Lecture 16 - Digestive System

GI tract has its own nervous system, referred to as

enteric nervous system - Also called "gut brain" -Contains more neurons than spinal cord

Enteric Nervous System made up of

enteric neurons that communicate extensively w/each other -Major nerve supply to GI tract wall that controls motility

What alters the tongues position?

extrinsic muscles

Lips (labia) composed of

fleshy orbicularis oris muscle

Mouth is where

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

splanchnic circulation

includes arteries that branch off aorta to serve digestive organs and the hepatic portal circulation

lamina propria of mucosa

Made up of loose areolar connective tissue Rich supply of capillaries located here -Needed for nourishment and absorption Also contains lymphoid follicles that help defend against microorganisms -Follicles are part of MALT (mucosa-associated lymphoid tissue)

mucosal epithelium

- Simple columnar epithelium and mucus-secreting cells in most of tract - Mouth, esophagus, and anus are made up of stratified squamous epithelium - Secretes mucus - Protects digestive organs from enzymes - Eases food passage - May secrete enzymes and hormones (e.g., in stomach and small intestine)

Functions of the tongue

-Gripping, repositioning, and mixing of food during chewing -Formation of bolus, mixture of food and saliva -Initiation of swallowing, speech, and taste

Digestive activity is provoked by a range of mechanical and chemical stimuli

-Receptors located in walls of GI tract organs -Respond to stretch, changes in osmolarity and pH, and presence of substrate and end products of digestion

Organs of digestive system fall into two groups:

1. Alimentary canal (gastrointestinal or GI tract or gut) 2. Accessory digestive organs

Three key concepts regulate GI activity

1. Digestive activity is provoked by a range of mechanical and chemical stimuli 2. Effectors of digestive activity are smooth muscle and glands 3. Neurons (intrinsic and extrinsic) and hormones control digestive activity

Processing of food involves six essential activities

1. Ingestion: eating 2. Propulsion: movement of food through alimentary canal, which includes: - Swallowing - Peristalsis: major means of propulsion of food that involves alternating waves of contraction and relaxation 3. Mechanical breakdown: includes chewing, mixing food with saliva, churning food in stomach, and segmentation 4. Digestion: series of catabolic steps that involves enzymes that break down complex food molecules into chemical building blocks 5. Absorption: passage of digested fragments from lumen of GI tract into blood or lymph 6. Defecation: elimination of indigestible substances via anus in form of feces

All digestive organs have the same four basic layers, or tunics

1. Mucosa 2. Submucosa 3. Muscularis externa 4. Serosa

Neurons (intrinsic and extrinsic) and hormones control digestive activity

1. Nervous system control 2. Hormonal controls

Major salivary glands include:

1. Parotid 2. Submandibular 3. Sublingual

oral cavity is

Bounded by lips anteriorly, cheeks laterally, palate superiorly, and tongue inferiorly

functions of saliva

Cleanses mouth Dissolves food chemicals for taste Moistens food; compacts into bolus Begins breakdown of starch with enzyme amylase

Submucosa

Consists of areolar connective tissue Contains blood and lymphatic vessels, lymphoid follicles, and submucosal nerve plexus that supply surrounding GI tract tissues Has abundant amount of elastic tissues that help organs to regain shape after storing large meal

Alimentary canal (gastrointestinal or GI tract or gut)

Continuous muscular tube that runs from the mouth to anus -Digests food: breaks down into smaller fragments -Absorbs fragments through lining into blood -Organs: mouth, pharynx, esophagus, stomach, small intestine, large intestine, anus

hepatic portal circulation

Drains nutrient-rich blood from digestive organs Delivers it to the liver for processing

mucosa made up of three sublayers

Epithelium Lamina propria Muscularis mucosae

peritoneal cavity

Fluid-filled space between two peritoneums Fluid lubricates mobile organs

Arteries that branch off aorta to serve digestive organs include

Hepatic, splenic, and left gastric arteries Inferior and superior mesenteric arteries

Hormonal controls

Hormones from cells in stomach and small intestine stimulate target cells in same or different organs to secrete or contract

Nervous system control - intrinsic + extrinsic controls

Intrinsic controls: involve short reflexes (ENS) Extrinsic controls: involve long reflexes (ANS)

whats changes the shape of the tongue?

