Human excretory system

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1. Human excretory system Kidneys, nephrons

2. What is human excretory system… The excretory system is a passive biological system that removes excess, unnecessary materials from the body fluids of an organism, so as to help maintain internal chemical homeostasis and prevent damage to the body. The dual function of excretory systems is the elimination of the  waste products of metabolism and to drain the body of used up and broken down components in a liquid and gaseous state. In humans and other  amniotes(mammals , birds and  reptiles ) most of these substances leave the body as urine and to some degree exhalation, mammals also expel them through sweating. Only the organs specifically used for the excretion are considered a part of the excretory system. In the narrow sense, the term refer to the urinary system. However, at excretion involves several functions that are only superficially related, it is not usually used in more formal classifications of anatomy or function.

3. Kidneys The  kidneys  are bean-shaped organs that serve several essential regulatory roles in vertebrates. They remove excess organic molecules from the blood, and it is by this action that their best-known function is performed: the removal of waste products of metabolism. Kidneys are essential to the urinary system and also serve  homeostatic functions such as the regulation of electrolytes, maintenance of acid–base balance, and regulation of blood pressure (via maintaining the salt and water balance). They serve the body as a natural filter of the blood, and remove water-soluble wastes which are diverted to the bladder. In producing urine, the kidneys excrete wastes such as  urea  and ammonium. They are also responsible for the reabsorption of water, glucose, and amino acids. The kidneys also

4. Excretion & Homeostasis Homeostasis is the process of maintaining the ideal internal conditions (i.e. correct temperature, right amount of water and glucose & other solutes) for the body to work at it’s optimum. Excretion is the process of removing metabolic waste products and other toxins. Osmoregulation is maintaining the correct balance between water and solutes. Excretion, which includes osmoregulation, is thus extremely important in maintaining homeostasis. Secretion is the release of useful substances, e.g. hormones, from the body. Thus, it is not excretion. Egestion, i.e. defecation, is also not excretion.

5. Removal of Waste Products Certain waste products would become highly toxic if they were to accumulate. This could damage tissues. An excess of water could also lead to a number of complications. Thus, the waste products must be removed – they continually move into the bloodstream, which carries them to the excretory organs.

6. Raw Materials (Food and 0 2 ) Useful Materials Useless Materials Egested (faeces) Metabolised Metabolic Waste Products (urea and CO2) E xcreted Useful Products

7. Excretory Organs There are four main excretory organs: Lungs Colon Skin Kidneys The liver is not an excretory organ, but produces many products which are excreted elsewhere. Toxins and drugs as well as alcohol, is broken down in the liver. Hence, an excess of smoking, medication and alcohol is extremely harmful to the liver.

8. The Lungs The carbon dioxide released from cellular respiration is carried to the lungs in the blood. It then diffuses across the respiratory membrane and is exhaled. A small amount of heat and water is excreted this way.

9. The Colon Bile pigments, from the break down of haemoglobin, and cholesterol are synthesised in the liver. They pass into the small intestine as bile and are finally excreted in the faeces as bile salts, from the colon. Mucus and bacteria are too excreted through the colon.

10. The Skin Sweat, which is excreted through the skin, contains water, salts and some urea. As the water in the sweat is excreted, heat is lost and the body is cooled. Sweat is a form of excretion as it rids the body of waste, as well as a form of secretion as it maintains the body temperature.

11. The Kidneys When amino acids and nucleic acids are broken down, nitrogenous wastes are released as ammonia, urea, uric acid and creatinine. Ammonia is toxic if it accumulates and is therefore converted to less toxic urea in the liver. The following substances are made in the liver and excreted by the kidneys: Urea , the main nitrogenous waste compound secreted. It is formed by the breakdown of excess amino acids in the process of deamination . Uric acid , the nitrogenous end product of nucleic acid metabolism. Creatinine is formed from creatinine phosphate, found in the muscle cells. Non-nitrogenous waste, e.g. CO2, excess water, ions, hormones, poisons and drugs.

12. The Urinary System The main function of the urinary system is to maintain homeostasis by regulating the volume and concentration of body fluids. It filters and reabsorbs certain materials from the blood. The urinary system is made up of the following parts: Two kidneys Urinary bladder urethra

13. Urinary Bladder Stores urine Is stimulated by impulses from a motor nerve, to contract to expel the urine. Has sphincter muscles at the base to control the flow of urine Urethra Carries urine from the bladder to outside the body

14. The Kidneys Found in abdominal cavity below the diaphragm, near the posterior, on either side of the vertebral column. Kept in position with connective tissue, the peritoneum, as well as renal blood vessels. They are wedged in with other organs. Externally they are bean-shaped, dark red and the size of a large bar of soap. The inner, concave border is called the hilum. Surrounded by three layers of protective tissue: A tough, fibrous renal capsule on the surface protects them from disease. A middle layer of adipose tissue cushions them against blows. An outer layer of fibrous connective tissue, the renal fascia, anchors the kidneys to surrounding structures.

