unit 3 objectivews

Describe the functions of the digestive system and differentiate between organs of the alimentary canal and accessory digestive organs.

• Alimentary canal is tube through body from mouth to anus

  • a) Lips

  • (b) Oral cavity

  • (c) Oropharynx

  • (d) Laryngopharynx

  • (e) Esophagus

  • (f) Stomach

  • (g) Small intestines

  • (h) Large intestines

  • (i) Anus

• accessory digestive organs are glands and organs involved in producing and secreting substances into the alimentary canal

  • (a) Salivary glands

  • (b) Pancreas

  • (c) Liver and gall bladder

• function

  • Involved in converting food into nutrients for absorption and transfer via the cardiovascular system for use and storage

  • Involves several steps that occur along the alimentary canal

    • 1) Ingestion

      • (a) Lips and oral cavity/teeth

    • 2) Mechanical breakdown

      • (a) Oral cavity/teeth

      • (b) Stomach

    • 3) Propulsion

      • (a) Oral cavity > anus

    • 4) Digestion

      • (a) Stomach

      • (b) Small intestines

    • 5) Absorption

      • (a) Small intestines

      • (b) Large intestine

    • 6) Defecation

      • (a) Large intestine

      • (b) Anus

Describe the location and function of the peritoneum.

• The peritoneal membrane, also known as the peritoneum, is a thin, transparent membrane that lines the abdominal cavity and covers the abdominal organs

• Serous membrane allowing for movement of organs within cavity

  • (a) Parietal peritoneum adjacent to abdominopelvic walls

  • (b) Visceral peritoneum adjacent to organ

  • (c) Peritoneal cavity between parietal and visceral peritoneum thin and filled with serous fluid

• Serous membranes folded to form double layer called the mesentery with several functions

  • (a) Provides routes for vasculature and nerves to organs

  • (b) Holds organs in place

  • (c) Stores fat

• Mesentery attaches to abdominal wall

  • (a) Dorsal attachments for most

  • (b) Ventral attachments for liver and stomach

• Most organs are within mesentery while others not

  • (a) Within mesentery = intraperitoneal/peritoneal organs

    • (i) Most organs

Define retroperitoneal and name the retroperitoneal organs of the digestive system.

• Covered only on one side by serous membrane = retroperitoneal

  • (i) Pancreas, duodenum region of small intestine, part of large intestines

Describe the tissue composition and general function of the four layers of the alimentary canal.

• Mucosa → facilitate digestion and absorption of nutrients while also acting as a protective barrier

  • 1) Epithelium

    • (a) Stratified squamous > protection

    • (b) Simple columnar > secretion and absorption

  • 2) Lamina propria —> supports the epithelium, provides a pathway for blood and lymphatic vessels, and plays a crucial role in immune responses.

    • a) Loose connective tissue

      • (i) Fibroblasts

      • (ii) Immune cells and aggregates

      • (iii) Collagen fibrils

    • (b) Capillaries

      • (i) Fenestrated blood

      • (ii) Lymphatic

    • (c) Smooth muscle

  • 3) Muscularis mucosa → enhancing the digestive and absorptive processes

    • (a) Smooth muscle

      • (i) Orthogonal layers (inner circular and outer longitudinal)

• Submucosa → support the mucosa, and houses blood and lymphatic vessels, nerves, and in some regions, glands

  • 1) Loose connective tissue

    • (a) Fibroblasts

    • (b) Immune cells

    • (c) Collagen fibers

    • (d) Elastic fibers

  • 2) Seromucous glands

  • 3) Nerve plexi (submucosal/Meisner’s)

  • 4) Vasculature

    • (a) Blood arterioles and venules

    • (b) Lymphatic Submucosa of Jejunum

• Muscularis → to propel food through the digestive tract via peristalsis and segmental contractions

  • 1) Inner circular layer

  • 2) Nerve plexi (myenteric/Auerbach’s)

  • 3) Outer longitudinal

• Serosa/adventitia → secretes fluid to reduce friction between organs and allow for smooth movement

  • 1) Visceral peritoneum for serosa

  • 2) Connective tissue for adventitia

Describe stimuli and controls of digestive activity.

