Week 3 Digestive System Flashcards
GASTROINTESTINAL TRACT ORGANS
Mouth Throat Oesophagus Stomach Large Intestine Small Intestine Rectum Anus
ACCESSORY ORGANS
ACCESSORY ORGANS are the SALIVARY GLANDS, the PANCREAS, the LIVER, and the GALLBLADDER
MOUTH
The GASTROINTESTINAL TRACT starts at the MOUTH with mastication (chewing) breaking food into smaller pieces. It also releases some enzymes to start carbohydrate digestion
secretes mucus
PHARYNX/THROAT and OESOPHAGUS
The PHARYNX/THROAT and OESOPHAGUS swallow and transport food from the mouth to the stomach
secretes mucus
STOMACH
The STOMACH begins digestion by releasing acid and mixing food
secretes gastric juice containing HCl pepsin and mucus
SMALL INTESTINE
The SMALL INTESTINE is made of the duodenum, jejunum and ileum, the majority of digestion and absorption occurs
secretes mucus salt enzymes
bile duct
The bile duct is a tube that carries bile from the liver and gallbladder, through the pancreas, and into the small intestine.
LARGE INTESTINE
The LARGE INTESTINE, or colon, absorbs the last of the water and salt and converts the luminal contents into faeces which end up in the rectum and anus
secretes mucus
MOTILITY
MOTILITY refers to muscular contractions that mix and move food along the digestive tract. Movements can be propulsive, such as peristalsis, or mixing, such as segmentation
SECRETION
EXOCRINE & ENDOCRINE GLANDS
SECRETION includes both exocrine and endocrine functions in both the gastrointestinal tract and accessory organs.
EXOCRINE glands secrete their substances through ducts into the body’s surfaces. ENDOCRINE glands secrete their substances directly into the bloodstream
DIGESTION
DIGESTION breaks down the three macromolecules; protein, carbohydrate and fat. Occurs via hydrolysis
hydrolysis
where a molecule is split into two by adding molecules of water via the catalytic actions of enzymes
ABSORPTION
ABSORPTION absorbs digestion end products with water and electrolytes to transfer to blood and lymph. Primarily occurs in the small intestine
BASIC STRUCTURE OF THE WALL OF THE GASTROINTESTINAL TRACT
Mucosa: MUCOUS MEMBRANE
LAMINA PROPRIA: LYMPHOID TISSUE
MUSCULARIS MUCOSA
THE SUBMUCOSA
MUSCULARIS EXTERNA:
INNER CIRCULAR LAYER
LONGITUDINAL LAYER SEROSA
MUCOSA
THE MUCOSA consists of the MUCOUS MEMBRANE, a protective barrier of epithelial tissue containing specialised cells for absorption or secretion.
LAMINA PROPRIA
LAMINA PROPRIA is a thin middle layer of connective tissue containing tiny blood vessels and LYMPHOID TISSUE
MUSCULARIS MUCOSA
MUSCULARIS MUCOSA is a very thin layer of smooth muscle that upon contraction can expose different areas of surface folding
THE SUBMUCOSA
THE SUBMUCOSA is a thick layer of connective tissue which gives elasticity and contains larger blood and lymph vessels and a nerve network
MUSCULARIS EXTERNA
MUSCULARIS EXTERNA is the smooth muscle on the outermost layer of the tube made up of the INNER CIRCULAR LAYER which decreases the diameter for contraction, and the outer LONGITUDINAL LAYER which decreases the length of contraction
SEROSA
SEROSA is a thin layer of connective tissue that secretes serous fluid for lubrication. This prevents friction between the digestive tract and the surrounding viscera
MECHANICAL DIGESTION
MECHANICAL DIGESTION: mastication (chewing) breaks food into small pieces, increasing the surface area for biochemical digestion
BIOCHEMICAL DIGESTION
BIOCHEMICAL DIGESTION: starts chemical digestion of carbohydrates with amylase, breaking down long carbohydrate molecules into shorter chains
SALIVA
SALIVA is 99.5% water, electrolytes and proteins. The water and mucus moisten food, flush away food particles, and act as a solvent. Also, contains lysozyme, an antibacterial enzyme, and bicarbonate as a buffer to neutralise acids
ENZYMATIC HYDROLYSIS:
ENZYMATIC HYDROLYSIS: A molecule is split into two by adding molecules of water via the catalytic actions of enzymes. Digestive enzymes are specific to bonds they can hydrolyse
STOMACH:
