GI system Flashcards
Give an account of the composition and function of saliva.
Saliva is mostly water but also contains Mucins, Electrolytes (Na+, Cl-, and HCO3-), Antibodies and Enzymes.
Its major functions are to keep mucosa moist, assist in the digestion of foods (both via breakdown of food and lubrication for swallow), act as a pH7 buffer,
Describe the anatomy of the salivary glands including the microstructure, ducts and important anatomical relations.
The basic microstructure of salivary glands involve ductal cells, serous cells, mucous cells. (serous appear dark (serous demilune) whereas mucous cells appear light)
There are 4 glands which are important for saliva poduction:
Parotid: Located superior to the masseter. Enters oral cavity via parotid duct. Associated with branches of the facial nerve which pass through it.
Submandibular: 1 duct which enter mouth at lingual papilla ( visible. Closely related to lingual nerve ( located in submandibular fossa of mandible.
Sublingual: 8-20 ducts enter oral cavity along the floor of the mouth at the sublingual fold. Located sublingual fossa.
Minor glands
Discuss the differences in saliva produced by the different salivary glands.
Parotid: serous gland which produce amylase.
Submandibular: seromucous gland with mixed secretions (contributes to most of rest secretions).
Sublingual: Mucous, lubricant
Minor Glands: mostly mucous for lubricant
Give a detailed account of the neural control of salivation.
Parasympathetic- secretomotor. Facial nerve (CNVII) and Glossopharyngeal (CNIX). The facial nerve doesnt supply the parotid and only passes through it. Sublingual and Submandibular • Preganglionic parasympathetic fibres originate from the superior salivatory nucleus in the brainstem • Pass through branch of facial nerve (chorda tympani) to reach the submandibular ganglion • Synapse with postganglionic parasympathetic fibres • Postganglionic parasympathetic fibres travel along lingual nerve (branch of CNV – trigeminal) to reach submandibular and sublingual glands • Lingual nerve also supplies sensory information i.e. pain. Parotid glands: • Preganglionic fibres originate from inferior salivatory nucleus in the brainstem • Pass through branch of glossopharyngeal nerve (lesser petrosal nerve to reach the otic ganglion • Synapse with postganglionic parasympathetic fibres • Postganglionic parasympathetic fibres travel along auriculotemporal nerve (branch of CNV – trigeminal) to reach parotid glands • Auriculotemporal nerve also supplies sensory information from parotid capsule and supplies overlying skin
Describe Frey’s syndrome
Parodectomy- many tumours occur in the parotid glands (some are malignant) but removal is complicated due to the relations with the facial nerve. Frey's syndrome- During parotidectomy, the auriculotemporal nerve can be damaged • Damaged sensory and parasympathetic fibres become mixed • Can result in parasympathetic fibres supplying skin (including sweat glands) • Consequences? • Salivary stimulus ( e.g. smelling food) results in sweating of skin over the parotid gland • Also called gustatory sweating • Treated with botulinum toxin
Describe the effects of Mumps on the salivary glands
• Mumps is a viral infection that primarily affects the parotid glands • Parotid glands become inflamed and enlarge • Parotid glands surrounded by tough, fibrous capsule • Stretching capsule stimulates the sensory fibres of the auriculotemporal nerve – very painful!
Describe salivary stones
A stone (calculus) may form in the salivary glands, particularly following infection • If the stone moves into the main duct it can block the duct • Saliva builds up in the gland causing swelling • Very painful, particularly at mealtimes
Give an account of the structure of the abdominal wall and it’s functions.
Extends from teh costal margins to the ileac crests and pubic bones. It consists of skin, superficial fatty fascia, scarpa’s fascia (membranous layer), 3 layers of muscle, a transverse fascia, an extraperitoneal fascia and a parietal peritoneum.
It supports and protects abdominal viscera, compresses the abdomen to increase pressure for expulsion, movement of trunk and maintenance of posture.
Describe the muscle of the abdominal wall including their innervation and blood supply
The outermost muscle layer is the:
External oblique
is found at the anteriolateral aspects of both sides of the cavity. Originates from ribs 5-12> anterior iliac crest and linea alba via a broad aponeurosis known as the rectus sheath.
Internal Oblique
Deep to the external oblique. thoracolumar fascia, iliac crest, 2/3 of inguinal lig. and pubic crest> ribs 10-12, linea alba and pubic crest. Both flex and rotate the trunk.
Transverse Abdominis
Deep to internal oblique. Thoracolcolumbar fascia, iliac crest, lateral 1/3 of the inguinal canal and ribs 7-12> linea alba and pubic cresr via conjoint tendon (formed by fibres of the internal oblique and transvers abdominis). Lined b transverse fascia.
Rectus Abdominis
Pubic crest and pubic synthesis> xiphoid process and 5th-7th costal cartilages. Seperated by tendonous intersections. (8). Flexes the trunk for sitting up and stabilizes the pelvis. Encosed in the rectus sheath
Cutaneous innervation T7-T12. The superior and inferior epigastric arteries lie posterior to rectus abdominis in the
rectus sheath
• Note that the linea alba is relatively devoid of blood vessels – avascular plane for
incisions.
Identify the key surface landmarks of the anterior abdominal wall
The key landmarks would be the linea alba which marks the midline of the abdominal cavity.
