Anatomy and Histology

1. Villi = 0.2–1mm high finger‐like projections, increase small intestinal surface area to 100‐200m2, important for water (and nutrient) reabsorption

2. Microvilli on the epithelial cells

3. Crypts = tubular depressions in the lamina propria, extending down to the muscularis mucosae, cell regeneration; rich in multipotent stem cells

4. Lamina propria well vascularised 

mittlere Abschnitt des Dickdarms

1. Ascending colon: ascends (retroperitoneal) from right groin with associated appendix through the right flank to just below the liver. Connected to small intestine by the cecum. Around 20cm 

2. Transverse colon: crosses the abdomen (intraperitoneal) ventrally to just below the spleen. From the hepatic flexure to the splenic flexure. Encased in peritoneum. 

3. Descending colon: descends (retroperitoneal) through the left flank into the left groin. From the splenic flexure to the beginning of the sigmoid colon. Store faeces that will be emptied into the rectum. 

4. Sigmoid colon: continues (intraperitoneal) dorsally in pubic region to the rectum ventral to the sacrum. S‐shaped. Muscular walls.

1. From the distal end of the ileum to the anus

2. Approx. 1.5m, larger diameter than small intestine

3. Absorbs fluids and salts, forming faeces

4. Caecum, appendix, colon, rectum anal canal

5. Caecum is first part of the large intestine, continuous with the ascending colon

6. Appendix is a narrow hollow, blind‐ended tube connected to the caecum

7. An immune organ containing large aggregations of lymphoid tissue, GALT

8. Only ca. 10% of digestion and nutrient absorption occurs in the colon. Other animals have much larger colons, more micro‐flora, better able to digest plant matter.

9. pH5.5‐7 

1. Intestine is rich in bacterial flora

2. Laminar propria is rich in immune cells

3. Single immune cells: T and B lymphocytes

4. Peyer’s plaques (lymph follicles) in small intestine

5. Lymphoid aggregates in the large intestine

6. Appendix vermiformes = immune organ rich in lymph follicles 

Wikipedia:

Das darmassoziierte lymphatische Gewebe (darmassoziierte Immunsystem) oder GALT (von engl. gut associated lymphoid tissue) ist der Teil des lymphatischen Systems im Bereich des Darms. Aufgrund der großen Oberfläche hat die Darmschleimhaut besondere Bedeutung für das Immunsystem. 70–80 % aller Zellen, die Antikörper produzieren, befinden sich in der Schleimhaut des Darmes.

Diffuse Ansammlungen von Lymphozyten oder lockere Verbände dieser (Lymphfollikel) findet man im gesamten Magen-Darm-Trakt, der durch die aufgenommene Nahrung besonders häufig mit Keimen und Fremdkörpern in Kontakt kommt. Im Krummdarm (Ileum) sowie im Wurmfortsatz (Appendix vermiformis) existiert organisiertes lymphatisches Gewebe in Form der Peyer-Plaques.

1. Rectum: short, dilated, terminal portion of the large intestine.

2. Very rich in goblet cells

3. Anal canal: stratified squamous epithelium. 2‐3cm. Surrounded by voluntary muscle (anal sphincter). Stratified squamous epithelium transitions to skin containing sebaceous glands and large apocrine sweat glands 

Wikipedia:

Rectum:
Der Mastdarm, eingedeutscht Rektum, Adjektiv rektal) ist ein Teil des Enddarms und damit des Dickdarms und dient der Zwischenspeicherung des Kots, d. h. der unverdaulichen und unverträglichen Nahrungsreste.

1. Retroperitoneal

2. Anal canal is inferior to the rectum

3. Transition from mucosal epithelium to stratified squamous non‐keratinized epithelium

4. Blood vessels in the lamina propria and submucosa may become distended = haemorrhoids 

1. Development: glandular outgrowth of the primitive foregut

2. Location: Upper right quadrant (right hypochondrium, and epigastric)

3. Form: largest visceral organ (~1.4kg), two surfaces

4. Diaphragmatic surface = anterior, posterior, superior

5. Visceral surface = inferior, covered by visceral peritoneum 

• Essential for survival
• Supports all other organs
• Only organ that can regenerate (Prometheus)
• Multifunctional, giant gland 
• Fat Metabolism -> oxidising triglycerides, synthesis of plasma lipoproteins, synthesis of cholesterol and phospholipid
• Carbohydrate Metabolism -> Conversion of carbohydrates into fatty acids and triglycerides, regulation of blood glucose by glycogenesis, glycogenolysis, glyconeogenesis
• Protein Metabolism -> synthesis of plasma proteins (albumin, coagulants), synthesis of non-essential amino acids, detoxification or metabolic waste (ammonia)
• Storage -> glycogen, vitamins A, D, K, B12, iron, copper
• Intermediary metabolism -> detoxification of drugs and toxins (e.g. alcohol, pharmaceuticals, industrial chemicals)
• Secretion -> bile for lipid emulsification and digestion, hormones (IGF, thrombopoietin, angiotensin) 

