DIGESTION Journey Glennon

Meghana Jami

Digestive Tracts

Not all animals have a digestive tract Ex: sponges’ digestion occurs in food vacuoles Ex: Hydras perform digestion in their

gastrovascular cavity and in their food vacuole

Most animals have some sort of gut or digestive tract that allows food to be digested into small nutrient molecules

Contribution to Homeostasis

Digestion provides the body with essential nutrients necessary for survival

The digestive tract allows The breakage of food into smaller molecules

that can cross plasma membranes Absorption of nutrient molecules Elimination of indigestible remains

Indigestible food is discharged in a process called egestion, or elimination. The food is released as feaces.

Adaptation to Diet

Some animals are.. Omnivores: eat both plants and animals Herbivores: only plants Carnivores: only other animals

Many invertebrates are filter feeders Mammal grazers (ex: cattle&sheep) have

large four-chambered stomachs and store partially chewed grasses into a part of the stomach called a rumen. The rumen contains microorganisms which

start digestion

Adaptation to Diet Cont.

Many mammals have adapted to their carnivorous lifestyle having pointed canine teeth (for tearing), sharp incisors (for biting), and pointed molars (for grinding).

Humans (omnivores) have varied 32 teeth to accommodate for eating plants and animals.

Continuous Feeders/ Filter Feeders

Continuous feeders are generally smaller, marine animals such as clams and marine fanworms.

Food particles are constantly filtered through the body and digestive enzymes are secreted by a large digestive gland. Amoeboid cells in the tract complete the digestive process

Small particles generally pass through and large particles are rejected

Discontinuous Feeders

These feeders require a storage area for food Can be a crop (storage area for food until it

can be processed), where no digestion occurs Can be a stomach, where digestion begins

Example: squids are discontinuous feeders because they prey on their food, which goes down their esophagus and to their stomach for digestion.

Incomplete Tracts

Incomplete Tract: Includes a single opening (usually called a mouth) in which food enters and also leaves as waste. Ex: Flatworms use an incomplete tract that

lacks many specialized parts.

Digestive enzymes are present to allow some extracellular digestion to occur, and diffusion itself is enough to distribute nutrient molecules

Complete Tract

The tract has a mouth and an anus Digestion can be extracellular within an

intestine The surface area of the digestive tract can be

increased for absorption of nutrient molecules Undigested molecules will then pass out

through the anus Allows more specialization of parts

The mouth leads to the pharynx, the esophagus, the stomach, the small and large intestines, and finally to the anus

Human Digestive Tract “Tube-within-a-tube” body plan Complete digestive tract, beginning with a

mouth and ending with an anus Digestion of food in humans is extracellular

Food particles are broken down into smaller, absorbable components outside the cell and in digestive system spaces.

Two major stages: mechanical digestion and chemical digestion Mechanical: physical breakdown of particles Chemical: requires the stomach and small intestine

Mouth/ Oral Cavity

The beginning of the digestive tract Consists of the anterior hard palate and the

posterior soft palate Three major pairs of salivary glands (parotid,

submandibular, and sublingual) send juices to the mouth via ducts

Saliva has the enzyme salivary amylase, which begins starch digestion.

Maltose (disaccharide) is generally the end product of salivary amylase digestion

Salivary amylase

Starch+ H2O maltose

Mouth/Oral Cavity Cont.

Food is controlled by a muscular tongue, which has touch and pressure receptors

Taste buds: sensory receptors that are stimulated by the chemical composition of food

The tongue is composed of striated muscle and an outer layer of mucous membrane

Saliva is mixed with the chewed food to form a mass called a bolus

The Pharynx and the Esophagus

Digestive and respiratory passages come together in the pharynx and then separate

The esophagus is a tubular structure (approx. 25 cm) that transports food to the stomach

Sphincters are muscles that encircle tubes and act as valves

tubes close when sphincters contract , and open when sphincters relax

The lower gastroesophageal sphincter is where the esophagus enters the stomach. As food enters the stomach, the sphincter relaxes and then closes again

The Pharynx and the Esophagus Cont.

