Nutrition and Digestion Flashcards
What are the different body cavities in the human?
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What layers are there in the gastro-intestinal tract?
THERE ARE 4 LAYERS:
- Mucosa, the innermost lining consisting of 3 layers, including a layer of muscle
- Submucosa, connective tissue. this is where blood vessels and nerves lie
- Muscularis, layers of smooth muscle and enteric (intestinal) nerves lie
- Serosa, the visceral layer of the peritoneum.
What drugs can be directly absorbed from the mouth?
Alcohol and GTN spray (for angina)
What is different about the mouth’s blood supply compared with the rest of the gut?
It goes straight to the circulatory system, which is different because of the rest of the gut’s blood vessels pass through the liver
What 3 sections is the pharynx split into?
Nasopharynx
Oropharynx
Larngopharynx
What is peristalsis?
The process in which food plus travels from one end of the GI tract to the other. it is involuntary, under the control of the contracting smooth muscles rather than striated muscles. Not based on gravity.
What are the 3 parts of the oesophagus?
Cervical (top)
Thoracic (thoracic cavity)
Abdominal
What is the oesophagus lined with?
Stratified squamous epithelium cells (thick and robust) until the last 1cm where it becomes columnar epithelium. between these is the Z line.
What are the muscles in the oesophagus?
Voluntary (striated) in the upper third
involuntary in the lower third (smooth) and mixed in the middle.
What are the roles of the sphincters?
Stops air getting into gut and acid/food reflux.
What are the two types of hiatal hernia?
Sliding is where the diaphragm has lessened and part of the stomach has slipped up. PHH is less common, part of stomach is next to oesophagus. Increases risk of reflux
What cells secrete acid?
The chief cells secrete enzymes of gastric juice (pepsin)
The parietal cells secrete hydrochloric acid.
What are the 3 areas of the small intestine?
The duodenum, the jejunum and ileum.
What is the function of the stomach, and what are the 4 sections of the stomach?
Stomach churns food and mixes it with gastric acid and breaks it down to chyme
The 4 sections are the cardia, fundus, body and antrum
What do the different specialised cells in the stomach do?
Glands secrete mucous which protects the mucosa from the acid
The chief cells secrete gastric huice (pepsin)
The pariertal cells secrete hydrochloric acid
Enfocrine cells excrete grelin, a hormone which promotes appetite and gastrin, a digestive hormone.
What are the 3 segments of the small intestine?
Duodenum, jejunum and ileum
What is the lining of the small intestine like?
The small mucosa of the small intestine is folded into villi to absorb food and water. Each vilius contains blood vessels and lymth vessels.
Surface cells- enterocytes have microvilli- known as the brush border
Digestive enzymes are found here
Also mucus secreting goblet cells and stem cells lying deep within crypts
Whar are the different areas of the colon/ large intestine?
Split into the caecum, colon (ascending/transverse/descending/sigmoid), the rectum and anal canal.
What is the appendix?
Starts at the base of thececum in a slit like opening, 2/3 are behind the cecum and others extend into the pelvis. Important to know it has a variable position.
Now thought to have a reservoir for gut microflora, still being studied.
What is the wall of the colon like?
What is the peritoneum?
It is continuous membrane that covers most abdominal organsSplit into two- visceral which lines their organs is their serosa and the parietal which lines the walls of the cavity
What is the gallbladder and what is it’s fuction?
The gallbladder lies below liver. Internally mucosa forms rugae which are thick folds in the lining. The function of the gallbladder is to store bile, which is crucial for fat absorption. When triggered by gut hormone (CCK) it empties.
The gallbladder empties into the cystic duct then joins with the common hepatic duct above it to form the common bile duct. Bile is formed in the liver. The common bile duct then runs through the pancreas.
What are the exocrine and endocrine functions of the pancreas?
The exocrine pancreas has a complex ductal collecting system that ends at the pancreatic duct which empties into the duodenum. It secretes pancreatic juice, i.e. digestive enzymes and sodium bicarbonate
The endocrine pancreas has islands of endocrine cells which secrete hormones systemically into capillaries. Most important is insulin from beta cells and glucagon from alpha cells.
What structures leave or enter the liver?
The portal vein is full of rich nutrients as it drains directly from the gut- any food absorbed, broken-down food is taken here.
The hepatic artery contains fully oxygenated blood.
Are are cells in the liver organised?
Cells are arranged in perforated plates, one cell wide. Between the plates are sinusoidal blood channels which are lined by endothelial cells- drain into central vein from the portal triad.
The portal triad is at corners of lobules, and consists of a branch of the portal vein, a branch of the hepatic artery and a bile duct. Blood flows towards the centre of a lobule, the central vein.
Where does blood in the central vein travel to?
Blood collected in the central veins goes to sublobular veins, then to collecting veins, and then hepatic veins leaving the liver.
What is the liver Acinus?
