Renal System: An Overview

Functions of Kidneys 1. Excretion of metabolic waste products, particularly of protein metabolism, such as urea, uric acid, creatinine and foreign substances such as drugs and the chemicals we ingest with our food

Functions of Kidneys ( Cont.) 2. Control of the body's fluid, electrolye & pH balance & osmolality. 3. Regulation of blood pressure by the renin- angiotensin- aldosterone system 4. Regulation of red blood cell production by secretion of the hormone erythropoietin (Endocrine function of Kidney) 5. Activation of vitamin D 6. Gluconeogenesis

Renin secretion: Role in Arterial BP Regulation Short Term- Minor role through Angiotensin Long Term- Renin activates : Renin-Angiotensin-Aldestrone System regulates Na+ and K+ balance & ECF volume which in turn Maintains blood pressure.

Endocrine Function (Cont.) Kidneys secrete: Active form of Vit. D ie 1,25 Dihydroxycholecalciferol (Calcitriol): (necessary for normal absorption of Ca+ from GIT & its deposition in bone) Erythropoietin:(Stimulates erythropoeisis )

Gross Anatomy of the Kidney

Nephron--

Cortical & Juxta-Medullary Nephrons

JGA

Urine Formation: Steps

THREE BASIC RENAL PROCESSES /Steps in Urine formation Glomerular filtration: Filtering blood into tubule Tubular reabsorption: Absorption of substances needed by body - from tubule to blood Tubular secretion: Secretion of substances to be eliminated from the blood into the tubule

Glomerulus

COMPOSITION OF GLOMERULAR FILTERATE Plasma minus proteins & cells. Main Constituents Na+ , K+ , Cl- , HCO3- , Urea, Uric acid, Creatinine, Glucose, Water

Tubular Mechanisms

Micturition Reflex Innervation of the Bladder Cystometrogram Facilitation & inhibition of Micturition Abnormalities in Bladder Function

?? Normal Features & Constituents of URINE

24 hour urinary volume Avg 1.5 litres (normal range: 0.6-2.5 L)/day. Physiologically, urinary volume varies with the intake of fluids (water, tea, coffee, alcohol, etc.), and losses of fluid (sweating, etc.). Oliguria (<500ml urinary excretion per day), anuria (<50ml) may be due to severe renal failure or more commonly due to severe dehydration, haemorrhage and shock). Polyuria Uri. Vol. ≥ 2.5 L/day

COLOR Light yellow color (varies--) due to the presence of urochrome pigment (a compound of urobilin and urobilinogen). On standing, the color deepens due to oxidation of urobilinogen to urobilin.

Osmolality (specific gravity). Normal urinary osmolality may vary from 50 to 1200 mOsm/kg (Sp. gr. 1.003 to 1.040), depends on the state of hydration of the body. Fixed urinary osmolality of 300 mOsm/kg (Sp. gr. 1.010) is an evidence of fairly advanced renal failure. It indicates failure of both urinary concentration and dilution mechanisms.

Urinary pH May vary from 4.5 to 8. Except for a short post-prandial alkaline tide, urinary pH remains acidic for most of the day. Intake of high protein diet shifts the urinary pH towards the lower side of normal range, Vegetarian food shifts it towards alkaline side. In certain congenital renal tubular disorders, there is failure of urinary acidification.

Composition of normal urine. Constituent Total excreted in 24 h urine Water 1.5 L Na+ 5g Cl– 9g K+ 2.2g PO42– 1.2 g HCO3– 0.1 g Ca2+ 0.2 g Urea 30 g Uric acid 0.8 g Creatinine 1.5 g Oxalate 20 mg

Abnormal Constituents of Urine In patients with certain renal or non-renal (metabolic) disorders, the urine may contain some abnormal constituents like: Glucose (glycosuria), Proteins, chiefly albumin (proteinuria) Bile pigments, Ketone bodies (ketonuria), Blood (haematuria), hemoglobin (hemoglobinuria) Microscopic examination: red blood cells, pus cells, or casts.

Glycosuria (glucose in the urine ) Diabetes mellitus -the most common cause Glucose appears in the urine when the blood glucose level exceeds the renal threshold for glucose (180 mg%). In some patients with congenital renal tubular defects, glucose may appear in the urine at relatively normal blood glucose level (renal glycosuria), Renal glycosuria is due to decreased renal threshold (TmG) for glucose. ( Normal Tmg = 300 to 375mg / min )

Proteinuria ( albuminuria ) Acute glomerulonephritis, Nephrotic syndrome, Pyelonephritis, Toxemia of pregnancy.

Ketonuria Ketone bodies (aceto -acetic acid, hydroxybutyric acid, and acetone) Severe diabetes mellitus Prolonged starvation Amino aciduria is seen in a variety of congenital renal tubular disorders.

Bile pigments Bilirubin appears in the urine in patients with elevated conjugated bilirubin levels, Hepatic jaundice. Post-hepatic jaundice

5. Hematuria Acute glomerulonephritis, renal stone disease malignancy of the urinary tract. Gross hematuria imparts red color to the urine. Microscopic hematuria may not change urine color

Learning Outcomes List functions of Kidney. Describe the functional unit of the kidney. State the excretory function of the kidney. State the role of kidney in maintenance of body fluid volume & concentration i.e in maintenance of stable environment of the cells / homeostasis. State the important role of kidneys in regulation of blood pressure through renin-angiotensin mechanism by secreting renin. Outline the role of kidneys in endocrine functions. List steps involved in urine formation. State normal color and composition of urine & State some of the common normal and abnormal constituents of urine.

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