week 12 urinary system - collin...

1

1

BIOL. 2402Anatomy & Physiology

WEEK 12

Urinary System

Collin County Community College

2

Main functions of the kidneys are

• regulate blood volume , water content• regulate blood composition e..g. Na, Cl, K, pH

• remove waste products and toxins

Kidneys are the guardians of the internal environment

They receive 25 % of cardiac output. Thus blood isfiltered every 4 minutes !

190 liters of fluid (plasma) is filtered daily to produce 1 liter of urine

INTRODUCTION

2

3

Urinary System Organization

• The kidneys– Produce urine

• The ureters• The urinary bladder

– Stores urine• The urethra

4


• Left kidney extendsslightly more superiorlythan right

• Both kidneys andadrenal glands areretroperitoneal

• Hilus– Entry for renal

artery and renalnerves

– Exit for renal veinsand ureter

3

5


6

• Outer capsule

• Under capsule is an

• outer cortex area• inner medulla

• Medulla contains pyramids.

• They contain the functional units ofthe kidneys = nephrons

Pyramid

Kidney Anatomy

4

7

Kidney Anatomy

8

• Nephrons perform 3 basic functions that result in urineformation

• filtration of blood

• re-absorption of essential elements back into the blood

• secretion of additional elements from blood into theforming urine

• The medulla consists of 6-18 renal pyramids• The cortex is composed of roughly 1.25 million nephrons

Kidney Anatomy

5

9

Bowman’s Capsule• always located in cortex

Proximal Convoluted Tubule• always located in cortex

Loop of Henle (dips into medulla)• Descending limb• Ascending limb

Distal Convoluted Tubule• located in cortex again

Collecting Tubules and duct• dips back into medulla

Nephron Anatomy

10

• Production of filtrate• Reabsorption of organic nutrients• Reabsorption of water and ions• Secretion of waste products into tubular fluid

This function of the nephron is correlated with thelining of the tubules; they are lined with simpleepithelials.

Nephron Anatomy/Function

6

11


12

What the nephrons excrete is equals to what is filtered out ofthe blood plus what is secreted from the blood minus what isreabsorbed back into the blood.


7

13


14

There are 2 kinds of nephrons

• cortical nephrons :the loop of Henle barelyreaches into the medulla

• juxta medullary nephrons :the loop of Henle dips deepinto the medulla

15 % of nephrons are juxtamedullary nephrons ; these arevery important in water re-absorption


8

15

• A Renal artery feeds the kidney. It then shows repeated branches– Segmental artery– Interlobar artery– Arcuate artery– Interlobular artery– Afferent arterioles

• Renal venules follow similar opposing pattern ending with renalvein

Renal Blood Supply

Since the nephrons are the filters of the blood, blood needs to becarried to the nephrons.

16

Renal Blood Supply

9

17

Renal Blood Supply

18

Bowman’s capsule of eachnephron is the filtering part andlocated in the cortex area.

Blood enters the Bowman’scapsule via the afferent arteriole.

Renal Blood Supply

10

19

Afferent arteriole• enters Bowman’s capsule

Glomerulus• capillary network

within Bowman’scapsule

Efferent arteriole• leaves Bowman’s capsule

Peritubular capillaries• surround the Proximal and Distal tubules

Nephron Blood Supply

20

Vasa Recta• peritubular capillaries that surround and follow the loop of Henle in

juxta medullary nephrons

Thus we have 2 capillary beds associated with the nephrons

• First one helps to produce the filtrate inside the lumen ofthe nephron (glomerulus)

• Second one functions in re-absorption and secretion aspectof urine filtration (peritubular capillaries)


11

21


22

Diagram of nephron with associated electron microscope pictures. Notethat all along the nephron, the cell layer of the tubules is only one cell layerthick ( indicates importance of diffusion, secretion, absorption).

12

23

Controls of Resistance are located at entrance and exit of glomerulus; thisallows for a steady pressure within the glomerulus ( which is important forhomeostasis of filtering process)

Vacular Resistance in Kidneys

24

RENAL PHYSIOLOGY

• Main function of the kidneys is to regulate bloodvolume and composition

• It does so by involving a process of excretion ofwaste products such as– Urea– Creatinine– Uric acid

13

25

RENAL PHYSIOLOGY

• Filtration– Blood pressure– Water and solutes across glomerular capillaries

• Reabsorption– The removal of water and solutes from the filtrate

• Secretion– Transport of solutes from the peritubular fluid into the

tubular fluid

Three basic mechanisms are involved :

26

RENAL PHYSIOLOGY

• Filtration occurs in the Bowmans Capsule at theGlomerulus

• Filtration is very non-specific. Filtration is modified by carriermediated transport, resulting in re-absorbption and/oradditonal secretion into the filtrate.– Facilitated diffusion– Active transport– Cotransport– Countertransport

• Carrier proteins have a transport maximum (Tm)– Determines renal threshold

• Diffusion and osmosis aid in kidney function.

14

27

RENAL PHYSIOLOGY

• Most regions of the nephron perform a combination offunctions

• General functions can be identified– Filtration in the renal corpuscle– Nutrient reabsorption along the PCT– Active secretion at PCT and DCT– Loops of Henle regulate final volume and solute

concentration

28

RENAL PHYSIOLOGY

• Most regions of the nephronperform a combination offunctions

• General functions can beidentified– Filtration in the renal

corpuscle– Nutrient re-absorption

along the PCT– Active secretion at PCT

and DCT– Loops of Henle regulate

final volume and soluteconcentration

15

29

Glomerular Filtration

• Filtration process that occurs in Bowman’s Capsule

• Blood is filtered and the filtrate ends up in the tubulesystem of the nephron

What creates the filter system ?