Controls of Digestive Activity:

• Mechanical Stimuli:

  • These include the physical stretching of the digestive tract walls as food enters, which is detected by mechanoreceptors. 

• Chemical Stimuli:

  • Changes in osmolarity, pH, and the presence of specific nutrients (like fats, proteins, and carbohydrates) in the digestive tract are sensed by chemoreceptors. 

• Neural Stimuli:

  • The sight, smell, and even thought of food can trigger digestive activity through the nervous system, preparing the body for digestion. 

• Hormonal Stimuli:

  • Various hormones, like gastrin, secretin, and cholecystokinin, are released in response to food and play a role in regulating digestive processes. 

Controls of Digestive Activity: 

• Intrinsic Nervous System (Enteric Nervous System):

  • This system, located within the walls of the digestive tract, has two nerve plexuses: the myenteric plexus, which controls muscle movement, and the submucosal plexus, which regulates secretions. 

• Extrinsic Nervous System:

  • The autonomic nervous system, including sympathetic and parasympathetic branches, influences digestive activity. Sympathetic nerves tend to inhibit motility, while parasympathetic nerves stimulate it. 

• Hormonal Control:

  • Hormones like gastrin, secretin, and cholecystokinin, released from the stomach and small intestine, regulate gastric secretions, pancreatic secretions, and gallbladder contractions. 

• Neural and Hormonal Interactions:

  • The brain also plays a role in digestion, with the cephalic, gastric, and intestinal phases of gastric control involving neural and hormonal responses.

Describe the gross and microscopic anatomy and the basic functions of the oral cavity and its associated organs.

• Anatomically delimited by the lips anteriorly, oropharynx posteriorly, hard and soft palate superiorly, tongue inferiorly, and cheeks laterally

  • 1) Lined mostly by stratified squamous epithelium

    • (a) Highly abrasive regions contain keratinized-like stratified epithelium

      • (i) Parts of tongue

      • (ii) Gums

• Lips and cheeks

  • Skeletal muscles within wall to contain and move food bolus about

    • Orbicularis oris for lips

    • (b) Buccinators for cheeks

  • Forms pouch for food > oral vestibule

• Palate

  • 1) Roof of mouth to facilitate mastication

  • 2) Hard palate supported by palatine bones of maxilla

  • 3) Soft palate contains skeletal muscle for closing off nasopharynx when swallowing

    • (a) Anchored laterally by palatoglossal arches

    • (b) Anchored posteriorly by palatopharyngeal arches

    • (c) Uvula projects downward at the posterior median

  • 4) Throat (oropharynx) is posterior most and delimited by palatopharyngeal arches

• teeth

  • Tooth is made of bone-like material and anchored into tooth sockets by connective tissue

• salivary glands

  • function

    • Secrete saliva with multiple functions

      • 1) Cleans the mouth

      • 2) Maintains teeth enamel

      • 3) Inhibits microbial growth

      • 4) Dissolve tastants

      • 5) Moistens food

      • 6) Proteins for partial digestion and protection

    • Gland parenchyma includes secretory cells, duct-lining, and muscle like cells for production and secretion of saliva into the oral cavity

      • 1) Two types of secretory cells arranged as tubes or acini (clusters)

        • (a) Mucous > secrete glycoproteins

          • (i) Tube organization

        • (b) Serous > secrete proteins

          • (i) Acini organization

Explain the dental formula and differentiate clearly between deciduous and permanent teeth.

• The dental formula is a shorthand way of indicating the numbers and relative positions of the different types of teeth in the mouth. This formula is written as a ratio, uppers over lowers, for one-half of the mouth.
  
  

• (2I,1C,2PM,3M)/(2I,1C,2PM,3M) X 2=32 teeth
  
  

• Primary Dentition consists of the deciduous teeth (decid = falling off), also called milk or baby teeth.
  
  

• Permanent Teeth enlarge and develop, the roots of the milk teeth are resorbed from below

Describe the composition and function of saliva and explain how salivation is regulated.

