Digestive System Chapter three

Learning Goal To learn in more detail about the digestive tract and its components To learn more about some disorders that affect the digestive tract

The digestive system The human digestive system is made up of organs working together to transform food The job of the digestive systems is to use the food we eat and break it down onto molecules that our body can easily use to keep us alive This is done in Four Steps: Ingestion Digestion   Absorption Elimination

The digestive system

Parts of the digestive system The function of digestion is to reduce a mouthful of food into smaller molecules so that our cells can use easier This reduction of food into smaller pieces happens as we chew our food, mix it up in our mouth, and churn it with our teeth = Mechanical Digestion The reduction of food in our mouth also uses enzymes = Chemical Digestion

Digestion in the Mouth The digestive structures in the mouth are the teeth and the salivary gland There are different types of teeth in your mouth, like fang shaped for biting into food or your molars at the back that grind your food into smaller pieces

Digestion in the Mouth Together all of your teeth start mechanical digestion of the digestive system In the mouth there are salivary glands that release saliva to help the breakdown of food into smaller pieces because inside our saliva are enzymes that help this digestion Chemical digestion begins with saliva

Digestion in the Mouth Mechanical Digestion also begins in your mouth as you bite, tear, and grind food into smaller pieces This also exposes more of the surface area of the food to the saliva, making it more accessible for chemical digestion

The Esophagus The chewed mass of food passes down your throat (pharynx) When you swallow, your epiglottis muscle opens for food to pass through the pharynx into the esophagus This is done using wave –like muscle contractions that push the food downward through peristalsis as muscles contract above the chewed food and relax below it A ring-like muscular structure called a sphincter controls how the food enters the stomach from the esophagus

The Esophagus

The Stomach The stomach is a J-shaped muscular bag that continues to carry our physical and chemical digestion It also temporarily stores food while further chemical and mechanical digestion take place The stomach is small when empty and can open up a lot when full (up to 4 L of food) Here, chunks of food are broken down into smaller pieces as peristalsis churns food in the stomach (breakdown)

The Stomach The stomach is filled with millions of gastric glands that secrete gastric juices, when food is present Gastric juice is made up of Hydrochloric acid (HCl), salts, enzymes, water, & mucous The mucous coats the walls of the stomach – protecting it from being attacked from strong acidic gastric juices Gastric juices continue chemical digestion within the body

The Stomach The mixture of food gets digested by the muscles in the stomach into smaller pieces and gastric juices that is churned up in the stomach becomes chyme At regular intervals small amounts of chyme are squirted from the stomach to the small intestine – where food will travel through next

The stomach The stomach is surrounded by a network of nerves that help regulate the activities of the digestive system These nerves start stomach contractions that release partially digested food into the small intestine (next phase)

The Small Intestine (SI) Chyme (mixture of food and gastric juices) enters the small intestine from the stomach contains molecules at different stages of being digested The 2 functions of the small intestine are to: Finish digesting nutrients in their smallest form Absorb these small molecules into the bloodstream so they can be transported to where they are needed

The Small Intestine (SI) The small intestine can be divided into 3 parts: duodenum, jejunum, and ileum Each section has different roles and functions that help absorb nutrients from the food we eat

The Small Intestine (SI) The Duodenum Makes up the first 25 cm of the small intestine Is the shortest and the widest of the 3 parts Large surface area IMPORTANT for ABSORBTION Helps the digestion of chyme from the stomach Ducts (like valves) connected to the duodenum from the liver and pancreas join together

The Small Intestine (SI) The Duodenum The surface of the duodenum has tiny finger-like projections along it called villi and even smaller microvilli that help increase the surface area for absorption Their job is to absorb the nutrients from food and allow them to enter into the blood system through lymph vessels from the circulatory system

The Small Intestine (SI)

The Small Intestine (SI)

The Small Intestine (SI) The Jejunum Is 2.5 meters long and continues nutrient digestion (if any left) and mainly absorption of nutrients into the blood stream The Ileum Is 3 meters long Contains less villi and microvilli than other parts of SI Its function is to absorb nutrients as well as push the remaining undigested food into the Large Intestine (LI)

Accessory organs Role of Accessory Organs Includes the pancreas, liver, and gall bladder These organs are not part of the digestive tract directly, but help it digest food

The Large Intestine (LI) The material that is left over from the small intestine after all the absorption of nutrients has taken place enters the large intestine Even though it is called the large intestine it’s actually shorter. We say “long” because its wider than the small intestine

The Large Intestine (LI) Digestion no longer takes place from the large intestine on – now it is strictly absorption, to be more specific, it’s the absorption of water Another name for the large intestine is colon Anything left over turns into feces – which leave the colon through the rectum and the anal canal

Time for Digestion?

Magic School Bus https://www.youtube.com/watch?v=BTjXdzxhc_w (7 – 20)

Things still questioning Post gizmo lab

1) Where does diffusion / osmosis take place? In the digestive tract, we have food broken down via mechanical and chemical digestion into smaller pieces Where our macromolecules (fat, protein, & carbohydrates) are broken down into smaller pieces (i.e carbs = glucose) These smaller pieces will DIFFUSE from the small intestine (duodenum & jejunum) into the capillary bed surrounding the small intestine or lymphatic system (only small amounts of fat will diffuse into the lymph system). Osmosis takes place mainly on the LARGE INSTESTINE where water is absorbed back into the body via the capillaries (end up increasing volume of interstitial space and blood volume)

2) Why does absorption increase with pancreas? The pancreas is responsible for releasing INSULIN to the small intestine to help with the absorption of carbohydrates (glucose). This is why when you add the pancreas to the duodenum (SI) that the % of absorption increases

What do parietal / Chief cells do A gastric chief cell is a cell in the stomach that releases enzymes that are part of the GASTRIC JUICES Parietal cells are another type of cell found in the stomach that work with the chief cells in helping the digestion of protein in the digestive system

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Bonus questions Thank you for brining this to my attention Haven’ t done them in the past, but see their rewards So I WILL try to add more bonus question in either assignments / final tests