Digestive System Flashcards
What makes up the digestive system?
Digestive tract organs
Glands
Accessory sturcture
What are the functions of the digestive system?
Ingestion Mastication/chewing Mixing and propulsion Secretion Digestion Absorption Elimination
What are the two types of digestion?
Mechanical- physical disruption of food into smaller parts
Chemical- enzymes break into constituent parts
What is meant by the digestive tract?
Tubular pathway from oral cavity to anus/cloaca
What organs are in teh foregut?
Oesophagus Stomach Liver Gall bladder Proximal duodenum Pancreas Spleen
What organs are in the midgut?
Distal duodenum Jejunum Ileum Caecum Appendix Ascending colon 2/3 transverse colon
What organs are in the hindgut?
1/3 transverse colon
Descending colon
Sigmoid colon
Rectum
What are the accessory organs in the digestive system and what are their roles?
Liver- degrade toxins, bile production
Gall bladder- store and concentrate bile
Pancreas- enzyme and hormone release
Spleen- lymphatic organ but shares digestive blood suply
Which aortic branches supply which regions of the GI system?
Coeliac trunk- foregut
Superior mesenteric artery- midgut
Inferior mesenteric artery- hindgut
How does blood drain from the GI system into the heart?
Into hepatic portal vein to the liver for detoxification then into inferior vena cava
What is the sympathetic innervation to the regions of the GI system?
Foregut- coeliac ganglion
Midgut- superior mesenteric ganglion
Hindgut- inferior mesenteric ganglion
What is the parasympathetic innervation to the regions of the GI systmem?
Foregut and midgut- vagus nerve
Hindgut- pelvic splanchnic nerve
Describe the lymphatic drainage from the GI tract
Inferior mesenteric (hindgut), superior mesenteric (midgut) and coeliac (foregut) lymph nodes drain to cisterna chyli then thorax then thoracic duct
What makes up the superior boundary of the abdominal cavity?
Diaphragm
What is the inferior boundary of the abdominal cavity?
Continuous with pelvic cavity ending at pelvic inlet
What are the layers of the abdominal walls?
Skin Superficial fascia Deep fascia Muscle Transversalis fascia Parietal peritoneum
Which spinal nerves innervate abdominal walls?
T7-L1
What is the blood supply to abdominal walls?
Superior epigastric artery- branch of internal thoracic artery from subclavian artery
Inferior epigastric artery- branch of external iliac artery
What is the rectus sheath?
Aponeurosis/flat tendon sheet enclosing muscles
What is the function of abdominal wall muscles?
Enclose and protect viscera
Manage abdominal pressure
What are the posterior abdominal wall muscles?
Quadratus lumborum- connects pelvis with inferior ribs
Psoas muscle- from vertebral column to hind limbs
Iliacus muscle- from ileum to hind limb
What are the ventrolateral muscles in order of superficial to deep?
Rectus abdominis- down front of abdomen, linea alba lies down the centre and tendons cross at intersections
External obliques- inferomedial from ribs to aponeurosis
Internal obliques- superiomedial from pelvis to aponeurosis
Transversalis abdominis- from rectus abdominals to vertebrae
How is the abdomen split into quadrants?
Median and transumbilical planes through the umbilicus
Define the peritoneum
Single cell layer of serous tissue lining the abdominal cavity
What does the different parts of the peritoneum cover?
Parietal- abdominal walls
Visceral- organs
Define retroperitoneal
Covered in peritoneum but not surrounded fully, behind the peritoneum
Define intraperitoneal
Organs fully surrounded by peritoneum
Define subperitoneal
Structures below the peritoneum
How are organs connected to the abdominal walls?
Ligaments
Define mesentary
Reflections of peritoneum surrounding blood vessels and nerves and holding intestines in place
Define omentum
Peritoneum connecting stomach to GI organs to hold everything in place
Explain the difference between the lesser and greater omentums
Lesser- stomach to liver
Greater- stomach to colon
What is the function of the oral cavity?
Mechanical digestion- mastication
Chemical digestion- salivary amylase
What are the boundaries of the oral cavity?
Roof- hard and soft palette
Floor- tongue
Anterior- Oral fissure and lips
Posterior- oropharyngeal istmus
What are the areas of the oral cavity?
Oral vestibule- space between the teeth and gums and lips and teeth
Oral cavity proper- cavity tongue is found
What are the components of the oral cavity?
