Excretory System Flashcards
Excretion
The removal of metabolic wastes from the body. Metabolic wastes are the waste products of chemical reactions in the cells.
Organs of Excretion
Lungs - Excretion of carbon dioxide produced in cellular respiration. Some water lost as vapour. CO2
Liver – processes certain materials so they can be excreted. Deamination of nitrogenous wastes
Sweat glands – secretes sweat to skin, contains water, salts, urea and lactic acid (by-products of metabolism). Metabolic Water
Alimentary canal – excretes bile pigments. Bile Salts
Kidneys – primary excretion organs, maintains constant concentration of materials in body fluids, excretes urea, uric acid and creatinine. Metabolic Water
The Kidneys
• Gets rid the body of wastes, especially nitrogenous wastes such as urea
• To Regulate the balance of fluid, salt, and pH (acidity of blood (how many Hydrogen ions floating through the blood))
• Performs these functions by:
Filtering the blood as it passes through the kidneys
Useful substances are returned to the body by the process of selective re-absorption
Waste substances are removed by the processes of filtration and tubular secretion
Urine
• It is collected in the bladder and eliminated through the urethra.
• The average amount of urine voided in 24 hours is about 1,200 cm3
• The composition of urine varies. Typically, urine contains:
95% water
5% other solutes (incl. organic molecules such as urea, creatinine and uric acid), ions (mainly sodium &
chloride ions) and other metabolic wastes.
Regulation of Urine and its composition
• Urine is regulated by using ADH (anti-diuretic hormone) as it increases the permeability of the distal tubule and collecting duct to water
Composition:
• When ADH is present, water is reabsorbed into the blood of the peri-tubular network by osmosis and the urine produced is more concentrated.
• If ADH is not present the membranes are impermeable to water.
• This results in less water passing back to the blood and greater volume of urine produced.
- ADH secretion is controlled by the Hypothalamus (part of brain).
- There are receptors in the hypothalamus which monitor the salt concentration in the blood.
- When the solute (e.g. Salt) concentration is high, the hypothalamus sends messages to the posterior pituitary which secretes ADH.
- The body reabsorbs water to dilute high solute concentration in the blood.
- When the solute concentration is low the hypothalamus stops sending messages to the posterior pituitary gland and the secretion of ADH is decreased.
Regulation of pH in the kidneys
If the blood is acidic (Low pH: too many H+ ions):
• The kidneys can excrete hydrogen ions (H+) and ammonia or…
• The body can reabsorb sodium ions (Na+) and bicarbonate ions (HCO3-) into the bloodstream.
If the blood is alkaline (High pH):
• Fewer hydrogen ions are excreted,
• Fewer sodium ions and bicarbonate ions are reabsorbed.
• All regulation is a balancing act: secreting more or less ADH, or more or less ions as required, constantly readjusting as needed.
Liver
- Liver’s functions:
- Deaminates amino acids
- Produces bile
- Converts glucose to glycogen
- Stores iron, and vitamins A, B12, D, E & K
- Synthesises vitamin A & plasma proteins
- Detoxicates drugs (including alcohol) and other toxins.
- Located in upper abdominal cavity.
- Processes excess protein so that it can be removed from the body.
- If the body has a sufficient supply of carbohydrates and lipids, or stored lipids, then protein is not used for energy.
- Excess protein cannot be stored in the cells so it must be removed.
Role of Liver in excretion
- Protein is broken down into amino acids, these are used to build new proteins that the body needs.
- However, if our other energy sources are used up, the body can metabolise proteins for energy.
Deamination (Liver in Excretion)
- Deamination is the stripping of nitrogen from amino acids and nitrogen bases (RNA).
- Nitrogen occurs in the amino (NH2) part of an amino acid and since nitrogen is toxic to the human body it must be removed.
- To metabolise proteins, the amino group (NH2) must be removed from the amino acid with the aid of enzymes.
- This converts the amino acid into ammonia (NH3)
- Process of Deamination: Amino acid + O2 → ammonia + organic compounds
- The remains of the amino acid which is mostly Carbon and Hydrogen is converted into a Carbohydrate which is used to release energy, CO2 and water.
- Ammonia is highly toxic so it is converted quickly into the less toxic UREA which can be easily excreted in urine or in sweat.
- Ammonia (very toxic) + CO2 + energy → urea (H2NCONH2) + H2O
- The liver also detoxifies alcohol and other drugs such as antibiotics.
- It deactivates hormones and converts them into a form that can be excreted by the kidneys.
