1 LECTURE - 1 Dr. Zahoor

Urinary System  Consists of Urine forming organs ○ kidneys Structures that carry urine from the kidneys to the outside for elimination from the body ○ Ureters ○ Urinary bladder ○ Urethra 2

3 Urinary System

Kidney Functions Urine formation Maintain H 2 O balance in the body Maintain osmolarity of body fluids, primarily through regulating H 2 O balance Regulate the quantity and concentration of most ECF ions e.g. Na +, Cl -, K +, Ca 2+, H +, HCO 3 -, PO 4 3- Maintain plasma volume 4

Kidney Functions (cont) Help maintain acid-base balance in the body Excreting (eliminating) the end products (wastes) of bodily metabolism e.g. urea, uric acid, creatinine, bilirubin Excreting - drugs, food additive Producing erythropoietin Producing Renin Converting vitamin D into its active form 5

6 Excretion of Metabolic Waste Products Eliminating waste products of metabolism that are not longer needed by the body Urea (from protein metabolism) Uric acid (from nucleic acid metabolism) Creatinine (from muscle metabolism) Bilirubin (from hemoglobin metabolism) Metabolites of various hormones

7 Regulation of Acid-Base Balance  Lungs  Body fluid buffers  Kidneys Excrete acids (kidneys are the only means of excreting non-volatile acids, such as sulfuric acid and phosphoric acid. Regulate body fluid buffers ( e.g. Bicarbonate)

Regulation and production of hormones and enzymes  The kidney produces: Erythropoietin Renin 1,25 dihydroxycholecalciferol ( also known as calcitriol) The active form of vitamin D that is important in calcium and phosphate metabolism. 8

9 Regulation of Erythrocyte Production O 2 Delivery Kidney Erythropoietin Erythrocyte Production in Bone Marrow Hypoxia Kidneys produce Erythropoietin: a hormone that stimulates bone marrow to produce red cells.

Renin production  It is an enzyme secreted by the kidneys from granular cells of the juxtaglomerular apparatus.  It activates the renin-angiotensin system by converting angiotensinogen to angiotensin I. 10

Metabolism of Hormones Most peptide hormones are metabolized and excreted by the kidney (e.g., insulin, angiotensin II, etc.) 11

Urinary System 12

Kidneys  The kidneys are a pair of bean-shaped organs that lie at the back of abdominal cavity.  Kidneys are Retroperitoneal ( behind the peritoneum )  Each kidney is about 4-5 inches (10-12 cm) in length 13

Kidneys (cont)  Each kidney is supplied with a renal artery and a renal vein  Acts on plasma, flowing through it to produce urine  Formed urine drains into the renal pelvis, Located at medial inner core of each kidney Urine is drained into ureters, and stored temporarily in the urinary bladder before it’s emptied through the urethra to outside the body. 14

Ureters  Smooth muscle-walled duct  Exits each kidney at the medial border in close proximity to renal artery and vein  Carry urine to the urinary bladder 15

Urinary Bladder  Temporarily stores urine  Hollow, distensible, smooth muscle- walled sac  Periodically empties to the outside of the body through the urethra 16

Urethra  Conveys urine to the outside of the body  In females Urethra is straight and short about 4cm long  In males Much longer about cm and follows curving course from bladder to outside Dual function ○ Provides route for eliminating urine from bladder ○ Passageway for semen from reproductive organs 17

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APPLIED  In male, Prostate gland lies below the neck of bladder and completely encircles the urethra.  Prostate gland enlargement occurs during middle to older age and can occlude (block) the urethra, therefore, obstructing the flow of urine. 19

Nephron  Functional and structural unit of the kidney  Approximately 1 million nephrons/kidney  Each nephron has two components ○ Vascular component ○ Tubular component 20

Nephron (cont)  Arrangement of nephrons within kidney gives rise to two distinct regions ○ Outer cortex Renal cortex (granular in appearance) ○ Inner medulla Renal medulla -made up of striated triangles called renal pyramids 21

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Nephron (Vascular component) Dominant part is the glomerulus  Glomerulus is a tuft of glomerular capillaries.  large amounts of fluid & solutes are filtered from the blood. 24

