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Course: High school biology > Unit 8
Lesson 4: The digestive and excretory systemsThe digestive and excretory systems review
Key terms
| Term | Meaning |
|---|---|
| Digestive system | The body system that converts food into energy and nutrients to fuel the body |
| Chemical digestion | The breaking down of food using chemical agents, such as enzymes and bile |
| Mechanical digestion | The breaking down of food by physical means, such as chewing |
| Absorption | The process by which nutrients pass through the walls of the digestive system into the blood |
| Excretory system | The body system that removes metabolic wastes from the body |
| Excretion | The process of removing wastes and excess water from the body |
The digestive system
The human digestive system breaks food down into small molecules that can be used by cells in the body.
Digestion begins when food enters the mouth (oral cavity). Both mechanical and chemical digestion occur in the mouth. Teeth grind and break up food (mechanical), while an enzyme in saliva called amylase begins to break down carbohydrates (chemical).
After it is swallowed, the chewed food (now called a bolus) moves down the esophagus. The esophagus acts as a connection between the mouth and the stomach, but no digestion occurs here.
The bolus then reaches the stomach, where more mechanical and chemical digestion take place. The muscles in the stomach walls churn the bolus (mechanical), allowing it to mix with digestive enzymes and gastric acids (chemical). This process converts the bolus into a liquid called chyme.
Digestion continues in the stomach for several hours. During this time, an enzyme called pepsin breaks down most of the protein in the food.
The chyme is slowly transported into the small intestine, where most chemical digestion takes place. Bile, which is made in the liver, is released from the gallbladder to help digest fats. In addition, enzymes from the pancreas and intestinal walls combine with the chyme to start the final part of digestion.
Most nutrient absorption occurs in the small intestine. Nutrients are absorbed through its walls into the circulatory system and by the time the chyme exits the small intestine, only water and undigestible substances are left behind.
The chyme then enters the large intestine. Here, water is removed and bacteria break down some undigestible materials, producing important compounds (such as vitamin K). The concentrated waste material that remains is called feces, which is passed into the rectum and eliminated from the body through the anus.
Accessory organs
Accessory organs help with digestion but are not part of the digestive tract. These include:
- Salivary glands: moisten food and begin chemical digestion of starches.
- Liver: creates bile for fat digestion, detoxifies blood, processes absorbed vitamins
- Gallbladder: stores bile produced by the liver
- Pancreas: secretes pancreatic juices to help digestion of proteins and carbohydrates
The excretory system
The excretory system removes metabolic wastes from the body.
The major organs of excretion are the kidneys, a pair of bean-shaped organs located below the liver. The kidneys filter blood and regulate water balance in the body.
There are several other organs that are also involved in excretion, including:
- the skin, which removes excess water and salt via sweat,
- the lungs, which exhale carbon dioxide, and
- the liver, which breaks down toxic substances in the blood and convert nitrogenous waste into urea
Urinary tract
The urinary tract is a major part of the excretory system. It filters wastes and water from the blood, and eliminates them from the body.
The kidneys produce a waste product called urine using special functional units called nephrons. The urine is then excreted from the body. This process takes place in three steps:
- Filtration: Blood enters a nephron, which filters out impurities.
- Reabsorption: The impurities move through tubules, while the rest of the blood is reabsorbed through capillary walls into the blood.
- Excretion: Urine is transported from the kidneys through the ureters and into the urinary bladder. It remains stored in the bladder until it is released through the urethra.
Common mistakes and misconceptions
- Digestion does not begin in the stomach. While some digestion occurs in the stomach, the process actually begins in the mouth, where chewing and salivary amylase act on the food.
- The digestive system does not produce urine. Some people think that the digestive system has two outlets - one for feces and one for urine. However, urine is a product of the excretory system, not the digestive system.
- The small intestine is actually longer than the large intestine. In fact, at approximately 20 feet in length, the small intestine is nearly four times as long as the large intestine (5 feet long)! However, the intestines are named for their diameters, not their lengths. The large intestine has a diameter of about 3 inches compared to the small intestine, with a diameter of about 1 inch.
Want to join the conversation?
So are stomach don't make urine(0 votes)
No, your kidneys do. The stomach does extract water from the food though. That water enters the blood and is used by cells, then extracted out of blood along with excess nitrogen in the kidneys.
So it kind of depends on what you mean by "make urine." The energy in urine was created at the big bang. The elements were created in stars and supernovas. The water was mostly extracted in the stomach, and the nitrogen waste was produced in cells all over the body. However, the thing only becomes actual urine in the kidneys, so we say the kidneys make urine.(41 votes)
How do cll affect the kidneys in the long run(5 votes)
Cancer starts when cells start to grow out of control. Cells in nearly any part of the body can become cancer and can spread to other parts of the body . Chronic lymphocytic leukemia (CLL) is the most common leukemia in adults. It's a type of cancer that starts in cells that become certain white blood cells (called lymphocytes) in the bone marrow. The cancer (leukemia) cells start in the bone marrow but then go into the blood.In CLL, the leukemia cells often build up slowly. Many people don't have any symptoms for at least a few years. But over time, the cells grow and spread to other parts of the body, including the lymph nodes, liver,kidneys, and spleen. i wish it can help(11 votes)
What path does water take to get from the mouth to the kidneys?(6 votes)
Water is absorbed into the body via the large intestine, at which point it enters the bloodstream. Blood is then filtered through the kidneys.(8 votes)
- what causes a person to need dialysis(3 votes)
- The waste component of urine is called Urea. If your kidneys stop working then that urea will build up and cause your body to stop functioning. It is toxic if not excreted through the kidneys. Therefore, the person needs dialysis to filter this urea (toxin) out of their body. The machine is doing the function of their kidneys. Person's can live on dialysis for years if they take care of their body through diet, exercise etc.(6 votes)
- Will you die if you get your two kidneys donated?(2 votes)
You cannot live without having at least one kidney.
Here's why....
So as the daughter of a man who worked with dialysis patients (kidney failure patients) your chances of survival without your kidneys is low. You will either need a kidney transplant or you will need dialysis. Dialysis won't prevent you from dying it will just allow you to live a little longer than having no kidneys at all.
Hope you find this answer helpful. :>(7 votes)
- what happens when the mucus secretion in stomach becomes abnormal ?(2 votes)
If there's no mucus in the stomach then an ulcer develops.(6 votes)
- will you die if the urter doesn't work(3 votes)
your ureter is one of the most important things in the urinary system. It is a tube that transports urine from your kidneys to the bladder. If your ureter doesn't work, then you will not be able to pee. There are artificial ureters that can be put in your body if your ureter does not work.(4 votes)
will you get the chance to eat dinner.(3 votes)
what is oral cavity(1 vote)
The oral cavity represents the first part of the digestive tube. Its primary function is to serve as the entrance of the alimentary tract (gastrointestinal tract) and to initiate the digestive process by salivation (through the salivary glands) and propulsion (through peristalsis) of the chewed up food into the pharynx. This is done with aid from the teeth, salivary glands, tongue, and lips. Basically, it's your mouth.(5 votes)
- What happens to the circulatory and excretory systems, if there is a disruption in the digestive system?(2 votes)
If the digestive system is disrupted, then less nutrients will not get to the circulatory system. Blood will still be filtered in the kidneys and excreted, though.(2 votes)
