Digestive and Excretory Systems

Did you know that your digestive

system measure about 30 feet long – from end to end?

Before you start

• In a healthy diet you should have:– Proteins– Healthy Fats– Vitamins– Minerals– Water – Carbohydrates

• Healthy sugars• Starches• Fiber

3 Functions of the Digestive System

1. Breaks down food into molecules the body can use = Digestion

2. Molecules are absorbed into the blood and carried throughout the body = absorption

3. Wastes are eliminated from the body

2 types of Digestion

• Mechanical Digestion• Begins with your first bite

of food– Teeth cut, slice and grind

the food – Saliva makes it slippery– Swallow food to continue

digestion

• Chemical Digestion• Breaks down food with

the help of enzymes – a protein that speeds up chemical reactions in the body

• Each enzyme in the body has a specific function– Spit – contains an enzyme

to break down starches into sugar molecules

– Have a cracker

Organs of the Digestive System - Esophagus

• At the back of your mouth there are two openings:– Epiglottis – a flap of tissue that seals off your

windpipe when you eat– Esophagus – a muscular tube that connects your

mouth to your stomach• Lined with mucus (a thick, slippery substance) that makes

food easier to be swallowed• Food is in your esophagus for about 10 seconds.• Peristalsis – involuntary waves of smooth muscle contraction

that pushes food to the stomach

The StomachA J-shaped muscular pouch.

As you eat it expands to hold your food – average about 2 liters.

• Mechanical Digestion– 3 layers of

muscles contract to churn food

– Similar to they way a washing machine works – mixing the contents with water

• Chemical Digestion – food is further broken down by digestive juices – produced by cells lining the inside of the stomach

Digestive Juices

• Pepsin – enzyme that chemically digests proteins in your food

• Mucus – protects your stomach lining from…

• Hydrochloric Acid – – provides an acidic environment for the pepsin

to function– Kills bacteria you swallow along with your

food.

Small Intestine – 6 meters long

• So now your food is a thick liquid…it enters the small intestine

• Starches and Proteins have been broken down…but fats haven’t

• Almost all chemical digestion and absorption of nutrients takes place here…with help from the liver and pancreas

Held together by the mesentery

Help from the liver…

• Largest and heaviest organ inside your body

• Produces bile (a substance that breaks down fat molecules)

• Bile moves from the liver to the gall bladder – stores bile until its needed in the small intestine

Help from the Pancreas…

• Between the stomach and the small intestine

• Produces 3 enzymes that continue the process of breaking down starches, proteins, and fat

Back to the small intestine

• After chemical digestion – nutrients are absorbed into the villi of the small intestine

• Villi line the walls and contain blood vessels

• The amount of villi greatly increases the surface area of the small intestine = greater absorption.

What’s left?

• By now most nutrients have been absorbed – except fiber (thickens the liquid material in the intestines and allows it to be pushed forward)

• The liquid food also still contains water

• It is pushed by involuntary muscle action into the large intestine.

Large Intestine

• A horseshoe shaped organ – 1.5 meters long

• Contains bacteria that feed on the material passing through = make vitamin K

• Water is absorbed into the bloodstream

• Remaining material enters the rectum and is compressed into solid waste

• Waste is pushed out through the anus

Traveling Tapeworms

• Traveling Tapeworm

Excretory System

The Excretory System…

• …is the system of the body that collects wastes produced by cells and removes the wastes from the body.

What is the waste that we need to get rid of?

1. Carbon Dioxide – more on this later with the respiratory system

2. Excess Water

3. Urea – a chemical that comes from the breakdown of protein

If your body didn’t take away these wastes, they would pile up and make you sick.

Organs of the Excretory System

• Kidneys – you have 2 of them – eliminate urea and excess water through urine.– As blood flows through the kidney they

remove waste from the blood– Urine flows from the kidney through 2 narrow

tubes called the ureters…..– To the urinary bladder – a sac-like muscular

organ that stores urine

How do you know you have to go?

• When the bladder is full enough that its walls are stretched – you feel a need to urinate.

• Urine flows out of the body through a small tube called the urethra.

What do the Kidneys actually do?

• Every drop of blood travels through your kidneys 300 times a day.

• Your kidneys contains about a million nephrons – tiny structures that remove waste from the blood and produce urine

Urine formation – 4 steps

1. Blood flows into a nephron

2. In the capillaries inside a nephron – urea, water, glucose, and other substances are filtered out of the blood. The filtered material passes into a capsule surrounding the capillaries

Urine formation – 4 steps

3. From the capsule – the materials that were removed from the blood pass into a long twisting tube. As the filtered material flows through the tube – glucose and water are reabsorbed, urea stays in the tube

4. After the re-absorption is complete – the liquid that remains in the tube is urine.

Urine and Disease

• What happens when you pee in a cup?– Normal urine contains no glucose or protien– Presence of glucose could = diabetes– Presence of protein = kidneys aren’t

functioning

Why is water so important?

• Remember that as urine is being formed, water is absorbed back into the bloodstream. The amount absorbed depends on…– Hot day - Sweat a lot with

little to drink – almost all of the water will be absorbed – little urination

– Cool Day – Little Sweat with a lot to drink – less water will be absorbed – more urination

– You need about 2 liters of water to maintain balance