Digestive System Part 2

Question 1

what are the parts of the small intestines?

Answer 1

• duodenum
• jejunum
• ileum

Question 2

what is the function of the small intestines?

Answer 2

• move chyme forward to continue its digestion with special juices secreted by its own intrinsic glands and accessory glands (liver and pancreas)
• absorb the nutrient material released by digestion into the blood and lymph vessels in its mucosa

Question 3

What are the four degrees of folding in the small intestine that amplify its absorptive surface area?

Answer 3

1. Plicae Circulares (Circular Folds): Large folds of the mucosa and submucosa that increase surface area and slow down food passage.
2. Villi: Finger-like projections of the mucosa that contain blood vessels and lymphatics for nutrient absorption.
3. Crypts of Lieberkühn (Intestinal Glands): Invaginations between villi that produce intestinal secretions and house stem cells for epithelial renewal.
4. Microvilli: Microscopic projections on the surface of epithelial cells (brush border) that maximize surface area for absorption.

Question 4

what are Goblet cells?

Answer 4

• unicellular, columnar mucus secreting cells, released by exocytosis

Question 5

what are the components of the mucus secreted by goblet cells and what is its function?

Answer 5

• 80% carbohydrates
• 20% proteins
• mucus hydrates to form a protective gel coat to shield the epithelium from mechanical abrasion and bacterial invasion

Question 6

what are Enterocytes/Absorptive Cells?

Answer 6

tall columnar cells primarily for absorption with a basally positioned nucleus whose microvilli contain lactase, maltase and sucrase

Question 7

what are Enteroendocrine Cells?

Answer 7

cells that produce various paracrine and endocrine hormones

Question 8

what are Paneth Cells?

Answer 8

cells that secrete antimicrobial agents that help maintain mucosal innate immunity, gut flora balance and protect against pathogens

Question 9

what are Microfold Cells (M Cells)?

Answer 9

modified enterocytes that cover enlarged lymphatic nodules in the lamina propria

Question 10

what is Lactose Intolerance an what does it cause?

Answer 10

• congenital lactase deficiency is an autosomal recessive disorder caused by mutations in the gene encoding lactase
• lactase deficiency gives rise to osmotic diarrhea because, in its absence, osmotically active lactose remains in the lumen

Question 11

what is associated with the microvillus brush board of Enterocytes and what is its role?

Answer 11

glycocalyx or cell coat, a cell surface glycoprotein complex containing mucins and sugars that focus to:
- Increase surface area
- Protect
- Digest
- Absorb

Question 12

what is the structure of the microvilli of Enterocytes?

Answer 12

• core of vertically oriented actin microfilaments
• extend into the apical cytoplasm and insert into the horizontally oriented terminal web
• attach to the intracellular density associated with the zonula adherens

Question 13

what is the function of junctional complexes that connect Enterocytes and what are they?

Answer 13

ensure tight adhesion between enterocyte apical-lateral surfaces, preventing leakage and regulating permeability by prevent the passage of macromolecules from the lumen into the intracellular spaces and lamina propria
- Zonula Occludens (Tight Junctions, ZO)
- Zonula Adherens (ZA)
- Macula Adherens (Desmosomes, MA)

Question 14

wha is the function of the baso-lateral cell membrane?

Answer 14

connects the basement membrane (blood) to the tight junction area with a lateral space between that has no digestive enzymes but is rich in Na, K- dependent ATPase

Question 15

what is Celiacs Disease and what does it lead too?

Answer 15

• autoimmune disorder that involves the formation of antibodies against gliadin, a component of gluten when ingested
• leads to deficient maturation of enterocytes and immune-mediated epithelial damage but the primary consequence is the loss of villi (villous atrophy) in the small intestine, reducing surface area for nutrient absorption, leading to malabsorption and gastrointestinal symptoms

Question 16

what is the function of Enteroendocrine Cells?

Answer 16

cells of the duodenum that secrete secretin and CCK in response to chyme stimulation

Question 17

what does the release of secretin and CCK by Enteroendocrine cells promote?

Answer 17

• pancreatic exocrine secretions
• CCK stimulates contraction of the gall bladder thus propelling bile into the common bile duct and then into the duodenum, secretin augmented CCK- induced contractions

Question 18

Where are Paneth Cells located and what type of granules do they contain and excrete?

Answer 18

• found at the base of the crypts (glands) of the small intestine, predominantly in the jejunum
• large eosinophilic secretory granules in their apical cytoplasm that secrete arginine-rich proteins, glycoproteins, lysozyme and antimicrobial peptides

Question 19

what are the antimicrobial agents secreted by Paneth Cells and how do they protect the intestine?

Answer 19

• Defensins (or cryptidins): Increase the permeability of microbial membranes, leading to their destruction.
• Lysozyme: Degrades bacterial peptidoglycan coats, breaking down their structure.
• Tumor Necrosis Factor-alpha (TNF-α): Produced in response to infections to mediate immune responses and tissue injury.

Question 20

What are Brunner’s Glands, and what is their function?

Answer 20

glands are found in the submucosa of the duodenum that
- secrete neutral or alkaline mucus rich in bicarbonate to neutralize stomach acid and protect the duodenal lining
- produce lysozyme, which has antibacterial properties
- secretion is stimulated by feeding and parasympathetic nervous system (PSN) activation.

