Anatomy & Physiology of Kidney and Glomerular Functions PDF

ANATOMY & PHYSIOLOGY OF KIDNEY AND GLOMERULAR FUNCTIONS Dr. Ashfaq Bukhari Assistant Professor- Physiology Learning Objectives At the end of the Lecture, Students will be able to: 1. Describe the structure of Kidney and its nephrons. 2. Discuss the functions of each part of kidney and nep...

ANATOMY & PHYSIOLOGY OF KIDNEY AND GLOMERULAR FUNCTIONS Dr. Ashfaq Bukhari Assistant Professor- Physiology Learning Objectives At the end of the Lecture, Students will be able to: 1. Describe the structure of Kidney and its nephrons. 2. Discuss the functions of each part of kidney and nephrons. 3. Explain the glomerular functions. The Kidneys- function The main purpose of the kidney is to separate urea, mineral salts, toxins, and other waste products from the blood. They also do the job of conserving water, salts, and electrolytes. At least one kidney must function properly for life to be maintained. The Human Kidney ❖bean shaped, reddish brown organs. ❖about the size of your fist. ❖It measures 10-12 cm long. ❖covered by a tough capsule of fibrous connective tissue- renal capsule ❖Adhering to the surface of each kidney-two layers of fat to help cushion them. The Human Kidneys ❖ concaved side having a depression where a renal artery enters, and a renal vein and a ureter exit the kidney. ❖ located in the upper rear region of the abdominal cavity just above the waistline. ❖ protected by the ribcage. ❖ The renal cortex, the renal medulla and the renal pelvis - major regions of the kidney. ❖ The left kidney lies slightly above the right kidney. The Kidney Diagram Kidneys and their structures ❑The Renal Arteries transport oxygenated blood from the heart and aorta to kidneys for filtration ❑The Renal Veins Transport the filtered, deoxygenated blood from kidneys to the posterior vena cava and finally the heart Kidneys and their structures ❑Renal Capsule (inferior/superior) Outer membrane which encloses and protects kidneys against infections and trauma. ❑The Renal Cortex Outer layer (granulated) of the kidney that contains most of the nephrons. Kidneys and their structures ❑Nephron Most basic microscopic structures of the kidneys Inside each kidney, there are about 1 million nephrons Physiological unit of the kidney used for filtration of blood, and reabsorption and secretion of materials Kidneys and their structures ❑The Renal Medulla Inner layer (radially striated) of the kidney contains renal pyramids, renal papillae, renal columns, renal calyces (minor/major),renal pelvis and part of nephron, not located in the cortex Site for salt, water and urea absorption Kidneys and their structures ❑The Renal Papillae The tips of the renal pyramids release urine into the calyces ❑The Renal Calyces Collecting sacs that surround the renal papillae Transport urine from renal papillae to renal pelvis Kidneys and their structure ❑The Renal Pelvis Cavity which lies in the centre of the kidney and which extends into the ureter Collects urine from all of the calyces in the kidney Kidneys and their structures ❑The Ureters (right/left) Tubes that transports urine from the renal pelvis to the bladder ❑The Urinary Bladder Hollow, expandable, muscular organ located in the pelvic girdle Functions as a temporary reservoir for urine The Kidney Nephron Diagram The two types of Nephrons ❑Cortical The loop of Henle does not extend past the cortex of the kidney. ❑Juxtamedullary Loop of Henle extends past the cortex and into the medulla of the kidney. Nephron structures and functions ❑Afferent Arteriole Transport arterial blood to glomerulus for filtration ❑Efferent Arteriole Transports filtered blood from glomerulus through the peritubular capillaries and the vasa recta, and to the kidney venous system Nephron structures and functions ❑Glomerulus The site for blood filtration operates as a nonspecific filter - removes both useful and non-useful material the product of the glomerulus – filtrate ❑Bowman’s Capsule A sac that encloses glomerulus transfers filtrate from the glomerulus to the Proximal Convoluted Tubule (PCT) Nephron structures and functions ❑Proximal Convoluted Tubule (PCT) A thick, constantly active segment of the nephron that reabsorbs most of the useful substances of the filtrate: sodium (65%), water (65%), bicarbonate (90%), chloride (50%), glucose (nearly 100%) The primary site for secretion (elimination) of drugs, waste and hydrogen ions. Nephron structures and functions ❑The loop of Henle U-shaped tube that consists of a descending limb and an ascending limb. begins in the cortex, receiving filtrate from the PCT, extends into the medulla, and then returns to the cortex to empty into the distal convoluted tubule(DCT). Nephron structures and functions ❑Decending Limb of the Loop of Henle fully permeable to water and completely impermeable to solutes (salt particles) receives filtrate from the PCT, allows water to be reabsorbed and passes “salty” filtrate to the next segment. “Saves water and passes the salt” Nephron structures and functions ❑Ascending Limb of the loop of Henle impermeable to water and actively transports (reabsorbs) salt (NaCl) to the interstitial fluid of the pyramids in the medulla. “Saves salt and passes the water.” the passing filtrate becomes dilute and the interstitium becomes hyperosmotic Nephron structures and functions ❑Distal Convoluted Tubule (DCT) Variably active portion of the nephron receives dilute fluid from the ascending limb of the loop of Henle Nephron structures and functions ❑Collecting Duct variably active portion of the Nephron receives fluid from the DCT The last segment to save