Digestive system - anatomy

Digestive systemDigestive systemMoath Nairat, MDMoath Nairat, MD

Function of the digestive systemFunction of the digestive system

• ingestion: taking food and liquid into mouth

• Secretion: total about 7 liter into lumen

• Mixing and propulsion: through GI muscle and peristalsis and motility

• Digestion: Breakdown of ingested food (mechanical and chemical)

• Absorption: Passage of nutrients into the blood

• Metabolism: Production of cellular energy (ATP)

• Defecation: waste substance leave the GI tract through anus

Organs of the Digestive SystemOrgans of the Digestive System

• Two main groups

• Alimentary canal or gastrointestinal tract – continuous coiled hollow tube from mouth to anus(5-7 meter)

• Accessory digestive organs: teeth ,tongue ,salivary gland ,liver ,gallbladder ,and pancreas

Organs of the Digestive SystemOrgans of the Digestive System

Organs of the Alimentary CanalOrgans of the Alimentary Canal

• Mouth

• Pharynx

• Esophagus

• Stomach

• Small intestine

• Large intestine

• Anus

Mouth (Oral Cavity) AnatomyMouth (Oral Cavity) Anatomy

• Lips (labia) – protect the anterior opening

• Cheeks – form the lateral walls

• Hard palate – forms the anterior roof

• Soft palate – forms the posterior roof

• Uvula – fleshy projection of the soft palate

Mouth (Oral Cavity) AnatomyMouth (Oral Cavity) Anatomy

• Vestibule – space between lips externally and teeth and gums internally

• Oral cavity – area contained by the teeth

• Tongue – attached at hyoid bone and styloid processes of the skull, and by the lingual frenulum

TongueTongue

• Dorsum (upper part of tongue covered with papillae taste receptor and buds)

• filiform papillae

• fungiform papillae

• circumvallate papillae

• Paltine tonsil and lingual tonsil

Salivary glands-Parotid gland: In the parotid fossa, three main structures transverse this gland – facial nerve, external carotid artery, and retromandibular vein. The parotid duct opens near the upper 2nd molar tooth. The gland is completely serous.

- Submandibular gland: Sitting most posteriorly in the submandibular triangle, it is supplied by the facial artery and vein. Submandibular ducts, which cross the lingual nerves, open on both sides of the tongue frenulum. It is mostly serous but partially mucus,.

- Sublingual gland: The smallest salivary gland sits beneath the oral mucosa in the floor of the mouth. It has multiple small openings. This gland is almost completely mucus-secreting.

Teeth• Teeth (mechanical breakdown)

– Incisors used for cutting– Canines used for stabbing

and holding– Molars large surface area

used for grinding

• Primary or deciduous teeth 20

• Secondary or permanent teeth 32

Structure of Teeth

Crown - exposed surface of tooth

Neck - boundary between root and crown

Enamel - outer surface (the hardest substance in the body 95% calcium salts)

Dentin – bone-like, but noncellular(70% calcium salts)

Pulp cavity - hollow with blood vessels and nerves

Root canal - canal length of root

gingival sulcus - where gum and tooth meet

Processes of the MouthProcesses of the Mouth

• Mastication (chewing) of food

• Mixing masticated food with saliva to produse easy digestied food called bolus

• Saliva contain 2 enzyme,salivary amylase and lingual lipase

• Initiation of swallowing by the tongue

• Allowing for the sense of taste

Layers of Alimentary Canal OrgansLayers of Alimentary Canal Organs

• Submucosa

• Just beneath the mucosa

• Soft connective tissue with blood vessels, nerve endings, and lymphatics also contain submucosal plexus

• Mucosa

• Innermost layer

• Moist membrane

1. Surface epithelium : secretion and absorbtion,renew every 5-7 days also contain enteroendocrine cells

2. Small amount of connective tissue (lamina propria): contain blood and lymphatic vessele also contain MALT

3. Small smooth muscle layer

• Muscularis externa – smooth muscle

1. Inner circular layer

2. Outer longitudinal layer

Between them is myenteric plexus

• Serosa

• Outermost layer – visceral peritoneum

• Layer of serous fluid-producing cells (mesothelium)

