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GI A&P

Alyssa Walsh GI disease unit infectious disease-MS Inglés

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GI A&P

ESOPHAGUS
- STOMACH
  - SMALL INTESTINE
    - LARGE INTESTINE
      - Appendix
      - Rectum
        Anus
        Consists of: APPENDIX, CECUM, COLON, RECTUM
        COLON
        Tons of goblet cells, no villi, tightly packed glands
        Mature cells at surface
        Stem cells (immature cells) at base of glands
        Electrolyte transport by intestinal epithelial cells
        APPENDIX
        In adults, may influence gut microflora and GALT more than digestion.
        In fetuses, may be more important for growth and development as a source of endocrine cells
        SIGMOID COLON
        Muscular, moves ingesta (feces)
        RECTUM
        Stores feces until elimination
        Colon Conserves Water
        follows osmotic gradient: equalizes when osmotic pressure in lumen = to that of plasma
        Absorption of Na+
        Electrogenic
        Na+ enters the apical epithelial sodium channels (ENaC) and exits basal Na+ K+ ATPase pumps
        Cl- follows passively
        Electroneutral
        ATP-dependent Na+/H+ pumps at the basolateral aspect of cells.
        Absorption of Vit k, Vit B12, thiamine, riboflavin
        bacterial metabolism products from microbiome
        Acetate, butyrate, proprionate
        Good for you
        1300ml in 200 out
    - Duodenum
      - Jejunum
        Ileum
        Empties into LI , 3 m
        Distal segment of SI
        Absorb vitamin B12 and bile acids
        Contains “Peyer’s Patches"
        Less of a role in digestion than jejunum
        ABSORPTION
        middle, 2.5 m
        Lots of plications and villi
        MAJOR SITE OF absorption of SUGARS, AMINO ACIDS, FATTY ACIDS
        MAJOR SITES OF WATER
        Electrolyte transport by intestinal epithelial cell control:
        water
        Uptake of glucose, amino acids, and bile acids across the apical (luminal) aspect of cells
        Electrochemical gradients are maintained by ATP-dependent Na+/H+ pumps at the basolateral aspect of cells
        Cl- is secreted to the lumen through the CFTR on epithelial cells
        Cystic Fibrosis Transmembrane Conductance Regulator
        Na+ and water follow
        Rehydrate mucus
        K+ secretion into GIT lumen
        Active
        Exchanged for Na+
        Passive
        Secreted into mucus
        Spatial distribution of transporters in SI matters
        Disease
        Pathogens can damage villi/microvilli
        Impairs absorption
        osmotic diarrhea
        secretory diarrhea
        Homeostasis
        Water and digestion products follow Na+ movement
        Secretion at crypts follow Cl- movement
      - Closest to stomach, short, 20-25 cm
        Receives gastric contents (“chyme”) mixes it with pancreatic enzymes and bile.
        Neutralizes the gastric acid with mucus and bicarbonate-rich solutions from Brunner’s glands
        Site of IRON absorption
    - Villi are unique to SI
      - Microvilli are surface projections from epithelial cells of villi
        Brush border= microvilli and glycocalyx on mature enterocytes
        Enterocytes with microvilli
        Filaments and terminal web are made of ACTIN
        Goblet cell filled with mucus droplets
        Enterocytes are attached to the basement membrane
        The glycocalyx contains glycoproteins and enzymes
        Dipeptidases split some amino acids
        Disaccharidases can split some sugars
    - Main location for digestion= Enzymes
      - Sucrase
        Lactase
        Isomaltase
        Aminopeptidase
        Dipeptidase
        Enteropeptidase
        Many enzymes are produced in an INACTIVE form and are CLEAVED in the lumen to an active form.- so we don’t digest ourselves
      - Pancreas= Trypsin
        activated by enteropeptidase
        Proteins/polypeptides
  - Rugal folds allow stretch
