Renal Anatomy and Absorption Control

kidneys

pair of retroperitoneal organs that filter waste from the blood

stones can manifest as back pain

ureter

tube that carries urine from the kidney to the urinary bladder

urinary bladder

temporarily stores urine

urethra

tube that carries urine from the bladder to the outside of the body for excretion

excretion: metabolic end products, drugs, and other exogenous compounds

regulation: filtering blood → regulates essential substances like ions, osmolarity, pH, arterial BP (homeostasis by selectively absorbing/secreting and altering their concentrations)

secretion: renin, EPO, and activates vitamin D

what functions is the urinary system responsible for?

cortex

outer layer of the kidney

medulla

inner part of the kidney

renal pyramids

triangular-shaped areas of tissue in the medulla of the kidney where many nephrons are found (in the tip)

papillae

tip/apex of renal pyramid where nephrons are "funneled" in/drain (contains terminal portions of nephron collecting ducts)

minor calyx

where papillae extend into

major calyx

where minor calyces converge into to form the renal pelvis

nephron

functional unit of the kidney; two types (cortical and juxtamedullary)

head of all of these is located in the the cortex

cortical nephron

nephrons with a shorter loop of henle responsible for filtration, reabsorption, and secretion

surrounded by peritubular capillaries

85% of nephrons

juxtamedullary nephron

nephrons with a long loop of hence that extended deeper in to the medullar responsible for concentrating urine

establish concentration gradient from cortex to deeper medulla; build osmolarity diff

surrounded by vasa recta and peritubular capillaries

peritubular capillaires

capillaries that surround the tubules of a nephron; site of secretion/reabsorption (nephrons are in very close contact with blood in vessels)

vasa recta

vessels that extend from peritubular capillary that accompanies the long loop of henle

corpuscle (bowman's capsule + glomerulus) and renal tubule (50 mm length)

Bowman's capsule → proximal convoluted tubule → loop of henle (hairpin/U-shaped structure) → distal convoluted tubule → collecting duct → drains into tip of medulla

what structures make up a nephron? list them in order

filtration, reabsorption, and secretion

excretion = filtration - reabsorption + secretion

urinary excretion of a substance depends on its ___? give the formula to determine this

excretion

how much filtration from capillary bed (glomerulus) into Bowman's space there is

filtration - reabsorption + secretion

reabsorption

once a substance has entered tubule, going back into the blood

lots throughout path of renal tubule

secretion

when a substance from the blood joins the renal tubule

mostly in proximal and distal tubules/collecting duct

glomerular filtration rate (GFR)

amount of plasma filtered from the glomeruli into Bowman's space (amount of filtrate formed) per unit time; volume/time

key indicator of kidney health → in average adult, average is about 125 mL/min or 180 L/day (entire plasma can be filtered by kidneys ab 60x/day)

20% of plasma is filtered each time by renal tubule, 80% bypasses it

glomerulus

capillary network encased in the upper end of a nephron where filtration of blood takes place

Bowman's capsule

beginning of tubule; cup-shaped strucutre of the nephron that encloses the glomerulus where filtration takes place

has parietal and visceral epithelium

parietal (outer) and visceral (inner) epithelium

visceral is in contact with capillaries and where filtration occurs

what are the two layers of Bowman's capsule?

renal corpuscle

glomerulus and bowman's capsule

the afferent arteriole brings blood in, the efferent arteriole is where blood exits (80% of blood leaves through here)

how does blood enter and leave the glomerulus?

filtration barrier

fenestrated capillary epithelium and basement membrane (basal lamina)

pores formed by podocytes, and leaky bc they are not in close contact with each other

podocytes

epithelial cells in the glomerulus that wrap around blood vessels and form a filtration barrier; make up visceral epithelium

resulting filtrate is protein-free dialysate of plasma; only RBCs and large proteins are left behind in blood during filtration

plasma inside capsule has ions, nutrients, etc.

what substances are found in the filtrate in nephron?

how much gets filtered depends on pressure; net glomerular filtration pressure = PH - Pfluid - π

favor filtration: PH (glomerular capillary hydrostatic pressure)

oppose filtration: Pfluid (Bowman's hydrostatic pressure) and π (colloid osmotic pressure)

what factors affect GFR? what is the equation for net glomerular filtration pressure?

