Appunti Anatomia (Anatomy, Anatomical and Physiological Bases of Organ Pathologies)

STOMACH

The stomach is the widest part of the alimentary tract and lies between the esophagus and the duodenum. It has several functions:

• Temporarily storage and mechanical breakdown of solid food
• Chemical digestion of proteins by enzymes and acid
• Secretion of intrinsic factors and hormones
• Microbial defense
• Absorption (only liquids, e.g. alcohol)

The position of the stomach is from posterior to anterior, from left to right. The mean capacity in adults is 1.0-1.5 L and its dimensions are variable.

The stomach is divided into several parts:

1. Fundus: dome-shaped, on the left of the esophageal arrival at the stomach (cardias orifice)
2. Body: the biggest part, it is a flattened cylinder when empty and can become bigger during digestion
3. Pylorus: divided into three parts, it is a sphincter, a muscular ring that can...

open and closeo p. antrum: expanded and then narrowedo p. canal: 1-2 cm long that ends intoo pylorus: real anatomical sphincter L12 sphincter: muscular ring that can open and close

internal configurationmany longitudinal folds of mucosa and submucosa rugae that become obliterated whenthe stomach is distended, with the exception of LESSER CURVATURE (a permanent foldconnecting esophagus to pylorus, shortcut where liquids can pass)

stomach wall is made up of 4 layers: mucosa, submucosa, muscular, sierosa

epithelium → cells of the epithelium have an important particularity: they produceand secrete large quantities of mucus that is stratified on the inner surface of the stomachthis mucus has to protect the stomach wall from the corrosive action of the gastric juice (pH 1-2)it is therefore a secretory epithelium- simple columnar mucus-secreting epithelium that covers the entire luminal surfacelongitudinal folds (rugae) of mucosa and submucosa that are obliteratedwhen the stomach is distendedinstead,

1. epithelium presents pits that are NOT obliterated➔ rugae ≠ pits
2. at the base of the pits, there are tubular gastric glands that differ in cellular composition in different parts of the stomach
1. principal glands
2. cardiac glands
3. pyloric glands

principal glands:

1. found in the body and fundus
2. 5 cell types
1. parietal cells: bear many microvilli rich in H /K ATPase antiporter channels that actively secrete H in the lumen-Cl follow the electrical gradient, many mitochondria, they also secrete intrinsic factors
2. chief (peptic) cells: secrete pepsinogen and chymosin (rennin), they contain secretory zymogen granules
3. mucous neck cells: secrete mucus
4. neuroendocrine cells: produce gastrin stimulates the stomach juice production, serotonin stimulates smooth muscle of stomach contractions, ghrelin stimulates hypothalamus and makes us hungry, histamine stimulates HCl production, somatostatin end of digestion
5. stem cells

submucosa → loose connective tissue with

Meissner's plexus (controls glands secretin and local bloodflow)

muscolaris externa → 3 layers

muscle activity is controlled autonomic nerve fibers which lie between the muscle circular and longitudinal layers (Auerbach's plexus)

the three-layered structure of its muscular wall enables the stomach to undergo powerful churning movements

interstitial cells of Cajal (ICCs) present in submucosa and muscular layers, they contact nerve fibers and have numerous gap junctions with each other's smooth muscular cells, and so are involved in the generation of rhythmic gastric slow-rate contractions

electric pacemaker for smooth muscle cells

most gastrointestinal contractions occur rhythmically, and this rhythm is maintained by slow waves that are NOT action potentials but slow undulating potential in the resting membrane, caused by Cajal cells (that so act as electrical pacemaker for smooth muscle cells)

innervation

both sympathetic and parasympathetic- sympathetic: splanchnic

nerves and branches of coeliac plexus- parasympathetic: branches of vagus nerve→CNS ANS➔ parasympathetic➔ sympatheticenteric nervous systemENS regulates many functions of the digestive systemit is considered as a separate entity from the orthosympathetic or parasympathetic nervous system, as ithas an autonomous reflex activityin connection with the autonomic nervous system + regulates many functions of the digestive system➔ submucosal (Meissner’s) and myenteric (Auerbach’s) plexus→o submucosal plexus located in the submucosal→o myenteric plexus between the two layers of smooth musclesensory neurons of the ENS (IPANs = intrinsic primary afferent neurons) analyze the mechanical andchemical conditions of the various hollow organs of the digestive tractmotor neurons regulate peristalsis, enzyme/hormonal secretion, caliber of the vessels

ANATOMY (16/11/2022)

SMALL INTESTINEplays the primary role in the digestion and absorption of nutrients (90%

