urinary phys II

anatomical components of urinary system

2 kidneys, 2 ureters, bladder, urethra, nephrons

how much nephrons do we have per kidney

a million

main kidney functinos

• responsible for maintaining stability of ECF volume, electrolyte composition, and osmolarity

• main route to eliminate toxic metabolic wastes and foreign compounds

overview of kidney functions

• Maintain H₂O balance in the body

• Maintain proper osmolarity of body fluids, thru regulating H₂O balance

• Regulate quantity and concentration of most ECF ions

• Maintain proper plasma volume

• maintain proper acid-base balance in the body

• eliminates wastes of bodily metabolism

• eliminates 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. dual function for eliminating urine and for semen

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 in cardiovascular system

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

Pathologically plasma-colloid osmotic pressure and Bowman’s capsule hydrostatic pressure can change

• 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 spontaneous changes)

  • Myogenic mechanism (muscle created)

  • Tubuloglomerular feedback (TGF)

• 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