BL Session 9 - Digestive System and Liver Flashcards
Outline the features of the hepatic portal system.
- The portal circulatory systems differ from the typical circulatory route in that blood passes through two sets of smaller vessels before returning to the heart.
- Blood from the first set of capillaries collects in portal vessels (sometimes called portal veins) which then begin to branch again to supply a capillary network to a second location before entering a series of veins which will lead to the heart.
What travels to the portal vein?
- Water
- Water soluble vitamins
- Electrolytes
- Carbohydrates (monosaccharides)
- Proteins – amino acids, dipeptides and tripeptides
- Intestinal hormones, particularly pancreatic hormones
- Toxins, including ammonia
In terms of the Krebs cycle, why is the liver important?
- The liver is the only organ in the body in which the complete urea cycle (Krebs cycle) is expressed.
- It converts ammonia to urea which can then be excreted in the urine.
What doesn’t travel through the portal vein?
- Lipids
I. Dietary lipid is mostly triglycerides, cholesterol and phospholipids
II. Digested by lipases, this process needs bile acids to form micelles
III. Lipids are taken into the cells and processed into chylomicrons
IV.Chylomicrons are taken up by lymphatics, called lacteals. Lacteals contain chyle
- Fat soluble vitamins (Vitamin ADEK)
Outline the functions of the liver.
- Storage: Iron; Vitamin, B12, D, Vitamin K and Glycogen
- Anabolism/production
I. Albumin
II. Glycogen
III. Numerous coagulation factors
- Catabolism/breakdown/ toxin degradation
I. Drugs and poisons (cytochrome P450)
II. Hormones - Insulin, Glucagon, Oestrogen and Progesterone
III. Haemoglobin
IV. Can take over removal of aged red cells after splenectomy
- Filtering function – macrophages are critical for the execution of this function
Outline the endocrine and exocrine functions of the liver.
- Exocrine function – bile is an exocrine secretion of the liver via the bile duct
- Endocrine function - it produces angiotensinogen, thrombopoetin, insulin like growth factor 1 (IGF – 1)
Outline the structure of hepatocytes
- Constitute 80% of liver cell population
- Can regenerate remarkably!
- Compared to other cells contain:
I. Numerous mitochondria
II. A lot of peroxisomes (organelles full of oxidising agents)
III. Numerous free ribosomes
IV. A lot of rER
V. A lot of sER
VI. Numerous Golgi complexes
VII. Glycogen deposits
Describe the structure and function of Kupffer cells.
- Kupffer cells are monocyte derived specialist macrophages that form part of the lining of the sinusoids.
- They patrol tiny vessels in the liver called sinusoids, recycling old red blood cells and ingesting pathogens.
- The endothelium of these vessels is perforated with large holes, allowing the Kupffer cells to migrate into liver tissue at sites of inflammation and damage.
Describe the structure of Stellate (Ito) cells.
Stellate (Ito) cells are full of cytoplasmic vacuoles containing Vitamin A.
What happens to stellate cells in the case of liver cirrhosis.
- In liver cirrhosis, hepatic stellate cells lose their vitamin A storage capability and differentiate into myofibroblasts.
- That synthesize and deposit collagen within the perisinusoidal space, resulting in liver fibrosis.
- This collagen surrounds the central vein, constricting it and leading to portal hypertension
What is a sinusoid?
- A sinusoid is an irregular tubular space for the passage of blood, taking the place of capillaries and venules in the liver, spleen and bone marrow.
- Its endothelial cells gas large gaps (perforated)
Describe the features of a liver acinus.
Describe the features of a liver lobule.
Describe the location of lymphatics in the liver.
Lymphatics arise from the periportal space of Mall and drain to the liver hilum and then onto the hepatic duct.
Identify the components of the alimentary canal.
Identify and describe the 4 layers of the gut wall.
- Mucosa (innermost)
I. Muscularis mucosae
II. Lamina propria
III. Epithelium
- Submucosa - a layer of connective tissue bearing glands, arteries, veins and nerves
- Two external muscle layers (muscularis externae) - circular and longitudinal muscle
- Serosa - a serous membrane
Identify the functions of the gastrointestinal tract.
- To provide a port of entry for food into the body
- To mechanically disrupt the food
- To temporarily store the food
- To chemically digest the food
- To kill pathogens in the food
- To move the food along the tract
- To absorb nutrients from the resultant solution
- To eliminate residual waste material
What is digestion?
Digestion: is the conversion of what we eat by physical and chemical disruption into a solution that is relatively sterile, neutral in pH and isotonic; from which we can absorb our nutrients (a few sugars, a few fatty acids, approx. 20 amino acids, some minerals and vitamins).
What is the role of saliva?