The small intestine, which is approximately 6 meters long, can be divided into:

1. Duodenum (approximately 25 cm long)
2. Jejunum (approximately 2.5 m long)
3. Ileum (approximately 3.5 m long)

The small intestine begins at the level of the pylorus, with a short section of the duodenum. The remaining segment is divided between the jejunum and ileum. The small intestine ends with the ileocecal valve, continuing into the large intestine. It occupies a large part of the digestive system and has the following functions:

• Completion of digestive processes started in the oral cavity and the stomach
• Absorption of nutrients after digestion

The surface area for nutrient absorption is increased by:

1. Circular folds (plica circulares of Kerckring)
2. Valves
3. Circular folds of mucosa and submucosa (permanent and easily visible by eye, unlike in the stomach)
4. Intestinal villi (fingerlike projections of the mucosa, barely visible by eye)

The transit time of chyme along the small intestine is approximately 5-6 hours.

Covered by a simple columnar epithelium (enterocytes), microvilli are extensions of the apical surface of enterocytes that are not visible by eye. The villi structure is responsible for nutrient absorption. The lymphatic circulation begins with the chyliferous vessels located centrally in the villi, draining into the lymphatic network of the submucosa. From the submucosa, lymph is collected in bigger vessels present in the serosa layers (lymphatic collecting vessels). Glycocalyx, which localizes enzymes that finish digestion, is found in the villi. Tuft or brush cells are important in gastrointestinal chemosensation and can also mediate inflammation.

Intestinal crypts, also known as crypts of Lieberkulm, are located at the base of the villi. These pockets extend deep into the underlying lamina propria. The cells of the crypts of Lieberkulm include enterocytes (columnar absorptive cells) and goblet cells, which are scattered among enterocytes and produce mucin for lubrication.

and protection of the epithelium

- Paneth cells: secrete lysozyme, an antibacterial enzyme, defensive proteins (defensins) and TNF

- stem cells

- neuroendocrine cells: secrete locally acting hormones that regulate intestinal mobility and secretion

- intraepithelial lymphocytes: mainly T cells

duodenum has a C shaped form, and the head of the pancreas lies with the concavity of the duodenum

important because it receives the bile duct and the pancreatic ducts

it is a mixing bowl that receives the chyme from the stomach and digestive secretions from pancreas and liver

almost all essential digestive enzymes enter the small intestine from the pancreas

divided in four parts with intervening flexures

- superior (duodenal bulb)

- descending

- horizontal

- ascending

total length of approx. 12 finger widths (from Latin duodeni, "twelve at a time")

internal appearance

there are two papillae (mucosal elevation surrounding opening of the ducts)

- major papilla (inferior) of Vater: common bile duct

and main pancreatic duct (of Wirsung) usually unite to form a common channel which pierce the medial wall in a dilated segment known as hepatopancreatic ampulla- minor papilla (superior): opening of secondary accessory pancreatic duct growing off the abdominal foregut are a dorsal pancreatic bud and a ventral liver diverticulum sprouting from the latter are gallbladder and ventral pancreatic buds jejunum and ileum 6-7 m in length, arranged in numerous convoluted loops a continuous tube that can be divided into

• jejunum (proximal 2/5 of length) from "ieiunus" it starts at the duodenojejunal flexure
• ileum (3/5 of length)

NO REAL SEPARATION BETWEEN THE TWO, it changes gradually becoming

• narrower: jejunum (external diameter 4 cm/internal 3 cm), ileum (external 3 cm/internal 2,5 cm)
• thinner: wall plicae circulars become progressively less high
• less vascularized: jejunal arteries are slightly larger than ileal regions of the small intestine have histological specializations

related to their primary function, the submucosa contains Brunner's glands which produce large quantities of mucous. This mucous protects the epithelium from the acid chyme arriving from the stomach because it contains buffers that help elevate the pH of the chyme.

By the beginning of the jejunum, the intestinal content changes from 1-2 to 7-8. From this jejunum, it can be distinguished from other tracts of the small intestine thanks to the presence of villi, which are fingerlike projections. The mucosa and submucosa are lifted up in plicae circularis or Kerckring.

The ileum can be distinguished from other tracts of the small intestine thanks to the following characteristics:

• Thinner wall: plicae circularis become progressively less high
• Increase in goblet cells
• Presence of Peyer's patches: aggregated lymphatic follicles that can reach considerable size, ranging from 2 to 10 cm. Oval-shaped, they surround the intestinal wall forming an incomplete ring.
• Usually, there are scarce villi to cover Peyer's plate and the