Renal system

purpose

• rid body of nitrogenous waste

• protein breakdown

• water and acid/base balance

• toxin/drug elimination

• breakdown product elimination

• produces hormones

types of nitrogenous waste

• ammonia

• uric acid

• urea

ammonia

• ammonotelic = aquatic animals

  • fish, aquatic invertebrates

  • water can reduce toxicity of ammonia

  • fish produce ammonia

    • tanks

    • nitrifying bacteria introduced to nitrogen cycle

• very toxic

• water soluble

uric acid

• uricotelic animals

• birds, reptiles

• renal portal system

• formed in the liver, concentrates, becomes precipitant

• semi-solid

• acidic

• requires little water, lots of energy

urea

• ureotelic animals

• mammals, amphibians, sharks

• allows water balance

• amount excreted dependent on conditions

• low toxicity

• build of of ura can cause problems 

kidneys basics

• retroperitoneal

  • separated in the abdominal cavity

  • have their own peritoneum

• smooth in most species

• lobulated in cattle and dolphins

• birds have elongated lobulated kidneys

• heart shape in horses

kidneys anat

• hilus

  • indentation where renal artery enters, renal vein and ureter leave

• cortex

  • outer, darker, rough

• medulla

  • inner, lighter, striated

• pyramids/peaks

  • within medulla

• pelvis

  • near hilus, space for urine collection/storage

• ureter

  • brings out urine

nepheron

• kidney cell

• functional unit

  • Glomerulus 

  • Bowman’s capsule

  • Proximal Convoluted Tubule (PCT)

  • Loop of Henle

  • Distal Convoluted Tubule (DCT) 

  • collecting tube or duct

  • vasa recta

• starts in cortex

  • extends down to medulla via descending loop

  • back up to nepheron via ascending loop

  • back down to medulla and exits via collecting duct

Glomerulus

• Capillary tuft

• Afferent arteriole: brings blood in

• Efferent arteriole: drains blood out

• This is the filter

Bowman’s capsule

• Podocytes = visceral layer

• Parietal layer = simple squamous epithelium

• Both podocytes and simple squamous epithelium necessary for filtration

• Sits above capillaries

• Receives filtrate

Proximal Convoluted Tubule (PCT)

• Simple cuboidal epithelium  

  • increases surface area

Loop of Henle

• descending limb

  • most simple squamous

  • does down into medulla

• ascending limb

  • thin = simple squamous epithelium

  • thick = simple cuboidal for strength

  • coes up to cortex

Distal Convoluted Tubule (DCT)

• simple cuboidal

  • increases surface area

  • convoluted

collecting tube or duct

• simple cuboidal

• no brush border

vasa recta

• capillary network in the medulla

• around loop of henle

• essential for flow of filtrate

ureters

• tubes from renal replica of the kidney to neck of urinary bladder

• angle prevents backflow

• trigone

  • area at neck of bladder where ureters enter and urethra leaves

• smooth muscle and loose connective tissue in walls

• lines with transitional epithelium

ureterovesicular junction

• oblique entrance of ureter into the urinary bladder

• Urine is conveyed to the urinary bladder from the renal pelvis by peristalsis and enters at the ureterovesicular junction. 

• During micturition (emptying of the urinary bladder), urine is directed through the neck of the bladder to the urethra. 

• Urine does not reenter the ureter because the ureterovesicular junction is closed by the hydrostatic pressure of urine

