Phys 1 Flashcards
how many nephrons in a kidney?
1 million
What are the 4 main functions of the nephron (aka blood processing unit)
- filtration
- reabsorption
- secretion
- excretion
functions of the kidney (there are a ton)
- filter plasma and produce urine
- excrete metabolic waste products
- reabsorb glucose and amino acids from filtrate
- regulate Ca and phosphate uptake
- regulate water homeostasis
- regulate extracellular vol. –> BP
- regulate electrolytes
- acid base homeostasis
- gluconeogenesis
- endocrine function
what are the endocrine components of the kidney? (4)
- kinins
- 1, 25-dihydroxycholecalciferol
- EPO
- renin
What 2 diseases cause the largest prevalence of kidney dysfunction?
- DM
2. HTN
What type of endothelium is found within the glomerulus?
fenestrated
characteristics of the afferent arteriole that feeds the glomerulus
- high resistance vessel
- high pressure
- larger diameter than efferent
what is the general function of the afferent arteriole?
to force fluid and solutes from the circulation to the glomerulus to form filtrate
mesangial cells
- where
- function
- between capillaries
- contractile cells that regulate the filtration rate and restrict large particles
What is the glomerular capsule aka bowman’s capsule?
- a blind sac of the nephron
- surrounds the glomerulus
- receives filtrate
podocytes
- cells that surround the capillaries
- they have foot like extensions that function as pores for another layer of filtration
PCT cell type
cuboidal
characteristics of the PCT
- high in mitochondria (think active transport occurring here)
- dense w/ microvilli
what mainly occurs at the PCT?
-active reabsorption of water and solutes (glc) from the filtrate
descending limb of the LoH
- thin
- squamous epithelium
- permeable to water
ascending lib of the LoH
- thick
- cuboidal epithelium
- solute secretion (i.e Na)
What are the 2 types of nephrons?
- cortical nephrons
2. jextamedullary nephrons
cortical nephrons
- make up 85% of nephrons
- short loops
juxtamedullary nephrons
- 15% (even though this is what we talk about the most)
- long loops
- have vasa recta
characteristics of the DCT
- cuboidal cells
- lack microvilli (b/c not as much reabsorption occurring)
- empty to collecting duct
peritubular capillaries arise from what?
the efferent arteriole
function and characteristics of the peritubular capillaries
- surround the renal tubule
- low pressure and porous
- readily absorb water and solutes
- return fluid to the renal vein
2 renal capillary beds
-function
- glomerulus
- produces filtrate - peritubular capillaries
- reabsorbs most of the filtrate
What is the point of contact between the DCT and the afferent arteriole?
juxtaglomerular apparatus
what are the 2 cell populations that make up the juxtaglomerular apparatus?
- juxtaglomerular cells
- macula densa
the juxtaglomerular apparatus functions to regulate what?
- blood volume
- BP
- GFR
juxtaglomerular cells (aka granular cells)
- where
- function
- in the afferent artery wall
- enlarged smooth muscle cells that function to produce and store renin in granules
juxtaglomerular cells sense what?
low BP
what juxtaglomerular cells release renin in response to low BP, what is the effect?
- vasconstriction (systemic)
- increases blood vol. which therefore increases BP
where is the macula densa located?
in the distal tubule
the macula densa is sensitive to what?
NaCl concentration in the late ascending limb
What is the outcome when the macula densa senses a decrease in NaCl concentration?
- vasodilation of afferent arteriole: this increases GFR
- increase in renin release: increases blood vol. and pressure
what coalesce to form the collecting ducts?
DCTs
The epithelium of the collecting ducts consist of what 2 cell types?
- principal cells (P cells)
2. intercalated cells (I cells)
principal cells of the collecting ducts function
- Na reabsorption
- H2O reabsorption in response to vasopressin
intercalated cells of the collecting ducts function
- acid secretion
- HCO3 transport
which cells have more microvilli and mitochondria, P or I?
I cells
vasopressin effect at the collecting duct
it opens pores creating an aquaporin to allow for a lot of water absorption
renal medullary interstitial cells (RMIC)
- where
- cell type
- in kidney interstitial tissue
- specialized fibroblast like cells
RMICs produce what (2)
- COX-2
- PG
- PGI2 - Prostaglandin synthase (PGES)
- PGE2
what effect does the COX2 produced by the RIMCs have?
vasodilation and anti-coagulation
what effect does the PGES produced by the RIMCs have?
vasodilation
how much blood to the kidneys receive at rest?
- 1.2-1.3 L/min
- just under 25% of the CO
- under close systemic and intrinsic control
pressure throughout the system
- systemic
- glomerular
- peritubular
- renal vein
- mean systemic arterial pressure: 100 mm Hg
- glomerular capillary P: 45 mm Hg
- peritubular capillaries: 8 mm Hg
- renal vein P: 4 mm Hg
comparing glomerular capillary pressure to systemic arterial pressure
glomerular P is about 40% of the systemic arterial pressure
innervation of the kidney
SNS via the thoracic and lumbar sympathetic trunk
innervation of the adrenal glands
thoracic sympathetic trunk
What is the effect of the SNS on renal circulation in times of stress?
- stimulation of adrenal medulla –> release of NE
- beta 1 adrenergic receptors:
- juxtaglomerular cells release renin
- renal tubular cells reabsorb water and Na
- alpha-1 receptors:
- vasocontrict the arterioles
what mechanism is responsible for autoregulation of renal blood flow?
- myogenic mechanism
- vascular smooth muscle tends to contract when stretched
how does the myogenic autoregulation mechanism work?
when BP increases, the afferent arteriole constricts to reduce the glomerular pressure
what makes up the tubuloglomerular feedback mechanism?
the macula densa cells of the JGA of the DCT
what does the tubuloglomerular feedback mechanism respond to?
- increased osmolality and flow
- this causes vasocontriction
- therefore slowing GFR and increasing processing time
(and vice versa)
EPO
- what
- prodcued by
- in response to
- protein hormone
- produced mainly by kidney interstiital cells (but also liver)
- in response to hypoxia
function of EPO
- circulates in response to hypoxia
- binds receptors on proeyrthroblasts in BM
- increases the production and maturation of RBCs
calcitriol
- aka
- what
- produced by
- aka 1,25 dihydroxyvitamin D3
- active form of vit. D
- produced by the kidney
calcitriol is produced in response to what?
PTH (increase in blood Ca)
what is the action of calcitriol?
- kidneys
- GI
- bone marrow
- kidneys: increase tubular reabsorption of Ca
- GI: increase absorption of Ca
- bone: release Ca from bone
