Edapt WK 4 Urinary System PDF

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INTRODUCTION TO GENERAL FUNCTIONS OF THE URINARY SYSTEM In this topic you will learn about the general function of the human urinary system: all major organs that are responsible for the functioning of this important system. Also, you will learn how human urinary system is integrated into the physiology other visceral systems. It is surprising to learn how many vital functions are integrated into homeostatic regulatory pathways.

GENERAL ANATOMY AND PHYSIOLOGY OF THE HUMAN URINARY SYSTEM Human urinary system consists of the following structures: 1. Kidneys: Central organs of the urinary system whose primary function is to filter blood. Arterial blood entering the kidneys is leaving as venous blood and allows for the removal of metabolic wastes and proper balance of electrolytes. 2. Ureters: Muscular tubes that function in conducting urine from the kidneys into the bladder. 3. Bladder: Collection chamber for urine, made of smooth muscle that will ultimately trigger micturition reflex (urination). 4. Urethra : Passageway through which the urine is expelled from the body. The male and female urethra vary in their general structure, length, and location. The male urethra is utilized by both the urinary and reproductive systems, as it conducts both urine and semen out of the body. The main functions of the urinary system include: 1. Excretion of nitrogenous wastes - human urinary system excretes metabolites; toxic byproducts of the body’s metabolism: urea and ammonia from the deamination of amino acids; creatinine from the breakdown of creatine phosphate; uric acid from the catabolism of nucleic acids; urobilin from the breakdown of hemoglobin.

The Major Nitrogenous Wastes a. Ammonia and uric acids are byproducts of protein synthesis that are extremely toxic compounds that would poison many organs and tissues if released into the bloodstream. It is for this reason that the liver detoxifies ammonia into less toxic urea, which is later filtered by the kidneys and excreted from the body. Creatinine is also a toxic byproduct of muscle metabolism that must be removed from the bloodstream by the kidneys. b. Previously you have learned of the importance of Na+, K+ , Cl− ions in the context of neuromuscular physiology, Ca2+ and HPO4 2- ions in the context of bone tissue development, and Ca2+ in the context of muscular contractions, neural synapses, and blood clotting. It is the urinary system that regulates the physiological balance of these essential ions (charged particles) in the human body. 2. Maintenance of blood osmolarity - osmotic concentration of various ions that preserves an equilibrium of volume of bodily fluids and cytoplasmic content of the body cells.

The Urinary System: (a) Anterior view. (b) Posterior view. Organs of the urinary system are indicated in boldface.

Pathways of Amino Acid Metabolism in Relation to Glycolysis and the Citric Acid Cycle. View this video on Kidney Anatomy and Urine Production to learn more.

GENERAL ANATOMY AND PHYSIOLOGY OF THE HUMAN URINARY SYSTEM, CONTINUED The main functions of the urinary system include (continued): 3. Regulation of blood pH: The maintenance of normal blood pH is essential for proper O2 and CO2 exchange during internal and external respiration. In fact, you have previously learned how the respiratory system regulates blood pH when it transiently deviates from homeostasis. The urinary system, in turn, regulates blood pH on a long-term scale. 4. Regulation of systemic blood pressure through regulation of blood volume: The kidneys work in conjunction with the cardiovascular center of the medulla oblongata, regulate mean arterial blood pressure by hormonal action, and regulate filtration rate (the rate at which kidneys filter the blood). 5. Production of hormones: Kidneys produce two essential regulatory hormones:  Calcitriol – Kidneys are at the final stage of the production of the hormone Calcitriol. This is the result of the activation of vitamin D, which began in the skin, and continues in the liver and skeletal muscle. Calcitriol functions in increasing calcium absorption by the small intestine, stimulates reabsorption of bone by osteoclasts, and promotes reabsorption of calcium by the kidneys.  Erythropoietin – The kidneys play a role in erythropoiesis by secreting the hormone erythropoietin, in response to hypoxic conditions. Erythropoietin targets the red bone marrow to produce red blood cells. 6. Regulation of blood glucose level: The kidneys carry out gluconeogenesis by converting noncarbohydrate substrates into glucose, thereby helping maintain blood glucose levels.

Calcitriol (Vitamin D) Synthesis and Action

Correction of Hypoxemia by a Negative Feedback Loop

INTRODUCTION TO URINARY SYSTEM ANATOMY In this concept we will discuss the both the gross and microscopic anatomical structures of the kidneys. While learning about the anatomy of the kidneys, we will also follow the path of filtrate as it moves through the nephron.