The umbilicus is also useful:
Above- the external oblique aponeurosis anterior, internal oblique aponeurosis divides –half anterior and half posterior
Transversus abdominis aponeurosis posterior.
Below- All 3 aponeurosis enter transverse fascia posterior.
Arcuate line demarcates a change in rectus sheath composition (into transverse fascia)
Describe the rectus sheath and its contents
Formed by aponeuroses
of the external and
internal oblique muscles
and transversus
abdominis
• Composition differs
above and below the
umbilicus (belly button)
Above- the external oblique aponeurosis anterior, internal oblique aponeurosis divides –half anterior and half posterior
Transversus abdominis aponeurosis posterior.
Below- All 3 aponeurosis enter transverse fascia posterior.
Give an acount of the inguinal canal including its boundaries and contents.
Inferior edge of external oblique aponeurosis attaches to the ASIS and the pubic tubercle • Inferior edge thickens and folds under to form a gutter – inguinal ligament • Aponeurosis of external oblique splits medial to the pubic tubercle to form the superficial inguinal ring • Allows the passage of the spermatic cord in males (round ligament of uterus in females) Starts at deep inguinal ring - an opening in the transversalis fascia • Passes through transversus abdominis, internal oblique and external oblique • Ends at superficial inguinal ring in external oblique aponeurosis
Discuss the anatomy of the inguinal canal in relation to inguinal hernias.
Anterior wall
External oblique aponeurosis
Lateral 1/3 reinforced by internal oblique muscle
Roof
Arching fibres of internal oblique and transversus abdominis muscles
Posterior wall
Transversalis fascia. Medial 1/3 reinforced by the conjoint tendon
Floor
Inguinal ligament
Note that reinforcement in the anterior and
posterior walls matches position of deep and superficial inguinal rings.
In a direct aquired inguinal hernia the bowel passes medial to the inferior epigastric vessels, pushing through the peritoneum and transversalis fascia in inguinal triangle to enter the inguinal canal.
In congenital inguinal hernias the bowel can pass lateral to the inferior epigastric vessels to enter the deep inguinal ring.
Give an account of the anatomy and innervation of the peritoneum including its reflections.
2 layers of serous membrane
(mesothelium) that are continuous with
each other
• Parietal layer covers the body wall
• Visceral layer surrounds internal organs
• Peritoneal cavity is a potential space
that only contains a thin film of fluid (5-
20 ml) between the visceral and parietal
layers.
Important for suspension of different organs to allow for GI motility.
An intraperitoneal organ is completely
covered by peritoneum
• A retroperitoneal organ lies posterior to
the peritoneum and is only partially
covered
• An infraperitoneal organ lies inferior to
the peritoneum and is only partially
covered
Mesentery – double layer of peritoneum that
connects an intraperitoneal organ to the
posterior abdominal wall e.g. small intestine
• Omentum – double layer of peritoneum that
extends from the stomach to another organ
e.g. greater omentum. It hangs like an apron from the greater curvature of the stomach and folds back to attach to the transverse colon. The greater omentum is highly mobile – often not located as depicted in diagrams
Multiple functions:
• Contains fat – insulation
• Contains milky spots – lymphoid tissue
• Policeman of the abdomen
• Peritoneal ligament – double layer of
peritoneum that attaches an organ to another
organ or the anterior abdominal
wall/diaphragm e.g. falciform ligament
Discuss how the anatomy of the peritoneal cavtiy relates to it’s embryological origins.
Derived from lateral plate mesoderm. Parietal layer of LP mesoderm= parietal peritoneum. Visceral layer of LP mesoderm= visceral peritoneum.
• 2 layers of LP mesoderm enclose intra-embryonic coelom = future serous cavities
• Visceral LP mesoderm surrounds gut tube
• Parietal LP mesoderm lines cavity wall. It is related to embryo folding stage.
Dorsal mesentery – from lower oesophagus to cloaca
• Ventral mesentery – from lower oesophagus to 1st part of duodenum
forms lesser omentum and falciform ligament.
The stomach rotates during wks 7/8 and subdivides into the peritoneal cavity. It rotates 90 degrees clockwise in a cranio-caudal axis creating space behind it- the lesser peritoneal sac (omental bursa). The remaining peritoneal cavity is now known as the greater sac. The epiploic foreman is the narrow opening that connects the greater and lesser sacs. The free ede of the lesser omentum contains the portal triad (hepatic artery, hepatic portal vein and bile duct).
Discuss the functions of the peritoneum and and relate these to diseased states.
Peritoneal adhesions:
Injured peritoneum can create
fibrotic adhesions with adjacent
intact peritoneum
• Fibrin is formed in response to the
injury
• Mesothelial cells can activate
degradation of fibrin to prevent
adhesions, however, requires a
delicate balance
• Imbalance in these mechanisms
leads to adhesions
• Most commonly occurs after surgery.
Peritoneal dialysis:
Peritoneum has a large surface area (1.8 m2
) and is a semipermeable membrane
• Can be used to filter excess water and waste products from blood in renal failure
• Dialysate is introduced into the peritoneal cavity where it comes into contact with
capillaries perfusing the peritoneum and viscera. Solutes diffuse from blood in the
capillaries into the dialysate
• A transmembrane pressure gradient is applied (osmotically) and results in
ultrafiltration of fluid from the capillaries into the dialysate
• Dialysate is then discarded