Intrinsic muscles

submandibular gland

Medial to body of mandible Duct opens at base of lingual frenulum

Walls of mouth lined with stratified squamous epithelium

Tough cells that resist abrasion Cells of gums, hard palate, and part of tongue are keratinized for extra protection

muscularis externa

Responsible for segmentation and peristalsis Contains inner CIRCULAR MUSCLE LAYER and outer LONGITUDINAL LAYERS Circular layer thickens in some areas to form sphincters

minor salivary glands

Scattered throughout oral cavity; augment slightly

salivary glands composed of 2 types of secretory cells

Serous cells + Mucous cells

Main functions of digestive system

Take in food Break it down into nutrient molecules Absorb molecules into the bloodstream Rid body of any indigestible remains

Effectors of digestive activity are smooth muscle and glands

When stimulated, receptors initiate reflexes that stimulate smooth muscle to mix and move lumen contents Reflexes can also activate or inhibit digestive glands that secrete digestive juices or hormones

oral orifice

anterior opening of the mouth

parotid gland

anterior to ear and external to masseter muscle Duct opens into oral vestibule next to second upper molar

sublingual gland

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

oral cavity proper

area that lies within the teeth and gums

lingual frenulum

attachment of tongue to floor of mouth

cheeks composed of

buccinator muscles

mechanical breakdown of food

chewing, mixing food with saliva, churning food in stomach, and segmentation

Ankyloglossia

congenital condition in wh. children are born with extremely short lingual frenulum -Often referred to as "tongue-tied" or "fused tongue" -Restricted tongue movement distorts speech Treatment: surgical snipping of frenulum

myenteric nerve plexus

controls GI tract motility

mucosa function

different layers perform one or all three -SECRETES mucus, digestive enzymes, and hormones -ABSORBS end products of digestion -PROTECTS against infectious disease

sympathetic system inhibits

digestion

Parasympathetic system enhances

digestive process

mesentary peritoneum

double layer of peritoneum; layers are fused back to back Extends from body wall to digestive organs Provides routes for blood vessels, lymphatics, and nerves Holds organs in place + stores fat

ingestion

eating

Mumps

inflammation of parotid glands caused by the mumps virus (myxovirus) -Common children's disease -Can spread from person to person via saliva -Symptoms: pain upon trying to open mouth or chew, moderate fever and pain when swallowing acidic foods, such as pickles, grapefruit, or juice -Mumps in adult males carries a 25% risk of infecting testes too, which could lead to sterility

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 Dangerous and lethal if it becomes widespread Treatment: debris removal and megadoses of antibiotics

Enteric neurons make up bulk of two main interconnecting

intrinsic nerve plexuses: -Submucosal nerve plexus -Myenteric nerve plexus

parietal peritoneum

lines the body wall

Segmentation

local constriction of intestine that mixes food with digestive juices

retroperitoneal organs

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

Most saliva produced by ______________ located outside the oral cavity

major (extrinsic) salivary glands

peristalsis

major means of propulsion of food that involves alternating waves of contraction and relaxation

labial frenulum

median attachment of each lip to gum

Short reflexes:

mediated by enteric nerve plexuses (gut brain); respond to stimuli in GI tract

organs of the alimentary canal

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

Associated organs include:

mouth, tongue, salivary glands, teeth

propulsion

movement of food through alimentary canal

MALT

mucosa-associated lymphoid tissue

but sublingual gland consists mostly of

mucous cells

tongue

occupies floor of mouth Composed of interlacing bundles of skeletal muscle

The mouth is also called the

oral or buccal cavity

Intraperitoneal (peritoneal) organs

organs that are located within the peritoneum

serosa

outermost layer, made up of the visceral peritoneum - Formed from areolar connective tissue covered with mesothelium (single layer of squamous epithelium) in most organs - Replaced by fibrous adventitia in esophagus (Dense connective tissue that holds esophagus to surrounding structures)

Mucous cells

produce mucus

Digestive glands

produce secretions that help break down foodstuffs

Serous cells

produce watery secretion, enzymes, ions, bit of mucin

oral vestibule

recess internal to lips and cheeks, external to teeth and gums

submucosal nerve plexus

regulates glands and smooth muscle in the mucosa

Long reflexes:

respond to stimuli arising inside or outside of gut, such as from autonomic nervous system -Parasympathetic system enhances digestive process -Sympathetic system inhibits digestion

Parotid and submandibular glands contain mostly

serous cells

peritoneum

serous membranes of abdominal cavity that consists of: -Visceral peritoneum: membrane on external surface of most digestive organs -Parietal peritoneum: membrane that lines body wall

Enteric nervous system participates in both

short and long reflex arcs

muscularis mucosae of mucosa

smooth muscle that produces local movements of mucosa

accessory digestive organs

teeth, tongue, gallbladder, digestive glands (salivary glands, liver, pancreas)

visceral peritoneum

the inner layer of the peritoneum that surrounds the organs of the abdominal cavity

mucosa

tunic layer that lines lumen Functions: different layers perform one or all three Secretes mucus, digestive enzymes, and hormones Absorbs end products of digestion Protects against infectious disease