GROSS AND MICROSCOPIC ANATOMY OF THE KIDNEY Kidneys are reddish, kidney bean–shaped retroperitoneal organs located just above the waist. The kidneys are encapsulated by three distinct layers of tissue. The three layers from deepest to most superficial include: 1. Renal capsule – deep layer, continuous with epithelium of the ureter and acts as a barrier against trauma, while maintaining the shape of the kidney. 2. Adipose capsule – a mass of fatty tissue that further protects the kidney from trauma and holds it in place 3. Renal fascia – superficial layer, a thin layer of connective tissue that anchors the kidney to surrounding structures and the abdominal wall Kidneys also have a Renal hilum; an indentation in the medial aspect of the kidney, which provides room for the ureter, blood vessels, lymphatic vessels, and nerves. Internal anatomy of the kidney includes:   

Renal cortex – superficial portion of the kidney  Outer layer = featuring cortical nephrons and juxtamedullary nephrons Renal medulla – inner region of the kidney  Consists of several triangular renal pyramids with the base of each pyramid (triangle) faces of cortex of the kidney.  Between each renal pyramid lies a band of tissue known as the renal column. Renal lobe – anatomical regions including  renal pyramid  overlying cortex area  ½ of each adjacent renal column

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The kidneys are large, bean-shaped organs located in a retroperitoneal position on the posterior abdominal wall on either side of the vertebral column. The hilum is located along the concave medial border where blood vessels and nerves enter and exit the kidney. It also serves as the point of exit for the renal pelvis, which transports urine to the ureter. The hilum is continuous with an expanded area within the kidney, known as the renal sinus. The kidney tissue is divided into an outer renal cortex, and an inner renal medulla. Extensions of the cortex called renal columns, project into the medulla between renal pyramids. The base of each pyramid is located at the junction of the cortex and medulla. The cortical medullary junction. The apex or tip of each pyramid, known as the renal papilla, projects into a funnel shaped structure in the renal sinus called a minor Catholics. Several minor catalyses merge to form larger structures called major catalyses, with each kidney containing two to three major calyces. Major catalyses merged to form a single funnel shaped renal pelvis. A human kidney is divided into eight to 15 lobes, each consisting of a renal pyramid with a renal column on each side. And the cortex external to the pyramid base. Blood is carried to each kidney for filtration through the renal artery. The renal artery branches in the renal scientists to form segmental arteries, which branch again to form interlobar arteries. Interlobar arteries pass through the renal columns to the cortical medullary junction, where they branch to form arcuate arteries. Arcuate arteries project along the base of renal pyramids to give off interlobular arteries that enter the renal cortex. Finally, each interlobular artery branches to form a series of efferent arterioles, each of which feeds a capillary network called the glomerulus. The glomerulus forms the vascular core of the renal core puzzle and is the initial filtering component of the kidney. The renal core puzzle and its associated Doug's form the functional filtration unit of the kidney, the nephron, the efferent arteriole that leaves each glomerulus enters a second capillary network. For nephrons in the renal cortex. A peritubular capillary network forms around the proximal and distal convoluted tubules. From this capillary network, blood leaves the cortex by flowing into interlobular veins, which drain into arcuate and interlobar veins, and finally the renal vein. Conversely, the efferent arterioles associated with nephrons at the cortical medullary junction enter a second capillary network along the nephron loop or loop of Henley. These capillaries are known as the vasa recta. From the vasa recta, blood flow sequentially into interlobular, arcuate and interlobar veins. And finally, the renal vein.

INTERNAL ANATOMY OF THE KIDNEYS Nephron – microscopic functional units of the kidneys that carry out filtration and reabsorption of the incoming blood plasma. Subdivided into the following regions: A. Renal corpuscle – site of filtration of blood plasma 1. Glomerulus – capillary network (knot of capillaries) formed by the afferent arteriole which delivers blood to the nephron, and the efferent arteriole which carries unfiltered blood away from the nephron (approximately 90%). Blood plasma percolates through the filtration membrane of glomerulus and enters the capsular space. 2. Glomerular (Bowman’s) capsule – double-walled cup surrounding glomerulus capturing the filtrate coming out of the glomerulus. 3. Bowman’s space (Capsular space) – exists within the capsule. Protein-free fluid (filtrate) travels from the glomerulus, into the capsular space before entering the Proximal Convoluted Tubule (PCT). 4. Filtration membrane of Bowman’s capsule:  Permits filtration of water and small solutes  Prevents filtration of most plasma proteins, blood cells and platelets  Blood in the glomerulus is separated from the fluid in Bowman’s space by a filtration barrier consisting of three layers:  Single-celled capillary endothelium with fenestrations  Basal Lamina - Noncellular layer of basement membrane