• Composition of saliva

  • 1) Water

  • 2) Electrolytes

    • (a) K+, Na+, Ca2+, Cl-, PO4- and HCO3-

  • 3) Metabolic wastes

    • (a) Urea and uric acid

  • 4) Enzymes

    • (a) Amylase for starch digestion

    • (b) Lipase for triglyceride to release fatty acid for taste

  • 5) Glycoprotein (mucins)

    • (a) Mucous for protection and lubrication

  • 6) Antibacterial proteins and peptides

    • (a) Lysozyme

    • (b) IgA

    • (c) Defensins

• salivary glands

  • function

    • Secrete saliva with multiple functions

      • 1) Cleans the mouth

      • 2) Maintains teeth enamel

      • 3) Inhibits microbial growth

      • 4) Dissolve tastants

      • 5) Moistens food

      • 6) Proteins for partial digestion and protection

• control

  • Parasympathetic motor activity stimulates activity to secrete protein-rich (serous) saliva

    • (a) Increase blood supply

    • (b) Increase saliva output

  • 3) Afferent signals from oral cavity chemoreceptors and mechanoreceptors to salivatory nuclei in brain stem stimulate parasympathetic activity

  • 4) Higher order input to salivary nuclei also can increase output

    • (a) Thinking about or seeing/smelling food

  • 5) Sympathetic stimulation decreases volume and favors mucous-rich secretion

    • (a) Decreases blood flow and subsequent secretion

Describe the anatomy and basic functions of the pharynx and esophagus.

The pharynx (throat) is a muscular funnel-shaped passageway at the back of the throat, serving as a common pathway for both the respiratory and digestive systems. It connects the nasal and oral cavities to the esophagus and trachea. The esophagus, on the other hand, is a muscular tube that primarily functions to transport food and liquids from the pharynx to the stomach

Describe the mechanism of swallowing

• Swallowing (deglutination) involves phases in the oral cavity and esophagus involving over 20 muscles

  • 1) Buccal phase

    • (a) Voluntary controls involved in forming a bolus of
      food for transport

      • (i) Mechanical breakdown moistening, and portioning to form bolus

    • (b) Close upper esophageal sphincter

    • (c) Push bolus posteriorly into oropharynx with
      tongue

  • Pharyngeal-esophageal phase

    • (a) Involuntary and controlled by swallowing center nuclei in the brainstem

      • Both skeletal and smooth muscle involved

        • Skeletal in tongue, oral cavity, and pharynx

        • Skeletal and smooth in esophagus

    • (b) Tongue blocks mouth

    • (c) Soft palate and uvula rise to close off nasopharynx

    • (d) Larynx rises to close off glottis via epiglottis

    • (e) Upper esophageal sphincter relaxes allowing food into the esophagus

    • (f) Pharynx muscle shorten forcing food into esophagus

    • (g) Upper esophageal sphincter closes

    • (h) Peristalsis moves food through the esophagus to the stomach

    • (i) Gastro-esophageal sphincter opens allowing food into stomach

    • (j) Gastro-esophageal sphincter closes to prevent backflow (regurgitation)

Describe stomach structure and indicate changes in the basic alimentary canal structure that aid its digestive function.

• Distensible chamber between esophagus and small intestine involved in mechanical, chemical, and enzymatic breakdown of food and some absorption

  • 50 ml expandable to 4L

  • Mucosa folds to form rugae when empty and
    collapse upon distention

• Located in left upper quadrant of peritoneal
  cavity posterior to liver and inferior to
  diaphragm

• Cardia, fundus, body, pylorus. Size varies depending on how much food it contains. Greater curvature (on outside), lesser curvature (on inside). The lesser and greater omentum tie the stomach to other digestive organs and the wall of the abdomen. 3 layers of muscle in stomach.

Name the cell types responsible for secreting the various components of gastric juice and indicate the importance of each component in stomach activity

• Parietal cells secrete hydrochloric acid and intrinsic factor. Chief cells produce pepsinogen and gastric lipase. Mucous neck cells secrete mucus. Additionally, enteroendocrine cells, specifically G cells, secrete the hormone gastrin. 

• Gastric juice is made up of HCl, pepsin (protein breakdown) and lipase (fat breakdown).

• HCl: makes stomach contents acidic which helps to denature proteins, breaks down cell walls of plant foods, and is harsh enough to kill many bacteria that may be ingested with foods.

