in the urine) and the GI system (bile & feces)
list the 5 major roles of the kidneys
- filter and excrete water soluble metabolic wastes
- regulate blood vol & bp
- production of erythropoietin
- regulation of electrolytes
- regulate pH
where are metabolic wastes filtered from? how are they excreted?
- filtered from the blood into filtrate
- excreted in the urine
list 3 metabolic wastes the kidneys filter & excrete
- urea
- uric acid
- creatinine
how are metabolic wastes produced?
- waste products are generated during metabolism in cells
what is urea
- waste product produced when we metabolize amino acids/the detoxification of ammonium
describe how the metabolism of amino acids forms urea; include whether or not ammonium is toxic to the body
- each amino acid contains an amino head & acid tail
- the amino head contains nitrogen
- when we break down proteins into amino acids & then break down the amino acids for fuel, the nitrogen in the amino head becomes ammonium
- ammonium is very toxic to the body & we do not want it to accumulate
- to avoid this accumulation, we deliver aa to the liver which removes the ammonium and creates urea thru the urea cycle
- urea is then put back into the blood & removed thru the kidneys
is urea toxic or non-toxic to the body
- no but its elevations are
what is uric acid
- waste product produced due to DNA and RNA catabolism
what 2 things does accumulation of uric acid cause?
- kidney stones
2. gout
what is creatine
- by-product produced from muscle tissue
- specifically it is a breakdown product of creatine phosphate
describe how creatine is formed from the breakdown of creatine phosphat
- creatine phosphate is what the muscle tissue uses to regenerate ATP when we use our muscles vigorously
- creatine phosphate donates a phosphate to ADP to create ATP
- and then we are left with creatinine
is creatine toxic to the body?
- it is not toxic itself, but it’s elevation is
how do the kidneys regulate blood volume & pressure? (3)
- alter the amt of urine produced
- release the enzyme renin into the blood
- antidiuretic hormone released from the pituitary gland acts on the kidneys
when is renin released? what is the function of renin?
- renin is released when blood volume &bp is low
- it then acts on angiotensignogen to convert it to angiotensin 1
describe the RAAS system
- renin is released when bp low
- turns angiotensinogen into angiotensin 1
- ACE turns angiotensin 1 into angiotensin 2
- angiotesin 2 causes vasoconstricition & aldo secretion
what is the function of aldo
- tells the kidneys to keep Na and water & get rid of K+
what is the function of ADH
- tells the kidneys to keep water
what triggers the kidneys to produce erythropoietin
- produces it in response to low blood O2 levels
what does erythropoietin do>
- stimulaed erythrocyte production in the bone marrow
list 5 main electrolytes the kidneys regulate
- Na
- K
- Ca
- Cl
- Phosphate
list 3 ways the kidneys regulate electrolytes
- alteration of the urine conc
- alteration of urine composition
- activation of vit D
describe why the kidneys need to activate vit D? what does this activation cause?
- when we absorb vit D into our skin via the sun it is inactive
- the kidneys then activate the vit D
- activation of vit D promotes Ca++ absorption in the small intestine
what other hormone promotes Ca++ absorption
- parathyroid hormone
how do the kidneys regulate the body’s pH
- control the amount of H+ secreted
- & the amount of HCO3- reabsorbed from the filrate
note: for every molecule of H+ secreted, one HCO3- is reabsorbed
where are the kidneys located? what are they partially protected by>
- located posterior to the peritoneum in the retroperitoneal area
- partially protected by the lower ribs
where do the kidneys receive blood from? where do these come from?
- the renal arteries
- these branch directly from the aorta
how do the kidneys return their cleansed blood to the heart?
- thru the renal veins into the inferior vena cava
describe the movement of urine (4 steps)
- it is produced in the kidneys
- travels down the ureters
- moves into the urinary bladder for storage
- then leaves the body thru the urthera using contraction of the bladder
each kidney is covered by ____ and _____
- a fibrous capsule
- layer of adipose tissue
where are pain receptors located in the urinary system? what does this mean
- none in the kidney
= pain only present when there is impingement on the renal capsule (fibrous capsule) or in the ureter (because these 2 have pain receptors) - no pain if shrunken, pain if swollen
where does blood go once it enters the kidney?
- it is transported by smaller arteries to the outer portion of the kidney = the cortex
where is the majority of blood in the kidney filtered?
- in the cortex
what is the innner portion of the kidney called
- the medulla
what is the function of the medulla (2)
- alters the composition of the filtrate (thru reabsorption)
- creates urine
which area of the kidney is highly suscpetible to ischemic damage? why?
- the medulla
- it is very metabolically active but has low O2 tension because blood goes to the cortex first
describe the shape of the medulla; what are these called
- arranged in triangular shaped structures = medullary pyramids
where does the urine go after the medulla alters the composition & forms urine?
