Renal System Physiology PDF

Renal System Presented by: Dr. Asmaa Seddek Lecturer of Physiology FOM/SCU  Introduction Excretion is the process by which the unwanted substances and metabolic wastes are eliminated from the body. Liver Lungs Skin RE...

Renal System Presented by: Dr. Asmaa Seddek Lecturer of Physiology FOM/SCU  Introduction Excretion is the process by which the unwanted substances and metabolic wastes are eliminated from the body. Liver Lungs Skin RENAL GIT SYSTEM Remove Excretes Bile pigments, Excretes carbon water, salts heavy metals, Has food dioxide and some drugs, toxins, bacteria, etc. residues and wastes + maximum in the water removes excretory through bile. form of vapor heat from capacity feces the body  produce the urine Renal system transport the urine to urinary bladder Store urine till it is voided Urine is voided through it  KIDNEYS FUNCTIONS OF KIDNEY 1. ROLE IN HOMEOSTASIS: During the formation of urine, kidneys regulate various activities in the body, such as: i. Excretion of Waste Products: Kidneys excrete the unwanted waste products, which are formed during metabolic activities: a. Urea (end product of amino acid metabolism) b. Uric acid (end product of nucleic acid metabolism) c. Creatinine (end product of metabolism in muscles) d. Bilirubin (end product of hemoglobin degradation) e. Products of metabolism of other substances ii. Maintenance of Water Balance: Kidneys maintain the water balance in the body by changing the urine volume in response to the body fluid content. iii. Maintenance of Electrolyte Balance: Maintenance of electrolyte balance, especially sodium is in relation to water balance. Kidneys retain sodium if its concentration in plasma decreases and eliminate sodium when its conc.in plasma increases. iv. Maintenance of Acid–Base Balance Body is under constant threat to develop acidosis, because of production of lot of acids during metabolic activities. In fact, kidneys are the only organs, which are capable of eliminating certain metabolic acids like sulfuric and phosphoric acids. 2. HEMOPOIETIC FUNCTION: Kidney secretes: i. Erythropoietin which stimulates production of erythrocytes. ii. Thrombopoietin which stimulates the production of thrombocytes. 3. ENDOCRINE FUNCTION: Hormones secreted by kidneys i. Erythropoietin ii. Thrombopoietin iii. Renin iv. 1,25-dihydroxycholecalciferol (calcitriol)(activation) 4. REGULATION OF BLOOD PRESSURE: Kidneys play an important role in the long-term regulation of arterial blood pressure by two ways: i. By regulating the volume of extracellular fluid ii. Through renin-angiotensin mechanism. 5. REGULATION OF BLOOD CALCIUM LEVEL: Kidneys play a role in the regulation of blood calcium level by activating 1,25-dihydroxycholecalciferol into vitamin D. Vitamin D is necessary for the absorption of calcium from intestine. FUNCTIONAL ANATOMY OF KIDNEY Kidney is a tubular gland formed of 3 layers: 1. Outer cortex: At intervals, cortical tissue penetrates medulla in the form of columns (renal columns ). 2. Inner Medulla: It is divided into 8 -18 medullary or Malpighian pyramids. Broad base of each pyramid is in contact with cortex and the apex projects into minor calyx. 3. Renal sinus: Renal sinus consists of the following structures: i. Upper expanded part of ureter called renal pelvis. ii. Subdivisions of pelvis: 2 or 3 major calyces and about 8 minor calyces. iii. Branches of nerves, arteries and tributaries of veins. iv. Loose connective tissues and fat.  Nephron  Nephron is defined as the structural and functional unit of kidney.  Each kidney consists of 1 to 1.3 millions of nephrons.  Each nephron is formed by two parts: 1. A blind end called renal corpuscle or Malpighian Corpuscle: Function of the renal corpuscle is the filtration of blood which forms the first phase of urine formation. It is formed of two parts: i. Glomerulus , ii. Bowman`s capsule 2. A tubular portion called renal tubule: Tubular portion of nephron is the continuation of Bowman capsule. It is made up of three parts: i. Proximal convoluted tubule ii. Loop of Henle iii. Distal convoluted tubule. Loop Of Henle  Malpighian Corpuscle I. Glomerulus  Glomerulus is a tuft of capillaries enclosed by Bowman capsule Glomerular capillaries arise from the afferent arteriole.  