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Chapter 23 part 4 (large intestine study)

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  • Length and diameter of the large intestine
    The large intestine is about 1.5 meters (5 feet) long and has a larger diameter than the small intestine.
  • Primary functions of the large intestine
    Propulsion and defecation, absorption of water, minerals, electrolytes, maintaining acid-base homeostasis, and housing beneficial gut microbiota.
  • Location and role of the cecum
    The cecum is the first portion of the large intestine, a blind pouch in the right lower abdomen; it connects to the appendix which plays a role in the immune system.
  • Cause and symptoms of appendicitis
    Blockage of appendix by fecal matter causes bacterial infection and inflammation; symptoms include right lower quadrant abdominal pain, nausea, and vomiting.
  • Potential complications of untreated appendicitis
    Appendix may rupture causing internal bleeding, peritonitis, and can be fatal if untreated.
  • Four portions of the colon
    Ascending colon, transverse colon, descending colon, and sigmoid colon.
  • Function of the internal anal sphincter
    Involuntary sphincter made of thickened circular muscularis externa, controlled by parasympathetic motor neurons.
  • Function of the external anal sphincter
    Voluntary sphincter composed of skeletal muscle, controlled by somatic motor neurons from the cerebral cortex.
  • Histological features of the large intestine mucosa
    Lacks villi and microvilli, contains numerous goblet cells that secrete mucus for protection and lubrication.
  • Role of gut flora in the large intestine
    Produce vitamins like vitamin K, metabolize undigested carbohydrates into fatty acids, and inhibit growth of harmful bacteria.
  • Proximal large intestine functions
    Consists of ascending and transverse colon; primary site for water and electrolyte absorption and bacterial activity.
  • Distal large intestine functions
    Includes descending and sigmoid colon, rectum, and anal canal; stores fecal material and absorbs small amounts.
  • Haustral contractions in the large intestine
    Occur every 30 minutes in ascending and transverse colon; aid water and electrolyte absorption; controlled by ENS.
  • Mass movements in the large intestine
    Propulsive peristaltic waves moving fecal contents toward distal colon; occur 3-4 times daily, often triggered by food intake.
  • Defecation reflex mechanism
    Rectal distension activates parasympathetic reflex causing sigmoid colon and rectum contraction, internal anal sphincter relaxation, and voluntary external sphincter control.
  • Effect of increased large intestine motility
    Less water absorption, resulting in diarrhea; insoluble fiber speeds up motility.
  • Effect of decreased large intestine motility
    Excess water absorption, causing hard feces and constipation; dehydration is a common cause.
  • Definition of digestion
    A catabolic process breaking down large molecules into monomers via hydrolysis.
  • Barriers for nutrient absorption in the alimentary canal
    Apical plasma membrane, cytosol, basal plasma membrane, and endothelial cells of capillaries.
  • Initial carbohydrate digestion
    Begins in mouth with salivary amylase breaking starch into oligosaccharides.
  • Completion of carbohydrate digestion
    Occurs in small intestine by pancreatic amylase and brush border enzymes producing monosaccharides.
  • Absorption of monosaccharides
    Glucose and galactose use active transport; fructose uses facilitated diffusion; all exit enterocytes by facilitated diffusion into blood.
  • Start of protein digestion
    Begins in stomach with pepsin activated from pepsinogen by chief cells.
  • Major site of protein digestion
    Small intestine with pancreatic enzymes activated by trypsin and brush border enzymes producing free amino acids.
  • Protein absorption mechanism
    Amino acids cotransported with sodium via active transport across apical membrane; exit by facilitated diffusion into capillaries.
  • Major dietary lipids and their digestion
    Mostly triglycerides; mechanical digestion breaks globules; emulsification by bile salts increases surface area for pancreatic lipase.
  • Role of micelles in lipid absorption
    Micelles formed by bile salts escort fatty acids and monoglycerides to enterocyte membrane for absorption.
  • Fate of absorbed lipids inside enterocytes
    Reassembled into triglycerides, packaged into chylomicrons, released by exocytosis into lacteals (lymphatic system).
  • Lipid transport after absorption
    Lipids enter lymph, then bloodstream; capillary enzymes break down chylomicrons into fatty acids and glycerol for energy or storage.