The Excretory System Chpt. 32

 Excretion is the removal of waste products of metabolism from the body.  The excretory system plays a role in homeostasis: (i) by maintaining the composition of an organism's fluids, including fluid balance and chemistry. (ii) by preventing the accumulation of poisonous wastes which might interfere with metabolism (iii) maintaining a constant temperature. Excretory System in Humans REMEMBER: Homeostasis is the maintenance of a constant internal environment within the body.

Organs of Excretion LUNGS – excrete water + CO 2 SKIN – excrete sweat (water & salts) KIDNEYS – excrete urine( water, salts & urea)

Our Excretory System

Temperature Regulation  Temperature influences the rate of enzyme- controlled reactions that sustain life.  Animals can be classified according to the method they use to control their temperatures: Ectotherms Endotherms

 Mammals and birds are endotherms (warm blooded) their source of heat is internal i.e. from their own metabolic heat.  They can operate in low temperature environments, as they can keep the rate of enzyme activity high. Endotherms:

 Most animals are ectotherms (cold blooded) — they lose or gain heat by moving into areas where temperature is suitable, e.g. fish, amphibians, reptiles. Ectotherms:

Temperature Regulation in Humans  Control of body temperature is an example of how homeostasis works in humans.  Our normal core body temperature is maintained at 37°C, the heat being mainly produced from metabolism in the liver.  Skin: - role of skin in homeostasis – Temperature Regulation - role of skin as excretory organ – Removal of Sweat

The Skin

1.Epidermis - Cornified Layer - outer layer is dead, hardened, flattened cells - Granular Layer - inner layer has living granular cells - Malpighian layer - makes new cells by mitosis and contain the pigment melanin The skin is made up of two layers: - outer epidermis - inner dermis

2. Dermis Consists of connective tissue containing a strengthening protein called collagen Contains blood vessels, sweat glands, sebaceous glands, hairs, nerves NOTE: Beneath these layers is SUBCUTANEOUS LAYER which contains fat rich cells called adipose tissue

Protection: Epidermis - protects against damage, water loss, entry of pathogens Dermis - protects internal organs Melanin - protects against UV radiation Sebum - keeps the epidermis intact Vitamin Production: Skin makes vitamin D following exposure to UV radiation Functions of the Skin:

Food Storage: Fat (in adipose tissue) stores energy Sense: Skin is an organ of touch ie. senses touch & temperature Excretion: Sweat glands act as organs of excretion Sweat removes water & salts from the body Functions of the Skin:

Temperature Regulation: Cold Conditions: Erector muscles contract causing hairs to stand up. These hairs trap a layer of warm air close to the skin reducing heat loss Blood vessels narrow to retain heat Shivering – muscles contract which generates heat to raise temp

Temperature Regulation: Sweating Blood vessels widen to lose heat and reduce body temp - glands release sweat (a weak salt solution) onto the surface of the skin—this perspiration cools the skin, by taking away some of the body heat when it evaporates

The Urinary System The urinary system consists of: - 2 kidneys - 2 ureters - the bladder - the urethra

The Kidneys: by controlling the amount of water and salts excreted the kidneys play a major role in the homeostasis of the fluid and chemical composition of the body fist sized organs, located just below diaphragm in small of the back

A section through the kidney shows an outer darker region (cortex) and a lighter inner zone (medulla). Cortex Medulla Pelvis Ureter

Kidney LS

The kidneys work by filtering the blood and then absorbing back what the body needs to keep. The wastes are allowed pass to the bladder, for storage and release. Cortex Medulla Ureter Pelvis Filtration Cortex Reabsorption Medulla As urine is produced, it flows into the renal pelvis, then into the ureter, to the bladder.

The bladder stores the urine, which flows through the urethra to the outside. Urine is composed of about 96% water, urea, salt and traces of other hormones such as hormones

Functions of the Kidney Filtration: in the outer cortex - glomerulus, small molecules glucose, amino acids, water, urea and salts filter out of the blood into narrow tubules Reabsorption: blood vessels reabsorb back useful nutrients from the tubules. Urea, excess salts and water, are allowed to continue down the tubule and on to the bladder this occurs in the proximal tubule of the MEDULLA

Secretion: is the production and release of chemicals from cells some substances, especially potassium and hydrogen ions, are secreted from the blood into the tubule in the cortex region when blood becomes to acidic, hydrogen ions are secreted into the urine by controlling the hydrogen ion concentration in the blood, the kidneys control blood pH

Osmoregulation: is the control of water and salt levels to ensure blood plasma has the same concentration as body cells

THE NEPHRON (Higher Level Only) More than a million nephrons per kidney Located in the cortex and medulla Structural and functional unit of the kidney i.e. makes urine