Combination of the membrane systems of thecapillaries and Bowman’s capsule cells

RENAL PHYSIOLOGY

30

Microscopic Anatomy of Bowman’s Capsule

Special cells, called Podocytes, cover the capillaries

16

31

Podocyte in Bowman’s capsule


Pedicels of podocytes (feet extensions) create filtration slits

32


Scanning electron microscope picture of thefingerlike filtration slits of the podocytes !

Compare this with the diagram on left sideand previous slide !

This system provides a filteringmechanism roughly similar to acoffee filter, but much more refined !

It houses 3 filtering mechanisms !

17

33

Capillary endothelial cellshave many pores

• let everything through exceptblood cells and large proteins

Basement membrane orBasal Lamina

• Is negatively charged andrepels most smaller proteins

Foot process of thePodocytes

• Form additional filtration slitsthat only let small moleculesthrough

Filtration System in Bowman’s capsule


34

What are the forces involved the filter system ?

• Similar forces that are involved in capillary fluidexchange in the tissues !

• Hydrostatic pressure from the blood ( = bloodpressure )

• Hydrostatic pressure in capsule from the filtrate

• Osmotic (oncotic) pressure from the blood


18

35


• Filtration occurs as fluids move across the glomerulus• The positive filtration pressure is the glomerular hydrostatic

pressure due to blood pressure in the glomerular capillaries(GHP)– Capsular hydrostatic pressure opposes (CsHP)– Blood colloid osmotic pressure opposes (BCOP)

• Net hydrostatic pressure (NHP) = GHP – CsHP• Filtration (FP) = GHP - CsHP - BCOP = NHP – BCOP

36

Net filtration pressure is thus a modest 10 mm Hg

Net filtration pressure is determined by the 3 forces


19

37

Net Filtration pressure (NFP)

• Pressure force that drives fluid out of the blood(out of the glomerulus) and into Bowman’scapsule

• Due to the characteristics of the ‘filter’, the filtratethat passes into the tubule system of the nephronequals blood minus formed elements and minusproteins

• Since proteins do not leave the blood stream, butwater does, the efferent arteriole will have a higherconcentration of proteins and blood cells ( will bemore viscous

Bowman’s capsule

38

Glomerular Filtration Rate (GFR)

Total amount of filtrate formed per minute by the kidneys.

Depends on :• NFP

• what happens when NFP = 0 ?• what happens to NFP when BP increases ?• what happens when afferent blood osmolarity

increases ? ( use next slide )• Total filtration area ( what happens with a unilateral

nephrectomy ? )

• Filtration membrane permeability ( what happenswhen some Glomeruli get clogged up ? )

Bowman’s capsule

20

39

Blood pressure changesaffect this force

Blood proteins changesaffect this force

Bowman’s capsule

40

Regulation of GFR

Regulation of the GFR is an important homeostatic process.

• If GFR is too high, we would produce a high rate of filtrateand re-absorption of essential elements would not beefficient.

• If GFR is too low, we would not be able to secreteimportant waste products fast enough

Regulation of the GFR occurs via 3 mechanisms

• Renal Auto-regulation• Neural regulation• Renin-Angiotensin Feedback

21

41

1. Renal Auto-regulation

a. Juxta Glomerular Apparatus (JGA) feedback

• Distal Convoluted tubule makes contact with afferentand efferent arteriole

• This region is called the JGA

• Contains 2 groups of cells that are important inkidney function

• Juxta glomerular cells : are part of the afferentarteriole wall and act as mechano-receptors andendocrine cells

• Macula Densa cells : are part of the DCT andthey act as chemoreceptors/endocrine cells.

Regulation of GFR

42

Regulation of GFR

22

43

44

b. Myogenic Effect

• Increased blood pressure willcause vasoconstriction in theafferent arteriole andcounteract a possibleincrease in NFP.

Regulation of GFR

1. Renal Auto-regulation

• When blood vessels and smooth muscles are stretched they tend tocontract

• Overall effect of auto-regulation is that GFR doesnot change much when aperson experiences acuteblood pressure changes.

23

45

2. Neural Regulation

• Mostly a sympathetic effect• Produces powerful vasoconstriction of afferent arteriole

• Decreases GFR and slows production of filtrate• Important for example during blood-loss ; prevents body from

excreting more urine ( fluid)

• Changes the regional pattern of blood flow• Alters GFR

• Also Stimulates release of renin by JGA

Regulation of GFR

46

Regulation of GFR

24

47

3. Renin-Angiotensin Feedback

The following will result in a Renin release by theJuxtaglomerular cells in JGA apparatus

• Drop in Blood pressure (reduced stretch in afferent arteriole)• Reduced release of the vasoconstrictor from the Macula Densa

cells ( thus, reduced Na+ flow in the DCT)• Direct stimulation of JG cells by sympathetic stimuli

• All these stimuli release Renin, resulting in Angiotensin II production• Efferent arterioles have more Ang II receptors than Afferent

arterioles ; thus this will increase the Pressure in the glomerulus (why ? )• Ang. II also results in release of Aldosterone and ADH

( what do they do ? )

Regulation of GFR

48

Regulation of GFR

25

49

Regulation of GFR

50

Regulation of GFR

week 12 urinary system - collin...

Documents