 Membrane of podocytes - single celled epithelial lining of Bowman’s capsule  Fluid filtered from glomerular capillaries enters capsular (Bowman’s) space B. Renal tubule – the passageway where filtrate is converted to urine 1. Proximal convoluted tubule (PCT) – cells that have microvilli which increase surface area for absorption. Hence the PCT, is where most reabsorption occurs. 2. Descending and ascending limbs of loop of Henle (nephron loop) - major site for reabsorption and regulation of urine concentration. Location and size of this loop differentiates nephrons into:  Cortical nephrons – with glomeruli near the periphery of the renal cortex, their superficial loops of Henle are located in the cortex of the kidney, producing highly dilute urine. Constitute approximately 85% of al nephrons  Juxtamedullary nephrons – with glomeruli located at the junction of the renal cortex and the medulla. They have a much longer loop of Henle, which is found deep into the medulla. Constitute approximately 15% of all nephrons. 3. Distal convoluted tubule (DCT) – major site of “fine tuning” the volume and overall concentration of the urine, sensitive to hormonal regulation.

Nephron Structure: In this diagrammatic representation, the nephron has been straightened out, with each component color-coded for clarity. Note that neither the collecting tubule nor the collecting duct is part of a nephron.

Conceptual Blood Supply of the Kidney INTERNAL ANATOMY OF THE KIDNEYS (CONTINUED) Urine is formed as nephrons drain the filtrate into the collecting ducts that are clustered at the tip of each renal pyramid within the renal medulla. Urine then drains into:     

Minor calyces (8-18) Major calyces (2-3) Renal pelvis Ureter Urinary bladder

Juxtaglomerular apparatus Regulates systemic blood pressure, Glomerular Filtration Rate (GFR) - the rate at which the glomerulus filters incoming blood plasma. Consists of the following regions: 

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Macula densa – patch of cells in the wall of the ascending limb as it becomes the DCT. Regulates Glomerular Filtration Rate. Normally releases the vasodilator, Nitrous Oxide (NO). As macula densa cells detect higher levels of sodium and chloride ions, NO is inhibited and Glomerular Filtration Rate is reduced Juxtaglomerular cells – secretory cells (secrete renin) of afferent arterioles that contain modified smooth muscle fibers. Renin triggers the release of Angiotensin II - a highly potent vasoconstrictor of systemic blood vessels including the afferent and efferent arterioles. Mesangial cells - regulate systemic blood pressure by increasing glomerular capillary surface

Gross Anatomy of the Kidney:. Posterior views. (a) Photograph of frontal section. (b) Major anatomical features. The adipose tissue that normally fills in the renal sinus is omitted to better reveal the other structures that occupy the sinus.

Juxtaglomerular Apparatus. With the nephron in the normal orientation, there is physical contact between the afferent arteriole and the adjacent distal convoluted tubule (DCT) forming the juxtaglomerular apparatus. The

juxtaglomerular apparatus is composed of granular cells of the afferent arteriole and macula densa cells of the distal convoluted tubule. The juxtaglomerular apparatus monitors blood pressure and releases renin into the blood in response to either low blood pressure or stimulation by the sympathetic division of the ANS. (PCT = proximal convoluted tubule)

