BIOL: Exam 3

Functions of the GI system

Ingestion, digestion, absorption, and elimination

What makes up the Ailmentary canal (GI tract or gut)

mouth, pharynx, esophagus, stomach, small intestine, large intestine, anus

What makes up the Accesory digestive organs

liver, gallbladder, pancreas, and saliva glands

What is the Ailmentary canal (GI tract or gut)

Contunuos muscular tibe that runs from the mouth to anus; digests food (breaks down into smaller fragments; absorbs fragments through intestinal lining into blood for nutrition

What is the Accesory digestive organs

Often called “digestive glands”: produce secretions that help break down foodstuffs

6 essential processes for processing food

Ingestion, propulsion, mechanical breakdown, digestion (chemical breakdown), absorption, and defecation

Ingestion

eating

Propulsion

Movement of food through GI tract; Peristalsis: major means of propulsion of food that involves alternating waves of contraction and relaxation; smooth muscle of GI tract squeezes food along

Mechanical breakdown

includes chewing, mixing food with saliva, churning food in stomach, and segmentation; Segmentation: local constriction of intestine that mixes food with digestive juices via backward/foward movements (uses circular muscles)

Digestion (chemical breakdown)

series of catabilic steps that involves enxymes that break down complex food molecules into chemical building blocks

Absorption

passage of digested fragments from lumen of GI tract into blood or lymph

Defecation

elimination of indigestible sibstances via anus in form of feces

Peritoneum

serous membranes of abdominal cavity that consists of visceral and parietal peritoneum

Visceral peritoneum

membrane that touches surface of most digestive organs (faces the organ)

Parietal peritoneum

membrane that lines body wall (faces the abdominal wall)

Peritoneal cavity

Fluid-filled space between two peritoneums; fluid lubricates mobile organs

Mesentery

double layer of peritoneum (layers are fused back to back); extends from body wall to digestive organs; provides routes for blood vessel, lymphatics, and verves; holds organs in place and also stores fat

Intrapereitoneal (peritoneal) organs

organs that are located within the peritoneum

Retroperitoneal organs

located outside, or posterior to, the peritoneum; includes most of pancreas, duodenum, and parts of large intestine

Peritonitis

Inflammation of the peritoneum; can be caused by piercing abdominal wound, perforating ulcer, or ruptured appendix; peritoneal coverings stick together, which helps localize infection; dangerious and lethal if it becomes widespread; treatment: debris removal and megadoses of antibiotics

4 basic layers of the digestive organs

mucosa, submucosa, muscularis externa, serosa

Mucosa

Innermost layer that lines lumen; Functions: secretes mucus, digestive enzymes, and hormones; absorbs end products or digestion; protects against infectious disease

Submucoua (exterior to mucosa)

Contains blood and lymphatic vessels, and submucosal nerve plexus that supply surrounding GI tract tissues; Has abundant amount of elastic tissues that help organs to regain shape after stretching to store a large meal

Musculatris externa

Muscle layer responsible for segmentation and peristalsis; contains inner curcular muscle layer and outer longitudinal layers-Circular layer thickens in some areas to form sphincters: muscle “rings” that open and close to control the flow of contents

Serosa

Outermost layer, which is made up of the visceral peritoneum

Enteric nervous system

Gi tract has its own nervous system (Enteric-intestines, Contains more neurons than spinal cord); Submucosal nerve plexus and Nyenteric nerve plexus

Submucosal nerve plexus

Regulates glands and smooth muscle in mucosa

Myenteric nerve plexus

Controls Gi tract mobility

Function of mouth

where food is chewed and mixed with enzyme-containing saliva that begins process of digesion, and swallowing process is initiated

Mouth (oral (buccal) cavity)

Bounded by lips anteriorly, cheeks laterally, palate superiorly, and tounge inferiorly; walls of mouth lined with stratified squamous epithelium (tough cells that resist abrasion)

Palate contains

Hard palate, soft palate, uvula

Tounge

Occupies floor of mouth, composed of skeletal muscle, Lingual frenulum: attachment to floor of mouth

Functions of tounge

Gripping, repositioning, and mixing food during chewing; formation of bolus of food, semi-solid lump of food (wetted by saliva); initiation of swallowing, speech, and taste

Ankyloglossia

Congenital condition in which children are born with an extremely short lingual frenulum; often referred to as “tongue-tied” or “fussed tongue”; restricted tongue movement distorts speech and prevents feeding for the infant; treatement=surgical snipping of frenulum

Parotid gland

anterior to the ear and external to the masseter muscle; parotid duct opens into oral cavity next to second upper molar

Submandibular gland

medial to body of mandible; duct opens at base of lingual frenulum

Sublingual gland

anterior to submandibular gland under tongue; opens via 10-12 ducts into floor of mouth