It represents a functional unit comprising parts of 3 or so lobules. Instead of having the central vein in the middle, the portal triad is in the middle.
Creates a metabolic zonation to deal with toxic agents- zone 1deals with sampling the components of blood and accordingly sends signals to the other zones eg glycogen being broken down to glucose and the blood sugar levels are higher by the time blood reaches central vein.
What are the sinusoids of the liver?
Sinusoids are low pressure vascular channels that receive blood from the portal triad and take it to the central vein. They are lined with fenestrated endothelial cells which are loosely attached and hold phagocytic Kupffer cells which detect and phagocytose intruders.
What are the hepatocyte cells of the liver?
- Main functional cells of the liver and perform many functions, 80% of liver mass
- In 3 dimensions, they are arranged in plates that anastomose with one another. Cells are polygon in shape and sides are in contact with either sinusoids (sinusoid face) or neighbouring hepatocytes (lateral faces).
- A portion of the lateral faces are modified to form bile canaliculi. Microvilli are present on the sinusoidal face.
- Can have more than 1 nucleus.
What happens in liver cirrhosis?
When the liver gets inflamed, inflammatory cells circulate the sinusoids and the Kupffer cells get activated (a phagocytic cell which forms the lining of the sinusoids of the liver) and the stellate cells get activated and produce collagen.
The fenestrations (openings) start closing up due to collagen deposition, the sinusoidal pressure increases. This is the start of cirrhosis and portal hypertension. Many of the hepatocytes die as it gets worse, and others get surrounded by fibrous tissue.
What are the bile pathways in the liver?
There is system of canaliculi between hepatic cells which travels the opposite way to blood. The system leads to the canal of Hering then to the bile ductulus between the cells, then to a larger bile duct in the portal triad
What are the spaces of disse in the liver?
The perisinusoidal space (or space of Disse) is a location in the liver between a hepatocyte and a sinusoid. It contains the blood plasma.
How is the liver involved in blood gluycose control?
The liver stores glucose as glycogen. If blood sugar levels are low the pancreas releases glucagon which tells the hepatic cells to break down glycogen.
What are the missing labels for this diagram?
What is the liver lymphatic system like?
Lymth is formed by filtration of plasma into the spaces of disse as blood flows through the sinusoids. it then filters to the portal tract, then the lymphatics run along side portal vessels
What are important functions of the liver that are not glucose metabolism?
Bilirubin metabolism
Haemoglobin is broken down to bilirubin, which is then conjugated in the hepatocyte cells.
Detox- turns toxins into water soluable waste products into the bile to stool, or kidneys to urine.
What is the bilirubin pathway from blood to excretion?
What is Jaundice?
Jaundice is the yellow appearance of skin and eyes, is caused by bilirubin in the skin, most often caused by liver and gallbladder disorders. If there is a blockage in the bile duct, eg gallstones or a tumour at the head of the pancreas this will cause jaundice.
What are two protection mechanisms that stop stomach acid hurting the body?
There are two sphicters in the stomach (top and bottom) that prevent acid leaving
There is a mucus barrier that protects the lining of the stomach
What are the primary stomach cells that produce acid?
Parietal cells
What is the broad name for cells that control acid secretion?
Neuroendocrine cells
What cells stimulate and inhibit gastric acid secretion?
STIMULATE= enterochrmaffin cells and G cells
INHIBIT= D cells
What do enterochromaffin cells secrete?
Histamine, stimulates acid secretion
What do G cells in the stomach produce?
Gastrin; stimulates secretion
What do D cells in the stomach produce?
Somatostatin, inhibits acid secretion
What to chief cells in the stomach release?
Pepsinogen, which is later activated to pepsin
What do mucus cells in the stomach release?
Mucus
What breaks down carbs and where is it secreted from?
Amylase is secreted by salivary glands in mouth and pancreas. Breaks down carbs to glucose.
How are fats digested?
Bile salts emulsify fats and allow lipase to break down. Lipase from pancreas
What can cause B12 deficency?
Poor dietary intake (alcoholics, elderly)
Small bowel Crohn’s disease (inflammation)
Pernicious anaemia
What is pernicious anaemia?
An autoimmune condition that affects the stomach
It causes the immune system to attack the cells in your stomach that produce the intrinsic factor that B12 binds to in order to be digested
What is folate and where is it found?
Found in animal products and leafy green vegetable
Has a key role in DNA synthesis and repair
What are the causes of folate deficiency?
Poor dietary intake
Coeliac or Crohn’s disease
Drugs, e.g. methotrexate
What are the two types of iron?
What is the problem with taking oral non-heme iron?
Non-heme iron is poorly absorbed (10-15%) and unabsorbed iron has side effects- diaherrea/constipation.
What is the basic overview of metabolism of proteins, fats and carbs?
protein, fat and carbs are broken down by catabolic pathways (oxidation) to intermediates. These breakdown pathways create energy (ATP) which goes on to work and heat as well as reducing power, NADPH. These both are required for biosynthetic anabolic pathways in which intermediates are converted to macromolecules and eventually assembled into cell structures.
