9.5 Excretory System

Learning GOals Learn and use the vocabulary Describe the anatomy of excretory system Describe how it works Know how this system maintains homeostasis Know how a change in the environment will affect this system (i.e. Drinking more or less, filtering toxins etc.) Pg 342-352 and 358-361

Excretory System Function Excretory systems needed to concentrate wastes and then excrete toxins into environment Regulates fluids and water within the body

Other Organisms Unicellular organisms can excrete toxic wastes via: Diffusion directly with environment Ex. Paramecium and contractile vacuoles (pump water out actively maintaining osmotic balance)

Terrestrial animals - Multicellular organisms need organ systems because they’re too large for diffusion to be efficient

Invertebrate Excretory Systems Metanephridium is a system of tubes and nephridopores that reabsorbs and excretes wastes out of worms

Invertebrate Excretory Systems Malpighian Tubules: system of tubes that deliver wastes to intestines in insects via reabsorption and excretion

Birds and Some Reptiles Excrete salt through glands on nose especially in salty environments

Human excretory system The major organ of this system is the kidney which is made up of specialized tubules called nephrons Other parts of the system include the bladder, the ureters and the urethra Wastes are filtered from the blood by the kidneys and passed to the bladder by the ureters The bladder have stretch receptors that send signals to the brain to let you know you have to urinate Urine passes through the urethra to exit the body

Human excretory system Renal = of the kidneys

Nephron Nephron is a microscopic unit of filtration in the kidney; acts like sieve for reabsorption and excretion of wastes Kidney contains millions of them

nephron The nephron is divided into regions that carry out specific steps involved in excretion: Blood enters nephron and collects in glomerulus The glomerulus is a capillary bed where waste moves from bloodstream into the Bowman’s Capsule and then into the Proximal Tubule

Filtrate enters the Proximal tubule Peritubular capillaries surround the entire nephron to reabsorb substances back into the blood Urine is formed in the nephron tubes

The proximal tubule leads to the Loop of Henle which helps reabsorb any useful materials (H2O, Na+, Cl- etc.) into the bloodstream The loop of henle leads to the Distal tubule and eventually to the Collecting ducts Collecting ducts drain into the renal pelvis Urine leads to ureters then bladder

Urine Formation: 3 steps 1. Filtration 2. Reabsorption 3. Secretion

Step 1. Filtration Fluids from the blood move through the afferent arteriole into glomerulus The capillaries of the glomerulus are under high pressure forcing dissolved solutes to move into Bowman’s Capsule from high to low pressure Water, sodium chloride (NaCl), glucose, amino acids, and hydrogen ions (H+) will move through the wall of the glomerulus But plasma proteins, blood cells, and platelets are too large and stay in the capillaries

Label where Filtration occurs in the image in your notes.

Step 2. Reabsorption Must reabsorb some substances from the filtrate that enters the nephron—otherwise we’d urinate 120mL per minute! Only 1 mL of urine is produce per 120mL of filtrate entering nephron

Step 2. Reabsorption Selective reabsorption so that only particular substances stay in the body Filtrate enters the proximal tubule H2O, ions and nutrients transferred back to interstitial fluid using both active and passive transport Active: Active ion pumps transport K+, Na+, & Cl- from filtrate into the fluid surrounding the tubule Glucose and amino acids are reabsorbed using active transport proteins

Step 2. Reabsorption The reabsorption process makes the filtrate hypo-osmotic to the interstitial fluid causing water to flow out of the tubule into the interstitial fluid by osmosis Movement of water can also be facilitated by membrane proteins called aquaporins

Step 2. Reabsorption The remaining filtrate (urea & other wastes) move into the descending Loop of Henle where additional water is reabsorbed In the ascending Loop of Henle more Na+ and Cl- are reabsorbed into the interstitial fluid using active and passive transport The filtrate now moves into the distal tubule where additional water and salts are removed Lastly, the filtrate moves into the collecting ducts where more water can be reabsorbed and then exits through the kidney to the bladder

Step 3. Secretion Is the removal of wastes from blood and interstitial fluid This occurs in the proximal, distal tubules and the collecting ducts Nitrogen-containing wastes, excess H+ ions, detoxified poisons (ex. Alcohol, medications...), and other minerals (K+) are balanced by secretions from the interstitial fluid into the nephron

Kidney Stones When calcium deposits build up in the kidneys Blocks urine flow Very painful to pass

History Is Cool Lithotomy is one of the first surgeries Removal of kidney stone through cut between anus and scrotal sack No anaesthetic or doctors—barber surgeons until 1800s

Dialysis When kidneys malfunction machines are used instead Patient must sit for hours several times a week to filter their blood artificially

Urinary System Game The class will be split into 2 teams and you will compete against each other to see if who completes this task first. Each person in your group will be assigned a part of the urinary system and must put it together from start to finish. When one team is done you will need to present it in order to me. One student can represent the wastes and flow through the system with each student explaining their function as they travel along.

Success Criteria Can you fill in the matching sheet and draw out the pathway? Can you fill out the table to determine the function of each section? Table 1 on page 342 is a great summery you should know.