Salivary Amylase: Begins Digestion of Starch in the Mouth

214 Digestive System

Mouth

Saliva:

Salivary amylase: begins digestion of starch in the mouth

Lingual lipase: begins fat digestion when activated by HCl in the stomach

Electrolytes: energy

Immunoglobulin A: inhibits bacteria growth

Lysozyme: enzyme that kills bacteria

Mucus: aids in swallowing

Sympathetic stimulation: produce less abundant, thicker saliva, with more mucus (flight or fight response, digestion slows down, energy routed to muscles and etc.)

Parasympathetic stimulation: salivary glands produce thin saliva, rich in enzymes

Exercise turns off digestion temporarily, so that’s why exercising right after you eat can cause stomach issues

Esophagus:

Top is skeletal muscle (voluntary swallowing) bottom is smooth muscle (involuntary)

Swallowing is an active process

1. Buccal phase: voluntary contraction of the tongue
2. Pharyngeal-esophageal phase: involuntary

Stomach

Parts of the stomach (label)**

Parietal Cells: produce HCl and intrinsic factor (vitamin b12 absorption)

HCl functions:

1. Activates pepsin and lingual lipase
2. Breaks down connective tissues and plant cell walls
3. Converts Fe3+ to Fe2+
4. Destroys ingested bacteria and pathogens

-Chief cells: secrete pepsinogen, which is activated and turned to pepsin by HCl

-Enteroendocrine cells: secrete chemical messengers to lamina propia (gastrin, serotonin)

-Gastrin- activated by an increase in stomach pH (so food basically), stimulates production of HCL, pepsinogen

Gastric Phases:

1. Cephalic phase: digestion stimulated by the thought or sight of food, stimulated by the vagus nerve which stimulates gastric secretion and motility
2. Gastric Phase: activated by the presence of food or semidigested protein (stretch or increase in pH)
3. Intestinal Phase: gastrin is released and gastric activity increases, but then the enterogastric reflex kicks in and the duodenum inhibits the stomach so it’s not constantly digesting things, prevents more food going into the duodenum than the duodenum can handle

Liver:

1. Process bloodborne nutrients
2. Store fat-soluble vitamins
3. Perform detoxification
4. Produce around 900 ml bile per day

Bile: Bilirubin (pigment) comes from the heme of hemoglobin during the breakdown of old RBC

-bile salts emulsify fats, breaking them down so that lipases have more surface area to absorb them

-also contains phospholipids

Gallbladder

-Stores bile that is not needed immediately for digestion, concentrates it by absorbing some of its water and ions

-Gallbladdercystic ductbile duct

Pancreas

(have to be activated so the pancreas doesn’t digest itself)

Trypsinogen Trypsin by enterokinase

Chymotrypsinogen chymotrypsin by trypsin

Procarboxypeptidasecarboxypeptidase by trypsin

Acini- clusters of secretory acinar cells surrounding ducts, secrete pancreatic jucie, exhibit zymogen granules

Zymogen granules- contain the inactive digestive enzymes

Pancreatic Islets- secrete insulin and glucagon

Pancreatic Juice: mostly water, electrolytes, and enzymes (mostly bicarbonate ions)

Normally the amount of HCl produced in the stomach equals the amount of bicarbonate in pancreatic juice (helps to neutralize chyme)

Bile salts: stimulate enhanced bile secretion, also secretin does this too

CCK: stimulates secretion of pancreatic juice, relaxes hepatosphincter so that bile and pancreatic juice can enter the duodenum (released to blood when fatty, acidic chyme enters duodenum)

Secretin: released in response to presence of HCl in the intestines, cause bicarbonate rich juice

CCK: causes enzyme rich pancreatic juice

Small Intestine

3 surface area enhancers:

1. Circular folds- force chyme to slowly spiral through lumen
2. Villi- epithelium made of columnar cells and lacteal
3. Microvilli- brush border enzymes that finish digestion of carbohydrates and proteins in small intestine

-Carbohydrates (lingual lipase in the stomach) and proteins (HCl/pepsin in stomach) are only partially degraded; Fat digestion has only begun

-A lot of stuff required for digestion are imported from liver and pancreas

-Segmentation is slow and aids absorption/digestion by giving it more time to do so

-Peristalsis: migrating motor complex, each wave starts distally to another

-Gastroileal reflex- increases the force of segmentation in the ileum and relaxes the sphincter, allows food to enter the cecum, helped by gastrin.

