Excretion
What is excretion? Excretion is the removal of metabolic waste from the body.
Excretion in Plants Plants produce very little waste products. Plants lose oxygen and water vapour through the stomata.
Homeostasis (temperature regulation in animals) Temperature in the body controls chemical (enzyme) reactions. Animals use two different methods to control their temperature: 1) Ectotherms: gain or lose heat from their environment. 2) Endotherms: generate their own heat from metabolic reactions.
Temperature regulation in humans The skin allows for temperature regulation in humans. Skin consists of two layers: Outer epidermis Inner dermis The subcutaneous tissue contains fat rich cells call adipose tissue.
Vertical section of skin Granular layer Malpighian layer
Epidermis The malpighian layer divide by mitosis to produce new epidermis cells. These new cells protein the water proof protein called keratin (nails, claws, horns and scales). Other cells in the malpighian layer produce a brown pigment called melanin. This gives the colour to the skin, hair and the coloured part of eye. Freckles and moles are where melanin is very concentrated.
Functions of Melanin Protects the skin against the harmful effects of ultra violet radiation. Production of melanin increases following exposure to sunlight.
Dermis Dermis consists of connective tissue containing a protein called collagen. Consists of sweat glands, hair follicles, sebaceous glands, nerve receptors and blood vessels. NOTE: Sebaceous glands produce an oil called sebum.
Functions of the skin Protection Vitamin D production Food store Sense organ Excretion Temperature regulation
Functions of the Skin: Epidermis: Protects the body from damage and prevents the entry of pathogens. Dermis: Protects internal organs from damage. Melanin: Protects the skin against UV rays Sebum: is an oil that keeps hair moist, flexible and prevents skin from drying out. Vitamin production: Vitamin D is produced in the skin by exposure to sunlight (vitamin D helps absorb calcium in the intestines).
Functions of the skin: Food store: Fat in the adipose tissue acts as a food store. Sense organ: Skin contains nerve receptors which detect temperature and sensations. Excretion: Sweat glands act as organs of excretion. Sweat contains salt and water.
Functions of the skin: Cold conditions: The skin can help retain heat. Erector muscles contract (form goose bumps) which cause the hair to stand up (piloerection). A layer of warm air is trapped close to the skin by the hairs which helps to reduce heat loss.
Functions of skin: Cold conditions: Blood vessels in the skin contract (vasoconstriction) which reduces heat loss. Finally, a part of the brain respond s to cold conditions by causing muscles to contract and relax to cause shivering which produces heat.
Functions of the skin: Warm conditions: Sweat is produced and released onto the skin (water evaporates to lower body temperature). Blood vessels in the skin expand (dilate) especially in the face. This increases heat loss through the skin and reduces body temperature.
Role of excretory system in homeostasis 1) Regulating body temperature 2) Controlling osmosis (salt and water balance of body) 3) Controlling concentration of body fluids 4) Removing waster products of metabolism from the body.
Organs of excretion: Lungs: excrete water and carbon dioxide Skin: excretes water and salts as sweat Kidneys: excrete water, salts and urea in the form of urine. NOTE: Kidneys controls the fluid and chemical composition of the blood (homeostasis)
The Urinary System
Facts on the Kidney Kidneys are located below the diaphragm in the small of the back. Aorta and renal arteries carry blood rich in waste products to the kidney. 20% of blood passes through kidneys every minute. Urinary system - The nephron - YouTube
Filtration Blood entering the kidneys is filtered which takes place in the outer cortex. Small substances are forced out of the bloodstream into the kidney.
Reabsorption Useful materials are taken back into the blood which is known as reabsorption. Takes place in the cortex and the medulla of the kidneys.
Secretion Substances are secreted from the blood into the cortex of the kidney (potassium and hydrogen ions). Kidneys control blood ph by controlling hydrogen ion concentration in the blood. Unwanted toxic substances are left in the kidney to form urine.
Purified blood leaves the kidneys through the renal veins and then the vena cava. Urine goes from the medulla into the ureter which carries the urine to the bladder. Filtration of small molecules in the renal artery Useful substances reabsorbed into the renal veins Urine flows to the bladder in the ureter
Urine Urine is composed of: 96 % water 2.5 % nitrogenous waste (urea) 1.5 % salts NOTE: Urea is formed in the liver (excess proteins are broken down deamination)
Bladder Can store up to 800ml of urine. Control of urination is caused by the ability to control the sphincter reflex.