•  Acinus: berry-shaped unity of the liver parenchyma centred on a portal tract. Lies between two or more terminal hepatic venules and blood flows from the portal tract through the sinusoids to the venules.

•  Three zones:

  •  Zone 1: periportal, i.e. closest to portal triad, well oxygenated, oxidative enzymes, gluconeogenesis, fatty acid oxidation, cholesterol synthesis

  •  Zone 2: transition

  •  Zone 3: centrilobular i.e. closest to centrilobular venule, poorly oxygenated, reductive enzymes, e.g. glycolysis, lipolysis, cytochrome P450. least oxygenated. 

Bilirubin from hemoglobin metabolism ‐> excess = jaundice (yellow discoloration of the tissues due to increased levels of bilirubin and associated deposition of bile pigments) 

1. Function: receives, concentrates and stores bile produced by the liver

2. Bile, or gall aids lipid digestion

3. 92% water, 6% bile salts, 0.3% bilirubin, 0.9- 2.4% fats

4. Excreted from hepatocytes into bile canaliculi, a network of canals between hepatocytes in the liver

5. Drain into interlobular bile ducts (bile ductules) -> hepatic duct -> common bile duct 

1. Small organ where the bile produced by the liver is stored and concentrated before its release into the small intestine.

2. Location: visceral surface of the right lobe of the liver, in a fossa between the right and quadrate lobes

3. Form: muscular pear‐shaped sack with three parts, fundus (rounded end), body, neck

4. 70‐100 mL volume

5. Feed by a branch of the right hepatic artery

6. Cystic duct branches off the common duct to the gallbladder for storage

7. Ducts lined with cuboid/columnar epithelium

8. Hollow organ 

1. Histologically similar to the rest of the GIT, except NO submucosal muscle

2. Muscular sac lined by simple columnar epithelium with mucous glands in the neck submucosa

3. Microvilli increase surface area for water reabsorption, and thus concentration of bile

4. Lamina propria + epithelium = mucosa

5. Submucosa is a thin layer of loose elastic connective tissue with smaller blood vessels, lymphatics. In the neck of the gallbladder mucus secreting glands

6. Muscular layer: Muscle fibers lie in longitudinal, oblique and transverse directions, NOT arranged in separate layers

7. Serosa is dense irregular connective tissue, continuous with the peritoneum 

Gallengangöffnung

1. Combines with the major pancreatic duct, feeding into the duodenum

2. Thus, bile and lipases are combined before injection into the small intestine

3. Sphincter oddi 

die Bauchspeicheldrüse

1. Pancreas: lobulated gland covered by a thin collagenous capsule which extends as a delicate septa between the lobules.

2. Location: posterior to the stomach, sits in the duodenal curvature, (secondary) retroperitoneal

3. Form: elongated, slender, pink, lumpy, with a head (sits in the duodenal curvature), neck, body and tail, ca. 80g, 20‐25 cm in length

4. Tail, body, neck, and head

5. Function: exocrine and endocrine gland 

Eine exokrine Drüse (exokrin „nach außen abgebend“) ist eine Drüse, die ihr Sekret an eine innere oder äußere Körperoberfläche abgibt.

