3: Digestion, Absorption, Metabolism Flashcards
What is Digestion
separates nutrients in food and breaks larger molecules into smaller ones so they can be absorbed
Individually, what do polysaccharides, triglycerides, and proteins break into? Why can’t they be absorbed?
- Polysaccharides → sugars
- Triglycerides → fatty acids
- Proteins → amino acids
cannot be absorbed as they are found in food, broken down to pass membranes of intestinal cells
What are the two types of digestion
Mechanical (physical), chemical digestion
Example of Mechanical/physical digestion
physical process like our teeth chewing and stomach churning to break food apart
- does not alter the chemical composition of the nutrients
Define Chemical digestion and give examples
uses enzymes to alter chemical structure of nutrients and reduces them to their building blocks
Ex: starch —> maltose —> glucose
Proteins —> dipeptides —> single amino acids
Define Enzymes and its reaction
speed up the rate of reaction
- Provide a location for chemical reactions to occur
- participate in hydrolysis and condensation reactions
Hydrolysis reaction
Input of water helps to break down larger molecule into a smaller one
Condensation reactions
Combine molecules by liberating a water molecule
Ex: binding amino acids into specific chain begins process of protein synthesis
What does the prefix of enzymes tell us
which substrate it acts on
- sucrase breaks down sucrose
- proteases break down protein
- lipases break down lipids
Define Hormones
chemical messengers that are required for many physiological processes, including digestion
How do hormones work
released from one area of the body and travel through the blood to different parts of body
- communicate info about specific parts of digestive tract to brain and other digestive structures
Give an example of hormone communication
fat and protein enter small intestine, local cells release hormone Cholecystokinin (CCK) signals brain theres food in small intestine, leading to decrease hunger
Digestive tract structure
long tube-like structure that begins in the mouth and ends in the anus
- length/various folds provide large SA for digestion and absorption
Sphincters
Circular muscle found between certain organs and regulate passage from one organ to the next
- 2+ days for material to pass through entire digestive tract
- food spends most time in large intestine
Factors that affect transit time in the digestive system
Age, activity levels, diet, gender, medication use, infection
What organs are accessory structures of the digestive tract
liver, gallbladder and pancreas are not part of digestive tract but are part of the digestive system and critical to its function
- all secrete into the digestive tract
List the digestive tract
Mouth - pharynx - esophagus - stomach - (liver) - (gallbladder) - (pancreas) - small intestine - large intestine
(Accessory organ)
Digestive tract is made of what four main layers
Lumen, submucosa, muscularis, serosa
Define Lumen and what is found
inner cavity of the small intestine tube; it is where you will find food and digestive secretions
Function of Mucosa
secretes mucus, keeps digestive tract moist and protects it from infection.
- plays a critical role in absorption, especially in the small intestine
Define Submucosa and what is found in it
connects the mucosa to the more superficial muscularis layer.
- Blood vessels, lymphatic vessels and nerves are found here
Nerve Plexus
500 million neurons arranged in a grouping
- various nerves and plexus makeup up the enteric nervous system
Enteric nervous system
communicates with the brain but can also function independently
- helps regulate muscular contractions, messaging and digestive tract secretions
Muscularis layer (smooth muscle)
- cant voluntarily control movement (autonomic, involuntary, control)
- two layers of muscles, inner layer is circular pattern along tubes circumference, outer layer longitudinal along long axis of tube
Function of the muscularis layer (smooth muscle)
responds to the movement needs of the digestive tract, pushing food forward and helping it mix with digestive secretions
Define Serosa and its function
Tracts outermost layer
- consists of a layer of connective tissue
- helps reduce friction with organs adjacent to tract/anchors into place
Mechanical process of Mouth
Mechanical: Teeth rip food apart, tongue pushes food towards teeth and mixes it with saliva
Function of Saliva
Secreted into the mouth to facilitate digestion
What are the three salivary glands
The parotid, submandibular and sublingual
- collectively release this water-based substance into the mouth to begin the digestion of food
Saliva contains what two enzymes
- Salivary amylase: digests amylose, type of starch
- Lingual lipase: digests lipids
T/F: There are no protein digesting enzymes in saliva
True, chemical digestion of protein begins in the stomach
Lysozyme
- antibacterial component in saliva
- disinfects material arriving in our food to help reduce the chances that an active infectious agent can enter
Bolus
food chewed and mixed with saliva, forms a uniform cohesive structure
What is the chemical digestion in the mouth
Salivary breakdown of lipids and starch
(Salivary amylase and lingual lipase)
Pharynx (throat)
- passageway for food and air
- when not eating, pharynx opens trachea, allowing air to float in and out of our lungs
Epiglottis
directs food from the pharynx into the esophagus instead of down the wrong tube into the trachea (windpipe)
Esophagus
- not directly add to the digestion process but a conduit for food from pharynx to stomach
- No active digestion or absorption
Peristalsis
waves of circular smooth muscle contraction to move a bolus of food forward
Lower esophageal sphincter
- found at end of the esophagus
- When open, food can enter stomach
Define Stomach and its time transit
temporary reservoir for food before entering the small intestine
- Food remains here 4-5 hours
- chemical digestion of protein begins
Chyme
When food leaves the stomach it is in a semi-liquid form
How does chyme enter the small intestine?