After entering the Bowman capsule, the afferent arteriole divides into smaller capillaries, which then finally reunite to form the efferent arteriole, which leaves the Bowman capsule. II. Bowman Capsule:  Bowman capsule is a capsular structure, which encloses the glomerulus. It is formed by two layers: i. Inner visceral layer ii. Outer parietal layer.  Visceral layer covers the glomerular capillaries. It is continued as the parietal layer at the visceral pole.  Parietal layer is continued with the wall of the tubular portion of nephron.  The cleft like space between the visceral and parietal layer is continued as the lumen of the tubular portion. Cleft like space  Functional histology of Malpighian Corpuscle  Glomerular capillaries are made up of single layer of endothelial cells. Endothelium has many pores called fenestrae or filtration pores. Diameter of each pore is 0.1 μ.  Both layers of Bowman capsule are composed of a single layer of flattened epithelial cells. Each epithelial cell is connected has cytoplasmic extensions Called pedicles or feet, rest on basement membrane. Epithelial cells with pedicles are called podocytes. Podocyte pedicles are separated by cleft like space called slit pore.  I. Glomerular Filtration (GF)  Glomerular filtration is the process by which the blood is filtered while passing through the glomerular capillaries by filtration membrane.  Filtration membrane is formed by three layers: 1. Glomerular capillary membrane 2. Basement membrane 3. Visceral layer of Bowman capsule. Process of Glomerular Filtration: When blood passes through glomerular capillaries, the plasma is filtered into the Bowman capsule. All the substances of plasma are filtered except the plasma proteins (because of their large molecular size).  The filtered fluid is called glomerular filtrate, and it contains all the substances present in plasma except the plasma proteins.  Glomerular filtration rate (GFR) is defined as the total quantity of filtrate formed in all the nephrons of both the kidneys in the given unit of time.  Normal GFR is 125 mL/minute or about 180 L/day. GFR is depends on three pressures: 1. Glomerular capillary pressure (PGC) It is the pressure exerted by the blood in glomerular capillaries. It varies between 45 - 70 mmHg (≈60 mmHg). It favors glomerular filtration. 2. Colloidal osmotic pressure in the glomeruli (ᴫGC) It is the pressure exerted by unfiltered plasma proteins in the glomeruli. It is about 25 mm Hg, and opposes glomerular filtration. 3. Hydrostatic pressure in the Bowman capsule (PBC)  It is the pressure exerted by the filtrate in Bowman capsule. It is also called capsular pressure. It is about 15 mm Hg. It also opposes glomerular filtration. Net filtration pressure= Glomerular capillary pressure – (Colloidal osmotic pressure + Hydrostatic pressure in Bowman capsule) =60-(25+15)= 60-40= 20mmHg 25 mmHg  Factors affecting glomerular filtration Increased Systemic Arterial Blood Increase Pressure Increased Renal PGC Increase Blood Flow Increase Glomerular Filtration Increased Concentration of ᴫGC Decrease Increase plasma proteins Urinary tract PBC Decrease Increase Obstruction  II- TUBULAR REABSORPTION  Definition: Tubular reabsorption is the process by which water and other substances are transported from renal tubules back to the blood.  When the glomerular filtrate flows through the tubular portion of nephron, large quantity of water (more than 99%), electrolytes and other substances are selectively reabsorbed by the tubular epithelial cells. The reabsorbed substances move into the interstitial fluid of renal medulla. And, from here, the substances move into the blood in peri-tubular capillaries.  