Question 21

What are the main characteristics of the Jejunum?

Answer 21

• villi are long, and the glands stain dark in the mucosa
• muscularis mucosae is quite thin
• lacks Brunner’s glands
• contains lacteals (specialized lymphatic vessels in the core of the villi)
• main function is nutrient absorption

Question 22

What are the distinguishing features of the Ileum?

Answer 22

• Peyer’s patches, key for immune surveillance and preventing infections
• ileum primarily absorbs vitamin B12, bile salts, and remaining nutrients

Question 23

What are Peyer’s Patches, and where are they located?

Answer 23

• large clusters of lymphoid follicles located in the wall of the ileum lined by the follicle-associated epithelium (FAE), which includes M cells and enterocytes
• located as part of the Gut-Associated Lymphoid Tissue (GALT) and play a role in immune response by uptake of antigens and interacting with antigen-presenting cells

Question 24

what is the structure of M Cells and what is their main function?

Answer 24

• specialized epithelial cells in the ileum overlying the
  lymphoid follicles of Peyer patches that have microfolds rather than microvilli on their apical surface
• selectively endocytose antigens and transport them to the underlying lymphocytes and dendritic cells

Question 25

what is the nerve supply of the digestive tube?

Answer 25

- controlled by the enteric nervous system - influenced by the central nervous system

Question 26

what is the Enteric Nervous System?

Answer 26

a complex nerve network in the walls of the gastrointestinal (GI) tract that operates independently of the central nervous system but can also communicate with it, often called the "second brain" of the gut that - receives stimuli - integrates sensory information - regulates GI function by changing motility or secretion

Question 27

What is the Myenteric Plexus (Auerbach's Plexus) and what is its function?

Answer 27

plexus located between layers of the muscularis externa that controls GI motility, smooth muscle contraction, and peristalsis to move food along the tract

Question 28

What is the Submucosal Plexus (Meissner's Plexus) and what is its function?

Answer 28

- plexus located in the submucosa of the intestinal wall that regulates secretion, blood flow, and muscle contraction of the mucosal layer to support digestion and absorption

Question 29

What are the main functions of the Enteric Nervous System (ENS)?

Answer 29

- Gastric Motility: Smooth muscle contraction for food movement - Secretion of Mucus and Enzymes: Done by mucosal secretory cells - Hormone Release: Enteroendocrine cells release hormones to regulate digestion - Immunomodulation: Mast cells secrete immune molecules to protect the gut

Question 30

What is Hirschsprung Disease, and how does it affect the intestine?

Answer 30

congenital defect in colonic innervation that occurs when neural crest cells fail to migrate the entire length of the bowel during development - results in a lack of enteric nerve cells in segments of the colon, causing obstructive constipation and failure to pass meconium in newborns

Question 31

what does Hirschsprung Disease primarily affect and how is it diagnosed and treated?

Answer 31

- primarily affects the rectum, sigmoid colon and the proximal part of the bowel is dilated, known as congenital megacolon - Diagnosis is confirmed through biopsy to show the absence of ganglion cells - the standard treatment is surgical resection of the affected segment

Question 32

What are the main sections of the Large Intestine?

Answer 32

- Cecum: proximal part, begins at the ileocecal valve, connected to the appendix - Colon: Includes ascending, transverse, descending, and sigmoid segments - Rectum: Distal portion, ends at the anal canal

Question 33

What is the function of the colon?

Answer 33

- Reabsorption of electrolytes (Na⁺, K⁺) and water to maintain body fluid balance by an Na⁺/K⁺ ATPase-driven transport, which actively pumps ions across the epithelium - Elimination of the remaining undigested food, along with waste products through compaction and excretion - Absorption of fat-soluble vitamins A, D, E, and K, which are produced by bacterial activity in the gut *i want to die

Question 34

What are the unique structural features of the Large Intestine?

Answer 34

- Omental Appendices: Fatty projections on the surface - Tenia Coli: Three distinct bands of longitudinal muscle allowing segmental contraction - Haustra: Sacculations created by the contraction of the tenia coli, aiding in fecal compaction

Question 35

What is the function of the Tenia Coli in the Large Intestine?

Answer 35

- Allows segments of the colon to contract independently - Aids in fecal compaction - Facilitates general peristalsis to move contents along the colon

Question 36

What are the features of the Appendix?

Answer 36

- a blind extension of the colon with no villi - contains Crypts of Lieberkühn, columnar cells with goblet cells, extensive lymphoid tissue, and a thick submucosa - primary role is immunological surveillance

Question 37

what is the Rectum and what is the Anal Canal?

Answer 37

- Rectum: dilated distal portion of the alimentary canal and its upper part is distinguished from the rest of the large intestine by the presence of folds called transverse rectal folds - Anal Canal: most distal portion of the alimentary canal

Question 38

What distinguishes the Rectum and Anal Canal?

Answer 38

- Rectum: Thick mucosa with simple columnar epithelium, long crypts with goblet cells, and prominent veins. - Anal Canal: Transition from simple columnar epithelium to stratified squamous epithelium, with prominent veins and long crypts - Contains sphincter muscles for voluntary and involuntary control of defecation.