Digestive Anatomy: Histological

Pharynx AnatomyPharynx Anatomy

• Nasopharynx – not part of the digestive system

• Oropharynx – posterior to oral cavity

• Laryngopharynx – below the oropharynx and connected to the esophagus

Pharynx FunctionPharynx Function

• Serves as a passageway for air and food

• Food is propelled to the esophagus by two muscle layers

• Longitudinal inner layer

• Circular outer layer

• Food movement is by alternating contractions of the muscle layers (peristalsis)

EsophagusEsophagus

• Runs from pharynx to stomach through the diaphragm( 25 cm)

• Conducts food by peristalsis (slow rhythmic squeezing): contraction of circular layer above the food and contraction of longitudinal below the food

• Passageway for food only (respiratory system branches off after the pharynx)

Esophagus- The esophagus is posterior to the larynx and trachea in the neck region and upper thorax. It travels on the right side of the descending aorta, passes through the diaphragm, and connects with the stomach.

-There are also inner circular and outer longitudinal muscle layers.

- The upper third is skeletal muscle (voluntary), middle third is mixed, and lower third is smooth muscle (involuntary).

-esophagogastric junction is located approximately at the level of the diaphragm. Contractions of the diaphragm create sphincter-like effects, preventing reflux of stomach acids and content. The esophagogastric junction is a

functional, not anatomical, sphincter.

Peristalsis in Esophagus

Bolus offood

Muscles relax,allowingpassagewayto open

Stomach

Musclescontract,constrictingpassagewayand pushingbolus down

Musclesrelax

Muscles contract

Muscles relax

Muscles contract

Stomach AnatomyStomach Anatomy

• Located on the left side of the abdominal cavity

• Food enters at the cardioesophageal sphincter

Site where food is churned into chyme Protein digestion begins

• Regions of the stomach

• Cardiac region – near the heart

• Fundus

• Body

• Phylorus – funnel-shaped terminal end

• Food empties into the small intestine at the pyloric sphincter

Stomach

• Rugae – internal folds of the mucosa

• External regions

• Lesser curvature

• Greater curvature

Stomach

• Layers of peritoneum attached to the stomach

• Lesser omentum – attaches the liver to the lesser curvature

• Greater omentum – attaches the greater curvature to the transverse colon which Contains fat to insulate, cushion, and protect abdominal organs

Stomach FunctionsStomach Functions

• Acts as a storage tank for food

• Site of food breakdown and mixing

• Chemical breakdown of protein begins

• Delivers chyme (processed food) to the small intestine

Specialized Mucosa of the Specialized Mucosa of the StomachStomach

• Simple columnar epithelium

• Mucous neck cells – produce a sticky alkaline mucus

• Gastric glands – secrete gastric juice

• Chief cells – produce protein-digesting enzymes (pepsinogens)

• Parietal cells – produce hydrochloric acid and Intrinsic factor(B12 absorption)

• Endocrine cells (G cell) – produce gastrin which stimulates both parietal and chief cells)

Structure of the Stomach MucosaStructure of the Stomach Mucosa

• Gastric pits formed by folded mucosa

• Glands and specialized cells are in the gastric gland region

Structure of the Stomach MucosaStructure of the Stomach Mucosa

Peritoneum

• Is the largest serous membrane of the body consist of mesothelium

• Divide into1. Parietal peritoneum: lines the wall of abdominopelvic

cavity internally2. Visceral peritoneum: cover some oh the organs in the

cavity 3. The space between them contain fluid and called

peritoneal cavity this cavity may be accumulated by several liters of fluid state called ascites

MembranesMembranesMesenteries - double sheets of peritoneum, surrounding and

suspending portions of the digestive organs

Peritoneal folds 1. falciform ligament:- attach the liver to anterior abdominal

wall and diaphragm2. Greater omentum - "fatty apron", hangs anteriorly from

stomach, double layer encloses fat

3. Lesser omentum - between stomach and liver

4. Mesentery proper - suspends and wraps the small intestine

5. Mesocolon - suspends and wraps the colon, parts arei. transverse mesocolonii. sigmoid mesocolon

• Ascending and descending ,pancreas, first 2 parts of the duodenum and kidneys are Retroperitoneal structure

peritoneum

Mesenteries

• Greater omentum and transverse colon reflected

Mesenteries

• Superficial view of the abdominal organs

Small IntestineSmall Intestine

• The body’s major digestive organ

• Site of nutrient absorption into the blood

• Muscular tube extending form the pyloric sphincter to the ileocecal valve

• Suspended from the posterior abdominal wall by the mesentery

Subdivisions of the Small IntestineSubdivisions of the Small Intestine

• Duodenum(25cm)

