Post on 01-Jan-2016
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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