(Renal Physiology 1)(Renal Physiology 1)

Renal Functions and Basic ConceptsRenal Functions and Basic Concepts

Dr Ahmad Ahmeda

aahmeda@ksu.edu.saCell phone: 0536313454

We drip, drip, drip, all day and all night, three to four times more by day than by night, drip from the kidneys into the silent pool of the bladder, an underground dripping into an underground lake.

(Gustav Eckstein 1817)

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Learning Objectives:Learning Objectives:• Enumerate general functions of the kidney.• Identify and describe that the nephron is the

structural and function unit of the kidney.• Explain glomerular filtration membrane & filtration

forces.• Describe mechanism of filtration & composition of

the glomerular filtrate.• Calculate the net filtration pressure using parameters

of Starling forces.

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Learning Objectives:Learning Objectives:

• Enumerate general functions of the kidney.• Identify and describe that the nephron is the

structural and function Unit of the kidney.• Explain glomerular filtration membrane & filtration

forces.• Describe mechanism of filtration & composition of

the glomerular filtrate.• Calculate the net filtration pressure using

parameters of Starling forces.

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Urinary System OrgansUrinary System Organs

• The Kidneys (The Kidneys (Shrewd Shrewd HousewifeHousewife)): They are the organs that perform the functions of the urinary system. The other components are accessory structures to eliminate the urine from the body.

• UretersUreters: transport urine from the kidneys to the bladder

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Urinary System OrgansUrinary System Organs

• Urinary bladderUrinary bladder: provides a temporary storage reservoir for urine

• UrethraUrethra: a thin-walled tube transports urine from the urinary bladder out of the body

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Urinary System OrgansUrinary System Organs

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Kidney FunctionsKidney Functions

1)1) FilterFilter 200 liters of blood daily, allowing toxins, metabolic wastes, and excess ions to leave the body in urine,

2)2) RegulationRegulation of water and electrolyte balance: Maintain the proper balance between water and salts, and acids and bases,

3)3) ExcretionExcretion of bioactive substances (hormones and many foreign substances, especially drugs) that affects body function,

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Kidney FunctionsKidney Functions

4) Regulation of arterial blood pressureblood pressure: by production of renin (vasoactive substances) and regulate volume and chemical makeup of the blood,

5) Regulation of red blood cells productionblood cells production: erythropoietin hormone to stimulate RBC production by bone marrow,

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Kidney FunctionsKidney Functions

6) Regulation of vitamin D productionvitamin D production : 25, cholecalciferol will be activated in the kidneys to 1,25 dihydrocholecalciferol D3,

7)7) GluconeogenesisGluconeogenesis: during prolonged fasting glucose can be synthesized in the liver and kidneys.

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Kidney Location and External Kidney Location and External AnatomyAnatomy

• The bean-shaped kidneys lie in a retroperitonealretroperitoneal position in the superior lumbar region and extend from the twelfth thoracic to the third lumbar vertebrae

• The right kidney is lower thanlower than the left kidney.

• The lateral surface is convex and the medial surface is concave, with a vertical cleft called the renal hilusrenal hilus leading to the renal sinus

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• Ureters, renal blood vessels, lymphatics, and nerves enter and exit at the hilus

• Layers of Tissue Supporting the Kidney

Renal capsule Renal capsule – fibrous capsule that prevents kidney infection Adipose capsule Adipose capsule – fatty mass that cushions the kidney and

helps attach it to the body wall Renal fascia Renal fascia – outer layer of dense fibrous connective tissue

that anchors the kidney

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Kidney Location and External Kidney Location and External AnatomyAnatomy

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Internal AnatomyInternal Anatomy

• A frontal section shows three distinct regions– CortexCortex: – the light

colored, granular superficial region

– MedullaMedulla: – exhibits cone-shaped medullary (renal) pyramids

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Internal AnatomyInternal Anatomy

Pyramids are made up of parallel bundles of urine-collecting tubules

Renal columns are inward extensions of cortical tissue that separate the pyramids

The medullary pyramid and its surrounding capsule constitute a lobe

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Internal AnatomyInternal Anatomy

• Renal pelvis Renal pelvis – flat, funnel-shaped tube lateral to the hilus within the renal sinus

• Major calyces Major calyces – large branches of the renal pelvis– Collect urine draining from papillae – Empty urine into the pelvis

• Urine flows through the pelvis and ureters to the bladder

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The NephronThe Nephron

• Nephrons are the structural and functional units that form urine, consisting of:– GlomerulusGlomerulus – a tuft of capillaries

associated with a renal tubule

– Glomerular (BowmanGlomerular (Bowman’’s) s) capsule capsule – blind, cup-shaped end of a renal tubule that completely surrounds the glomerulus

