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UNIT 5: Systems involved in nutrition I: Digestive and respiratory systems
1- Systems involved in nutrition
There are four systems involved in nutrition:
-Digestive system: Transforms food into nutrients which can be used by our cells.
-Respiratory system: Captures oxygen and eliminates carbon dioxide and water produced by cell
respiration.
-Circulatory system: Transports substances (nutrients and waste products) through the body.
-Excretory system: Cleans the blood eliminating waste products produced by cell metabolism.
2- Digestive system structure
The Mouth has different parts:
-Teeth:
(Grind food)
(Grind food)
(Cut food)
(Pierce and
tear food)
-Tongue: has taste buds.
-Salivary glands: Parotids, submandibular and sublingual glands. They produce saliva.
Salivary glands
Epiglottis
Cardias
Transverse colon
Duodenum
Small
Jejunum
intestine
Descending colon
Ascending colon
Illeum
Caecum
Large
intestine
Rectum
Appendix
Anus
The epiglottis is a flap at the entrance of the pharinx which closes when we swallow and
forces food to go down the esophagus instead of the respiratory system.
3- How does the digestive system work?
We can be observed five steps in the digestive systems:
1-Ingestion: Food enters the gastrointestinal tract through the mouth. In the mouth two things
occur:
-Physical (mechanical) digestion: teeth and tongue are involved in breaking apart
food.
-Chemical digestion: In the mouth, salivary glands produce saliva which contains
the enzyme amylase which acts on starch, breaking it into maltose.
2-Swallowing (deglutition): After swallowing, the bolus (ball of food made by the actions of the
teeth, tongue, and saliva) moves to the stomach through the esophagus which uses waves in its
wall called pesristaltic movements to move the bolus.
3-Digestion:
Digestion in the stomach:
-Physical: the stomach is a muscular storage organ that churns the food.
-Chemical: gastric juice, produces by gastric glands, mixes with bolus. Gastric juice
contains:
a) Pepsin: enzyme that breaks down protein.
b) HCl: hydrochloric acid. It allows pepsin to work.
c) Mucus: protects the stomach from HCl damage.
The stomach contents are now called chyme.
Digestion in the intestines:
Gland involved
Juice involved
Salivary gland
Saliva (amylase)
(mouth)
Gastric glands
(Stomach)
Intestinal glands
(duodenum)
Pancreas
Gastric juice
(pepsin)
Intestinal juice
Nutrient
Carbohydrates
(starch)
Final product
Glucose
Proteins
Amino acids
Carbohydrate
Glucose
Proteins
Amino acids
Pancreatic juice
Carbohydrate
Glucose
(Duodenum)
Proteins
Amino acids
Lipids
Small lipids
Liver
(bile) Gallbladder Lipids
Small lipids
(Duodenum)
*The table shows digestion in the intestines and in the rest of the digestive system.
4-Absorption:
Absorption is the transport of nutrients from the intestines to the blood. Most of nutrients are
absorbed in jejunum and illeum. Water and mineral salts are absorbed in the colon. The intestinal
wall is covered by villi (folds formed by cells with microvilli in their surface) which increase the
absorption surface. Inside the villi there are blood capillaries which pick up nutrients to be carried
through the body.
5-Egestion:
Egestion is the discharge of undigested food (as feces) from the digestive tract via the anus.
Feces are formed when food is transformed by bacteria in the large intestine.
3- Digestive system disorders
 Cavities: When we eat or drink something that contains sugar, the bacteria uses it to
produce acids. These acids destroy tooth's emanel and dentine, making small holes in them.
You should brush your teeth after eating and go to the dentist regularly.

Constipation: When an individual has hard feces that are difficult to expel. It occurs when
the colon has absorbed too much water from the food that is in the colon. To avoid
constipation we should consume foods rich in fiber, drink a lot of water and do exercise.

Ulcers: Are painful sores that can be found in the stomach lining or small intestine.
Stomach ulcers are caused by excess acid. Treatment will vary depending on the cause of
your ulcer. Most ulcers can be treated with:
- Acid blockers
- In serious cases, surgery may be required.

Gastroenteritis: is inflammation of the gastrointestinal tract caused by viral or bacterial
infections. It provokes symptoms like diarrhea, vomiting, and abdominal pain. The primary
treatment for gastroenteritis is rehydration (by drinking rehydration solution to recover
water and mineral salts lost) and then to go on a bland diet.

Hepatic cirrhosis: is the severe damage of the liver caused by long-term exposure to
toxins such as alcohol or viral infections.
4-Respiratory system
-Function:
Is to take in oxygen from atmoshere (which is be used by cell respiration) and release carbon
dioxide and water (produced in that process).
-Structure:
Nasal cavity
Oral cavity
Pharinx (with epiglottis)
Larynx (vocal cords)
(cartilaginous rings)
(protected by pleura)
-Breathing process:
Inhalation
Diaphragm:
Contracts and
curves down
Intercostal muscles:
Air
Contract
Enters the body
exhalation
Relaxes and
curves up
Relaxe
Moves out
-Gas exchange:
Gaseous exchange occur in alveoulus by diffusion. This alveolus is surrounded by blood
capilaries. In diffusion, oxygen which is more in concentration in alveolus and low in blood, go to
the blood from alveolus and carbon dioxide which is more in concentration in pulmonary capillary
and low in alveolus go to the alveolus from pulmonary capillary blood.
-Respiratory disorders:
 Bronchitis is an inflammation or swelling of the bronchi. There are two types:
-Acute bronchitis: Due to viral infections (like flu).
-Chronic bronchitis: Due to toxic substances in smokers.
 Asthma is the inflammation and narrowing of the bronchial tubes.
 A cold is a bacterial or viral infection. Some symptoms are: runny nose, coughing,
sneezing, headache, temperature.
 Tuberculosis is a bacterial infection that destroys the lung tissue.