Essential substances such as glucose, amino acids and vitamins are completely reabsorbed from renal tubule. Whereas the unwanted substances like metabolic waste products are not reabsorbed and excreted through urine  SITE OF REABSORPTION Reabsorption of the substances occurs in almost all the segments of tubular portion of nephron. Proximal convoluted tubule Distal It reabsorb 88% of the Loop convoluted filtrate, including : Of tubule glucose, amino acids, Henle sodium, sodium, potassium, sodium, calcium, calcium, bicarbonates, and bicarbonates chlorides, phosphates, Chloride. , and water urea, uric acid and water  I. Transport from tubular lumen to renal interstitium Active Transport: Passive Transport:  It is the movement of  It is the movement of molecules against the electrochemical gradient. It molecules along the needs energy (ATP). electrochemical  Examples: Substances gradient. It does not reabsorbed actively from the need energy. renal tubule are sodium,  Examples: Substances calcium, potassium, reabsorbed passively phosphates, sulfates, bicarbonates, glucose, amino are chloride, urea and acids, ascorbic acid, uric acid water. and ketone bodies. iI. Transport from renal interstitium to peri-tubular capillary The substrances are transported from renal interstitium to the peri-tubular capillar by Bulk Flow, which depends on pressure gradients The normal rate of peri-tubular capillary reabsorption is about 124 ml/min. MECHANISMS OF TUBULAR REABSORPTION Interstitial fluid  The reabsorptive forces include: (1) hydrostatic pressure inside the peritubular capillaries (peritubular hydrostatic pressure [Pc]), which opposes reabsorption; (2) hydrostatic pressure in the renal interstitium (Pif) outside the capillaries, which favors reabsorption; (3) colloid osmotic pressure of the peritubular capillary plasma proteins (πc), which favors reabsorption; and (4) colloid osmotic pressure of the proteins in the renal interstitium (πif), which opposes reabsorption REGULATION OF TUBULAR REABSORPTION  Tubular reabsorption is regulated by three factors: 1. Glomerulo-tubular balance: = Balance between the filtration and reabsorption of solutes and water in kidney. When GFR increases, the tubular load of solutes and water in the proximal convoluted tubule is increased. It is followed by increase in the reabsorption of solutes and water. 2. Nervous factors: Activation of sympathetic nervous system increases the tubular reabsorption (particularly of sodium) from renal tubules, how? a. directly: Sympathetic stimulation causes vasoconstriction of efferent arterioles, decreasing the blood hydrostatic pressure inside the peritubular capillaries (PC), increasing reabsorption. b. Indirectly: sympathetic stimulation increase renin production which ultimately stimulate Angiotensin II, which stimulate Na+ reabsorption.  3. Hormonal factors: A number of hormones regulates the peri-tubular re- absorption, such as; Hormone Effect Aldosterone Increases sodium reabsorption in ascending limb, distal convoluted tubule and collecting duct Angiotensin II Increases sodium reabsorption in proximal tubule, thick ascending limb, distal tubule and collecting duct (mainly in proximal convoluted tubule) Antidiuretic Increases water reabsorption in distal hormone convoluted tubule and collecting duct  III- TUBULAR SECRETION  Tubular secretion is the process by which the substances are transported from blood into renal tubules. Secreted substances are secreted into the lumen from the peri- tubular capillaries through the tubular epithelial cells.  Examples: 1. Potassium is secreted actively by sodium potassium pump in proximal and distal convoluted tubules and collecting ducts 2. Ammonia is secreted in the proximal convoluted tubule 3. Hydrogen ions are secreted in the proximal and distal convoluted tubules. 4. Urea is secreted in loop of Henle.  III- TUBULAR EXCRETION The final form of collected fluid containing wastes , ions , water , etc. Passes from renal collecting ducts to both ureters then to urinary bladder waiting there till getting out of the body