Human Phys Midterm 3

Main functions of kidneys

removal of metabolic waste products from blood and their excretion in urine, gluconeogenesis, balance ions in ECF, production of enzymes/hormones

renal system is responsible for

maintaining a proper osmolarity and tonicity in ECF

primary organs of urinary system

kidney, ureter, bladder, urethra

sections of a human kidney

renal cortex (outer layer), renal medulla (inner layer)

renal cortex

renal corpuscles, convoluted tubules, cortical nephrons

renal medulla

long loops of henle, collecting ducts

the nephron

functional unit of kidney

Nephron tubules

bowman’s capsule (part of corpuscle), proximal convoluted/straight tubule, loop of henle, distal convoluted tubule, collecting duct

Nephron equals

glomerular (renal) corpuscle + renal tubule

nephron blood supply

renal artery, afferent arteriole, glomerular capillaries, efferent arteriole, peritubular capillaries, renal vein

renal corpuscle

glomerular capillaries + bowman’s capsule

portal system

arrangement by which blood is collected from one set of capillaries passes through a large vessel to another set of capillaries before returning to systemic circulation

two types of nephrons

juxtamedullary (15%) and cortical (85%)

Juxtamedullary nephrons

extend into medulla, long loops of henle, generates gradient important for water reabsorption, concentrate the filtrate

cortical nephrons

short or no loops of henle, located in cortex, do not contribute to hypertonic medullary interstitium, change volume and composition of filtrate

basic renal processes

glomerular filtration, tubular secretion, tubular reabsorption

glomerular filtration characteristics

movement of plasma and substances in plasma from blood stream into renal tubule (bowman’s capsule), 1/5 plasma is filtered

glomerular filtration

plasma proteins and cells too big for filtration, filtration = blood plasma except for RBCs and proteins, GFR = 125 ml/min (180L/day)

tubular secretion

80% that wasn’t filtered could get filtered later

tubular reabsorption characteristics

reabsorb from filtrate and put back into plasma, prevents excretion of urine

Urinary Excretion

Filtration + Secretion - Reabsorption

Drugs, toxins

freely filtered and 100% secreted

Na+ and ions

freely filtered and partially reabsorbed

Glucose and amino acids

freely filtered and 100% reabsorbed

3 layers of glomerular filtration

capillary endothelium, basement membrane, bowman’s epithelium

capillary endothelium

50x more leaky than other typical capillary bed

basement membrane

negative charge

bowman’s epithelium

podocytes

filtered load (mg/min)

GFR (ml/min) * [P] (mg/ml), how much of a certain substance is filtered

excreted load (mg/min)

V (urine flow rate, ml/min) * [U] (concentration in urine, mg/ml), how much actually came out in the urine

EL < FL

net reabsorption

EL > FL

net secretion

reabsorption of water, ions, nutrients, etc

is almost complete

reabsorption of wastes

is incomplete, excreted

tubular lumen

carries future urine

luminal membrane

part of tubular epithelial cell that is touching lumen

basolateral membrane

part of tubular epithelial cell that is not touching lumen

reabsorption travels from

tubular lumen, tubular epithelial cell, peritubular capillary, renal vein

diffusion reabsorption

lipid soluble substances that don’t need carriers

mediated transport reabsorption

large/charged substances (glucose)

transcellular route (across cell)

luminal membrane, basolateral membrane, renal interstitial fluid, peritubular capillaries

paracellular route (between cells)

tight junctions, renal interstitial fluid, peritubular capillaries

substances needing protein carriers have

transport max

tubular secretion

usually active process, coupled with Na+ reabsorption, secondary active transport, foreign chemicals and toxins, most secretion occurs in proximal tubules, transport max

renal plasma clearance

volume of plasma per unit time from which all of a substance is removed by the kidneys and excreted in the urine

RPC can be used to determine

how well kidneys are functioning or how a substance is handled by the kidney

inulin

freely filtered but not secreted or reabsorbed

RPCinulin = (renal plasma clearance)

GFR (125 ml/min)

RPC > GFR

net secreted

RPC < GFR

net reabsorbed

renal plasma clearance of creatine

more practical and less invasive way of determining GFR, produced by muscles at a constant rate, byproduct of normal skeletal muscle metabolism, freely filtered, not reabsorbed, slightly secreted, RPC ~ to true GFR

renal plasma flow

volume of plasma going through kidneys per minute, normal is 625 mL/min

PAH is

freely filtered and 100% secreted

detrusor smooth muscle, sensory afferent to CNS

parasympathetic, causes contraction, inhibited during filling, stimulated during urination

internal urethral sphincter smooth muscle, sensory afferent to CNS

sympathetic, causes contraction, stimulated during filling, inhibited during urination

external urethral sphincter skeletal muscle, sensory afferent to CNS

somatic motor, causes contraction, stimulated during filling, inhibited during urination

