Anatomy and Histology

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.

1. Function is to break down food for absorption into the body

2. Occurs in 5 steps: ingestion, fragmentation, digestion, absorption, elimination

3. Digestion is the enzymatic breakdown of food particles

4. Outside in, i.e. external environment contained within us, i.e. epithelial lining

5. Mucous membrane is: protective, secretory, absorptive

6. Muscular tube

7. Because of it’s contact with the outside, it is lined with protective immune tissue (gut-associated lymphoid tissue, GALT) 

die Nahrungsaufnahme

die Zertrümmerung (Fragmentierung)

Ausfaulung

die Aufnahme

Beseitigung

1) Protein

Denaturation by gastric juices

Enzymatic hydrolysis into polypeptides (trypsin, chymotrypsin, elastase, carboxypeptidases)

Membrane bound peptide hydrolases produce amino acids

Carrier enzymes actively transport individual amino acids 

Carbohydrates

Enzymatic hydrolysis (salivary and pancreatic amylase)
Membrane bound di- and oligosaccharidases, glucose, fructose, galactose
Absorbed by facilitated diffusion 

Lipids

Triglycerides converted to a coarse emulsion in the stomach

Converted into a fine emulsion by combination with bile acids in the duodenum

Pancreatic lipases break triglycerides down into monoglyceride and two free fatty acids

Absorbed and then re-synthesised 

Schleimmhaut

The mucosa is made up of three components: the epithelium, a supporting lamina propria and a thin smooth muscle layer, the muscularis mucosae, which produces local movement and folding of the mucosa. At four points along the tract, the mucosa undergoes abrupt transition from one form to another: the gastro- oesophageal junction, the gastroduodenal junction, the ileocaecal junction and the rectoanal junction. 

This layer of loose collagenous connective tissue supports the mucosa and contains the larger blood vessels, lymphatics and nerves. 

The muscular wall proper consists of smooth muscle that is usually arranged as an inner circular layer and an outer longitudinal layer. In the stomach only, there is an inner oblique layer of muscle. The action of the two layers, at right angles to one another, is the basis of peristaltic contraction (see textbox). 

This outer layer of loose supporting tissue conducts the major vessels, nerves and contains variable adipose tissue. Where the gut lies within the abdominal cavity (peritoneal cavity), the adventitia is referred to as the serosa (visceral peritoneum) and is lined by a simple squamous epithelium (mesothelium). Elsewhere, the adventitial layer merges with retroperitoneal tissues. 

Image: top left

This type is found in the oral cavity, pharynx, oesophagus and anal canal. The surface epithelium is of stratified squamous type and, although not keratinised in humans, it may be keratinised in some animals that have a coarse diet (e.g. rodents, herbivores). A stratified mucosal lining of this type is well suited to sites of potential frictional trauma, such as that associated with the passage of food during mastication and swallowing, or during the passage of faeces through the anal canal. 

found in: oral cavity, pharynx, oesophagus, anal canal 

Image: top right

This type of mucosa occurs only in the stomach. It consists of long, closely packed tubular glands that are simple or branched, depending on the region of the stomach. These glands act to produce various combinations of acid and digestive enzymes in order to facilitate digestion of food whilst also 

Image: bottom right

This mucosal form is typical of the entire small intestine. The mucosa is arranged into finger-like projections called villi which serve to dramatically increase surface area of the mucosa, with intervening short glands called crypts. In the duodenum, some crypts extend through the muscularis mucosae to form submucosal glands called Brunner’s glands. This is the major histological feature that differentiates the duodenum from the jejunum and ileum. 

Image bottom left

This form lines the entire large intestine. The mucosa is arranged into closely packed, straight tubular glands consisting of cells specialised for water absorption, as well as mucus-secreting goblet cells to lubricate the passage of faeces. 

1. Primary method for propelling food forward through the GI tract

2. Only the extreme ends of the GI tract are under voluntary control

3. Autonomic control primarily via parasympathetic innervation

4. Muscularis propria = smooth muscle wall, two layers, inner circular and outer

   longitudinal, peristaltic contraction

5. Constriction of both the luminal diameter as well as shortening of its 

1. Strong muscular tube

2. Conveys food from the oropharynx to the stomach

3. Voluntary initiation of swallowing skeletal muscles of oropharynx

4. Upper third is voluntary skeletal muscle, lower 2 thirds is autonomic smooth muscle

5. Thoracic oesophagus descends from the oral cavity, ventral to the spine, together with the aorta and vena cava

6. Goes through the diaphragm (vertebra TX) together with two vagal nerves (ant, left and post, right)

7. Abdominal oesophagus (1‐2cm long) feeds straight into the stomach at an acute angle

8. Gastro‐oesophageal sphincter prevents acid reflux 

1. Oesphageal mucosa is deeply folded, allowing for distension

2. Lumen is lined with a thick stratified squamous non‐keratinized epithelium

3. Submucosal glands (glandulae oesophageae), similar to those in the mouth, secrete lubricating mucous

4. A: lower third of the oesophagus: relaxed mucosa deeply folded allows distension during the passage of food

5. Lumen: stratified squamous epithelium, narrow lamina propria, with scattered lymphoid aggregates

6. Muscularis mucosa very thin

7. Submucosa loose, rich in elastin fibres (distension). Rich in seromucous glands 9lubrication)

8. Thick muscularis propria with clearly distinguishable inner circular and outer longitudinal layers of smooth muscle cells.

9. Bundles of skeletal muscle only on the upper third of the oesophagus 

1. Most dilated part of the GI‐tract. Distensible organ.

2. Retains the food for 2 or more hours

3. Mechanical and chemical breakdown of food chyme

4. Only absorbs water, alcohol and some drugs

5. Has four regions: cardia, fundus, body (corpus) and pylorus (pyloric antrum)

6. Cardia: surrounds the oesophageal opening. Small area of mucus secreting glands. In some individuals it may be only a few milometers or incomplete or totally absent

7. Fundus: area superior to the oesophageal opening glands that secrete acid‐ pepsin gastric juices as well as protective mucus.

8. Body: largest region glands that secrete acid‐pepsin gastric juices as well as protective mucus.

9. Pyloric part: pyloric antrum and pyloric canal, distal to the stomach end glands that secrete mucus of two different types and there are associated endocrine cells which secrete gastrin 

area superior to the oesophageal

opening glands that secrete acidpepsin gastric juices as well as protective mucus. 

largest region

glands that secrete acid‐pepsin gastric juices as well as protective mucus. 

pyloric antrum and pyloric canal, distal to the stomach end

glands that secrete mucus of two different types and there are associated endocrine cells which secrete gastrin 

Dünndarm

Small intestine is approx. 6‐7m long, plicae + villi + microvilli ‐> 200m2 Mucosa and submucosa arranged in folds called plicae circularis or valves of Kerckring (very numerous in jejunum) Mucosa surface made of finger like projections – villi
Microvilli at the luminal surface of the enterocytes
Duodenum: neutralise stomach acid, enzymatic digestion of chyme
Jejunum: further enzymatic digestion, nutrient absorption
Ilium: further enzymatic digestion, nutrient absorption