Heartburn can occur from acid reflux, which is when some of the stomach’s contents enters the esophagus.

Once food is swallowed, the soft palate in the mouth moves back to close off the nasopharynx.

The Pharynx and the Esophagus Cont.

After the nasopharynx is closed, a flap of tissue classed the epiglottis covers the glottis(an opening into the trachea)

The bolus then moves through the pharynx and into the esophagus to begin peristalsis

Peristalsis: a rhythmical contraction that moves the contents along the digestive tract

Stomach

The stomach is a thick-walled organ shaped like a J

Divided into three sections- Cardiac region, body, and pyloric region

It lies underneath the diaphragm on the left side of the body

The wall of the stomach contains deep folds called rugae that disappear as the stomach fills This is what allows humans to eat

large meals and still continue with daily activities

Stomach Cont.

The stomach contains muscular walls which contract vigorously and mix food with juices that are secreted when food enters the stomach

These juices, called gastric juices, contain HCl and a substance called pepsin

The gastric juices are produced by gastric glands which are located in the gastric pits of the epithelial lining of the stomach So much HCl is produced in the gastric juices

that the stomach usually has a pH of about 2

Stomach Cont.

This acidity in the stomach is usually enough to kill any bacteria in the food

A thick layer of mucus protects the wall of the stomach from enzymatic action

However, sometimes an ulcer- an open sore in the wall caused by gradual destruction of the tissues- occurs in individuals These ulcers usually occur when an acid-

resistant bacterium called Heliobactor pylori attaches to the epithelial lining and forces the cessation of the mucus production

Stomach Cont.

Eventually, when the food has been mixed with gastric acid it’s contents become what is called chyme, a thick consistency.

At the base of the stomach is a narrow opening controlled by a sphincter (a muscle surrounding a tube that helps it to open and close)

When the sphincter relaxes, a small amount if chyme passes through the tube into the small intestine. The chyme entering the small intestine sets off a neural reflex that makes the sphincter close temporarily.

Stomach Cells

Mucus cells- produce mucus Parietal cells- produce hydrochloric acid

and intrinsic factor (necessary for absorption of vitamin B)

Chief cells- in gastric glands, produce pepsinogen Pepsinogen is converted to the active form

(pepsin) when in contact with HCL

Small Intestine

The small intestine averages 6 meters in length and consists of three parts (duodenum, jejunum, and the ileum)

Where most enzymatic digestion takes place The first 25 cm of the small intestine is called the

duodenum A duct brings bile from the liver and gallbladder and

pancreatic juice from the pancreas into the small intestine

Bile emulsifies fat (breaks it down into another liquid), in this case water

The intestine has a basic pH due to sodium bicarbonate in the pancreatic juice, thus chyme is neutralized

Small Intestine Cont.

The enzymes in the pancreatic juice and the enzymes produced by the intestinal wall complete the process of food digestion

After nutrients are absorbed, they are eventually carried to all the cells of the body by the bloodstream

Villi and Microvilli

The wall of the small intestine contains fingerlike protrusions called villi, which give the intestinal wall a soft, smooth appearance.

Nutrients are absorbed into vessels of the villi (which contain blood capillaries)

The purpose of villi is to increase surface area for digestion and absorption

Microvilli on the cells of the mucosa further increase the surface area Without microvilli, some of the nutritional value of

food would be lost and not absorbed.

Large Intestine

The large intestine is made up of: the cecum (located at the junction of the small and large intestines), the colon, the rectum, and the anus

It is approximately 1.5 meters in length

It absorbs water, salts, and some vitamins however no digestion occurs in the large intestine

It can also be used to store indigestible material until it can be eliminated through the anus

Main function is to eliminate waste

Large Intestine Cont.