1. Tubuloacinar Exocrine gland makes up the bulk (ca. 99%) of the organ

2. Acinus made up of an irregular cluster of pyramid‐shaped secretory cells.

3. Adjacent acini separated by supporting tissue with numerous capillaries.

4. Secretes 1.5‐2 L d‐1 of an enzyme‐rich alkaline “digestive juice” into the duodenum

5. High HCO3‐ neutralises acid

6. Luminal digestion = pancreatic enzymes breakdown proteins, carbohydrates, lipids and nucleic acids

7. Duodenal neuroendocrine cells release secretin which stimulates pancreatic secretions

8. Pancreas also richly innervated by ANS 

1. Endocrine gland constitutes ca. 1‐2%

2. Endocrine cells are found in scattered groups, islets of Langerhans

3. Ca. 1‐2 million islets

4. Islets are well vascularised (fenestrated capillaries) for delivery of hormones into blood

5. Primarily four cell types α‐, β‐, δ‐, and F or PP‐cells

6. α‐cells secrete glucagon, increasing glycogen breakdown and liver glucose release, raising blood sugar

7. β‐cells secrete insulin, increasing glucose uptake and utilization, lowering blood glucose

8. δ‐cells secrete somatostatin, inhibits glucagon and insulin, slowing food absorption

9. F or PP‐cells secrete pancreatic polypeptide, inhibiting gallbladder and some

   pancreatic enzyme production, controlling nutrient absorption 

Abdominal muscles:

•  Rectus abdominis – paired muscle running vertically on both sides of the anterior

  abdominal wall

•  External oblique – largest and most superficial. Flat muscle. Lateral anterior

  abdominal wall

•  Internal oblique – lies immediately bellow the external oblique and just above the

  transverse abdominal muscles. Lateral anterior abdominal wall

•  Transverse ‐ muscle layer of the anterior and lateral (front and side) abdominal wall

  which is deep to (layered below) the internal oblique muscle. 

Funktion

Dabei bilden die seitlichen Bauchmuskeln mit ihren Aponeurosen – das heißt flächenhaften Sehnen – die sogenannte Rektusscheide, in die der gerade Bauchmuskel zu liegen kommt.

Vorne befindet sich der gerade Bauchmuskel, er kann den Oberkörper nach vorne beugen oder den vorderen Beckenrand anheben. Er ist damit der direkte Gegenspieler der Wirbelsäulenmuskulatur und wirkt dem Hohlkreuz entgegen. Er gehört ähnlich wie die vordere Oberschenkelmuskulatur, die Gesäßmuskulaturund die Rückenmuskulatur zu den Muskeln, die für den aufrecht gehenden Menschen besonders wichtig sind. Eine gut trainierte Bauchmuskulatur erleichtert eine gute Körperhaltung.

Die beiden schrägen Bauchmuskeln können den Oberkörper zur Seite neigen und drehen. Der quere Bauchmuskel kann eine Bauchpresse erzeugen, z. B. beim Stuhlgang. Außerdem sind die Bauchmuskeln Hilfsmuskeln bei der Ausatmung.

Rectus abdominis – paired muscle running vertically on both sides of the anterior 

abdominal wall 

External oblique – largest and most superficial. Flat muscle. Lateral anterior

abdominal wall 

Internal oblique – lies immediately bellow the external oblique and just above the

transverse abdominal muscles. Lateral anterior abdominal wall 

Transverse ‐ muscle layer of the anterior and lateral (front and side) abdominal wall

which is deep to (layered below) the internal oblique muscle. 

1. Assists during breathing, relaxing during inspiration, contracts during expiration

2. Contraction causes a significant increase in intra‐abdominal pressure, BUT the

   diaphragm must be held in position, i.e. filled with air, stop breathing

3. Assist in voiding the bladder (urination), rectum (defecation), during child birth

   (micturition)

4. Liver, gallbladder and stomach are below the dome of the diaphragm, this protected by the thoracic wall

5. Kidneys lie (partially) behind the lower ribs

6. The reminder is protected and supported by the muscular wall 

1. Cylindrical chamber

2. From the inferior margin of the thorax (diaphragm) to the superior margin of the

   pelvis

3. Enclosed by the abdominal wall: abdominal muscles and the spine posteriorly

4. Encloses the large peritoneal cavity

5. Organs are suspended by mesenteries, double layer of peritoneum

6. Location of tube‐like organs of the digestive tract and solid organs: stomach, small

   intestine, colon, appendix, liver, gallbladder, pancreas, spleen, kidneys, adrenal glands 

Becken

or spinal column

Wirbelsäule

Dünndarm

• Small intestine: part of the gastrointestinal tract between the stomach and the large intestine, and is where most of the end absorption of food takes place.

• Three distinct regions:

  • Duodenum ‐ receives bile and pancreatic juice through the pancreatic duct,

    controlled by the sphincter of Oddi

  • Jejunum – absorption of small nutrient particles, previously digested by

    enzymes in the duodenum.