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The NephronThe Nephron

– Renal corpuscleRenal corpuscle – the glomerulus and its Bowman’s capsule

– Glomerular endotheliumGlomerular endothelium – fenestrated epithelium that allows solute-rich, virtually protein-free filtrate to pass from the blood into the glomerular capsule

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Anatomy of the Glomerular CapsuleAnatomy of the Glomerular Capsule

• The external parietal layer is a structural layer

• The visceral layer consists of modified, branching epithelial podocytespodocytes

• Extensions of the octopus-like podocytes terminate in foot processes

• Filtration slits – openings between the foot processes that allow filtrate to pass into the capsular space

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Renal TubuleRenal Tubule

• Proximal convoluted tubule Proximal convoluted tubule (PCT) – composed of cuboidal cells with numerous microvilli and mitochondria– Reabsorbs water and solutes from filtrate and

secretes substances into it

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Renal TubuleRenal Tubule

• Loop of Henle Loop of Henle – a hairpin-shaped loop of the renal tubule– Proximal part is similar to the proximal convoluted

tubule– Proximal part is followed by the thin segment

(simple squamous cells) and the thick segment (cuboidal to columnar cells)

• Distal convoluted tubule Distal convoluted tubule (DCT) – cuboidal cells without microvilli that function more in secretion than reabsorption

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Connecting TubulesConnecting Tubules

• The distal portion of the distal convoluted tubule nearer to the collecting ducts

• Two important cell types are found here– Intercalated cellsIntercalated cells

• Cuboidal cells with microvilli • Function in maintaining the acid-base balance of the

body

– Principal cellsPrincipal cells• Cuboidal cells without microvilli• Help maintain the body’s water and salt balance

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Types of NephronsTypes of Nephrons

• Cortical nephrons Cortical nephrons – 85% of nephrons; located in the cortex

• Juxtamedullary nephrons:Juxtamedullary nephrons:– Are located at the cortex-medulla junction– Have loops of Henle that deeply invade the

medulla – Have extensive thin segments– Are involved in the production of concentrated

urine

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Juxtaglomerular Apparatus (JGA)Juxtaglomerular Apparatus (JGA)

• Where the distal tubule lies against the afferent (sometimes efferent) arteriole

• Arteriole walls have juxtaglomerular (JG) cells– Enlarged, smooth muscle cells – Have secretory granules containing renin– Act as mechanoreceptors

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Juxtaglomerular Apparatus (JGA)Juxtaglomerular Apparatus (JGA)

• Macula densaMacula densa– Tall, closely packed distal tubule cells – Lie adjacent to JG cells – Function as chemoreceptors or osmoreceptors– The cells of the macula densa are sensitive to the

ionic content and water volume of the fluid in the tubule

– produce molecular signals that promote renin secretion by the juxtaglomerular cells

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Juxtaglomerular Apparatus (JGA)Juxtaglomerular Apparatus (JGA)

• Mesanglial cellsMesanglial cells – Have phagocytic and contractile properties– Influence capillary filtration– Intraglomerular mesangial cells provide

structural support and regulate blood flow of the glomerular capillaries by their contractile activity

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Filtration MembraneFiltration Membrane

• Filter that lies between the blood and the interior of the glomerular capsule

• It is composed of three layers– Fenestrated endothelium of the glomerular

capillaries (Pores are 50-100 nm in diameter)– Visceral membrane of the glomerular capsule

(podocytes)– Basement membrane composed of fused basal

laminae of the other layers.

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Filtration MembraneFiltration Membrane

• Glomerular filtration membrane is highly permeable to water and small molecules (less than 10.000 MW)

• Large molecules (more than 70.000 MW especially proteins are not filtered due to their large size and negative electrical charge because their passage is repulsed by negatively charged glycoproteins present on endothelial pores, basement membrane and podocytes.

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Composition of Glomerular Composition of Glomerular FiltrationFiltration

• Glomerular Filtrate has almost the same composition as that of plasma, except that it has no significant amount of proteins (it has about 0.003%)

• It is less than 1/2000 protein as compared with plasma.

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Innervation of the kidneyInnervation of the kidney

• Sympathetic nerves supply renal blood vessels, regulate blood flow, filtration, water reabsorption, rennin secretion.

• ↑ sympathetic = constriction, ↓ blood flow

• There is no parasympathetic innervation

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