Excretion vs. Elimination

Excretion vs. Elimination

• Your body makes several kinds of waste, which fall into two groups:

–Undigested solid wastes

–Wastes made by cells

Elimination• Undigested solid waste

leaves your body through the large intestine– Water is removed

from the wastes in the large intestine, which allows for the formation of a solid (feces).

– The solid wastes moves from the large intestine to the rectum.

– From the rectum, the solid waste is excreted through the anus.

Excretion• When waste products made by cells

(water, heat, carbon dioxide, salts, urea) leave your body

• In many animals, CO2 leaves the body through the lungs

• The liquid waste, urine, is made in the kidneys

• Urine: made up of water, heat, harmful chemicals (urea), and some salts

• Perspiration: when heat, water, and salt are excreted by the body through skin (i.e. sweating)

Write the correct waste product next to the excretory organ:1. Skin = 2. Large intestine = 3. Lungs = 4. Kidneys =

(word bank: carbon dioxide, solid wastes, salt, harmful chemicals, water, heat)

The waste products are:Skin = water, heat, saltLarge Intestine = solid wasteLungs = carbon dioxideKidneys = harmful chemicals, heat, salt

The Excretory System

• The group of organs responsible for removing waste products from the body = the excretory system

• The main organs are:– Lungs– Kidneys– Skin

Lungs• When we breathe, we excrete CO2

waste, and small amounts of heat and water

• Fact: your lungs are capable of removing alcohol from the blood; this is how a breathalyzer is able to determine a person’s blood alcohol level

Skin• Largest organ; excretes most of the

body’s waste heat

• Also removes some water, salts, and very small amounts of urea

• Perspiration: helps the body ‘cool off’– When sweat evaporates from the skin, it

cools the body, removing heat

Kidneys• Fist sized, bean shaped (i.e. kidney

bean) organs found on either side of the lower spine

• Main job is to filter out wastes from the blood, making them more concentrated in preparation for excretion and, in the process of doing this, retaining as much water as possible

• The blood enters the kidney through the renal arteries; renal veins carry blood back from the kidneys to the body

• A ureter connects each kidney to the urinary bladder; once urine has formed, the ureter carries the urine (produced after the blood has been filtered for wastes) from the kidney to the bladder

• Another tube, the urethra, carries the urine out of the body

• In males, the urethra passes through the penis; in females, it lies between the pubic bone and the front wall of the vagina

Label the diagram: bladder, kidney, renal artery and vein, ureter, urethra

Nephrons• The filtration of the blood takes

place in minute structures called nephrons, found in the cortex, which is the outer layer of the kidney

• The nephrons estimate at more than 1 million per kidney

• In spite of their size, the kidneys filter more than 180 L of blood every 24 hours

– Most is reclaimed by the body, only 1.5 L of urine is passed each day

– Your blood passes through the kidneys 300 times per day

Label the Kidney: cortex, medulla, renal artery, renal pelvis, renal vein, ureter

Liver• A secondary organ of excretion

• Does not excrete wastes, but is important for excretion

• Handles cell wastes in several ways:1) Breaks down dead red blood cells: pass into digestive tract, then eliminated with solid waste by the bowels

2) Weakens certain harmful substances

3) Changes some harmful substancesEx: the liver makes bile from harmful substances – bile is important in fat digestion – after bile works on fat, it is eliminated from the bowels

4) Combines certain harmful chemicalsEx) liver combines ammonia and some CO2 – forms urea, which the blood carries to the kidneys where it becomes part of the urine

Disorders Affecting the Excretory System

Urinary Tract Infection-Most common problems treated by doctors-Caused by bacteria invading the kidneys, bladder or urinary tract-Examples of infections include cystitis (sis-ti-tis), bladder infection, kidney infection and nephritis-Common symptoms for urinary infections include pain or burning sensation during urination and a sense of needing to pass urine frequently, although the volume passed may be small; urine may be cloudy, foul smelling or bloody; symptoms many be accompanied by fever, chills, lower back pain ***it is possible to have an infection with no symptoms at all-Doctors usually prescribe antibiotics or medication to reduce pain

Kidney Stones-Sometimes some of the salts found in the urine form small crystals that are hard and insoluble called kidney stones-They can form almost anywhere in the urinary tract, but are usually found in the kidneys-When they are painful and obstruct the flow of urine they may have to be surgically removed-Ultrasound is also used to shatter the stones so that the pieces may be passed with urine-Using flexible fibre optics – a tube is passed up through the urethra or through a small hole in the kidney; optic fibres allow the surgeon to see into the kidney and locate the stones, which can then be removed by suction

Note: Urine-In addition to the wastes that we would expect to find in urine, some usable substances are present as well. Physicians use the analysis of urine samples as a common diagnostic technique. The presence or absence of a particular substance in the urine may direct the physicians attention to a problem or provide information about the malfunction of a particular organ

*Drug testing*Pregnancy tests