- drains into collecting ducts in the medulla
- then goes through the renal calcyes which combine to form one big funnel called the renal pevlis
- the urine goes from the renal pelvis into the ureters for transport to the urinary bladder
why is blood pressure to the kidneys importanT
- important to maintain filtration
- NOT to satisfy the metabolic needs of the tissue
at rest, the kidneys receive ___% of the cardiac output
25%
list 2 things that cause less cardiac output to go to the kidneys
- exercise
- exertion
what is the average blood pressure in the glomerular capillaries
- ~55 mmHg
what 2 things maintain glomerular blood pressure? what is the formula
- flow through the afferent arteriole (BFG)
- high resistance to flow in the efferent arteriole (RG)
BPg = BFg x Rg
the glomerular blood pressure is the driving force for what?
- to create filtration
describe the relation between BFg and BPg; what would cause BPg to increase? decrease?
- if BFg increases with afferent arteriole dilation = increased BPG
- if BFG decreases with afferent aertiorole constiction = decreased BPG
describe the relation between RG and BPG; what would cause BPG to increase? decrease?
- RG is increased with efferent constriction = increased BPG
- RG is decreased with efferent dilation = decreased BPG
what effect does increased BPG have on filtration? decreased?
- increased BPG = increased filtration
- decreased BPG = decreased filtration
the glomerular capillaries are formed from…?
- the afferent arteriole
what are glomerular capillaries composed of? (3)
- fenestrations
- basement membrane in between
- podocytes
what is the glomerulus?
- a tuft of capillaries surrounded by bowman’s capsule
what are fenestrations
- endothelial cells with holes in them
what are podocytes
- epithelial cells with foot-like structures & slits
does fluid first go thru the fenestrations or podocytes
- fenestrations –> basement membrane –> podocytes
what is Bowman’s capsule continuous with?
- the renal tubule
what is the juxtaglomerular apparatus? what is it made of?
- regulatory unit composed of:
1. afferent arteriole
2. efferent arteriole
3. juxtaglomerular cells
4. macula densa
what is the function of the juxtaglomerular cells
- secrete renin in response to low BP or SNS stimulation
what is the function of the macula densa (3)
- part of the distal tubule
- senses changes in the conc of the filtrate
- can dilate or constrict the arterioles appropriately
what is the function of the fenestrations in the glomerular capillaries
- only allow particles less than 8 nm to pass
what is a con to the size limit of the fenestrations? how do we overcome this?
- proteins like albumin are smaller than 8 nm
- the capillary basement membrane contains negatively charged proteoglycan which repels other anions (negatively charged molecules) like albumin
describe the role/relation between inflammation & the immune system to the glomerulus
- the glomerulus is commonly injured by immune complexes
- this complexes get caught in the fenestrations or slits
- this produces an inflammatory response in an attempt to destroy the immune complex thru phagocytosis
what is nephritic syndrome
- occurs if the immune complexes are within the endothelial layer (on the fenestration side of the basement membrane) & accessible to phagocytes
what is nephrotic syndrome
- occurs if the immune complexes lie within the epithelial cells (podocytes) and are not accessible to phagocytes
what does inflammation of the glomerulus cause
- allows protein to inter the filtrate & urine
describe the urine in nephritic vs nephrotic syndrome
- nephritic = there are blood cells in the urine = hematuria
- nephrotic = there are not
what 3 forces regulate filtration thru the glomeruluar capillaries
- glomerular (blood) hydrostatic P
- blood colloid osmotic P
- capsular hydrostatic P
what does the glomerular blood hydrostatic P cause? what is the pressure exerted?
- pushes fluid out of the glomerulus
= 55 mmHg
what does the blood colloid osmotic P cause? what is the amt of pressure exerted?
- pushed water back into the glomerular capillary because there are more proteins in the blood
= 30 mmHg
what does the capsular hydrostatic pressure cause? what is the amt of pressure exerted?
- pushes a small amount of fluid back into the capillary
= 15 mmHg
what helps increase the permeability of the glomerular capillaries? (2)
- fenestrations
- higher bp compared to other capillaries
what is the glomerular filtration rate
- the amount of blood plasma filtered thru the capillaries in 1 min
what is the typical glomerular filtration rate?
125 mL/min
how is GFR primarily regulated
- by altering the BPg (and therefore altering BFg and Rg)
what 2 things cause an increase in GFR
- afferent dilation = increased flow thru the capillaries
- efferent constriction = increased resistance to flow
what 2 things cause a decrease in GFR
- afferent constriction = decreased flow thru the capillaries
- efferent dilation = decreased resistance
