Functions of the Kidney Flashcards
explain the role of the kidney in regulating blood pressure (BP):
- does it regulate short term or long term BP?
- list the key ions, transporters, ect. involved in this process
- kidney manages long term regulation of blood pressure
- key ion: Na+
- key transporter: Na+/K+ ATPase
- the process:
the kidney regulates long term BP by modulating effective cirulating volume (ECV). it does this via the paired (or “coupled”) reabsorption of Na+ and water. movement of Na+ into the peritbular capillaries (aka reabsoprtion), is immediately followed by movement of water. thus, this process is isotonic: there is no change in solute concentration as Na+/water move together.
reabsorption of water into capillaries –> changes ECV –> changes BP –> modulates flow to tissues (tissue perfusion)
explain the role of the kidney in regulation of plasma osmolality
- list pertinent molecules/transporters/ions ect involved.
- outline the process
- what does the resultant plasma osmolality determine?
- key molecules: ADH (anti-diuretic hormone)
- process:
- ADH is released base on patient’s thirst and water intake
- ADH makes parts of the nephron more permeable to water
- free water moves between tubules/capillaries based on a solute concentration gradient
- thus, water moves by itself (not along with sodium) and this process is NOT isotonic
- plasma osmolality determines intracellular fluid volume
- control of intracellular fluid volume allows kidney to conserve water by retaining free water and producing a maximally concentrated urine
explain the role of the kidney in maintaining pH.
- note important ions, transporters, metabolites, ect.
regulation of body pH contingent on
- secretion of H+
- reabsorption of HCO3-
- formation of titratable acid (PO4) and NH4 in the urine
key takeaway: for every H+ excreted, HCO3- reabsorbed
generally, the kidney excretes what substances?
metabolism ends products
non metabolizable dietary substances
undesirable substances that must get cleared (drugs, chemicals)
constrast the regulation of blood pressure with the regulation of plasma osmolality (by the kidney) in terms of
- reabsorptive process
- physiological purpose
blood pressure regulation
- isotonic reabsorption of Na+/water
- purpose: maintainence of effective circulating volume (ECV) –> BP –> perfusion of tissues
plasma osmolality
- reabsorption of free water (NOT isotonic)
- purpose: denotes ability to converse water and produce concentrated urine
renin:
- what triggers its release?
- what cells release it?
- what does it do?
- renin release triggered increased SNS outflow, usually in response to a low volume state
- adrenergics (NE, E) bind to B1 receptors juxtaglomerular cells lining afferent arterioles
- the juxtaglomerular cells release renin
- renin triggers RAAS system, which induces isotonic reabsorption of Na/water –> restores blood pressure
what is erythropoiten and when is it released?
erythopoitin is a hormone released by the kidney in response to chronic hypoxdemia
- what is urodilatin?
- when is it released?
- what does it do?
- urodilatin is an atrial neuretic peptide: these are peptides that causes “naturesis” - aka increased sodium excretion
- it is released in response to increased ECV (effective circulation volume)
- increased Na+ secretion –> increased water excretion
discuss how the kidney modulates Ca++ concentration
- parathyoid hormone (PTH) is released from the parathyroid glands in response to low Ca++ states
- the kidney detects PTH, and in response, activates vitamin D3
- increased amount of activated D3 aids increased absoprtion of Ca++
contrast “cortical” nephrons and “juxtamedullary nephrons”
differences based on: 1. length of loop of henle and 2. location of glomerulus
cortical nephron:
- the glomerulus found near superficial cortex (outermost kidney layer)
- loop of henle found in the inner & outer stripes of the outer medulla, but NOT in the inner medulla
juxtamedullary nephron:
- glomerulus sits right at the “juxtamedullary margin” - margin between cortex and outer medullar
- loop of henle found in both the outer AND inner medulla
afferent arterioles:
- what are they made of?
- how do they respond to sympathetic ouflow?
the afferent arteriole is made up of 1. smooth muscle and 2. j_uxtaglomerular cells_. in response to sympathetic stimulation (due to a low volume state)
- the smooth muscle contracts, leading to afferent arteriole vasoconstriction: in isolation, this decreases both flood flow into the glomerulus and glomerular hydrostatic pressure, decreasing the amount of fluid filtered from capillaries
- the juxtaglomarular cells release renin, which promotes Na+/water reabsorption
macula densa
- what forms it?
- what is its role?
- an area of closely packed specialized cells lining a portion of DCT (distal convoluted tubule) that is directly adjacent to the glomerulus
- the macula densa communicates characteristics of the filtrate in the tubular system to dictate filtration at the glomerulus. this communication is called “tubuloglomerular feedback”
bowman’s capsule
- definition and characteristics
- the capsule encasing the glomerular capillaries
- receives the fluid/solutes filtered out of the glomerular capillaries, and this thus the first component of the tubular filtration system in nephrons
- has NO plasma proteins
- thus, its oncotic pressure is zero
the proximal tubule:
- has what epithelial lining and characteristics
- discuss its permeability/solute movement that occurs here
histology: allows high resorptive capacity/metabolic activity:
- cuboidal cells with well developed brush border
- abundant mitochondria
permeability:
- 65% of filtered water, Na+, HCO3, K+, glucose and amino acids reabsorbed here
thin descending limb
- has what epithelial lining?