Blood enters the kidney through the RENAL ARTERY This divides into renal arterioles and then smaller afferent (incoming) arterioles Each afferent arteriole divides into a cluster of capillaries called GLOMERULUS Glomerulus found in each BOWMAN’S CAPSULE Blood leaves glomerulus in efferent (outgoing) arteriole Efferent Arteriole Capillaries Renal Venules Renal Vein

THE NEPHRON (HL must know diagram)

Urine formation in the nephron occurs in two stages: Stage 1: Blood entering the kidney is filtered through the Glomerulus into the Bowman’s Capsule Stage 2: As the glomerular filtrate passes through the proximal tubule, loop of Henle and distal tubule, its composition and volume are changed by Reabsorption and Secretion, to form urine

Stage 1: Filtration (Ultrafiltration): Due to high pressure in the glomerulus small molecules such as glucose, amino acids, vitamins, urea, salts are forced out of the blood into BOWMANS CAPSULE forming GLOMERULAR FILTRATE larger molecules such as proteins, red & white blood cells etc. cannot pass through the pores *Note: Blood enters glomerulus under pressure because: - comes from renal artery which is a branch of aorta - efferent arteriole is narrower than the afferent arteriole, which offers greater resistance to the flow of blood

FILTRATION

*NOTE: Active Transport: means that energy is used to move molecules, often against a concentration gradient, i.e. from low concentrations to high concentrations

Stage 2: Reabsorption & Secretion: Reabsorption: In rest of nephron water, most salts and useful substances are reabsorbed back into the blood The glomerular filtrate passes through Bowman capsule into the PROXIMAL TUBLULE where useful substances e.g.. Glucose, AA’s, H 2 O are REABSORBED into the blood due to active transport, osmosis or diffusion Structure of PCR helps reabsorption: - thin wall – 1 cell thick - long - numerous infoldings in its cells– microvilli - cells have mitochondria – provide energy for Active Transport

Reabsortpion in PCR: 1.Glucose/AA’s/Vitamins, (All) Salts Active Transport 2.Uric Acid & Urea Passive Diffusion 3.Water (80%) Osmosis

Reabsorption: Loop of the Henle: Descending Limb: permeable to water approx 5% of water passes out by osmosis therefore increasing salt conc. in loop. Ascending Limb: permeable to salts Na +,Cl -. In this region salts move out of nephron into medulla. Fluid in medulla now becomes more conc. than fluid in tubule causing removal of water from the descending limb and the collecting ducts by osmosis. Role of the Loop of the Henle: to help conserve water in the body, by increasing the salt conc. in the medulla tissue, causing reabsorption of water from collecting duct.

Reabsorption: Distal Convulted Tubule: - controls water, salt and pH values of the blood - up to 10% of the water and some salts can be reabsorbed from the tubule into the blood Collecting Duct: - permeable to water - up to 4.9% of the water in the filtrate can pass out of the collecting duct by osmosis (high salt conc. in medulla) The rest (urine) passes into the PELVIS, the URETER and finally the BLADDER for storage

Secretion: Potassium (K + ), Hydrogen (H + ) and ammonium (NH 4 + ) ions may pass from the blood into the nephron via diffusion and active transport.

SubstanceRegionProcess glucoseProximal convoluted region Active transport Amino acidsPCRActive transport vitaminsPCRActive transport saltsPCRActive transport Na + / Cl - Ascending loop of henle Active transport & diffusion Na + /Cl - Distal convoluted region Active transport & diffusion waterCollecting ducts PCR, Loop of henle osmosis Summary of Substances Reabsorbed

Control of Urine Volume  The kidney regulates the amount of water in the body by varying the amount of urine produced.  This is known as osmoregulation, and it is an example of homeostasis.  ADH [Anti-diuretic hormone] (made in pituitary gland) controls whether the distal tubule and collecting ducts reabsorb water or not.

Why is the kidney referred to as an Osmoregulatory Organ???? becasue it can vary the amount of water and salts it reabsorbs from the glomerular filtrate in order to maintain a constant plasma, water and solute concentration. The ways in which human body gains and loses water: GainsLosses Drinking Urination Eating Defaecation Aerobic Respiration Sweating Exhalation

Too little water may cause salt conc. of plasma to rise, subsequently plasma may become more conc. than blood cells. High salt concentration Hot day, Little water drunk HYPOTHALAMUS in the brain detects high salt concentration in the blood & sends message to PITUITARY GLAND to release ADH ADH travels to the kidneys Causes walls of DISTAL TUBULE & COLLECTING DUCTS to become more permeable to water More water is reabsorbed from the nephron Urine low in volume ( concentrated)

Excessive Water Intake, Low Salt Concentration Too much water consumed, plasma becomes diluted subsequently plasma becomes less concentrated than blood cells Hypothalamus detects low pH of blood ADH is not produced Walls of distal tubule and collecting ducts become less permeable to water Lots of urine produced (dilute)