- Haemoglobin from dead Red Blood cells is broken down in the liver to produce bile pigments, which are passed out with faeces.
Metabolising Proteins
- Remove the amino group - deamination.
- Convert the amino group to ammonia and then to urea, in the liver.
- Eliminate the urea in the urine. The remaining part of the amino acid is primarily made of carbon and hydrogen.
- These are converted to carbohydrates and then broken down to form energy.
Kidneys
Structure:
• Cortex - the outer layer of the kidney, it surrounds the whole kidney and appears reddish-brown
• Medulla - inside the cortex and is slightly darker in colour
• Renal pyramids - striated, triangular structures within the medulla
• Renal papillae - tips of the pyramid, project towards the renal pelvis, they are separated by the columns of the cortex
• Major calyces - cup- like extensions which divide into minor calyces
• Renal pelvis - funnel- shaped, expanded upper end of the ureter, holds the urine formed by the kidneys
Function:
• The function of the kidneys is to expel wastes, especially nitrogenous wastes such as urea from the body.
• They also regulate the body’s balance of fluid, salt and pH.
• They achieve these by filtering the blood as it passes through the kidneys.
• Waste substances are removed by the processes of filtration and tubular secretion.
• Useful substances are returned to the body by the process of selective reabsorption.
Nephron:
• The functional unit of the kidneys is called the Nephron and is where urine is formed.
• There are about 1.2million nephrons in each kidney
Each nephron consists of a:
• Renal corpuscle
• a Renal tubule
• surrounded by a network of blood capillaries.
The Nephrons (Kidneys)
- The Nephron starts with the Renal Corpuscle, which is made up of the glomerulus and the glomerular capsule (aka Bowman’s capsule).
- The Glomerulus is a knot of arteriole capillaries which is formed from the Afferent Arteriole and then recombine to form the Efferent Arteriole.
- The Glomerular Capsule is a double walled cup that surrounds and almost encloses the glomerulus.
- Leading away from the renal corpuscle is the Renal Tubule which is about 5cm long.
- This begins with the Proximal Convoluted Tubule which is highly convoluted section that leads away from the glomerular capsule. (Proximal meaning close)
- The tubule then turns into a straight hairpin like section called the Loop of Henle, with a Descending Limb heading downwards and an Ascending Limb heading back upwards.
- The tubule then becomes convoluted again with the Distal Convoluted Tubule. (Further Away)
- The distal convoluted tubules of a few nephrons join to form a Collecting Duct which open into a funnel shaped structure called the Renal Pelvis, which holds the urine until it is passed through the Ureter.
- Nephrons start in the cortex section of the kidney and finish in the medulla.
- The kidneys are supplied with blood from the Renal Artery which divides into smaller afferent arterioles.
- The efferent arteriole that leaves the glomerular capsule then forms the capillary network that surround the renal tubule.
- This network is known as the Peritubular Capillaries
- The capillaries recombine to venules which connect to the Renal Vein
Urinary System
- Kidneys – pair of reddish-brown organs located in the abdomen roughly 11cm long. They regulate blood composition.
- Ureter – transports urine from kidney to bladder.
- Bladder – stores urine.
- Urethra – discharges urine from the body.
Glomerular Filtration (Kidneys)
- Takes place in the renal corpuscle.
- Materials are filtered out of the blood in the glomerulus (mass of blood capillaries) and collected in the glomerular capsule.
The structure of the glomerulus is suited to its function of filtration (site of filtration):
• The efferent arteriole leaving the glomerulus is much narrower compared to the afferent arteriole entering it.
• This increases resistance to blood flow in the efferent arteriole, which creates a high pressure in the capillaries which forces water and undissolved blood components through the capillary membranes into the capsule.
• The glomerular capsule directly surrounds the glomerulus and the walls of both the capillaries and the capsule are only one cell thick, which allows the filtrate to pass efficiently into the capsule.
• Blood is also continually flowing which maintains the concentration gradient.
Filtration is the process where fluid is forced out of the blood in the afferent arteriole due to the high-pressure cause by the:
• Netted capillaries of the Glomerulus
• Decreased diameter of the efferent arteriole
• Proximity to the aorta
Filtrate
• The filtrate will consist of all the components of blood, except Red blood cells, White blood cells and Plasma proteins as they are too large to pass through the membrane.
Therefore, the filtrate will contain: • Water, Various Ions, and Salts • Amino acids, Fatty acids, Glucose • Urea, Uric acid, and Creatinine • Vitamins, Hormones and Toxins