https://cdnapisec.kaltura.com/index.php/extwidget/preview/partner_id/2363221/uiconf_id/43522921/entry_id/1 _4p306d4u/embed/dynamic The functional filtration unit of the kidney is a microscopic structure called the nephron. Each kidney contains approximately 1.3 million nephrons. Each nephron consists of a renal core puzzle and a renal tubule. The renal core puzzle is a bulbous structure in the renal cortex, consisting of a capillary network called the glomerulus and a surrounding glomerular capsule, also known as Bowman's capsule. Blood vessels enter and exit the renal core puzzle at its vascular pole. The tubular pole is continuous with the renal tubule. Glomerular capsule has two layers. The visceral layer envelops the capillaries of the glomerulus. It is composed of specialized epithelial cells called podocytes, which have multiple interdigitating foot like processes, called petit cells. The parietal layer is a simple squamous epithelium that forms a capsule around the glomerulus. The capsular space lies between these two layers. Water and some solutes of blood plasma pass through a filtration membrane formed by three components of the glomerulus. Small pores in the capillary endothelium called fenestration. A basement membrane between the endothelium and the podocytes, and narrow spaces called filtration slits between Peter cells. The renal tubule is composed of a proximal convoluted tubule are nephron loop and the distal convoluted tubule. The extensively coiled proximal convoluted tubule originates at the tubular pole of the renal core puzzle and is continuous with the nephron loop. Each U-shaped nephron loop, also known as the Loop of Henle, consists of a descending limb that extends into the medulla and it ascending limb that returns to the cortex. The nephron loop is divided into thick and thin segments. The thick segments are lined with simple cuboidal epithelium. And the thin segments are lined with simple squamous epithelium. Beyond the ascending limb of the nephron loop, the renal tubule coils again to form the distal convoluted tubule. Several distal convoluted tubules drain into collecting ducts that pass through the medulla of the kidney. These merge to form papillary ducts that drain into a minor Catholics. As fluid passes through the renal tubule, useful solutes move out of the tubular fluid and returned to the blood. And waste products in the blood move into the tubular fluid ultimately to be excreted in the urine. Two types of nephrons can be identified based on their location within the renal cortex. Cortical Nephrons, which account for 85% of the Nephrons, have their glomerulus near the periphery of the cortex. Nephron loops in the outer medulla. The remaining nephrons are called juxtamedullary nephrons because their glomeruli are located at the cortical medullary junction and have relatively long nephron loops that extend deep into the medulla. Blood from interlobular arteries enters the vascular pole of each glomerulus through an afferent arteriole. A juxtaglomerular apparatus is located at the point where the afferent arterial enters the renal core puzzle. The juxtaglomerular apparatus has three parts. The Macula Densa, composed of specialized cells of the distal convoluted tubule, modified smooth muscle cells known as juxtaglomerular cells and extra glomerular mesangial cells. The efferent arteriole from each glomerulus enters a second capillary network. For Cortical Nephrons, a peritubular capillary network surrounds the proximal and distal convoluted tubules. This capillary network drains into interlobular veins. In contrast, efferent arterioles associated with juxtamedullary nephrons enter capillaries known as the vasa

recta that surround the descending and ascending limbs of the nephron loop. From the vasa recta. Blood also flows into interlobular veins.

*FILTRATION SLITS* BLOOD SUPPLY OF THE KIDNEYS Although the kidneys constitute less than 0.5% of total body mass, they receive 20-25% of resting cardiac output. The kidney filters blood as it circulates throughout systemic circulation. However, blood is not ENTIRELY cleared from all toxins. Rather, a small percentage of toxins are still present in blood (however, these are at physiologically tolerable levels). Human kidney functions like a swimming pool filtration pump: the pump filters water in the swimming pool when water is present without the necessity of draining all the water from pool for cleaning. The left and right renal arteries enter each kidney and subsequently branch into segmental, interlobar, arcuate, interlobular arteries. It is at this point that blood reaches the glomerulus. Finally, each nephron receives one afferent arteriole (input of blood to be filtered) and one efferent arteriole (blood that has not been filtered) Only 10% of delivered blood becomes filtrate = liquid to be cleared of all toxins throughout the nephron. With the total Cardiac Output=7,560L/day; 1,890L of blood is delivered to the kidneys per day or approximately 6 bathtubs! 180 L of filtrate is formed each day resulting in 1.5 -2.0 L liters of urine produced/day, the rest is reabsorbed. Reabsorbed plasma and filtrate is taken back to the general circulation by: 1. efferent arteriole conducting not filtrated blood from glomerulus 2. peritubular capillaries – network of capillaries entangling the cortical nephron 3. vasa recta - network of capillaries s entangling the juxtamedullary nephron Furthermore, venous blood is drained into Peritubular venule, interlobar vein, with the renal vein exiting each kidney to enter Inferior Vena Cava.

Gross Anatomy of the Kidney: Posterior views. (a) Photograph of frontal section. (b) Major anatomical features. The adipose tissue that normally fills in the renal sinus is omitted to better reveal the other structures that occupy the sinus.

Conceptual Blood Supply of the Kidney

INTRODUCTION TO URINARY TRACT ANATOMY Gross and microscopic anatomy of the urinary tract; we will identify and describe the gross anatomy of ...