Large Intestine

CecumColon (ascending, transverse, descending)sigmoid colon-rectum

-No villi, microvilli because most food is absorbed before reaching the large intestine

-Mucosa is thicker and goblet cells are present to help ease passage of feces, protect wall

Motility: haustral contractions are slow in colon, haustra contract in sequence (distention in one part causes it in the next)

Gastrocolic reflex- presence of food in the stomach causes this, three to four powerful peristaltic waves in the colon (mass movements)

Bacterial flora- all of the bacteria present in the LI, ferment cellulose, synthesize vitamin B and K

Gas: most is swallowed air, but HS, indole, skatole make odor

Diarrhea occurs when too little water has been absorbed from feces (pass to quickly, high concentration of solute-lactose)

Digestion of Stuff

Carbohydrates:

-Polysaccharidesmonosaccharides

-Monosaccharides can be absorbed easily

-Absorbed by microvilli in small intestine

-Salivary amylase is in saliva- digests starch, begins in the mouth, ends in the stomach when amylase is inactivated by stomach acid

-Starchy foods or other carbs that are missed by amylase in the mouth are broken down in the small intestine by pancreatic amylase

-These products further digested into monosaccharides by brush border enzymes

-OFFICIALLY ends in small intestine (digestion)

Proteins:

-Begins in the stomach when pepsinogen (chief cells) is activated by HCl and turns into pepsin

-Operates best with acidic pH/environment; therefore becomes inactivated when mixes with pancreatic juice that is more basic in the duodenum

-Protein fragments entering small intestine are cleaved by trypsin/chymotrypsin from pancreas, carboxypeptidase splits off one amino acid at a time, aminopeptidase and dipeptidase liberate the final amino acid products

Lipids/Fats:

-Lipases: major fat-digesting enzymes

-Lingual lipases is found in saliva in the mouth, not activated until gets to acidic stomach

-Bile salts emulsify fats because they have nonpolar regions that cling to fat molecules and polar regions that allow them to repel each other

-Lipases make free fatty acids and monoglycerides, which associate with bile salts to form micelles which “ferry” them to intestinal mucosa

-Fatty acids leave micelles to diffuse into epithelial cells and are recombined/repackaged to form chylomicrons

-Chylomicrons are extruded by exocytosis and enter lacteals and are carried away in lymph

Nucleic Acids:

-Pancreatic nucleases in pancreatic juice break them down to nucleotides, then brush border enzymes

Absorption:

-Most nutrients are absorbed through active transport

-Enter the blood and transported to liver in hepatic portal vein to liver

Respiratory System

Functions:

1. Breathing
2. Supplying O2
3. Removing Co2, heat, and water

-Respiratory zone:

-Site of gas exchange

-Includes respiratory bronchioles, alveolar ducts, and alveoli

-Conducting zone:

-Conduit to gas exchange sites (transports air basically)

-Every other respiratory structure

-Filters, heats, and humidifies air

Muscles:

-External intercostal muscles-breathe in

-Internal intercostal muscles-breathe out

-Diaphragm

Nose:

-Nasal cavities divided by nasal septum

-Hair inside them (vibrissae) filter coarse particles from inspired air

-Mucus-secreting cells make sticky mucus that traps inspired dust, bacteria and other debris

-Cilia move mucus toward pharynx, where we swallow and digest it

-Nasal cilia become sluggish on cold days causing runny nose

-Air is warmed to 37 degrees C by capillaries and thin-walled veins under the epithelium, air saturated with H2O vapor, which protects the alveoli from drying out

Carina- point where the trachea branches into the two main bronchi, if a foreign object touches it, causes you to cough violently

Alveoli:

-External surfaces covered in a cobweb of pulmonary capillaries, this plus alveoli surface= respiratory membrane (blood/air barrier) with blood flowing past on one side and gas on the other

-Gas exchange occurs by diffusion across the respiratory membrane (O2 alveolusblood, CO2 bloodalveolus)

1.Surrounded by fine elastic fibers

2. Alveolar pores connect adjacent alveoli allow pressure to be equalized and provide alternative routes to any alveoli whose bronchi have collapsed due to disease

3. Alveolar macrophages on internal alveolar surface engulf bacteria

Dead Space

-Anatomical dead space: typically 150mL, inspired air that fills the conducting respiratory passageways but never contributes to gas exchange in the alveoli

-Alveolar dead space: space occupied by alveoli that cease to act in gas exchange due to collapse or obstruction

Alveolar Ventilation: flow of gases into and out of the alveoli during a particular time

AVR= frequency (breaths/min) x (TV-dead space) (mL/breath)

Boyles Law:

P1V1=P2V2

-Pressure and volume are inversely related (increase in lung volumedecrease in intrapulmonary pressureair enters the lungs)

Expiration depends more on the lung’s elasticity than on muscle contraction

When PpulPatm, air rushes out

When PpulPatm, air rushes in

Surface tension

-Acts to draw the liquid molecules closer together and reduces their contact with the dissimilar gas molecules, and resists any force that tends to increase surface area of a liquid

-Water has high surface tension and coats alveoli, so it is always trying to reduce the size of alveoli

-Surfactant: lipids and proteins that reduces the surface tension of alveolar fluid and tries to make them not collapse (steroids help make surfactant in preemies-Infant respiratory distress syndrome)

Daltons Law: total pressure exerted by a mixture of gases is the sum of the pressures exerted by each gas

Alveolar Gas

-More CO2 and water vapor and much less O2: gas exchange puts CO2 into alveoli, O2 out of body), humidification of air causes water vapor, mixing of alveolar gas in each breath