• Attached to the stomach

• Curves around the head of the pancreas

• Fixed retroperitoneal structure

• Jejunum (2.5m)

• Attaches anteriorly to the duodenum

• Ileum (3.5m)

• Extends from jejunum to large intestine

RegionsRegions of Small Intestine of Small Intestine

Small intestine

Duodenum and Related Organs

LiverBile

Gall-bladder

Duodenum ofsmall intestine

Acid chyme

Pancreaticjuice

Intestinal enzymes

Stomach

Pancreas

Chemical Digestion in the Small Chemical Digestion in the Small IntestineIntestine

• Source of enzymes that are mixed with chyme

•Intestinal cells

•Pancreas

• Bile enters from the gall bladder

Villi of the Small IntestineVilli of the Small Intestine

• Fingerlike structures formed by the mucosa

• Give the small intestine more surface area

Figure 14.7a

Microvilli of the Small IntestineMicrovilli of the Small Intestine

• Small projections of the plasma membrane

• Found on absorptive cells

Figure 14.7c

Structures Involved in Absorption Structures Involved in Absorption of Nutrientsof Nutrients

• Absorptive cells

• Blood capillaries

• Lacteals (specialized lymphatic capillaries)

Figure 14.7b

Folds of the Small IntestineFolds of the Small Intestine

• Called circular folds or plicae circulares

• Deep folds of the mucosa and submucosa

• Do not disappear when filled with food

• The submucosa has Peyer’s patches (collections of lymphatic tissue)

Digestion in the Small IntestineDigestion in the Small Intestine

• Enzymes from the brush border

• Break double sugars into simple sugars

• Complete some protein digestion

• Pancreatic enzymes play the major digestive function

• Help complete digestion of starch (pancreatic amylase)

• Carry out about half of all protein digestion (trypsin, etc.)

Figure 14.6

Digestion in the Small IntestineDigestion in the Small Intestine

• Pancreatic enzymes play the major digestive function (continued)

• Responsible for fat digestion (lipase)

• Digest nucleic acids (nucleases)

• Alkaline content neutralizes acidic chyme

Absorption in the Small IntestineAbsorption in the Small Intestine

• Water is absorbed along the length of the small intestine

• End products of digestion

• Most substances are absorbed by active transport through cell membranes

• Lipids are absorbed by diffusion

• Substances are transported to the liver by the hepatic portal vein or lymph

Propulsion in the Small IntestinePropulsion in the Small Intestine

• Peristalsis is the major means of moving food

• Segmental movements

• Mix chyme with digestive juices

• Aid in propelling food

Digestive Secretions: (≈7 L / Day From Tissues into

Lumen)• Salivary glands

• Pancreas

• Water

• Enzymes

• Mucus

• Ions: H+, K+, Na+

• HCO3-, Cl-

• Mass Balance (H2O)

Large IntestineLarge Intestine

• Larger in diameter, but shorter than the small intestine

• Frames the internal abdomen

Large IntestineLarge Intestine

Figure 14.8

CecumCecum –– pocket at proximal end with Appendix

ColonColon

Ascending colon - on right, between cecum and right colic flexure

Transverse colon - horizontal portion

Descending colon - left side, between left colic flexure and

Sigmoid colon - S bend near terminal end

Regions of Large IntestineRegions of Large Intestine

RectumRectum –– terminal end is anal canal - ending at the anus - which has internal involuntary sphincter and external voluntary sphincter

1. Mucosa - abundant goblet cells, stratified squamous epithelium near anal canal

2. No villi

3. Longitudinal muscle layer incomplete, forms three bands or taenia coli

4. Circular muscle - forms pockets or haustra between bands

Histology of Large IntestineHistology of Large Intestine

Functions of the Large IntestineFunctions of the Large Intestine

• Absorption of water

• Eliminates indigestible food from the body as feces

• Does not participate in digestion of food

• Goblet cells produce mucus to act as a lubricant

Structures of the Large IntestineStructures of the Large Intestine

• Cecum – saclike first part of the large intestine

• Appendix

•Accumulation of lymphatic tissue that sometimes becomes inflamed (appendicitis)

•Hangs from the cecum

Structures of the Large IntestineStructures of the Large Intestine

• Colon

• Ascending

• Transverse

• Descending

• S-shaped sigmoidal

• Rectum

• Anus – external body opening

Food Breakdown and Absorption in Food Breakdown and Absorption in the Large Intestinethe Large Intestine

