3020 Lecture 18
Amber Stokes・2 minutes read
The large intestine and appendix in humans are vestigial organs from our ancestors, but the appendix now plays a crucial role in producing the microbiome, influencing immune system function. Herbivores have longer digestive tracts with a large cecum and four-chambered stomach for enhanced digestion of cellulose, while marine vertebrates actively regulate internal ion and water concentrations to match their external environment.
Insights
- The appendix, once considered vestigial, is now recognized for its role in producing the microbiome, which influences immune system function and overall health, leading to ongoing research and the use of probiotics.
- Ruminants, such as cows, possess four-chambered stomachs and a large cecum to aid in breaking down cellulose, showcasing specialized digestive adaptations for herbivorous diets, including rumination for enhanced digestion and methane production.
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Recent questions
What is the role of the large intestine?
The large intestine absorbs water, electrolytes, and vitamins.
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Summary
00:00
The Appendix: Vestigial Organ with Vital Role
- The large intestine is shorter and wider than the small intestine, surrounding it and receiving its contents at the ileocecal valve.
- The cecum, resembling a tail, and the appendix are considered vestigial organs, no longer essential in humans but still functional in herbivores.
- Vestigial organs are structures once used by ancestors but now unnecessary, like the cecum and appendix in humans.
- Recent research suggests the appendix plays a role in producing the microbiome, influencing immune system function and overall health.
- The microbiome, comprising gut bacteria, has significant impacts on health, prompting ongoing research and the use of probiotics.
- The book "I Contain Multitudes" delves into the microbiome's importance, offering accessible insights into its role and ongoing research.
- The large intestine does not digest food but absorbs water, electrolytes, and vitamins like vitamin K, preparing waste for expulsion.
- Feces are compacted in the large intestine, passing to the rectum for short-term storage before expulsion, controlled by the anus's smooth and skeletal muscles.
- Herbivores rely on microbes in their digestive tracts to break down cellulose, with a longer digestive tract, large cecum, and potential ruminant modifications aiding in digestion.
- Ruminant herbivores, like cattle, possess four-chambered stomachs to further break down cellulose, with a large cecum housing bacteria and protists for enhanced digestion.
22:31
Digestive Systems and Osmoregulation in Animals
- Herbivores have long digestive tracts, with the large intestine looping extensively, aiding in breaking down plant material.
- Insectivores and carnivores possess shorter intestines, with a vestigial cecum or none at all, making protein digestion easier in the stomach.
- Humans, as omnivores, have longer intestines than carnivores but still possess a vestigial cecum.
- Ruminants, like cows, have a four-chambered stomach, with the abomasum being the true stomach where food is digested.
- Ruminants chew food, which then goes through the rumin, reticulum, omasum, and finally the abomasum for digestion.
- Rumination evolved multiple times, not just once, as seen in monkeys off the coast of Africa, who are also ruminants.
- Ruminants produce methane due to the breakdown of plant matter, leading to gassiness.
- Osmoregulation involves regulating water and ion concentrations in the body, primarily through the kidneys.
- Water and ions are exchanged through various body systems like the skin, lungs, GI tract, and kidneys, with excess water and ions excreted through urine.
- Osmosis involves water moving from a dilute to a less dilute solution, while osmolarity measures the number of osmotically active moles of solute per liter of solution, and tonicity determines a solution's ability to change a cell's volume by osmosis.
46:16
Cell Solutions: Hypertonic, Isotonic, Hypotonic
- The text discusses the different solutions in which a cell can be found: hypertonic, isotonic, and hypotonic.
- In a hypertonic solution, the cell has lower solutes and higher water compared to the external environment.
- Water and solutes move in opposite directions based on the relative concentrations of solutes inside and outside the cell.
- In a hypotonic solution, the cell has a high concentration of solutes and a low concentration of water compared to the external environment.
- Water moves from high to low concentration, causing the cell to swell, potentially leading to bursting.
- In a hypertonic solution, water leaves the cell, causing it to shrink and dehydrate.
- In an isotonic solution, the concentrations of solutes and water inside and outside the cell are equal, resulting in no net movement of water or solutes.
- Marine invertebrates are osmoconformers, matching the ion concentrations of their environment to be isotonic.
- Freshwater vertebrates are osmoregulators, actively regulating their internal ion and water concentrations to be hypertonic to the environment.
- Marine vertebrates are also osmoregulators, maintaining a hypotonic internal environment compared to the saltwater they live in.
01:09:48
Osmosis and Water Regulation in Animals
- Inside cells have higher water concentrations, while the outside has high solute concentration and low free water, leading to osmosis from inside to outside.
- Fish and sea turtles take in solutes from the environment, leading to water loss through osmosis, resulting in concentrated urine production.
- Marine animals drink seawater to intake water, producing concentrated urine with low volume and high solutes, while actively transporting solutes out and using salt glands to expel excess salt.
- Terrestrial vertebrates, like humans, lose water through evaporation via skin and respiratory evaporation, with osmo Regulatory mechanisms evolving to retain water, especially in arid environments like the desert-dwelling kangaroo rat.