Functions of saliva

Cleanses mouth'; dissolves food chemicals for taste; moistens food; compacts into bolus; begins breakdown of starch with enzyme “salivary amylase”

Xerostomia

dry mouth, uncomfortable condition caused by too little saliva being made; lack of moisture may lead to dificulty with chewing and swallowing, as well as oral infections (ulcers, canker sores)

Causes of Xerostomia

many common medications, diabetes mellitus, HIV/AIDS and associated treatments, Sjogren’s syndrome (autoimmune disease affecting moisture-producing glands throughout body)

Teeth

Teeth lie in sockets in gum-covered margins of mandible and maxilla

Mastication

process of chewing that tears and grinds food into smaller fragments

Dentition

Primary dentition consists of 20 deciduous (baby) teeth, that erupt between 6 and 24 months of age; 32 deep lying permanent teeth that occur around 6-12 years of age

Three areas of the pharynx

Nasopharynx, Oropharynx, and Laryngopharynx

The muscles of the pharynx are used to

move foods, fluids, and air

The esophagus

the muscular tube that runs from the laryngopharynx to the stomach (collapsed when not in use)

Where does the esophagus pierce the diaphragm

esophageal hiatus

where does the esophagus join stomach

Cardial orifice

What surrounds teh cardial orifice

gastroesophageal (cardiac) sphincter which keeps the orifice closed when food is not being swallowed.; mucus cells on both sides of sphincter help protect esophagus from acid reflex

how is heartburn caused

caused by stomach acid regurgitating into the esophagus; excess food/ drink, extreme obesity, pregnancy, alcohol, coffee, etc; hiatal hernia-structural abnormality where part of the stomach protrudes above the diaphragm→ can lead to esophagitis, esophageal ulcers, or even esophageal cancer

heartburn is the first symptom of

gastroesophageal reflux disease (GERD)

deglutition (swallowing) muscles and phases

coordination of 22 muscle groups and two phases

Two phases of deglutition

Buccal and Pharyngeal-esophageal phase

Buccal phase

voluntary contraction of tounge

Pharyngeal-esophageal phase

involuntary phase that primarily involves the vagus nerve; controlled by swallowing center in the medulla and lower pons

Stomach

temporary storage tank that starts the chemical breakdown of protein digestion; converts bolu so f food to paste-like chyme; in empty stomach, mucosa forms many folds of tissue called rugae

6 major regions of the stomach

Cardial part (cardia)- surrounds cardial orifice; Fundus- dome-shaped region beneath diaphragm; Body- midportion; Pyloris part- lower end that joins with duodenum of small intestines; Greater curvature- convex lateral surface of stomach- Lesser curvature- the concave medial surface of the shock

glands in fundus and body produce most what

gastric guice

Four primary cells that exist inside the stomach

Mucous, parietal, chief, enteroendocrine cells

Mucous cells

produce very viscous, bicarbonate-rich mucus; protects stomach lining from abrasion and acidic contents

Parietal cells

Hydrochloric acid (HCL)- pH 1.5-3.5; denatures protein, activates pepsin, and kills many bacteria; Intrinsic factor-glycoprotein required for absorption of vitamin B12 in small intestine

Chief cells

Pepsinogen: inactive enzyme that is activated to pepsin by HCl and begins protein digestion; Lipases: digests ~15% of lipids

Enteroendocrine cells

Secretes chemical messengers; Serotonin- promotes peristalsis, segmentation, and inflammation; Gastrin- promotes GI mobility and acid release; Histamine- regulates acid secretion; Somatostatin- reduces secretions and mobility

Stomachs Mucosal barrier

Harsh digestive conditions require the stomach to be protected

mucosal barrier protects the stomach and is created by three factors

• Thick layer of bicarbonate-rich mucus

• Tight junctions between epithelial cells

  • Prevents juice seeping underneath tissue

• Damaged epithelial cells are quickly replaced by division of stem cells

  • Surface cells replaced every 3-6 days

Gastritis

Inflammation caused by anything that breaches stomach’s mucosal barrier

Peptic/gastric ulcers

Can cause erosions in the stomach wall

• If erosions perforate the wall, it can lead to peritonitis and hemorrhage

Most ulcers are caused by the bacterum Helicobacter pylori (H. Pylori)

Can also be caused by non-steroidal anti-inflammatory drugs (NSAIDs), such as aspirin

Digestive processes in the stomach

Carries out breakdown of food

Serves as holding area for food

Delivers chyme (liquified stomach mixed food) to small intestine

Denatures proteins by HCl

Pepsin carries out enzymatic digestion of proteins

Intrinsic factor

Only stomach function essential to life (vitamin B12 absorption)

