Patho Exam 4: Renal System

ways in which the renal system regulates homeostasis

• removes waste and toxins (medications)

• regulates body’s fluid, electrolyte, acid-base balance

• releases hormones that regulate BP and Ca2+

• produce active forms of Vitamin D

• controls production of RBCs

location of glomerulus of nephrons

renal cortex

how much blood flows through kidneys each minute

1200 mL

blood flow through kidney in order

• renal artery

• afferent arteriole

• glomerulus

• efferent arteriole

• peritubular capillary

• renal vein

arteriole entering glomerulus

afferent arteriole

arteriole leaving glomerulus

efferent arteriole

if a patient has less than ___ nephrons, dialysis is required

360,000

urinary excretion rate

glomerular filtration + tubular secretion - tubular reabsorption

in nephrons, filtration occurs in the

glomerulus

what kind of capillary is the glomerulus

fenestrated

in order for a substance to enter renal tubules, it must pass through in order

• fenestrated epithelium of glomerular capillary

• basement membrane

• podocytes (foot processes)

function of nephrin

transmembrane protein that supports structure of podocytes

main determinant of what gets filtered through the glomerulus

podocytes (foot processes)

size of pores in the fenestrated epithelium of the glomerulus capillary

large, 70-100 nm in diameter

function of heparin sulfate in the basement membrane of glomerulus

protein filtration via charge: blocks negatively charged proteins like albumin

function of type IV collagen and laminin in the basement membrane of glomerulus

protein filtration by size: blocks large proteins like albumin

area between epithelial podocytes is called

slit diaphragm/filtration slits

what does not get filtered through glomerulus

RBCs and proteins

ions, drugs, toxins are actively pumped into

distal tubule

increased renal perfusion pressure (BP) causes

increased sodium and water excretion, reduced extracellular fluid returns blood pressure back to normal

renin-angiotensin-aldosterone system (RAAS) in controlling blood pressure

increased BP inhibits RAAS axis, reducing the vasoconstrictor effects of angiotensin II, decreases solute resorption in proximal and distal tubules

Natriuresis

Na+ excretion from the kidneys

what promotes natriuresis

ventricular and atrial natriuretic peptides, calcitonin

what inhibits natriuresis

aldosterone

where is angiotensinogen secreted

the liver

what converts angiotensinogen to angiotensin I

renin from the kidney, released by a decrease in renal perfusion

what converts angiotensin I to angiotensin II

ACE from lungs and kidney

effect of angiotensin II on nervous system

increases sympathetic activity

effect of angiotensin II on kidney

increased tubular Na+ and Cl- resorption, K+ secretion, water retention

effect of angiotensin II on adrenal gland

increased aldosterone secretion

effect of angiotensin II on BP

arteriolar vasoconstriction, increased BP

effect of angiotensin II on pituitary gland

increased ADH secretion

what inhibits renin secretion form the kidney

water and salt retention, effects of angiotensin II (negative feedback)

ADH effect on distal tubule and collecting duct

increases permeability by inserting more aquaporins, more water reabsorbed

alcohol effects on ADH

inhibits ADH release from pituitary

caffeine effects on ADH

interferes with ADH activity

hydrostatic pressure in glomerulus

higher than other capillary beds, 50 mmHg

nutrients (salts, amino acids, vitamins, etc.) are moved out of nephron tubules via

active transport

water is moved out of nephron tubules via

osmosis

some ions, drugs (antibiotics, beta blockers, digoxin), and toxins are secreted into distal tubule via

active transport

what is secreted out of the collecting duct

water and urea

why is a high sodium, low potassium diet problematic

Na+ is actively recovered in the renal system, K+ is pumped out. high sodium diet disrupts this equilibrium, causes HTN

how does the kidney regulate blood pressure

increased renal perfusion BP leads to a rise in sodium and water excretion, decreasing blood volume and BP (pressure natriuresis)

relationship between RAAS and pressure natriuresis

increased BP inhibits the RAAS axis, reducing the vasoconstrictor effects of angiotensin II on afferent arterioles, decreasing solute reabsorption in nephron

effects of ADH (vasopressin)

more water retained in the kidneys, increases permeability of the distal tubule and collecting duct by inserting more aquaporins into the membrane

alcohol and caffeine are classified as

diuretics

extrinsic control of arterial diameter

sympathetic nervous system

continuous capillary

• most common, least permeable

• intercellular clefts and transcellular cytosis allows for exchange of molecules

• abundant in skin and muscle

fenestrated capillary

• pores in the endothelial membrane

• found in the kidney

sinusoidal/discontinuous capillary

• most permeable and least common

• big holes in the endothelial membrane, big clefts between cells

• seen in liver, spleen, bone marrow

pathways of movement of water and solutes across capillaries

• paracellular via endothelial pores

• transcellular directly through the cell membrane via vesicles

exchange of small macromolecules through capillary

• smaller molecules can diffuse through interendothelial clefts through fenestrae <1 nm in diameter

• positively charged molecules are more permeable than negative

• most plasma proteins have a negative charge

exchange of large macromolecules through capillary

• macromolecules with diameter > 1 nm can cross at a very slow rate through intercellular clefts, fenestrations, paracellular gaps

• transcellular transcytosis via vesicles is predominant pathway

diffusion of water and solutes through capillary: via endothelial pores (paracellular pathway)

• the determinant of permeability (more junction proteins means decreased pores/pore size and decreased diffusion/permeability)

• mostly water and ions