Na+ reabsorption in proximal tubule

65% Na+ reabsorption occurs here and is non-regulated

Na+ reabsorption in distal tubule and cortical collecting duct

regulated by hormones, no Tm

water follows Na+ passively by osmosis via two routes

paracellular and transcellular

paracellular osmosis

main water route in proximal tubule (leaky tight junctions), non-regulated

transcellular osmosis

main water route in distal tubules and collecting ducts (very tight junctions), requires insertion of aquaporins (regulated by ADH/Vasopressin)

renal medullary gradient

active transport of NaCl (reabsorption) from ascending limb, ascending limb is impermeable to water, water reabsorption via osmosis from descending limb, recycling of urea from collecting duct

concentration of the urine

because of hyperosmotic medullary ISF filtrate can become highly concentrated with a low ADH volume, results in excretion of low volume of highly concentrated urine

Hydrostatic Pressure

Pgc (pressure of glomerular capillaries)

Oncotic Force

πgc, πbs

Pgc

gets pushed into bowman’s capsule

Pbs

gets pushed into glomerular capillaries

πgc

gets pushed into glomerular capillaries from bowman’s capsule

Decreased GFR

constrict afferent arterioles or dilate efferent arterioles, decreased Pgc

Increased GFR

constrict efferent arterioles or dilate afferent arterioles (caffeine), increased Pgc

water

99% reabsorbed

glucose

100% reabsorbed

renal sodium regulation

Nexcreted = Nfiltered - Nreabsorbed

why is sodium so important in renal system

most abundant ECF ion

Na+ filtered =

GFR * [Na+]plasma

Na+ reabsorption regulation

renin/angiotensin/aldosterone system

Na+ reabsorption regulation steps

kidney releases renin enzyme from jg cell promotion, liver releases angiotensinogen, renin converts angiotensinogen to angiotensin 1 inactively, ACE converts angiotensin 1 to angiotensin 2, targets systemic arterioles or adrenal cortex on kidneys, vasoconstriction in artioles or Na+ and water retention in kidneys, increase in blood pressure

water regulation

1) excess water ingested

2) decrease fluid osmolarity (increase water concentration)

3) lower firing by hypothalamic osmoreceptors

4) decrease in vasopressin secretion in posterior pituitary gland

5) decrease in plasma vasopressin

6) tubular permeability to water decreases and water reabsorption decreases in collecting ducts

7) increase in water excretion

if ADH is not present

water cannot be reabsorbed in distal nephron, stuck

main function of vasopressin/ADH is to

regulate plasma osmolarity

JGA

juxtaglomerular cell patch and macula densa cell patch

juxtaglomerular cell patch

from afferent arteriole, senses pressure and releases renin when it is low

macula densa cell patch

distal convoluted tubule, senses flow and sends paracrine signals to afferent arterioles

sweat comes out of blank and contains

ECF, water and NaCl

water and NaCl must both be preserved after sever sweating

to maintain blood volume and osmolarity

severe sweating leads to

loss of hypooosmotic salt solutions

loss of hypoosmotic salt solutions leads to

lower plasma volume and higher plasma osmolarity (lower water concentration)

lower plasma volume leads to

lower GFR, increased plasma vasopressin, increased plasma aldosterone, both lead to lower Na+ excretion

higher plasma osmolarity leads to

higher plasma vasopressin, lower water excretion

kidneys can excrete ingested water and Na+ but can only reduce the rate, not completely excrete when

you don’t eat/drink enough

fluid loss occurs even during

dehydration

what leads to thirst

lower plasma volume (increase in angiotensin 2), higher plasma osmolarity, dry mouth, metering of water intake by GI tract

respiratory acidosis

increase in H+, increase in HCO3-, increase in CO2

respiratory alkolosis

decrease in H+, decrease in HCO3-, decrease in CO2

metabolic acidosis

increase in H+, decrease in HCO3, decrease in CO2

metabolic alkolosis

decrease in H+, increase in HCO3, increase in CO2

causes of HCO3 change in respiratory acidosis and alkalosis

renal consumption

causes of HCO3 change in metabolic acidosis and alkalosis

primary abnormality

causes of CO2 change in respiratory acidosis and alkalosis

primary abnormality

Causes of CO2 change in metabolic acidosis and alkalosis

reflex ventilatory compensation