water for the body Nephron structures and functions ❑Peritubular Capillaries transport reabsorbed materials from the PCT and DCT into kidney veins and eventually back into the general circulation help complete the conservation process (reabsorption) that takes place in the kidney BASIC RENAL PROCESSES ⚫There are three basic Renal processes: ⚫Glomerular filtration. ⚫Tubular reabsorption ⚫Tubular secretion BASIC RENAL PROCESS Urine formation: ⚫ Filtration from of plasma from the glomerular capillaries into the Bowman‟s space. ⚫ Movement from the tubular lumen to the peritubular capillaries is the process called tubular reabsorption ⚫ Movement from the peritubular capillaries to the tubular lumen is the process known as tubular secretion ⚫ Once in the tubule the substance need not be excreted , it can be reabsorbed. ⚫ These processes do not apply to all substances. E.g. - Glucose (completely reabsorbed.) - Toxins ( Secreted and not reabsorbed) Glomerular Filtration ⚫ The filtration of plasma from the glomerular capillaries into the Bowman‟s space is termed glomerular filtration. ⚫ The filtrate is termed glomerular filtrate or ultrafiltrate ⚫ Filtrate contains all plasma substances except protein. Table 1: Constituents of the Glomerular filtrate Filtered Not filtered Low molecular weight Most plasma proteins ie. substances (including Albumins & Globulins. smaller peptides) water Plasma calcium and fatty acids ⚫ Fenestrations found in the glomerular capillary walls are not large enough to allow the passage of large proteins from the plasma, smaller proteins however are allowed to pass. ⚫ Glycoproteins in the basement membrane discourage the filtration of small plasma proteins. ⚫ Glycoproteins are negatively charged and therefore they repel small molecular weight proteins such as albumin which is also negatively charged. ⚫ Less than 1 % of albumin molecules escape the Bowman‟s capsule. Those that do are removed by exocytosis in the proximal tubule Forces involved in filtration Table 2 : Forces involved in the Glomerular filtration Favouring filtration Opposing filtration Glomerular capillary blood Fluid pressure in Bowman‟s pressure space Osmotic force due to protein in plasma Forces involved in glomerular filtration  RATE OF GLOMERULAR FILTRATION ( GFR ) ⚫GFR : the volume of fluid filtered from the glomeruli into the Bowman‟s space per unit time Normal GFR: 125 ml/min ⚫ Determined by :1. Net filtration pressure 2. Permeability of the corpuscular membranes 3. Surface area available for filtration Decreased GFR Increased GFR ⚫ Constriction if afferent ⚫ Constriction of the efferent arteriole arteriole causes a decrease in results in an increase in hydrostatic hydrostatic pressure in the pressure in the glomerular glomerular capillaries, this capilleries. Results in increased GFR results in decreased GFR ⚫ Dilation of the efferent ⚫ Dilation of afferent arteriole causes an arteriole results in a increase in hydrostatic pressure in the reduction in hydrostatic glomerular capilleries. This results in pressure in the glomerular an increase in GFR capillaries resulting in a decreased GFR Changes in GFR by constriction or dilation of afferent (AA) or efferent (EA) arterioles 5 Tubular Reabsorption ⚫ Movement of substances from the tubular lumen to the interstitial fluid does not occur by bulk flow due to inadequate pressure differences and permeability of the tubular membranes ⚫ Tubular reabsorption involves the reabsorption of certain substances out of filtrate by either diffusion or mediated transport ⚫ Substances are then returned to capillary blood which surround the kidney tubules. ⚫ Tubular reabsorbtion mainly occurs in the Proximal tubule and the Loop of Henele Data for a few plasma components that undergo filtration and reabsorption. ⚫ Diffusion usually occurs across the tight junctions connecting the epithelial cells ⚫ Mediated transport requires the participation of transport protiens in the membranes of the tubular cells. Methods of Tubular reabsorption Diffusion Mediated Transport Water reabsorption creates Reabsorption coupled with the concentration gradient across reabsorption of sodium. tubular epithelium. Requires the use of transporters. Example: Urea , variety of Example : glucose , amino lipid soluble organic acids substances Tubular secretion ⚫ Involves the transport of substances from peritubular capillaries into the tubular lumen. ⚫ Secretion occurs via diffusion and transcellular mediated transport. ⚫ Organic anions and cations are taken up by the tubular epithelium from the blood surrounding the tubules and added to the tubular fluid. ⚫ Hydrogen ions and potassium are the most important substances secreted in the tubules. ⚫ Other noteworthy substances secreted are metabolites such as choline and creatinine and chemicals such as penicillin. Division of labour in the tubules ⚫ The primary role of the proximal tubule is to reabsorb most of the filtered water and filtered plasma solutes after the filtration in the Bowman‟s capsule. ⚫ Proximal tubule is a major site for solute secretion. ⚫ Henle‟s loop also reabsorbs relatively large quantities of major ions and to a lesser extent water. It therefore ensures that the mass of water and solute is smaller as it enters the following segments of the nephron ⚫ The distal segments determine the final amount of substances excreted in the urine. ⚫ Homeostatic controls act more on the distal segments of the tubule. The kidneys: I am happy that now you know An Excretory organ or a more about me!!! Regulatory organ?!!! https://www.youtube.com/watch?v=CShAIAD-ask https://www.youtube.com/watch?v=Yif_nhNg57E