Digestive system (ch.20)

List and describe the four phases of digestive processes

1) Digestion (nutrients that are broken down) 2) Absorption (small enough nutrients) 3) Motility (move things through the tract) 4) Secretion (secreted in lumen of the tract to help digestion process)

List and describe the three phases of gastrointestinal control

1.) Cephalic Phase: -stimuli originate in head (brain) -thoughts, taste, smell -requires input from CNS (long reflexes) 2.) Gastric Phase: -stimuli originate in stomach -long & short reflexes. & GI hormones 3.) Intestinal Phase: -stimuli originate in small intestine -long & short reflexes & GI hormones

Describe the transport mechanisms involved in absorbing glucose

2ndary active transport across apical membrane & Facilitated diffusion across basolateral membrane

What mechanism is used to absorb glucose & galactose?

2ndary active transport across apical membrane and facilitated diffusion across basolateral membrane

Describe the autonomic nervous system control of stomach secretions

Acid secretion is stimulated by parasympathetic nervous system; the hormone gastrin that's made by the stomach & histamine can stimulate acid secretion by the parietal cells.

Describe the two major components of pancreatic juice and how the two components' secretions are regulated*

Acinar cells & duct cells. Acinar cells are small volume of primary secretion. Water, electrolytes, & digestive enzymes. Duct cells large volume. Bicarbonate- rich secretion. Both regulated separately by enzyme and bicarbonate secretion

Compare and contrast cephalic and gastric phase regulation of stomach secretions*

Cephalic Phase regulation of secretion by stimuli increase in acid and pepsinogen by sight of food, taste, smell, chewing, and swallowing. Activate the parasympathetic nervous system & stimulates gastrin secretion. Gastric phase regulation of secretion stimuli of gastric secretion by proteins, peptides, & amino acids. Distension of stomach. Short & long. reflex pathways trigger gastrin, acid, & pepsinogen release

State the pathway of chylomicrons to end up in the bloodstream

Chylomicrons are mixtures of proteins & lipids, bile salts, cholesterol, & fat-soluble vitamins. The Golgi apparatus will combine some lipids or these triglycerides with some bile salts, fat soluble vitamins, & Cholesterol molecules which creates lipoproteins. Chylomicrons make up part of the LDL & HDL. Chylomicrons are made by the Golgi & exported across the basal lateral membrane of the enterocytes into the interstitial fluid by exocytosis. Chylomicrons don't enter into the blood directly instead they enter into the lymphatic system. at the lacteal. They'll enter into the blood supply at the subclavian veins where the lymphatic system joins w/ the circulatory system so they don't go directly into the capillaries.

List and describe the major functions of the gastrointestinal system*

Consumed food is too large to enter directly into the bloodstream. Consumed. foods. are converted into smaller nutrient molecules, so the molecules that make up our food (usually proteins, carbohydrates, & lipids) are broken downing their basic building blocks

Describe how epithelial cells of the small intestine process absorbed fatty acids and monoglycerides and transport them across the basolateral membranes. Include the organelles involved, what they do and the name of the final product of enterocyte processing*

Enterocytes are the brush border cells. Some fatty acids across basolateral side into the interstitial space & into the capillaries. Most fatty acids that diffuse into the epithelial cell are processed inside the cell. Enters smooth ER and can re-form triglycerides & other lipids (like phospholipids) where they're sent into the Golgi to be packaged up into chylomicrons. Triglycerides can't move across the membrane

In general, state the mechanisms of absorption of fat-soluble and water-soluble vitamins.

Fat soluble vitamins absorbed w/ lipids. So as the lipids get broken down by the lipases the bits & pieces come in & some of the fat soluble vitamins diffuse across the apical brush border and can also diffuse across the basolateral brush border or can get get packaged up into chylomicrons & sent through our lymphatic system to our blood. Dissolve in lipid droplets, micelles, & chylomicrons. Water-soluble vitamins are hydrophilic molecules. These require special transport proteins like facilitated diffusion transporters or active transport

List the products of enzymatic digestion of triglycerides by lipases and describe how they are transported across the apical membrane of epithelial cells in the small intestine

Free form fatty acids can be absorbed by passive diffusion across the apical. membrane of the epithelium.