15. Renal pyramid Interlobular artery Renal artery Renal vein Renal hilum Renal pelvis Ureter Minor calyx Renal capsule Inferior renal capsule Superior renal capsule Inter lobular vein Nephron Minor calyx Major calyx Renal papilla Renal column

16. The damage of the kidneys Pyelonephritis  (infection of kidney pelvis): Bacteria may infect the kidney, usually causing back pain and fever. A spread of bacteria from an untreated bladder infection is the most common cause of pyelonephritis. Glomerulonephritis : An overactive immune system may attack the kidney, causing inflammation and some damage. Blood and protein in the urine are common problems that occur with glomerulonephritis. It can also result in kidney failure. Kidney stones  (nephrolithiasis): Minerals in urine form crystals (stones), which may grow large enough to block urine flow. It's considered one of the most painful conditions. Most kidney stones pass on their own but some are too large and need to be treated. Nephrotic syndrome : Damage to the kidneys causes them to spill large amounts of protein into the urine. Leg swelling (edema) may be a symptom. Polycystic kidney disease : A genetic condition resulting in large cysts in both kidneys that impair their function. Acute renal failure  (kidney failure): A sudden worsening in kidney function. Dehydration, a blockage in the urinary tract, or kidney damage can cause acute renal failure, which may be reversible.

17. ……. Chronic renal failure : A permanent partial loss of kidney function. Diabetes and high blood pressure are the most common causes. End stage renal disease (ESRD): Complete loss of kidney function, usually due to progressive chronic kidney disease. People with ESRD require regular dialysis for survival. Papillary necrosis: Severe damage to the kidneys can cause chunks of kidney tissue to break off internally and clog the kidneys. If untreated, the resulting damage can lead to total kidney failure. Diabetic nephropathy : High blood sugar from diabetes progressively damages the kidneys, eventually causing chronic kidney disease. Protein in the urine (nephrotic syndrome) may also result. Hypertensive nephropathy: Kidney damage caused by high blood pressure. Chronic renal failure may eventually result.

18. …….. Kidney cancer : Renal cell carcinoma is the most common cancer affecting the kidney. Smoking is the most common cause of kidney cancer. Interstitial nephritis: Inflammation of the connective tissue inside the kidney, often causing acute renal failure. Allergic reactions and drug side effects are the usual causes. Minimal change disease: A form of nephrotic syndrome in which kidney cells look almost normal under the microscope. The disease can cause significant leg swelling (edema). Steroids are used to treat minimal change disease. Nephrogenic diabetes insipidus : The kidneys lose the ability to concentrate the urine, usually due to a drug reaction. Although it's rarely dangerous, diabetes insipidus causes constant thirst and frequent urination. Renal cyst : A benign hollowed-out space in the kidney. Isolated kidney cysts occur in many normal people and almost never impair kidney function.

19. Blood Supply of Kidney The kidney needs to have a constant supply of blood in order to control the composition of body fluids. The renal artery, a branch from the aorta, enters the kidney at the hilum. It supplies blood rich in nitrogenous waste, oxygen and nutrients. The renal vein carries purified, deoxygenated blood to the inferior vena cava, and then to the heart.

20. Glomerulus Efferent arteriole Bowman’s capsule Proximal convoluted tubule Cortical collecting duct Distal convoluted tubule Henle’s loop Papillary duct Peritubular capillaries Arcuate vein Arcuate artery Afferent arteriole Juxtaglomerular apparatus

21. Functioning of nephrons The nephron carries out nearly all of the kidney's functions. Most of these functions concern the reabsorption and secretion of various  solutes  such as ions (e.g., sodium),carbohydrates (e.g., glucose), and  amino acids (e.g., glutamate). Properties of the cells that line the nephron change dramatically along its length; consequently, each segment of the nephron has highly specialized functions. The loop of Henle, is a U-shaped tube that extends from the proximal tubule. It consists of a descending limb and an ascending limb. It begins in the cortex, receiving filtrate from the proximal convoluted tubule, extends into the medulla as the descending limb, and then returns to the cortex as the ascending limb to empty into the distal convoluted tubule. The primary role of the loop of Henle is to concentrate the salt in the interstitium , the tissue surrounding the loop .

22. Bowman’s capsule Bowman's capsule  is a cup-like sac at the beginning of the tubular component of a nephron in the mammalian kidney that performs the first step in the filtration of blood to form urine. A glomerulus is enclosed in the sac. Fluids from blood in the glomerulus are collected in the Bowman's capsule (i.e., glomerular filtrate) and further processed along the nephron to form urine. This process is known as ultrafiltration .  The Bowman's capsule is named after Sir William Bowman, who identified it in 1842.