Food that is consumed must be broken down into smaller soluble particles that can be absorbed into the blood stream. This process is known as
digestion .
The digestive process consists of the following:
Ingestion – food is taken in
Digestion – food is broken down
Absorption – food particles in the bloodstream
Egestion – excretion of undigested food
Digestion may be
mechanical (chewing of teeth and peristalsis) or
chemical (enzymes).
1. What is peristalsis?
2. Which adaptation of human beings makes peristalsis possible?
3. What are enzymes?
4. Where do enzymes come from?
5. What happens to food particles after they have been absorbed into the bloodstream?
The human digestive system
Study the sketch and write down the captions and their functions:
Regions of the digestive tract
Mouth:
Teeth chew food mechanically until fine so that enzymes can operate.
Saliva from the salivary gland contains mucus to form the chewed food into a
BOLUS , as well as
AMYLASE , which digests starch. The mucus facilitates swallowing.
Throat to stomach:
The bolus is swallowed through the pharynx or throat and follows the
oesophagus or
gullet to the stomach.
PERISTALSIS propels the food, even against the force of gravity.
The
EPIGLOTTIS prevents food from slipping into the trachea (windpipe) and thus preventing choking.
Stomach:
The powerful muscles of the stomach grind the food to
CHYM within a few hours.
Enzymes and gastric juice help with the further breakdown of food particles.
The chym is passed through the
pyloric sphincter to the small intestine / ileum.
Ileum:
GALL from the liver helps with the digestion of fats by
emulsifying it.
PANCREATIC JUICE from the pancreas contains many enzymes that assist in completing digestion.
The intestinal wall is folded and has millions of small projections known as
VILLI .
The villi are responsible for the
ABSORPTION of nutrients.
Large intestine:
This is divided into a rising section, a horizontal section and a descending section.
The
COLON reabsorbs water, minerals and vitamins to conserve body fluid.
Undigested remains are stored temporarily in the last part of the large intestine, the RECTUM, until DEFECATION occurs through the ANUS.
ANSWER THE QUESTIONS THAT FOLLOW:
DIGESTIVE TRACT
1. Explain the role of the liver in the processing of toxic substances.
2. Amylose signifies starch. What is amylase?
3. What are the building blocks referred to in an earlier table?
4. What is the gastric juice referred to earlier and from where is it derived?
5. Why doesn’t acid destroy the wall of the stomach?
6. What is an ulcer? How does it develop?
7. What is a sphincter?
8. What is a spastic colon and how is it caused?
9. What is the role of roughage in the digestive process?
10. What purpose do the millions of villi in the small intestine serve?
11. Explain how the ileum is adapted to its purpose.
12. Complete the captions to clarify the structure of the villus:
Structure of a villus
Beneficial bacteria of the digestive tract
A variety of harmless bacteria are present in the alimentary canal. Some assist in the digestion of food by producing enzymes, while other bacteria produce vitamin K, which plays a role in blood clotting.
Questions & Answers
Explain the following terms .
(1) Abiotic factors in an ecosystem
Abiotic factors are non living components of ecosystem.These include physical and chemical elements like temperature,light,water,soil,air quality and oxygen etc