• Pepsin: relies on acid environment made possible by HCl. Protein digesting enzyme.

• Lipase: fat digesting enzyme.

Describe the three phases of gastric secretion.

• Cephalic phase > thinking about it

  • (a) Stimulates secretion before there are contents in the stomach

  • (b) Stimulated by olfactory, gustatory, ocular and vestibulocochlear systems to CNS

  • (c) CNS > hypothalamus > vagus nerve > parasympathetic ganglia > postganglionic terminal > Ach

    • (i) Stimulate secretion

• Gastric phase > something in the stomach

  • (a) Mechano and chemoreceptors involved that sense stretch and stomach contents

  • (b) Mechano-receptors stretch > afferent via vagal nerve > brain stem > vagal nerve (motor) > parasympathetic ganglia > postganglionic terminal > Ach

  • (c) Peptides and pH detected by chemoreceptors on enteroendocrine G cells

    • (i) Peptides and high pH > enteroendocrine G cells within antrum > gastrin secretion

    • (ii) Gastrin > enteroendocrine (enterochromaffin- like) cells > histamine

• Intestinal phase > metering things out of the stomach into the duodenum

  • (a) Balance between stimulation and inhibition to meter the acidic chyme (partially digested food) into the duodenum

  • (b) Stimulation initially upon entry of chyme into the duodenum mediated by intestinal enteroendocrine G cells > gastrin

  • (c) Inhibition subsequently to slow gastric secretion caused by

    • (i) Distension

    • (ii) Acidic chyme

    • (iii) Fatty chyme

    • (iv) Hypertonic chyme

  • (d) Inhibition mechanism involves neuronal and hormone pathways

    • (i) Enterogastric reflex via short and long range neural pathways

    • (ii) Enterogastrone via the hormones secretin and cholecystokinin (CCK)

Explain how gastric secretion and stomach motility are regulated.

Gastric secretion and stomach motility are regulated by neural and hormonal mechanisms. These mechanisms involve both intrinsic (within the stomach) and extrinsic (outside the stomach) inputs, working to coordinate digestion. The enteric nervous system plays a key role in coordinating digestion, while the autonomic nervous system (sympathetic and parasympathetic) and various hormones influence gastric function. 

Define and account for the alkaline tide.

refers to a condition, normally encountered after eating a meal, parietal cells also secrete bicarbonate ions across their basolateral membranes and into the interstitial fluid causing an increase in pH.

Describe how the stomach and duodenum interact to regulate emptying of the stomach.

The stomach and duodenum regulate gastric emptying through a feedback loop involving both neural and hormonal mechanisms. The duodenum monitors the contents entering it from the stomach and signals the stomach to slow down or speed up gastric emptying based on factors like acidity, fat content, and distension. 

Identify and describe structural modifications of the wall of the small intestine that enhance the digestive process.

• Has a modified muscularis layer. It has a smooth muscle layer that runs obliquely and allows stomach to churn, mix and pummel food.

• Modified mucosa is a simple columnar epithelium composed entirely of goblet cells and gastric glands.

  • Glands in the fundus, where most chemical digestion occurs, produce majority of stomach secretions including from secretory cells.

Differentiate between the roles of various cell types of the intestinal mucosa.

Histology Of The Wall:
a. Simple columnar epithelial tissue with tight junctions and goblet cells
b. The intestinal crypts, or the crypts of Lieberkühn, secrete intestinal juice that serves as a carrier fluid for absorbing nutrients from chyme.
c. Enteroendocrine cells and the enterogastrones secretin and cholecystokinin
d. Intraepithelial lymphocytes [IELs]
e. Paneth cells: defensins and lysozyme
f. Peyer's patches: part of GALT

Define the functions of intestinal hormones and paracrines.

• Cholecystokinin (CCK):

  • Potentiates secretin's actions on liver and pancreas

  • Increases output of enzyme-rich pancreatic juice in pancreas

  • Stimulates gallbladder to contract and expel stored bile

  • Relaxes hepatopancreatic sphincter to allow entry of bile and pancreatic juice into duodenum

• Gastrin:

  • Increases HCI secretion in stomach (parietal cells)

  • Stimulates gastric emptying (minor effect)

  • Stimulates contraction of intestinal muscle in small intestine

  • Relaxes ileocecal valve

  • Stimulates mass movement in large intestine

• Histamine:

  • Activates parietal cells to release HCI in stomach

• Intestinal Gastrin:

  • Stimulates gastric glands and motility in stomac

List the major functions of the large intestines.