• No digestive enzymes are produced

• Resident bacteria digest remaining nutrients

• Produce some vitamin K and B

• Release gases

• Water and vitamins K and B are absorbed

• Remaining materials are eliminated via feces

Propulsion in the Large IntestinePropulsion in the Large Intestine

• Sluggish peristalsis

• Mass movements

• Slow, powerful movements

• Occur three to four times per day

• Presence of feces in the rectum causes a defecation reflex

• Internal anal sphincter is relaxed

• Defecation occurs with relaxation of the voluntary (external) anal sphincter

SalivaSaliva

• Mixture of mucus and serous fluids

• Helps to form a food bolus

• Contains salivary amylase to begin starch digestion

• Dissolves chemicals so they can be tasted

Chemistry of Digestion: Carbohydrates

Enzymes in Small Intestine

PancreasPancreas

• Produces a wide spectrum of digestive enzymes that break down all categories of food

• Enzymes are secreted into the duodenum

• Alkaline fluid introduced with enzymes neutralizes acidic chyme

• Endocrine products of pancreas (langerhans island)

• Insulin

• Glucagons

• Somatostatin

Exocrine Pancreas: Histology

Composition and Function of Pancreatic Juice

• Examples include

• Trypsinogen is activated to trypsin

• Procarboxypeptidase is activated to carboxypeptidase

• Active enzymes secreted

• Amylase, lipases, and nucleases

• These enzymes require ions or bile for optimal activity

• Retroperitoneal :compose of head, body and tail

• Endocrine and exocrine gland

• Common bile duct and major pancreatic duct lead to ampulla of vater then to second part of duodenum through sphincter of oddi

PancreasPancreas

LiverLiver

• Largest gland in the body

• Located on the right side of the body under the diaphragm

• Consists of four lobes suspended from the diaphragm and abdominal wall by the falciform ligament

• Connected to the gall bladder via the common hepatic duct

On right under diaphragm, largest organ made up of 4 lobes (left and right, caudate, and quadrate)

Hilus (porta hepatis) – underside "entry" point

Gall bladder

Microscopic anatomy: Liver lobules and triads

Microscopic Anatomy of Liver

Visceral Surface of the Liver

Role of the Liver in MetabolismRole of the Liver in Metabolism

• Several roles in digestion

• Detoxifies drugs and alcohol

• Degrades hormones

• Produce cholesterol, blood proteins (albumin and clotting proteins)

• Plays a central role in metabolism

BileBile

• Produced by cells in the liver

• Composition

• Bile salts

• Bile pigment (mostly bilirubin from the breakdown of hemoglobin)

• Cholesterol

• Phospholipids

• Electrolytes

Gall BladderGall Bladder

• Sac found in hollow fossa of liver

• Stores bile from the liver by way of the cystic duct

• Bile is introduced into the duodenum in the presence of fatty food

• Gallstones can cause blockages

Figure 14.6

Gallbladder• Stores and concentrates bile to ten folds

• Expels bile into duodenum– Bile emulsifies fats

Processes of the Digestive SystemProcesses of the Digestive System

• Ingestion – getting food into the mouth

• Propulsion – moving foods from one region of the digestive system to another

• Peristalsis – alternating waves of contraction

• Segmentation – moving materials back and forth to aid in mixing

Figure 14.12

• Mechanical digestion

• Mixing of food in the mouth by the tongue

• Churning of food in the stomach

• Segmentation in the small intestine

• Chemical Digestion

• Enzymes break down food molecules into their building blocks

• Each major food group uses different enzymes

• Carbohydrates are broken to simple sugars

• Proteins are broken to amino acids

• Fats are broken to fatty acids and alcohols

• Absorption

• End products of digestion are absorbed in the blood or lymph

• Food must enter mucosal cells and then into blood or lymph capillaries

• Defecation

• Elimination of indigestible substances as feces

Control of Digestive ActivityControl of Digestive Activity

• Mostly controlled by reflexes via the parasympathetic division

• Chemical and mechanical receptors are located in organ walls that trigger reflexes

NutritionNutrition

• Nutrient – substance used by the body for growth, maintenance, and repair

• Categories of nutrients

• Carbohydrates: simple sugars, starches, fiber

• Lipids: triglycerides, phospholipids, fatty acids

• Proteins: amino acids

• Vitamins

• Mineral

• Water

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