Describe the mechanism of gastric motility and its regulation

Function of gastric motility is to mix food & secretion into chyme; regulate gastric emptying. Its mechanism is Peristalsis which is the type of motility that helps to move material along the tract and is controlled by enteric nervous system

List the stimuli that inhibit gastric and intestinal phase GI functions

Gastric phase: -exit of food removes stimuli for secretion - increased acidity inhibits gastrin release Intestinal phase: - effects of food entry into the duodenum -increased osmolarity, fat & acid, & dissension. -long and short reflex pathways inhibit acid & pepsinogen secretion

Describe the release locations and actions of gastrin, cholecystokinin, secretin, and glucose-dependent insulinotropic peptide*

Gastrin: -Location: stomach -Actions: Stimulates gastric secretion and motility; stimulates ileal motility &relaxes ileocecal sphincter; stimulates mass. movement colon Cholecystokinin: -Location: duodenum & jejunum -Action: Inhibits gastric secretion & motility; potentiates actions of secretin on pancreatic bicarbonate secretion; stimulates pancreatic enzymes secretion; stimulates bile secretion. by liver; stimulates gallbladder contraction and relaxation of sphincter of Oddi Secretin: -Location: Duodenum & jejunum -Action: Inhibits gastric secretion & motility; stimulates pancreatic bicarbonate secretion; potentiates actions of CCK on pancreatic enzyme secretion; stimulates bile secretion. by liver Glucose-dependent insulinotropic peptide (GIP): -Location: Glucose, fats, or acid in duodenum; dissension of duodenum _Action: Inhibits gastric secretion & motility; stimulates insulin secretion by pancreas

Describe the interaction of pepsinogen and hydrochloric acid and how they function to denature and digest proteins in the stomach.

HCL can cleave pepsinogen into a quasi active form that then eventually converts other pepsinogens into pepsin. Once its pepsin, it can breakdown proteins into smaller peptide fragments. HCL can also disrupt the tertiary structure of proteins & can cause some proteins to be cleaved anyway because of chemical properties of the amino acids. HCL serves to activate pepsinogen into pepsin & can directly break down proteins. HCL can disrupt the tertiary structure of proteins & can cause some proteins to be cleaved away because of chemical properties of the amino acid. HCL serves to activate pepsinogen into pepsin & can directly breakdown protein

Describe the two types of large intestine motility and the motility reflexes of this structure*

Haustrations: occurs in proximal colon, like segmentation but slower, mixes contents near contraction site Mass Movement: occurs throughout entire colon; propels bolus (material) towards rectum; similar to but not peristalsis; contraction lasts longer than relaxation Colonocolonic reflex: Distension of colon in one area causes relaxation of other areas of colon Gastrocolic Reflex: Food in stomach increases colonic motility Defecation: emptying of the rectum

List the hormones that regulate bile secretion and how each one affects this process

Hormones that regulate bile secretion are secretin & CCK. Secretin stimulates bile secretion from liver & CCK stimulates gallbladder secretion & relaxation of hepatopancreatic sphincter. Allows pancreatic juice & bile entry into the duodenum

Describe the hormones and neural elements that regulate food intake in the short-term

Hormones: insulin, CCK, & Leptin Neural inputs: Mechanoreceptors & chemoreceptors

Describe what is meant that bile salts are amphipathic molecules and how this property relates to their function in lipid digestion

Its means that it is both polar/non-polar. Lipids don't mix well with water, so that where bile salts come into play since lipids and bile salts mix well and bile salts can mix with water making it easy for lipids to be digestible. This allows from processing of lipids more easily.

Describe how leptin secretion by adipose tissue leads to a reduction in eating and an increase in metabolism throughout the body

Leptin is a hormone released from adipose cells when calories eaten exceed demands. When leptin is released, it suppresses hunger & increases metabolism. So when things suppress hunger and increase Metabolism it is called satiety signals. Leptin then stimulates the release of aMSH & CART (cocaine and amphetamine related transcript) Adipose tissue releases leptin & sends it through our blood. In our hypothalamus we have receptors for leptin. Those receptors activate cells that release alpha MSH & CART into the blood. They cause lateral hypothalamus to release tropic hormones. These releasing hormones enter into the portal vein that the hypothalamic pituitary portal vein & find their way to the anterior pituitary.

Describe the source of release for lipases and bile salts, and how they aid in digesting lipids*

Lipids are digested by enzymes called lipase's. Secreted from pancreas and sent through the pancreatic duct to the small intestine. Lipase's begin to break down the lipid molecules, but usually lipids from these large droplets and the enzymes can only act on the lipids at the very surface of the droplet. Most of the lipids in a droplet are in the inside where lipase's can't get too. Bile salts are ampipathic molecules so they are polar/non-polar. Lipids don't mix with water, so they dissolve w/ bile salts making it easier to be digestible since bile salts mix w/ water.