• major function is processing the undigested material and ejecting it from the body

  • 1) Formation of feces and defecation

Describe the regulation of defecation.

• Feces forced into the rectum by mass movements stretch the rectal wall and initiate the defecation reflex.

• This spinal cord-mediated parasympathetic reflex causes the sigmoid colon and the rectum to contract, and the internal anal sphincter to relax.

  • As feces are forced into the anal canal, messages reach the brain allowing us to decide whether the external (voluntary) anal sphincter should be opened or remain constricted to stop feces passage temporarily.

  • If defecation is delayed reflex contractions end within a few seconds, and the rectal walls relax.

  • With the next mass movement, the defecation reflex is initiated again—and so on, until the person chooses to defecate or the urge to defecate becomes unavoidable.

Describe the functional anatomy of the liver and gall bladder

liver

• Sits right below the diaphragm protected by the ribcage

• Composed of 4 lobes that are separated by connective tissue and fissures

  • Right lobe

  • Left lobe

  • Caudate

  • Quadrate

• The liver is enclosed and suspended by a mesentery , which is  type of ligament that suspends and separates from the diaphragm and the anterior abdominal wall

  • Also separates the different lobes

• Round ligament → remnant of umbilical vein, a blood vessel that carried oxygenated blood from placenta to fetus

• Porta hepatis or hilum which contains the vasculature from liver and bile ducts draining the liver

  • Hepatic portal vein

  • Hepatic artery

  • Common hepatic bile duct

• The liver is comprised of lobules that look like hexagons

• Periphery lobules contains the hepatic vasculature

  • Portal vein/venule

  • Hepatic artery/arteriole

  • Bile duct/ductules

• Center of lobule contains central vein

• Liver cells include

  • Hepatocytes → preform most of the liver functions

  • Cholangiocytes  → lining of bile ductules and ducts

  • Macrophages à remove debris

  • Capillary endothelial cells → sinusoidal capillaries allowing exchange between hepatocytes and the blood

  • Fibroblast à secrete proteins that form stroma

• functions

  • Exocrine > produces, recycles, and secretes bile

  • Endocrine > produces blood proteins

  • Energy processing > carbohydrates and fatty acids

  • Energy storage > glycogen and fats

  • Detoxification of substances in blood

gallbladder

• Main function is to store bile collected from the liver and to secrete it when stimulated

• The gall bladder is an expandable container that is wrapped in smooth muscle

• Bile drained by hepatic ducts from left and right lobes

• The right and left ducts come together to form the hepatic duct

• The cystic duct branches to fill the gall bladder

• The bile duct continues on to the duodenum

Describe the functional anatomy of the exocrine and endocrine pancreas.

The exocrine pancreas, composed of acinar cells, secretes digestive enzymes into the small intestine via ducts. The endocrine pancreas, consisting of islets of Langerhans, produces hormones like insulin and glucagon, which regulate blood sugar levels and are released directly into the bloodstream

Explain the roles of exocrine products of the liver and pancreas in digestion

The liver and pancreas both play crucial roles in digestion through their exocrine secretions. The liver produces bile, which aids in fat digestion by emulsification, while the pancreas secretes digestive enzymes and bicarbonate into the small intestine. These pancreatic enzymes break down carbohydrates, proteins, and fats, and the bicarbonate neutralizes stomach acid to create a suitable environment for enzyme activity. 

Describe the regulation of liver and pancreas exocrine secretions into small intestine.

The exocrine secretions of the liver (bile) and pancreas (digestive enzymes and bicarbonate) into the small intestine are primarily regulated by hormones and neural signals. Hormones like secretin and cholecystokinin (CCK) play key roles, while the nervous system, particularly the enteric nervous system, also contributes to the regulation

Describe the general process of digestion and absorption.

