Advanced A&P - Unit 9 Study Guide: Kidney Physiology

pathway of blood thru major vessels that supply nephron (to glomerulus)

adb. aorta → renal artery → segmental artery → interlobular artery → arcuate artery → cortical radiate artery → afferent arteriole → glomerulus

pathway of blood thru major vessels that drain nephron (from glomerulus)

glomerulus → efferent arteriole → peritubular capillaries or vasa reta → cortical radiate vein → arcuate vein → interlobular vein → renal vein → inf. vena cava

cortical nephron

most abundant, have a short nephron loop, reside almost entirely in the renal cortex with their renal corpuscles nearer to the surface of the kidney

juxtamedullary nephron

about 15% of nephrons, neprhon loops project well into renal medulla, renal corpuscle reside deep in renal cortex

juxtaglomerular apparatus

located @ end of the ascending limb of nephron loop where tubules comes in contact with the afferent arteriole

JG cells

smooth muscle cells of afferent arteriole that monitor bp in afferent arteriole; secrete renin when bp decreases

macula densa cells

elongated cells in tubule that monitor concentration of sodium chloride in tubular fluid; when sense low sodium chloride, JG cells will secrete renin

glomerular (bowman’s) capsule

ultrafiltration

glomerulus

filtration; especially efficient at filtering blood because bp (a hydrostatic pressure) is higher in glomerulus compared to systemic capillaries

• this is due to narrower diameter of the efferent arteriole compared to the afferent arteriole

filtrate

as blood flows through glomerulus, water & small substances are filtered into glomerular capsule. result is ____ which is similar to plasma/tissue fluid

composition of filtrate

mostly water, same solutes as blood plasma, both contain glucose

• only plasma has protein

Glomerular Hydrostatic Pressure (GHP)

bp in glomerulus; favors filtration

glomerular osmotic pressure (GOP)

due to protein in plasma, draws water back into blood by osmosis; opposes filtration

capsular hydrostatic pressure (CHP)

pressure in glomerular capsule due to filtrate accumulation; opposes filtration

capsular osmotic pressure (COP)

normally zero due to absence of protein in the filtrate

NFP (net filtration pressure)

net effect of all forces

• forces that favor filtration - forces that oppose filtration

NFP equation

NFP = GHP + COP - (GOH + CHP)

GFR (glomerular filtration rate)

total amount of filtrate produced per minute

• directly proportional to NFP (change that increases NFP will increase GFR and vice versa)

rise in NFP and GFR

increased bp

reduce NFP and GFR

decreased bp

decrease NFP and GFR

afferent arteriole constricts

increase NFP and GFR

afferent arteriole widens

increases NFP and GFR

efferent arteriole constricts

decreases NFP and GFR

efferent arteriole widens

increases NFP and GFR

low blood protein

decrease NFP and GFR

high blood protein

decreases NFP and GFR

obstruction

autoregulation (intrinsic)

maintain GFR at steady rate despite bp fluctuations during the day

• if bp rises, afferent arteriole constricts

• if bp decreases, afferent arteriole dilates

extrinsic mechanisms

goal is to bring bp back to normal

• if bp too low → increased sympathetic impulses

• if bp too high → decreased sympathetic impulses

Renin-angiotensin mechanism

• extrinsic mechanism

• used when bp drops too low

• JG cells of juxtaglomerular apparatus release renin into blood → renin converts angiotensinogen into angiotensin I and an enzyme from the lungs converts angiotensin I to angiotensin II

Angiotensin II

• causes constriction of systemic arterioles

• increases aldosterone secretion

• increases ADH secretion

• increases thirst

Tubular reabsorption

movement of substances from tubular fluid into peritubular capillary; substances of value to the body will be absorbed

• over 99% of volume of original filtrate will be absorbed

• 70% occurs in proximal tubule

Glucose

• freely filtered from glomerulus and is reabsorbed in proximal tubule by active transport pumps

water

• reabsorbed by osmosis in proximal tubule

renal plasma threshold

maximum amount of glucose that can be reabsorbed

• typical blood glucose is 80-120mg/dL

tubular secretion

movement of substances from blood in peritubular capillary into the tubular fluid

• hydrogen ions

• potassium

• medications or breakdown products of medications

• metabolic waste

ADH

released by post. pituitary gland when we are dehydrated. when present, large amounts of water can be reabsorbed by distal tubule and collecting duct, resulting in a smaller volume or more concentrated urine

Aldosterone

secreted by adrenal cortex in response to low blood sodium levels, high blood potassium, or thru activation of renin-angiotensin-aldosterone system. Causes sodium reabsorption in distal tubule and water follows by osmosis; decreases urine volume and concentrate urine

countercurrent mechanism

creates a very hypertonic environment deep in medulla of kidney; creates an osmotic gradient for water to be reabsorbed from distal tubule and collecting duct

cc multiplier

invovles nephron loop and creates the hypertonic environment

cc exchanger

involves vasa recta; exchange of solutes in vasa recta maintains hypertonic environment and ensures blood doesn’t pick up all solutes and carry them away

collecting duct

reabsorption of water by osmosis

normal urine composition

• water, nitrogenous waste (urea, uric acid, creatinine) and electrolytes

• not normal: RBCs, WBCs, protein, glucose, ketones, hemoglobin

afferent

vessel that supplies blood to the nephron is also an ______ arteriole