Lips Soft palette Hard palette Teeth Tongue Salivary glands
Describe the structure of the lips and their role
Musculofibrous folds surrounding the mouth
Close oral cavity, taking in food and communication
What is the orbicularis oris?
Sphincter of the mouth
What is the role of the soft palette?
Depresses to close opening to pharynx
Elevates to separate nasopharynx and oropharynx
What is the structure of the soft palette?
Muscle lined with mucosa
What is the structure of the tongue?
Muscular organ covered in mucus membrane of non keratinised stratified squamous epithelium
Root attaches to hyoid bone and mandible and body sits in oral cavity
What does the intrinsic and extrinsic muscles of the tongue do?
Intrinsic- changes tongue shape
Extrinsic- moves tongue around cavity
What is the role of the tongue in digestion?
Swallowing
Speech
Taste
What bones make up the oral cavity?
Maxilla- upper jaw
Mandible- lower jaw
What makes up the mandible?
Condylar process- joint with upper jaw Coronoid process- extension in front of condylar process Ramus- vertical body Angle- corner Body- horizontal body
What makes up the hard palette?
Premaxilla (quadrupeds)
Maxilla
Palatine- centre and behind maxilla
What is the lining of the hard palette?
Thick mucosa with rugae
Keratinised in epithelium in herbivores
Describe the muscles of mastication
Temporalis- closes jaw by pulling up mandible
Masseter- closes jaw and allows lateral movement
Lateral pterygoid- opens jaw
Medial pterygoid- closes jaw
What is the nervous supply of the muscles of mastication?
Trigeminal nerve
What are the components of the teeth?
Enamel- protects tooth
Dentine
Pulp- contains nerve
Periodontal ligament- holds tooth in root
What are the different tooth positions?
Acrodont- emerge from jaw with no root
Pleurodont- rooted on one side
Thecodont- anchored in jaw on both sides of root
What is meant by diphyodonts and polyphodonts?
Di- animals with deciduous and permanent set of teeth
Poly- animals with multiple sets of teeth
What are the different shapes of teeth?
Incisors
Canines
Premolars
Molars
What are major and minor salivary glands?
Major- paired glands away from oral cavity, drain by long ducts
Minor- present throughout oral cavity mucosa
What is produced by salivary glands?
Produce watery secretions containing amylase and antimicrobial agents
Where are the different major salivary glands located?
Parotid- under and slightly below ear
Buccal- behind maxilla bone below eye
Sublingual- below tongue
Mandibular- behind mandible
What are the functions of the salivary glands and their secretions?
Digestion Mineralisation of teeth Antimicrobial roles Lubrication Agglutination of bacteria Taste Hydration detection
Which salivary gland is only present in quadrupeds?
Buccal
Describe the components of the pharynx
Nasopharynx
Oropharynx
Laryngopharynx
Combined respiratory and digestive tract
What are the pharynx regions lined by?
Nasopharynx- respiratory epithelium
Oropharynx and laryngopharynx- non-keratinised stratified squamous epithelium
What is the purpose of the oesophagus?
Carry food from pharynx to stomach
What is the oesophagus lined with?
Stratified squamous epithelium mucosa
What are the muscles or the oesophagus?
Inner circular- constricts lumen
Outer longitudinal- shortens tract
List the functions of the stomach
Food storage
Mechanical digestion by churning
Chemical digestion
List the anatomical parts of stomach structure?
Lower oesophageal sphincter
Lesser curvature
Greater curvature
Pyloric sphincter
What are the regions of the stomach?
Cardia- small area under oesophageal sphincter
Fundus- area above oesophageal sphincter
Body- main bulk of the stomach
Pylorus- tapered end of the stomach
What muscle types are present in the stomach?
Circular
Longitudinal
Oblique
What allows stomach distension?
Rugae
Describe the stomach lining of horses
Glandular and non-glandular lining separated by margo plicatus
Describe the avian stomach
Oesophagus joins glandular proventriculus which connects to muscular ventriculus/gizzard where ingested pebbles aid digestion
What is foregut fermentation?
Specialised ruminant stomach for cellulose digestion by commensal bacteria
Why is the stomach enlarged in foregut fermentors?
Increased surface area for bacteria and absorption of free fatty acids produced by bacteria
What is the ruminoreticula grove?