  • Ileum ‐ mainly to absorb vitamin B12 and bile salts and whatever products of

    digestion were not absorbed by the jejunum

• Primary function: absorption of nutrients and minerals from food 

1. Peritoneum: serous membrane that line the abdominal cavity. Layer of mesothelium (single layer of epithelial cells), supported by a thin layer of connective tissue. Lines the abdominal cavity

2. Abdominal organs are suspended by mesenteries, double layer of peritoneum enclosing the organs of the abdominal cavity

3. Parietal peritoneum lines the abdominal wall

4. Visceral peritoneum covers suspended organs

5. Organs fill the abdominal cavity, thus parietal and visceral lie against each other

6. Intraperitoneal: suspended in mesentery

7. Retroperitoneal = between parietal and abdominal wall, e.g. kidney, ureters 

Wikipedia:

Das Peritoneum oder Bauchfell kleidet als seröse Haut den Bauchraum aus. Es umgibt die meisten inneren Organe unterhalb des Zwerchfells bis zum Eingang des kleinen Beckens. Es ist durch ein einschichtiges, flaches Epithel gekennzeichnet.

Das Bauchfell beherbergt die Blutgefäße, die Lymphgefäße und die Nerven der Bauchorgane.

• Greater omentum: fold of visceral peritoneum that hangs down from the stomach.

• Function: fat deposition, immune systems (macrophage collection), infection and

  wound isolation

Wikipedia:

Das Omentum majus (großes Netz,englisch Greater Omentum) ist beim Menschen und anderen Säugetieren eine vom Bauchfell (Peritoneum) überzogene fett- und bindegewebsreiche Struktur, die von der großen Krümmung des Magens und dem quer verlaufenden Teil des Dickdarms (Colon transversum) schürzenartig herabhängt und die Dünndarmschlingen normalerweise vollständig bedeckt. Bei geschlachtetem Vieh spricht man vom Fettnetz.

Das Omentum majus ist verantwortlich für die Immunabwehr im Bauchraum. Es enthält eine große Anzahl Makrophagen und Lymphozyten, die sich im Falle einer Entzündung vermehrt auf die betroffenen Bereiche legen und so vor einer Bauchfellentzündung schützen. Außerdem spielt es eine Rolle sowohl im Rahmen der Fettspeicherung als auch bei der Regulation des Flüssigkeitsgleichgewichts im Peritonealraum.

Mesentery: double layer of visceral peritoneum that attaches to the gastrointestinal tract. There are often blood vessels, nerves, and other structures between these layers. The space between these two layers is technically outside of the peritoneal sac, and thus not in the peritoneal cavity. 

Wikipedia:

Gekröse

Als Gekröse (lat. Serosa intermedia) wird eine Bauchfellfalte an einem inneren Organ bezeichnet, die in der Regel als Aufhängeband fungiert und das Organ mit der Leibeswand verbindet. Es handelt sich um eine Serosa-Doppellamelle, die zwischen Organüberzug (Peritoneum viscerale) und der Wandauskleidung (Peritoneum parietale) verkehrt.

Entsprechend der Organbeteiligung wird das Gekröse unterteilt in das

• Mesenterium ist der Oberbegriff für das Aufhängeband des Darms. In der Human- und Veterinäranatomie wird der Begriff auch einschränkend speziell für das Gekröse des Dünndarms, genauer des Jejunum (Mesojejunum) und Ileum (Mesoileum) verwendet.
• Mesocolon: das Aufhängeband des Dickdarms
• Mesogastrium: der embryonalen Aufhängeapparat des Magens, unterteilt in vorderes und hinteres Mesogastrium (in der Tieranatomie Mesogastrium dorsaleund ventrale), nach der Geburt als Omentum majus und Omentum minus.
• Mesovarium: den Aufhängeapparat des Eierstocks
• Mesosalpinx: jenen des Eileiters
• Mesometrium: die Bauchfellduplikatur beidseits der Gebärmutter

Parietal peritoneum – outer layer of the peritoneum. Attached to the abdominal wall and the pelvic wall. 

Wikipedia:

Die Auskleidung der Innenseite der Bauchwand nennt man Peritoneum parietale (parietales Peritoneum), den Überzug der Organe Peritoneum viscerale (viszerales Peritoneum), wobei nur das Peritoneum parietale sensibel innerviert wird, d. h. empfindlich für Schmerzen ist. Das viszerale Peritoneum ist dünner als das parietale Peritoneum.