urinary bladder

• three layers

  • serosal epithelium

  • large layer of smooth muscle

    • detrusor muscle

  • transitional epithelium

    • lines lumen

    • cells slide apart and flatter to fewer layers as organ fills with urine

urethra

• caudal continuation of the bladder

• tube from neck of urinary bladder to outside

• longer in males

  • goes through penis

  • less prone to UTIs

• starts in transitional epithelium lining lumen

  • changes to moist stratified squamous

    • adds protection

• urine is sterile until it exits the body

formation of urine

• glomerular filtration

• ultrafiltrate

• tubular reabsorption

• tubular secretion

• PCT

• loop of henle

• DCT and CD

• secretion

• countercurrent mechanism

• fluid flow through tubules

glomerular filtration

• glomerulus

  • fenestrated capillaries

  • species between glomerular endothelial cells

• substances from leaky capillaries goes to bowman’s capsule

• most plasma leaves blood

  • dissolved nutrients, waste, electrolytes

• large molecules stay inside

  • blood cells

  • most proteins

  • osmotic effect to keep some water

ultrafiltrate

• product of filtration

• not urine yet

tubular reabsorption

• from glomerular filtrate ->

  • cells of tubules of nephron->

    • blood

tubular secretion

• from blood ->

  • cells of tubules of nephron ->

    • fluid in tubules

• rest of nephron needs to recover lost nutrients

  • most of water

  • fine tune water

  • acid/base balance

PCT

• ultrafiltrate

• glucose reabsorption by active transport

• 65% of water that enters gets sent back to eh blood via osmosis

• amino acids coupled with sodium cotransport

  • needs energy

• peritubular capillary reabsorption

  • NaCl and K

  • water will follow NaCl back into the blood

  • 90% of bicarbonate is reabsorbed back into the blood

loop of henle

• after PTC

• filtrate goes from cortex to medulla

• medulla has higher osmolarity than cortex and filtrate

• descending

  • water permeable, solute impermeable

  • water follows by osmosis via channel

• ascending

  • sodium and chloride reabsorbed by active transport

  • not followed by water

  • bottom of loop

    • most concentrated area

DCT and CD

• sodium reabsorbed by active transport

  • influences by aldosterone

• water reabsorbed by osmosis

  • influenced by antidiuretic hormone

• hydrogen ion and some drugs secreted by active transport

  • acid/base balance

secretion

• anything in the blood sent out to urine

• toxins, bicarb, H, drugs, meds

countercurrent mechanism

• flow of urine

• opposite floes

  • creates concentration gradient

  • pass material from one table to another

• medulla

  • hypertonic

    • sodium and ura in interstitial fluid

  • driving force of water going out is high, solute concentration on outside if high

• cortex

  • isotonic to hypotonic

fluid flow through tubules

• hypotonic

  • fluid in to loop of henle

• becomes hypertonic

  • bottom of loop

  • loses water on the way down and becomes concentrated

• hypotonic

  • during ascent

  • closed sodium/solutes and becomes dilute

• hypertonic

  • in collecting duct

  • loses water

• urine excreted

  • hypertonic to plasma

  • unless if excess water or osmotic effects draw water out

• countercurrent flow in descending and ascending limbs but also in vasa recta

control of urine formation 3

• blood pressure

• autoregulation

• thirst and osmolarity

blood pressure

• increase BP yields increase glomerular filtration rate

  • forces more blood into the glomerulus

  • urine forms faster

• lower BP slows urine formation

• specifically changes afferent or efferent arteriole diameter

  • dilate afferent arteriole

    • more blood flows

    • increases GFR

  • constrict efferent arteriole

    • also increase GFR

autoregulation

• juxtaglomerular apparatus JG

  • JG cells and macula densa cells of DCT

  • macula densa cells

    • chemoreceptors around DCT

    • sense increase NaCl in tubular fluid

    • slows GFR to increase sodium reabsorption

• JG cells around afferent and efferent arterioles

  • acts as baroreceptors

  • secrete renin

    • causes Angiotensin I to form AII

    • causes efferent arteriole constriction

      • decrease GFR

    • also causes Aldosterone production

      • reabsorption of sodium and water

    • decrease urine output, increases blood pressure

thirst and osmolarity

• cycle of events for the relief of hyperosmolality

• increase thirst

  • predominant factor for the correction of hyperosmolality

  • regulated by ADH

• diabetes insipidus

  • no ADH is produced

  • can’t send water to body

  • animal will keep drinking

  • increased urination

• Atrial natriuretic hormone

  • ANH

  • causes sodium to be secreted into urine at the CD

    • water follows

  • increased urine volume

    • decreases urine concentration

control of urine formation

• sympathetic nerve stimulation

• vasoconstriction of afferent arteriole

  • decreased GFR