The pyloric sphincter must open
T/F: A small amount of absorption occurs in the stomach
True, limited to the partial absorption of water and amino acids
How does a stomach churn food?
3 layers of muscles allow stomach to churn
- Lower esophageal sphincter and pyloric sphincter close as stomach churns food and mixes it with gastric juice
What are the three muscle layers in the stomach?
Longitudinal - outer layer
Circular - middle layer
Diagonal - inner layer
What is the mechanical digestion when the stomach churns?
Stomach churning, promotes mechanical digestion
What is the chemical digestion when the stomach churns?
mixing foodstuffs with enzymes
Crypts
increase SA to allow more stomach cells to be involved in digestion
- different cells (secrete mucus, pepsinogen)
Gastric juice
Cells in stomach crypts secrete contents of gastric juice for digestion
(Mucus, gastric lipase, hydrochloric acid, pepsinogen)
Mucus
Lubrication, medium for chemical reactions
- also lines the stomach’s inner walls, creating a protective layer that stops stomach acid and juices from damaging the stomach wall
Hydrochloric acid (HCl)
- highly corrosive acid (pH = 2)
- unravel proteins, exposing sites where enzymes can further break them down
- activates pepsinogen
Pepsinogen
proenzyme secreted by certain stomach cells
- becomes an active enzyme when acted upon by HCl, converting pepsinogen into active form, pepsin, which digests protein
Pepsinogen
proenzyme secreted by certain stomach cells
- becomes an active enzyme when acted upon by HCl, converting pepsinogen into active form, pepsin, which digests protein
Gastric lipase
- continues the breakdown of lipids that lingual lipase began in the mouth
- accounts for approximately 30% of lipid digestion
T/F: Enzyme salivary amylase found in mouth is inactivated in stomach, since there are no carb-digesting enzymes secreted by stomach
True, negligible carbohydrate digestion occurs in the stomach
Small intestine
Primary site of digestion and absorption
- Long length (~6m), large circular folds, villi, microvilli contribute to its large surface area
What are the three parts of the small intestine?
Duodenum, jejunum, ileum
Duodenum
- first part of the small intestine
- hooked tube, about 25 cm in length
- small opening that receives secretions from liver, gallbladder and pancreas
Jejunum
- Middle part of small intestine
- 2m in length
Ileum
- terminal part
- 3 m in length
Villus (plural = villi)
increase the SA and slow passage of food along its path
- invaginations of small intestine wall
- Main functional unit of small intestine
Microvilli (brush border)
- tiny finger-like projections
- extensions which secrete enzymes on the surface of villus
- part of the enterocyte and are oriented towards the lumen
How do nutrient sub units enter the blood or lymph?