What happens when ATP is hydrolysed?
It creates ADP and Pi, 60kJ of energy released
How are fats, carbohydrates and proteins converted into energy? (diagram)
What are the different types of carbs?
Amylose
Amylopectin
Sucrose
Lactose
All broken down by various pathways to glucose
Where does anaerobic and aerobic metabolism of glucose take place, and how much ATP does each path produce?
AEROBIC= ~30 ATP per glucose, occurs in mitochondria
ANAEROBIC= 2 ATP, occurs in cytoplasm
How and where is fat stored in the body?
Most fat is stored as insoluable triacylglycerol in adipose, muscle and liver tissue
How is fat moved around the bodies?
Converted into triacylglyerole and secreted into the blood in the form of chylomicrons- these are lipo-proteins
Core of triacylglycerole surrounded by phospholipids
What enzyme converts chylomicrons to fatty acids in muscle and adipose tissue?
Lipoprotein lipase
What enzyme converts triacylglycerol from adipose tissue to fatty acids in the blood? And when does this occur?
Hormone-sensitive lipase
Occurs under starvation or exercise.
Why is secretion of proteinases dangerous for cells?
May digest the cells that make them.
For that reason, they are secreted as inactive precursors called zymogens
What causes different zymogens to activate?
Pepsinogen is activated by an increase in H+ (stomach acid)
Trysinogen can autoactivate
Trypsin can activate different zymogens
How are excess proteins excreted?
Amino acids converted to ammonia which can be converted to urea in the urea cycle in the liver then transported to the kidneys.
Can also be turned into glutamine which is converted to ammonia and excreted directly into urine
What are the different types of amino acids?
Glucogenic= can be broken down to glucose
Ketogenic= can be broken down to ketones
Some are both
Essential= amino acids that cannot be made in the body
What is the storage form of glucose and where can it be used?
Glycogen- present in liver and muscle mainly.
Liver glycogen used in blood sugar homeostasis
Muscle glycogen cannot be released into plasma and so has to be used in muscle
What happens to glucose, proteins and adipose tissue triacylglycerole during starvation?
Hormone status will be low insulin and high glucagon- promotes glycogen breakdown in the liver
TAG is broken down by hormone-sensitive lipase to fatty acids, or ketones
Protein broken down to amino acids
How are ketone bodies produced?
During starvation, TCA cycle becomes saturated and acetyl-CoA is converted into ketone bodies.
These can be used by muscle, kidney, heart and brain
What energy can/cannot pass the blood/brain barrier?
Glucose and ketone bodies can be used as energy
Fatty acids cannot be used
What is gluconeogenesis?
The formation of glucose from other intermediates
What is insulin exocytosis?
Where insulin (stored in beta cells in the pancreas) is released
When glucose reaches the beta cells, this triggers the fusion of the vesicles with the plasma membrane, releasing the insulin
What are the effects of insulin on the liver?
Glycogen synthesis increased
Breaking down of glucose, glycogenolysis, decreased
Gluconeogenesis decrased.
What are the effects of insulin on adipose tissue?
Glucose uptake increases
Triacylglycerole synthesis increases
Lipolysis (break down of TAG) decreases
What are the effects of insulin in muscle?
Glucose uptake increases
Glycogen synthesis increases
Glycogenolysis (breakdown of glycogen) decreases
Protein synthesis increases
What is the difference between type 1 and type 2 diabetes?
Type 1= failureof insulin production
Type 2= loss of insulin sensitivity
What are the effects of insulin on the liver, muscle and adipose tissue with type 1 diabetes?
Opoosite to usual
What are the symptoms of type 1 diabetes?
Weight loss
Hyperglycaemia
Drinking and peeing alot
What is an effect of type 1 diabetes that does not occur with type 2?
TAG synthesis and lipolysis still occur because insulin is still being produced in type 2
Therefore, there is no production of ketone body production
What is the most common drug given to treat diabetes type 2 and what are it’s effects?
Metformin
Inhibits gluconeogenesis and activates AMP-activated protein Kinase
AMPPK stimulates glucose uptake and inhibits fatty acid synthesis and glycogen synthesis
What is Leptin?
Hormone released by adipocytes (adipose cells)
There are leptin receptors in the brain, including the hypothalamus which control behaviour and development.
Leptin regulates food intake, motivation to feed, rewards for feeding and satiety (how full one feels)
What is ghrelin?
Secreted by gastic cells
Increases hunger, levels fall after feeding
What is cholecystekinin
Secreted by duodenum
Stimulates secretion of digestive enzymes and bile
What is gastric inhibitory peptide
Secreted by small intestine
Inhibits gastric acidifaction, slows digestion
What are common treatment plans for obese people?
Dieting
Gastric surgery- part of stomach and digestive tract are reduced in size
Injections of leptins