Describe the unique problem our bodies face when digesting and absorbing lipids and the molecules our body uses to solve or reduce this problem.*

Lipids don't mix well with stomach or intestinal contents especially water. So what happens is when you eat fatty foods, you chew it up with your mouth and mix w/ saliva and slide it down your stomach & mix it w/ acid & water & other things but the fat forms little fat droplets that don't dissolve into the chyme. Just like when you mix water with oil, they don't dissolve. They separate from each other, not compatible molecules. Lipids turn into fat droplets, but don't mix well with our body because our body is mostly water. If the lipids keep turning into fat droplets it is hard for digestion and absorption, and they can disrupt membranes and cause physiological problems. Lipase's & Bile Salts (amphipathic molecule: has a polar/non-polar region) help reduce the problem

Define essential and non-essential amino acid*

Non-essential amino acids can be synthesized in the body from other molecules and essential amino acids must be obtained from food

Describe the type of carbohydrate molecule that can be absorbed (in general) and the processes that digest larger carbohydrates into ones that can be absorbed. Include the site(s) of digestion and absorption of carbohydrates.*

Only monosaccharides can be absorbed. Disaccharides & polysaccharides must be digested to break down monosaccharides. This is done by enzyme digestion beginning in the mouth w/ saliva. Digest pancreatic amylase in our mouth & small intestine. End product is a disaccharide; also get limit dextrin which amylase can't break down.

List the orexigenic factors discussed in class and how they oppose satiety factors in the long-term to promote eating and decrease metabolism

Opposite of Leptin, Orexigenic factors signals to start eating. Neuropeptide Y & Agouti-related peptide (AgRP) are released in the hypothalamus & lead to an increase in parasympathetic activity which will make us slow down & rest & digest and eat. Cause a decrease in sympathetic activity and inhibit other hormones.

Describe the mechanism of acid production carried out by parietal cells of the stomach. Be sure to include the role carbonic anhydrase, carbon dioxide, and chloride ions*

Parietal cells produce hydrochloric acid (HCL). Carbonic anhydrase converts carbon dioxide & water into carbonic acid. Carbonic acid in water dissociates into a proton & bicarbonate molecule. The protons made from carbonic anhydrase will be exchanged to the lumen of the gastric gland. For potassium ions, so as potassium ions are absorbed an ATP is used & that powers potassium movement against its concentration gradient & pushes protons against their concentration gradient into the gastric gland. The gastric gland lumen is continuous w/ the lumen of the stomach. Protons are pumped into the lumen of the stomach that came from water & the carbon dioxide that came together to make carbonic acid. Enter into the blood and buffer it & exchanged for chlorides. Chloride gets pumped against its concentration gradient into the parietal cells & then leaks into the lumen of the stomach through ion channels for chloride

Describe the roles of the autonomic nervous system in controlling GI functions*

Part of the autonomic nervous system is the enteric nervous system which manages GI functions. The CNS can influence the GI tract through the enteric nervous system, and there. are many sensory receptors that are used to inform both the enteric system and the central nervous system about the chemical composition of the contents of our GI tract, and also whether the fuller the tract the more stretched out it is

Describe how gastric secretions aid in digestion of food*

Pepsinogen secretion is regulate in sync w/ acid secretion. Both linked because pepsinogen is a zymogen form of pepsin which is an enzyme that breaks down proteins. A high acidic environment & a low pH converts pepsinogen into pepsin. The acid is released that helps to break down & denature proteins. The acid activates pepsinogen into pepsin & helps to cleave up & breakdown those denatured proteins which is the chemical digestion of proteins done in the stomach.

Describe the processes of gastric mixing and emptying

Peristalsis will move chyme along when its time to do Segmentation which mixes contents. Peristalsis stops & the same muscles move in different patterns to mix up the food

Describe the type of protein molecule that can be absorbed (in general) and the processes that digest larger proteins into absorbable components. Include the site(s) of digestion and absorption of proteins*

Protease can be absorbed and secreted into the stomach and lumen of intestinal tract. Dipeptides, tripeptides, and amino acids can digest larger proteins in absorbable components

Define protease and zymogen and describe their relationship

Proteases is an enzyme that breaks down proteins. Breaks down into amino acids, dipeptides, and tripeptides. They are secreted into the stomach & into the small intestine. Zymogen is an inactive storage form of proteases; stored in granules; secreted by exocytosis; activated by proteolysis (zymogen is activated by an active protease. Another protease comes in & cleans them & makes them active)

pancreatic protease

Proteins that breakdown small peptides into amino acids; made in pancreas & secreted into the small intestine

Describe the neural and hormonal regulation of small intestine motility and the motility reflexes of this structure

Regulated by our autonomic nervous system where the parasympathetic branches excites the movements & the sympathetic branch inhibit it. Hormones like gastrin will stimulate reflexes to cause mixing & movement of material in the small intestine. Trigger for reflexes is distension where there is more material inside the lumen of the small Intestine it activates intestine-intestinal reflex which is injury or severe stress inhibits intestinal contractions, ileogastric reflex which is dissension of ileum inhibits gastric motility , & gastroileal reflex presence of chyme in stomach increases motility. in ileum.