Adaptation in young ruminants to allow ingested milk to skip fermentation and rumen as closes when suckling and connect oesophagus directly to omasum
What are the chambers of foregut fermenters stomach and their order from oesophagus to duodenum?
Rumen
Reticulum
Omasum
Abomasum
What is the function and structure of the rumen?
Receive, hold and ferment swallowed food
Lots of bacteria present
Regurgitation, remastication and reswallowing
Distinctive papillated mucosa lining
What is the structure and function of the reticulum?
Small accessory chamber with distinctive honey comb mucosa
Very contractile to slosh chyme back and forth with rumen
What is the structure and function of the omasum?
Epithelium folded in laminae
Pumps food into abomasum
What is the structure and function of the abomasum?
Simple columnar glandular epithelium lightly folded
Enzymatic digestion of protein and fat, highly acidic
What marks the foregut-midgut divide?
Major duodenal papilla- where common bile duct and main pancreatic duct drain into duodenum
What are the different parts of the pancreas?
Exocrine- digestive enzyme production
Endocrine- regulate blood sugars by producing hormones
What is the gall bladders structure and lining?
Pear shaped sac under right lobe of liver
Lined with simple columnar epithelium
Describe how bile travels from the liver
Ducts collect bile from left and right lobes of liver which connect and drain into gall bladder
Then drains into duodenum
Describe the anatomical lobes of the liver from anterior and posterior views
Anterior view- right and left lobes separated by falciform ligament
Inferior view- right and left lobes, quadrate lobe close to gall bladder, caudate lobe close to inferior vena cava
Explain the role of bile
Emulsifies fat making it easier for enzymes to digest
What is the portal triad?
Found in centre of the four lobes containing hepatic portal vein, hepatic artery and common bile duct
What is meant by a lobule of the liver and what is it made up of?
Functional unit of the liver
Central hepatic venule going to hepatic vein surrounded by hepatic sinusoids, portal veins, bile ductules and hepatic arteries
What are lobules separated by?
Interlobular connective tissue
What is the function of the liver?
Produce and secrete bile
Detoxify blood from GI tract
What is the role of the different parts of the spleen?
Red pulp- removes particles from circulation including old erythrocytes
White pulp- lymphocyte production and immune response
Where is the spleen located in relation to other structures in the abdomen?
Under diaphragm and behind stomach
What are the functions of the small intestine?
Chemical digestion by pancreatic and intestinal juice
Absorption of fat, protein and carbohydrates
Where is the duodenum located?
Encircling pancreas, fixed in position by short messentary
What is the purpose of bruners glands in the duodenum?
Secrete alkaline mucus to neutralise digestive contents from stomach
Where is the jejunum and ileum located?
Jejunum- mainly in upper left quadrant
Ileum- mainly in lower right quadrant
Both mobile from long mesentery
What is the structure of the jejunum?
Highly folded lining, plicae circularis covered in villi and microvilli
Thin mesentery with simple blood supply
Describe the structure of the ileum?
Thin walls with peyers patches and gut associated lymphoid tissue
Thick fat filled mesentery with complex blood supply
What is the caecum?
Saclike structure at start of colon with connection to ileum called ileocecal junction
Where is the appendix and what species dont have one?
Connected to inferior caecum
Horse, dog or ox
What is meant by midgut fermentation?
Cellulose digestion by commensal bacteria in hugely expanded caecum and ascending colon
How do commensal bacteria aid midgut fermentation?
Produce enzymes that breakdown cellulose to volatile fatty acids with them being absorbed by the caecum and ascending colon
Describe the stomachs of midgut fermentors
Single chambered with no rumination
How does midgut fermentation compare to foregut?
Faster but less efficient so need constant grazing
Soluble sugars are absorbed before fermentation
What is caecotrophy?
Form of midgut fermentation where caecotrophs are produced in caecum and proximal colon
Explain the process of caecotroph production
Fusus coli regulates colonic contraction and segmental and haustral contractions separate ingesta into solids and liquids
Caecotrophs are eaten from the anus, swallowed and redigested allowing maximun nutrient absorption
Explain the structure of the colon
Taeniae coli- longitudinal muscles along length of colon pulls to form haustra/bulges
Explain the different arrangements of the colon in pigs and cows
Spiral loop
Pigs- conical
Cows- flat
Describe the lining of the colon
Smooth mucosa to absorb salt and water
Walls contain intestinal glands
What is the role of the levator ani muscle in the pelvic floor and what muscles make it up?
