Kidney Anatomy Physiology

L105: RIC Core Training, Level1Kidney Anatomy & Physiology

31/01/2014 © Year, Legal owner2 L105 RIC Core Training: Kidney Anatomy & Physiology

Content

• GENERAL ANATOMY

• KIDNEY FUNCTION

• THE NEPHRON

• URINE FORMATION

• GLOMERULAR FILTRATION

• CLEARANCE


Guiding Questions

• What constitutes the Urinary System ?

• How much blood flows through the kidneys in 24 hours ?

• What are the excretory functions of the kidney ?

• What are secretory functions of the kidney ?

• What are the two major components of the Nephron ?

• In what part of the kidney is the urine formed ?

• What is the meaning of GFR ?

• How is Estimated GFR and Creatinine Clearance measured ?


The Urinary System

The kidneys are principal organs of the urinary system

Organs of Urinary System

The Kidneys, functions,coverings,

Size, weight

Location

Blood Supply

Urine production & flow

Adrenal Glands


Kidney Anatomy


How many ml of blood flows through the

kidney in one minute ?

What percent of total cardiac output

(blood pumped by the heart) does this

volume represent ?


Anatomy of the Kidney

Approximately 1,200 ml of blood or 25 % ofCardiac Output flows through the kidney in one minute

Renal arteryand vein

Fibrous capsule Cortex

Pyramid (medulla)

Ureter

Pelvis

Deep inside the cortex and

the medulla regions are long

hairpin-like structures called

nephrons, these are the

functional urine producing

unit of the kidney


Kidney Function

Function is both excretory and secretory

Impaired renal function has adverse effects on:

• blood chemistry

• blood pressure

• fluid balance

• nutrient intake

• general state of health.


Kidneys Excretory Functions

Needed to maintain Homeostasis in the body

Regulate electrolyte levelsRemove waste products

Remove excess fluid Regulate acid/base balance

The excretion product of the kidney is urine

Urea & Creatinine


Kidneys Secretory function

Hormonal function of the kidneys

Renin: regulate blood pressure

EPO: regulate red blood cell production

Vitamin D: regulate calcium uptake

Secretion of three different hormones


The Nephron is the urine producing part

of the kidney. What are the approximate

number of Nephrons in each kidney ?


The Nephron

The urine producing part of the kidney

Distal tubule

Collecting ductLoopof Henle

Peritubularcapillaries

Proximal tubule

Bowman’scapsule

Glomerulus Afferent arteriole(wider)

Efferent arteriole(narrow)

There are one million Nephrons in each kidney

The efferent arteriole, whichis narrower than the afferentarteriole, creating ahydrostatic pressure inglomerulus


The Nephron


Urine Formation

In the Nephron, divided into a three step processes

Tubular secretion

Glomerular filtration

Tubular reabsorption


How many liter of primary urine

(glomerular filtrate) does the kidneys

produce each day ?

What percent of this volume

constitute the “final” urine ?


Glomerular Filtration

Primary urine is formed

Step 1

Glomerular filtration (unspecific) :

filtration of the blood when a large

amount of primary urine is formed,

containing water and low molecular

weight substances (resembles plasma

without proteins)

Approximately 180 liter of glomerular

filtrate is produced every 24 hours

Filtration is taking place due to the hydrostatic pressure in the glomerulus


Tubular Reabsorption

Most of primary urine (99%) is reabsorbed

Step 2

Tubular reabsorption:

most substances needed by the body that

were filtered into the primary urine (99%)

are selectively reabsorbed to the blood

• Creatinine, which a waste product from muscle catabolism,is not reabsorbed at all

• Glucose, amino acids, vitamins and bicarbonate (substances that are needed inthe body) are normally completely reabsorbed into the blood

• Electrolytes are absorbed in varying amounts to regulate the electrolyte balance inorder to maintain homeostasis


Tubular Secretion

Active transport from blood to urine

Step 3

Tubular secretion:

some specific substances, often of high

molecular weight, are selectively

transported from the blood to the urine

Hydrogen ions (H+, acid) are secreted from blood

into the tubuli and in the very same process

bicarbonate is regenerated (maintenance of acid-base balance)

The final composition of the urine is determined by hormones;

anti-diuretic hormone (ADH) and aldosteron.


A constant GFR is maintainedthrough “autoregulation” but thisprocess will only go so far.

At what mean arterial pressure isautoregulation impaired ?


Glomerular Filtration Rate (GFR)

Volume of plasma cleared of a given substance per minuteBest estimate of renal function

1,200 ml/min

120 ml/min

1,080 ml/min

A constant GFR is maintained through a process called autoregulation


Autoregulation

Selective vasoconstriction or dilatation to maintain organ bloodflow at a constant rate, despite changes in perfusion pressure

Ability to maintain renal perfusion pressure through autoregulation islimited; only until MAP reaches approximately 60 - 80 mmHg.

MAP is dependent on a number of important systemic factors

• Blood Volume (dehydration, hemorrhage)

• Blood flow; reduced Cardiac output (congestive heart failure, infarct)

• Albumin level in blood (disease of liver and starvation) affects intravascular volume

• Hypotension from severe vasodilatation (anaphylactic shock, sepsis)


What is Creatinine and why is it usedto measure kidney function ?


Creatinine Clearance (K) and GFR

A screening to estimate kidney function

and a 24 hour urine collection on which Creatinine is measured

Blood measurement of Creatinine

• the volume of blood from which a substance is completely clearedby the kidneys per unit time (ml/min)

• calculated based on level of creatinine in blood and urine

• a commonly used laboratory test - easily performed

• gives a close estimate of the actual GFR

Creatinine a breakdown product from the

muscle, is a substance freely filtered in the

glomeruli but neither absorbed nor secreted -

it therefore has a the clearance (ml/min) that

equals the GFR (ml/min) of the kidneys.

Well functioning kidneys have a Creatinine

Clearance of approximately 120 ml /min.


KEYPOINTSApproximately 1200 ml of blood or 25 % of Cardiac Output flows through

the kidneys in one minute

The excretory function of the kidneys is needed to maintain homeostasis in

the body, it is essential for the regulation of the water and electrolyte

(dissolved salts) balance and for the body to maintain normal acid-base

balance

The secretory function or the hormonal function of the kidneys includes

the secretion of three different hormones; Renin, Erythropoietin & Vit.D

The Nephron is the urine producing part of the kidney, there are about

one million in each kidney


KEYPOINTSThe formation of urine in the kidney is divided in three different steps

Approximately 180 liter of glomerular filtrate is produced every 24 hours,

as much as 99% is reabsorbed

GFR is the volume of plasma cleared by the kidneys of a given substanceper minute

Autoregulation is the ability of an organ to maintain a constant blood flowdespite changes in perfusion pressure

Creatinine is freely filtered by glomeruli, it has a clearance that equals GFR

Well functioning kidneys have a Creatinine clearance and therefore GFR ofapproximately 120 ml / min

Adapted in part from Gambro Basics

Further references and reading:

http://www.uhmc.sunysb.eduRENAL BLOOD FLOW-GLOMERULAR FILTRATIONRATEGeorge N. Coritsidis, MD

http://en.wikipedia.org/wiki/Glomerular_filtration_rate

http://www.labtestsonline.org/understanding/analytes/gfr/sample.html

Kidney Anatomy Physiology

Documents

Transcript of Kidney Anatomy Physiology