Serves many crucial functions relating to homeostasisAnd performs excretion of wastes
Blood is filtered to remove water and small dissolved molecules Then nutrients are reabsorbed from the filtrate Remaining water and dissolved wastes are excreted
Protonephridia= the first specialized excretory structure that arose during evolution Still used by flatworms › Regulates water balance › Which consists of tubes that branch throughout the body End in flame cells (single celled bulbs) Named for the cilia that extends into the bulb Water is filtered into the bulbs › The continuously beating cilia conduct the fluid through the tubes › More waste is added and some nutrients are reabsorbed › Then it reaches a pore and leaves through diffusion
Earthworms, mollusks, and several others have simple kidney like structures (nephridia) › Fluid fills the body cavity (coeluom) and surrounds the organs collecting wastes › Flows through the nephrostome that reabsorbs salts and nurtients into the blood › Leaves behind water and wastes that is stored in a bladder area of the nephridium Then waste is excreted through the excretory pores (an opening in the body wall) › Each segment of an earthworm has its own nephridia
Excretory systems must eliminate dissolved wastes without losing too much water in the process › Water may also still contain nutrients Kidneys collect and absorb extra nutrients from blood and other bodily fluids › At the same time wastes and dangerous chemicals, to be excreted, are also filtered out
Regulating blood levels of ions such as sodium, potassium, chloride, and calcium Regulates water content of blood Maintains pH of blood Retains nutrients like glucose and amino acids Secretes hormones such as erythropoietin which stimulates red cell production Eliminates cellular waste such as urea
Urea is a product of amino acid metabolism › Digestive system breaks proteins into amino acids Those are absorbed Some used for new proteins Others lose their amino groups (-NH2) and used for energy or to synthesize new molecules The amino groups are released as ammonia (NH3) which is toxic This travels in blood to the liver where it is converted to urea (far less toxic)
The Urea is then filtered from the blood by the kidneys › Excreted in urine (fluid containing water, dissolved wastes, and excess nutrients) Mammals avoid ammonia’s dilapidating effects by excreting it in water › But then we lose water › Reptiles excrete it in uric acid with little loss of water
amino acid R O NH2 CH C OH 1 In cells, amino acids are broken into simpler molecules, releasing ammonia. ammonia (NH3) carried in blood 2 In the liver, ammonia is combined with CO2 to produce urea. urea NH2 C NH2 O carried in blood3 In the kidneys, urea and otherwater soluble wastes areconverted into urine. excreted in urine
The Urinary System Consists of the: Kidneys- paired organs located on either side of the spinal column and extending slightly above the waist where blood carrying cellular waste enters to be filtered. Renal Artery- The artery which blood enters each kidney. Renal Vein- The vein which blood exits each kidney. Ureter- Muscular tube through which urine leaves each kidney to reach the bladder. Bladder- Hollow, muscular chamber which collects and stores urine. › Muscles contained in the walls of the bladder are capable of considerable expansion. Urine is retained in the bladder by two sphincter muscles located at its base. Urethra- Through this narrow tube, urine exits the body. 1.5 inches long in females and 8 inches long in males.
Structure of the Kidneys: Each kidney contains a soldouter layer where urine isformed, which consists ofthe renal cortex overlyingthe renal medulla, and asubdivided inner chambercalled the renal pelvis, thatcollects urine and funnels itinto the ureter. More the one million tiny,Individual filters calledNephrons are pack into theOuter layer of each kidney.
The three major parts of the nephron are the glomerulus, the tubule, and the collecting ducts. With the help of these three structures. Each individual nephron is able to filter the blood and produce urine to be excreted.
GLOMERULUS: Within a cup-shaped portion of the nephron- Bowman’s Capsule- the arteriole, which supplies each nephron with blood and branches from the renal artery, branches further into the microscopic capillaries that intertwine in a mass called the glomerulus. Within its water permeable walls, pressure is created through difference in diameter between the larger incoming arteriole and the smaller outgoing arteriole. This process is termed filtration, and the resulting fluid is called filtrate. This fluid collects into the Bowman’s Capsule and through the nephron. Blood after passing through the glomerulus is more concentrated.
Tubule: Through the processes of tubular reabsorption, which occurs primarily in the proximal tubule and tubular secretion, which occurs primarily in the distal tubule, the tubule of the nephron will restore needed nutrients and most of the water to the blood to the filtrate in the Bowman’s Capsule. This will be done while retaining wastes for elimination, maintaining a balance required for homeostasis.
Loop of Henle/Collecting Ducts: Urine can become concentrated because there is an osmotic concentration gradient of salts and urea in the interstitial fluid that surrounds the loop of Henle and the collecting ducts. As filtrate passes through this area, additional water may leave the filtrate through walls of the collecting ducts, while wastes are left behind. This filtrate, as is passes through the ducts, is now called urine. It is important to produce concentrated urine when water is scarce, and to produce dilute, watery urine when there is excess water in the blood. All this depends on the permeability of the collecting duct to water, which is, in turn, controlled by the amount of antidiuretic hormone.
Disorders of this system include: › Gout, also known as gouty arthritis, is incredibly common and painful. People with gout usually first experience pain in the joint of the big toe. › A kidney stone, also known as a renal calculus is a solid concretion or crystal aggregation formed in the kidneys from dietary minerals in the urine. › Pyelonephritis is an ascending urinary tract infection that has reached the pyelum or pelvis of the kidney. It can lead to kidney failure and death.
The kidneys regulate the water content of the blood Human kidneys filter out about half a cup of fluid from blood each minute Without reabsorption of water, your body would produce 50 gallons of urine daily The amount of water reabsorbed is controlled by an antidiuretic hormone (ADH)
Kidneys produce two hormones that are essential to regulating blood When blood pressure fails, the kidneys release renin into the bloodstream › Renin is an enzyme that speeds up the formation of the second hormone, angiotensin › Angiotensin is a protein that causes arteries to constrict, raising blood pressure
In response to low oxygen levels, the kidneys release erythropoietin Erythropoietin travels to the bone marrow, where the marrow is stimulated to produce more red blood cells Kidney failure leads to anemia , because the kidneys do not produce enough erythropoietin to make the minimal number of red blood cells
Different types of mammals have different kidney structures depending on the availability of water in their habitat The longer the Henle, the more concentrated the urine is, which means more water is conserved A loop of Henle is what recycles water, the longer the loop, the less diluted the urine is