• B12 is needed for red blood cells to mature

• Lack of intrinsic factors causes pernicious anemia

• Treated with B12 injections

Vomiting (emesis) caused by

extreme stretching

intestinal irritants, such as bacterial toxins excessive alcohol, spicy food, certain drugs

Vomitting (emesis)

Chemicals and sensory impulses stimulate the emetic center of the medulla

Excessive vomiting can lead to dehydration and electrolytes and acid-base imbalances (alkalosis)

3 Accessory organs associated with small intestine

Liver, gallbladder, and pancreas

Liver

digestive function is production of bile

Bile: fat emulsifier (allows fat to be more easily digested)

Gallbladder

chief function is storage/concentration of bile

Pancreas

supplies most of enzymes needed to digest chyme, as well as bicarbonate to neutralize stomach acid

4 primary lobes of the liver

Common hepatic duct: leaves liver

Cystic duct; connects to gallbladder

Common bile duct: formed by union of common hepatic and cystic dicts

Cm. Hepatic+Cystic= Common Bile Duct

Hepatocyte

the functional “liver cell”unit

produces ~900 ml bile per day and processes bloodborne nutrients

Stores fat-soluble vitamins (D, E, A, K)

Perform deotxification

Bile

Yellow-green, alkaline solution containing:

• Bile salts: cholesterol derivates that function in fat emulsification and absorption

• Bilirubin: pugment formed from heme

  • Bacteria break down in intestin to stercobilin that gives brown color of feces

Pathologies of the Liver

Hepatitis and Cirrhosis

Hepatitis

Usually viral infection, drug toxicity, wild mushroom poisoning

• Hepatitis B and C are more worrisome

Cirrhosis

Progressive, chronic inflammation fro chronic hepatitis or alcoholism

Liver→ fatty, fibrous→ portal hypertension

Are liver transplants sucessful?

Yes, but livers are scarce

Liver can regenerate to its full sixe in 6-12 months after 80% removal

The gallbladder

A thin-walled muscular sac on the ventral surface of the liver

functions to store and concentrate bile

muscular contractions release bile via systic duct, which flows into common bile duct

Gallstones

caused by too much cholesterol or too few bile salts

• can obstruct flow of bile from gallbladder

• painful when gallbladder contracts against sharp crystals

• Obstructuve jaundice: blockage can cause bile salts and pugments to build up in blood, resulting in jaundiced (yellow) skin

  • Jaundice can also be caused by liver failure

Gallstone treatment

crystal-dissolving drugs, ultrasound vibrations (lithotripsy), or surgery (cholecystectomy)

Pancreas location

mostly retroperitoneal, deep to greater curvature of stomach

• head is encircled by duodenum; tail butts up against spleen

Pancreas exocrine function

produce pancreatic enxymes and secretin

• ducts: secrete to duodenum via main pancreatic duct

Pancreas endocrine function

secretion of insulin and glucagon by pancreatic islet cells

Composition of pancreatic juice

1200-1500 ml/day is produced

contains alkaline solution containing sodium bicarbonate to neutralize acidic chyme coming from stomach

digestive enzymes

• proteases (for proteins)

• amylase (for carbohydrates)

• lipase (for lipids)

• nucleases (for nucleic acids)

Proteases

secreted in an inactive form; they are activated after they reach duodenum

• Enterpeptidase: converts trypsinogen to trypsin

• once trypsin is activated it can then activate

  • more trypsinogen

  • procarboxypeptidase to activate carboxypeptidase

  • chymotrypsinogen to activate chymotrypsin

Hepatonpancreatic sphincter (sphincter of oddi)

controls entry of bile and pancreatic juice into duodenum

Are bile and pancreatic juice secretions stimulated by neural or hormonal controls?

Both!

hormonal controls include

• Cholecystokinin (CCK)

• Secretin

Small intestine

major organ of digestion and absorption

15-20 ft long from pyloric sphincter to ileocecal valve

• duodenun (~10.0 in long)

• jejunum (~8 ft long)

• ileum (~12 ft)

Blood supply

superior mesenteric artery brings blood supply

veins (carrying nutrient-rich blood drain into superior mesenteric veins, then into hepatic portal vein, and finally into liver

nerve supply

parasympathetic innervation via vagus verve, and sympathetic innervation from thoracic splanchnic nerves

How does small intestine’s length and stuctural modifications help?

provide huge surface area for nutrient absorption

Modifications of small intestine

circular folds

villi

microvilli

Circular folds

permanent folds that force chyme to slowly sprial through lumen, allowing more time for nutrient absorption

Villi

fingerlike projections of mucosa

microvilli

extensions of mucosal cells that give a fuzzy appearance called the brush border

• Contains brush border enzymes, used for final carbohydrate and protein digestion

what is chemotherapy

targets rapidly dividing cells, such as cancer cells