7 Excretion.docx

Name: ( ) Date: Class: -- ----------------------------- ------------------------ **Peirce Secondary School** **Science Department** -- ----------------------------- ------------------------ a. define *excretion* and explain the importance of removing nitrogenous and other compou...

Name: ( ) Date: Class: -- ----------------------------- ------------------------ **Peirce Secondary School** **Science Department** -- ----------------------------- ------------------------ a. define *excretion* and explain the importance of removing nitrogenous and other compounds from the body The Need for Excretion {#the-need-for-excretion.ListParagraph} ====================== - Waste products from metabolic processes (*chemical activities that occur within body cells*), toxic substances and substances that are in excess can build up in the human body. - Hence, they must be removed regularly to prevent them from causing harm to the body. Excretion refers to the removal of metabolic waste products, toxic substances, and substances that are in excess, from the body. These substances can harm the body if they are allowed to accumulate. - Aerobic respiration and deamination are processes through which excretory waste products are produced. - During aerobic respiration, glucose and oxygen react and carbon dioxide and water are produced. - Urea is produced when excess amino acids are deaminated in the liver. Note: - Excretion is not the same as egestion. Egestion is the removal of undigested material from the alimentary canal. The undigested material is not formed within cells. Egested material is not a product of metabolic processes. Excretion in Humans {#excretion-in-humans.ListParagraph} =================== 1. Waste products and their mode of excretion: **excretory product** **organ** **mode of excretion** ----------------------- ----------- ----------------------- **\ ** **The human urinary system** \(b) identify the kidneys, ureter, bladder and urethra and state their functions in excretion **Structure of a human kidney:** **Structure of a nephron:** **Blood circulation at the nephron:** 1. Blood enters the kidney via the [renal artery]. The renal artery branches into many arterioles. 2. The arterioles branch into a mass of blood capillaries called the [glomerulus]. Blood leaves glomerelus and enters blood capillaries surrounding the nephron. 3. These blood capillaries converge to form venules that lead to the renal vein. Blood exits the kidney via the [renal vein]. \(c) outline the function of the nephron with reference to ultra-filtration and selective reabsorption in the production of urine Urine Formation {#urine-formation.ListParagraph} =============== Urine formation involves two main processes within the nephron: [ultrafiltration] and [selective reabsorption]. **Ultrafiltration** 1. Ultrafiltration occurs at the [renal corpuscle] (= Bowman's capsule + glomerulus). 2. Ultrafiltration is a passive process that requires [high hydrostatic blood pressure] at the glomerulus. The high pressure forces small molecules through the [basement membrane] of the glomerular capillaries, and into the Bowman's capsule. 3. The [partially permeable] basement membrane acts as a [filter]. a. Small molecules such as water, glucose, amino acids, mineral salts and nitrogenous waste products are able to pass through. These molecules form the [filtrate] in Bowman's capsule. b. Large molecules such as [plasma proteins] and [red blood cells] remain in the glomerulus. +-----------------------------------+-----------------------------------+ |  | An analogy to show how different | | | diameters of afferent and | | | efferent arterioles increase | | | blood pressure | | | | | | - the afferent arteriole is | | | wider than the efferent | | | arteriole | | | | | | - this creates a high blood | | | pressure in the glomerulus | | | | | | - hydrostatic blood pressure | | | provides the main force for | | | ultrafiltration | +-----------------------------------+-----------------------------------+ **\ ** **Selective reabsorption** 1. = reabsorption of [useful substances] from the filtrate to the bloodstream. +-----------------------------------+-----------------------------------+ | **Part of nephron** | **Substance(s) selectively | | | reabsorbed and the processes | | | involved** | +===================================+===================================+ | Proximal convoluted tubule | - Some water reabsorbed | | | by osmosis | | | | | | - All glucose and amino acids | | | reabsorbed by active | | | transport | | | | | | - Most mineral salts reabsorbed | | | by diffusion and active | | | transport | +-----------------------------------+-----------------------------------+ | Loop of Henlé | - Some water reabsorbed | | | by osmosis | | | | | | - Some mineral salts reabsorbed | | | by active transport | +-----------------------------------+-----------------------------------+ | Distal convoluted tubule | - Some water reabsorbed | | | by osmosis | | | | | | - Some mineral salts reabsorbed | | | by active transport | +-----------------------------------+-----------------------------------+ | Collecting duct | - Some water reabsorbed | | | by osmosis | +-----------------------------------+-----------------------------------+ 2. The remaining fluid that passes out of the collecting duct into the renal pelvis forms [urine]. Urine contains the excess water, excess salts and metabolic waste products such as urea, uric acid and creatinine. A kidney nephron **\ ** \(i) outline the role of anti-diuretic hormone (ADH) in osmoregulation -- refer to Homeostasis Osmoregulation: {#osmoregulation.ListParagraph} =============== 1. The water potential of the blood plasma depends on the amount of [water] and [solutes] in the plasma. 2. The [anti-diuretic hormone] (ADH) produced by the [hypothalamus] and released by the [pituitary gland], controls the water potential of blood plasma. Increased ADH secretion increases [water absorption] by the nephron. **The mechanism of osmoregulation:** **\ ** \(d) outline the mechanism of dialysis in the case of kidney failure Kidney Failure {#kidney-failure.ListParagraph} ============== 1. Kidneys are [excretory organs] and [osmoregulators]. 2. Kidney failure can be treated with a kidney transplant or [dialysis]. A dialysis machine mimics the function of a kidney. **How dialysis works:** 1. Blood is drawn from a [vein] in the patient's arm and pumped into the dialysis machine through a tubing. 2. In the dialysis machine, the tubing is [partially permeable] and bathed in a [dialysis fluid]. a. Small molecules, including metabolic waste products, [diffuse] out of the blood and into the dialysis fluid because of the [concentration gradient] between the blood and the dialysis fluid. b. Blood cells, platelets and large molecules remain in the tubing. 3. The [filtered blood] is returned to a [vein] in the patient's arm. -- -- -- -- The diagram represents the arm of a patient who is being treated by a machine.