Digestion

Question 0

Oral cavity

Answer 0

• mechanical digestion in the mouth in a process called mastication, involves the breaking up of large food particles into smallr particles by using the teeth, tongue, and lips
• this increases the surface area of the food particles for a more efficient chemical digestion
• saliva contains salivary amylase, also known as ptyalin and lipase
• ptyalin is capable of hydrolyzing starch into smaller sugars like maltose and dextrin, whereas lipase catalyzes the hydrolysis of lipids

Question 1

Epithelium

Answer 1

• in most of our body cavity (for example nasal cavities, inner eyelids, mouth, G.I. tract) these epithelia are known as mucous membranes
• helps to prevent fluid loss and by allowing for selective absorption of materials that our bodies require
• epithelium is bound to connective tissue layer known as the basement membrane that gives it stability
• cells maybe cuboidal, columnar, and squamous (scale like)

Question 2

Pharynx

Answer 2

The cavity that leads from the mouth and nose to the esophagus

Question 3

Esophagus

Answer 3

-A muscular tube that starts out with striated muscle and transitions into smooth muscle in the thorax
-The majority of the Esophagus is under involuntary control through the autonomic nervous system
-The continuation of the muscular contraction in the Esophagus in the form peristalsis is involuntary
As the bolus approaches the stomach, a muscular ring known as the lower esophageal sphincter opens to allow the passage of food

Question 4

Stomach

Answer 4

• gastric glands respond to signals from the brain which are activated by the site taste and smell of food
• three gastric gland cell types are: mucous cells, chief cells and the parietal cells
• mucous cells produce the mucus that protects the muscular wall from the harshly acidic and proteolytic environment of the stomach
• gastric juice is the combination of secretions from the other two cell types in the gastric glands
• –> chief cells secrete pepsinogen which is the zymogen form of the proteolytic enzyme pepsin; pepsin digest proteins by cleaving peptide bonds near aromatic amino acids resulting in short polypeptide fragments; pepsin which is most active at a pH of two that is maintained by the hydrochloric acid concentration (parietal cells secrete hcl), is unique among human enzymes, most of which are active in neutral to slightly basic pH ranges
• pyloric glands secrete gastrin which is a hormone that induces our stomach to secrete more HCl into the contents of the stomach – produces chyme
• increases surface area of food particles so absorption of nutrients by the intestines can be maximized
• The stomach is primarily a site of digestion not absorption

Question 5

Small intestines

Answer 5

• Food leaves the stomach through the pyloric sphincter entering the duodenum of the small intestine
• The surface of the inner wall of the small intestine is covered in projections called villi each of which is covered in its own set of microvilli—these increase the relative surface area to over 300 square meters which increases the absorptive capabilities of the small intestine
• digestion occurs in the duodenum
• pancreatic juice is a complex mixture of several enzymes in a bicarbonate solution to neutralize chyme
• The enzymes produced by the pancreas are most active around a pH of 8.5
• –> these enzymes digest all three types of nutrients: carbohydrates, fats, and proteins
• —–pancreatic amylase breaks down large polysaccharides
• —–pancreatic peptidases (trypsinogen, chymotrypsinogen, elastinogen, and carboxypeptidases) released in their zymogen form but once activated are responsible for protein digestion
• —–the pancreas secretes lipase which is capable of breaking down fats to free fatty acids
• bile is a complex fluid made up of bile salts bile pigments and cholesterol it is produced by the liver and stored in the gallbladder
• —> gallbladder releases bile into the duodenum byway of the bile duct in response to the hormone CCK which is released by the small intestines in response to the movement of chyme out of the stomach and into the intestine; the pH of bile is between 7.5 and 8.8; it is alkaline to help neutralize the acidity from the stomach
• —-> bile salts allow fat to be emulsified and cholesterol to form micelles : this get the fats into the solution and increases their service area by placing them in micelle, then lipase can come into hydrolyze ester bonds holding the lipids together
• Chyme in the duodenum causes the small intestine to release disaccharide (maltase, lactase, sucrase), peptidases, Enterokinase, secretin, and CCK
• –> collectively called the brush border enzymes

-The autonomic nervous system can exert control over the digestive system. The parasympathetic division is involved in stimulation and the sympathetic is involved in inhibition of digestive activity

• the absorptive process is mostly occur in the jejunum and ileum
• -> simple sugars and amino acids are absorbed by active transport and facilitated diffusion into the epithelial cells lining the gut, into intestinal capillaries = the absorbed molecules then go to the liver via the hepatic portal circulation
• -> fats do not need transporters to move into the epithelial cells; larger fats, glycerol, and cholesterol move separately into the intestinal cells but then reform into triglycerides; the triglyceride and esterified cholesterol molecules are packaged into insoluble chylomicrons and rather than entering the bloodstream they enter the lymphatic circulation through lacteals, small vessel that form the beginning of the lymphatic system
• chylomicrons are processed directly in the bloodstream into low density lipoprotein LDL the bad cholesterol; LDL are taken up by the liver where they can be repackaged into high-density lipoprotein HDL the good cholesterol, very low density lipoprotein VLDL, or more LDL
• fat soluble vitamins: A, D, E, K
• water soluble vitamins: everything else

Question 6

Large intestine

Answer 6

Primarily involved in water absorption

• three major sections: cecum,colon, rectum
• cecum has appendix; connects small to large
• colon absorbs water and salt in the undigested material from the small intestine
• rectum stores poop; contain indigestible material, water, bacteria, certain digestive secretions that aren’t reabsorbed
• external sphincter is under voluntary control but the internal sphincter is under in voluntary control (anus)