Nutrient subunits are absorbed into the center of the villus where they then enter the blood or the lymph
Villi in small intestine:
Lacteal
lymphatic vessels are one-way tubes filled with watery, non-blood liquid that removes material from tissues
- absorbs larger lipids and fat-soluble vitamins
Thoracic duct
Material that ends up in the lacteal will eventually drain into the bloodstream through thoracic duct
Villi in small intestine:
Capillary bed
all nutrient subunits are absorbed here, except for larger lipids and fat-soluble vitamins
Methods of no transporter required
Osmosis (water), passive diffusion (lipids, fat, soluble vitamins)
Methods of protein transporter required
Facilitated diffusion (fructose),
Active transport (glucose, amino acids)
Villi in small intestine:
Enterocytes
in contact with the small intestine lumen
- helps increase total SA, needed to perform a wide range of digestive and absorptive functions
Function of Enterocytes
in contact with the small intestine lumen
- helps increase total SA, needed to perform a wide range of digestive and absorptive functions
Osmosis
- Water can move across walls of the enterocytes without a transporter
- moves in response to differences in dissolved particles. If there are more dissolved particles within the villus, water moves into this area to decrease their relative concentration
Passive (Simple) diffusion
move from an area of high concentration to one of low concentration
Ex: lipids, fat soluble vitamins
T/F: Fatty acids and fat-soluble vitamins do not require a transporter
True, they can be absorbed along the spaces between phospholipids in the enterocyte cell membrane
Facilitated diffusion
tunnels that allow material to pass from an area of high concentration to low concentration
What nutrient used the absorption process, facilitate diffusion?
Certain sugars such as fructose require a protein transporter
Active transport
move from an area of lower concentration to one of higher concentration
- movement against a concentration gradient also requires energy
- contributes to our daily total energy expenditure
What nutrients use the absorption process, active transport
glucose and amino acids move from an area of lower concentration to one of higher concentration
What digestive enzymes are stored at the brush border (microvilli)
lactase, sucrase and maltase
Where do the secretions of accessory organs drain into?
Secretions from the pancreas, liver and gallbladder collect into a common tube that drains into the duodenum
Pancreas
Glands with two types of functions (endocrine and exocrine)
What is the endocrine function of the pancreas?
blood glucose-regulating function, due to the production and secretion of the hormones insulin and glucagon
What is the exocrine function of the pancreas?
pancreas secretes pancreatic juice into the small intestine
- secretions are called pancreatic juice
Pancreatic juice contains what
Digestive enzymes: protein-digesting protease, lipase and carbohydrate-digesting amylase
Bicarbonate: important buffer that neutralizes the highly acidic chyme
Liver
Metabolism, detoxification, digestion
- production of bile, which promotes lipid digestion
Gallbladder
Bile is made in liver BUT stored in the gallbladder for quick secretion when needed
Bile
lipid emulsifier – it breaks larger lipid globules into smaller ones and allows them to be suspended in a watery environment
What do the salts within bile contain?
a hydrophilic (water-loving; lipid-hating) head and a hydro- phobic (water-hating; lipid-loving) tail
Micelle
Allow lipids to be suspended and freely move around the small intestine lumen
- also allow lipase to act on lipids
- arrange itself so lipids groups together in smaller mixtures within a ring of bile salts
Emulsification
Breakdown of large lipid globules through bile salts that create the micelle structure for enzyme lipase to digest lipids
Large intestine
- Approx 1.5 m in length
- colon is main part of large intestine
- any unabsorbed material is either:
Packaged for removal or Acted upon by bacteria Microbiota
What are the four sections of the large intestine?
ascending, transverse, descending and sigmoid colons
What is the first part of the large intestine?
Cecum, material moves from the ileum of the small intestine into the cecum
Segmentation of the large intestine
break material into smaller components while mixing it with digestive juices
Segmentation of the large intestine
break material into smaller components while mixing it with digestive juices
What movements occur in the large intestine
- Slow waves of peristalsis due to contractions of its muscularis layer
- segmentation
How is waste created?
large intestine draws water out and packages waste into solid feces, which is easier to excrete
Rectum
stores feces until it is ready to be excreted
Distal anus
- muscular sphincter that regulates passage of material out from the rectum
- sphincter is regulated by both involuntary and voluntary muscle
Microbiota
- total composite of non-human microorganisms found in our bodies
- 300-500 different species
Ex: viruses, fungi and other microorganisms, but mainly bacteria
Microbiome
genetic material of the non-human organisms found in our body
- 150 times more genes than human DNA – greatly expanding our own DNA potential
The Microbiome
largest population of non-human cells is found in the large intestine
- contribute to both health and disease
What roles does the microbiota have?
- Vitamin synthesis (vitamin K, B2, B12)
- Energy harvesting
- Health/disease
T/F: Diet does not alter the composition of the Microbiome
False, processed foods high in refined carbs can negatively affect diversity of the microbiome, altering its metabolic capacity and potentially leading to higher energy harvesting
What digestive tract structure secrete mucus?
Pharynx, esophagus, stomach, small intestine, large intestine
