Digestive system part 1 Flashcards
Digestion
Digestion- is the process of breaking down nutrients and absorbing them into the blood and carrying it to cells.
The digestive system is the group of organs that work together to carry out digestion.
Connected to the circulatory system. The digestive system breaks the food down into nutrients and the circulatory system transports them to the cells.
Four main steps:
Ingestion- _____taking in nutrients__________________________________
Digestion- ___chemical and physical breakdown____________________________________
Absorption- _____the transfer of digested nutrients to the circulatory system. _________________________________
Egestion- ___the removal of waste food materials from the body._____________________________________
Specialized Digestive Systems
Simple animals have a digestive sac with a single opening into a gastrovascular cavity. The opening is an entrance for food and an exit for waste. Often surrounded by tentacles to capture prey. The nutrients are absorbed by diffusion through the cavity and the waste is expelled. Ex) Jellyfish.
More complex animals digest food along a tract with two openings- one for intake and one for waste elimination. Along the tract is are specialized regions that enable breakdown and absorption. This design is referred to as a complete digestive system.
Human Digestive System
The human system is a ____complete _____________ system.
The digestive tract is referred to as the gastrointestinal tract (GI tract),
Approximately __7-9 m_______long depending on age and size.
Interaction with other systems: circulatory to transport nutrients, nervous and endocrine system system regulates digestion.
The gastrointestinal tract consists of: mouth, pharynx, esophagus, stomach, small intestine, large intestine, rectum & anus.
The ____acessory organs____________________are: salivary glands, pancreas, liver and gall bladder.
The Journey
__Mouth_______________
____Esophagus______________
___stomach_______________
____small intestine______________
_____large intestine_____________
____rectum and anus______________
The accessory organs also aid in digestion.
The Mouth(physical digestion)
Physical digestion- food is broken down into smaller pieces by teeth.
The incisors and canines are specialized for ___grabbing___________ and ___cutting_________ food.
The pre-molars and molars are broad and flattened specialized for ___grinding_________ and ____crushing_________ food.
The teeth an animal has is directly related to its diet. Ex) Herbivores have more molars and mammals have canines.
The mouth(chemical digestion)
breaking food down using chemicals, specifically saliva and acid.
The presence of food is often enough to trigger the salivary glands to secrete saliva.
Saliva contains enzymes, which are chemicals that increase the rate of chemical reactions. The most important enzyme is saliva is ____amylase_____________.
Amylase breaks down starch into disaccharides (known as chemical digestion).
Saliva also dissolves food particles, making it possible to ___taste___________ food.
It also contains mucus, a protective secretion that acts as a lubricant to aid in swallowing.
You produce approximately _____0.75 to 1.5 L___________ of saliva each day.
The Bolus
The water in saliva moistens the food and a bolus, or ___ball of foood__________________, is formed from chewing.
The tongue pushes the bolus to the back of the mouth for swallowing.
The bolus is then pushed into the pharynx and a soft palate is raised to prevent food from entering the ___lungs______________________.
At the same time, the larynx is raised against the epiglottis which covers the entrance to the trachea preventing the food from entering the _____lungs_________.
This process of taking food in and swallowing it is known as ingestion.
The Esophagus
Food moves from the mouth to the stomach via the esophagus.
Long muscular tube.
2cm diameter.
The walls stretch because of the food which activates the smooth muscles which undergo rhythmic wave-like contractions called ___peristalsis_______________.
The first contraction involves a ___circular ____________ muscle which squeezes the food bolus, the second involved a _______longitudinal ______________l muscle which moves the bolus down.
It takes about 8 s for food to travel down the esophagus to the stomach.
The Stomach
J-shaped, muscular organ.
Mechanical and chemical digestion.
The stomach can expand and hold up to ____2 L_____.
The inside is covered in thick layers of folded smooth muscle known as rugae which allow the stomach to expand and aid in churning.
Proteins are partly digested in the stomach and the small intestine. Lipids and carbohydrates are not digested in the stomach.
Movement of food into and out of the stomach is controlled by circular muscles called ___sphincters___________.
The gastroesophageal (cardiac) sphincter is located where the esophagus meets the stomach. When relaxed, food enters the stomach, when contracted food cannot move back into the esophagus.
Layers of the Stomach
The stomach has ____4_____layers_______.
The innermost layer is extensively folded and is called the mucosa. Secretes gastric juice (digestive enzymes + acid + mucus).
The cells of the mucosa divide rapidly to heal any damage.
The next layer is the submucosa which is connective tissue that connects nerves and blood vessels.
The next is muscularis which consists of smooth muscles that churn and mix the food with gastric juices to create a semi-liquid material called ___chyme_______________.
The outermost layer is the smooth serosa which holds the stomach in place and secretes a lubricating fluid to eliminate friction between organs.
Chemical digestion in the stomach
Digestion is controlled by enzymes, hormones and nerves.
Nerves in the submucosa detect when food is present and initiate the release of the hormone Gastrin- which is released into the bloodstream and goes to the gastric cells which release gastric juice.
Gastric juice is made of mucus, acid and digestive enzymes. The mucus coats and protects the lining of the stomach from the acid and digestive enzymes.
The acid is very strong (pH 2-3) and kills many harmful microorganisms ingested with food. It stops the action of amylase but activates other digestive enzymes like pepsinogen.
When pepsinogen is activated it becomes pepsin which begins the digestion of proteins into amino acids.
Nerve endings in the lining of the stomach are stimulated when food enters which releases signals to cause the stomach to increase muscular contraction and mix food with gastric juice.
Acid Reflux
If the gastroesophageal sphincter does not close completely, acid from the stomach can enter the ____esophagus_______________.
This causes a burning sensation in the lower throat known as heartburn or__acid reflux_______________________.
An overfilled stomach can force some acid into the esophagus.
Smoking can also be a contributing factor because it relaxes the sphincter and stimulates the production of acid.
Stomach Ulcers
Stomach acid is strong enough to kill most bacteria that enter the stomach, except for Helicobacter pylori which survives and burrows through the mucosa.
These bacteria prevent enough mucus from being produced so the lining of the stomach is not protected and an open sore, or ulcer can develop.
Ulcers can bleed and be quite painful.
H. pylori can be transmitted through food or water or the saliva of people with ulcers. This bacteria can usually successfully be eliminated with antibiotics.