Pulls up anus and supports rectum
Iliococoygeus, pubococcygeus and puborectalis muscles
What is the function of puborectalis muscle?
Wraps around rectum causing it to bend, tonicly contracted and further contracts to prevent defecation, relaxes to straighten rectum allowing defecation
Describe the structure of the cloaca
Coprodeum- entry of colon
Urodeum- entry of ureters
Proctodeum- entry of reproductive system
What is the purpose of the rectum?
Store faecal mass before defecation
Describe the relations of the rectum
Superior- peritoneum and abdominal viscera
Posterior- sacrum, coccyx and pelvic floor
Anterior- vagina/prostate and bladder
Inferior- anus
What is the innervation of external anal sphincter?
Pudendal nerve
What is the innervation of the internal anal sphincter?
Splanchnic nerve
What is the pectinate line?
Separates the visceral and parietal parts of the anus
What are the origins, innervation and blood supply of the anus above the pectinate line?
Endoderm derived epithelium
Visceral motor and sensory innervation
Blood drains to hepatic portal vein
What are the origin, innervation and blood supply of the anus below the pectinate line?
Ectoderm derived keratinised squamous epithelium
Somatic motor and sensory innervation
Blood drains to systemic circulation
What germ layer does the primitive gut tube arise from?
Endoderm
How does the primitive gut tube fold in the embryo?
Lateral folding- lateral sides of embryo roll in to form primitive gut tube
Longitudinal folding- way of establishing foregut, midgut and hindgut, reduces connection of gut tube to yolk sac to a small connection
Describe the development of the midgut
Rapidly lengthens to exceed capacity of abdominal cavity
Forms U-shaped loop that leaves the cavity
Top of loop becomes jejunum and upper ileum, bottom becomes the rest of the midgut
Counter clockwise 90 degree rotation brings lower loop to embryos left side
As embryo grows cavity gets bigger allowing gut tube to return to abdomen
180 degree rotation brings appendix to upper right quadrant before growth forces it to lower right quadrant
How does the cloaca become separated into the genital, urinary and anal tracts?
Urorectal septum divides cloaca into urogenital sinus and dorsally into rectoanal canal
Describe the development of the stomach
Fusiform dilation of foregut embryo
90 degree rotation brings left side ventrally and right side dorsally
Differential growth establishes greater and lesser curvatures as left side grows more quickly
Craniocaudal rotation tips pylorus superiorly
Describe how the liver develops
Foregut endoderm adjacent to septum becomes liver under signals from the heart and septum transversum
Made up of endoderm buds surrounded by mesoderm
Explain how the pancreas develops
2 outgrowths caudal to forming liver become ventral and dorsal pancreatic ducts
Explain how the oesophagus is developed
2 tracheoesophageal folds divide cranial foregut into trachea and oesophagus
Lengthens as embryo grows
Explain the congenital abnormality of a stenosis
Oesophagus becomes filled in so needs to recanalize before birth, failure causes regurgitation after feeding
Explain the congenital hiatal hernia
Oesophagus doesn’t lengthen properly so stomach gets pulled up through oesophageal hiatus making hiatus weak and other structures move into thorax
Describe the midline incision
Cut from xiphoid process to pubis, entering through rectus sheath
What are suprapubic incisions used for?
Gynaecological or pregnancy operations
What does the subcostal incisions allow access to?
Liver, biliary tree and spleen
What incision should you use for exploratory procedures?
Longitudinal
What is the incision for appendectomy?
McBurneys
When are flank incisions used?
Rumenectomy
What is the benefits of laparoscopic procedures?
Less pain
Complications
Better recovery
Define a gastrointestinal anastomoses
Reduction of stomach capacity and absorptive region of small intestine using jejunum as a graft
What is a gastric sleeve?
Portion of stomach removed creating tube like stomach
What is a gastric bypass?
Small amount of stomach connected to retracted small intestine to bypass digestion, grafted to cardia
What is a jejunal anastomoses?
Reduction in jejunum length
What is the name for a gall bladder removal?
Cholecystectomy
What is a whipple procedure?
Removal of head of pancreas, duodenum, gall bladder and bile duct with remaining organs reattached to allow normal digestion
Where does pain from organs refer to?
Foregut- epigastric/upper centre of abdomen
Midgut- umbilicus/ middle of abdomen
Hindgut- pubic region/lower abdomen