urinary phys II

how much nephrons do we have per kidney

a million

main kidney functions

• maintain stability of ECF volume, electrolyte composition, and osmolarity

• eliminate toxic wastes and foreign compounds

overview of kidney functions

• Maintain H₂O balance

• Maintains proper osmolarity of body fluids

• Regulate quantity and concentration of most ECF ions

• Maintain proper plasma volume

• maintain proper acid-base balance

• removes wastes of bodily metabolism

• removes many foreign compounds

• produces erythropoietin

• produces renin

• converts vitamin D into its active form

what are the kidneys

• pair of bean-shaped organs that lie in back of abdominal cavity

Each kidney is supplied with

a renal artery and a renal vein

what acts on plasma flowing through it to produce urine

nephrons in kidneys

formed urine drains into the

renal pelvis

where is renal pelvis located

at medial inner core of each kidney

ureters (muscle, exits, carries, and forms what)

• smooth muscle walled duct

• exits each kidney at the medial border close to renal artery and vein

• carry urine to urinary bladder

• formed by confluence of major calyxes

urinary bladder (stores, muscle, empties, includes)

• stores urine

• hollow, distensible, smooth muscle walled sac

• empties to outside of body thru urethra

• includes internal and external sphincter

urethra (muscle, conveys)

• smooth muscle

• conveys urine to outside of body

urethra in females

straight and short

urethra in males

much longer and follows curving course from bladder to outside

functional unit of kidney

nephron

smallest unit that can perform all functions of kidney

nephron

2 components of nephron

vascular component and tubular component

outer region of nephrons

renal cortex (looks granular)

inner region of nephron

• renal medulla

• made up of striated triangles called renal pyramids

dominant part of vascular component

glomerulus

what is the glomerulus

ball like twine of capillaries

what is filtered through glomerulus as blood passes through it

water and solutes

describe the basic renal process

• Filtered fluid passes thru nephron’s tubular component

• From renal artery, blood passes thru afferent arterioles which deliver blood to glomerulus

• Efferent arteriole transports blood from glomerulus

• Efferent arteriole breaks down into peritubular capillaries which surround tubular part of nephron

• Peritubular capillaries join into venules which transport blood into the renal vein

tubular component (nephron itself)

• hollow, fluid filled formed by a single layer of epithelial cells

components of nephron

• Bowman’s capsule

• Proximal tubule

• Loop of Henle

  • Descending limb

  • Ascending limb

• Juxtaglomerular apparatus

• Distal tubule

• Collecting duct or tubule

two types of nephrons

they are distinguished by location and length of structures

• juxtamedullary nephrons

• cortical nephrons

basic renal processes (urine results from these)

1. Glomerular filtration

2. Tubular reabsorption

3. Tubular secretion

glomerular filtration

• Fluid filtered from the glomerulus into Bowman’s capsule pass through three layers of the glomerular membrane

3 layers of glomerular membrane

• Glomerular capillary wall

  • Single layer of endothelial cells

  • More permeable to water and solutes than capillaries elsewhere in the body

• Basement membrane

  • Acellular gelatinous layer

  • Composed of collagen and glycoproteins

• Inner layer of Bowman’s capsule

  • Consists of podocytes that encircle the glomerulus tuft (ball of twine)

3 physical forces involved in glomerular filtration

• Glomerular capillary blood pressure

• Plasma-colloid osmotic pressure

• Bowman’s capsule hydrostatic pressure

Glomerular Capillary Blood Pressure + depends on

• Fluid pressure exerted by blood within glomerular capillaries

• Major force producing glomerular filtration

• 55 mm Hg

• Depends on

  • contraction of heart

  • resistance to blood flow offered by afferent and efferent arterioles

plasma colloid osmotic pressure

measures the pressure exerted by proteins in blood plasma, ensuring proper fluid pass in and out of capillaries at proper rate

Bowman’s Capsule Hydrostatic Pressure

• pressure exerted by fluid in first part of tubule

• push fluid out of bowman’s capsule

• opposes filtration

• 15 mm Hg, pushes out 55 mm Hg

glomerular filtration rate

Net filtration pressure =  glomerular capillary blood pressure – (plasma-colloid osmotic pressure + Bowman’s capsule hydrostatic pressure)

Glomerular filtration rate (GFR) depends on

• Net filtration pressure

• How much glomerular surface area is available for penetration

• How permeable the glomerular membrane is

Unregulated influences on the GFR

• plasma colloid osmotic pressure

  • Severely burned patient ↑ GFR

  • Dehydrating diarrhea ↓ GFR

• bowman’s capsule hydrostatic pressure

  • kidney stones/enlarged prostate ↓ filtration and ↑ capsular hydrostatic pressure

controlled adjustments in GFR

Glomerular capillary blood pressure can be controlled to adjust GFR to suit the body’s needs

two major control mechanisms in GFR

• Autoregulation (aimed at preventing sudden changes)

  • Myogenic mechanism (muscle created)

  • Tubuloglomerular feedback (TGF): enlarged prostate, kidney stones

• Extrinsic sympathetic control (aimed at long-term regulation of arterial blood pressure)

  • Mediated by sympathetic nervous system input to afferent arterioles

  • Baroreceptor reflex

The kidneys receive __ to __ percent of the cardiac output

20 to 25

total blood flow through the kidneys average ___ per minute.