Describe the mechanism of water (re)absorption in the GI tract

Secretions by our pancreas & our stomach add water into our GI tract. We secrete 7 liters a day and drink about 2 liters a day. When we want to absorb or reabsorb water, its done passively by osmosis through aquaporins.

Describe where and how sodium, chloride, potassium, bicarbonate, calcium, and iron are absorbed from the GI tract

Sodium: co-transported w/ water reabsorption and absorbed in jejunum, ileum, & colon. Active transport to transport more sodium back into our blood Chloride: Same as sodium Potassium: Absorbed passively either through potassium channels on the brush border or through facilitated diffusion transport by passive means Bicarbonate: absorbed in jejunum where its passively absorbed and later in the ileum of the small intestine and into the large intestine. Gets its part of a secondary active transport so it can be absorbed or secreted in exchange for chloride. Secrete it as a way to help manage pH of chyme in the small intestine Calcium: Actively absorbed in duodenum & jejunum. Binds to a protein in the apical surface of the small intestine epithelium (calcium-binding protein). Transported into he cells & absorbed across the basolateral membrane by primary active transport pump. Vitamin D helps to increase calcium absorption by increasing the concentration of calcium-binding proteins. Iron: Transferrin is secreted by epithelial cells into the lumen of the small intestine. Transferrin is iron bound to a transport molecule. T iron can be secreted into our small intestine to pick up iron we've eaten. After transferrin binds w/ iron, its done by endocytosis. To store iron, brush border cells can store it for later absorption to ferritin to make f iron. Some iron is transported into blood as t iron.

Describe how di/tripeptides are transported across the apical and basolateral membranes of epithelial cells of the small intestine*

They cross the apical membrane by active transport across the apical membrane. Usually, dying tripeptides are broken down into amino acids inside the brush border cells. They move across the basolateral membrane the same way as through facilitated diffusion

Describe the patterns of motility generated in the small intestine and how they affect absorption and movement of material through this structure.*

Waves of smooth muscle contraction that move from one end of the stomach to the other is called peristalsis. Peristaltic movements begin at the cardiac/ fungus end of the stomach. Moves as a wave toward the pyloric end. Muscle contractions increase in strength as they approach pylorus. When pyloric sphincter is closed contraction serve to mix chyme. When its open contractions cause gastric emptying causing strong contractions to push stuff out. Factors of emptying rate is volume of chyme in the stomach & strength in gastric peristalsis. Smooth muscle contractions serve to mix & move material through the tract

State the stimuli that lead to saliva secretion and the area of the CNS that control the saliva glands.

What triggers it are the taste and textures of foods the stimulate mechano & chemo receptors in our mouth. The cephalic phase can also cause salivation by anticipating food. Medulla Oblongata controls salivary glands

Describe how amino acids are transported across the apical and basolateral membranes of epithelial cells of the small intestine*

absorption of amino acids across the apical membrane is usually done by sodium linked secondary active transport or facilitated diffusion. Facilitated diffusion can be used when the concentration gradient is such that the concentrations are higher in the lumen of the small intestine than inside the brush border cells. Secondary active transport is used when the concentration of amino acids inside the brush border cells is higher than in the lumen, so we need to move things up against their concentration gradient. To cross the basolateral membrane, we use facilitated diffusion. This moves amino acids from the brush border cells into the interstitial fluid, where they can be taken up by capillaries and to the liver

when pyloric sphincter is closed

contractions serve to mix chyme

zymogen

inactive storage form of proteases, stored in zymogen granules, secreted by exocytosis, activated by proteolysis

In general, describe the relationship between GI regulation, homeostasis and absorption of nutrients from food

regulation of GI function is not based on the concept of homeostasis. Gi function is regulated to maximize absorption, regardless of whether or not nutrients are needed. Helps us ingest nutrients that we can use as building blocks & energy at a later time. Stop Glucose as glycogen in our liver & body fat is the idea of savingsometching for later that we don't need now. When it comes to regulating absorption, homeostasis is not adhered to it

Define emulsify

to break up fat globules into smaller ones

absorption

transport of nutrients from lumen of GI tract to blood