    - The stomach does not have villi. Some cells have microvilli but the microvillli are not as abundant or obvious as the brush border of the small intestine.
      - Function
        Mucus protects our stomach from the stomach acid
        Parietal cells increase their SA when producing acid
        Vitamin absorption
        PCs produce intrinsic factor which helps w/Vit B12 absorption
        PCs contain many mitochondria to produce ATP
        Microvilli and vesicles
        Increase the area that H+ and Cl- can be secreted from
        Acid production increased by:
        Gastrin
        Histamine
        Acetylcholine
        Hydrochloric acid = pH2-3
        Hydrolysis of macromolecules and lipase
        Inhibit bacterial growth
        Shigella spp.
        Some E. coli
        ***Listeria monocytogenes
        Parasite oocysts
        Pathogens that survive stomach acid
        Gastric secretions add 2.5L/day to GIT contents
        FUN FACT
        Liquefy, mix, and break down ingesta into small particles
        Peristalsis
        Acid
        Enzymes
        Pepsin
        Breaks down proteins/polypeptides
        Activated to pepsin by Hal
        Lipase
        Triglycerides
        Regulates flow into duodenum
    - Store ingested meal
      - Peristalsis
- MOUTH
- SALIVARY GLANDS
- Break down food
  - Mechanical
  - Enzymatic
    - Amylase breaks down starch
- Saliva
  - IgA
  - Lysozyme
  - Mucins
  - Alkaline
    - Balances acidic pH in stomach
!!Big Picture!!
- Structure
  - Convoluted tube with invaginations and surface projections.
    - Most anatomic divisions are separated by sphincters
      - Convolutions: 30-300 m2 for avg adult
        Important for small intestine
        Convolutions of the jejunum= plicae, villi, and microvilli
        As the cells differentiate they migrate towards the tips as they mature
        Plicae are permanent folds in the mucosa and submucosa
        In all parts of the large intestine and jejunum of SI
        SI does not like to stretch
        They do not like to stretch
    - Lumen is inside your body but OUTSIDE your tissues
      - Pathogens interact with the mucus and mucosa first
        Mucosa: epithelial cell layer and the subjacent tissue of the lamina propria
- Function
  - Maximize surface area for enzymatic digestion, absorption, secretion
    - Control flow
      - Increase SA, provide flexibility
        Stretching of stomach/colon/rectum
        Storage of food and feces
        Digestion and absorption
Briefly covered
- Bile normal functions
  - Bile is alkaline solution produced by liver and stored in gall bladder
    - Bile salts (bile acids)
      - synthesized from cholesterol
      - Act as detergents to emulsify lipids for absorption
      - Antimicrobial
        Some pathogens like Salmonella Typhi can survive in bile
        Some pathogens use bile components as signals to adapt.
        Salmonella, Vibrio, Cryptosporidium
    - Bile pigments
      - Derived from hemoglobin
      - Brown, green, yellow
- Hormones that regulate GIT
  - Gastrin
    - Gastric epithelial cells, stimulates acid secretion, pepsin production, growth of GIT mucosa
  - Secretin
    - SI endocrine cells
      - Inc bicarbonate, dec acid secretion
  - Cholecytokinin (CCK)
    - SI endocrine cells
      - Gall bladder contraction, pancreatic secretion
- PERISTALSIS
  - A reflex initiated by lumen stretching, resulting in contraction behind the stretch and relaxation in front.
    - VOMITING!!= REVERSE Peristalsis
      - REMOVES stomach & upper GIT CONTENTS and PROTECTS the airway.
      - STIMULI= irritants to mucosa like infection or inflammation, chemoreceptors in brain, links to limbic system
  - Requires intact innervation, smooth muscle coordination, and multiple types of neurotransmitters that we are not covering

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Descripción: infectious disease-MS GI disease unit Mapa Mental sobre GI A&P, creado por Alyssa Walsh el 16/10/2021.
Creado por: Alyssa Walsh
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GI A&P

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