1,140 ml

The kidneys need to receive 1,140 ml flow to

monitor and control the ECF

tubular reabsorption

• transfer of substances from tubular lumen into peritubular capillaries

• Highly selective and variable process

• Involves transepithelial transport

transepithelial transport tubular reabsorption - crossing 5 barriers

• leave tubular fluid, cross luminal membrane of tubular cell

• pass through cytosol from side of tubular cell to the other

• cross basolateral membrane of the tubular cell, enter interstitial fluid

• diffuse through interstitial fluid

• penetrate capillary wall, enter blood plasma

passive reabsorption

• No energy is required for the substance’s net movement

• Occurs down electrochemical or osmotic gradients

active reabsorption

• Occurs if any one of the steps in transepithelial transport of a substance requires energy

• Movement occurs against electrochemical gradient

sodium reabsorption

• sodium potassium pump in basolateral membrane is essential

• sodium is not reabsorbed in the descending limb

• Water follows reabsorbed sodium by osmosis - affects blood volume and blood pressure

Of total energy spent by kidneys, __ percent is used for Na⁺ transport

80

Proximal tubule: % of sodium reabsorbed and role

67% - reabsorbs glucose, amino acids, H₂O, Cl^-, and urea

ascending limb of the loop of Henle: % of sodium reabsorbed and role

25%. kidneys’ ability to produce urine of varying concentrations

Distal and collecting tubules: % of sodium reabsorbed and role

8%. subject to hormonal control; regulates ECF volume

• last effort to balance and regulate fluid

Renin-angiotensin-aldosterone system (RAAS)

• hormonal system involved in regulating Na⁺

• Aldosterone increases Na+ reabsorption by the distal Convoluted tubules

Atrial Natriuretic Peptide (ANP) are released by…

atrial myocytes (cells in the atria of the heart) in response of raised blood pressure, water, sodium, and adipose loads to return to normal levels

ANP

• main function: inhibit Na⁺ reabsorption in distal tubule

• Secreted by atria: stretches sodium retention, expands ECF volume, increase in arterial pressure

• promotes natriuretic, diuretic, and hypotensive effects to correct original stimulus that brought about release of ANP

glucose and amino acids are reabsorbed by..

sodium-dependent, secondary active transport

Reabsorption

• The proximal tubule has separate carrier systems for reabsorbing electrolytes other than sodium.

• Water reabsorption increases urea concentration in the tubule = creates gradient —> puts urea into the interstitial fluid.

• Waste products not needed aren't reabsorbed.

tubular secretion

• Transfer of substances from peritubular capillaries into the tubular lumen

• Kidney tubules can add some substances to the substances already filtered

• reverse of transepithelial transport

tubular secretion transepithelial transport

• substances from the peritubular capillaries enter the interstitial fluid.

• substances then cross the basolateral membrane into the epithelial cells of the renal tubule.

• move across the apical membrane from the epithelial cells into the tubular lumen.

most important substances secreted by tubules (3)

Hydrogen

• regulate acid-base balance

• Secreted in proximal, distal, and collecting tubules

Potassium

• Maintains plasma K+ levels for normal muscle and nerve function.

• Secreted in distal and collecting tubules under control of aldosterone

Organic ions

• more efficient elimination of foreign organic compounds from the body

• Secreted only in the proximal tubule

Plasma clearance

• How much material is being cleaned in the kidney per minute

• inulin

inulin

• carbohydrate from Jerusalem artichokes.

• not absorbed or secreted.

• injection helps measure GFR clinically.

• determines plasma clearance

urine excretion ECF

• too much water in ECF creates hypotonic ECF

• water deficit creates hypertonic ECF

urine excretion osmotic gradient

• exists between the tubular lumen and the surrounding interstitial fluid

• basically water and sodium playing bakck and forth so there is a balance

vasopressin (antidiuretic hormone)

• Peptide hormone that regulates reabsorption in kidney tubules by affecting tissue permeability.

• Plays a key role in homeostasis and regulates water, glucose, and salt levels in the blood.

• Prevents dehydration by causing the kidneys to retain water.

• blood test to test ADH level

where is vasopressin produced and stored in

hypothalamus and posterior pituitary —> release of substance signals distal tubule and collecting duct of reabsorption of water

during water deficit, secretion of vasopressin

increases

during excess of water, secretion of vasopressin

decreases

causes of renal failure

• Infectious organisms

• Toxic agents

• Inappropriate immune responses

• Obstruction of urine flow

• An insufficient renal blood supply

Stimulated stretch receptors signal smooth muscle in bladder wall by __ neurons

parasympathetic

micturition reflex

relaxation of 2 sphincters and detrusor muscle to relax