26-1

Human Urogenital System

26-2

Urogenital System Functions

• Filtering of blood, Removal of wastes and

metabolites

• Regulation of

– blood volume and composition

– concentration of blood solutes

– pH of extracellular fluid

– blood cell synthesis

• Synthesis of Vitamin D

• Reproduction and sexual function

26-3

Urinary System Anatomy

26-4

Location and External Anatomy

of Kidneys

• Location

– Lie behind peritoneum on

posterior abdominal wall

on either side of vertebral

column

– Lumbar vertebrae and rib

cage partially protect

– Right kidney slightly lower

than left

• External Anatomy

– Renal capsule

• Surrounds each kidney

– Perirenal fat

• Engulfs renal capsule and acts as

cushioning and source of energy

– Renal fascia

• Anchors kidneys to abdominal

wall, separates from abdomen

– Hilum

• Renal artery and nerves enter and

renal vein and ureter exit kidneys

26-5

Internal Anatomy of Kidneys

• Cortex: Outer area

– Renal columns

• Medulla: Inner area

– Renal pyramids

• Calyces

– Major: Converge to form

pelvis

– Minor: Papillae extend

• Nephron: Functional unit

of kidney

– Juxtamedullary

– Cortical

26-6

The Nephron

26-7

Histology of the Nephron

26-8

Internal Anatomy of Kidneys

• Renal corpuscle

– Bowman’s or Renal capsule

• Parietal layer

• Visceral layer

– Glomerulus

• Network of capillaries goes into another capillary bed called the peritubular Capillaries

- Arterioles

– Afferent

• Blood to glomerulus

– Efferent

• Drains not into veinule but another arteriole

• Tubules

– Proximal (convoluted) tubule

– Loops of Henle

• Descending limb

• Ascending limb

– Distal (convoluted) tubules

• Collecting ducts

26-9

Renal Corpuscle

26-10

Kidney Blood Flow

26-11

Ureters and Urinary Bladder

• Ureters

– Tubes through which

urine flows from

kidneys to urinary

bladder

• Urinary bladder

– Stores urine

• Urethra

– Transports urine from

bladder to outside of

body

– Difference in length

between males and

females

– Sphincters

• Internal urinary

• External urinary

26-12

Ureters and Urinary Bladder

26-13

Urine Formation

26-14

Filtration

• Filtration

– Renal filtrate

• Plasma minus blood

cells and blood proteins

• Most (99%) reabsorbed

• Filtration membrane

– Fenestrated

endothelium, basement

membrane and pores

formed by podocytes

• Filtration pressure

– Responsible for filtrate formation

– Glomerular capillary pressure (GCP) minus capsule pressure (CP) minus colloid osmotic pressure (COP)

– Changes caused by glomerular capillary pressure

EFP = GCP – CP – COP

Where Effective filtration pressure = EFP

26-15

Filtration Pressure

26-16

Tubular Reabsorption• Reabsorption almost 90%

takes place in Proximal tubule via

– Passive transport

– Active transport

– Cotransport

• Specialization of tubule segments

• Distal tubule and collecting duct affected by hormones like ADH & Aldosterone

• Substances transported

– Active transport moves Na+ across nephron wall

– Other ions and molecules moved by cotransport

– Passive transport moves water, urea, lipid-soluble, nonpolar compounds

26-17

Reabsorption in Proximal Nephron

26-18

Reabsorption in Loop of Henle

26-19

Reabsorption in Loop of Henle

26-20

Tubular Secretion

• Substances enter proximal or distal tubules

and collecting ducts

• H+, K+ and some substances not produced in

body are secreted by countertransport

mechanisms

26-21

Secretion of Hydrogen and

Potassium

26-22

Urine Production

• In Proximal tubules

– Na+ and other substances removed

– Water follows passively

– Filtrate volume reduced

• In descending limb of loop of Henle

– Water exits passively, solute enters

– Filtrate volume reduced 15%

• In ascending limb of loop of Henle– Na+, Cl-, K+ transported out of

filtrate

– Water remains

• In distal tubules and collecting ducts– Water movement out

regulated by ADH

• If absent, water not reabsorbed and dilute urine produced

• If ADH present, water moves out, concentrated urine produced

26-23

Filtrate and Medullary

Concentration Gradient

26-24

Medullary Concentration and

Urea Cycling

26-25

Urine Concentration Mechanism

• When large volume of

water consumed

– Eliminate excess

without losing large

amounts of electrolytes

– Response is kidneys

produce large volume

of dilute urine

• When drinking water

not available

– Kidneys produce small

volume of concentrated

urine

– Removes waste and

prevents rapid

dehydration

26-26

Urine Concentrating Mechanism

26-27

Hormonal Mechanisms

• ADH

– Secreted by posterior

pituitary

– Increases water

permeability in distal

tubules and collecting ducts

• Aldosterone

– Produced in adrenal cortex

– Affects Na+ and Cl-

transport in nephron and

collecting ducts

• Renin

– Produced by kidneys,

causes production of

angiotensin II

• Atrial natriuretic

hormone

– Produced by heart when

blood pressure increases

• Inhibits ADH production

• Reduces ability of kidney

to concentrate urine

26-28

Effect of ADH on Nephron

26-29

Aldosterone Effect on Distal

Tubule

26-30

Autoregulation and

Sympathetic Stimulation

• Autoregulation

– Involves changes in

degree of constriction

in afferent arterioles

– As systemic BP

increased, afferent

arterioles constrict and

prevent increase in

renal blood flow

• Sympathetic stimulation

– Constricts small arteries

and afferent arterioles

– Decreases renal blood

flow

26-31

Clearance and Tubular Load

• Plasma clearance

– Volume of plasma

cleared of a specific

substance each minute

– Used to estimate GFR

– Used to calculate renal

plasma flow

– Used to determine

which drugs or other

substances excreted by

kidney

• Tubular load

– Total amount of

substance that passes

through filtration

membrane into

nephrons each minute

– Normally glucose is

almost completed

reabsorbed

26-32

Tubular Maximum

• Tubular maximum

– Maximum rate at

which a substance can

be actively absorbed

– Each substance has its

own tubular maximum

26-33

Urine Flow and

Micturition Reflex

• Urine flow

– Hydrostatic pressure

forces urine through

nephron

– Peristalsis moves urine

through ureters

• Micturition reflex

– Stretch of urinary

bladder stimulates

reflex causing bladder

to contract, inhibiting

urinary sphincters

– Higher brain centers

can stimulate or inhibit

reflex

26-34

Micturition Reflex

26-35

Effects of Aging on Kidneys

• Gradual decrease in size of kidney

– Decrease in kidney size leads to decrease in renal blood flow

• Decrease in number of functional nephrons

• Decrease in renin secretion and vitamin D synthesis

• Decline in ability of nephron to secrete and absorb

26-36

Kidney Dialysis