BIO288 Introductory Physiology Lecture 23 PDF

BIO288: Introductory Physiology (04/30/2024) Reminders & Due Dates: SRTI ○ You should have received an email prompting you to complete these! ○ But why would you? They help the instructor analyze ways to make the class better They are also known to be biased ○ What we do know is that the more input,...

BIO288: Introductory Physiology (04/30/2024) Reminders & Due Dates: SRTI ○ You should have received an email prompting you to complete these! ○ But why would you? They help the instructor analyze ways to make the class better They are also known to be biased ○ What we do know is that the more input, the better! To incentivize this, I will give 2 extra credit points if we reach 90% completion for the class Upcoming Assignments: ○ HW#9 → Available Thursday (05/02/2024) ○ QUIZ #5 → Available Thursday (05/02/2024) Review from the last lecture: (4) Stages of digestion ○ Ingestion → The process of taking food into the gastrointestinal tract ○ Digestion → The physiological process of breaking down food into its component molecules ○ Absorption → The physiological process of moving molecules into cells from the intestinal lumen ○ Assimilation → Converting food molecules into cell components ○ Elimination → The excretion of undigested/unused food Ingestion (Step 1): The primary route that an animal uses to gain access to environmental chemicals. Most animals absorb nutrients across the epithelium of their gastrointestinal tract. Some assimilated nutrients are degraded to liberate chemical energy; the rest are used as building blocks. “Bringing the food into the body” (ex. Using hands) The two parts of digestion (Step 2): Physical digestion → like chewing and/or peristalsis Chemical digestion → like stomach acids and/or enzymes Digestive Enzymes: Digestion of specific nutrients requires specific enzymes. There are multiple enzymes required for digestion ○ At different physical locations in the digestive tract ○ At different times during the digestive process Most enzymes function best at a pH of 7.3-7.5 ○ However, the stomach's pH is 4-5 when empty and 1-2 after a high-protein meal. Examples of enzymes: ○ Carbohydrates → Amylase (breaks down carbohydrates into glucose) ○ Proteins → Pepsin (breaks down proteins into amino acids) ○ Fats → Lipase (breaks down fats into fatty acids & glycerol) Intraluminal → enzymes that mediate extracellular digestion in the gut lumen Membrane-associated → enzymes mediate extracellular digestion via binding food molecules at the intestinal epithelium’s apical membrane surface Intracellular → enzymes mediating digestion inside the cell Saliva contains enzymes that initiate the chemical breakdown of food molecules ○ Amylase → carbohydrates ○ Lingual Lipase → lipids ○ Saliva contains intraluminal enzymes (they are not associated with a membrane and not within a cell) Saliva also provides a fluid substrate for taste receptors. * This chart shows (4) digestion “pathways,” which use multiple enzymes to breakdown macromolecules into their smaller units Carbohydrate Digestion: Only monosaccharides are absorbed by the body Disaccharides and polysaccharides must be digested to monosaccharides Step 1: Digestion of starch ○ Enzymes of digestion Salivary amylase Pancreatic amylase ○ End-product Disaccharides (maltose) Limited dextrins Amylase → breaks down starches into their components monosaccharides and disaccharides Sucrase → Breaks down sucrose Lactases → Breaks down milk sugars ○ Both Sucrases and Lactases are found in the small intestine (disaccharidases) Protein Digestion: Typical diet: 125 grams/day of protein No protein digestion in the mouth (no enzymes for proteins in the mouth) Protein digestion products: ○ Proteases (trypsin, chymotrypsin) break down proteins into shorter polypeptides ○ Peptidases are proteases that clear off amino acids ○ Dipeptidase breakdown dipeptides into amino acids Lipids: Bile salts ○ Synthesized in the liver from cholesterol (stored in the gallbladder) ○ Bile salts increase the surface area of droplets by breaking each large droplet into several small droplets via emulsification. ○ Emulsify fat ○ By increasing the surface area, you allow for a better probability of digestion. Lipid Digestion: Enzymes of digestion: lipases (intraluminal enzymes) Secreted from pancreas Lipases can only act on molecules near the edge of a fat droplet Lipase operate at lipid/water interface ○ Bile salts (from Gallbladder) emulsify lipids This creates tiny, bile-salt encrusted lipid globules suspended in the aqueous gut contents Bile salts lipase binding during gut transit Active lipase binds to the surface of the fat globule and begins hydrolyzing surface triglycerides into usable fatty acids iClicker #1: Which of the following substances emulsifies fats? A) Salivary amylase B) Lingual lipase C) Bile salts D) Endopeptidases Reason: (A) breaks down carbohydrates, (B) breaks down lipids (not that same as emulsification; needs to be emulsified first), (D) breaks down proteins into amino acids, (C) does emulsify fats Why do you have lingual lipases inside the mouth? ○ To start breaking down some of the large fat droplets (cannot break all of them before emulsification) iClicker #2: Proteins are cleaved by which enzymes? A) Amylase B) Sucrase C) Lipase D) Chymotrypsin Reason: (A) breaks down carbohydrates, (B) breaks down sucrose, (C) breaks down lipids, (D) is a type of protease which breaks down proteins into shorter polypeptides Absorption (Step 3): Extracellular absorption is the process by which digestive products are transferred across epithelia into the living tissues of the animal. Structure of Gastrointestinal Wall: Mucosa ○ Mucous membrane → thin layer of epithelial cells of various types (contains absorptive cells; i.e. transport nutrients to blood) ○ Lamina propria → layer of connective tissue containing small blood vessels, nerve, and lymphatic vessels ○ Muscularis mucosae → thin layer of smooth muscles that make the mucosa fold Submucosa ○ Layer of dense connective tissue ○ Has large blood vessels and lymphatic vessels ○ Nerves (Enteric Nervous System; ENS) innervates Muscularis Externa ○ Involved in mechanical processing, movement of materials along digestive tracts (motility) ○ Coordinated by the Enteric Nervous System (ENS) Serosa ○ Consists of the inner layer of fibrous connective tissue which provides structural support ○ Also secretes a lubricating fluid which makes it easier for organs to slide past one another Moving Food through the Gut: Gut muscles are arranged in… ○ An outer layer of longitudinal muscles ○ An inner layer of circular muscles Gut motility is generated by… ○ Peristalsis Wavelike muscle contractions that causes propulsion towards the anus ○ Segmentation Organized circular muscle contractions that causes mixing which promotes absorption ○ Tonic contraction → prevents movement of food (sphincter) iClicker #2: Proteins are cleaved by which enzymes? E) Amylase F) Sucrase G) Lipase H) Chymotrypsin Reason: (A) breaks down carbohydrates, (B) breaks down sucrose, (C) breaks down lipids, (D) is a type of protease which breaks down proteins into shorter polypeptides Important of Surface Area: We know that animals with diets that are difficult to digest often have longer guts ○ This increases digestion efficiency This means that herbivores have longer guts than carnivores (longer digestion and absorption for herbivores than carnivores) But we can also alter the surface of the gut to increase surface area Each villi is made up of microvilli → high surface area (increase digestion efficiency) Enterocytes: Site of Absorption: Intestinal villi provide vast surface area for absorption ○ More surface area = more absorption Polar nutrients are transported across the apical surface of intestinal epithelia via… ○ Secondary active cotransporter ○ Secondary active counter transporters ○ Secondary active transport explanation (review) Glucose cannot move across the plasma membrane by itself; sodium wants to move into the cell (due to Na/K pump); sodium will pull glucose with it into the cell (cotransport = movement of both substances in the same direction) Nonpolar nutrients move through the apical surface via simple diffusion Student Questions: Where does salvia originate? ○ Your saliva glands secrete saliva inside your mouth. Inside the saliva, some enzymes break down food. What would happen during digestion if your stomach's pH became too basic instead of acid or neutral? ○ Your stomach cannot break down proteins → can’t absorb amino acids → excrete Will we need to know all the enzymes? ○ Yes (only know the five or six of them) What is a lumen? ○ The hollow component of a tubular organ. What is propulsion? ○ Movement of macromolecules from the mouth to the anus. What is the difference between intracellular and intraluminal enzymes? ○ Intracellular → find enzymes inside a cell ○ Intraluminal → found in the hollow component of a tubular organ (technically the outside environment) Do you vomit enzymes? ○ Yes How does breaking fat globules into smaller droplets increase the surface area? ○ The surface area of a sphere to volume is not a linear relationship; the smaller the volume, the higher the surface area (ratio). The more spheres (tiny), the more surface area Is pepsin a protease? ○ Yes Why is it encouraged to eat a lot of carbs before an athletic activity like a big game? ○ Breaks down into glucose (sugar) → required by oxidative phosphorylation (or any type of phosphorylation) → you get ATP → thus you get more ATP production (short-form energy source) Does sodium directly bind to glucose? ○ Sodium and glucose do not interact; they move through the same cotransporter together (cotransport; secondary active transport)