Vascular Component  Renal Artery enters the kidney and forms afferent arteriole, which supplies each nephron.  Afferent arteriole delivers blood to the glomerulus.  Glomerular capillaries rejoin to form another arteriole – the efferent arteriole.  The blood that was not filtered in the glomerulus goes to efferent arteriole. 25

Vascular Component (cont)  Efferent arteriole gives second set of capillaries, the peritubular capillaries, which supply the renal tissue and are important in exchange with tubular system. (Peritubular means around the tubular system)  Peritubular capillaries rejoin to form venules, that drain in renal vein. 26

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Nephron (Tubular component) Hollow, fluid-filled tube ○ single layer of epithelial cells Components ○ Bowman’s capsule ○ Proximal convoluted tubule ○ Loop of Henle Descending limb (thin) Ascending limb (thin and thick part) ○ Distal convoluted tubule ○ Collecting duct or tubule ○ Juxtaglomerular apparatus 28

Tubular component (cont)  Bowman’s capsule – expanded double walled invagination that cups around the glomerulus to collect fluid from the glomerular capillaries.  From bowman’s capsule, filtered fluid passes into PCT. PCT lies entirely in the cortex.  From PCT, fluid passes into loop of Henle [LH]. 29

Tubular component (cont)  Loop of Henle – form U-shaped or hair pin loop, LH dips into renal medulla.  LH – descending limb of LH goes from cortex to medulla, and ascending limb of LH passes from medulla to cortex.  Ascending limb of LH, forms distal convoluted tubule (DCT), DCT lies in cortex. 30

Tubular component (cont)  DCT empties into the collecting tubule or duct.  Collecting tubule gets fluid from about 8 nephron (DCT).  Collecting tubule passes from cortex to medulla and empties into renal pelvis. 31

32 Nephron

Juxtaglomerular apparatus ○ Distal convoluted tubule, afferent and efferent arterioles are specialized to form Juxtaglomerular apparatus (JGA). ○ Cells in the DCT are called Macula densa and the cells in the afferent (mainly) and efferent arteriole which contain secretary cells are called Juxtaglomerular cells. ○ The combination of Macula Densa and JGC is called JGA. ○ JGA secretes Renin in blood. 33

Juxtaglomerular apparatus 34

Nephron  Two types of nephrons  Distinguished by location and length of their structures Juxtamedullary nephrons Cortical nephrons 35

 Cortical nephrons - About 80% nephron -have glomeruli located in the outer cortex. -have short loops of Henle that penetrate only a short distance into the medulla, -In cortical nephron, peritubular capillaries do not form vasarecta, but go around the short loop of Henle -Involved in solute reabsorption. Regional differences in nephron structure 36

Regional differences in nephron structure (cont.) 37  Juxtamedullary nephrons. -About 20 per cent of the nephrons -have glomeruli that lie in the inner layer of the renal cortex near the medulla -have long loops of Henle that dip deeply into the medulla. - have peritubular capillaries called vasarecta (straight vessels) which run with the loop of Henle - Play important role in concentration mechanism of urine

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URINE FORMATION Basic Renal Processes  Glomerular filtration  Tubular reabsorption  Tubular secretion Urine results from these three processes. 39 Excretion = Filtration – Reabsorption + Secretion

IMPORTANT  All nephron originate in the cortex.  Glomeruli of cortical nephron lie in the outer layer of cortex and glomeruli of Juxta medullary nephron lie in the inner layer of the cortex near the medulla  The kidney cannot regenerate new nephrons.  Aging causes a gradual decrease in nephron number. 40

What You Should Know  list the general functions of the kidney  Identify the different parts of nephron  Describe in sequence the tubular segments through which ultrafiltration flows after it is formed at Bowman’s capsule  Identify each structure as being located in the renal cortex or renal medulla.  Compare Cortical with Juxtamedullary nephron  Correlate the structure of nephron with functions  Describe in sequence the blood vessels through which blood flows when passing from the renal artery to the renal vein  Describe juxtamedullary apparatus and its function 41

THANK YOU 42