PH (glomerular capillary hydrostatic pressure)

blood coming in from capillaries; very little pressure in Bowman's space normally, but glomerulus does have pressure from fluid

driving force of filtration by acting as primary mechanism for physiological regulation of GFR (increase in this = increase in GFR)

Pfluid (Bowman's hydrostatic pressure)

once fluid moves into Bowman's space, it creates pressure opposing original fluid that came in

π (colloid osmotic pressure)

protein left behind in blood creates osmotic pressure gradient that drives fluid back into the capillaries (glomerulus)

arterial pressure (systemic BP, buffered by autoregulation), afferent arteriole resistance (blood coming in), and efferent arteriole resistance (blood going out)

what are the 3 factors that influence PH?

autoregulation of GFR

maintains GFR despite (wide range of) changes in systemic BP; even if systemic BP (MAP) changes, GFR will be buffered and not change as much bc of myogenic response, TGF, and hormones (RAAAS)

afferent: less blood flow in → hydrostatic pressure in glomerulus (PH) and thus GFR will decrease → renal blood flow (blood flow to kidneys) will also decrease bc less input = less output → more blood will flow to other organs

efferent: more blood flow in (less out) → PH and thus GFR will increase

renal blood flow will still decrease if both efferent and afferent are restricted an equal amount

how would constricting the afferent and/or efferent arterioles affect PH?

myogenic response

increase in renal BP (stretch in arteriole) = constrict smooth muscle in afferent arteriole to oppose it (and vice/versa)

stretch from increased BP → Ca in → activate calmodulin and MLCK → contraction

similar to autoregulation in other systemic arterioles

tubuloglomerular feedback (TGF)

paracrine control/feedback; increase in GFR → increasing NaCl (osmolarity in renal tubule) sensed by macula densa → send signals to juxtamedular cells → smooth muscle of afferent arteriole contracts

macula densa

osmoreceptors in distal tubule; modified epithelial cells that detect osmolarity change and send signals based on that to granular cells

granular cells (juxtaglomerular cell)

modified smooth muscle of afferent arteriole that receive signals from macula densa cells and act accordingly

secrete renin (paracrine signal from NO)

GFR increase → flow through tubule increases → flow past macula densa increases → paracrine signals from macula densa go to afferent arteriole (granular cells) → granular cells contract (afferent arteriole constricts) → resistance in afferent arteriole increase → hydrostatic pressure in glomerulus decreases → GFR decreases

describe the feedback loop of TGF of lowering GFR in response to an increase in it

use adenosine: if you have too much GFR, you constrict afferent arteriole to decrease how much blood gets through

Adenosine causes vasoconstriction and NO causes vasodilation. When GFR increases, the macula densa cells will release which paracrine signal as part of the TGF response?

renin

hormone secreted by the kidney that raises BP and converts angiotensinogen into angiotensin I

secreted in response to BP drop, sympathetic activation, and low osmolarity of tubular fluid (through macula densa) from granular cells

angiotensin-converting enzyme (ACE)

converts angiotensin I to angiotensin II, made by lung endothelial cells

angiotensin II

increases BP by causing arteries to constrict, increases CO, and triggers secretion of ADH (hypothalamus) and aldosterone

decreases GFR → water retention (not excreted in urine) → higher BP from higher blood volume

made by liver and causes thirst as well

aldosterone

triggered by angiotensin II, causes nephron to reabsorb more Na → increase blood volume and maintain osmolarity

from adrenal glands (kidneys), increases BP

antidiuretic hormone (ADH)

increases water reabsorption (insertion of aquaporins into nephron)

from posterior pituitary (made in hypothalamus), increases BP

atrial natriuretic peptide (ANP)

dilates afferent arterioles to increase GFR and inhibit renin secretion in response to high BP (antagonist of RAAAS)

increases excretion of Na in urine; increases GFR and decreases reabsorption of Na by nephrons

from heart (atrial myocytes)

correct answer is E because aldosterone secretion is suppressed, not increased

answer the question and explain your answer