- Starts digestion (amylase and lipase)
- Bacteriostatic (contains Immunoglobin A antibody (IgA))
- High calcium (protects teeth)
- Alkaline
- Assist swallowing
- Protects the mouth
- Maintains moisture
Outline the oesophageal mucosa.
- Epithelium – stratified squamous non-keratinized (withstands abrasion).
- Lamina propria – loose connective tissue bearing blood & lymph vessels, some smooth muscle cells & many cells of immune system.
- Muscularis mucosae – thin layer of smooth muscle cells
Outline the structure of the other layers of the oesophageal wall.
- Submucosa – subtending layer of connective tissue containing mucus-secreting glands.
- Muscularis externa – smooth muscle layers (inner – circular; outer – longitudinal) which move food by peristalsis.
- Adventitia – thin outermost layer of connective tissue (no peritoneal enfolding of this portion of GI tract).
What are the 3 layers of smooth muscle in the stomach (part of the muscularis externa)
- Oblique
- Circular
- Longitudinal
What are rugae?
Folds of gastric mucosa forming longitudinal ridges in the empty stomach
Identify and describe the components of the gastric gland.
- The gastric pit is lined by mucus secreting cells, very much like goblet cells.
- The isthmus is the region in which stem cells divide to populate the gland by upward or downward migration
- Parietal cells secrete H+ ions into the lumen and HCO3- ions into nearby capillaries, which move it to surface mucous cells
- Chief cells secret pepsinogens which are converted into pepsin which partly hydrolyse proteins
- Enteroendrocrine cells include G cells which secrete gastrin. The wider gastric mucosa responds to this hormone by secreting acid.
Outline the role of surface mucous cells in the gastric pit.
- Surface mucous cells are abundant in the gastric pits.
- Their secreted mucus is resistant to pepsin (enzymatic) degradation.
- The mucus is released in response to distension, stomach contents, and acid secretion from gastric glands.
- Alcohol or aspirin can damage the mucous cells but they are quickly replaced by mitosis in deeper cells in the neck of the gastric pit
- The secreted mucus contains HCO3- ions which neutralise the effect of H+ ions and thereby protect the stomach lining.
Describe the structure of the duodenum
- Proximal portion of small intestine
- Curves around head of pancreas
- Walls contain Brunner’s glands which secrete bicarbonate–rich mucus, to neutralise acidic chyme.
Outline the components of the small intestine and explain what they do.
- Duodenum/Jejunum/Ileum – Most active absorption proximally
- Duodenum absorbs iron
- Jejunum absorbs most of sugars, amino acids and fatty acids
- Ileum absorbs Vitamin B12, bile acids and remaining nutrients by the terminal Ileum
What are plicae circulares?
- Circular folds of mucosa and submucosa project into the gut lumen
- Seen in the jejunum
What does the large intestine consist of?
- Caecum
- Ascending colon
- Transverse colon
- Descending colon
- Sigmoid colon
- Right hepatic flexure
- Left splenic flexure
Outline the role of the large intestine.
- Continues water recovery over a 20 hour transit.
- By end of large intestine contents semi-solid
I. Contents await expulsion in colon (not rectum)
II. At certain times rapidly propelled into rectum
Outline the role of the bacteria of the large intestine.
- Colon contains most of the GI tract’s bacteria
- 99% of these anaerobic and most lost in faeces (1011/g)
- Involved in:
I. Synthesis of vitamins K, B12, thiamine and riboflavin
II. Breakdown of bile acids
III. Conversion of bilirubin to non-pigmented metabolites - (all readily absorbed)
Outline the neural (somatic and autonomic) control of the gut.
- Somatic (innervating striated muscle)
I. Ingestion (mouth and first ⅓ of oesophagus)
II. Excretion (last sphincter of anus)
- Autonomic nervous system controls the rest
I. Post ganglionic neurones form plexuses
A. One between muscle layers of gut wall
B. One between submucosa and muscularis externa
II. The ‘gut nervous system’ (the ‘gut brain’)
III. Range of neurotransmitters
Outline the role of gastrin.
- Released by:
I. G cells of pyloric antrum of stomach
II. Pancreas
III. Duodenum
- Promotes production of HCl (gastric acid) by the parietal cells of the stomach.
Outline the role of cholecystokinin
- Synthesised and secreted by enteroendocrine cells of the duodenum
- Promotes release of digestive enzymes from the pancreas
- Promotes release of bile from gall bladder (stimulates it to contract)
- Is a hunger suppressant
Outline the role of secretin.
- Promotes HCO3- (bicarbonate) secretion from duct cells of pancreas
- Promotes bile production by the liver
- Inhibits secretion of acid by parietal cells of stomach