The Vermiform Appendix is a blind sac that projects from the cecum Does not have much

known function in the human body- may contribute to immunity

Considered to be a vestigial structure: structure that previously had a greater physiological significance in an ancestor than at present.

Large Intestine Cont.

The last 20 cm is the rectum

The large intestine has a large population of bacteria which break down indigestible material

Intestinal flora produce vitamin K and some B that can be absorbed

Digestive waste leave the body via the anus

Fecal material is formed by dehydration

Pancreas

The pancreas is located deep in the abdomen, resting up against the posterior abdomen wall

Most pancreatic cells produce pancreatic juice which contains sodium bicarbonate and digestive enzymes Amylase digests starch Trypsin digests protein Lipase digests fat

Liver

The largest gland in the body which lies in the upper right quadrant of the abdomen under the diaphragm

A bile duct in the liver takes bile away from the liver

Bile- solution containing bile salts, pigments, cholesterol, salts, and lecithin

Blood moves from the intestines to the liver via the hepatic portal vein

Digestive Function of the Liver

Aids in homeostasis by removing and adding nutrients to the blood

Converts glucose to glycogen, which is also stored in the liver

Converts amino acids to fatty acids and urea (organic compound that is important for metabolism)

Stores iron and fat-soluble vitamins (A, D, E, & K)

Liver Cont.

Liver Disorders Liver is very regenerative although it can

be hard to fix itself when it is in liver failure Jaundice occurs in many patients with liver

failure which is the yellowing of the skin and the whites of the eyes

Hepatitis can occur form many sources however its effects can lead to liver inflammation

Cirrhosis is a liver disease in which the organ becomes fatty and then the liver tissue is replaced by scar tissue

Gallbladder

Pear shaped, muscular sac attached to the side of the liver

Excess bile from the liver is stored in the gallbladder

The bile leaves through the common bile duct into the duodenum

Digestive Enzymes

Digestive enzymes present in the digestive juices mentioned previously help to break down carbs, proteins, nucleic acids, and fats.

Some important enzymes involved in the breaking down of these main elements of food are: Salivary amylase Maltase Pepsin Peptidases Pancreatic amylase Bile salts Trypsin Lipase

Carboyhdrates

Carbs are present in food in the form of sugars, starch, and fiber

After being absorbed from the digestive tract to the bloodstream, all sugars are converted to glucose

Starch is digested into glucose in the digestive tract

Fiber is technically indigestible, however it can aid movement in the large intestine

Lipids

Lipids present in the form of fats and oils Cholesterol is one lipid that is essential to

the body and can be synthesized by the body

Cells use cholesterol to make compounds such as bile

Elevated blood cholesterol levels are associated with an increased risk for cardiovascular disease This is the number one killer of Americans

Proteins

Proteins are digested to amino acids which cells in the body use to synthesize hundreds of cellular proteins

Nine out of the twenty amino acids are essential in the human diet

When amino acids are broken down, the liver uses parts of it to form urea, which is excreted in urine

In some cases, high protein diets can increase calcium-loss in the urine and encourage the formation of kidney stones

Type 2 Diabetes

Diabetes is indicated by the presence of glucose in the urine

There is too high a level of glucose in the blood Type 2 diabetes patients are usually

overweight and display impaired insulin production and insulin resistance

All diabetics are at risk for blindness, kidney disease, and cardiovascular disease

Healthy dieting and exercise habits can help increase insulin production in diabetes patients

Cardiovascular Disease

Includes hypertension, heart attack, and stroke

CV disease is usually caused to blocked arteries from plaque

This plaque is made up of saturated fats and cholesterol

The American Heart Association recommends limiting our cholesterol intake to 300 mg per day

Vitamins and Minerals

Vitamins are organic compounds that regulate various metabolic activates

Vitamins are excessively present in fruits and vegetables

The body also needs about 20 elements called minerals for various physiological functioning which include Regulation of biochemical reactions Maintenance of fluid balance

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