- discuss permeability
- simple squamous epithelium
- impermeable to solute
- permeable ONLY to water: which moves out tubule (reabsorbed) along concentration gradient
thin asending
- what epithelial lining
- permeability
thin ascending limb
- simple squamous epithelium
- permeable only to solute: NaCl exits tubule here (reabsorbed) along concentration gradient
- NOT permeable to water
thick ascending limb
- epithelial lining/characteristics
- permeability
histology:
- cuboidal cells
- rich in mitochondria
permeability:
- like thin ascending limb, is impermeable to water & permeable to solute
- ACTIVELY transports Na+ out of tubule into blood
discuss the resistance of the afferent arterioles, glomerular capillaries, and efferent arterioles
afferent and efferent arterioles: high resistance
glomerular capillaries:
- are aligned in parallel
- thus, total resistance at the glomerular capillaries is low
discuss the three components of the distal nephron
distal convoluted tubule - has macula densa
cortical connecting tubules
- connecting tubule cells
- intercalated cells that: handle movement of H+, HCO3-, K+
cortical collecting tubules
- principle cells that: handle movement of Na+, K+
- intercalated cells that: handle movement of H+, HCO3-, K+
medullary collecting tubules: same makeup as cortical collecting tubules
afferent arterioles come from what arteries?
Renal artery –> interlobar arteries –> arcuate arteries –> interlobular arteries –> afferent arteriole
how blood from efferent arterioles enter venous circulation
efferent arterioles –> peritubular capillaries –> vasa recta (extend into medullary region) –> interlobular veins –> arcuate veins –> interlobar veins –> renal vein
agents that vasoconstrict renal vasculature
(a) Epinephrine and norepinephrine
(b) Angiotensin II
(c) Vasopressin (Antidiuretic Hormone, ADH)
(d) Endothelin
vasodilators?
- NO
- PGI
- bradykinin
- ANP (atrial natriuretic peptide)
- BNP (brain natiuretic peptide)
- ACh
- dopamine
- serotonin
- adenosine
define filtration, secretion, reasroption
filtration: fluid is filtered into bowman’s capsule (thus the tubular system) from glomerular capillaries
absorption: fluid moving from tubules into peritubular capillaries
secretion: fluid moving from peritubular capillaries back into tubules
how much fluid is filtered thorugh the kidney per day?
125 ml/min, or
180 L/day
relationship between filtration, reabsorption, and what is not reabsorbed
- 98-99% of what is filtered is reabsorbed by the nephron
- What is left in the tubules is excreted as urine
what are the means by which contents in the filtrate are reabsorbed
- passive diffusion: down existing solute gradients
- paracellular: between cells thru intercellular junctions
- trancellular: across cell membrane - water utilizes aquaporins, non specific solute carriers/channels
- facilitated diffusion: down existing solute gradients, using solute specific carriers
- active transport
- movement directly paired with ATP
- secondary: movement coupled to passive diffusion of a solute down a concentration gradient set up by ATP
how is urea reabsorbed?
va facilitated diffusion (no energy expenditure, urea specific transporter used)
symport
- define
- give examples found in kidney
type of secondary active transport
- Na+ gradient set up of Na/K ATPase
- solutes move along with Na+ down gradient (co transport): Na-glucose, Na-amino, 2Na+ phosphate
antiport
- definition
- examples in kidney
type of secondary transporter
- Na+ gradient set up by Na/K ATPase
- Na+ moves down gradient, drives solute movement in opposite direction: Na-H+ antiporter
secretion is movement of solutes from where to where?
The opposite of reabsorption; solutes move into the tubular lumen from either the:
- tubular cells
- interstitial space
- peritubular capillaries
secretion key in movement of what ion
NH3/NH4
what solutes are freely filtered and
- not reabosrbed or secreted
- partly reabsorbed, not secreted
- ALL reabsorbed, not secreted
- ALL secreted, not reabsorbed
- NEITHER reabosrbed or secreted: creatinine, inulin
- partly reabsorbed, not secreted: phosphate, urea
- ALL reabsorbed, not secreted: glucose
- ALL secreted, not reabsorbed: PAH
discuss balance of starling forces in the glomular capillaries and peritubar capillaries
balance of starling forces determines movement of water
glomerular capillaries:
hydrostatic force > oncotic force –> net fluid filtration
peritbular capillaries:
oncotic force > hydrostatic force –> water reabsorption