• Wetted with saliva and secretions to facilitate mechanical breakdown

• Mechanical breakdown to increase surface area for hydrolase activity

  • Oral cavity

  • Stomach

• Chemically release ions and denature proteins

  • Stomach

• Release and emulsify fats to increase water-exposed surface
  area for hydrolase activity

  • Some in stomach

  • Mostly in duodenum

• Absorption of monomeric units of biomolecules is done by enterocytes in the small intestine

  • Tight junctions at apical domain of cells prevents transport between cells

  • Go through the cell via various mechanisms not between the cells

  • Mostly mediated by transporters and passive diffusion

    • (a) Channels

    • (b) Carriers

      • (i) Secondary active

      • (ii) Facilitated transport

    • (c) Pumps > primary active

  • Many biomolecules transported against their gradient by secondary active transport

    • (a) Use Na+ gradient for import into cytosol via Na+ -driven symporter

      • (i) Na+/K+ pump to maintain gradient

    • (b) Amino acids, mono-saccharides, and nucleotide components

  • Some passively diffuse in then actively transported out in vesicles

    • (a) Lipids via micelles and chylomicrons

  • Microvilli (brush border) on apical membrane have hydrolases attached that primarily degrade short polymers into monomers

    • (a) Maltase, lactase, sucrase, and dextrinases for di- and oligosaccharides

    • (b) Peptidases for peptides

List the enzymes involved in digestion and name the foodstuffs on which they act.

•salivary amylase - Chemical digestion of carbohydrates begins in the mouth, where salivary amylase breaks large polysaccharides into smaller fragments.

•Pepsin - secreted by the chief cells, begins the chemical digestion of proteins in the stomach.

•Rennin - is produced in infants and breaks down milk proteins.

•Pancreatic enzymes - such as trypsin and chymotrypsin, further break down proteins in the small intestine.

•The brush border enzymes - carboxypeptidase, aminopeptidase, and dipeptidase work on freeing single amino acids in the small intestine.

•Lipases are secreted by the pancreas and are the enzymes that digest fats after they have been pretreated with bile.

List the end products of protein, fat, carbohydrates, and nucleic acid digestion.

• Protein

  • Amino acids are absorbed by cotransport with sodium ions.

  • Some dipeptides and tripeptides are absorbed via cotransport with H+ and hydrolyzed to amino acids within the cells.

  • Amino acids leave the epithelial cells by facilitated diffusion, enter the capillary blood in the villi, and are transported to the liver via the hepatic portal vein.

• Fat

  • Fatty acids and monoglycerides enter the intestinal cells via diffusion.
    oFatty acids and monoglycerides are recombined to form triglycerides and then combined with other lipids and proteins within the cells, and the resulting chylomicrons are extruded by exocytosis.

  • The chylomicrons enter the lacteals of the villi and are transported to the systemic circulation via the lymph in the thoracic duct.

  • Some short-chain fatty acids are absorbed, move into the capillary blood in the villi by diffusion, and are transported to the liver via the hepatic portal vein.

• Carbohydrate

  • Monosaccharides (simple sugars), the monomers of carbohydrates, are absorbed immediately

  • Glucose and galactose are absorbed via cotransport with sodium ions.
    oFructose passes via facilitated diffusion.

  • All monosaccharides leave the epithelial cells via facilitated diffusion, enter the capillary blood in the villi, and are transported to the liver via the hepatic portal vein.

• Nucleic Acid

  • Units enter intestinal cells by active transport via membrane carriers.
    oUnits are absorbed into capillary blood in the villi and transported to the liver via the hepatic portal vein

Describe the process by which breakdown products of foodstuffs are absorbed in the small intestine

1.Large fat globules are emulsified (physically broken up into smaller fat droplets) by bile salts in the duodenum.

2.Digestion of fat by the pancreatic enzyme lipase yields free fatty acids and monoglycerides. These then associate with bile salts to form micelles which "ferry" them to the intestinal mucosa.

3.Fatty acids and monoglycerides leave micelles and diffuse into epithelial cells. There they are recombined and packaged with other lipoid substances and proteins to form chylomicrons.

4.Chylomicrons are extruded from the epithelial cells by exocytosis. The chylomicrons enter lacteals. They are carried away from the intestine by lymph.