STOMACH: Hydrochloric acid (HCl) inhibits amylase, halting biochemical digestion
Produces chyme
SMALL INTESTINE
The small intestine contains villi: folds in the small intestinal wall, with a lamina propria with blood vessels and lymphatic vessels, covered with small intestinal epithelial absorptive cells, ENTEROCYTES
Enterocytes
Enterocytes also have small projections called microvilli which make up the brush border
The large surface area and transport mechanisms of enterocytes in the small intestine allow for absorption
Pancreas
Pancreatic amylase into small intestine for digestion
BREAKDOWN OF POLYSACCHARIDES
Amylase from saliva and pancreas breaks down polysaccharides into disaccharides
Indigestible polysaccharides,
form indigestible fibre or
are broken down by the gut microbiome
BREAKDOWN OF DISACCHARIDES:
Disaccharidases in the brush border of the small intestine breakdown disaccharides into monosaccharides
MONOSACCHARIDE ABSORPTION
absorbed into the enterocytes through sodium-glucose cotransporter symporter (SGLT)
passively enters cell
through a protein called GLUT-5
monosaccharides exit the cell by passive facilitated diffusion via a protein called GLUT-2
Carbohydrate Digestion
Mouth breaks down food
Saliva and amylase break down carbohydrates and neutralise bacteria and acid
Stomach churns food
Small intestine breaks down further using pancreatic amylase and absorbs via microvilli on enterocytes using a Na+ dependant symport
Protein Structure
Amino acids with peptide bonds between them. On one end is the amino terminal, and on the other end is the carboxy terminal.
STOMACH
Secretes gastric juice, containing HYDROCHLORIC ACID and PEPSINOGEN
HYDROCHLORIC ACID
Secreted from parietal cells
Kills bacteria, denature proteins and activates pepsinogen
Tight junctions between epithelial cells of the stomach, mucous, and bicarbonate protect the stomach from HCl
PEPSINOGEN
secreted by chief cells in the stomach
Activated by HCl to form pepsin. forming process where pepsin molecules activate pepsinogen to form more pepsin
Pepsin splits certain amino acid linkages in proteins to release peptide fragments
PANCREAS
Secretes proteolytic enzymes (trypsinogen) into the small intestine
Enteropeptidase in the small intestine converts trypsinogen into trypsin.
Trypsin then activates other pancreatic enzymes
PROTEIN HYDROLYSIS
ENDOPEPTIDASE
EXOPEPTIDASE
ENDOPEPTIDASE hydrolyse peptide bonds within the protein molecules, forming two smaller peptide chains
EXOPEPTIDASE hydrolyses peptide bonds at the terminals of the protein molecules.
PROTEIN ABSORPTION
Amino acids are absorbed across enterocytes with symporters which are selective for different amino acids
peptides entering the cell that wasn’t hydrolysed
broken down by intracellular peptidases
Amino acids then enter the circulation by simple diffusion
Protein Digestion
Pepsinogen creates pepsin in the stomach breaking down amino acids in proteins
Trypsinogen from the pancreas converts to trypsin and activates other pancreatic enzymes to hydrolyse proteins within or at the terminals
Then absorbed across enterocytes and Na+ dependant symport and entering circulation via simple diffusion
Fat
triglycerides
Dietary fat comes in the form of large fat globules composed of triglycerides
The triglycerides are turned into liquid chyme in the stomach
SMALL INTESTINE
Chyme
stimulates enteroendocrine cells to secrete a pair of hormones
hormones then stimulate
gallbladder, causing bile to travel through the bile ducts into small intestine
BILE
BILE is made by the liver and stored and concentrated in the gallbladder
Bile emulsifies fats to prevent fat molecules from clumping together increasing are for enzymes to break them down into fatty acids and monoglycerides
pancreas
the pancreas is also triggered by hormones from enteroendocrine cells to release pancreatic juice including lipases
Fat absorption
micelles carry the end product of fat digestion to cell membrane to diffuse through, then resynthesising into triglycerides coated in lipoprotein to form chylomicrons