Functions of the kidneys 1) Excretion: remove waste products from the blood and converts them to urine 2) Osmoregulation: i) Water content: controls water content in body (varies water content in urine). ii) Salt concentration: controls salt concentration of the body fluids (varies amount of salt released in urine). Example: if we consume to much salt, the kidneys will increase the amount of salt excreted in urine.
Functions of the kidney 3) ph control: controls the ph of the blood fluids (varies the acidity of the urine) NOTE: ph of blood is 7.4
The nephron Each kidney contains more than a million nephrons. A nephron is a tube about 3 cm long. Nephrons are located in the cortex and medulla of the kidney. Nephrons make urine.
Blood supply to nephron Blood enters kidney through renal arteries which divide into smaller afferent arterioles (incoming). Each afferent arteriole divides into capillaries called glomerulus (located in Bowman s Capsule). Blood leaves the nephron through the efferent arteriole (outgoing).
Bowman s capsule and the blood vessels
Urine production Urine is produced in the nephron It involves three processes: 1) Filtration 2) Reabsorption 3) Secretion
Filtration Filtration: 1) Blood entering the nephron in the afferent arteriole contains waste products. 2) Filtration takes place in the glomerulus (glucose, amino acids, vitamins, hormones, urea, salts and water are forced out of plasma into the Bowman s capsule) 3) The materials that are filtered are called the glomerular filtrate.
Filtration Adaptions of the glomerulus for filtration: Pressure in the glomerulus is greater than normal blood pressure (efferent arteriole is narrower than afferent arteriole). Surface area of capillaries in the glomerulus is large (increases area for absorption). Walls of capillaries are very porous. Wall of Bowman s capsule is one cell thick.
Filtration Large substances do not enter the glomerular filtrate (red and white blood cells, platelets, antibodies).
Reabsorption After the Bowman s capsule, all the useful substances are reabsorbed back into the blood. 99% of the glomerular filtrate is reabsorbed.
Reabsorption (proximal tubule) Along the proximal tubule most of the water is reabsorbed by osmosis. Glucose and amino acids are reabsorbed back into the capillaries by diffusion and active transport. What is active transport? energy is required to move molecules against the concentration gradient (low to high)
Adaptions of the proximal tubule for absorption: Adaptions: 1) Thin walled 2) Long 3) Numerous infoldings 4) A lot of mitochondria (energy for active transport)
Reabsorption Descending loop of Henle: 5% of water is reabsorbed here by osmosis. Ascending loop of Henle: Permeable to salts and reabsorbs water. NOTE: Main function of Loop of Henle is reabsorption of water.
Reabsorption Distal convoluted tubule: water and salts are reabsorbed (controls water, salt and ph values).
Collecting duct Permeable to water which is reabsorbed due to osmosis. NOTE: the liquid passing from collecting duct is called urine.
Secretion Some substances pass from the blood into the nephron. How does glomerular filtrate differ from urine: Glomerular filtrate has more water than urine. Contains useful substances (glucose and amino acids).
Condition Controlling urine volume Effect on blood ADH Distal tubule and collecting duct Urine Thirsty or Hot day or Salty diet Low water content and high salt concentration Produced Makes it more permeable to water Low volume of water, higher salt concentration (low volume of urine produced) Excess water intake or Very lo salt concentration High water content and low salt concentration Not produced Less permeable to water High volume of water, low salt concentration (high volume of urine) High protein diet Increased concentration of urea No effect No effect Increased urea concentration (same volume of urine, high levels of urea)
Role of ADH: NOTE: ADH = anti diuretic hormone ADH travels to kidneys to make walls of distal tubule and the collecting ducts more permeable to water. ADH allows for the reabsorption of more water from the nephron.
Reabsorption in the nephron
Control of urine volume Blood plasma to concentrated: 1) If you lose to much water (sweating) the salt concentration of plasma rises. 2) Receptors in brain are triggered which causes the pituitary gland to release the hormone ADH (anti diuretic hormone) 3) ADH travels to kidney in the blood which causes the wall of distal tubule to become more permeable to water. 4) ADH causes more water to be reabsorbed fro the nephron which reduces salt concentration in the blood plasma. 5) A lower volume of urine is then produced
Control of urine volume Blood plasma concentration normal of too dilute: 1) If to much water is reabsorbed, the plasma becomes to be diluted. 2) ADH is not produced, which means the distal tubule and collecting ducts become relatively impermeable to water. 3) Water is not reabsorbed from the distal tubules. 4) A larger volume of dilute urine is produced.